FR2602364A1 - Method of recording and reading information on a medium, and information medium for implementing this method - Google Patents

Abstract

The information is recorded in the form of variations in transparency on a tape 1 as a track consisting of transverse track divisions 3 and the information is read by making sequential transverse sweeps of the tape 1 with at least one radiation beam during the (slow) forward motion of the tape, the information being restored in the form of modulated electrical signals in photoelectric sensors.

Description

Method for recording and reading information on a medium, and information medium for implementing this method.

 The present invention relates to a method of recording and reading information on a mobile medium comprising an information track with optical reading, as well as to an information medium for the implementation of this method.

 Apart from the recording and reading of information by magnetic means (on tape or on disc), there are known optical methods using as support a disc on which the information is materialized in the form of microcuvettes arranged in a track in spiral, the information being read by reflection or refraction, using a radiation beam, in particular a laser beam.

 The advantages of this technique of recording on disc with optical reading, compared to recording on magnetic tape (simpler manufacturing, reduced cost price, absence of wear due to the absence of contact disc-reading head , high degrees of precision, video definition, audio fidelity) are important, but the capacity of discs, that is to say the amount of information likely to be recorded on a disc, is relatively limited.

 The object of the present invention is to provide a method for recording and reading information by optical means, which retains the advantages of optical reading while offering increased recording capacity, that is to say the possibility of '' save more information under a given footprint.

 According to the method in accordance with the invention of recording and reading information on a mobile medium comprising an optical reading information track, the information is recorded on a tape in the form of a track formed by a longitudinal strip. of transverse track fractions, materializing the information by variations of transparency of the ribbon. The information of the ribbon track fractions is read by carrying out sequential transverse scans of the ribbon using at least one beam of radiation during the longitudinal advancement movement of the ribbon, collecting on photoelectric sensors the radiation having passed through the ribbon, to restore, in the form of modulated electrical signals, the information recorded on the track fractions of the ribbon.

 These characteristics make it possible to remedy the difficulties encountered a priori in adapting to the tape the optical recording and reading of information, namely the arrangement of the information track and the speed of travel of the track in front of the means of reading. Indeed, if the disc has the advantage of having a spiral track, therefore a compact, manageable and easy to manufacture carrying surface, the ribbons in principle have a longitudinal information track. For certain applications of optical reading, the scrolling speed must be of the order of 20 m / second, which means that the length of ribbon necessary for a capacity close to that of a disc would be considerable and would pose problems of volume of the reels or cassettes receiving this ribbon , as well as serial reproduction problems. In the nth order of idea, problems would arise to realize special sequences (accelerated, sudden stops, reverse, fast searches).

 By providing several parallel tracks on the same ribbon, it would be possible to remedy to a certain extent the problem of the capacity, but there would remain the problems relating to the speed of taper. In addition, there would arise, at the end of each length of track, an insoluble problem in the continuity of reading the information.

 The technique of optical reading, by virtue of the scrolling speeds which it requires, also poses, for its adaptation to the ribbon, problems of linearity of the information track and flatness of the information carrying surface. For the use of a longitudinal track, these problems would be very difficult to solve, taking into account the rigidity necessary for the formation of microcuvettes according to the engraving technique used for the disc, and this leads to rigidity necessary for reading. In this regard, it should be noted in particular that it is inconceivable to give a ribbon the thickness required by the optical reading technique on disc.

The method according to the invention overcomes all these difficulties, thanks to the fact that while retaining certain characteristics of the optical disc disc technique, it constitutes a specific adaptation of this technique to an information medium in the form of ribbon, namely
a) the track on the tape is not longitudinal and continuous as following the usual techniques for recording information on tape, for example magnetic, but is transverse and fractional,
b) the optical reading is not done by reflection or diffraction, but by detection of the variations in transparency of the ribbon,
c) the reading is done by sequential transverse scans of the ribbon using radiation beams, that is to say that the reading speed is no longer determined by the speed of movement of the ribbon, but by the displacements sequential transverse reading spots.

 The main advantage of the process according to the invention lies in the capacity for recording information on the tape. Thus, in the case of a tape having for example transverse fractions of tracks of 10 mm long, with a pitch (spacing of two transversal fractions) of 1.61ut, a reading speed of the track of 20 m / s results in a longitudinal advance speed of the ribbon of 3.2 mm / s (i.e. 2000 fractions per second), which represents 11.52 m / hour. Such a 100 m long tape would have an information capacity corresponding to 8 hours of reading.

