HK1006048B - A pre-engraved movable information carrier and an optical radial-tracking device which can be used with said carrier - Google Patents

Description

The present invention relates to a mobile information medium, in particular a disc-shaped one, which contains pre-engraved material tracks along which optically readable information can be recorded.

Many radial track tracking methods have been described in the art. When recording information in sequential form, for example video information, usually the tracks are not materialized in advance but rather created in real time at the time of recording. The information is recorded along tracks that are in the form of a single spiral extending from the peripheral area of the disk to a central area or vice versa or in the form of concentric circles centered on the axis of rotation of the disk.

In the simplest systems, the precision of the forward organs of the recording head is relied upon to create this track. When reading, information recorded, for example in the form of micro-reliefs, interferes with a focused reading beam in the plane of the recording face of the disc. The scrolling of these micro-reliefs under the focusing task modulates the beam and this modulation is detected by photoelectric cells converting light intensity variations into electrical signals.

The process described above requires that the front of the recording head must be very stable, so that two successive grooves do not overlap or at least are not easily distinguishable when reading. In order to improve the system described above, a process using the last recorded track or one of the previously recorded tracks as a reference was proposed in the French patent application No. 2 366 636.

US-A-3 919 697 is also known to track a runway in the middle of a set of adjacent elements already recorded by subdividing each runway element into alternating information-reserved sites and specific patterns to counteract any tendency of the exploration spot to deviate from its ideal trajectory. These specific patterns occupy regions that are not vis-à-vis data blocks and are centered with respect to each runway element. The re-centering of the exploration spot depends exclusively on optical interactions with the patterns on the surrounding runway elements. The measurement of eccentricity is indirect and does not depend on the variation of the runway.

However, when information is to be recorded at random, for example in computer applications, it is no longer possible to use the processes described above or similar processes. It is usually necessary to materialise in advance the tracks in front of which information can be recorded. To do this, it is customary to create a pre-engraving in any form. In an example of a realization described in the French patent application published under number 2 365 854, when manufacturing the support, the tracks are materialised in the form of a groove smoothed into a crease layer of this support.

In a preferred variant of the known art, pre-recorded tracks can be confused with the regions in which the information is recorded, resulting in a so-called mono-track system.

It is known from GB-A-2 067 313 to use a first optically detectable and periodic modulation for information elements whose period is a frequency for which the recorded digitally coded information energy spectrum shows a zero of the curve to generate a clock signal during recording and/or playback and where, to generate a follow-up radial signal during recording or playback, a second modulation is superimposed on the first modulation in which the runway position is modulated in a radial direction.

A special combination of runway periodic modulation is obtained if the period of the first and second modulation are equal with a fixed phase relationship that renders synchronous detection superfluous.

In other processes, the pre-recorded track or tracks are separate from the tracks along which the information is recorded. This results in systems called bi-tracks or multi-tracks. To distinguish between these two types of tracks, pre-recording can be made to consist of a signal that can be decomposed into a first frequency spectrum and the information that can be decomposed into a second disjoint frequency spectrum.

The main disadvantage of the method described above is that it does not allow for a maximum recording density since it requires at least one additional pre-engraving track for a pre-engraved information track.

The single track media, which have a pre-engraving, are not without disadvantages: they usually require the use of two beams, one for recording and the other for radial tracking.

It is also known from the patent EP-A-0 077 644, the contents of which are included in the state of the art in accordance with Articles 54 (3) and 54 (4) ), an information medium containing pre-engravings with a first centered pattern of specific thickness allowing its detection followed by two patterns offset from the centre axis of the track.

The present invention proposes a disk-shaped, pre-engraved mobile information carrier structure that overcomes the known drawbacks of the art and is compatible with single-beam single-track systems.

The invention therefore concerns a mobile information medium comprising at least one face intended for recording, along tracks arranged in a predetermined arrangement, optically readable information, the medium being a pre-engraving intended to be detected by optical means of radial tracking of the tracks of an optical tracks radial tracking device containing in addition at least one radiant energy source associated with a lens, to form on a reference surface of the disc at least one track exploration spot when the medium is set in motion, the first discovery being a discrete pre-engraving consisting of discrete noncontiguous elements materializing the mean axis of the tracks, excluding the interfaces of the frames and the second discovery being a discrete axis for the characterization of the tracks, by means of which at least one hundred discrete elements are used for the characterization of the areas, and the second discovery being based on the fact that the tracks are at least one hundred times wider than the tracks, and that the tracks are at least one hundred times larger than the tracks, and that the second discovery is based on the fact that the tracks are at least one hundred times larger than the tracks, and that the tracks are at least one hundred times larger than the tracks.

