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Claims  |
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I claim:
1. In a method for identifying objects appearing at random positions, in
random orientations, and at random times on an image window and having, on
a surface facing the image window, an identification in the form of a data
field which includes on at least one data track contrasting symbols and
one or more contrasting line patterns identifying the position and
orientation of the data track, the line pattern being defined by a
plurality of lines with variable spacing and/or line widths, wherein the
window is opto-electronically scanned line-by-line to generate a video
signal which corresponds to a scanned contrast sequence appearing at the
window, the method including, as a first step, detection scanning the
image window in a raster having relatively widely spaced raster lines at
different detection angles .alpha. until the contrasting line pattern has
been intersected by the raster lines at least twice during the last scan;
as a second step determining the position and orientation of the data
track relative to the image window; and, as a third, reading step, readout
scanning the data field in direction of the data track in a reading raster
having a relatively narrow line spacing to read and decode the symbols on
the data track, the improvement comprising:
(a) scanning the raster lines point by point;
(b) during the scanning step continuously counting already scanned raster
lines and already scanned points on the raster lines currently being
scanned to thereby form first and second numerical values which define the
numerical coordinates (x, y) of the raster point currently being scanned
in a corresponding raster-constant numerical coordinate system;
(c) during the last raster scan of the first step and upon simultaneous
identification of a contrasting line pattern storing the selected
detection angle (.alpha..sub.l) and the numerical coordinates (x.sub.p,
y.sub.p) of the point of intersection between raster lines and contrasting
line pattern,
(d) during the second step, determining an angle of intersection .beta.
between the raster lines of the last detection scanning step and the data
track from the stored numerical coordinates (x.sub.p, y.sub.p), and
(e) during the third step, scanning through the reading raster at an angle
equal to the sum of the determined angle of intersection .beta. and the
last selected detection angle (.alpha..sub.l), and reading the contrasting
symbols on the data track.
2. A method according to claim 1, including the step of identifying the
size of the data field with the position of the contrasting line pattern,
spacing adjacent raster lines during detection scanning sufficiently close
in relation to the length of the contrasting line pattern so that a
plurality of raster lines intersect the contrasting line pattern during
its identification, determining in the numerical coordinate system of the
last detection scan and in the numerical coordinate system of the reading
scan the size of the data field from the numerical coordinates, stored at
the end of the first step and corresponding to the points of intersection
between the first and the last raster lines and the contrasting line
pattern, and thereafter limiting the size of the reading raster to about
the size of the data field.
3. In an apparatus for identifying objects appearing at random positions,
in random orientations, and at random times on an image window and having,
on a surface facing the window, an identification in the form of a data
field which includes on at least one data track contrasting symbols and at
least one contrasting line pattern identifying the position and
orientation of the data track, the line pattern being defined by a
plurality of lines, the apparatus including an image window, a vidicon
including a target onto which the image window is projected, the target
being scanned line by line by a deflection system that includes an
electronically rotatable scanning raster, the vidicon emitting as its
output a video signal corresponding to the scanned image field and
sequentially reproducing the contrasting pattern of the scanned lines as a
substantially binary amplitude sequence, a decoder for identifying scanned
contrasting line patterns which characterize the position and the
orientation of the data track, a deflection system having a first
deflection generator for periodically emitting a line deflection signal
for deflection in the x-direction and a second deflection generator for
emitting a line advance signal for deflection in the y-direction after the
line deflection signals for a given raster line have been emitted, pairs
of deflection coils which are offset with respect to each other by
90.degree., the coils being positioned and arranged so that their magnetic
fields deflect a scanning beam of the vidicon, a circuit for
electronically rotating the raster through selected angles, means for
directing the deflection signals to the raster rotating circuit and for
weighting and coupling the signals so that the coils effect the rotation
of the raster through a desired angle, the improvement comprising:
(a) a decoder adapted to identify one or more different contrasting line
patterns and which, upon identification, emits an identification signal
characterizing the respective contrasting line pattern;
(b) a first deflection generator which includes a first counter having a
given pulse frequency and a maximal counting interval, a first digital to
analog converter coupled with the counter for continuously or
incrementally converting the count of the counter into a line deflection
signal which correspondingly increases, proportional to the count,
continuously or incrementally and which is fed to the raster rotating
circuit, the maximal counting interval corresponding to the largest
