FR2500675A1 - Video disc player head - detects video data and reference signals recorded as variations in geometrical configuration on the surface of a disc - Google Patents

Abstract

The video disc played by this machine has four rasters of pulse-code-modulated video information on each rotation of a spiral track of depressions. Each track, which is 1.5 micron wide, is bounded by two reference signal tracks which are used by the play-back machine to keep the pick-up centred on the track, thus relieving the need for pick-up guide tracks. A third reference signal is used by the play-back machine to discriminate between data and reference signals. The detected signal is amplified, and fed in modulated form to standard video processing equipment. It is also demodulated, filtered and fed to discriminators which measure the levels of the reference signals and feed back a servo signal to a motor control circuit which keeps the pcik-up on the track.

Description

 The present invention relates generally to apparatusi for reproducing or reading rotary recording mediums, and in particular an apparatus for reproducing or reading a rotary recording medium of the type where three types of reference signals intended for the Track follow-up command by a playback element which follows the track are recorded on opposite sides of a continuous spiral track, the reference signals being recorded so that a drive command from a reproducing transducer is performed by means of one of the above reference signals without using special control signals.

 A system has already been proposed which records an information signal under strong variations of geometrical shape along a spiral track based on a rotary recording medium, without there being a guiding groove to guide a reproduction style, or stylus. According to this system, an information signal such as a television video signal, first and second reference pilot signals intended for the control of the tracking of the track and a third signal pilot or reference intended to switch the first and second reference signals ~ - reference during the reproduction or reading are recorded on the rotary recording medium (which will be designated hereinafter siipleient by disc). The first and second reference signals are recorded alternately in the radial direction of the disc in intiorediary positions situated between the axes of adjacent tracks containing the information signal. The third reference signal is recorded in a predetermined position on each track of the information signal. A reproduction or playback system reproduces the information signal, as well as the first, second and third reference signals using a As a reading element following the track, a track following control signal is formed from the first and second reference signals which are switched by the third reference signal separated from the reproduced signal.

Track tracking by the playback element is controlled by this track tracking control signal. as a result, although a guide groove is not provided, the reading element which follows the track can follow precisely this track containing the information signal.

 In a disc of this type, the pitch of the track has an extremely low value, for example 1.4 m, in order to obtain a high recording density. For this reason, the accuracy of the recording system must be extremely high so that it sends a light beam along the radial direction of the disc to record the information signal on the disc. It is therefore very difficult to form a portion of large pitch and containing no recording in the so-called start of playback section near the external periphery of the disc, as is the case with conventional audio discs.

 In the type of disc above, the track is therefore formed in the normal pitch from the outermost peripheral part to the innermost peripheral part of the disc. To start reading the information signal, for example within five seconds of the point at which the playback element following the track is lowered on the outermost peripheral part of the disc, the element must of reading that follows the track is lowered on this outermost peripheral part of the disc to an area of 105 / µm (which is the result of 1.4 x 13 x 5 r 103) because the disc spins at a speed of 900 rpm when four frames of video signals are recorded for each turn of the disc. From the point of view of mechanical precision, it is extremely difficult to lower the playback element which tracks the track precisely on the disc in one very narrow admissible area which is of the order of 105 pt.

 On the other hand, if the admissible zone in which the reading element which follows the track can be lowered is large, the time which elapses between the moment when the reading element which follows the track is lowered and the the moment this element reaches the track on which the information signal is recorded, it is important to start reading.

 It was therefore very feasible in this field of technology to produce a disc of which the admissible area for lowering the reading element which follows the track is large and the time necessary for starting playback from the moment the element of playback that follows the track is lowered on this disc to be short. it was also desirable to develop a system allowing rapid selection of a desired program, on the basis of the recorded information signal, to start the playback of this chosen program.

 Furthermore, it is desirable to automatically return the playback transducer to a rest position other than the position on the disc, and return the playback transducer to a state that precedes the start of playback when the playback element playback that follows the track reaches the innermost peripheral portion of the disc and ends playback.

 Among the methods making it possible to satisfy the requirements indicated above, it is possible to implement the so-called direct access method known in this field of the technique. In this direct access method a signal of address is recorded on the entire track, including the tracks located on the outermost peripheral part of the disc. The playback device reads the address difference between the address number of the track on which the playback item following the track has been lowered, and the address number of the track. of the first information signal, and quickly moves the reading element which follows the track until the difference between the addresses becomes zero; in addition, the method also provides for an operation during which the reproduction transducer is returned to its rest position when the number of the final address is read.

 In this method, however, the address signal must be recorded on the disc beforehand and the reading system tends to become complicated. It is further necessary to provide circuits for detecting the address and performing the direct access control in the reading apparatus, and this apparatus becomes complicated and comatose.

