Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
117'79S~
E~ACKGROUN~ OF TlIE INVENTION
~rhe present invention generally relates to rotary
~recording mediums and recording systems thereof, and more
l~particularly to a rotary recording medium of a type wherein three
¦kinds of reference signals for controlling tracking of a
~reproducing tracing element are recorded on opposite sides of a
continuous spiral track, in which the reference signals are
~recorded so that a feeding control of a reproducing transducer is
~performed by use of one of the above reference signals without the
~use of special control signals, and further, to a system for
recording such a rotary recording medium.
¦ ~ system has previously been proposed which records an
¦information signal as variations in geometrical configuration along
a spiral track on a rotary recording medium, without providing a
guide groove for guiding a reproducing stylus. An information
signal such as a television video signal, first and second pilot
or reference signals for tracking control, and a third pilot or
reference signal for switching the first and second reference
~signals upon reproduction, are recorded on the rotary recording
¦medium (hereinafter simply referred to as a disc) by this system.
¦The first and second reference signals are alternately recorded
¦along the radial direction of the disc at intermediate positions
¦between center lines of adjacent information signal tracks. The
¦third reference signal is recorded at a predetermined position
¦on every information signal track. A reproducing system
¦reproduces the information signal, and the first, second, and
¦third reference signals by use of a reproducing tracing element.
¦A tracking control signal is formed from the first and second
¦reference signals which are switched by the third reference
¦signal separated from a reproduced signal. The tracking of the
- 2 - ~
11'7'79~i~
1 reproducing tracing element i9 controlled by this tracking
control signal. Accordingly, although the guide groove is not
I provided, the reproducing tracing element can accurately trace over
I the information signal track.
¦ In a disc of this type the track pitch is of an
exceedingly small value, for example, l.4 ~m, in order to obtain a
~high recording density. For this reason, extremely high precision
¦is required in a recording system, to feed a light beam along the
¦radial direction of the disc in order to record the information
~signal onto the disc. Accordingly, it is very difficult to form an
¦unrecorded portion of large pitch at the so-called lead-in part in
¦the vicinity of the outermost peripheral part of the disc, as in the
¦conventional audio record disc.
~ ¦ Therefore, in the above type of a disc, the track is
~formed with the normal pitch, from the outermost peripheral part
¦to the innermost peripheral part of the disc. ~ence, in order to
¦start reproducing the information signal within five seconds from
¦the time when the reproducing tracing element is lowered onto the
1~ ¦outermost peripheral part of the disc, for example, the reproducing¦tracing element must be lowered onto the outermost peripheral part
f the disc within a range of l05 ~m (calculated from 1.4 x 15 x 5
- 105), since the disc i8 rotated ~t a rotational qpeed of ~00 rpm
when four fields of video signals are recorded for one revolution
of the disc. As a matter of mechanical precision, it is extremely
difficult to accurately lower the reproducing tracing element onto
the disc within a very narrow allowable range in the order of
105 ~m.
On the other hand, if the allowable range for lowering
the reproducing tracing element is set to a large value, the time
between the time when the reproducing tracing element is lowered
117'795~
1 land the time when the reproducing tracing element reaches the track
~which is recorded with the information signal to start reproduction,
;becomes long.
Therefore, it was highly desirable in the art to realize
a disc in which the allowable range for lowering the reproducing
tracing element is large, and the time required until the
repro~uction is started from the time when the reproducing tracing
element is lowered onto the disc is short. Moreover, it was
~ desirable to enable an operation in which a desired program is
~quickly selected from the recorded information signal, to start
the reproduction from the selected program.
Furthermore, it is desirable to automatically return the
¦reproducing transducer to a resting position other than the position
~ on the disc, to return the reproducing transducer to a state before
¦starting of the reproduction when the reproducing tracing element
¦reaches the innermost peripheral part of the disc to complete
reproduction.
As a method of realizing the above demands, the
application of the so-called random-access method known in the art
appears to be possible. In the random-access method, an address
signal is recorded over the entire track, including the tracks at
tne outermost peripheral part of the disc. The reproducing
apparatus reads out the address difference between the address
¦number of the track onto which the reproducing tracing element
~was lowered, and the address number of the track of the first
¦information signal, and ~uickly moves the reproducing tracing
¦element until the address difference becomes zero. In addition,
¦an operation is also performed in which the reproducing transducer
¦is returned to the resting position when the final address number
¦is read out.
- 4 -
il7'7~5~
1 ~ However, in this method, the address signal must ~e
~recorded on the disc beforehand, and the recording system tends to
¦become complicated. Moreover, it becomes necessary to provide
l circuits for carrying out address detection and random access
control in the reproducing apparatus, and the reproducing apparatus
becomes complex and expensive.
