GB1585547A - Information signal reproducing system - Google Patents

Description

(54) INFORMATION SIGNAL REPRODUCING SYSTEM (71) We, NIPPON VICTOR KABUSHIKI KAISHA, of NO. 12, 3-Chome, Moriya-Cho, Kanagawa-Ku, Yokohama City, Kanagawa-Ken, Japan, a Japanese Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates generally to systems for reproducing information signals from recording mediums, the information signals being recorded on the recording mediums, and more particularly to a system for reproducing an information signal and a reference signal from recording medium, said information signal having been recorded with high density and said reference signal at specific positions for tracking control.

One example of a system for recording and reproducing with high density an information signal such as a video signal and/or an audio signal on and from a recording medium is a system in which a laser beam is used to record and reproduce the information signal optically on and from a rotating recording medium. In the reproducing system of this system, it is necessary to exercise tracking control so that the laser beam for reproduction will trace accurately the recording track on the rotating recording medium.

One example of a system for accomplishing this tracking control known heretofore has been a system wherein a light beam obtained by dividing a light beam for reproducing reflected from the recording medium is used for tracking control. Another tracking control system known heretofore is a system wherein a light beam for reproducing is divided into one main light beam for reproducing and two subsidiary light beams for tracking, and tracking control is achieved by these subsidiary light beams.

All of these known tracking control systems, however, have been accompanied by problems such as complicated and expensive apparatus, unstable operation, and incapability of accomplishing positive and accurate tracking control.

Accordingly, a possible system for solving these problems accompanying known tracking control system would appear to be a system wherein a single laser beam for recording a main information signal is deflected at a specific part on the main information track thereby to record a tracking signal on this specific part. In this system, however, at least the main information signal is disturbed or interrupted by the deviation. Consequently, a continuous reproduced signal of high quality cannot be obtained. Furthermore, since means for compensating for the interrupted signal is necessary, the reproducing apparatus becomes complicated and expensive.

Another example of a system for recording and reproducing information signals is a system which records and reproduces an information signal as a variation of electrostatic capacitance or as a variation of mechanical vibration. A rotating recording medium to be reproduced by these systems is provided with a spiral guide groove formed thereon for guiding a tracing stylus for signal reproduction. Along the bottom part of this guide groove, there is formed a track of an information signal recorded as a variation of geometrical configuration. The tracing stylus is guided by this guide groove in tracing the bottom thereof and thus reproduces the recorded information signal.

However, a recording and reproducing system of this known type has been accompanied by various problems as enumerated below.

(a). In the case where a video signal is to be recorded as an information signal, the groove pitch on the recording medium unavoidably must be made less than a number of calm, because the frequency band of a video signal is wide and is recorded with high density. As a consequence, the area of contact with the recording medium and the shape of the tracing stylus are limited by the groove pitch dimension. For this reason, the contacting force per unit area at the contacting parts between the tracing stylus and the recording medium is very large. As a consequence, the serviceable life of the tracing stylus and that of the groove of the recording medium are very short.

(b). If, in order to suppress abrasive wear of the tracing stylus, the stylus pressing force is reduced to a minute value of 30 mgr., for example, jumping of the stylus will occur frequently.

(c). As the abrasive wear of the tracing stylus progresses, it becomes increasingly easy for the tracing stylus to vibrate within the guide groove. tinder this condition, the reproducing operation becomes unstable, and, furthermore, the wear of the tracing stylus is further promoted. This vibration phenomenon is attributable to the sticking and slipping phenomena of the tracing stylus which occur within the guide groove at the time when the tracing stylus is being compulsorily guided by the guide groove.

(d). When the tracing stylus vibrates, a great pressure is applied locally in aconcen- trated manner on the side walls of the guide groove, whereby the film on the groove side wall surface is scraped off. Particularly, at the outer peripheral part of a rotating recording medium where the relative velocity of the tracing stylus and the recording medium is large, it is observed that the guide groove wall surfaces are rendered by abrasive scraping into the state of fish scales.

(e). As another consequence of the above described abrasive scraping, fine pieces of film thus scraped off adhere to the tracing stylus and give rise to frequent interruption or skipping and deterioration of the reproduced signal. As a result of our observation by analysis of the foreign matter adhering to the tracing stylus under these circumstances, the inventors discovered that the foreign matter comprised the dielectric material covering the recording disc surface and the underlying metal film material. In some cases, it was found that the foreign matter further contained polyvinyl chloride (PVC), which is the material of the recording disc. This result verifies the fact that the foreign matter deposited on the tracing stylus is not any substance which has infiltrated from the outside but comprises almost entirely materials scraped off from the recording disc.

(f). Because of the nature of the mechanism wherein a tracing stylus is compulsorily guided by the guide groove, special modes of reproduction such as still motion, slow-motion, intermittent frame-by-frame, high-speed searching of reproduction start point, and information search etc. are theoretically impossible.

(g). The tracing stylus and the guide groove are very fine and intricate in shape, and are difficult to form into their shapes.

(h). Since the signal groove has been formed on the recording disc, the process of recording the information signal on the original disc is laborious and complicated.

Accordingly, in order to overcome the various above described problems which arise from the fact that the guide groove has been provided, the inventors have realized the recording of an information signal as variation of geometrical form on a rotating recording medium without providing a guide groove.since there is no groove.

However, since there is no groove for compulsorily guiding the tracing stylus, it is necessary to provide means for causing the tracing stylus to trace positively and accurately over the recorded track. Accordingly, the inventors have realized a system for accomplishing tracking control of the tracing stylus so that it will trace accurately and positively over the recorded track and have made possible the realization of a system in which the tracing stylus traces accurately following tracks on a medium which does not have a guide groove as described above.

