JP2748721B2 - 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 which scans a bar code by scanning light such as a laser beam, converts the reflected light into an electric signal and binarizes the signal. About.

[0002]

2. Description of the Related Art Conventionally, in this type of apparatus, the amplitude of an output signal from a light receiving element for receiving reflected light from a bar code and converting the reflected light into an electric signal depends on the material and color of the object to be detected and the object to be detected. The amplitude of the output signal from the light-receiving element is changed by an automatic gain adjustment circuit (auto gain control circuit: AGC circuit) because it changes depending on conditions such as the irradiation angle of light to the object and the distance between the object to be detected and the reader. ) (Hereinafter A)
It is called an amplifier with GC circuit. ), And then binarized after adjusting to a certain width.

[0003]

However, the AGC circuit is
Because the feedback circuit adjusts the amplification factor of the amplifier based on the output signal, if the scanning speed of the projection light projected on the bar code is increased, the operation of the AGC circuit may not be able to follow the amplitude fluctuation of the output signal. For this reason, in the conventional barcode reading device, when the scanning speed of the projection light is increased in order to increase the reading speed of the barcode,
There is a problem that the amplitude of the output signal from the light receiving element cannot be corrected to a constant width by the amplifier with the AGC circuit, and the output signal cannot be binarized accurately.

The present invention has been made in view of such a problem. In a bar code reader that reads a bar code by emitting and receiving laser light or the like, even if the scanning speed of the projection light is increased, the amplitude of the output signal from the light receiving element is increased. The purpose is to correct the fluctuation so that an accurate binary signal is always obtained.

[0005]

That is, the present invention, which has been made to achieve the above object, comprises a light projecting means for generating light,
Scanning means for scanning the light from the light projecting means in a predetermined direction at a predetermined period; and receiving reflected light reflected from the outside by scanning of the light by the scanning means, and generating an electric signal corresponding to the received light amount. A bar code reader having a binarizing means for binarizing an electric signal from the light receiving means, the electric signal path from the light receiving means to the binarizing means, A filter circuit for removing a DC component from the inside, and a first circuit having a non-linear amplification characteristic for amplifying an electric signal after removing the DC component that has passed through the filter circuit with a larger amplification factor as the amplitude of the signal is smaller. An amplifier and a second amplifier having an automatic gain adjustment circuit for amplifying an output signal from the first amplifier so that the amplitude becomes a predetermined width are provided.

[0006]

In the bar code reader according to the present invention, the scanning means scans the light from the light projecting means, and the light receiving means reflects the light reflected from the outside by the scanning of the light. It receives light and generates an electrical signal corresponding to the amount of received light. Then, the electric signal from this light receiving means is
First, a DC component is removed by a filter circuit. The electric signal from which the DC component has been removed is amplified by the first amplifier at a larger amplification factor as the amplitude is smaller.
Further, the signal is adjusted to a signal of a predetermined amplitude by the second amplifier, and then input to the binarizing means.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 2 is an explanatory diagram illustrating a configuration of a barcode reading device according to an embodiment to which the present invention is applied.

As shown in FIG. 2, the bar code reader according to the present embodiment has a so-called hand-held type bar code reader having a hand-held support portion 3 below the main body case 1 for a user to support by hand. It is. An operation switch 5 for inputting a bar code reading command to the device by the user operating the index finger or the like is provided on the hand-held support unit 3.
Is provided.

Further, inside the main body case 1, there are provided a light projecting device 12 as a light projecting device for emitting a laser beam, a light receiving device 14 as a light receiving device for receiving the laser beam and generating an electric signal corresponding to the received light amount, The laser beam from the projector 12 is projected onto an external barcode label 10 on which a barcode is printed, and the laser beam (scattered light) reflected from the barcode label 10 by the projection of the laser beam is transmitted to the light receiver 14. A scanning mirror 16 for rotating the scanning mirror 16 at predetermined intervals, and a laser beam from the bar code label 10 reflected from the scanning mirror 16
4, an optical system including a condenser lens 19 for condensing light, a driving circuit for driving the light projector 12 and the scanning motor 18 in accordance with a read command input from the operation switch 5, and an electric signal from the light receiver 14 are processed to generate a bar code. A circuit board (not shown) in which a signal processing circuit for outputting a binary signal corresponding to a bar code printed on the label 10 is formed is housed.

The light projector 12 is a laser diode, H
The light receiving device 1 includes a light emitting element made of e-Ne laser or the like, a focusing lens made of a plano-convex lens, and an aperture stop.
Reference numeral 4 denotes a light receiving element including a photodiode, a phototransistor, and the like, and the same wavelength as the laser light projected from the projector 12 (the wavelength 67 when the light emitting element is a laser diode)
0 nm, wavelength 63 when the light-emitting element is a He-Ne laser
(0 nm).

