Note: Descriptions are shown in the official language in which they were submitted.
HOLOGRAP~IC SYSTEM FOR GENE~ATING
DUAL SCAN PATTERNS
Technical Field
The present invention relates to optical
scanners and more particularly to a holographic
system for generating dual scan patterns.
Background of the Invention
For sound business reasons, more and more
supermarkets have begun to use bar code scanners
at their checkout stands. Generically speaking,
all such scanners direct a light beam across a
UPC (Universal Product Code) label on a product
being checked and detect variations in the
level of light reflected from the label. The
electrical representation of the detected optical sig-
nal is decoded to establish the digital value of the
UPC label. The digital value is used to access
a lookup table which contains the price and
description of the item carrying the label. The
price and description are used to prepare the custo-
mer rece.pt tape. The ~ame information can be used for
,
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inventory control or other store management
purposes.
One of the reasons for using bar code scanners
in checkout operations is that such scanners can
significantly increase throughput at a checkout
stand when the scanner is operating properly and
is being used properly. However, operators sometimes
fail to use a scanner correctly by not holding a
product in such a way that the UPC label passes
through the region or "gate" required for a
successful scan. This "gate" is, of course,
adjacent the scanner window in the surface of the
checkout stand.
Specific scan patterns have been designed to
make this "gate" as large as possible. Examples of
such patterns include a stitch bar pattern having
several vertical scan lines and a single horizontal
scan line, a lissajous pattern having overlapped,
out-of-phase sinusoids forming side-by-side Xs,
and single or multiple X patterns either with or
without horizontal scan lines.
For any single pattern, the size of the "gate"
established by that pattern is necessarily limited.
This, in turn, places restraints on the checkout
operator who must take the time to be certain that
the UPC label passes the scanner window within this
limited gate.
Summary
To increase the size of the "gate" through which
the UPC label must pass, a scanner built in accor-
dance with the present invention generates at least
two scan patterns which operate with optimum reading
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efficiencies in spatially displaced regions above-the
scanner window. ~~
A scanner constructed in accordance with the
invention includes a rotating circular member with
a plurality of beam-deflecting holographic elements
arranged in a multi-segment annular track. The
holograms are divi~ed into a plurality of sets with
each hologram in each set being capable of focussing
an incident collimated beam of radiation at a pre-
determined distance from the hologram. The scanner
further includes means for directing a collimated
beam of radiation along a predetermined path in-
tersecting with the annular track of holographic
segments. The circular member rotates about a
fixed axis to move each holographic segment through
the path of the collimated beam. The relative
movement of the circular member and the beam causes
the beam to be deflected along a scan line deter-
mined by the function of the segment characteristics.
The scanner further includes an optical system
for redirecting the deflected beams to form a
number of scan patterns equal to the number of
sets of holograms. The scan patterns are spatially
displaced relative to one another.
In one embodiment, the scan patterns are similar
but are focussed in different regions above the
scanner window. In another embodiment, dissimilar
scan patterns are generated.
.
Brief Description of the Drawings
While the specification concludes w~th claims - -
particularly pointing out and distinctly claiming
that which is regarded as the present invention,
further details of preferred embod~ments of the
invention may be more readily ascertained from
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the following technical description when read in
conjuction with the accompanying drawings, wherein:
Figure 1 is a simplified perspecti.ve view
showing the physical relationship between various
components of a scanner constructed in accordance
with the invention;
Figure 2 is a schematic diagram of an optical
arrangement used to generate each holographic seg-
ment or holofacet of a scanner disk employed in
the present invention;
Figure 3 shows various planes in which scan
patterns generated in accordance with one embodi
ment of the invention are to be viewed;
Figure 4 shows one set of scan patterns at
the scanner window;
Figures 5-7 are perspective views of scan traces
and are used to more fully illustrate the three-dimen-
sional configuration of the scan patterns shown in
^ Figure 4;
Figures 8-12 are at least partial views of the
scan pattern taken at various planes de~ined in
Figure 3;
.
~ 30 Figure 13 is a top view showing one arrangement
; of beam folding mirrors for generating the scan
patterns described with reference to the foregoing
figures;
Figure 14 is a perspective view of the beam
folding mirrors;
.
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Flgure 15 is a view of dissimilar scan pattern-s
which can be generated; ---
Figure 16 is a perspective view showing the
three-di~ensional traces of certain of the scan lines
in the pattern illustrated in Figure 15; and
Figure 17 is a top view of a beam folding
mirror arrangement suitable for generating the
pattern shown in Figure 15.