Another method may be considered in which a synchronizing
signal of the video signal is not recorded at the outermost
~peripheral part of the disc. The existence or non-existence of the
¦synchronizing signal can be detected in the reproducing apparatus
~and the reproducing transducer can be returned to the resting
¦position when no synchronizing signal is detected. However, in a
PCM disc, an audio signal is pulse code modulated and recorded, and
there accordingly is no synchronizing signal. Hence, if an attempt
¦is made to reproduce the PCM disc, the reproducing apparatus will
¦detect that there is no synchronizing signal ~ust before starting
¦reproduction, and the reproducing transducer will be returned to
~the resting position. Thus, this method has a disadvantage in that
¦the PCM disc cannot be reproduced.
~ owever, when the information signal is a video signal
¦in the disc having the above recording format, ~he above described
¦first, second, and third reference signals are used regardless of
whether the audio signal is a PCM audio signal. The third reference
signal is used to detect the swit~hing position of the first and
second reference signals, to switch a tracking control signal
forming circuit system. It is sufficient to detect the existence or
non-existence of the third reference signal, and the recording
l~ngth of the third reference signal is not important. Therefore,
in the present invention, the third reference signal is recorded by
varying the recording length (recording range), and the above
11'7'795~
1 I described various discrimination is performed by detecting the
length (size) of the recording length (recording range) of the thirc
~ reference signal.
SUMMARY OF THE INVENTION
Accordingly, it is a general ob~ect of the present
invention to provide a novel and useful rotary recording medium and
a recording system thereof, in which the above demands have been
realized and the above disadvantages have been overcome.
~ Another and more specific object of the present invention
is to provide a rotary recording medium and a recording system
¦ thereof, in which the recording format of one reference signal of
¦ reference signals for tracking control originally present in a
~ rotary recording medium, is different at a predetermined position
~ from the recording format at other recording positions. According
¦ to the rotary recording medium of the present invention, there is
no need to record a special control signal for controlling the
¦ reproducing transducer movement in the reproducing apparatus, and
~ the recording with respect to the rotary recording medium can be
easily performed.
Another ob~ect of the present invention is to provide a
rot~ry recording medium and a recording sys~em thereof, in which
the recording length of one reference signal at a position where
the reproducing transducer movement is controlled, is different
rom the recording length at other positions. This recording
¦ length of the reference signal is a length in accordance with the
control state of the reproducing transducer movement. Hence, the
¦ reproducing apparatus can easily perform control with respect to
I the reproducing transducer movement, by discriminating the above
recording length of the reference sisnal.
117'79S~
1 Other ob~ects and further features of the present
invention will be apparent from the following detailed description
when read in conjunction with the accompanying drawings.
l .
~BRIEP DESCRIPTION OF THE DRAWINGS
FIG.l is a plan view, with a part cut away, for explaining
a recording pattern of an embodiment of a rotary recording medium
according to the present invention;
1 FIG.2 is a perspective view in an enlarged scale, ~howing
~ a part of a rotary recording medium together with a tip end part of
a reproducing stylus;
FIGS.3, 4, and 5 respectively show a relationship between
a recording range of a reference signal which constitutes an
1 essential part of the present invention, along a circumferential
~ and radial directions of a rotary recording medium, and a recording
range of an information signal program along the radial direction
of the rotary recording medium, with respect to each embodiment of
the rotary recording medium according to the present invention;
~ FIG.6 is a systematic block diagram showing an embodiment
¦ of a rotary recording medium recording system according to the
present invention;
FIG,7 i9 a systematic block diagram showing an example of
an apparatus which reproduces the rotary recording medium according
l to the present invention;
¦ FIG.8 is a systematic block diagram showing an example of
an essential part of the block system shown in FIG.7; and
FIGS.9(A) through 9(F) respectively show signal waveforms¦
1 at each part of the block system shown in FIG.8.
1 DETAILED DESCRIPTION
il~7'î :~5~
1 1 ~ recording pattern of an embodiment of a rotary recording
medium according to the present invention, is shown in FIG.l. In
FIG.l, parts P indicated by oblique lines on a disc 10, are recorded
regions of a main information signal such as a video signal and a
PCM audio signal. Shaded parts R indicate recorded regions of a
third reference signal fp3, and remaining blank (white) parts
¦indicate unrecorded regions.
The main information signal is recorded on a spiral
~track on the disc 10, in the recorded regions P. When the main
~ information signal is a video signal, a video fignal of two frames,
that is, four fields, is recorded for each revolution of the disc
10, along a spiral track of pits formed according to the information
contents of the video signal. A part of this track is shown in an
~ enlarged scale in FIG.2. Track turns of a single continuous spiral
~ track corresponding to each revolution of the disc 10, are
i designated by tl, t2, t3, ... . Each track is constituted by the
formation of pits 11 of the main information signal, along the
plane track path, and has no stylus guide groove formed therein.
With respect to one track turn tl, for every horizontal scanning
l period (lH) correspondiny to the horizontal blanking period, pits
12 of a first reference signal fpl are formed on one lateral
side of the track when viewed along the direction of the track path.
Pits 13 of a second reference signal fp2 are formed on the other
l side of the track.
