Note: Descriptions are shown in the official language in which they were submitted.
61
BACKGROUND OF THE INVENTION
This invention re].ates to a method and apparatus for
correcting tracking errors in a transducer which scans successive,
parallel tracks of a record medium and, more partic-llarly, to such
a rnlthod and apparatus wherein the position of the transducer rela-
tive to the track being scanned can be adjusted when a tracking
error condition is sensed.
Signal recording and/~r reproducing apparatus are known
wherein a rotary head assembly scans successive parallel tracks
on a record medium so as to record signal.information by scanning
the record medium with the rotary head or heaas. The record medium
generally used in such apparatus is magnetic tape, magnetic sheets,
magnetic discs and various other types of media. In additi.on to
rotating the head or heads across the record medium, the medium
also is moved. One particular use o such apparatus is to record
video signal inEormation on, for example, mac3rletic tape, wherein
parallel slant tracks are recorded in skewed relation to the
longitudinal axis of the tape. In addition to video si~nal informa-
tion, such apparatus is capable of recordinq other types of analog
signals or, if desired, digital signals representing various types
of information. In the interest of simplification, the following
explanation and description refers to video signal recorders which
use magnetic tape, such as the video tape recorder (VTRl However,
it should be understood that this explanation and description also
is applicable to different types of recordi.ng apparatus ~such. as
other types of analog or digital recorders) which use different
media.
A typical VTR includes one, and preferably twc, record/
playback heads mounted on a suitable rotary assembiy so as to
rotatably scan a magnetic tape which is helically wrappe~ about
.
... . ,
~11961
at least a portion of a guide drum. During recording, a tracking
servo system synchronizes the movement of the tape to the rotary
movement of the heads, and control signals wh;ch can be used for
thi.s type of synchronism during a reproducing operation are recorded
on the tape. ~lence, during reproduction, this same servo control
system is used to synchronize the movement of the tape to the rota-
tion of the heads. Consequently, a generally accurate video picture
can be displayed in response to t~e reproduced video sLgnals. That
is, this servo control system is operative to control the relative
movement between the rotary heads and the tape such that each head
scans substantially the same track during reproduction as was
scanned during recording. :
However, even with this servo control system, there are
instances wherein ~he path traversed by the heacls during reproduc-
lS tion does not coincide satisfactorily with the recorded record
track. This is particularly true when the video signals are
recorded by one VTR and are reproduced Erom the tape.by a different
VTR. If the orbits of the magnetic heads in these di.fferent ~TRIs
are not equal to each other, the servo control system may not be
effective to bring the heads into coincidence with the recorded
~ tracks during reproduction. Other factors also may be present
which prevent successful operation of the servo control system.
Consequently, the scanning magnetic heads may exhibit tracking
errors during reproduction.
The tracking errors mention.ed above may not be partic-
: ularly noticeable or objectionable for VTR apparatus wherein parallel
tracks are recorded with guard bands separati.ng adjacent track.s ...
or when the magnetic tape is transported at a sufficiently higher
speed. However, the problems caused by these tracking errors
~2-
. .
~ . . . . . . . .
- . . : : - . -
961
during signal reproduction may not be acceptable if the guard
bands between adjacent tracks are reduced and if the speed at ~,
which the magnetic tape is transported is reduced. The desirable
effect of eliminating the guard bands, and thus increasing the
recordi,ng density (tracks per inch), and oE reducing the transport
speed of the magnetic tape is to increase the amount of video
signal information which can be recorded on a magnetic tape of
- given lengths. This, in turn, increases the recording capacity
(generally expressed as a measure of time) of the VTR without
requiring a concommitant increase in the supply or length of
recording tape. In particular, for these so-called "longer-
playing" VTR's, tracking errors may reduce the signa]-to-noise
ratio and may otherwise deleteriously affect the reproducing
characteristics.
OBJ~CTS OF THE XNVENTIO~
Therefore, it is an o~jec-t of the present invention to
provide an improved method and apparatus for correcting tracking
errors which may occur in rotary head recording/reproducing apparatus
Another object of this invention is to provide a method
and apparatus for correcting tracking errors in a rotary head
recording/reproducing system so as to correct for deviations
between the scanning path of a head and a record track on the
record medium.
A further object of this invention is to provide a method
and apparatus for correcting tracking errors in a rotary head
recording/reproducing system wherein the scanning path of the
rotary head is adjusted so as to coincide with a previously
recorded track.
,
. ' .. ' ' .'
,' ' , . ' ' , '
6~
An addi-tional object of this invention is to provide a
method and apparatus for correcting tracking errors of a scanning
head which tra.verses a scanning path that may deviate from a
desired path, this deviation being corrected by di.splacing the
support member upon wh.ich the head is mounted durincJ the scanning
operation.
Yet another object of this invention is to correct for
tracking errors which may occur in a video signal reproducing
device wherein a playback head may deviate from a record track
on a record medium having parallel, adjacent record tracks.
A still further object of this invention is to provide
a method and apparatus for controlling the scanning of a record
track by a scanning head during a reproducing operation so as to
avoid deleterious effects upon the reproduced siynals.
Another object of this invention is to provide a method
and apparatus for recording particular signal.s on a record medium
in a video signal recorder, which signals .3re de-tected and used
during a reproducing operation to correct ~or tracking errors of
the reproducing transducers in, for exam~l~, a long-playi.ng vi.deo
recorder.
Various other objects, advantages and features of the
present invention will become readily apparent from the ensuing
. .
detailed description, and the novel features will be parti.cularly
pointed out in the appended claims.
SUMMARY OF THE INVF.NTION
In accordance with the present invention, predetermined
signals are recorded in successive traclcs of a record ~edium such
that when these predetermined signals are reproduced, as by a rotary
transducer, tracking errors of that transducer may be easily correcte
such that the transducer accurately scans a record track. The record
-4-
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.~ . ' ' , '' : '' ,. ' . , ~ : ,-'
61
medium is provided with parallel, adjacent record tracks
in which information signals and the aforementioned predetermined
signals aré recorded. During a reproducing operation, at least
one cross-talk predetermined signal which is recorded in at least
one adjacent track is reproduced. ~rhis cross-talk predetermined
signal is detected and a control signal is produced in response
to the level of the detected cross-talk predetermined signal.
