JPH11174320A - Optical projection system and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical projection system and an image forming device capable of improving image quality by enhancing the density of a light spot formed on a projection surface. SOLUTION: A semiconductor laser array 2 emits plural laser beams in parallel with an optical axis direction Z. The respective laser beams from the laser array 2 are extended only concerning the lateral magnification of an image-formation lens system 4 and made incident on a variable power optical system 5. The respective laser beams made incident on the optical system 5 are reflected by the 1st mirror 50 of the optical system 5 and the reflected light beams by the mirror 50 are reflected by a 2nd mirror 51. The reflected light beams reflected by the mirror 51 are reflected by the mirror 50 again, and further reflected by the mirror 51, then projected on a photoreceptor drum 3 and formed into an image. Plural elliptical light spots long in a main scanning direction X are formed on the drum 3 so as to form an electrostatic latent image in accordance with an image signal.

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, etc., and more particularly, to a projection optical system capable of increasing the density of a light spot formed on a projection surface and improving image quality. The present invention relates to an 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. 9-200431. The image forming apparatus includes a plurality of laser elements arranged two-dimensionally in a main scanning direction and a sub-scanning direction, and a laser array that emits a plurality of laser beams from the plurality of laser elements based on an image signal. The laser beam moves in the sub-scanning direction and forms an electrostatic latent image by each of the laser beams emitted from the plurality of laser elements, and the respective laser beams emitted from the plurality of laser elements are projected onto the photoconductor and combined. And a magnifying projection optical system for imaging. When each laser beam emitted from a plurality of laser elements is projected and imaged on a photoconductor by a magnifying projection optical system, a plurality of circular light spots having a diameter of 20 to 30 μm are formed on the photoconductor at a pitch of 20 to 30 μm. Then, an electrostatic latent image is formed on the photoreceptor by the plurality of light spots. After this electrostatic latent image is developed with toner, the toner image is transferred and fixed on paper, and 1200
An image is formed at a resolution of about dpi.

[0003]

However, according to the conventional image forming apparatus, the interval between the light spots has a lower limit due to the restrictions on the production of the laser array and the magnifying projection optical system, so that the distance between the light spots on the photosensitive member is small. There is a problem in that the density of the formed light spot is limited and the image quality cannot be improved.

Accordingly, the present invention provides a projection optical system and an image forming apparatus capable of increasing the density of light spots formed on a projection surface and improving image quality.

[0005]

In order to achieve the above object, the present invention provides an imaging lens system for projecting light emitted from a light source onto a projection surface to form an image, and the imaging lens system and the projection surface. An elliptical light spot on the projection surface which is longer or shorter in the vertical or horizontal direction by enlarging or reducing incident light from the imaging lens system by different magnifications in the vertical and horizontal directions. And a variable power optical system for forming a projection optical system. In order to achieve the above object, the present invention provides a laser array having at least a plurality of laser elements arranged in an array in a main scanning direction, and emitting a plurality of laser beams from the plurality of laser elements based on an image signal. And an image carrier that moves in the sub-scanning direction relative to the laser array and forms a latent image with the plurality of laser beams from the plurality of laser elements;
An imaging lens system that projects the plurality of laser beams from the plurality of laser elements onto the image carrier to form an image; and the imaging lens system is disposed between the imaging lens system and the image carrier. The plurality of laser beams from the system are enlarged or reduced by a magnification in the main scanning direction that is larger than the sub-scanning direction to form a plurality of elliptical light spots long in the main scanning direction on the image carrier. An image forming apparatus comprising a variable power optical system is provided.

[0006]

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 main scanning direction, Y indicates the sub-scanning direction, and Z indicates the optical axis direction. FIG. 2A is a schematic configuration diagram on the XZ plane, and FIG. 2B is a schematic configuration diagram on the YZ plane. The image forming apparatus 1 has a plurality of laser elements arranged two-dimensionally in a main scanning direction X and a sub-scanning direction Y, and can independently and simultaneously emit a plurality of laser beams from each laser element in parallel. Semiconductor laser array 2 and photosensitive drum 3 rotated by a drum drive circuit 6 described later
An imaging lens system 4 of an enlargement optical system for projecting a plurality of laser beams emitted in parallel from each laser element of the semiconductor laser array 2 onto the photosensitive drum 3 to form an image, and A variable power optical system 5 for expanding each laser beam at different magnifications in the main scanning direction X and the sub-scanning direction Y to form a plurality of elliptical light spots on the photosensitive drum 3 in the main scanning direction X; A drum driving circuit 6 that drives the photosensitive drum 3 to rotate and outputs a timing signal synchronized with the rotation of the photosensitive drum 3, an image memory 7 that stores image signals, and reads image signals from the image memory 7. A signal processing circuit 8 that processes an image signal and outputs a recording signal corresponding to a recording pattern; a laser driving circuit 9 that inputs a recording signal from the signal processing circuit 8 to drive the semiconductor laser array 2; In synchronization with the timing signal from the driving circuit 6 are outputs a control signal to the laser drive circuit 9 and a control circuit 10 for controlling the drive by the laser drive circuit 9. Note that a projection optical system is composed of the imaging lens system 4 and the variable power optical system 5.