 Another precedent which can be taken into account consists in not recording a video signal synchronization signal on the outermost peripheral part of the disc. The existence or non-existence of the synchronization signal can be detected in the reading apparatus, and the reproduction transducer can enter into its rest position when no synchronization signal is detected. However in an HIC (pulse code modulation) disc, an audio signal is modulated by code pulses and recorded, and therefore there is no synchronization signal. If we therefore try to play a HIC disc, the playback device will detect the absence of a synchronization signal Jus ** before the start of reading, and the reproduction transducer will be returned to its rest position. This process therefore has the drawback of not being able to read an HIC disc.

 However, when the information signal is a video signal recorded on the disc and having the above recording format, the first, second and third reference signals indicated above are used regardless of whether the signal audio is a HIC audio signal. The third reference signal is used to detect the switching position of the first and second reference signals and to switch a circuit which forms the tracking control signal I1 is sufficient to detect the existence or non-existence of the third signal reference length, and the length of the recording of the third reference signal is unimportant. Therefore, in the disc which is reproduced or played by an apparatus according to the present invention, the third reference signal is therefore recorded by changing the length of the recording (recording area), and the discrimination of the type described above is carried out by detecting the value (dimension) of the recording length (recording area) of the third reference signal.

 Accordingly, a general object of the present invention is to create a rotary recording medium reproduction or playback apparatus which is new and particularly useful and in which the above requirements are met and in which the disadvantages are met. ~ mentioned are eliminated.

 Another object of the present invention is to create an apparatus for reproducing or playing a rotary recording medium in which the recording format of one of the reference signals intended for the tracking control which is present from the start on a rotary recording medium is different, in a predetermined position, from the recording format in other recording positions, the rotary recording medium reproduced or read by the device according to the present invention makes it unnecessary to record a special control signal for controlling the movement of the reproducing transducer of the playback apparatus, and recording on the rotary recording medium can be performed easily.

Another object of the present invention is to provide an apparatus for reproducing or playing a rotary recording medium in which the recording length of a reference signal, in a position where the movement of the transducer reproduction is ordered, is different from the recording length in other positions. This signal recording lenguer
reference is a length which corresponds to the state of control of the movement of the reproduction transducer. The playback apparatus can therefore easily effect control of the movement of the reproduction transducer by detecting the above recording length of the reference signal.

 Other objects and features of the present invention will appear more clearly on reading the following description, with reference to the attached drawings.

 Fig. 1 is a plan view with partial cutaway presented to explain a recording pattern of an embodiment of a rotary recording medium which must be reproduced or read by an apparatus according to the present invention.

 Fig. 2 is a perspective view on a larger scale showing part of the recording medium as well as the end of a reading style.

 Figs. 3, 4 and 3 respectively represent the ratio between a recording area of a reference signal along the circumferential and radial directions of a rotating recording medium, and a recording area of a recording program information signal in the radial direction on the rotary recording medium with respect to each example of a rotary recording medium.

 Fig. 6 is a block diagram showing an example of a recording system of a rotary recording medium.

Fig. 7 is a block diagram showing an embodiment of an apparatus according to the invention making it possible to reproduce or read a recording medium
Fig. 8 is a block diagram showing an embodiment of an essential part of the block diagram of FIG. 7.

 Figs. 9 (A) to 9 (F) respectively represent signal waveforms in certain parts of the block diagram shown in fig. 8.

 A recording pattern of an exemplary rotary recording medium to be reproduced or read by an apparatus according to the present invention is shown in FIG. 1. In this fig. 1, the parts P indicated by oblique hatching on the disk 10 constitute the regions carrying a recording of the main information signal such as a video signal and an HIC audio signal.

The shaded part R designates the regions carrying a third reference signal fp3, and the remaining parts which are white indicate the regions not carrying any recording.

The main information signal is recorded on a spiral track on the disc 10, in the regions P carrying the recordings. When the main information signal is a video signal, a video signal of two images, that is to say of four fields, is recorded for each revolution of the disc 10, along a spiral track formed by dip depending on the information content of the video signal. Part of this track is shown on a larger scale in fig. 2.The turns of a single continuous spiral track corresponding to each revolution of the disc 10 are designated in tl, t2, t3, ... Each track is formed by the formation of pits 11 corresponding to the main information signal, along the flat track which does not include a guide groove for the read head. If we consider a turn tl of the track, during each horizontal scanning period (1H) and in a position corresponding to the horizontal blanking period, dips 12 of a first reference signal fpl are formed, on a lateral side of the runway, in the direction of travel of the runway. Dips 13 of a second reference signal fp2 are trained on the other side of the track
In an intermediate position between the axes of the adjacent turns of the track, only depressions of any of the types 12 and 13 of the first and second reference signals are formed above. In addition, as regards a given track, the sides on which the recesses 12 and 13 are formed are reversed for each turn of the track.

In other words, if the recesses 12 and 13 are formed respectively on the right and left sides of a turn of the track for example, the recesses 12 and 13 are formed respectively on the left and right sides of each adjacent turns of this track.