 There is also a marked improvement in the accessibility of the sequences compared to traditional tape reading techniques, in the sense that a rapid tape speed (excluding reading) of 5 m / s would make it possible to explore in a few seconds. dozens of meters of a numbering or sequence tracking track which can be entered longitudinally in the margin, which would represent the exploration of a length of ribbon corresponding to several hours of normal reading.

 It should be noted. that the transverse optical reading of a ribbon is already known per se, for example by the U.S. patent

 No. 3,210,466. However, it is a ribbon designed for direct optical projection of information on a screen (each information appearing on this ribbon representing only one point of a line of an original image has project on the screen, the recording of each point being done by mechanical means), and not of a tape with optical reading variations of transparency of a tape by sequential transverse scanning of the tape (scanning to read fractions transverse of the optical track in continuity of information, the recording of the information being done by optical means) using beams of radiation with a view to obtaining modulated electrical signals, similarly to the reading of a track as on the optical disc.

 According to a preferred characteristic of the process according to the invention, the information recorded on the tape is read using two beams of radiation alternately scanning the track fractions. This ensures the continuity of the reading, the phase of scanning of a fraction of track by one of the beams starting at the moment when the scanning of another fraction of track by the other beam of radiation ends.

 The recording of information in transverse track fractions on a tape can advantageously be carried out, according to the invention, by the fact that information is recorded to be recorded in the form of a helical strip on a cylinder of revolution bearing externally at minus a photosensitive layer and an opaque layer, by making one or two beams of radiation modulated as a function of the information to be recorded, on the cylinder animated by a movement of rotation around its axis and a slow movement relative to the (x) beam (x) of radiation, of sequential scans transverse to said helical strip # dale, of an amplitude less than the pitch of the helical strip, for recording the information in transverse fractions of track on the photosensitive layer. After development of the photosensitive layer and etching of the opaque layer, the information etched on the cylinder is optically transferred onto a ribbon comprising at least one photosensitive layer and an opaque layer, by passing said ribbon over the cylinder along said helical band, by insulating it through the formed layer of the cylinder, developing the photosensitive layer of the ribbon and etching the opaque layer of the latter.

Following this engraving, the ribbon can advantageously be covered on the engraved side with a transparent layer giving the ribbon a uniform thickness.

 Preferably, in the case of scanning reading using two beams of radiation, the transverse track fractions are extended at their two ends by short sequences of information contained in the preceding and following track fractions. , in the vicinity of the ends of these fractions of track, by maintaining during recording and during reading the two beams of radiation simultaneously in service for a period of time corresponding to these duplicated information sequences.

 This ensures perfect continuity of reading the information, even in the event of inaccuracies during recording and if the tape undergoes, during reading, transverse deviations due for example to vibrations or shocks.

 To produce the sequential transverse scans by two beams of radiation, on reading the tape, but also when engraving the cylinder, it is advantageous that the two sequential transverse scans are obtained by the reflection of two beams of radiation on two concentric rows of mirrors arranged around the periphery of a disc driven in rotation.

 Thus, by its displacement due to the rotation of the disc, each mirror, when it receives a beam of radiation in a fixed direction of incidence, produces a beam of reflected radiation carrying out a scanning movement in the direction of movement of the mirror.

 For the implementation of the method of reading according to the invention, it is advantageous to have the tape carrying the information in a cassette comprising two spaced coils used alternately, one for winding reel and the other for unwinding reel ment, and vice versa. This cassette comprises, between said two coils, a transparent roller for deflecting the ribbon, comprising two cheeks spaced apart by a distance corresponding to the width of the ribbon. The casing of the casette has two opposite transparent wall parts in such a way that during reading, the radiation beams used for the sequential transverse scanning of the ribbon can pass through said wall parts, said roller and the ribbon when the latter passes over it. said roller.

