JPH10268217A - Optical scanning device of multicolor image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily compensate the curvature of a scanning line corresponding to each beam in an optical scanning device using a plastic lens for a lens for forming the image of each beam transmitted from plural laser beam sources on a photosensitive body. SOLUTION: A deflection adjusting means 1 for bending a toroidal lens 18 in the sub-scanning direction is integrally provided on the upper surface of the toroidal lens 18 as a plastic lens. The deflection adjusting means 1 is composed of holding protrusions 2, 2 integrally formed with the rib 18b of the toroidal lens 18, a supporting plate 3 engaged between the holding protrusions 2, 2 and an adjusting screw 8 hinged on the supporting plate 3, by revolving the adjusting screw 8 for correcting the curvature of a scanning line, the toroidal lens 1 is bent and the focal line 18d is also bent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in an optical writing system of an image forming apparatus such as a digital copying machine or a laser printer, and more particularly, to an electrostatic scanning device on a photosensitive drum by a plurality of beams. The present invention relates to an optical scanning device of a multicolor image forming apparatus that forms an image and obtains a multicolor image by superimposing the images, and more particularly to an optical scanning device of a multicolor image forming apparatus using a plastic lens.

[0002]

2. Description of the Related Art In recent years, at least two different locations on a photosensitive drum are simultaneously exposed with a light beam, and the respective exposed areas are developed and superimposed by different color developing units, and are transferred once to output paper. To form a two-color image, or to arrange four photosensitive drums side by side in the transport direction of the output paper, and simultaneously expose the photosensitive drums with light beams corresponding to the respective photosensitive drums, thereby different colors (yellow, magenta, cyan, black) 2. Description of the Related Art Digital copiers and laser printers, which sequentially transfer images developed by a developing device and superimpose to form a full-color image, have been put to practical use.

In such a multicolor image forming apparatus, beams emitted from a plurality of laser light sources are scanned using respective lens groups, images are formed, and the images are superimposed to form a multicolor image. However, in this case, how to accurately overlap the scanning lines of the respective beams is a point for improving the image quality.

[0004] The form of the overlapping error of each scanning line includes a deviation of the sub-scanning position, a deviation of the inclination, and a bending. Typically,
The deviation of the sub-scanning position is corrected by controlling the writing start timing, and the deviation of the inclination is adjusted by adjusting the folding mirror in the optical path to improve the image quality, but the bending is easily adjusted. At present, there is no means capable of improving the relative arrangement accuracy of the lens groups, which is a cause of the bending, and the deterioration of image quality is avoided by making the absolute amount of the scanning line bending close to zero. For example, Japanese Patent Laying-Open No. 4-127115 discloses an example of an optical scanning device capable of maintaining relative positioning accuracy by storing a plurality of scanning means at predetermined positions in a single optical housing.

In recent years, plastic lenses have been used from the viewpoints of low cost, easy handling, and the like. However, plastic lenses have a higher coefficient of thermal expansion than an optical housing that supports them. If the binding force of the optical housing to the plastic lens is large, there is a problem that the plastic lens itself is distorted due to an environmental change, that is, a temperature fluctuation, and the scanning line is bent. In order to cope with such a problem, for example, Japanese Patent Application Laid-Open No. 63-15212 discloses that an anti-warp body having a slit for allowing a laser beam to pass therethrough is fixed to an optical housing and a plastic lens is housed therein. There is disclosed a technique in which the longitudinal direction of a plastic lens is not restricted. The restraint by the warpage preventing body prevents the plastic lens from being warped and deformed over time, and allows a longitudinal expansion and contraction displacement due to a temperature change.

[0006]

In the method of individually correcting the scanning line bending corresponding to each beam by increasing the arrangement accuracy of each lens group, there is a problem that the correction operation is troublesome and requires skill. In the case of a plastic lens, the focal line of the lens is likely to bend due to distortion during molding due to resin characteristics. In this case, the scanning line may be bent.
Since the technology disclosed in Japanese Patent No. 15212 is merely a technology for preventing warpage over time after the lens group is arranged, when using a plastic lens with distortion during molding, in order to reduce errors due to the distortion, The arrangement of the lens groups must be adjusted. That is, in the related art, after all, it is necessary to rely on a troublesome method in which the arrangement accuracy of each lens group is increased and individually corrected. Also, the distortion of the plastic lens during molding is completely different from the lens group arrangement error as the cause of the scanning line bending. Therefore, depending on the degree, the lens group arrangement adjustment (in a broad sense, the optical system element) May not be possible.

