Note: Descriptions are shown in the official language in which they were submitted.
1150836
VIDEO DISC PLAYER
TECHNICAL FIELD
The present invention relates to the method 2nd
means for reading a frequency modulated video signal
stored in the form of successively positioned reflectlve
and non-reflective regions on a plurality of lnformation
tracks carried by a video disc. More specifically, an
optical system is employed for directlng a reading be~m
to impinge upon the information track and for gather'ng
10 ~the reflected signals modulated by the reflective and
non-reflective regions of the information track. A
frequency modulated electrical signal ls recovered fr~m
the reflected llght modulated ~lgnal. The recovered
frequency mGdulated electrical slgnal ls applied to a
signal processing section wherein the recovered fre-
quency modulated signal is prepared for appllcatlon to
a standard television receiver and/or monitor. me
recovered light modulated signals are applied to a
plurality of servo systems for providing control 8ign~1s
which are employed for keeplng the lens at the optim~m
focus positlon with relation tothe information beari-.g
surface Or the video disc and to maintain the focuse~
llght beam ln a position such that the focused llght
spot implnges at the center Or the lnformatlon track.
BRIE~ 5~ OF THE INVENT~ON
The present lnvention is dlrected to a video
dlsc player operating to recover rrequencY modulated
video signals from an information bearing surrace Or a
vldeo disc. The frequency modulated video informaticn
.
.i ~
.
1150836
--2--
is stored in a plursllty of concentric circles or a
single splral extending over an informatlon bearing
portion of the video disc surface. The frequency modu-
lated video signal ls represented by lndicia arranged in
track-like fashion on the inrormation bearing surface
portlon Or the video dlsc. The indicia comprise suc-
cessively positioned reflective and non-reflective
regions in the inrormation track.
A laser is used as the source of a coherent
light beam and an optical system is employed for focus-
ing the light beam to a spot having a diameter approxl-
mately the same as the width Or the indicla positloned
in the information track. A microscopic ob~ective lens
is used for focusing the read beam to a spot and for
gathering up the reflected light caused by the spot
impinging upon successively positioned light reflective
and light non-reflective regions. The use of the
microscopically small indicia typically 0.5 microns in
~ width and ranging between one micron and 1.5 microns in
length taxes the resolving power Or the lens to its
fullest. In this relationship, the lens acts as a low
pass filter. In the gathering of the rerlected light
and passing the reflected light through the lens when
operating at the maximum resolution of the lens, the
gathered light assumes a sinusoldal-shaped like modulat~
beam representing the frequency modulated video signals
contained on the video disc member.
The output from the microscopic lens is ap-
plied to a signal recovery system wherein the reflected
3 light beam is employed ~irst as an information bearing
light member and second as a control signal source for
generating radial tracking errors and focus errors.
The information bearing portion of the recovered fre-
quency modulated video slgnal is applied to an FM
processing system for preparation prior to transmission
to a standard TV rece~ver and/or a TV mon tor.
The control portlon of the recovered freQuency
modulated video slgnal is applied to a plurality of
servo subsystems for controlling the position of the
t
-3~ 836
reading beam on the center of the in~ormatlon track and
for controlling the placing of the lens for gatherlng
the maximum reflected li~ht when the lens is posltloned
at its optimum focused posltion. A tangentlal servo
subsystem ls employed ror determining the time base error
introduced into the readin~ process due to the mechanics
of the reading system. This time base error appears as
a phase error in the recovered frequency modulated
video signal.
The phase error is detected by comparing a
selected portion of the reco~ered frequency modulated
signal with an internally generated signal having the
correct phase relationship with the predetermined por-
tion of the recovered frequency modulated video signal.
The predetermined relationship is established during
the original recording on the video disc. In t,he pre-
ferred embodiment, the predetermined ~rtion of the
recovered frequency modulated video signal ls the color
burst signal. The internally generated reference
rrequency ls the color subcarrier frequency. The color
burst signal ~as originally recorded on the video disc
under control of an identical color subcarrier fre-
quency. The phase error detected in this comparison
process is applied to a mirror moving in the tangential
direction which ad~usts the location at which the focused
spot impinges upon the information track. The tangential
mirror causes the spot to move along the lnformation
track either in the forward or reverse direction for
providing an ad~ustment equaltothe phase error detected
ln the comparison process. The tangential mirror in lts
broadest sense is a means for ad~usting the time base
of the signal read from the video disc member to ad~ust
for time base errors in~ected by the mechanics of the
reading system.
3~ In an alternatlve ~orm of the invention, the
predetermined port;on of the recovered frequency modu-
lated video signal is added to the total recorded
frequency modulated video signal at the time of record-
lng and the same frequency is employed as the operating
J
4 1~50B36
point for the hi~hly controlled crystal oscillator used
in the comparison process.
In the preferred embodiment when the vldeo disc
player is recovering frequency modulated vldeo slgnals
representins television pictures, the phase error
comparison procedure is performed for each line of
television information. m e phase error ls used for the
entire line of television information for correcting the
time base error for one full line of television infor~a-
tion. In this manner, incremental changes are appliedto correct for the time base error. These are con-
stantly being recomputed for each line of television
information.
A radial tracking servo subsystem is employed
15 for maintaining radial tracking of the focused llght
spot on one information track. The radial tracking
servo subsystem responds to the control signal portion
of the recovered frequency modulated signal to develop
an error signal indicating the offset from the preferred
center of track position tothe actual position. This
- tracking error is employed for controlling the movement
of a radial tracking mirror to bring the light spot back
into the center of track position.
The radial tracking servo subsystem operates
in a closed loop mode o~ operation and in all op~n loop
mode of operation. In the closed loop mode of operation,
the diff~rential tracking error derived from the re-
covered frequency modulated video signal is continuously
applied through the radial tracking mirror to bring the
focus spot ~ack to the center of track position. In
the open loop mode of operation, the differentlal
tracklng error is temporarily removed from controlling
the operation of radial tracking mirror. In the open
loop mode of operation, various combinations of slgnals
take over control o~ the movement of the radial track-
ing mirror for directing the point of impingement Or
the focused spot from the preferred center of track
; position on a first track to a center of track position
on an adjacent track. A first control pU~.C causes the
115~836
trac~ing mirror to move the focused spot Or llght rrom
the center of track position on a ~irst track and move
towards a next adjacent track. This rirst control pulse
terminates at a point prior to the rocused sp~t reaching
the center Or track position in the next adjacent track.
After the termination Or the rirst control pulse, a
second control pulse is applied to the radial tracking
mlrror to compensate for the additional energy added
to the tracking mirror by the first control pulse. The
second control pulse ls employed for bringing the
focused spot into the preferred center Or track rOcus
position as soon as possible. The second control pulse
is also employed for peventing oscillation of the read
spot about the second inrormation track. A residual
portion of the difrerential tracking error is also
applied to the radial tracking mirror at a point cal-
culated to assist the second control pulse ln bringing
the focused spot to rest at the center of track focus
~ position in the next ad~acent track.
A stop motion subsystem is employed as a means
for generating a plurality of control signals for
application to the tracking servo subsystem to achieve
the movement of a focused spot tracking the center of a
first information track to a separate and spaced loca-
tion in which the spot begins tracking the center Or
the next adjacent information track. The stop motion
subsystem performs its function by detectlng a predeter-
mined signal recovered from the frequency modulated
video signal which indicates the proper position wlthin
the recovered frequency modulated video signal at whlch
time the ~umping operatlon should be lnitiated. This
detection function ls achieved, in part, by internally
generating a gatlng circuit indicating that portlon of
the recovered frequency modulated vldeo slgnal within
whlch the predetermlned s~gnal should be located.
In response to the predetermlned signal, whlch
is called ln the re~erred embodiment a white ~lag, the
stop motion servo subsystem generates a first control
slgnal ror appllcatlon to the tracking servo subsystem
~ 150836
--6--
fcr temporarily interrupting the appllcation of the
differential tracking error to the radial tracking
mirrors. The top motion subsystem generates a second
control signal for appllcation tothe radial tracking
mirrors for causing the radial tracklng mirrors to leave
the center of tracklng position on a first information
track and ~ump to an adjacent information track. The
stop motion subsystem terminates the second control
signal prior to the focus spot reaching the center of
the focus position on the next adjacent inrormation track.
In the preferred embodiment, a third control
signal is generated by the stop motion subsystem at a
time spaced from the termination of the second control
pulse. The third control pulse is applied directly to
the radial tracking mirrors for compensatlng for the
effects on the radial tracking mirror which were added
to the radial tracking mirror by the second control
pulse. ~ile the second control pulse is necessary to
~ have the reading beam move from a first information
track to an ad~acent lnformation track, the spaces in-
volved are so small that the ~umping operation cannot
al~ays reliably be achieved using the secor.d control
signal alone. In a preferred embodiment haYlng an im-
proved reliable mode of operation, the third control
signal is employed for compensating for the effects of
the second control ~ump pulse on the radial tracking
mirror at a point in time when it is assured that the
focus spot has, in fact, left the first information
track and has yet to be properly positioned in the center
of the next adjacent information track. A further em-
bodiment gates the differential error signal throu~h to
the radial tracking mirror at a tlme calculated for the
gated portion of the differential tracking error to
assist the compensation pulse in bringlng the focus spot
under control upon the center of track position of the
- next ad~acent information track.
The video disc player employs a splndle servo
subsystem for rotating the video disc member positioned
upon the spindle at a predetermined frequency. In the
.t
.
~lSV836
--7--
preferred embodlment the predetermined frequency is
1799.1 revolutions per minute. In one revolution of
the video disc, a complete frame of television informa-
tior. is read from the video disc, processed in elec-
tronic portion of the video disc player and applied to astandard television recelver and/or television monitor
in a form acceptable to each such unit, respectively.
~oth the television receiver and the television monitor
handle the signals applied thereto by stan~ard internal
circuitry and display the color, or black and white
slgnal, on the receiver or monitor.
The spindle servo subsystem achieves the accur-
ate speed of rotation by comparing the actual speed of
rotation with a motor reference frequency~ The motor
reference frequency is derived from the color sub-
carrier frequency which is also used to correct for
time base errors as described hereinbefore. Py utlliz-
ing the color subcarrier frequency as the source of the
~ motor reference slgnal, the spindle motor itself removes
all fixed time base errors which arise ~rom a mismatch-
ing of the recording speed with the playback speed. The
recording speed is also controlled by the color fre-
quency subcarrier frequency. The use of a single highly
controlled frequency in both the recording mode and the
reading back mode removes the ma~or portion of time
base error. While the color subcarrier rrequency is
shown as the preferred source in generating the motor
reference frequency~ other highly controlled rrequency
signals can be used in controlling the writing and
reading of frequency modulated video signal on the video
disc.
A carriage servo subsystem operates in a close
loop mode of operation to move the carriage assembly
to the specific location under the direction of a
plurality of current generators. The carriage servo
subsystem con~rols the relative posit;icning of 'he video
disc and the optical system used to form the read beam.
A plurality of individual current sources are
indlvldually activated by command signals from the
1150836
functlon generator for directlng the movement Or the
carriage servo.
A first command slgnal can direct the carriage
servo subsystem to move the carrlage assembly to a
predetermined location such that the read beam lnter-
sects a predetermined portion of the informatlon bear-
ing surface of the vldeo dlsc member. A second current
source provides a continuous blas current for directing
the carriage assembly to move ln a fixed direction at a
predetermined speed. A further current source generates
a current signal of fixed magnitude and variable length
for moving the carriage assembly at a high rate of speed
ln a predetermined direction.
A carriage tachometer current ~eneratlng means
ls mechanically connected to the carriage motor and is
employed for generating a current indicating the
instantaneous position and speed of the carriage motor.
The current from the carriage tachometer ls compared
~ with the sum of the currents being generated in the
current sources in a summation circuit. The summation
circuit detects the difference between the current
sources and the carriage tachometer and applies a
different signal to a power amplifier for moving the
carrlage assembly under the control of the current
generators.
~RIEF DESCRIPTION OF THE DRA~NGS
The foregoing and other ob~ects, features and
advantages of the invention will be apparent rrom the
following more particular descrlptlon of a preferred
3 embodiment of the inventlon as lllustrated ln the
accompanying drawlngs whereln:
FIGURE ~ shows a generallzed block dlagram of
a video dlsc player;
FIGURE 2 shows a schematic diagram of the opti~
3~ cal system employed with reference to the video disc
player sho~Jn ir, Figure l;
FIGURE 3 shows a block diagram of the spindle
servo subsystem employed in the video dlsc player shown
ln Figure l;
1150836 ~
FIGURE 4 shows a block diagram of the carriage
servo subsystem employed in the video disc player shown
in Flgure l;
FIGURE 5 shows a block dlagram of the focus
servo subsystem employed in the vldec disc player shown
in Figure l;
FIGURES 6a, 6b, and 6c show various waveforms
illustr~ing the operation of the servo subsystem shown
ln Figure 5;
FIGURE 7 shows a partly schematic and partly
block diagram vlew of the signal recovery subsystem
employed ln the video disc player shown in ~lgure l;
FIGURE 8 shows a plurallty of waveforms and
one sectional vlew used ln explaining the operation of
the signal recovery subsystem shown in Flgure 7;
FIGURr 9 shows a block dlagra~ of the tracking
servo used in the video disc player shown in Figure l;
FIGURE 10 shows a plura~.ity of waveforms
~ utilized in the explanation of the operation of the
20 tracking servo shown in Figure 9;
FIGURE 11 shows a block diagram of the tangen-
tial servo emplo~red in the video disc player shown in
Figure l;
FIGUR~ 12 shows a block diagram of the stop
motion subsystem utilized in the video disc player of
Figure l;
FIGUP~.S 13A, 13~, and 13C show waveforms gen-
erated in the stop motlon subsystem shown with reference
to Figure 12;
FIGURE 14 is a generalized block diagram of
the FM processing subsystem utilized in the video disc
player shown with reference to Figure l;
FIGURE 15 is a block dlagram of the FM correc-
tor circuit utilized ln the FM processing clrcuit shown
in Figure 14;
FIGURE 15 shows a plural~ty Or waveforms and
one transfer runction utilized in explaining the opera-
tion of the FM corrector shown in Figure 15;
FIGURE 17 is a block diagram Or the FM
11~0836
-- --10--
detector used in the FM processing circuit shown ln
Figure 14;
FIGU~E 18 shows a plurality Or waveforms used
in explaining the operation of the FM detector shown with
reference to Figure 17;
FIGU~ 19 shows a block diagram of the audlo
processing circuit utilized in the video disc player
shown with reference to Figure l;
FIGURE 20 shows a block diagram of the audio
demodulator employed in the audio processing circuit
utilized in the video disc player shown with reference
to Figure 19;
FIGUR~ 21 shows a plurality of waveforms useLul
in e~plaining the operation of the audio demodulator
sho~n with reference to ~igure 20;
FIGURE 22 shows a block diagram of the audic
voltage controlled oscillator utilized ln the audio
processing circuit shown with reference to Figure 19;
FIGURE 23 shows a plurality of waveforms avail-
able in the audio voltage controlled oscillator sho-"n
with reference to Figure 22;
FIGU~E 24 shows a block diagram of the RF modul~-
tor utilizing the video disc player shown in Figure l;
FIG~E 25 shows a plurality of waveforms uti-
lized in the explanation of the ~F modulator shown withreference to Figure 24;
FIGURE 26 shows a schematic view of a video
dlsc member illustrating the eccentricity effect of
uneven cooling on the disc;
FIGU~E 27 is a schematic view o~ a video disc
illustrating the eccentricity effect of an orf-center
relationship Or the information tracks to the central
aperture;
FIGURE 28 is a logic diagram demonstrating the
3~ normal acquire focus mode of operation of the focus
servo employed in the video disc sh~n in Figure l; and
FIGURE 29 is a logic diagram demonstrating
other modes of operation of the focus servo shown with
reference to Figure l;
.
_
11~0133S
D~TAILED DESCRIPTION OF THE I~TENTION
The same numeral will be used in the several
vlews to represent the same element.
Referring to Figure 1, there ls shown a sche-
matic block diagram of a video disc player system in-
-dicated generally at 1. The player 1 employs an optical
system lndlcated at 2 and shown in greater detail ln
Figure 2.
Referring collectlvely to Figures 1 and 2, ~he
optical system 2 includes a read laser 3 employed for
generating a read beam 4 which ls used for readin~ a
frequency modulated encoded signal stored on a video
disc 5. The read beam 4 is polarized in a predetermined
direction. The read beam 4 is directed to the video
disc 5 by the optical system 2. An additional function
of the optical system 2 is to focus the light beam dc;~n
to a spot 6 at its point of lmpingement with the video
disc 5.
~ A portion of an information bearing surface 7
of the video disc 5 is shown enlarged within a circle 8.
A plurality of information tracks 9 are formed on the
video d~sc 5. Each track is formed with successive
light reflective regions 10 and light non-reflective
regions 11. The direction of reading is lndlcated by an
arro~ 12. The read beam 4 has two degrees o~ movemer.',
the first of which is in the radial direction ~s indi-
cated by a double headed arrow 13; the ~econd of wh ^h
is the tangential direction as indicated by a double
headed arro~.~ 14. The double heads of each of the arrows
3 13 and 14 indicate:that the read beam 4 can move in
both directions in each of the radial degree and tan-
gential degree.
Referrlng to Figure 2, the optical system ccm-
prises a lens 15 employed for shaping the beam to fully
flll an entrance aperture 16 of a microscopic ob~ectlve
lens 17. The ob~ective lens is employed for forming
the spot 6 of light at its point of lmpingement with
the video disc 5. Improved results have been found
when the entrance aperture 16 is overfllled by the
1150~336
-12-
readlng beam 4. Thls results in maximum light intenslty
at the spct 6.
After the beam 4 ls properly formed by the lens
15, it passes through a di~raction grating 18 which
splits the read beam into three separate beams (not
shown). T~o of the beams are employed for developing a
radial ~racking error and the other is used for develop-
ing both a focus error signal and the information signal.
These three oeams are treated ldentically by the remaln-
ing portiDn of the optical system. Therefore, they arecollectively referred to as the read beam 4. The output
for the di~fraction grating 18 is applied to a beam
splltting prism 20. The axis of the prism 2Q ls
slightly offset from the path of the beam 4 for reasons
that are explalned with reference to the descriptlon of
the performance of the optical system 2 as it relates
to a reflected beam 4'. The transmitted portion of the
beam 4 is applied through a quarter wave plate 22 which prc-
~Vldes a forty-~1ve degree shift in polarization of the
light forming the beam 4. The rear beam 4 next impinges
upon a fixed mirror 24 which re-directs the read beam 4
to a first artlculated mirror 26. The function of the
first articulated mirror 26 is to move the light beam
in a first degree of motion which is tangential to the
25 s urface ~ the video dlsc 5.to correct for time base
error errors introduced into the reading beam 4 because
of eccentricities in the manufacture of the disc 5.
The tangential direction is in the forward and/or back-
ward direction o~ the information track on the video
disc 5 as indicated by the double headed arrow 14. The
read beam 4 now impinges upon the entrance aperture 16,
as previously described, and is foc~sed to a spot 6
upon the information bearing track 9 of the video disc
5 by the lens 17.
The first articulated mirror 26 directs the
lighf beam to a second articulated mirror c8. The
second articulated mirror 28 is employed as a tracking
mirror. It is the function of the tracklng mirror 28
to respond to tracking error signals so as to sli~htly
` 1150836
--13-
change its physical posltlon to dlrect the polnt of
impingement S of the read beam 4 so as to radlally
tracl; the lnformatlon carrylng lndlcla on the surface
of the video dlsc 5. The second artlculated mlrror 28
has one degree of movement whlch moves the llght beam
ln a radial dlrection over the surface o~ the video
dlsc ~ or indlcated by the double headed arrow 13.
In normal playing mode, the focused beam
of llght lmplnges upon successively positioned llght
reflective regions 10 and light non-reflectlve regions
11 representlng the frequency modulated lnformation.