The invention also concerns an optical track radial tracking device according to claim 6 implementing such a support.

The invention will be better understood and other features will be shown by the following description in reference to the figures annexed, among which: Figures 1 represent a disc of the known art and a track-tracking device on such a disc; Figures 2 to 6 represent a pre-engraving of a disc according to several embodiments conforming to the invention; Figures 7 to 9 represent electrical schematics of track-tracking devices according to several embodiments conforming to the invention; Figures 10 and 11 are explanatory diagrams of the operation of the device of the invention.

The invention concerning a pre-engraved type of media and a device for radial tracking of one of the tracks of such media, it is useful to recall the main components of a recording and/or reading system of media, in particular optically readable and inscribble disc-shaped media.

Figure 1 shows a known information medium 5 of the art in the form of a circular disc which can rotate in a plane XOY around an axis parallel to the third axis of a reference triad XYZ. The lower side of this disc is here assumed to be smooth; the upper side which is parallel to it is also smooth, but has a pre-engraved track 7 in the form of a smooth track of substantially constant width of the order of or less than the micrometer.

The disc, for example, of about 30 cm in diameter, is driven by a rotational motion communicated by a solid drive motor of the chassis of the optical recording-reading system. In this embodiment, the access device has a track comprising a predetermined part of the disc comprising a fixed part comprising two sources of light energy (not shown in Figure 1) and a moving part comprising the recording-reading head.The latter consists of an Ob-type microscope lens, a solid of an electromagnetic coil B moving in the magnetic field of a permanent magnet (not represented) providing vertical servoing and an M1 galvanometric mirror providing radial servoing. Light energy sources, as it is also known, include laser sources, e.g. He Ne or semiconductor gas lasers. Gas lasers deliver a polarized parallel beam with a very small cross section.To achieve this requirement, it was proposed in French patent application FR-A-2 462 758 to interconnect between the light energy sources and the mobile recording-reading head an optical system of the focal type.

For reading, a parallel f1 laser beam produced by a laser source (not shown in Figure 1) is magnified by means of an aphocal, whose magnification is such that the emerging beam, also parallel, covers the input pupil of the Ob lens. The M1 mirror deflects the rays propagating parallel to a direction parallel to the OX axis. The Ob lens focuses the reading beam at point 3 on the information carrier disc.

The same afocal is then used for the fe recording beam, which has been modulated beforehand. To differentiate between the read and recording spots on the disc, the fe recording beam is inclined very slightly with respect to the f1 reading beam so that the decentrication of the recording beam on the lens input pupil is very limited and the displacement of the beam during a radial head movement can be neglected.

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In the recording phase of the disc, the insulation of the sensitive layer used for the recording is carried out by a spot whose intensity is modulated, for example, by an electrical signal in slots of variable or constant widths depending on the applications that constitute the information carrier.

To detect the reading beams reflected by the disc, a semi-transparent blade M2 is placed on the path of the beam f1 and the reflected beam is then sent to photo-detector and signal processing devices which can deliver an error signal ε which allows the motor 2 to be controlled to control the position of the mirror M1, thus achieving radial enslavement, and an error signal ε ′ which allows the OB solidary B coil to be controlled to achieve focus enslavement.

The processing means can also give a signal S(t) representative of the useful information recorded on the disc, because when scrolling through the elements recorded on the tracks 7, a signal S(t) is collected in reading which faithfully translates the temporal variations of the signal recorded on the track.

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Although only a surface corresponding to the width of a single track is required, in contrast to processes which use one or two pre-engraved tracks adjacent to or framing the useful track, the known state-of-the-art process just mentioned in relation to Figure 1 has some disadvantages.

From a detection point of view, it is as if the tracks were darker than the inter-track areas. Any deviation from the track can therefore be easily detected by this amplitude contrast. When the layer covering the support is subjected to inscribing radiation, the inscribed areas can be illuminated for some heat sensitive materials, which helps to create a good contrast along the track. However, these illuminated areas tend to be confused with the lower density of the surrounding inter-tracks, which radially loses the contrast needed to ensure good track tracking.

