JP3005829B2 - Barcode reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bar code reader for irradiating a printed bar code with light and reading the reflected light.

[0002]

2. Description of the Related Art A bar code reader for irradiating a bar code with light and receiving the reflected light by a light receiving element to obtain a digital signal has a schematic configuration as shown in FIG. 4, for example.

Reference numeral a denotes a light source for irradiating a bar code b serving as an object with light, which emits light when driven by a driving unit g.

A light receiving element c receives reflected light from the bar code b and outputs a light receiving signal.

The light receiving signal of the light receiving element c is amplified by the amplifier circuit d and input to the threshold value generating circuit e and the comparing circuit f.

The threshold value generation circuit e and the comparison circuit f are, for example,
The configuration is as shown in FIG.

The threshold value generating circuit e performs charging and discharging based on the output signal A of the amplifier circuit d, and generates a threshold value signal B.

In the comparison circuit f, the output signal A of the amplification circuit d
Is compared with the threshold value signal B, and the detection signal C as shown in FIG.
Occurs.

[0009]

In such a bar code reader, if there is a minute defect in the bar code, there is a risk of erroneous detection.

[0010] For example, as shown in FIG. 6, there is a problem that when a void is present in a bar portion of a bar code or when a space portion is dirty, this is detected.

To alleviate this, it is conceivable to lower the detection sensitivity by changing the diode of the threshold value generating circuit, but it becomes difficult to accurately detect a thin bar.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a bar code reader capable of reducing erroneous detection due to a bar code void or dirt and reliably detecting a thin bar. is there.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a light source for irradiating a bar code as an object with light, and a light receiving signal generated by receiving reflected light from the bar code. A light receiving unit, a threshold value generation circuit that generates a threshold value signal based on the light receiving signal of the light receiving unit, a comparison circuit that compares the light receiving signal of the light receiving unit with the threshold value signal and outputs a detection signal, A threshold value control circuit that controls a threshold value of the threshold value generation circuit based on a detection signal output from the comparison circuit;
The threshold value control circuit constitutes a bar code reader characterized in that the threshold value signal of the threshold value generation circuit approaches the light receiving signal for a certain period from the rise and fall of the detection signal.

[0014]

The bar code reader according to the present invention is configured as described above, and the light emitted from the light source is reflected by the target bar code and received by the light receiving element.

The light receiving signal of the light receiving element is input to a comparison circuit and also to a threshold value generating circuit.

The threshold value signal generated by the threshold value generation circuit is controlled by the threshold value control circuit so as to approach the light receiving signal for a certain period of time from the rise and fall of the detection signal output from the comparison circuit. The sensitivity goes up.

Since the detection sensitivity is high in the vicinity of the rise and fall of the light receiving signal, a thin bar can be accurately detected without overlooking it.

In a thick bar portion, the detection sensitivity is lowered, so that even if there is a void, it is not erroneously detected, and also in a space portion, dirt is not erroneously detected as a bar.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on illustrated embodiments.

FIG. 1 is a simplified block diagram showing the configuration of the present invention.

Reference numeral 1 denotes a light source for irradiating light to the surface of the bar code 2 as an object, and generally scans light obtained from a light emitting element such as a semiconductor laser by a polygon mirror or the like.

Reference numeral 3 denotes a light receiving section which receives the reflected light from the bar code 2 and outputs an electric signal, and sequentially outputs a light receiving signal corresponding to the bar code 2 in accordance with the scanning of the light source 1. .

Reference numeral 4 denotes a threshold value generation circuit for generating a threshold value signal for detecting the falling of the light receiving signal of the light receiving section 3 from High to Low and the rising from Low to High.

Reference numeral 5 denotes a threshold value generating circuit 4
And outputs a comparison result as a detection signal.

Reference numeral 6 denotes a threshold value generating circuit for bringing the threshold value signal closer to the light receiving signal for a certain period from the rise and fall of the detection signal.

FIG. 2 is a circuit diagram of an embodiment of a threshold value generating circuit and a threshold value control circuit used in the present invention.

The light receiving section 3 in FIG. 1 includes a light receiving element for generating an analog electric signal corresponding to the amount of received light, and an amplifier circuit 31 for amplifying an output signal of the light receiving element.

The output signal A of the amplifying circuit 31 is input to the comparator 51 of the comparing circuit 5 and also to the threshold value generating circuit 4.

The threshold value generating circuit 4 has a capacitor 41 for charging and discharging based on the output signal A of the amplifier circuit 31. A plurality of diodes D1 and D3 are connected in a direction in which the capacitor 41 is charged. Diodes D2 and D4 are connected in a direction to discharge the capacitor 41.

An output signal A of the amplifying circuit 31 is input to a minus terminal of the comparator 51, and a threshold signal B of the threshold value generating circuit 4 is input to a + terminal.

The output of the converter 51 is a binarized detection signal C, which is input to the threshold control circuit 6.

The threshold value control circuit 6 detects a rise of the detection signal C and generates a pulse signal of a predetermined width to generate a rise detection one-shot timer circuit 61, and detects a fall of the detection signal C and generates a pulse signal of a predetermined width. And a falling detection one-shot timer circuit 62 for generating a pulse signal.

