GB2035661A - Disc record having flat-top playing surface - Google Patents

Abstract

Signals are mechanically recorded on a disc master 10 such that the direction and the contour of a spiral groove cut by a chisel-shaped tip of a recording stylus on the master is opposite to the direction and the contour of a spiral raised portion disposed on a resulting disc record. The resulting spiral raised portion disposed on the record surface contains undulations representative of signal elements defining an information track therein. In the master, a spiral ridge separates the tracks. This ridge produces a separating groove in the pressed record which separates tracks formed by the raised spiral portion. <IMAGE>

Description

SPECIFICATION Disc record and master recording This invention relates to a method for electromechanically recording a master suitable for producing a disc record having a spiral land portion disposed on the surface thereof and containing signal representative geometric variations defining an information track thereon.

In certain video disc systems, information is stored on a disc record in the form of geometric variations in the bottom of a continuous spiral groove disposed on the record surface. The variations in capacitance between an electrode incorporated in a grooveriding stylus and a conductive coating disposed on the record surface are sensed to reproduce the stored information. In one signal format, the recorded signal comprises a picture carrier frequency modulated in accordance with video information, and a sound carrier frequency modulated by the sound accompaniment thereof. A capacitance-type video disc system is illustratively described in U.S.

Patent No. 3,842,194 (Clemens). U.S. Patent No.

4,022,968 (Keizer), describes a signal format of the type mentioned above.

In systems of the type mentioned above, an FM signal is recorded along the bottom of a spiral groove disposed on the record. While such a grooved disc format is desirable because it permits simple stylus tracking apparatus in the player, there are some applications for which a flat-type or grooveless disc record is advantageous. An example of such an application is where it is desirable to translate the playback stylus across information tracks for providing active record scanning and special effect features (e.g., repeat play, fast forward and reverse motion).

A problem associated with the flat-type disc format is the difficulty involved in being able to electro-mechanically record a disc master suitable for making records having generally flat-top playing surfaces. U.S. Patent No. 4,044,379, issued to J.B.

Halter, describes an apparatus for electromechanically recording a disc master suitable for making grooved records. Substitution of a flat-bottom cutting stylus for a V-tipped cutting stylus used in the Halter's recorder would produce ridges between the information tracks. If the depth of cut were increased in such apparatus, the information tracks would overlap. A technique which overcomes the foregoing problems is herein described.

In accordance with this invention, signals are electromechanically recorded on a disc master such that the direction and the contour of the spiral groove cut on the master is opposite to the direction and contour of the spiral land portion disposed on the disc record. The land portion disposed on the record surface contains signal elements defining an information track.

In the drawings: Figure 1 is a simplified block diagram representation of a system for electromechanically recording a disc master suitable for making disc records having flat-top playing surfaces in accordance with the instant invention; Figure 2 schematically illustrates the recorded master of Figure 1, and shows signal-representative trenches disposed transversely along a clockwiseinward spiral groove disposed on the surface thereof; Figure 3 is a diagrammatic illustration of a flat-top disc record derived from the recorded master generated in accordance with Figures 1 and 2, and shows corresponding signal-representative trenches disposed transversely along a counterclockwise-inward raised spiral portion disposed on the surface thereof;; Figures 4 and 5 schematically represent greatly enlarged views of the recorded master generated in accordance with Figures 1 and 2; Figure 6 shows an enlarged perspective view of the tip portion of a recording stylus suitable for cutting the disc master in accordance with Figures 1 2 and 4 - 5; and Figures 7and 8 diagrammatically illustrate greatly enlarged portions of the flat-top record of Figure 3.

In Figure 1 a disc master 10 is disposed on a turntable 12 of an electromechanical recording apparatus 14. A cutterhead 16, comprising a cutting stylus 18 and a piezoelectric element 20, is disposed on a carriage 24. The recording apparatus 14 is provided with rails 26 for guiding the carriage 24 along a path that is radially disposed relative to the turntable 12. A carriage driving mechanism translates the carriage 24 in correlation with the speed of rotation of the turntable 12. The position of the cutting stylus 18 relative to the disc master 10 is adjusted in the vertical direction to obtain a proper groove depth. The turntable rotational speed, the carriage translational speed and the depth of cut are all precisely controlled during recording.The piezoelectric element 20, responsive to relatively high frequency signals (e.g., 4.5 MHz), vibrates the cutting stylus 18 secured thereto in order to effect short wave length modulation (e.g., 0.5 micrometers) of the groove bottom.

