JPH0814832B2 - Barcode reader - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bar code reader using an image sensor.

2. Description of the Related Art Processing for reading a barcode includes (1) binarizing an image sensor signal, (2) counting a binarized barcode width with a reference clock, and (3) counting data. It consists of decoding processing based on.

Generally, when reading a high-density printed thin bar code, the output signal of the image sensor is small, so that it cannot be binarized unless the gain is increased. Therefore, conventionally, the gain of the circuit for amplifying the output signal of the image sensor is controlled to be switched to a plurality of stages to obtain an appropriate binarized signal. FIG. 3 shows a typical conventional example. Where 1 is a barcode and 2
Is a light source for illuminating a barcode, 3 is a lens system for collecting reflected light from the barcode, 4 is an image sensor, 5 is a drive circuit of the image sensor, 6 is a filter circuit, 7 is a gain control circuit, and 8 is 2 A digitization circuit, 9 is a microcomputer, 10 is a communication interface for transmitting read data to the outside, and 11 is a case. FIG. 4 is an example of barcode detection in the example of FIG. Here, A is an output waveform of the image sensor 4 in FIG. 3, and a reset waveform appears for each shift clock (cycle t) for each pixel as shown in B in which the portion A is enlarged. Filter 6 to obtain the envelope waveform corresponding to the barcode from
The waveform of C is obtained through. The shift clock (cycle t) of the image sensor 4 is constant, so that one scanning cycle (fourth cycle)
(Corresponding to T in the figure) is also constant. Then, although this filter output signal is binarized, in the case of a fine bar code, it cannot be binarized unless the gain is increased. That is, the fourth
By increasing the gain as shown in FIG. D, comparison with the binarized reference voltage becomes possible, and as shown in FIG.
A digitized waveform can be obtained. The gain control circuit 7 shown in FIG. 3 is composed of an operational amplifier 13 and an analog switch 12, for example, as shown in FIG. 5, and the analog switch 12 is switched according to a cycle preset by the microcomputer 9.

However, in the conventional example, since the filter is used to obtain the envelope signal corresponding to the bar code, the waveform is distorted and it is difficult to detect the accurate bar code width. Moreover, when the signal detected in one scanning cycle T is binarized and the width is counted by the bar width measurement clock as shown in FIGS. It often happened that the accuracy deteriorated and the decoding became impossible.

Further, in the case of configuring a gain control circuit, a complicated circuit is required when the control has multiple stages, and it takes time to input an optimum value because switching is performed according to a preset cycle.

Means for Solving the Problems In order to solve the conventional problems, the barcode reader of the present invention is an image sensor, and a sample and hold means for obtaining an envelope signal from the output value of each pixel of the image sensor, A microprocessor for controlling the exposure time of the image sensor and a binarization circuit for converting the output of the sample and hold means into a digital signal corresponding to a bar code are provided, and the microprocessor outputs the binarization circuit output. The frequency is detected, and the exposure time of the image sensor is controlled so that the frequency becomes maximum.

Since the output of the working image sensor is sampled and held by the sample and hold means, an accurate bar code-corresponding signal without distortion can be obtained as compared with the conventional method using a filter.

Further, by changing the scanning period of the pixels, the exposure time of the image sensor can be changed and the gain of the signal can be equivalently changed. Further, as shown in FIGS. 6C, 6D and 6E, for example,
If the scanning cycle is set to 2T, the detection pulse width of the bar code signal is doubled as compared with the case of the cycle T, so that the count value of the bar width measurement clock increases and accurate detection is possible. Further, by providing a means for measuring the frequency of the output of the means for converting into a digital signal (binarization means), and a means for controlling the exposure time so that the frequency becomes maximum, it is determined as in the conventional case. The optimum signal can be acquired faster than the method of setting the gain in order.

Embodiment FIG. 1 is an embodiment of the present invention. Here, 1 is a barcode, 2 is a light source that illuminates the barcode, and 12 LEDs
Are arranged in the direction perpendicular to this paper surface. 3 is a lens system that collects the reflected light from the bar code, which is a combination of a Tessa lens with a focal length of 30 mm and an optical filter that cuts infrared light of 700 nm or more. 4 is a 2048 pixel CCD
The image sensor 5 is a drive circuit of the image sensor, and the frequency of the shift clock of the pixel is set and controlled by the microcomputer 9. Reference numeral 14 is a sample and hold circuit which is composed of an operational amplifier or the like, but it may be incorporated in the image sensor to obtain the peak output envelope for each pixel of the image sensor. Reference numeral 8 denotes a binarization circuit, which is a comparator made up of an operational amplifier or the like, and here is made up of a fixed binarization method.
The floating binarization method may be used. Reference numeral 9 is a microcomputer, which observes the binarized data of the binarization circuit 8 and counts its width with an internal bar width measurement clock, and stores it in a memory.
Decoding processing is performed based on it. The microcomputer 9 also controls the lighting of the light source 2, outputs a drive clock to the drive circuit of the image sensor, and outputs the read data to the communication interface 10 which transmits the read data to the outside. Note that 11 is a case. FIG. 2 shows the first
This is the output waveform of the main part of the figure. Here, one scanning cycle is T
The figure shows the case of controlling from 2T to 2T. 2A is an output waveform of the sample hold circuit of the image sensor 4 of FIG.
A part B is enlarged and shown as B, and C is a waveform obtained by binarizing the output waveform of A. When T was set to 9.8 milliseconds and the bar width measurement clock period was set to 35 microseconds, the conventional barcode reading resolution was 0.17 mm, but a barcode reading resolution of 0.13 mm could be obtained. The reading field width is 80 mm. The frequency of the binarized signal was measured by the internal counter of the microcomputer 9 while changing the pixel scanning period up to 4 times, and the data when the frequency was maximized was input, and the width was counted and the decoding processing was controlled. However, reading could be made about 30% faster than when this control was not performed.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to obtain an accurate bar code detection waveform with less distortion, and further improve the bar width detection accuracy by controlling one scanning cycle of the image sensor. It is possible to dramatically improve the reading of barcodes printed with high density and barcodes with poor contrast. Further, the reading performance can be improved without adding a complicated gain control circuit as in the past, an inexpensive configuration is possible, and the industrial value is extremely high.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a bar code reader showing an embodiment of the present invention, FIG. 2 is a waveform diagram of a main part of the bar code reader, and FIG. 3 is a block circuit diagram of a conventional bar code reader. FIG. 4 is a waveform diagram of the main part of the bar code reader, FIG. 5 is a concrete circuit diagram of a conventional gain control circuit, and FIG.
The figure is a waveform diagram for explaining bar width measurement. 1 ... bar code, 2 ... light source, 3 ... optical system, 4 ...
Image sensor, 5 ... Image sensor drive circuit, 6 ...
... filter, 7 ... gain control circuit, 8 ... binarization circuit, 9 ... microcomputer, 10 ... communication interface, 11 ... case, 12 ... analog switch, 13
…… Op Amp, 14 …… Sample hold circuit.

Claims (1)

[Claims] 1. An image sensor, a sample hold means for obtaining an envelope signal from an output value of each pixel of the image sensor, a microprocessor for controlling an exposure time of the image sensor, and an output of the sample hold means. Is provided to the digital signal corresponding to the bar code, the microprocessor detects the frequency of the output of the binarization circuit, and the exposure of the image sensor is performed so that the frequency becomes maximum. A barcode reader that controls the time.