possible number of raster points on each raster line, successive numerical
counting values of the counter being associated with adjacent raster
points via the line deflection signal;
(c) a second deflection generator which includes a second counter, the
count of which is changed by a predetermined amount when the first counter
reaches the upper limit of its counting interval, a second digital to
analog converter coupled with the second counter for converting the count
of the second counter into a line advance signal which changes
proportional to the count of the second counter and which is fed to the
raster rotating circuit, a control circuit which also receives the line
advance signal for reactivating the first counter after a predetermined
time interval following a change in the count of the second counter, the
largest counting interval of the second counter corresponding to the
largest possible number of raster lines in the raster, successive counts
of the second counter being associated with adjacent lines via the line
advance signal;
(d) a memory for storing the current counts of the first and second
counters as raster-constant numerical coordinates when a raster line
intersects a contrasting line pattern and the decoder identifies the
contrasting line pattern and emits a corresponding recognition signal to
the memory;
(e) the control circuit including means for deactivating the first and
second counters after the contrasting line pattern has been identified a
sufficient number of times and the associated numerical coordinates have
been stored in the memory and identified with the recognized contrasting
line pattern, the control circuit further advancing the detection angle
.alpha. by a given increment .DELTA..alpha. and storing the detection
angle in the memory after the second counter has reached its upper
counting interval and has thereby initiated the last cycle of the first
counter, the control circuit further reactivating the first counter to
commence another detection raster scan when, during the last detection
raster scan, the contrasting line pattern has been identified less than m
times;
(f) the control circuit including a processor for determining the angle of
intersection .beta. between the raster lines of the detection raster and
the data tracks of the data field from the stored numerical coordinates of
the given position of the associated contrasting line pattern on the data
field and the current detection angle .alpha..sub.l, and
(g) means for thereafter reactivating the first and the second deflection
generators for a renewed scan through the reading raster while the reading
raster is rotated by the raster rotating circuit through an angle
corresponding to the sum of the last stored detection angle .alpha..sub.l
and the calculated angle of intersection .beta..
4. Apparatus according to claim 3, wherein the control circuit is defined
by software of the processor.
5. Apparatus according to claim 3 wherein the first counter includes means
for adjusting the upper and lower limits of its counting interval to
thereby correspond the limits to the desired beginning and end of the
raster lines during scanning.
6. Apparatus according to claim 3 wherein the second counter includes means
for adjusting the lower and upper limits of its counting interval to
thereby correspond the limits to a desired group of raster lines that are
to be scanned.
7. Apparatus according to claim 3 wherein the counters are incrementally
advanced, and including means associated with the counters for varying the
increments by which the counters are advanced.
8. Apparatus according to claim 3 including means operatively coupled with
the first and second digital to analog converters for adjusting the line
deflection signal or line advance signal emitted by the respective
converters.
9. Apparatus according to claim 3 wherein the raster rotating circuit
includes a memory for storing the sine and cosine values of all possible
angles of rotation, a digital to analog converter coupled to each output
of the memory, first and second analog multipliers for multiplying the
line deflection signal with the cosine value and the negative sine value
of the angle of rotation supplied by the memory, third and fourth analog
multipliers for multiplying the line advance signal with the cosine value
and the sine value of the angle of rotation supplied by the memory, a
first adding unit coupled with the first and fourth multipliers for adding
their respective outputs, and a second adding unit coupled with the second
and third multipliers for adding their respective outputs, and means for
applying the outputs of the adding units to the respective deflection
coils.
10. Apparatus according to claim 3 including a low-pass filter operatively
coupled with the input of the deflection coils. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a method for identifying objects appearing at
random positions, in random orientations, and at random times on an image
window and having, on a surface facing the image window, an identification
in the form of a field which includes on at least one data track
contrasting symbols and a plurality of given contrasting line patterns, or
a product identification code (PIC). The latter identifies the position
and orientation of the data track(s) and comprises a plurality of lines
having a variable line spacing and/or line widths. In use, the image
window is opto-electronically scanned line-by-line and a video signal is
generated which reflects to the scanned contrast sequence.
In a first method step, the image window is scanned in a fixed or
stationary detection raster configuration (hereinafter simply "raster")
and, upon identification of the individual contrasting line patterns,
their position or orientation within the detection raster is determined.
