JPH0369909A - Scanning optical system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a scanning optical system for a laser printer or the like using a semiconductor laser as a light source.

(Prior Art) Conventionally, scanning optical systems using semiconductor lasers as light sources have been used in many printers, copiers, and
It was put into practical use as AX, etc., and achieved remarkable development.

In general, a scanning optical system uses a collimator lens to collimate the light beam emitted by a semiconductor laser into a parallel light beam, which is then deflected by a rotating polygon mirror, and an fθ lens to produce a beam at a constant velocity with respect to the rotational speed of the rotating polygon mirror and a predetermined beam diameter. An image is formed on the photoreceptor as a beam of light.

In addition, the pitch unevenness due to the surface tilt of the rotating polygon mirror is compensated for by IE.
It has a function to do that. For example, JP-A-57-144
No. 515 discloses an optical system composed of an fθ lens consisting of a glass spherical lens and a single lens having a toric surface. In addition, in recent years, advances in plastic materials have led to the development of plastics that have optical properties and environmental resistance close to those of glass.Compared to glass lenses, plastic lenses have excellent impact resistance and mass production, and are inexpensive and lightweight. There is also an optical system. As an example, JP-A-62-18
There is an invention disclosed in Japanese Patent No. 2709, which is a scanning optical system composed of an aspherical fθ lens.

(Problem to be solved by the invention) However, the conventional scanning optical system is
Optical designs using glass, such as the invention in Publication No. 515, are mainstream, and not only do they have high material costs, poor workability, and lack mass production, they also require a large number of man-hours for positioning, making them expensive, and it is difficult to reduce weight. There was a problem of difficulty. Furthermore, in a scanning optical system using only lenses with a low refractive index, the radius of curvature is small and there is no degree of freedom in the refractive index, so there is a problem that high-performance optical characteristics cannot be obtained.

On the other hand, in a scanning optical system for a plastic lens such as the invention disclosed in JP-A-62-182709, since an aspherical lens is used, not only the shape of the molding surface of the lens mold becomes complicated, but also the molding conditions It is necessary to strictly control the accuracy of the lens, and there is also the problem that the accuracy of the lens (a) (q constant) is complicated, and problems remain in the evaluation method.

The present invention solves the above problems and provides a high-performance, inexpensive scanning optical system that is easy to process or position during molding.

(Means for Solving the Problems) In order to solve the above problems, 1 the present invention uses a rotating surface with one circular arc as a generatrix as a lens surface, and pasting together two lenses of the same kind with a low refractive index. The scanning section is composed of a plurality of lenses each having a flat surface for positioning.

(Function) With the above structure, excellent mass production and low cost can be obtained regardless of whether the lens material is glass or plastic.
6. 1tI impact resistance and weight reduction can be achieved. Since the shape of the lens surface is simple, it is easy to measure and evaluate accuracy. Furthermore, a high-performance scanning optical system can be obtained using a material with a low refractive index.

(Example) Three embodiments of the present invention will be described with reference to FIGS. 1 to 6. 1, 2, and 3 are a perspective view, a plan view seen from a main scanning cross section, and a side view seen from a sub scanning cross section, showing the configuration of a scanning optical system according to the present invention.

In FIG. 1, the scanning optical system includes a semiconductor laser 1, a collimator lens 2 that converts the light emitted from the semiconductor laser 1 into parallel light, a columnar lens 3 that forms a linear image of the light beam from the collimator lens 2, and a columnar lens 3 that forms a linear image of the light beam from the collimator lens 2. A rotating polyhedral mirror 4 that has a reflective surface near the crystal plane of the lens 3 and deflects the light flux, an incident side having a negative cylindrical surface having a central axis parallel to the rotation axis 4a of the rotating polyhedron 4JIt4, and an exit side having a convex spherical surface. The curved rod-shaped first fθ lens 5, the incident side has a negative cylindrical surface whose central axis is at the same angle as the rotational axis 4a, and the output side has a convex arc-shaped generatrix, is connected to the rotational axis 4a. parallel to,
A second arcuate fθ lens 6 each formed of a rotational surface rotated about a central axis on the incident side;
The light beams focused by the second fθ lenses 5 and 6 are scanned. The photoreceptor 7 has a rotation axis perpendicular to the rotation axis 4a described above.

