JPS6037951B2 - Barcode detection circuit - Google Patents

Description

[Detailed Description of the Invention] For example, as a means of detecting unique information of moving objects such as vehicles and containers at a cargo handling field, information encoded in binary code or numerically is transmitted to each moving object in black and white bars of different widths. Conventionally, a barcode plate with a combination of and alternating arrays is attached, and a barcode detection device installed at a fixed point optically scans and detects the barcode to read the barcode. For barcode detection, the intermediate tone between black and white is used at the slice level.
) to detect black bars and white bars.

FIG. 1 is an explanatory diagram of a conventional detection method. A is an example of a bar code, in which black bars and white bars are arranged alternately, and the width of each bar is selected to be long or short based on the center of the code. b is a level diagram in which the code of a is optically scanned and detected using, for example, the movement of a moving object and converted into an electrical signal, where the black bar outputs the B level and the white bar outputs the W level. For such detected waveforms, black and white bars are distinguished by setting the intermediate S level between black and white as the slice level, but in reality, barcode boards often get dirty in various ways.
It is not always possible to obtain a detection waveform in which black and white can be easily detected. For example, if the barcode plate becomes dirty and the reflection decreases toward the black side, the waveform may be biased toward the B level side, as shown in the c waveform, and the W level side may not be output. On the other hand, if there is dirt on the white side and the black reflection becomes large,
Like the d waveform, the B level side may not be output because it is biased towards the W level side. In this way, there are cases where the signal does not intersect with the S level, and in this case, the detection of the barcode becomes ambiguous, and black or white bars are detected continuously, making it impossible to discuss the entire width of the bar. . The present invention relates to a barcode detection circuit which eliminates the above-mentioned drawbacks.The barcode plate is dirty and optically ideal black and white level detection cannot be performed. The feature is that the black and white levels are compressed so that even if there is dirt that makes black and white indistinguishable, accurate discrimination can be made, and this will be described in detail below.

FIG. 2 is a diagram showing an example of the configuration of a barcode detection circuit according to the present invention.

In the figure, 1 is a barcode board, 2 is a light source such as infrared rays, 3 is a photoreceiver consisting of a photoelectric converter, 4 is an operational amplifier (hereinafter abbreviated as OBE amplifier), 5 is a rectifier, 6, 7, and 8 are OBE amplifiers, 9 is an amplitude modulator, an oscillator for an AC signal or a carrier wave, 11 is a slide-back type detector, and 12 is a square wave conversion output circuit. Further, FIG. 3 is an operation waveform diagram of each part of FIG. 2, and the operation of FIG. 2 will be explained using this diagram. Second
In the figure, it is assumed that the barcode plate 1 displays, for example, the barcode shown in FIG. 3a.

B is a black bar and W is a white bar. The plate 1 is irradiated with, for example, infrared rays from a light source 2, and the light receiver 3 receives the reflected light from the black and white bars of the barcode as the moving body moves, and thus the barcode plate 1 moves relative to the light source 2. It is converted into an electrical signal and output. Note that in order to ensure detection and also to enable barcode detection when the moving object is stopped, the light source 2 and the light receiver 3 may be combined with a mechanism for scanning the barcode plate. Here, considering the case where the barcode plate 1 runs at a constant speed, as shown in the waveform g in Fig. 3, the W of the barcode a has a white bar level W, the B has a black gs level wave, and the bar level B has a gs level wave. It is output from the light receiver 3.
In addition, g's eww and bell are assumed to be the maximum white bar (maximum reflection by the white bar), and eBB is the maximum black level (the non-reflection level by the black bar, which is actually the lowest level, but hereinafter referred to as the maximum black level). It is. Therefore, even if the barcode board is dirty, gs is output at a level within the range of e88 and e side. Note that the broken line portions at both ends of the gs correspond to non-reflective black bars without a barcode plate. Receiver 3
The output gs is input to the e terminals of the amplifiers 4 and 7.

