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Description  |
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TECHNICAL FIELD
The invention relates to optical data information storage and more
particularly to a method for making information cards containing both eye
readable images and laser recorded machine readable data.
BACKGROUND ART
Identification cards have used magnetic data strips in conjunction with
photographs of the card holder.
In U.S. Pat. No. 4,236,332, Domo discloses a medical record card containing
a microfilm portion having some data visible to the eye and other data
visible by magnification. The directly visible data is alphanumeric
character codes pertaining to emergency medical conditions of the patient
and the magnifiable data portions detail the medical history.
In U.K. patent application No. 2,044,175, Maurer et al. teach a card having
eye readable, machine readable and security verification information. The
machine readable data may be laser recorded or magnetic data.
Silverman et al. teach, in U.S. Pat. No. 4,213,038, an access control
system with an identification card. The card has machine recordable
indicia used to choose a master microspot pattern from the machine's
memory. This master pattern is compared with an identical pattern on the
card for verification. The card also has space for a picture and a
signature. Similarly, Idelson et al., in U.S. Pat. No. 4,151,667, teach an
identification card having a photograph and a phosphorescent bar code
pattern used for verification.
The amount of information these cards can hold is extremely limited. Data
visible to the eye occupies a considerable amount of space on a card,
which further limits the amount of information that can be stored. In the
patent to Idelson et al., the photograph and bar code pattern overlap.
Random microspot patterns can only be used for verification, while bar
codes can only represent a small amount of specific data.
In prior application Ser. No. 822,067, assigned to the assignee of the
present invention, a data card was disclosed having both eye readable
images and laser recorded machine readable data. More specifically, a data
card was disclosed having laser recording material which could either be
prerecorded or recordable in situ. The data card also included an
eye-readable visual image, such as a photograph. One of the problems
encountered in manufacturing such cards is in achieving registration
between the eye readable data and the machine readable data when data
cards are mass produced.
An object of the invention was to devise a card manufacturing method which
would achieve registration between eye readable and machine readable data.
Another object of the invention was to provide quality control for data
cards by identifying cards having flaws or errors and rerecording the same
cards.
SUMMARY OF THE INVENTION
The above object has been met with a method for forming a data card by
merging two webs, one from a roll containing visible images, and one from
a roll containing pre-formatted high resolution optical recording
material. As the two webs are merged, they are joined together and then
cut to card length, with eye readable and machine readable images disposed
in back-to-back relationship. Alternatively both types of data could be
read from the same side. The eye readable image contains a machine
readable identifier so that automatic optical inspection and acceptance
may be performed on finished cards. If such an inspection reveals flaws or
data errors, the image is identified by the machine readable data and may
be re-recorded for a second attempt to make the card. In this manner, the
merger of two webs, and subsequent cutting, provides an opportunity for
precise registration in forming large numbers of data cards and the
remaking of only those cards which failed inspection.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of the manufacturing method of the present invention.
FIG. 2 is a top view of a film segment employed in the card manufacturing
method shown in FIG. 1.
FIG. 3 is a cross sectional view of a double sided card with eye readable
and machine readable images on opposite sides.
FIG. 3a is a cross sectional view of a single sided card with eye readable
and machine readable images on the same side of the card.
FIG. 4 is a perspective plan view of tape rolls spooling optical recording
tape employed in the present invention.
FIG. 5 is a side sectional view of the optical tape of FIG. 4.
FIG. 6 is a detail magnified about line 6a--6a in FIG. 5.
FIG. 7 is a side view of an apparatus for forming the optical tape of FIG.
4.
FIGS. 8-10 are top views of portions of strips of optical recording tape,
showing prerecorded servo track guides disposed on the tape in various
directions.
FIG. 11 is a top plan view of a data card with optical tape mounted
thereon, showing prerecorded tracks.
FIG. 12 is a top plan view of the card of FIG. 11 with initialized stop and
start marks.
FIG. 12a is an enlarged view of a portion of the card in FIG. 12.
FIGS. 13a, 13b and 13c are schematic views of data tracks at various stages
of recording.
FIG. 14 is a flow chart illustrating a method of recording data on the card
of FIG. 11.