According to the invention there is provided an information signal reproducing system comprising: means for reproducing an information signal and first, second and third reference signals from a recorded disc, said information signal being recorded on information signal tracks on the recorded disc, said first and second reference signals being recorded on reference signal tracks, said first and second reference signals being recorded alternately on the reference signal tracks during each rotation of the recorded disc, and said third reference signal being recorded at positions corresponding to the positions where the first and second reference signals switch; means for individually separating said first, second and third reference signals from the signals reproduced by said reproducing means; means for producing a tracking control signal from the separated first and second reference signals switched in response to the separated third signal; and means for controlling tracking in response to said tracking control signal so that said reproducing means traces the information signal track on the recording disc.

According to another aspect of the invention there is provided an information signal reproducing system comprising: means for reproducing an information signal and first, second and third reference signals from a recorded disc, said information signal and first, second and third reference signals being recorded on a recorded disc as variations of geometrical configuration, said information signal being recorded on information signal tracks on the recorded disc, said first, second and third reference signals having respectively different frequencies, said first and second reference signals being recorded on reference signal tracks, said first and second reference signals being recorded alternately on the reference signal tracks during each rotation of the recorded disc, and said third reference signal being recorded at predetermined positions corresponding to the positions where the first and second reference signals switch during each rotation of the recorded disc; means for individually separating said first, second and third reference signals from the signals reproduced by said reproducing means; means for alternately deriving said separated first and second reference signals responsive to the separated third reference signal; means for detecting the delived first and second reference signals; means for producing tracking control signal in response to a difference between the detected first and second reference signals; and means for controlling tracking in response to said tracking control signal so that said reproducing means traces the information signal track on the recording disc.

The present invention will be further described by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing a first embodiment of a recording system for making recording on a recording medium to be reproduced by a reproducing system of the present invention; Fig. 2(A) through Fig. 2(D) and Fig. 3(A) through Fig. 3(D) are signal waveform diagrams respectively for explaining the operation of a block diagram shown in Fig. 1; Fig. 4A through Fig. 4D are successively enlarged views showing a portion of a track pattern of a first embodiment recorded and formed on a rotating record medium in accordance with a recording system illustrated in Fig. 1; Fig. 5 is an enlarged view showing a second embodiment of a track pattern recorded and formed in accordance with a recording system in Fig. 1; Figs. 6A and 6B are respectively a perspective view showing one embodiment of tracing reproduction means usable in a reproducing system of the present invention, and an enlarged perspective view, as viewed from the bottom, showing a tip portion of the tracing stylus; Fig. 7 is a perspective view showing another embodiment of the reproducing tracing means; Fig. 8 is a block diagram showing a first embodiment of the reproducing system according to the present invention Fig. 9(A) through Fig. 9(E) are signal waveform diagrams for explaining the operation of the block diagram in Fig.

Fig. 10 is a block diagram showing an essential part of a second embodiment of the recording system; Fig. 11(A) through Fig. 11(J) are respectively signal waveform diagrams for explaining the operation of the block diagram in Fig. 10; Fig. 12 is a block diagram showing an essential part of a modification of the embodiment in Fig. 10; and Fig. 13 is a block diagram showing an essential part of a second embodiment of the reproducing system according to the present invention.

A first embodiment of a recording system is described with reference to Fig. 1 through Fig. 3.

With reference to Fig. 1, a part of a laser beam projected from a laser light source 11 is reflected, by a half-mirror 1 , and is supplied to a light beam modulator 24. On the other hand, the remaining part of the projected laser beam passes through the halfmirror 12, and is then reflected by a reflecting mirror 13, and is thereafter supplied to a light beam modulator 16. A recording information signal including color video signal and an audio signal introduced through an input terminal 14 is supplied to a frequency modulator 15 and frequencymodulates a carrier thereat. The output frequency modulated signal is applied, as a modulation signal, to the light beam modulator 16 and modulates the above described laser beam thereat. The above described color video signal is indicated in Fig. 2(A) with a unit of a vertical synchronizing pulse 40, and in Fig. 2(C) with a unit of the hozizontal synchronizing pulse 41. A first modulated light beam, which has been modulated by the frequency modulated signal at the light beam modulator 16, is reflected by a reflecting mirror 26 and passes through a polarization prism 27 and is then reflected by a reflecting mirror 28.

The first modulated light beam thus reflected enters as an incident beam into an objective lens 29. The beam passed through the lens 29 is focused in such a manner that a focal point of the lens 29 coincides with a sensitive material 31 coated on an original recording disc 30 made of materials such as glass, whereby a spiral main track or a concentric circle-formed main track is recorded and formed with variation of geometrical configuration.

Switching pulses are applied to oscillators 20, 21 and 2 through input terminals 17, 18, and 19, respectively. The switching pulses cause, for instance, the oscillators 20, 21 and 22 to perform oscillating operation during the interval of positive polarity, and to stop oscillating operation during the interval of negative polarity. The oscillators 20, 21, and 22 oscillate at their normal frequencies and generate signals having respectively single frequency fpl (e.g., 700 KHz), fp2 (e.g., 500 KHz), and fp3 (e.g., 300 KHz).

Here, when every two-frame video signal is to be recorded on the recording disc 30 for every one rotation thereof, for instance, first and second pulses obtained as described hereinbelow are used alternately every two-frame interval, as the input switching pulse to be supplied to the input terminals 17 and 19. The first switching pulse is obtained by separating the vertical synchronizing pulse 40 indicated in Fig.

2(A) from the recording color video signal, and then by subjecting the pulse 40 to a 1/4 count-down operation. The first switching pulse thus obtained is a pulse having a period of two-frame as indicated in Fig.

(B). The second switching pulse is a pulse which is obtained by separating the horizontal synchronizing pulse 41 indicated in Fig.

2(C) from the input video signal every 1H (H: horizontal scanning period), and then by processing it so that the pulse width thereof is synchronized with a horizontal blanking period (abbreviated as H.BLK hereinafter). The aforementioned pulse width is selected so that a reference signal for tracking control does not affect a color burst signal 42 indicated in Fig. 2(C). Consequently, the signal fpl is sent out from the oscillator 20 for two-frame interval (1/15 second) in a time-phase relationship as indi cated in Figs. 2(C) and 2(D) respectively.

