Note: Descriptions are shown in the official language in which they were submitted.
~1~'75~5S
:.
I .I BACKGROUND OF THE INVENTION
The present invention generally relates to rotary
recording medium reproducing apparatuses, and more particularly
Il to an apparatus for reproducing a rotary recording medium of
1 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.
A 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
l 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
- 2 -
I the third reference signal separated from a reproduced
signal. ~he tracking of the reproducing tracing element is
controlled by this tracking control signal. Accordingly,
although the guide groove is not provided, the reproducing
tracing element can accurately trace over the information
signal track.
~n a disc of this type, the track pitch is of an
exceedingly small value, for example, 1.4 llm, 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. Hence,
in order to start reproducing the information signal within
five seconds from the time when the reproducing tracing
element is lowered onto the outermost peripheral part of the
disc, for example, the reproducing tracing element must be
lowered onto the outermost peripheral part of the disc
within a range of 105 ~m (calculated from 1.4 x 15 x S =
105), since the disc is rotated at a rotational speed of 900
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
il'7'7955
I ~ range in the order of lOS ~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 and 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 reproduction 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 the 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
i~ î '7~55
1 ~I number of the track of the first information signal, and
quickly moves the reproducing tracing element until the
address difference becomes zero. In addition, an operation
I is also performed in which the reproducing transducer is
returned to the resting position when the final address
number is read out.
However, in this method, the address signal must
be recorded on the disc beforehand, and the recording system
~ tends to become complicated. Moreover, it becomes necessary
1~ 1 to provide 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 synchronizin~
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 just 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.
¦ However, when the information signal is a video
signal in the disc having the above recording format, the
above described first, second, and third reference signals
are used regardless of whether the audio signal is a PCM
ii'~'7~55
I audio signal. The third reference signal is used to detect
the switching position of the first and second reference
signals, to switch a tracking control signal forming circuit
I system. It is sufficient to detect the existence or non-
existence of the third reference signal, and the recording
length of the third reference signal is not important.
l Therefore, in the disc which is reproduced by an apparatus
I according to the present invention, the third reference
l signal is recorded by varying the recording length (recording
l range), and the above described various discrimination is
performed by detecting the length (size) of the recording
length (recording range) of the third reference signal.
SUMMARY OF THE INVENTION
~ Accordingly it is a general object of the present
1 invention to provide a novel and useful rotary recording
¦ medium reproducing apparatusj in which the above demands
¦ have been realized and the above disadvantages have been
1 overcome.
~ Another and more specific object of the present
invention is to provide a rotary recording medium reproducing
apparatus for reproducing a rotary recording medium, 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.
¦ The rotary recording medium reproduced by the apparatus
~ according to the present invention, need not be recorded
¦ with a special control signal for controlling the reproducing
1 transducer movement in the reproducing apparatus, and the
117'7955
i
1 ll recording with respect to the rotary recording medium can be
easily performed.
Another object of the present invention is to
l provide a rotary recording medium reproducing apparatus for
reproducing a rotary recording medium in which the recording
length of one reference signal at a position where the
I reproducing transducer movement is controlled, is different
from the recording length at other positions. This recording
l 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 the reproducing transducer movement, by
discriminating the above recording length of the reference
~ signal.
~ Other objects and further features of the present
¦ invention will be apparent from the following detailed
description when read in conjunction with the accompanying
1 drawings.
2~ ~ BRIEF 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 which is to be reproduced by a reproducing
apparatus according to the present invention;
FIG.2 iS a perspective view in an enlarged scale,
showing 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 along a
circumferential and radial directions of a rotary recording
~1~7'7~55
1 I medium, and a recording range of an information signal
i program along the radial direction of the rotary recording
medium, with respect to each example of the rotary recording
medium;
FIG.6 is a systematic block diagram showing an
example of a rotary recording medium recording system;
FIG.7 is a systematic block diagram showing an
embodiment of an apparatus according to the present invention
l for reproducing the rotary recording medium;
1 FIG.8 is a systematic block diagram showing an
embodiment of an essential part of the block system shown in
FIG.7; and
FIGS.9(A) through 9(F) respectively show signal
~ waveforms at each part of the block system shown in FIG.8.
l DETAILED DESCRIPTION
A recording pattern of an example of a rotary
recording medium which is to be reproduced by a reproducing
~ apparatus according to the present invention, is shown in
~ FIG.l. In FIG.l, parts P indicated by oblique lines on a
disc lO, 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 lO, in the recorded regions P.
When the main information signal is a video signal, a video
¦ signal of two frames, that is, four fields, is recorded for
1 each revolution of the disc lO, along a spiral track of pits
¦ formed according to the information contents of the video
il7'~S5
1 ¦ signal. A part of this track is shown in an enlarged scale
Il in FIG.2. Track turns of a single continuous spiral track
I corresponding to each revolution of the disc 10, are 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 period (lH) corresponding to the horizontal blanking
l 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 side of the track.
