EP0126147A1 - Data storage devices - Google Patents

Abstract

To obtain a data memory in which a data carrier (T) can contain a large amount of data and ensure rapid access, a format of parallel tracks is used, each starting with a unique track identity number and a unique relationship. on one or more longitudinal control tracks (B, C) allowing a search in high speed mode and a localization in low speed mode, using videotape recording servo systems in a particularly advantageous manner. Coarse localization of a desired group of tracks can be achieved by sequences of coded signals on a control track (B1) and individual tracks identified by a sequence of coded signals in another longitudinal control track (B2). In one embodiment, only the control track accepts the passage of a read head in the high speed mode, and in the slow mode, the support is wound to half surround a helical analyzer cylinder carrying a plurality of heads . Fixed memory devices are used as reference sources in library or computer installations possibly with multi-bus and / or multi-user capacities. If necessary, recording and / or output of stored data can be included, but the sequence of control tracks is preferably prerecorded and constant. The data carrier can be, in a preferred embodiment, a flexible strip in a cassette, but open reel-to-reel systems, semi-rigid cards, rigid plates or cylinders can be used. The recording process can be of the magnetic or optical type, and the data can be computer data, text, videographic information, or any combination of these data.

Description

DATA STORAGE DEVICES

The invention relates to data stores, and in particular to a novel form of data storage on a data carrier, to read-out apparatus for reading from such data carriers, and to data store recording devices providing for entering data on the carrier as required, and performing selective read-out, erasure and rerecording.

Presently available data carriers for highdensity storage comprise solid-state matrices of relatively limited capacity but rapid access, disc or drum storage devices giving considerably increased capacity, with only a slight access time delay at the expense of a considerable increase in financial outlay for mechanisms and circuitry of high complexity, and finally there are tape spool units which can make a mammoth capacity available, but require provision to be allowed for prolonged access time in some adverse conditions. One object of the present invention is to so dispose data on a carrier that a maximum packing density can be achieved without incurring the prolonged access time required for stores using large tape spools, by exploiting to surprising advantage the sophisticated servo-control systems that have been widely developed for video-recorders In accordance with, the present invention there is provided a data store in which a rectilinear data carrier (as hereinafter defined) is provided with at least one longitudinal control track along a path that is normal to or inclined with respect to a plurality of mutually parallel data storage tracks, each extending across said data carrier from a respective point adjacent said control track each said data storage track carrying a signal sequence comprising a data synchronising signal providing a unique track-identification code number, any data recorded on that track, and an end of line signal,and in which said longitudinal control track carries a sequence of said unique track-identification code signals in numerical order, each preceded by a start-of-track code signal and a start-of-code signal, and each followed by an end-of-code signal and an endof-track code signal, the signals in said sequence on said control track being so recorded that they can be read-out by relative movement of said control track with respect to a read-out head in either direction, and said start-of-track code signals either being aligned with the start of the related data storage track or spaced from that track by a predetermined distance in a predetermined direction along said control track path.

The term rectilinear data carrier is used here to refer to a carrier which provides a surface for a plurality of mutually parallel data tracks that extend in a direction normal to or inclined with respect to the longitudinal control track path, which may be on the reverse face. The data storage tracks may be straight, or may display a limited degree of S-distortion symmetrical about a respective straight path. The surface may be flat during use, or may be curved into a part-cylindrical or fully cylindrical surface.

In one advantageous embodiment the datacarrier is a flexible tape or card, preferably of magnetic material. The coded signals are conveniently recorded in a tri-phase code adapted to provide a plurality of errors-checking facilities.

The recorded data may be a video signal, possibly complete with a chroma signal if coloured images are being recorded, and/or computer data, each storage track preferably holding a complete video field, possibly with interleaved or superimposed computer data.

As an alternative to magnetic recording, optical means may be used to effect the writing in of the recorded data and to achieve read-out, using various forms of laser devices in recording techniques that are now available and this includes the use of a photo-lithographic data carrier, as will be described later. Read-out apparatus for use with such a data store may comprise drive means provided to move said data carrier relative to a control track read-out head in such a manner that the signals on said control track are read-out, selection means being provided to request that the data carrier is automatically driven to a required data-storage track, logic means being provided to determine the direction of travel required to reach the required track, said drive means initially causing a relatively high-speed mode if required, until further logic means detect the approach of the required track, whereupon a relatively slow-speed mode is initiated by the "start-of-track" code signal at said control track read-out head, and said tape is caused to fold about and partly embrace a rotating drum which carries a plurality of data read-out heads positioned to sweep along said required data-storage tracks, said drive means is caused to continue said movement in a relatively slow-speed mode until the required trackidentification code §ignal is readout, when said tape is either held stationary with respect to said controltrack read-out head, or moved by said drive means at a rate to bring the start of the succeeding data storage track into alignment at the end of sweep of said required track. A complete data recording device may be provided, in which the read-out apparatus is combined with erase and recording facilities.