In a second method step, the angle .beta. at which the data tracks(s) and
the lines of the detection raster intersect is determined. In a third
method step, sometimes referred to as the reading step, the data field is
scanned in direction of the data track(s) in a readout raster which is
rotated by the angle .beta. to thereby read and decode the symbols or
indicia on the data track(s). Alternatively, the the detection raster is
rotated in predetermined angular increments .DELTA..alpha. and scanned.
The readout raster is then rotated in direction of the data track(s) by
the angle .beta. and the angular increments .DELTA..alpha..
Such method and apparatus are already known. The objects to be identified
are, for example, commercial products, department store articles or the
like which bear machine readable markings. For this purpose, appropriate
identifications are applied to the objects by imprinting thereon a desired
code, for example the well-known OCR code. The encoded information may
relate to the quality, size, price, the number of articles, and the like
and is applied to the surface of the goods in any desired manner.
It is difficult to machine read such information since the objects vary in
size and since the information is frequently printed on adhesive labels
which are applied to the article at random locations. Therefore, it cannot
be assumed that the information is present at a specific location with a
fixed orientation and at predetermined time intervals. Thus, the reading
of such codes cannot be compared with the reading of punched cards or the
like, where a card is available in a precisely defined position at
precisely fixed times. In the present case, the exact opposite applies.
The data field on the object appears with only rough approximation at a
specific place, and the orientation of the data field is relatively
arbitrary.
Such methods and apparatus for the identification of objects are used, for
example, at the check-out counters of supermarkets and the like in order
to identify the price and/or the number of articles which a customer
wishes to buy and which he has brought to the counter for this purpose.
The articles, such as boxes of varying shapes and sizes, bottles, cartons,
cans, and the like, are then placed individually over an image window with
the surface bearing the data field directed toward the window. The data
fields on the various objects thus appear in variable orientations at
differing locations within the image window. The data fields also do not
appear at the scanning station at fixed time intervals. Thus, the scanning
station must be able to search for the data field and, once found, must
read the data track symbols in the direction of the data tracks of the
field. The read symbols can then be fed to the cash register in the form
of electric impulses so that the register can print out on the receipt the
price, the number of the articles, its classification, etc.
The data field applied to the article includes a contrasting line pattern
or product identification code ("PIC") which is formed by a plurality of
parallel lines of varying spacing and/or line width. The contrasting line
pattern reliably and clearly distinguishes the data field, for example the
printed label, from other indicia or line patterns which may be present on
the object in the vicinity of the data field. Further, within the data
field the contrasting line patterns have given positions and orientations
which can be used to ascertain the position and orientation of the data
tracks relative to the raster lines in order to subsequently generate a
raster in direction of the data tracks so that the symbols on the data
tracks can be read.
German Offenlegungsschrift No. 2,338,561 discloses a method and an
apparatus of the above described type wherein the identification of the
contrasting line pattern occurs only when the lines of the pattern are
oriented substantially perpendicularly to the scanning direction and the
resulting pulse sequence of a video signal generated thereby equals a
predetermined pulse sequence which corresponds to the contrasting line
pattern used. Thus, the disclosed method is a correlation method. In the
method and the corresponding apparatus described in the German
Offenlegungsschrift the line deflection signal is a constantly and
linearly ascending saw tooth signal which results in a constant scanning
of the individual raster lines. The relative position of the contrasting
line pattern--and thereby of the data tracks--to the raster lines is
determined by storing the amplitudes of the line ramp generator and the
line advance ramp generator for the point of intersection between a raster
line and the contrasting line pattern, when the latter has been recognized
by the PIC decoder. The detection operation is continued until at least
two points of intersection A, B appear between the raster lines and the
contrasting line pattern. The relative angular position between the
contrasting line pattern and the raster lines can be calculated on an
analog basis from the amplitude coordinates of the points of intersection.
Storage of the analog amplitude signals for the points of intersection
between the raster lines and the PIC for the subsequent analog calculation
of the relative position of the PIC--and of the data tracks--is
cumbersome. It is also disadvantageous because in addition to the line
pulse counters for identifying the PIC, suitable analog circuits are
required. Finally, the stored analog amplitude values are subject to time
and heat drift, and there is no assurance for an accurate correlation
between the line deflection voltage, which constantly varies in time, with
specific points of intersection within the line raster. Thus, the
determination of an angle between the raster lines and the contrasting
line pattern or the data tracks lacks accuracy.