In the preferred embodlment, the llght non-reflectlve
reglons 11 are light scatterlng elements carrled by
the vldeo disc 5. The modulated llght beam ls a light
equivalent of the electrlcal fsequenc~ modulated slgnal
ccntaining all the recorded lnformation. This modulated
light beam is generated by the mlcroscopic objectlve
lens 17 by gat~ering as much reflected light from the
~ successlvely positloned llght reflective region 10
and light non-reflective regions 11 on the vldeo disc
5. The re~lected portion of the read beam is lndicated
at 4'. The reflected read beam 4' retraces the same
path previously explained by impinging ln sequence
upon the second articulated mirror 28, the first arti-
culated mirror 26, and the fixed mlrror 24. The re-
flected read beam 4' next passes through the quarter-
wave plate 22. The quarterwave plate 22 provldes an
additional forty-five degree polarization shift re-
sultlng ln a total of nlnety degrees in shift of polar-
ization to the reflected read beam 4'. The reflectedread beam 4' now impinges upon the beam splitting prism
20, which prism dlverts the reflected read beam 4' to
lmpinge upon a signal recovery subsystem indicated
generally at 30.
The function of the beam splitt~ng prism ls to
prevent the total reflected read beam 4' rrom re-
entering the laser 3. The efrect o~ the returnlng read
beam 4' upon the laser 3 would be to upset the mecAanism
whereby the laser oscillates ln lts predetermlned mode
1150836 (
--14--
of operation. Accordingly, the beam splitting prlsm 20
redirects a significant portion of the reflected read
beam 4' for preventing feedback into the laser 3 when
the laser 3 would be affected by this feedback portion
of the reflected read beam 4'. For those solid state
lasers which are unaffected by the feedback of the re-
flected light beam 4', the beam splitting prism 20 is
unnecessary. The solid state laser 3 can function as
the photo detector portlon o~ the signal recovery sub-
system 30 to be described hereinafter.
Referring to Figure 1, the normal operatingmode of the signal recovery subsystem 30 is to provide a
plurality of informational signals to the remaining
portion of the player 1. These informational signals
fall generally into two types, an informational signal
itself ~:hich represents the stored lnformation. A
second type Or signal is a control slgnal derived frcm
the informational signal for controlllng various por-
~ tions of the player. The informational signal is a
cO ~requency modulated signal representing the lnformatlon
stored on the video disc 5. This informational signal
is applied to an FM processing subsystem indicated at
32 over a line 34. A flrst contrpl signal generated by
the signal recovery subsystem 30 is a differentlal focus
error signal applied to a focus servo subsystem indica-
ted at 3~ over a line 38. A second type of control
signal ger,erated by the signal recovery subsystem 30 is
a differential tracking error signal applied to a track-
lng servo subsystem 40 over a line 42. The differential
tracking error signal from the signal recovery sub-
system 30 is also applied to a stop motion subsystem
indicated at 44 over the line 42 and a second line 46.
Upon receipt of the START pulse generated in a
function generator 47, the first function o~ the video
disc player 1 is to activate the laser 3, activate a
spindle motor 48, causing an integrally attached spindle
49 and its video disc member 5 mounted thereon to begin
spinning. The speed of rotation of the splndle 49,
as provided by the spindle motor 48, is under the
115083~ f
control of a spindle servo subsystem 50. A splndle
tachometer (not shown) ls mounted relatlve to the
spindle 49 to generate electrical signals showing the
present speed of rotation of the spindle 49. The
tachometer comprises two elements which are located one
hundred eighty degrees apart with reference to the
spindle 49. Each of these tachometer elements generates
an output pulse as is common in the art. Because they
are located one hundred eighty degrees out of phase with
each other, the electrical signals generated by each
are one hundred eighty degrees out of phase with each
other. A line 51 carries the sequence of pulses gener-
ated by the first tachometer elements to the spindle
servo subsystem 50. A line 52 carries the tachometer
pulses from the second tachometer element to the spindle
servo subsystem 50. Wher the spindle servo subsystem 50
reaches its predetermined rotational velocity of 1799.1
revolutions per minute, it generates a player enable
~ signal on a line 54. The accurate rotational speed
of 1799.1 revolutions per minute allo~s 30 frames of
television in~ormation to be displayed on a standard
television receiver.
The next major functioning ~ the video disc
player 1 is the activation of a carriage servo sub-
system 55. As previously mentioned, the reading of thefrequency modulated encoded information from the video
disc 5 is achieved by dlrecting and focusing a read
beam 4 to impinge upon the successively positioned light
reflective region 10 and a lig'nt non-re~lective region 11
3 on the vid~ disc 5. For optimum results, the read
beam 4 should impinge upon the plane carrying the encoded
information at right angles. To achieve this geometric
configuration requires relative movement between the
combined ~tical system 2 and the Yideo disc 5. Either
the video disc 5 can move under the fixed laser read
beam 4 or the optical system 2 can move relative t~ 'ne
fixed video disc 5. In this embodiment, the optical
system 2 is held stationary and the video disc 5 ls
moved under the reading beam 4. The carrlage servo
1150836
--16--
su~system controls this relative movement between the
video disc 5 and the optical system 2.
As completely described hereina~ter, the
carriage servo subsystem adds a degree Or flexibility
to the overall functioning of the video disc player 1 by
dlrecting the aforementioned relatlve movement in a
number Or different modes o~ operation. In its ~irst
mode of operation the carriage servo subsystem 55 re-
sponds to the player enable signal applied to it over
the line 54 to move a carriage assembly 56 such that
the read beam 4 impinges upon the video disc 5 perpendi-
cular to the information bearing surface of the video
disc 5. At this time it would be important to note
that the term carriage assembly is used to identify the
structural member UpOil which the video disc is carried,
This also includes the spindle motor 48, the spindle 49,
the spindle tachometer (not shown) a carriage motor 57
and a carriage tachometer generator 58. For the purpose
~ of not unduly complicating the broad block diagram shown
in Figure 1, the carriage assembly ls not shown in great
detall. For an understandlng of the summarized opera-
tlon of a vldeo dlsc player, it ls important to note
at this time that the function of the carriage servo
subsystem is to move the carriage to its initial posi-
tion at which the remaining player functions will beinitiated in sequence, Obviously, the carriage servo
subsystem can position the carriage at any number of
fixed locations relative to the vldeo disc pursuant to
the deslgn requlrements of the system, but for the
purposes ~ this description the carriage is posltloned
at the beginning of the frequency modulated encoded
- information carried by the video disc. The carriage
motor 57 provides the driving force to move the carriage
assembly 56. The carriage tachometer ger.erator 58 is
a current source for generating a current lndicating
the instantaneous s~eed and direction ~ movement of
the carriage assembly.
The spindle servo subsystem 50 l~as brought the
spindle speed up to its operational rotational rate of
1150836
-17--
1793.1 rpm at ~hich tlme the player ena~le slgnal is
generated on the line 54. The player enable slgnal on
the llne 54 is applied to the carrlage servo subsystem
55~for controlling the relative motlon between the
carrlage assembly 56 and the optlonal system 2. The
next sequence in the PLAY operation is for the focus
servo subsystem 36 to co-,ltrol the movement of the lens
17 relative to the video disc 5. The focusing opera-
tlon includes a coil (not shown) moving the lens 17
under the direction of a plurallty of separate elec-
trlcal waveforms which are summed within the coil ltself.
These waveforms are completely descrlbed ~ith reference
to the descriptlon ~iven for the focus servo subsystem
in Figures 6a 6b and 6c. A volce coll arrangement as
found ln a standard loud speaker has been found to be
suitable for controlllng the up and do~n motlon of the
lens 17 relati e to the video disc 5. The electrlcal
signals for controllil~ the volce coll are generated by
~ the focus servo subsystem 36 for appllcation to the coil
over a ~ine 64.
The inputs to the focus servo subsystem are
applled from a plurallty of locations. The first of
hich is applied from the slgnal recovery subsystem 30
over the line 38 as previously descrlbed. The second
input signal is from the FM processing circuit 32 over
a llne 66. The FM processing subsystem 32 provides the
frequency modulated slgnal read from the surface of the
video disc 5. A third input signal to the focus servo
subsystem 36 is the ACQUIRE FOCUS enabling loglc signal
30 generated by the act of puttlng the player lnto its
pla~y mode by selectlon of a functlon PIAY button within
the function generator 47.
The function of the focus servo subsystem 36
is to position the lens 17 at the optimum distance from
35 the video disc 5 such that the lens 17 is able to gather
and/or collcct the maximum lig;lt reflected from the
video disc 5 and modulated by the successively posi-
tioned light reflective region 10 and light non -
reflective region 11. This optimum range is approxi-
11~;083~i
--18-
mately .3 microns in length and is located at a distance
of one micron above the top surface of the video disc 5.
The focus servo subsystem 36 has several modes of oper-
at~on all of which are descrlbed hereinafter ln greater
detail with reference to Figures 5, ~a, .ib and ~c.
At the present time it is important to note
that the focus servo subsystem 36 utilizes its three
input signals in various combinations to achieve an
enhanced focusing arrangement. me dlfferential focus
error signal from the signal recovery subsystem 30
provides an electrical representatlon of the relative
distance between the lens 17 and the video disc 5. Un-
fortunately, the dlfferential focus error signal ls
relatively small in amplitude and has a uave shape
containing a number of positlons thereonJ each of which
lndicate that the proper point has been reached. All
but one o~ such positions are not the true optlmum
focusing positions but rather carry false information.
~ Accordingly, the dlfferentlal focus error slgnal ltself
is not the only signal emplo~Jed to indicate the optlmum
focus condition. I~hile the use of differential focus
error itself can oftentimes result ~nthe selectlon of
the optlmum ~ocus positlon, lt cannot do so rellably
on every focus attempt. Hence, the combination of the
dlfferential focus error slgnal with the slgnal indica-
tive of reading a frequency modulated slgnal from the
vldeo disc 5 provldes enhanced operatlon over the use of
uslng the dlfferentlal focus error slgnal ltself.
Durln~ the focus acquiring mode of operation,
3 the lens l7 is moving at a relatlvely high rate of speed
towards the video disc 5. An uncontrolled lens detects
a frequency modulated sl~nal from the informatlon
carried by the video disc 5 in a very narrow spaclal
range. This very narrow spaclal range ls the optimum
focusing range. Accordlngly, the combination of the
detected frequenc~J modulated slgnal and the differential
focus error signal provides a reliable system for ac-
qulring focus.
The focus servo subsystem 36 herelnafter
11S083`f~ ~
-19-
described cont2ins additional improvements. One Or
these improvements is an additioll of a further fixed
signal to those alraady described whicll further helps
the focus servo subsystem 36 acquire proper focus
on the initial attempt to acquire focus. Thls addi-
tional signal is an internally generated kickback
signal ~hich is initiated at the time when a frequency
modulated signal is detected by the FM processing
subsystem 32. This internally generated klckback
pulse is combined with the previously discussed signals
and applied to the voice coil so as to independently
cause the lens tc physically move back through the
region at ~hich ~ frequency modulated signal was read
f~om the disc 5. This internally generated fixed
kickback pulse signal gives the lens 17 the opportunity
to p2SS through the critical optimum focusing point a
number of times during the first transversing of the
lens 17 to~ards the video disc 5.
F~rther improvements are described for handling
momentary loss of focus during the play mod~ of opera-
tion caused `D~J 1mperfection in the encoded frequency
modulated signal which caused a momentary loss of the
frequency modulated signal as detected by the FM
processing subsystem 32 and applied to the focus servo
subsystem 36 over the line 66.
A tangential servo subsystem 80 receives its
first input signal from the FM processlng subsystem 32
over a line 82. The input signal present on the line 82
is the frequency modulated signal detected from the sur-
face of the video disc 5 by the lens 17 as ampliried inthe signal recovery subsystem 30 and applied to the FM
processing subsystem 32 by a line 34. The signal on the
line 82 is the video signal. me second input signal to
the tangential servo subsystem 80 is over a line 84. The
signal on the line 84 is a variable DC signal generated
by a carri~e position potenti3met2r. T~e amplitude of
the variable voltage signal on the line 84 indicates
the relative position of the point Or impact of the
readlng spot S over the radial distance indicated b~ a
1150836
-20-
double headed arrow 86 as drawn upon the surrace of the
video disc 5. This variable voltage adJusts the gain of
an internal circuit for ad~usting lts operatlng charac-
teristics to track the relative position Or the spot
as it transverses the radial positlon as indicated by
the length of the line 85.
The function of the tangential tlme base error
correction subsystem 80 is to adjust the signal detected
from the video disc 5 for tangential errors caused by
eccentricity of the informatlon tracks 9 on the disc 5
and other errors introduced into the detected signal
due to any physical imperfection of the video disc 5
itself. The tangential time base error correction
subsystem 80 performs its runction by comparing a signal
read from the disc 5 wlth a locally generated slgnal.
The difference between the two signals ls lndlcatlve of
the instantaneous error in the signal being read by the
player 1. More specially, the signal read from the disc
~ 5 ls one which was carefully applied to the dlsc with a
predetermined amplitude and phase relative to other
signals recorded therewith. For a color televislon FM
signal this is the color burst portion of the vldeo
signal. The locally generated signal is a crystal con-
trolled oscillator operating at the color subcarrier
frequenc~T of 3.579545 megahertz. The tangentlal time
base error correction subsystem 80 compares the phase
dlfference between the color burst slgnal and the color
subcarrier oscillator frequency and detects any differ-
ence. ~his dlfference ls then employed for ad~ustlng
the phase ~ the remainlng portion of the llne of FM
lnformation which contalned the color burst signal.
The phase difference of each succeeding ~ine is gener-
ated in exactl~ the same manner for providlng continuous
tangential tlme base error correction for the entire
signal read from the disc.
In other embodlments storing in~ormation
signals which do not have a portlon thereof comparable
to a color ~urst slgna~ such ~8~ ~ having predeter-
mlned amplitude and phase relative to the remalning
` 1150836 ~
-21-
slgnals on the disc 5 can be periodlcally added to the
information when recorded on the dlsc 5. In the play
mode, this portion of the recorded lnformation can be
selected out and compared witll a locally generated
sisnal comparable to the color subcarrier oscillator.
In thls manner, tangential time base error correction
can be achieved for any signal recorded on a video disc
member.
The error signal so detected in the comparison
of the signal read from the video disc 5 and the inter-
nally generated color subcarrier oscillator frequency is
applied to the first articulated mirror 25 over lines
88 and 90. The signals on lines 88 and 90 operate to
move the first articulated mirror 26 so as to re-
direct the read beam 4 forward and backwards along thelnformation track, in the dlrection of the double
headed arrow 14, to correct for the time base error
injected due to an imperfection from a manufacture of
the video disc 5 and/or the reading therefrom. Another
output signal from the tangential ti~e base error cor-
rection subsystem 80 is applied to the stop ~otion sub-
system 44 over a line 92. Thls signal, as completely
described hereinafter, is the composite sync signal
which is generated in the subsystem 80 by separating the
composite sync signal from the remainlng video slgnal.
It has been found convenient to locate the sync pulse
separator in the tangential time bsse error correction
subsystem 80. This æync pulse separator could be
located in any other portion of the player at a point
where the complete video signal is available from the
FM processing subsystem 32.
A further output signal from the tangential
subsystem is a motor reference frequency applied to the
spindle servo subsystem 50 over a line 94. The genera-
tion of the motor reference frequency in the tangentialsubsystem 80 is convenient because of the presence of
the color subcarrier osclllator frequency used in the
comparison operation as previously described. This
color subcarrier oscillator frequency is an accurately
115U836 (
. ~
gener2ted signal. It is dlvided down to a motor re~er-
ence frequenc~t used in the control of the spindle servo
speed. ~- utili~ing the color subcarrier frequency as
a control frequency for the speed Or the spindle, the
speed of the spindle is erfectively locked to this
color subcarrie- frequency causing the spindle to rotate
at the precise frame frequency ra~e required for maximu~.
fidelity in the display of the information detected
from the video disc 5 on either a televisicn receiver
indicated at 95 and/or a TV monitor indi-ated at 98.
The tracking servo subsystem 40 receives a
plurality of input signals, one of which is the pre-
viously descri~ed differential tracking error signal
generated by a signal recsvery subsystem 30 as applied
thereto over a line 42. A second input signal to the
tracking servo subsystem 40 is generated in a function
generator 47 over a line 102. For the purpose of clar-
ity, the function ge!lerator 47 is sho~n as a single
block. In the preferred embodiment, the function gener-
ator 47 includes a remote control function generatorand a series of switches or buttons permanently mounted
on the ^onsole of the video disc player 1. The specific
functions so generated are described in ~ore detail in
the detailed description Or the carriage servo sub-
system $5 contained hereinafter.
The signal contained on the line 102 is asignal which operates to disable the normal functionin&
of the tracking servo 40 during certain functions
initi~ted by the function generator 47. For example,
the function generator 47 is capable Or generating a
signal for causing the relative move~.ent of the carriage
assembly 56 over the video disc 5 to be in the rast
for~ard or fast reYerse condition. By definiticn, the
lens is traversing the video disc 5 in a radial direction
as represented by the arrow 13, rapidly sklpping over the
tracks at the rate o~ 11,000 tracks per inch and tracking
is not expected in this condition. Hence, the slgnal from
the functlon generator 47 on the line 102 disables the
tracking servo 40 so that it does not attempt to operate in
..... ... _ _ .
.
` 11S0836 (
-23 -
its normal tracking mode.
A thlrd input signal to the tracking servo
subsystem 40 is the stop motion compensation pulse gene~
ated in the stop motion subsystem 44 and applied over a
line 104. An additional input sigr.al applled to
tracking servo subsystem 40 is the subsystem loop
interrupt signal generated by the stop motion subsystem
44 and applied over a line 10~. A thlrd lnput slgnal to
the tracking servo subsystem 40 ls the stop motion pulse
generated by the stop motion subsystem 44 and applied
over a line 108.
The output slgnals from the tracking servo sub-
system 40 include a first radial mirror tracking signal
over a llne 110 and a second radial mlrror control on
a line 112. The mirror control signalson the line 110
and 112 are applied to the second articulated mirror 28
which is emplo~ed for radial traclcing purposes. The
control signals on the lin~s 110 and 112 move the second
articulated mirror 28 such that the reading beam 4
impinging thereupon ls moved in the radial direction and
- becomes centered on the information track 9 illuminated
by the ~ocused spot 6.
A further output signal from the tracking servo
subsystem 40 is applied to an audio processing subsystem
114 over a line 116. The audio squelch signal on the
line 116 causes the audio processing subsystem 114 to
stop transmitting audio signals for the ultimate appli-
catlon to the loud speakers contained in the TV receiver
96, and to a pair o~ audio ~acks 117 and 118 respec-
tlvely and to an audio accessory block 120. The audio~acks 117 and 118 are a convenient point at which exter-
nal equipment can be lnterconnected with the video disc
player 1 ~or recelpt of two audio channels for stereo
applicatlon.
A further output signal from the ~racking servo
subsystem 40 is applied to the carriage servo subsystem
55 over a line 130. The control signal present on the
llne 130 is the DC component ~ the tracking correctlon
signal which is employed by the carriage servo subsystem
1150836
--24 -
for providlns 8 rurther carriage control slgnal indica-
tive o~ now closely the tracking servo subsystem 40 ls
following the directions glven by the ~unction generator
47. For example, if the function generator 47 glves an
instruction to the carriage servo 55 to provide carriage
movement calculated to operate with a slo~ forward or
slow reverse movementJ the carriage servo subsystem 55
has a further control signal for determining how well it
is operatlng so as to cooperate with the electronic
control signals generated to carry out the instruction
from the function generator 47.
The stop motion subsystem 44 ls equlpped with a
plurality of input signals ~ne of which ls an output
signal o~ the function generat~r 47 as applied over a
1~ line 132. The control signal present on the llne 132
ls a STOP enabling signal lndicating that the video disc
player 1 should go into a stop motion mode of operation.
A second input signal to the stop motion subsystem 40
is the frequency modulated signal read off ~f the vldeo
disc and generated by the FM processing subsystem 32.