Technical Description
Figure 1 shows the relative physical positions
of major elements of a scan pattern generator con-
structed in accordance with the present invention.
Complex elements, such as sets of beam folding mirrors
or specific scan patterns, are shown only in dotted
box outline in order to simplify the illustration.
These complex elements are described later in more
detail with reference to other figures.
In a preferred embodiment, the beam deflecting
element of the scanner is a rotating glass disk 20
which carries an annular track 22 consisting of
sectorial holographic film segments or holofacets.
Preferably, the holofacets are sealed between two
thin glass disks to prevent ph~sical damage to the
film material.
The light beam which is deflected by the indivi-
dual holofacets in the track 22 is generated by a
conventional laser 24. The laser beam is deflected
through a right angle in a horizontal plane by a
small mirror 26. The beam leaving mirror 26 is
reflected from a larger mirror 28 toward the under-
side of disk 20 along a path intersecting the path
of travel of the holofacets in track 22. While
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the beam which strikes the disk 20 is stationary,
rotation of dis~ 20 causes individual holofacets
to move through the beam at a high speed. The rela-
tive movement between the holofacets and the beam
causes the emerging beam to be deflected along an
arc. Generally speaking, the elevation of the arcu-
ate scan line above the disk surface and the amount
of skew, either forward or backward in the direction
of disk rotation, are dependent upon the characteris-
tics of the individual holofacets. As will be
explained in more detail later, these charac-
teristics are fixed at the time the holofacet
is generated.
The deflected emerging beam is dire~ted into a
set 30 of beam folding mirrors which are located
eccentrically above the disk 20. Specific preferred
arrangements of mirrors will be described later
with reference to Figures 13, 14 and 17. The mirrors
in the set 30 will redirect the deflected beam
through a scanner window 32 in the surface of a
checkout stand (not shown). Normally, items being
processed at the checkout stand would be moved
over the scanner window 32 in the direction
indicated by arrow 34. At least two complete
scan patterns are generated. To increase the
size of the "gate" through which the UPC label
must pass, the first pattern may be focussed
in a region 36 located near the surface of the
scanner window 32. The second scan pattern may
be focussed in another region 38 located further
above the surface of the scanner window 32. The
second region 38 may also be advanced in the direc-
tion of oncoming products depending upon the particu-
lar scan pattern which is employed.
The scanner is preferably a retro-reflective
system in which the light reflected from a label re- -
turns along at least part of the path followed by the-
emerging beam. More specifically, light reflected
from a label would follow a path including scanner
window 32, beam folding mirrors within the set 30,
disk 20 and mirror 28. The beam of returning light
reflected from mirror 28 has a cross-sectional area
substantially larger than the cross-sectional
area of mirror 26. Most of the returning light by-
passes mirror 26 and is focussed by a planoconvex
lens 40 onto a photosensitive element 42 such as a
photodetector or a photomultiplier tube. The function
of the photosensitive element 42 is to generate an
electrical signal having an amplitude which is pro-
portional to the amplitude of the optical signal.
The electrical signal is transmitted to a decoder/
utilization system 44 which performs the conventional
functions of finding and decoding the detected label.
The generated scan patterns are a function of
the paths traversed by the holofacet-deflected beams
and of the particular configuration of beam folding
mirrors within the set 30. The paths which are
traversed by the deflected beams are, in turn, a
function of the characteristics of the particular
holofacet being traversed. These characteristics are
fixed when the holofacet is recorded, preferably in
accordance with an off-axis technique described below
with reference to Figure 2.
The individual holofacets are optical diffrac-
tion gratings formed by interfering two coherent beams
of light at a photosensitive film 46. The film ma-
terial may be a conventional photographic film, such
as a silver halide film, or any other light sensitive
material, such as a dichromated gelatin material. The
light source is a laser 48 which produces a collimated,
coherent light beam 50. The beam 50 is directed to a
beam splitter 52 which reflects one beam component 54
towards a mirror 56 while allowing another beam com-
ponent 58 to continue along its original path toward
a beam expander 60. The expanded, collimated
beam 62 leaving beam expander 60 is directed
onto the photosensitive film 46 as a reference
beam. seam 54 is reflected from mirror 56, and passes
through a beam converging lens 64 to a spatial filter
66. The spatial filter 66 acts as a point source for
a diverging object beam 68 which strikes the photo-
sensitive film 46 in registry with the collimated
reference beam 62. The interference of the two
beams at film 46 creates an optical diffraction
grating which can be developed and fixed by conven-
lS tional techniques.