FIG. 15 is a flow chart detailing steps for advancing to the first
unrecorded track and setting the track number in accord with the method of
FIG. 14.
FIG. 16 is a flow chart illustrating a method of recording data on the card
of FIG. 11 and checking for defects in that card.
FIG. 17 is a simplified plan view of a system for reading and recording on
the data card in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
With reference to FIG. 1, a film roll 11 provides a continuous web 13 of
unexposed, undeveloped photographic film. This film is moved from supply
roll 11 past a recording beam 15 derived from a beam source 17, such as a
laser, and a scanner 19 which sweeps the beam across the film in a
scanning fashion, reproducing an image. Such film recorders are known and
typically reproduce digitally recorded images. In this manner, a data base
having a large number of images may produce a series of pictures as output
and each picture is transferred to film, as needed. In the present
invention, images are to be mounted on cards and so the sequence of images
corresponds to a sequence of cards to be produced. Such a situation arises
in production of identification cards, drivers licenses, student
registration cards and the like. Together with picture data, low
resolution machine readable indicia, such as bar code, are also recorded
for subsequent use in quality control.
The film web is advanced by means of edge sprockets or friction rolls 21
and 23 which turn the film into a film developing and processing bath 25.
After the film web is developed, the film web is merged with a web 31 of
preformatted high resolution laser, direct-read-after-write (DRAW) optical
recording tape from supply roll 33. The optical recording tape has
approximately the same lateral dimensions as the film. The recording
surface of the tape is disposed in either front-to-back or back-to-back
relation with the film. The two may either be thermally bonded using the
heaters 27 and 35, or may be adhesively joined. The formatting of the
optical data tape is discussed below. If the webs are joined back-to-back,
film and data are read from opposite sides of the composite web as
discussed with reference to FIG. 3. If the webs are joined front-to-back,
film and data are read through one of the substrates on the same side and
the images must be laterally separated as discussed below with reference
to FIG. 3a.
The tape or the film, or both, carries a backing member which when joined
to the other forms a self-supporting structure which will be subsequently
cut into cards. After joinder of the two webs, film and data web portions
undergo quality control scanning by laser scanners 41 and 43. Each scanner
has associated scanner mirrors 45 for areawise simultaneous reading of
front and back sides of the card. Detector 47 receives the image from
laser 41 while detector 49 receives the image from laser 43. The image
which has been scanned by laser 47 should correspond to the image
originally recorded by film recording laser 17. Detector 49 checks for the
presence of prerecorded formatting on the high resolution laser recording
material.
A computer 51 receives data from the scanners and notes any failures, such
as lack of an image, or lack of data tracks. In this situation, the
computer may order a re-recording of the eye readable information. Since
the preformatted high resolution laser optical recording tape is
continuous preformatted web of similar material, no rerecording is
necessary. Advancement of the supply roll will provide a new portion to
receive a rerecorded visual image and once again attempt to form a proper
back-to-back combination which will pass inspection. After inspection, the
joined webs pass to a cutter 53 which forms individual data cards 55.
FIG. 2 shows the upper surface of a film web portion 61 having opposite
sprocket holes 63 for advancement and machine readable indicia 65 which
are used to identify the face photographs 67 during quality control
review. The sprocketted holes are shown for illustration and unsprocketted
film is preferred. The indicia 65 are low resolution machine readable
code, although high resolution indicia may also be used. The film shown in
FIG. 2 is similar to common 35 mm film except that the machine readable
indicia are on the inside of the sprocket holes, rather than on the
outside. This is because if they are used the sprocket holes may be
trimmed away after joinder with the machine readable web portion. Note
that precise registration is not needed since the high resolution optical
recording tape is continuously formatted.
In FIG. 3, the cross section of the joined webs may be seen to comprise a
first emulsion layer 71 having filamentary silver particles 77 therein,
characteristic of developed silver halide films. Emulsion 71 is adhered to
a Mylar substrate 73 and has a protective coating 75 disposed over the
emulsion. The layers 71, 73 and 75 comprise the photographic film web
portion which is joined to the laser recording material.
The preformatted high resolution laser recording tape may consist of a
Mylar substrate 83 which may be coated with a very thin metal layer 85.