SUMMARY OF THE INVENTION
In contrast, it is an object of the invention to provide a method and an
apparatus of the above described type which enable a rapid and reliable
scanning of the data field and a precise and reliable determination of the
angle between the raster lines and the contrasting line pattern during the
detection step. This assures during the subsequent reading operation that
the contrasting symbols on the data tracks are correctly read.
This object is achieved in accordance with the invention with the method of
the above described type wherein:
(a) each contrasting line pattern has lines which are closed within
themselves and extend at a constant spacing between them;
(b) during scanning through, the lines which have already been scanned are
counted and are available as a first count, and a second count
proportional to the length of the currently scanned track is generated and
available, the two counts representing the "actual coordinates" (x, y) of
the currently scanned raster point in a corresponding raster-constant
numerical coordinate system;
(c) the numerical coordinates (x.sub.p, y.sub.p) corresponding to the
points of intersection between raster lines and contrasting line patterns
(PIC) are stored while scanning through the detection raster when the
respective contrasting line pattern (PIC) is simultaneously identified;
and
(d) in the second method step, the raster-constant central coordinates
(x.sub.z, y.sub.z) of the contrasting line pattern are calculated from the
stored numerical coordinates (x.sub.p, y.sub.p), and the angle of
intersection .beta. between the lines of the detection raster and the data
track(s) is calculated from the central coordinates (x.sub.z, y.sub.z).
An alternative embodiment of the invention step (a) provides that a
contrasting line pattern of a first type defined by parallel lines is
imprinted on the data field and given a first line spacing sequence in a
first direction, and a contrast line pattern of a second type--also of
parallel lines--is imprinted and given a second line spacing sequence in a
second direction. After completion of steps (b), (c), the angle of
intersection .beta. between the raster lines of the detection raster and
the track(s) of the data field are calculated pursuant to method step (d)
from the stored numerical coordinates (x.sub.p, y.sub.p).
A further alternative embodiment of the invention provides at least one
given contrasting line pattern (PIC) of a plurality of parallel lines on
the data field. In a first step, the detection operation, the field is
scanned in a raster having a relatively large line spacing and at varying
angles until the contrasting line pattern or patterns is or are
intersected by at least two raster lines and thereby is or are identified.
In a second step, the data field is calculated from the angle of
intersection between the raster lines of the last scan through the
detection raster and the data track(s). In a third step, the field is
scanned in a reading raster with a relatively small or narrow line
spacing. The reading raster is oriented so that its lines are at an angle
which is equal to the sum of the calculated angle of intersection .beta.
and the last-adjusted detection angle .alpha..sub.l.
The invention also provides an apparatus for practicing the above outlined
method of the invention.
An advantage of the invention is that both a line deflection and a line
advance signals are generated by a digital counter followed by
digital/analog converters (DAC) so that, in addition to an incremental or,
alternatively, a continuously rising line deflection and line advance
signal, corresponding counts or numerical values are available which
define the currently scanned raster point.
The counts form a raster-constant numerical coordinate system, so that the
currently scanned raster point is always available as a digital number in
both counters. The coordinates of the point of intersection required for
determining the angle .beta. between the raster lines and the contrasting
line patten (PIC) are therefore available in digital form when a PIC is
identified and can be stored for further processing. A precise and
reliable identification of the required coordinates of the point of
intersection in digital form is therefore possible--without further
electronic devices--merely from the deflection generators. The angle
between the PIC and the raster lines can then be digitally determined with
great precision and the raster can be precisely adjusted for the reading
of the data tracks, thus reducing the probability of errors during readout
of the symbols in the data tracks.
In a particularly preferred embodiment, the DAC which follows the first
counter converts the count of the latter into a line deflection signal
which advances as a function of time incrementally or continuously, and
makes possible a point-by-point scanning of the raster lines.