If the developed film is illuminated with a
collimated reconstructing beam directed along the
path 70 which is opposite to the path o beam 62 as
the film is being moved along an arcuate path ~as
it would be during disk rotation), a substantial
beam component is diffracted along path 68. The
angle ~ between the central axis of beam 68 and a
continuation of the axis of beam 70 is equal to
; 25 the angle between the axes of beams 62 and 68 used
to generate the holofacet.
The diffracted beam 68 is a reconstructed image
of the optical conjugate of the diverging object beam
68 and will converge to a point focus at a distance
from the film 46 determined by the original distance
d between the film 46 and the spatial filter 66. B~v
varying the angle between the reference be`am and the
object beam and by varying the distance d between the
spatial filter 66 and the film 46 when making indivi-
dual holofacets, the beam paths traced by deflected
beams are fixed. The deflected beams strike mirrors
within the set 30 along different lines and are
redirected by those mirrors to generate a desired
scan pattern or patterns. --
Scan patterns are three-dimensional and are
not readily described by normal two-dimensional
drawings. To more fully describe preferred scan
patterns, it is necessary to describe those
patterns as they would appear at various viewing
planes which are defined with reference to Figure
3. That figure shows the scanner win~ow 32 and
the directional arrow 34 indicating the direction
from which label-bearing products approach the
window 32. Scan patterns generated in accordance
with one embodiment are shown in Figure 4 as those
patterns appear on the surface of window 32 when
looking along the direction indicated by arrow
72. The same patterns are also described as
those patterns would appear in four different
planes when viewed along the direction indicated
by arrow 74. Plane P8 (Fig. 8) extends along the center
line of window 32 at a normal to the scanner
surface. Plane P9 (Fig. 9) is also normal to the scanner
surface extending from that surface at the leading
edge of the scanner window 32. Plane P10 (Fig. 10)
extends along a normal intersecting the scanner surface
at a distance on the order of 1"-2" in front of the
leading edge of window 32. Plane Pll (Fig. 11) also
extends along a normal to the scanner surface at a
distance approximately equal to twice the distance
between plane P10 and the leading edge of window 32.
Finally, certain scan lines are shown in Fig. 12 as
they would be viewed along a line 12-12 to illustrate
how corresponding lines in the different patterns are
focussed at different distances from the scanner window
32. Line 12-12 represents a viewing plane which
extends at a normal to the scanner surface at an
angle of '15 relative to the leading edge of the
scanner window.
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When scanner window 32 is viewed from above or
along arrow 72, the scan patterns generated in one
embodiment appear as a number of intersecting lines
and horizontal lines. Referring to Figure 4, two
complete scan patterns are shown. Generally speaking,
the two patterns are similar with each line in one
pattern having a corresponding but displaced line
in the other pattern. The direction of displacement
is not the same for all corresponding lines in both
patterns.
The first pattern consists of scan lines S1-SlO.
Of these, scan lines S1, S2, and S3 are generally
parallel right hand diagonals while scan lines S4,
S5 and S6 are similarly parallel left hand diagonals.
These scan lines are paired (Sl-S6, S2-S5, S3-S4) to
form an interlaced X pattern which covers substantially
all of the scanner window area. This scan pattern
further includes relatively flattened intersecting
scan lines S7 and S8 forming an asymmetric X.
Finally, the pattern includes two horizontal scan
lines S9 and S10 extending paral}el to the leading
and trailing edges of scanner window 32.
The second scan pattern consists of scan lines
Sll-S20. The scan lines Sll, Sl2, Sl3 correspond to
the scan lines Sl, S2, S3 but are displaced toward
the leading edge of window 32 relative to those scan
lines. Similarly, scan lines Sl4, Sl5, and Sl6 corres-
pond to scan lines S4, S5, S6 and are also displaced
towards the leading edge of window 32. In contrast,
scan lines Sl7 and Sl8 are displaced toward the trailing
edge of the window 32 relative to the corresponding
scan lines S7 and S8. The horizontal scan lines Sl9
and S20 in the second of the two patterns are also
displaced toward the trailing edge of window 32 rela-
tive to the corresponding scan lines S9 and SlO in
the first of the two patterns.
ll
While it is a common practice to consider
scan patterns in terms of the two-dimensional
traces which those patterns make at the scanner
window, the traces alone do not clearly define the
three-dimensional scan pattern which is being generated.
For example, scan lines S4, S5, and S6 appear only as
left hand diagonal lines in Figure 4. Referring
to Figure 5, it can be seen that the scan lines in
scanner window 32 represent only two of the three
dimensions traced by the emerging beams.