The video si~nal from the FM processing subsystem 32 ls
applied to the stop motlon subsystem 44 over a line 134.
Another lnput slgnal to the stop motion subsystem 44 ls
the dlfferentlal tracklng error as detected by the
2~ signal recovery subsystem 30 over the llne 45.
The tangential servo system 80 ls equipped with
a plurality of other output signals in addition to the
ones previously ldentifled. The first of which is
applled to the audio processing subsystem 114 over a
llne 140. The signal carried by the line 140 is the
color subcarrier oscillator frequency generated in the
tanentlal servo subsystem 80. An additlonal output
signal from the tangential servo 80 is applied to the
FM processing subsystem 32 over a llne 142. The signal
3~ carried by the line 142 ~s the chroma portlon of the
vldeo slgnal generated ln the chroma separator fllter
portion of the tangentlal ~ervo subsystem 80. An addi-
tlonal output slgnal from the tangentlal servo 80 is
applied to the FM processlng subsystem 32 over a line
1~508(36
-25-
1~4. The signal carried by the line 144 ls a gate enab-
ling signal generated by a first gate separator portion
Or the tangential servo system ~0 wllich indlcates the
instan~neous presence o~ the burst ~ime period in the
received video signal.
The focus servo receives its ACQUIRE FOCUS
signal on a line 14~.
me power output from the spindle servo sub-
system 50 is applied to the spindle motor 48 over a line
14~.
The power generated in the carriage servo 55
for driving the carriage motor 57 is applied thereto
over a line 150. The current generated i~ the carriage
tacnometer generator 58 for application to the carriage
15 servo subs~Jstem 55 indicative of the instantaneous speed
and direction of the carriage, is applied to the carriage
servo subsystem 55 over a line 152.
The FM processing unit 32 has an additional
plurality of output signals other than those already
described. A ~irst output signal from the Fr~ processing
subsystem 32 is applied to a data and cloc~ recovery
subsystem 152 over a line 1~4. The data and clock re-
covery circuit is of standard deslgn and it is employed
to read address information contained ln a predetermined
25 portion of the in~ormation stored in each spiral and/or
circle contained on the sur~ace of the vldeo.dlsc 5.
The address information detected in the video signal
~urnished by the FM processing unit 32 ls applied to the
runction generator 47 ~rom the data and clock recovery
subsystem 152 over a line 15~. The clocki~g lnformation
detected by the data and clock recovery subsystem is
applied to the function generator over a line 158. An
additional output signal from the FM processir.g unit 32
ls applied to the audio processing subsystem 114 over a
line 1~0. The signal carried by the line 160 is a fre-
quency modulated video signal from the FM dlstribution
ampliflers contained in the Frl processir.g unit 32. An
addltional outpu~ signal from the Fi~ processing subsystem
32 is applied to an RF modulator 152 over a line 164.
-~6- 11S083~
The line 16', carries a video output signal from the FM
detector portion of the FM processins unlt 32. A final
output signal from the FM processin~ unit 32 ls applied
to the TV monitor 9& over a line 155. ~he llne 166
c~rries a video signal o~ the type displayable in a
standard TV monitor 98.
The audio processing system 11~ receives an
additional input signal from the function generator 47
over a line 170. The signals carried by the line 170
from the function generator 47 are such as to switch
the discriminated audio signals to the various audio
accessory systems used herewith. The audio contained
in the Fr~ modulated signal recovered from the video
disc 5 contains a~plurality of separate audio signals.
More specifically, one or two channels Or audio can be
contained in the FM modulated signal. These audio
channels can be used in a stereo mode of operation. In
one of the preferred modes of operations, each channel
contains a different language explaining the scene shown
on the TV receiver 96 and/or TV monitor 98. The si~nals
- contained on the line 170 control the selection at ~hich
the audio channel is to be utilized.
The audio processing system 114 is equipped witl
an additional output signal for application to the RF
modulator 1~2 over a line 172. The signal applied to
the R~ modulator 152 over the line 172 is a 4.5 mega-
hertz carrier frequency modulated by the audio informa-
tion. The modulated 4,5 megahert~ carrier further
modulates a channel frequency oscillator having its
center frequency selected for use wlth one channel of
the TV receiver. This modulated channel ~requency
oscillator is applied to a standard TV receiver 96
such that the internal circuitry of the TV recelver
demodulates the audio contained in the modulated
3~ channel frequency signal in its standard mode of oper-
ation.
The audio signals applied to the audio acces-
sory unit 120 and tlle audio ~acks 117 and 118 lies
~ithin the normal audio ran6e suiiable for driving a
1150836
-27 -
loudspea~er b~ mealls Or the audio jacks 117 and 118.
The same audio ~requencies can be the ir.put to a
stereophonic audio ampll~ier when such is employed as
the audio accessory 120.
In the pre~erred embodiment, the output ~rom
the audio processing system 114 m~dulates the channel 3
frequency oscillatDr be~ore applicaticn to a standard
TV receiver 96. l~hile Channel 3 has been conveni-
ently selected ror this purpose, the oscillating ~re-
quency of the channel frequency oscillator can be
adapted f~r use with any channel of the standard TV
receiver 96. The output o~ the RF modulator 162 is
zpplled to the rrv receiver 96 over a line 174.
An additional output slgnal ~rcm the function
generator 47 is applied to the carrlage servo subsystem
55 over a llne 180. The llne 180 represents a plural-
it~J of individual lines. Each individual line is not
shcwn in order to keep the main block dia~ram as clear
as possible. Each of the individual lines, schematic-
ally indicated by the single line 180, represents an
~ lnstruction ~rom the ~unction generator lnstructlng
the carrlage servo to move ln a predetermined direction
at a predetermined speed. Thls is described ln greater
detail when describing the detailed operation of the
carriage servo 55.
NORMAL PLAY MODE - SEQI~ENCE OF OPERATION
The depression of the play button generates a
PLhY slgnal from the runctlon generator followed by an
ACQUIRE FOCUS slgnal. The PLAY signal is applied to
the laser 3 by a line 3a ~or generating a read beam 4.
The PLAY signal turns on the spindle motor subsystem 50
and starts the splndle rotatlng. After the spindle
servo subsystem accelerates the splndle motor to its
proper rotational speed of 1799.1 revolutions per
minute, tlle spindle servo subsystem 50 generates a
PLAYER ENA~LE signal for appllcation to the carriage
servo subsystem 55 ~or controlling the relative move-
ment between the carriage assembly and the optlcal
assembly 2. The carriage servo subs~stem 55 dlrects
1151~836
-28
the movement of the carriage such that the read beam
4 is positioned to impinge upon the beglnning portion
of the inform~tion stored on the video disc record 5.
Once the carriage servo subsystem 55 reaches the approx-
imate beginnins Of the recorded information, the lensrOcus servo subsystem 3~ automatically moves the 1~n9
17 towards the video disc surface 5. The mo-~ement of
the lens is calcul~ted to pass the lens through a point
at which optimum focusing is acllieved. The lens ser~o
system preferably achieves optimum focus in com~ina-
tion with other control signals generated by reading
information recorded on the video disc surface ~. In
the preferred embodi~ent, the lens servo subsystem has
a built-in program triggered by information read from
the disc ~lhereby the lens is caused to move tllrough
the opti~um ~ocusing point several times by an oscilla-
tor~ type microscopic retracing of the lens path as the
lens 17 moves t'nrough a single lens focusing acquiring
procedure. As the lens moves through the optimum
focusing point, it automatically acquires information
from the video disc. This information consists of a
total FM signal as recorded on the video disc 5 and
additionally includes a differential focus error signal
and a differential tracking error signal. The size of
the video lnformation signal read from the disc is used
as a feedback signal to tell the lens servo subsystem
35 that the correct point of focus has been success-
full~J located. ~hen the point of optlmum focus has
been located, the focus servo loop is closed and the
3 mechanically initiated acquire focus procedure ls
terminated. The radial tracking mirror 28 is now
responding to the di~ferential trackin~ error generated
from the informaticn gathered by the reading lens 17.
The radial tracking error is causing the radial track-
ing m~rror 2~ to follow the information track andcorrect for any radial de~artures fro~ a ~erfect spiral
or circle track configuration. Electronic processing
of the detected video FM signal generates a tangential
error signal which is applied to the tangential mirror
" 115()8~6
-29 -
26 for correctin~ phase error in the reading process
caused by small physical deformatles in the surface of
the video disc 5. Durin~ the normal play mode, the
servo subsystems hereinbefore described continue their
normal mode Or operation to maintain the read beam 4
properly in the center of the informa~ion track and to
maintain the lens at the optimum focusing point such
that the light gathered by the lens generates a high
quality si~nal for display on a standard television
receiver cr in a television monitor.
The frequency modulated signal read from the
disc needs additional processing to achieve optimum
fideliJy during the display in the television receiver
9~ and/or television monitor 98.
Immediately upon recovery from the video disc
surface, the frequency modulated video signal is applied
to a tan~ential servo subsystem 80 for detectlng any
phase difference Eresent in the recovered video signal
and caused by the mechanics of the reading process.
The detected phase difference is employed for driving a
tangential mirror 26 and ad~ustin6 for this phase
difference. The movement of the tangential mirror 26
functions for changing the phase of the recovered
video signal and eliminating time base errors intro-
duced into the reading process. The recovered videosignal is F~ corrected for achieving an equal amplitude
FM signal over the entire FM video spectra. This re-
quires a variable amplification of the FM signal over
the FM video spectra to correct for the mean transfer
function of the readin~ lens 17. More specifically,
the high frequency end of the video spectrum is atten-
uated more by the reading lens than the lo~ frequency
portion of the frequency spectrum of the frequency
modulated slgnal read from the video disc. This
equalization ls achieved through amplif~v~ing the higher
frecluency portion more than the lower frequency por-
tion. After the frequency modulation correction is
achieved, the detected signal is sent to a discrimina-
tor board whereby the discrimil~ted video is produced
1150~336
3o-
~or applicaticn to the remaini;~ portions Or the board.
Rererring to Figure 3 there ls sho~n a gen-
erali~ed blocl~ diagram Or the spindle servo subsystem
indicated at ~0. One o~ the ~unctlons o~ the spindle
servo subsystem is to maintain the speed o~ rotation
o~ the spindle 4g by the spindle motor 48 at a constant
speed of 1799.1 rpm. Obviously this ~i~ure has beei~
selected to be compatible with the scanni~g rrequency
Or a standard television receiver. me standard tele-
vision receive~ receives 30 rrames per second and theln~ormation is recorded on the video disc such that
one complete ~rame of television in~ormation is con-
tained in one spiral and/or track. ObviouslyJ when the
time requirements Or a television receiver or tele-
vision moritor differ rrom this standard then thefunction o~ the spindle servo subsyste~ ls to maintain
the rotational speed at the new standard.
The function ger.erator 47 provides a START
pulse to the spindle motor. As the motor begins to
turn the tachometer input sig~l pulse train ~rom the
first tachometer element is applied to a Schmitt trig-
ger 200 over the line 51. The tacho~.eter lnput signal
pulse train rrom the second tachometer element is
applied to a second Schmitt trigger 202 over the line
25 52. A 9.33 KHz motor reference ~requency is applied
to a third Schmitt trigger 204 ~rom the tangential
servo subsystem 80 over a line 94.
The output from the Schmitt trigger 200 is
applied to an edge generator Cil'CUit 206 through a
30 divide by t~o network 208. The output rrcm the Schmitt
trigger 202 is applied to an edge generator 210 through
a divided by two network 212. Tlle output from the
Schmitt trigger 204 is applied to an edge generator
circuit 214 througll a divided by two network 216. Each
3~ o~ the edge generators 206 210 and 214 is employed
ror gererqting -q sllarp pulse corres?ond}ng to bo~h the
positive gOiilg e~e and the negative ~oing edge o~ the
signal applied respectively fro~ the divlded by two
net-,~orks 208 212 and 215.
1150836 ~
The output from the ed~e generator 214 is
ap~iied as the reference phase si~nal to a rirSt ph~3e
detector 218 and to a second phase detector 220. The
phase detector 218 has as lts second input signal the
OUtp~lt from the edge generator 206. The phase genera-
tor 220 has as its second input signal the output of
the edge generator 210. The phase de'ectors operate to
lndicate any phase difference between the tachometer
input signals and the motor reference frequency. The
output from the phase detector 218 is applied to a
summation circuit 222. And the output from the ph~se
detector 220 is also applied as a second input to the
summation circuit 222. The output from the summation
circuit 222 is applied to a lock detector 224 and to a
power amplifier 22S. The function of the lock detector
224 is to indicate when the splndle speed has reached a
predetermined rotational speed. This can be done by
sensing the output signals from the summ~tion circuit
222.
In tne preferred embodiment ls has been deter-
mlned that the rotational speed of the spindle motor
should reach a predetermined speed before the carriage
assembly is placed in motion. When a video disc is
brou~ht to a relatively high rDtational speed, the disc
rides on a cushion of air and rises slightly vertical
against the force of gravity. Additionally, the
centrifugal force of the vldeo disc causes the video
disc to some~ at flatten considerably. It has been
found that the vertical movement against gravity
caused by the disc riding on a cushion of air and the
vertical rise caused by the centrirugal force both
lift the video disc from its position at rest to a
stabillzed position spaced from its lnitial rest posi-
tion and at a predetermined p~sition with reference
to other internal fixed members of the video disc
player cabinet. The dynamics ol a spinnin~ disc at
1799.1 rpm Wit~1 a predetermined weight and density
can be calculated such as to insure that the dlsc ls
spaced from all lnternal components and ls not ln
1150836
,,
contact ~itll anJ such i~lternal components. An~J con-
tact between the disc and the player cabinet causes
rubbing, an~ the rubbing causes dama~e to the video
disc throu~h abrasion.
In the preferred embodiment, the lock detector
224 has been set to generate a PIAYER ENAELE pulse on
the line 54 when the spindle speed is up to its full
1799.1 rpm speed. A speed less than the full rota-
tlonal speed can be selected as the point at which the
player enable si~nal is generated provided that the
video disc has moved sufficiently from its initial
position and has attained a position spaced from the
internal components of the video disc player cabinet.
In an alternate embodiment, a ~ixed dela~-, after apply-
ing the START signal to the spindle motor, is used tostart t'ne carriage assembly in motion.
During the normal operating mode of the vi~eo
disc player l; the tachometer input si~nals are con-
tinuously applie~ to the Schmitt triggers 200 and 202
over the lines 51 and 52, respectively. These actual
ta~hometer input signals are compared against the moto~
reference si~nal and any deviation therefrom is detected
in the summation circuit 222 for applic~tion to the
poJer amplifier 225. The power amplifler 226 provides
2~ the driving force to the spindle motor 48 to maintain
the required rotational speed of the spindle 49.
Referring to Figure 4, there is shown a sche-
matic block diagram of the carriage servo subsystem ~5.
The carriage servo subsystem ~ comprises a plurality
of current sources 230 through 235. The function of
each Or these current sources is to provude a predeter-
mined value of current in response to an input signal
from the function generator 47 over the line 180. It
was previously described that the line 180, shown with
reference to Figure 1, comprlses a plurality of in-
dividual llnes. For the pur?oses of ~his description,
each of these lines will be identlfied as 180a through
l~Oe. The outputs of the current sources 230 throu~h
23~ are applied to a summation circuit 238. The
~150836 ~
-33-
ouiput from the summation clrcuit 23~ is applied to a
p^wer ampli~ier 240 over a line 242. The output from
the power ampll~ier 240 is applied to the carriage motor
57 over t~le line 150. A dashed line 244 extending
between the carriage motor 57 and the carriage tachometer
member 58 indicates that these units are mechanically
connected. The output ~rom the carriage tachometer 58
is applied to the summation circuit by the line 152.
The STAP~T pulse is applied to the current
so~rce 232a over a line 180al. The current source 232a
functions to provide a predetermined current for moving
the carriage assembly from its initial rest position to
the desired start of tracl~ position. As previously
mentioned, the carriage assembly 55 and the optical
system 2 are moved relative one to the other. In the
standard PLAY mode of operation, the optical system 2
and carriage assembly 56 are moved such that the read
beam 4 from the laser 3 is caused to impinge upon the
~ start Or the recorded informatlon. Accordingly, the
current source 232 generates the c~rrent for applica-
tion to the summation circuit 238. The summ~tion
circuit 238 runctions to sense the several incremental
amounts Or current being generated by the ~arious
current sources 230 through 235 and compares this sum
25 of the currents against the current being ~ed into the
summation circuit 238 from the carriage tachometer
s~Jstem 58 over the line 1~2. It has been previously
mentioned that the current generated by the carria~e
tachometer 58 indicates the instantaneous speed and
position of the carriage assembly 5S. This current
on the line 152 is compared with the currents being
generated by the current sources 230 through 235 and
the resulting difference current is applled to the
po~Jer ampli~ier 240 over the line 242 fo~ generating
35 the power required to move the carriage motor 57 to the
desircd locatio.l.
Onl~J for purposes of example, the carriage
tachometer 58 could be generatil~ a negative current
indicating that the carriage assembly 56 is positioned
~15083~
-3~-
at a first location. The current source 232a ~ould
gener2te a SeCOlld cu~rent indicati~.~ the desired posi-
tion for the carriage assembly 56 to reacn for start-
up time. The summation circuit 23~ compares the two
currents and 6enerates a resulting difrerence current
on the line 2~2 for application to the pol~er amplifier
240. The output from the amplifier 240 is applied to
the carriage motor 57 for driving the carriage motor
and moving the carriage assembly to the indicated
position. As the carriage motor 57 moves, the carriage
tachometer 58 also moves as indicated by the mechanical
linkage sho~n by the line 244. As its pos ~ion changes,
the carriage tachometer 58 generates a nell 2nd differ-
ent signal on t',le line 152. When the carri~ge tachom-
eter 58 indicates that it is at the same position asindicated b~ the output signal from the cur ent source
232a~ the summation circuit 238 indicates a COr~PAR~
E~UAL condition. No signal is applied to the po-.~ler
amplifier 240 and no additional power is applied to
the carriage motor 57 causing the carria~e motor 57
~o stop.
The START sign21 on t'ne line 180al causes the
carriage motor 57 to move to its START positlon. When
the spindle servo subs~Jstem 50 has brought the speed of
rota~ion of the spindle 49 up to its reading speed, a
PLAY ENA~LE signal is generated by the spindle servo
subsystem 50 for application to a current source 230
over a line 54. The current source 230 generates a
constant bias current sufficient to move the carriage
assembly 56 a distance of 1.6 microns for each revolu-
tion of the disc. This bias current is applied to the
summation circuit 238 for providing a cor.stant current
input signal to the po~er amplifier for driving the
carriage motor 57 at the indicated distance per revo-
lution This constant input bias currer.t frcm thecurrPnt so-,rce 230 is fur~her ~delli;ifled as a first
fiY~ed bias control signal to the carriage motor 57.
The current source 231 receives a FAST FORtJARD
E~APLE signal from the functicn generator 47 over the
115~836
~5
llne 180`o. ~ne ~ast for~l~.d current source 231 gener-
aies an output current signal for applicatlon to the
summation circuit 238 and the power amplifier 240 for
activating the carriage motor 57 to move the carriage
assembly 56 in the fast forl~ard direction. For clari-
fication, the directions referred to in this section
of the description refer to the relative movement of
t'..e carriage assembly and the reading beam 4. These
movements are directed generally in a radial direction
0 2S indicated by the double headed arrow 13 shown in
Figure 1. In the fast forward mode of operation, the
video disc 5 is rotating at a very high rotational
speed and hence the radial tracking dces not occur in
a straight line across the tracks as indicated by the
double arrow 13. More specifically, the ca-riage
servo subsystem ls capable of providing relative motion
between the carria~e assembly and the optical s~Jstem 2
such as to traverse the typically four inch wide band
of infcrmatio:l bearing surtace ~ the video disc 5 in
approximately four secon~s from the outer periphery to
the inner periphery. The average speed is one inch per
second. During the four second period, the reading
head moves ac;oss appro~imately forth-four thousand
tracks. The video disc is revolving at nearly thirty
revolut~ons per second and hence, under idealized con-
ditions, the video disc 5 rotates one hundred and
t~enty times while the carriage servo subsystem 55
provides the rela~ive motion from the outer periphery
to the inner periphery. Hence, the absolute point of
3o impact of the reading beam upon the rotatin~ video disc
is a spirally shaped line having one hundred and t~lenty
spirals. The net effect of this movement is a radial
movement of the point of impingement of the reading
beam 4 ~ith the video disc 5 in a radial direction as
indicated by a double headed line 1~.