Referring to the accompanying drawings, there will be described below in more detail an illustrative and non-limiting embodiment of the method according to the invention for recording and reading information, and an example of a cassette for tape serving as an information carrier; on the drawings
FIG. 1 is a plan view of a portion of ribbon carrying optical reading information recorded in transverse track fractions;
FIG. 2 is a partial plan view of a disk carrying two concentric rows of mirrors for producing sequential transverse scans using two beams of radiation;
Figure 3 is a section, on a larger scale, along
III-III of FIG. 2, showing the manner in which each mirror produces a scan of a fraction of the strip track;
FIG. 4 represents an overall diagram of the various elements involved in the reading by sequential scanning of the transverse fractions of the strip track; ;
FIG. 5 very schematically represents the principle of the first phase of recording information, namely the initial engraving on a cylinder;
Figures 6a to 6h illustrate the different phases of recording information according to the method according to the invention;
FIG. 7 is a section through a cassette intended for an information support tape used according to the method according to the invention.

 A ribbon 1, a section of limited length of which is shown in FIG. 1, carries information inscribed in a tongitudinal band 2 in the form of successive transverse fractions of track 3 of length a. The information is materialized on the track fractions 3 in the form of variations in transparency of the ribbon 1, these variations of transparency being able to be detected using concentrated beams of radiation, with long focusing, exploring the ribbon 1 animated by a slow longitudinal advancement movement, by sequential transverse sweeps of the ribbon 1.

 Preferably, the ribbon 1 is scanned by two beams of radiation alternately scanning fractions of track 3 which can either follow each other directly or be distant from one another in the longitudinal direction of the ribbon. It is sufficient that this same offset of the track fractions has been respected at the time of recording the information so that the continuity of the information is ensured at the time of reading.

 It is also recognized, in FIG. 1, that each fraction of track 3 is extended, at each end, by a section of track 4, 5 (represented in dashes) of length b, c having the same content of information as the section 5, 4 at the end or at the beginning of the fraction of track which precedes or which follows in the continuity of the information. Thus, when one of the radiation beams takes over from the other during reading, the continuity of the information is respected noème if the ribbon makes a lateral deviation from, for example, vibrations or shocks.

 FIG. 2 shows a possibility for producing the sequential transverse scanning of the ribbon 1 using two radiation beams 6 and 7. These two radiation beams 6, 7 are directed parallel to each other in two concentric rows mirrors 8, 9 arranged on the periphery of a disc 10 driven in rotation about its axis 11.

 As shown in FIG. 3 for the radiation beam 6 and a mirror 8, the position, on the ribbon 1, of the part of the beam 6 reflected by the mirror 8 depends on the position of the mirror 8, which position varies during the disc rotation movement 10.

 By choosing the angle of incidence i of the beam 6 on the mirror 8 and the angle of inclination 4 of the mirror 8, it is possible to ensure that the reflected part of the radiation beam 6 performs, during the incidence of the beam 6 on a mirror 8, a displacement of an amplitude at least equal but preferably slightly greater than the length has transverse fractions of track 3 in the plane carrying information of the ribbon 1.

 FIG. 4 illustrates the general diagram of the reading of the ribbon 1 by sequential transverse scans using two beams of radiation 6, 7 reflected by two rows of mirrors 8 and 9 according to FIG. 2.

 A radiation source 12, for example a laser, produces a concentrated beam which is divided into two beams 6, 7 by a diffraction grating 13. Each beam 6, 7 is directed on a distribution mirror 14, 15. The two mirrors distribution 14, 15 have the function not only of directing the beams 6, 7 on the movable mirrors 8, Y of the rotary disc 10, but also of ensuring the corrections of track deviation (as that # a is well known in the optical disc technique, for example for tangential deviation or radial deviation corrections). To this end, the distribution mirrors 14, 15 are equipped with servo # lateral deviation correction mechanisms 16, 17. The means of concentration and long focusing of the beams, if necessary, are state of the art and were not represented.

 In FIG. 4, the two mirrors 8 and Y occupy the position in which the ray 6 reflected by the mirror 8 has just finished scanning a transverse fraction of the track of the ribbon 1, while the ray 7 reflected by the mirror 9 has just started scanning the transverse fraction of track which is the following in the continuity of the information.

The beams 6, 7, modulated with the passage of the ribbon 1 as a function of the variations in transparency that the ribbon 1 presents on the track fractions explored by said beams, fall on photoreceptors 18, 19 producing electrical signals modulated accordingly, that is to say based on the information on the ribbon
To ensure the continuity of the information written on the tape 1, the alternating sequential operation of the photoreceptors 18, 19 must be synchronized with the rotation of the disc carrying the two rows of mirrors 8, 9. Such synchronization, for example by clock quartz, state of the art.