 The position where the sides on which the recesses 12 and 13 of the first and second reference signals are recorded exists only in one position of each turn. This position is in alignment, in a terminal part of the recorded region R, along the radial direction of the disc 10 in FIG. 1. The third reference signal fp3 is originally recorded to switch the first and second reference signals fpl and tp2 which are reproduced by the playback device.

 The recorded region R of the third signal of reference ~ - reference fp3 on the outermost peripheral part of the disc 10 comprises a region A carrying a recording over the whole of an angular zone of 279 and of center 0 for each revolution of the disc 10 (ie a duration of 3 x seconds for a revolution of the disc 10 in time) and comprising approximately 2,230 periods of rotation (length requiring approximately two minutes and thirty seconds for a read head moving in the radial direction of the disc to a normal speed of movement for normal reproduction), a region B1 comprising a recording on an angular zone of 9- for a revolution of the disc 10 (that is to say a duration of 1.66 x 10 -3 seconds for a revolution of the disc 10 in time) and comprising approximately 33 periods of rotation (length requiring approximately two seconds for the read head to move in the radial direction of the disc 10 during normal reproduction), and a region C1 recorded in an area angular of 3 for a revolution of the disk 10 (i.e. a duration of 3.35 x 10 -4 seconds for a revolution of the disk 10 over time) and comprising approximately 430 periods of rotation (length requiring approximately thirty seconds for the test of reading moves in the radial direction of the disc 10 in normal reproduction).

 The relationship between the positions of the region R on which the third reference signal rp3 is recorded and the region P carrying a recording is indicated in FIG. 3. In fig. 3, the horizontal axis indicates the time necessary for the read head to move along the radial direction of the disc 10 at a speed equal to the normal reproduction speed. On the horizontal axis, the left side corresponds to the external periphery of the disc, and the right side corresponds to the internal periphery of the disc. With regard to the recorded region R, the vertical ase indicates the angle at the center of vertex 0 corresponding to the center of the disc 10 and carrying a recording. The signal which is in the part corresponding to the region A of the disc 10 is used as start of playback signal. The signal which is in the region B1 is used as a signal indicating a duration of between approximately three seconds and one second before the position to start playback of a first program recorded P1. The region C1 is situated in a range between approximately one second before and thirty seconds after the starting position of the recorded program P1.

A region B2 is formed for the same purpose as the region B1 and is provided in a space located between a second recorded program P2 and the first recorded program P1, with the same angle at the center and the same interval as the region Bl. C2 is formed with the same angle at the center and the same interval as the region Cl. In addition, between each of the above regions, regions D1, D2, ... Dn in which the third reference signal rp3 is recorded are included in an angle at the center of 1. for a revolution of the disk 10 (i.e. a duration of 1.83 x 10 seconds for a revolution of the disk 10 in time), as a function of each of the programs Pl,
P2, ... Pn.

 In addition, a recorded region E included in an angle at the center of 81- for a revolution of the disc, from a position located immediately after the last program Pn (i.e. a duration of 13 x 10 3 seconds for a revolution of the disc 10) and comprising approximately 2,700 periods of rotation (ie a length requiring approximately three minutes for the read head to move in the radial direction on the disc 10) exists as shown in FIG. 1. The signal in this region E is used as the end of reading signal.

Initial positions in the registered region
R corresponding to each revolution of the disc 10 are aligned in a straight line in the radial direction of the disc, as shown in fig. 1.

 As described above, five types of regions, ie regions A, B, ..., E, are respectively expected, and they are included in a center angle less than 90 ~. The angular ratio between each region is chosen so that the angle at the center of region C is three times greater than that of region D, that the angle at the center of region B is three times greater than that of region C, that the angle at the center of region A is three times greater than that of region B and that the angle at the center of region E is three times greater than that of region A. We choose the angle at the center of the region Dl (D2, ..., Dn) on which the program signal is recorded so that sbn angle is the narrowest and of so as not to restrict the recording area reserved for the main information signal.

 It is desirable that the recording area of region A which is used for the playback start signal is relatively long. We therefore choose an angle at the center of 27 for region A. In addition, the read head may suffer damage if the end of read signal is not detected due to a vacuum or the like, and when the head reading is not automatically returned to its standby position. This is why the recording area of the region E is chosen, which is used as the end of reading signal, so that its maximum center angle is 810.

 In the example described above, the recorded regions B1 (B2 to Bn) and C1 (C2 to Cn) are formed before the program signal P1 (P2 to Pn). However, a method for detecting the starting position of the program signal P1 (P2 to Pn) may consist in assuming that the starting position of the program signal P1 (P2 to Pn) is detected when the reading of region A has been finished. This is shown in Fig 4 which shows an example of a pattern for recording the third reference signal fp3.