Following this, the signal fp2 is sent out from the oscillator 21 for following twoframe interval in the time-phase relationship as indicated in Figs. 2(C) and 2(D) respectively. Then, similarly as in the preceding case, the signals fpl and fp2 are thereafter sent out every two-frame period successively and alternately.

In correspondence to the time point when the switching of the signals fpl and fp2 takes place, a third reference signal fp3, as an index pulse at the time of reproducing mode, is sent out from the oscillator 22.

Here, in order to carry out a special reproduction such as a still-motion reproduction or a slow-motion reproduction, particularly in the case where the information signal to be recorded is principally a video signal, it is required to effect a kick-back control for shifting or transferring forcibly a reproducing tracing means tracing on a certain track to another track within a vertical blanking period (abbreviated as V.BLK hereinafter). In taking account of this kickback control operation, the signal fp3 is recorded at V.BLK part of the video signal.

Fig. 3(A) shows the V.BLK part of the video signal. Here, it is considered that pulses, designated by 45a in Fig. 3(A), during two or three H periods at the initial horizontal synchronizing pulse part following equalizing pulses, proJecting toward white side, may be recorded as the above described signal fp3. However, when the tracing stylus is actually subjected to the kick-back operation by the signal fp3 at the time of stitl-motion reproduction or slow motion reproduction mode, the tracing stylus does not stabilize on a predetermined track immediately after jumping over the tracks but is accompanied by hunting to some extent. Further, interrelatedly with a response characteristic of the mechanism for moving the tracing stylus, some noises may appear on the picture at the upper part thereof caused by the influence of the kickback operation.

Therefore, in order to carry out the kickback operation within the V.BLK interval completely, it is sufficient that the switching operation at the time of signal recording and reproducing mode is carned out just before or just after the respective ends of the video signal intervals. In consequence, it is desirable that the signal fp3 is inserted and recorded at a position designated by 45b in Fig. 3 (A) with respect to the recording video signal.

The present invention is not limited to the case of reproducing the video disc on which at least the video signal has been recorded, but may be contemplated so as to reproduce the video disc and the audio disc on which the audio signal has been recorded, interchangeably. Here, since the audio signal does not contain any periodic signal such as horizontal or vertical synchronizing pulses, it is not appropriate to record the signal fp3 with the timings indicated by 45a and 45b in Fig. 3(A), from point of view of compatibility. Accordingly, the signal fp3 may be recorded in such a manner described hereinafter.

()) The signal fp3 having a frequency lower than the frequency range of the main information signal to be recorded is oscillated for an appropriate period of time, and is then superimposed, at a proper level thereof, on a predetermined part of the main information signal at an adder 34 indicated in Fig. 1. The signal thus superimposed is recorded by the first modulated light beam on the same one track.

Q2 The signal fp3 is supplied, together with the signals fpl and fp2, to an adder 23 for a predetermined period of time as indicated in Fig. 2(D) and Fig. 3(A), and is then recorded as a second modulated light beam described hereinafter.

The above described method 0 does not affect the recording video signal because the signal fp3 is inserted within the V.BLK period, but causes deleterious effects such as beat disturbance or buzz against the audio signal. On the contrary, the above described method Q2 does not cause a deleterious effect on the main information signal to be recorded, but leads to a favourable result as a fundamental arrangement in the case of reproducing the video disc or audio disc by the above described same reproducing apparatus.

Accordingly, the method (2) will be described in detail hereinafter. An output signal of the adder 23 becomes as indicated in Fig. 3(C) or Fig. 3(D). Fig. 3(C) indicates a waveform wherein the signal fp3 is recorded at a switching position of the signal fpl and the signal fp2 as an intermittent oscillation pulse over two or three-H periods of time. Fig. 3(D) indicates a waveform in the case where the signal fp3 is recorded continuously for a relatively longer predetermined period of time.

Fig. 3(B) indicates a reference pulse for controlling the rotation of the recording disc 30 with accuracy, in the case of recording only the H period pulse which is synchronized in phase thereof with the video signal to be recorded, or the audio information. In the case of recording the video signal, the interval designated by numeral 46 corresponds to the V.BLK period of the video signal. The H period pulse has relationships with the reference signals fpl and fp2 in their phases, as indicated Figs. 3(B), 3(C), and 3(D), respectively.

As a modification, the signals fpl and fp2 may be inserted or disposed successively and alternately even in the part where the signal fp3 has been inserted. Further, even if the signals fpl and fp2 are dropped out for three or four-H periods by recording the signal fp3, any deleterious effect does not substantially arise in the tracking servo operation.

The output signal of the adder 23 is applied, as a modulation signal, to the light beam modulator 24. The output second modulated light beam from the light beam modulator 24 is subjected to an attenuation by a light filter 25, where the brightness (beam light quantity) is adjusted so as to be attenuated appropriately in comparison with the quantity of light of the above described first modulated light beam. The second modulated light beam thus attenuated thereafter advances to a polarization prism 27, where the polarization lane of the light beam is deviated by 90 with respect to the polarization plane of the first modulated light beam.

The second modulated light beam which has passed through the polarization prism 27 is, together with the first modulated light beam, reflected by the reflecting mirror 28 and passes through the objective lens 24, and then irradiates the sensitive material 31 on the rotating recording disc 30. The irradiation part on the rotating disc 30 moves in the radial direction thereof by a predetermined pitch, whereby the spiral track, for instance, is formed as a change of the geometrical configuration in accordance with the recording information signal. The second modulated light beam follows a light path through the objective lens 29 which is displaced with respect to the first modulated light beam by the polarization prism 27. As a result of this displacement, the second modulated light beam records and forms a sub-track, separated by approximately 1/2 track pitch from a main track formed by the first modulated light beam. Here, the track pitch refers to a distance between two tracing center lines of adjacent tracks. Further, in the above described recording system, a guide groove for guiding the reproducing tracing stylus is not formed even in the case of a disc which is adapted to the reproducing system of using the tracing stylus as reproducing tracing means.