The position of the scanning transducer is adjusted wlth respect
to the track ~eing scanned in accordance with the control signal.
In one embodiment, the information signals are video signals having
periodic horizontal blanking intervals recorded in each record
track. The horizontal blanking intervals in a given trac}; are
displaced from the horizo~tal blanking intervals in an adjacent
track in ~he direction of scanning. This displacement faci~itates
the detection of the cross-tal~ predetermined signals which are
recorded in predetermined locations of the horizontal blanXing
intervals.
More particularly, there is provided:
A method of recording tracking-error correcting
signals added to a video signal on a record medium for use in
detecting errors in the scanning path of a
scanning transducer which scans parallel record tracks across
said medium, comprising scanning successive record tracks across
said medium to record periodic video signals in said record !
tracks, said video signals containing periodic horizontal-
synchronizing pulses; generating pilot signals during pre-
determined portions of the horizontal synchronizing signals in
said vldeo signals; and recording said pilot signals in said
successive tracks such that the portion of a pilot signal in
one track is shifted with respect to the position of a pilot
signal in an adjacent track.
~ . .
_5_
61
There is also provided:
A method of correcting tracking-errors of a
scanning transducer which scans successive parallel, adjacent
recor,~ tracks of a record medium to reproduce video signals
therefrom , said video signals including pilot signals recorded
dur.ing predetermined portions of the horizontal blanking inter-
vals of said video signals, said method comprising reproducing
said video and pilot signals when said tracks are scanned, ¦
said reproduced pilot signals including the pilot signal ¦
recorded in the trac~ being scanned by said transducer together
with at least one cross-talk pilot signal recorded in at least
one adjacent track; detecting said at least one crioss-talk :
pilot signal; producing a control signal in response to the
level of the detected cross-talk pilot signal; and adjusting
the position of said transducer with respect to said track
being scanned by said transducer as a function of said control
signal.
There is also provided: - .
Apparatus for recording tracking-error correcting
signals on a record medium for use in detecting tracking errors
in the scanning path of a transducer as said transducer scans
said record medium to reproduce video signals recorded thereon,
said video signals being recorded in successive, adjacent,
parallel tracks wherein each track is pro~ided with a plurality
of horizontal blanking intervals with the horizontal blanking ¦
intervals of one track being offset with respect to the
horizontal blanking intervals of an adjacent track, said .
apparatus comprising at least one transducer for recording
said video signals onto said record medium; video signal ~:
processing means for supplying a video signal to said trans-
ducer for recording on said record medium; and means for
~ , ,.
-5a-
.
:~ A
.. . . . .. ... . . ... ~ .. .. ~.... . . ..... .
361
supplying a pilot signal to said transducer during predetermined
portions of said horizontal blanking intervals for recording
on said record medium.
There is further provided:
Apparatus for correcting tracking errors in a
video signal reproducing system of the type wherein at least
one transducer scans successive, adjacent, parallel tracks on
a record medium in which video signals including horizontal
synchronizing signals are recorded, said video signals being
provided with pilot signals recorded during certain portions of
the horizontal blanking intervals of said video signals, said ,
apparatus comprising:
transducer means adapted for relative motion with
respect to said record medium for reproducing the signals
recorded in a given track together with a cross-talk component
o~ at least the pilot signals recorded in an adjacent track;
sensing means for sensing said cross-talk component
of said pilot signals recorded in said adjacent track~
level detecting means for detecting the level of said
sensed cross-talk component of said pilot signals;
control signal generating means for generating a j
control signal as a function of the detected level of said
sensed cross-talk component of said pilot signals; and
adjustable support means for said trans~ucer means,
said adjustable support means being responsive to said control I ¦ :
signal to displace said transducer means transversely of said :
given track in accordance with said control signal and in a
direction to restore said control signal to a quiescent value.
5~
:: ., , ... , , ., , . , . . ,, , , ~: .
- . . -
, ,~, ., ., .. .. :
BRIEF DESCRIPTION OF THE: DRAI~I~GS
- The following ~etailed descri~t.ionr given by wa~ of. ~
e~ample, will best be understood in conjunct;on with the accompany-
in~ drawings in wh;ch:
FIG. 1~ is a schematic top view of rotary head recording/
reproduc;ng apparatus;
FIG. lB is a schematic side view of the apparatus shown .
in FIG. lA; . ! :
FIG. 2~ represents parallel tracks on a record medium
having guard bands between a~ cent trac);s; ¦ . . .
. FIG. 2B represents parallel tracl~s on a record medium l .
wherein successive tracks are adjacent each other; I
'
.
. , ~ . , . . ~ . ~.
- ' '': ~ ~ . .
FIGS. 3A-3C are schematic side views of a piezo-electric
support member which can be used with the present invention;
FIG. 4~ is a side view of one embodiment of a head support
assembly which can be used with the present invention;
FIG. 4B is a bottom view of the assembly shown in FIG. 4A;
FIG. 5 is a block diagram of video signal recording appara~
tus which can be used to record tracking-error correcting signals;
FIGS. 6A-5D are waveform diagrams which are useful in
understanding the operation of the apparatus shown in FIG. 5;
FIG. 7 represents different positions of a scanning
transducer relative to the record tracks shown, for example, in
FIG. 2B;
FIG. 8 is a block diagram of signal reproducing apparatus
which can be used to correct tracking errors of a scanning trans-
ducer;
FIGS. 9A-9E are waveform diagrams whih are useful in
understanding the operation of the apparatus shown in F~G. 8; and
FIG. 10 is a graphical representation showing ~he relation-
ship between tracking errors and particular s;gnals which are pro-
duced by components o~ the apparatus shown in FIG. 8.
DETAILED DESCRIPTION OF CERTAIN PREFERRED E~ODIMENTS
The following detailed description, given by way of
example, will best be understood in conjunction with the accompany-
ing drawings. For the purpose of simplification, and in order to
facilitate an understanding of the present invention, the following
description is limited to the environment of a video signal recorder
and, more particularly, to a VTR. However, it will become readily
apparent that the present invention can be used in other types of
signal recorders, such as analog or digital recorders wherein moving
heads scan a record medium. Furthermore, although the record medium
.
-6-
- .... . , -: ................ . . . .
-~" : ' ' ' ' ' '
6~
described herein is, illustratively, magnetic tape~ it should
be readily apparent that other types of record media, such as
ma~Jnetic sheets, magnetic discs, and the li.ke can be used.