In this example, a recording region Aa is formed using a recording area starting from the outermost periphery of the disc up to the starting position of the first program P1, with an angle at the center of 27.

 Another example of the recording pattern of the third reference signal fp3 is shown in FIG. 3.

A region F intended for the signal to start playback and on which this signal is recorded is formed on the external peripheral side of the disc, with an angle at the center of 270 (or 9 *), for rotation periods equivalent to two minutes and thirty seconds which are necessary for the read head to move along the radial direction of the disc during normal playback. A recorded region having an angle at the center of 1 is formed between the recorded region F and the position of start of the first program signal Pî. In addition, a recorded region Gl (G2 to Gn) is formed over the entire area corresponding to twenty seconds and which are necessary for the read head to move in the radial direction of the disc during normal reproduction from the starting position of each program P1 (P2 to Pn), with a center angle of 3 ~. Recorded regions H1 to Ha are formed respectively within each program signal having an angle at the center of 1, following each of the recorded regions G1 to Gn. A recorded region I is used as the end of playback signal, as in the case of the recorded region E, and has an angle at the center of 81 (or 27 ~).

 In the present example and unlike the examples described above, the regions recorded G1 to Gn are provided. Consequently, it is not necessary to know in advance the positions which are three seconds before the start of each recorded program and to modify the recording mode of the third reference signal fp3. This recording system therefore makes it possible to carry out the recording with ease.

 Although not shown in the drawings and this constituting another modification, the recording area of the recorded regions A, Aa and F for one turn of the disc which are used for the signal to start playback can be determined for a duration of l of 2.3 x 10 -3 seconds, and the recording area of the recorded regions E and I for one turn of the disc which is used for the end of playback signal can be controlled over a period of order of 14.46 x 10 -3 seconds for example. In addition, the recording interval in the radial direction of the disc can also be chosen according to the number of programs to be recorded, the duration, the speed of movement of the playback head when searching at high speed, and the like.

 We will now describe with reference to fig. 6 year example of a system with reference to fig. 6. A main information signal such as a video signal and an HIC audio signal is sent to an adder 24 by a terminal 20. Signals relating to the start of a start of read signal, of a program signal and of an end of reading signal are respectively applied to a gate circuit 27 by terminals 21, 22 and 23. A signal of predetermined frequency and obtained from a master oscillator 25 is sent to a circuit generating reference signals. Bramble 26. The reference signal generator circuit 26 generates first and second reference signals fpl and fp2 having mutually different frequencies in the vicinity of 0.6 MHz, for example for each horizontal scanning period, and only during the period of horizontal suppression excluding the interval where the color burst signal exists. The first and second reference signals fpl and fp2 thus generated are sent to a switching circuit 29. In addition, a third reference signal fp3 having a frequency different from that of the reference signals fpl and fp2 is generated for a predetermined interval (for a period of time corresponding to the recording range having the center angle of 81 above, i.e. 13 x 10 3 seconds) by the reference signal generation circuit 26, in function of the switching of the first and second reference signals fpl and fp2 which will be described later. The third reference signal fp2 is sent to the gate circuit 27.

 When no signal is applied to any of the input terminals 21 to 23 of the gate circuit 27, this gate circuit 27 lets through the third reference signal fp3 which is obtained from the reference signal generator circuit 26 during a period corresponding to the angle at the center of 1- above, that is to say 1.85 x 1 10 seconds for each period of rotation of an original disc 42. If the signal d main information which is recorded is a video signal, the period during which the third reference signal fp3 passes is located during the vertical blanking period. When a signal is applied to the input terminal 21, the gate circuit 27 lets through the third reference signal fp3 obtained from the reference signal generator circuit 26 for a period corresponding to the angle at the center of 27e, that is to say for approximately two minutes and thirty seconds in units of 3 x 10 seconds of time for each period of rotation of the original disc ne 42.

 A signal is applied to the input terminal 22 for an interval of between three seconds and one second before the recording of each program of the main information signal which has to be recorded, begins, for a period corresponding to a center angle. of 90, that is to say of 1.66 x 10 3 seconds for each period of rotation of the original disc 42. In addition, the input terminal 22 receives a signal for thirty seconds from a point in time which is located one second before the start of the recording of each program, for a period corresponding to the angle at the center of 3 ~, that is to say 5.55 x 10 seconds, for each period of rotation of the original disc 42.The circuit 27 carries the third reference signal fp3, coming from the reference signal generator circuit 26, during the period when the signal is applied to the input terminal 22 .

 When a signal is applied to the input terminal 23, the gate circuit 27 allows the third reference signal fp3 from the reference signal generator circuit 26 to pass in its state.

 The third reference signal fp3 which has passed through the gate circuit 27 is added in the adder 24 to a recorded main information signal. A signal from the adder 24 frequency modulates a carrier in the modulator 28. A frequency modulated output signal is sent to a light modulator 35.