Moreover, in the case where it is not appropriate to divide the beam into two beams by the half-mirror 12 on account of matters such as beam power of the laser light source 11, another laser light source 32 indicated by a dotted line in Fig. 1 may be additionally provided. In this case, the light beam intenslty and the modulation index, and the like of the beam projected from the laser light source 32 is adjusted appropri- ately with respect to the first modulated light beam.

The light beam projected from the laser light source 32 is reflected by a reflecting mirror 33 and is then supplied to the light beam modulator 24. Moreover, interrelatedly with the provision of the laser light source 32, the half-mirror 12 is omitted and the light beam projected from the laser light source 11 is supplied to only the light beam modulator 16.

In the case where the recording main information signal is of a color video signal, the above described respective reference signals may be obtained by frequency dividing a chrominance sub-carrier of the color video signal.

Further, instead of recording with the use of the light beam, the recording may be carried out by an electron beam in the form of double beams.

Accordingly, a track pattern recorded on the recording disc by the recording system indicated in Fig. 1 resultingly becomes as indicated in Fig. 4A through Fig. 4D, for instance. The signals fpl, fp2, and fp3 are recorded in alignment in the radial direction of the disc 50. Fig. 4B shows schematically the first embodiment of the track pattern encircles on the disc indicated in Fig. 4A, for the sake of convenience of description. A track pattern indicated in Fig. 4C is shown by magnifying an essential part of the track pattern in Fig. 4B in the form resembling the actual pattern. In Fig. 4B, numerals (1), (2), (3), .... respectively indicate parts where the first, the second, the third .....

horizontal synchronizing signals of the first frame of the video signal are recorded, and numerals (521)', (522)', .... (525)' respectively indicate parts where the 521st, the 522nod .... the 525th horizontal since hronizing signals of the second frame of the video signal. That is, in the present embodiment, two frames of the video signal having 525 horizontal scanning lines per one frame are recorded every rotation of the disc.

In Fig. 4C, reference marks tl, t2, t3, .

respectively designate the first, the second, the third .... main tracks which are recorded and formed every rotation of the disc 50 by a number of intermittent pits 50.

The reference signals fpl and fp2 are recorded alternately with a period of one rotation, and formed at an intermediate part between the adjacent main tracks by intermittent pits which are shallow in comparison with the depth of the pits of the main track.

Further, although the illustration is omitted in Fig. 4B for the sake of simplification, the reference signal fp3 is recorded as a timing pulse at a position 52 where the recording of the signals fpl and fp2 is switched (which position corresponds to a position (525)' in Fig. 4B) as indicated by a broken line in Fig.

4C.

In the case where the main information signal comprises at least the video signal, recording of the reference signals is effected similarly as in the preceding description.

That is, for the purpose of preventing the beat disturbance of cross modulation bet ween the reference signals and the video signal, the signals fpl and fp2 are recorded within a H.BLK interval indicated by the numeral 53 in Fig. 4C, and the signal fp3 is recorded at a V.BLK part 52. Each of signals fpl, fp2, and fp3 is not therefore recorded in the video information period 54.

Further, for the purpose of recording and reproducing the signals fpl and fp2 with higher sensitivity, the present embodiment is arranged in such a manner that the positions where the signals fpl and fp2 are respectively recorded separately along every track are alternately located at positions of the H.BLK period with a period of 2H interval. Furthermore, the recording of the signals fpl and fp2 is effected in such a manner that the recording positions of the signals fpl and fp2 located within the H.BLK period at positions separated or deviated by every 1H alternately with respect to the adjacent tracks. According to this recording arrangement of the signals fpl and fp2, the recording of the signals fpl and fp2 is carried out without affecting the main information signal. Further, since the reference signals can be recorded with wider dimension even in the case of recording the main information signal with very small track pitch, i.e., with high density, the reference signals can be reproduced in a stable manner, thereby being advantageous with respect to the stabilization of the tracking control operation. However, when reducing into practice, the signals fpl and fp2 may be recorded at positions corresponding to every H.BLK of the video signal. Further, by using the single frequency of low frequency, i.e., of longer wavelength as the reference signals as described hereinbefore, the reference signal can be reproduced in a stable manner.

Fig. 4D indicates a part of track pattern indicated in Fig. 4B, with further enlargement. The track pattern is formed by recording a main track with track pitch 58 (e.g., 2.8 ,um) blanking period of the main information signal recording track. This can be done by recording the signals fpl and fp2 intermittently with periods 2H, 3H, etc., for example.

As is known, in the case where the main information signal is an audio signal, there is no periodic signal such as a horizontal synchronizing pulse in the audio signal. However, in this case, also, by recording the reference signals fpl and fp2 with different phases respectively front and rear in the rotational direction at the opposite lateral side parts of the audio signal track, tracking control can be accomplished even more advantageously than in the above described case herein the reference signal recording position is limited to the part corresponding to the horizontal blanking period.

As is also known in this connection, the horizontal scanning frequency of a television video signal of the NTSC system is 15.75 KHz. Since the rotational speed of the disc 50 in the case of the embodiment of the invention is 900 rpm, the fundamental error period at the time of disc eccentricity is merely 15 Hz, and this period interval is ample as the information quantity for tracking control.

Moreover, instead of using the signal fp3, the system is so adapted that, for instance, the deficient part is detected and discriminated from the other recording part by causing the reproduced signals fpl and fp2 to pass an integration circuit at the time of reproducing mode, without recording the signals fpl and fp2 during 2H through 3H intervals within V.BLK period.

One embodiment of reproducing tracing means suitable for use in the reproducing system according to the present invention is shown in Fig. 6A. A disc-shaped recording medium (disc) 71 has on its surface a thin metal film coated thereto. On this disc surface, pits of the main information signal and reference signals fpl and fp2 on opposite lateral sides thereof as shown in Figs. 4 and 5 are respectively recorded. The disc 71 is positioned on and rotates with a turntable 3 rotated synchronously by a disc motor (not shown) at, for example, 900 rpm. in the arrow direction 72 at the time of reproducing. A tracing stylus 74, which is, for example, of a signal pickup form of the electrostatic capacitance type, is positioned to contact and slide over the disc 71 thereby to reproduce a video signal of two frames every rotation of the disc 71 by a method described hereinafter.

