JP2604358B2 - Barcode demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] In a two-beam scanner, data to a demodulation unit is switched according to an output of a bar code scanning start detection circuit.

[Industrial applications]

The present invention relates to a bar code demodulation device, and aims to improve a reading rate without making the device expensive.

2. Description of the Related Art A bar code is printed on wrapping paper of a product, and is used for printing out a product name, its price, and a total amount, creating sales data, and the like. As is well known, a barcode is configured by combining white bars of a plurality of widths. FIG. 5 shows an example. At both ends and at the center there is a guide bar GB containing two black bars, and the numbers 9,0,3,… between these guide bars.
There is a character bar that represents ... The width of the black bar and white bar (space between the black bars) of the character bar is the unit width, part 2
There are a plurality of types such as double and triple, and each numerical value is composed of two black bars and two white bars. A large space is placed before and after the bar group, which indicates the start and end of the bar group together with the guide bars at both ends.

In general, a bar code is read by scanning a bar group with a light beam, photoelectrically converting the reflected light, and examining the width of each pulse of the obtained rectangular wave signal. A laser scanner is sometimes used for scanning with light beams.In this case, the scanning light is generated all the time during operation, and when the product is placed on the laser scanner with the barcode printing surface down, the laser beam is scanned. The code is read. In this case, the scanning trajectory of the bar group by the laser beam is not constant, and is deviated from a horizontal line passing through the center of each bar, and then becomes oblique or partially missing. The laser scanner is provided with a polygon mirror that rotates at a high speed and performs repetitive scanning. Further, the scanning trajectory of each scanning is different, and the scanning may be performed completely apart from the bar group.
However, when an item is placed on or over a laser scanner, a number of scans will traverse the bars, producing a code reading output.

Such a scanning method in which the scanning light trajectory is irregular eliminates the need to accurately position the product at the time of reading,
Operability can be improved.

If the scanning light trajectory crosses the bar group, it first enters the space, then enters the leading guide bar GB, enters the subsequent character bar, and so on.
The width of each pulse of the rectangular wave obtained by photoelectrically converting the reflected light is measured by a counter that counts clocks. FIG. 3 shows an example of this measurement circuit. Reference numeral 10 denotes a bar width counter to which a bar code signal (obtained by photoelectrically converting, amplifying, and shaping the reflected light) indicated by BCS in FIG. 4 is input, and the H (high) level of this rectangular wave
The clock CLK is counted during each L (low) level period, and the count value indicates the length of each H, L level period. In FIG. 4, this count value is assumed to be 100, 25, 23,... Since there is a large space at the tip of the bar group, the pulse width in this portion is large, and the counter 10 overflows. Detection circuit 16 detects this, give signals S ₁ to the write control circuit 18 of the FiFo memory 12.

The FiFo memory 12 has a capacity of about 64 words and functions as a buffer. That is, laser scanners are quite fast,
Each word (25, 23,..., Etc.) is 1 in 0.5 μs
However, the demodulation circuit 14 can process only about 1/2 to 1/3 thereof. Therefore, each word generated in one scan is buffered in the memory 12 and sequentially processed by the demodulation circuit 14. When data is accumulated in the FiFo memory 12 (64 in this example)
Since further writing is not possible (when the word is accumulated), the input signal IR is set to the L level to notify that writing is not possible. Only during write control circuit 18 and a signal IR of H level, and after the overflow signals S ₁ arrives, when the rise of the bar code signal BCS, the signal S ₂ indicating a falling entering, FiFo
The write signal WE is output to the memory 12. When the signal WE is input, the FiFo memory 12 takes in the count value of the counter 10 at that time and writes it into an address indicating a pointer (not shown). The counter 10 outputs its count value at the rise / fall of the barcode signal BCS, and resets itself to start the next count.

The demodulation circuit 14 sequentially retrieves the data from the FiFo memory 12 (in the order of writing because it is FiFo), and determines a guard bar or a numerical value from a combination of pulse widths.