The operation of the scanning optical system configured in this way will be explained. The light beam from the semiconductor laser t passes through the collimator lens 2
The light is made into a substantially parallel light beam by the columnar lens 3, then focused near the reflection point of the rotating polygon mirror 4, deflected by the 1-turn polygon mirror surface, and then transmitted onto the photoreceptor 7 by the 1st and 2nd fO lenses 5 and 6. The image is formed by scanning at a constant speed to create a latent image corresponding to one image data.

Note that the columnar lens 3 maintains an optical conjugate relationship between the first and second fθ lenses 5 and 6 and the image plane of the photoreceptor 7, thereby correcting tilting.

Next, the lens surfaces of the t-th and second fO lenses 5 and 6 are set to Nα1 to Nα4 in order from the incident direction.

The minor radius of curvature centered on the central axis parallel to the rotation axis 4a is r, and the half curvature a centered on the perpendicular central axis is P'1. The distance from the reflective surface of the rotating polygon mirror 4 to the first fθ lens 5. is d0, the distance between the lens surfaces of the first and second fO lenses 5 and 6 is d4 to d2, and the refractive index of the first and second fO lenses 5 and 6 is nl and n2, and the three embodiments are shown in Table 1 to Table 3 shows its optical performance, and FIGS. 4 to 6 show its optical performance.

Embodiment ↓ Table 1 Units of r, r', and d ml Embodiment 2 Table 2 r , r d , = 60.41 + m f = 180nn d , >:lOm = f / 6 Embodiment 3 Table 3 r , r, unit of d n, = n, ≦1.6, unit of d nm d, = 59.57 nm f = 180 no n
,=n2≦1.6d o)30na=f/6d,=47.02mm f=180on d,)30n plate=f/6 nwork=n2≦1. The fθ characteristic is expressed by the following equation.

As described above, each embodiment obtained a good optical system.

In addition, in such a pine-shaped optical system, when do becomes f/6 or less, the fθ characteristic deteriorates significantly, making it difficult to obtain a good optical system.

(Effects of the Invention) As explained above, according to the present invention, not only glass but also plastic can be used, so there is a wide range of materials to choose from, and the problems of mass production, weight reduction, precision, and
Not only does it eliminate costs and the difficulty of positioning the lens, but the simple lens shape also makes the plastic mold less expensive, and the lens evaluation method is simplified.
1, so it is easy to improve accuracy and the like.

[Brief explanation of drawings]

1, 2, and 3 are a perspective view showing the configuration of the main scanning optical system, a plan view as seen from the main scanning section, a side view as seen from the sub-scanning section, and FIGS. 4 to 6. The figures are characteristic diagrams showing the optical characteristics of each embodiment, that is, (a) shows spherical aberration, (b) shows astigmatism, and (c) shows fO characteristics. 1... Semiconductor laser, 2... Collimator lens, 3... Column lens, 4... Rotating polyhedral mirror,
5... 1st f17 lens, 6... 2nd fθ lens, 7... Photoreceptor.

Claims (1)

[Scope of Claims] A semiconductor laser, a first optical section that converts the emitted light beam of the semiconductor laser into parallel light beams, and a second optical section that includes a columnar lens that images the parallel light beam from the first optical section into a horizontal line. a deflector that has a reflective surface near the imaging surface of the second optical section and deflects the light beam in the main scanning direction; and a third optical section that forms an image of the light beam deflected by the deflector on the photoreceptor. In the scanning optical system, the third optical section includes a first fθ lens consisting of a two-element fθ lens, the entrance side of which is a negative cylindrical surface perpendicular to the main scanning surface, and the exit side of which is a convex spherical surface; A second fθ lens includes a negative cylindrical surface parallel to the main scanning plane, and a convex rotating surface whose output side is a convex arc perpendicular to the scanning cross section as a generatrix, and the deflector reflecting surface and the first fθ lens The distance between the surfaces is d_0, and the first f
When the refractive index of the θ lens is n_1, the refractive index of the second fθ lens is n_2, and the focal length in the main scanning section is f, the following conditions are satisfied: n_1=n_2≦1.6, d_0≧f/6 Features a scanning optical system.