JP5284115B2 - Bar code reader - Google Patents

Description

  The present invention relates to an apparatus for reading bar code information.

  The bar code reader reads the code information by projecting a laser beam or the like onto a bar code composed of a black bar and a white bar, receiving the reflected light, and performing electrical processing. In this electrical processing, a signal processing circuit that converts a barcode reading signal, which is an analog signal photoelectrically converted by the light receiving element, into a digital signal greatly affects the reading accuracy.

  As a conventional signal processing circuit for barcode reading signals, for example, the one shown in FIG. 8 is known. First, the barcode read signal photoelectrically converted in the CCD 101 is amplified in the amplifier 102 and noise is removed in the filter 103. An output signal from the filter 103 is input to a differentiation circuit 105 including a resistor 108 and a capacitor 109 via an operational amplifier 104 that is a buffer, and a threshold signal is generated. A signal from the filter 103 that is directly input to the non-inverting input terminal of the operational amplifier 106 and a threshold signal from the differentiation circuit 105 that is input to the inverting input terminal of the operational amplifier 106 are calculated by the operational amplifier 106 and binarized digital signal. And input to the decoder 107. Then, as shown in FIG. 9, a point at which the threshold signal generated by the differentiation method and the analog signal waveform cross each other is regarded as an inflection point, and this inflection point is regarded as a signal polarity switching edge in the digital signal waveform. Was generated.

  There is also a binarization processing method in which a change point where the shape of the analog signal waveform changes most greatly is obtained, and this change point is used as a switching edge of the digital signal waveform.

  When finding the inflection point or maximum change point of an analog signal waveform as described above, the input analog signal is composed of a signal waveform with less deformation and distortion, and the input analog signal can be accurately converted to a digital signal. Is on the premise.

  However, the bar code reading signal that has been subjected to photoelectric conversion may be greatly affected by the wear or stain of the bar code, the surface irregularity of the article to which the bar code is attached, and the like, and may become a distorted signal. In such a case, even if an inflection point is detected by obtaining a threshold value from an analog signal waveform by a differentiation method, a correct inflection point cannot be detected from a distorted analog signal waveform, and accurate bar code information cannot be obtained. is there.

  In order to solve such a problem, for example, in Patent Document 1, an analog signal composed of a photoelectrically converted barcode read signal is subjected to waveform shaping, converted to a waveform having the same polarity, input to a comparator, and set in advance. When an analog signal is converted into a binary digital signal with a certain threshold, the rising start point and end point of the analog signal waveform from the bottom region and the falling start point and end point of the peak region from the analog signal waveform The inflection point, which is the midpoint between each start point and end point, is obtained, and the obtained inflection point is regarded as a signal polarity switching edge of a binary digital signal waveform and binarized. A method has been proposed.

JP-A-10-293805

  However, even in the signal processing method described in Patent Document 1, when an analog signal composed of a photoelectrically converted barcode read signal is a dull (distorted) signal due to barcode wear or contamination, it is not always necessary. The correct inflection point cannot be detected, and there is a problem that accurate bar code information cannot be obtained.

  Therefore, the present invention has an object to enable accurate reading of barcode information even when the analog signal subjected to photoelectric conversion is a dull (distorted) signal due to barcode wear or dirt. And

  In order to solve the above problems, the barcode reader of the present invention inputs an analog signal composed of a photoelectrically converted barcode read signal to a comparator and compares it with a predetermined threshold value. When the period is longer than the first period (T1) and shorter than the second period (T2) and continuously longer than the threshold, the first digital signal is output, and the analog signal is output from the second period (T2). ) Is a bar code reader that outputs a second digital signal when continuously larger than the threshold value for a longer period of time than the threshold value, and includes a threshold value changing means for changing the threshold value, wherein the threshold value changing means includes the analog When the rising level of the signal waveform reaches the first threshold value (VR1), the first threshold value is applied only during the period not less than the first period (T1) and not more than the second period (T2). And changes to a higher than a second threshold (VR2) VR1).

  According to the present invention, it is possible to suppress detection errors even when an analog signal composed of a barcode read signal subjected to photoelectric conversion is a dull (distorted) signal due to wear or dirt on the barcode. it can.

It is an example of the barcode which concerns on this invention. 1 is a block diagram of a barcode reading apparatus according to a first exemplary embodiment of the present invention. It is a figure for demonstrating the analog output waveform from the amplifier 23, and the digital signal waveform from the conventional threshold value fixed comparator 24. FIG. It is a figure for demonstrating the analog output waveform from the amplifier 23, and the digital signal waveform from the conventional threshold value fixed comparator 24. FIG. It is a figure for demonstrating the analog output waveform from the amplifier 23, and the digital signal waveform from the conventional threshold value fixed comparator 24. FIG. It is a figure for demonstrating the digital signal waveform (B) from the threshold variable comparator 24 in the example of embodiment of this invention. It is a figure for demonstrating the digital signal waveform (B) from the threshold variable comparator 24 in the example of embodiment of this invention. It is a block diagram which shows the processing circuit of the barcode reading signal of a prior art example. It is a figure for demonstrating the signal processing method of a prior art example.