This layer is used to enhance the optical contrast of the laser recording
tape. Disposed over thin metal layer 85 may be an emulsion layer 87 which
has regions of one reflectivity characterized by metal particles 89 and
regions of a second reflectivity 91, indicated by vertical dashed lines,
which are prerecorded and which expose the highly reflective metal layer
85 which is more reflective than the region wherein the metal particles 89
reside. A transparent coating 93 is applied over the recording layer.
Other preformatted or unformatted laser recording tapes known in the art
may also be used.
With reference to FIG. 3a, the cross section of the joined webs comprises a
first web having a film substrate 72 and a photographic emulsion coating
74 extending across the lateral extent of the substrate. A picture does
not occupy the full lateral extent because room is left in a field of view
from one side of the card for a superposed strip of optical recording
material 76 carried by the Mylar substrate 78 forming the second web. The
first and second webs are joined together such that the emulsion 74 and
the optical recording material 76 are optically in side by side
relationship. The optical recording material may be of the type described
below with reference to FIGS. 5 and 6. A protective transparent cover
layer 88 may be disposed over the recording medium 76. A thin reflective
metallic layer 80 is disposed between the optical recording material 76
and substrate 78 to enhance optical contrast. Emulsion layer 74 is seen to
contain filamentary silver particles 82, characteristic of developed
silver halide films. Optical recording material 76 is seen to contain
metal particles 84 whose reflectivity may be altered by a laser beam.
Contrast is enhanced by means of the metallic layer 80. Both the
photographic image in emulsion 74 and optical data in recording medium 76
may be read from the same side. In this situation, reading optics for both
the film and the recording medium would exist on the same side of the
joined webs.
The formation of the preformatted tape and the initializing of data cards
has been the subject of prior applications by the assignee of the present
invention. The procedure is described below.
A. An Example of the Formation of One Type of Pre-formatted Optical Tape
With reference to FIG. 4, a supply tape hub 111 is seen dispensing a tape
web 113 to a tape take-up hub 115, the tape passing around turning or
support posts 117 and 119. The tape is an optical recording medium capable
of laser writing. The tape has a width ranging from 1 cm to 5.5 cm and is
relatively thin, about 400 microns or less, although this is not critical.
Tape web 113 is typically about 300 meters long. A linear array 121 of
semiconductor diode lasers records parallel, spaced-apart servo tracks on
the tape by displacing, modifying or agglomerating absorptive metal
particles in the tape medium. Alternatively, a single laser emitting a
beam that repeatedly scans laterally across the tape as the tape is
advanced past a scanning station may be used. The writing system guides
the laser beam so that data are written or read in parallel paths. It is
important that parallelism be maintained accurately, so a mechanical
alignment mechanism, not shown, may be used to insure that the position of
the tape passing in front of laser array 121 is proper. Moreover, all
portions of the tape should experience uniform lateral tension so that the
tape is not squeezed together between opposite edges.
The tape path illustrated in FIG. 4 is a very simple path with drive power
being applied directly to one of the hubs by a transport mechanism. The
tape may be reversed in direction of travel by applying power to the
opposite hub. Hubs may be driven directly by motors or by belts attached
to pulleys in power communication relation to the hubs. Sometimes more
complicated systems of posts and tape paths are used for high-speed tape
transport. Typically, tape may be advanced in either direction at a rate
of about 5 meters per second. A read head could be combined with the laser
bar writing mechanism 121 to form a read/write system. The read head would
consist of a number of photo diodes or CCD elements in a linear array,
spaced similarly as the laser bar 121, except being vertically movable, as
by a servo controlled piezoelectric element in order to maintain the read
elements in a data path following position so as to confirm the writing.
The recording material which is selected should be compatible with the
laser used for writing on it. Some materials have a higher recording
sensitivity than others at certain wavelengths. Good recording sensitivity
to near-infrared light is preferred because semiconductor lasers creating
the required light beams are readily available. The selected recording
material should have a favorable signal-to-noise ratio and form high
contrast databits with read/write systems with which it is used. The
material should not lose data when subjected to temperatures of about
140.degree. F. (60.degree. C.) for long periods. The material should also
be capable of recording at speeds of at least several thousand bits per
second. This generally precludes the use of materials that require long
heating times or that rely on slow chemical reactions in the presence of
heat, which may permit recording of only a few bits per second.