The formulation of the relatively high frequency signals (the time variation of which is represented by the spatial variation in the groove bottom) will now be described by way of an example. Illustratively, a video camera 30 scans an image 32 for developing a video signal at the output thereof. The video signal may include components representative of the luminance and the chrominance of the scanned image 32. The output signal of the video camera 30 is slowed down (e.g., by a factor of 2) by a video slow down processor 34 in order to accommodate the bandwidth of the cutterhead 16. A video modulator 36, coupled to the video slow down processor 34, frequency modulates a slowed-down high frequency video carrier over a high frequency deviation range (e.g., of the order of 4.3/2 to 6.3/2 Mhz) in accordance with the slowed-down video signal.

A microphone 40 picks up an audio signal accompaniment of the video signal from a speaker 42. The output signal of the microphone 40 is likewise slowed down (e.g., also by a factor of 2) by an audio slow down processor 44 in order to synchronize the audio signal to be recorded with the slowed-down video signal. An audio modulator 46 coupled to the audio slow down processor 44, frequency modulates a slowed down low frequency audio carrier over a low frequency deviation range (e.g., of the order of 716/2 +50/2 KHz) in accordance with the sloweddown audio signal developed at the output of the microphone 40. An audio/video modulator 48 modulates the once-modulated, slowed-down high frequency video carrier in accordance with the once modulated, slowed-down, low frequency audio carrier.A relatively high frequency signal at the output of the audio/video modulator 48 (e.g., 4.5MHz) energizes the cutterhead 16 during the recording operation in order to effect short wavelength modulation of the groove depth (e.g., 0.6 to 1.6 micrometers) while cutting a groove in the disc master 10 at a slowed-down recording speed (e.g., 450/2 rpm).

Several alternative modes of operation of the audio/video modulator 48 (i.e., alternative methods for modulating the once-modulated high frequency video carrier in accordance with the once-modulated low frequency audio carrier) are possible. For example - (1) superposition, (2) amplitude modulation, (3) duty cycle modulation, and (4) negative peak modulation. U.S. Patent No. 4,044, 379 (Halter) further elaborates an electrochemical recording system of the type shown in Figure 1.

The relationship between the direction of rotation of the disc master 10 and the direction of translation of the cutting stylus 18 pursuant to this invention is such that the direction and the contour of the spiral groove 50 cut in the master is the reverse of the direction and the contour of the signal elementcontaining spiral land portion 52 disposed on the surace of a disc record 54. Figures 2 and 3 schematically illustrate such a relationship between a recorded master and a flat-top disc record derived therefrom.

The direction of the spiral on the recorded master 10 is clockwise-inward as shown in Figure 2 whereas the disc record 54 has a counterclockwise-inward spiral in the manner shown in Figure 3.

In systems where one starts with a given direction of rotation, say counterclockwise, of a disc on a player and a given radial direction of translation of a pickup during playback, e.g., from the outer convolutions toward the record center, it is possible to establish the relationship between the master and record which is shown in Figures 2 and 3 as follows.

During recording, the master is rotated in the opposite or clockwise direction and the radial translotion of the recording head is from the outside and progressing toward the center of the master. In this case, the progression of signals supplied to the recording head during recording is the same as the progression of signals recovered during playback.

That is, the programming begins on the outer convolution of both the master and the record produced from the master.

It is also possible to generate the relationship between master and record, as shown in Figures 2 and 3, in another manner. Here, the direction of rotation of the master is the same as the direction of rotation of the disc during playback. In this case the direction of radial translation of the recording head is opposite to the direction of radial translation of the pickup during playback. Thus, if the radial translation of the pickup is from outer convolutions of the record to inner convolutions thereof, the recording head over the master would be translated from an inner point on the master along a radial line toward the outside of the master. Now the progression of signals supplied to the master would be opposite to the progression of signals recovered during playback.That it, during the recording steps the end of the programming would be recorded first toward the inside of the master so that the beginning of the programming ends at the outside of the master. A record produced from such a master would then be played back from the outside of the record and progress toward the inside of the record.

