TRANSMISSIVELY READ QUAD DENSITY OTPICAL DATA SYSTEM

Abstract: An optical data storage and retrieval system using a length of optical recording material (19) in which data in the form of microscopic spots (39, 41) is disposed in cells (43, 45, 47) forming a regularly spaced grid. While the material is being moved in a lengthwise direction by a transport (11), rows of cells are being read by a linear CCD array (21), one row at a time. A servo system (59) advances the material so that successive rows can be read, while a second servo (58) adjusts the position of the material in the crosswise direction for proper alignment with the CCD array.

Description: Trans issively Read Quad Density Optical Data System Background Art In prior U.S. patent No. 4,360,728, assigned to the assignee of the preset invention, a banking card is disclosed suitable for use with automatic teller machines (ATMs) . The patent describes a card having optical data written by a laser which forms pits in the medium. The medium itself is described as a thin metallic recording layer made of reflective metal. Types of reflective recording material suitable for use in such cards are described in U.S. patents 4,269,917; 4,304,848 and 4,363,870, all assigned to the assignee of the present invention. This material is characterized by reflective silver particles in a gelatin matrix. The silver parti¬ cles form a reflective field which may be modified by laser writing or, in some instances, by photographic prerecording of information. Since the material des¬ cribed in the patents is based upon silver halide emul¬ sions, exposure of data patterns and subsequent devel¬ oping of the patterns leads to recording of data in a manner similar to laser writing. In either case, data is represented by spots or pits in a reflective field. Reflective spots in an absorptive field would also work. In many optical data recording and retrieval systems, data has been recorded in linear tracks, analo¬ gous to magnetic recording. Data is read by following tracks, usually by means of servo systems. Attempts have been made to increase the data density of optical storage media without increasing the read error rate. Some lengthwise compression of data has been achieved in both magnetic and optical systems by means of clever modula¬ tion schemes, such as FM and MFM. In U.S. patent No. 3,980,818, Browning teaches data storage in a grid of perpendicular contiguous non-overlapping rows and columns. The data is read with a single detector in a raster scan-like manner. In U.S. patent No. 4,105,926, Reno et al. teaches a transparent film containing indicia through which a light beam passes. A mirror behind the film reflects the beam so that it illuminates a small area of the film from behind. In the absence of opaque indicia at the illuminated spot, light is transmitted to a photo- detector. The spots represent data bits with opaque spots representing ones and transparent spots repre¬ senting zeros. In practice, there may be N parallel tracks and N respective photodetectors. Unfortunately, a. signal "crosstalk", i.e. de¬ tection of unwanted light from adjacent areas around an illuminated spot, often occurs when data spots and tracks are spaced too closely, due to the fact that some of the light from each track reaches photodetectors intended to receive light from other nearby tracks. In order to reduce crosstalk, the parallel tracks are typically not closely spaced and substantial blank space is provided between bit positions. Others, such as Browning, sacri¬ fice speed in reading data for higher density by using only a single detector. An object of the present invention was to de- vise a means for formatting optically recorded data for a data card, or the like, in a way that increases data density, while at the same time minimizes error resulting from crosstalk and other sources. Disclosure of the Invention The above object has been achieved in an opti¬ cal data storage and retrieval system in which data is stored in a high density format and is read at a high rate with minimum error. The system includes an optical storage medium, such as a data card with a strip of optical data storage material disposed thereon, and a linear CCD array. High density is achieved by encoding data as microscopic spots aligned in specified data cell positions of a grid of perpendicular, non-overlapping, rows and columns of cell positions. The optical medium is read transmissively by moving it relative to a linear array of optical detec- tors. The detector array is disposed for reading on an opposite side of the medium from a light source. The detector array is alligned perpendicular to the direction of lengthwise card motion for simultaneously reading each cell position in a row of cell positions. A plurality of detector cells read each specified cell position for minimizing error. Groups of similar cells simultaneously