¦ At an intermediate position between center lines
¦ of adjacent track turns, 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 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 a 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 of 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 direction 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.
;117'7~55
1 I The recorded region R of the third reference
signal fp3 at the outermost peripheral part of the disc lO,
comprises a region A recorded throughout a central angle of
I 27 with respect to a center O for one revolution of the
disc lO (a range of 5 x lO 3 seconds for one revolution of
the disc lO 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 lO with a normal moving speed
l upon normal reproduction), a region Bl recorded throughout a
central angle of 9 for one revolution of the disc lO (a
range of l.66 x lO 3 seconds for one revolution of the disc
lO in time) and having approximately thirty rotational
~ periods (a length requiring approximately two seconds for
¦ the reproducing stylus to move along the radial direction of
the disc lO upon normal reproduction), and a region Cl
recorded throughout a central angle of 3 for one revolution
of the disc lO (a range of 5.55 x lO seconds for one
¦ revolution of the disc lO 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 lO upon normal reproduction).
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
9SS
l I to the inner periphery of the disc. With respect to the
recorded region R, the vertical axis indicates the recorded
central angle with respect to the center O of the disc lO.
I 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 Bl 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 objective as
the region Bl, and exists in a space between a second recorded
program P2 and the first recorded program Pl, with the same
central angle and interval as the region Bl. A region C2 is
formed with the same central angle and interval as the
region Cl. Furthermore, between each of the above regions,
recorded regions Dl, D2, ... , Dn of the third reference
signal fp3 are recorded with a central angle of 1 for one
revolution of the disc lO (a range of 1.85 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 revolution 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
:117'7955
1 ¦ 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 straight
¦ line along the radial direction of the disc as indicated in
FIG.l.
, As described above, five kinds of regions, that
¦ is, the regions A, B, ... , E are respectively set with a
l __ _
central angle which is less than 90. The angular relationship
~ between each region is selected so that the central angle of
l the region _ 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 region A. The central angle of the region
15 l Dl (D2, , Dn) recorded within the program signal, is
selected to the narrowest angle of 1 so as not to restrict
the recording range of the main information signal.
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 example, the recorded regions Bl
(B2 through Bn) and Cl (C2 through Cn) are provided
before the program signal Pl (P2 through Pn). However, as
another method of detecting the starting position of the
- 12 -
117'7~355
1 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 example in
1 FIG.4 showing a recording pattern of the third reference
signal fp3. In this example, 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,
I and having a central angle of 27.
Next, still another example of a recording pattern
of the third reference signal fp3, is shown in FIG.5. A
lead-in signal recorded region _ 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 time required for the reprodu~ing
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 a
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 Hl through Hn 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).
i~7'7955
'I
I ¦ In the present example, unlike in the above described
examples, the recorded regions Gl through Gn are formed.
Accordingly, it is not necessary to know positions which are
1 three seconds before start of each recorded program beforehand,
1 and vary the recording pattern of the third reference signal
fp3. Thus, the recording can be performed with ease in the
¦ recording system.
¦ Although not shown in the drawings, as a further
¦ modification, the recording range of the recorded regions A,
¦ Aa, 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 x 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
I lead-out signal, can be set in the order of 14.46 x 10
¦ 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
example of a disc recording system by referring to FIG.6. A
main information signal such as a video signal and a PCM
audio signal, is supplied 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
~1~7'7~5
1 and fp2 having mutually different frequencies in the vicinity
of a frequency of 0.6 MHz, for example, for every horizontal
scanning period, and only during the horizontal blanking
~ period excluding the interval wherein the color burst signal
1 exists. The first and second reference signals fpl and fp2
thus generated, are supplied to a switching circuit 29.
Moreover, a third reference signal fp3 having a different
I frequency from the reference signals fpl and fp2, is generated
l 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 is passed is
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 thirty seconds in units of 5 x 10 3 seconds in
S5
1 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 is started, for a period
corresponding to the central angle of 9, that is, l.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, 5.55 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 is supplied to a light
modulator 35.
The first and second reference signals fpl and fp2
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
signals thus alternately switched, are respectively supplied
117'795~
1 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 adjusting the light
quantity, by a light quantity control signal from the light
quantity control 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
objective lens 41. The original disc 42 is formed by covering
a disc made of glass and the like with a photosensitive
11'7'79~5
1 1 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 modulated 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 l/2 track pitch from the main track, on the
¦ original disc 42.
l The original disc 42, the turntable 43, and the
¦ motor 44 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 modulated
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 which is in accordance with the detected position is
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 which is in accordance with the above detected
¦ position. ~ence, 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
11'~'7955
1 speed. In addition, the first and second reference signals
fpl and fp2 exist within an interval corresponding to the
horizontal blanking period of the video signal, other than
~ the interval of the color burst signal. Because the light
I modulator 33 is controlled by the control signal from the
light quantity control signal generating circuit 30, the
light intensity of the light beam is decreased during the
I interval in which the first and second reference signals fpl
l and fp2 exist compared to other intervals. Therefore, the
1 depth of the pits of the main track is maintained constant,
without being affected by the first and second reference
signals.
