JP2000249915A - Projection optical system and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection optical system and an image forming device by which a viewing angle can be made large and high resolution is realized without increasing the number of lenses. SOLUTION: An image forming lens part 4 which is provided with the aspherical-surface lenses 41 and 42 having a 1st shape for correcting the aberration of plural laser beams in the 1st direction and a 2nd shape for correcting the aberration in a 2nd direction orthogonally crossing the 1st direction and whose object side is formed to be telecentric is arranged. Then, a diaphragm 43 is arranged between and the lens part 4 and a photoreceptor drum 3. Thus, the viewing angle can be made large and the high resolution is realized without increasing the number of lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system and an image forming apparatus suitable for a printer, a copying machine, and the like, and more particularly, to realize a wide angle of view and high resolution while suppressing an increase in the number of lenses. The present invention relates to a projection optical system and an image forming apparatus.

[0002]

2. Description of the Related Art As a conventional image forming apparatus, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 9-193450. The image forming apparatus includes a laser array having a plurality of laser light emitting elements arranged in an array, a field lens for condensing a plurality of laser lights emitted from each laser light emitting element at a converging point, and a A projection optical system including a lens group that forms a plurality of laser beams emitted from the element onto respective image forming points, and a photosensitive drum that can position an exposure area at each of the plurality of laser light image forming points A plurality of laser beams emitted from each laser light emitting element according to an image signal are condensed at a converging point by a projection optical system, and are imaged on a photoconductor as a plurality of light spots. The photosensitive drum rotates at a predetermined speed in the sub-scanning direction, and an electrostatic latent image corresponding to an image signal is formed on the surface thereof. After the electrostatic latent image is developed with toner, it is transferred and fixed on a recording sheet as a toner image to form a recorded image.

In such an image forming apparatus, a plurality of laser beams emitted from a laser array are condensed so as to have a predetermined light spot diameter required for image formation, and are formed into an image on a photosensitive member. A large-angle, high-resolution projection optical system is required.

[0004]

However, according to the conventional image forming apparatus, when the angle of view of the projection optical system is increased, an aberration occurs in a light spot formed on the photoreceptor. Will be difficult to do. If a lens for correcting this aberration is provided, the number of components increases and the cost of the apparatus increases. In addition, if the angle of view is reduced to suppress aberration, there is a problem that the size of the projection optical system increases in the optical axis direction and the entire apparatus becomes large. Accordingly, an object of the present invention is to provide a projection optical system and an image forming apparatus capable of increasing the angle of view and achieving high resolution without increasing the number of lenses.

[0005]

In order to achieve the above object, the present invention provides a light source for emitting image signal light based on image information and a first light source for correcting aberration in a first direction of the image signal light. An imaging lens unit having a shape and a lens having a second shape for correcting aberrations of the image signal light in a second direction orthogonal to the first direction, wherein the object side is telecentric; A projection optical system having a stop between an imaging lens unit and a projection plane is provided.

In the above-described projection optical system, the imaging lens unit corrects aberration in one of the main scanning direction and the sub-scanning direction of the image signal light based on the first shape, and adjusts the image based on the second shape. It is preferable to correct aberration in a main scanning direction or a sub-scanning direction that is a second direction orthogonal to the first direction of the signal light.
It is preferable to have different aspherical shapes in the direction. According to the projection optical system, the aberration is corrected in the first direction of the image signal light based on the first shape, and the aberration is corrected in the second direction orthogonal to the first direction based on the second shape. By correcting the light and irradiating the light onto the projection surface via the aperture, it is possible to increase the angle of view and realize high resolution.

Further, the present invention achieves the above object,
A light source that has a plurality of laser elements arranged in an array and emits a plurality of laser beams based on image information, and an image carrier that forms an electrostatic latent image by being irradiated with the plurality of laser beams A first shape for correcting aberrations in a first direction of the plurality of laser beams, and a second shape for correcting aberrations in the plurality of laser beams in a second direction orthogonal to the first direction And an image forming apparatus having an imaging lens section having a telecentric object side, and an aperture between the imaging lens section and the image carrier.

In the above-described image forming apparatus, the imaging lens unit corrects aberration in one of the main scanning direction and the sub-scanning direction of the plurality of laser beams based on the first shape,
It is preferable that aberration is corrected in a main scanning direction or a sub-scanning direction, which is a second direction orthogonal to the first direction of the plurality of laser beams, based on the second shape. And the second direction preferably have different aspherical shapes. According to the image forming apparatus, the aberration is corrected in the first direction of the plurality of laser beams based on the first shape, and the aberration is corrected in the second direction orthogonal to the first direction based on the second shape. Is corrected, and by irradiating the image carrier through the aperture, the angle of view can be increased and high resolution can be realized.