 The first and second reference signals fpl and fp2 obtained from the reference signal generating circuit 26 are switched alternately, for each period of rotation of the original disc 42, by the switching circuit 29. The reference signals which are thus switched alternately are sent respectively to a light quantity control signal generator circuit 30 and to a light modulator 36.

 A laser beam emitted by a laser light source 31 is reflected by a mirror 32, then adjusted in terms of quantity of light by a light modulator 33 which regulates the quantity of light by means of a quantity control signal. light from a light quantity control signal generator circuit 30 and a control signal from a DC amplifier 46. The laser beam which has passed through the light modulator 33 is partially reflected by a semi-miter reflective 34 before reaching the light modulator 35, and the remaining part of the laser beam passes through the reflecting semi-mirror 34 to reach the light modulator 36. The laser beam which has reached the light modulator 35 is modulated by a signal coming from the modulator 28. An output signal from the light modulator 35, that is to say a first modulated light beam, is reflected by a mirror 38 and strikes 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 signal from the light modulator, that is to say a second modulated light beam , is reflected by a mirror 37 and strikes the polarizing prism 39. The first modulated light beam above is deviated from the polarization plane by an angle of 90, relative to the second modulated light beam, by the polarizing prism 39 .

 The first and second modulated light beams coming from the polarizing prism 39 are respectively reflected by a mirror 40, then concentrated on the original disc 42 by an objective lens 41 The original disc 42 is constituted by covering a glass disc or the like of a photosensitive agent. This original disc 42 is placed on a turntable 43 and driven at a rotation speed of 900 rpm by a motor 44. The photosensitive recording concerning the main track is carried out by the first modulated light beam, and the recording photosensitive concerning the track of the reference signals is carried out by the second modulated light beam concentrated in a position separated by half of the pitch of the track, relative to the main track, on the original disc 42.

 The original disc 42, the plate 43 and the motor 44 are continuously moved together in the direction of an arrow X at a predetermined speed, by a movement mechanism (not shown). At the same time as the movement of the original disc 42, the plate 43 and the motor 44 indicated above, the main track and the secondary track are formed in a spiral, starting from the external periphery and towards the internal periphery of the original disc 42, by means of the first and second light beams modulated above. In addition, 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 is thus obtained which corresponds to the detected position. This DC voltage is applied to the light modulator 33 by means of a DC amplifier 46.

 The light modulator 33 is controlled by the DC voltage which is in agreement with the position detected above. Therefore, even when the relative speed of the first and second modulated light beam relative to the original disc 42 changes according to the position along the radial direction of the original disc 42, the light intensity of the beam light is adjusted so that there are no undesirable effects from the change in the relative linear speed indicated above. In addition, the first and second reference signals fpl and fp2 are present in an interval corresponding to the horizontal blanking period of the video signal, other than the interval of the color burst signal. Because the light modulator 33 is controlled by the control signal from the light quantity control signal generator circuit 30, the light intensity of the light beam decreases, during the interval during which the first and second reference signals fpl and fp2 are present, by comparison with other intervals. The depth of the troughs of the main track is therefore kept constant, without being affected by the first and second reference signals.

The original disc thus exposed is subjected to a known development process. In addition, the original disc 42 is subjected to known disc manufacturing and stamping processes, which ultimately makes it possible to obtain the disc 10. This disc 10 is made of a conductive material obtained by mixing carbon with polyvinyl chloride (CPV) for example. Rows of depressions are formed on the disc 10, as shown in FIG. 2
We will now describe with reference to FIG. 7 an embodiment of an apparatus according to the present invention for reproducing or playing a disc. The disk 10 is placed on a plate 30 and driven in rotation with the plate 30 at a speed of 900 rpm by a motor 31.

A reproduced signal is detected from disk 10, by a reproduction style or read head 15 belonging to the signal reading device 52, in the form of tiny variations in electrostatic capacitance. This read signal is sent to a preamplifier 33 comprising a resonant circuit. The resonant frequency of the resonant circuit varies according to variations in the electrostatic capacitance, and the level of the signal sent to the preamplifier 53 is modified according to a predetermined level. The output of the preamplifier 33 is demodulated to obtain the original information signal by a demodulator 54, and outputted to a terminal 33.

 The output signal of the preamplifier 33 passes through a low-pass filter 36 and an automatic gain control circuit 57, and it is then sent respectively to amplifiers 38, 39 and 60. In the present case, each of the amplifiers 38, 59 and 60 is a type of bandwidth amplifier designed to have a very sloping pass frequency characteristic respectively only for the frequent fpl, fp2 and fp3. The first and second reference signals fpl and fp2 obtained respectively from amplifiers 58 and 59 have their level adjusted by the level adjusters 61 and 62. The signals thus obtained from the level adjusters 61 and 62 are sent to a gate switching circuit 63.

