JP2002341274A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffraction optical device adjusting mechanism whose cost is reduced without deteriorating optical performance and by which the bending of a scanning line is easily adjusted. SOLUTION: A bending adjusting member is made to abut on the surface of a diffraction optical device in parallel to an optical scanning plane, and force is applied in a direction in parallel with a lens surface, so that the diffraction optical device is turned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for an apparatus such as a laser beam printer or a color digital copying machine having a color electrophotographic process, which records color image information while suppressing a scanning line shift between colors. The present invention relates to a scanning optical device used in a color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a laser beam printer (LB) has been used.
P) and a scanning optical device used in a digital copying machine or the like, a light beam which is light-modulated and emitted from a light source means in response to an image signal is periodically deflected by, for example, a rotating polygon mirror (polygon mirror) by an optical deflector. The light is focused into a spot on a photosensitive recording medium (photosensitive drum) surface by a scanning optical element (imaging element) having fθ characteristics, and the surface is optically scanned to record an image.

FIG. 3 is a schematic view of a main part of a conventional scanning optical device of this kind. For convenience, the main scanning direction of image formation is the y direction, the sub scanning direction is the x direction, and the direction perpendicular to the xy plane is z.
Direction.

In FIG. 1, a divergent light beam emitted from a light source means 91 is converted into a substantially parallel light beam by a collimator lens 92, and the light beam (light amount) is restricted by a stop 93, and a cylindrical light beam having a predetermined refractive power only in the sub-scanning direction. The light is incident on the lens 94. Of the substantially parallel light beams incident on the cylindrical lens 94, they are emitted as they are in the state of substantially parallel light beams in the main scanning section. In the sub-scanning section, the light is converged and formed as a substantially linear image on the deflection surface (reflection surface) 95a of the optical deflector 95 formed of a rotating polygon mirror (polygon mirror).

The light beam deflected and reflected by the deflecting surface 95a of the optical deflector 95 is a scanning optical element (fθ
A photosensitive drum surface 9 as a surface to be scanned through a lens 96
8, light is scanned in the direction of arrow B on the photosensitive drum surface 98 by rotating the light deflector 95 in the direction of arrow A. Thus, an image is recorded on the photosensitive drum surface 98 as a recording medium.

FIG. 4 is a schematic diagram of a main part of a color image forming apparatus which simultaneously uses a plurality of the above-described scanning optical devices, records image information for each color on different photosensitive drum surfaces, and forms a color image. .

In FIG. 1, 111, 112, 113, 1
14 is a scanning optical device, 131, 132, 133, 1
Numeral 34 denotes photosensitive drums as image carriers, 121 and 12 respectively.
Reference numerals 2, 123, and 124 denote developing units, respectively, and 141 denotes a transport belt. In the color image forming apparatus shown in the figure, four scanning optical devices (111, 112, 113, 114) are arranged, and each color is C (cyan), M (magenta), Y (yellow), and B (black). The image signals are recorded on the surfaces of the photosensitive drums 131, 132, 133 and 134 in parallel, and a color image is printed at a high speed.

In such a color image forming apparatus, since a plurality of scanning lines are superposed to form an image, it is particularly important to reduce a scanning line shift between the respective colors (hereinafter also referred to as "registration shift"). .

As a method of adjusting (correcting) this scanning line deviation, for example, each resist detection image (cyan, magenta, yellow, black) is formed on a transfer material conveyed accurately on a transfer belt, and each resist is detected. There is a method in which the position of a detected image is detected by a detecting means and electrically adjusted based on the detected signal.

However, there is a problem that it is very difficult to electrically adjust the scanning line deviation, and the cost is high in terms of cost.

Conventionally, in a color image forming apparatus having a plurality of scanning optical devices, the bending of the scanning line in each scanning optical device is adjusted by displacing the position of the diffractive optical element of the diffractive portion of each scanning optical device. By doing so, a registration shift between respective colors can be suppressed with a simple configuration, and a position displacement mechanism of a diffractive optical element suitable for a compact color image forming apparatus suitable for high-definition printing is provided.

FIG. 5 shows the adjustment (correction) of the scanning line bending.
This will be described with reference to FIG. In the figure, the same elements as those shown in FIG. 3 are denoted by the same reference numerals. It adjusts (corrects) errors in mounting optical components such as lenses and light sources, and scan line distortions that occur during lens molding.

In FIG. 1, a photosensitive drum 98 is provided as described above.
A light beam L that scans the surface is emitted from a laser unit 91 including a light source unit, a collimator lens, and an aperture stop, passes through a cylindrical lens 94 having a predetermined refractive power in the sub-scanning direction, and After being deflected and reflected by 95 and passing through the toric lens 61 and the diffractive optical element 10c, it irradiates the surface of the photosensitive drum 98.