¦ At an intermediate position between center lines of
adjacent track turn3, only one of the pits 12 and 13 of the above
¦first and second reference signals are formed. Moreover, with
respect to one track, the sides on which the pits 12 and 13 are
l formed, are alternated for each track turn. That is, if the pits
¦ 12 and 13 are respectively formed on the right and left sides of
'7'.35~
1 la certain track turn, for example, the pits 12 and 13 are
~respectively formed on the left and right sides of each track
¦adjacent to that certain track.
~ The position where the sides on which the pits 12 and 13
lof the first and second reference signals are recorded switch,
~exists at only one position in each track. This position is
aligned at an end part of the recorded region R along the radial
àirection of the disc 10 in FIG.l. The third reference signal fp3
~ is originally recorded for switching the first and second reference
signals fpl and fp2 reproduced by the reproducing apparatus.
TAe recorded region R of the third reference signal fp3
at the outermost peripheral part of the disc 10, comprises a region ¦
A recorded throughout a central angle of 27 with respect to a
center O for one revolution of the disc 10 (a range of 5 x 10
seconds for one revolution of the disc 10 in time) and having
approximately 2,250 rotational periods (a length requiring
approximately two minutes and thirty seconds for a reproducing
stylus to move along the radial direction of the disc 10 with a
normal moving speed upon normal reproduction), a region Bl recorded
throughout a central angle of 9 for one revolution of the disc 10
(a ranqe of 1.66 x 10 3 seconds for one revolution of the disc 10
in time) and having approximately thirty rotational periods (a
length requiring approximately t~o seconds for the reproducing
stylus to move along the radial direction of the disc 10 upon
normal reproduction), and a region Cl recorded throughout a central
angle of 3 for one revolution of the disc 10 (a range of 5.55 x
10 4 seconds for one revolution of the disc 10 in time) and having
approximately 450 rotational periods (a length requiring
approximately thirty seconds for the reproducing stylus to move
along the radial direction of the disc 10 upon normal reproduction),
g
il'7'7~5~
1 I The positional relationship between the recorded region
¦R recorded with the third reference signal fp3 and the recorded
. region P, is indicated in FIG.3. In FIG.3, the horizontal axis
indicates the time required for the reproducing stylus to move
¦along the radial direction of the disc lO with a moving speed equal
to that upon normal reproduction. In the horizontal axis, the left
side corresponds to the outer periphery of the disc, and the right
side corresponds to the inner periphery of the disc. ~lith respect
¦to the recorded region R, the vertical axis indicates the recorded
1~ ~central angle with respect to the center O of the disc lO. The
¦signal at the part corresponding to the region A of the disc
lO, is used as a lead-in signal. The signal at the region ~l
~is used as a signal for indicating a range between approximately
~ three seconds to one second before a starting position of a first
¦recorded program Pl. The region Cl exists in a range between
¦approximately one second before to approximately thirty seconds
¦after the starting position of the recorded program Pl.
~ A region B2 is formed with the same ob~ective as the
2 ¦region Bl, and exists in a space between a second recorded program
O ¦P2 and the first recorded program Pl, with the same central angle
¦ and interval as the region Bl. A region C2 is ~ormed with the
¦ same central angle and interval as the region Cl. Furthermore,
¦ between each of the above regions, recorded regions Dl, D2, ... .
1 Vn of the third reference signal fp3 are recorded with a central
¦ angle of 1 for one revolution of the disc lO (a range of l.85 x
lO 4 seconds for one revolution of the disc lO in time), in
accordance with each of the programs Pl, P2, ... , Pn.
In addition, a region E recorded with a central angle of
81 for one revolution of the disc, from a position immediately
after the last program Pn (a range of 15 x lO 3 seconds for one
11'7'7~54
1 Irevolution of the disc lO in time), and having approximately
~2,700 rotational periods (a length requiring approximately three
¦minutes for the reproducing stylus to move along the radial
direction of the disc lO in time), exists as indicated in FIG.l.
~The signal at this region E is used as a lead-out signal.
Initial positions in the recorded region R for each
~revolution of the disc lO, is aligned in a ~traight line along the
radial direction of the disc as indicated in FIG.l.
~ As described above, five kinds of regions, that is, the
¦ regions ~, B, ... , E are respectively set with a central angle
which is less than 90. The angular relationship between each
~region is selected so that the central angle of the region C is
¦three times that of the region D, the central angle of the region B
~ is three times that of the region C, the central angle of the region
~ A is three times that of the region B, and the central angle of the
¦region E is three times that of the xegion A. The central angle of
¦the region Dl tD2, ... , Dn) recorded within the progr~m signal, is
~selected to the narrowest angle of 1 so as not to restrict the
¦recording range of the main information signal.
