US3800100A - Method for storing and playing back signals on a carrier - Google Patents

Abstract

In a signal storage system in which signals are stored in the form of spatial undulations in a resiliently compressible surface and played back by compressing the undulation peaks with a substantially motionless pressure responsive transducer, the transducer output having a component whose frequency represents the frequency at which successive undulation peaks are scanned, a second signal is recorded in the form of variations in the ratio of undulation peak length to total undulation length.

Description

O v United States Patent 1 1 3,800,100

Runge A Mar. 26, 1974 METHOD FOR STORING AND PLAYING [56] References Cited BACK SIGNALS ON A CARRIER UNITED STATES PATENTS [75] Inventor: Wilhelm Runge, Ulm/Donau, 3,691,317 9/1972 Dickopp.... 179/100.41 P Germany 3,482,038 12/1969 Warren 178/66 A [73] Assignee: TED Bildplatten Aktiengesellschaft AEG Telefunken TELDEC g, Primary Examiner Raymond F. Card1llo, Jr. Attorney, Agent, or Fzrm--Spencer & Kaye Switzerland [22] Filed: July 3, 1972 [57] ABSTRACT [21] Appl. No.: 268,553 In a signal storage system in which signals are stored in the form of spatial undulations in a resiliently compressible surface and played back by compressing the [30] Foreign Apphcamm Pnonty Dam undulation peaks with a substantially motionless pres- July 3, 1971 Germany 2133130 Sure responsive transducer, the transducer output ing a component whose frequency represents the fre- Eg g 'g 100'4 7% quency at which successive undulation peaks are W 9 d d d 5' s1 Field ofSearch ..179/100.4 R, 100.4 0, a Sewnd s'gnal e m the 179/1004 M, 100.41 P, 100.41 13,15 BM; 178/66 A, 6, DIG. 3; 325/139 variations in the ratio of undulation peak length to total undulation length.

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SHEET 3 [IF 3 THRESHOLD GAIN CONTROLLED zggggg g c/Rcu/T AMRL/F/ER 'L/M/TER E INTAEGRATORX AMPLIFIER g- I SIC Ya I D CL dI e f T CONTROLLED THRESHOLD 5 F c/Rcu/T METHOD FOR STORING AND PLAYING BACK' SIGNALS ON A CARRIER BACKGROUND OF THE INVENTION The signal scanning from this carrier is effected by av pickup provided with a mechanical-electrical transducer responsive to pressure variations. As disclosed in the above-cited patents, the scanning surface of the pickup remains, during playback, substantially motionless in the direction of the force exerted thereon by the surface portions of the carrier, while the surface portions are compressed as they pass under the pickup surface and thus exert a pressure force on the pickup surface due to their being compressed. The characteristic shape of this pressure force during the passage of the surface portions under the pickup surface is used by the transducer to derivean electrical value which corresponds to the stored signals.

This technique is particularly useful for the storage and playback of signals which contain a broadbanded frequency mixture, for example television picture sig nals.

A number of specific proposals have been made regarding the form in which the information is recorded on the carrier. Inter alia, it has been proposed to keep the amplitude of the undulations of the carrier surface tage, for example, when the recorded signal value is a carrier oscillation which is frequency modulated with the signal.

SUMMARY OF THE INVENTION It is an object of the present invention to store a second information signal on the carrier, simultaneously and without any additional space requirement, in addition to the previously proposed hill-and-dale frequency modulated information signal, while maintaining the frequency-independent amplitude of these undulations on the carrier surface, and to play the second signal back therefrom. If, for example, the first information signal is the luminance signal of a television program, the second information signal may be the chrominance signal or the'audio signal, possibly also a superimposition of these two signals.

The present invention thus involves a method for storing and playing back signals on a carrier along a certain track where the signals are constituted by undulations in mechanically depressable surface portions. During playback the peaks of these undulations, due to their being compressed by a pressure sensitive pickup, exert a pressure force on the scanning surface of this pickup. This pressure force is converted into an electrical ducer.

The objects according to the present invention are achieved by using the undulations, whose number per unit of scanning path length corresponds to the instanvoltage by a mechanical-electrical transtaneous frequency of a first signal, for the simultaneous storing of a second signal which is independent of the first signal, and giving each undulation peak such a length along the scanning path that the ratio between this length and the total length of the associated undulation period corresponds to the respective characteristic value of the second signal.

The two signals to be recorded are thus stored, according to the present invention, by frequency modulation of the first signal and an additional pulse duration modulation of the second signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are idealized elevational views of a portion of one track of a carrier with hill-and-dale recording for two successive positions of a cooperating pickup stylus.

