JPH0120791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a barcode reading device that reads a barcode recorded on a recording medium by scanning the barcode.

Conventionally, the reading level of the reading sensor changes due to variations in illuminance on the surface of the card on which the desired barcode is printed, or variations in the distance between the card and the reading device, making it difficult to read barcodes with high accuracy. However, as shown in, for example, Japanese Unexamined Patent Publication No. 51-93128 and Japanese Utility Model Application No. 55-124050, the gain of an amplifier that amplifies the read signal is adjusted according to the read signal of the read sensor, It is known that this improves reading accuracy.

However, although the above device can adjust the overall level of the signal read by the reading sensor, it does not properly amplify the video signal included in this read signal, that is, the identification information signal itself corresponding to the white bars and black bars of the barcode. It could not be adjusted, and therefore it was still insufficient to improve reading accuracy.

The present invention further improves the reading ability compared to the above-mentioned conventional device, and when there is a change in the irradiation light for irradiating the barcode or a reduction in reflected light due to dirt on the barcode, the image can be imaged by the change. It is an object of the present invention to provide a barcode reading device that can eliminate fluctuations in signal amplitude, obtain a stable video signal, and always accurately read barcodes.

Therefore, the present invention provides a reading sensor that converts a barcode into a multi-bit video signal by scanning a reading line that intersects the bar symbol on a bar code in which bar symbols of at least two different widths are sequentially arranged; A holding means for holding the peak value of each bit of the video signal and converting it into a continuous signal, a differentiating means for differentiating this continuous signal and outputting a differentiated signal, and an amplification gain according to the smoothed output of this differentiated signal. The present invention is characterized by comprising an amplifying means for adjusting and amplifying the differential signal to a predetermined level, and a shaping means for shaping the output signal of the amplifying means into a rectangular wave.

An embodiment of the present invention shown in the drawings will be described below.

In the overall configuration diagram of FIG. 1, 1 is the irradiation light 1a
2 is a light receiving section that receives reflected light from an object based on the irradiation light of the light transmitting section 1;
Reference numeral d denotes an image sensor that constitutes a reading sensor in which a plurality of reading points are continuously arranged on a reading line, and receives a read image on the reading line depending on the intensity of the reflected light 1b from the object that the irradiation light 1a hits, and also receives a clock pulse. When the clock pulse is applied, the plurality of reading points are cyclically read (swept) in sequence to generate a series of video signals corresponding to the intensity of the reflected light. 2b is a lens that focuses the reflected light onto the image sensor 2a.

Reference numeral 3 denotes a card serving as a recording medium, and barcode information in which four barcodes are grouped in a linear arrangement of wide and narrow bar symbols 3a is printed and recorded on the surface of the card. A reflected light signal from a black and white line at a linear reading position 3b perpendicular to the linear direction is given to the image sensor 2a, and the bar symbol 3 is applied on the reading surface 3c.
It moves in the direction of the arrow that coincides with the linear direction of a.

4 is an analog amplification unit that amplifies the discrete and weak video signal synchronized with the clock pulse generated by the image sensor 2a, converts it into a continuous signal, and further shapes it to obtain a rectangular wave that is inverted for each bar symbol;
5 is a digital converter that converts the output signal of the analog amplifier 4 into a parallel digital signal corresponding to the bar code; 6 is a digital converter that generates a clock pulse of a constant frequency to connect the image sensor 2a, the analog amplifier 4 and the digital converter; 5, and a reference clock generating section 7 which generates other synchronized clock pulses, and 7, an arithmetic processing section having a microcomputer, which performs digital arithmetic processing on the digital signal converted by the digital converting section 5. Reference numeral 8 denotes a card feeding device which automatically moves the card 3 in the direction of the arrow, and is composed of a motor, a belt, a pair of rollers, etc., and inserts the card 3 between the rollers to feed the card. It is something to do.

Next, the general operation of the above configuration will be explained.