So we can see that the inscription interferes with the proper radial tracking of the tracks in all the areas where the layer has stored data.

In addition, two different beams must be implemented, at least during the registration periods: a writing beam and a reading and/or radial monitoring beam.

The invention proposes a pre-engraved type optical disc which, among other advantages, allows simultaneous single-beam configuration and requires the use of a single beam, without interference of the pre-engraving with the engraving representing the useful information.

The main feature of the invention is that the pre-engraving is in the form of discrete elements or flags which alone define the centre axis of the track to be followed. This track is therefore virtual. Given the speed of rotation of the disc, the spatial distribution of these pre-engraving elements must be sufficient to satisfy the Shannon criterion: typically on a disc 30 cm in diameter with a crown 8 cm wide representing the useful recording area, approximately 40,000 tracks are available and each contains about 3500 flags.

The following, without limitation, describes a medium on which the tracks are distributed in concentric and equidistant circles, as the main application envisaged in the present invention is the recording of digital data.

The useful information is recorded between two successive flags, so that if a block recording configuration is desired, the spatial distribution of the flags is preferably uniform.

Figure 2 illustrates a first example of state-of-the-art engraving. Pre-engraving is in the form of stretches of 71 smooth tracks defining the central axis of 70 tracks along which information can be recorded. As just mentioned, between two identical 71 flags there is a blank area where no information 72 before recording is available.

It should be understood that track 7 in the figure is a virtual track whose centre axis 70 represents the ideal path to be followed by a writing beam.

To do this, the signals necessary for radial servoing of the writing head will be derived from the detection of flags 71 by means of track-tracking which will be described in more detail below. The recording head may be a head similar to that shown in Figure 1. When the pre-engraving elements 71 pass under the focusing point of a track-tracking beam which may be the reading beam or as will also be detailed later, the writing beam, a track-tracking signal can be generated in a classical manner.Err1:Expecting ',' delimiter: line 1 column 102 (char 101)The amplitude and sign of this signal is representative of the direction and amplitude of this decentering.

Unlike known processes, signal processing devices must store the measurement during the time interval between two successive flags passing in the area illuminated by the track-tracking spot.

It is also necessary, if information is to be recorded only in the useful area 72 located between two successive flags 71, to inhibit the writing beam when one of these flags is in the area illuminated by the writing task.

Figure 3 illustrates this achievement: each flag 71 is divided into several sections 710, 711 whose lengths and spatial distribution define a code that allows an unambiguous identification of a flag.

To improve the quality of radial servoing, it is also known to wobble the tracking beam by printing a slight oscillation at a fixed frequency on either side of the track's center axis. In a preferred variant of the invention, this wobble can be created using patterns asymmetric to the track's 70th axis. To do this, each flag has, in addition to one or more sections centered on the track's center axis and indicating the beginning of the flag, one or more other sections offset from that center axis.

In a first, simplest variant, shown in Figure 4, a first flag 71 has a 710-section centered on the mid-axis of runway 70 and a second 711-G-section offset to the left of that axis. The next flag 71′ also has a first 710-section centered on the mid-axis 70 and a second 711-D-section offset to the right of the axis. This sequence is repeated. The gap between the offset sections and the runway 70 axis is on the order of a fraction of the width of the tracking spot.

In a second variant, each flag has at least one left-shifted and one right-shifted section. This variant is illustrated in Figure 5. This variant has the advantage of offering a sample rate of track error signal twice that of the previous variant, since it is not necessary to wait for two successive flags to pass to develop a track error signal.

Finally, it may be advantageous to combine the advantages of the structure illustrated in Figure 3 with those of the structure illustrated in Figure 5. Such a configuration is illustrated in Figure 6. One associates with the main flag 71, comprising offset sections on either side of the middle axis 70 used to generate a radial tracking error signal, a second flag 73 used to generate a timing signal. Preferably the flag 73 represents a special code that allows it to be identified selectively from other recorded information.

The precise manner in which the information is recorded is beyond the scope of the invention. Any known process may be used. Flags 71, 71′ and useful information recorded in zones 72 may, without limitation, be made up of hollow or bumpy micro-reliefs, for example by removal of a surface layer using the laser beam of writing.

