JPH0511201A - Synthetic resin lens for scanning optical system - Google Patents

Abstract

(57) [Abstract] [Purpose] It enables vapor deposition of the effective part of a synthetic resin lens having a collar part. [Structure] In a strip-shaped synthetic resin lens 5 having a collar portion 6 on the outer circumference of the lens, apex of each surface of the lens in a cross section in the lateral direction
When the distance from P3, P4 to the brim tips Q3, Q4 on each surface side in the lens optical axis direction is d3, d4, the effective ray diameter of each lens surface is E1, and the inner diameter of each lens surface is E2. , 0 <d3 (d4)
<0.6 · (E2-E1), and the distance d3,
d4 is substantially constant in the longitudinal direction of the lens 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device f.
The present invention relates to a strip-shaped synthetic resin lens used for a θ lens or the like.

[0002]

2. Description of the Related Art Conventionally, a glass material was generally used for an fθ lens of a light beam scanning device or the like, but in recent years, a synthetic resin material has been used for cost reduction and high performance. Various fθ lenses have been proposed. For example, as shown in the main-scan sectional view of FIG. 7 and the sub-scan sectional view of FIG.
The optical system, which is emitted from the laser light source 1, is scanned by the polygon mirror 2, and is guided to the photosensitive drum 3, includes a plano-convex lens 4 made of a glass material and a meniscus thin aspherical toric lens 5 made of a synthetic resin material. F of two
A θ lens or the like may be used. Such an fθ lens has a so-called strip shape that is long in the main scanning section and short in the sub scanning section.

When a synthetic resin material is used for a lens having such a shape, a collar portion 6 is formed on the outer peripheral portion of the synthetic resin lens 5 as shown in the plan view of FIG. 9 due to strength problems and easy handling. It is general that the flange portion 6 is provided so as to have a rectangular shape.

[0004]

However, in the case of the strip-shaped synthetic resin lens as in the above-mentioned conventional example, from the apex of the lens 5 in the cross section in the lateral direction, the tip portion of the collar portion 6 on each surface side. Is not constant over the longitudinal direction, as shown in FIG. 10 which is an enlarged sectional view taken along the line AA in FIG. 9 and FIG. 11 which is an enlarged sectional view taken along the line BB. In FIGS. 10 and 11, P1 and P2 are vertices of the surface r1, Q1 and Q2 are flange tips on the surface r1 side, and d1 and d2 are distances of P1, P2 and Q1 and Q2 in the lens optical axis direction. .. As described above, the distance d1 in FIG. 10 and the distance d2 in FIG. 11 are not constant, but gradually change in the longitudinal direction, which causes the following problems.

First, when a synthetic resin lens is used as the fθ lens of the light beam scanning optical system, in order to prevent ghosts due to surface reflection and adhesion of dust due to static electricity, or due to the problem of surface hardness, antireflection is performed. Film deposition is required. However, in the case of the synthetic resin lens 5 having the rectangular flange 6 as described above, it is impossible to perform uniform vapor deposition in the longitudinal direction in the vapor deposition process.

This will be described with reference to FIGS. 10 and 11.
When vapor deposition of the surface r1 is considered, when the vapor deposition material flies from the left side of the figure at an angle θ with respect to the optical axis and vapor deposits on the lens surface, in FIG. 11 which is an end cross section in the longitudinal direction, the surface r1 is Although vapor deposition can be performed on almost the entire surface, in FIG. 10, which is the longitudinal center cross-section, the entire surface of the surface r1 cannot be vapor-deposited uniformly due to the influence of the shadow of the collar portion 6 shown by diagonal lines. In other words, as described above, the distance from the apex of each surface of the lens in the cross section in the lateral direction to the tip of the flange on each surface gradually changes in the longitudinal direction, so that the entire effective portion can be vapor-deposited uniformly. It will be impossible.

Secondly, due to the same reason, even in the molding step, there arises a problem such as a difference in shrinkage ratio between the central portion and the peripheral portion in the longitudinal direction, and it is difficult to obtain uniform surface accuracy in the longitudinal direction.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a synthetic resin lens for a scanning optical system, which enables vapor deposition over the entire surface in the longitudinal direction.

[0009]

A synthetic resin lens for a scanning optical system according to the present invention for achieving the above object is used for an fθ lens of a light beam scanning optical system and is a strip provided with a collar portion on the outer circumference of the lens. -Shaped synthetic resin lens, the distance in the lens optical axis direction from the apex of each lens surface of the cross section in the lateral direction to the tip of the flange on each surface side is d, the effective ray diameter of each lens surface is E1, each lens surface is When the inner diameter of the surface is E2, the condition of 0 <d <0.6 · (E2-E1) is satisfied, and the distance d is substantially constant in the longitudinal direction of the lens. Is.

[0010]

The synthetic resin lens for a scanning optical system having the above-described structure is a strip-shaped synthetic resin lens having a flange portion on the lens outer peripheral portion used for an fθ lens or the like, and is provided with certain conditions to prevent reflection. Eliminates the influence of the shadow of the collar in the film deposition process.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. 1 to 3 show a first embodiment of the present invention, FIG. 1 is a plan view in the longitudinal direction of a synthetic resin lens 5 of the present invention, in which a hatched portion indicates a lens portion and a solid line portion indicates a lens outer periphery. The collar part 6 is shown. 2 and 3 are enlarged cross-sectional views in the lateral direction of the synthetic resin lens, and FIG. 2 is a cross-sectional view taken along the line AA which is the central portion in the longitudinal direction of FIG.
Similarly, FIG. 3 is a cross-sectional view taken along the line BB which is an end portion in the longitudinal direction. Here, in FIG. 2, P3 and P4 are lens surfaces r1 and r2, respectively.
, Q3, Q4 are the tip ends of the flanges on the respective surface sides of the surfaces r1, r2, E1 is the effective ray diameter in the lateral direction of the synthetic resin lens 5, and E2 is the inner diameter in the lateral direction.

