JPH07234913A - Bar code reader - Google Patents

Abstract

PURPOSE:To prevent the read error of a bar code from occurring. CONSTITUTION:The detection signal level for a thin bar or space of the detection signal of the bar code 14 outputted from a phototransistor 16 is decreased due to the low resolution of a sensor part, etc. The cutoff frequency and the slope of attenuation characteristic of a high-pass filter 24 are set so as to supply a high gain to a comparatively high frequency equivalent to the width of the thin bar or space, and to supply a low gain to a comparatively low frequency equivalent to the width of a thick bar or space. Therefore, the fluctuation of a detecting level due to the difference of thickness of the bar or space can be compensated by passing the detecting output of the phototransistor 16 through the high-pass filter 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bar code reading device for reading a bar code and prevents reading errors.

[0002]

2. Description of the Related Art As is well known, a bar code is a combination of a bar having a different thickness and a space in which numbers and characters are expressed in a machine-readable form.

A conventional bar code reader for reading a bar code is shown in FIG. The light 12 emitted from the light emitting diode 10 is projected on the barcode 14, and is scanned manually or automatically. The reflected light 12 ′ is received by the phototransistor 16. The received light signal output from the phototransistor 16 has its direct current component removed by the coupling capacitor 18 and is amplified by the amplifier 20.
Entered in. The comparator 22 compares the output signal of the amplifier 20 at a constant threshold level, binarizes it, and outputs it.

FIG. 3 is a waveform diagram of the portions shown in (a) to (d) of the circuit of FIG. The light reception signal (a) output from the phototransistor 16 is a signal in which an AC component due to a bar code is added to a DC component. The magnitude of the DC component varies depending on the phototransistor 16 used,
Since it fluctuates due to temperature, aging, ambient light intensity, etc., if the received light signal (a) is directly compared with a predetermined threshold level, the barcode information may not be correctly detected. Therefore, the phototransistor 1
By inserting the coupling capacitor 18 on the output side of 6,
As shown in (b), the DC component is removed and the AC component, that is, the barcode component is extracted. The amplifier 20 is driven by, for example, a single power source of +5 V, amplifies the + side waveform of this AC component, and outputs the waveform as shown in (c). Comparator 2
2 corresponds to a bar code by comparing this signal with a predetermined threshold level.
The binary signal of (d) is output.

[0005]

The bar code reader is
The signal changes only when the barcode is being detected,
Others are constant levels, so coupling capacitor 1
If the DC is simply cut in step 8, the result shown in Fig.
As shown in, since the DC level changes gradually, a part of the bar code information may be lost and a read error may occur. Further, when the resolution of the sensor portion (the portion from the light emitting diode 10 to the phototransistor 16) is low, or when the bar code 14 is printed small in size, the received light signal is as shown in FIG. 4 (a). , The signal level does not fall completely in the thin bar portion, and the signal level does not rise completely in the thin space portion. For this reason, the received light signal level may fluctuate greatly, and as shown in FIG. 4D, a part of the bar code information may be further lost, resulting in a reading error.

The present invention intends to solve the above problems in the prior art and to provide a bar code reading apparatus which prevents reading errors.

[0007]

The invention according to claim 1 is
The light emitting means, the light receiving means for receiving the light emitted from the light emitting means and reflected by the bar code, and the gain for the frequency corresponding to the width of the thin bar or space of the bar code with respect to the light receiving output of the light receiving means. And a gain giving means for giving a gain by making it larger than the gain for a frequency corresponding to the width of a thick bar or space.

According to a second aspect of the present invention, the gain imparting means is composed of a high-pass filter or a band-pass filter, and the frequency corresponding to the width of at least the thickest bar or space of the bar code is the filter. It is characterized in that the cutoff frequency on the low frequency side of the filter and the slope of the attenuation characteristic are set so as to be on the slope of the attenuation characteristic on the low frequency side.

The third aspect of the present invention is characterized in that the high-pass filter is an RC first-order high-pass filter.

[0010]

According to the invention described in claim 1, for the light receiving output of the light receiving means, the gain for the frequency corresponding to the width of the thin bar or space of the bar code and the gain for the frequency corresponding to the width of the thick bar or space are set. Since the gain is given by making the gain larger than that, it is possible to compensate the fluctuation of the received light signal level due to the thickness of the bar or the space even if the resolution of the sensor unit is low. Further, the above-mentioned slow fluctuation of the DC level does not occur when the coupling capacitor is used. Therefore, this can prevent read errors.

According to a second aspect of the present invention, the gain applying means is constituted by a high-pass filter or a band-pass filter, and the frequency corresponding to the width of at least the thickest bar or space in the bar code is The cutoff frequency on the low frequency side of the filter and the slope of the attenuation characteristic are set so that they are on the slope of the attenuation characteristic on the low frequency side of the filter. You can

Then, the high-pass filter can be simply constituted by an RC first-order high-pass filter, as in the invention described in claim 3, for example.

[0013]

FIG. 1 shows an embodiment of the present invention. The light 12 emitted from the light emitting diode 10 as the light emitting means is
It is projected on the barcode 14 and scanned manually or automatically. The reflected light 12 'is received by a phototransistor 16 as a light receiving means. The received light signal output from the phototransistor 16 passes through the high pass filter 24, is amplified by the amplifier 20, and is input to the comparator 22. The comparator 22 compares the output signal of the amplifier 20 at a constant threshold level, binarizes it, and outputs it.