The present invention provides an optical scanning apparatus for a multi-color image forming apparatus capable of easily correcting a scanning line curve when a plastic lens is used, regardless of the kind of the cause of the curve, and improving the image quality. (Claim 1). According to the second aspect of the present invention, further,
The provision of an optical scanning device of a multicolor image forming apparatus capable of simultaneously solving a plastic lens distortion problem due to temperature fluctuation,
With that purpose. It is still another object of the present invention to provide an optical scanning device of an image forming apparatus capable of further facilitating a correction operation.

[0008]

A plastic lens is easily deformed as compared with a glass lens, so that it is easy to cause a scan line to bend. However, the deformation can be intentionally operated by utilizing the material property which is easily deformed. By doing so, it is possible to easily correct the scanning line bending. Since the cause of the bending itself is directly operated, the correction operation is extremely easy as compared with the operation for improving the arrangement accuracy of the lens groups. This is the purpose of the present invention. More specifically, according to the first aspect of the present invention, there is provided a multi-color image forming apparatus in which a lens group for forming beams emitted from a plurality of laser light sources on corresponding photosensitive members is provided for each beam. In the apparatus, a slit-shaped plastic lens is used as one of the lenses constituting the lens group, and a curvature adjusting means for forcibly bending the plastic lens in the sub-scanning direction is provided. Has been adopted. By adjusting the curvature of the plastic lens by the curvature adjusting means, it becomes possible to correct the scanning line bending due to the lens group arrangement error or the distortion during molding of the plastic lens.

According to a second aspect of the present invention, in the configuration of the first aspect, the curvature adjusting means is provided integrally with the plastic lens. Since the bending adjusting means is not restricted by the optical housing, it is possible to avoid the displacement of the plastic lens in the longitudinal direction due to the temperature fluctuation of the plastic lens due to the presence of the bending adjusting means.

According to a third aspect of the present invention, in the configuration of the first aspect, the bending of the scanning line is corrected by bending each plastic lens corresponding to each beam in the same direction by the corresponding bending adjusting means. To do. Since the procedure of the correction operation by the curvature adjusting means becomes uniform, the operation of correcting the scanning line bending is further facilitated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to FIGS. 5 and 6 show the overall configuration of an optical scanning device to which the present invention is applied. Light source units 11, 12 and 13, 14 each including a semiconductor laser and a collimator lens (not shown) are arranged to face a polygon mirror 15 as a rotating polygon mirror, and are supported by a mounting surface formed on the optical housing 10. ing. In the present embodiment, the average incident angle θ of the light source units 11 and 14 to the polygon mirror 15 is set to 60 °, and the light source units 12 and 13 are set to 75 °. In FIG. 5, reference numerals 35 and 36 indicate mirrors, and reference numerals 32, 33 and 34 indicate beam detection sensors.

The laser beams emitted from the light source units 11, 12, and 13 and 14 are deflected by a polygon mirror 15 and are deflected by fθ mirrors 16 and 17 which are concave curved mirrors each having a coaxial aspherical surface and having fθ characteristics. Plastic toroidal lenses 18, 19, 2 forming a surface tilt correction system
Spots are formed on the surfaces of the photoconductors 28, 29, 30, and 31 through 0 and 21 to record a latent image. These latent images are visualized sequentially with black, yellow, magenta, and cyan toners and are transferred to output paper to form a color image.

The polygon mirror 15 has a thickness of 3 mm and is stacked in two stages on the motor reference plane in phase with each other. The fθ mirrors 16 and 17 are also integrally formed of resin in two stages with a center distance of 3 mm. Each normal line direction is inclined by α opposite to the sub-scanning direction with respect to the incident light beam.
Therefore, according to the drawing, the beam 1 emitted from the light source unit 11 is deflected by the lower polygon mirror 15, reflected by the lower stage of the fθ mirror 16, and reflected by the mirror 2.
2 through the toroidal lens 18 and the mirror 24
The image is formed on the photoreceptor 28 through the. On the other hand, the light source unit 1
2 emitted from the upper polygon mirror 1
5, is reflected by the upper stage of the fθ mirror 61,
The light passes through the toroidal lens 19 via the mirror 26 and forms an image on the photoconductor 29. The flow of the beams 3 and 4 of the light source units 13 and 14 scanned oppositely is the same, but since the rotation direction of the polygon mirror 15 is specific, the scanning direction is opposite. That is, if the light source units 11 and 12 scan from the beginning to the end of the sentence, the light source units 13 and 1
In 4, the scanning is performed from the end of the sentence to the beginning of the sentence.

