JPH10154201A - Symbol information reading device having disturbance light correcting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a symbol information reading device having a disturbance light correcting function for correctly reading the information of barcode signal even in the environment in which a disturbance light such as an artificial light and the sunlight or the like originally unneeded is made incident. SOLUTION: This information reading device is composed of a current-voltage converting part 1 for generating an information signal from a reflected light from a symbol, an operational amplifying part 9 for extracting a pulsating flow signal of the diffused external light (AC component) from the information signal and amplifying it in the case where the disturbance light is superimposed on the information when in reading, a rectifying part 7 for converting the pulsating signal into a DC voltage signal, and a current (light quantity) resistance converting element 6 for converting a resistance value into that proportion to the converted amount of the DC voltage signal. This device has the disturbance light correcting function for restraining an waviness in an output voltage owing to the disturbance light and a sudden change in AC by varying the synthesizing feedback resistance of the current- voltage converting part 1 corresponding to the change quantity of the DC voltage obtained by the signal intensity of the disturbance light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reader having a scanning element for optically reading a symbol such as a bar code symbol, and more particularly to a symbol information reader for reading a signal component of a symbol without being affected by disturbance light. Related to the device.

[0002]

2. Description of the Related Art In general, a symbol is irradiated with a light beam,
A device that converts the reflected light into an electric signal and reads information to be described is known. As a representative example of this symbol, for example, a bar code symbol configured by arranging a plurality of bars and spaces is known. The information of the barcode symbol is irradiated with the laser beam light converged to a desired spot diameter by the optical element to scan the barcode symbol, and receives the reflected light from the barcode symbol,
The intensity of light obtained by the difference in reflectance of the reflected light is converted into an electric signal and read. Generally, such a reading apparatus employs a semiconductor laser diode (LD) as a light source.

[0003] The bar code symbol is printed on an article or an outer package for packing the article, or is printed and attached on a sticker or the like. Therefore, the reading of the barcode symbol is often performed under sunlight or some sort of lighting at a place where articles are distributed, for example, outdoors or in a warehouse. For this reason, the barcode symbol must be read in the presence of disturbance light such as artificial light or sunlight, which is originally unnecessary on the surface of the barcode symbol. Unnecessary light is mixed in, and in the current-voltage conversion circuit of the reading device, a signal due to disturbance light is superimposed on the read information signal of the bar code symbol, which greatly affects the reading performance.

[0004] When the amount of disturbance light reflected further increases, the ratio of the disturbance light signal to the read information signal increases, and eventually, even if a bar code symbol is read, the information described is read. No situation.

As a technique for solving these problems, Japanese Patent Application Laid-Open Nos. 5-62002 and 5-19114 have been proposed. Of these, Japanese Patent Application Laid-Open No. 5-622002
Japanese Patent Laid-Open Publication No. 2000-214, proposes an optical reading device that adds an integrating circuit to a current-voltage conversion circuit that converts an output signal due to reflected light received by a light receiving element into a DC voltage signal, and corrects a DC component of an output voltage of the current-voltage circuit. Have been.

Japanese Patent Publication No. 5-19114 discloses that a feedback current is generated by charging and discharging a capacitor of a feedback circuit including a capacitor for feeding back a low frequency component to an output signal of a light receiving element, and only a signal component is output. Devices that have taken the approach have been proposed.

FIG. 4 shows a schematic circuit configuration of a conventional apparatus for reading symbol information such as bar code symbols. In this configuration, when reading a barcode symbol, the scanning mirror 3 is driven by a light source driving circuit 32 using a light emitting element such as a semiconductor laser diode as the light source 31.
3 is irradiated with an output beam. And the scanning mirror driving unit 3
4, the scanning mirror 33 is swung, the emitted beam is scanned on the bar code symbol 35, and the reflected light from the bar code symbol 35 is captured by the current-voltage conversion circuit 36 and converted into an electric signal. Output signal is differentiated by a differentiating circuit 3
7, the noise is removed by an amplifying / filtering circuit 38 and an AGC circuit 39, amplified to a predetermined voltage value, binarized by a binarizing circuit 40, and read by a data processing circuit 41. Circuit configurations for processing data are known.

