GB2039125A - A method of producing a disc shaped record carrier - Google Patents

Abstract

A method of producing a disc shaped record carrier having a helical, information-carrying, dam- shaped track (3) for pressure transducer playback, comprises cutting a groove forming a base modulated by the signal with the width of the base equal to the width of the elevation (2), into a master and producing the final record carrier as a negative of this master. The groove cutting stylus can be subjected to a low frequency lateral oscillation to provide on playback a signal for guiding the playback head. <IMAGE>

Description

SPECIFICATION A method of producing a disc shaped record carrier This invention relates to a method of producing a disc shaped record carrier. It is known to record a sound or video signal along a helical track of a disc. In preferred manner it is common in video recording to record a number of complete frames on one circuit of the track, each frame comprising two half frames. Recording may be carried out optically or mechanically. Scanning may in turn be carried out optically, mechanically or even capacitatively.

In known pressure scanning (German Patent Specification No. 1574489), the deformations caused by scanning with the scanner which is held rigidly in position for example, are compressed and provide force pulses in this scanner which are converted into electrical signals by a pressure transducer coupled to the scanning element.

However cross-talk may occur in these record carriers between the information of adjacent portions of the track even if the scanner, guided along the groove is guided perfectly in the groove and does not leave it. This socalled geometric cross-talk is caused in particular by the high groove density which is of the order of magnitude of 300 to 500 grooves/mm.

Geometric cross-talk occurs where adjacent tracks overlap between the grooves overlap at the dam-like ridge, and this leads to crosstalk. The scanner 12 is also in contact with the over-lapping areas and this leads to crosstalk.

When recording one complete frame per rotation this cross-talk is relatively insignificant because the adjacent portions of the track correspond both in time and space to the same lines of successive frame and therefore the information is not very different. Moreover, with this type of recording, in accordance with German Patent Specification No.

2042434, the type of modulation of the colour recording is so similar that there are no significant errors when there is cross-talk between the colour signals.

However it has become apparent that particularly in the case of certain picture contents, such as horizontal edges for example, errors may arise where the information is very different in a vertical direction. Moreover, the type of recording just described with one frame per rotation cannot be utilized when, in known manner, the recording takes place at a constant tangential speed, i.e. when one line or one frame always covers the same circumferential distance, both at the outer edge and at the inner edge of the recording surface.

Similarly with a frequency-modulated sound recording, more particularly are having several channels, substantial errors arise.

It is known (German Offenlegungsschrift No. 1942 648) to record the signal for an optical recording along the surface of a helical and dam-like elevation which is formed by a continuous groove-shaped helical depression.

Such a recording has the advantage that when the scanner is being guided exactly on the dam-like elevation there is no cross-talk because adjacent portions of the dam-like elevation are separated in each case by groove portions.

With mechanical recording, this type of record carrier is relatively difficult to produce because the signal has to be recorded on the dam-like elevation.

The invention seeks to create a method by means of which a record carrier of the type last described and having mechnical recording may be produced simply.

According to the invention, there is provided a method of producing a disc-shaped record carrier for electrical signals in which the signal track passes along the surface of a spiral and dam-like ridge which is delimited by a continuous spiral groove-like depression wherein a groove having a flat base containing the signal first cut into a master in order to achieve mechanical recording and the width of this groove base is equal to the width of the eventual elevation; and wherein the final record carrier is produced as a negative from this master.

With the method of the invention, the sig nal initially stored at the bottom of a depression by means of mechanical deformation is transferred to the surface of a dam-like ridge in the desired manner by production of a negative. The recording or cutting stylus therefore produces a depression during the cutting process having a modulation at the base of this depression which afterwards forms a ridge having a mechanical modulation at the surface of this ridge.

The invention will now be described in greater detail by way of example, with reference to the drawings in which: Figure 1 shows a section through a known disc having an obtuse groove base angle.

Figure 2 shows a section through a record carrier, which can be produed by the method in accordance with the invention: Figure 2a shows a plan view of this carrier: Figure 3 shows the method in accordance with the invention, and Figure 4 shows the low-frequency modulation of the depression in outline.