With reference to FIGS. 5 and 6, one example of the optical recording media
comprises a film substrate layer 123, a highly reflective metallic layer
124 deposited on substrate layer 123 and a selected, thin black silver
planar crust 126, generally less than one-half micron thick, within
gelatin layer 125. The latter layer is generally one to six microns thick,
disposed on metallic layer 124, which is generally 100 Angstroms to 1000
Angstroms thick. During the optical medium manufacturing process the
surface of the silver-halide emulsion, distal to the substrate, is
developed to dark or black by exposure to actinic radiation and then to
photographic development. Black and clear images can be created if desired
by using a photomask. The exposing image is a pattern of control indicia
such as tracks or data location grids to be pre-recorded. The depth of the
dark layer is typically 0.3 to 0.5 microns. The undeveloped remainder of
the emulsion layer which is essentially gelatin remains clear. Other laser
recordable tapes known in the art may also be used. Substrate layer 123
should be self-supporting, yet sufficiently flexible so that the tape is
spoolable, i.e. so that a length of tape may be wound on a tape hub. A
transparent, planar protective layer 128 may be disposed over the laser
recording layer 126. Polycarbonate plastic material is one of the
preferred cover layers and may be a thin laminating sheet adhered over the
tape or, alternatively, other clear plastics or a lacquer coating may be
used.
Film substrate layer 123 may be composed of polyesters, cellulose acetate,
Mylar, or other materials commonly used as film bases. Metallic layer 124
is typically composed of either gold, copper, silver, aluminum or alloys
thereof. The layer is on the order of 100 to 1,000 Angstroms thick.
Gelatin layer 125 originally was the gelatin matrix containing a silver
halide emulsion, i.e. a photographic emulsion layer. The gelatin colloid
matrix should be made from material which is substantially transparent to
a read beam wavelength in the near infrared, and may be further selected
to be substantially more absorptive at an actinic wavelength thereby
enhancing the antihalation properties of the recording medium during the
preformatting process. Gelatin layer 125 is typically under 3 microns
thick, but could be as thick as 10 microns. The gelatin layer 125
containing crust 126 is shown having been exposed to actinic radiation and
then developed to be substantially dark only at its surface. Wavy lines in
planar crust 126 represent black filamentary or oblong silver particles
embedded in the gelatin colloid matrix.
Areas 118 and 120 represent data spots which have been laser recorded by
displacement, modification and/or agglomeration of metal particles in the
crust 126 to be predominantly clear, revealing an underlying reflectivity
in the metallic layer 124 when illuminated by light of a read beam
wavelength, typically in the near infrared. Clear areas 118 are preferably
sharply defined, rather than diffuse or otherwise blurred. The optical
density of background areas 122 at the read beam wavelength of gelatin
layer 125 should be at least 0.5 and preferably greater than 1.0. The
optical density of the spot areas 118 of gelatin layer 125 should be not
more than 0.2 and preferably less than 0.1.
Metallic layer 124 is placed onto a flexible self-supporting film substrate
123 by vacuum or vapor deposition and then applying the thin, planar
photosensitive emulsion layer 125 over a reflective metallic layer 124 or
alternatively a thin photosensitive emulsion layer over a gelatin layer
covering a reflective metallic layer. Alternatively, the thickness of the
laser sensitive recording layer can be controlled in the manufacture of
the photosensitive starting material of the present invention.
Very thin (0.25-0.5 .mu.m) photosensitive silver halide emulsion can be
coated over clear gelatin to achieve the thin recording layer. The
resulting photosensitive web is then processed by exposure, development
and fixing, as described in greater detail below, to produce a laser
sensitive, but not photographic sensitive medium. Track guides and other
control indicia may be photolithographically prerecorded during the
processing of the photosensitive web, if desired, by imagewise exposure
through a mask. A planar, transparent protective layer 128 may finally be
adhered over optical storage layer 125. To simplify registration with the
photographic images only the track guides would be recorded.
