JPH06110001A - Polygon mirror for projection optical system - Google Patents

Abstract

PURPOSE:To provide a polygon mirror which can freely be varied in projection distance and installed in a small space. CONSTITUTION:This polygon mirror 1 can be made to operate as a concave or a convex surface mirror by forming its respective reflecting surfaces concavely or convexly. The projection optical distance can freely be varied by varying the curvature and the depth of focus can freely be varied by combining the polygon mirror with a projection lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polygon mirror for a projection optical system for projecting and scanning a light beam on a predetermined area.

[0002]

2. Description of the Related Art For example, as an optical reading device for reading a bar code symbol on a bar code label, as shown in FIG. 6, a semiconductor laser (LD) 100 as a light source,
It is known to include a light projecting lens group 101, a half mirror 102, and a light projecting optical system 104 including a polygon mirror 103. In the figure, reference numeral 105 is a bar code label, 106 is a light receiving lens group, and 107 is a photoelectric element.
07 constitutes the light receiving optical system 108.

[0003]

By the way, in such an optical reading apparatus, the projection lens group 1 provided in the projection optical system is provided.
For example, a combination of three lenses is used as 01, but there is a certain limit to the depth of focus, so if there is a large variation in the optical distance to the barcode label to be read, it may not be possible to read. There is also. Especially when reading a bar code symbol having a narrow bar width, the beam is narrowed down and the depth of focus becomes shallow, so that the above-mentioned problem becomes more serious. Therefore, an object of the present invention is to provide a polygon mirror for a projection optical system, which can change a projection distance freely and can be installed in a small space.

[0004]

That is, the present invention provides a projection optical system for projecting a beam of light toward an object to be projected while scanning light from a light source through a projection lens and a polygon mirror. The reflecting surface of the polygon mirror is formed in a concave or convex shape having a specific curvature, and the focal length of the light projecting lens is changed based on the difference in the curvature.

[0005]

According to the present invention, each reflecting surface of the polygon mirror is formed into a concave or convex shape so that it can function as a concave mirror or a convex mirror. Optical distance can be freely expanded and contracted, and by combining with a projection lens,
You can also change the depth of focus freely.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an optical reading apparatus equipped with a polygon mirror 1 for a projection optical system according to the present invention. As the polygon mirror 1, as shown in FIG. It is composed of a flat surface portion 11, a concave surface portion 12, and a convex surface portion 13 that form a concave mirror and a convex mirror, and a focal length (depth of focus) is obtained by combining with a light projecting lens group 101 having a focal length F (depth of focus ± Δx).
As shown in FIG. 3, it substantially expands and contracts between F _{A and} F _C. In the figure, the same parts as those in the related art are designated by the same reference numerals to avoid redundant description. In the plane portion 11, the beam light emitted from the light source 100 and reflected here is just the standard distance S (S = F + D, where F is the focal length of the light projecting lens group, D is the light source 100 and the light projecting lens group 101). The distance is set to (2) when the light is projected onto the bar code label 105B. Concave part 1
2 is concavely curved with a constant curvature in the radial direction of the polygon mirror 1, and when combined with the light projecting lens group 101, the focal length F _A is, as shown in FIG. Compared with the case of reflection at the portion 11, the length is shortened by a substantially constant length. Convex portion 13
Is curved in a concave shape with a constant curvature in the radial direction of the polygon mirror 1, and in combination with the light projecting lens group 101, the focal length F _C is, as shown in FIG. The reflection is increased by a substantially constant length.

Therefore, according to the projection optical system using the polygon mirror 1 of this embodiment, when the bar code label 105C is at the standard position as shown in FIG.
Beam light reflected by 1 is just the barcode label 105C
You can focus on the top and read the bar code symbol in the best possible condition. Further, as shown in FIG. 4, as compared with the bar code label 105A in the standard position, the projection lens group 101
When the light beam is displaced by more than the depth of focus Δx and passes in a close state, the beam light reflected by the concave portion 12 is focused on the barcode label 105A and can be read in the best state. Similarly, as shown in FIG. 5, the barcode label 1
When 05C is displaced at a depth of focus Δx or more of the projection lens group 101 and passes in a state away from the standard position of 05C, the beam light reflected by the convex surface portion 13 is focused on the barcode label 105C. , Can be read in the best condition. In this embodiment, 15 polygon mirrors are used.
Although the prismatic shape is used and the concave surface portions 12 having the same curvature are provided adjacent to each other at five places, and the convex surface portions 13 having the same curvature are provided adjacent to each other at five places, the present invention is not limited to this. For example, it is possible to use a prism having 15 or more or 15 or less side surfaces, and form a concave mirror or a convex mirror having different curvatures on each side surface.

[0008]

As described above, according to the polygon mirror for a projection optical system according to the present invention, each reflecting surface of the polygon mirror is formed in a concave shape or a convex shape so that it can be used as a concave mirror or a convex mirror. It can be made to function, and the projection optical distance can be freely expanded and contracted by changing the curvature, so by combining with the projection lens, the depth of focus can be increased without using a zoom lens or the like. You can change it freely,
A device suitable for cost reduction and device miniaturization can be provided.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing an optical reading device using a polygon mirror according to the present invention.

FIG. 2 is a perspective view showing a polygon mirror according to the present invention.

FIG. 3 is a graph showing the operation of the polygon mirror of the present invention.

FIG. 4 is a graph showing the operation of the polygon mirror according to the present invention.

FIG. 5 is a graph showing the operation of the polygon mirror according to the present invention.

FIG. 6 is an optical path diagram showing a conventional optical reading device.

[Explanation of symbols]

 1 Polygon Mirror 11 Plane 12 Concave 13 Convex 101 Projection Lens Group

Claims (1)

[Claims] 1. A light projecting optical system for projecting a beam of light from a light source through a light projecting lens and a polygon mirror toward a light-projected object, wherein each reflecting surface of the polygon mirror is specified. A polygon mirror of a projection optical system, characterized in that it is formed in a concave or convex shape having a curvature, and the focal length of the projection lens is changed based on the difference in the curvature.