Next, as shown in FIG. 1, the signal processing circuit for processing the electric signal from the light receiver 14 is an electric signal corresponding to the amount of reflected light from the bar code label 10 output from the light receiving element 20 of the light receiver 14. And an amplifier 22 for amplifying the DC component from the output signal from the amplifier 22,
In addition, a band-pass filter 23 that passes only a predetermined frequency component of the signal, a LOG amplifier 24 that amplifies the signal that has passed through the band-pass filter 23 with a larger amplification factor as the amplitude is smaller, and a LOG amplifier 24 An amplifier 26 with an AGC circuit for amplifying an output signal, and a binarization circuit 28 for binarizing the output signal by comparing the output signal from the amplifier 26 with an AGC circuit with a reference voltage. .

In the signal processing circuit configured as described above, the electric signal output from the light receiving element 20 is first amplified by the amplifier 22, and then input to the band-pass filter 23 as a filter circuit. The pass frequency band of the band-pass filter 23 is set in accordance with the change period of the reflected light from the bar code determined by the rotation speed of the scan mirror 16 by the operation motor 18 and the type of bar code read by the device. The band-pass filter 23 cuts a direct-current component from the output signal from the amplifier 22 and, at the same time, cuts a noise component unnecessary for reading a barcode. The electric signal passing through the band-pass filter 23 is input to a LOG amplifier 24 as a first amplifier.

For this reason, even if the electric signal from the light receiving element 20 fluctuates in amplitude and the output signal from the band-pass filter 23 fluctuates in amplitude as shown in FIG. From the amplifier 24, (b1) in FIG.
Or, as shown in (b2), an output signal having a substantially constant amplitude is output.

Next, an output signal from the LOG amplifier 24 is supplied to an amplifier 26 having an AGC circuit as a second amplifier.
Therefore, even if the amplitude of the output signal from the LOG amplifier 24 is different as shown in (b1) or (b2) of FIG. 3, the amplifier 26 with the AGC circuit outputs (c1) of FIG. ) Or (c2), a signal having a constant amplitude is always output. That is, the amplifier with AGC circuit 2
6 is removed by the LOG amplifier 24, the amplifier 26 with the AGC circuit only needs to be able to make the swell and level of the entire input signal constant. Even if the scanning speed is high, the response speed of the AGC circuit is not required, and a signal with a constant amplitude can always be output.

Therefore, in the bar code reader of this embodiment, even if the scanning speed of the scan mirror 16 by the scanning motor 18 is high, the binarizing circuit 28 has no amplitude fluctuation and the amplitude is always constant. The signal is input, and as shown in (d1) or (d2) of FIG. 3, it is possible to always binarize the electric signal from the light receiving element 20 accurately in the binarization circuit 28. .

In FIG. 3, (a1), (b1),
(C1) and (d1) show signal waveforms when the distance between the barcode reader and the barcode label 10 is relatively short and an electric signal with a large amplitude is output from the light receiving element 20. (B2), (c2), and (d2) show signal waveforms when the distance between the barcode reader and the barcode label 10 is long and an electric signal with a small amplitude is output from the light receiving element 20.

In this embodiment, the LOG amplifier 24 is used as the first amplifier. However, as the first amplifier, a non-linear amplifier capable of amplifying the input signal with a larger amplification factor as the amplitude of the input signal is smaller is used. As long as the amplifier has characteristics, it is not always necessary to use a LOG amplifier, and an amplifier having amplification characteristics as shown in FIG. 4 may be configured by combining a plurality of amplifier circuits having different amplification characteristics.

[0018]

As described above, in the bar code reader of the present invention, even when the scanning speed of the light by the scanning means is high, an electric signal having a constant amplitude is always input to the binarizing means. As a result, the binarizing means can always accurately binarize the electric signal from the light receiving element. Therefore, according to the present invention, the bar code can be read at a high speed by increasing the scanning speed of the light by the scanning means.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a barcode reading device according to an embodiment.

FIG. 2 is a block diagram illustrating a configuration of a signal processing circuit according to the embodiment.

FIG. 3 is a diagram illustrating a signal waveform of each part of the signal processing circuit.

FIG. 4 is a diagram illustrating amplification characteristics when the first amplifier is configured by a large number of amplifier circuits.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Bar code label 12 ... Emitter 14 ... Receiver 16 ... Scan mirror 18 ... Scan motor 19 ...
Condensing lens 20 ... Light receiving element 22 ... Amplifier 23 ... Band pass filter 24 ... LOG amplifier 26 ... Amplifier with AGC circuit
28 ... Binarization circuit

Claims (1)

(57) [Claims] 1. A light emitting means for generating light, a scanning means for scanning light from the light emitting means in a predetermined direction in a predetermined cycle, and reflected light reflected from the outside by scanning of light by the scanning means. And a light receiving means for generating an electric signal according to the amount of received light, and a bar code reader including a binarizing means for binarizing the electric signal from the light receiving means,
An electric signal path from the light receiving means to the binarizing means, a filter circuit for removing a DC component from the electric signal,
A first amplifier having a non-linear amplification characteristic for amplifying an electric signal after removing the DC component that has passed through the filter circuit with a larger amplification factor as the amplitude of the signal is smaller; and an output from the first amplifier. A second amplifier having an automatic gain adjustment circuit for amplifying a signal so that the amplitude has a predetermined width; and a second amplifier.