JPH0614186Y2 - Beam scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a beam scanning device of a laser beam printer for deflecting a laser beam by a rotating polygon mirror and forming an image by imaging this beam on a photoconductor. It is a thing.

[Conventional technology]

The optical system of a laser beam printer, which deflects the laser beam with a rotating polygon mirror and forms an image on the photoconductor, forms an image.The deflection angle after the deflection with the rotating polygon mirror and the image height of the image on the photoconductor. Must be in a proportional relationship. That is, when the deflection angle is θ in FIG. 3, the image height is Y, and the focal length of the imaging lens is f, it is necessary that Y = fθ. A general image forming lens has a relationship of Y = ftan θ. When this lens is used, when a beam is deflected by a rotating polygon mirror at a constant speed and a photoconductor is scanned, the peripheral portion of the image has a deflection angle larger than that of the central portion. The movement of the image point with respect to the change is large, and the image extends in the scanning direction toward the peripheral portion. In order to prevent this, the distortion is corrected differently from that of a general lens to obtain a relation of Y = fθ. This is called an fθ optical system. A laser beam printer converts a laser beam emitted from a light source into a parallel light beam of a certain diameter, reflects it by a rotary polygon mirror, forms an image on a photoconductor by an fθ optical system, and rotates the rotary polygon mirror to a photoconductor by an fθ lens. Scanning laser spot image created above. In this case, if there is a large variation in the tilt of the rotary polygonal mirror in the direction of the rotation axis of the rotary polygonal mirror, the height of the spot image on the surface of the photoconductor that is formed by the reflection of each surface will be different, and the photoconductor that rotates at a constant speed will be constant. , It is not possible to scan at intervals, causing unevenness in the image. To prevent this, Fig. 4 (a),
An optical system is used as shown in (b). As shown in FIG. 4 (b), the parallel laser beam is passed through a cylindrical lens 3 having a generatrix in the direction of the beam deflecting surface, and a cross section perpendicular to the deflecting surface is imaged on a rotating polygon mirror 11 to be parallel. The parallel cross section reflects the parallel light flux on the rotating polygon mirror 11, and the lens 6 has different curvatures in the direction parallel to the deflecting surface and in the direction perpendicular to the deflecting surface. It is incident on the imaging lens having the fθ characteristic. In the cross section parallel to the deflecting surface as shown in FIG. 4A, the parallel light flux reflected by the rotary polygon mirror 11 is fθ.
The light imaged on the photoconductor by the lens and reflected by the rotary polygon mirror 11 in the vertical section as shown in FIG. 4 (b) is a divergent light beam, but the fθ lens also exposes this divergent light beam. The refractive power is made larger than that of the parallel cross section so that an image is formed on the body 12.

That is, in the cross section perpendicular to the deflecting surface, the surface of the rotary polygon mirror and the surface of the photoconductor have a conjugate relationship. In this case, the height of the beam on the surface 12 of the photoconductor does not change even if the tilt of each surface of the rotary polygon mirror 11 varies. This optical system is called a tilt correction optical system.
This tilt correction optical system comprises a cylindrical lens 3, a spherical lens 5 and a toric lens 6. When incorporating this into the frame, some assembly errors are unavoidable. This error appears as various phenomena, and one of them is that the scanning locus of the spot image does not become a straight line but is bent as shown in FIG. When forming an image with a single laser spot scanning device, this bending is not very noticeable, but when forming an image using a plurality of laser spot scanning devices, as shown in FIG. Naturally, the bending state is different for each, and when they are overlapped as shown in FIG.

[Problems that the device is trying to solve]

As described above, the frame incorporating the conventional fθ tilt correction optical system adjusts the position of the cylindrical lens 3 in the optical axis direction in order to correct the deviation of the image forming position in the cross section perpendicular to the deflecting surface due to the processing error of the component. Although there was a mechanism, there was no other adjustment mechanism, and the bending of the spot scanning locus remained unchanged. The present invention corrects the curvature of the spot scanning locus so that the scanning loci are aligned and the images of the respective scanning devices can be matched even when images are formed by a plurality of laser spot scanning devices.

[Means for solving problems]

According to the present invention, in a beam scanning device for deflecting a laser beam modulated by an image signal by a rotary polygon mirror or a galvano mirror and forming an image of the beam on a surface to be scanned by an fθ optical system to scan the beam. At least one of the lenses forming the f.theta. Optical system can be moved in parallel in a direction perpendicular to the beam deflection surface, and a mechanism for adjusting the amount of movement can be provided to correct the bending of the spot scanning locus. Is.