1 It is desirable for the recording range of the region A,
which is used as the lead-in signal, to be relatively long. Hence,
a central angle of 27 is given to the region A. Furthermore, an
accident may occur to damage the reproducing stylus, if the lead-out
signal is not detected due to dropout and the like and the
reproducing stylus is not automatically returned to a waiting
position. Thus, the recording range of the region E, which is
used as the lead-out signal, is selected to have the maximum
central angle of 81.
In the above embodiment of the invention, the recorded
regions Bl (B2 through Bn) and Cl (C2 through Cn) are provided
il~7'~95~
1 before the program signal Pl (P2 through Pn). ~1owever, as another
method of detecting the starting position of the program signal Pl
(p2 through Pn), it may be assumed that the starting position of the
program signal Pl (p2 through Pn) has been detected when the
reproduction with respect to the region A is completed. This is
shown in an embodi~lent in FIG.4 showing a recording pattern of the
third reference signal fp3. In this embodiment, a recorded
region Aa is formed with a recording range from the outermost
¦peripheral part of the disc to the starting position of the first
¦program Pl, and having a central angle of 27.
¦ Next, still another embodiment of a recording pattern of
the third reference signal fp3, is shown in FIG.5. A lead-in
signal recorded region F is recorded and formed at the outer
~ peripheral side of the disc with a central angle of 27 (or 9),
~ for rotational periods equivalent to two minutes and thirty seconds
in ti~le required for the reproducing stylus to move along the
radial direction of the disc upon normal reproduction. A recorded
¦region with a central angle of 1, is formed between the recorded
~region F and the starting position of the first program signal Pl.
¦Moreover, a recorded region Gl (G2 through Gn) is formed throughout
la range corresponding to twenty seconds in time required for the
¦reproducing stylus to move along the radial direction of the disc
¦upon normal reproduction from the starting position of each program
¦Pl (P2 through Pn), with a central angle of 3. Recorded regions
~l through E~n are respectively formed within each program signal
with a central angle of 1, succeeding each of the recorded regions
Gl through Gn. A recorded region I is used as the lead-out signal
as in the case of the recorded region E, and is formed with a
central angle of 81 (or 27).
In the present embodiment of the invention, unlike in the
,11'7'~95~
1 ~above described embodiments, the recorded regions Gl through Gn are
~formed. Accordingly, it is not necessary to know positions which
l are three seconds before start of each recorded program beforehand,
5 and vary the recording pattern of the third reference signal fp3.
Thus, the recording can be performed with ease in the recording
i system.
Although not shown in the drawings, as a further
modification, the recording range of the recorded regions A, Aa,
l and F for one revolution of the disc, which are used as the lead-in
signal, can be set in the order of 2.5 ~ 10 3 seconds, and the
recording range of the recorded regions E and I for one revolution
of the disc, which are used as the lead-out signal, can be set in
the order of 14.46 x 10 3 seconds, for example. Further, the
~recording interval along the radial direction of the disc may also
¦be selected according to the number of programs which are to be
¦recorded, the time, the moving speed of the reproducing stylus
¦upon high-speed search, and the like.
¦ Next, description will be given with respect to an
embodiment of a disc recording system according to the present
invention, by referring to FIG.6. A main information signal such
as a video signal and a PCM au~io signal, is ~upplied to an adder
24 through a terminal 20. Signals related to the start of a lead-in
signal, a program signal, and a lead-out signal, are respectively
applied to a gate circuit 27 through terminals 21, 22, and 23.
A signal having a predetermined frequency obtained from a master
oscillator 25, is supplied to a reference signal generating
circuit 26. The reference signal generating circuit 26 generates
first and second reference signals fpl and fp2 having mutually
different frequencies in the vicinity of a frequency of 0.6 ~Hz,
for example, for every horizontal scanning period, and only
11~7'7~
I
1 during the horizontal blanking period excluding the interval wherein
t,he color burst signal exists. The first and second reference
signals fpl and fp2 thus generated, are supplied to a switching
ll circuit 29. Moreover, a third reference signal fp3 having a
different frequency from the reference signals fpl and fp2, is
generated for a predetermined interval (for a time period
corresponding to the recording range having the above central
angle of 81, that is, 15 x lO 3 seconds) by the reference signal
generating circuit 26, according to the switching of the first and
second reference signals fpl and fp2 which will be described
hereinafter. This third reference signal fp3 is supplied to the
gate circuit 27.
When no signal is applied to any of the input terminals
21 through 23 of the gate circuit 27, the gate circuit 27 passes
the third reference signal fp3 which is obtained from the reference
signal generating circuit 26 for a period corresponding to the
above central angle of 1, that is, 1.85 x 10 4 seconds in time,
for every rotational period of an original disc 42. If the main
information signal which is to be recorded is a video signal, the
period during which the third reference signal fp3 i9 passed i9
within the vertical blanking period. When a signal is applied to
the input terminal 21, the gate circuit 27 passes the third
reference signal fp3 obtained from the reference signal generating
circuit 26 for a period corresponding to the central angle of 27,
that is, for approximately two minutes and ~hirty seconds in units
of 5 x lO 3 seconds in time, for every rotational period of the
original disc 42.