The tracing stylus 74 has a tip shape as shown in Fig. 6B. The tracing stylus proper is made of a material such as diamond or sapphire. The entering or leading part 88 of this tracing stylus 74 is formed by the acute vertex of the sliding surface. An electrode 86 made of a metal such as titanium is secured to the back part of the stylus by a sputtering process. The width 87 of the electrode is selected to correspond substantially to the pit width, being approximately 2 ,um.

in the present embodiment. For preserving the serviceable life of the stylus over a long period, the area of the contacting and sliding part 89 of the stylus tip should be made large. For this purpose, the dimensions of the contact in the longitudinal and transverse directions are made large thereby to make the width and area of contact with the disc surface amply large relative to the information pit. Accordingly, the sliding surface 89 contacts a plurality of pits simultaneously at the time of contact, but the above mentioned electrode width 87 is made to correspond to the information width of a single pit. Therefore, while the contact area is amply large, pit information can be picked up in the form of variation of electrostatic capacitance successively with high sensitivity from the electrode part 86.

The tracing stylus 74 is secured to a moving shaft 78 of a moving coil mechanism 80 respectively by way of a thin leaf spring 75, a shock-absorbing member 76, and a bracket 77. The provision of the spring 75 and the shock-absorbing member 76 affords stable contact of the sliding tip of the tracing stylus 74 against the information surface on the disc 71 with a light pressing force of approximately 30 mg. Furthermore, the light pressing force in the up-and-down direction of the tracing stylus 74 is imparted to a signal pickup part 79, which is so constructed that it does not move in the leftand-right direction. The above mentioned moving coil mechanism 80 is constructed on the basis of the same operational principle as a sound loudspeaker and comprises a permanent magnet, a driving coil, and a yoke (all not shown). The part is axially supported by a damper and is provided with the moving shaft 78. This moving shaft 78 is displaced by a specific quantity in its radial direction, that is, an arrow direction 81, which is the disc radial direction, in response to the direction and magnitude of the electric current supplied to the above mentioned driving coil.

By this construction wherein the signal pickup structure 79 including the tracing stylus 74 is mounted on the moving shaft 78, the tracing stylus 74 is capable of accomplishing high-speed control driving in the direction perpendicular to the signal track traced on the disc 71 by the tracing stylus 74. Furthermore, the signal pickup structure 79 and the moving coil mechanism 80 are mounted on a traversing mechanism (not shown) and are thus caused to travel in a straight line at a low speed synchronized with the rotational speed of the disc 71 in the radial direction 82 of the disc 71 at the time of signal recording or reproducing.

Another embodiment of reproducing tracing means is illustrated in Fig. 7. In Fig.

7, those parts which are the same as corres ponding parts in Fig. 6A are designated by like reference numerals. In this tracing device, a bracket having a horizontal exten sion 85 is mounted on the moving shaft 78 of the moving coil mechanism 80. A pair of cantilever members 83a and 83b are coupled together at their outer ends and at their inner base ends are connected to and sup ported by the horizontal extension 85 of the bracket through dampers 84a and 84b at positions respectively spaced apart in the horizontal direction. The tracing stylus 74 is fixedly mounted on the coupled outer end of the cantilever members 83a and 83b. By this structural arrangement, wherein the two cantilever members 83a and 83b and the bracket extension 85 form a triangular structure, the tracing stylus 74 is effectively limited in its free displacement in the hori zontal direction relative to the bracket extension 85 but can undergo displacement freely in the vertical direction, accompanied by flexuous deformation of the dampers 84a and 84b.

The bracket extension 85 fixed to the moving shaft 78 is caused to traverse, together with the moving coil mechanism 80, in the radial direction of the disc 71 in synchronism with the rotation of the disc. At the same time, the bracket extension 85 is caused to undergo fine displacements in the disc radial direction by the operation of the moving coil mechanism 80 itself in response to an output signal from a tracking servo circuit. As a result, the tracing stylus 74 is caused to traverse at a very low constant speed, unitarily with the bracket extension 85, in the disc radial direction toward the center of the disc. The stylus 74 thereby traces accurately and positively the main signal recording track. Furthermore, the tracing stylus 74 undergoes displacement in the vertical direction, accompanied by flex uous deformation of the dampers 84a and 84b and thus faithfully follows the undula tions of the disc surface.

Next, a first embodiment of the reproduc ing system according to the present inven tion will now be described with reference to Fig. 8 and 9.

In the system shown in Fig. 8, a repro duced signal picked up as a minute variation of electrostatic capacitance by the tracing stylus 74 from the disc 71 is supplied to a preamplifier 95 having a resonance circuit whose resonance frequency varies in response to this variation in electrostatic capacitance and is rendered into a signal of a desired level. The resulting output of the preamplifier 95, on one hand, is demodulated into the original information signal by a demodulator 96 and is sent out as output through an output terminal 97.

The output signal of the preamplifier 95, on the other hand, is supplied respectively to amplifiers 98, 99, and 100. Here, each of the amplifiers 98 and 99 is a kind of bandpass amplifier, the amplifier 98 being designed to have a steep passing frequency characteristic at only the frequency fpl, and the amplifier 99 being designed to have a steep passing frequency characteristic at only the frequency fp2. As a result, the signal of frequency fpl as indicated in Fig.

9(A) and the signal of frequency fp2 as indicated in Fig. 9(B) are obtained separately from the amplifiers 98 and 99, respectively, and respectively passed through level adjustors 101 and 102, where their levels are adjusted. The resulting signals are then supplied to a gate switching circuit 103. These reproduce signals fpl and fp2 are pulse trains of 2H period and, moreover, of coinciding phase in the horizontal blanking period of the reproduced video signal.