 The third reference signal fp3 obtained from the amplifier 60 is sent to a detector circuit 64. An output signal from the detector circuit 64 is sent to a flip-flop 65 so as to operate # this flip-flop 63. An output of the flip-flop 63 is applied to the gate switching circuit 63 as a switching pulse.

 Each time the output switching pulse from flip-flop 65 is applied to the gate switching circuit 63, the connection state of the gate switching circuit 63 is switched from a connection state indicated by the solid lines in a connection state indicated by the dashed lines in fig. 7.

Thanks to this switching operation, the first reference signal fpl is supplied alternately to the detector circuits 66 and 67, while the second reference signal fp2 is supplied alternately to the detection circuits 67 and 66 each time the pulse of switching is applied to the gate switching circuit 63. As a result, the sides on which the first and second reference signals fpl and fp2 are recorded relative to the track change with each revolution of the track, but the reference signal located d 'a track catie (on the outer side in the radial direction of the disc for example) is always sent to the detector circuit 66 for each revolution of the track, while the reference signal located on the other side of the track (on the internal side in the radial direction of the disc for example) is always sent to the detector circuit 67.

 The detector circuits 66 and 67 detect the envelopes of their respective input reference signals, and convert the signals into direct current voltages.

These direct current voltages are sent to the input terminals of a differential amplifier 68. The differential amplifier 68 compares the output signals of the detector circuits 66 and 67 which vary as a function of the reproduced levels of the reference signals fpl and fp2. Therefore, the differential amplifier 68 generates a track following control signal which is in agreement with the direction of the track following error and the amount of track following error. This track following control signal is further amplified to a predetermined level by a known circuit, then applied to a track following control winding of the signal detector device 32.

 When the tracking position of the track of the read head 13 deviates from the correct track which it must follow towards the side of an adjacent track, the level of one of the reference signals fpl and fp2 became higher than that of the other. Thus, a level difference is introduced between the output signals from the tester circuits 66 and 67. A track follow-up control current is obtained from the differential amplifier 68 and sent to the track control control winding. Consequently, the read head 15 is moved in a direction perpendicular to the longitudinal direction of the track, as a function of the amplitude and direction of the track following control current, and the track following command. track is made so that the read head 13 follows the track precisely.

 From another input, the signal detected at the output of the third reference signal fp3 by the detector circuit 64 is sent to a discriminator circuit of length 69. The length (corresponding to the angle at the center described above) of the period during which the third reference signal fp3 exists for one revolution of the track is discriminated by the length discriminating circuit 69. The discrimination can therefore be carried out on the place, that is to say on the region, where the third signal of reference fp3 which is reproduced and detected has been recorded. An output discrimination signal from the length discrimination circuit 69 is sent to a drive control circuit 70 of the motor. The speed of rotation and the direction of rotation of the motor 72 are controlled by the control circuit. motor 70, and the motor 72 advances the signal detection device 52 in the radial direction of the disc 10 by means of an advance mechanism 73.

 For example, the length discriminator circuit 69 is constituted as shown in FIG. 8. The output of the detector circuit 64 is sent successively to the integrator circuits 81a to 81, the time constants of which are mutually different, via a terminal 80. When a third reference signal fp3 of different length as shown in FIGS. 9 (A) or 9 (D) is sent to the detector circuit 64, so a detected output is obtained indicated in fig. 9 # B) or 9 (E). The detected output is sent to the integrator circuits 81a to 81d of the length discriminator circuit 69 shown in FIG. 8. An integrating circuit belonging to the integrating circuits 81a to 81d having a time constant in agreement with the period of existence of the detected output produces an output whose level is indicated in figs. 9 (C) or 9 (F). Schmidt trigger circuits 82a to 82d are respectively connected to integrator circuits 81a to 81d A Schmidt trigger circuit which is connected to an integrator circuit producing an output reaching the TL level of the trigger circuit is therefore actuated. A logic circuit 83 is connected to the Schmidt trigger circuits 82a to 82d. The logic circuit 83 produces a control signal according to which the Schmidt trigger circuits have been actuated, and sends this control signal to the control circuit 70 motor drive via terminal 84.

For example, when the third reference signal fp3 contained in region A whose angle at the center is 27e is reproduced, the outputs of the integrator circuits 81a to 81c exceed the threshold level of the Schmidt trigger circuits 82a to 82c, and operate these Schmidt 82a to 82c trigger circuits. In addition, the logic circuit 83 produces a signal to start reading. When the third reference signal fp3 in the region B1 (B2 to Bn) having an angle at the center of 9 is reproduced, the outputs of the integrator circuits 81a and 81b exceed the threshold levels of the Schmidt trigger circuits 82a and 82b. As a result, logic circuit 83 detects that seals the Schmidt trigger circuits 82a and 82b have been actuated, and it produces a signal which indicates that the region Bl (B2 to
Bn) has been read. When the third reference signal fp3 in the region C1 (C2 to Cn) whose angle at the center is 38 is reproduced, only the output of the integrator circuit 81a exceeds the threshold level of the Schmidt trigger circuit 82a. Thus, the logic circuit 83 detects that only the Schmidt trip circuit 82a has worked, and it produces a signal which indicates that the region Cl (C2 to Cn) has been read. When the third reference signal fp3 in the region Dl (D2 to Du) whose angle in the center is of le is reproduced, none of the outputs of the integrated circuits 81a to 81d exceeds the threshold levels of the circuits k triggering from Schmidt 82a to 82d, and all the circuits triggering from Schmidt 82a to 82d are therefore activated. In my case, the logic circuit 83 produces an end of reading detection signal. The output signal from the logic circuit 83 above is sent to the motor drive control circuit 70.