Now, when the card 3 moves on the reading surface 3c in the direction of the arrow shown in the figure and reaches the reading position 3b of the light receiving section 2, the reflected light signal obtained from the card 3 passes through the lens 2b, and a read image is displayed on the image sensor 2a. Tie. At this time, since the image sensor 2a has a plurality of photoelectric conversion elements arranged on the reading line, reflected light signals with different reflectances from the black and white bar symbols on the straight line at the reading position 3b are read on the image sensor 2a. Tie the statue.

Therefore, the image sensor 2a irradiated with the reflected light signal receives the clock pulse from the reference clock generator 6 and reads the plurality of reading points arranged on the reading line, so that the image sensor 2a converts the reading line into a serial video signal. Convert to This video signal is amplified and waveform-converted by the analog amplifier 4, and is converted into a logic signal in which, for example, the white line code symbol is at the "1" level and the black line code signal is at the "0" level. The logic signal is determined in the digital converter 5 as to whether it is a wide bar symbol or a narrow bar symbol, and is converted into a parallel digital signal, that is, an information code of a bar code. The information code is then sent to the arithmetic processing section 7 where various processes such as barcode information confirmation processing are performed.

Next, the detailed configuration and operation of the analog amplifying section 4 shown in FIG. 1 will be explained.

FIG. 2 is an electrical wiring diagram showing the detailed configuration of the analog amplifying section 4, in which the white bar symbol is amplified and converted to the "1" level and the black bar symbol to the "0" level upon receiving the video signal from the image sensor 2a. are doing. 4
Reference numeral 1 denotes an amplifier for amplifying the very small video signal, and performs differential amplification of the video signal with respect to a feedback input applied to a resistor 41a. Reference numeral 42 denotes a sampling circuit, and includes sampling pulse generators 42a and 42 that receive the clock pulse from the reference clock generator 6 and generate sampling pulses synchronized therewith.
It has b. Reference numeral 43 denotes a sample and hold circuit which serves as a holding means for sampling and holding the video amplified signal from the amplifier 41 using the sampling pulse and converting a discrete signal synchronized with the clock pulse into a continuous signal; 43a is a sample and hold circuit that is closed by the sampling pulse; 43b is a capacitor that holds the signal level sampled by the analog switch 43a until the next sampling point, and 43c is a capacitor that increases the signal level held by the capacitor 43b by about three times. This is a high input impedance amplifier circuit. Reference numeral 44 denotes a feedback low-pass filter which extracts low frequency components from the continuous signal from the sample and hold circuit 43 and supplies the feedback input to the amplifier 41, and sets its cutoff frequency to the frequency of the continuous signal corresponding to the wide width of the bar signal. The frequency is set to be lower than the frequency. This negative feedback removes low frequency noise components such as low frequency fluctuations related to the illuminance of the irradiated light 1a from the light transmitting section 1 from the video signal. 45 is a high pass filter that differentiates the continuous signal from the sample hold circuit 43;
The point of change in the continuous signal is detected, and the cutoff frequency is set at a frequency higher than the frequency of the continuous signal corresponding to the narrow width of the bar symbol. Reference numeral 46 denotes an automatic gain control circuit (hereinafter referred to as AGC circuit) which amplifies the differential output signal of the high-pass filter 45 by automatically varying the gain.
This is achieved by changing the impedance between the drains. The gate voltage is controlled by amplifier 4.
This is performed using the average value of the differential output signal of 6a. That is, the differential output signal is rectified, and the rectified signal is sampled at a constant period by the analog switch 46b, and the signal is held by the capacitor 46d until the next sampling point. 4
6e is a reset circuit for instantaneously discharging the charge of the capacitor 46d, and is composed of a transistor and the like. 47 is a shaping circuit that shapes the differential signal of the AGC circuit into a rectangular wave, 47a and 47b are diodes connected in anti-parallel, and 47c is a capacitor, which reduces the forward voltage drop of the diode with the diodes 47a and 47b connected in anti-parallel. The reference signal is obtained by reducing the amplitude of the differential signal by a predetermined potential difference and shifting the phase. 47d is a comparator that compares the reference signal and the differential signal to obtain a rectangular wave. A pulse generator 48 applies a timed pulse to the reset circuit 46e upon receiving an unreadable instruction signal from the arithmetic processing section 7.