Turning now to FIG. lA, there is schematically illus-
tra.ted a top view of a typical rotary head scannin~ device, such
as a VTR. As is conventional, this devi.ce îs formed with two
magnetic record/playback heads la, lb (hereinafter, merely heads)
which are adapted for rotation about a central axis. A guide drum
2 is adapted to receive a r cord medium, such as tape 3, wrapped
helically thereabout for at least 180. Heads la and lh may be
mounted on diametrically opposed arms which are rotated to as to
scan successive, parallel, skewed tracks across tape 3~ Alterna-
tively, heads la and lb may be mounted on a portion of the guide
drum, which portion is adapted to be rotated so as to serve the
dual purpose of guiding tape 3 -thereabou-t and rotating heads la
and lb so as -to scan para].lel tracks across ~he tape. Thus, the
heads rotate in the direction :indicated by the arrow while tape 3
is advanced so as to record signal inforrnati:on thereon.
If, as shown in FIG. lB, guide drurn 2 is formed of two
drums 2a, 2b, disposed in face-to-face conflguration and spaced
apart so as to define a scanning gap therebetween, tape 3 is
helically wrapped about a portion of the surface of the guide.
drum and heads la, lb which are supported by, for example., drum 2a,
are rotated to scan parallel tracks across the tape. Although
FIG. lA shows the preferred scanning apparatus wherein two heads
are used, it is possible that only a single head may be provided.
Nevertheless, if two heads are used, alternate tracks are recorded
thereby such that first one track is recorded by head la and then
the next adjacent track is recorded by head lb, and then the follow-
ing track is recorded by head la, and so on.
'
6~
During a signal reproducing operation, the relative speedof tap~ 3 with respect to heads la and lb is the same as during a
sigmal recording operation. A suitable servo control system (not
shown) is provided to account for relatively small changes .in tape-
drive and head-drive motor speeds, tape shrinkage, tape stretching,
differences from the recording apparatus to the reproducing appara-
tus, and the like. To this effect, a head-position generator 5
is provided to generate pulsés when hea~s la, lb rotate into pre-
determined position, such as when head la first contacts tape 3.
A magnetic element 4 ;s secured to the rotary drive shaft which is
used to rotate heads la, lb so as to rotate relative to head-
position generator 5 while the heads rotate. Head-position gen-
erator 5 may comprise a magnetic pick-up sensor for generating a
position detecting pulse when magnetic element 4 rotates therepast.
lS In a typical video recording device, each head records a complete
field in a respective record track, and heads la, lb are rotated
at a speed of 30 rps. Consequently, the posi.tion detecting pulses
generated by pick-up sensor 5 have a frequency of 30 Hz.
As shown in FIG. 2A, video signals are recorded by heads
la, lb in parallel slant tracks Tal, Tbl, Ta2, ..~ As one example,
head la records alternate tracks Tal, Ta2, ...; and head lb records
the remaining alternate tracks Tbl, Tb2, ... In a typical VTR,
each track Tal, Tbl, ... has a field of video signals recorded
therein such that a plurality cf horizontal line intervals separated
~5 by horizontal blanking intervals is recorded in each track. During
a reproducing operation, heads, such as heads la, lb, scan the
parallel recoxd tracks Tal, Tbl, ... so as to reproduce the previ-
ously recorded video signals. The aforement.ioned servo control
system adjusts the relative speed of tape 3 and heads la, lb such
that the scanning path traversed by the heads substantially
'; ' ' ' :~
coincides with the respective record tracks. However, the servo
control system may not be sufficient to achieve precise coincidence
between the scanning path and record tracks. This means that the
head will not be aligned precisely with a record track and, there-
Eor, will include a portion of its ~ir gap which ex-tends beyond
the longitudirlal margins of the track. For the embodiment wherein
tracks Tal, Tbl, ... are spa~ed from each other by guard bands,
as shown in FIG. 2A, this lack of coincidence between the path
traversed by the scanning head and the record track may not produce
noticeable deterioration in the video picture which ultimately is
reproduced. However, if the information density of the magnetic
tape is increased, as by recording parallel, adjacent record
tracks without separating guard bands therebetween, and by reducing
the transport speed of tape 3, the problem of imprecise coincidence
between the path or trace of the scanning head and each adjacent
record track is noticeable. ~hat i5, if the ~canning head deviates
significantly from the reco~d track, undesired cross-tallc s;gnals
are picked up from the adjacent track. These cross-talk signals
may interfere with the video picture which ultimately is reproduced.
Furthermore, tracking errors of this type may reduce the signal-
to-noise ratio, thus degrading the quality of the reproduced video
picture.
As a numerical example of the foregoing, the width of
each record track shown in FIG. 2A may be 30 microns. Similarly,
the width of each guard band also m~y be 30 microns. Hence, the
track pitch is 60 microns. Now, if the tape transport speed is
reduced to one third of the speed used to record the xecord tracks
shown in FIG. 2A, the successive parallel tracks will be adjacent
each other as shown in FIG. 2B. Although the inclination of the
parallel tracks shown in FIG. 2B closely resembles the inclination
:`
_9_
.
61
shown in FIG. 2A, because of the much hi~her rotary speed of the
heads rela-tive to the transport speed of the tape in both examples,
it may be appreciated that the track pitch in FIG. 2B is reduced
to one third the pitch shown in FIG. 2A. That is, the track
pitch, or width of each record track, sho~n in FI~. 2B is 20
microns. If the size of the reproducing head used to reproduce
the video signals recorded in the tracks shown in FIG. 2A is equal
to the size of the reproducing head used to reproduce the signals
recorded in the tracks shown in FIG. 2B, then the gap leng-th is
30 microns. Preferably, when this head is used with the record
tape shown in FIG. 2B, the scanning path of the head must be con-
trolled so as to scan only a 10 micron width portion of aajacent
record tracks. That is, if head lb scans track Tblduring a repro-
ducing operation, this head must scan only a 5 micron portion of
track Tal and only a 5 micron portion of track Ta2. I~ the scanlling
path or trace of head lb deviates from the foregoing limitations,
interference due to cross-talk from the adjacent record tracks
(tracks Tal, Ta2) tends to deteriorate the video picture which is
reproduced.
