JPH06231290A - Device for shaping light receiving signal for bar code reader - Google Patents

Abstract

PURPOSE:To read various bar codes at a low cost. CONSTITUTION:The device for shaping light receiving signal is the device for bar code reader irradiating the light on bar codes, receiving the reflection light from the bar code, and outputting a read signal. In the device, a filter circuit 31 of the light receiving circuit and a gain circuit 32 have plural shaping characteristics. Using one of the shaping characteristics, the light receiving signal is shaped and outputted. The shaping characteristic of the filter circuit 31 and the gain circuit 32 is changed by a gain switching circuit 36 to conform to the shape characteristic of the bar code of the object to be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a signal shaping device, and more particularly to
The present invention relates to a light reception signal shaping device of a bar code reading device.

[0002]

2. Description of the Related Art A bar code is a code that represents characters such as numbers by arranging bar-shaped images called bar code symbols, and was developed for use in a distribution information system. The bar code reader scans the vicinity of the center of the bar code symbol with a laser beam and measures the width of the bar code symbol to read the displayed code. This bar code reader usually includes a laser light source for emitting a laser beam, a scanning section having a polygon mirror, and a receiving section for receiving the laser beam reflected from the target bar code and converting it into an electric signal. . The electric signal received by the receiving unit is shaped by the received light signal shaping device, and then it is determined by the comparison circuit whether or not it is the barcode symbol portion, and the determination result becomes the reading result.

[0003]

There are various kinds of bar codes, such as one having a thin bar code symbol as a whole and one having a thick bar code symbol as a whole. It is difficult to reliably read these various barcodes using a constant laser beam. For example, it is conceivable to narrow down the spot of laser light to read thin barcodes reliably and to increase the spot of laser light to read thick barcodes reliably, but with that configuration, the mechanism becomes complicated,
Manufacturing cost is high.

An object of the present invention is to enable reliable reading of various bar codes at low cost.

[0005]

A light receiving signal shaping device according to the present invention is for a bar code reading device which irradiates a bar code with light and receives reflected light from the bar code to output a read signal. Is. This received light signal shaping device includes a shaping means and a characteristic changing means. The shaping means is
It has a plurality of shaping characteristics, and the received light signal is shaped and output using one of the shaping characteristics. The characteristic changing unit changes the shaping characteristic of the shaping unit to match the shape characteristic of the barcode to be detected.

[0006]

In the light receiving signal shaping device according to the present invention, when the light emitted from the bar code and reflected from the bar code is received as the light receiving signal, the shaping means shapes the light receiving signal using one of the shaping characteristics. Output. Here, the shaping means has a plurality of shaping characteristics, and the characteristic changing means changes the shaping characteristics so as to match the shape characteristics of the barcode to be detected. The signal shaping adapted to it and the signal shaping adapted to the thick bar code are performed, so that the bar code can be reliably read.

In this case, the bar code can be reliably read by changing the shaping characteristics of the shaping means instead of changing the light source, so that the cost can be reduced.
It enables reliable reading of various barcodes.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a bar code reader 1 according to an embodiment of the present invention employs a laser beam 5 directed toward a bar code 4 of a bar code label 3 attached to an object to be measured 2.
It is designed to irradiate. An LCD 6 for display and a switch group 7 including a push switch 7a for changing shaping characteristics are arranged on the front surface of the barcode reader 1. A programmable controller 10 (an example of a signal output target) is connected to the signal transmitting / receiving connector portion 8 of the barcode reader 1 via a cable 9.

The bar code reader 1 is, as shown in FIG. 2, a detection section 11 for scanning a bar code 4 with a laser beam 5.
And a control unit 12 that controls the detection unit 11 and outputs the detection result. The detection unit 11 includes a semiconductor laser diode 14, a laser lighting circuit 15 that drives the laser diode 14, a scanning unit 17 having a polygon mirror 16, a light receiving element 18 including a photoelectric conversion element such as a photodiode, and a light receiving element. A light receiving circuit 19 that performs analog processing such as shaping on the output signal of 18 is provided.

The control unit 12 includes a main control unit 20 composed of a microcomputer. The main control unit 20 controls the laser lighting and decodes the bar code information by the signal from the light receiving circuit 19. The main control unit 20 includes a scanning unit 17, a laser lighting circuit 15,
The light receiving circuit 19 is connected to them, and the main controller 20 controls the driving of them. Further, the main control unit 20 outputs an A / D converter 21 for converting an analog signal obtained by the light receiving circuit 19 into a digital signal, a memory 22 for storing decoded bar code information and the like, and a decoding result. The output circuit 23 is connected. The LCD 6 and the connector section 8 described above are connected to the output circuit 23. Further, the connector 8 and the switch group 7 described above are connected to the main controller 20.