In the conventional scanning optical device, the photosensitive drum is rotated by rotating the diffractive optical element 10c in the direction C in the figure around the y-axis which is the central axis in the longitudinal direction of the diffractive optical element. The light beam L scanned on the surface 98 scans in a curved manner as shown by a dotted line D in FIG.

FIG. 5B shows the diffractive optical element indicated by an arrow C2.
Of the scanning line on the photosensitive drum when it is tilted only once in the direction of. Since the amount of rotation (inclination angle) of the diffractive optical element and the amount of curvature (bending) of the scanning line are substantially proportional to each other, diffraction is performed by an amount necessary to correct the bending of the scanning line based on data checked in advance. By rotating the optical element, the bending of the scanning line can be adjusted.

That is, by adjusting the angle of inclination of the diffractive optical element with respect to the scanning surface and the angle of rotation about the optical axis, it is possible to eliminate a color shift due to a scan line shift of each scanning optical device.

Next, the structure for rotating (rotating) the diffractive optical element will be described. FIG. 6 shows an adjustment mechanism for correcting a deviation in curvature. The diffractive optical element 10 is held by a holding member 14 by a spring material 11.
The rotation shaft 8 of 0 is held by a rotation support section 140 so as to be rotatable with respect to the optical box 15. Further, an adjustment screw fixing member 13 for holding the adjustment screw 12 is also fixed to the holding member 14. In the figure, an adjusting screw 12 applies a force in a direction perpendicular to the lens surface of the diffractive optical element 10 (x-axis direction).

The diffractive optical element 10 is rotated in the rotational direction B by an adjusting screw 12 and a pressing portion 110 provided on the spring material 11.
Is determined, the diffraction optical element 10 can be rotationally moved by moving the adjusting screw.

[0019]

However, in the above method, the holding member 14 is required, and the cost of parts of the holding member and the cost of assembling the diffractive optical element to the holding member are required.

In order to avoid the high cost, there is a method in which the holding member is abolished and the diffractive optical element is directly operated by the adjusting screw. The acting direction is a direction perpendicular to the lens surface (yz surface) on the x-axis.
As shown in (1), the element itself bends and bends in the x-axis direction. The amount of deflection Δd at the center becomes maximum, and the deformation of the lens deteriorates the optical performance of the lens.

There is also a method for increasing the rigidity of the diffractive optical element itself. When the diffractive optical element is molded of resin,
Usually, as shown in FIG. 8, the outer shape of the lens 20 is provided with a rib 22 for protecting the lens effective surface 21. The rib 22 also has the function of increasing the rigidity of the lens. However, in the molding method as described above, it is difficult to increase the length and thickness of the rib because a long molding time is required and the accuracy of the lens surface may be impaired.

An object of the present invention is to solve the above-mentioned problems, and to provide a diffractive optical element adjustment mechanism which can be easily adjusted at low cost without deteriorating optical performance.

[0023]

That is, in the image forming apparatus of the present invention, a light beam emitted from a light source is guided to an optical deflector, and the light beam deflected by the light deflector is diffracted by at least one sheet. It has a scanning lens system having an optical element, and has an adjusting member for displacing the position of the diffractive optical element, and the diffractive optical element displaces the position of the diffractive optical element so that the light beam is projected onto the surface to be scanned. In a scanning optical device that adjusts a curvature and performs scanning, the diffractive optical element abutting portion of the adjusting member is parallel to a scanning plane on the surface of the diffractive optical element where the light beam passes through the diffractive optical element and scans. It is characterized by being provided on a suitable surface.

The operation is a bending adjustment mechanism that causes little deformation such as warping or bending of the diffractive optical element that occurs during the adjustment of the diffractive optical element. Even if deformation occurs, an image is generated as a "bend" Therefore, the correction can be made by using the bending adjustment mechanism of this configuration. The color shift and the tilt shift of the four colors on the image forming apparatus can be adjusted with higher precision, and a high-definition color image can be formed.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of the present invention will be described with reference to FIG. In the figure, a light beam L for scanning on the surface of a photosensitive drum 98 is emitted from a laser unit 1 including a light source means, a collimator lens, and an aperture stop, and has a cylindrical lens 4 having a predetermined refractive power in a sub-scanning direction. After being deflected and reflected by the optical deflector 5 and passing through the toric lens 65 and the diffractive optical element 30c, the light is irradiated onto the surface of the photosensitive drum 98.