 It should be noted that due to the circular movement of the mirrors 8, Y, each of these mirrors, while ensuring the transverse scanning movement of a radiation beam, actually describes a curved path. The same applies to the path of the transverse scans by the radiation beams 6, 7. However, taking into account the reduced length of the transverse track fractions, this curvature has practically no effect.

 The mirrors 8, 9 can be attached to a carrier disc 10, it is also possible to produce the disc with the mirrors in one piece by molding, in a suitable material or treated in an appropriate manner, the mirrors then being constituted by facets of predetermined orientation of the molded part.

 The recording of the information in fractions of transverse track 3 on a tape 1 can be carried out as described below with reference to FIGS. 5 and 6.

 According to FIG. 5, the information to be recorded is recorded, using two radiation beams 20, 21 modulated as a function of the information to be recorded, and carrying out sequential scans comparable to those of the radiation beams 6, 7 used during reading, in the form of transverse track fractions along a strip 22 in a helix on a coating of photosensitive resin applied externally to a cylinder 23. For this purpose, the cylinder 23 is rotated about its axis and a relative displacement of the cylinder 23 relative to the radiation beams 20, 21, along the axis of cylinder 23, is ensured for example by displacement of the etching means 24 relative to cylinder 23, or vice versa.

 It should be noted that the etching means 24 not only comprise means for modulating the beams: ink is means ensuring the alternation of the two beams. Such alternation means are known per se and are synchronized, for example by quartz clock.

 This initial engraving is illustrated in more detail in FIGS. 6a to 6e.

 According to Figure óa, a thin and regular layer 25 of conductive plastic (for example PVC) is applied to the outer face of the cylinder 23 constituted by a hollow glass cylinder.

Then, by electrolytic means, a metal layer 26 is applied to the conductive layer 25. This metal layer 26 is in turn covered with a layer of photosensitive resin 27.

 According to FIG. 6b, the photosensitive resin layer 27 undergoes exposure to the radiation beams 20, 2lmodules, according to the information to be recorded.

 According to FIG. 6c, the exposed parts 28 of the photosensitive layer 27 are developed and eliminated by passage through a revealing bath (formation of microcuvettes).

 According to FIG. Ód, the underlying metal layer 26 is subjected, using an appropriate acid, to an etching (29) at the bottom of the microcuvettes 28 of the photosensitive layer 27.

 According to FIG. 6e, the photosensitive resin layer has been removed using an appropriate acid, to expose the etched metal layer 26 - (at 29).

 According to FIG. 6f, after application of a transparent leveling and anti-adhesion layer 30 on the metal layer 26 etched at 29, the information from the cylinder 23 is transferred onto a ribbon which is helically wound around the cylinder 23 following the same layout as the strip 22 of transverse track fractions during the engraving of the cylinder Z3. This tape is composed of a support of conductive plastic material 31, for example PVC, on which is applied electrolytically a metal layer 32 itself covered with a layer of photosensitive resin 33. Through the holes of the layer metallic Z6 etched from the cylinder 23, the photosensitive resin of the layer 33 of the ribbon is exposed using a light source 34 placed inside the hollow cylinder 23. After development of the photosensitive layer 33 and elimination of the exposed parts 35 (formation of microcuvettes), the metal layer 32 is etched at the bottom of the microcuvettes 35 with the aid of an appropriate acid, for example by placing the ribbon by the support layer 11 on a cylinder, after removing the ribbon from the cylinder 23 (figure 6g).

 Finally, after removing the rest of the photosensitive resin layer 33, a layer 37 of transparent plastic is applied to the metal layer 32 etched at 36.

 The ribbon thus produced corresponds to the optical reading ribbon 1, on which the information is written in the form of transparency variations in transverse fractions of optical reading track by transverse scans using radiation beams.

 According to FIG. 7, the tape 1 with optical reading is packaged inside a cassette 38 containing, in a manner known per se, two reels 39, 40 which can serve in turn as a take-up reel and a take-up reel . the drive in rotation of one or the other of these coils is carried out in a manner known per se when the cassette is inserted into a reader, the operating diagram of which is illustrated in FIG. 4 and of which only the two photodetectors 18, 19 are shown in FIG. 7. The casing of the cassette 38 has two transparent windows 41, 42 in two opposite walls (sections), so as to allow the two beams of radiation 6, 7 to pass through the cassette 38. the path of passage of the beams 6, 7 through the cassette 38, the latter contains a transparent roller 43 comprising two cheeks spaced apart by a distance corresponding to the width of the ribbon 1. This roller 43 constitutes a deflection roller for the ribbon 1 when the latter passes from one of the two coils 39, 40 to the other. Thus, the ribbon 1 is perfectly guided relative to the radiation beams 6, 7, which ensures reading accuracy.