[0008]

FIG. 5 (a) shows the reading of a bar code symbol in a state where disturbance light such as artificial light or sunlight exists on the surface of the bar code symbol as described above.
As a result, a signal waveform shown as a signal S1a is obtained. Like this
Unnecessary disturbance light is incident on the light receiving element at each scanning cycle at the same time as reflected light from the bar code symbol surface, and as a result, a steep amplitude change occurs in the output voltage of the current-voltage conversion circuit at a change in the light amount, and A large swell is generated in the signal as in the waveform shown by S1b.

As described above, if the obtained signal is distorted, not only is it not correctly converted by the current-voltage conversion circuit, but also an unnecessary signal is generated by the differentiating circuit. Correct digital data (signal S1c) is not generated, which greatly affects decoding performance.

FIG. 5B shows an enlarged signal waveform when the disturbance light shown in FIG. 5A is simultaneously incident, and should be output as indicated by A in the signal S2c. 2
The digitized signal is missing due to the influence of disturbance light.

Accordingly, the present invention provides a symbol information reading apparatus having a disturbance light correction function for accurately reading bar code symbol information even in an environment where disturbance light such as artificial light or sunlight which is originally unnecessary is incident. The purpose is to provide.

[0012]

According to the present invention, in order to achieve the above object, a symbol representing arbitrary information with a code having a different reflectance is scanned while irradiating with a light beam.
In a symbol information reading device that reads information expressed based on the intensity of the reflected light, feedback control is performed to generate a reflected light from the symbol into an information signal. When an information signal is generated from the reflected light in an environment in which the reflected light includes disturbance light, only a pulsating component generated by the disturbance light is extracted from the information signal generated from the reflected light including the disturbance light, and a level signal proportional to time is extracted. A symbol information reading device comprising disturbance light correction means for suppressing the output fluctuation caused by the pulsating current by varying either the feedback resistance value or the feedback current in the feedback control of the current-voltage conversion means. provide.

In the symbol information reading apparatus having the disturbance light correcting function having the above-described structure, when the disturbance light is incident on the light receiving element at the same time as the information signal light obtained by reading the bar code symbol, the output voltage of the current-voltage conversion means is reduced. The pulsating signal of only the pulsating component of the disturbance light is extracted from the swell of the signal generated in the step (1) and is converted into a DC voltage. Then, a current (light quantity) resistance conversion element that converts the resistance value into a resistance value proportional to the DC voltage conversion amount,
Varying the combined feedback resistance of the current-voltage conversion means, or
A feedback current is controlled by a voltage resistance element in proportion to the amount of conversion of the DC voltage, and output fluctuations of the current-voltage conversion means caused by the pulsating component are suppressed.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of a disturbance light correction / current / voltage conversion circuit that reads barcode symbol information while eliminating the influence of disturbance light in a symbol information reading device according to a first embodiment of the present invention. . In the present embodiment, components other than the disturbance light correction / current-voltage conversion circuit are the same as those of the conventional reader shown in FIG. 4, and only the characteristic portions will be described in the description of the present embodiment. I do.

The disturbance light correction / current / voltage conversion circuit of the present embodiment is a circuit corresponding to a current / voltage conversion circuit for receiving a reflected light beam reflected by a bar code symbol and generating a bar code information signal by photoelectric conversion. , A circuit provided before the differentiating circuit having the conventional configuration as shown in FIG.

The disturbance light correction / current / voltage conversion circuit is roughly divided into a current / voltage conversion unit 1 for converting reflected light from a bar code symbol into an electric signal, and a disturbance light mixed in an output signal of the current / voltage conversion unit 1. Only the pulsating current component (AC component) generated by the above is extracted and amplified, converted to a DC voltage, and converted by a current (light amount) resistance conversion element in accordance with the amount of change in the DC voltage obtained by the signal intensity of the disturbance light. A disturbance light correction unit that varies the combined feedback resistance (transimpedance) r of the current-voltage conversion unit 1 and suppresses the swell of the output voltage from the current-voltage conversion unit 1 and abrupt AC changes to reduce the influence of disturbance light. And 2.