A signal is applied to the input terminal 22 during an
interval between three seconds to one second before recording of
each program of the main information signal which is to be recorded
~7'7~S~
1 is started, for a period corresponding to the central angle of 9,
that is, 1.66 x lO 3 seconds in time, for every rotational period
of the original disc 42. In addition, the input terminal 22 is
applied with a signal for thirty seconds from a point in time
which is one second before recording of each program is started,
¦for a period corresponding to the central angle of 3, that is,
15.S5 x lO 4 seconds in time, for every rotational period of the
¦original disc 42. The gate circuit 27 passes the third reference
signal fp3 from the reference signal generating circuit 26,
during the period in which the signal is applied to the input
terminal 22.
When a signal is applied to the input terminal 23, the
gate circuit 27 passes the third reference signal fp3 from the
~ reference signal generating circuit 26 as it is.
~ The third reference signal fp3 which has passed through
the gate circuit 27, is added to a recorded main information signal
at the adder 24~ A signal from the adder 24 frequency-modulates a
~ carrier at a modulator 28. An output frequency-modulated signal
1 is supplied to a light modulator 35.
The first and second reference signals fpl and p~
obtained from the reference signal generating circuit 26 are
alternately switched over for every rotational period of the
original disc 42, at the switching circuit 29. The reference
l signals thus alternately switched, are respectively supplied to
~ a light quantity control signal generating circuit 30 and a light
modulator 36.
A laser beam emitted from a laser light source 31 is
reflected by a mirror 32, and then adjusted of the light quantity
¦ at a light modulator 33 for ad~usting the light quantity, by a
¦ light quantity control signal from the light quantity control
il'7'795~
1 signal generating circuit 30 and a control signal from a DC
amplifier 46. The laser beam which has passed through the light
~modulator 33, is partly reflected by a half mirror 34 to reach the
light modulator 35, and the remaining part of the laser beam
passes through the half mirror 34 to reach the light modulator 36.
¦The laser beam which has reached the light modulator 35, is
¦modulated by a signal from the modulator 28. An output of the
light modulator 35, that is, a first modulated light beam, is
~ reflected by a mirror 38 and becomes incident to a polarizing
prism 39. The laser beam which has reached the light modulator 36
is modulated by the first and second reference signals fpl and
fp2 obtained from the switching circuit 29. An output of the
light modulator, that is, a second modulated light beam, is
reflected by a mirror 37 and becomes incident to the polarizing
prism 39. The above first modulated light beam is shifted of the
polarizing plane by an angle of 9O with respect to the second
modulated light beam, at the polarizing prism 39.
: The first and second modulated light beam from the
~ polarizing prism 39 are respectively reflected at a mirror 40, and
~ then focused on the original disc 42 through an ob~ective lens 41.
The original disc 42 is formed by covering a disc made of glass
and the like with a photosensitive agent. This original disc 42
¦is placed onto a turntable 43, and rotated at a rotational speed of
¦9oo rpm by a motor 44. Photosensitive recording with respect to
¦the main track is performed by the first modulate'd light beam, and
¦photosensitive recording with respect to a reference signal track
is performed by the second modulated light beam focused at a
position separated by 1/2 track pitch from the main track, on the
original disc 42.
The original disc 42, the turntable 43, and the motor 44
1 as a whole is continuously moved in the direction of an arrow X at
a predetermined speed, by a moving mechanism (not shown).
~Accompanied by the above movement of the original disc 42, the
~turntable 43, and the motor 44, the main track and the sub track
~are formed in a spiral manner from the outer periphery to the inner
periphery of the original disc 42, by the above first and second
~nodulated light beams. Moreover, the position of the light beam
along the radial direction of the original disc 42, is detected by
a position detector 45 comprising a potentiometer. A DC voltage
1 which is in accordance with the detected position i8 thus obtained.
This DC voltage is applied to the light modulator 33 through the
DC amplifier 46.
~ The light modulator 33 is controlled by the DC voltage
1 ~ which is in accordance with the above detected position. Hence,
1 even when the relative linear speed of the first and second
modulated light beam with respect to the original disc 42 changes
according to the position along the radial direction of the original
~ disc 42, the light intensity of the light beam is adjusted so that
~ no undesirable effects are introduced by the above change in the
relative linear speed. ~n addition, the first and second reference
signals fpl and fp2 exist within an interval corresponding to the
horiæontal blanking period of the video signal, other than the
interval of the color burst signal. Because the light modulator 33
l is controlled by the control si~nal from the light quantity control
~ signal generating circuit 30, the light intensity of the light beam
is decreased during the interval in which the first and second
reference signals fpl and fp2 ex st compared to other intervals.
Therefore, the depth of the pits of the main track is maintained
constant, without being affected by the first and second reference
¦ signals.