Further, the vertices P3 and P4 of the lenses on the surfaces r1 and r2
And the distances of the brim tips Q3 and Q4 on the respective surface sides in the optical axis direction are d3 and d4, in this embodiment, the size of the brim portion 6 is 0 <d3 (d4) <0. 6 · (E2-E1) is satisfied. In other words, if d3 (d4) becomes a negative value, the vertex P3 (P4) of the lens 5 will protrude beyond the brim tip Q3 (Q4), and the surface of the lens 5 is easily scratched. There is no problem.

When d3 (d4) is 0.6 × (E2-E1) or more, it is impossible to uniformly deposit the effective portion in the effective portion due to the shadow of the collar portion 6 in the vapor deposition step as described above. Is not preferable. That is, the condition under which the shadow of the collar portion 6 is not affected in the vapor deposition process can be approximated as E2> E1 + 2 · d · tan θ when expressed using the diameters E1 and E2, the distance d and the angle θ in FIG.

Under ordinary vapor deposition conditions, θ is 0 to 40.
In order to prevent the influence of the shadow even at a maximum angle of 40 ° by substituting θ = 40 ° into the above equation, d <
It becomes 0.6 · (E2-E1), and if this condition is not satisfied, it will be impossible to uniformly deposit vapor in the effective portion.

Further, in the embodiment, as shown in FIG. 3, at the peripheral portion in the longitudinal direction, from the lens vertices P3 and P4 to the tip of the collar.
Distances d3 and d4 to Q3 and Q4 are substantially the same as the central portion in the longitudinal direction of FIG. That is, on the surface r1, the distance d3 in FIG.
And the distance d3 in FIG. 3 and the distance d4 in FIG.
The distances d4 are set to be almost equal. In other words, by setting the shapes of the brim tip portions Q3 and Q4 on both the surfaces r1 and r2 to have a radius of curvature substantially equal to the radius of curvature in the longitudinal direction as shown in FIG. Not only is it possible to deposit evenly over the entire length, but also in the molding process there is no problem such as a difference in shrinkage ratio between the central part and the peripheral part in the longitudinal direction, and the surface accuracy is uniform over the entire longitudinal direction. It is possible to put out.

In the first embodiment, the case where the cross-sectional shape of the synthetic resin lens 5 in the lateral direction is a meniscus convex lens has been described. However, even in the case of the biconvex lens 5 shown in FIG. 4 and the meniscus concave lens 5 shown in FIG. The same effect can be obtained by setting the conditional expression within the range.

Further, in the first embodiment, in the case of a meniscus-shaped convex lens having a relatively small radius of curvature in the longitudinal direction as shown in FIG. 1, the shape of the tip of the brim is substantially equal to the radius of curvature of the lens 5. However, in the case of the lens 5 which is close to a plano-convex lens having a relatively large radius of curvature as in the second embodiment shown in FIG. 6, the shape of the brim tip Q3 on the surface r1 side having a large radius of curvature is set. , May be approximated to a straight line. That is, if the distance d3 in the optical axis direction from the lens surface apex P3 to the flange tip portion Q3 is made substantially constant in the longitudinal direction, the same effect can be obtained.

[0018]

As described above, the synthetic resin lens for a scanning optical system according to the present invention is a strip-shaped synthetic resin lens having a collar portion on the outer peripheral portion of the lens used for the fθ lens of a light beam scanning device. By satisfying the distance d in the optical axis direction from the lens apex of the cross section in the lateral direction to the tip of the collar under certain conditions and setting the distances d to be substantially equal in the longitudinal direction, the strength is sufficient and the handling is easy, and Not only is it possible to perform uniform vapor deposition over the entire effective portion, but it is also possible to improve the molding accuracy.

[Brief description of drawings]

FIG. 1 is a horizontal sectional view in a longitudinal direction of a synthetic resin lens according to a first embodiment.

FIG. 2 is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a cross-sectional view taken along the line BB of FIG.

FIG. 4 is a cross-sectional view of a modified example.

FIG. 5 is a cross-sectional view of a modified example.

FIG. 6 is a horizontal sectional view of the second embodiment.

FIG. 7 is a plan view of a conventional optical scanning optical system.

FIG. 8 is a side view of a conventional optical scanning optical system.

FIG. 9 is a horizontal sectional view of a conventional synthetic resin lens.

10 is a cross-sectional view taken along the line AA of FIG.

11 is a cross-sectional view taken along the line BB of FIG.

[Explanation of symbols]

 5 Toric lens 6 Collar P P Apex of lens surface Q Collar tip d Optical axis distance E1 Effective diameter of light E2 Effective diameter of inner diameter

Claims (1)

Claim: What is claimed is: 1. A strip-shaped synthetic resin lens used for an fθ lens of a light beam scanning optical system and provided with a collar portion on the lens outer periphery, from the apex of each surface of the lens in a cross section in the lateral direction, The distance in the lens optical axis direction to the tip of the flange on each surface side is d, the effective ray diameter of each lens surface is E1, and the inner diameter of each lens surface is
When E2, the condition 0 <d <0.6 · (E2-E1) is satisfied, and the distance d is substantially constant in the longitudinal direction of the lens. Resin lens.