read a plurality of specified data cell positions. Since the linear detector array is perpendicu¬ lar to the direction of motion, there is no need for "track following" in the traditional sense. Data spots are disposed in positions, termed cells, which are rows and columns of a regular grid. Each transverse row of cells is usually read more than one time and these cells must be in alignment with the linear detector array. Since the entirety of a row is read almost simultaneous¬ ly, a new error checking scheme is possible. For exam¬ ple, cells at opposite edges of a row may always have spots, or specified spot patterns. Each row of cells contains a discrete set of cells which collectively make up usable data. This row can be called a "track". Each row is read out by the detector array in parallel with a single scan of the contents of the array. The image of the "track" is smaller than the total view of the detec¬ tor array. This allows electronic tracking to be accom¬ plished with no alignment motion of the card or the electronics. The card can be moved in (1) an incremental fashion, where the card or optics is stepped to each new row and the data is recovered, or (2) a uniform motion where the electronics continuously reads rows of data until a high quality read is found. The electronics can detect a new row of data by special marks on the ends of the row. The system minimizes error resulting from crosstalk and other sources by having a plurality of detectors of the array observe each data cell, output from the number of detectors observing a cell can be poled to determine whether or not a spot existed within a cell. For exam¬ ple, if two of three detectors have voltage levels indic¬ ative of a spot, then presence of the spot is assigned to that particular cell. However, if only one detector cell indicates a spot, the cell is determined to be empty. Such poling is also helpful because spots may not be centered in a cell or have a geometrically optimal shape. Brief Description of the Drawings Fig. 1 is a front plan view of an optical data storage and retrieval system in accord with the present invention. Fig. 2 is a frontal blowup view of a data strip having optically readable digital data thereon. Fig. 3 is a plan view of data spots arranged in cells in accord with the present invention. Fig. 4 is a detail of detector cells aligned for reading data spots in accord with the present invention. Fig. 5 is a plan view of data spots in a cen- tral band and neighboring bands, with a CCD array span¬ ning the central band and portions of the neighboring bands. Fig. 6 is a block diagram of optical, mechani¬ cal and electrical components of a data strip reader mechanism in accord with the present invention. Best Mode for Carrying Out the Invention With reference to Fig. 1, a card transport 11 is shown. The transport includes a rail 13 which sup¬ ports a card 15, such as a credit card. The transport 11 includes a readout head 17 mounted for scanning a strip 19 carried by card 15. Strip 19 is an optical storage medium, preferably of the transmissive type, such as one formed from a silver-halide emulsion which has been pho- tolithographically exposed through a mask to actinic radiation and developed to produce a medium with trans¬ parent spots in an opaque field. Strip 19 may also be 5 formed from diazo or vesicular type films. These ma¬ terials are commercially available from Xidex Corporation and others. The medium may also be produced with opaque spots in a transmissive field. Other types of reflective or transmissive material, which can support pre-encoded 0 data, formed by laser or other optical techniques, such as those previously mentioned in U.S. patents 4,269,917; 4,304,848 and 4,363,870, can be used. The readout head 17 holds a linear array 21 of optical detectors, such as a CCD array. The linear array 5 has a line of detectors which spans at least one row of data on strip 19 at a time. Card 15 may have other indicia thereon, such as alphanumeric indicia 23 serving as eye-readable identification information. As the card is moved in the direction shown by the arrow A, by an o automatic card advancing mechanism, strip 19 moves past the readout head 17 so that the strip 19 passes beneath the linear detector array 21. This allows microscopic data spots on the strip to pass beneath the readout head 17. 