JPH0795613B2 - Laser light output fluctuation prevention device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A laser light output fluctuation prevention device applicable to a bar code scanner or the like as a POS terminal, which suppresses fluctuations in laser light output to prevent bar code reading from becoming inaccurate. In order to prevent fluctuations in output, a laser tube having a resonance length in which the longitudinal mode is one or two, and in order to prevent fluctuations in output, the S-polarized light and the P-polarized light emitted from the laser tube are circularly polarized. It is configured to include a quarter-wave plate for conversion and an optical element for reflecting the circularly polarized light converted by the quarter-wave plate.

[Industrial application field]

The present invention relates to a laser light output fluctuation preventing device, for example,
The present invention relates to a laser light output fluctuation prevention device applicable to a barcode scanner as a POS terminal.

[Conventional technology]

Bar code scanners currently used as POS terminals are becoming smaller and thinner, and the laser tubes used as their light sources are also becoming smaller accordingly. On the other hand, there is a result that the angle at which the laser light emitted from the laser tube enters each optical element inside becomes shallow.

[Problems to be solved by the invention]

As described above, due to the miniaturization of the laser tube, its resonance length is shortened, and the longitudinal mode of the emitted laser light is one or two. Therefore, S-polarized light and P-polarized light alternate with each other during the longitudinal mode shift, and due to the influence, according to the experiment,
There is a 30% output variation.

Further, the shallower the angle of the light ray when entering each internal optical element, the larger the difference between the ratios of the S-polarized light and the P-polarized light in the reflected light and the refracted light. Therefore, if the longitudinal mode is one or two and the S-polarized light and the P-polarized light alternate with each other when the longitudinal mode is moved, the difference between the ratios of the S-polarized light and the P-polarized light in the reflected light and the refracted light remains as they are. It appears as a fluctuation in the output after passing through the optical element.

Due to the above two factors, the output fluctuation becomes remarkable, and the output of the laser tube is determined in consideration of the fluctuation, but the upper limit output is limited by the safety standard, so the output is sufficiently high with sufficient margin. Cannot be set. Therefore, there is a problem that the barcode reading becomes inaccurate when the output becomes small due to the fluctuation due to the above factors.

The present invention has been made in view of such a point, and an object thereof is to provide a laser light output fluctuation preventing apparatus that suppresses fluctuations in laser light output and prevents bar code reading from becoming inaccurate. I am trying.

[Means for solving problems]

FIG. 1 is a block diagram of the principle of the laser light output fluctuation preventing device of the present invention.

In the figure, the laser tube 111 has a resonance length in which the longitudinal mode is one or two.

The quarter-wave plate 113 is provided in order to prevent output fluctuations.
Each of the S-polarized light and the P-polarized light emitted from the laser tube 111 is converted into circularly polarized light.

The optical element 115 reflects the circularly polarized light converted by the quarter-wave plate 113.

Therefore, as a whole, the S-polarized light and the P-polarized light emitted from the laser tube 111 are converted into circularly polarized light by the quarter-wave plate 113, and the circularly polarized light is reflected and transmitted through the optical element 115. ing.

[Work]

Laser tube with resonance length of 1 or 2 longitudinal modes 11
S-polarized light and P-polarized light are emitted from 1 and each is a quarter
It is converted into circularly polarized light by the wave plate 113. Quarter wave plate 1
The circularly polarized light converted by 13 is reflected and transmitted by the optical element 115.

In the present invention, by converting the S-polarized light and the P-polarized light emitted from the laser tube 111 into circularly polarized light, fluctuations in the output are prevented.

〔Example〕

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

FIG. 2 shows the outline of a bar code scanner to which the laser light output fluctuation preventing device in one embodiment of the present invention is applied.

I. Correspondence between Embodiment and FIG. 1 Here, the correspondence between the embodiment of the present invention and FIG. 1 will be described.

The laser tube 111 corresponds to the laser tube 211.

The quarter-wave plate 113 corresponds to the quarter-wave plate 213.

The optical element 115 corresponds to the mirror 215, the condenser mirror 217, the pattern combining mirror 219, the window glass 221, and the polygon mirror 225.

An embodiment of the present invention will be described below on the basis of the above correspondence.