11'7'~9~
1 I The original disc 42 thus exposed, is subjected to a
known developing process. Further, the original disc 42 is
¦ subjected to known disc manufacturing process and stamping process,
and the disc 10 is finally obtained. This disc 10 is made from a
1 conductive material obtained by mixing carbon into polyvinyl
chloride (PVC), for example Rows of pits are formed on the disc
10 a-~ shown in FIG.2
Next, description will be given with respect to an
example of a reproducing apparatus for reproducing a disc according
~ to the present invention, by referring to FIG.7. The disc 10 is
placed onto a turntable 50, and ro~ated together with the turntable
50 at a rotational speed of 900 rpm by a motor 51. A reproduced
signal is picked up from the disc 10 by a reproducing stylus 15 of
~ a signal pickup device 52 as minute variations in electrostatic
capacitance. This reproduced signal is supplied to a preamplifier
53 having a resonant circuit. The resonant frequency of the
resonant circuit varies according to the variations in the
electrostatic capacitance, and the level of the signal supplied to
the preamplifier 53 is changed into a predetermined level. An
¦ output of the preamplifier 53 is demodulated into the original
¦ information signal by a demodulator 54, and produced through an
¦ output terminal 55.
¦ The output signal of the preamplifier 53 passes through
¦ a lowpass filter S6 and an automatic gain control circuit 57, and
is then reQpectively supplied to amplifiers 58, 59, and 60. Here,
each of the amplifiers 58, 59, and 60 is a kind of a bandpass
amplifier, designed to have a steep passing frequency characteristi~ :
at only the frequency fpl, fp2, and fp3, respectively. The first
and second reference signals fpl and fp2 respectively obtained
from the amplifiers 58 and 59, are adjusted of their level at level
117'795~ ~
1 llad~ustors 61 and 62. The signals thus obtained from the level
adjustors 61 and 62 are supplied to a gate switching circuit 63.
. The third reference signal fp3 obtained from the amplifier
60, is supplied to a detecting circuit 64. An output signal of the
5 1l detecting circuit 6~ iS supplied to a flip-flop 65, to operate
~this flip-flop 65. An output of the flip-flop 65 is applied to the
gate switching CirCuit 63 as a switching pulse.
Every time the output switching pulse of the flip-f lop 65
~ is applied to the gate switching circuit 63, the connection state
¦ of the gate switching circuit 63 is switched over between a
connection state indicated by solid lines and a connection state
indicated by a dotted line in FIG.7. By this switching operation,
the first reference signal fpl is alternately supplied to detecting
l circuits 66 and 67, while the second reference signal fp2 is
¦ alternately supplied to the detecting circuits 67 and 66, every
time the switching pulse is applied to the gate switching circuit
63. Accordingly, the sides on which the first and second
reerence signals fpl and fp2 are recorded with respect to the
l track switches for each track turn, however, the reference signal
l on one side of the track (on the outer side along the radial
direction of the disc, for example) is always supplied to the
detecting circuit 66 for each track turn, while the reference signal
on the other side of the track (on the inner side along the radial
l direction of the disc, for example) is always supplied to the
¦ detecting circuit 67.
The detecting cirCuits 66 and 67 detect the envelopes of
their respective input reference signals, and convert the signals
into DC voltages. These DC voltage~ are supplied to input terminal~
l of a differential amplifier 68. The differential amplifier 68
¦ compares the output signals of the detecting circuits 66 and 67
11'7'7954
1 Iwhich vary according to the reproduced levels of ~he reference
signals fpl and fp2. Accordingly, the differential amplifier 68
generates a tracking control signal which is in accordance with
~the direction of the tracking error and the tracking error quantity.
1 This tracking control signal is further amplified to a predetermined
levèl by a known circuit, and then applied to a tracki~g control
~coil of the signal pickup device 52.
When the tracing position of the reproducing stylus 15
¦shifts from the proper tracing track towards the side of an adjacent
~track, the level of one of the reference signals fpl and fp2
becomes higher than the level of the other. Thus, a level
difference is introduced between the output signals of the detecting
circuits 66 and 67. A tracking control current is obtained from
¦the differential amplifier 68, and supplied to the tracking control
¦coil. Accordingly, the reproducing stylus 15 is moved in a
direction perpendicular to the longitudinal direction of the track
according to the magnitude and direction of the tracking control
current, and tracking control is performed so that the reproducing
¦stylus 15 accurately traces over the track.
¦ On the other hand, the output detected signal of the
¦third reerence signal fp3 detected at the detecting circuit 64, is
¦supplied to a length discriminating circuit 69. The length
¦(corresponding to the above described central angle) of the period
¦during which the third reference signal fp3 exists for one track
turn, is discriminated at the length discriminating circuit 69.
Discrimination can thus be performed on where, that is, in which
region, the reproduced and detected third reference signal fp3 was
recorded. An output discrimination signal of the length
discriminating circuit 69 is supplied to a motor drive control
circuit 70~ The rotational speed and the rotational direction of
il'i'795~
1 a feed motor 72 are controlled by the motor drive control circuit
~70, and the feed motor 72 feeds the signal pickup device 52 along
the radial direction of the disc 10 through a feeding mechanism 73.
