JPS6131911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a barcode information reading method, and more particularly to a new reading method for accurately and stably extracting a digital signal corresponding to the bar width.

Recently, department stores, supermarkets, etc. are trying to simplify product management and save labor.
A Point of Sales system is adopted. This system records product information in the form of barcodes on price tags attached to products, and optically reads the barcodes as input to an information processing device.
Generally, this information is included in the bar width.

Conventionally, as a method for reading such a bar width, a method is known in which a second-order differential operation is performed on an analog signal corresponding to a barcode, and a digital signal corresponding to the bar width is extracted from the second-order differential output. . However, in such a reading method, S/
In addition to being unable to obtain a stable digital output due to the poor N ratio, it also required a wideband amplifier and had the disadvantage of a complicated circuit configuration. especially,
Since the former reading accuracy greatly influences the next stage of signal processing, improvement is desired.

The present invention aims to provide a new reading method capable of extracting an accurate and stable digital signal corresponding to the bar width of a bar code from the above-mentioned situation. Briefly stated, the present invention is an apparatus that optically reads barcode information written on a recording medium, and after differentiating an analog signal corresponding to the barcode information, corresponds to differential signals of positive polarity and negative polarity. The bar width of the desired barcode information is obtained by extracting the two delayed signals, level slicing the original differential signal output using these two delayed signals as a reference, and combining the sliced outputs of both systems. It is characterized by being able to obtain digital signals compatible with

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic system diagram showing the configuration of an example of the reading method according to the present invention, and the differential circuit 11 as a whole is shown in FIG.
, a delay circuit 12 , two systems of envelope circuits 13 and 14 , slice circuits 15 and 16 , and a digital signal extraction circuit 17 . The differentiating circuit 11 differentiates the analog signal corresponding to the barcode whose signal input is input from the terminal 1, and the delay circuit 12
is for delaying this differential signal output by a predetermined time. The two envelope circuits are each used to obtain an envelope waveform of the delayed signal output, and 13 derives a positive polarity waveform and 14 derives a negative polarity waveform, respectively.

The slice circuit 15 inputs the differential output and the positive envelope waveform, and levels slices the differential waveform using the envelope waveform. Further, the slicing circuit 16 is for level slicing the differential output using a negative envelope waveform. These slice circuits use comparators with appropriate hysteresis characteristics.

In short, the leading edge and trailing edge of a unit barcode are individually detected by the circuit described above. The digital signal extraction unit 17 extracts each edge signal, that is, the slice output (digital signal).
are respectively input, and in response to these two input signals, their output states are inverted, and as a result, a digital signal corresponding to the bar width of the unit bar code is extracted.

Note that the reference numeral 2 in the figure is a signal output terminal.

In the above configuration, it is assumed that the analog signal shown in FIG. 2b corresponding to the barcode symbol shown in FIG. do. The analog signal is first differentiated by a differentiating circuit 11, and then branched into three systems. FIG. 2c shows such a differential waveform. The differential output of one of these channels is passed through a delay circuit 12 and derived as a signal waveform delayed by a predetermined time, and then further branched into two channels and applied to envelope circuits 13 and 14, respectively. These circuits produce positive and negative envelope waveforms that straddle the zero level as shown by dotted curves A and B in FIG. is input as a slice level signal.

At this time, the differential outputs of each of the two systems are individually input to the other input terminals of these slice circuits 15 and 16, so that the levels of these differential outputs and each of the envelope waveforms are sequentially compared. . Here, at points _P'1 and _P2 where the level difference between both input signals becomes zero, the slice circuit generates digital outputs as shown in FIGS. 2d and 2e. The digital signal extraction circuit 17 first responds to the rise of the digital output waveform of the positive side slice circuit 15 and inverts its output state from the logical value "0" to "1", that is, forms the rise of the output waveform. Next, in response to the rise of the digital output waveform of the negative polarity side slice circuit 16, its output state is inverted from "1" to "0", that is, a fall of the output waveform is formed. FIG. 2f shows such a digital signal waveform. Thereafter, such operations are repeated.

In this way, digital signals corresponding to the bar widths of each unit barcode in the barcode symbol are extracted in time series from the digital signal extraction circuit 17. According to the above embodiment,
Since the configuration is such that a level comparison is made between a stable first-order differential signal and a delay envelope waveform corresponding to the differential signal, accurate and stable reading processing can be performed even with frequency fluctuations and light amount fluctuations.

On the other hand, FIG. 3 is a schematic system diagram showing a modification of the reading method of the present invention, in which the signal processing system between the differentiating circuit and the two slice circuits is greatly different from that in FIG. 1. Therefore, only this signal processing system will be described in detail here. As a whole, this includes two systems of clip circuits 21,
22 and delay circuits 23 and 24. The clip circuit 21 clips the negative polarity of the differential output, and the clip circuit 22 clips the positive polarity of the differential output. In addition, each delay circuit 2
Numerals 3 and 24 further delay the clipped waveform by a predetermined time as in FIG. However, the two systems of slicing circuits 15 and 16 each input the clipped waveform and each delayed waveform, level slice the clipped waveform using the delayed waveform, and when the level comparison result becomes zero, the same Outputs digital signals corresponding to the leading and trailing edges of the barcode. Thus, in response to the rising edge of each of these digital output waveforms, the digital signal extraction circuit 1
7 are operated in sequence, a digital signal corresponding to the bar width of each unit barcode is extracted as described above.

In the reading method according to this modification, as in the above-described embodiment, good reading processing can be performed with respect to frequency fluctuations and light amount fluctuations.

As is clear from the above description, the barcode information reading method of the present invention has the advantage of being able to accurately and stably extract digital signals corresponding to bar widths. Therefore, this invention can be applied to, for example, POS.
It would be extremely advantageous if applied to the system.

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram showing one embodiment of the barcode information reading method according to the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the first light, and FIG. It is a schematic system diagram showing an example of. 1...Signal input terminal, 2...Signal output terminal, 1
1...differentiation circuit, 12, 23 and 24...delay circuit, 13 and 14...envelope circuit, 1
5 and 16...Slice circuit, 17...Digital signal extraction circuit, 21 and 22...Clip circuit.

Claims (1)

[Claims] 1. In a device that optically reads barcode information written on a recording medium, after differentiating an analog signal corresponding to the barcode information, two systems of delayed signals corresponding to positive polarity and negative polarity differential signals are generated. The original differential signal output is level-sliced using these two delayed signals as a reference, and the sliced outputs of both systems are combined to obtain a digital signal corresponding to the bar width of the desired barcode information. A method for reading barcode information, which is characterized in that: