JPH0192888A - Bar code detector - Google Patents

Abstract

PURPOSE:To prevent the generation of misreading by providing the title device with a voltage dividing circuit for outputting a 1st signal with intermediate potential, a subtractor for outputting a 2nd signal with lower potential and a comparator for selecting and outputting the lower signal and switching a threshold level of a binarizing circuit. CONSTITUTION:The subtractor 19 and the comparator 20 are added. The potential of a signal selected by the comparator 20 out of the 1st and 2nd signals is used as the threshold level of the binarizing circuit 15 without always using the 1st signal generated from the output of the voltage dividing circuit like an ordinary method. Even when an analog signal to be binarized is oscillated by dirt on a bar code or noise, binarization is executed by using the 2nd signal as the threshold level, so that a accurate binarizing processing can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a barcode detection device that binarizes an analog signal obtained by scanning a barcode in a barcode reading device.

BACKGROUND OF THE INVENTION FIG. 4 shows a barcode reading device. A barcode 1 to be read is scanned by a laser beam 4 of a laser beam generator 3 via a rotatably supported scanning mirror 2. The reflected light 5 of the laser beam 4 is focused by a condensing lens 6 and received by a photodiode 7.

The analog signal 8 generated at the output of the photodiode 7 is binarized via a barcode detection bag e19 as described below. FIG. 5 shows a specific circuit of the barcode detection device 9.

Analog signal 8 is input to envelope circuit 11 via ms circuit 10. The envelope circuit 11 is a first peak value hold circuit 1 configured with an operational amplifier OP1.
2 and an operational amplifier OP2, and the output of the first peak hold circuit 12 is a signal of the higher peak change of the analog signal 8 (hereinafter, a positive envelope signal). A] is generated, and a signal B (hereinafter referred to as a negative envelope signal) of the lower peak change of the analog signal 8 is generated at the output of the second peak hold circuit 13. The positive envelope signal A and the negative envelope signal B are applied to a voltage divider circuit 14, and the output of the voltage divider circuit 14 is sometimes a divided voltage signal C at an intermediate potential between the positive envelope signal A and the negative envelope signal B.
occurs. The binarization circuit 15 binarizes the analog signal 8 using the occasional level V1 of the divided voltage signal as a threshold as shown in FIG.

Problems to be Solved by the Invention In such a conventional configuration, the threshold value in the binarization circuit 15 changes depending on the level of the analog signal 8 to be binarized.
Even if the level of the analog signal 8 changes somewhat overall, it can be stably binarized.

Such a binarization method is generally called a floating slice level method.

However, if the barcode 1 is dirty or if the analog signal 8 contains large noise, it is not possible to obtain a binarized output corresponding to the target barcode 1. FIG. 7 shows the binarization operation in this case, in which noise 16 is superimposed on analog signal 8. When the level of the analog signal @8 changes due to the noise 16, a state will occur where it crosses this level ■1 with respect to the level ■1 of the divided voltage signal C. There is a problem in that erroneous binarized output occurs in interval 17 and interval 18 immediately following.

The present invention provides barcode detection that enables more accurate binarization than conventional methods even when the barcode is dirty or has noise in floating slice level binarization processing. The purpose is to provide equipment.

Means for Solving the Problems The barcode detection device of the present invention includes an envelope circuit that detects a positive envelope signal and a negative envelope signal of an analog signal obtained by scanning a barcode, and a a voltage divider circuit that divides the output potentials of positive and negative envelope signals to output a first signal at an intermediate potential between the two envelope signals; a subtraction circuit that outputs a second signal at a potential; a comparison circuit that selects and outputs a signal with a lower level from the first signal and the second signal; The present invention is characterized in that it further includes a binarization circuit that binarizes the analog signal using an output potential as a threshold value.

Effects According to this configuration, when the binary circuit is broken, the first signal generated at the output of the voltage divider circuit is not always used, but only one of the first and second signals is used. , the potential of the signal selected by the comparison circuit is used as the threshold. therefore,
Even if the analog signal to be binarized is vibrating due to barcode dirt, noise, etc., in this case, binarization is performed using the second signal as a threshold, and accurate binarization processing is performed.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3. Components having the same functions as those shown in FIGS. 4 and 5 showing the conventional example will be described with the same reference numerals.