The light receiving circuit 19 has a structure as shown in FIG. The signal from the light receiving element 18 (FIG. 2) is input to the filter circuit 31. The filter circuit 31 is for removing a noise component included in the input signal,
The filter characteristic can be switched in three stages. The output signal of the filter circuit 31 is input to the gain circuit 32. The gain circuit 32 amplifies the input signal.
The amplification characteristic can also be switched in three stages. The output signal of the gain circuit is input to the comparison circuit 33.

The comparison circuit 33 is a circuit for comparing the input signal from the gain circuit 32 and the threshold value signal of the threshold value generation circuit 34, and the comparison result is used as a detection signal for the A / D converter 21 (FIG. 2). Output to. The threshold generation circuit 34
It is a circuit that generates a threshold signal for detecting the falling and rising of the output signal from the gain circuit 32. The threshold value generation circuit 34 is connected to a threshold value control circuit 35 which brings the threshold value signal closer to the light receiving signal for a certain period from the rising and falling.

The filter circuit 31 and the gain circuit 32
The gain switching circuit 36 switches its filter characteristic and gain characteristic. The gain switching circuit 36 and the threshold control circuit 35 are connected to the main controller 20.
(FIG. 2). Details of the filter circuit 31, the gain circuit 32, and the gain switching circuit 36 are shown in FIG.

The filter circuit 31 is an active filter type circuit using an operational amplifier 41. Operational amplifier 4
The output signal from the light receiving element 18 (FIG. 2) is input to the first non-inverting terminal via a pair of resistors 42a and 42b connected in series. Two pairs of resistors 43a, 43b, 44a, 44b are further connected in parallel to the resistors 42a, 42b. Connection / disconnection of these resistors 43 to 44 is switched by four analog switches 47, 48, 49 and 50. Note that, for example, the resistors 42a, 4
2b is 6.8 KΩ and resistors 43a and 43b are 3.
3KΩ, 44a and 44b are 750Ω.

The gain circuit 32 is an amplifier circuit using an operational amplifier 51, and is provided with three types of resistors 52, 53, 54 as feedback resistors for determining its amplification characteristic.
The resistor 52 always functions as a feedback resistor, but the remaining resistors 53 and 54 change the connection / disconnection state by switching the analog switches 55 and 56. The amplified output signal from the operational amplifier 51 is used as a comparison circuit 33.
(Fig. 3). Note that, for example, the resistance 52 is 4
The resistance 53 is 33 KΩ, and the resistance 54 is 15 KΩ.

The gain switching circuit 36 is composed of a pair of switching circuits 57 and 58 using transistors. ON / OF of both switching circuits 57 and 58
F is Hi / L of the control signal input to the gain control terminals 59 and 60 connected to the main control unit 20 (FIG. 2).
It is switched by o. Switching circuit 57 is OF
In the F state, the analog switches 47, 48, 55 are turned on and the resistors 43a, 43b, 53 function. When the switching circuit 58 is turned off, the analog switches 49, 50, 56 are turned on and the resistors 44a, 44b, 54 function.

Next, the operation of the above embodiment will be described. The laser diode 14 is driven by the laser lighting circuit 15 and the polygon mirror 16 is rotated, so that the barcode 4 is scanned with the laser light 5. The light receiving element 18 outputs an output signal to the light receiving circuit 19 according to the reflected light from the bar code 4 which is incident on the light receiving element 18.

In the light receiving circuit 19, the input signal is filtered by the filter circuit 31 and then amplified by the gain circuit 32. The amplified signal is input to the comparison circuit 33 and the threshold value generation circuit 34. The threshold value generation circuit 34 compares the threshold value signal with the comparison circuit 3 based on the input signal and a command from the threshold value control circuit 35.
Output to 3. The comparison circuit 33 compares the input signal from the gain circuit 32 with the threshold value signal, determines the presence / absence of a bar code, and outputs the bar code to the main control unit 20. Here, since the threshold value generation circuit 34 operates so that the detection sensitivity becomes high in the vicinity of the rising and falling edges of the detection signal, reliable detection is possible even if the bar code symbol is a thin bar.