Although not shown, the image forming apparatus 1 is provided with image forming means such as a charger, a developing unit and a transfer unit around the photosensitive drum 3, and a transfer unit is provided in front of the transfer unit. 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.

FIG. 3 shows an imaging lens system 4 and a variable power optical system 5. The imaging lens system 4 includes the semiconductor laser array 2
A first lens 401 having a negative power and a concave surface facing the (object side), a second lens 402 having a positive power and a convex surface facing the object side and bonded to the first lens 401,
Third lens 4 having a positive power and a convex surface facing the object side
03 and a fourth power having a positive power with the convex surface facing the object side.
A lens 404, a fifth lens 405 having a positive power with a convex surface facing the object side, a sixth lens 406 having a negative power with a concave surface facing the object side, and a sixth lens 406 having a convex surface facing the object side A seventh lens 407 having a positive power, an eighth lens 408 having a positive power having a convex surface facing the object side, and a ninth lens 409 having a negative power having a concave surface facing the object side. A tenth lens 410 having a negative power with the concave surface facing the object side, and an eleventh lens 41 having a positive power with the concave surface facing the object side
1 and the twelfth having negative power with the concave surface facing the object side.
Lens 412, fifth lens 405 and sixth lens 406
And an aperture 420 disposed between the lens and the object side, and the object side is a telecentric optical system.

The variable power optical system 5 has a first mirror 50 which has a negative power in the sub-scanning direction Y and reflects an incident beam having no power in the main scanning direction X on the surface, and a positive mirror in the sub-scanning direction Y. And a second mirror 51 that reflects an incident beam having no power in the main scanning direction X on the surface. Here, the absolute value of the radius of curvature of the first mirror 50 in the sub scanning direction Y is set to be larger than the absolute value of the radius of curvature of the second mirror 51 in the sub scanning direction Y.

Next, the operation of the apparatus 1 will be described. The signal processing circuit 8 reads an image signal from the image memory 7, processes the image signal, and outputs a recording signal corresponding to a recording pattern to the laser driving circuit 9. The drum drive circuit 6 drives the photosensitive drum 3 to rotate at a constant rotation speed and outputs a timing signal synchronized with the rotation of the photosensitive drum 3 to the control circuit 10. The control circuit 10 outputs a control signal to the laser drive circuit 9 in synchronization with the timing signal from the drum drive circuit 6. The laser drive circuit 9 drives the semiconductor laser array 2 by inputting a recording signal from the signal processing circuit 8 based on a control signal from the control circuit 10.
The semiconductor laser array 2 emits a plurality of laser beams from each laser element in parallel with the optical axis direction Z. The plurality of laser beams emitted from the semiconductor laser array 2 are magnified by the lateral magnification of the imaging lens system 4 and enter the variable power optical system 5. Each laser beam incident on the variable power optical system 5 is reflected by the first mirror 50 of the variable power optical system 5, and the reflected light is reflected by the second mirror 51. The reflected light reflected by the second mirror 51 is reflected again by the first mirror 50, and further reflected by the second mirror 51.
And is projected on the photosensitive drum 3 to form an image.
A plurality of elliptical light spots long in the main scanning direction X 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,
The image is transferred to a recording sheet fed from a sheet feeding unit by a transfer unit, further fixed by a fixing unit, and discharged to a sheet discharging unit. Thus, a high-quality image is formed on the recording paper.

According to the above configuration, the following effects can be obtained. (A) Since the shape of the light spot projected on the photosensitive drum 3 is an ellipse long in the main scanning direction X, the pitch of the light spot in the sub-scanning direction Y can be reduced, and the light spot in the sub-scanning direction Y Density can be improved. As a result, the image quality can be improved, and it is possible to cope with a high-quality printer or the like. (B) Since the variable power optical system 5 is formed of a reflection mirror, the distance from the imaging lens system 4 to the photosensitive drum 3 can be reduced, and the size of the apparatus 1 can be reduced. (C) Since the photosensitive drum 3 side of the imaging lens system 4 is constituted by a lens having a negative power (the twelfth lens 412), the angle of view is increased, and each laser beam from the semiconductor laser array 2 is used as a photosensitive member. The image can be projected on the entire area on the drum 3. (D) Since the object side of the imaging lens system 4 is a telecentric optical system, the semiconductor laser array 2 can be used as a light source, and high resolution can be obtained.