[0009]

1 and 2 show a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In the figure, X indicates the sub-scanning direction, Y indicates the main scanning direction, and Z indicates the optical axis direction. FIG. 2 is a schematic configuration diagram in the XZ plane. The image forming apparatus 1 has a plurality of laser elements arranged two-dimensionally in a sub-scanning direction X and a main scanning direction Y, and can emit a plurality of laser beams from each laser element simultaneously in parallel and independently. A semiconductor laser array 2, a photosensitive drum 3 rotated by a drum driving device 5 described later, and a plurality of laser beams emitted in parallel from each laser element of the semiconductor laser array 2 are projected on the photosensitive drum 3 to form an image. An imaging lens unit 4 for rotating the photosensitive drum 3, a drum driving device 5 for outputting a timing signal synchronized with the rotation of the photosensitive drum 3, an image memory 6 storing an image signal, and an image memory 6, a signal processing circuit 7 that reads out an image signal, processes the image signal and outputs a recording signal corresponding to a recording pattern, and receives a recording signal from the signal processing circuit 7 Semiconductor laser array 2 Te
And a control circuit 9 that outputs a control signal to the laser drive circuit 8 in synchronization with a timing signal from the drum drive device 5 to control the drive by the laser drive circuit 8. .

The imaging lens unit 4 includes a first anamorphic aspheric lens 41 formed in an aspherical shape different in the sub-scanning direction X and the main scanning direction Y, and a sub-scanning direction X and a main scanning direction Y.
Second anamorphic aspheric lens 42 and a second anamorphic aspheric lens 4
And a stop 43 disposed on the side of the second photoconductor, and the object side is a telecentric optical system.

Although not shown, the image forming apparatus 1 is provided with image forming means such as a charging device, a developing device, and a transfer device around the photosensitive drum 3, and a transfer device is provided in front of the transfer device. A fixing unit for fixing the toner image transferred to the recording paper,
And a paper discharge unit for discharging the recording paper on which the toner image is fixed.

Next, the operation of the present apparatus will be described. The signal processing circuit 7 reads an image signal from the image memory 6, processes the image signal, and outputs a recording signal corresponding to a recording pattern to the laser driving circuit 8. The drum driving device 5 drives the photosensitive drum 3 to rotate at a constant rotation speed,
A timing signal synchronized with the rotation of the photosensitive drum 3 is output to the control circuit 9. The control circuit 9 outputs a control signal to the laser driving circuit 8 in synchronization with the timing signal from the drum driving device 5. The laser drive circuit 8 inputs the recording signal from the signal processing circuit 7 based on the control signal from the control circuit 8 and drives the semiconductor laser array 2. The semiconductor laser array 2 emits a plurality of laser beams from each laser element substantially parallel to the optical axis direction Z. Semiconductor laser array 2
Are emitted from the imaging lens unit 4
Are projected on the photosensitive drum 3 to form an image. A plurality of light spots are formed on the photosensitive drum 3, and an electrostatic latent image corresponding to an image signal is formed. Thereafter, the electrostatic latent image on the photosensitive drum 3 is developed with toner by a developing device, and the toner image is transferred to a recording sheet fed from a feeding unit by a transfer unit, and further fixed by a fixing unit. The paper is discharged to the paper discharge unit. In this way, a high quality image is formed on the recording paper.

According to the above configuration, the following effects can be obtained. (A) By using an anamorphic aspherical lens as the lens constituting the imaging lens unit 4, aberration correction necessary for forming a high-quality image on the photosensitive drum 3 can be achieved while keeping the minimum number of lenses. It becomes possible. (B) In the imaging lens unit 4, the aperture 43 is disposed outside the first anamorphic aspheric lens 41 and the second anamorphic aspheric lens 42, that is, on the photosensitive drum 3 side, so that the angle of view is increased, and In addition, the lens diameter can be reduced, and each laser beam from the semiconductor laser array 2 can be projected on the entire area on the photosensitive drum 3. (C) Since the object side of the imaging lens unit 4 is a telecentric optical system, the semiconductor laser array 2 having a small divergence angle can be used as a light source, and high resolution can be obtained. (D) Since the configuration can be made with the minimum number of lenses, the total optical path length of the imaging lens unit 4 and the optical system can be shortened, and the image forming apparatus can be downsized.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Assuming that the horizontal coordinate with the optical axis as the origin is X and the vertical coordinate is Y, the sag amount z of the plane parallel to the Z axis
(X, y) is represented by Equation 1 shown below.

(Equation 1)

Table 1 shows lens data of the imaging lens unit 4 of the image forming apparatus according to the embodiment of the present invention. In the table, the # column indicates the surface number, # 0 indicates the emission surface of the semiconductor laser array 2, # 1 to # 2 indicate the first anamorphic aspheric lens 41, and # 3 to # 4 indicate the surface. 2
An anamorphic aspheric lens 42 is shown.
3, and # 6 indicates the surface of the photosensitive drum 3, that is, the image plane. The column of the radius of curvature r indicates the radius of curvature of each surface. The column of the thickness or the surface distance d indicates the distance from each surface to the next surface. The column of refractive index indicates the refractive index of the material forming the first anamorphic aspheric lens 41 and the second anamorphic aspheric lens 42.

