OPTICAL SCANNING APPARATUS AND IMAGE FORMING APPARATUS USING SAME

Abstract

An optical scanning apparatus allowing reduction in the size of the overall apparatus and the size of an imaging optical system LB with the use of an optical deflector that swings back-and-forth and an image forming apparatus using such an optical scanning apparatus, comprising: light source means; a condense optical system that condenses a light beam emitted from the light source means; an optical deflector that deflects the light beam emergent from the condense optical system; and an imaging optical system that images the light beam deflected by a deflection surface of the optical deflector on a scanning surface, wherein the optical deflector has a function of moving the deflection surface back-and-forth, the light beam emergent from the condense optical system converges in a sub-scanning cross section, and the convergence position is on the light source side of the deflection surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of the relevant portion of an optical scanning apparatus according to a first embodiment of the present invention taken along the main scanning direction.

FIG. 2 illustrates the structure of an optical deflector used in the first embodiment of the present invention.

FIG. 3 is a diagram for illustrating the principle of the optical deflector used in the first embodiment of the present invention.

FIG. 4 is a diagram of a model used in studying a resonance optical deflector having two movable plates.

FIG. 5 is a graph showing the deflection angle 2θ₁ of the light beam reflected by the optical deflection in the first embodiment.

FIG. 6 is a cross sectional view in the sub scanning direction of the relevant portion of a system in which an optical face tangle error correction optical system is not used.

FIG. 7 is a cross sectional view in the sub scanning direction of the relevant portion of a system in which an optical face tangle error correction optical system is used.

FIG. 8 is a cross sectional view in the sub scanning direction of the optical scanning apparatus according to the first embodiment of the present invention.

FIG. 9 is a diagram for illustrating the beam width in the sub scanning direction on the deflection surface.

FIG. 10 is a graph showing curvature of field in the main scanning direction and the sub scanning direction at room temperature in the first embodiment.

FIG. 11 is a graph showing curvature of field in the main scanning direction and the sub scanning direction when the temperature of the apparatus has risen by 25° C. in the first embodiment.

FIG. 12 is a graph showing changes in the image plane (defocus) in the main scanning direction and the sub scanning direction when the temperature of the apparatus rises by 25° C. in the first embodiment.

FIG. 13 is a graph showing curvature of field in the main scanning direction and the sub scanning direction at room temperature in a comparative example.

FIG. 14 is a graph showing curvature of field in the main scanning direction and the sub scanning direction when the temperature of the apparatus has risen by 25° C. in the comparative example.

FIG. 15 is a graph showing changes in the image plane (defocus) in the main scanning direction and the sub scanning direction when the temperature of the apparatus rises by 25° C. in the comparative example.

FIG. 16 is a graph showing changes in the image plane in the sub scanning direction in the case where a cylindrical lens is mounted with a position error of 0.1 mm toward the deflection surface along the optical axis in the first embodiment.

FIG. 17 is a graph showing changes in the image plane in the sub scanning direction in the case where a cylindrical lens is mounted with a position error of 0.1 mm toward the deflection surface along the optical axis in the comparative example.

FIG. 18 is a graph showing deviations in the imaging position in the sub scanning direction that occur with an error in the angle of a mirror in the first embodiment.

FIG. 19 is a graph showing deviations in the imaging position in the sub scanning direction that occur with an error in the angle of a mirror in the comparative example.

FIG. 20 is a diagram for illustrating a deviation of the imaging position in the sub scanning direction that occurs with an error in the angle of the mirror.

FIG. 21 is a sub scanning cross sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 22 is a sub scanning cross sectional view of a color image forming apparatus according to an embodiment of the present invention.

Claims

1. An optical scanning apparatus comprising: light source means,a condense optical system that condenses a light beam emitted from said light source means;an optical deflector that deflects a light beam emergent from said condense optical system for scanning; andan imaging optical system that images the light beam deflected and scanned by a deflection surface of said optical deflector on a surface to be scanned,wherein said optical deflector has a function of moving the deflection surface back and forth in a main scanning direction, andthe light beam emergent from said condense optical system converges in a sub scanning cross section, the convergence position being in an optical path between said condense optical system and the deflection surface of the optical deflector.

2. An optical scanning apparatus according to claim 1 further comprising a mirror provided in an optical path between said condense optical system and said optical deflector, wherein the following condition is satisfied: L1×β≦11.46 (mm)

3. An optical scanning apparatus according to claim 1, wherein the following condition is satisfied:

4. An optical scanning apparatus according to claim 1, wherein said imaging optical system comprises at least one imaging optical element made of plastic.

5. An optical scanning apparatus according to claim 1, wherein said optical deflector is a resonance optical deflector in which the deflection surface of the optical deflector is driven by resonance drive.

6. An image forming apparatus comprising an optical scanning apparatus according to claim 1, a photosensitive member disposed at said surface to be scanned, a developing device that develops an electrostatic latent image formed on said photosensitive member by a light beam scanned by said optical scanning apparatus as a toner image, a transferring device that transfers the developed toner image onto a material to be transferred, and a fixing device that fixes the transferred toner image on the material to be transferred.

7. An image forming apparatus comprising an optical scanning apparatus according to claim 1, and a printer controller that converts code data input from an external device into an image signal and input it to said optical scanning apparatus.