JPH0746175B2 - Scanning device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning device, and in particular, a light beam from a laser light source is reflected by a rotating polygon mirror and then scanned on a surface to be scanned via a condenser lens. Display and record information, eg laser printer, laser facsimile, laser COM (C
The present invention relates to a scanning device suitable for an optical output microfilm).

(Prior Art) Conventionally, a light beam from a laser light source is guided to a rotating polygon mirror, and a reflected light beam from the rotating polygon mirror is a condensing lens f-.
Various scanning devices have been proposed in which the scanning surface is scanned by focusing on the scanning surface via a θ lens and rotating a rotary polygon mirror.

For example, FIGS. 4 and 5 are schematic views of an optical system of a conventional scanning device, FIG. 4 is a sectional view in the main scanning direction in which scanning is performed by rotating a rotary polygon mirror, and FIG. 5 is a main scanning direction. FIG. 6 is a partial cross-sectional view in the sub-scanning direction orthogonal to the direction.

In FIG. 4, among the light beams from the light source 10, the light beam in the main scanning direction passes through the cylindrical lens 4 having no refracting power in the main scanning direction, and then enters the rotating polygon mirror, and the rotating polygon mirror 1
After being reflected by, the light is focused on the surface 3 to be scanned by the condenser lens 2 which is an f-θ lens system.

On the other hand, the light flux in the sub-scanning direction shown in FIG. 5 is converged by the cylindrical lens 4 and is reflected at a predetermined position on the reflecting surface of the rotary polygon mirror 1.
After focusing by PF, it is focused on the scanned surface 3 by the focusing lens 2.

Here, the focusing lens 2 has a toric surface and corrects the error due to the surface tilt of the rotary polygon mirror by making the conjugate relationship of the image formation in the main scanning direction and the sub-scanning direction different.

In general, it is desirable that the focusing lens is constructed so that the focal point position coincides with the scanning surface in the scanning direction and the sub-scanning direction over the entire scanning width.

However, since various aberrations remain in the focusing lens in reality, the focal position is scanned because the position where the cylindrical lens 4 forms an image on the rotary polygon mirror 1 in the sub-scanning direction changes depending on the rotation angle of the rotary polygon mirror. It was very difficult to match the face perfectly.

FIG. 6 shows the deviation of the focus position on the scanning surface in FIGS. 4 and 5 with the horizontal axis representing the amount of image plane curvature and the vertical axis representing the scanning angle. In the figure, the solid line indicates the focal position in the sub scanning direction, and the broken line indicates the focal position in the main scanning direction. As shown in the figure, the spot shape varies due to the focus error depending on the scanning position on the scanning surface, and as a result, there is a limit to reduce the light beam diameter and perform scanning with high resolution.

On the other hand, U.S. Pat. No. 4,496,209 proposes a method of correcting the focal position of the image plane by using a bending cylindrical lens. However, since this method has a refractive power in the scanning direction, it is very difficult to independently correct a complicated image surface curvature in both the scanning direction and the sub-scanning direction.

(Problems to be Solved by the Invention) In the present invention, when a light beam from a light source is reflected by a rotating polygon mirror and focused on a surface to be scanned by a condenser lens for scanning, the focus is mainly at the scanning position in the sub-scanning direction. It is an object of the present invention to provide a scanning device capable of excellently correcting misalignment, so-called image curvature, and having high resolution and capable of scanning a large screen.

(Means for Solving Problems) A light beam from a light source is guided to a rotary polygon mirror through a cylindrical lens having no refractive power in the main scanning direction, and in a sub-scanning direction orthogonal to the main scanning direction. In a scanning device which forms an image on the reflecting surface of the rotating polygon mirror, and focuses the periodically deflected reflected light flux from the rotating polygon mirror on a scanning surface through a condenser lens having a toric surface for scanning. An optical element having no refracting power in the main scanning direction but having only refracting power in the sub-scanning direction is arranged between the condenser lens and the scanning surface, and refraction of the optical element in the sub-scanning direction is performed. The force is that it continuously changes from positive to negative and positive from the central portion of the optical element in the main scanning direction toward the peripheral portion.

(Embodiment) FIGS. 1 and 2 are schematic views of an optical system of a scanning device of the present invention, respectively. FIG. 1 is a sectional view in a main scanning direction of a scanning direction by rotation of a rotary polygon mirror, and FIG. The figure is a cross-sectional view in the sub-scanning direction orthogonal to the main scanning direction.

In FIGS. 1 and 2, reference numeral 1 is a rotary polygonal mirror, and a rotary shaft 11
It is rotating around. A condenser lens 2 is composed of an f-θ lens system. Reference numeral 3 is a surface to be scanned, 4 is a cylindrical lens, 10 is a light source, and 5 is an optical element having no refracting power in the main scanning direction but only in the sub-scanning direction. A sectional view and FIG. 3B show sectional views at positions A, B, C, D, and E orthogonal to the respective positions in FIG.

The difference between the scanning device of this embodiment shown in FIGS. 1 and 2 and the conventional scanning device shown in FIGS. 4 and 5 is that between the rotary polygon mirror 1 and the surface 3 to be scanned in this embodiment. Optical element 5 having the above-mentioned shape
Is arranged to correct the image plane curvature in the sub-scanning direction due to the residual aberration of the condenser lens 2.