When this horizontal blanking period is approximately 11 microseconds, for example, and the frequencies fpl and fp2 are set at 500 KHz and 300 KHz, respectively, the signals fpl and fp2 become repeated waveforms of approximately 5 cycles and approximately 3 cycles, respectively.

In the case where the recorded signal is a color video signal, and there is a possibility of the recording and reproducing of the reference signals fpl and fp2 affecting the color burst signal, it is desirable that the color burst signal position be avoided in the recording of the signals fpl and fp2.

The gate switching circuit 103 is supplied through an input terminal 104 with a switching pulse generated with the position designated by reference numeral 52 in Fig. 4C (V.BLK part in the case where the recorded main information signal is the video signal) as a reference and thus carries out switching of the signals fpl and fp2 every revolution period of the disc 71. Since the disc rotational speed in the present embodiment of the invention is 900 rpm. as mentioned hereinbefore, two frames of the video signal are recorded for each revolution of the disc 71. As a result, in response to a switching pulse which undergoes inversion of polarity every two frames (1/15 second), the gate switching circuit 103 supplies a signal as indicated in Fig. 9(C) and a signal as indicated in Fig. 9(D) respectively to detecting circuits 10 and 106.

The aforementioned band-pass amplifier 100 is designed to have a band-pass filter characteristic by which it separately filters only the signal of frequency fop3. The signal fp3 as indicated in Fig. 9(E) which has been separated and amplified in this band-pass amplifier 100 is supplied to an integration circuit 107, where it is subjected to waveshaping so as not to be affected by noise and other influences. The signal thus waveshaped is then applied to a flip-flop 108 to trigger the same. The resulting output of this flip-flop 108 is sent out through an output terminal 109 and applied to the aforementioned input terminal 104.

In order to suppress the effects of interruption or dropouts and noise, etc., in the signal from the tracing stylus 74 in this case thereby to obtain an even more stable and accurate switching pulse from the terminal 109, it is desirable to use, instead of the flip-flop 108, means such as a flywheel oscillator which performs its free running oscillation at 15 Hz or an AFC circuit capable of accomplishing the same function.

The detecting circuits 105 and 106 detect envelopes of their respective input reference signals and convert the same into DC voltages, which are then supplied respectively to the input terminals of respective differential amplifiers (not shown) within a tracking servo circuit 110. This tracking servo circuit 110 compares the output signals of the detecting circuits 105 and 106 which vary in response to the reproduced levels of the signals fpl and fp2 thereby to generate as output a tracking error signal responsive to the tracking error direction and error quantity. This error signal is further amplified to a specific level by a known circuitry and then applied through an output terminal 111 to the moving coil mechanism 80 of the tracing stylus 74 thereby to control this mechanism. Thus, the tracing stylus 74 is stably tracking controlled by the resulting closed loop.

Here, the operational state wherein the reproduction of the track t2 is to start, continuing from the recording position 52 of the signal fp3 upon completion of the reproduction of the track tl of the tracing stylus 74 in Fig. 4B will be considered. In the instant embodiment of the invention as described above, the reference pulse signal fp3 is extracted from the reproduced signal after reproduction of the track tl. With this signal fp3 as reference, the polarities of the signals fpl and fp2 are inverted at the time of reproduction of the track t2, and the control direction by the signals fpl and fp2 is inverted from that at the time of reproduction of the track tl thereby to control the aforementioned moving coil mechanism 80.

For this reason, at the time of reproduction of the track t2, tracking control is so carried out that the tracing stylus is controlled and actuated toward the outer periphery of the disc 71 by the reproduction of the signal fpl and toward the center of the disc by the reproduction of the signal fp2. Therefore, it is possible this time to trace accurately and positively in succession over the track t2.

Then, for the reproduction of the track t3 upon completion of tracing of the track t2 per revolution, by the inversion again of the polarities of the signals f 1 and fp2 at the recording position 52 of the signal fp3, tracing and tracking of the track t3 is similarly carried out. Similarly thereafter, the signal pickup structure 79 shown in Fig. 6A accurately and positively traces and reproduces the successive track paths following one after another by moving with a specific pitch in the radial direction of the disc 71, for example, from the outer periphery toward the center of the disc. Thus, a normal reproduced picture is obtained.

In accordance with the present invention, reproduction of a still motion picture by continuous reproduction of the same track and reproduction of slow-motion pictures by repeated reproduction of each track can also be carried out. For example, upon completion of the first time reproduction of the track tl, a pulse obtained from the pulse signal fp3 detected from the signal recording position 52 and having a compulsory power with respect to the tracking servo circuit 110 is applied from outside, and a signal is applied from a tracking servo amplifier (not shown) to the moving coil mechanism 80, the tracing stylus being caused to jump or kick back at the position 52. In this manner, continuous tracing of only the track tl can be effected.

Furthermore, it is also possible by reducing to 1/3 the traversing speed of the signal pickup structure 79 in the disc radial direction as the above described operation is repeated three times for reproduction of succeeding tracks in a desired reproduced picture, for example, and, inter-relatedly with this, processing the switching pulses of the signals fpl and fp2 so that the number of reproducing tracings of the same track will be three times each, a 3:1 slow-motion picture can be obtained. In addition, depending on the necessity, various operations such as high-speed searching, determination of the starting point of reproducing and forwardreverse reproduction can be carried out as desired.

Another embodiment of the recording system will now be described in conjunction with Figs. 10 and 11. For convenience in description, the case wherein a video signal of 4 fields is recorded and reproduced every revolution period of the disc will be considered as one example.

In the system shown in Fig. 10, a video signal a indicated in Fig. 11(A) with a field taken as a unit is introduced through an input terminal 171 and is supplied to a synchronizing signal separation circuit 172 and a mixer 184. The output synchronizing signal thus separated by the synchronizing signal separation circuit 172 is supplied respectively to a vertical synchronizing signal separation circuit 173 and a gate circuit 179.

