CA1177955A - Rotary recording medium reproducing apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A rotary recording medium reproducing apparatus reproduces a rotary recording medium having at least one surface which has a spiral main track comprising a multiplicity of successively adjacent track turns, and a reference signal track disposed between center lines of mutually adjacent track turns of the main track, wherein the surface of the rotary recording medium comprises at least one information part comprising track turns of the main track having an information signal recorded thereon, where first and second reference signals are alternately recorded in the radial direction of the rotary recording medium on the reference signal track, and a third reference signal is recorded at positions where track turn numbers change for every revolution of the rotary recording medium, and at least one predetermined region in which one of the first, second, and third reference signals is recorded with an existence period longer than that at other normal regions, for one track turn.
The rotary recording medium reproducing apparatus comprises a reproducing tracing element for reproducing a signal from the rotary recording medium, a comparing circuit for comparing level differences between first and second reference signals reproduced by the reproducing tracing element, to produce an output control signal, a switching circuit for switching the reproduced first and second reference signals in response to a third reference signal reproduced by the reproducing tracing element, and for supplying the signals thus switched to the comparing circuit, a tracking control circuit supplied with the output control signal, for controlling the tracking of the reproducing tracing element, a discriminating circuit for discriminating the reference signal which is recorded in the predetermined region with an existence period longer than that at other normal regions, for one track turn, and reproduced by the reproducing tracing element, and a feed control circuit for controlling feeding of the reproducing tracing element by an output of the discriminating circuit.

Description

~1~'75~5S
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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 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 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 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.

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 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~

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A reproducing apparatus for reproducing a rotary recording medium having at least one surface which has a spiral main track comprising a multiplicity of successively adjacent track turns, and a reference signal track disposed between center lines of mutually adjacent track turns of the main track, said surface of the rotary recording medium comprising:
at least one information part comprising track turns of the main track having an information signal recorded thereon, first and second reference signals being alternately recorded in the radial direction of the rotary recording medium on the reference signal track, a third reference signal being recorded at positions where track turn numbers change for every revolution of the rotary recording medium; and at least one predetermined region in which one of said first, second, and third reference signals is recorded with an existence period longer than that at other normal regions, for one track turn, said rotary recording medium reproducing apparatus comprising:
a reproducing tracing element for reproducing a signal from said rotary recording medium;
comparing means for comparing level differences between first and second reference signals reproduced by said reproducing tracing element, to produce an output control signal;
switching means for switching the reproduced first and second reference signals in response to a third reference signal reproduced by said reproducing tracing element, and for supplying the signals thus switched to said comparing means;
tracking control means supplied with said output control signal, for controlling the tracking of said reproducing tracing element;
discriminating means for discriminating the reference signal which is recorded in said predetermined region with an existence period longer than that at other normal regions, for one track turn, and reproduced by said reproducing tracing element; and feed control means for controlling feeding of said reproducing tracing element by an output of said discriminating means.

2. A reproducing apparatus as claimed in claim 1 in which the reference signal recorded in said predetermined region of said rotary recording medium with an existence period longer than that at other normal regions, for one track turn, is the third reference signal, said reproducing apparatus further comprises separating means for respectively separating said first, second, and third reference signals, and said discriminating means discriminates that the third reference signal separated by said separating means exists for a period longer than a predetermined length, to control said feed control means.

3. A reproducing apparatus as claimed in claim 1 in which said predetermined region in said rotary recording medium is a lead-out track region provided on the inner side from an innermost periphery of the main track recorded with the information signal, and said feed control means feeds said reproducing tracing element to a resting position other than a position opposing said rotary recording medium from said lead-out region.

4. A reproducing apparatus as claimed in claim 1 in which said predetermined region in said rotary recording medium is a lead-in track region provided on the outer side from an outermost periphery of the main track recorded within the information signal, and said feed control means feeds said reproducing tracing element to a position at the outermost periphery of said main track from said lead-in region.

5. A reproducing apparatus as claimed in claim 1 in which said predetermined region is provided at a plurality of different specific positions, and the reference signal recorded in each of said predetermined regions is recorded with a longer existence period than that at other normal regions, and differ in length of the existence period in each of said predetermined regions, for one track turn, and, said discriminating means discriminates the length of said reference signal to operate said feed control means with a mode in accordance with the discriminated length.

6. A reproducing apparatus as claimed in claim 5 in which said reference signal recorded in eaah of said predetermined regions with said different length of existence period for one track turn, is recorded with different number of tracks in each o said predetermined regions in said rotary recording medium.