FIG. 7 illustrates photographic processing for producing a laser sensitive
optical tape medium from a photosensitive web. Photosensitive web 135,
stored on a reel 131, is driven by a tape advancing mechanism 133 beneath
a source 137 of actinic radiation. Source 137 may be a laser bar or other
source of green, blue or ultraviolet light which illuminates the web
surface. Typically, the actinic light has a wavelength in the blue-green
range of 0.4 to 0.6 microns, although ultraviolet light with wavelengths
less than 0.4 microns may also be used. Web 135 is thus exposed to create
a latent image. The entire mechanism in FIG. 7 is shielded in a protective
housing which preserves the light sensitive character of web 135.
The emulsion layer is preferably a fine grain silver-halide emulsion in a
gelatin matrix. The smaller the grain sizes of the silver-halide emulsion,
the higher the resolution of the final pre-recorded product of this
invention. The emulsion grain size should be less than 5% of the recording
data spot size for best results, and emulsions with grain size on the
order of 0.05 microns are commercially available. Antihalation dyes, also
known as attenuating or accutance dyes, may also be added to the
photographic emulsion to increase the absorptivity of the emulsion at the
actinic wavelength thereby concentrating the exposure to the top surface
of the emulsion. This can help create a thin black recording crust. It can
also reduce any halation effect and give higher resolutions. Such dyes are
commonly used and are water soluble and thus are not present when the
emulsion has been converted to the optical storage media.
If pre-recording of track guides is desired, a shielding mask may be placed
over unexposed web 135. The mask would typically have two degrees of
transmissivity to actinic radiation, being substantially clear over most
of its extent, except for an imagewise pattern of optically dense lines
for forming track guides.
Turning idlers 139 and 141 advance the exposed tape web into a processing
solution 143 where the web is developed and fixed. Additional tanks, not
shown, are used for this process. Exposure by web 135 to actinic radiation
creates a latent image in which silver halide is activated substantially
to saturation. The exposed web is developed to produce a medium which is
substantially dark over most of its extent, but which may have an
imagewise exposure pattern of partially clear track guides revealing the
underlying reflectivity in the metallic layer for light of read beam
wavelength. Development of the surface layer may be a surface development
occuring typically within the top 0.3 to 0.5 micron of the emulsion layer
in a plane distal from the substrate. Such development occurs by
contacting the light exposed image layer with a concentrated development
solution for a very short period, before the development solution can
diffuse into the material or by means of a slow-diffusing developer such
as tertiary butylhydroquinone.
Alternatively, a viscous developer thickened with carboxymethylcellulose
may be used. This material is syrupy in consistency and is rolled on. It
may be washed off and development stopped with a spray stop bath. It then
is treated with a fixing bath. Crusts as thin as five to ten percent of
the thickness of a ten to fifteen micron emulsion layer have been made.
During development, areas containing black filamentary or oblong silver
particles are formed from activated silver-halide areas. The volume
concentration of activated silver halide at the emulsion surface
determines the volume concentration of filamentary silver, which in turn
determines the optical density of the emulsion layer. Areas containing
filamentary silver should exhibit an optical density as measured with red
light of a photographic densitometer of at least 0.5 and preferably
greater than 1.0, while any unexposed track guide areas should have
densities less than 0.2. Subsequent to development, fixing and rinse steps
remove the remaining silver halide from emulsion layer 135 leave just
silver in the gelatin matrix.
The tape is advanced past idler 145 and beneath a drying unit 147 after
processing has converted it into an optical recording material. The laser
sensitive medium is then wound on a takeup hub 149 and stored for future
use.
FIGS. 8-10 show the placement of servo track guides on optical tape. In
FIG. 8, the track guides 181, 183 and 185 extend longitudinally parallel
to the lengthwise direction of the tape web. The track guides are spaced
apart at least wide enough to accommodate data spots between the guides,
although several writing areas could be associated with one track guide.
As an example, the track guides may be 10 microns apart, with data spots
having a size of three microns between the guides and a servo track guide
line width of three microns.