A track tracking device of a type bearing pre-engravings conforming to the invention, i.e. consisting of discrete elements distributed along a track and delimiting useful areas for recording data, will now be described. The recording-reading system of information on the disc may be analogous to that described in relation to Figure 1. The identical elements will not be described again. Only the circuit detected 1, which produces the radial tracking error signal, is specific.

Figure 7 illustrates a first, simplified variant of such a circuit. This variant is particularly suitable for pre-engravings of the type shown in Figure 2. It comprises a photoelectric detector 10 and a measuring circuit 11 producing the radial tracking error signal ε. The detector 10 may comprise two cells as previously recalled. The output signals from these VD cells are transmitted to measuring circuits 11 which may also comprise a differential amplifier as described.If data recording is organized by block, a clock signal H needed to synchronize the measurement can be deduced from the block length and disk rotation rate. These clock pulses can be transmitted to a clock input terminal of a blocking sampling circuit receiving the signal produced by the differential amplifier at its input and generating at its output a signal ε, stored from one pulse to the next, representing the radial tracking gap. This signal can be smoothed out using a low pass filter.

Figure 8 illustrates a second circuit variant which applies more particularly to pre-engravings of the type shown in Figure 3, i.e. coded and self-identifiable. The VD signals are transmitted to sampling circuits 12 including a decoder generating a synchronisation signal H transmitted to the measuring circuits when the code read corresponds to the specific flag code.

Figure 9 illustrates a third variant of track monitoring device specially adapted for type flags with portions offset from the centre axis of the tracks and more particularly for the pre-engraving of the type illustrated in Figure 6 comprising a first synchronisation flag 73 and a second flag used for the purpose of developing a track monitoring error signal.This decoder selectively detects the passage of the synchronization flags 73 in the area illuminated by the track tracking spot and generates a VAE sampling authorization signal transmitted to the 12 sampling circuits. The generation of a radial tracking error signal can be done in two main ways, either by crest sampling or, when the shifted portions are of equal lengths, by integration.In the second case, when an integration process is used, these circuits may be made up of an integrator associated with a memory circuit. As is known, the integration circuit may be based on a controlled integrator associated with an analogue memory (e.g. capacitor). The sampling circuits 12 whose operation is allowed by the synchronization signal are intended to produce H1 and H2 signals synchronizing the measurements taken on the left and right offset portions of the flags 71 respectively. These signals are transmitted to the second and first processing circuits 110 and 111.These sampling circuits also receive the signals generated by the detector 10.

The diagram in Figure 10 illustrates the three characteristic possibilities of the position of the track-tracking spot relative to the centre axis of the runway 70. At the top of the diagram, the curve V1 illustrates the case where the track-tracking spot is offset to the left of the centre axis of the runway, with the understanding that the direction of rotation is that indicated by the arrow R in Figure 6. In this case, the interaction of the section 711-G on the track-tracking beam is greater than that of the section 711-D. The curve V1 represents the absolute value of the amplitude of the electrical signal provided by the means of detection 10.The V1 signal has a greater amplitude variation during the time window θ1 corresponding to the passage through the area illuminated by the track-tracking spot of the 711-G section than the amplitude variation during the time window θ2 corresponding to the passage through the 711-D section. The amplitude and signal differences between these two signals are representative of the direction and amplitude of the spot's shift from the mean axis of the track.

In the middle part of the diagram, the curve V2 illustrates the case where the track tracking spot is centered on the centre axis of the track.

On the lower part of the diagram, the curve V3 represents the case where the track-tracking spot is shifted to the right in relation to the mean track-tracking axis.

If an integration process is used, the sampling circuits generate from the electrical signals provided by the sensing means 10 and the authorization signal of the VAE decoder two pulses H1 and H2 coinciding with the time windows θ1 and θ2.

If the peak sampling process is implemented, then it is necessary to supply the two sampling-blocking circuits 110 and 111 with two short-duration pulses, H1 and H2, centred on the times t1 and t2 between the windows θ1 and θ2. Each sampling-block takes into account, for example, on the front of the pulse transmitted to it, the signal provided by the detection means 10. The value of the signals thus sampled is then stored until the next measurement. The outputs of the two signal processing circuits 110 and 111 are connected to the inputs of an amplifier 112 which can be operated by a differential amplifier and which provides a signal at its output representing the radial error factor ε. To be truly tracked, it is useful to use the ε-based amplifier 113 to monitor the signal.