The current source 23, receives its ~ T ~E-
VERSE E~J~LE signal from the function generator 47 over
the line 180c. The fast reverse current source 233 pr~-
vides its output directly to tl.e summation ci,cuit 238.
115~836
-36-
The current source 234 is a SLOW FORWARD cur-
rent source and receives its SLOW FORWARD ENABLE input
signal from the function generator 47 over a line 180d.
The output signal from the slow forward current source
234 is applied to the summation circuit 238 through an
adjustable potentiometer circuit 246. The function of
the adjustable potentiometer circuit 246 is to vary
the output from the slow forward current source 234 so
as to select any speed in the slow forward direction.
The current source 235 is a SLOW REVERSE cur-
rent source which receives its SLOW REVERSE ENABLE
signal from the function generator 47 over the line
180e. The output from the slow forward current source
235 is applied to the summation circuit 238 through
an adjustable potentiometer circuit 248. The adjust-
able potentiometer circuit 248 functions in a similar
manner with the circuit 246 to adjust the output signal
from the slow reverse current source 235 such that the
carriage servo subsystem 55 moves the carriage assembly
56 at any speed in the slow reverse direction.
The DC component of the tracking correction
signal from the tracking servo subsystem 40 is applied
to the summation circuit 238 over the line 130. The
function of this DC component of the tracking correc-
tion signal is to initiate carriage assembly movement
when the tracking errors are in a permanent off-
tracking situation such that the carriage servo sub-
system should provide relative motion to bring the
relative position of the video disc 5 and the read
beam 4 back within the range of the tracking capability
of the tracking mirrors. The DC component indicates
that the tracking mirrors have assumed a position for a
substantial period of time which indicates that they
are attempting to acquire tracking and have been unable
to do so.
CARRIAGE SERVO -_NORMAL MODE OF OPERATION
The carriage servo sybsystem 55 is the means
for controlling the relative movement between the
carriage assembly on which the video disc 5 is located
836
-37-
and the optical system in which the reading laser 3 is
located. A carrige tachometer is mechanically linked
to the carriage motor and operates as a means for
generating a highly accurate current value representing
the instantaneous speed and direction of the movement
of the carriage assembly 56.
A plurality of individually activated and
variable level current sources are employed as means
for generating signals for directing the direction and
speed of movement of the carriage assembly. A first
current source for controlling the direction of the
carriage motor generates a continuous reference current
for controlling the radial tracking of the read beam
relative to the video disc as the read beam radially
trakcs from the outer periphery to the inner periphery
in the normal mode of operation. A second current
source operates as a means for generating a current
of the same but greater amplitude to direct the carriage
assembly to mo~e at a higher rate of speed in the same
direction as the bias current. This second type of
current ceases to operate when the carriage assembly
reaches its predetermined position.
An additional current source is available for
generating a current value of opposite polarity when
compared with the permanently available bias current
for causing the carriage motor to move in a direction
opposite to that direction moving under the influence
of the permanently available bias current.
A summation circuit is employed for summing
the currents available from the plurality of current
sources for generating a signal for giving directions
to the carriage motor. The summation circuit also sums
the output current from the carriage tachometer indi-
cating the instantaneous speed and location of the
carriage assembly as the carriage assembly move pur-
suant to the various commands from the input current
generators. The summation circuit provides a differ-
ence output signal to a power amplifier for generating
the power required to move the carriage assembly such
ffr ~
1150836
that the current generated in the carrlage tachometer
matches the current generated from input current
sources.
Referring collectlvely to Flgure 5 and Figures
5 oA through 6F, there ls shown and described a schematlc
block diagram of the focus servo subsystem 36, a plur-
ality of d~r~erent wave~orms which are employed wlth
the rOcus servo subsystem and a plurallty of single
logic dia~rams showlng the sequence of steps used in
10 the focus servo to operate in a plurality of different
modes of operation. The rOcus error signal from the
slgnal recovery subsystem 30 ls applied to an ampll~ier
and loop compensatlon circuit 250 over the line 38.
The output ~romthe ampli~ler and loop compensatlon cir-
15 suit 250 is applied to a kiclcback pulse generator 252over a llne 25~ and to a focus servo loop switch 256
over the line 254 and a second l~ne 258. The output
~rom the kickback pulse generator 252 ls applied to a
driver circult 260 over a line 202. The output ~rom
the focus servc loop switch 256 is applied to the
- driver circuit 260 over a llne 264.
The FM vldeo slgnal is applled from the dls-
tribution amplifler portlon o~ the FM processing sub-
system 32 to a FI~ level detector 270 over the llne
25 66. The output from the FM level detector 270 is ap-
plled to an acquire focus logic circuit 272 over line
274. The output of the FM level detector 270 is ap-
plied as a second alternative input signal to the gener-
ator 252 over a line 275. The output from the acquire
30 ~ocus logic clrcult is applled to the ~ocus servo loop
swltch 256 over a llne 276. A second output slgnal
from the acquire focus loglc clrcuit 272 ls applled to
a ramp generator clrcuit 278 over a llne 280. The
acquire ~ocus loglc clrcuit 272 has as its second input
35 signal the acquire ~ocus enable signal generated by
the ~unctioll generator 1,7 over the line 146. The
output o~ the ramp generator 278 is applied to the
drlver clrcult 260 over a line 281.
The acquire focus enable signal applied to the
1150~336
acquire rOc-ls logic 272 over the line 145 is shown o.,
line A of Figure 6A. ~asicall~, this signal ls a two-
le~el sigial generated by the function generator 47
and haYi~ a disabling lo~ler condition indicated at
282 and an enabli,lg condition indicated ger.erally at
284. The functiorl generator produces this pulse when
the video disc player 1 is in one of its play modes and
it is necessary to read the information stored on the
video disc 5.
Referring to line ~ of Figure 6A, there is
shol-~n a typical ramping voltage waveform generated by
the ramp generator circuit 2~8. During the period of
time corresponding to the disabling portion 282 of the
acquire focus signal, the focus ramp wave~orm is in a
quiescent condition. Coincidental ~ith the turning on
of the acquire ~ocus enable si~nal, the ramp generator
2~8 generates its ramping voltage waveform shown as a
sa-.~Jtooth type output waveform going from a higher
position at 286 to a lo~er position at 288. ThiS is
sholn as a linearl~ cnanging signal and has been found
- to be the most useful waveform for this purpose.
Referring to line C of Figure 6A, there is
shown a representation of the motion of the lens itself
during a number of operatlng modes of the video disc
25 player. Prior to the generation of the acquire focus
enabie signal, the lens is generally in a retracted
positlon indicated generally at 290. Upon the receipt
of the acqulre focus enable slgnal, the lengs begins
to move ln a path indicated by the dash/dot line 292.
30 The dash/dot line 292 begins at a point identifled as
the upper limit of lens travel and moves through an
intersection with a dotted line 294. This point of
intersection ls identifled as the lens in focus posi-
tlon 293. Whell focus is not acquired on the first
35-attempt, the lens continues along th~ dash/dot line
292 to a p~int 295 identi e~ a5 10~Jer lir`~i t Or lens
travel. lJhen the lens reaches point 295, the lens
remains at the lower limit cr lens travel throu~h the
portinn o~ t~.e line indicated generally at 296. The
115083~
~o-
lens continues to follow the dash/dot line to a point
~ndicated at 297 ldentified as the RAMP R~SET point~
This is also shown on line A as 288. ~ur lng the ramp
reset ti~e the lens is drawn back to the upper limit of
lens travel portion Or the waveform as indicated at 298.
In this first mode of operation the lens fails
in its firs~ attempt at acqulring focus. The lens
passes through the lens in rOcus position as indicated
by the dotted line 294. After failing to acquire focus
the lens then moves all the way to its lower limit of
lens travel at 296 before retracting to its upper limit
of lens travel indicated at 298. The upper limit of
lens travel position and the lower li~.it Or lens travel
position are sensed by limit switches in tlle lens driver
subassembly not shown.
Duri~g a successful attempt to acquire focus
the path of lens travel changes to the dotted line
indicated at 294 znd remains there until focus is lost.
The lens is ~ormally one micron above the video disc 5
20 ~hen in the focus position Also the in-focus posi-
~ tion can varT over a range of 0.3 microns.
The output signal fro~ the ramp generator 278to the driver 250 on the line 281 has the configuration
shown on line ~ of Figure 6A.
2~ The ~aveform shown on line G of Figure 6A
shows the wave shape of the signal applied to the FM
level detector 270 over the line 66. The ~lave~orm shown
on line G illustrates two principal conditions. The
open double sided sharp pulse indicated generally at
300 is generated by the signal recovery subsystem 30 as
the lens passes through focus. This is shown by the
vertical line 301 connecting the top of the pulse 300
with the point on line 292 indicatlng that the lens has
passed through the in~focus position as indicated by
its intersection with the dotted line 294. Correspond-
ing to the description previously given ~ith reference
to line C of Figure 6A the lens passes through focus
and the sharp pulse retracts to its no activity level
indicated generally at 302.
8 3
-4;-
I~ the second illustration, the waveform shownon line G Or Flgure 6A lllustrates the output from the
F~ distribution amplirier on t`ne line 56 ~hen the len~
acquires ~ocus. This is indicated by the envelope
generally represented by the crossed hatched sections
between lines 304 and 30S.
Referring to the waveform shown on line H of
Figure 6A, there is shown a dash/dot line 308 repre-
senting the output from the FM level detector 270 corres-
ponding to that situation when the lens does not acquirefocus in its first pass through the lens in focus posi-
tion by line 294 of line C of Figure 6~. The output of
the level detector represented by the dotted iine 311
shows the loss of the FM signal by the detector 270.
1~ The solid line 312 shows the presence of an FM slgnal
detected by the FM level detector when the lens ac-
quires focus. The continuing portlon of the waveform
at 312 indicates that a Frl signal ls available in the
focus servo subsystem 35.
Referring to line I of Figure 6A, there is
~ shown the output char~cteristic of the focus servo loop
switch 255. In the portion of its cperating character-
istics generally indicated by the portion Or the line
indicated at 314, the switch is in the Or, condition
representing the unfocused condition. The position of
the line 316 represents the focused condition. The
vertical transition at 318 indicates the time at which
rOcus is acquired. The operating mode of the video
disc player ~uring the critical period Or acquiring
focus is more ~ullJ described with reference to the
waveforms shown in Figure 6C. Line A of Flgure 6C
represents a corrected differential focus error gener-
ated by the signal recovery system 30 as the lens
follows its physical path as previously described with
3~ reference to line C 3f Figure ~A. At point 319 Or the
waveform A shown in Figure 5C, the difrerential focus
error corresponds to a portivn Or the lens ~ravel during
which no focus errors are available. At the region
indicated at 320, the first false in-focus error signal
15~83
-42-
is available~ There is ftrst a momentary rise in focus
error to a first maximum initial level at point 322.
.'~t pOillt 3~2, the differential rOcus error begins to
rlse in ~he opposlte direction until it peaks at a point
5 324. ~rhe difrerenti~l focus error begins to drop to a
second but opposite maximum at a point 325. At a point
328, halfway between the points 324 and 325, is the
optimum in-focus position for the lens. At this point
328, the lens athers maximum reflected light from the
video disc surface. Continuing past point 326, the
differential focus error begins to fall towards a
second false in-focus condition represented at this
p~int 330. The differential focus error rises past
the ln-focus position to a lower maximum at 332 prior
to falling back to the position at 333 where no focus
error inrorma~ioll iS available. No focus error in-
formation is available because the lens is so close to
the video disc surface as to be unable to distinguish
a difference of the diffused illumination presently
20 bat~ng the two focus detectors.
Referring to line ~, there is shown a waveform
representing the frequency modulated signal detected
from the video disc surface 5 through the lens 17 as
the lens is moving tol~Jards the video disc 5 ln an
attempt to acquire focus. It should ~e noted that the
frequency modulated signal from the video disc 5 is
detected only over a small distance as the lens reaches
optimum focus, and then passes through optimum focus.
This small distance is represented by sha~p peaks 334a
and 334b of the FM detected video as the lens 17 moves
through this preferred in-focus position ~Ihen focus is
missed.
I~Jhlle focus can be achieved using only the
differential focus error signal shown with reference
to line A of Fi~ure 6C, one embodiment of the present
invention utili~es the differential focus error signal
as shown on line A of Figure 6C in combination with
the signal shown on line ~ of Figure Gc to achieve more
reliable acquisition of focus during each attempt at
1~5~836
-~i3 -
f~us.
Figure ~ of line 6C shows an lnverted ideal-
i~ed focus error signal. This ldealized error signal
is tilen differentiated and the results shown on llne D
Or Fi~ure 6C. The differentiation of the ideallzed
focus error signal is represented by the line 339.
Small portions of this line 339 shown at 340 and 342
lyinO above the zero point indicated at 344 give false
indication of proper focusing regions. The region
345 falling under the line 339 and above the zero
ccndition represented by the llne 344 indicates the
range wiihin which the lens should be positioned to
obtain proper and optimum focus. The region 346 repre-
sents approximately 0.3 mlcrons of lens travel and
1~ corresponds to the receipt of an FM input to the FM
level detector as shown in line B. It should be noted
that no Fl'i is shown on line ~ correspondi~ to regions
340 and 342. Xence~ the FM pulse shown on line ~ is
used as a gating signal to indicate when the lens has
been positioned at the proper distance above the
video disc 5 at which it can be expected to acquire
focu~.
The signal representing the differentiation
cr the idealized focus error is applied to the gener-
ator 252 for activating the generator 252 to generate
its kickback waveform. The output from the F~ level
detector 270 is an alternative input to the kickback
generator for generating the ki~kbacl{ waveform ~or
application to the driver 260.
Referring back to line ~ of Figure 6A and
continuing the description of the waveform shown there-
on, the dot/dash portion beginning at 285 represents
the start of the output signal from the ramp generator
27~ for moving the lens through the optimum focusing
3~ range. This is a sawtooth signal and it is calculated
to move the lens smoothly through the point at which
Fr1 is detected b~ the FM level detector 270 as lndi-
cated by the waveform on line H. In a flrst mode of
operation, the focus ramp follows a dot-dash portion
- 1~50836
44
?8/ of the waveform to a p~lnt 287a corresponding to
the ti~e at which the output of the FM level detector
shows the acquisition of ~ocus b~ generatlng the sisnal
le~el at 312a in line I~. The output si~nal from the
5 acquire ~ocus lo~;ic bloclc 272 turns off the ramp ~;en-
erator over the line 280 indicatin~ that rccus has been
acquired. Uhen focus is acquired, the output from t'ne
ra~p generator follows the dash line porticn at 287b
indicating that focus has been acquired.
Referring to line A of Figure 6~, a portion o~7
the focus ramp is shown extending between a first upper
voltage at 285 and a second lower voltage at 288. The
optimum 170cus point is located at 287a and corresponds
with the pe2k of the FM signal applied to the FM
level detector 270 as shown on line C of Fi~ure 6~.
Line P ls a simplified version of the lens position
transfer function 290 as shown more specifically With
reference to line C of Figure 6A. The lens position
transfer func'~io, line 290 extends between an u~per
limlt of lens travel indicated at point 292 and a lower
llr~it of lens travel indicated at point 295. The
optimum lens focus position is indicated b~T a line 295.
The optimum lens focus point is therefore located at
299 .
Referring to line D of Figure 6E, there is
shown the superlmposing of a kickback sawt~oth wave-
form indicated generally ln the area 300 upon the lens
posltion transfer line 292. This indicates that in the
top portion of the three kickback pulses are located at
302, 304 and 306. The lower portion of the three
kickback pulses are located at 308, 310 and 312, re-
spectively. The line 295 again shows the point of
optimum focus. The intersection of the line 296 with
the line 292 at points 296a, 296~, 295c and 296d shows
that the lens itself passes through the optimu~, lens
focus position a plurall'~T of ti~es dul71rlct one acquire
focus enable function.
Referring to line E of Figure 6P, the input
to the FM level oetector indicates that during an
~;
_ .
115083S
-45-
oscillaior~ motlon Or the lens through the optimum
~ocus position as shown by the combined lens travel
functlon characteristic shown in Figure D, the lens
has the opportunity to acquire focus Or t~.e FM si~nal
at rour locations indicated at the peaks Or waveforms
314, 316, 318 and 320.
The waveforms shown with rererence to Figure
6~ demonstrate that the addition Or a high frequenc~
oscillatln~ sawtooth klckback pulse upon the ramping
signal generated by the ramp generator 278 causes the
lens to pass through the optimum lens focus position a
plurality of times or each attempt at acquiring lens
focus. This lmproves the reliability of achieving
proper lens ~ocus during each attempt.
The rOcus servo system employed in the present
invention functions to position the lens at the place
calculated to provide optimum focusing Or the reflected
read spot a~ter impinging upon the information track.
In a first mode of operation, tlle lens servo is moved
under a ramp voltage waveform from its retracted
position towards its fully down position. When focus
is not acquired during the traverse of this distance,
means are provided for automatically returning the
ramping voltage to its original position and retracing
tl~e lens to a point corresponding to the start of the
ramping voltage. Thereafter, the lens automatlcally
moved through lts focus acquire mode of operation and
through the optimum focus position at which focus is
acquired.
In a third mode Or operation, the fixed ramp-
ing waveform ls used in comblnation with the output
rrom an FM detector to stabilize the mirror at the
optimum focus position which corresponds to the point
at which a frequency modulated signal is recovered from
the information bearin~ surface Or the video disc and
an output is indicated at an Fi;i detector. In a further
embodiment an oscillatory waveform is superimposed
upon the ramping voltage to help the lens acquire
proper focus. The oscillatory waveform is triggered
`` ` 115083
-46 -
by a num~er of alternative input signals. A first
such illpUt si~nal is the output from the ~M detector
indicating that the lens has reac~led the optimum focus
point. A second tri6gering signal occurs a fixed time
after the beginning of the ramp voltage ~aveform. A
third alternative input signal is a derivation of the
differential tracking err~r indicating the point at
which the lens is best calculated to lie within the
range at which optimum focus can be achieved. In a
further embodiment of the present invention, the focus
servo is constantly monitoring the presence of FM
in the recovered frequency modulated signal. The focus
servo can maintain the lens ln focus even though there
is a momentary loss of detected frequency modulated
signal. This is achieved by constantly monitoring
the presence o~ FM signal detected rom the video disc.
Upon the sensing of a momentary loss of ~requency
modulated signal, a timing pulse is generated which is
calculated to restart the focus acquire mode of oper-
ation. However, i~f the frequency modulated signalsare detected prior to the termination of this fixed
perlod of time the pulse terminates and the acquire
focus mode is skipped. If FM is lost for a period of
time lon~er thall this pulse, then the focus acquire
mode is automatically entered. The focus servo con-
tinues to attempt to acquire focus until successful
acquisition is achieved.
FOCUS SERVO SU~SYSTEM - NORMAL MODE OF OPERATION
The principal function of the focus servo sub-
system is to drive the lens mechanism towards the video
disc 5 until the ob~ective lens 17 acquires optimum
focus of the light modulated signal bein~ refl2cted
from the surface of the video disc 5. Due to the re-
solving power of the lens 17, the optimum focus point
is located approximately one micron from the disc
surface. The range of ler.s travel at wllich optimum
focus can be achieved is 0.3 microns. The information
bearing surface of the vldeo disc member 5 upon which
the light reflective and light non-reflective members
_. _
-47~-
are pcsitioned, are ortentimes distorted due to imper-
fections in tihe manufacture of the video disc 5. The
video disc 5 is manufactured according to standards
which ~ill make available for use on video disc players
those video disc members 5 having errors which can be
handled by the focus servo system 36.