That is, in this embodiment, as shown in FIG. 1, of the light beams from the light source 10, the light beams in the main scanning direction are reflected by one reflecting surface of the rotary polygon mirror 1 through the cylindrical lens 4 having no refractive power in the main scanning direction. After that, the light is guided to the scanned surface 3 through the optical element 5 by the condenser lens 2.

As shown in FIG. 3 (A), the optical element 5 has no refractive power in the main scanning direction, so that the light beam passes through as it is and reaches the surface 3 to be scanned.

On the other hand, as shown in FIG. 2, the light beam in the sub-scanning direction is focused on one point PF of one reflecting surface of the rotary polygon mirror 1 in order to correct the surface tilt of the rotary polygon mirror 1 by the cylindrical lens 4.
Then, the light is focused again on the surface 3 to be scanned by the condenser lens 2 and the optical element 5.

Then, the surface to be scanned 3 is rotated by rotating the rotary polygon mirror 1.
Scanning over.

In the image forming relationship in this embodiment, the surface to be scanned 3 is in a conjugate relationship with the infinite object through the cylindrical lens 4, the focusing lens 2 and the optical element 5 in the main scanning direction. Further, in the sub-scanning direction, the surface to be scanned 3 is configured to have a conjugate relationship with the reflection point PF of the rotary polygon mirror 1 via the condenser lens 2 and the optical element 5.

Generally, of the aberrations in the condenser lens, the meridional image plane curvature in the main scanning direction can be corrected relatively easily as compared with the sagittal image plane curvature in the sub scanning direction, as is apparent from the aberration diagram in FIG. You can

For this reason, it is important to correct the sagittal image plane curvature in the sub-scanning direction in the condenser lens of many scanning devices. However, it is generally very difficult to satisfactorily correct the sagittal image plane curvature in the sub-scanning direction inside the condenser lens.

Therefore, in the present embodiment, the sagittal image plane curvature in the sub-scanning direction is considered in consideration of the amount of curvature for each image height, and an optical element having a shape as shown in FIGS. By arranging it between the scanning surface 3 and the scanning surface 3, the correction is excellent.

That is, the optical element 5 has no refracting power in the main scanning direction but only in the sub-scanning direction.
As shown in (B), the shape has positive, negative, and positive refracting power from the central portion to the peripheral portion in the main scanning direction. In addition, the change in refracting power at this time is measured by the condenser lens
In accordance with the amount of curvature of the image surface at each image height, the refractive power is changed continuously so as to have positive, negative, and positive refracting powers.

As a result, it is possible to satisfactorily correct the image plane curvature in the sub-scanning direction, and it is possible to scan the light beam on the surface to be scanned in a small focused state over the entire scanning range.

In the present embodiment, the case where the surface tilt correction of the rotary polygon mirror and the image plane curvature in the sub-scanning direction are corrected by the combination of the condensing lens having the toric surface and the optical element is shown. Alternatively, the objective of the present invention can be achieved in the same manner even if a condenser lens having a cylindrical lens is provided with the function of the optical element.

Also, the optical element shown in FIG. 3 has a positive and negative refractive power in the sub-scanning direction, and has a shape in which the refractive power is continuously changed. Only the shape may be continuously changed.

(Effects of the Invention) According to the present invention, when the light beam from the light source is reflected by the rotary polygon mirror and focused on the surface to be scanned by the condenser lens for scanning, the optical element having the above-described shape is arranged at a predetermined position. By doing so, the image formation position of the light beam can be made to coincide with the scanning surface, and scanning can be performed with high resolution, and furthermore, the curvature of the image plane of the condenser lens can be satisfactorily corrected, so that scanning can be performed with high resolution over a wide scanning width. A scanning device can be achieved.

[Brief description of drawings]

1 and 2 are schematic views of an optical system in a main scanning direction and a sub scanning direction according to an embodiment of the present invention, and FIGS. 3 (A) and 3 (B) are explanatory views of an optical element according to the present invention. , FIG. 4 and FIG. 5 are schematic diagrams of a conventional optical system in the main scanning direction and the sub-scanning direction, respectively.
The drawing is an explanatory view showing the deviation of the focal point position on the scanning surface in the scanning device shown in FIG. In the figure, 1 is a rotary polygon mirror, 2 is a condenser lens, 3 is a surface to be scanned, 4 is a cylindrical lens, 5 is an optical element, and 10 is a light source.

Claims (1)

[Claims] 1. A light beam from a light source is guided to a rotary polygonal mirror through a cylindrical lens having no refractive power in the main scanning direction, and the rotary polygonal mirror of the rotary polygonal mirror is guided in a sub-scanning direction orthogonal to the main scanning direction. In the scanning device, an image is formed on a reflecting surface, and the reflected light beam periodically deflected from the rotary polygon mirror is focused on a scanning surface through a condensing lens having a toric surface to perform scanning. And an optical element having no refracting power in the main scanning direction and having only refracting power in the sub-scanning direction between the scanning surface, and the refracting power in the sub-scanning direction of the optical element is the optical A scanning device characterized by continuously changing from positive to negative and positive from a central portion of the element in the main scanning direction to a peripheral portion.