JPH0666010B2 - Laser optical scanning device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a laser beam scanning device used as an optical scanning unit of a bar code reading device.

Background of the Technology Recently, in order to save labor in register operations in supermarkets and the like, a bar code reading device that reads a bar code printed on the exterior of a product and inputs it into a computer has come to be used. Laser safety standards have been established for devices using such lasers.For example, in the case of bar code readers used in POS systems, the standard is BRH class IIa in the United States and IEC class I in Europe. It is necessary to protect each. However, in order to improve the reading performance, it is preferable to increase the light amount of the laser emitted from the window of the barcode reading device as much as possible.

2. Related Art and Problems Conventionally, in a laser beam scanning device used in a POS system or the like, a laser scanning pattern emitted from a reading window is usually composed of scanning lines scanning in a plurality of directions. Further, in order to increase the number of times of scanning, it is usual to scan each direction a plurality of times with one rotation of the rotating body (rotating polygon mirror, hologram disk, etc.).

FIG. 1 is a diagram for explaining a rotary polygon mirror of a laser light scanning device using a conventional mirror, where a is a side view, b is a view of the a view from below, and c is the state of the a view. It is a figure which shows the state when rotating 180 degrees. In the figure, 1 is a rotary polygon mirror (two-sided mirror in the figure), 2 is its rotation axis, 3 is the first mirror, and 4
Is the second mirror, 5 is the incident beam, 6 is the incident beam incident point, 7
Indicate scanning beams, respectively.

The operation of this rotary polygon mirror will be explained. In FIG. A, an incident beam 5 incident from below in parallel to the rotation axis 2 is reflected obliquely downward by the first mirror 3 as shown in FIG. Scan by rotating to. The tilt angles of the mirror surface are different between the first and second mirrors 3 and 4, and are θ ₁ and θ ₂ , respectively. Therefore, when the state shown in FIG. 10A is rotated 180 ° to the state shown in FIG. 7C, the direction of the scanning beam 7'changes by 2 (θ ₂ -θ ₁ ) in comparison with the case shown in FIG.

FIG. 2 is a view showing a laser beam scanning device using the rotary polygon mirror shown in FIG. 1, a is a side view of a main part, and b is a top view of a reading window. In the figure, 1 is a rotating polygon mirror, 5 is an incident beam, 7 is a scanning beam by a first mirror, 7'is a scanning beam by a second mirror, 8 is a window glass, 9 is a reading window cover, 1
Reference numeral 0 indicates a reading window, and reference numerals 11 and 12 indicate reflection mirrors.
This laser light scanning device changes the scanning light 7,7 'by the first mirror and the second mirror as described in FIG.
The opening was set to 7 mm or more in the reading window 10. This is because if the two scan lines are separated by more than the human pupil diameter (about 7 mm), the two scan lines do not enter the pupil at the same time, which increases safety.

However, this method has a drawback that the opening of the reading window 10 becomes large and the window glass is damaged by dropping of the article, or the window glass is easily scratched or soiled.

SUMMARY OF THE INVENTION The present invention has been made in view of the above drawbacks of the prior art, and an object of the present invention is to provide a laser beam scanning device capable of reducing the opening of a reading window and increasing the amount of laser emission light.

According to the present invention, the object of the present invention is to provide a laser beam scanning device for reflecting a laser beam by a rotary polygon mirror and scanning the laser beam through a reading window, wherein the rotary polygon mirror is a scanning beam from each surface. Is provided by providing a step between each surface so as to intersect in the vicinity of the reading window, and the emission point of the scanning beam is different for each surface.

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

FIG. 3 is a diagram for explaining a rotary polygon mirror used in the laser beam scanning device according to the present invention, in which a is a side view and b is a diagram showing a state rotated by 180 ° from the state of FIG. In the figure, 20 is a rotary polygonal mirror (two-sided mirror in the figure), 21 is its main body, 22 is a rotation axis, 23 is a first mirror, 24 is a second mirror, and 25.
Is the incident beam and 26 and 26 'are the scanning beams. In this embodiment, the first mirror 23 and the second mirror 24 have a step h, and are attached to the main body 21 of the rotary polygon mirror with the respective surface inclination angles θ ₁ and θ ₂ . In this embodiment having such a configuration, in the state of FIG.
It is incident on the mirror 23 of the
Scan with the rotation of. Next, the rotation advances 180 degrees and the third
In the state of FIG. B, the reflection point of the incident beam moves upward by h with respect to the figure a, and the reflection direction of the scanning beam 26 ′ is 2 (θ ₂ −θ ₁ ) with respect to the scanning beam 26 of the figure a. Approach at an angle of.