The current-voltage converter 1 includes a light receiving optical system 3 for condensing reflected light from a bar code symbol and a light receiving element (photo signal) for photoelectrically converting the condensed reflected light to generate a photoelectric signal (information signal). PD) 4, an operational amplifier 5 for amplifying the information signal to a predetermined current / voltage value, feedback resistors R1, R2 and a capacitor C1 connected to input / output terminals of the operational amplifier 5.
It is composed of

The combined resistance of the resistors R1 and R2 connected in series between the inverting input terminal 5a and the output terminal 5b of the operational amplifier 5 becomes the transimpedance when converting a current to a voltage. A capacitor C1 connected in parallel with these resistors R1 and R2 is provided with an LPF (Low Pass Filtration) for removing unnecessary high frequency component noise contained in the signal.
ter). Also, one resistor R2 of the feedback resistor includes:
The variable resistance element r in the cadmium cell Cds6 is connected in parallel. The cadmium cell Cds6 is one of current (light) resistance conversion elements for converting a resistance value proportional to a conversion amount of a DC voltage rectified by a rectification unit 7 including a diode bridge described later.

The output terminal 8 of the current-to-voltage converter 1 is connected to a differentiating circuit 37 (equivalent to that shown in FIG. 4) for generating a differential signal in which edges of the information signal output from the current-to-voltage converter 1 are emphasized. , And the disturbance light correction unit 2.

The disturbance light correction unit 2 includes a current / voltage conversion unit 1
An amplifying unit 9 for amplifying a pulsating signal (AC component) from the information signal output by the rectifying unit 7 for converting the amplified pulsating signal into a DC voltage signal, and a transformer of the current-voltage converting unit 1 The cadmium cell Cds6 is connected to an impedance and varies the transimpedance according to the amount of change in the DC voltage obtained by the signal intensity of the disturbance light.

The operational amplifier 9 includes a non-inverting type AC amplifier 10 for amplifying only the AC component generated by disturbance light, and the degree of amplification is determined by the resistors R3 and R4. The capacitor C2 connected in parallel to the resistor R3 is equivalent to the capacitor C1, and removes unnecessary high-frequency component noise included in the signal. The capacitor C3 connected to the resistor R4 is a capacitor for blocking a direct current, and determines a passing frequency. The frequency band of the AC amplifier 10 is configured with a time constant such that the vicinity of the scan frequency of the output beam is a pass band and the frequency of the information signal is a stop band.

The signal component of the disturbance light appropriately amplified by the AC amplifier 10 is subjected to full-wave rectification by the rectification unit 7 in which the diodes d1, d2, d3, and d4 are bridge-connected, and is rectified to substantially direct current. Is supplied through the resistor R5 to the light emitting element of. The capacitor C4 connected between the common cathode terminal of the diodes d1 and d2 and the common anode terminal of the diodes d3 and d4 of the rectifier 7 is a decoupling capacitor for further stabilizing a substantially DC voltage.
The current rectified by the rectifier 7 and flowing through the light emitting element inside the Cds 6 is proportional to the intensity of the disturbance light. When the signal component of the disturbance light is large, the light emission amount of the light emitting element inside Cds6 increases, and equivalently, the resistance value of the variable resistance element inside Cds6 decreases. As a result, since the combined resistance of one feedback resistor R2 of the current-voltage converter 1 is reduced, the total feedback resistance (transimpedance) is reduced, and the output voltage of the current-voltage converter 1 is reduced. This decrease in the output voltage also leads to a decrease in the voltage of the information signal at the same time. However, the signal light amount in the near field where the disturbance light affects the light receiving section can be obtained relatively sufficiently, and furthermore, the automatic gain at the subsequent stage can be obtained. Adjustment circuit (AGC shown in FIG. 4)
By amplifying the signal to an appropriate amplitude in the circuit 39), the reading performance does not deteriorate.