II. Configuration of Embodiment In FIG. 2, inside the barcode scanner 200,
There is a laser tube 211 that emits a laser beam for reading a barcode of a product, and a 1/4 wavelength plate 213 is arranged at a position where the laser beam emitted from the laser tube 211 is first received. The quarter-wave plate 213 is adjusted so as to form an angle of 45 ° with respect to each of P-polarized light and S-polarized light in the laser light.
Mirror at the position to receive the laser beam that has passed through the quarter-wave plate 213
215 is arranged, and the polygon mirror 225 is arranged at a position for receiving the laser beam reflected by the mirror 215. Also,
There are a plurality of pattern combining mirrors 219 at the positions where the laser light struck by the polygon mirror 225 is received, and the upper window glass 2
It is arranged so that the laser light is directed to 21.

On the other hand, a condensing mirror 217 for collecting the light reflected and scattered from the bar code of the product (not shown) is arranged in the vicinity of the pattern combining mirror 219, and further the sensor 223 for sensing the light. Are arranged so as to face the condenser mirror 217.

III. Operation of Embodiment With reference to FIG. 2, an outline of operation of the barcode scanner 200 is shown. The laser light emitted from the laser tube 211 is composed of P-polarized light and S-polarized light, and is converted into circularly polarized light by the 1/4 wavelength plate 213 that passes first. The laser light that has passed through the quarter-wave plate 213 is then reflected by the mirror 215 toward the polygon mirror 225. The laser light reflected by the polygon mirror 225 is shaken by the rotation of the polygon mirror 225 and is applied to the plurality of pattern combining mirrors 219. The laser light inverted to the plurality of pattern combining mirrors 219 then passes through the window glass 221 on the upper side and is irradiated on the barcode of the product there.

The laser light emitted to the bar code is reflected there to become scattered light, and follows the opposite path and again the pattern synthesizing mirror 21.
Go to 9. Further, the light is reflected to the polygon mirror 225, and the light further reflected there is directed to the condenser mirror 217 in this case. The light that reaches the condenser mirror 217 is condensed by being reflected there, and finally the sensor.
Detected at 223. The information of the bar code detected by the sensor 223 is converted into an electric signal and then used for searching the PLU of the POS terminal device (not shown).

The above is the outline of the optical system of the barcode scanner 200. Here, as described above, the laser light emitted from the laser tube 211 first passes through the quarter-wave plate 213. The quarter-wave plate 213 has a function of converting S-polarized light and P-polarized light into circularly polarized light, so that the laser light thereafter is circularly polarized light. As a result, when the quarter-wave plate 213 does not exist and the light is passed through each optical system with random polarization, the output variation of the optical system is hardly seen.

IV. Summary of Examples As described above, the laser light composed of S-polarized light and P-polarized light emitted from the laser tube 211 is converted into circularly polarized light by the 1/4 wavelength plate 213, and the circularly polarized light is converted into each optical element (mirror 215). The polygon mirror 225, the pattern combining mirror 219, the window glass 221, and the condenser mirror 217) are reflected and transmitted.

Therefore, it is possible to prevent the output of the laser beam emitted from the laser tube 211 from varying after passing through each optical element.

V. Modified Embodiment of the Invention In the embodiment of the present invention described above, the 1/4 wavelength plate 2
Although 13 is provided to convert the randomly polarized light into circularly polarized light and prevent the output from varying during reflection and transmission, a greater effect can be expected if a non-reflection coating is applied to the incident surface of the window glass.

Further, although the correspondence between FIG. 1 and the present invention has been described in “I. Correspondence between Example and FIG. 1”, the present invention is not limited to this, and there are various modifications. Those skilled in the art can easily guess.

〔The invention's effect〕

As described above, according to the present invention, the vertical mode is one or two.
By converting S-polarized light and P-polarized light emitted from a laser tube having a resonance length of a book into circularly polarized light by a quarter-wave plate, it is possible to prevent fluctuation in output after passing through each optical element. The code information can be read accurately, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the laser light output fluctuation preventing apparatus of the present invention, and FIG. 2 is a configuration diagram of a bar code scanner to which the laser light output fluctuation preventing apparatus according to an embodiment of the present invention is applied. In the figure, 111 is a laser tube, 113 is a quarter wave plate, 115 is an optical element, 211 is a laser tube, 213 is a quarter wave plate, 215 is a mirror, 217 is a converging mirror, and 219 is pattern composition. A mirror, 221 is a window glass, 223 is a sensor, and 225 is a polygon mirror.

Claims (1)

[Claims] 1. A laser tube (111) having a resonance length in which the longitudinal mode is one or two, and S-polarized light and P-polarized light emitted from the laser tube (111) in order to prevent output fluctuation. A quarter-wave plate (113) for converting each of them into circularly polarized light, and an optical element (115) for reflecting the circularly polarized light converted by the quarter-wave plate (113). A laser light output fluctuation preventing device characterized by: