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Disclosed is a bar code scanner using a holographic disk designed for improved readability of bar code symbols scanned in the "picket fence" orientation.
English (United States)
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Holographic Scanner Design for Reading "Picket Fence" Bar Codes
Disclosed is a bar code scanner using a holographic disk designed for
improved readability of bar code symbols scanned in the "picket fence"
The term "picket fence" describes bar code symbols whose bars are oriented
nominally perpendicular to the direction of symbol motion. The nominal scan line
for reading "picket fence" bar codes sweeps in a direction parallel to the direction
of symbol motion, intersecting all bars in the symbol.
Rotations of the symbol due to positioning tolerances increase the likelihood
that the nominal scan line will not intersect all bars in the symbol. The scan
pattern shown in the figure and described below allows a greater range of symbol
Using well known holographic scanning techniques, a set of scan lines (1) is
projected straight ahead, sweeping parallel to the direction of symbol motion. A
second set of scan lines (2) is projected to the left of the first set of lines. When
intersecting the symbol plane, these scan lines are tilted, sweeping at an angle
relative to the direction of symbol motion. A third set of scan lines (3) is projected
to the right of the first set of lines. These lines tilt in a direction opposite the tilt of
the second set of lines.
The tilted scan lines can read tilted symbols (4) that would be missed by the
nominal, untilted scan lines.