For example, the length discriminating circuit 69 has a
1 construction shown in FIG.8. The output of the detecting circuit 64
is successively supplied to integrating circuits 81a through 81d
having mutually different time constants, through a terminal 80.
When a third reference signal fp3 of different length as indicated
in FIG.9(A) or 9(D~ is supplied to the detecting circuit 64, a
detected output indicated in FIG.9(B) or 9(E) is accordingly
obtained. The detected output is supplied to the integrating
circuits 81a through 81d of the length discriminating circuit 69
shown in FIG.8. An integrating circuit of the integrating
~circuits 81a through 81d having a time constant which is in
accordance with the existing period of the detected output,
produces an output having an output level indicated in FIG.9(C) or
9(F). Schmidt trigger circuits 82a through 82d are respectively
connected to the integrating circuits 81a through 81d. A Schmidt
~trigger circuit connected to an integrating circuit producing an
¦output reaching a triggex level TL, is accordingly operated. A
¦logic circ~it 83 is connected to the Schmidt trigger circuits 82a
¦through 82d. The logic circuit 83 produces a control signal
~according to which Schmidt trigger cixcuit was operated, and
¦supplies this control signal to the motor drive control circuit 70
¦through a terminal 84.
¦ For example, when the third reference signal fp3 in the
¦region A having the central angle of 27 is reproduced, the outputs
¦of the integrating circuits 81a through 81c exceed the threshold
¦levels of the Schmidt trigger circuits 82a through 82c, to operate
the Schmidt trigger circuits 82a through 82c. Moreover, the logic
1;1~7'7~S4
`I
1 circuit 83 produces a lead-in detection signal. When the third
reference signal fp3 in the region Bl (B2 through Bn) having the
central angle of 9 is xeproduced, the outputs of the integrating
l circuits 81a and 81b exceed the threshold levels of the Schmidt
trigger circuits 82a and 82b. Hence, the logic circuit 83 detects
that only the Schmidt trigger circuits 82a and 82b have operated,
and produces a signal indicating that the region B1 (B2 through Bn)
has been reproduced. When the third raference signal fp3 in the
~region Cl (C2 through Cn) having the central angle of 3 is
~ reproduced, only the output of the integrating circuit 81a exceeds
~the threshold level of the Schmidt trigger circuit 82a. Thus, the
logic circuit 83 detects that only the Schmidt trigger circuit 82a
~has operated, and produces a signal indicating that the region Cl
¦(C2 through Cn) has been reproduced. When the third reference
¦signal fp3 in the region Dl (D2 through Dn) having the central
¦angle of 1 is reproduced, none of the outputs of the integrating
~circuits 81a through 81d exceed the thre~hold levels of the Schmidt
trigger circuits 82a through 82d, and thus, all the Schmidt trigger
circuits 82a through 82d are operated. In this case, the logic
circuit 83 produces a lead-out detection signal. The output
signal of the above logic circuit 83, i9 supplied to the motor
drive control circuit 70.
The motor drive control circuit 70 is constructed from
a micro-computer, for example. This motor drive control circuit 70
applies a motor driving signal having a level and polarity which
are in accordance with the output signal of the length
¦discriminating circuit 6~ or the control signal from an input
¦terminal 71. ~escription will hereinafter be given with respect to
¦the feed operation control of the signal pickup device 52 performed
¦by the motor drive control circuit 70.
il'7'7~5~
1 ll In a state before starting of the reproduction, the signal
pickup device 52 is at a waiting position separated from above the
disc 10. As the reproduction is started, a reproduction start
instruction signal is applied to the motor drive control circuit 70
from the terminal 71. Accordingly, the signal pickup device 52 is
fed to a position in the vicinity of the outermost peripheral
part of the disc 10, from the waiting position, and the reproducing
stylus 15 is lowered onto the disc 10~ Here, the position where
~ the reproducing stylus 15 is lowered onto the disc 10, is
considerably towards the outer peripheral side of the disc from
the starting position of the first program. This is done by
considering the mechanical accuracy of the feeding mechanism 73,
¦ eccentricity of the disc, and the like, so that reproduction is
~ not started at an intermediate point of the first program.
~ When the lowered reproducing stylus 15 reproduces the
¦ third reference signal fp3 in the region A, this operation is
discriminated at the length discriminating circuit 69. Hence, the
motor drive control circuit 70 feeds the signal pickup device 52
¦ towards the inner periphery of the disc at a relatively high ~peed~
2~ ¦ Therefore, the reproducing stylus 15 moves towards the inner
¦ periphery of the disc in the region A, within a relatively short
¦ period of time.