FIG. 4 is a diagram showing a laser beam scanning device according to the present invention, in which (a) is a cross-sectional view of an essential part and (b) is a top view of a reading window.
In the figure, 20 is a rotary polygon mirror, 22 is its rotation axis, 23 is a first mirror, 24 is a second mirror, 25 is an incident beam, and 26, 26 '.
Is a scanning beam, 27 and 28 are reflection mirrors, 29 is a window glass, 30 is a reading window cover, and 31 is a reading window.

This embodiment uses the rotary polygon mirror 20 shown in FIG. 3, and the scanning beam 2 reflected by the first and second mirrors 23 and 24 is used.
6,26 'meet one point at the reading window 31. Then, the scanning beams 26 and 26 'intersect each other at an intersection angle of 1.45 ° or more (the solid angle at which each scanning start point is seen from the beam intersection point is 5 ×
Equivalent to 15 ^-4 sr. ) Beam reflection angle difference 2 (θ ₂ -θ
₁ ) is set to 1.45 ° or more. Also, the step h in FIG.
It must be determined by the emission path of the scanning beams 26, 26 'in the figure and the optical path length to the reading window, and the beam reflection angle difference θ.

Since the scanning beams 26 and 26 'cross each other at the reading window portion in this embodiment, the reading window 31 can be made smaller than the conventional one as shown in FIG. 4B, and each scanning is started from the beam intersection point. Since the solid angle that allows points is 5 × 10 ^-4 sr or more (this value is specified in the laser safety standard IEC), it also meets the safety standard. In the case of laser safety standard BRH, this solid angle is 10 ^-3 sh (about 2 °).

FIG. 5 is a diagram for explaining another embodiment of the rotating polyhedron, a is a side view, b is a diagram showing a state when rotated 180 ° from the state of FIG. A, the same as FIG. The parts are denoted by the same reference numerals. In the present embodiment, the rotary shaft 22 is removed from the center instead of the step h between the mirrors shown in FIG. Even with this, the first mirror 23 and the second mirror
24 is equal to a step on the center line of the rotary shaft 22
The same effect as that in the figure can be obtained.

Effects of the Invention As described above in detail, the laser light scanning device of the present invention satisfies the safety standard by using the rotating polygon mirror that can move the reflection point of the incident beam by providing a step between the mirrors, In addition, the reading window becomes smaller than the conventional one.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a rotary polygonal mirror of a conventional laser beam scanning device, FIG. 2 is a diagram for explaining a laser beam scanning device using a conventional rotary polygonal mirror, and FIG. 3 is the present invention. For explaining a rotary polygon mirror used in the laser light scanning device of
FIG. 4 is a diagram for explaining the laser beam scanning device according to the present invention, and FIG. 5 is a diagram for explaining another embodiment of the rotary polygon mirror. In the drawing, 20 is a rotary polygon mirror, 21 is its main body, 22 is a rotation axis, 23 is a first mirror, 24 is a second mirror, 25 is an incident beam, 26, 26 'are scanning beams, and 27, 28 are Reflective mirror, 29
Is a window glass, 30 is a reading window cover, and 31 is a reading window.

Claims (2)

[Claims] 1. A laser beam scanning apparatus for reflecting a laser beam by a rotary polygon mirror and scanning the laser beam through a reading window, wherein the rotary polygon mirror has scanning beams intersecting in the vicinity of the reading window. As described above, the laser beam scanning device is characterized in that a step is provided between the respective surfaces, and the emission point of the scanning beam is different for each surface. 2. The laser beam scanning device according to claim 1, wherein the rotary polygon mirror is provided with a rotation axis of the rotary polygon mirror off the center instead of providing a step between each surface. apparatus.