In a first mode of operation, the focus servo
su~system 3~ responds to an enabling signal telling the
lens driver mechanism when to attempt to acquire focus.
A ramp generator is a means for generating a rampins
voltage for directlng the lens to move from its upper
retracted position down towards the video disc member
5. Unless interrupted by external signals, the ramcing
voltage continues to move the lens through the optimum
focus position to a full lens down position correspond-
ing to the end of the ramping voitage. The full lens
do~n position can also be indicated by a limit switch
which closes ~1'nen the lens reaches this position.
~ The lens acqulre period equals the time of the
ramping voltage. At the end of the ramping voltage
period, automatic means are provided for automatically
resetting the ramp generator to its initial posltlcn at
the start of the ramping period. Operator interven-
tion is not required to reset the lens to lts lens
acquire mode in the preferred embodiment after focus
was not achieved during the flrst attempt at acqulring
focus.
In the recovery of FM video information from
the video dise surface ~, lmperfections on the dlsc
surface can cause a momentary loss of the FM signal
being recovered. A gating means is provlded ln the
lens servo subsystem 36 ~or detecting this loss FM
~rom the recovered FM video signal. This FM detecting
means momentarily delays the reactivation of the ac-
quire focus mode of operation of the lens servo sub-
system 35 fcr a predetermlned time. Duri:;g this pre-
determined time, the reacquisition of the FM slgnal
prevents the FM detector means from causing the servo
subsystem to restart the acquire focus mode of operation.
11~0836
~ ,~
In the event that F~l ls not detected during this flrst
predetermiiled time the FM detector means reactivates
the ramp generator for generating the ramping signal
which causes the lens to rollow through the acquire
fccus procedure. At the end of the ramp generator
period J the FM detector means provides a further
signal for resetting the ramp generator to its initial
position and to follow through the ramping and acquire
focus procedure.
In a third embodiment, the ramping voltage
generated by the ramp generator has superimpcsed upcn
it an oscillatory sequence of pulses. me oscillatory
sequence of pulses are added to the standard ramping
voltage in response to the sensing of recovered F~
from the video disc surface 5. The combination of the
oscillatory waveform upon the standard ramping voltage
is to drive the lens through the optimum focus position
in the direction towards the disc a number of times
during each acquire focus procedure.
In a further embodiment, the generation of
the oscillatory waveform is triggered a fixed time
after the initiation of the ~ocus ramp signal. ~nile
this is not as efficient as USillg the Fi~ level detector
output signal as the means for triggering the oscilla-
tor~r waveform ger.erator it provides reasonable and
reliable results.
In a third embodiment, the osclllatory wave-
form is triggered by the compensated tracklng error
signal.
Referring to Figure 7, there is shown a
schematic block diagram of the signal recovery sub-
system 30. The waveforms shown in Flgure 8, lines P,
C and D, illustrate certain of the electrical waveforms
available within the signal recovery subsystem 30
during the normal operation of the player. Re~erring
to Figure 7, the reflected light beam is indlcated at
4' and is divided into three principal beams. A first
beam impinges upon a first tracking photo detector
lndicated at 330, a second portion o~ the read beam 4'
~150~36`
4~
l~pinges UpOIl a second trackin~ photo detector 382 and
the central information beam ls shown impinglng upon a
concentric rin~ detector indicated generally at 384.
The concentric ring detector 384 has an inner portion
at 386 and an outer portion at 388, respectively.
The output from the first track~n~ photo de-
tector 380 is applied to a first trackin~ preamp 390
over a line 392. The output from the second tracking
photo detector 382 is applied to a second tracking
preamp 394 over a line 395. The output from the inner
portion 386 of the concentric ring detector 384 ls
applled to a first focus preamp 398 over a line 400.
The output from the outer portion 388 of the concen-
tric ring detector 384 is applied to a second focus pre-
amp 402 over a line 404. The output frcm both portions
386 and 388 of the concentric rin~ focusing element 384
are applied to a wide band amplifier 405 over a line
405. Al alternative embodiment to that sho~n would
include a summation of the signals on the llnes 400
20~ and 404 and tne appllcation of this sum to the wide
band ampllfier 405. The showlng of the llne 405 is
schematic in nature. The output from the wide band
ampllfier 405 is the time base error corrected fre-
quency modulated slgnal for application to the FM
25 processing subsystem 32 over the line 34.
The output from the first focus preamp 398
is applied as one input to a dlfferentlal ampllfier
408 over a line 410. The output from the second focus
preamplifier 402 forms the second lnput to the differ-
3 ential amplifier 408 over the line 412. The outputfrom the difrerential ampllfier 408 is the differential
focus error signal applied to the focus servo 36 over
the line 38.
The output from the first tracking preampll-
fier 390 forms one input to a differentlal amplifier414 over a line 415. The output ~'romthe second track-
ing preamplifier 394 forms a secona in,out to trle diffe~
ential amplifier 414 over a line 418. The output from
the differential amplifier 414 is a differentlal track-
-5~- 1150836
in~ error si~nal applied to the trackln~ servo syste-,
o~er the line 4 and applled to the s~op m~tion sub-
system over the line 42 and an additional line 45.
Line A of Fi~ure 8 shows a cross-sectlonal
view taken in a radial directlon across a video dlsc
member 5. Light non-reflective elements are shown a'
11 and intertr~ck regions are shown at lOa. Such int~
traclc re~ions lOa are slmilar ln shape to llght re-
flective elements 10. The ligh~ reflectlve regions 10
10 are planar in nature and normally are hi~hly polished
surfaces, such as a thin aluminum layer. The light n~
reflective regions 11 in the preferred embodiment are
light scattering and appear as bumps or elevations
above the ~7anar surf~ce represented oy the light re-
flective regions 10. The lengths of the line indicatedat 420 and 421 shows the center to center spacing of
two adjacently positioned tracks 422 and 423 about a
center traclc 424. A point 425 ln the line 420 and a
polnt 425 in the llne 421 represents the crossover pclnt
20` between each of the adjacent tracks 422 and 423 ~hen
- leavlng the central track 424 respectively. The cross-
over polnts 425 and 425 are each exactly halfway be-
tween the central track 424 and the tracks 422 and 423
respectively. The end points of line 420 represented
at 427 and 428 represent the center of lnformation
tracks 422 and 424, respectively. The end Or line 421
at 429 represents the center of information track 423.
The waveform shown in line B o~ Figure 8
represents an idealized form Or the ~requency modulat~d
si~nal output derived from the modulated light beam "'
during radlal movement of the read beam 5 across the
tracks 422, 424 and 423. This shows that a maximum
frequency modulated signal ls avallable at the area
indicated generally at 430a, 430b and 430c which
correspond to the centers 427, 42~ and 429 of the in-
formation tracks 422S 42~ an~ 423, reslJectively. A
minimum ~requency modulated si~nal ls av~ilable at
431a and 431b which corresponds to the crossover points
42~ and 426. The waveform shown on line ~ o~ Flgure 3
` ` ` ~150836
-51_
ls generaied by radially moving a focused lens across
the surface Or a vldeo disc 5.
Referrillg to line C of Figure 8, there ls
shown the dlfferentlal tracking error signal generated
ln the differentlal amplifier 414 shown ln Flgure 7.
The differential tracklng error signal ls the same as
that shown ln lil~e A of Figure 6C e~cept for the detalls
shown ln the Figure 6C for purposes Or explanation of
the focus servo subsystem peculiar to that mode of
operation.
Referrlng again to Flgure C of line 8, the
differential tracking error signal output shows a
first maximum traching error at a pOillt indicated at
432a and 432b which is intermediate the center 428 of
an lnformaticn traclc 424 and the crossover point indi-
cated at 425 or 426 depending on the direction of beam
travel frcm the central track 424. A second maximum
tracking erro~ is also shown at 434a and 434b corres-
ponding to a track location interm~dlate the crossover
points 425 and 425 between the informa'ion track 424
and the next adjacent tracks 422 and 423. Minlmum
focus error is shown in line C at 440a, 440b and 440c
corresponding to the center of the information tracks
422, 424 and 423, respectively. Minimum tracking error
signals are also shown at 441a and 441b corresponding
to the crossover points 425 and 426, respectively. This
corresponds with the detailed description given with
reference to Figure 6C as to the importance ~ ldenti-
fying which of the minimum differentlal tracking error
signal outputs corresponds with the center of track
location so as to insure proper focusing on the center
of an information track and to avoid attempting to
focus upon the track crossovers.
Referring to line D of Figure 8, there ls
shown the differential focus error si~nal output wave-
form generated by the differenti~l amplifier 408. The
waveform is indicated generally by a line 442 which
moves in quadrature with tne differential tracking
error signal silown with reference to line C of Figure 8.
115(~836
--5~--
Rel'erring to Fl~ure 9, there ls shown a
schematic block dia~ram of the tracking servo subsystem
40 emplo~red ln the vldeo disc pla~er 1. The dlfferen-
tial trackins error ls applled to a trackln~ servo loop
5 lnterrupt swltch 4SO, over the llne 46 fro~ the signal
recovery system 30. The loop lnterrupt signal ls ap-
plied to a gate 482 over a llne 108 from the stop
motion subsystem 44. An open fast loop command slgnal
ls applied to an open loop fast gate 484 over a line
180~ from the function generator 47. As previously
mentioned, the function generator includes both a re-
mote control unit from which commands are received and
a set of console switches from which commands can be
received. Accordingly, the command signal on line
15 180b is diagra~matically shown as the sa~e signal
applled to the carriage servo fast forward current
generator over a line 180b. The console s~itch is
shown entering an open loop fast gate 48~ over the line
~ 180b ' . The fast reverse command from the remote con-
20 trol portion of the function generator 47 is appliedto the open loop ~ast gate 484 over the line 180b.
The fast reverse command from the console portlon of
the function generator 47 is applied to the open loop
fast gate 486 over the line 180b ' . The output from the
25 gate 484 is applied to an or gate 488 over a line 490.
The output from the open loop fast gate 480 is applied
to the or gate 488 over a line 492. The first output
from the or gate 488 is applied to the audio processing
system 114 to provide an audio squelch output signal on
3 the line 116. A second output from the or gate 488 ls
applied to the gate 482 as a gating signal. The output
from the tracking servo open loop switch 480 is applied
to a ~unction 496 connected to one side ~ a resistor
498 and as an input to a tracking mirror amplifier
driver 500 over a line 505 and an ampllfier and fre-
quenc~r compens~t1on network 510. The other end of th~
resistor 498 is c onnected to one side of a capacitor
502. The other side of the capacitor 502 is connected
to ground. The amplifier 5C0 receives a second input
115~)836
-53-
si~r.al from the stop motion subsystem 44 over the llne
106. The slnal on tne line 106 is a stop motlon com-
pensation pulse.
The fuilction of the amplifier 510 is to provide
a DC component of the trackln~ error, developed over
the combination of the resistor 498 and capacitor 502,
to the carriage servo system 55 during normal tracking
periods over a line 130. The DC component from the
junction 496 is gated to the carriage servo 55 by the
play enabling signal from the function generator 47.
The push/pull amplifier circuit 500 generates a first
trac~ing A signal for tlle radial tracking mirror 28 over
the line 110 and generates a second tracking ~ output
signal to the radial tracking mirror 28 over the line
112. The radial mirror requires a maximum of 600 volts
across the mirror for maximum operating efficiency when
bimorph type mirrors are used. Accordingly, the pùsh/
pull amplifier circuit 500 comprises a pair of ampli-
fier circuits, each one providing a three hundred
volta~e swing for driving the tracking mirror 28.
~ Together, they represent a maximum of six hundred volts
peak to peak signal for application over the lines 110
and 112 for controlling the operation of the radial
tracking mirror 28. For a better understanding of the
tracking servo 40, the description of its detailed
mode of operation is combined with the detalled descrip-
tion of the operation of the stop motion subsystem 44
shown with reference to Figure 12 and the waveforms
shown in Figures 13A, 13~ and 13C.
TRACKING SERVO SUPSYSTEM - NO~MAL MODE OF OPERATION
The video disc member 5 being played on the
video disc player 1 contains approximately eleven
thousand information tracks per inch. The distance
from the center of one information track to the next
ad~acent information trac~ is in the range ~ 1.6
microns. The informalion indicia al~gned n an informa-
tion track is approximately 0.5 microns in width. This
leaves approximately one micron of empty and open space
bet~een the cutermost reGions of the indicia positioned
54 llS0836
in adjacent ir.formation bearing tracks.
The function of the tracklng servo ls to
direct the impin~ement of a focused spot of llght to
impact directl~J upon the center Or an information track.
5 The focused spot of light ls approximately the same
wl~th as the inrormation bearing sequence of lndlcia
which form an information track. Obviousl~, maximum
signal recovery ls achieved when the focused beam of
llght ls caused to travel such that all or most of
the light spot impinges upon the successively positioned
light reflective and light non-reflectlve regions of
the lnformation track.
The tracking servo is further identified as
the radlal tracking servo because the departures from
15 the lnformation track occur in the radial direction
upon the disc surface. The radial tracking servo is
continuously operable in the normal play mode.
The radial tracking servo system is interrupted
or released frcm the differential tracking error signal
20 generated from the FM video information signal recov-
ered from t;le video disc 5 in certain modes of oper~-
tion. In a first mode ~ operation, when the carriage
servo is causing the focused read beam to radially
traverse t'ne information bearing portion of the video
25 disc 5, the radial tracking servo system 40 is released
from the effects of the differential tracking error
signal because the radial movement of the reading beam
is so rapid that tracking is not thought to be neces-
sary. In a ~ump back mode of operation wherein the
3 focused reading beam 4 is caused to ~ump from one track
to an ad~acent track, the differential tracking error
is removed from the radial tracking ser~-o loop for
ellminating a signal from the tracking mirror drivers
which tend to unsettle the radlal mirror and tend to
35 require a longer period of time prior for the radizl
trqc~{ing ~ervo subs~Jstem to reacquire proper tracking
of the neYt adjacent informatioll track. In this embod-
iment of operation where the differential tracking error
is removed from the tracking mirror drivers, a substitute
_55_ 1~50836
pulse is genera~ed for giving a clean unambiguous slgnal
to t!le tracking mirror drivers to direct tl~e tracking
mirror to move to itS next assigned location. This
signal in the preferred embodiment is identified as
the stop motion pulse and comprises regions Or pre-
emphasis at the beginning and end of the stop motion
pulse which are tailored to direct the tracking mirror
drivers to move the focused spot to the predetermined
next traclc location and to help maintain the focused
spot in the proper tracking position. In review, one
mode ~ operation Or the video disc player removes the
differential tracking error signal from application to
the trac~cing mirror drivers and no additionPl signal
is substituted therefor. In a further embodiment of
operation o~ the video disc player, the differential
tracking error signal is replaced by a particularly
shaped stop motion pulse.
In a still further mode of opera'ion of the
tracking mirror servo subsystem 40, the stop motion
pulse which is employed for directing the focused
beam to leave a flrst information traclc and depart for
a second adjacent information track is used in combina-
tion with a compensatlon signal applied directly to the
radial tracking mirrors to direct the mlrrors to main-
~ain focus on the next adjacent track. In the preferr~embodir,ent, the compensation pulse is applied to the
tracking mirror drivers after the termination of the
stop motion pulse.
In a still further embodiment of the tracking
servo subsystem 40s the differential tracking error
signal is interrupted for a period less than the time
necessary to perform the stop motion mode of operation
and the portion Or the differential tracking error
allowed to pass into the tracking mirror drivers is
calculated to assist the radial traclcing mlrrors to
achie~Je proper radial tracking.
Re~erring to Figure 11, there is shown a block
diagram of the tangential servo subsystem 80. A first
input signal to the tangential servo subs~Jstem 80 is
115~836
--,6--
applled from the FM processing system 32 over the line
82. The signal present on the line 82 is the video
signal available frcm the vodeo distribution ampli-
fiers as contained in the FM processing system 32. The
video sigllal on the line 82 is applied to a sync pulse
separator circuit 520 over a line 522 and to a chrom~
separa~or filter 523 over a line 524. me video signal
on the line 82 is also applied to a burst gate separa-
tor circuit 525 over a line 525a.
The function of the vertical sync pulse separ-
ator circuit 520 is to separate the vertical sync
signal from the video signal. The vertical sync signal
is applied to the stop motion su~system 44 over the
line 92. The function of the chroma separator filter
523 's to separate the chroma portion fro~ the total
video si~nal received from the Fl~ processing circuit 32,
The output from the chroma separator filter 523 is ap-
plled to the FM corrector portion of the FM process-
~ ing circuit 32 over the line 142. The output signal
from the chroma separator filter 523 is also applied
to a burst phase detector circuit 526 over a line 52~.
The burst phase detector circuit 526 has a second input
signal from a color subcarrler oscillator circuit 530
over a llne 532. The p~rpose of the burst phase de-
tector circuit 526 is to compare the instantaneousphase of the color burst signal with a very accurately
generated color subcarrier oscillator signal generated
in the oscillator 530. The phase difference detected
in the burst phase detector circult 526 is applied to a
sample and hold circuit 534 over a line 535. The
function Or the sample and hold circuit is to store a
voltage equivalent of the phase difference detected in
the burst phase detector circuit 526 for the tlme during
which the f'ull line of video information containing
that color burst signal, used in generatin~ the phase
difference, is read from the disc 5.
The purpose of the burst gate separator 525
ls to generate an enabling signal lndicating the time
during which the color bu-st portion Or the video
l tS0836
-57-
waverorm is received from the FM processing unit 32.
The output ignal from the burst gate separator 52
is applied to the FM corrector portion Or the FM
processing system 3~ over a llne 144. The same burst
5 ~ate timinG sig~al is applied to the sample and hold
circuit 54 over a line 538. The enabling signal on
the line 53S gates the input from the burst phase de-
tector 526 into tlle sample and hold circuit 534 during
the color burst portion of the video signal.
The color subcarrier oscillator circuit 530
applies the color subcarrier frequency to the audio
processing circuit 114 over a line 140. The color
s~bcarr~er oscillator circuit 530 supplies the color
subcarrier frequency to a divide circuit 540 over a
line 541 which divides the color subcarrier frequency
by three hundred and eighty-four for generating the
motor reference frequency. The motor reference fre-
quency signal is applied to the spindle servo subsystem
~0 over the line 94.
The output from the sample and hold circuit
~ 53l' is applied to an automatic ~ain contrclled ampli-
fier circuit 542 over a line 544. The automatic gain
controlled amplifier 542 has a second input signal from
the carriage position potentiometer as applled thereto
over the line 84. The function of the signal on the
line 84 is to change the gain of the amplifier 542 as
the reading beam 4 radially moves from the inside track
to the outside track and/or conversely h~hen the reading
beam moves from the outside track to the inside track.
The need for this adjustment to change with a change in
the radial position is caused by the formation of the
reflective regions 10 and ..on-reflective regions 11
with different dimensions from the outisde track to the
lnside track. The purpose of the const~nt rotational
speed from the spindle motor 48 is to turn the disc 5
t'nrough nearly thirty revol~tions per second to provide
thlrty frames of in~ormation tothe television receiver
96. me length of a track at the outermost circum-
ference is much longer than the length of a track at
li501~36
-5~
tlle innermost circumrerence. Since the same amount of
lnformation is stored in one revolution at ~cth the
inner and outer circumfere~ce~ the si~e Or the reflec-
tive and non-reflective re~ions 10 and 11, respectively~
are adjusted from the inner radius to the outer radius.