In the present embodiment, the gist of the invention is embodied for the toroidal lenses 18, 19, 20, 21 in the lens group. Among these toroidal lenses 18, 19, 20, and 21 as plastic lenses, the toroidal lens 1 corresponding to the beam 1 of the light source unit 11
8 will be described with reference to FIGS. As shown in FIG. 2, the toroidal lens 18 has a slit shape extending in the main scanning direction from a lens portion 18a and a rib 18b provided so as to surround the lens portion 18a.
As in the prior art, the optical housing 10 is supported in contact with the positioning reference surface.
The bottom surfaces of the ribs 18b are placed on the inclined support pieces 6, 6 fixed to the projections 18 and the projections 18 formed on both ends of the ribs 18b.
c is applied to the inclined surfaces 7a of the columns 7, 7 fixed to the optical housing 10, and the front surfaces of the projections 18c and the upper surfaces of the ribs 18b are pressed and held by leaf springs 4, 5 screwed to the columns 7, 7. It is done by things. The same applies to the toroidal lens 20 that is supported in an inclined manner.

On the upper surface of the toroidal lens 18, there is integrally provided a curvature adjusting means 1 for forcibly bending the lens in the sub-scanning direction.
2). The curvature adjusting means 1 includes an inverted L-shaped 2 integrally formed on the sub-scanning side surface of the rib 18 b of the toroidal lens 18.
The holding projections 2, 2, a support plate 3 made of sheet metal, which is rigid in the longitudinal direction and is engaged between the holding projections 2 and 2 in the upward direction so as not to come off, and is formed at the center of the support plate 3. And an adjusting screw 8 screwed into the screw hole 2a. The holding projections 2 are provided at positions substantially equidistant from each other from the center O of the rib 18b having a total length of 2l.

As shown in FIG. 1, when the adjusting screw 8 is turned in the direction in which the screwing proceeds, the support plate 3 rises because the tip of the adjusting screw 8 is in contact with the side surface of the rib 18b. Is stopped by the holding projections 2, 2, the tip of the adjusting screw 8 gradually presses the toroidal lens 18, whereby the toroidal lens 18 bends and its focal line 18
d also curves. The pitch of the adjusting screw 8 in the present embodiment is about 500 μm, so that one rotation of the adjusting screw 8 is 50 μm.
The 0 μm toroidal lens 18 can be deformed. Although not shown, other toroidal lenses 19 and 2
At 0 and 21, the adjustment structure is the same as that of the toroidal lens 18.

Next, a specific operation of correcting the scan line bending will be described. In this embodiment, each toroidal lens 1
The bending adjustment means 1 in 8, 19, 20, and 21 is a one-sided installation structure that can only perform pressure adjustment in one direction, that is, if there is a convex scanning line bend in the same direction as the pressure direction before adjustment. Since all the toroidal lenses 18, 19, and 2 have
At 0 and 21, a correction is made to deflect in the same direction (claim 3). For example, the scanning line curves corresponding to black Bk, yellow Y, magenta M, and cyan C are shown in FIG.
In the case where the scan lines are present in a state as shown in FIG. 3A, these scan line bends are not made close to zero as in the related art, but, for example, based on the scan line bend corresponding to black Bk as shown in FIG. As shown in ()), a correction is made so that another scanning line curve approaches this.

It is not always necessary to approach zero in the correction of the scanning line bending, and it is important to suppress the size of the scanning line bending to 0.2 mm or less, which does not affect the image, and to reduce the deviation between the scanning line bendings. It is. In the example of FIG. 3, since the scanning line curve corresponding to black Bk is a reference, there is no need to perform correction by the curvature adjusting unit 1, and the scanning lines corresponding to the other three (yellow Y, magenta M, and cyan C). Correction is made only for bending. In this case, in the correction of each scanning line bend, a result of further increasing the bend generated before the correction, that is, forcibly causing the scan line bend in a range of 0.2 mm or less that does not affect the image. With respect to the scan line curve corresponding to cyan C, a large adjustment amount from the − range to the + range is obtained. As is clear from FIG. 3, the magnitude of the adjustment amount of each scanning line bending is in the order of Y <M <C.

FIG. 4 is an experimental graph actually corrected by the curvature adjusting means 1 based on the above-described concept of correcting the scanning line bending. As is apparent from FIG. 4, the absolute amount of the overall scanning line bending is as large as 125 μm (200 μm or less).
The deviation between each scanning line bend is within the range of ± 25 μm. Therefore, color shift can be suppressed.

As described above, the lens (here, the toroidal lenses 18, 19, and 2) that causes the scanning line to be bent is used.
0,21) by directly and forcibly deforming itself, the scan line bend can be easily nullified regardless of the type of cause such as lens group arrangement error and lens focal line bend, that is, does not affect the image. You can do so. Also,
In the above embodiment, the curvature adjusting means 1 is replaced with each toroidal lens 1.
8, 19, 20, and 21, there is no constraint between the bending adjustment means 1 and the optical housing 10, and the toroidal lenses 18 and 1 by the bending adjustment means 1 are provided.
No distortion occurs due to temperature fluctuations of 9, 20, 21.