FIG. 3 is a curve of the force acting on a pickup during scanning of the carrier according to FIGS. 1 and FIG. 4 is a curve illustrating the behavior of the pickup scanning the hill-and-dale recording applied to the carrier.

FIG. 5a is an idealized cross-sectional view of a carrier with the hill-and-dale recording according to the present invention.

FIG. 5b is a curve of the time sequence of the second information recorded on the carrier of FIG. 5a.

FIG. 5c is a pair of curves showing the force produced by the carrier on the pickup during scanning of the carrier of FIG. 5a.

FIG. 6 is a diagram of a playback arrangement with a filter for use with a carrier produced according to the invention.

FIG. 7 shows a block diagram of the arrangement to produce the modulation signal according to the invention.

arrangement shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 illustrate a carrier 1 provided with groove undulations in the manner described in the above-cited patents. These figures show a cross section along a scanning track in which the frequency modulated information is recorded according to the hill-anddale technique. The recording is in the form of a train of undulations, with each undulationvbeing composed of a projection la, 1b, 1c, 1d, 12, 1f, etc., and a space or gap. The length of each projection is B and the total length of each undulation, composed of a projection and its succeeding gap, is A. The undulation projections have a constant height vertical to the scanning direction, and a constant length B. The groove width is constant. The distance A between the leading edges of two identical groove undulations, or the spatial wavelength of the undulations, varies as a function of the recorded signal frequency. For reasons of simplic ity it is shown to be constant in the figures.

A pickup 2 of the type disclosed in the above-cited patents is disposed on the groove undulations 1b to 1e in FIG. 1. This pickup extends over many groove undulations in the scanning direction, in practice for example or more undulation projections. The pickup 2 moves from the left to the right in the plane of the drawing which is equivalent to the actual conditions of a stationary pickup and a carrier moving to the left.

The pickup 2 is positioned so that its lower surface is below the tops of the projections la-lf when the latter are not stressed.

In the type of system under consideration, the pickup 2 is much less resilient in a vertical direction than the carrier material so that the movement of the pickup across the undulation projections produces an elastic compression of the carrier material. In order to permit a sliding movement of pickup 2 over the groove undulation peaks, its scanning shown in the drawing has a skid shape so that the pressure acting on this skid over a path of about 1 to 100 wavelength A, (1 wavelength distance between the leading edges of two groove undulation projections) decreases in the direction of movement of the pickup relative to the carrier. The trailing skid edge, which is to the left in the drawings, is moreover so designed that the pressure thereat drops from a maximum to zero over a path of travel having a length of no more than one-half a wavelength (A/2).

In FIG. 1 the groove undulation projections 1b to 1e are compressed by pickup 2 to an increasing extent from the right toward the left due to the particular shape of the pickup. The displaced portions of these groove undulation projections are shown by hatching. If the pickup 2 slides over the hill-and-dale recording of FIG. 1, the time curve shown in FIG. 3 results for the force exerted by carrier 1 on the pickup.

FIG. 3 shows that the total force F is greatest when the trailing edge of the pickup 2 is disposed at the leading edge of an undulation projection seen in the scanning direction, this being the left-hand edge. This force will be identified as F B in the further discussion. Thus, at this point, F,,,, F,;. Such a position is taken up by the pickup in FIG. 1. Thetotal force F,,,, is lowest when the trailing edge of the pickup, as shown in FIG. 2, lies at the trailing edge of a groove undulation projection. The difference between this force and F will be called AF. There thus results for this pickup position the force To further aid understanding of the present invention certain relationships for F and AF will be set forth below.

Under the above-mentioned conditions of constant width transverse to the scanning direction of the groove undulations and of the elastic behavior of the carrier material, a force component B T is produced by an undulation projection having the length B and which has been compressed by a depth T, which force component directly corresponds in magnitude to the area of the hatched portion of the groove undulation 1b. The total force F F which corresponds to the pickup location of FIG. 1 and which originates from all of the undulations lb to 1e is thus:

un a /A (T2) B k where L is the effective length of the pickup, A the distance between the leading edges of two successive groove undulations or an undulation wavelength, and k a constant.

If the pickup 2 moves to the right into the position shown in FIG. 2, the total force decreases by the amount T B k. During this further movement of the pickup each of the groove undulation projections 1c to 1f is additionally compressed by the amount D B T/L and, since their number is L/A, the force originating from these groove undulations increases by the amount If the pulse ratio or duty factor, B/A is represented by i, this results in AF=TA-i(li)'k and F =(TL/2 )'i-k FIG. 3 shows the curve of the force acting on pickup 2 and originating from carrier 1 in the course of the scanning process. Here the maxima correspond to the pickup position of FIG. 1 and the minima to that of FIG. 2.