Accordingly, this change in size requires ~hat certain
adjustmentsin the processing of the detected signal
read from ihe video disc 5 are made for optimum opera-
tion. 0ne of the required adjustments is to adjust the
gain of the amplifier 542 which adjusts for the time
b~se error as t!~e reading pOiilt radially changes from
an inside to an outside circumference. The carriage
position potentiometer (not shown) generates a suffi-
ciently accurate reference voltage indicating the
radial position of the point of impingement of the
reading beam 4 onto the video disc 5. The output from
the amplifier 542 is applied to a compensation circuit
545 over a line 5~6. The compensation netv:ork 545 is
employed for preventing any system oscillations and
instability. The output from the compensation network
545 is applied to a tangential mirror dr~ver circuit
500 over a line 550. The tangential mirror driver
circuit ~00 was described with reference to Figure 9.
The circuit 500 comprises a pair of push/pull ampll-
fiers. The output from one ~ the push/pull amplifiers
(not shown) is applied to the tangential mirror 26
over a line 88. The output fromthe second push/pull
ampllf~er (not sho~1n) ls applied to the tangential
mirror 2~ over a llne 90.
TIME ~ASE ERROR CORPECTION MODE: OF OPERATION
,
The recovered FM video signal, from the surfaceof the video disc 5 is corrected, for time base errors
introduced by the mechanics Or the reading process, in
the tangential servo subsystem 80. Time base errors
are introduced into the reading process due to the
minor imperfections in the video disc 5. A time base
error introduces a slight phase change into the re-
covered F~ video signal. A typical tlme base error
base correction system includes a highly accurate
115(~836
-59 -
oscillator for generating a source of slgnals used as
a phase standard for comparlson purposes. In the pre-
ferred embodimentJ the accurate oscillator is conven-
iently chosen to oscillate at the color subcarrier
frequency. T:~e color subcarrier rrequency is also
used during the wrlting process for controlling the
speed of revolution of the writing disc during the
writing process. In this manner, the reading process
is phase controlled by the same highl~J accurate oscil-
lator as was used in the writing process. The outputfrom the highly controlled oscillator is compared with
the color burst signal of a Fr~ color video signal. An
alternative system records a highly accurate frequency
at any selected frequency during the writing process.
During the reading process, this frequency would be
compared ~ith a highly accurate oscillator in the player
and the phase difference between the t~o signals is
sensed and is employed for the same purpose.
The color burst slgnal forms a small portion
of the recovered FM video signal. A color burst signal
is repeated in each line of color T.V. video information
in the recovered FM video signal. In the preferred
embodiment, each portion of the color burst signal is
compared ~.~ith the highly accurate subcarrier oscillator
signal for detecting the presence of any phase error.
In a different embodiment, the comparison may not occur
during each availability of the color burst signal or
its equivalent, but may be sampled at randomly or pre-
determined locations in the recovered signal containing
the recorded equivalent of the color burst signal.
~en the recorded information is not so highly sensi-
tive to phase error, the comparison may occur at greater
spaced locations. In general, the phase di~ference
between the recorded signal and the locally generated
signal is repetitively sensed at spaced locations on the
recording surface for adjusting for phase rrors in the
recovered signal. In the preferred embodiment this
repetitive sensing for phase error occurs on each line
of the FM video signa.
~1~W836
-6~-
The detected phase error ls stored for a
period of time extendin~ to the next sampllng process.
This phase error ls used to ad~ust the readlng posl-
ticn of ~le reading beam so as to lmpinge upon the
vldeo dlsc st a locatlon such as to correct for the
phase error.
Repetitlve comparison of the recorded signal
with the locally generated, highly accurate frequency,
contlnuousl~ ad~usts for an incremental portion of the
recovered video signal recovered durlng the sampllng
periods.
In the preferred embodiment, the phase error
changes as the reading beam radially tracks across the
information bearing surface portion of the video disc 5.
In this embodiment, a further si~nal is required for
ad~usting the phase error according to the lnstan-
taneous location of the reading beam to adjust the
phase error according to its lnstantaneous locatlon on
the lnformation bearlng portion of the video disc 5.
This addltional signal ls caused by the change ln
ph~Jsical slze of the lndicia contalned on the video
disc surface as the radlal tracking posltion changes
from the inner location to the outer locztion. The
same amount of informatlon is contained ~t an inner
radius as at an outer radlus and hence the lndicia must
be smaller at the inner radius when compared to the
lndlcia at the outer radlus.
In an alternatlve embodiment, when the size
of the indlcia ls the same at the lnner radlus and at
the outer radius, this additlonal slgnal for adjustlng
for lnstantaneous radlal positlon ls not required.
Such an embodiment ~ould be operable with vldeo disc
members which are in strip form rather than ln disc
form and when the informatlon ls recorded uslng lndicla
3~ of the same size on a vldeo dlsc member.
In the pre~erred embodiment, a tangentlal
mirror 26 ls t~le mechanism selected for correcting the
time base errors introduced by the mechanlcs ~ the
reading system. Such a m~rror is electronically
1150836
-5:1-
controlled and ls a means for changlng the phase ~ the
recovered video signal read from the dlsc by changing
the time base on which the signals are read from the
disc. This is achieved by directing the mirror to
read the information from the disc at an incremental
point earlier or later ln tine when compared to the
time and spacial location during which the phase error
~:~as detected. The amount of phase error determines
the degree of chan~e in location and hence time in which
10 the information ls read.
~ hen no phase error is detected in the time
base corr4cting system the point Or i~pingement of the
read beam with the video disc surrace 5 is not moved.
l~hen a phase error is detected during the comparison
15 period, electronics signals are generated for changing
the point of impingement so that the recovered informa-
tion from the video disc is available rOr processing
at a point in time earlier or later when compared to
~ the comparison perlod. In the preferred embodiment,
this is achieved by changing the spacial location of
the point of intersection of the read beam ~ith the
video disc surface 5.
Re~erring to Figure 12, there is shown a block
diagram of the stop motion subs~stem 44 employed in
the video disc player 1. The ~aveform shown with
reference to Figures 13A, 13B and 13C are used in
conJunction with the block diagram shown in Flgure ~2
to explain the operation of the stop motlon system.
The video signal from the FM processing unit 32 is
3 applied to an input buffer stage 551 over the line 134.
The output signal from the burrer 551 is applied to a
DC restorer 552 over a line 554. The function Or the
DC restorer 552 is to set ~he blanking voltage level
at a constallt uniform level. Variations in signal
recording and recover~J oftentimes result in video
signals available on the line 134 with dirrerent blank-
ing levels. The output from the DC restorer 552 is
applied to a wllite flag detector circuit 55O over a
line 558. The runction Or the wnite flag detector 556
11$~836
is to idellti~ the presence of ar. all whlte 'evel v~deo
s~gn~l existin~ during an entire line of one or both
fields contained in a frame Or television information.
'~'hile the white 1'1ag detector has been described 2S
being detectin~ an all white video signal durlng a
complete line interval of a frame of television in-
formation, the white flag may take otller forms. Cne
such form would be a special number stored in a line.
Alternativel~, the white flag detector can respond to
the address indicia found in each video frame for the
same purpose. Other indicia can also be employed. How-
ever, the use of an all white level signal during an
entire line interval in the television frame of in-
formation has been found to be the most reliable.
The vertical sync signal from the tangential
servo 80 is applied to a delay circuit 550 over a line
92, The output from the delay circuif 560 is supplied
to a vertical window generator 552 over a line 5~4.
~ The function of the window Oenerator 5S2 is to gener-
20 ate an enabling signal for application tothe white flag
detector 55~ over the line 55~ to coincide with that
line interval in which the white flag signal ha~ been
stored. The output signal from the generator 5~2
gates the predetermined ~rtion of the video sign 1
from-the Fl~ detector and generates an output white
flag pulse whenever the white flag is contained in the
portion of the video signal under surveillance. The
output from the white flag detector 556 is applied to a
stop motion pulse generator 567 over a line 558, a gate
30 569 and a further line 570. The gate 569 has as a
second input signal, over the line 132, the STOP MOTION
~ODE enabling signal from the function generator 47.
The differential tracking error from the signal
recovery subsystem 30 is applied to a zero crossing
detector and delay circuit 571 over the lines 42 and
45. The function o~ the zero crossing detector circuit
571 is to identify when the lens crosses the mid-points
425 and/or 425 between two ad~acent tracks 424 ~nd 423.
~ :1508~6
-~3 -
It ~ important to note that the dlrferentlal tracklnG
si~nal output also indlcates the same level signal at
polnt 440c which identifies the optlmum focusing point
at which the tracking servo system 40 seeks to position
the lens in perfect tracking aligrlment on the mid-point
429 Or the track 423 when the tracklng suddenly ~umps
from track 42~ to track 423. Accordingly, a means
must be pro-~ided for recogni~ing the dif~erence between
points 4~1b and 440c on the differential error signal
10 shown in line C of Figure 8.
The output of the zero crossing detector and
delay circuit 571 is applied to ~he stop motion pulse
generator 5~7 over a line 572. The stop motion pulse
genera~ed in tlle generator 567 is applied to a plurality
o~ locati~ns the first Or ~Jhich is as a loop interrupt
pulse to the trackin~ servo 40 over the line 108. A
second output sigr,al from the stop motion pulse gener-
ator 5~7 is applied to a stop motion compensation se-
quence generator 573 over a line 574a. The function of
the stop motio!l compensation sequence generator 573
is to generate a compensation pulse waveform for appli-
cation to the radial tracking mirror to cooperate with
the actual stop motion pulse sent directly to the track-
ing mirror over the line 104. The stop motion compen-
sation pulse is sent to the tracking servo over theline 10~.
~ ith reference to line A of Figure 8, the
center to center dlstance, indicated by the line 420,
between adjacent tracks is presently fixed at 1.6
microns. The tracking servo mirror gains sufficient
inertia upon receiving a stop motion pulse that the
focused spot from the mirror ~umps from one track to
the next ad~acent track. The inertia of the tracking
mirror under normal operation conditions causes t~e
mirror to s~ing past the one track to be ~umped.
Briefl-~J, the stop motion ~uise on the line 104 causes
the radial tracking mirror 2~ to leave the track on
hich it is tracking and ~ump ~o the next sequential
track. A short time later, the radial tracking mirror
ilsds~6
-~4-
re~eives a stop motion compensation pulse to remove the
added inertia and direct the tracklng mlrror into
tra~king the next aàjacent track wl~hcut skipping one
or more tracks before selecting a track for tracking.
In order to insure the optimum cooperation
betlleen the stop motion pulse from the generator 567
and the stop motion compensation pulse frcm the gener-
ator 573 the loop interrupt pulse on line 108 is sent
to the tracking servo to remove the di~rerential
trackil2 error signal from being applied to the track-
ing error amplifiers 500 during the period of time
that the mirrcr is purposely caused to leave one track
und~r direction of the stop motion pulse from the
generator 5~7 and to settle upon a ne;~t adjacent track
under the direction of the stop motion compensation
pulse from the generator 573.
As an i~.troduction to the detail understand-
ing of the interaction between the stop motion system
~ 44 and the tracking servo system 40 the waveform
s~lown in Figures 13A 13~ and 13C are described.
Refer.ing to line A of Figure 13A there is
shown the normal tracking mirror drive signals to the
radial trackin& mirror 28. As previously discussed
there are two driving si~nals applied to the tracking
mirror 28. The radial tracking A signal represented
by a line 574 and a radial tracking ~ signal represented
by a line 575. Since the information track is normally
in the shape Or a spiral there is a continuous track-
lng control signal being applied to the radial tracking
mirror for following the spiral shaped configuration
of the information track. The time frame of the
information shown in the waveform shown in line A
represents more than a complete revolution of the disc.
A typlcal normal tracking mirror drive signal waveform
for a single revolution of the disc is represented by
the lengt!l of the line indicated at 57~. The two dis-
continuities s~owll at ~78 and 580 on waveforms 574 and
575 respectively indicate the portlon of the normal
trackin~ period at which a stop motion pulse is given.
liS083~
. , .
-s5-
The stop motlon pulse is also referred to as a Jump
back slænal and these two terms are used to describe
the outpu~ rom the gener tor 567. me stoo motion
pulse is represented b~J the small vertical'~ dlspose~
discontinuity present in the llnes 574 and 575 at
polnts 578 and 580, respectively. The rem2~n ~g wave-
forms contained in Figures 13A, 13~ and 13C are on an
expanded time base and represent those electrlcal
signals which occur ~ust before the beginning of thls
Jump back perlod, through the ~ump back perlod and
continulng a short duration beyond the ~ump back period.
The stop motion pulse generated by tne stop
motlon pulse generator 5S7 and applled to the tracking
servo system 40 over the llne 104 ls represented or.
line C o~ Figure 13A. The stop motion pulse ls ide~lly
not a squarewa~e but has areas of pre-emphasis located
generall-~ at 582 and ~84. These areas o~ p.e-emphasls
insure ~timum reliability ln the stop motion system
44. The stop motion pulse can be described as rlsing
to a first higher voltage level during the inltlal
period of the stop motion pulse perlod. Next, the
stop motlon pulse gradually falls o~f to a second
voltage level, as at 583. m e level at 583 is ma'n-
tained during the duratlon o`f the stop motion pulse
period. At the termination o~ the stop motion pulse,
the waveform falls to a negztive voltage level at 585
below the zero voltage level at 586 and rises gradually
to the zero voltage level at 586.
Line D of Flgure 13 represents the d~f~eren-
3 tial tracking error signal received ~rom the recover~system 30 over the llnes 42 and 46. The wave~orm
shown on line D of Figure 13A is a compensated differ-
entlal trackin~ error achieved through the use o~ the
comblnatlon of a stop motion pulse and a stop motlon
compensatlon pulse applied to the radial trac~ing
mirror 28 according to the teachlr.g o~ the present
lnventlcn.
Line G o~ Figure 13A represents the loop inte~
rupt pulse generated by the stop motlon pulse 2enerator
~,, l iS~)836
5~7 and applied to the tracl;ills servo subs~stem 40 over
the line loS. A~ previously mentioned, lt ls best to
remove the differentlal tracking error sign~l as repre-
sented b~ the waveform on line D from appllcatlon to
the radial tracking mirror 28 during the stop motion
interval period. The loop lnterrupt pulse shown
line G achieves this gatlng function. However, by
lnspection, it can be seen that the differential
tracking error slgnal lasts for a period longer than
the loop interrupt pulse shown on line G. The waveform
sho~n on line E is the portion of the differential
tracking error signal shown on line D which survives
the gatlng by the loop interrupt pulse shown on line G.
~he waveform shown on line E is the compensated track-
ing error as ir.terrupted by the loop interrup~ pulsewhich is applied to the tracking mirror 28. Referrlng
to line F, the high frequency signal represented gener-
ally under the bracket 590 indicates the output waveform
of the zero crossing detector circuit 571 in the stcp
motion system 44. A zero crossing pulse is generated
each time the di ferential error tracking slgnal sho~n
in line D of Figure 13A crosses through a zero bias
level. I~ile the information shown under the bracket
590 is helpf ul in maintaining a radial tracking mirror
28 in traclsing a slngle information track, such in-
formation must be gated off at the beginning of the
stop motion interval as indicated by the dashed lines
592 connecting the start of the stop motion pulse in
line C of Figure 13A and the absence of zero crossing
3 detector pulses shown on line F of Figure 13A. ~y
referrin~ again to line D, the differential tracking
error signal rises to a first maximum at 594 and falls
to a second opposite but equal maximum at 596. At
point 598, ~IIe tracking mirror is passing over the
zero crossing point 426 between two ad~acent tracks 424
and 423 as shown witll re~erence f o line .~ of Fi~ure 8.
This means that the mirror has traveled half way ~rom
the first track 424 to tlle second track 423. At thls
point indlcated by ~he number 598, the zerc crossin~
1150836
-67-
detector generates an output pulse indicated at 600.
The output pulse 600 terminates the stop motion pulse
shown on line C as represented by the vertical line
segment 602. This termination of the stop motion pulse
starts the negative pre-emphasis period 584 as pre-
viously described. The loop interrupt pulse is not
affected by the output 600 of the zero crossing de-
tector 571. In the preferred embodiment, improved
performance is achieved by presenting the differential
tracking error signal from being applied to the radial
tracking mirror 28 too early in the jump back sequence
before the radial tracking mirror 28 has settled down
and acquired firm radial tracking of the desired track.
As shown b reference to the waveform shown in line F,
the zero crossing detector again begins to generate
zero crossing pulses when the differential tracking
error signal reappears as indicated at point 604.
Referring to line H of Figure 13A, thereis shown a
waveform representing the stop motion compensation
sequence which begins coincidental with the end of the
loop interrupt pulse shown on line G.
Referring to Figure 13B, there is shown a
plurality of waveforms explaining the relationship
between the stop motion pulse as shown on line C of
Figure 13A, and the stop motion compensation pulse
waveform as shown on the line H of Figure 13A and re-
peated for convenience on line E of Figure 13E. The
compensation pulse waveform is used for generating a
differential compensated tracking error as shown with
reference to line D of Figure 13E.
Line A of Figure 13B shows the differential
uncompensated tracking error signal as developed in
the signal recovery subsystem 30. The waveform shown
om Figure A represents the radial tracking error signal
as the read beam makes an abrupt departure from an
information track on which it was tracking and moves
towards one of the adjacent tracks positioned on either
side of the track being read. The normal tracking
error signal, as the beam oscillates slightly down the
lSV~3 6
-5~ -
i~formatio~l tracl;~ ls sho~n at the region 610 Or Llne A.
- The tracking error represents the slight side to side
(radial) ~otion of the read beam 4 to the successively
positiored reIlective and non-reflecti~e reglons on the
disc 5 as prevlously described. A point 612 represents
the star~ of a stop motion pulse. The uncompensated
trac~ing error 1~ increasing to a first maximum indi-
cated at 514. The region between 612 and 614 shows an
increase in tracking error ind~cating the departure
of the read beam from the track being read. From point
61~ the dirferential tracking error signal drops to a
pcint indicated at 616 which represents the mid-poir.t
of an information track as shown at point ~2s in line A
Or Figure 8. Hot~ever the distance traveled by the
read beam between poi.nts 512 and 616 on curve A in
Figure 13E is a movement o~ o.8 microns and is equal
to lengtll of line 617. The uncompensated radial trao~:-
ing error rises to a second ma.~imum at point 618 as the
read beam begins to approach the neY~t ad~acent track
20 423. The tracking error reaches zero at point 622
but is unable to stop and continues to a new maximum
at 624. The radial track~ng mirror 28 possesses suffi-
cient inertia so that it is not able to instantaneously
stop in response to the differential trackir.g error
signal detecting a zero error at point 622 as the read
beam crosses the next adjacent information track.
Accordingly the raw tracking error increases to a
point indicatcd at 624 wherein the closed loop servo-
ing effect of the tracking servo subsystem slows the
30 mirror do~n and brings the read beam back towards the
lnformation track represented by the zero crossing dif-
ferential tracking error as indica~ed at point 625.
Addltional peaks are ldentifled at 626 and 628. These
show a gradual damping of the differential tracking
35 error as the radial tracklng mirror becomes graduall~
positicned in its proper location to generate a zero
tracking error such as at points 612 622, 625. Addi-
tlonal zero crossing locations are indicated at 630 and
632. The po~tion of tne wavefo~m shot~n in line A
1~5081~6
59
e.~isting arter point 632 shows a gradual return of the
raw tracking error to its ~ero positlon as the read
spot gradually comes to rest on the next ad~acent track
423.
Point ~16 represents a ralse indication of
~ero tracki!l~ error as the read beam passes over the
cer.ter 425 of t'ne region between ad~acent tracks 42
anà 423.
For optimum operation in a stop motion situa-
tior. wnerein the read beam ~umps 'o the ne~t adjacent
trac~, the time allowed for the radial tracking mirror
28 to reacquire proper radial tracking is 300 micro-
seconds. This is indicated b~r the length of the line
634 sho~ln on line ~. ~y observation, it can be seen
that the radial tracklng mirror 28 has not yet reac-
quired zero radial error position at the expiration of
tlle 300 microsecond time period. Obviously, if more
time ~ere available to achieve tllis result, the wave-
~ ~crm shown wlth re~erence to Figure A would be suitable
~or those systeMs having more time ror the radialtrac~ing mirror to reacquire zero differential trackin~
error on the center of the next adjacent track.