The invention will now be described with reference to the drawings; in which:-

Figure 1 is a plan view of a fragmentary portion of a data carrier on which coded control signals and inclined tracks storing data are disposed in accordance with a preferred embodiment of the invention;

Figure 2 is a set of explanatory waveforms illustrating details of a preferred tri-phase coding using unique combinations of error-checking pulses to indicate pre-determined code signal positions in addition to providing parity-checking safety-measures;

Figure 3 is a set of explanatory waveforms illustrating the data arrangement within the data storage track;

Figure 4 is a block schematic circuit diagram showing details of the essential mechanical features and circuitry of an exemplary playback apparatus;

Figure 5 is a simplified perspective view of the mechanical arrangement used in the exemplary embodiment shown in Figure 4;

Figure 6 is a block schematic circuit diagram showing details of an exemplary recording device complete with record, erase and selective re-recording features;

Figure 7 is a set of explanatory waveform diagrams for usie in explaining the means adopted to facilitate compensation for any drop-sout of data during replay;

Figure 8 is a set of explanatory waveform diagrams explaining the drop-out compensation process;

Figure 9 is a set of fragmentary detail views showing the relationships between recorded track path and head scanning path in different states of operation;

Figure 10 is a simplified representation of one exemplary embodiment using a laser to write or read from a data carrier that is in the form of a flexible strip; Figure 11 is a schematic exploded view of an apparatus for feeding a strip or card into an annular rotating circular guide assembly to surround a read-out head unit; and

Figure 12 is a set of fragmentary detail views of sections of the embodiment represented in simplified form in Figure 11.

The preferred data store is a cassette with VTR reelto-reel operation, but it is possible to use an open reelto-reel system, or short strips of tape in the manner of data cards, with relevant mechanisms. Read means (and erase and record) (if provided) will be adapted to the physical nature of the data carrier and the form of recording selected.

If a rigid plate is used this may be scanned by a laser using compensating optics, or a magnetic head drive could be provided to perform a scanning function in two directions in a common plane parallel to the plate.

If semi-rigid plastics material is used, the mechanism can form this into a cylinder, or a rigid drum could be utilised, turning on its axis co-axial with a rotating readout means, (and/or record or erasure means if necessary). In these latter cases the control track may be annular and the recording tracks axially extending or vice versa, and the drive mechanisms will use the seryo control functions of VTR to the same advantageous effect. Other optical recording and/or replay systems than those specifically described may be used, for example a thermal-magnetic optical laser technique. The layout of the data on the carrier is shown in Figure 1, and in general terms the configuration is of the conventional type used in helical scan recording. We will assume that the carrier is a magnetic tape housed in a cassette, although this is not essential to the underlying principles of the invention, and other materials and recording techniques could be used, for example a thermal-writing laser could be used to record the data on a suitable material. Furthermore instead of a great length of tape wound from one reel to another, a relatively short length in the form of a flexible strip or a "credit card" format could be employed, assuming that an appropriate conveyor drive is provided to move the carrier with respect to the apparatus, as will be described later.