Figure 11 shows an example of shift change δ of radial tracking spot 3 relative to the mean axis 70 of a track c as a function of time. On the bottom of the same diagram, the corresponding shift in the error signal ε as a function of time is shown by the dotted curve. The shift in the numerical error signal ε N is also shown on the same diagram.

In a preferred variant of the invention, a single beam is used. To do this, during information recording periods, the write beam is used sequentially as a track-tracking beam during the 71 flag pass intervals in the area illuminated by the spot produced by this beam and as a write beam in the other time intervals. To do this, the write circuits are inhibited during the passing of the flags. The signal produced by the decoder 12 can be used: VAE, possibly after logical inversion, inhibits the writing circuits.

The invention therefore presents the simultaneous advantages of single-beam systems, i.e. maximum registration density, given that flags occupy only a small area in relation to useful information, and of single-beam systems, i.e. simplicity and cost reduction.

The invention is not limited to the exemplary embodiments described above for illustration purposes, and in particular to the flag configurations shown in Figures 2 to 6.

Claims (8)

1. Movable information carrier (5) comprising at least one face intended for the recording, along tracks (7) arranged in a predetermined arrangement, of optically readable information, the carrier being furnished with pre-engraving intended to be detected by optical means for radially tracking the said tracks of an optical radial-tracking device furthermore including at least one source of radiant energy associated with an objective (O_b), in order to form on a reference surface of the disc, at least one track scanning spot (4) when the carrier is set into movement, the said pre-engraving consisting of non-contiguous discrete elements (71) giving physical representation to the mid-line (70) of the said tracks (7) forming intercalary areas and flanking areas (72) intended for the recording of the said information, characterized in that the discrete elements comprise at least one first pattern centred on the mid-line generating the synchronization and at least one second pattern, offset in relation to the mid-line used for the tracking, to the exclusion of centred patterns of width greater than the width of the tracks.
2. Carrier according to Claim 1, characterized in that the second patterns of each intercalary area are constituted by a pattern (711-L) offset on one side of the said mid-line (70) of the track (7) and a pattern (711-R) offset on the other side.
3. Carrier according to Claim 1, characterized in that the second pattern (711-L) of an intercalary area is offset on one side of the said mid-line (70) of the track (7) and the second pattern (711-R) of the next inter-calary area is offset on the other side of the said mid-line (70) of the track (7), the combination of the two seconds patterns being used for the tracking.
4. Carrier according to any one of Claims 1 to 3, characterized in that the first pattern or patterns are arranged so as to represent a particular code enabling the area to be identified.
5. Carrier according to any one of Claims 1 to 3, characterized in that the first and second patterns of an intercalary area are arranged so as to represent a particular code enabling the area to be identified.
6. Optical radial-tracking device which can be used with a carrier according to any one of Claims 1 to 5, the said device including photodetector means (10) delivering, in response to the radiation emerging from that portion of the said reference surface illuminated by the said spot, an electrical signal (V_D) sensitive to the transverse shift of the said spot in relation to the said track elements and means (11) for measuring the variations from one pre-engraving to the next, the said measuring means being sensitive to those values of the said signal registered exclusively during the scanning of the said intercalary areas and generating a compensating signal (ε) intended to keep the said read spot between the ideal paths of the two flanking track elements, characterized in that decoding means analyze the said electrical signal so as to generate a synchronization signal making it possible to produce a sampling authorization signal (V_AE) transmitted to the sampling circuits (13) which then deliver, after processing, a signal (ε) indicating the optical interaction of the said spot with a pre-engraving pattern contributing to giving physical representation to the optical mid-line of the track element during scanning; the said compensating signal changing value in a discrete manner by altering the contents of a memory circuit included in the measuring means.
7. Optical device according to Claim 6, characterized in that the said compensating signal (ε) arises from comparing two components of the said electrical signal (V_D), respectively produced by two adjacent photodetector cells belonging to the said photodetector means (10); the said components representing the interaction of the said spot with a centred pre-engraving pattern located in each of the said intercalary areas (71).
8. Optical device according to Claim 6, characterized in that the said compensating signal (ε) arises from comparing two samples coming from the same output terminal of the said photodetector means (10); the said samples representing the successive interactions of the said spot with two pre-engraving patterns having offsets which are equal and of opposite sign in relation to the said mid-line; the said offset patterns being located in the said intercalary areas (71).