As mentioned above, the usual servo control system provided
with VTR's of the type shown in FIGS. lA and lB may not be capable
of controlling the scanning trace of the heads within the afore-
noted-limitations. It is one purpose of the present invention
to provide an adjustable support assembly for heads la, lb so that
the scanning traces of these heads can be adjusted so as to correct
; the tracking errors which may not be fully compensated by the usual
servo control system. A preferred embodiment of such an adjustable
head support assembly is formed of piezo-electric material which is
responsive to a voltage applied thereto so as to bend or deflect
accordingly. Thus, if heads la and lb are supported by such piezo-
electric material, the controlled deflection thereo~ can be used
--10--
.
. . - -
6~
to compensate for such trackin~ errors.
One type of head support assembly which can be used with
the present invention is shown schematically in FIGS. 3A-3C. This
assembly is formed of a pair of leaf members 7 and 9, each being
constructed of piezo-electric material whose directions of polariza-
tion are represented by the illustrated arrows. The opposite
surfaces of piezo-electric leaf member 7 are plated with electrodes
6a and 6b, respectively; and the opposite surfaces of piezo-electric
leaf member 9 likewise are plated with electrodes 8a and 8b, respec-
tively. When piezo-electric leaf members 7 and 9 overlie each
other such that electrodes 6b and 8a are in contact, the assembly
will deflect if a variable voltage is applied across the respective
members. For example, and as shown in FIG. 3B, if voltages are
applied to the electrodes in the manner shown, then piezo-electric
leaf mem~er 7 tends to e~pand in its lengthwise direction while
piezo-electric leaf mer~er 9 tends to compres~. As a re~uJ.t of
these oppositely-acting forces, the illustrc~l:ed head support
assembly bends, or deflects, by an amount which is a function of
the strength of the electric field applied across each member.
The variable voltage source thus repres~nts that a variable
electric field can be applied across members 7 and 9 so as to
adjustably deflect the head support assembly. If the po]arity
of this electric field is reversed, the direction in which the
; assembly bends, or deflects, correspondingly is reversed~
The head support assembly comprised of the pair of piezo-
electric leaf members having respectively opposite surfaces plated
with electrodes hereinafter is referred to as a bi-morph leaf or
bi-morph assembly~
` : -
If the direction of polarization of the plezo-elec-tric
members is made opposite to each other, that is, if elec~rode 6a
of leaf member 7 now contacts electrode 8a of leaf member 9, the
manner in which voltaye is applied to th~ bi-morph assembly to
5 e~fect a displa~ement thereof i.s as shown in FI~3C. Hence, a
voltage need not be applied to the electrodes which are in common
contact with each other, as in the FIG. 3s embodiment. Instead,
if a bias voltage, for example, V /2 is applied to electrode 8b
and if a variable voltage V is applied to electrode 6b, then the
illustrated bi-morph assembly will bend in a downward direction
if the variable voltage V is less than the bias voltage Vo/2.
Conversely, the bi-morph assembly will bend in an upward direction
if variable voltage V exceeds bias voltage Vo/2. It can be assumed
that variable voltage V is variable over a range from zero to VO
volts.
~ practical embodiment o~ a head support assemb].y formed
of a bi-m9rph leaf is illustrated in FIGS. ~A and 4B, whi.ch are
side and bottom views, respectively. In FIG. 4A, it is assumed
that the head support assembly is mounted on -the lower surface of
upper, rotatable guide drum 2a (FIG. lB~. The head support assembly
includes a mounting base 10 adapted to receive the bi~morph assemhly
which may be secured to this mounting base by a suitable adh~sive 11
The bi-morph assembly extends outward from the base toward the
periphery of guide drum 2a, and magnetlc head la or lb is mounted
on the free end of the bi-morph assembly.
Preferably, damping members 13a and 13b are provided to
damp free or resonant oscillation of the bi-morph assembly which
may be caused by the forces exerted in response to the bending
voltages applied to the respective electrodes. Damping members
13a and 13b are attached to tabs 12a anfl 12b, respectively, these
-12-
' ' ' : ,
' ' ~ '` ' .' ' ',: "' ' ~ . '. ` ' ' :
G~
tab~ extendiny from a damping member mounting plate 14 which, as
shown, extends outwardly from base 10. Dam~iny action is achieved
when the damoing members are pressed between the sides of the bi-
morph assembl~ and tabs 12a and 12b with suitable force to prevent
oscillation but not so g~ea-t as to prevent deflection of the bi-
morph assembly in response to the drlve voltage applied thereto.
As also shown, conducting leads are secured to the respective
electrodes of the bi-morph assemhly for receiving the drive or
deflecting vol-tage.
In accordance with the present invention, the drive
voltaye which is applied to the bi-morph asse~bly is produced
during a reproducing operation. This dr;ve voltage represents
the deviation of the scanning trace of head la, lb from the pre-
viously recorded track. The extent of this deviation is determined
by detecting the magnitude of a cross-talk component which is
picked up by the scanning transducer fxom a track adjacent the
particular track which is scanned. For example, and wi~h reference
to FIG. 2B, if head lb scans track Tbl, the deviation between the
scanning trace of this head and track Tbl can be representea by
the level of a cross-talk signal picked up from track Tal and/or
track Ta2. It is one aspect of the present invention to record a
predetermined signal, such as a pilot signal, together with the
video signals which normally are recorded in each track so that,
during a reproducing operat;on, a cross-talk comp~nent of the pre-
determined, or pilot signal can be detected and used as an indica-
tion of the extent of a tracking error.
Referring to FIG. 5, there is illustrated therein a block
diagram of video signal recording apparatus which can be used to
record both a video signal and a predetermined, or pilot signal on
the recording medium. The illustrated recording apparatus is
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' ' ' ` ` ' . `
capable oE recording ~oth monochrome (black-and-white) video
si~nals and color video signals on the record medium. For the
purpose of the present discussion, it will be assumed that this
apparatus is supp].ied with a composite color video signal, includ-
ing lumlnancc and chrominance components, and -the usual synchron.iz-
ing signals, for recording. In one embodiment, the recording
apparatus is comprised of a luminance signal channel, formed of
a low-pass filter 16, frequency modulator 18 and high-pass filter
19, and a chrominance s;gnal channel formed of a band-pass filter
17, frequency converter 21 and low-pass filter 22. As is conven-
tional, the respective circuits in each of the aforementioned chan-
nels are connected in series for the purpose of separating the
luminance and chrominance signals from each other, and then frequency-
modulating the separated luminance signals to a higher frequency band
15 while frequency~converting the chrominance si~nals to a lower fre-
quency band. These band-separated s:ignals are co~inea in an add-
ing circuit 20 to be supplied to heads la, lb ~or recording on
the record medium. In an alternative e~odi:ment of recording appa-
ratus, the composite color video signal may be suppliedr through
suitable filtering and amplifying circuits, to a :Erequency modulator,
and the frequency-modulated composite color video signal then may
be recorded on the medium.