 The motor drive control circuit 70 is produced from a microcomputer for example. This motor drive control circuit 70 applies a motor drive signal having a level and a polarity which are in agreement with the output signal of the length discriminator circuit 69 or the control signal from an input terminal. 71. The control of the movement of the signal detector device 32 which is produced by the motor drive control circuit 70 will now be described.

 In a state preceding the reading, the signal detector device 52 is in a standby and separate position above the disc. When the reading has started, a read start instruction signal is applied to the motor drive control circuit 70, from the terminal 71. Consequently, the signal detecting device 52 is brought to a position at the in the vicinity of the outermost periphery of the disc 10, starting from its standby position, and the read head 15 is lowered onto the disc 10. At this time, the position in which the read head 15 is lowered onto the disc 10 is located at a great distance in the direction of the outer periphery side of the disc from the start position of the first program. This arrangement is taken into account to take into account the mechanical precision of the advance mechanism 73, the eccentricity of the disc and the like, so that playback is not started at an intermediate point of the first program.

 When the read head 15 which is lowered reads the third reference signal fp3 in region A, this operation is discriminated by the length discriminator circuit 69. As a result, the motor drive control circuit 70 makes advancing the signal detector device 52 / towards the internal periphery of the disc, at a relatively high speed The read head 15 therefore moves towards the internal periphery of the disc in region A, the duration of this movement being only relatively short.

 Region B1 is recorded for two seconds. Because the disc spins fifteen times per second, thirty tracks are therefore formed for two seconds. The B1 region is therefore made up of the thirty tracks. When the advance speed is set so that the region B1 is followed at least once during a period of rotation (1/15 of a second) of the disc when the read head is advanced to the start play position , the above feed speed can be set to run 450 (2 30 x 15) tracks per second. But if the feed speed is set to this type of speed, it would take a significant amount of time. about two minutes for the entire disc to be explored during a high-speed search. This is why, in the present embodiment of the invention, the speed of advance when there is a search is set to a speed which is fifteen times higher than the speed above. disc can therefore be explored for a short period of time which is approximately eight seconds.

When the signal detector device 32 is advanced at the above high speed, the possibility that the read head 15 will follow a track and read it in the region B1 is low. However, because there are 450 tracks in the region Cl, this region Cl is followed and read at least once per revolution of the disc 10. When the discriminator circuit of length 69 detects that the region Cl has been read, the motor control circuit 70 produces a signal to slowly advance the signal detecting device 32 toward the outer periphery of the disc, at a speed lower than the speed above.
Cl is therefore read when the read head 13 returns towards the external periphery of the disc, then it is the region il which is read. When the length discriminator circuit 69 detects that the region B1 has been read, the motor drive control circuit 70 produces a signal which advances the signal detector device 52 towards the internal periphery of the disc at a speed which is The one used for normal reproduction. Although this is unlikely to happen, when the read head 13 directly reads region B1 after following the track in region A, the motor drive control circuit 70 produces a signal to immediately advance the signal detection device 52 towards the internal peripheral side of the disc at normal playback speed, so the start of playback operation takes place quickly for a short time and playback begins at start of the first P1 program. w
Then, if the second program P2 is to be read from the beginning of the program - when the first program P1 is being read, an instruction signal indicating the above operation is sent to the control circuit 70. motor drive, from terminal 71.

In response to this instruction signal, the motor drive control circuit 70 advances the signal detection device towards the internal periphery of the disc at high speed. The motor drive control circuit 70 controls the motor 72 so that normal reading takes place immediately when the region B2 is read, but when the region B2 is not read and when it is the region C2 which is read, the signal detection device is returned in the internal peripheral direction of the disc at low speed to perform normal playback when the region B2 is read.

 In addition, if the eighth program P8 is to be read from the start of the program when the first program P1 is being played, a certain number of pulses (seven in this case) corresponding to the number of programs which must be skipped are applied to the input terminal 71. Thus, normal reading is immediately carried out when the region B8 is read, and when the region B8 is not read and the region C8 is read, the detection device of signal is brought back at slow speed towards the external periphery of the disc to perform normal reading when the region B8 is read following the command carried out by the motor drive control circuit 70 which controls the motor 72.