According to the above-derived relationships for F, and AF these two values are dependent on the pulse ratio i. F B is directly and linearly proportional to i. The function AF(i) is shown in FIG. 4.

In the'region i AF is always more than percent of its maximum value and can thus be considered constant to a first approximation. Outside of these preferred limits given for i, AF rapidly drops toward zero, the signal to noise ratio correspondingly deteriorates in this range with decreasing AF.

For the simultaneous recording of a second, more slowly varying, information signal, the pulse ratio is correspondingly changed and thus becomes directly proportional to F The course of F during scanning over a distance s thus results from the superposition of the path of F and the AF fluctuations representing the frequency modulated recording.

Since F and AF represent separate sources of information, they must be separable. They must thus lie far enough apart in frequency that they can be separated with frequency selective filters. The smallest frequency difference between the two is with respect to the upper frequency limit of the second signal, which is one-half the lowest frequency occurring during the frequency modulation of the first signal. The latter frequency is represented by the greatest value of the length A occurring in the hill-and-dale recording. As already mentioned, AF increases proportionally to A according to the equation:

AF=TA-i(l i)-k. Since the signal derived from AF is to remain as constant in amplitude as possible, however, it can be corrected during its electrical amplification by the factor NA f/v, where f is the respective frequency of the AF signal and v is the linear speed of the pickup 2 relative to the carrier 1.

A carrier with hill-and-dale recording according to the present invention, which simultaneously carries a first frequency modulated signal and a second signal S, recorded by a duration or length modulation of the groove undulation projections is shown in FIG. 5a. The frequency values of the first signal are represented by the wavelengths A1, A2, A3, A4, etc., the amplitude of the second signal S, by the respective lengths of the intervals B1, B2, B3 and B4. The amplitude waveform of the second signal S, which results in the illustrated projection length modulation is shown in FIG. 5b. The derivation of the length of the undulations B1 to B4 was based on the particularly favorable operating range Ai i 4. This range results for the following value of B, in dependence on A:

S is the peak value of S If the dynamic range of the recording of the second signal S2 is limited, eg to 2/5 i 3/ 5, the upper frequency limit of the second signal can be made higher. FIG. 5c shows the variation of the force exerted on the pickup by the carrier of FIG. 5a during the playback process. For the sake of better clarity the dimensions of AF in FIG. 5c, particularly for the fluctuation of force per wavelength, are exaggerated.

The pressure pickup converts this force variation into a correspondingly varying electrical voltage. The thus derived electrical signal consists, as shown in FIG. 50, of the rapid voltage fluctuations corresponding to the frequency modulation (AF) and a total amplitude variation (F (8 which corresponds, in the form of an amplitude modulation, to the second stored signal. These signals can be separated by known electronic means, for example frequency selective filters.

FIG. 6 shows the basic structure of this type of playback device. A mechanical-electrical transducer 11 is placed directly onto a pickup 10. The electrical voltage appearing at the output of transducer 11 travels through a frequency selective filter arrangement 12 to the system 13 in which the stored signals are displayed. In the case where a television picture is recorded the system 13 will be a television receiver. In the filter arrangement 12 the two recorded signals which were picked up by pickup are electrically separated, by techniques which are abundantly well-known in the art.

As can be seen in FIG. 5a, all groove undulations have the same height. This fact is of great advantage during manufacture of the carrier. Due to the extremely high information density of the present highdensity storage system the cutting processes during manufacture of the carrier, which up to now were mechanical processes, must be very precise, which results in a relatively low cutting speed. Methods utilizing the electron beam technique and the laser technique have been proposed to substantially increase the cutting speed. The use of known circuit measures from the electronic art make it easily possible to produce an electrical signal from the two sources of information to be stored, which signal corresponds in frequency as well as in its pulse ratio to the two signals. This electrical signal can then be used, according to the abovementioned prior proposals, to control an electron or laser beam effecting the recording.

Such circuits are known, for example, from the book Theorie und Technik der Pulsmodulation [Theory and Technique of Pulse Modulation] by l-Ic'ilzler and Holzwarth, published by Springer Verlag, 1957, particularly on pages 17 and 55, and from US. Pats. Nos. 1,917,102, 2,171,150 and 2,479,947.