5 Fig. 2 shows a detail of the strip. The card 15 has a strip edge 25 a few millimeters from the upper edge of the card. The optical data strip spans the length of the card, similar to a magnetic data strip on a credit card. Inward from edge 25 is a first data area or Q band between parallel lines 27 and 29. A second data area or band exists between lines 29 and 31. The second data area or band is approximately the same size as the first. The lines 27, 29 and 31 are dark, straight, parallel, spaced apart lines which assist in playback of 5 information. Any number of such data areas may be dis¬ posed on a data strip, depending upon its width. The width of each data area is governed by the size and number of cells disposed across the area. At least one row in one band passes beneath the readout head. In the case of multiple, parallel bands, the detector array overlaps bands, as described below. A small quantity of spots 39 is shown. Here, the spots are disposed in two rows across the first data recording area. The spots are microscopic in size, typically have a dimension greater than 3 microns, with the preferred dimension being about 10 microns, and a range of dimensions for an edge or diameter being between 1 to 35 microns. 0 The data spots and their positions may be seen in Fig. 3. The dashed horizontal lines 35 and the dashed vertical lines 37 are imaginary, serving to indicate cells wherein data is written either photographically or by means of a laser. The cells are generally square, 5 although this is not necessary. Within the cells, spots 39 may be present or absent. The field in which the spots appear may be opaque. The presence of a spot may increase the transmissivity of the field to an extent that a detector can detect light transmitted through a o spot and produce a corresponding signal. Previously described line 29 is seen defining the edge of a re¬ cording area. The spots need not be round, as shown, but may have any regular shape, such as square. There is no 5 required number of cells in a row and no required numbers of columns of cells between spaced apart parallel lines. However, the number of cells in each row is preferably equal. Preferably, the spots are positioned such that they touch each other when adjacent, i.e. contiguous, in Q lateral and lengthwise directions. Fig. 4 shows a linear detector array 21 passing over a portion of a grid having the data spot 41 within data cell 43. Data cells 45 and 47 are empty, as well as the other data cells which are pictured. 5 The linear detector array 21 has a plurality of detectors 51, 53, 55 disposed for sensing light trans¬ mitted to each cell. In this case, three detectors observe cell 43 and in the process detect spot 41. Since the detectors are typically CCD devices, the detector output is sensed by shifting charge levels from one end of the linear array to the other. The charge levels are measured in terms of voltages, with a high amount of 5 transmissivity defined as the highest or lowest voltage condition and the lowest amount of transmissivity defined as the opposite voltage condition. A threshold level is defined between the maxima and the output from the number of detectors observing one cell can be polled to deter- 0 mine whether or not a spot existed within a cell. For example, if two of three detectors have voltage levels indicative of a spot, then presence of the spot is as¬ signed to that particular cell. However, if only one detector cell indicates a spot, the cell is determined to 5 be empty and the single detector reporting a spot is believed to have detected foreign material within the cell. With reference to Fig. 5, a portion of a data card is shown with three adjacent bands of data spots 0 including central band 38 and neighboring bands 36 and 10. Band 36 is between parallel lines 28 and 30. Band 38 is between parallel lines 30 and 32. Band 10 is between parallel lines 32 and 34. Each band of data has 46 data cells between the transparent columns immediately 5 adjacent to the opaque parallel lines on either side of a band. The linear detector array 21 has a total of 256 detector cells uniformly spaced along the array. In reading data the detector array is over-filled with more than one band. Approximately one-half of each neigh- Q boring band 36 and 10 is captured, as well as the entire¬ ty of the central band 38, which is primarily of in¬ terest. The linear detector array is preferably read several times so that ambiguities may be resolved by comparing successive reads of the same row. This is 5 described further below. The central band 38 may be followed electronically by identification of the parallel lines 30 and 32, each having white, i.e. transparent, columns on either side of the line, such as the columns 42 and 44 and data bits forming track marks at the end of each row. The track marks may indicate track numbers so that the address of each track is established. Once a band is read, such as band 38, the card, or the optics disposed above the card may be moved so that the next band of data may be read. This constitutes electronic tracking of data with very fine separation of relevant data from other data or non-data areas of the card. With reference to Fig. 6, an optical data stor- 0 age medium 46 is shown to be supported in a card trans¬ port 11 driven by a motor 57 via a belt 48. The card is held firmly in place by guides 13, seen in Fig. 1, serving to locate