Re~erring briefly to line D o~ Figure 13,
line 634 is redrawn to lndicate that the compensated
radial tracking error signal shown in line D does not
include those large peaks shown with re~erence to
line A. The compensated di~rerential tracl~ing error
shown in line D is capable of achieving proper radial
tracking by the tracking servo subsystem within the
3 time frame allowed ror proper operation Or the video
disc player 1. Referring briefly to line E Or Figure
13A, the remaining tracking error signal available a~ter
interruption b~y the loop interrupt pulse is o~ the
proper direction to cooperate with the stop motion
compensatlon pulses descrlbed hereinarter to brlng the
radial ~rac';_ng mirrcr ~o ~ts op~imllm ra~ial trackin~
position as soon as possible.
The stop motion compens~tion generator 573
shown wlth reIerence to F~gure 12, applies the wave~orm
7~, ~150836
sho~n in line E of Figure 13E to the radlal trackin~
mirror 28 b~y ~ay of the line 10~ and the amplifier 500
sho~n ir. Figure 9. The stop motion pulse directs the
radi~l tr~cking mirror 28 to leave the tracking of one
information track and begin to seek the tracklng of the
next ad~acent track. In response to the pulse from the
zero crossing detector 571 sho~n in Figure 12, the stop
motion pulse generztor 557 is caused to generate the
stop motion compensation pulse s'nown in line E.
lC Referring to line E of Figure 13E, the stop
motioll co~pensation pulse waveform comprises a plural-
ity of individual and separate regions indicated at
540, 542 and 544, respectively. The fi~t region 540
of the stop motion compensation pulse begins as the
15 differential uncompensated radial tracking error at
point 515 cross the zero reference level indicating
that the mirror is in a mid-track crossing situation.
At this time, the stop motiorl pulse generator 557
generates the first ~ortion 540 of the compensation
20 pulse ~.~hich is applied directly to the tracking mirror
2~. The generation of tl~e flrst portion 640 of the
stop motion compensation pulse has the effect of re-
ducing the peak 624 to a lo~ler radial tracking displace-
ment as represented by the ne~ peak 524 ~ as shown in
line ~. It should be kept ln mind that the waveforms
sholln in Figure 13B are schematic only to show the
overall lnterrelationship of the various pulses used
in the tracking servo subsystem and the stop motion
subsystem to cause a read beam to ~ump from one track
30 to the next adjacent track. Since the peak error 624
is not as high as the error at peak 624, this has the
effect of reducii~ the error at peak error point 526
and generally shifting the remainlng portlon of the
~Javeform to the left such that the rero crossings at
35 ~2~', 630' and 632' all occur sooner than they would
have occurred ~Jit;lout the presence of the stop motion
compensation pulse.
~ eferring back to llne E of Fl~ure 13~, the
second portion 642 of the stop motion compensatlon
. .. .
8 3 6
-7i-
pulse is of a second polarlty when compared to the
rirst region S40. The second portlon 642 of ~he stop
motion compensation pulse occurs at a polnt in time
to compensate for the tracking error shown at 626' of
line ~. This results in ar. eYen smaller radial track-
ing error being generated at that time and this smaller
radial tracking error is represen~ed as point 526" on
line C. Since the degree of the radial tracking error
represented by the point 626" of line C is significantly
smaller than that sllown with reference to point 626'
Or ;ine ~, the maximum error in the opposite direction
shown at poir.t 525' is again significantly smaller
than that represented at point 625 of line A. This
counteracting of the natural tendency of the radial
trackinO mirrcr 2~ to oscillate baclc and forth over
the information track ls furtller dampened as indicated
b~ the furth2r movement to the left of points 628" and
525 with reference to their relative locations show
in lines P and A.
Referring again to line E of ~igure 13~ and
the t'ni~d region 544 of the stop motion compensation
pulse, this region 644 occurs at the time calculated
to dampen the remaining long term traclcing error as
represented that portion of the error signal to the
ri~ht of the zero crossin~ point 532" shown in line C.
Region 644 is shown to be approximately equal and
opposite to this error signal which would exist if the
portion 644 of compensation pulse did not exist. Re-
ferring to line D of Figure 13~, there is shown the
differential and compensated radial tracking error
representative of the motion Or the light beam as it
is caused to depart from one information track being
read to tlle next adjacent traclc under the control of
a stop motion pulse and a stop motion compensation
pulse. It should ~e noted that the waveform shown in
line-D of Figure 13~ can represent the movement in
either directLon although tlle polarity of various
signals would be changed to represent the difrerent
direction of movement.
-` ~150836
~ he cooperatlon ~etwee.l the stop motion sub-
system 44 and the tracking se;vo subsystem 40 duril~ a
stop motion period wlll now be described r:~th reference
to Figures 9 and 12 and their rela~ed wave~orms. Re-
fe ring to ~igure 9A the tracking servo su~s~stem 40ls in operation ~ust prior to the initiaticn of a
stop mction mode to maintain the radial tr~cking mlrror
~8 in its position centered directly atop o~ infor~ation
track. In order to maintain this position the di~fer-
10 ential traclcing error is detected in the s~gnal recoverJsubsystem 30 and applied to the tracking servo subsystem
40 by the line 42. In this present operating mode
the differential tracking error passes di-ectly thro~gh
the tr-c~.ing servo loop s~itch 480 the a~?lifier 510
15 and the pusll/pull amplifiers 500. Th~t pc-tion of the
waveform showr. a' 591 on line D of Figure 13A as being
traversed.
Tl-e function generator 47 gener2tes a stop
motion mode signal for applica~ion to the stop motion
mode gate 5S9 over a line 132. The function of the
stop motion mode gate 569 is to generate ~ pulse in
response to t`ne proper location in a televlsion frame
for the stop motion mode to occur. This pcint is de-
tected bJ the combined operation of the total video
signal from the FM processing board 32 be~ng applied
to the white flag detector 556 over a line 134 ln com-
blnation with the vertical sync pulse developed in the
tangential servo system 80 and applied ~er a ltne 9~.
The wlndo~; gener~tcr 562 provides an enabling signal
which corresponds with a predetermined po-tion of the
vldeo signal containing the white flag indicator. The
~hite flag pulse applied to the stop motion mode gate
569 is gated to the stop motion pulse generator 567 in
response to the enablillg signal received rom the
function generatcr 47 over the line 132. The enabling
slgnal from the stop motion mode gate ~59 nltiates
the stop motion pulse as shown with reference to line C
of Figure 13A. The output from the zero crossing de-
tector 571 indicates the end of the stop ~otion pulse
.
l.t~0~36
-73-
period by application Or a si~nal to the stop motion
pulse ~er.erator ~57 over the line 57~. The stop
~otion pulse rrom the generator 567 is applied to the
traclcing servo loop interrupt switc`ll 430 by way Or the
gate 482 and the line 108. The function of the track-
in~ servo loop interrupt swi ch ~80 is to remove tlle
dilferential tracking error currently being generated
in the signal recovery subsystem 30 ~rcm the pusy/pull
am?li~iers 500 driving the radial tracking mirror 2~.
10 Accordingly, the switch 480 opens and the differential
tracking error is no longer applied to the amplifiers
500 for driving the radial tracking mirror 28. Simul-
taneously, the stop motion pulse rrom the generator
567 is applied to the ampli~iers 500 over the line 104.
The stop motion pulse, in essence, is substituted for
the difrerential tracking error and provides a driving
si~nal to the push/pull amplifiers 500 ror starting
the read spot to move to the next adjacent information
track to be read.
Tlle stop motion pulse ~rom the generator 567 is
also applied to the stop motion compensation sequence
generator 573 wnerein the waveform shown ~i'h reference
to line H of Figure 13A and line r~ of Figure BR iS
generated. ~y inspection of line H, it is to be noted
that the ccmpensation pulse sholYn on line H occurs at
the termination of the loop interrupt pulse on line G,
which loop interrupt pulse is triggered by the start of
the stop motion pulse shown on line C. me compensa-
tion pulse is applied to the push/pull amplifiers 500,
3 over the line lOZ shown in Figures 9 and 12, for damp-
ing out any oscillation in the operation of radial
tracking mirror 28 caused by the applicatlon of the
stop motion pulse.
As previously mentioned, the compensation
pulse is initiated at the termination of the loop
interrupt signal. Occurring simultaneousl~r wit'n the
generation Or the compensation pulse, the tracking
servo loop interrupt switch 480 closes and allows the
di~ferential tracking error to be reapplied to the
~ 3 ~
-74-
push/pull amplifiers 500. The typical waverorm avall-
a`cle at this point is shol~n in line E of ~igure 13A
which cooperates ~th the stop motion com~ensatlon
pulse to ~uickly bring the radial tracking mirror 28
into suitable radial tracking alignment.
Referring briefly to line A of Fig~lre 13C, two
frames of televisicn video information beinO read from
the video disc 5 are shown. Line A represents the
differential tracking errcr signal hav~ng a~rupt dis-
con~inuitles located at 550 and 652 representing thestop motion mode of operation. Discontinuities of
smaller amplitude are shown at 654 and 656 to show the
effect of errors on the surface of the video disc
sur~ace in the differential track~ng error signal.
Line B of Figure 13C shows the FM envelo~e as it is
read from the video disc surface. The stop motion
periods at 653 and 660 show that the FM envelope is
temporarily interrupted as the reading spot jumps
tracks. Changes in the FM envelope at 662 and 664
show the tempcrary loss of FM as tracking errors cause
the trackillg beam to temporarily leave the informatlon
track.
In review Or the stop motlon mode of opera-
tion, the following combinatio~s occur in the preferred
2~ embodiment. In a first embodiment, the differential
tracklng error signal ls removed from the tracking
mirror 28 and a stop motion pulse is substltuted
therefor to cause the radial tracking mirror to ~ump
one track fromthat track belng tracked. In this
3 embodlment, the stop motlon pulse has areas of pre-
emphasis such as to help the radlal tracking mirror to
regain tracking of the new track to which it has been
positioned. The differential tracking error is re-
applied into the tracking servo subsystem and cooperate
3~ with the ~top motion pulse applied to the radial track-
inO mirror to reacquire radial tracl~in~. The dif~eren-
tlal tracking error can be re-entered into the tracklng
servo system for optimum results. In this e~bodiment,
the duration of the loop lnterrupt pulse is varied for
-75- 1150836
gating crr the a~plicatlon of the differential track-
in~ error into the push/pull ampliflers 500. The stop
motlon pulse is of fixed lenr~th ln thls embodiment.
Al alternative to thls fixed lengtll of the stop motion
pulse is to lnitiate the end of the stop motion pulse
at the flrst zero crossing detected after the ~eginning
of the stop motion pulse was initiated. Suitable
del~ys can be entered into this loop to remove an~
extraneous signals that may slip throu3h due to mis-
alignment of the beginnil~ of the stop motion pulseand the detection of zero crossings in the detector
571.
A further embodiment includes any one of the
above combinations and further includes the generation
of a stop motion aompensation sequence. In the pre-
ferred embodiment, the stop motion compensatlon se-
quence is initiated with the terminatlon of the loop
interrupt period. Coincldental with the termination
Or the loop interrupt period, the differential track-
20~ ing error is reapplied into the tracking servo sub-
- system 40. In a further embodiment~ the stop motion
compensation pulse can be entered into the tracking
servo subsystem over the line 106 at a period fixed
in time from the beginnin~ of the stop motion pulse as
opposed to the ending of the loop interrupt pulse. The
stop motion compensation sequence comprises a plurality
of separate and distinct regions. In the preferred
embodiment, the first region opposes the tendency of
the tracking mirror to overshoot the next adjacent
track and directs the mirror bacl; lnto radial tracking
of that next ad~acent particular track. A second
region is of lower amplitude than the first region and
of opposite polarity to further compensate the motion
of the radial tracking mirror as the spot again over- -
shoots the center portion of the next adjacent track
but in the opposite direction. ~he third re~ion sf
the stop moiivn compensation sequence is of the same
polarit~ as the first region, but Or si~nificantly
lower amplitude to further compensate any te~dency of
75 ~ 836
the radial trackillg mlrror having the rOcus spot again
leave the in~ormation track.
lhile in the preferred embodlment, the various
resions of the stop motion sequence are sho~Yn to consist
of separ~te individual regions. It is possible for
these re&ions to be themselves broken down into in-
dividual pulses. It has been found by experiment that
the various regions can provide enhanced operation
when separated by sero level signals. More specific-
ally, a zero level condition exists between re~ionone and region tl~o allowing the radial tracking mirror
to move under its own inertia without the constant
appllcation of a portion of the compensation pulse.
It has also been found by experiment that this quiescent
1~ period of the compensation sequence can coincide with
the reapplication of the differential trackin2 error
to the radial tracking mirrors. In this sense, region
one, showll at 640~ of the compensation sequence cooper-
ates with the pcrtion ~04 sho~n in line E of Figure 13A
from the dirrerential trackin~ error input into the
tracking loop.
~ y observatlon of the compensation waveform
shcwn in line E of Figure 13~, lt can be observed that
the various regions tend to begin at a high amplitude
and fall off to very low compensation signals. Tt
can also be observed that the period of the various
regions begin at a first relatively short time period
and gradually become longer in duratlon. Thls coin-
cides with the energy contained in the ~raclcln~ mirror
as it seeks to regain radial trackin~. Initially ln
the track ~umping sequence, tlle energy is high and the
early portions of the compensation pulse are appro-
priately hi~h to counterac'c this energy. ~hereafter,
as energy is removed ~rom the tracking mirror, the
correcticns become less so as to bring the radial
tracking mirror back into radial al~gnment as soon as
possible.
P.efe-rin~ to Flgure 1~, there is shown a
block diagram of the F~l processing system 32 employed
77 1~5083~
in the videQ disc pla-~er 1. The frequency modulated
video sign~l recovered from the dlsc 5 fo ms the input
to the F~l processing unit 32 over the line 34. The
frequency modulated video slgnal is applied to a dis-
tribution amplifler 670. The distributicn amplifierprcvides three equal unloaded representations ~ the
received signal. The first output signal from the
distribution amplifier is applied to a FM corrector
circuit 572 over a line 673. The F~ corrector circult
672 operates to provide variable gain amplification
to the received freauency mcdulated video signal to
compensate for the mean transfer function of the lens
17 as it reads the frequency modulated vldeo slgnal
from the disc. The lens 17 is operating close to its
absolute resolving po:~er and as a result, recovers the
frequency modulated video signal with dif~erent ampli-
tudes correspGnding to different frequencies.
The output froM the FM corrector 672 is
applied to an Fl~ detector 574 over a llne 675. The
FM detector gellerates discrimi,lated video for applica-
tio.. to the remainlng circuits requiring such dis-
crimirated video in the video disc player. A second
output slgnal from the distribution amplifier 670 is
applied to the tangential servo subsystem 80 over a
line 82. A rurther output signal from the distrlbu-
tion ampli~ier 670 is applied to the stop motion sub-
system 44 over the line 134.
Referrlng to Figure 15, there is shown a more
detalled block diagram of the FM corrector 672 sho~ln ln
3 Figure 14. The FM video signal from the amplifler 570
is applied to an audio subcarrier trap circult 576
over the line 673. The ~unction of the subcarrler trap
circuit 676 is to remove all aud~o components ~rom the
frequency modulated video slgnal prior to appl~cation
to a ~requency selectlve variable gain amplifier 678
o~ e 5~.
The control signals ror operating the amplit'ler
678 include a first burst gate detector 582 having a
plurality of input slgna's. A first input slgnal is the
-78- 115083~
chro~ portion Or the FM video siænal as applied over a
llne 1~. The second lnpu slgnal to the burst gate
682 ls the burst gate enable signal ~rom the tanger.tial
servo system 80 over the llne 144. The function Or the
burst gate 582 is to gate lnto an amplitude detector
68~ over a line 685 that portion o r the chroma signal
corresponding to the color burst slgnal. The output
from the amplitude detector 684 i s applied to a summa-
tion circuit 588 over a line 690. A second input to
10 the summation circuit 588 is from a variable burst
level adjust potentiometer ~92 over a line 594. The
runction Or the amplitude detector 584 is to deter~ine
the first order lol~er chroma side band vector and apply
it as a c~rrent representation to the summation circuit
15 688. The burst level ad~ust si~nal on the line 694
from the potentiometer 692 operates in conJunction l1ith
this vector to develop a control signal to an ampli~ier
696. The output from the summation circuit is applied
to the amnlifier 595 over the line 698. ~ne output
from the amplifier 696 ls a control voltage for applica-
tion to tlle ampli~ier 678 over a line 700.
Rererrins to Figu~e 15 there is shown a numoer
Or wave~or~s helpful in understanding the operation of
the FM corrector sh~n in Figure 15. The ~aveform repre-
sented by the line 701 represents the FM correctortransfer ~unction in generating control vol~ages ~or
application to the amplifier 678 over the line 700.
- The line 702 includes four sections Or the curve indi-
cated generally at 702 ~ 7~4 706 and 708. These
segments 702, 704~ 70~ and 708 represent the various
control voltages generated in response to the com-
parison with the instan aneous color burst signal
amplitude and the pre-set level.
Line 710 represents the mean trans~er ~unction
3~ Or the objective lens 17 emplo-~-ed ror re~ding the
successive li~ht rerlective regions ~ ar.d li~ht non-
reflective reOions 11. It can be seen up~n inspection
that the gain versus frequency response o~ the lens
falls o~ as the lens reads the rrequency modulated
.. . .
79 115V836
rep~eselltatlons of the vldeo signal. ~eferrin~ to
the remair.lng portion of Flgure 16, there ls sho~n the
frequenc~- spectrum of the frequency modul~ted sigr.als
as read from the video disc. Thls lndicates that the
5 video sigllals are located prlncipally between the 7.5
and 9.2 megahertz region at which the frequenc~l re-
sponse Or the lens shown on line 710 is showing a sig-
nificant decrease. Accordingly, the control voltage
from the amplifier 696 is variable in nature to com-
pensate for the frequency response of the lens. Inthis m~nner the effective frequency respcnse of the
lens is brought into a normalized or uniform region.
FM CORR~CTOR SU~SYSTEM - NORr~L MODE OF OPERATIOM
The FM corrector subsystem functions to adjust
the FM video signal received from the disc such that
all recovered Frl signals over the entlre ~requency
spectra of the recovered FM signals are all amplified
to a level, relative one to the other to reacquire thelr
substantially identlcal relationships one to the other
as they existea during the recording process.
The microscopic lens 17 employed in the video
disc player 1 has a mean transfer characteristic such
that it attenuates the higher frequencies more than it
attenuates t!le lower frequencies. In this sense, the
lens 17 acts similar to a low pass filter. The function
of the FM corrector is to process the received FM
video signal such that the ratio of the luminance sig-
nal to the chrominance signal is maintained regardless
of the position on the disc ~rom which the FM video
slgnal is recovered. This is achieved by measuring the
color burst signal in the lower chroma side band and
storing a representation of lts amplitude. This lo~.ler
chroma side band signal functions as a reference ampli-
tude.
The FM video signal is recovered from the
vide~ disc as previously described. The chrominance
signal is removed from the FM video signal and the
burst gate er.able signal gates the color burst signal
present on each line of Frl video information into a
_ . . .
-80- ~ ~ ~ ~ 6
ccmparison operatio!l. The comparlson opera~lon e~rec-
tively operates for sensing the dir~erence between
tlle actual amplitude Or the color burst signal re-
covered from the video disc surface with a reference
amplitude. The reference amplitude has been ad~usted
to the correct level and the comparlson process indi-
cates an errcr slgnal between the recovered amplltude
Or the color burst signal and the reference color burst
signal indicating the difrerence in ampl~tude between
the two signals. The error signal generated in this
comparison operation can be identi~ied as the color
burst error amplitude signal. This color burst error
amplitude signal is employed for ad~usting the gain of
a variable gain amplifier to amplify the signal
presently being recovered from the video disc 5 to
ampli~y the chrominance signal more than the luminance
signal. This variable amplification provides a var-
iable gain over the ~requency spectrum. mhe higher
frequencies are ampli~ied more than the lower fre-
quencies. Since the chrominance signals are at thehlgher frequencies, they are amplified more than the
luminance signals. This variable amplification of
signals results in e~fectively maintaining the correct
ratio Or the luminance signal to the chrominance signal
as the reading process radially moves ~rom the outer
periphery to the inner periphery. As previously men-
tioned, the lndicia representing the FM video signal on
the video disc 5 change ln size from the outer periphery
to the lnner periphery. At the lnner periphery they
3 are smaller than at the outer perlphery. The smallest
size lndicia are at the absolute resolution power of
the lens and the lens recovers the FM si~nal represented
by thls smallest size lndicla at a lower amplltude
value than the lower frequency members which are larger
ln slze and spaced farther apart.
