JPS5991414A - Optical symbol reader - Google Patents

Abstract

PURPOSE:To stabilize a read performance by a simple device constitution by using an optical beam spot of a ''0'' order diffracted light which transmits a hologram, for detecting a light source output. CONSTITUTION:An information of a reflected light from a scanning face 32 is condensed onto a photoelectric converting element 32, and the condensed light is converted to an electric signal by the photoelectric converting element 34, attains a video signal and is amplified by an amplifying circuit 35 of a signal processing circuit 41. On the other hand, an optical beam spot 36 being a ''0'' order diffracted light, which is made incident to a hologram disk 30 and transmits it is converted to an electric signal by a photoelectric converting element 37, and is inputted to the amplifying circuit 35. The amplifying circuit 35 is controlled so that the amplitude of a video signal outputted from the amplifying circuit 35 is made constant by the potential of the electric signal. The video signal is sent to a signal comparing circuit 38, and is converted to a pulse train corresponding to variable density of a bar-code. This pulse train is sent to a recognizing circuit 39 from a logical circuit, is decoded and read.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical symbol reading device that scans a hologram with a light beam and receives reflected light from an object to be scanned to read barcode information.

FIG. 1 shows the configuration of a conventional optical barcode reading device.

In general, a hologram can be equivalently regarded as a convex lens composed of a diffraction grating, but when used as a scanning device,
By itself, it can simultaneously polarize the light beam, converge the light beam on the surface to be scanned, collect the reflected light from the surface to be scanned, remove the disturbance light contained in the focused light, and rotate the mirror. It is a much cheaper device than optical systems using . 1st
In the figure, this hologram is placed around the disk,
This shows the case where it is used as a scanning device.

To explain FIG. 1 in detail, a light beam emitted from a light source 1 is divided by a beam splitter 2 into a light beam 3 for reading scanning and a light beam 402 for measuring the light source output.
Divided into books. The light beam 3 passes through the lens 5 and then through the hole in the mirror 6 and enters the hologram disk 7 . In the hologram disk 7Kb, as the disk rotates, polarization is performed by the hologram segments 8, resulting in scanning lines 10 on the scanning surface 9.

This scanning line 10 scans a barcode label 1 moving on a scanning surface 9. The information in the barcode, which is composed of black bars on a white paper background, is converted into the intensity of reflected light and enters the hologram 8. This reflected light is focused onto the photoelectric conversion element 12 by the hologram 8 via the mirror 6.

The focused light is converted into an electric signal by the photoelectric conversion element 12 and becomes a video signal, and the amplification circuit 1 of the signal processing circuit 40
It is amplified at 6. As shown in FIG. 2, the amplified video signal 13 is sent to a signal comparison circuit 17 operating at a certain set threshold value 14 and converted into a pulse train 15 corresponding to the density of the bar code. The pulse train 15 is sent to a recognition circuit 18 consisting of a logic circuit, decoded, and read out.

In such a reading operation, in order to perform stable reading, it is necessary that the video signal amplitude does not change and is always converted into a pulse train at an optimal threshold value.

By the way, as the light source 1, generally a gas or semiconductor laser oscillator is used in consideration of the convergence of the light beam on the scanning surface 9. When this laser oscillator is used for a long time, the light beam output decreases due to physical deterioration. Moreover, contamination of the optical system also causes a decrease in the optical output of the device and a decrease in light receiving efficiency.

As a result, the video signal amplitude becomes small, an optimal threshold value for the video signal is no longer secured), and reading performance deteriorates.

Conventionally, in order to avoid this phenomenon, as shown in Figure 1,
The light beam of the light source 1 is split, this light beam 4 is converted into an electric signal by the photoelectric conversion element 19, a change in the output of the light source 1 is detected based on the potential of this signal, and the electric signal is converted to the video signal amplification circuit 16. A method for controlling the amplitude of the video signal output from the amplifier circuit 16 to be constant in response to fluctuations in the light beam output of the light source 1 by inputting the input into the signal comparison circuit; The first method is to control the conversion into a pulse train. ing.

However, since this method uses a light beam splitter, the optical system becomes complicated, and there is no measure against contamination of the optical system. There is also a conventional method in which the scanning beam is detected and a sampling circuit is used to detect the laser light output, including dirt on the optical system, but this requires a sampling circuit and the electrical circuit becomes complicated. There are drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, to provide an optical symbol reading device that detects a decrease in light beam output due to contamination of the optical system and a decrease in light beam output of a light source, and has a simplified device configuration.