[Table 1] In Table 1, the aspherical surface is indicated by *, and is defined by Expression 1, and the value of the coefficient in Expression 1 for each surface is shown by Table 2 below.

[Table 2]

In the imaging lens unit 4 having the lens data shown in Table 2, the wavelength λ, the focal length f, and the total angle of view 2
θ, execution FNo, magnification M, λ = 775 nm, f = 70.000 mm, 2θ = 52 de
g, FNo = 16, and M = 6.

FIG. 3 shows the aberration of the imaging lens unit 4 described above, and FIG. 3A shows the spherical aberration of the imaging lens unit 4 and FIG.
FIG. 3B shows the astigmatism of the imaging lens unit 4, and FIG.
4 shows distortion aberration of the imaging lens unit 4. According to the imaging lens unit 4 described above, aberrations are suppressed as shown in the figure, whereby a high-resolution image can be obtained. In FIG. 3B, S (dashed line) indicates astigmatism in the sub-scanning direction, and T (solid line) indicates astigmatism in the main scanning direction.

FIG. 4 shows an MTF (Modulation).
FIG. 4 is a diagram showing a Transfer Function curve. M corresponding to object height 0mm, 15mm, 30mm
4 shows a TF curve. As shown, the MTF curve extends to high spatial frequencies and has high resolution. In addition, as described above, the total angle of view 2θ is 52 degrees, and a projection optical system having a large angle of view can be obtained.

Further, the projection optical system according to the present invention is telecentric on the object side, so that the emission points of the laser array arranged two-dimensionally can be accurately enlarged and projected on the photosensitive member.

In the above-described image forming apparatus, the configuration using the photosensitive drum as the image carrier has been described. For example, a belt photosensitive member, a drum-shaped or a belt-shaped dielectric may be used. Further, the present invention can be applied to an image forming apparatus having an intermediate transfer member.

[0021]

As described above, according to the present invention,
A lens having a first shape for correcting aberration in a first direction of the image signal light and a second shape for correcting aberration of the image signal light in a second direction orthogonal to the first direction; Since the object side is telecentric and the projection optical system has a stop between the imaging lens unit and the projection surface, the angle of view can be increased without increasing the number of lenses, and high resolution can be realized. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an XZ of the image forming apparatus according to the embodiment of the present invention;
Schematic configuration diagram in plane

3A and 3B show aberrations in the projection optical system according to the embodiment of the present invention, wherein FIG. 3A shows spherical aberration, FIG. 3B shows astigmatism,
(C) is distortion aberration

FIG. 4 is an explanatory diagram showing an MTF curve in the image forming apparatus according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1, image forming apparatus 2, semiconductor laser array 3, photosensitive drum 4, imaging lens unit 5, drum driving device 6, image memory 7, signal processing circuit 8, laser driving circuit 9, control circuit 41, first anamorphic non Spherical lens 42, 2nd anamorphic aspheric lens 43, diaphragm

Claims (6)

[Claims] A light source that emits image signal light based on image information; a first shape that corrects aberration in a first direction of the image signal light; and a second shape that is orthogonal to the first direction. A lens having a second shape that corrects the aberration of the image signal light with respect to a direction, an imaging lens unit having an object side telecentric, and a stop between the imaging lens unit and a projection surface. A projection optical system, characterized in that: 2. The image forming lens section corrects aberration in one of a main scanning direction and a sub-scanning direction of the image signal light based on the first shape, and corrects the image based on the second shape. The projection optical system according to claim 1, wherein aberration is corrected in a main scanning direction or a sub-scanning direction that is the second direction orthogonal to the first direction of the signal light. 3. The projection optical system according to claim 1, wherein the lens has a different aspherical shape in the first direction and the second direction. 4. A light source having a plurality of laser elements arranged in an array and emitting a plurality of laser beams based on image information; and forming an electrostatic latent image by irradiating the plurality of laser beams. An image carrier to be corrected; a first shape for correcting aberrations in a first direction of the plurality of laser beams; and a correction for aberrations in the plurality of laser beams in a second direction orthogonal to the first direction An image forming apparatus, comprising: an imaging lens unit having a lens having a second shape to be telecentric on the object side; and an aperture between the imaging lens unit and the image carrier. . 5. The imaging lens section corrects aberration in one of a main scanning direction and a sub-scanning direction of the plurality of laser beams based on the first shape, and corrects the aberration based on the second shape. The image forming apparatus according to claim 4, wherein aberration is corrected in a main scanning direction or a sub-scanning direction that is the second direction orthogonal to the first direction of the plurality of laser beams. 6. The image forming apparatus according to claim 4, wherein said lens has a different aspherical shape in said first direction and said second direction.