The contrasting line pattern comprising a plurality of closed lines
extending at a constant spacing from each other are preferably concentric
circular lines. This form has the advantage that the contrasting line
pattern can be scanned and identified at an angle. In particular, with
this type of contrasting line pattern it is possible to calculate in a
simple manner the center coordinates of the contrasting line pattern with
a substantially central scan. Once the central coordinates of the
concentric contrasting line patterns imprinted on the data field are
known, the orientation of the data tracks relative to a straight line,
which is determined by the center coordinates of the line patterns, can be
calculated in a second step. Most preferred is the provision of three
circular concentric line patterns arranged on a straight line in the data
field so that the orientation of this straight line can be determined
redundantly.
If, on the other hand, an image field projected onto a target is scanned in
a detection raster the angular orientation of which is incrementally
varied, it is preferred to employ a contrasting line pattern (PIC) having
a plurality of straight lines of variable width and spacing for
determining the position and orientation of the data tracks.
In the third method step (reading step) the raster is of a smaller size as
compared to the raster employed in the first method step (detection step).
The raster size is adapted to the data field to be read out and has the
greatest possible raster line density. This enables the scanning of the
data field during the reading step in the shortest possible time.
It is particularly preferable that the length of the individual contrasting
line patterns or their spacing also defines the size of the data field.
For this purpose, a plurality of line patterns of a given size may for
example be imprinted ahead of and behind the data tracks. The spacing
between adjacent raster lines in the detection operation is sufficiently
small so that during passage of the last scan through the detection raster
a plurality of raster lines intersect the contrasting line pattern or
patterns. The center coordinates of the contrast line patterns--and
thereby the length or size of the data field--are then calculated in the
numerical coordinate system of the last detection raster from the
numerical intersection coordinates. The length of the data field is
subsequently calculated in the numerical coordinate system of the reading
raster which is rotated relative to the detection raster by the angle of
intersection .beta.. The reading raster is thereupon limited to about the
size of the data field. For this purpose, the lower and the upper limits
of the count interval of first and the second counters are set to value
correspond to the size of the data field.
Alternatively, only one contrasting line pattern with parallel lines of a
given length is used, from which the length of an edge of data field to be
scanned can be determined. The length of the other side of the data field
is then predetermined.
The contrasting line pattern is then, for example, in front of or behind
the data tracks and extends prependicular with respect to the data tracks
(FIGS. 8, 10 and 11). Alternatively, the contrasting line pattern is
located beneath the data tracks and extends parallel to them (FIG. 9).
If, according to another embodiment of the invention, contrasting line
patterns of the first and second type having a first and a second line
spacing sequence of parallel lines are used, a contrasting line pattern of
the first type preferably extends parallel to the data track of the data
field, and the contrasting line pattern of the second type is
perpendicular to the data track. At least one contrasting line pattern of
the first type and one contrasting line pattern of the second type are so
long that, during scanning through the detection raster, they are
intersected by at least two raster lines so that the direction of the line
patterns can be calculated from the coordinates of the point of
intersection between the raster lines with the line patterns.
A line pattern of the second type is preferably disposed directly ahead of
a line pattern of the first type. In addition, or alternatively, a further
line pattern of the second type is disposed immediately behind the line
pattern of the first type. All three line patterns extend over a given
distance perpendicular to the data tracks. The length of the line pattern
of the first type preferably corresponds substantially to the length of
the data tracks. Alternatively, the line patterns of the second type may
also be disposed beneath the line pattern of the first type. With such a
length and arrangement of the line patterns, at least one line pattern of
the first or second type is intersected by at least two raster lines
during scanning through the detection raster. The coordinates of the point
of intersection can thereby be determined and they are sufficient for
calculating the orientation of the respective line patterns and thereby
also of the orientation of the data tracks. A particular advantage of the
above arrangement is that the data tracks are free of line patterns, so
that the eye of an observer can readily recognize the symbols contained in
the data tracks.
In another embodiment of the invention, the contrasting line patterns of
the first and of the second type--which have parallel lines extending
perpendicularly to each other--are alternatingly disposed in a contrasting
line pattern track. The orientation of this track relative to the data
track or tracks is known and the line pattern track preferably extends at
a given distance beneath the data tracks. The length of the contrasting
line patterns is such that during scanning through the detection raster
each line pattern is at least once intersected by a raster line. The angle
of intersection between the raster lines of the detection raster and the
data tracks is calculated from the stored numerical coordinates when at
least all line patterns of the first type or all line patterns of the
second type are intersected within the contrasting line pattern track.