[0012]

Embodiment 1 Table 1 shows the results of an embodiment of the imaging lens system 4.
This shows the lens data. In the same table, Ri (i = 1,
2, ..., 22) indicate the radius of curvature of the lens.
For example, R₁Is the radius of curvature of the concave surface of the first lens 401
And R_TwoAre a first lens 401 and a second lens 402
Is the radius of curvature of the bonding surface. D₁, D_Two, D_Four,
D ₆, D₈, D_Ten, D₁₁, D₁₃, D_Fifteen, D₁₇, D₁₉, D
_{twenty one}Is the thickness of each of the first to twelfth lenses 401 to 412
Respectively, and D_Three, D_Five, D₇Are the second to fifth records
Distance between adjacent lenses of lenses 402 to 405
D₁₂, D₁₄, D₁₆, D₁₈, D₂₀Are the seventh to
Between the adjacent lenses of the 12 lenses 407 to 412
, And D₉Is the fifth lens 405 and aperture
420, D_TenIs the stop 420 and the sixth lens 40
6 are shown. Also, the first lens 40
The first and second lenses 402 and the tenth lens 410 and
The eleventh lens 411 is bonded with zero surface spacing. Ma
N₁~ N₁₂Indicates the refractive index at a wavelength of 780 nm.
doing.

[Table 1]

An imaging lens system 4 having the above lens data
Focal length f, the effective F _NO of the magnification M is respectively set to _{f = 65, F NO = 17} , M = 6.

The radius of curvature of the first mirror 50 and the second mirror 51 in the sub-scanning direction Y are 600 and 373.8, respectively.
It is set to 2. Note that the radius of curvature, lens thickness, surface distance, and the first mirror 50 and the second mirror 51 in Table 1 are used.
The unit of the numerical value of the radius of curvature in the sub-scanning direction Y is mm.

FIGS. 4A and 4B show the spherical aberration and astigmatism of the imaging lens system 4 of this embodiment, respectively. In addition, FIG.
, The symbol S (solid line) indicates astigmatism in the sagittal direction, and the symbol T (dashed line) indicates astigmatism in the tangential direction.

FIG. 5 shows the MT of the imaging lens system 4 of this embodiment.
It is a figure showing an F curve. H is the object height (0, 17, 25m
m), symbol S indicates an MTF curve in a sagittal direction, and symbol T indicates an MTF curve in a tangential direction. The MTF curve extends to a high spatial frequency as shown in the figure, indicating that it has a high resolution.

The length of the main scanning direction X is 30 μm and the length of the sub-scanning direction Y is 25 μm on the photosensitive drum 3 by the projection optical system including the imaging lens system 4 and the variable power optical system 5.
Could be formed. Accordingly, the pitch of the light spots in the sub-scanning direction Y is made smaller than the pitch in the main scanning direction X, and the density of the light spots is about 1.
Since it can be doubled, the image quality can be improved.

The present invention is not limited to the above-described embodiment, but can take various forms. For example, the projection lens system may be a reduction optical system. Further, as the image carrier, a belt-shaped photoconductor, a drum-shaped or a belt-shaped dielectric may be used in addition to the above-described photoconductor drum. The present invention is also applicable to an image forming apparatus using an intermediate transfer member. Further, in the above embodiment, the reflection mirror is used as the variable power optical member. However, only the lens may be used, or the reflection mirror and the lens may be combined.

[0019]

As described above, according to the present invention, since the light spot formed on the projection surface is made elliptical by the variable power optical system, the density of the light spot in the minor axis direction of the ellipse can be increased. Thus, image quality can be improved.

[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.

2A is a schematic configuration diagram on an XZ plane of the image forming apparatus according to the embodiment of the present invention, and FIG. 2B is a schematic configuration diagram on a YZ plane of the image forming apparatus according to the embodiment of the present invention; is there.

FIG. 3 is a configuration diagram of an imaging lens system and a variable power optical system according to the present embodiment.

FIG. 4A is a spherical aberration diagram of the laser beam optical system according to the embodiment, and FIG. 4B is an astigmatism diagram of the laser beam optical system according to the embodiment.