Which of the resistors 42 to 44 of the filter circuit 31 is used and the resistor 52 to 52 of the gain circuit 32 are used.
Which one of 54 is used is determined by ON / OFF of the switching circuits 57 and 58 of the gain switching circuit 36. This change is performed by the operator operating the push switch 7a of the switch group 7.

Both switching circuits 57 and 58 are turned on.
In this state, among the resistors 42 to 44, the resistors 42a and 42b
Only is effective, and the cutoff frequency of the filter circuit 31 is low. Further, in the gain circuit 32, only the resistor 52 among the resistors 52 to 54 is effective, and the amplification factor is high. When the switching circuit 57 is turned off, the analog switch 4
7, 48, 55 are turned on and the resistors 42a, 42
In addition to b and 52, the resistors 43a, 43b and 53 function effectively. As a result, the cutoff frequency of the filter circuit 31 becomes medium, and the amplification factor of the gain circuit 32 becomes medium.

When the switching circuit 57 is turned on and the switching circuit 58 is turned off, the resistor 42 is turned on.
a, 42b, 52 and the resistors 44a, 44b, 54 effectively function, and the cutoff frequency of the filter circuit 31 becomes high. Further, the gain of the gain circuit 32 becomes low. The cutoff frequency of the filter circuit 31 and the amplification factor of the gain circuit 32 can be changed by an operator operating the push switch 7a of the switch group 7. FIG. 5 shows a part of a control flowchart of the main control unit 20 here.

In FIG. 5, in step S1, it is determined whether or not the push switch 7a has been operated. If it has not been operated, the processing here is terminated. If the push switch 7a is operated, the process proceeds to step S2. In step S2, it is determined whether or not the gain is high (the switching circuits 57 and 58 are in the ON state). If it is determined that the gain is high, step S
Then, the switching circuit 57 is turned off. As a result, the cutoff frequency of the filter circuit 31 is set to a medium level, and the gain of the gain circuit 32 is set to a medium level. When the processing in step S3 ends, the processing here ends.

If it is determined in step S2 that the gain is not set high, the process proceeds to step S4.
In step S4, it is determined whether or not the gain is set to a medium level (the switching circuit 57 is in the OFF state and the switching circuit 58 is in the ON state). If it is determined that the gain is set to the medium level, the process proceeds to step S5. In step S5, only the switching circuit 58 is turned off. As a result, the cutoff frequency becomes high in the filter circuit 31, and the amplification factor becomes low in the gain circuit 32. When the processing in step S5 ends, the processing here ends.

If it is determined in step S4 that the gain is set low, the process proceeds to step S6. In step S6, the switching circuits 57 and 58 are both turned on. As a result, the cutoff frequency becomes low in the filter circuit 31, and the amplification factor becomes high in the gain circuit 32. When the processing in step S6 ends, the processing here ends.

In this way, the operator pushes the push switch 7a.
You can change the gain adjustment in three steps by pressing. As a result, it is possible to reliably read various types of barcodes 4 at low cost without adjusting the laser emission portion. The resistors 42 to 44 and the resistor 52
Settings may be enabled using all of ~ 54. Further, instead of the switching by the push switch 47a and the control of FIG. 5, the gain switching circuit 36 may be directly driven by the switch.

[0026]

In the light-receiving signal shaping device of the bar code reader according to the present invention, the shaping means has a plurality of shaping characteristics, and the characteristic changing means shapes the shape of the barcode to be detected so as to match the shape characteristics. Since the characteristics are changed, various barcodes can be reliably read at low cost.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a usage state of a bar code reader adopting an embodiment of the present invention.

FIG. 2 is a schematic block diagram showing an internal configuration of the barcode reader.

FIG. 3 is a schematic block diagram showing a configuration of a light receiving circuit of the barcode reader.

FIG. 4 is a partial circuit diagram showing details of the light receiving circuit.

FIG. 5 is a flowchart showing a part of a control function of the barcode reader.

[Explanation of symbols]

 1 bar code reader 4 bar code 19 light receiving circuit 31 filter circuit 32 gain circuit 36 gain switching circuit

Claims (1)

[Claims] 1. A light reception signal shaping device of a bar code reading device, which irradiates a bar code with light, receives reflected light from the bar code, and outputs a reading signal, wherein the light receiving signal shaping device has a plurality of shaping characteristics. Shaping means for shaping and outputting a received light signal using one of the shaping characteristics; and characteristic changing means for changing the shaping characteristics of the shaping means so as to match the shape characteristics of the barcode to be detected. Receiving signal shaping device for barcode reader.