I The region Bl is recorded for two s~conds in time. Since
¦ the disc rotates fifteen times per second, thirty tracks are
¦ formed in two seconds. Accordingly, the region Bl is formed
¦ throughout the thirty tracks. When the feeding speed is set so
¦ that the region Bl is traced at least once during one rotational
period (1/15 seconds) of the disc upon feeding of the reproducing
stylus to the lead-in position, the above feeding speed must be
set to a speed so as to move by 450 (- 30 x 15) tracks per second.
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il7'795~ 1
1 IlHc,wever, if the feeding speed is set to this kind of a speed, it
will take a long time of approximately two minutes when the entire
disc is to be searched upon high-speed search. Hence, in the
l present embodiment of the invention, the feeding speed upon search
is set to a speed which is fifteen times the above speed.
Therefore, the entire disc can be searched within a short period
o time o~ approximately eight seconds.
When the signal pickup device 52 is fed at the above
high speed, the possibility of the reproducing stylus 15 tracing
and reproducing the region Bl is small. However, since 450 tracks
are formed in the region Cl, this region Cl is traced and
reproduced at least once per revolution of the disc lO. When the
length discriminating circuit 69 discriminates that the region Cl
has been reproduced, the motor drive control circuit 7~ produces a
signal to slowly feed the signal pickup device 52 towards the
outer peripheral direction of the disc at a speed slower than the
above speed. Hence, the region Cl is reproduced as the reproducing
stylus 15 returns towards the outer peripheral direction of the
disc, and then, the region Bl is reproduced. When the length
discriminating circuit 69 discriminates that the reglon Bl has
been reproduced, the motor drive control circuit 70 produces a
signal for feeding the signal pickup device 52 towards the inner
peripheral direction o~ the disc at a feeding speed used upon
normal reproduction. Although it is unlikely that it will happen,
when the reproducing stylus 15 directly reproduces the xegion Bl
after tracing the region A, the motor drive control circuit 70
produces a signal for immediately feeding the signal pickup device
52 toward~ the inner peripheral side of the disc at the normal
reproducing ~peed. There~ore, the lead-in operation is quickly `~
performed within a short period of time, and reproduction is
il~7'i'95~
1 started from the beginning of the first program Pl.
Next, if the second program P2 is to be reproduced from
the beginning of the program when the first program Pl iS being
~reproduced, an instruction signal indicating the above operation is
;~applied to the motor drive control circuit 70 from the terminal 71.
In response to this instruction signal, the motor drive control
circuit 70 feeds the signal pickup device towards the inner
peripheral direction of the disc at a high speed. The motor drive
~ control circuit 70 controls the motor 72 ~o that normal reproduction
~ is immediately performed when the region B2 is reproduced, and
when the region B2 is not reproduced and the region C2 is
reproduced, the signal pickup device is returned towards the inner
peripheral direction of the disc at a low speed to perform normal
l reproduction when the region B2 is reproduced.
Furthermore, if the eighth program P8 is to be reproduced
~from the beginning of the program when the first program Pl is
being reproduced, a number of pulses (seven in this case)
¦corresponding to the number of programs which are to be advanced,
¦are applied to the input terminal 71. Thus, normal reproduction
¦ is immediately performed when the region B8 i9 reproduced, and
¦when the region B8 is not reproduced and the region C8 is
¦ reproduced, the signal pickup device is returned towards the outer
¦ peripheral direction of the disc at a low speed to perform normal
¦ reproduction when the region B8 is reproduced, by the control
performed by the motor drive control circuit 70 with respect to
the motor 72.
Similarly, when a desired program at the outer peripheral
side of the disc from the program which is being reproduced is to `
be reproduced from the beginning of the program, the control
operation is performed in a similar manner as in the case described
117'795~
above, except in that the feeding direction of the ~ignal pickup
device is different in this case.
When reproduction of the program signal is completed
and the reproducing stylus traces and reproduces the third
reference signal fp3 in the region E, this is discriminated at the
llength discri~inating circuit 69. Thus, the motor drive control
Icircuit 70 controls the rotation of the motor 72 ~o as to return
the signal pickup device 52 to the waiting positlon at a high
l speed.
The construction of the length discriminating circuit 69
is not limited to the construction shown in FIG.8. The functions
of the length discriminating circuit 69 may be performed by a
micro-computer. In addition, in the above embodiment of the
invention, the third reference signal fp3 is used as the signal to
vary the existing period. However, either one or both of the first
and second reference signals fpl and fp2 may be used instead.
Moreover, the reproducing system is not limited to the electrostatic
capacitance type using the reproducing stylus, but the reproducing
system may be an optical system in which a light beam is used or
reproduction.
According to the disc of the present invention, it is
unnecessary to record a special control signal to perform the
above described operations. Recording of the disc is simple
~ since only one of the three reference signals originally used for
¦ tracking control, is used. Furthermore, it is unnecessary to
provide a special control signal detecting circuit in the
reproducing apparatus, and the circuit construction of the
reproducing apparatus is accordingly simplified.
Further, the present invention is not limited to these
embodiments, but various variations and modifications may be made
117'7~5~
I w:ithout departing from the scope of the present invention.
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