A pilot signal oscillator 24 is provided to generate a
pilot signal having a predetermîned frequency fp. If the recording
apparatus is of the illustrated type wherein a frequency-modulated
; luminance signal and a frequency-converted chrominance signal are
combined for simultaneous recording, the frequency fp of the pilct
signal generated by pilot signal oscillator 24 preferably is less
than the band of frequency-modulated luminance s.ignals and is
; 30 capable of being detected or discriminated from the frequency-
converted chromin~nce signals. Pilot si~n~l oscillator 24 is
coupled through a gate ~ircuit 25 to an adding circuit 23. Gate
circuit 25 is responsive to a gating signal applied thereto so
as -to transmit a predetermined duration of pilot signal to adding
circu:it 23. It is one feature of the i.llustrated recording appara-
tus to record the pilot signal only during predetermined times oE
the video signal. Preferably, and in order to insure that the
pilot signal will not interfere with the video si~nal during a
reproducing operation, the pilot sianal is recorded during a certain
portion of the horizontal blanking interval. For this purpose, the
gating signal applied to gate circuit. 25 is derived from the hori-
zontal synchronizing signal included in the composite color video
signal. Accordingly, a horizontal synchroniæing separator circuit 26
is connected to separate the horizontal synchronizlng signal from
the composite color video signal. As shown, horizontal synchroniz-
ing separator circui.t 26 is coupled to the output of l.ow-pass fi.lker
16. The separated horizontal synchronizi.ng si`gnal is applied to a
monostable multivibrator 27 to -trigger the latter for generating a
gating signal which, in turn, is applied to gate circuit 25~
In operation, the luminance and chrominance signal channel.s
operate in conventional manner and, therefore, need not he further
described. Horizontal synchronizing separator circuit 26 also
operates in a conventional manner so as to separate the horizontal
signal, shown in FIG. 6A, from the composite color video si.gnal
which is applied to input terminal 15. The separated horizontal
synchronizing signal triggers monostable multivibrator 27 to produce
a gating pulse of limited duration as shown in FIG. 6C~ The pilot
siynal, shown in FIG. 6B, is supplied from pilo~ signal oscillator
24 to gate circuit 25 and is gated through the gate circuit during
30 . the interval of the gating pulse of FIG. 6C. Accordingly, the
6~
pilot signal is supplied to adding circui-t 23 during a predeter-
mined portion of the horizontal blanking interval, such as durin~
an initial portion of the horizontal synchronizing pulse, as shown
in FIG. 6D. The gated pilot signal is combined with the frequency-
modu]ated luminance signal and the frequency~converted chrominancesignal for recordin~ on the record medium by heads la and lb durin~
alternate scans of the medium. In one embodiment, this pilot signal
is recorded during each horizontal blanking interval. I~oweve~, if
desired, the pilot signal may be recorded during selected horizontal
blanking intervals. Thus, in successive, ad~acent parallel tracks,
a pilot signal is recorded at predet~rmined locations, i.e., during
a selected portion of the horizontal blanking interval r Of the
horizontal line interval.
As mentioned above, one aspect of this invention is to
utilize the cross-talk component of the recorded pilot signal
which is picked up from adjacent txacks as cl~ indication of the
trackirlg error of the scanning transducer dt~ring a reproducin~
operation. As may be appreciated, if the horizontal blanking
intervals in adjacent tracks all are in aliynment in a d~rection
tranversely of such tracks, there may be difficulty in discriminat-
ing between a cross-talk pilot signal and the pilot signal which
is recovered from the track being scanned. This difficulty may
be avoided if the pilot signal is of a different frequency for
the different tracks. That is, if the pilot signal recorded by
head la is of a frequency fpa and if the pilot si~nal recorded by
head lb is of a frequency fpb, then suitable frequency detectors
can be used to detect the cross-talk pilot signal during signal
reproduction. In the preferred embodiment described herein, the
frequency of the pilot signal is the same for all tracks. There-
fore, in order to facilitate the detection of the cross-talk componen
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, . . ' ' '` :
- .. . . .
- - . - : .. .
of the pilot signal, the position of the horizontal blanking
in-tervals which are recor~ed in one track is shifted or displaced
w;th respect to the position of the horizontal blanking intervals
recorded in an adjacent tr~ck. This is illustrated in FIG. 7
which shows tracks Tal, Tbl and Ta2, in which are recorded hori-
zontal blanking intervals Hl, H2 and H3, respectively. As shown,
these horizont~l blanking intervals are not ali~ned. Rather,
hori~ontal blanking intervals H2 are displaced or shifted with
respect to horizontal blanking intervals Hl, and horizontal blank-
ing intervals H3 are displaced, or shifted, with respect to hori-
zontal blanking intervals H2. This displacement or shifting of
the horizontal blanking intervals relative to each other in success-
ive, adjacent tracks, can be attained by suitably selecting the
diameter of tape guide drum 2/ by suitably selecting the transport
speed of the m~ynetic tape, or by selectin~ other paramet:ers in
the VTR, as is well known. For example, in the NTSC system, one
frame of video signals is formed of 525 horizontal lin~ intervals.