The carrier T has a control track B along its edge and a further control track C may be provided along the other edge of the carrier, for use as a sound track, or for special control functions, such as "inhibit erasure" or "request ident before read-out", to give safeguards and security. Such signals can also be incorporated in the control track B. When in use, the carrier may or may not be stationary with respect to a rotatable "head-drum" about which the carrier T is wound for approximately 180 when in the data record or playback mode. The fast rotation of the rotatable "head-drum" will lead to the writing of a slanting or inclined track that has an angle a with respect to the longitudinal axis of the carrier. If we assume that the tape is held stationary during data recording or replay, and that the head-drum is rotating so as to carry a recording head along the inclined track without tracking error, correct synchronisation has been established by a synch-pulse recorded at a position dictated by the control track signal sequence. It will be appreciated that the slant action is produced because the tape is wound on a helical path about the head-drum, and the head itself does not in fact move off of its circular path. The length of the recording on a single track, and the amount of data that can be recorded thereon is determined by the duration d and in equipment based upon video recording equipment this will be the duration of one field, i.e. a period less than one fiftieth of a second. Obviously, the actual duration available will depend upon the width of the tape the speed of rotation and overall diameter of the head-drum, and the aperture of the recording head. The important point to be considered is the need to locate a particular track if selected data is to be readily available, whether it be a television video field, the data store of a computer, or map or typescript displays, or the binary number system used by a computer, all of which can be readily converted into the signal to be laid down upon a single track. In order to locate the individual tracks the carrier T is provided with a specific track identification signal for each track recorded thereon. This must be laid upon the control track and may be the control track B or the control track C. In a typical case these tracks will have a width of from 0.75 mm to 1mm. It is necessary to ensure that the duration between the portion of control track aligned with the beginning of one data track and the beginning of the next data track, which has a length f in the illustration shown in Figure 1, has to accommodate sufficient coded data to identify each given track and mark the position of the beginning of the track with reference to a control track reading head which is a known distance on the control track path from the beginning of the indicated data track. It is possible to conceive of a configuration which would permit a single control track signal containing a sequence of the individual identification codes, but because of the physical arrangement of the tape and the need for high speed search it might be most inconvenient to attempt to arrange for such a facility. Therefore in a preferred embodiment a first track identification code signal is recorded as one path along a control track B1, and this contains a group identification code for a group of data tracks, and in a typical case each group contains one hundred tracks. As a modification of the normal high speed mode or re-wind action, the intention would be to have the control head in contact with the control track during the high speed winding action and the process control apparatus would search for the required group identification. As will be described later with reference to the apparatus, when the group identification signal is located, or when the track identification code is approaching in the case where a single control code track is used, the machine will be switched to a slow speed search mode with the tape path lifted to embrace the head-drum and continue at a slower speed until such time as the particular track identification code is read out from a track B2, when the machine will stop or reduce to normal replay speed with the required data track aligned with the sweeping head of the head-drum. To achieve the identification of a very large number of data storage tracks (e.g. up to one million) the coded identification must be accurate and recognisable but exceedingly short in duration, and therefore the preferred embodiment employs a separate track, for the individual data storage track identification codes in addition to the group identification track. Indeed, in some cases it might be advantageous to employ a plurality of individual data storage track identification coded signal paths laid side-by-side along the control track B and/or possibly on the control track C, since by increasing the number of tracks the available duration for a given signal is increased as will be readily apparent. It is anticipated that the carrier T will have a width t of 1/2", and the width of a data track will be 49 μ . Before turning to details of the preferred coding of the control signals it should perhaps be stated for the sake of clarity that the essential format of the tracks corresponds closely to that of a video recording, although in normal use for data storage the recording can be made with the tape stationary, and therefore the track will automatically be correctly read-out when a stationary tape play-back mode is employed, provided the head-to-tape speed is approximately the same as when recorded. However, it is possible to arrange for the recording of successive fields of a video signal with the tape moving in the conventional manner if such a facility should be required, and in such a case controlling could be used in known manner to record or replay the field of a video-signal, including the use of a four-head drum to improve a "still-field" facility, if desired. In a preferred embodiment of the data carrier the group or storage track identification signals will be pre-recorded on one or more paths, to provide for group identification if necessary, and to provide for the one or more data track identification code signal paths. With such a pre-recorded control signal it is only necessary to insert the tape carrier in recording apparatus and run the tape for an initial number of tracks in order to insert synchronisation pulses at the requisite points indicated by the prerecorded control signals, so that the normal servo system control can come into operation. It is anticipated that when a data carrier is intended to hold a large quantity of pre-determined data the initial data tracks can be used to contain a detailed index giving the location of the particular items of data under some form of key word and the microprocessor which forms an intelligent controller for the apparatus can then be used to read-out the index into memory, and then serve to move directly at high speed mode to reach the required data track in the main body of the store. As a further refinement it is possible to utilise at least one audio signal path on one of the longitudinally extending control paths, which would enable key words to be entered for the coarse identification of a block of stored data, and/or for use in recording video sound in apparatus that has been adapted to replay such video signals with a moving tape carrier.

The preferred form of identification code will now be described with reference to the set of waveforms shown in Figure 2. It will be understood that various forms of coding can be utilised, but the code to be described, which is termed a tri-phase code, incorporates a number of safety measures to ensure that an accurate identity is read out during high speed wind in either direction, and that the required start of track point is accurately defined. The code also incorporates provision to indicate to the "intelligent controller" formed by a standard micro-processor, that the particular sections of each coded signal are detectable to play their own individual roles in guiding the controller to respond.