While lengthwise servo tracks are preferred, it is also possible to have
side-to-side servo tracks. As seen in FIG. 10, the track guides 197, 199,
200 and so on, are again parallel, but transverse to the lengthwise
direction of the tape. Such tracks are known as lateral tracks, to
distinguish them from the lengthwise tracks previously described. Lateral
tracks consist of parallel, closely spaced tracks with a line-to-line
separation, approximately the same as for longitudinal tracks. The spacing
must be sufficient to accommodate a data path between adjacent tracks or
in some relation to a track, such as overlying it, with enough room for
adjacent paths.
Lateral data paths would be written by a scanning laser which sweeps across
the width of the tape as the tape is advanced past a scanning station. In
the read situation, data could be detected by a linear array of detector
elements, such as a CCD array. An adjacent servo track, if any, would be
detected when a continuous line is observed by the array. The linear array
would be aligned parallel to the servo tracks with tape motion
synchronized with detector electronics, allowing the detector array a
sufficient time to observe a pattern on the tape as the tape advances past
the detector array. The tape need not stop for observation, but may move
continuously past the detector array.
In FIG. 9, the track guides run in two perpendicular directions. For
example, guides 187, 189 and 191 extend longitudinally parallel to the
lengthwise direction of the tape web while guides 193 and 195 are aligned
laterally, i.e. transverse to the direction of the tape web. In this case,
a read system could follow either set of guides or treat the guides as
forming a data location grid in which data are written in relation to the
grid, either on the lines or tracks, or inside of the rectangles formed by
the tracks. Data could be located by counting line crossings from marked
reference positions. The grid pattern could also be used as a reference
guide when strips of the tape are used for laser recording of data. The
grid pattern forms can be used for alignment of data spots.
The final result of these processing steps is a superior laser recording
medium comprised of a very thin black silver crust within one of the
planar surfaces of a gelatin layer and a reflective underlayer which
achieves good recording sensitivity, high contrast and resolution for
laser recording of data. Laser recording on this medium is efficient,
because the filamentary silver particles in the crust are absorptive
causing a rise of temperature at the top surface of the crust, thereby
facilitating the particle modification, displacement or agglomeration of
the crust layer. Also, since the crust is thin, very little time is
required for the laser beam to modify the crust to reveal the reflective
metallic layer beneath the gelatin layer. These filamentary particles are
absorptive of light energy over a very wide spectrum range from
ultraviolet to near infrared, permitting a wide variety of lasers to be
used for recording.
B. Card Formation
With reference to FIG. 11, a data card 211 comprises a card base 213 and a
strip 215 of laser recordable optical data storage tape disposed thereon.
The photograph of FIG. 2 is on the opposite side of the card and is not
shown. A plurality of generally parallel tracks 217 are prerecorded on
strip 215 by laser or photolithography. Data card 211 is preferably a
wallet size card with a width dimension of approximately 54 mm and a
length dimension of approximately 85 mm. These dimensions are not
critical, but preferred because such a size easily fits into a wallet and
has been adopted as a conventional size for automatic teller machines and
the like. Card base 213 is a dielectric, usually a plastic material, such
as polycarbonate, polyvinylchloride or similar material. Card base 213 may
be either opaque or transparent but should have low specular reflectivity,
preferably less than 10%, when used with strips 215 which are reflective
media. Card base 213 must be transparent when used with strips 215 which
are transmissively read. Strip 215 is typically about 10 mm to 35 mm wide
and extends the length of the card. Alternatively, strip 215 may have
other sizes and orientations. The strip may be applied by any convenient
method which achieves flatness and adherence to the card base. A
transparent protective laminating sheet made of polycarbonate plastic or
other material may cover strip 215 to protect it from dust and scratches.
The laser recordable optical data storage material which forms strip 215
may be one of the reflective recording materials which have been developed
having direct-read-after-write capability. Many such materials are known
in the art. Typical recording media used by the assignee are described in
U.S. Pat. Nos. 4,314,260, 4,278,758, 4,278,756, 4,298,684, 4,269,917, and
4,284,716, all assigned to the assignee of the present invention. These
media contain suspensions of reflective metal particles in organic
colloids and form highly reflective low melting temperature laser
recordable media. Data are recorded by forming higher reflectivity spots
which contrast with the surrounding field of the reflective layer itself.