If a complete field is recorded in a record track, each track will
include 262.5 horizontal line intervals. As shown in PIG. 2B,
the beginning portion of one track is shiEted relative to the
beginning portion of an adjacent track because of the movement
of the tape. If this displacement is equal to one-half of a
horizontal line interval (0.5 H), then the parallel tracks are
recorded with their horizontal blanking intervals aligned with
each other in a direction transversely of the tracks. This is
the so-called H alignment which is attained by suitably selecting
the diameter of the tape guide drum, the transport speed of the
tape, or other parameters. Hence, the displacement, or shifting
o~ the horiæontal blanking intervals as shown in FIG~ 7 can be
achieved in accordance with the selection of one or more of these
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parameters. Preferably, the displace~ent of the horizontal
b]anking intervals, that is, the displacement between horizontal
bla.nk;.nc3 interval Hl and horizontal blanking interval H2, as well
as the di.sp].acemen-t between horizont~l blanking interval. H2 and
hor:izontal blanking interval H3 is such that, in this displacement
interval,neither a chrominance signal nor a burst signal is recorded.
That is, since the burst signal usually is provided during the back
porch of the horizontal synchronizing pulse, the displacement be-
tween, for example, horizontal blanking interval Hl and horizontal
blanking interval H2 is less than the distance between the leading
portion of horizontal blanking interval Hl and the beginning of the
burst signal on the back porch of horizontal. blanking interval Hl.
A similar displacement is provided between horizontal blanking
intervals H2 and H3. As will soon become apparent, this displace-
lS ment enables the cross-talk components of the pilot s.1.gnals to be
detected and, fur~hermore, avoids interferer)ce which may be caused
by cross-talk between the pilot signal recorded in one track and
the burst or chrominance signals recorded .i.n the adjacent track.
Turning now to FIG. 8, there is illustrated a block diagram
of apparatus for reproducing the video sign~ls record.ed by the
apparatus shown in FIG. 5 and ~or controlling the scanning trace.
of the reproducing head during reproauction~ It will be assumed,
for the purpose of the present discussion, that the horizontal
: blanking intervals recorded in adjacent tracks are dîsplaced, or
~ 25 shifted from each other, in the manner shown in FIG. 7~ It also; will be assumed that the pilot signals are recorded during eachhorizontal blanking interval at the location represented i.n FIG. 6D. .
The video signal reproducing apparatus includes a luminance signal
channel.and a chrominance signal channel coupled to heads la, lb.
The luminance signal channel includes a high-pass filter 31, a
' ' , .
.
- ~
lim:iter 33, a frequency demodulator 34 and a low-pass filter 35,
all connected in series as shown, as is conventional. The chromi-
nance signal channel includes a low-pass fi.lter 32, a frequency
re-converter 37 and a band-pass filter 3~, al] connected in series
as shown, and as is conventional. An addi.ng circuit 36 is couplecl
to the outputs of the luminance and chrominance si~nal channels
so as to recombine the recovered luminance and chrominance components
in order to reconstitute the composite color video signal for further
application to an output terminal 39.
The reproducing apparatus illustrated in FIG. 8 is compat-
ible with the recording apparatus described previously with respect
to FIG. 5. Accordingly, if the recording apparatus includes merely
a frequency modulator for modulating the composite video signal,
that is, if separate luminance and chrominance signal channels
lS are omitted in the recording apparatus, the reproducing apparatus
likewise may include a ~requency demodul~tor ~or demodula.ting the
composite color video signal, thereby omitting the separate lwminance
and chrominance signal channels.
The apparatus for controlling the scanning trace of heads
la, lb, that is, the tracking-error correctin~ circuitry, is com-
prised of a horizontal synchronizing separator circuit 42, mono-
stable multivibrators 43, 44 and 45, gate circuits 40 and 41, band-
pass filters 46 and 47, level detectors 48 and 49 and a comparator
50. Horizontal synchronizing separator circuit 42 may be simi.lar
to aforede5cribed horizontal synchronizing separator cîrcuit 26
and is coupled to the output of the luminance signal channel so
as to separate the horizontal synchronizin~ signal from the recovered
luminance signal. The output of horizontal synchronizing separator
circuit 42 is coupled in common to monostable multivibrators 43
and 45, with monostable multivibrator 43 being further coupled to
.
--19--
:
monos-table mul-tivibrator 44, Monostable multivihrator 43 is
responsive to the separated horizontal synchronizing signal for
producing a pulse of prede-termined duration. This pulse is applied
to monostable multivlbrator 4~ whi~h, .in turn, is adapted to produce
a gating pulse Pl. Depending upon the time constant of monostable
mu].tivi.brator ~3, it is appreci.ated that gating pulse Pl is c~elayed
from the separated hori~ontal synchronizing signal. In the embodi-
ment described herein, this delay is slightly less than a horizontal
line interval (lH) and, more particularly, is approximately equal
to the delay between horizontal blanking interval H2 and the next
succeeding horizontal blanking interval Hl, shown in FIG. 7.
Monostable multivibrator 45 is responsive to the separated hori-
zontal synchronizing signal for producing a gating pulse P2 at a
time delayed from the start of the separated horizontal synchroniz-
ing signal. More particularly, gating pulse P2 is adapted to beproduced at a delayed time approximately correspQndin~ to the
delay between hoxizontal blanki.ng interval H2 and horizontal blank-
ing interval H3, shown in FIG. 7.
Gate circuits 40 and 41 have signa] inputs connected in
common to the output of the chrominance signal channel, ~hese gate
circuits being adapted to receive both the chrominance signal and
the pilot signal which are transmitted through this chrominance
signal channel. Gate circuit 40 includes a gating input adapted
to receive gate pulse Pl; and gate circuit 41 similarly includes
a gating input adapted to receive gate pulse P2. The outputs of
gate circuits 40 and 41 are coupled through band-pass fi].ters 46 and
47, respectively, to level detectors 48 and 49, respectively.
Level detectors 48 and 49 each are comprised of peak level detectors,
such as envelope detectors, or the like, adapted to produce signals
El and E2, respectively, which are a function of the signal level
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- . ' :- ., . ~ , : : . : .
... . .. ` ~ - . . : ~ .. :
1113.961
of the pilot signals applied thereto by band-pass filters 46
and 47. For this purpose, the pass-band oF these ~and-pass
filters preferably may be relatively narrow so as to pass sub-
stantially only the reproduced pilot signals~ As will be described
in greater detail below, these band-pass filters pass cross-talk
components of the reproduced pilot signals.
Comparator 50 is adapted to compare the signal levels
of the passed pilot signals and to produce an output voltage in
accordance with the difference therebetween. Accord;ngly, the
comparator may comprise a differential amplifier having a pair
of inputs adapted to receive signals El and ~2 The output of
comparator 50 is used as the drive or deflection voltage V for
application to the bi-morph assembly so as to correspondîngly
deflect or bend the head support assembly 80 as to adjust the
transverse position o heads la, lb relative t:o the record tracks
-~ as these heads traver~e such tracks.