The resulting vertical synchronizing signal b as indicated in Fig. 11(B) led out from the vertical synchronizing signal separation circuit 173 is counted down by 1/2 by a flipflop 174 and is further counted down by 1/2 by a flip-flop 175. The respective output pulses of the flip-flops 174 and 175 have pulse recurrence frequencies which, as indicated at c and din Figs. 11(C) and 11(D), are 1/2 and 1/4 of the field frequency and are both supplied to the gate circuit 179.

On one hand, the vertical synchronizing signal from the separation circuit 173 is rendered into pulses having a suitable position and width by monostable multivibrators 176 and 177 connected in cascade arrangement and is further synchronized with a synchronizing signal by a J-K flip-flop 178 and thus rendered into the pulses e indicated in Fig. ll(E). These pulses e are supplied to the gate circuit 179. As a result, pulses of a 4-field period and, moreover, a pulse width made equal to 1 to a number of H (H being the horizontal scanning period) within the vertical blanking period of the video signal a, as indicated in Fig. 11(F) are gated and derived from the gate circuit 179.

Fig. ll(G) shows vertical synchronizing signals and equalizing pulses within the vertical blanking period of the video signal a.

Fig. 11(H) shows an enlarged waveform in the vicinity of pulse width fl of the output pulses f of the gate circuit 179. The output pulse fl of the gate circuit 179 is supplied to a pulsed oscillator 180, an inverting amplifier 181, and a monostable multivibrator 182. The pulsed oscillator 180 is a circuit, as well known, for generating a sinusoidal wave only when the input pulse is a logical "1" or "0", and, in the present embodiment, is adapted so as to oscillate only when the logical "0" is attained. Accordingly, the output signal of the pulsed oscillator 180 becomes as indicated by i in Fig. 11(I), and which signal is supplied to a mixer 184. The output oscillation frequency of the pulsed oscillator 180 is required to be sufficiently high in compared with the frequency of the synchronizing signal. A preferable result can be obtained, in practice, by selecting the above frequency at about 1 MHz to 2 MHz.

The pulse inverted and amplified by the inverting amplifier 181 is supplied to the mixer 184, where it is mixed with the signal i and the video signal a at a predetermined level ratio. Accordingly, a video signal j (Fig. 11(J)) wherein the sinusoidal wave is superimposed, at its gray level, on a portion (equalizing pulses, in this case) following the vertical synchronizing signal within the V.BLK period is derived from the mixer 184 and through an output terminal 185.

The video signal j is then supplied to the input terminal 14 in Fig. 1.

It will be understood from the description set forth that the parts where the sinusoidal wave and the gray level are superimposed each other in the above described video signal j appear every four-field period, i.e., in a period of one rotation of the rotating recording medium.

On one hand, a monostable multivibrator 182 is triggered by the front edge (the falling part, in the present embodiment) of the output pulseffrom the gate circuit 179, and supplies to a flip-flop 183 a pulse in which cut-in parts such as the equalizing pulses within the V.BLK period is eliminated. The flip-flop 183 therefore sends out, from the terminals Q and Q thereof to the output terminals 186 and 187, the pulses which are of opposite phase and are inverted in a period of four fields respectively. The output pulses Q and Q from the output terminals 186 and 187 are respectively applied to the pulsed oscillators (corresponding to the oscillators 20 and 21 in Fig. 1) for oscillating the reference signals fpl and fp2 which are used for tracking control operation, and cause the pulsed oscillators to effect the oscillation operation alternately every four-field period. The reference signals fpl and fp2 are selected so that the frequencies thereof differ mutually and are in a frequency range, for instance, lower than the range of the main track recording signal.

Further, the reference signals fpl and ap2 are recorded, similarly as in the case described with reference to Fig. 1, alternately every period of single rotation of the rotating recording medium (every four-field interval, in this case) at an intermediate point between the adjacent main tracks as a change of geometrical configuration, thereby forming the sub-track.

Accordingly, the track pattern on the rotating recording medium, the illustration thereof being omitted, is composed of a spiral-formed or coaxial circle-formed main track on which at least a frequency modulated video signal has been recorded as a change of geometrical configuration, and a sub-track of the signals fpl and fp2 formed at the both sides of the main track. In the present embodiment, at least either the gray level signal or the single frequency signal (sinusoidal wave) is further inserted, as the reference signal fp3, to a partial section or the whole section of the V.BLK period of the recording video signal of the main track, which period corresponds to the recording switching position of the signals fpl and fp2.

In the present embodiment, both of the gray level signal and the single frequency signal are inserted and recorded.

The detection of the recording switching points between the signal fpl and the signal fp2 may be effected by only the gray level signal thus recorded. However, it is more advantageous of recording the single frequency signal from the point of view of S/N ratio, because a band-pass filter is used in the reproducing system as described hereinafter. Further, in the case of recording both the gray level signal and the single frequency signal, the recording amplitude of the recording video signal may be enlarged to the allowable limit, thereby being advan ta eous in the point of S/N ratio.

Fig. 12 indicates the block diagram of the essential part of a modification of the recording system in Fig. 10. In Fig. 12, the parts which correspond to those in Fig. 10 are designated by the like reference numerals. In the embodiment in Fig. 10, the signals fpl and fp2 are recorded even in the V.BLK period where the detection signal for indicating the recording switching position of the reference signals fpl and fp2.

However, when the switching timing is taken into consideration, it is advantageous of not existing the signals fpl and fp2 within the period the detection signal is inserted therein.

The system of this modification is adapted so as to satisfy the above described requirement, and is arranged by providing gate cir cuit 188 and 189 for gating the output Q and Q of the flip-flop 183 and by using commonly the output pulse of the monostable multivibrator 182 as gate pulses of the gate circuits 188 and 189. The pulse width of the output pulse of the monostable multivibrator 182 is of the same order as the pulse width of the output pulse of the monostable multivibrator 177 for adjusting pulse width indicated in Fig. 10. The gate circuits 188 and 189 are rendered into their "close" state only over the period of the pulse width.

Accordingly, from the output terminals 190 and 191 of the gate circuits 188 and 189, any pulses are not derived during the detection signal insertion period, in a period of four fields. Therefore, during the above described period, the oscillation operation of the pulsed oscillator for oscillating the signals fpl and fp2 is caused to be stopped.

