JPS6154571A - Bar code reader - Google Patents

Abstract

PURPOSE:To prevent misdetection with a bar code reader by sampling the bar code analog signal to compare the sample values with each other and deciding the rise and fall from the preceding and next values and at the same time deciding the width of the bar code when the value of dV/dt exceeds a reference level. CONSTITUTION:For the bar code analog signal, the 1st holding circuit 3 holds the value Vn which is sampled by the clock given from a clock oscillator 2. Then the 2nd holding circuit 4 holds the sample value Vn-1 preceding by a step, and a detecting circuit 5 compares both values with each other to decide the rise and the fall. Then the data signal is outputted 1 and at the same time the absolute value of the voltage difference is outputted. This absolute value is compared with the reference voltage Vc given from a reference voltage generator 7 by a dV/dt comparator 6. Then the pulse signal is outputted when the absolute value of the voltage difference exceeds the voltage Vc. This pulse signal and the data signal are supplied to a flip-flop circuit 8. Then the bar code digital signals are outputted.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a barcode reader, and more specifically, the invention relates to a barcode reader that is affected by waveform distortion and noise generated in a barcode analog signal read by a reading head. The invention relates to a barcode reader that can accurately decode data without any problems.

[Conventional technology]

In recent years, bar and code readers have come to be widely used in warehouses, distribution centers, factories, etc. for automatically collecting product information, automatically sorting, giving work instructions, etc.

A barcode reader uses reflected light from the barcode label surface (
It is a device that recognizes data by receiving (or transmitted light) and includes a reading head section and a decoder section incorporating a microprocessor (CPU) for decoding the contents of a barcode.

The main components of the barcode reader will be explained with reference to the drawings.

Diagram M3 is a block diagram of the barcode reader.

As shown in the figure, the analog signal of the barcode taken in by the reading head section 10 is sent to the decoder section 2o. The decoder section 20 includes an A/D converter 21 that shapes the waveform of the analog signal and converts it into a digital signal;
It is equipped with a counter 22 that converts the output of the D converter 21 into 8 elements (counts the waveform and examines the pattern), and a judgment circuit 23 that decodes the contents of the barcode from the output of the counter 22. The code data is transferred to an external device (host computer) 30 via an interface 24.
It is now output to . Incidentally, the A/D converter 21 for converting the barcode analog signal into a barcode digital signal has conventionally had a circuit configuration as shown in FIG. 4, for example.

That is, a white peak hold circuit 211 holds the peak of the white part of the input barcode analog signal, a black peak hold circuit 212 holds the peak of the dot part, and the output of the above peak hold circuits 211 and 212 is used to A threshold detection circuit 21 that determines whether the input analog signal is white or black and at the same time determines the signal width at the midpoint between the white and black holds.
3, and a comparator 214 that converts the output of the threshold detection circuit 213 into a barcode digital signal and outputs it.
It is configured with.

[Problem to be solved]

In the conventional A/D converter described above, a conversion operation as shown in FIG. 5 is performed. That is, when a barcode as shown in FIG. 5(a) is read and the barcode analog signal shown by the solid line in FIG. 5(b) is input to the A/D converter, the white and black peak hold circuits 211 and 212 are
The white peak and black peak are held as shown by dotted lines and broken lines in FIG. 5(b). Each peak hold circuit discharges at a fixed predetermined time constant in order to sequentially hold the peaks of the input barcode analog signal. The threshold detection circuit 213 finds the intermediate value between the white and black peak values, extracts the signal width at the intermediate value, and converts it into a barcode digital signal as shown in FIG. 5(C) by the comparator 214. .

Incidentally, the input barcode analog signal is affected by the position and angle when the reading head unit 10 scans the barcode label surface (effects due to defocusing of the scanning light beam, etc.), and is also affected by noise (barcode In some cases, the waveform may be distorted as shown in Figure 5 (<d'') due to the effects of uneven printing, external light, etc. In this case, it becomes impossible to detect the peak value of the input signal. However, as a result, accurate threshold detection (extracting the intermediate value) becomes impossible, and a digital signal as shown in Figure 5(e) is output.In other words, the data from the read barcode label surface is There is a problem that it is not deciphered correctly.

The present invention was made to solve these problems, and an object of the present invention is to provide a barcode reader that can accurately decode data even if the barcode analog signal is distorted. It is.

Means for Solving Problem C] The cause of the above-mentioned problem is that the discharge time constant of the peak hold circuit is fixed and that accurate threshold detection may become impossible. The circuit configuration had an essential flaw. Therefore, A/ of the present invention
The D converter is constructed using a new circuit that is completely different from conventional circuits.