When viewed in "time~lapse" perspective, scan
lines S4, S5, S6 appear as beams which sweep upwardly
from the scanner window 32 in a vertical fan-shaped
configurations. The fan-shaped beams are shown as
terminating along arcs. These arcs simply repre-
sent the points at which the beams are most
sharply focussed. The beams begin to diverge at
points beyond the arcs. The scan lines Sl-S3 are
described by the same fan-shaped representation as
lines S4-S6. While lines S4-S6 are directed from
right to left, lines Sl-S3 are directed from left to
right.
Figure 6 is a time-lapse representation of scan
lines S7 and S8. Scan line S7 emerges from the scanner
window at an angle of approximately 45 sweeping from
the left hand trailing edge toward the right hand
leading edge of window 32. Scan line S7 is focussed
along a nearly linear arc which is generally parallel
to the scanner window surface. Scan line S8 is
similar to scan line S7 but sweeps from right to
left beginning at the trailing edge window 32.
Figure 7 shows horizontal scan lines S9 and
S10. Each of these scan lines emerges from the
scanner window 32 at an angle of roughly 45.
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Each is focussed along a nearly linear arc which
generally parallels the leading and trailing edges
of window 32 at a uniform distance above the window
surface.
The general three-dimensional configuration
of the scan lines of the second pattern are similar
to those for corresponding lines in the first pattern.
The scan lines in the second pattern are, however,
displaced relative to corresponding lines in the
first pattern and are focussed at different dis-
tances from the scanner window. For example, scan
lines S14, S15, and S16 would be located to the
right of scan lines S4, S5, S6 shown in Figure 5
but would have an arc of focus located further
away from the scanner window in the direction of
arrow 34.
Figures 8, 9 and 11 show various scan lines
in one of the two patterns in the corresponding planes
P8, P9 and Pll defined with reference to Figure 3.
Figures 10 and 12 show certain scan lines in both
of the scan patterns when viewed in plane P10 and
along the vertical plane defined by line 12 12. If
! 25 Figures 8-11 are viewed in se~uence, it will be seen
that the vertical scans Sl-S6 are initially centered
in scanner window 32. As the viewer moves forward
from one viewing plane to the next or toward the
arrow 34, it can be seen that scan lines Sl-S3 shift
to the right as they diverge and become elevated.
Scan lines S4-S6 similarly shift to the left, diverge,
and become elevated. Scan lines S7 and S8 increase
in elevation when viewed in successive planes.
3~ Scan lines S9 and S10 are substantially
parallel to the upper surface of the scanner and
increase in elevation when viewed in successive plançs.
Referring to Figure 10 specifically, the pro-
jected scan lines from the pattern made up of
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scan lines S10-S20 are also shown. ~hose figures show
that the sca~ pattern made up of scan lines S10-S20
is shifted both vertically and horizontally rela-
tive to the scan pattern made up of scan lines Sl-
S10. The relative displacement of the two patterns
increases the size of the "~ate" through which a
UPC label must pass if it is to be successfully
scanned.
Figure 12 shows only certain of the scan lines
from the two patterns. It can be seen that corres-
ponding scan lines are focussed at different horizon-
tal and vertical distances from the leading edge of
window 32, to greatly enlarge the volume which defines
the "gate" discussed above.
Figures 13 and 14 are plan and perspective views,
respectively, of a set of beam folding mirrors which
can be used to generate the scan patterns described with
reference to Figures 4 through 12. The laser light beam
which is reflected from the mirror 28 beneath disk
; 20 impinges on the disk 20 at a fixed point 76. As
each holofacet is rotated through the point of inter-
section, the emerging beam is deflected through an
arc centered on point 76. The elevation and skew
of the arc, as previously discussed, are functions
of the holofacet characteristics. The deflected
beams may strike the same sets of mirrors in
different places to produce parallel scan lines
such as scan lines Sl-S3 or S9, S10. The beams
may also strike different sets of mirrors to produce
intersecting scan lines such as scan lines S7, S8.
The set 30 of beam folding mirrors includes
~ 35 a first triad of mirrors, consisting of mirrors
; ~ 78A, 78B and 78C, located adjacent the edge of
disk 20. The bottom e~ge of each of the mlrrors
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78A-78C is parallel to the surface of disk 20 while
the reflecting surfaces are at an angle of approxi-
mately 135 to the disk surface. A second triad 80A,
80B, 80C of mirrors is located directly above the
surface. These mirrors also have bottom edges parallel
to the disk surface. The set 30 further includes a
long mirror 82 located well above and away from the
surface of the disk 20. The reflecting surface of
the mirror 82 faces downwardly or towards the disk.