Next, the operation of the above configuration will be explained with reference to the signal waveform diagrams of each part shown in FIGS. 3 and 4. Figure 3 shows the state during normal reading, where a is the amplifier 4.
1, b shows the continuous waveform b from the sample and hold circuit 43, and c shows the amplified video signal a from sample hold circuit 43.
A differential waveform c of the AGC circuit 46 is shown, and d shows a rectangular wave d from the integer circuit 47. In this state, the white line bar symbol is scanned from time t ₁ to t ₂ , from t ₃ to t ₄ , from t ₅ to t ₆ , and from time t _{1 to time t 1} , from t ₂ to t ₃ ,
From t ₄ to t ₅ and after t ₆ , the black line bar symbol is scanned.
Then, the video signal from the image sensor 2a is amplified approximately 400 times by an amplifier 41 to obtain a discrete video amplification signal a shown in FIG. 3a. Only the negative peak value of this amplified video signal a is sampled and held in a sample hold circuit 43 to obtain a continuous signal shown in FIG. 3b. Next, the continuous signal is differentiated and amplified by the high pulse filter 45 and the AGC circuit, resulting in a signal waveform shown by the solid line in FIG. 3c. At this time, the gain of the AGC circuit is determined by the average value of the signal c, for example, GI. Furthermore, the differential signal c
is added to the shaping circuit 47, so the capacitor 4
A reference signal indicated by a broken line in FIG.
d, and a rectangular wave d shown in FIG. 3d is obtained.
In this rectangular wave d, the black bar symbol in the bar code is at the "0" level, and the white bar symbol is at the "1" level.

Further, FIG. 4 shows a state in which the bar code surface of the guard 3 is dirty, and the amplitude of the continuous signal a has decreased, making it difficult to distinguish between black line portions and white line portions. This is more noticeable in narrow bar symbol areas. b indicates a differential signal, but since the amplitude fluctuation of the continuous signal a is small, the differential signal also becomes small, making it impossible to obtain an accurate rectangular wave corresponding to the barcode. Therefore, the gain of the AGC circuit 46 is changed by the average value voltage of the differential signal of b, that is, the gain is increased, so that a normal differential signal like waveform c can be obtained at the next scan of the image sensor 2d, and at the same time the waveform As shown in d, accurate rectangular waves corresponding to the black line and white bar symbols are obtained.

Next, according to the waveform diagram shown in Fig. 5, the AGC circuit 4
6 will be explained in more detail. a indicates a continuous signal that is the output of the sample and hold circuit 43,
The interval T ₁ is one reading period of the image sensor 2a,
Between _T2 is the barcode video signal. Also, the difference between T ₂ and T ₂ ′ is that the video signal between T ₂ and normal barcode reading is different from the image signal during T ₂ ′ when a dirty barcode is being read, as is clear from the figure. It's getting smaller. The differential signal of the AGC circuit 46 at that time is e. Waveform b indicates the average value voltage of the differential signal, and this voltage is applied to the sampling pulse generator 42b.
The AGC shown in d is sampled by a sampling pulse c with a period of T ₃ and connected to a capacitor 46d.
The reference voltage is obtained. The sampling pulse c has a waveform b after scanning or reading the barcode.
It is set so that it is output when the average voltage of is stabilized. The gain of the AGC circuit 46 is determined by the reference voltage held in the capacitor 46d at the time.
Up to _T4 , the bias is large and negative. Therefore, the FET 46c is heavily biased negatively, so the impedance between the source and drain of the FET 46c becomes large, and therefore the gain becomes small. Therefore
The differential signal between T ₅ has become smaller, but at time T ₄ , the reference voltage of the AGC circuit is sampled and held with the new average voltage between T ₅ , so the gain increases and the differential output signal also increases as shown in e. . Furthermore, when reading is not possible for a certain period of time (a certain number of scans), the pulse generator 4 receives an instruction signal from the arithmetic processing section 7.
A timed pulse is generated from 8, and the reset circuit 46e
This operates to maximize the gain by discharging the charge in the capacitor 46d, that is, by setting the reference voltage of the AGC circuit to "0".