[Problems to be solved by the invention]

Barcode scanning by laser beam is irregular, which has the advantage of not requiring positioning accuracy,
There is also a disadvantage that a read failure may occur.

Various means are considered to improve the reading rate, and the number of scans per unit time by a laser beam is increased.
Is a powerful tool. In a laser scanner, a rotating polygon is used for beam scanning, and the number of scans per unit time can be increased by increasing the rotation speed of the polygon.
Therefore, using a DC motor to drive the rotating polygon is one method. That is, while the maximum speed is 3000 rpm for the AC motor, it is easy to obtain about 6000 rpm for the DC motor, and the number of scans can be increased. However, DC motors are more expensive than AC motors and have maintenance difficulties.

When a plurality of laser beams are projected onto the rotating polygon from different angles, a plurality of scanning lights are obtained, and the number of scans can be increased. FIG. 6 shows the system configuration in this case.
Laser light sources 20, 20a generate laser light, respectively, and project the laser light onto a rotating polygon 24 through lenses 22, 22a.
The rotating polygon 24 is rotated by a motor 26,
Generates 28 and 28a. The light reflected by the barcode enters the sensors 30 and 30a along the reverse path, and is photoelectrically converted to the barcode signal BCS. The bar code signal enters the demodulation circuits 14 and 14a through analog / digital converters 32 and 32a shown in FIG. 3 as counters and FiFo memories, and the bar code is decoded. The decoding result should be the same in both systems. After checking this by the matching circuit 34, it is output as bar code data.

In this two-beam system, the number of scans can be equivalently doubled, and the rotation speed of the rotating polygon has not necessarily increased. Therefore, the data generation speed in each system is the same as that in the case of one beam. The same is true, and it is not necessary to increase the speed of the processing circuit. However, there is a disadvantage that the apparatus is duplicated. In particular, the demodulation circuits 14 and 14a are LSIs having about 10,000 gates, and the necessity of double this increases the cost.

An object of the present invention is to provide a laser scanner having a simple configuration while employing a multi-beam system such as a two-beam system.

[Means for solving the problem]

According to the present invention, a bar code is scanned by generating two beams whose scanning timings are temporally shifted, and a bar having a pulse width corresponding to the bar code is provided for each of the two beams. An optical system (36) for outputting a code signal; a circuit (38) for detecting a start of a bar code from a pulse width of each of two bar code signals corresponding to each of the two beams; A demodulation circuit (14) provided in common for the two barcode signals, and a multiplexer for switching the start detection circuit so that the barcode signal whose start is detected first is input to the demodulation circuit (14). (40).

[Action]

According to this apparatus, the scanning frequency is increased by scanning the barcode with a time lag between the two beams, so that the reading speed and the reading rate can be improved. Since the driving speed of the rotating polygon of the laser scanner is not increased, an inexpensive and robust AC motor can be used, and there is no need to speed up the processing circuit. Further, since only one demodulation circuit is required, the configuration can be simplified and the cost can be reduced.

〔Example〕

FIG. 1 shows an embodiment of the present invention. Here, for simplification of description, an example of a two-beam system is adopted. Therefore, the optical system 36 is shown as a laser light source, a lens, a rotating polygon, and a sensor in FIG.
The bar code is scanned by generating two scanning lights. The analog / digital converters 32 and 32a are counters in FIG.
And the FiFo memory 12 is omitted. As shown in FIG. 5, there is a space at the beginning of the bar code, and the pulse width of the pulse signal after photoelectric conversion of the reflected light in this portion is wide. The start detection circuit 38 detects this, and may simply be an overflow pulse extraction circuit of the counter 10. Since the laser beam is projected onto the rotating polygon from different directions, the two scanning lights hardly scan the bar code at the same time, and the scanning is shifted in time. The multiplexer 40 selects one of the outputs of the A / D converters 32 and 32a and inputs it to the demodulation circuit 14, and the output is selected by the output of the start detection circuit 38. In the present invention, the demodulation circuit 14 is 1
There are only two systems, and the two systems up to A / D conversion (pulse width measurement) share a demodulation circuit.