The set further includes smaller mlrrors 84A and 84B,
the reflective surfaces of which are at compound
angles relative to the disk surface. Generally speaking,
those reflective surfaces face down and inwardly rela-
tive to the disk. Finally, the set includes two
relatively large mirrors 86A, 86B, the reflective
surfaces of which face the scanner window 32.
The path followed by a deflected beam will
be generally described for various groups of
scan lines making up the previously described
scan patterns. Scan lines S4-S6 are generated by
directing the deflected beam along a beam path 88
including mirrors 84A and 86B. The beam reflected
from mirror 86B is directed upwardly through the
scan window 32. The separation between scan lines
S4, S5, S6 is established by sweeping mirrors 84A
and 86B along spaced parallel lines. The same set
of mirrors is used in generating scan lines S14, S15,
S16 of the second scan pattern.
A complementary set of mirrors is used in
generating scan lines Sl, S2, S3 in the first
pattern and Sll, S12, S13 in the second pattern.
The complementary set consists of small mirror
84B and larger mirror 86A. The beam path is
from the surface of the disk 20 to mirror 84B
to mirror 86A and through the scanner window 32.
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Scan line S7 and its corresponding scan line
S17 in the other scan pattern are generated by
means of mirrors 82, 80C and 78C. The beam path
for both of these scan lines is beam path 90 ~rom
disk 20 to mirror 82 to mirror 80C to mirror 78C
and through the scanner window. Scan lines S8 and
S18 are generated using a complementary set of
mirrors consisting of mirrors 78A, 80A and 82.
The horizontal scan lines S9, S10 and comple-
mentary scan lines Sl9, S20 are generated by
sweeping mirrors 82, 80B and 78B in sequence, as
shown by beam path 92.
Dissimilar scan patterns may be generated
using the holographic disk and sets of beam folding
mirrors to take advantage of the desirable charac-
teristics of each pattern. One such pattern is
shown in Figure 15 as it would appear at the scanner
window. The illustrated pattern is a combination
of a stitch-bar pattern and a double X pattern. The
stitch-bar pattern consists of a horizontal line
S21 and the plurality of upwardly emerging lines S22-
S27 which are generally parallel to the side edges
of a scanner window 94. The second scan pattern
consists of four diagonal scan lines. Scan lines
S28 and S29 can be described as right hand lines,
while scan lines S30 and S31 can be described as
left hand diagonal lines. The scan lines S28
through S31 have the general three-dimensional
configuration described with reference to Figure
6. Scan line S21 would have the same general
three-dimensional configuration as either scan
line S9 or S10 described in Figure 7. The three-
dimensional configuration of scan lines S22-S27
are illustrated in Figure 16. Each of these scan
lines sweeps upwardly from beneath the surface
of scanner window 94.
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~igure 17 is a plan view of a set of beam
folding mirrors suitable for generating the dis-
simllar scan patterns illustrated in Flgure 15.
A number of mirrors in the set occupy the same
relative positions as in the set described with
reference to Figures 13 and 14 since those mirrors
are used to generate the same type of scan lines.
More specifically, the set shown in Figure 17
includes a first triad of mi.rrors 96A, 96B, 96C
and a second triad of mirrors 98A, 98B, 9~C. The illus-
trated set further includes a relatively long hori~ontal
mirror 100. These mirrors are used to generate
the scan lines S21 and S28-S31. The beam path
for generating scan line S21 includes, in sequence,
mirrors 100, 96B and 98B. The beam paths for scan
lines S28 and S29 include, in sequence, mirrors 100,
96C and 98C. Scan lines S30 and S31 are generated
by directing a beam through the sequence of mirrors
100, 96A and 98A.
The set further includes smaller mirrors 102A
and 102Bj the reflecting surfaces of which generally
face down and in toward the surface of a rotating
disk 104. The mirrors 102A and 102B are located
above much larger mirrors 106A and 106B. The
mirror sequence for generating scan lines S22, S23,
and S24 consists of mirror 102B and 106A. The
mirror sequence for generating scan lines S25,
S26 and S27 consists of small mirror 102A and
larger mirror 106B.
A detailed embodiment of the invention has
been described. Variations and modifications in
the embodiment will occur to those skilled in
the art once the invention becomes known to them.
It is intended that the appended claims shall be
construed to include both the detailed embodiment
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as described and all such variations and modifica-
tions which fall within the true spirit and scope
of the invention.