edges of the card. Motor 57 may be a stepper motor under control of motor servo 59. The 5 transport is capable of moving card 46 back and forth, with extreme positions of the transport signaled by opti¬ cal limits 61 which are electrically connected to motor servo 59. A beam source, such as a laser 40, generates a o radiation beam 49 directed toward the data bands on card 46 by means of optics 63 typically a focusing lens. Light transmitted through the card is directed toward a linear detector array 50 by means of a lens 52. Light source 40 and detector 50 are mounted on opposite sides 5 of the card on a movable support 54 which is driven by a motor 56. Light source 40 is a semiconductor laser operating at infrared wavelengths. The motor is a step¬ per motor which is controlled by a second motor servo 58. Both the first motor servo 59 and the second motor servo Q 58 are connected to a data bus 80 for computer control. The first servo 59 forces motor 57 to advance card 46 in a lengthwise direction so that successive rows of data may be read by the linear array 50. On the other " hand, stepper motor 58 provides crosswise motion control so 5 that various bands of data may be read. The linear array 50 is able to read successive rows of data, asynchronously scanning the data, in a sense, as the data is shifted out of the linear array. The start of each scan is indicated by means of a start pulse. As previously mentioned, a CCD driver 60 receives incoming data bits along line 62 and produces a start pulse along line 64 once the start of data is recognized. Since the data is self-clocking, clock pulses may be generated from the data stream arriving on line 62 and these clock pulses are sent to other system components along line 66. Undecoded data is transmitted along line 68 to a data decoder circuit 70 having memory with vari- ous data patterns. Clock pulses provide timing marks so that data patterns may be recognized. Data is also transferred to a reference line follower circuit 72 which recognizes the lines which mark the edges of each band. One of the data patterns to be decoded consists of trac marks on the card. Such marks are embedded in each row which, as previously indicated, is termed a "track". Reference line information is transmitted from reference line follower 72 to decoder circuit 70 so that track marks can be located adjacent to the reference lines. The memory of the bit decoder 70 contains a map indi¬ cating where data should be expected. A counter in the bit decoder cooperates with the map in order to match the data stream along line 68 to decoded data bits. The linear array 50 is clocked at a rate so that each row of data is read at least a few times before the optics passes on to the next row. Each scan from the linear array is tested to find out if it is a new track. If it is a new track, then the best previous pattern match from the previous track is transferred to the data bus. Other scans from the previous track are discarded. Each scan of the same track is compared to the previous best decoded track until the best data pattern for that row has been selected when the next row scan is ini¬ tiated. The best row is measured by reading track marks at the end of each row. Each track also may be checked for parity. Decoded data is transmitted to a line buffer 74 which converts data to parallel bytes for transmission to bus 80. A computer is, connected to the data bus for testing data as described above and for providing error correction. The computer also provides control for the motor servos 59 and 58 using known servo correction and feedback techniques. As previously mentioned, each card carries opaque, straight, parallel reference lines separating bands of data. After a band has been read, the second servo 58 positions the optics for reading the next band. Instead of moving the optics, the card could have been moved in the crosswise direction. In the present invention, the motors 56 and 57 provide coarse positioning of the card so that the linear array can scan a row of cells, plus neighboring cells on either side of the row. The CCD array separates the row utilizing the track marks within each row and in this manner performs electronic tracking of the data. This may be considered to be fine tracking of the data which cooperates with the coarse tracking. While the preferred embodiment has described a card having a strip of opaque material with transparent spots thereon, it will be realized that a continuous strip could be wound on hubs, like tape. Moreover, the material need not be opaque with transmissive spots but could be transmissive with opaque spots or reflective. Reflective material would be read by light reflecting from the material onto a detector array on the same side of the material relative to the source. The material need not be a film material. Most types of laser data storage media can be used.