The charge-side diodes D1,
Of the D3, the diode D3 is connected to the analog switch 42.
Are connected in parallel, and the section of the diode D3 is short-circuited for a certain period by a pulse signal of the falling detection one-shot timer circuit 62.

Similarly, an analog switch 43 is connected in parallel to the diode D4 of the discharge-side diodes D2 and D4 of the threshold value generation circuit 4, and the pulse signal of the rise detection one-shot timer circuit 61 causes a predetermined period of time. The section of the diode D4 is short-circuited.

Here, the operation of the present invention will be described with reference to FIG.

The light receiving signal A of the light receiving section is output as a low analog signal in a bar portion and a high analog signal in a space portion based on a bar code as an object.

When the light receiving signal A is High, the capacitor 41 is charged, and the threshold signal B is at a level lower than the light receiving signal A by the voltage due to the resistance of the diodes D1 and D3.

In the bar portion of the bar code, the light receiving signal A changes to low, and the detection signal C of the comparator 51 becomes high at the moment when the light receiving signal A falls below the threshold value signal B.

At this time, the output signal D of the rise detection one-shot timer circuit 61 generates a pulse signal of a predetermined width.
The analog switch 43 short-circuits the section of the diode D4 for a certain period.

As a result, the electric charge of the capacitor 41 becomes the signal D
Is discharged only through the diode D2 during the period of the pulse signal, and the threshold value signal B approaches the light receiving signal A.

When the pulse signal of the signal D goes low, the analog switch 43 is turned off and the capacitor 4
Since the discharge from 1 is performed via D2 and D4, the threshold signal B moves away from the light receiving signal A.

When the bar portion of the bar code ends, the level of the light receiving signal A rises, and the detection signal C becomes low at the moment when the level exceeds the threshold value signal B.

At this time, the output signal E of the falling detection one-shot timer circuit 62 generates a pulse signal of a predetermined width.
The analog switch 42 short-circuits the section of the diode D3 for a certain period.

From this, charging of the capacitor 41 is performed only through the diode D1 during the period of the pulse signal of the signal E, and after this period, the charging of the capacitor 41 is performed through the diodes D1 and D3. During the period of the pulse signal, the threshold value signal B approaches the light receiving signal A, and moves away when the pulse signal becomes Low.

Therefore, since the detection sensitivity is high in the vicinity of the rise and fall of the detection signal C, even if the bar portion is a thin bar, the width of the bar portion or the space portion can be reliably detected without being overlooked. Is possible.

Furthermore, the detection sensitivity is lowered after a certain period from the edge of the detection signal, so that erroneous detection of a void in a thick bar portion and a stain in a space portion can be reduced.

By appropriately changing the number of diodes in the threshold value setting circuit 4, an optimum threshold value can be set.
By changing the pulse width output from the rise detection one-shot timer circuit 61 and the fall detection one-shot timer circuit 62, it is possible to correspond to barcodes of any width.

In addition, the configuration of the present invention is not limited to the embodiment.

[0049]

According to the present invention, as described above, the threshold value for obtaining the detection signal approaches the light receiving signal for a certain period from the rise and fall of the detection signal, and the sensitivity increases. In addition, the width of the bar portion and the space portion can be accurately detected without overlooking the narrow space.

Also, after a certain period from the rise and fall of the detection signal, the detection sensitivity is lowered by moving the threshold value signal away from the light receiving signal, thereby reducing erroneous detection of voids in the bar portion and dirt in the space portion. You can do it.

[Brief description of the drawings]

FIG. 1 is a block diagram corresponding to a claim of a barcode reader according to the present invention.

FIG. 2 is a circuit diagram of an embodiment of a threshold value generation circuit and a threshold value control circuit used in the present invention.

FIG. 3 is a time chart showing a signal waveform of each unit according to the embodiment of the present invention.

FIG. 4 is a block diagram of a conventional example.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is a time chart showing a signal waveform of each section of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Barcode 3 ... Light receiving part 4 ... Threshold value generation circuit 5 ... Comparison circuit 6 ... Threshold value control circuit 31 ... Amplification circuit 41 ... Capacitor 42 ... Analog switch 43 ... Analog switch 51 ... Comparator 61 ... Rise detection one Shot timer circuit 62: Fall detection one-shot timer circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G06K 7/10 G06K 7/00

Claims (1)

(57) [Claims] 1. A light source for irradiating a bar code to be an object with light, a light receiving unit for receiving a reflected light from the bar code to generate a light receiving signal, and a threshold value based on the light receiving signal of the light receiving unit. A threshold value generating circuit for generating a signal; a comparing circuit for comparing a light receiving signal of the light receiving section with the threshold value signal to output a detection signal; and a threshold value generating circuit based on the detection signal output from the comparing circuit. And a threshold value control circuit that controls a threshold value of the threshold value, wherein the threshold value control circuit brings the threshold value signal of the threshold value generation circuit closer to the light receiving signal for a certain period from the rise and fall of the detection signal. Barcode reader.