Numerical coordinates of the points of intersection are stored and can be
used for determining the presence and the direction of the line pattern
track. It is an advantage that the individual contrasting line patterns
can be relatively small, that only one line pattern track is present
beneath the data tracks so as to not impair the legibility of the symbols
on the data tracks, and, particularly, that the orientation of the
contrasting line pattern track can be determined with a high degree of
redundancy since either all line patterns of the first type or all line
patterns of the second type are intersected at an angle which is larger
than 45.degree.. In such an arrangement, the entire contrasting line
pattern is of about the same size as a single line pattern of relatively
long lines located beneath the data tracks. Because of the perpendicular
line patterns of the first and second type alternate, the group of line
patterns of the first type or the group of patterns of the second type are
always precisely identified on the image screen irrespective of the
orientation of the data field and without the need for rotating the
detection raster incrementally relative to the data field.
During reading the raster line density is preferably as high as possible.
For this purpose, the incremental advance of the second counter is at the
lowest possible value, the value 1. The increments of the line advance
signal thereby have the smallest possible value which insures a line
advance from one line to the next adjacent one.
In contrast, during the detection operation, the increment of the second
counter preferably has a relatively high value, for example the value 10.
The incremental line advance signal thereby has the tenfold value as
compared with the reading operation, so that at the end of a line a jump
of ten lines is made, that is, only each tenth line is scanned.
The raster rotating circuit preferably has a read-only memory (ROM) which
stores the sine and cosine values of all possible angles of rotation. Each
output of the ROM is applied to a digital-analog converter. The raster
rotating circuit further has a first analog multiplier which multiplies
the line deflection signal with the cosine of the desired angle of
rotation, a second analog multiplier which multiplies the line deflection
signal with the negative sine of the angle of rotation, a third analog
multiplier which multiplies the line advance signal with the cosine of the
angle of rotation, and a fourth analog multiplier which multiplies the
line advance signal with the sine of the angle of rotation. The output of
the first and fourth multipliers is added in a first adding unit and the
sum is fed to the first output of the raster rotating circuit. The output
of the second and third multipliers is added in a second adding unit and
its sum is fed to the second output of the raster rotating circuit. In
this embodiment it is of particular advantage that the cosine and the sine
of all desired angles of rotation are stored in a memory and can be read,
for example by a central processor, into the raster rotating circuit.
Thus, the digital storage of the required sine and cosine values makes a
precise rotation of the raster possible.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a first embodiment of a data field with three identical,
self-enclosed contrasting line patterns;
FIG. 2 shows a second embodiment of the data field having a plurality of
different contrasting line patterns;
FIG. 3 shows a third embodiment of a data field with two different
contrasting line patterns which precede and follow a data track;
FIG. 4 shows a fourth embodiment of a data field having a contrasting line
pattern track defined by alternating contrasting line patterns of a first
and of a second type;
FIG. 5 is a block diagram of an apparatus constructed in accordance with
the present invention;
FIGS. 6a and 6b are a schematic representation of a scanning raster rotated
in a stationary coordinate system;
FIGS. 7a and 7b are a block diagram of a deflection system of the apparatus
of the invention;
FIG. 8 shows a fifth embodiment of a data field having a contrasting line
pattern of parallel lines;
FIG. 9 shows a sixth embodiment of a data field having a contrasting line
pattern of parallel lines;
FIG. 10 shows a seventh embodiment of a data field having a contrastiing
line pattern of parallel lines and two data tracks; and
FIG. 11 shows an eighth embodiment of a data field having two parallel
contrasting line patterns of parallel lines and a data track.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 4 show a variety of identifications 70, for example price tags
which may be affixed to containers, packages, a product, paper, forms or
the like. They appear in random positions and orientations on an image
window 2 of a vidicon 3, see FIG. 5.
The identifications 70 define a data field which includes contrasting
symbols 72 in at least one data track 71 for identifying the object or
article to which it is applied. The contrasting symbols are preferably
optical character signals of one of the known, machine readable types as
OCR-A or OCR-B characters.
A plurality of contrasting line patterns 74, 75, 76, hereinafter sometimes
referred to as product identifying code, or PIC, are disposed on the data
field in predetermined positions and orientations relative to the data
track. The PIC comprises a plurality of lines having a given line spacing
and a given line width and positioned adhead, beneath, above, or behind
the data track or tracks.