In order to achieve such an object, the present invention provides a light source that emits a light beam, a fixed plane mirror having a portion that transmits the light beam, and a hologram light deflector that polarizes and scans the light beam and irradiates the object to be scanned. A photoelectric conversion element that receives reflected light from an object to be scanned and converts it into a video signal, and a signal processing circuit that processes the video signal and decodes the information. In the symbol reading device, a photoelectric conversion element is provided to receive the 0th order light transmitted through the hologram light deflection element, and the output of the photoelectric conversion element is inputted to the signal processing circuit to keep the amplitude of the video signal constant. The invention is characterized in that it is configured to be held and controlled.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a diagram showing the principle of deflection of a light beam by a hologram. In the same figure, a light beam 2 is placed on a hologram 21.
0 is incident and the hologram 21 is moved as shown by the arrow 22, a scanning line 24 formed by the first-order diffracted light is formed on the scanning surface 23.
A scanning line 25 of −1st-order diffracted light and a light beam spot 26 of 0th-order light are generated. The diffracted light goes +2 to the +1st order side.
Next, +3rd order, . . . , -1st order, 12th order, -3rd order, etc. continue indefinitely, but here, +1st order diffracted light is used as a scanning line for reading.

The present invention provides a light beam spot 26 which is the 0th order diffracted light.
A photoelectric conversion element is placed on top to detect the light beam output of the light source. According to this method, the output of the light beam of the light source is reduced and the contamination of the optical system is reduced. This makes it possible to detect a decrease in the output of a light beam due to a simple device configuration, and it is possible to stabilize reading performance and ensure reading reliability at the same time.

FIG. 4 is a perspective view showing an outline of an embodiment of the optical symbol reading device of the present invention. In the figure, the device of the present invention includes a light source 27 that emits a light beam, a lens 28, and a hole 2 in the center.
9a, a hologram disk 30 that has a plurality of segments 31 and is rotatably arranged and deflects the light beam, and the reflected light from the object to be scanned is collected through the hologram disk 31 and the mirror 29. a photoelectric conversion element 34 that receives light and converts it into a video signal; a signal processing circuit 41 that includes an amplifier circuit 35, a signal comparison circuit 38, and a recognition circuit 39 and processes the video signal and decodes information; It is configured to include a photoelectric conversion element 37 that receives a light beam spot 36 that is the next diffracted light and detects the output of one light source.

The optical symbol reading device of the present invention constructed as described above will be explained in more detail along with its operation.

The light beam emitted from the light source 27 passes through the lens 28 and further passes through the hole 29a of the mirror 29 to enter the hologram disk 30. In the hologram disk 30, as the disk rotates, the hologram segments 31
Deflection is performed by , resulting in a scanning line 33 on the scanning plane 32 .

The information of the reflected light from the scanning surface 32 is incident on the hologram segment 31 . This reflected light is focused on the photoelectric conversion element 34 via the mirror 29 by the hologram.

The collected light is converted into a 11A signal by the photoelectric conversion element 34 and amplified by the amplifier circuit 35 of the signal processing circuit 41 to become a video signal.

On the other hand, a light beam spot 36 that is the 0th order diffracted light that enters the hologram disk 30 and passes through the photoelectric conversion element 3
The signal is converted into an electrical signal at step 7 and input to the amplifier circuit 35.

The amplification circuit 35 is controlled by the electric potential of the electric signal so that the amplitude of the video signal output from the nuclear amplification circuit 35 is constant. The video signal is sent to a signal comparison circuit 38 and converted into a pulse train corresponding to the density of the bar code. This pulse train is processed by a recognition circuit 39 consisting of a logic circuit.
The first . Ru.

As described above, the present invention has a configuration in which the light beam spot of the 0th-order diffracted light that passes through the hologram is used for detecting the light source output, thereby further stabilizing the reading performance with a simple device configuration. realizable.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a conventional optical symbol reading device;
Figure 2 is a waveform diagram to explain video signal processing, Figure 3 is a waveform diagram to explain video signal processing.
This figure is a diagram showing the principle of hologram scanning, and FIG. 4 is a perspective view showing an outline of an embodiment of the optical symbol reading device of the present invention. 27...light? w, 28...lens 29...
Mirror 30...Porogram disk 31...Segment 32...Scanning surface 33...Scanning line 34.37...Photoelectric conversion element 35...Amplification circuit 36...Light beam spot 38... Signal comparison circuit 39...Recognition circuit 41...Signal processing circuit Applicant: NEC Corporation

Claims (1)

[Scope of Claims] A light source that emits a light beam, a fixed plane mirror that has a portion that transmits the light beam, a holographic optical deflection element that deflects and scans the light beam and irradiates the object to be scanned, and an object to be scanned. An optical symbol reading device that reads information in an optical symbol, comprising a photoelectric conversion element that receives reflected light from a light source and converts it into a video signal, and a signal processing circuit that processes the video signal and decodes the information. , disposing a photoelectric conversion element that receives the zero-order pointing light transmitted through the hologram light deflection element, and inputting the output of the photoelectric conversion element to the signal processing circuit to control the amplitude of the video signal to be kept constant. An optical symbol reading device characterized in that it is configured as follows.