Figure 4 diagrammatically illustrates a greatly enlarged view of a portion of a partially recorded disc master 10 suitable for making flat-top disc records. The recording stylus 18 with a chiselshaped tip cuts the spiral groove 50 having signal representative trenches disposed transversely along the flat groove bottom on the master surface as shown in Figure 5. Figure 6 shows a greatly enlarged perspective view of the tip portion of the cutting stylus 18 suitable for making flat-top records. The width "W" of the tip portion of the cutting stylus 18 is equal to the width of the raised spiral information track 52 disposed on the disc record surface.

Figures 7 and 8 schematically illustrate greatly enlarged views of the flat-top disc record 54 derived from the recorded master 10 of Figures 1 - 2 and 4 - 5.

The disc record 54 may be replicated from the recorded master 10 in any known manner. For example, a stamper having the same groove direction and contour as the spiral groove on the recorded master 10 is electroformed. The stamper is then used in conjunction with a record molding machine to press flat-top disc records from plastic materials. The resulting record has a relatively flat-top with the signal elements located in the land portions and having slight grooves on either side of such land portions. The small grooves are the reverse of the projections shown in Figure 4.

Illustratively, the dimensions are as follows: (1) tracks per inch = 9,620, (2) turn-to-turn pitch = 2.67 micrometers, (3) information track width = 2.2 micrometers, (4) recording stylus width = 2.2 micrometers, (5) peak-to-peak signal amplitude = 600 angstroms, (6) signal element dimension along the spiral information track = 0.5 micrometers, (7) the width of the playback stylus = 2.2 micrometers, and (8) the dimension of the playback stylus shoe along the spiral information track = 5. micrometers.

Since the disc record has flat-top playing surfaces, the record player is provided with a tracking system for keeping the playback stylus centered over the information track during playback. U.S. Patent Application, Serial No. 938,963, filed in behalf of Clemens describes an active tracking system suitable for use with flat-top disc records (Japanese Applications 54-111637 and 54-111638).

Thus, the present invention provides a means in an electromechanical mastering operation which will ultimately enable the production of records having flat-top information tracks, i.e., records where the information signal is located on a flat surface as compared to records where the information signal is located in geometric variations at the bottom of a groove.

Claims (10)

1. A method for electromechanically recording a master suitable for making a disc record having signal elements in the form of geometric variations disposed along a raised spiral information track on the surface thereof; said method comprising the steps of: causing said master to rotate; translating a recording head along a path disposed radially of said master while said master is rotating to impress a spiral groove thereon; and supplying signals to said recording head for modulating the bottom of said spiral groove; wherein the relationship between the direction of rotation of said master and the direction of translation of said recording head is such that the direction and the contour of said modulated spiral groove impressed on said master is opposite to the direction and the contour of said raised spiral information track disposed on said disc record.

2. The method as defined in Claim 1 wherein the direction of rotation of said master during recording is opposite to the direction of rotation of said disc record during playback; wherein the direction of translation of said recording head relative to said master during recording is the same as the direction of translation of a signal pickup relative to said disc record during playback; wherein the progression of signals supplied to said recording head during recording is the same as the progression of signals appearing at the output of said signal pickup during playback.

3. The method as defined in Claim 4 wherein the direction of rotation of said master during recording is the same as the direction of rotation of said disc record during playback; wherein the direction of translation of said recording head relative to said master during recording is opposite to the direction of translation of a signal pickup relative to said disc record during playback; wherein the progression of signals supplied to said recording head during recording is opposite to the progression of signals derived at the output of said signal pickup during playback.

4. The method as defined in Claim 1 suitable for use with a recording head comprising a recording stylus for cutting said modulated spiral groove thereon, and means coupled to said recording stylus for translating said signals into signal representative motion.

5. The method as defined in Claim 4 wherein said recording stylus has a relatively straight cutting edge in the plane of the master surface being recorded, said stylus cutting edge having a width slightly less than the turn-to-turn pitch dimension of said spiral groove on said master and representing the width of said raised spiral information track.

6. The method as defined in any of Claims 1-5 further including the steps of: duplicating said recorded master to generate a stamper; and replicating said stamper to generate a disc record.

7. A disc record having a spiral land portion interposed between successive groove convolutions disposed on the surface of said disc record; said land portion containing geometric variations representative of signal elements defining a raised spiral information track.

8. A disc record as defined in Claim 7 wherein the width of said land portion is less than the turn-toturn pitch dimension thereof.

9. A disc record generated from the method of Claim 6.

10. A method of recording a master or a disc record produced from such master substantially as hereinbefore described with reference to any Figure.