The operation of the reproducing apparatus shown in
FIG. 8 now will be described. It is recalled that the ~requency
fp of the pilot signal which is recorded during the horizontal
blanking intervals is less than the frequency band of the frequency-
modulatèd luminance signal. Hence, during reproduction, the pilot
signal is passed by low-pass filter 32 in the chrominance signal
channel. In bne embodiment, this pilot signal i.s frequency converted
by a freguency reconverting signal whose frequency is f5 so as to
~ form a freguency-converted pilot signal of a frequency ~fs-fp).
This frequency-converted pilot signal is passed through band-pass
filter 38 and applied to adding circuit 36 as well as to gate cir-
, ,
cuits 40 and 41. If desired, suitable circuitry may be providedto prevent this frequency-converted pilot signal from being applied
30 to the adding circuit.
A
~ -21-
6~ '
In an alternative embodiment, the reproduced pilot
signal which is passed by low pass filter 32 merely is applied
dlrectly throu~3h a hand-pass filter ~o gate circuits 40 and 41
without passi.ng through a frequency converting circuit, such as
frequency converter 37. In either embodlment, it is appreciated
that a detectable pilot signal is applied to gate circuits 40 and
41. Also, in bo-th emb~diments, the pilot signal may be blocked
so as not to be applied to adding circuit 36.
Let it first be assumed that head lb scans track Tbl.
Let it further be assumed that, since the length of the gap of
this head is greater than the width of track Tbl, the head scans
this track symmetrically, as shown in FIG. 7. This corresponds
to a desired scanning trace and is assumed to be error-free.
Since substantially equal portions of tracks Tal and Ta2 are
scanncd by head lb, it may be appxeciated -that, as track Tbl is
~canned, cross-talk components of the pilot signals recorded in
tracks Tal and Ta2 are recovered, which cross-talk components
have substantially equal signal levels. When hea~d lb scan.s
horizontal blanking interval H2 on track Tbl f the horizon.tal
blanking pulse and horizontal synchronizing pulse are reproduced.
Since these signals had been recorded with the frequency-modulated
luminance component, they are recovered at the output of low-pass
filter 35 and are separated from the luminance component by
horizontal synchronizing separator circuit 42. The se.parated
signals trigger monostable multivibrator 43 which, in turn,
triggers monostable multivibrator 44 to produce a gating pulse Pl.
The time of occurrence of gating pulse Pl i:s delayed from the
reproduction of horizontal blanking interval H2~ In particular,
if it is assumed that the pilot signal recorded during horizontal
blanking interval H2 is represented as signal Sb shown in FIG. 9A,
~ ~ .
: -22-
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then ~ating pulse Pl is delayed therefrom, as shown by pulses
Pl in FIG. 9B.
The separated horizontal synchronizing signal also
tr.i.ycJers rnonostab].e multivlbrator 45 to produce pulses P2 as
showr1 in FIG. 9C.
As head lb scans track Tb], first a cross-talk component
of the pilot signal, designated S l' recorded in horizontal blank-
ing interval Hl is reproduced, then the pilot signal, designated
as Sb, recorded in horizontal blanking interval H2 is reproduced,
and then the cross-talk component of the pilot signal, designated
as Sa2, recorded in horizontal blanking intexval ~13 is reproduced.
The time and amplitude relationship between pilot signals Sal, Sb
and Sa2 are shown in FIG. 9A. A comparison of FIGS. 9A-9C lndi-
cates that gating pulse Pl substantially co.incides with the cross-
talk component of pilot signal Sal, and gating pulse P~ substan-
tially coincides with the cross-talk componer)t of pilot signal Sa2.
However, no gating pulse is provided to coincide with.pi:lot signal
Sb. Accordingly, gate circuit 40 responds to gat1ng pulse Pl to
extract the cross-talk component of pilot signal Sal ~rom the repro-
duced video signals; and gate circuit 41 responds to gating pulseP2 to extract the cross-talk component of pilot signal Sal from
the reproduced video signal. The extracted pilot signals pass
through band-pass f;lters 46 and 47 having signal levels El and
E2, respectively, as shown in FIGS. 9D and 9E. These signal
levels are detected by level detectors 48 and 49, respectively,
and are compared in comparator 50. Since it is assumed that head
lb correctly scans track Tbl, si~nal level ~l of the cross-talk
component o~ pilot signal Sal is equal to signal level E2 of the
cross-talk component of pilot signal Sa2. Accordingly, the differ-
ence therebetween is substantially equal to zero. This means that
.
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6~ .
comparator 50 applies a drive vol~age of vo/2 to the bi-morph
assembly, whereby head lb is not deflected d~ring its scanning
trace of track Tb1.
Let it now be assurned that head lb deviates from its
desired scanrling trace in the manner represented by the left-most
example shown in FIG. 7~ Hence, head lb deviates toward track T 1
such that a yrea-ter portion of this track is scanned by the h~ad
than track Ta2. As described above, when the horizonta] blanking
intervals H2 are scanned, horizontal synchronizing pulses are
separated from the reproduced video signals, and monostable multi-
vibrators 43, 44 and 45 are triggered so as to produce gating
pulses Pl and P2, as shown in FIGS. 9B and 9C. Gating pulse Pl
actuates gate circuit 40 to gate the cross-talk component of pilot
signal Sal, recorded in track Tal and reproduced by head lb.
Similaxly, gating pulse P2 actuates gate circl:lit 41 so a8 to pass
the cross-talk component of pilot signal Sa~ which is recorded in
track Ta2 and is reproduced by head lb. In view of the deviation
of head lb with respect to its desired scanning trace, the levels
of the gated pilot signals, as passed through band-pass filters
46 and 47 are as shown in FIGS. 9D and 9E, respectively. Conse-
quently, signal level El, detected by level d~tector 48, exceeds
signal leveL E2, detected by level detector 4~. These detected
signal levels are compared in comparator 50 and the difference
therebetween is used to derive the drive voltage which is applied
to the bi-morph assembly. As may be appreciated, this drive volt-
age is of a polarity and magntiude so as to deflect the bi-morph
assembly in a direction whereby head lb is restored to its desired
scanning trace. That is, head lb is deflected in a direction to
minimize the tracking error. This means that the detected signal
~ 30 levels of the cross-talk pilot signaIs which are reproduced from
: - .