〔Example〕

1 (a) and 1 (b) show an embodiment of the present invention, and FIG. 1 is a drawing showing the features of the present invention at best. In FIG. 1, 1 is a laser chip as a light source, and 2 is a drawing. Is a collimator for collimating a diverging laser beam into a parallel light beam, 3 is a cylindrical lens for forming an image on the rotary polygon mirror only in a cross section perpendicular to the deflecting surface, and leaving a parallel light beam in the cross section parallel to the deflecting surface,
Reference numeral 4 is a rotary polygon mirror, 5 is a spherical lens, 6 is a toric lens having different refracting powers in a cross section parallel to the deflecting surface and a cross section perpendicular to the deflecting surface, 7 is a frame into which the lens is incorporated, and 8 is a lower surface of the toric lens. A lens receiving plate having three points for receiving the light, 9 is a washer for adjusting the height of the member of 8, and 10 is a plate for fixing the toric lens from above.

The principle of correcting the curve of the scanning line
This will be described with reference to FIG. In the present invention, the spherical lens 5 and the toric lens 6 form an fθ optical system.

Since the fθ optical system has negative distortion,
As shown in the figure, when the cells are imaged, the image becomes barrel-shaped. Further, as shown in FIG. 11, when a parallel line is imaged, a straight line is formed on the optical axis, but an upward arc shape is formed above the optical axis and a downward arc shape is formed below the optical axis.

By utilizing this phenomenon, when the scanning line has an upward arc shape as shown by broken lines in FIGS. 12 and 13, the position of the toric lens 6 is moved upward and the position of the optical axis is shifted upward. As a result, the scanning line becomes a straight line like a solid line due to the distortion.

First, the toric lens 6 is placed at a design reference position, and the position of the cylindrical lens in the optical axis direction is adjusted so that the image forming position of the cross section perpendicular to the deflection surface coincides with the image forming position of the parallel cross section. The height of the spot image on the surface on which the photoconductor is located is measured from the end toward the center and further toward the other end. By plotting the measurement results on a graph as shown in FIG. 6 and connecting the measurement points at both ends with a straight line, the curve of the spot scanning locus can be seen. If the bend is within the allowable value, Fig. 2 (a)
However, if the allowable value is exceeded, the thickness of the washer 9 below the toric lens receiving plate 8 must be adjusted to correct the bending as shown in FIG. 2 (b) or c. The correction amount of the washer thickness and whether to increase or decrease the thickness depend on the optical system.

[Effect of device]

As described above, by making the toric lens mounting part of the frame in which the optical system is incorporated in the laser beam scanning device in the laser beam printer a mechanism that allows the height of the toric lens to be adjusted, It becomes possible to correct the bending of the scanning locus of the spot image, and even when the image is formed by the laser spot scanning apparatus for copying, if the scanning locus is a straight line, the folding mirrors 13, 13 'are provided.
Alternatively, the scanning position from the laser spot scanning device for copying can be easily matched as shown in FIG. 7 by adjusting the frame bodies 14 and 14 '.

[Brief description of drawings]

1 (b) is a plan view of an embodiment of the present invention, FIG. 1 (a) is a sectional view taken along the line AA 'of FIG. 1 (b), FIG. 2 (a), FIG. 2 (b), FIG. 2 (c) is a diagram for explaining the method of adjusting the height of the toric lens by enlarging the mounting portion of the toric lens of FIG. 1 (b), and FIG. 3 is a diagram showing the relationship of the characteristic Y = fθ of the fθ lens. 4, FIG. 4 is a diagram for explaining the tilt correction optical system, FIG. 5 is a diagram showing the bending of the spot image scanning locus, FIG. 6 is a diagram after correcting the bending of the spot image scanning locus, and FIG. Fig. 8 is a diagram in which the loci are matched by the laser spot scanning device of Fig. 8, Fig. 8 is a diagram showing an example in which an image is formed by a plurality of laser spot scanning devices, and Fig. 9 is a diagram in which the loci are corrected by a plurality of laser spot scanning devices. FIG. FIG. 10 is a diagram showing a case where a mesh is imaged by the fθ optical system. FIG. 11 is a diagram showing a case where parallel lines are imaged by the fθ optical system. FIG. 12 is a diagram showing a state in which the toric lens is moved to correct the curve of the scanning line. FIG. 13 is a diagram showing a state in which the toric lens is moved to correct the curve of the scanning line. 1 is a laser chip, 2 is a collimator, 3 is a cylindrical lens, 4 is a rotary polygon mirror, 5 is a spherical lens, 6 is a toric lens, 7 is a frame of an optical system, 8 is a toric lens receiving plate, 9 is a washer and 10 Is a lens fixing plate.

Claims (1)

[Scope of utility model registration request] 1. A laser beam modulated by an image signal is deflected by a rotating polygon mirror or a galvanometer mirror,
In a beam scanning device for forming an image of this beam on a surface to be scanned by an fθ optical system and scanning it, at least one lens of the lenses constituting the fθ optical system is finely moved in a direction perpendicular to the beam deflecting surface. A beam scanning device characterized by having a mechanism capable of parallel movement and adjusting the amount of movement.