 Likewise, when a desired program located on the side of the external periphery of the disc with respect to the program which is being played is to be read from the beginning of this program # e, the control operation proceeds in a manner similar to that of the case described above, with the exception that the direction of movement of the signal detector device is different in this case.

 When the reading of the program signal is finished and when the reading head follows the turn and reads the third reference signal fp3 in the region E, this movement is discriminated by the length discriminator circuit 69. Thus, the control circuit 70 motor drive controls the rotation of the motor 72 so as to return the signal detector device 52 to its standby position at high speed.

 The constitution of the length discriminator circuit 69 is not limited to that shown in FIG. 8. The functions of the length discriminator circuit 69 can be fulfilled by a microcomputer. In addition, in the above embodiment of the invention, the third reference signal fp3 is used as a signal to modify the existing period. However, either or both of the first and second reference signals fpl and fp2 can be used in place of the signal fp3. Furthermore, the reading system is not limited to the electrostatic capacitance type using the reading head, and this reading system can be an optical system in which a light beam is used for reading.

 In the disc which is reproduced or read by the apparatus according to the present invention, there is no need to record a special control signal to obtain the operations described above. Disc recording is simple, since only one of the three reference signals originally used for track tracking is used. In addition, there is no need to provide a special control signal detection circuit in the reading apparatus, and the construction of the circuit of the reading apparatus is therefore simplified.

 It goes without saying that the present invention is not limited to the embodiments which have been described, and various variants and modifications can be made to it without departing from its scope.

Claims (6)

 1 - Apparatus making it possible to reproduce or read a rotary recording medium of which at least one surface has a main spiral track constituted by a large number of adjacent and successive turns (tl, t2, ...) and a track for signals of reference arranged between the axes of the mutually adjacent turns of the main track, this surface of the rotary recording medium comprising at least one part reserved for information and constituted by turns of the main track on which a signal is recorded. information, first and second reference signals (fpl, fp2) being alternately recorded in the radial direction of the rotary recording medium on the reference signal track, a third reference signal (fp3) being recorded at positions where the numbers of the turns of the track change with each revolution of the rotary recording medium, the reproducing or reading apparatus comprising a reading element (15) for reproducing a signal from the rotary recording medium, comparison means (68) for comparing differences in levels between first and second reference signals reproduced by said reading element to produce a signal for controlling output, switching means (63) for switching the first and second reference signals reproduced in response to a third reference signal reproduced by the reading element and for applying the signals thus switched to said comparison means, tracking control means receiving said output control signal to control tracking of the track by the playback element, characterized in that said recording medium comprises at least one predetermined region (A, B1 - Bn , C1 - Cn, E, F, G1 -, I) in which one of said first, second and third reference signals is recorded with a longer period of existence than that which 'it has in other normal regions (D1 - D), for a turn of the track, and in that the reproducing or reading apparatus further comprises discriminating means (69) making it possible to detect the reference signal which is recorded in said predetermined region with a longer period of existence than that which it has in other normal regions, for a turn of the track, and which is reproduced by said reading element, and displacement control means (70, 72, 73) for controlling the advance of the read element using the output signal of the discrimination means.  2 - Apparatus according to claim 1, further comprising separation means (58, 60) for separating first, second and third reference signals respectively, characterized in that the reference signal recorded in the predetermined region of the recording medium rotary with a longer period of existence than that which it has in other normal regions, for a turn of the track, is the third reference signal (fp3), and in that the means of discrimination detected as the third reference signal separated by said separation means exists for a period longer than a predetermined length in order to control said movement control means.  3 - Apparatus according to claim 1, characterized in that the predetermined region of the rotary recording medium is a region (E, I) comprising the end of reading track provided on the internal side from the innermost periphery of the main track on which the information signal is recorded, and in that the movement control means advance the reading element towards a rest position other than a position opposing the rotary recording medium from the end of reading region.  4 - Apparatus according to claim 1, characterized in that the predetermined region (A, F) of the rotary recording medium is a region containing the start of playback track provided on the external side from the outermost periphery of the main track on which the information signal is recorded, and in that the movement control means advances the playback element to a position located on the outermost periphery of the main track from the region start of reading.  5 - Apparatus according to claim 1, characterized in that the predetermined region is provided in several specific and different positions, in that the reference signal which is recorded in each of these predetermined regions is recorded with a longer period of existence than that which it has in other normal regions, its period of existence being different in length in each of the predetermined regions, for a turn of the track, and in that said discrimination means (69) detect the length of said reference signal in order to actuate the displacement control means according to a mode conforming to the length thus detected.  6 - Apparatus according to claim 5, characterized in that the reference signal which is recorded in each of the predetermined regions with a period of existence of different length, for a turn of the track, is recorded on a different number of tracks in each of the predetermined regions of the rotary recording medium.