Therefore, at the time of reading a bar code symbol, even if disturbance light is present, the output signal of the disturbance light correction / current / voltage conversion circuit becomes saturated, and large undulation of the signal waveform can be suppressed. An appropriate differential signal can be obtained without generating an unnecessary signal waveform at the time of the differential signal conversion in the differential circuit of the stage.

The disturbance light correction / current / voltage conversion circuit according to the first embodiment having the above-described configuration causes the signal S3a shown in FIG.
Thus, an output signal which is not affected by disturbance light is obtained, and a binarized signal as shown by a signal S3c can be obtained from a binarization circuit at a subsequent stage.

Therefore, according to the present embodiment, a pulsating signal (AC component) is detected from the output signal (information signal) converted by the current-voltage converter by the disturbance light incident on the light receiving element, and converted into a DC voltage. The output voltage of the current-to-voltage conversion unit is controlled by changing the feedback resistance value of the current (light amount) resistance conversion element based on the DC voltage, and the components of disturbance light, such as artificial light and sunlight, which are originally unnecessary. Even when the bar code symbol is read, the information signal of the bar code symbol can be accurately read without being affected by the disturbance light even under bad conditions in which disturbance light exists.

FIG. 2 is a diagram showing a configuration example of a disturbance light correction / current / voltage conversion circuit of a symbol information reading device as a second embodiment according to the present invention. This embodiment is an embodiment in which the current (light quantity) resistance conversion element in the above-described first embodiment is replaced with a voltage resistance conversion element, and other configurations and operations are substantially the same. In the present embodiment, components other than the disturbance light correction / current / voltage conversion circuit are:
The components are the same as those of the conventional reading apparatus shown in FIG. 4, and only the characteristic portions will be described here.

The disturbance light correction / current / voltage converter circuit is roughly divided into a current / voltage converter 11 for converting reflected light from a bar code symbol into an electric signal, and an A signal generated by the disturbance light.
A change in the DC voltage obtained by the signal strength of the disturbance light, for example, by extracting and amplifying only the C component from the output signal from the current-to-voltage converter 11 and converting the amplified signal into a DC voltage The combined feedback resistance (transimpedance) r of the current-to-voltage converter 11 is varied according to the amount to suppress the swell of the output voltage from the current-to-voltage converter 11 and a rapid AC change, thereby reducing the influence of disturbance light. And a disturbance light correction unit 12.

The current-voltage converter 11 includes a light receiving optical system 13 for condensing reflected light from the bar code symbol and a light receiving element (photo signal) for photoelectrically converting the condensed reflected light to generate a photoelectric signal (information signal). PD) 14 and an operational amplifier 15 for amplifying the information signal to a predetermined current / voltage value. A feedback resistor R11 and a capacitor C11 described later are connected to the inverting input terminal of the operational amplifier 15. This capacitor C
11 forms an LPF for removing high-frequency component noise contained in the signal.

The output terminal 16 of the current / voltage converter 11
Is connected to the differentiating circuit 37 (equivalent to that shown in FIG. 4) for generating a differential signal in which the edge of the information signal output from the current-voltage converter 11 is emphasized, and to the disturbance light correcting unit 12.

The disturbance light correction unit 12 includes an operational amplifying unit 17 for amplifying a pulsating signal (AC component) from the information signal output from the current / voltage converting unit 11 and a DC voltage converting unit. It comprises a rectifier 18 for converting into a signal, and a feedback current variable unit 19 connected to the feedback resistor R11 and the capacitor C11 of the current / voltage converter 11 to vary the feedback current applied to the current / voltage converter 11.

The operational amplifier 17 extracts and amplifies a pulsating signal (AC component) from the output signal from the current-voltage converter 11 when disturbance light components are present in the reflected light from the bar code symbol. A non-inverting type AC amplifier 20 is provided.