Next to be described with reference to Fig. 13 is an essential part of a second embodiment of the reproducing system according to the present invention.

A reproduced signal introduced through an input terminal 192 is supplied to a synchronizing signal separation circuit 193 and to a gate circuit 196. A synchronizing signal separated in the circuit 193 is supplied to a vertical synchronizing signal separation circuit 194, where only the vertical synchronizing signal is separated, and is then supplied to a gate pulse generator 195, where a gate pulse of a period of four fields is generated.

The gate pulse thus generated is supplied to a gate circuit 196 thereby rendering it "open" state only during the detection signal insertion period. Accordingly, from the output side of the gate circuit 196, the sinusoidal wave of the single frequency superimposed in a period of four fields for 1H to several H period within the V.BLK period, among the reproduced video signal introduced through the input terminal 92 is derived. The sinusoidal wave thus derived is discriminated by a narrow band-pass amplifier 197 having the passing frequency band having a center frequency which equals to the oscillation frequency of the pulsed oscillator 180 indicated in Fig. 10. The output signal of the band-pass amplifier 197 is detected by a detector 198 and is then applied to a flip-flop 199 as trigger pulse.

Therefore, the flip-flop 199 produces the pulse which is inverted every period of single rotation of the rotating recording medium. This pulse is derived from an output terminal 200 and is used as a pulse for switching the signals fpl and fp2 supplied to the input terminal of the tracking control circuit.

In the case where only the gray level signal is superimposed, as a detection signal, on the video signal, a circuit for detecting the direct current level may be used instead of the band-pass amplifier 197. Accordingly, the recording switching position of the fpl and fp2 is detected, in a electronic manner, by the output pulses of the output terminal 200, whereby the inversion of the tracking error voltage is carried out.

Further, by using the narrow band-pass amplifier in the reproducing system, the above described superimposed signal is reproduced in a stable manner even if the S/N ratio of the demodulated video signal is deteriorated. Still further, since the gray level signal or the single frequency signal, or the signal the both signals being superimposed exists continuously for a certain period within the V.BLK period, the influence of the drop-out or deficiency thereof may be almost eliminated.

The embodiments set forth are described in the case of reproducing the disc 71 recorded in the pit pattern form by means of, particularly, the tracing stylus of the type of detecting electrostatic capacitance. The reproducing tracing means is not limited to the tracing stylus type, but the laser beam, for instance, may be used.

The system of the present invention is applicable not only to the recording and reproducing of video signals but also to operations such as recording and reproducing audio signals only by a high dynamic range with high quality and recording an audio signal with multichannels on the same single track thereby to carry out reproducing and tracking this recorded information track similarly as described hereinbefore.

In addition, while the case wherein respective single-frequency signals are used for the signals fpl and fp2 was described in the foregoing disclosure, signals which have been produced by frequency modulating audio signals, for example, and which have been continuously recorded may be used as the reference signals fpl and fp2. Further modifications such as frequency converting the carrier color signal in a color video signal to a low-frequency range by a known technique and applying it to the reference signals fpl and fp2 are also possible. The essential requirement is that the reference signal is recorded and reproduced in a signal form which can be applied to at least tracking control.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope of the invention.

Attention is drawn

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. track similarly as described hereinbefore. In addition, while the case wherein respective single-frequency signals are used for the signals fpl and fp2 was described in the foregoing disclosure, signals which have been produced by frequency modulating audio signals, for example, and which have been continuously recorded may be used as the reference signals fpl and fp2. Further modifications such as frequency converting the carrier color signal in a color video signal to a low-frequency range by a known technique and applying it to the reference signals fpl and fp2 are also possible. The essential requirement is that the reference signal is recorded and reproduced in a signal form which can be applied to at least tracking control. Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope of the invention. Attention is drawn to our copending application no. 14533/77 (Serial No.

1 585 546) out of which the present application has been divided.

WHAT WE CLAIM IS: 1. An information signal reproducing system comprising: means for reproducing an information signal and first, second and third reference signals from a recorded disc, said informa tion signal being recorded on information signal tracks on the recorded disc, said first and second reference signals being recorded on reference signal tracks, said first and sec ond reference signals being recorded alternately on the reference signal tracks during each rotation of the recorded disc, and said third reference signal being recorded at positions corresponding to the positions where the first and second reference signals switch; means for individually separating said first, second and third reference signals from the signals reproduced by said reproducing means; means for producing a tracking control signal from the separated first and second reference signals switched in response to the separated third signal; and means for controlling tracking in response to said tracking control signal so that said reproducing means traces the information signal track on the recording disc.

2. An information signal reproducing system as claimed in claim 1 in which said tracking control signal producing means comprises means for alternately deriving said separated first and second reference signals responsive to the separated third reference signal, means for detecting the derived first and second reference signals, and means for producing the tracking control signal in response to a difference between the detected first and second reference signals.

3. An information signal reproducing system comprising: means for reproducing an information signal and first, second and third reference signals from a recorded disc, said information signal and first, second and third reference signals being recorded on a recorded disc as variations of geometrical configuration, said information signal being recorded on information signal tracks on the recorded disc, said first, second and third reference signals having respectively different frequencies, said first and second reference signals being recorded on reference signal tracks, said first and second reference signals being recorded alternately on the reference signal tracks during each rotation of the recorded disc, and said third reference signal being recorded at predetermined positions corresponding to the positions where the first and second reference signals switch during each rotation of the recorded disc; means for individually separating said first, second and third reference signals from the signals reproduced by said reproducing means; means for alternately deriving said separated first and second reference signals responsive to the separated third reference signal; means for detecting the derived first and second reference signals; means for producing a tracking control signal in response to a difference between the detected first and second reference signals; and means for controlling tracking in response to said tracking control signal so that said reproducing means traces the information signal track on the recording disc.

4. An information signal reproducing system substantially as described with reference to the accompanying drawings.