  Hereinafter, embodiments of the present invention will be exemplarily described based on the drawings. However, the specific numerical values and the like described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

(Example embodiment)
FIG. 1 is an example of a bar code label. The bar code label 10 is divided into 25 sections, and is composed of a narrow black bar 11, a wide black bar 12 having a width twice that of the narrow black bar 11, and a space (white bar) 13.

  FIG. 2 is a block diagram of the bar code reader according to the present example. This bar code reader outputs an LO signal (first digital signal) corresponding to the narrow black bar 11 and outputs it to the wide black bar 12. Correspondingly, an HI signal (second digital signal) is output, and a zero signal is output corresponding to the space (white bar) 13.

  First, the barcode label 10 is scanned at a predetermined speed by the photo interrupter 21. The reflected light from the bar code label is read and photoelectrically converted by the photo interrupter 21, noise is removed by the low-pass filter 22, and the analog output signal (A) amplified by the amplifier 23 is input to the comparator 24. In the barcode reader of this example, the analog output signal (A) takes a value of 0 to 5 V, the analog output signal (A) is low when a space (white bar) is detected, and the analog output signal (A) when a black bar is detected. A) is configured to be high.

  On the other hand, a threshold value generated by the microcomputer 25 (or a threshold value generated by a CR circuit or the like from the analog output signal (A)) is input to the comparator 24 and compared with the analog output signal (A) from the amplifier 23. A digital signal waveform (B) having a pulse width corresponding to an amplitude portion equal to or greater than the threshold value of the analog output signal (A) is generated. This digital signal waveform (B) is input to the microcomputer 25. In this example, the microcomputer 25 detects the detection signal of the narrow black bar 11 when the pulse width of the digital signal waveform (B) is longer than 0.5 ms and shorter than 2 ms. When the pulse width of the digital signal waveform (B) is longer than 2 ms, the HI signal is output as the detection signal of the wide black bar 12.

  FIG. 3A is a diagram showing an output waveform from the amplifier 23 and its timing when the uncontaminated barcode is read. When the barcode is not contaminated, the analog output waveform (A) from the amplifier 23 has little distortion rising corresponding to the narrow black bar 11 and the wide black bar 12, as shown in FIG. It becomes a waveform.

FIG. 3B shows the digital signal waveform (B) from the comparator 24 and its timing when the threshold value is set to 1/2 (2.5 V) of the peak value (5 V) of the analog output waveform (A). It is a figure.
As shown in FIG. 3B, when an uncontaminated barcode is read, the pulse width corresponding to the narrow black bar 11 is 1.8 ms, and the pulse width corresponding to the wide black bar 12 is 3.6 ms. Thus, the microcomputer 25 outputs the LO signal corresponding to the narrow black bar 11 and outputs the HI signal corresponding to the wide black bar 12, so that the barcode information can be read correctly.

  However, when the bar code is contaminated with, for example, hand dirt, the analog output waveform (A) from the amplifier 23 becomes unstable, and some narrow black bars 11a as shown in FIG. There is a case where the corresponding waveform is extended. Further, the distance between the barcode and the photo interrupter 21 varies depending on the surface irregularity state of the barcode label, and the wave height corresponding to some narrow black bars 11b becomes lower than usual as shown in FIG. There is.

When the analog output waveform (A) as shown in FIG. 4A is always input to the comparator 24 with a constant threshold value and compared with the analog output waveform (A), the following problems occur.
For example, when the threshold value is set to 1/2 (2.5 V) of the peak value (5 V) of the analog output waveform (A), the digital signal waveform (B) from the comparator 24 becomes as shown in FIG. Although the pulse width corresponding to the narrow black bar 11a exceeds 2 ms and the LO signal should be output originally, the microcomputer 25 outputs the HI signal and cannot read the barcode information correctly.
On the other hand, when the threshold is set high, for example, to about 4/5 (4V) of the peak value (5V) of the analog output waveform (A), the digital signal waveform (B) from the comparator 24 is analog as shown in FIG. Due to the size of the output waveform (A), the pulse width is likely to be uneven, and the pulse width corresponding to the narrow black bar 11b whose wave height is lower than usual may be less than 0.5 ms. The LO signal corresponding to the signal cannot be output, and the barcode information cannot be read correctly.

  Therefore, in the present invention, the analog output signal (A) composed of the photoelectrically converted barcode reading signal is longer than the first period T1 (0.5 ms in this example) and longer than the second period T2 (2 ms in this example). If the first digital signal (LO signal in this example) is continuously output for a shorter period than the threshold, the analog output signal (A) is longer than the second period T2 (2 ms in this example). In the barcode reader that outputs the second digital signal (HI signal in this example) when it is continuously larger than the threshold value, the detection error is suppressed by using the following means.