In a preferred mode of operation, the audlo
signals contained in the F:~ video signal are removed
from the FM vldeo signal be~ore application to the
variable gain amplifier. The aud~o inrormation ls
8 1 :lS0~36
-- 1--
contqined around a number Or FM subcarrier slgnals
and it has ~een found by experlence that the removal
Or these FM subcarrler audlo slgnals provides enhanced
correction Or the remainin~ video FM signal in the var-
iable gain amplifier.
In an alternatl~e mode of operation thefrequency band width applied to the variable galn
amplifier is that band width which is affected by the
mean transfer function Or the ob~ective lens 17. More
specifically, when a portion of the total FM recovered
from the video disc lies in a range not affected by
the mean transfer functlon, then this portion of the
total waveform can be removed from that portlon of the
F~l signal applied to the variable gain amplifier. In
this manner, the operation of the variable ~ain ampli-
fier is not complicated by signals having a frequency
which need not be corrected because of the resolution
characteristics of the objective lens 17.
The Fl~q corrector functions to sense the ab-
solute value of a signal recovered from the video disc,which signal is known to suffer an amplitude change due
to the resolution power of the objective lens 17 used
in the video disc signal. This known signal is then
compared against a reference signal indicating the
amplitude that the known signal should have. The out-
put from the comparison ls an lndlcation of the addl-
tional amplification required for all of the signals
lying in the frequency spectra affected by the resolv-
ing power of the lens. The amplifier is designed to
provide a variable gain over the frequency spectra.
Furthermore, the varlable gain is ~urther selective
based on the amplitude Or the error signal. Stated
another way for a first error signal detected between
the signal recovered from the disc and the reference
frequency, the variable gain amplifier is operated at
a first level of variable amplification over the entire
frequency range of the afrected signal. For a sec~nd
level of error signal, the gain across the frequency
spectra is ad~usted a different amount when compared
~50836
82-
for the first color burst error amplitude signal.
~ eferring to Fi6ure 17, there ls sho~n a block
di~gram of the FM detector circuit 674 shown with refer-
ence to Figure 14. The corrected frequency modulated
slgnal from the FM corrector 672 is applied to a
llmiter 720 over the line 675. The output from the
limiter is applied to a drop-out detector and compen-
satlon circuit 722 over a line 724. It is the function
of the limiter to change the corrected FM video signal
into a discriminated video signal. The output from
the drop-out detector 722 is applied to a lo~ pass
filter 725 over a line 728. The output from the low
pass fllter 726 is applied to a wide band video dis-
tribution amplifier 730 ~hose function is to provide a
plurality of output signals on the line 66, 82, 134,
154, 156, 164 and 16~, as previously described. The
function of the FM detector is to change the frequency
modulated video signal into a discriminated video
signal as shown with reference to lines A and ~ of
Figure 18. The frequency modulated video signal is
~ represented by a carrier frequency having carrier
variations in time changing about the carrier fre-
quency. The discriminated video signal is a voltage
varying in time signal generally lying within the zero
to one volt range suitable for display on the television
monltor 98 over the line 166.
Referrlng to Figure 19, there ls shown a
block diagram of the audio processing circuit 114. The
frequency modulated video slgnal from the distribution
3 amplifier 670 of the FM processing unit 32, as shown
with reference to Figure 14, applies one of lts lnputs
to an audio demodulator clrcuit 740. The audio demodu-
lator circuit provides a plurality of output signals,
one of which is applled to an audio variable controlled
3~ oscillator circuit 742 over a line 744. A first audio
output is available on a llne 74;~ for application to
the audio accessory unit 120 and a second audio output
signal is available on a line 747 for application to
the audio accessor~J unit 120 and/or the audio ~acks
.
-8,- li50836
117 and 11~. The output from the audio volta6e con-
trolled osclllator is a 4.5 megahert~ signal for appli-
c~tion to the RF modulator 162 over the line 172.
Referring to Figure 20, there is shown a block
diagram of the audio demodulator circuit 740 shown
with reference to Figure 19. The frequency modulated
video signal is applied to a first band pass filter
750 having a central band pass frequency of 2.3 mega-
hert~, over the line 160 and a second line 751.. The
10 frequenc~J modulated video signal is applied to a second
band pass filter 752 over the line 160 and a second line
754. The first band pass filter 750 strips the first
audio channel from the FM video signal, applies it to
an audio FM discriminator 755 over a line 758. The
audio F~ discriminator 75~ provides an audio signal
in the audio range to a SWitCi~ g circuit 760 over a
line 752.
The second band pass filter 752 havin2 a
central frequenc~T of 2.8 megahert~ operates to strip
20 the second audio channel from the FM video input signal
- and applies this frequenc~ spectra Or the total FM
signal to a second video FM discriminator 764 over a
line 765. The second audio channel in the audio fre-
quenc~J range applied to the switching circuit 750 over
a line 768.
The s~itching circuit 760 is provided with a
plurality of additional input signals. A first of
which is the audio squelch signal from the trackin~
servo subsystem as applie~ thereto over the line 116.
3 Thc second input signal ls a selection command signal
from the function generator 47 as applied thereto over
the line 170. The output from the switc~ g circuit
ls applied to a first amplifier circuit 770 over a
line 771 and to a second amplifier circuit 772 over a
line 77~. The lines 771 and 773 are also connected to
a summation circuit indicated at 774. The output from
the summation circuit 774 is applied to a third ampli-
fier circuit 7~5. The output from the first amplifier
770 is the channel one audio signal for application to
` 1150836
-84-
the audio jack 117. The output from the second ampli-
fier 772 is the second channel audio slgnal ~or
application tothe audio ~ack 118~ The output rrom
the thlrd amplifier 776 is the audio si~nal to the
audio VC0 742 over the llne 744. Referring briefly
to Fi~ure 21, there is shown on line A the rrequenc~J
modulated envelope as received from the distribution
amplifier in the F~ processing unit 32. me output of
the audio FM discriminator for one channel ls shown on
line ~. In th~s manner, the FM signal is changed an
audio frequency signal for applicatlon to the switch-
lng circuits 760, as previously descrlbed.
Xeferring to Figure 22, there is shown a
block diagram of the audio voltage controlled ~scilla-
tor 742 as shown with reference to Figure 19. Theaudio signal ~rom the audio demodulator is applied to
a band pass ~ilter 780 over the llne 744. The band
pass filter passes the audio frequency signals to a
summation circuit 782 by way of a pre-emphasis circuit
784 and a first line 786 and a second line 788.
The 3.58 megahertz color subcarrier frequency
from the tangentlal servo system 80 is applled to a
divide circuit 790 over tne line 140. The divide
circuit 790 divides the color subcarrier frequency by
2048 and applies the output signal to a phase detector
792 over a line 794. The phase detector has a second
lnput slgnal from the 4.5 megahertz voltage controlled
oscillator circuit as applied to a second divide clr-
cuit 798 and a flrst line 800 and 802. The divlde
3 circuit 798 divides the output of the VC0 796 by 1144.
The output from the phase detector ls applied to an
amplitude and phase compensatlon clrcuit 804. The
output from the clrcult 804 is applled as a thlrd
input to the summation circult 782. The output from
the voltage controlled oscillator 796 ls also applied
to a low pass filter 806 ~ the line 800 and a ~cond
line 806. ~he output from the filter 806 ls the 4.5
megahertz ~requency modulated slgnal for appllcatlon
to the RF modulator 182 by the line 172. The function
115~836
-85 -
oI' the audio voltage controlled osclllator clrcult is to
prepare the audio signal received rrom the audio demod-
ulator 740 to a frequency wi~ich can be applied to the
~F modulato~ 152 so as to be processed by a standard
televislon recelver 9S.
Referring brlefly to Figure 23, there can be
seen on line A a waveform representlng the audio signal
received from the audio demodulators and available on
the llne 744. Line ~ of Figure 23 represents the 4.5
megahertz carrier frequency. Line C of Figure 23
represents the 4.5 megahertz modulated audio carrier
~hich is generated ln the VC0 circuit 796 for applica-
tion to the RF modulator 152.
Re~erring to Figure 24, there ls shown a
15 block diagram of the RF modulator 162 employed in the
video disc player. The video information signal from
the Frl processing circuit 32 is applied to a DC re-
storer 81~ over the line 154. The DC restorer 810
read~usts the blanking level of the received video
signal. The output from the restorer 810 is applled
to a first balanced modulator 812 over a line 814.
The 4.5 megahertz modulated signal from the
audio VC0 is applied to a second balanced modulator 81O
over the~llne 172. An osclllator circuit 818 functlons
25 to generate a suitable carrier frequency corresponding
to one of the channels of a standard televislon re-
celver 96. In the preferred embodiment, the Channel 3
frequency is selected. The output rrom the oscillator
818 is applied to the first balanced modulator 812 over
a line 820. The output from the oscillator 818 is
applied to the second balanced modulator 816 over the
line 822. The o~tput from the modulator 812 is ap-
plied to a summation clrcuit 824 over a llne 826. The
output from the second balanced modulator 816 ls
35 applied to the summatlon circuit 824 over the llne
828. Referring briefly to the wave~orm shown in
Figure 25, llne A sho~s the 4.5 megahertz frequellcy
modulated signal received rrom the audlo VC0 over the
llne 172. Line ~ o~ Figure 25 shows the vldeo signal
115~36
-8~-
received fro~ the FM processing clrcuit 32 over the
line 154. The output from the summation circuit 824
is showll on line C. The signal shown on line C ls
suitable for processing by a standard television re-
ceiver. me signal shown on line C is such as to causethe standard television receiver 96 to display the
sequential ~rame in~ormation as applied thereto.
Rererring briefly to Figure 26, there is shown
a video disc 5 having contained thereon a schematic
10 representation of an information track at an outside
radius as represented by the numeral 830. An informa-
tion track schematically shown at the inside radius
is shown by the numeral 832. The uneven form of the
infor~ation track at the outside radius demonstrates
15 an eY.treme degree of eccentrlcity arising from the
effect of uneven cooling of the video disc 5.
Referring briefly to Figure 27, there is shown
a schematic view o r a video disc 5 having contained
~thereon an in~ormation track at an outside radius
- 20 represented bJ the numeral 834. An information track
at an inside radius is represented by the numeral 836.
This Figure 27 shows the eccentricity efI'ect of an
off-center relationship of the tracks to a central
aperture indicated generally at 838. More specifically,
25 the off-center aperture effectively causes the dlstance
represented by a llne 840 to be effectively different
from the length of the llne 842. Obviously, one can
be larger than the ot~er. This represents the off-
centered position of the center aperture hole 838.
Referring to Figure 28, there is shown a logic
diagram representing the first mode ~ operation Or
the focus servo 36.
The logic diagram shown wlth reference to
Figure 28 comprises a plurality oi AND functlon gates
35 shown at 850, 852, 854 and 856. The AND function gate
850 has a pluralit~ of inpu~ signals3 ~!le first of
which is the r~N~ JA~L~ applied over a line 858. The
second input signal to the AND gate 850 is the ~OCUS
SIGNAL applied over a llne 860. The AND gate 852 has
.
-87- 1 1S~B3 6
a plur21it-~ of input si~nals, the ~irst Or whlch is
the FOCUS SI~i~AL applied thereto ~or the line 860 and
a second lille 862. The second input si&nal to the AND
function gate 852 is the lens enable sigilal on a llne
5 804. The output rrom the AND runction gate 852 is the
ramp enable signal which is available for the entire
period the ramp signal is being generated. The output
frcm the AND function gate 852 is also applied as an
input signal to the AND runction gate 854 over a line
lo 866. The AND ~unction gate 854 has a second input
signal applied over the llne 868. The signal on the
line 868 is the FM detected signal. The output from
the AND function gate 854 ~s the focus acquire signal.
This focus acquire signal is also applied to the ramp
generator 278 for disalbing the ramping wave~orm at
that ~int. The AND function gate 856 is equipped with
a pluralit~J of input signals, the first of which is
the FOCUS ~IGi~lAL applied thereto over the line 860
~nd an additional lire 870. The second input signal
20 to the A~D function gate 855 is a ramp and signal
applied over a line 872. The output signal from the
AND ~unction gate 856 is the withdraw lens enabling
signal. ~rierly, the logic circuitry shown with refer-
ence to Figure 28 generates the basic mode o~ operation
25 o~ the lens servo. Prior to the function generator 47
generating a lens enable signal, the LENS ENA~LE signal
is applied to the AND ~unction ~ate 850 along wlth the
FOCUS SIGNAL. This indicates that the player is in an
inactivated condition and the output si~nal from the
3 AND runction gate indicates that the lens is ln the
fully withdrawn position.
~ en the ~unction generator generates a lens
enable signal for application to the AND gate 852,
the second input signal to the AND gate 852 indicates
that the video disc pla~e. 1 is not in the focus mode.
AccGrdingl~, the output signal rrom the .~ND gate 852
is the ramp enable signal which initiates the ramping
waveform shown with re~erence to l~ne P of Figu-e 6A.
The ramp enable signal also indicates that the focus
~- ~0836
-8~ -
ser~o is in the acqulre focus mode ~ operatlon and
this enabli2~ signal forms a flrst lnput to the AND
function gate 85~. The second input slgnal to the AND
function gate 854 indicates that ~M has been success-
rully detected and the output from the A~TD ~unctiongate 854 is the focused acquire signal indicatir~ that
the normal play mode has been successfully entered and
frequency modulzted video signals are being recovered
rrom the surface of the vldeo dlsc. The output from
10 the AND function &ate 856 lndicates that a successful
acquisitlon of focus was not achieved in the first
focus attempt. The ramp end signal on the lir.e 872
indicates that the lens has been fully extended towards
the video disc surface. The FOC~tS SIGI~qL on the llne
15 870 indicates tilat focus was not successfully acquired.
Accordingl~, the output from the AND function gate
855 ~ithdraws the lens to its uppe~ position at whlch
time a focus acquire operation can be reattempted.
Referring to Figure 29, there is sho,1n a logic
20 dlagram illustrating the additional mcdes o~ operation
of the lens servo. A first AND gate 880 is equipped
witll ~ pluralit~J of input signals, the first Or which
~s the focus signal generated by the A~ gate 854 and
applied to the AND gate 880 over a line 853. The
25 FM DETECl' SIGNAL is applied to the AND gate 880 over a
line 8~2. The output from the AND gate 880 is applied
to an OR gate 84 over a line 886. A second input
signal is applied to th4 OR gate ~84 over a llne 888.
The output from the OR function gate 884 is applied to
30 a first one-shot circuit shown at ~90 over a line 892
to drive the one-shot into its state for generating an
output signal on the line 894. Tlle output slgnal on
the line 894 is applied to a delay circuit ~96 over a
second line ~98 and to a second AND function gate 900
35 over a line 902. The AND function gate 9CO ls equlpped
with a second input signal on whic~l the FM detect
signal is applied over a line 90l~. The output from
the AND function gate-900 is applied to reset the first
one-shot ~90 over a line 90S.
_.. ~ . ... . .. . .. .
1'150836
sg -
The output from the delay circuit 895 ls ap-
plied as a first input signal to a third AND f~nction
g~te 908 over a line 910. The AND function gate 908
is equipped with a second input signal which is the
RAriP KE~ IGi~L applied to the AND function gate 908
over a line 912. The output from the AND function gate
908 is applied as a first input signal to an OR circuit
914 over a line 916.
The output from the OR function gate 914 is
the ramp reset enabling signal which is applied at least
a fourth AND functlon gate 918 over a line 920. The
second inpu~ sl~nal to the AN~ function gate 918 is the
output signal from the rirst one-shot 890 over the line
894 and a secon~ line 922. The output f~om the AND
function gate 918 is applied to a second one-shot cir-
cuit 924 over a line 926. The output from the second
one-shot indicates the timing period of t~le focus ramp
voltage sho;wn on line B of Figure 6A. The lnput signal
on line 925 activates the one-s'not 924 to generate its
output signal on a line 928 for application to a delay
circuit 930. The output from the delay circult 930
forms one input to a sixth A~ function gate 932 over a
line 934. The AI~D function gate 932 has as its second
irput signal the FOCUS SIGiJAL available on a line 936.
The output fro~ the AND function gate 932 is applied
as the second input signal to the OR function gate 914
over a line 938. The output from the AND function gate
932 ls also applied to a third ~e-shot circuit 940
over a line 942. The output from the third one-shot
3 is applied to a delay circuit 942 over a line 944. As
previously rnentioned, the output from the delay clrcuit
942 is applied to the OR functlon gate 884 over the
line 888.
The one-shot 890 is the circuit employed for
generating the timing waveform shown on lir.e D of
Figure 6Q. The second one-shG~ 9211 is employ d ~or
generatin~ a waveform shown on line ~ of Figure oA.
The third one-shot 940 is employed for generating the
waverorm shown on line F of Figure 6A.
~o llS0836
In one form of operation, the logic circultry
shown in Fig ure 29 operates to delay the attempt to
reac~uire focus due to momentary losses cf FM caused by
imperfections on the video disc. This ls achieved in
5 tlle following manner. The AND function gate 880 gener-
ates an output signal on the line 885 only when the
video disc player is in the focus mode and there ls a
temporary loss of FM as lndicated by the FM DEr~CT SIGl~AL
on llne 882. The output signal on the llne 885 triggers
10 the first one-shot to generate a tim~ng perlod of pre-
determined short length during which the video disc
player will be momentarily stopped from reattemptin~;
to acquire lost focus superficially indicated by the
availability of the FM DEl`~CT SI~NAL on the line 882.
15 The output from the first one-shot forms one lnput to
t;le AND function gate 900. If the FM detect signal
ava~lable on 9~4 reappears prior to the timlng out of
the tlme period of the first one-shot, the output from
the Ai~D circuit 900 resets the first one-shot 890 and
20 the video disc player continues reading the reacquired
FM signal. Assuming that the first one-shot is not
reset, 'chen the following sequence of operation occurs.
The output from the delay circuit 895 is gated through
the AND function gate 908 by the ~AMP R~:SET SIGNAL
25 available on line 912. The RAMP RESET SIGNAL ls avail-
able in the normal focus play mode. The output from
the AND gate 908 is applied to the OR gate 914 for gen-
erating the reset signal causing the lens to retrack
and begin lts focus operation. The output from the OR
30 gate 914 is also applied to a turn on the second one-
shot which establishes the -shape of the ramping wavefo~m
shown in Figure B. The output from the second one-shot
924 is essential coextensive in tine with the ramping
period. Accordingly, when the ot~tput from the second
35 one-shot is generated, t;he machine is ca-;sed to return
to the attempt to acquire ~ocus. When fecus is success-
fully acquired, tlle ~()CU~ ~LGi~lAI. on 1 Lne 936 does not
gate the output from the delay circuit 930 through to
the OR function gate 914 to restart the automatlc focus
~1
;~
.
1150~36
--91-
procedure. HoweYer, when the video disc player does
not acquire focus the FOCUS SIGNAL on line 935 gates
the output from the delay circuit 930 to restart auto-
matically the rOcus acquire mode. When focus is success-
fully acquired, the output from the delay line is notgated through and the pla~er continues in its focus
mode.
While the invention has been particularly
shown and described with reference to a preferred embod-
iment and alterations thereto, it would be understood bythose skilled in the art that various changes in form
and detail may be made therein without departing from
the spirit and scope of the invention.