The AC amplifier 20 has a function of amplifying only the AC component generated by the disturbance light and extracting only the swell component of the disturbance light. The frequency band of the AC amplifier 20 includes resistors R12 and R13 and capacitors C12 and C12.
13 is connected, and has a time constant such that the vicinity of the scan frequency of the output beam is set in the pass band and the frequency of the obtained information signal is set in the stop band.

Further, the rectifier 18 includes capacitors C14 and C14.
15 and a diode D11, D12 to form a half-wave rectification type voltage doubler rectifier circuit, which generates a pulsating current signal (signal component of disturbance light) appropriately amplified by the operational amplifier 17 into a substantially DC voltage and outputs the DC signal. The voltage is fed back to the variable FET 19
The voltage is applied to the gate of the transistor 21.

The feedback current variable section 19 is composed of an FET transistor 21 and resistors R15 and R16. The feedback current variable section 19 is connected to the feedback resistor R11 and the capacitor C11, and the amount of change in the DC voltage obtained by the signal intensity of disturbance light. , The feedback current applied to the current-voltage converter 11 is varied. The FET transistor 21 employs a P-channel type MOSFET in which the on-resistance Rds between the drain and the source changes in proportion to the DC applied voltage.

The transimpedance here is the on-resistance Rds connected between the inverting input terminal and the output terminal of the operational amplifier 15 and between the resistors R11 and R15 and further between the resistor R16 and the drain and source of the FET transistor 21.
Is determined by the combined resistance formed by the parallel connection of A resistor R14 inserted between the gate of the FET transistor 21 and GND defines a potential applied to the gate when the FET transistor 21 is off, and a capacitor C1.
5 is determined.

With such a configuration, the voltage of the information signal output from the disturbance light correction / current / voltage conversion circuit increases when the signal component of the disturbance light is large, and the voltage applied to the gate terminal of the FET transistor 21 increases. Therefore, equivalently, the on-resistance Rds between the drain and the source increases, and the combined resistance of the feedback resistors of the current-to-voltage converter decreases, so that the output voltage of the disturbance light correction / current-to-voltage converter decreases.

Accordingly, even if there is disturbance light, the output signal of the disturbance light correction / current / voltage conversion circuit is saturated, and a large swell of the signal waveform is suppressed. An appropriate differentiated signal can be generated without performing this.

As described above, according to the present embodiment, when disturbance light enters the light receiving element simultaneously with signal light,
From the swell of the signal generated in the output voltage of the current-voltage converter, only the pulsating component of the disturbance light is extracted, the pulsating signal is rectified and converted into a DC voltage, and the DC voltage is converted by a current (light amount) resistance conversion element. By converting the resistance value into a resistance value proportional to the voltage conversion amount, the combined feedback resistance (transimpedance) of the current-to-voltage conversion unit can be changed or the voltage can be changed according to the change amount of the DC voltage obtained by the signal intensity of the disturbance light. The feedback current is varied in proportion to the DC voltage conversion amount by the resistance conversion element, thereby suppressing the swelling and abrupt AC change of the output voltage of the disturbance light correction / current / voltage conversion circuit. At the same time, even if disturbance light enters, the signal headroom of the current-voltage conversion circuit is prevented from being reduced.

Therefore, by suppressing the output fluctuation of the current-voltage conversion circuit according to the intensity of the ambient disturbance light signal,
Even when ambient disturbance light is incident on the light receiving element simultaneously with the signal light during the reading scan, the signal does not saturate or generate an unnecessary signal waveform due to a sharp signal change, thereby improving the accuracy of the read information.

Although the above embodiments have been described, the present invention includes the following inventions. (1) A bar code symbol affixed to an article or printed on a reading tag or the like is scanned with a laser beam, a symbol in a portion having a different reflectance is detected, and converted into a signal voltage by a current-voltage conversion circuit. In a device for reading information of a bar code symbol, the edge of a signal is emphasized by a differentiating circuit, further amplified to a desired signal voltage by an automatic gain adjustment circuit (AGC circuit), and binarized to read information. DC voltage converting means for converting a resistance value of a feedback resistor of a circuit into a substantially DC voltage proportional to a pulsating current (AC) component of disturbance light obtained by superimposing the resistance value on a signal amplitude; A bar code information reading device comprising: current (light) resistance conversion means for varying the resistance value of a feedback resistance of a conversion circuit.