Figure 2 (a) shows the basic waveform in which the individual elements are of predetermined duration, and may have any one of three states, the different states being represented by respective frequencies or amplitudes, or by pulse coding. Assuming that a bias oscillator is provided we will refer to the three states as potential levels for the sake of simplicity. Preferably the intermediate level is zero, so that one binary state can be indicated by a positive pulse of magnitude Vp, and the other binary state indicated by a negative pulse of magnitude Vn. The pulse periods are determined by clocks in the controller, and the central level (a zero voltage signal in the present preferred embodiment) will be referred to as an X signal to serve both as a form of parity checking and as a flag marking for the particular sections of a code sequence. Thus in Figure 2(a) we have a basic representation of the three possibilities formed by a check signal, followed by a binary 1 signal, followed by a binary 0 signal, followed by a check signal. In the proposed apparatus, in order to ensure recognition of the signals when reading at high speed mode, this particular combination is not used, but the simplified figure serves to lead into a description of Figure 2(b) which constitutes the "start of track" code signal. It will be seen that the duration of the individual pulses has been trebled to facilitate read-out when the tape is being fed at high speed mode and the combination comprises three check periods, followed by three "1" state signals, followed by three check signals, followed by three "0" state signals, followed by three check state signals. This start-of-track code signal is intended to represent the precise point on the tape at which the tape feed, must be stopped in order to read the required data track, as will be described. Figure 2(c) shows a "start code" combination, in which two check signals are followed by two "0" state signals, which are followed, by two check signals and two "1" state signals, with a final two check signals. Thus this combination is a mirror Image of the shape of the "start of track" code signal, but is shorter in duration, and is used to indicate to the control computer that the following sequence of signals will be the actual group or data storage track identification code and we will term this sequence the "start of code" sequence. Figure 2(d) shows by way of example a typical sequence of four-bit code track numbering signals, each four-bit pulse sequence being preceded and followed by a pair of check signals, and in the illustrated example there are five pulse sequences comprising four "1" state signals followed by a final signal in which there are three "1" state signals immediately followed by a "0" state. We will assume that this represents the identity of the first track in the sequence, and in order to ensure that the control computer receives the identity correctly when the tape is moving in one direction or in the other direction this entire sequence is now repeated in reverse order ending with an "end of code" sequence in reverse order to that shown in Figure 2(c), in turn followed by an "end of track" sequence which is in the reverse order to that shown in Figure 2(b), to give the full group of data storage track identification in the form of a sequence of 126 bits, as shown in Figure 2(e), which must be scanned in 49μ for normal operation. With this type of check sequence to separate the sections of the code signal it will be seen from Figure 2(e) that the end of one sequence and the beginning of the next result in there being a unique combination of six check signals, whilst the point separating the end of the "start of track" signal and the beginning of the "start of code" signal is identified by a unique combination of five check signals, which appears in mirror image fashion between the "end of code" signal and the "end of track" signal. A further unique combination comprising four check, signals in sequence appears at the centre of the identification track signals and at each end of the identification sequence, that is to say between the end of the "start of code" signal and the beginning of the code identification, and at the end of the code identification and the commencing of the end of code signal. Finally there is the recognisable combination of two check signals which appears between each coded digit in the identification signal itself, and at the centre of the "start of code" signal, and the middle of the "end of code" signal. The presence of these unique combinations enables the microprocessor to analyse the identification signals in a clear manner during high speed wind or re-wind, and for simplicity, in the present embodiment, when the controller recognises that it is approaching the group of tracks including the required data track and a slow speed mode is initiated, the coding on the one or more individual track identification paths is formed in like manner. The point on the control path forming the junction of the termination of one "end of track" code and the immediately following "start of track" code for the next track identifies the alignment of the data storage track whose identity has been given by the identification code signal just read out, in the normal direction of travel, in this embodiment.

Figure 3 (a) shows in simplified schematic form the waveform envelope as recorded on each data storage track, the horizontal synchronising pulse HS being followed by a data synchronising signal DS to establish the timing of the data pulses within the block of data recorded in the period terminating with an ELS end of line signal, which may correspond to a horizontal synch pulse. Along each track a sequence of 305 lines of data blocks, or video signals, or both, can be recorded as indicated in Figure 3 (b) the data arrangement being preceded by an equalising pulse EQ to provide settling time for the servo system used, and act as a track synchronising signal. One or more lines DCL within the field hlanking period are utilised for identification and other control functions, and the remaining lines hold the recorded data, coded in the required manner in known fashion. Figure 3 (c) shows a typical control data arrangement within one horizontal line. The track identification code is given first, and this may be followed by a signal providing the user with an indication of the following data content, using a content identification code, and there is room available for further control signals for security, restriction of access or safeguarding against erasure, by the use of appropriate code signals recognised by control system signal analysis means provided to trigger the necessary functions, as the case may be. The control line uses a eight-bit coding system, and computer data storage can be effected in a similar manner, but this is not essential, and any form of signal coding can be utilised, possibly being varied to increase security, the relevant coding process being given by a control function code signals in the period following the content identification code (if used) . As far as the coding on the control tracks B1,B2 is concerned the use of four-bit signals in the three-state mode described above enables ten different digits to be identified by binary coded signals, but preferably a non-standard sequence is used, to make unauthorised access more difficult.

