JP3021150B2 - Barcode reading synchronization circuit - Google Patents

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 synchronization circuit which is most suitable for reading a bar code label, particularly for reading a curved bar code label.

[0002]

2. Description of the Related Art In recent years, inventory management using barcodes has been carried out for most distribution products. This barcode is composed of a combination of a plurality of thin lines and thick lines, and is printed directly on a product bag or the like, or is temporarily printed on a label or the like and is affixed to the product. The barcode is generally read using a barcode scanner using infrared light as reading light.

In a register used in a retail store such as a supermarket, a stationary bar code reader is generally used. However, since money is exchanged with customers, accurate reading is required. On the other hand, depending on the product, the printing surface or the sticking surface of the barcode is often curved, and its performance is determined by whether or not it can be accurately read by a decoder. As a means for solving this problem, for example, a method has been proposed in which one module is obtained from several bar codes in the vicinity that have been read before (Japanese Patent Application No. Hei 3-16243).

[0004]

However, in the above-mentioned prior art, since the previously read data is used as a basis, there is a possibility that a read error may occur in the first read area from the margin to the start bar (guard bar). Is high.

[0005] In addition, four-level bar codes (WPC,
In the case of CODE93 and CODE128), when one module is obtained from previously read data, the calculation is made from the widths of black bars and white bars of four different thicknesses. Appropriate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bar code reading synchronization circuit capable of reading a curved label on which a 4-level bar code is written with high accuracy.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a character interval counter for detecting a character interval from bar code image data obtained from a bar code scanner and counting one character width by a reference clock. A circuit, a division circuit that divides the count value counted by the circuit by the number of character bits to obtain one module width data, a one module width data delay circuit that delays one module width data output from the division circuit, An image data delay circuit for temporarily delaying the bar code image data, reading based on each of an output of the image data delay circuit, a clock having a frequency twice as high as a reference clock, and an output of the one-module width data delay circuit Read clock generation circuit for generating a clock for It is way.

[0008]

According to the above-described means, one module width data is obtained by dividing the value obtained by detecting and counting the character interval from the bar code image data by the number of character bits, and the one module width data and twice the reference clock are obtained. The reading clock can be obtained based on the clock of the frequency. As a result, the reading interval of the character bit varies in accordance with the width of each character in character units, and the bar code of the curved label can be read, so that the reading accuracy can be improved and the reading error can be reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a bar code reading synchronous circuit according to the present invention.

Image data output from a bar code scanner is serially input to a character interval counting circuit 1 for counting character intervals. The character interval counting circuit 1 is connected to a 1/2 frequency dividing circuit 2 which divides the double clock by 1/2 to generate a reference clock. The parallel output of the character interval counting circuit 1 is 1 / n
(Where n is the number of character bits) is connected to a division circuit 3, to which a one-module-width data delay circuit 4 for delaying one-module-width data is connected. An image data delay circuit 5 for delaying the image data and outputting the number of character bits.
Is provided. A read clock generation circuit 6 is provided to generate a read clock based on the output of the one-module width data delay circuit 4, the double clock, and the output of the image data delay circuit 5.

Next, a case where the POS bar code WPC is read will be described. Here, the length of one character bit waveform is one module.

The image data from the bar code scanner is input to the character interval counting circuit 1 and to the image data delay circuit 5. In the character interval counting circuit 1, the width of the character interval is counted from the falling edge of the input data (the point of change from the black bar to the white bar) using the reference clock, and the result is sent to the division circuit 3 as a binary value. Applied. The division circuit 3 divides the input binary value by the number of character bits to obtain 1
Per module (or per character bit)
Is obtained. This binary value is sent to the next one-module width data delay circuit 4 and is temporarily stored.

On the other hand, the image data delay circuit 5 temporarily stores the input data until the character interval counting circuit 1 finishes counting the entire character width. After the character widths of all the characters have been obtained, the stored image data is transmitted, and this image data is input to the read clock generation circuit 6.
The read clock generation circuit 6 detects all edge signals from the image data and uses them for bit synchronization. The binary value temporarily stored in the one-module width data delay circuit 4 is used for character synchronization, sent to the read clock generation circuit 6 for each character, and becomes the basis of the read clock generation cycle. It should be noted that the bit synchronization is adjusted so that each edge of the image data always coincides with the 0 phase (one reference edge) of the read clock.