 We also recognize in FIG. 7, two shutters 44, 45 which serve as protection for the windows 41, 42 and which, when the cassette 38 is introduced into the reader, are separated automatically, for example by pivoting around asrs 47, against the action of springs not shown.

 To allow the cassette 38 to operate in both directions, it is sufficient to write the information on the tape 1 so that every second track fraction is used for one direction of tape travel and the other track fractions for the other direction of scrolling, and adapt the reader accordingly.

 It goes without saying that the embodiment described above and illustrated by the drawings has been given for information only and is not limitative and that numerous variants and modifications are possible within the framework of the invention. This is particularly so with regard to the different phases of engraving on a cylinder and of transfer to tape for recording, which can be replaced by analogous operations known per se, for example in the printed circuit technique, to the extent that they provide the same end result, namely the recording of information by variations in the transparency of a tape-shaped information medium.

 The transverse scans, on reading, but also on recording, can also be produced by means other than rotating mirrors, for example by electronic means such as vacuum tubes, according to a principle revealed for example by demand. French Patent No. 2,248,569.

Claims (7)

 1. Proceda c record and read information on a mobile medium comprising an information track with optical reading, characterized in that the information is recorded on a tape (1) in the form of a track formed by a longitudinal strip (2) of transverse track fractions (3) materializing the information by variations of transparency of the ribbon, and that the information of the track fractions of the ribbon is read by carrying out sequential transverse scans from the ribbon to the using at least one beam of radiation (6,7) during the longitudinal advancement movement of the ribbon by collecting on photoelectric sensors (18, 19), the radiation having passed through the ribbon, to restore, in the form of modulated electrical signals, the information recorded on the tape track fractions.  2. Method according to claim 1, characterized in that the information recorded on the tape is read using two beams of radiation (6, 7) - alternately sweeping the track fractions.  3. Method according to claim 1 or 2, characterized in that the information to be recorded is written in the form of a helical strip (22) on a cylinder of revolution (23) externally carrying at least one photosensitive layer ( 27) and an opaque layer (26) by causing a beam of radiation or two beams of radiation (20, 21) operating alternately, modulated (s) according to the information to be recorded, on the animated cylinder (23) a rotational movement around its axis and a slow axial movement relative to the beam (s) of radiation, sequential scans transverse to said helical band, of an amplitude less than the pitch of the helical band , to enter the information in transverse track fractions on the photosensitive layer, and that after development of the photosensitive layer and etching of the opaque layer, the information etched on the cylinder is optically transferred onto a ribbon comprising t at least one photosensitive layer (33) and an opaque layer (32), by passing said ribbon over the cylinder along said h # licoidal strip, by insulating it through the etched layer of the cylinder, by developing the photosensitive layer of the ribbon and engraving the opaque layer of the latter.  4. Method according to claim 3, characterized in that after etching the opaque layer of the tape, a transparent layer of equalization and protection (37) is applied to the etched layer.  5. Method according to any one of claims 2 to 4, characterized in that the transverse track fractions (3) are extended, at each of their ends, by track sections (4, 5) containing short sequences of information already contained in the end sections of the preceding and following track fractions, which are maintained, during recording and reading, the two radiation beams simultaneously in service for a period of time corresponding to these sequences of duplicated information.  6. Method according to any one of claims 2 to 5, characterized in that the sequential transverse scans by two radiation beams (6, 7; 20, 21) are obtained by the reflection of the two beams on two concentric rows of mirrors (8, 9) arranged on the periphery of a disc (10) driven in rotation.  7. A tape-shaped information medium for implementing the method according to any one of the preceding claims, said tape being placed in a cassette comprising two spaced spools serving alternately as a take-up reel and a take-up reel, characterized in that the cassette comprises, between said two reels (39, 40), a transparent roller (43) for deflecting the ribbon, comprising two cheeks spaced apart by a distance corresponding to the width of the ribbon, and that the housing of the cassette (38) has two opposite transparent wall parts (41, 42) arranged in such a way that during reading, the radiation beams (6, 7) can pass through said transparent wall parts, said roller and the ribbon in passing of the latter on said roller.