First of all, in obeamp 4, the above eww is input via the other input terminal.
3, the hs level of the h waveform shown in FIG. The charging time constant of the rectifier 5 is set to a value of 4 mm that can sufficiently follow the bar code detection speed, and the discharging time constant is set to a value sufficiently larger than the bar code detection speed. Therefore, when the input hs level is rectified, the hd level in FIG. 3 becomes the output. This hd level is equal to the level of the difference between the assumed maximum level e side of the white bar and the black bar envelope of the output gs of the photoreceiver 3, but it is input to the next stage oven amplifier 6 and is equal to the assumed maximum level eBB of the black bar. Calculate the difference between the relative value e88 and e'88 (e'BB>0), which is the sign-inverted level of the difference between e88 and e's cape (Fig. 3 h waveform), and output the e8d level of the i waveform to the obe amplifier 8. do. On the other hand, the output gs of the photoreceiver 3 is inputted to the e terminal of the oven amplifier 7, and the difference with the eBB level given to the terminal is calculated here, and the is level of the i waveform is output, and the output is input to the ■ terminal of the oven amplifier 8. Enter.

Note that the level of the black bar B of this j waveform holds the difference level eB from the eBBta level. The obeamp 8 calculates the difference between the eBd level of the i waveform and the is level of the i waveform, and outputs the ks level of the k waveform. To summarize the above, the maximum level of the black bar and white bar for eww > gs > e88 is set to 0, and for obeamp 4, eww-
g9=hs......[1
The rectifier 5 in the next stage performs envelope detection of the black bar B level and outputs hd, and the amplifier 6 outputs the difference between e'8B equivalent to eBB and hd (e'cB>hd) data hd
1e'88neeeBd (outputs 21).

On the other hand, in oven amplifier 7, the difference between eBB and gs (g3>eBB
)eBB1gs=113 “””…'3}
On the other hand, in the OBE amplifier 8, eBd-ls=k3 "" from the input of -eBd and -i30.
“…[4'] is output.

The difference between the black bar B level of gs and eBB is e8,
Since e'B8 is the level equivalent to eBB, eB=e
Since it is Bd and therefore ks=EB-j3, the black bar B level becomes zero level here as shown in the k waveform.
Next, the amplitude modulator (MOO) 9 is inputted to the k waveform as a modulation input, while the oscillator 10 outputs a frequency L that is sufficiently higher than the bar code detection speed - for example, if the detection speed is 10 kbaud, then 100 KHz ~ A carrier wave of - taken on 50 days 2 is input, on-off type amplitude modulation is performed, and one waveform shown in FIG. 3 is outputted to the next stage slide-back type detector 11.

FIG. 4 is an example diagram of a configuration circuit of a slide-back type detector (DET), and FIG. 5 is an example diagram of waveforms of each part of FIG. 4.

In FIG. 4, T is a coupling transformer, w,, w2 are secondary windings of T, and the turns ratio is w. /w2=2. D, , D2 are diodes, C, , C2 are capacitors, and R, , R2 are resistors. In addition, the time constants due to C and R are small enough to follow the barcode detection speed, the charging time constants due to D2 and C2R2 are enough to follow the barcode detection speed, and the discharging time constant is set to a value sufficiently larger than the barcode detection speed. Configure each of them. For example, if the 1' waveform in FIG. 5 is input to the transformer T, then w, . The detection circuit composed of D,,C,,R outputs the p waveform in Figure 5, and w2, D2, C
A q waveform is output from the rectifier circuit composed of 2 and R2, and a p waveform is output.
Since q has positive polarity and q has negative polarity, the output of the detector obtained by differentially combining these in series becomes an Enoki current signal as shown in the waveform r in Fig. 5. Returning to Figure 2, in DETII, the input of one waveform is output as m waveform in Figure 3, and from the next stage square wave conversion output circuit (for example, a flip-flop circuit is used). The zero level of the m waveform is used as a conversion level, and a square wave n is output, which is converted from a positive bell input to an H level, and from zero and negative level inputs to an L level, and has a duration corresponding to the width of the bar. It is clear that this n waveform is the information output from reading the barcode. Next, for example, barcode a is stained towards Kuroyanagi and the third
When the gs level of the waveform g in the figure becomes smaller and is biased toward eBB, e8 naturally becomes smaller. Furthermore, the h3 level of the h waveform increases, and therefore the eBd of the i waveform decreases. On the other hand, the black bar B level of the i waveform is large, and therefore gB of the i waveform is small. By subtracting these i and i waveforms, e8=
e8d is subtracted, and a k waveform with black bar B at zero level is output. As mentioned above, the i and i waveforms differ depending on the state of dirt on the barcode plate, but the fact remains that the ks amplitude level of the k waveform hardly changes and the black bar B is subtracted to zero level. Therefore, although the amplitude of the 1.m waveform is different from that in the case of no dirt, a double flow signal of the m waveform is output.
A square wave n is obtained which is a code output depending on whether the bar is black or white and its width. This can be expressed by the formula m~{4} as follows, and the influence of the level bias Δ does not appear on the ks level as in the formula [4}'. (Actually, Δ is not common to all waveforms, and the amplitude of ks changes somewhat depending on the dirt.
) {1r eWW-(g31△)=hS-△'2r h
d+△-e'BB=-eBd+△'3}' eBB-(
gS-△)=-is+△'4r e8d-△-Js=k
sAlso, even if the barcode a is dirty towards the white side, the bias △ of the opposite level to the above is processed, so the same result is obtained and the m waveform is output, so the barcode can be detected accurately. be able to.

