JPH05182008A - Agc circuit in decoding processing part for bar code reader - Google Patents

Abstract

PURPOSE:To permit an AGC circuit to hold the amplitude of a bar code label read waveform, which changes by a distance to a bar code label, a PCS value and bar width, to be specific. CONSTITUTION:The AGC circuit composed of a pulse value difference detector 2, of a differential amplifier 4 inputting a bar code read signal to an inversion input terminal through a peak value detector 1 and inputting a pulse value difference reference value 3 to a non-inversion input terminal, an A/D converter 5 which A/D-converts the detection signal of the differential amplifier 4 and of a comparator inputting the bar code read signal and inputting the output signal of the A/D converter 5 to the variable resistor of a feedback circuit as feedback quantity is provided for the amplifier circuit of a decoding processing part in a bar code reader.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an AGC circuit in an amplifier circuit of a decoding processing unit in a bar code reader to keep the read bar code signal level constant.

[0002]

2. Description of the Related Art As shown in FIG. 5, a decoding processing section of a bar code reader in the prior art inputs a bar code signal obtained by reading a bar code label printed on the surface of an article by optical means, and outputs this signal. Photoelectric conversion circuit 10
1, the amplification circuit 102, the binarization processing circuit 103, and the decoder 104, and outputs as bar code information. Generally, a barcode label reading signal by a barcode reader is determined by the distance from the reading portion of the barcode reader to the barcode label printed on the surface of the article, the PCS value (Print Contrast Signal) and the bar width of the barcode label. The signal level changes due to the influence. In order to reduce the fluctuation of the bar code signal level due to the above-mentioned factors, the decoding processing section is provided with the amplifier circuit 102, and the bar code signal input by the amplifier circuit 102 is amplified by a constant amplification factor.

[0003]

The read signal of the bar code label by the bar code reader is influenced by the working environment, the surface condition of the article on which the bar code label is printed, and the handling method of the operator. Amplification of the code signal at a constant amplification factor is not sufficient, and the signal may be too small or may be saturated, and the bar code label may not be read accurately. The present invention has been made in order to solve the above-mentioned drawbacks of the decoding processing circuit according to the prior art, and provides the decoding processing unit with an AGC circuit capable of holding the read bar code signal level constant.

[0004]

In order to solve the above-mentioned problems, the AGC in the decoding processing unit according to the present invention.
The circuit inputs the bar code signal read by the optical means to the differential amplifier via the signal waveform peak detection circuit and the peak value difference detection circuit, and sets the peak value difference reference value preset in the differential amplifier. The detected value of the differential amplifier is compared with the detected value of the peak value difference detection circuit to detect the difference, and the detected value of the differential amplifier is fed back to the variable resistor provided in the feedback circuit of the operational amplifier for inputting the read bar code signal. By
The output signal level is kept constant by eliminating the difference between the level of the read signal waveform of the barcode label and the reference signal level.

[0005]

In the differential amplifier, the maximum peak value difference of the bar code label read signal is compared with a preset peak value difference reference value to obtain the difference, and this detected value is provided in the feedback circuit of the operational amplifier. Input to variable resistor. Since this variable resistor is of a digital signal input type, it gives the operational amplifier a feedback amount precisely corresponding to the detected value of the A / D converted differential amplifier. As a result, the bar code label read signal input to this operational amplifier is corrected by the detection value of the differential amplifier, and the output signal level (AGC output) is held constant.

[0006]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block circuit diagram showing a circuit configuration of an AGC circuit according to the present invention. In FIG. 1, the bar code label read signal is a signal waveform peak detection circuit 1
And the peaks of the space portion and the bar portion in the barcode label are detected. The peak signal of the space portion and the bar portion is input to the peak value difference detection circuit 2, and is input to the inverting input terminal of the differential amplifier 4 as the difference (maximum peak value) of the peak value of the space portion and the bar portion. Since the preset peak value difference reference value 3 is connected to the non-inverting input terminal of the differential amplifier circuit 4, the maximum peak value detected by the peak value difference detection circuit 2 and the peak value difference reference value are Is input to the variable resistor 15 provided in the feedback circuit of the operational amplifier 6 via the A / D converter 5. The variable resistor 15 is of a digital signal input type and includes a differential amplifier 4
The resistance value is precisely adjusted to the detection signal from.
Therefore, the operational amplifier 6 for inputting the bar code label read signal has the resistor 16 and the variable resistor 15 provided in the feedback circuit.
Since the feedback amount is precisely adjusted by, the difference between the bar code label read signal label and the reference signal label can be eliminated and the AGC output signal can be kept constant.

