Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1998-04-02
2001-02-20
Lee, Michael G (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462250
Reexamination Certificate
active
06189794
ABSTRACT:
BACKGROUND OF THE INVENTION
(1). Field of the Invention
The present invention generally relates to a bar-code reader, and more particularly to a bar-code reader in which the light beam is shaped by using an aperture so that a beam spot is an circle.
In a laser unit used as a light source of a bar-code reader, the laser beam spot is generally elliptically shaped. The laser beam is shaped by using an aperture so that a beam spot of the laser beam is a circle. In this case, the laser beam is diffracted by the aperture (the Fresnel diffraction). The influence of the Fresnel diffraction strongly appears on a part of the laser beam which is located at the upstream side of the beam west of the laser beam.
In recent years, bar-code readers are required to be operated at a high speed and have high performance. A bar-code reader in which scanning beams are output in various directions so that bar codes on articles can be read in various directions has been popularized. To accurately read a bar code, it is necessary to adjust an optical path length of a scanning beam so that a beam west of the scanning beam is located in a reading area in which a bar code should be read.
However, in a case where the scanning beams are output in various directions, it is difficult to adjust the beam west of every scanning beam is located in the reading area in which the bar code should be read. Thus, the parts of some of the scanning beams in which the influence of the Fresnel diffraction strongly appears may be located in the reading area.
(2). Description of the Related Art
FIG. 1
shows a conventional bar-code reader using a differential operation.
Referring to
FIG. 1
, the conventional bar-code reader has a photoelectric conversion unit
201
, an amplifier (AMP)
202
, a differentiating circuit
203
, a peak detecting circuit
204
, a gate generating unit
205
, a black-edge generating unit
206
, a white-edge generating unit
207
, and a B-W width counter
208
. The photoelectric conversion unit
201
converts reflected light from a bar code into electric signals. The AMP
202
amplifies infinitesimal signals into signals which can be processed. The differentiating circuit
203
differentiates the signals generated by the AMP
202
so as to generate differential waveform signals. The peak detecting circuit
204
detects minus and plus peak points of the differential waveform signals. The gate generating unit
205
generates enable signals to cause the peak detecting circuit
204
to detect the peak points. The black-edge generating unit
206
generates edge signals corresponding to the minus peak points detected by the peak detecting circuit
204
. The white-edge generating unit
207
generates edge signals corresponding to the pulse peak points detected by the peak detecting unit
204
. The B-W width counter
208
counts a distance between change points corresponding to the respective edge signals.
The bar-code reader using the differential operation detects peak points of the differential waveform of an electric signal, so that change points between white and black areas of a bar code can be detected. For example, in the bar-code reader as shown in
FIG. 1
, a bar code as shown in
FIG. 4A
is scanned by a scanning beam having an intensity distribution as shown in FIG.
4
D. In this case, the reflected light from the bar code is converted into an electric signal by the photoelectric conversion unit
201
and the AMP
202
amplifies the electric signal so as to generate an electric signal, as shown in FIG.
4
B, which can be processed by a circuit will be described later.
The differentiating circuit
203
differentiates the electric signal generated by the AMP
202
so as to generate the differential waveform signal as shown in FIG.
4
C. The peak detecting unit
204
detects peak points of the differential waveform signal generated by the differentiating circuit
203
so as to obtain change points between black and white areas of the bar code. The peak detecting unit carries out a process for detecting peak points while a gate signal generated by the gate generating unit
205
is in an enable state (e.g., “1”). The gate generating unit
205
checks the differential waveform signal generated by the differentiating circuit
203
. When the level of the differential waveform signal exceeds a specific voltage value, the gate generating unit
205
supplies an output of “1” to the peak detecting circuit
204
. The specific voltage value is set at a value by which the change points can be detected.
In addition, the differential waveform signal generated by the differentiating circuit
203
, as shown in
FIG. 4C
, has plus peak points corresponding to change points at each of which the bar code is changed from the black area to the white area and minus points corresponding to change points at each of which the bar code is changed from the white area to the black area.
When the peak detecting unit
204
detects a peak point of the differential waveform signal, the black-edge generating unit
206
and the white-edge generating unit
207
respectively generate edge signals in synchronism with the minus peak point and the plus peak point. The B-W width counter
208
counts a period of time between times at which the edge signals are generated.
In the conventional bar-code reader, in order to read the bar code, the B-W width counter
208
counts a period of time between times at which the edge signals are generated, that is, the difference between the change points is measured.
However, in the conventional bar-code reader, a part of a scanning beam affected by the Fresnel diffraction so as to have an intensity distribution as shown in
FIG. 5D
may scan a bar code in the reading area. In this case, the intensity distribution of the scanning beam greatly affects the electric signal into which the reflected light from the bar code is converted. In the differentiating operation in which the electric signal generated after the photoelectric conversion of the reflected light is differentiated, the intensity distribution of the scanning beam corresponds to the differential waveform.
That is, when the part of the scanning beam affected by the Fresnel diffraction as shown in
FIG. 5D
scans the bar code as show in
FIG. 5A
, the signal as shown in
FIG. 5B
is generated by the photoelectric conversion unit
201
. Thus, the differential waveform has a plurality of peaks corresponding to edges of stripes of the bar code, so that a plurality of change points for each edge of a stripe are detected.
Thus, due to the influence of the Fresnel diffraction, the true change point and false change points are detected. If the distance between the false change points is measured, the bar code is erroneously read.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to provide a novel and useful bar-code reader in which the disadvantages of the aforementioned prior art are eliminated.
A specific object of the present invention is to provide a bar-code reader in which the true change points corresponding to edges of stripes of a bar code can be detected by use of the scanning beam scanning a bar code in a reading area affected by the Fresnel diffraction can be detected.
The above objects of the present invention are achieved by a bar-code reader having photoelectric conversion means for converting reflected light from a bar code into an electric signal and changing point detecting means for detecting, from the electric signal generated by the photoelectric conversion means, a changing point at which a white stripe is changed to a black stripe in the bar code or a black stripe is changed to a white stripe in the bar code wherein the bar code is read based on a plurality of changing points detected by the changing point detecting means, the bar-code reader comprising: determination means for determining, based on measurement of a distance between changing points, whether a changing point is detected as a true changing point at which a white stripe or a black stripe is changed to a black stripe or a white
Itoh Motohiko
Iwaguchi Isao
Kawai Hiroaki
Satoh Shin-ichi
Watanabe Mitsuo
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Lee Diane I.
Lee Michael G
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