JPH0618335Y2 - Beam scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is a beam scanning of a laser beam printer that forms an image by deflecting a laser beam with a rotating polygon mirror or a carbano mirror and forming an image on the photoconductor. It relates to the device.

[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 imaging lens has a relation 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 is compared with the central portion in terms of deflection angle. 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 the relationship of Y = fθ. This is called an fθ optical system. A laser beam printer makes a laser a parallel light beam of a certain diameter, which is reflected by a rotating polygon mirror, forms an image on the photoconductor by the fθ optical system, and the rotating polygon mirror is rotated to form a laser spot image on the photoconductor by the fθ optical system. Are scanning. In this case, if there is a large variation in the tilt of the rotating polygon mirror in the direction of the rotation axis of the rotating polygon mirror, the height of the spot image on the photosensitive member surface caused by the reflection of each surface will be different, and the photosensitive member rotating at a constant speed will be constant. It is not possible to scan at intervals and the image becomes uneven. To prevent this, an optical system is used as shown in FIGS. 4 (a) and 4 (b). As shown in FIG. 4 (b), the parallel laser beam is passed through the cylindrical lens 3 having a generatrix in the direction of the beam deflecting surface, and the cross section perpendicular to the deflecting surface is imaged on the rotary polygon mirror 11 to be parallel. A lens 6 with a different cross section is reflected on a rotating polygon mirror in the state of parallel light flux, and has different curvatures in the directions parallel to and perpendicular to the deflecting surface and with different refracting power (hereinafter referred to as a toric lens).
It is incident on the imaging lens having the fθ characteristic using. In a cross section parallel to the deflecting surface as shown in FIG.
The parallel light flux reflected by is imaged on the photoconductor by the fθ lens, and in the vertical section as shown in FIG.
Although the light reflected by is a divergent light beam, the fθ lens has a refracting power larger than that of the parallel cross section so that this divergent light beam is also imaged on the photoconductor 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 an image is formed by 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 bent 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, a beam scanning device in which a laser beam modulated by an image signal is deflected by a rotary polygon mirror or a galvano mirror, and the deflected beam is imaged and scanned on a surface to be scanned by a beam scanning optical system. In this case, by providing at least one of the lenses constituting the beam scanning optical system with an adjusting mechanism capable of minutely rotating in a plane perpendicular to the deflection surface including the optical axis of the beam scanning optical system, This is to correct the bending of the scanning locus.

〔Example〕

FIG. 1 is a drawing best showing the features of the embodiment of the present invention. In FIG. 1, 1 is a laser chip as a light source, and 2 is a laser chip.
Is a collimator that collimates the diverging laser light,
3 shows only the cross section perpendicular to the deflection surface is imaged on the rotary polygon mirror,
Cylindrical lens that keeps parallel light in the section parallel to the deflecting surface, 4 is a rotary polygon mirror that deflects the laser beam, 5 is a spherical lens, and 6 is different in refracting power between the section parallel to the deflecting surface and the section perpendicular to the deflecting surface. Toric lens, 7 is a frame in which an optical system is incorporated, 8 is a receiving plate for receiving the lower side of the toric lens having one supporting point, and 8'is a receiving end for receiving the cylindrical side of the lower toric lens. A plate with two support points, 9 is 8
A washer for adjusting the height of the receiving plate of No. 9 and a receiving plate 9'for adjusting the height of the receiving plate of No. 8 '.

The principle of correcting the curve of the scanning line
This will be described with reference to FIG.

As shown in FIG. 10, the deflected light beam is imaged on the surface to be scanned by the spherical lens 5 and the toric lens 6. A state in a cross section perpendicular to the deflecting surface of the light beam toward the center of the surface to be scanned and the light beam toward the periphery is shown by broken lines in FIGS. 11 (a) and 11 (b).

Here, focusing on the lens cross section [FIG. 11 (a)] through which the central light beam passes and the lens cross section [FIG. 11 (b)] through which the peripheral light beam passes, the toric lens 6 has a lens thickness at the center that is equal to that at the periphery. Larger than the lens thickness. Therefore, the principal point distance (HH ') of the lens is larger in the center than in the periphery.

Therefore, the toric lens 6 is shown in FIGS. 11 (a) and 11 (b).
As shown by the solid line, when the same amount of inclination is made in the plane perpendicular to the deflecting surface, the amount of deviation of the image on the optical scanning surface is larger in the central light flux than in the peripheral light flux.

As shown in FIG. 12A, when the scanning line is a broken straight line, if the toric lens 6 is rotated downward,
The scan line is a downward bow of the solid line. Further, as shown in FIG. 12 (b), when the scanning line is a broken straight line, when the toric lens 6 is rotated upward, the scanning line becomes a solid upward curve.

By utilizing this phenomenon, the bending of the scanning line is corrected. First
When the scanning line has an upward bow shape as shown in FIG. 3A, the scanning line is corrected to a straight line by rotating the toric lens 6 downward. When the scanning line has a downward arcuate shape as shown in FIG. 13B, the scanning line is corrected to a straight line by rotating the toric lens 6 upward.

First, the toric lens 6 is placed at the 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 deflecting surface coincides with the image forming position of the parallel cross section. The height of the spot image on the surface where the body 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 bending is within the allowable value, it remains as shown in FIG. 2 (a), but if it exceeds the allowable value, the thickness of the washers 9 and 9'under the receiving plates 8 and 8'of the toric lens is adjusted. The spot image scanning locus is corrected. The angle of rotation and the direction of bending differ depending on the lens. As shown in FIGS. 2 (b) and 2 (c), the rotation of the washer 9 below the receiving plate 8 on the toric surface side of the toric lens and the thickness of the washer 9'below the receiving plate 8'on the cylindrical surface side. Adjust the thickness.

[Effect of device]

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

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (b) is a plan view of an embodiment of the present invention, and FIG. 1 (a).
Is a sectional view taken along the line AA 'in FIG. 1 (b), and FIGS. 2 (a), 2 (b) and 2 (c) are enlarged views of the torque lens mounting portion in FIG. 1 (b). FIG. 3 is a diagram for explaining a method of adjusting the elevation of the torque lens, FIG. 3 is a diagram showing the characteristic of the fθ lens, a relation of Y = fθ, FIG. 4 is a diagram for explaining the tilt correction optical system, and FIG. 5 is a spot image scanning. Fig. 6 is a diagram showing the curve of the locus, Fig. 6 is a diagram after correcting the curve of the spot image scanning locus, Fig. 7 is a diagram in which the loci are matched by a plurality of laser spot scanning devices, and Fig. 8 is a plurality of laser spots. FIG. 9 is a diagram showing an example of a case where an image is formed by a scanning device, and FIG. 9 is a diagram showing a case where a locus is not corrected by a plurality of laser spot scanning devices. FIG. 10 is a diagram illustrating a beam scanning optical system. 11 (a) and 11 (b) are views showing how the toric lens is moved in order to correct the bending of the scanning line. 12 (a) and 12 (b) are diagrams showing bending of the scanning line when the toric lens is moved. 13 (a) and 13 (b) are views showing a state in which the bending of the scanning line is corrected. 1 is a laser chip, 2 is a collimator, 3 is a cylindrical lens, 4 is a rotating 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, 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 a deflected beam on a surface to be scanned by a beam scanning optical system and scanning the same, at least one lens constituting the beam scanning optical system is provided in the beam scanning optical system. A beam scanning device characterized by having an adjusting mechanism capable of minutely rotating in a plane including the optical axis of and perpendicular to the deflecting surface.