FIG. 1 shows three identical PIC patterns 74 of concentric circular lines
having differing widths and which are disposed beneath the data track 71.
Alternatively, the line patterns can have a rectangular, square,
triangular or similar shape. However, as compared with other closed PIC
patterns, the circular shape shown in FIG. 1 is advantageous because when
it is scanned in a raster having raster lines 80 the relative position of
the data field 70 is of no effect. Thus, the central coordinates of the
PIC patterns 74 are readily calculated from the coordinates of the points
of intersection which can then be stored in the circuitry shown in FIG. 5.
A straight connection line 73 between the two outer PIC patterns 74--and
thereby also the angle .beta. between the raster lines 80 and the
connection line--can then be calculated. According to FIG. 1 the
connection line 73 is parallel to the data track 71. Thus, the relative
position of the data track 71 in the coordinates system of the detection
raster is also known, which permits the subsequent rotation of the raster
as may be required.
FIGS. 2 to 4 show data fields having a variety of PIC patterns of parallel
lines with differing line spacings and line widths. FIG. 2 illustrates a
contrasting line pattern of the first type 74, located beneath the data
track 71, followed by a contrasting line pattern of a second type 75,
which in turn is followed by a contrasting line pattern of a third type
76. The line patterns of the first and third types 74, 76 extend
perpendicularly to the direction of the data track 71 and the line pattern
of the second type 75. This arrangement of the PIC patterns has the
advantage that raster lines 80 will normally intersect the line pattern 75
with sufficient frequency that they can be identified. The points of
intersection are stored for the subsequent determination of the
intersection angle .beta.. In the event the angle .beta. is so small that
the raster lines 80 fall to intersect the PIC pattern 75--that is, in the
event the raster lines are substantially parallel to the lines of the PIC
pattern 75--the raster liines will intersect the pattern lines of the
first and third type 74, 76 at a relatively large angle. Thus, so long as
the PIC pattern 74, 76 has a sufficient minimum length it will be
identified.
FIG. 3 shows a contrasting line pattern of the first type 74 ahead of the
data track 71 and a contrasting line pattern of the second type 75, which
is parallel to the data track, in the lower corner of the data field 70.
This arrangement of PIC patterns also insures that at any random position
of the data field 70 one of the PIC patterns 74, 75 will be intersected by
a sufficient number of raster lines to assure the identification of the
relative position and orientation of at least one PIC pattern. From that
the necessary intersection angle .beta. can be calculated in the
raster-constant coordinate system.
FIG. 4 shows a further arrangement of contrasting line patterns in a
contrasting line pattern track 73a beneath and parallel to data track 71.
Contrasting line patterns of the first type 74 comprising a plurality of
parallel lines extend perpendicularly to data track 71 and they alternate
with contrasting line patterns of the second type 75, the lines of which
are parallel to the data track. The PIC patterns 74, 75 have a sufficient
length so that during scanning through the detection raster each PIC
pattern 74, 75 is intersected by at least one raster line. In an
exceptional case when the raster lines are substantially parallel to the
track 73a, each PIC pattern of the first type 74 is intersected, and the
corresponding coordinates of the intersection are stored. Conversely, when
the raster lines are substantially perpendicular to track 73a, all PIC
patterns of the second type 75 are intersected by them and the coordinates
of these intersection points are stored. In all other cases the PIC
patterns of the first type 74 as well as the PIC patterns of the second
type 75 are intersected. In all cases, a sufficient number of intersection
coordinates are available for calculating the track direction 73a and
thereby the intersection angle .beta. between the raster lines and the
data track 71. The arrangement of FIG. 4 has the advantage that the
direction of the track 73a and thereby the needed intesection angle .beta.
can be calculated with a high degree of redundancy. Further, the uniform
appearance of the PIC patterns beneath the data track 71 does not
interfere with the visibility of the symbols on data track 71.
Although the drawings only show PIC patterns having three lines, PIC
patterns having more than three lines can also be used. Further, the PIC
patterns can be arranged in positions and in orientations relative to the
data tracks which vary from what is shown in FIGS. 1-4. It is equally
possible to use PIC patterns with lines which are parallel to each other,
curved or undulated, although their i | | |