Furthermore, even if the amplitude levels B and W of the black bar and white bar of the output g waveform of the photoreceiver 3 are extremely small, a 1, m waveform proportional to the amplitude level is output, so the level of the m waveform is the square wave conversion output. As long as the hysteresis of the circuit 12 is exceeded, barcode detection is possible. Therefore, c in Figure 1
, d waveform, even if a photoreceiver output occurs, c. Black and white bars can be distinguished by slice level setting processing that assumes the center level of the amplitude of the d waveform, so the drawbacks of the conventional method can be eliminated. In the above explanation, the difference eBd between the envelope level of the black bar B level of the receiver output g and the non-reflection level eBB of the black bar is calculated, and by subtracting this difference and the difference eo between g and eBB, It was shown that the black bar B level of g is set to zero level, but on the contrary, g
Calculate the difference between the envelope level of the white bar W level and the maximum reflection level eww of the white bar, and calculate this level, g and ew
A similar result can be obtained by using means for setting the white bar W level of g to zero from the calculated value of the difference in w.

Also, as explained above, the reason for detecting the difference e8d between the envelope of the gs black bar B level and the temporary black bar maximum level eBB is that the output g of the light receiver 3 in the absence of a barcode plate is the reflected light. Since there is little, the black bar level is output (the B level wavy lines at both ends of the waveform in Figure 3 are this output), but next, the white background (white bar) and black bar at the beginning of the barcode are read. This is to make it possible to detect the above-mentioned bell at an early stage.

As explained above, this detection circuit allows barcode analysis to match the intermediate level between the black and white bar detection levels to the slice level even if the barcode board is soiled toward either the black or white side. By configuring the circuit in such a way, it will be possible to distinguish between black bars and white bars, and this will enable accurate detection of the widths of black and white bars. Automatic negotiation of information required for control has been realized, and can greatly contribute to the management of mobile objects and their labor savings.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional barcode detection method, FIG. 2 is an example of the configuration of the circuit of the present invention, FIG. 3 is an example of the operation waveforms of each part in FIG. FIG. 5 is an example circuit diagram of a slide-back type detector, and FIG. 5 is an example diagram of waveforms of each part of FIG. 4. 1...Barcode board, 2...Light source, 3
......Photodetector, 4,5,6,8...Operation amplifier, 5...Rectifier, 9...Amplitude modulator, 10... AC generator, 11...Slideback type detector, 12...Square wave conversion output circuit. Juice 1 figure Uwa 2 figures ★ 4 figures Juice 5 figures Spear 5 figures

Claims (1)

[Claims] 1 Binary code information is arranged alternately and the length corresponding to the code,
A light source and a light receiver that optically scan the barcode display surface and convert reflected light into electrical signals, as a circuit for detecting codes from the barcode display surface represented by short white bars and black bars. and a step that calculates the difference between the white bar maximum level value set as the maximum value of the white bar reflected output of the light receiver or the black bar minimum level set as the non-reflection minimum level of the black bar and the bar code detection output of the light receiver. 1 arithmetic unit and a detector that performs envelope detection of the output of the first arithmetic unit; The reflection level of the black bar or white bar of the barcode and the minimum of the black bar are comprised of a second calculating unit that calculates the difference between the maximum level setting value and the sign-inverted level value of the difference between the black bar minimum level value and the minimum level value of the black bar. a circuit group for calculating the difference level from the level setting value; a third calculating unit for calculating the difference between the minimum level of the black bar or the maximum level setting value of the white bar and the barcode detection output of the light receiver; a fourth arithmetic unit that calculates the difference between the output of the arithmetic unit and the output of the arithmetic circuit group; amplitude modulation means that uses the output of the fourth arithmetic unit as a modulation input; and detection that performs slide-back type detection of the output of the modulation unit. and a square wave converter that converts the output of the detector into a square wave and outputs a binary code.