'
. .
:. . . . :,
.: . . . . ~ - , . . . , - ..
.. . . .
6~
tracks Tal and Ta2 become equal to each other.
Now let it be assumed that head lb deviates from its
des:ired scanni.ng trace in the manner represented by the right-
most example shown in FIG. 7 wherein he~d lb overlies a greater
portion of track T 2 than track T 1 It is appreciated that,
in accordance with this assumed tracking error, the level of the
cross-talk component of pilot signal S 1' which is recorded in
track Tal and reproduced by head lb, is less than the cross-talk
com~onent of pilot signal Sa2, recorded in track Ta2 and repro-
duced by head lb. Co~parator 50 senses that signal level E2exceeds signal level El and applies a drive voltage to the bi-
morph assembly having a magnitude and polarity which deflects
the bi-morph assembly in a direction so as to restore head lb
to its correct scanning trace.
'rhe relationship between the detected signal levels of
the cross-talk components of the pilot signals which are recorded
in tracks adjacent track Tbl and the track.ing error or deviation
in head lb as it scans track Tbl is graphically depicted i.n FIG. lO
and particularly the solid lines shown therein. Thus, when si.gnal
. level El is equal to signal level E2, the tracking error, or
deviation, is equal to zero ~en.signal level E2 exceeds signal
level El, the tracking error is in one direction Conversely, if
signal level El exceeds signal level E2, the tracking error is in
the opposite direction. As an alternative embodiment, the gap
length of head lb (and head la) may be equal to the width. of a
record track. With such a construction, it is appreciated that
a c.ross-talk component can be recovered from only one of the
adjacent tracks and not from both. That is, if head lb traverses
its correct scanning trace, no cross-talk component of the pilot
signals will be reproduced, and E2=El=0. However, if a cross-talk
~ :
6~L
component of a pilot signal is detected with a level equal to E2,
then a tracking error is present wherein head lb overlaps with a
port.i.on of trac~ Ta2 Conversely, if the cross--talk component of
pilot signal S 1 is reproduced with a signal :I.evel E1, then head
lb overlaps with a portion of track T 1 Hence, detected signal
levels E2 and E1, which may be of opposite polarities, can be
used to derive respective drive votlages to he applied to the
bi-morph assembly so as to deflect head lb in a direction to
correct the tracking error. The relationship between signal
levels El and E2 and the tracking error for the construction
wherein the gap length of héad lb is substant.ially equal to the
width of the record track is represented by the broken lines
shown in FIG. 10. As may be appreciated, with this construction, ..
a diode switching arrangement may be provide~l to selecti:v~ly apply
signals El and E2 to the bi.-morph assembly as a drive voltage there-
for; or, alternatively, comparator 50 may be used in a manner
similar to that described hereinabove.
While the present invention has been particularly shown
and described with reference to preferred embodiments and applica-
tions thereof, it should be readily apparen-t to one of ordinary
: skill in the art that various modifications in form and details
may be made without departing from the spirit and scope of the
invention. For example, although two scanning heads la, lb have
been described, it is appreciated that the tracking-error correcting
technique disclosed herein is equally applicahle to a recording/
reproducing device employing only a single head, or to such a
device employing more than two heads. Also, and with reference
to FIG. 8, horiæontal synchronizing separator circuit 42 has been
shown as being connected to the output o~ low-pass filter 35 so
as to receive the recovered, demodulated horizontal synchronizing
-26
6 IL
signal. If desired, a suitable frequency detector or discriminator
may b~ coupled to the output of limiter 33 and -tuned to the partic-
ular frequency which represents -the horizontal synchronizing signals.
Such a frequency detector or discriminator can he used to tri~ger
monostable multivibrators 43-45, in a manner similar to -that de-
scribed above. Still further, the pilot signal which is recorded
during predetermined portions of the horizontal blanking intervals
need not be generated solely by pilot signal oscillator 24 (FIG. 5)
As an alternative, the ~urst signal which normally is provided on
the back porch of the horizontal synchronizing signal can be used
as the pilot signal. In such an alternative, the burst signal
recorded in the displaced, or shifted horizontal blanking intervals
Hl, H2 and H3 can be detected such that the signal levels of the
cross-talk components of such burst signals may be used to repre-
~en~ the extent of the tracking error of the scanning head, thisoperation being performed in a manner quite s;milar to the fore-
going operation discussed in conjunction with the embodiment
shown in FIG. 8. Additionally, although the bi-morph assembly
is preferred for the head support assembly, other adjustable
head support structures can be used, if desired.
The present invention need not be limited only to an
NTSC-type color video signal. Rather, the present invention is
applicable to the PAL system and SECAM system as well~ As men-
tioned previously, tracking-error correction can be attained if
the recorded and reproduced video signals are monochrome signals.
Still further, the luminance and chrominance sîgnal
channels in both the recording and reproducing apparatus may be
of the type wherein crosstalk components which are picked up from
adjacent tracks are suppressed. For example, the azimuth angles
of heads la and lb may differ from each other so that a cross-talk
.
:: -, - .
6~
component of -the luminance signal picked up from an adjacent
track is suppressed by reason of the attendant azimuth loss.
Cross-talk components of the chrominance si~nal may be suppressed
by providinc3 di.fferent frequency-convertiny carriers in the record-
ing apparatus, the frequencies of these carriers exhibiting aninterleaved relationship. By usincJ this technique, cross-talk
components which are reproduced from adjacent tracks can be
eliminated by providing a comb filter through which the repro- ..
duced chrominance components are passed.
10Hence, it may be appreciated that tracking errors are
detected during each horizontal line interval so that heads la
and lb can be suitably controlled so as to scan a correct trace
across each record track during a reproducin~ operation. This
tracking error correction system is of part:icular advantage when
the width of each record track is reduced and the tape tran.spoxt
~peed is of a relatively low value so as to .increase the recording
density, and thus the recording time, for the record medium~
It is,therefore, intended that the appended claims be.
interpreted as including all of the aforedescribed changes and
modifications, as well as various other such changes which will
become apparent to one of ordinary skill in the art. :
.
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