Next, detailed circuit configurations of the signal waveform peak detection circuit 1 and the peak value difference detection circuit 2 of the bar code label read signal are as shown in FIGS. 2 and 3, and signals at respective points constituting the circuit are shown. A waveform time chart is shown in FIG. The signal waveform peak detection circuit 1 is composed of the waveform differentiating circuit 21 and the peak value detecting circuit 22 in FIG. 2, and the peak value difference detecting circuit 2 is the peak value detecting circuit 23, the peak hold circuit 24 in FIG. The amplification circuit 25 and the maximum peak value detection circuit 26 in FIG.

The waveform differentiating circuit 21 includes a buffer 31, an operational amplifier differentiating circuit 32, two comparators 33 ₁ ,
33 ₂ is constituted by a read signal of the bar code label entered in the buffer 31 becomes a differentiated waveform at the output of the differentiating circuit 32 becomes a square wave at the output of the comparator 33 _1, it is shown in FIG.

The peak value detection circuit 22 has two flip-flops.
The output signals from the output terminals of the flops 35 ₁ and 35 ₂ are the space peak signal and the bar peak signal, respectively, as shown in FIG.

The peak value detecting circuit 23 includes a buffer 34, and two analog switches 36 ₁ and 36 ₂ and 3 respectively.
7 ₁ and 37 ₂ , and the space section crest signals sent from the analog switches 36 ₁ and 36 ₂ and the bar crest value signals sent from the analog switches 37 ₁ and 37 ₂ are shown in FIG. On the street.

The peak hold circuit 24 is composed of _two peak hold circuits 38 ₁ and 38 ₂ , and the space portion sample hold signal and the bar portion sample hold signal from the respective output terminals are as shown in FIG.

The amplifier circuit 25 is composed of two operational amplifiers 39 ₁ and 40 ₁ and 39 ₂ and 40 ₁ , respectively, and a differential signal a at its output terminal is as shown in FIG.

The maximum peak value detection circuit 26 is composed of three operational amplifiers 41, 42, 43 and a transistor 44. The maximum peak value (Pmax) b is output from the output terminal of the operational amplifier 42, and its signal waveform is shown in FIG. As shown in. The operational amplifier 43 and the transistor 44 are provided for erasing the maximum peak value (Pmax) of the data.

[0015]

As described above, the AGC circuit in the decoding processing unit of the bar code reader according to the present invention compares the peak value difference peak of the read bar code signal with the peak value difference reference value in the differential amplifier. By returning the difference signal to the operational amplifier, the read bar code signal level is held constant. Therefore,
Since the amplification of the barcode label reading waveform that changes depending on the distance to the barcode label, the PCS value, the barcode width, etc. can be made constant, errors in reading the barcode label can be reduced.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an AGC circuit in a decoding processing section showing an embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a circuit configuration of a signal waveform peak detection circuit and a crest value difference detection circuit.

FIG. 3 is a block circuit diagram showing a circuit configuration of a peak value difference detection circuit.

FIG. 4 is a time chart of signal waveforms.

FIG. 5 is a block circuit diagram showing a circuit configuration of a decoding processing unit of a conventional example.

[Explanation of symbols]

 1 signal waveform peak detection circuit 2 crest value difference detection circuit 3 crest value difference reference value 4 differential amplification circuit 5 A / D converter 6 operational amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinichi Kato 1-10-12 Ueno, Taito-ku, Tokyo Nidec Electric Seiki Co., Ltd.

Claims (1)

[Claims] 1. A decoding processing unit of a bar code reader which reads a bar code label printed on the surface of an article by optical means, processes the read bar code signal and sends out the bar code information as bar code information. The difference between the crest value difference of the waveform in the code signal and the preset crest value difference reference value is detected by a differential amplifier, and through a variable resistor provided in the feedback circuit of the operational amplifier for inputting the read bar code signal. An AGC circuit in a decoding processing unit of a bar code reader, wherein the detection value of the differential amplifier is fed back to adjust the read signal level of the bar code label to a reference signal level.