FIG. 5 is an MTF curve diagram of the laser beam optical system according to the present embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming apparatus 2 semiconductor laser array 3 photoreceptor drum 4 imaging lens system 5 variable power optical system 6 drum drive circuit 7 image memory 8 signal processing circuit 9 laser drive circuit 10 control circuit 50 first mirror 51 second mirror 401 first 1 lens 402 2nd lens 403 3rd lens 404 4th lens 405 5th lens 406 6th lens 407 7th lens 408 8th lens 409 9th lens 410 10th lens 411 11th lens 412 12th lens 420 Aperture

Claims (14)

[Claims] An imaging lens system configured to project light emitted from a light source onto a projection surface to form an image; and an incident light from the imaging lens system disposed between the imaging lens system and the projection surface. And a variable power optical system that expands or contracts at different magnifications in the vertical direction and the horizontal direction to form the elliptical light spot long in the vertical direction or the horizontal direction on the projection surface. Projection optical system. 2. The projection optical system according to claim 1, wherein said variable power optical system includes a plurality of variable power optical members having different powers in said vertical direction and said horizontal direction. 3. The variable power optical system has a negative power in the vertical direction or the horizontal direction and a first variable power optical member having no power in the horizontal or vertical direction. 2. The projection optical system according to claim 1, further comprising a second variable power optical member having a positive power in the horizontal direction and having no power in the horizontal direction or the vertical direction. 3. 4. The projection optical system according to claim 3, wherein said first variable power optical member and said second variable power optical member are constituted by reflecting mirrors for reflecting the incident light from said imaging lens system on a surface. system. 5. The first variable magnification optical member comprising the reflection mirror, wherein the absolute value of the radius of curvature in the vertical direction or the horizontal direction is equal to the absolute value of the second magnification variable optical member in the vertical direction or the horizontal direction. 5. The projection optical system according to claim 4, wherein the projection optical system has a configuration in which the absolute value of the radius of curvature in the lateral direction is set to be larger than the absolute value. 6. The optical system according to claim 4, wherein said first variable power optical member and said second variable power optical member comprising said reflecting mirror reflect said incident light from said imaging lens system at least twice. Projection optics. 7. The projection optical system according to claim 1, wherein said imaging lens system includes a telecentric optical system on said light source side. 8. The imaging lens system has a first lens having a negative power with a concave surface facing the light source, and a positive power having a convex surface facing the light source with the first lens. A second lens, a third lens having a positive power with the convex surface facing the light source side, a fourth lens having a positive power with the convex surface facing the light source side, and a positive lens having a positive power facing the light source side. A fifth lens having a negative power, a sixth lens having a negative power with the concave surface facing the light source side, and a seventh lens having a positive power with the convex surface facing the light source side and bonded to the sixth lens An eighth lens having a positive power with a convex surface facing the light source side, a ninth lens having a negative power with a concave surface facing the light source side, and a negative power having a concave surface facing the light source side. A tenth lens having
An eleventh lens having a concave surface facing the light source and having a positive power, a twelfth lens having a concave surface facing the light source and having a negative power, and the fifth lens and the sixth lens are arranged between the fifth lens and the sixth lens. The projection optical system according to claim 1, wherein the projection optical system has a configuration provided with a stop. 9. A laser array having at least a plurality of laser elements arranged in an array in the main scanning direction, and emitting a plurality of laser beams from the plurality of laser elements based on an image signal; An image carrier that relatively moves in the sub-scanning direction and forms a latent image with the plurality of laser beams from the plurality of laser elements; and an image carrier that holds the plurality of laser beams from the plurality of laser elements. An imaging lens system for projecting and forming an image on a body, disposed between the imaging lens system and the image carrier, and the plurality of laser beams from the imaging lens system being larger than the sub-scanning direction. A variable-magnification optical system that forms a plurality of elliptical light spots elongated in the main scanning direction on the image carrier by enlarging or reducing the magnification in the main scanning direction. Forming apparatus. 10. The variable power optical system has a first variable power optical member having no power in the sub-scanning direction and no power in the main scanning direction, and a positive power in the sub-scanning direction. The image forming apparatus according to claim 9, further comprising: a second variable power optical member having no power in the main scanning direction. 11. The optical system according to claim 10, wherein said first variable power optical member and said second variable power optical member are constituted by reflecting mirrors for reflecting the plurality of laser beams from said imaging lens system on the surface. Image forming device. 12. The first variable magnification optical member comprising the reflecting mirror, wherein the absolute value of the radius of curvature in the sub scanning direction is equal to the radius of curvature of the second variable magnification optical member comprising the reflecting mirror in the sub scanning direction. The image forming apparatus according to claim 11, wherein the image forming apparatus is configured to be set to be larger than an absolute value of (i). 13. The optical system according to claim 1, wherein said first variable power optical member and said second variable power optical member comprising said reflecting mirror reflect said plurality of laser beams from said imaging lens system at least twice. 12. The image forming apparatus according to item 11. 14. The image according to claim 9, wherein said variable magnification optical system has a configuration in which a pitch in said sub-scanning direction of said plurality of light spots formed on said image carrier is smaller than a pitch in said main scanning direction. Forming equipment.