Reflectivity of the strip field of about 10% with a reflectivity of a spot
in the field of more than 50% is preferred, thus creating a contrast ratio
of at least five to one, although a contrast ratio of two to one or even
lower may be sufficient for reading the data. Alternatively, media which
have reduced reflectivity spots in a highly reflective field and media
which are read by light transmission through the card may also be used.
Erasable, direct-read-after-write materials, such as magneto-optic and
amorphous-to-crystalline recording materials, may also be used.
With reference to FIG. 12, data card 211 is seen to have been initialized,
i.e. marked with start and stop marks 219 and 221, so as to demarcate the
ends of the usable recording area 223. Once initialized, a card
writer/reader will not write data too close to a "stop" point for a given
machine. The stop point is determined by the reading and writing optics of
a card writer/reader and may vary for each machine type. Beyond the stop
point, in areas 225 and 227, data writing is either impossible or subject
to an unacceptably high level of read errors. In the event that the stop
point for a particular card writer/reader is sufficiently large to be
beyond an edge of the card, card initialization demarcates the effective
edge of the card. The effective edge of the card need not be identical to
the physical edge of the card. The smaller the distance between the data
areas and the physical card edge, the more accurate must be the cutting of
the card during production. Accurate cutting implies relatively
sophisticated and expensive equipment in addition to a greater number of
rejected cards. Accordingly, depending on the tolerances indicated for a
particular type of card, the effective card edge may be set a certain
distance away from the physical card edge.
Start and stop marks 219 and 221 are laser recorded as a series of lines
across the narrow dimension of the cards. The marks can be continuous as
shown or consist of dashed lines across each track. Prerecorded track
lines 217 generally extend the length of card 211. Initialization may be
performed on a dedicated apparatus or on a data card writer/reader, such
as the apparatus in FIG. 17, with appropriate software. Each start and
stop mark 219 and 221 may comprise one or a pair of parallel lines, as
shown, or a series of lines in a predetermined pattern, as in FIG. 13B.
The pattern forms a code which when read indicates the location of data
areas, i.e. were data are to be written or read. Alternatively, the
pattern may indicate other information, such as the number of data sectors
on a track or the particular data encoding scheme being used.
The position of the start and stop marks 219 and 221 corresponds to the
stop points for a particular card writer/reader, with the edgemost lines
in marks 219 and 221 preferably coinciding with the stop points. The marks
thus define a user recordable area 223 therebetween and nonusable areas
225 and 227 between the start and stop marks 219 and 221 and their nearest
card edge 226 and 228 respectively. On cards which are intended to be
inserted in only one particular direction into a card writer/reader, a
stop mark 221 need not be recorded during initialization. Then the start
mark 219 defines a user recordable area 223 between the mark 219 and the
furthest edge 228. Appropriate track indicia may also be written during
initialization or when the card is being recorded upon by the user.
FIG. 12A shows an enlarged portion of data card 211. Tracks 217 may be
prerecorded either photolithographically, by laser recording, by molding,
or other means. One type of photolithographic prerecording involves
exposing photosensitive material which is to form strip 215 to actinic
radiation through an imagewise pattern on a mask. The material is
subsequently processed to form the strip 215 of laser recordable optical
data storage material. One such photolithographic recording process is
described in U.S. Pat. Nos. 4,304,848 and 4,278,756, assigned to the
assignee of the present invention. As mentioned above, start and stop
marks 219 and 221 are laser recorded across the narrow width of the card.
As seen in FIG. 12A, start mark 219 forms a series of lines recorded
crosswise over the prerecorded tracks.
The user recordable area 223 defined by marks 219 contains laser recorded
spots 229. Spots 229 represent data bits as well as track indicia,
including but not limited to synchronization marks, error codes and track
numbers. Spots 229 are generally greater than about 1 micron in size,
preferably about 2 to 5 microns, but may be any size in the range from
about 1 micron to 35 microns. Spots 229 may be either round or oblong and
are typically recorded in paths between tracks 217 with a separation
dependent upon spot size and code scheme. Tracks 217 are | | |