Figure 4 shows details of the mechanical and electrical arrangement for a dedictated playback apparatus which is an apparatus that will be used in cases where it is essential or highly desirable that there can be no accidental erasure or re-recording of data, and such apparatus may be used for example in a library situation where the vast amount of data stored can be rapidly accessed using the deposit of indexing data in the initial data tracks so that any inserted data store can be initially played to enter the index information in the control micro-processor storage array, and the operator can then indicate by normal instruction entries the particular data track required to be displayed upon a local visual display unit, or to be transmitted to a remote source, or to be used in whatever computer system or communication system that is utilising the data store. The control apparatus includes a storage facility to indicate to the intelligent controller unit the position of the tape at any instant. When an operator inserts an instruction command that leads to a request to have access to a particular data track, he or she inserts the appropriate command which identifies the address, either directly or via a programme, possibly after reference to the index, and the circuitry within the micro-processor determines whether it is necessary to go into a high speed mode in one direction or the other and initiates this mode if necessary. When the appropriate group identification signal is located, assuming such group identity is a feature of the particular system, the apparatus switches to a slow speed mode to lock onto the particular required data track. For this purpose the apparatus is such that high speed winding is not affected directly from reel to reel, but the track path is taken via a code head, and there is a pinch wheel on the track path together with lefthand and righthand torque tension sensors to indicate to torque comparison amplifiers the track tension and facilitate rapid response when a required identification signal is read out. When the group identity is found the apparatus switches to the slow mode which causes two guide arms GA to lift the tape up and around a head-drum so that the tape adopts a helical path about the head-drum and is approximately 180° around the drum surface. There is a pre-tension guide arm which cooperates with the forward and reverse pinch caps to give precise servo control of the tape position. The control head is intended to detect the pulse at the beginning of the recorded data track and may stop the tape in order that the head/drum can read out the data track. As described with reference to Figure 3 the initial portion of each data storage track contains the track identification code number, followed by a consumers content reference or index code and possibly pre-programmed routines for access, safeguard and security functions, and this is compared with the required track identity and other coding contained in the controller, to ensure that the apparatus is operated correctly. Should there not be correlationship between the required identity and the track pulse that is being scanned the scan will continue without read out display until reaching the end of track signal which forms part of that data storage track, when the controller will automatically cause the servo to re-adjust the tape position in the direction indicated by the error between the data track identities. Thus, assuming the control head has fed a signal to the amplifier to supply the control circuit with a signal showing that it has located the correct address code that has been requested by an operator, the lefthand and righthand torque tension motors will stop and the forward and reverse motor will lock in. The head-drum will now sample the data to check the identity of the storage track number against that of the control track sequence, and can immediately cause further tape feed if there is not identity. Alternatively, as mentioned above the data read out can be suppressed and the track sweep completed to be terminated by the "end of track" code signal which is itself recorded on the data storage track. Should fine adjustment be required the pretension guide arm PTA will operate in one direction or the other to draw the tape further or to allow the tape to be drawn back, in order to obtain precise alignment of the data track with the heads on the head-drum. The left-hand torque tension motor will have been controlled by the apparatus to indicate the precise tension of the tape and the guide arm GA and maintain that tension with respect to the pinch wheel FR.

Whilst in this condition the righthand torque tension motor is set to give sufficient torque to avoid there being any slack tape between the cassette and the pinch wheel. Thus, if the required address is some distance away the guide arms GA will be in their respective positions A so that the tape is passing the control track code reading head or heads, and high speed winding can be continued until the approach of the required identity track indicates to the control computer that it is time to convert to the slow speed mode, when the guide arms GA will move the tape to the respective positions B indicated schematically in Figure 4.

Figure 5 shows a simplified schematic perspective view of the mechanical apparatus that is provided, the parts being identified by the references used in Figure 4, and the operation will be readily understood from the description of Figure 4, and will therefore not be repeated, it merely being necessary to refer to the fact that three possible positions of the guide arms are shown, including the rest state permitting direct reel to reel winding.

Figure 6 shows the additions required for a complete, recorder and read out device. The mechanical arrangements have already been described with reference to Figure 4 and it only remains necessary to consider the additional circuitry that is required to provide for recording. When a recording function is required a new tape is inserted and the code head will record onto the tape a number of synchronising pulses as it reads the pre-recorded track identity code sequences. In some cases it may be considered more desirable to intially record the track identity code signals via the apparatus but present experience suggests that more reliable and consistent results will be obtained if these tracks are in fact pre-recorded. An initial coding signal may be inserted to indicate the total number of data tracks that can be recorded onto the particular tape.

A suitable computer circuit is such as a dedicated controller to control the read, write and erase apparatus, plus logic to automatically drive the apparatus to any required data storage track in either high speed mode or slow speed mode, control being provided for the input and output functions and any other appropriate functions, and/or multi-user bus facilities.

Video tape recorders normally incorporate some form of compensation for drop-out, which is a momentary loss of signal, possibly due to dirt on the tape or the heads, or to a loss of oxide coating on the tape.

The form of compensation most often used is to replace the missing piece of information by the last relevant piece of information replayed. This process can be used when video recordings are made., but is inappropriate when recording computer information, so that a new method of dropout compensation will be used, which will now be described with, reference to Figure 7. Ail computer information will be recorded twice, as shown in Figure 7 Ca) the third horizontal line, following an initial two data control lines DCL, will contain seventeen data words, and the same words are recorded in the fourth horizontal line, shown in Figure 7 (b) . If a drop-out occurs in the third line as shown in Figure 8a, a positive pulse DD is produced by a drop out detector to give the waveform shown in Figure 8b. This pulse changes a drop-out compensation switch so that the waveform is completed, by the insertion in the delayed signal, from the third line, Fig.8 (a), of part Fig .8(d) of the fourth line. Fig. 8(.c). In view of the plurality of recording modes that may be employed, including video signal with sound, video combined or interleaved with computer read-out, and direct computer read-out or static text or graphic readout, there may be problems introduced due to the different modes of record and replay that may be involved. As there may be a significant misalignment of the recorded track path and the read-out scanning sweep of a read-out head it is necessary to provide correction means. Figure 9(a) shows a typical format of recorded tracks produced on a stationary record carrier and Figure 9 (b) shows the precise alignment of the head path that can be obtained if read-out is effected from a stationary record carrier. If replay is effected with the record carrier moving at normal speed to bring successive tracks into alignment there is a misalignment, as shown in Figure 9(c), but by canting the feed using a solenoid energised by circuit board mounted with the head-drum, precise alignment can be regained, as shown in Figure 9(d). This process is reversible, so that correction can be achieved by canting if a recording mode on a moving carrier needs to be read-out from a stationary carrier. The movemeφt required is precise, but of very small magnitude, and is in opposite directions for the first described correction and the second described correction. The invention is not restricted to the use of a magnetic recording medium, and as there are a number of optical data storage techniques becoming available, which permit writing , reading , and in some cases erasure.