[0041]

As described above in detail, according to the present invention, even in an environment where disturbance light such as artificial light or sunlight which is originally unnecessary is incident, the disturbance light for accurately reading the information of the bar code symbol can be obtained. A symbol information reading device having a correction function can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a disturbance light correction / current / voltage conversion circuit of a symbol information reading device as a first embodiment according to the present invention.

FIG. 2 is a diagram illustrating a configuration example of a disturbance light correction / current / voltage conversion circuit of a symbol information reading device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a signal waveform read when disturbance light does not exist when reading a barcode symbol.

FIG. 4 is a diagram showing a schematic circuit configuration of a symbol information reading apparatus according to the related art.

FIG. 5 is a diagram illustrating a signal waveform read when disturbance light is present at the time of reading a barcode symbol.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Current-voltage conversion part 2 ... Disturbance light correction part 3 ... Light receiving optical system 4 ... Light receiving element (PD) 5 ... Operational amplifier 5a ... Inverting input terminal 5b ... Output terminal 6 ... Cadmium cell Cds (current (light quantity) resistance conversion element) 7) Rectifier 8 Output terminal 9 Operational amplifier 10 AC amplifier 21 FET transistor (voltage resistance conversion element) 37 Differentiator

Claims (3)

[Claims] 1. A symbol information reading device which scans a symbol, in which arbitrary information is represented by a code having a different reflectance, while irradiating a light beam, and reads information represented by the intensity of the reflected light. A current-voltage conversion unit that is feedback-controlled and generates reflected light from the symbol into an information signal; and when the information signal is generated from the reflected light in an environment where disturbance light exists by the current-voltage conversion unit, a disturbance light is generated. Only the pulsating flow component generated by the disturbance light is extracted from the information signal generated from the reflected light including the above, and a level signal proportional to time is generated, and the feedback resistance value or the feedback in the feedback control of the current-voltage converting means is generated. A disturbance light correction means for varying any one of the currents to suppress output fluctuations caused by the pulsating flow. Le information reading device. 2. A symbol information reading apparatus which scans a symbol, which represents arbitrary information with a code having a different reflectance, while irradiating a light beam and reads the information from the intensity of the reflected light. Current-voltage conversion means for generating reflected light from the symbol into an information signal; and when generating an information signal from the reflected light in an environment where disturbance light is present by the current-voltage conversion means, includes disturbance light. A pulsating current extracting means for extracting and amplifying only a pulsating current component generated by the disturbance light from the information signal generated from the reflected light as a pulsating current, and converting a pulsating current signal extracted by the pulsating current extracting means into a DC voltage A rectifying means for converting the DC voltage signal from the rectifying means into a resistance value proportional to the amount of conversion of the DC voltage signal with a current (light quantity) resistance conversion element over time; An output control unit that varies a feedback resistance value in feedback control of the current-voltage converter with a resistance value and suppresses output fluctuations caused by the pulsating current component. Symbol information reading device. 3. A symbol information reading apparatus which scans, while irradiating a light beam, a symbol representing arbitrary information with a code having a different reflectivity and reads the information from the intensity of the reflected light. Current-voltage conversion means for generating reflected light from the symbol into an information signal; and when generating an information signal from the reflected light in an environment where disturbance light is present by the current-voltage conversion means, includes disturbance light. A pulsating current extracting means for extracting and amplifying only a pulsating current component generated by the disturbance light from the information signal generated from the reflected light as a pulsating current; Rectifying means for converting to a signal, and in proportion to the amount of conversion of the DC voltage signal from the rectifying means,
Output control means for varying a feedback current in the feedback control of the current-to-voltage converter over time by a voltage resistance conversion element and suppressing output fluctuations caused by the pulsating current component. A symbol information reading device having a correction function.