According to the above-described embodiment, the following effects can be specifically obtained.

In the bar code image data,
By measuring the character interval and dividing the measured value by the character bit number n, the jitter component in the character becomes 1 / n, so that highly accurate module width data can be calculated. For example, if one character is 7
If the number of bits is n, then n = 7. Therefore, assuming that the jitter distribution of the image data is within ± 40% of one module, the distribution of one module width data calculated from this is ± 5.7%. Decreases within. As a result, since a more accurate reading clock can be generated, the conversion (reading) from the image data to the character bits is
This is done correctly as shown in FIG. The accuracy of the read clock cycle in this case is as follows.

When calculated from only the narrowest bar: 1 ± 0.
4 modules When calculated from 1 character width: 1 ± 0.057 modules By measuring the character interval, 1 module width data corresponding to each character is calculated. Therefore, even if the barcode label is curved, Optimum one-module width data according to the degree is calculated for each character. For this reason, the period of the read clock can be appropriately changed for each character, and the reading of the curved label becomes easy as shown in FIGS.

FIG. 2 is a timing chart showing an example of reading a flat label. FIGS. 3 and 4 are timing charts showing examples in which two types of curved labels are read. Referring to FIG. 2, a character interval pulse is generated at the detection timing of the guard bar of the image data, and counting is started by the character interval counting circuit 1 at the same time. When the counting of one character width is completed, the read clock is output from the read clock generation circuit 6 by the double clock with the character synchronization signal output in synchronization with the end point as a start timing. FIG.
4 are the same as those in FIG.

In the above description, application to WPC, which is a bar code for POS, has been described as an example. However, the present invention is not limited to this, and is applicable to all NRZ code type bar codes having a constant character width. It is. For example, F
FIG. 6 shows the case of CODE 93, 128 of a four-level bar code for A (factory automation).

[0020]

As described above, the present invention provides a character interval counting circuit for detecting a character interval from bar code image data obtained from a bar code scanner and counting one character width by a reference clock;
A division circuit for dividing the count value counted by the means by the number of character bits to obtain one module width data;
A one-module width data delay circuit for delaying one-module width data output from the division circuit; an image data delay circuit for temporarily delaying the bar code image data; an output of the image data delay circuit; Since a read clock generating circuit for generating a read clock based on each of a clock having a double frequency and an output of the one-module width data delay circuit is provided, the accuracy of reading a bar code on a curved label is improved. In addition, reading errors can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a barcode reading synchronization circuit according to the present invention.

FIG. 2 is a timing chart showing an example of reading a flat label.

FIG. 3 is a timing chart showing an example of reading a curved label.

FIG. 4 is a timing chart showing an example in which another curved label is read.

FIG. 5 is an explanatory diagram showing a state of occurrence of jitter in image data and a conversion from image data to character bits when one character is composed of 7 bits.

FIG. 6 shows CODE93, a four-level barcode for FA.
It is explanatory drawing which shows conversion in case of 128.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Character interval counting circuit 2 1/2 frequency dividing circuit 3 Dividing circuit 4 1 Module width data delay circuit 5 Image data delay circuit 6 Read clock generation circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G06K 7/016

Claims (1)

(57) [Claims] 1. A character interval counting circuit for detecting a character interval from bar code image data obtained from a bar code scanner and counting one character width by a reference clock, and dividing a count value counted by the circuit by the number of character bits. And a 1-module width data delay circuit for delaying 1-module width data output from the division circuit, and an image data delay circuit for temporarily delaying the barcode image data. A read clock generation circuit for generating a read clock based on each of an output of the image data delay circuit, a clock having a frequency twice as high as a reference clock, and an output of the one-module width data delay circuit. Bar code reading synchronous circuit.