Note that, even if the curvature adjusting means 1 is provided on both sides of the toroidal lenses 18, 19, 20, and 21 to adjust the curvature of each scanning line to be straight (zero), the correction work is much easier than in the past. However, in the case where the adjustment direction is the same by providing only one side as described above, the operation of correcting the scanning line bending becomes simpler and uniform, which is further facilitated.

In the above embodiment, each of the toroidal lenses 18, 19, 20, and 21 is flexed by pressing with the adjusting screw 8, but the invention is not limited to this. For example, as shown in FIG. 7, an adhesive is applied to the gap between the support plate 3 and the solidifying operation from the outside in a state where the toroidal lens 18 is curved to an amount to be corrected by applying an external pressure. An adhesive, for example, an ultraviolet-curing adhesive 9,
The curved shape may be fixed. In the above embodiment, the curvature adjusting means 1 is provided integrally with the lens. However, as shown in FIG. 8, the curvature adjusting means 100 provided on the optical housing 10 presses the central portion of the toroidal lens 18. Further, as shown in FIG. 9, both ends of the toroidal lens 18 whose center is supported by the support member 40 may be bent by the bending adjusting means 10 provided on the optical housing 10.
It is also possible to adopt a configuration in which a pressure is applied at 1, 101 to bend.

[0023]

According to the first aspect of the present invention, since the curvature adjusting means for forcibly bending the plastic lens is provided, the scanning line is bent without adjusting the arrangement of the delicate and troublesome lens group. Can be easily corrected, a high-quality multicolor image without color shift can be obtained, and the advantages of the plastic lens, which is low in cost and easy to handle, can be fully utilized.

According to the second aspect of the present invention, since the curvature adjusting means is provided integrally with the plastic lens, the plastic lens itself is forcibly attached to the optical housing even if there is a temperature fluctuation, as in the related art. Since the plastic lens can be configured so that no force is exerted, that is, the plastic lens can freely expand and contract in its longitudinal direction, in addition to the effect of claim 1, it is possible to prevent image distortion and the like due to distortion of the plastic lens due to temperature fluctuation. .

According to the third aspect of the present invention, since the lens corresponding to each beam is bent in the same direction, the adjustment by the curvature adjusting means becomes uniform, and the first aspect of the present invention provides a method for adjusting the curvature of the lens.
In addition to the effects described above, it is possible to further facilitate the operation of correcting the scanning line bending.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a relationship between a plastic lens and a curvature adjusting unit of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a relationship between a plastic lens and a curvature adjusting unit.

FIGS. 3A and 3B are schematic diagrams showing a correction method according to the present invention for scanning line bending in each plastic lens, where FIG. 3A shows a state before correction, and FIG. 3B shows another example based on a specific scanning line bending. It is a figure which shows the state which reduced the deviation by combining.

FIG. 4 is a graph showing data obtained by actually correcting scan line bending by the correction method shown in FIG. 3;

FIG. 5 is a schematic plan view showing the overall configuration of the optical scanning device according to the present invention.

FIG. 6 is a schematic sectional view showing the overall configuration of the optical scanning device according to the present invention.

FIG. 7 is a cross-sectional view illustrating a relationship between a plastic lens and a curvature adjusting unit according to another embodiment.

FIG. 8 is a schematic diagram showing the relationship between the plastic lens and the curvature adjusting means when the curvature adjusting means is attached to the optical housing.

FIG. 9 is a schematic diagram showing the relationship between another example of a plastic lens and the curvature adjusting means when the curvature adjusting means is attached to the optical housing.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Curve adjustment means 11, 12, 13, 14 Light source unit as a laser light source 18, 19, 20, 21 Toroidal lens as a plastic lens 28, 29, 30, 31 Photoconductor

Claims (3)

[Claims] 1. An optical scanning device of a multicolor image forming apparatus, wherein a lens group for forming a beam emitted from a plurality of laser light sources on a corresponding photosensitive member is provided for each beam. A slit-shaped plastic lens is used as one of the lenses to be bent, and a curvature adjusting means for forcibly bending the plastic lens in the sub-scanning direction is provided. Scanning device. 2. The plastic lens according to claim 1, wherein said curvature adjusting means is provided integrally with said plastic lens.
An optical scanning device for the multicolor image forming apparatus according to the above. 3. The bending of a scanning line is corrected by bending each plastic lens corresponding to each beam in the same direction by a corresponding curve adjusting means.
An optical scanning device for the multicolor image forming apparatus according to the above.