Figure 10 illustrates one exemplary embodiment of a laser system, using a flexible strip of tape, so that the mechanical feed arrangements can be as shown in Figures 4 and 5. A relatively high-power laser L1 may be provided in units which are required to provide a recording facility and erasure function. A lower powered laser L2 is used for the read-out function. If both lasers are provided a common path is formed by a beam-splitter BS . In a data storage device which is only required to provide read -out then there is only a need for the laser L2 , and this has the advantage of positively guarding against erasure or over-recording to change the content of the stored data . A polarisation sensitive beam- splitting

Prism serves to pass light from the read laser L2 on a path via a quarter-wave plate Q and mirror M to a finetracking deflection mirror-surface which is mounted to be movable over a small angle to facilitate precise tracking , the movement being controlled by a transducer in known manner . The tape is wound in helical form to partly surround a hollow drum that is formed by two sections defining a slit for the focussed laser beam to track the exposed surface of the data carrier . The drum sections are supported and rotated by external drive means, which must be designed to avoid obstruction of the tape feed system, which can be as shown in Figure 5.. Reflected light, modulated in time by the stored data content due to surface variations of the data carrier, passes back along the optical path to the mirror M, which def lects it to return via the quarter-wave plate Q to the polarisation sensitive beam-splitting prism PBS, and due to the double passage through, the quarter-wave plate, the returning light is polarised at right-angles to the light projected from the laser L2, and the prism PBS deflects this light to a sensor assembly SA to produce a read-out signal of the recorded data, be it a video signal, text or computer signals, or a combination thereof. The sensor assembly SA can be used to detect defocussing or tracking error in known manner, to control the tracking mirror TM, and possibly any of the focussing lenses that may be provided.

The data carrier may be provided with a pre-recorded magnetic control stripe or stripes along its edges, for use in the manner described with reference to Figures 4 to 6. However, as the laser L2 is not in use during the high-speed mode of transport, a light component can be deflected from the read laser L2 to pass to a prism positioned in place of the code heads shown on path A of Figures 4 and 5, so that the reflected light is passed back to the sensor assembly SA, which in this mode of operation will feed its output to the dedicated digital servo controller and logic (Figure 4) . For example the data carrier may comprise a layer of tellurium suboxide containing germanium, indium and lead, a change in reflectivity can be achieved by converting the surface of the layer from a crystalline to an amorphous layer, and the process can be reversible, using lasers of differing energy output, either in terms of power or frequency, depending upon the particular materials of the data, carrier recording layer.

A purely photographic material can be used for the data, carrier, if the device is to be used for read-out only, a master negative being exposed and developed in the usual manner to provide a monochrome record of the data content, of whatever form, and a reflective rear coating then being applied to reflect back the laser beam during read-out. The control tracks can be magnetic strips or optically-readable tracks, as discussed with reference to Figure 10.

Another exemplary embodiment for use in laser-operated devices utilises an ultra-violet laser with a data carrier of photo-lithographic material to effect recording by ablative photo-decomposition. An argon-fluoride laser is suitable, and the photolithographic material may be a synthetic resin film carrying polymeric material, probably organic, the molecules of which are disrupted by a high-intensity UV laser, and it is believed that the resultant small molecules vaporise at relatively low temperatures and so carry away excess energy. By selective exposure it is thus possible to record monochrome signals varying from black to white, which can form images or binary data to be read out from a data storage device. The embodiments so far described in detail have been mechanically based on the type of design commonly used for video-tape recording. As in television applications, a cassette can hold any arbitrary length of tape. If short strips of such tape are used, then the feed mechanism can be adopted to pick-up a strip from a feed port and apply it to the head-drum, and even a short strip of narrow tape could hold a very significant quantity of data, either computer data, text and graphics, or full visual images, alone or in combination.

R_γ simple modification, the. combination of the control track and data storage tracks can utilise the same type of sophisticated serya-control to read, write or re-record data on a relative stiff medium such as a synthetic resin card, which may open up fields comparable to computer punched card or floppy disk applications, whilst offering a greatly increased storage capacity.

Even a rigid card can be used, with appropriate feed mechanisms, since with laser read-out the passage of a card along a tangential path with respect to a head-drum of the type shown in Figure 10 can be utilised if one or more optical correction lenses are incorporated to compensate for the different path deflections required to correctly scan the tracks and one or more of the mirrors or lenses of the optical focussing system are moved to allow for the varying optical path length.