Fig. 2 shows part only of a disc shaped record carrier in a sectional plane which is perpendicular to the plane of the disc surface and is taken along a radial line. A spiral damlike elevation 2 is formed by a continuous spiral groove-like depression 1. The signal is stored in the form of a spiral recording track 3 in the form of a frequency-modulated carrier at the surface of the elevation 2. The transducer 4 (e.g. a pressure scanner), which converts the force pulses P into a voltage U is guided along the track 3 and supplies the signal S to the output terminals 5. The scanner 4 may be guided by mechanical control with the aid of a control signal recorded in the depression 1. t is also possible for a guide element for the scanner 4 to engage into the depression 1 with its projections and to guide the scanner 4 itself.

In Fig. 2a. the modulation along the track 3 is indicated by horizontal lines. These lines are intended to represent successive elevations in a direction along the track these elevations being modulated in frequency in accordance with the signal and being able to be scanned for example, in accordance with the principle of pressure scanning. It may be seen that the overlapping areas 11, in which cross-talk between adjacent portions of the track occurs, are not detected by the transducer 4 in a manner which is advantageous.

In Fig. 3, the profile which is shown on the left of the recording or cutting stylus 6 is cut into the carrier material 8, for example comprising lacquer foil or copper, by the recording or cutting stylus 6 which has a flat edge 7 at the bottom which agrees with, corresponds to the recording of the signal track. This cutting process is implemented so that nothing at all of the original surface 9 of the carrier material remains. Thus a particularly uniform shape of the elevations 10 thus formed is achieved.

This so-called deep cutting is described in greater detail in German Patent Specification No. 15 47 064. If a negative produced from the original carrier cut in the cutting process a counterpart of the original carrier in accordance with Fig. 2 is formed i.e. the ridges 10 in Fig. 3 then form the depressions 1 in Fig.

2. The final record carrier is therefore obtained as a negative from the carrier 8 in accordance with Fig. 3 after one or more reproduction stages.

Fig. 4 shows an additional modulation of the depression 1 which is modulated at a low frequency in accordance with a control signal also evaluated by the transducer 4. The con trol signal thus obtained in the form of an amplitude modulation of the signal supplied by the transducer 4 may be used in known manner to control the position of the scanner 4. The position of the scanner is controlled in a direction identified in Fig. 2 by the brokenline double arrow and the direction of signal scanning is identified by the solid-line double arrow.

In known devices operating by means of laser beam recording a similar pattern of modulation serving the same purpose is provided when recording by means of appropriately guided laser beams. The mechanical cutting device is so formed in accordance with a further embodiment of the invention that the recording or cutting stylus performs a lowfrequency movement (lateral recording) perpendicular to and in addition to movements implementing the useful vertical recording. In Fig. 3 the solid-line double arrow shows the movement of the recording or cutting stylus 6 when producing the vertical recording which contains the signal, while the broken-line double arrow perpendicular thereto illustrates the direction of recording of control modulation.

Claims (4)

1. A method of producing a disc-shaped record carrier for electrical signals in which the signal track passes along the surface of a spiral and dam-like ridge which is delimited by a continuous spiral groove-like depression, wherein a groove having a flat base containing the signal is first cut into a master in order to achieve machanical recording and the width of this groove base is equal to the width of the eventual elevation; and wherein the final record carrier is produced as a negative from this master.

2. A method according to Claim 1, wherein the cutting process takes place to such a depth that there are no parts of the original surfaces of the master left.

3. A method according to Claim 1, wherein a mechanical cutting device is used which has a recording or cutting stylus which performs a low-frequency movement lateral to the groove for producing the control track for maintaining the scanner in its track the lateral movement being in addition to and perpendicular to the movement (vertical recording) which is required for recording the signal.

4. A method of producing a disc-shaped record carrier substantially as described herein with reference to Figs. 2 to 4 of the drawings.