FIG. 1 shows a barcode reading device employing the barcode detection device of the present invention, in which a subtraction circuit 19 and a comparison circuit 20 are shown.
The only difference from the conventional configuration shown in FIG. 4 is that . A subtraction circuit 19, a variable resistor 21 for voltage setting, and an operational amplifier OP for subtraction operation as shown in FIG.
3, a positive envelope signal A is applied to the non-inverting input terminal (+) of the operational amplifier OP3 via the buffer-connected operational amplifier OP4, and a variable resistor is connected to the inverting input terminal (-) of the operational amplifier OP3. 21 output voltage ΔV is applied. The output of the subtraction circuit 19 is a second signal subtracted by Δ■ from the occasional level of the positive envelope signal A.
A signal @D [see Fig. 3(a)] is generated. In the following explanation, the voltage dividing signal C [ generated at the output of the voltage dividing circuit 14]
Refer to FIG. 3(b)] will be referred to as the first signal @C.

The comparison circuit 20 includes a switching diode 22 and a resistor 2.
3, and its output has a first signal C and a second signal C.
The signal with the lower level is generated. 2
In the value converting circuit 15, the third
The analog signal 8 is binarized using the level of the signal E as a threshold.

FIG. 3(C) shows how the binarization circuit 15 performs binarization. The situation is as follows. In the interval 17 immediately before and the interval 18 immediately after reading the barcode 1, the level of the second signal C is lower than that of the first signal C, so the comparing circuit 20 detects the third signal C. Second as E
In the binarization circuit 15, the analog signal 8 is binarized using the occasional level of the second signal as a threshold. As shown in FIG. 3(C), the level of the third signal E in this section is lower than the level of the analog signal 8 which is vibrating due to dirt on the bar code, noise, etc., so in this section 17.18. No erroneous binary output is generated as in the conventional case. Target barcode section 2
4, the third signal E becomes the first signal C, which is the same as the conventional one, and the binarization circuit 15 performs 2m conversion using the same threshold as the conventional one.

In this way, by adding the reduction circuit 19 and the comparison circuit 20 and switching the threshold of the binarization circuit 15, it is possible to obtain an initial start margin when reading a barcode, and it is possible to obtain the initial start margin when reading a barcode. Even if the analog signal @8 is vibrating, accurate binary output corresponding to the target barcode can be obtained.

Effects of the Invention As described above, according to the present invention, there is provided a voltage divider circuit that outputs a first signal at an intermediate potential between positive and negative envelope signals generated from an analog signal to be binarized, and a a subtraction circuit that outputs a second signal with a potential lower by a predetermined level from the divided voltage signal; and a comparison circuit that selects and outputs the lower level signal of the first signal and the second signal from time to time. Since it is configured to switch the threshold of the binarization circuit, even with the floating slice level method,
The starting margin can be made larger than before,
Even if the analog signal to be binarized is vibrating due to dirt or noise on the barcode, it is possible to obtain accurate binarized output corresponding to the target barcode. This can contribute to avoiding the situation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the barcode detection device of the present invention, FIG. 2 is a specific configuration diagram of the device, and FIG. 3 is an explanatory diagram of threshold values for binarization processing in the device. Fig. 4 is a block diagram of a conventional barcode detection device, Fig. 5 is a specific configuration diagram of the same device, and Fig. 6 is an explanatory diagram of binarization processing when the analog signal to be converted to 2tn is not vibrating. , FIG. 7 is an explanatory diagram of the binarization process when the analog signal to be binarized is oscillating. 1... Barcode, 8... Analog No. 48, 9...
・Barcode detection device, 11...envelope circuit,
14... Voltage dividing circuit, 15... Binarization circuit, 19...
- Reduction circuit, 20... Comparison circuit, A... Positive envelope signal, B... Negative envelope signal, C...
First signal, D... second signal. Agent Yoshihiro Moriki 1st figure p... 2nd license figure 4 figure 2 figure 7

Claims (1)

[Claims] 1. An envelope circuit that detects the positive envelope signal and negative envelope signal of the analog signal obtained by scanning the barcode, and divides the output potential of the positive and negative envelope signals generated at the output of the envelope circuit. a voltage divider circuit that outputs a first signal at an intermediate potential between the two envelope signals, and a subtraction circuit that outputs a second signal at a potential lower by a predetermined level from the divided voltage signal generated at the output of the voltage divider circuit; a comparator circuit that selects and outputs a signal with a lower level from time to time between the first signal and the second signal, and binarizes the analog signal using an output potential generated at the output of the comparator circuit as a threshold; A barcode detection device equipped with a binarization circuit.