Due to the operation of the AGC circuit 46 as described above,
Accurate square waves corresponding to black line and white bar symbols can be obtained.

In the above embodiment, scanning of the reading line intersecting the bar symbol on the bar code is performed electronically using clock pulses, but a laser beam may be scanned on the reading line instead of the image sensor 2a. A laser scanning sensor that converts the reflected light into discrete electrical signals may also be used.

In addition, although AGC is shown in which a discrete video signal is converted into a continuous signal and then applied to a differentiated signal, it is applied to the part that converts the discrete video signal into a continuous signal, that is, the amplifier 43c of the sample-and-hold circuit 43 in FIG. equivalent results can be obtained.

In addition, we have shown that the reset circuit is activated when the card cannot be read for a certain period of time, but a card detector is installed and the reset circuit is activated when a card reaches the reading surface, maximizing the gain of the AGC circuit. You can do it like this.

Furthermore, the barcode information may have any code form.

As described above, the present invention particularly includes a reading sensor that converts a barcode into a multi-bit video signal, a holding means that holds the peak value of each bit of this video signal and converts it into a continuous signal, and a Differentiating means for differentiating a signal and outputting a differentiated signal; and amplifying means for amplifying the differentiated signal to a predetermined level by adjusting an amplification gain according to the smoothed output of the differentiated signal, the continuous signal being differentiated. The differential signal is amplified to a predetermined level, and this amplified differential signal is
Since it is used as a signal source for value conversion, even if the signal level of the video signal included in the read signal of the reading sensor becomes small, the change in the video signal (that is, the differential signal) can be extracted and amplified to a predetermined level. Therefore, the ability to read video signals can be further improved. As a result, the amplification gain for the differential signal can be quickly adjusted even if there are fluctuations in the light irradiating the barcode, dirt on the barcode surface, or variations in the printing density of the barcode, and the white line can always be accurately adjusted. , it has the excellent effect of being able to be converted into a rectangular wave corresponding to the black line bar symbol and read.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of the barcode reading device according to the present invention, FIG. 2 is an electrical wiring diagram showing the detailed configuration of the analog amplification section in FIG.
4 and 5 are signal waveform diagrams of various parts for explaining the operation of the circuit shown in FIG. 2. DESCRIPTION OF SYMBOLS 1... Light transmitting part, 2... Light receiving part, 2d... Image sensor forming a reading sensor, 2b... Lens, 3
...Card serving as a recording medium, 3a...Bar symbol,
4...Analog amplification section, 5...Digital conversion section, 6...Reference clock generation section, 7...Arithmetic processing section, 41...Amplifier, 42...Sampling circuit, 43...Sample hold circuit forming holding means , 44... Return low-pass filter, 45...
High pass filter, 46... Automatic gain control circuit serving as amplifying means, 47... Shaping circuit serving as shaping means.

Claims (1)

[Scope of Claims] 1. A reading sensor that converts the barcode into a multi-bit video signal by scanning a reading line that intersects the bar symbol on the bar code in which bar symbols of at least two different widths are sequentially arranged; A holding means for holding the peak value of each bit of this video signal and converting it into a continuous signal, a differentiating means for differentiating this continuous signal and outputting a differentiated signal, and an amplification gain according to the smoothed output of this differentiated signal. A barcode reading device comprising: amplifying means for adjusting the differential signal and amplifying the differential signal to a predetermined level; and shaping means for shaping an output signal of the amplifying means into a rectangular wave.