In the conventional scanning optical device, the photosensitive drum is rotated (rotated) in the direction E in the drawing around the y-axis which is the longitudinal central axis of the diffractive optical element 30c. The light beam L scanned on the surface 98 scans in a curved manner as shown by a dotted line F in FIG.

Next, a structure for rotating (rotating) the diffractive optical element will be described with reference to FIG. Diffractive optical element 3
Rotation shaft members 28 are provided on the y-axis at both ends in the longitudinal direction (y-direction) of 0. The rotating shaft member 28 is integrally formed with the diffractive optical element 30 or, when the diffractive optical element 30 is a separate part, firmly fixed to the diffractive optical element 30. The rotation shaft member 28 is held by a rotation shaft holding portion 29 of the optical box 24 so as to be rotatable.

An adjusting screw fixing member 23 for holding the adjusting screw 22 is also fixed on a plane (xy plane) parallel to a scanning plane on which light passing through the diffractive optical element 30 scans. A spring 11 is provided at a portion opposing the portion acting with the adjusting screw with the diffractive optical element 30 interposed therebetween, and the position of the diffractive optical element 30 is determined. Therefore, the diffractive optical element 30 can be rotationally moved by moving the adjusting screw 22.

Although a part of the xy plane is pressed during the bending adjustment, the amount of deformation of the diffractive optical element 30 that occurs is extremely small. The lens (diffractive optical element) is less deformed, and the scanning line can be corrected without adversely affecting the image. “Even if the lens (diffractive optical element) is deformed, the scanning line appears as a bend on the photoreceptor in the present configuration, so that the correction can be performed by performing the bend adjustment of the present embodiment. No problem occurs. "(Second Embodiment) A configuration for rotating (rotating) the diffractive optical element of the second embodiment will be described with reference to FIG. At both ends in the longitudinal direction (y direction) of the diffractive optical element 40, similarly to the first embodiment, a rotating shaft member 38 is provided on the y axis, and the rotating shaft member 38 is optically rotated. It is held by the rotating shaft holder 39 of the box. In the diffractive optical element 40, an adjustment contact portion 35 is provided on a plane (xy plane) parallel to a scanning plane on which light passing through the diffractive optical element 40 scans. An adjustment screw fixing member 33 that holds the adjustment screw 32 is also fixed to the optical box 34. This adjustment screw 32
Is a plane (xy plane) parallel to the scanning plane where light scans
The spring 21 is provided in a portion of the adjustment contact portion 35 where the adjustment screw 32 faces, and the diffraction optical element 4
Since the position of 0 is determined, the diffractive optical element 40 can be rotationally moved by moving the adjusting screw 32. In the present embodiment, when the amount of bending correction of the diffractive optical element 40 is severe, the shape and length of the adjustment contact portion for each scanning optical device are intended to make the effective amount (sensitivity) of the rotational movement amount insensitive. You just have to change it and decide. As in the first embodiment, also in this configuration, deformation of the lens (diffractive optical element) can be suppressed, and even if deformed, it can be corrected by bending adjustment.

[0030]

As described above, in a color image forming apparatus in which the inclination of the scanning line and the bending of the scanning line are adjusted by displacing the position of the diffractive optical element of each scanning optical apparatus, the light of the diffractive optical element scans the curvature deviation. By pressing a surface parallel to the scanning surface to be adjusted, the force applied to the diffractive optical element during adjustment can be reduced as much as possible. In addition, components for increasing the rigidity of the diffractive optical element are not required, and the configuration can be made at low cost.

[Brief description of the drawings]

FIG. 1 is a detailed view of a first embodiment.

FIG. 2 is a detailed view of the first embodiment.

FIG. 3 Conventional example

FIG. 4 is a conventional example (schematic view of a main part of a color image forming apparatus).

FIG. 5 Conventional example

FIG. 6: Conventional example

FIG. 7: Conventional example

FIG. 8: Conventional example

FIG. 9 is a detailed view of the second embodiment.

[Explanation of symbols]

 10, 20, 30, 40 Diffractive optical element 22, 32 Adjustment screw

Claims (2)

[Claims] 1. A light beam emitted from a light source means is guided to a light deflector, and the light beam deflected by the light deflector is converted into at least one light beam.
A scanning lens system having a number of diffractive optical elements,
A scanning optical device for adjusting the position of the diffractive optical element and displacing the diffractive optical element to adjust the bending of the light beam onto the surface to be scanned and scan the light; The scanning optics, wherein the diffractive optical element abutting portion of the member is provided on a surface of the diffractive optical element parallel to a scanning plane through which the light beam passes and scans the diffractive optical element. apparatus. 2. The scanning optical apparatus according to claim 1, wherein the diffractive optical element contact portion is provided outside a lens effective portion of the diffractive optical element.