The high-pass filter 24 may be either a passive filter or an active filter, but in the simplest case, it can be constituted by an RC filter in which a capacitor 26 and a resistor 28 are combined as shown in FIG. .

FIG. 6 shows a characteristic example of the high-pass filter 24. Here, the cutoff frequency is set so that the frequency f1 corresponding to the width of the thinnest bar or space of the bar code is the frequency at which the attenuation starts, and the slope slope of the attenuation characteristic is appropriately set, The frequency difference f2 corresponding to the width of the thick bar or space is set on the slope of the attenuation characteristic, and the gain difference between the two is set to 3 dB. As a result, it is possible to compensate for variations in the received light signal level due to the thickness of the bar or space due to low resolution of the sensor unit (the portion from the light emitting diode 10 to the phototransistor 16). Specifically, in the case of a bar code in which a bar and a space are indicated by two types of thickness, the high-pass filter 24 can be configured by an RC first-order high-pass filter, and the cutoff frequency in that case is, for example, 340 Hz ± 20%. (Slope slope-6 dB / oct) can be set.

FIG. 7 is a waveform diagram of the portions shown in (a) to (d) of the circuit of FIG. The received light signal (a) output from the phototransistor 16 is a signal in which the DC component is an AC component due to a bar code. Due to the low resolution of the sensor part, the signal level of the received light signal does not drop in the thin bar part, and the signal level does not rise in the thin space part.Therefore, the signal level becomes large due to the thickness of the bar or space. It is fluctuating.

When this received light signal is passed through the high-pass filter 24, the output thereof has a direct current component removed as shown in (b), and the signal level due to a wide bar or space is attenuated, so that (a). The fluctuation of the signal level of is compensated. Therefore, the output of the amplifier 20 is as shown in (c) (when driven by a single + power supply), and the level of the portion corresponding to the narrow space can be sufficiently high. Therefore, if this is compared in the comparator 22 at a constant threshold level, an output corresponding to the barcode 14 exactly as shown in (d) can be obtained.

Either the amplifier 20 or the comparator 22 may be provided depending on the output signal level of the high-pass filter 24 and the characteristics of the input of the next stage for inputting the output (d) of the circuit of FIG. . That is, the output signal level of the high-pass filter 24 is the same as that of the comparator 22.
If the size is such that the logical levels of "1" and "0" can be correctly determined even when they are compared with each other, the amplifier 20 is unnecessary. Further, if the output signal of the amplifier 20 is input to the logic circuit of the next stage as it is, the comparator 22 is not necessary as long as it is properly converted into the logic level of "1" or "0".

Further, in the characteristics of FIG. 6, the attenuation is started from the frequency corresponding to the thinnest bar or space, but the attenuation start frequency can be set lower or higher than this. Further, in the above-described embodiment, the gain applying means is composed of a high-pass filter, but it may be structured as a band-pass filter also having a function of removing noise by cutting the high frequency side of the bar code frequency band together. Further, the present invention can be applied to bar code readers of various types such as a hand type, a stationary type and the like.

[0020]

As described above, according to the first aspect of the invention, the gain for the frequency corresponding to the width of the thin bar or space of the bar code is increased with respect to the light output of the light receiving means. Since the gain is applied by making the gain larger than the gain corresponding to the frequency corresponding to the width, it is possible to compensate the fluctuation of the received light signal level due to the thickness of the bar or the space even if the resolution of the sensor unit is low. Further, the above-mentioned slow fluctuation of the DC level does not occur when the coupling capacitor is used. Therefore, this can prevent read errors.

According to the second aspect of the present invention, the gain applying means is constituted by a high-pass filter or a band-pass filter, and the frequency corresponding to the width of at least the thickest bar or space in the bar code is The cutoff frequency on the low frequency side of the filter and the slope of the attenuation characteristic are set so that they are on the slope of the attenuation characteristic on the low frequency side of the filter. You can

Then, the high-pass filter can be simply constructed by an RC first-order high-pass filter, as in the invention described in claim 3, for example.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a bar code reading device of the present invention.

FIG. 2 is a block diagram showing a conventional device.

3 is an operation waveform diagram of each part of the apparatus of FIG.

4 is an operation waveform diagram of each part of the apparatus of FIG. 2 when the resolution of the sensor part is low.

5 is a circuit diagram showing an embodiment of the high pass fill of FIG.

6 is a diagram showing a characteristic example of the high-pass filter of FIG.

7 is an operation waveform diagram of each part of the apparatus of FIG. 1 when the resolution of the sensor part is low.

[Explanation of symbols]

 10 light emitting diode (light emitting means) 12 light 12 'reflected light 14 bar code 16 phototransistor (light receiving means) 24 high-pass filter (gain applying means)

Claims (3)

[Claims] 1. A light emitting means, a light receiving means for receiving light emitted from the light emitting means and reflected by a bar code, and a light receiving output of the light receiving means within a width of a narrow bar or space of the bar code. A bar code reading apparatus comprising: a gain applying unit that applies a gain by making the gain for the corresponding frequency larger than the gain for the frequency corresponding to the width of a thick bar or space. 2. The gain applying means is composed of a high-pass filter or a band-pass filter, and a frequency corresponding to the width of at least the thickest bar or space in the bar code has a low-frequency side attenuation characteristic of the filter. 2. The bar code reader according to claim 1, wherein the cutoff frequency on the low frequency side of the filter and the slope of the attenuation characteristic are set so as to be on the slope of. 3. The bar code reader according to claim 2, wherein the high-pass filter is an RC first-order high-pass filter.