In other words, each intermediate value of the barcode analog signal waveform (
In order to find the value corresponding to the width of each bar, two holding means sample the input barcode analog signal waveform and sequentially hold the sampled values, and the differential coefficient ( dV/d
A rising/falling detection circuit is provided which sequentially obtains the voltage t (where ■ is the voltage and t is the sampling time) and outputs a data signal by detecting its absolute value (voltage value) and whether it is rising or falling.

A/D conversion outputs a pulse signal when the absolute value voltage output of this detection circuit exceeds a predetermined reference voltage 0 V/d
This is done by a flip-flop circuit that inputs a t comparator, the pulse signal output from the dV/dt ratio comparator, and the data signal detected as rising or falling, and outputs a barcode digital signal. did.

[Effect]

The A/D converter of the barcode reader of the present invention converts the barcode analog signal into a clock of a predetermined frequency (at 1 adt
>, and calculate the voltage difference (dV) before and after the sample value.
) and directly converts it into a barcode digital signal, and the peak value of the barcode analog signal is irrelevant, so it is accurate even if the input barcode analog signal is distorted or the level is low. can be converted into a digital signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of an A/D converter of a barcode reader of the present invention, and FIG. 2 is a waveform diagram for explaining its operation. In FIG. 1, 1 is an input terminal into which a barcode analog signal is input, 2 is a clock oscillator that generates a clock signal for sampling, and 3 is a first
The new sample value Vn (V+,
V:.

■3...) [see Figure 2 (a)]; 4 is a second hold circuit; similarly, the previous sample value V1-+ (Vo, V +, V
2...) [see Fig. 2 (a)].

5 is a rising/falling detection circuit, and the first and second hold circuits 3 and 4 are shown in bold! Input Vn and Vl-9, compare them, and if V t-+ > V n, it is determined that the barcode analog signal is in a falling state, and V t
If +l < V n, it is determined that the barcode analog signal is in the rising state, and the data signal [Figure 2 (b)
), the absolute value of the voltage difference at that time l
It outputs Vt-1-Vnl [see FIG. 2(C)].

6 is a dV/dt ratio calibrator, and the above absolute value voltage! Vx-+
-Vn I is compared with the reference voltage ■c from the reference voltage generator 7 [see Figure 2 (C)], and when the absolute g1 voltage exceeds the predetermined reference voltage Vc, a pulse signal [Figure 2 (d) ) reference] is output.

8 is a flip-flop circuit, and a rising/falling detection circuit 5
A data signal indicating the rising or falling state that occurred [
A barcode digital signal (9721m (e)) is generated at the output terminal 9 by inputting the pulse signal [Fig. 2(d)] generated by the dV/dt comparator 6 as shown in Fig. 2(b)]. .

〔effect〕

As explained above, the A/D converter of the present invention samples the input barcode analog signal, sequentially compares each sample value, and determines the rise and fall of the waveform directly from before and after. Since the width of the barcode is determined by detecting the point where the value of dV/dt exceeds the reference voltage value VC, there is no possibility of missing barcode detection as in the past, and accurate digital signals can be obtained. conversion is performed. Therefore, the barcode reader of the present invention equipped with this A/D converter does not have the disadvantage of not being able to decode the barcode read by the reading head.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the A/D converter of the barcode reader of the present invention, FIGS. 2(a) to (e) are waveform diagrams for explaining the operation of the A/D converter, and FIG. 3 is a block diagram of the A/D converter of the barcode reader of the present invention. A block diagram of a barcode reader, Figure 4 shows the A/D of a conventional barcode reader.
The block diagram of the converter and FIGS. 5(a) to 5(e) are waveform diagrams for explaining the operation of a conventional A/D converter. 2...Clock oscillator, 3...First hold circuit, 4...Second hold circuit, 5...Rise and fall detection circuit, 6・・・・・・
dV/clt comparator, 7...Reference voltage generator, 8...Flip-flop circuit, 10...
-Reading head section, 20...decoder section, 21...A/D converter.

Claims (1)

[Claims] 1. Barcode data comprising a reading head section that reads a barcode from the barcode label surface and an A/D converter that converts the barcode analog signal output from the reading head section into a digital signal. A barcode reader comprising a decoder unit for decoding a barcode, and the A/D converter includes two holding means for sampling an input barcode analog signal waveform and sequentially holding the sampled values. , sequentially compares the sample values before and after held by the two holding means, detects whether the barcode analog signal waveform is in a rising or falling state, generates the data signal, and at the same time outputs the sample values before and after. a rising/falling detection circuit that outputs the absolute value voltage of the difference in values; a dV/dt comparator that outputs a pulse signal when the absolute value voltage from the rising/falling detection circuit exceeds a predetermined reference voltage; 1. A barcode reader comprising a flip-flop circuit that receives a data signal and the pulse signal and outputs a barcode digital signal.