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 lO is finally obtained. This disc lO
~ is made from a conductive material obtained by mixing carbon
¦ into polyvinyl chloride (PVC), for example. Rows of pits
~ are formed on the disc lO as shown in FIG.2.
¦ Next, description will be given with respect to an
¦ embodiment of a disc reproducing apparatus according to the
¦ present invention, by referring to FIG.7. The disc lO is
placed onto a turntable 50, and rotated 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 lO 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
11 7'7355
I I 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
1 output terminal 55.
The output signal of the preamplifier 53 passes
through a lowpass filter 56 and an automatic gain control
circuit 57, and is then respectively supplied to amplifiers
l 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 characteristic 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 adjustors 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 detecting circuit 64 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-
flop 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 circuits 66 and 67, while
the second reference signal fp2 is alternately supplied to
t55
1 ¦ 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 reference signals
¦ fpl and fp2 are recorded with respect to the track switches
for each track turn, however, the reference signal 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
j on the other side of the track (on the inner side along the
~ radial 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 voltages are supplied to
~ input terminals of a differential amplifier 68. The differential
¦ amplifier 68 compares the output signals of the detecting
circuits 66 and 67 which vary according to the reproduced
levels of the reference signals fpl and fp2. Accordingly,
the differential amplifier 68 generates a tracking control
l signal which is in accordance with the direction of the
tracking error and the tracking error quantity. This tracking
control signal is further amplified to a predetermined level
hy a known circuit, and then applied to a tracking 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 ~ecomes 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
il'7';'955
1 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
ll the third reference 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 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 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
117'~955
1 I 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
I 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
l connected to the integrating circuits 81a through 81d. A
~ Schmidt trigger circuit connected to an integrating circuit
producing an output reaching a trigger level TL, is accordingly
operated. A logic circuit 83 is connected to the Schmidt
trigger circuits 82a through 82d. The logic circuit 83
produces a control signal according to which Schmidt trigger
~ circuit 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
i 82a through 82c, to operate the Schmidt trigger circuits 82a
through 82c. Moreover, the logic circuit 83 produces a
lead-in detection signal. When the third reference signal
~ fp3 in the region sl (B2 through Bn) having the central
¦ angle of 9 is reproduced, the outputs of the integrating
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
l 82a and 82b have operated, and produces a signal indicating
~ that the region Bl (B2 through Bn) has been reproduced.
- 23 -
117'7955
1 When the third reference 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 threshold 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, is 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 69 or the control signal
from an input terminal 71. Description 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.
In a state before starting of the reproduction,
the signal pickup device 52 is at a waiting position separated
from above the disc lO. As the reproduction is started, a
reproduction start instruction signal is applied to the
motor drive control circuit 70 from the terminal 71. Accordingly,
117'7~S5
1 the signal pickup device 52 is fed to a position in the
v:icinity of the outermost peripheral part of the disc lO,
from the waiting position, and the reproducing stylus 15 is
lowered onto the disc lO. Here, the position where the
I reproducing stylus 15 is lowered onto the disc lO 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
I 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 speed. Therefore, the reproducing stylus
15 moves towards the inner periphery of the disc in the
~ region A, within a relatively short period of time.
~ The region Bl is recorded for two seconds 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. However, 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
.117'7955
1 be searched upon high-speed search. Hence, in the present
embodiment of the invention, the feeding speed upon search
is set to a speed which is fifteen times the above speed.
I Therefore, the entire disc can be searched within a short
~ period of time of 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,
l since 450 tracks are formed in the region Cl, this region Cl
¦ is traced and reproduced at least once per revolution of the
disc 10. When the length discriminating circuit 69 discriminates
¦ that the region Cl has been reproduced, the motor drive
control circuit 70 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 region 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 of 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 region Bl after tracing the region
A, the motor drive control circuit 70 produces a signal for
immediately feeding the signal pickup device 52 towards the
inner peripheral side of the disc at the normal reproducing
speed. Therefore, the lead-in operation is quickly performed
within a short period of time, and reproduction is started
- 26 -
11'7'7955
1 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
l 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
l disc at a high speed. The motor drive control circuit 70
~ controls the motor 72 so 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 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 is 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
117'7955
1 program, the control operation is performed in a similar
manner as in the case described above, except in that the
feeding direction of the signal pickup device is different
in this case.
I 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 length discriminating circuit 69. Thus, the motor
l drive control circuit 70 controls the rotation of the motor
72 so as to return the signal pickup device 52 to the waiting
l position at a high speed.
i 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 for reproduction.
In the disc which is reproduced by the reproducing
apparatus according to 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
11'7'7955
1 circuit in the reproducing apparatus, and the circuit construction
of the reproducing apparatus is accordingly simplified.
I Further, the present invention is not limited to
¦ these embodiments, but various variations and modifications
may be made without departing from the scope of the present
invention
~0~
- 29 -