Assuming a card is sufficiently flexible it can be used with a conventional configuration of head-drum, and any of the recording methods discussed above can be used.

However, a preferred embodiment for use with such a data storage carrier is shown in Figure 11. Figure 11 shows in simplified form the guide assembly of a data storage device for using strips or cards having a flexibility sufficient to permit their being driven into a pair of rotating circular guides and adopt a substantially cylindrical format about a head-drum, which may be provided with magnet heads or comprise a laser write and read arrangement as described with reference to Figure 10. It is possible to provide a dual or multi-function arrangement designed to read from any given, type of data carrier, and to write if the recording medium is one of those providing for erasure and recording. An opposed pair of U-shaped entryguides EG are provided to feed each card up to a pair of guide-gates GG which form part of a pair of rotating circular guides RCG, and can be closed to complete a circular path at each, edge of an inserted strip or card, or pivot to open and accept the insertion of a strip or card from the entry guides EG. With the strip or card inserted the head-drum is rotated within the assembly, which rotates the circular guides RCG to give the required head-to-surface speed, conforming to the requisite television standard video format, with provision for PAL or SECAM, as the case may be. The guides RCG move together relative to their control axis to facilitate the formation of helical tracks and move to any selected track, if continuous video is to be reproduced. Intermittent axial motion can be utilised if the storage tracks are in a plane normal to the axis. Alternatively, a compromise functional arrangement may provide for a canting action of one end edge of the inserted strip or card relative to the adjacent edge, to form a virtually continuous helical track. The internal surface of the data carrier can be freely selected to suit the precise requirements of the data to be stored in any given field of application, and the control track is provided on the outer face, to be read by a code head and provide for setting of the head-drum tracking path relative to the storage tracks by relative axial movement of the guide assembly or the head-drum. Preferably one or more magnetic control tracks will be used, with respective co-operating code heads, but optical means can be employed if so desired. Control of the positioning of the head-drum of the rotating circular guides in both their axial and angular movements, and of the guide gates (together with canting, if employedl is effected by the digital servo controller and logic, as in the previously described embodiment. Figure 12 gives a set of explanatory fragmentary details of the embodiment shown in Figure 11. Figure 12(a) shows a section, of one of four guide, supports which each carry a sleeve firmly linking two common rotary guide raisl RGR so as to be slidable on the guide supports by drive means (not shown) . Each guide rail RGR has a cross-section R, as shown in Figure 12(b). The connecting links between the sleeve portion and the upper guide rail is ringed by a broken-line circle A, and the corresponding link for the lower guide rail by a broken-line circle B, and these portions are indicated by similar broken-line circles for each guide support in the general view shown in Figure 12(e) . This gives a rugged positive support for the rotatable section, where each rotating circular guide RCG has a support strap S extending to a flange wall W which engages in the associated rotary guide rail, and thereby positively locates the associated U-shaped rotating circular guide whilst permitting free rotation thereof, under the control of further drive means (not shown) .

To read the control track on the external face of the data carrier code heads are carried by an elevation control arm E, positively secured to a pair of parallel vertical fixings F, as shown in Figure 12(d).

To eject data carrier cards, a separate gating mechanism could be provided, but it is obviously more economical to utilise the same gates for insertion and ejection by indexing the rotational movement, especially as this enables the guides to provide a positive stop.

Depending upon the requirements imposed by any particular storage system characteristic with regard to head-to-surface speed, track length and playing time, axially extending recorded tracks, possibly with both moving guide assembly and head in the axial direction could be used, or record tracks that extend around the internal face of the cylinder, in like manner.

This type of format is equally applicable to a rigid drum that can be fed onto the head in an axial direction, if not a permanent assembly.

Claims

CLAIMS : ¬

1. A data store in which, a rectilinear data carrier as hereinbefore described is provided with at least one longitudinal control track along a path that is normal to or inclined with respect to a plurality of mutually parallel data storage tracks, each extending across said data carrier from a respective point adjacent said control track each said data storage track carrying a signal sequence comprising a data synchronising signal providing a unique track-identification code number, any data recorded on that track, and an end of line signal, longitudinal control track carries a sequence of said unique track-identification code signals in numerical order, each preceded by a startof-track code signal and a start-of-code signal, and each followed by an end-of-code signal and an end-oftrack code signal, the signals in said sequence on said control track being so recorded that they can be read-out by relative movement of said control track with respect to a read-out head in either direction, and said start-of-track code signals either being aligned with the start of the related data storage track or spaced from that track by a predetermined distance in a predetermined direction along said control track path.