In FIG. 7 is shown as an example an arrangement for forming carrier modulation according to the invention.

FIG. 8 shows the several signals in this arrangement. By a standard frequency-modulated oscillator the signal S is transformed into a course of oscillations the frequency of which corresponds to the signal S as is given in FIG. 8a. By means of a low threshold circuit 20 this signal is transformed into a course of rectangular pulses the frequency of which corresponds to the frequency modulated signal a and the ratio B/A of pulse duration B to pulse distance A is A, as is shown in FIG. 8b.

This Signal (FIG. 8b) is processed by an integrator 22 of the arrangement shown in FIG. 7 and gives a triangular sequence of pulses the amplitude of which is inversely proportional to the frequency of the pulses, as is shown in FIG. 8c. This sequence of triangular pulses feeds a gain controlled amplifier 23, the gain of which is steered either by an automatic gain control or a volume control in dependence on the signal 8,, in such a way that the amplitude of the triangular pulses remains constant.

The result of this operation is shown in FIG. 8d. This sequency of triangular pulses of constant amplitude but of a frequency corresponding to the frequencymodulated signal (FIG. 8a) is applied to a controlled threshold circuit 24 the height of the threshold of which is derived from the second signal 8,. The result .of this process is shown in FIG. 8e.

Now the signal is amplified by an amplifier 25 (FIG. 7) and clipped by the voltage limiter 26. The result is the signal shown in FIG. 8f. If the signal S should be zero, by the arrangement is produced a rectangular pulsetrain the frequency of which corresponds to the modulating signal shown in FIG. 8a, and the ratio of pulse duration to pulse distance is again 1%.

But if the threshold differs from zero, the ratio of pulse duration to pulse distance corresponds to the value of the threshold and correspondingly to the signal S The frequency of the train of pulses (FIG. 8f) corresponds to signal S and the ratio of pulse duration to pulse distance corresponds to the signal S The train of pulses according to FIG. 8f is the signal wanted for modulation of an electron beam or laser for producing a record according to the invention.

It is not necessary that the pulses have an exact rectangular wave form. However, the duration of the slopes should be smaller than one-half of the duration of the part of the pulse of constant amplitude.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. In a method for storing signals on a carrier having a deformable surface portion by which the signals are stored in mechanical form; the deformable surface portion being arranged along a path over which there is to be relative movement between the surface portion and, a pressure sensitive pickup which converts changes in the mechanical pressure thereon into electrical signals, the relative movement subjecting the pickup to different pressures as it moves along the path while in engagement with the surface portion, in consequence of which, upon such relative movement with the pickup engaging the surface portion and remaining in substantially constant spatial relationship with the undeformed position of the surface portion, the surface portion is deformed and the pickup produces electrical signals which correspond to the signals that are stored in mechanical form, the surface portion having, in its undeformed state, the form of a series of spatial undulations, each undulation being composed of a to correspond to a characteristic value of the second signal.

2. A method as defined in claim 1 wherein the ratio between the length of a projection and the total length of its associated undulation is greater than A and less than "$4.

3. A method as defined in claim 1 wherein the highest recorded frequency of the second signal is lower than the lowest recorded frequency of the first signal.

Claims (3)

1. In a method for storing signals on a carrier having a deformable surface portion by which the signals are stored in mechanical form; the deformable surface portion being arranged along a path over which there is to be relative movement between the surface portion and a pressure sensitive pickup which converts changes in the mechanical pressure thereon into electrical signals, the relative movement subjecting the pickup to different pressures as it moves along the path while in engagement with the surface portion, in consequence of which, upon such relative movement with the pickup engaging the surface portion and remaining in substantially constant spatial relationship with the undeformed position of the surface portion, the surface portion is deformed and the pickup produces electrical signals which correspond to the signals that are stored in mechanical form, the surface portion having, in its undeformed state, the form of a series of spatial undulations, each undulation being composed of a projection and an adjacent space, the improvement comprising: forming said undulations to give all of said projections a uniform undeformed height above a reference plane; recording a first signal by causing the number of said undulations per unit length of the path to correspond to the frequency representative of the first signal; and recording a second signal, superimposed on, and independent of, the first signal, by causing the ratio of the length of each projection to the total length of its associated undulation along the path to correspond to a characteristic value of the second signal.

2. A method as defined in claim 1 wherein the ratio between the length of a projection and the total length of its associated undulation is greater than 1/4 and less than 3/4 .

3. A method as defined in claim 1 wherein the highest recorded frequency of the second signal is lower than the lowest recorded frequency of the first signal.

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