  That is, in this example, when the rising level of the analog output signal (A) from the amplifier 23 reaches the first threshold value (VR1), the microcomputer 25 is equal to or longer than the first period T1 (0.5 ms) and the second period. The threshold value is changed to a second threshold value (VR2) higher than the first threshold value (VR1) for a period of 2 ms that is equal to or less than T2 (2 ms). Specifically, in this example, the first threshold value (VR1) was set to 2.2V, and the second threshold value (VR2) was set to 3.5V.

  The threshold value in this example for the analog output waveform (A) of FIG. 6A when the uncontaminated barcode is read is as shown in FIG. 6B, and the digital signal waveform (B) from the comparator 24 is As shown in FIG. Thus, the pulse width of the digital signal waveform (B) corresponding to the narrow black bar 11 is 1.7 ms, the pulse width of the digital signal waveform (B) corresponding to the wide black bar 12 is 3.5 ms, and the microcomputer 25 Outputs a LO signal corresponding to the narrow black bar 11 and outputs an HI signal corresponding to the wide black bar 12, so that the barcode information can be read correctly.

  Further, the threshold in this example for the analog output waveform (A) in FIG. 7A when a contaminated barcode is read is as shown in FIG. 7B, and the digital signal waveform (B) from the comparator 24 is as follows. Is as shown in FIG. Thus, the pulse width of the digital signal waveform (B) corresponding to the narrow black bar 11a extended is 1.8 ms, the pulse width corresponding to the narrow black bar 11b whose wave height is lower than normal is 0.7 ms, and normal narrow. The pulse width of the digital signal waveform (B) corresponding to the black bar 11 becomes 1.5 ms, and the microcomputer 25 correctly outputs the LO signal corresponding to all the narrow black bars 11, and corresponds to the wide black bar 12. Since the HI signal is output, the barcode information can be read correctly.

As described above, in the present invention, by changing the threshold value, which is the reference voltage input to the comparator 24, for a predetermined period, reading errors caused by fluctuations (delays) in black bar detection time due to bar code contamination and the like are reduced. can do.
When the rising level of the analog output signal (A) reaches the first threshold value (VR1), the threshold value is set to the first period T1 (0.5 ms in this example) or more and the second period T2 (2 ms in this example). ) Since only the following period is changed, it affects the detection of the wide black bar that is detected when the pulse width of the digital signal waveform (B) is continuously longer than the threshold for a period longer than the second period T2. Without giving it, it is possible to correctly read a narrow black bar that easily causes a detection error.

  In the present invention, if the first threshold value (VR1) is set too low, the digital signal waveform (B) rises even with slight wear or dirt on the barcode, and an error in detecting a nonexistent black bar is likely to occur. If the first threshold value (VR1) is set too high, an error in which a black bar cannot be detected is likely to occur depending on the surface irregularity state of the barcode label. For this reason, the first threshold value (VR1) is preferably set to 2/5 or more and 3/5 or less of the peak value of the analog output waveform (A), and particularly preferably set to about 1/2.

  In the present invention, the second threshold value (VR2) can be arbitrarily set to a value higher than the first threshold value (VR1), but the second threshold value (VR2) is set to the first threshold value (VR1). If the value is set too close to the value, the effect of the present invention is reduced. Therefore, the second threshold value (VR2) is preferably set to 3/5 or more and 4/5 or less of the peak value of the analog output waveform (A). It is particularly preferable to set the threshold value (VR1) and the vicinity of the intermediate value between the peak values of the analog output waveform (A).

  In the present invention, the first period T1 and the second period T2 take values that are appropriately determined by the width of the black bar (or white bar) of the barcode, the scanning speed by the reading device, and the like.

10 Barcode Label 11 Narrow Black Bar 12 Wide Black Bar 21 Photointerrupter 22 Low Pass Filter 23 Amplifier 24 Comparator 25 Microcomputer 101 CCD
102 Amplifier 103 Filter 104 Operational Amplifier 105 Differentiation Circuit 106 Operational Amplifier 107 Decoder 108 Resistor 109 Capacitor

Claims (1)

An analog signal composed of a bar code reading signal that has been photoelectrically converted is input to a comparator and compared with a predetermined threshold value. At least the analog signal is longer than the first period (T1) and longer than the second period (T2). A first digital signal is output if it is continuously longer than the threshold for a short period, and a second is output if the analog signal is greater than the threshold for a period longer than the second period (T2). A barcode reader that outputs a digital signal,
A threshold changing means for changing the threshold;
When the rising level of the analog signal waveform reaches the first threshold value (VR1), the threshold value changing unit is configured to perform the first period only during the period not less than the first period (T1) and not more than the second period (T2). The bar code reader is changed to a second threshold value (VR2) higher than the threshold value (VR1).

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