2. A data store as claimed in Claim 1, in which said data-carrier is a flexible tape.

3. A data store as claimed in Claim 2. in which, said tape is. mounted on a reel.

4. A data store as claimed in Claim 2, in which said tape is mounted on reels in a cassette.

5. A data store as claimed in Claim 1, in which said data-carrier is an elongate free strip of tape.

6. A data store as claimed in Claim 1, in which said data-carrier is a semi-rigid elongate card or strip.

7. A data store as claimed in Claim 1 , in which said data-carrier is a rigid strip or plate.

8. A data store as claimed in any preceding Claim, in which said data-carrier is of magnetic material.

9. A data store as claimed in any one of Claims 1 to 7, in which said data-carrier is of a photographic material and said or each control track is optically formed.

10. A data store as claimed in any one of

Claims 1 to 7, in which said data-carrier is of a photographic material and said or each control track is a magnetically recorded track.

11. A data store as claimed in any one of Claims 1 to 7, in which said data-carrier is of a photo-lithographic form, including a pre-recorded control track or tracks.

12. A data store as claimed in Claim 11, in which said data-carrier is of a photo-lithographic form, and said or each control track is a magnetically recorded track..

13. A data store as claimed in. Claim 11 or Claim

12, in which said data-carrier is of a tellurium suboxide including germanium, indium and lead.

14. A data store as claimed in Claim 11 or

Claim 12, in which said data-carrier is of a material optically processable by ultra-violet radiation to record by ablative photo-decomposition.

15. A data store as claimed in any preceding

Claim, in which said data storage tracks are helically formed.

16. A data store as claimed in any preceding Claim, in which said coded control signals are recorded in a tri-phase code.

17. A data store as claimed in any preceding Claim, in which said recorded data consists of or includes binary signals comprising computer code signals.

18. A data store as claimed in any preceding

Claim, in which said recorded data consists of or includes a video-signal in analogue or digital-coded form.

19. A data store as claimed in any one of Claims 1 to 17, in which said video-signal is recorded as a frequency modulated signal.

20. A data store as claimed in Claim 18 or Claim 19, in which said video-signal includes a chroma signal.

21. A data store as claimed in any one of Claims

18 to 2α, in which, computer data is superimposed on said video-signal.

22. A data store as claimed in any preceding Claim, in which said recorded data is in the form of pulse-code-modulation signals.

23. A data store as claimed in any preceding Claim, in which, said control track is a fine-setting control track, and an auxiliary coarse-setting control track is provided containing a similar sequence of signals identifying respective groups of said data storage tracks.

24. A data store having a data-carrier substantially as described with reference to Figures 1 to 3, 7, 8, 10 or 11 and 12.

25. Data store read-out apparatus for use with a data store as claimed in any preceding Claim in which drive means are provided to move said data carrier relative to a control track read-out means in such manner that the signals on said control track are read-out, selection means being provided to request that the data carrier is automatically driven to a required data-storage track, logic means being provided to determine the direction of travel required to reach the required track, said drive means initially causing relatively high-speed mode if required, until further logic means detect the approach of the required track, whereupon a relatively slow-speed mode is initiated by the "start-of-track" signal in said control track, and said data-carrier is moved at a relatively slower speed whilst a rotating drum which, carries data read-out means positioned to sweep along said required data-stora.ge tracks, said drive, means continuing said relatively slow-speed mode until the required track-identification, code signal is read-out, when said data carrier is either held Stationary with respect to said control-track read-out means, or moved by said drive means at a rate to bring the start of the succeeding data storage track into alignment at the end of sweep of said required track.

26. A data store read-out apparatus for use with a data store as claimed in any one of Claims 2 to 5, or any one of Claims 8 to 24 when dependant upon one of Claims 2 to 5, in which drive means are provided to move said data carrier relative to a control track readout means in such a manner that the signals on said control track are read-out, selection means being provided to request that the data carrier is automatically driven to a required data-storage track, logic means being provided to determine the direction of travel required to reach the required track, said drive means initially causing relatively high-speed mode if required, until further logic means detect the approach of the required track, whereupon a relatively slow-speed mode is initiated by the "start-of-track" signal at said control track, read out head, and said tape is caused to fold about and partly embrace a rotating drum which carries data read-out means positioned to sweep along said required data-storage tracks, said drive means is caused to continue said movement in a relatively slow-speed mode until the required track-identification code signal is read-out, when said tape is either held stationary with respect to said control-track read-out means, or moved by said drive means at a rate to bring the start of the succeeding data storage track into alignment at the end of sweep of said required track..

27. Data, store read-out apparatus as claimed in Claim 25 or 26 when dependent upon Claim 21, in which said slow-speed mode is initiated by said coarse-setting control track signal, and data read-out initiated by the signals on said fine-setting control track.

28. Data store read-out apparatus as claimed in Claim 25 or Claim 26 when dependent upon any one of Claims 18 to 21, in which said drum carries four heads, spaced equally about the drum, and interlaced static display of the normal recorded video data signal is achieved by switching to alternate heads during replay.

29. A data store recording device comprising apparatus as claimed in any one of Claims 25 to 28, in combination with respective erase and recording circuits for connection to said data read-out means.

30. Data store read-out apparatus substantially as described with reference to Figures 4 and 5, 10 or 11 and 12.

31. A data recording device substantially as described with reference to Figures 6, 10, or 11 and 12.