That is, two bar code signals are output from the optical system 36 by two-beam scanning, and the pulse width of these signals is A / D.
The start of the bar code is detected by the conversion devices 32 and 32a, and the pulse width is wider than that of the character portion. When the start of the bar code is detected, the circuit 38 operates the multiplexer 40 to set the A / D on the side where the start is detected.
The output of the converter is supplied to the demodulation circuit 14. The demodulation circuit 14 decodes the bar code from the supplied pulse width measurement value group and outputs bar code data. When the two scanning beams generated by the optical system 36 perform bar code scanning in less than 1/2 of one cycle, and are shifted from each other by 1/2 cycle, when bar code scanning and decoding in one system are completed. , Barcode scanning in another system starts. Therefore, the start detection circuit 38
Switches the multiplexer 40 to the other A / D converter side,
The output is input to a demodulation circuit 14 for decoding. Any decoding result may be adopted, thus enabling quick decoding. If the decoding results of the two systems are matched, a so-called dual system is obtained, and the reliability of the decoding results can be improved.

FIG. 2 shows another embodiment of the present invention. 2 as described above
The scanning by the beams is not synchronized, so the two beams may start barcode scanning at the same time with a slight time difference. FIG. 2 is a diagram for coping with this, in which a priority order determination circuit 46 is provided, to which the outputs of the start detection circuits 38 and 38a and the demodulation end signal from the demodulation circuit 14 are inputted.
By operating the multiplexer 40 with the output of 46, the A / D conversion output on the side that first detected the start is demodulated,
During demodulation, the multiplexer 40 is not operated even if a start is detected in the other system. In this Fig.
Fo memories 12 and 12a are also used, and when the start is detected by the AND gates 42 and 42a, the subsequent A / D conversion output is F
It is written to iFo memory sequentially. A write control circuit is provided as in FIG. 3, but is not shown in this figure.

〔The invention's effect〕

As described above, according to the present invention, the scanning frequency can be increased by scanning a barcode with a time lag with two beams, and the reading speed and the reading rate can be improved. Since the driving speed of the rotating polygon of the laser scanner is not increased, an inexpensive and robust AC motor can be used, and there is no need to speed up the processing circuit. Further, since only one demodulation circuit is required for two operation outputs by two beams, the configuration can be simplified and the cost can be reduced.

[Brief description of the drawings]

1 and 2 are block diagrams showing an embodiment of the present invention, FIG. 3 is a block diagram showing a conventional example, FIG. 4 is a waveform diagram for explaining the operation of FIG. 3, and FIG. FIG. 6 is a block diagram showing a configuration of a two-beam scanner. 1 and 2, 36 is an optical system, 38 is a start detection circuit,
40 is a multiplexer, 14 is a demodulation circuit, and 46 is a priority determination circuit.

Claims (2)

(57) [Claims] 1. A bar code is scanned by generating two beams whose scanning timings are shifted in time, and each of the two beams has a pulse width corresponding to the bar code. An optical system (36) for outputting a bar code signal; and a circuit (38) for detecting the start of the bar code from the pulse width of each of the two bar code signals corresponding to each of the two beams. A demodulation circuit (14) provided in common for the two barcode signals, and a circuit for detecting the start is switched so that the barcode signal for which the start is detected first is input to the demodulation circuit (14). A bar code demodulation device comprising a multiplexer (40). 2. The bar code signal which has been switched to be inputted after the circuit for detecting start has been switched to input the bar code signal which has detected the start first to the demodulation circuit (14). A priority determination circuit (4) that keeps the state until demodulation of the code is completed.
The bar code demodulation device according to claim 1, further comprising (6).