Claims: Claims 1. An optical data storage and retrieval system com¬ prising, an optical data storage medium having optically readable digital data encoded by microscopic spots in specified data cell positions on said medium thereby changing transmissivity of the medium, said data cell positions forming a grid with perpendicular, non-over¬ lapping rows and columns of cell positions, said columns aligned with the length of said medium, and a linear CCD array aligned perpendicular to said columns of cell positions on a side of said medium opposite a light source, said array having a plurality of fixed position detector cells imaging each specified data cell position in a row of cells, wherein at least two detector cells image a specified data cell position, with groups of detector cells simultaneously imaging a plu¬ rality of cell positions. 2. The system of claim 1 wherein said storage medium comprises a strip of opaque optical data storage material with transparent microscopic spots. 3. The system of claim 2 wherein said strip of optical data storage material is mounted on a wallet-size card. 4. The system of claim 1 wherein a first group of rows is separated from a second group of rows by a lengthwise optically absorptive line. 5. The system of claim 1.further comprising a first servo for adjusting the crosswise position of the storage medium relative to the CCD array. 6. The system of claim 5 further comprising a second servo for incrementally advancing the lengthwise position of the storage medium. 7. An optical data storage and retrieval system com¬ prising, a data card having a length and a width with a strip of an optical recording medium thereon, said strip having microscopic data spots aligned in data cell posi¬ tions forming a grid with non-overlapping elements in said lengthwise and widthwise directions, a data readout head having a linear photodetec- tor cell array disposed on a side of said data card opposite a light source to transmissively read data spots on the strip in a direction across the width of said card, wherein said readout head has a plurality of detec¬ tor cells of said linear detector cell array for each cell position in a row of cell positions, with groups of detector cells simultaneously imaging a plurality of cell positions and card transport means for advancing said card relative to said head in a direction parallel to the length of said card. 8. The system of claim 7 further comprising a first servo for adjusting the crosswise position of the medium relative to the CCD array. 9. A data card read system comprising, a data card having non-overlapping parallel rows of data cells arranged in groups of parallel col¬ umns, each data cell capable of holding a single bit of data approximately the size of a laser beam diameter, each group of columns of data cells spaced from a neigh¬ boring group of columns, thereby forming parallel bands of data,' a card transport having means for moving the card, a beam source means for directing a radiation beam onto the card and beam detector means on an opposite side of said data card from said beam source means for reading said radiation beam after transmission through the card, said beam detector means capable of simul¬ taneously reading a row of data cells, wherein said beam detector means include a linear array of fixed position detectors, wherein at least two detectors read each data cell, with groups of detector cells simultaneously imaging a plurality of cell positions, and card transport means for advancing the card relative to the beam source and the beam detector means so that successive rows of data can be read. 10. The apparatus of claim 9 wherein parallel bands of data are separated by parallel, absorptive lines. 11. The apparatus of claim 9 wherein each row of data cells has track marks at opposed ends, said track marks identifying a row. 12. The apparatus of claim 9 wherein said detector means comprises a linear array having a width greater than a row of data, said linear array having detector cells imaging data in a row plus some data from rows in neigh¬ boring bands. 13. A data card comprising, a substrate capable of supporting an optical data storage medium, and an elongated data storage medium on the sub¬ strate having a rectangular non-overlapping array of storage cells, including a length dimension and a width dimension, some of the storage cells having data spots therein of microscopic size, the remaining storage cells being empty, said spots being mainly transmissive of light in comparison to the surrounding field which is mainly opaque to light, the data being arranged in tracks along the widthwise direction, at least one end of each track having spots marking the presence of the track, each of the storage cells in a track having a size capa¬ ble of being imaged by a plurality of adjacent detector cells in a linear array. 14. The data card of claim 13 wherein said rectangular array of storage cells is divided into a plurality of bands by parallel, absorptive lines, each band containing a plurality of tracks. 15. The data card of claim 13 wherein the size of said spots is between 1 to 35 microns along an edge or a diameter. 16. The data card of claim 13 wherein at least some of said data spots are contiguous in both lengthwise and widthwise directions. 17. The data card of claim 13 wherein said spots are photographically prerecorded in a photosensitive emulsion having an optically contrasting field surrounding the spots, said emulsion forming said storage medium.

Inventors: BUXTON JAMES L, PIERCE GERALD A, BUXTON, JAMES, L., PIERCE, GERALD, A.
Applicants: DREXLER TECH, DREXLER TECHNOLOGY CORPORATION
Application year: 1987
Main classification: G06K7
IPC codes: B42D15, G06K7, G06K17, G06K19, G11B7