JPH11223783A - Color picture forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact color picture forming device suitable for highly precise printing in which color deviation or picture non-uniformity or the like can be reduced in a simple constitution. SOLUTION: This color picture forming device is provided with plural scanning optical devices 11, 12, 13, and 14 having a light source means including a semiconductor laser and an optical element including a refracting part and a diffracting part, and plural light fluxes outgoing from each scanning optical device 11-14 are introduced to the faces of plural corresponding image carriers 21, 22, 23, and 24, and the faces of the plural image carriers 21-24 are scanned with the plural fluxes so that a color picture can be formed. In this case, the plural scanning optical devices 11-14 are constituted so that aberration change in a main scanning direction on the faces of the image carriers 21-24 due to the environmental fluctuation of the scanning optical devices can be corrected by power change between the refracting part and the diffracting part of the optical element and the wavelength fluctuation of the semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus having a plurality of scanning optical devices, and more particularly, to a color image forming apparatus using a plurality of light beams emitted from a plurality of scanning optical devices in which aberration fluctuation due to environmental fluctuation (temperature fluctuation) is suppressed. Color image formation suitable for devices such as a laser beam printer or a color digital copier having a color electrophotographic process, wherein a single or a plurality of image carriers are optically scanned to record color image information. It concerns the device.

[0002]

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

FIG. 14 is a schematic view of a main part of a conventional scanning optical apparatus of this type.

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. The light beam (light amount) is restricted by a stop 93, and a cylinder having a predetermined refractive power only in the sub-scanning direction. The light is incident on a lens (cylindrical lens) 94. Of the substantially parallel light beams incident on the cylinder 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 a deflecting surface (reflection surface) 95a of an optical deflector 95 formed of a rotating polygon mirror (polygon mirror).
Is formed almost as a line image.

The light beam deflected and reflected by the deflecting surface 95a of the optical deflector 95 is converted into a scanning optical element (fθ
A photosensitive drum surface 9 serving 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.

[0006]

FIG. 15 shows a color image forming apparatus which uses a plurality of the above-described scanning optical devices simultaneously, records image information for each color on different photosensitive drum surfaces, and forms a color image. It is a principal part schematic diagram.

In FIG. 1, 101, 102, 103, 1
04 is a scanning optical device, 111, 112, 113, 1 respectively.
Numeral 14 denotes photosensitive drums as image carriers, 121 and 12 respectively.
Reference numerals 2, 123, and 124 denote developing units, respectively, and 131 denotes a transport belt. In the color image forming apparatus shown in the figure, four scanning optical devices (101, 102, 103, 104) 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 111, 112, 113 and 114 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 superimposed to form an image, a scanning line deviation between the respective colors (hereinafter referred to as "registration deviation"), an image density unevenness between the respective colors, and the like. It is important to reduce For this reason, the scanning optical device must:-compensate for a change in magnification (spot displacement) in the main scanning direction due to environmental fluctuations (temperature fluctuations) such as temperature rise;-environmental fluctuations (temperature fluctuations) such as temperature rise ) Is required to be compensated for in the main scanning direction and the focus change in the sub-scanning direction.
Alternatively, it is necessary to provide a configuration that does not cause misregistration between respective colors or image unevenness even if there is a difference in the use environment of a plurality of scanning optical devices.

Conventionally, glass lenses, glass mirrors, and the like having little characteristic fluctuation due to environmental fluctuations have been used in such a scanning optical apparatus. However, aberration changes due to wavelength fluctuations of a semiconductor laser remain, and an aspherical surface is used. Due to the inability to perform advanced aberration correction and the high cost, it is required to perform environmental fluctuation compensation with a scanning optical element using plastic.

JP-A-7-174999 discloses an example in which a scanning optical system of a scanning optical device is composed of a glass spherical lens having a positive power and a plastic toric lens having a positive power in a main scanning direction and a sub-scanning direction. It is. In this publication, a magnification (position) shift in the main scanning direction due to a temperature rise of + 25 ° C. is 80 μm, and a focus shift in the sub-scanning direction is +
2.1 mm. However, this scanning optical device,
For example, in a color image forming apparatus using a plurality of colors, there is a problem that registration deviation between respective colors, image density unevenness, and the like easily occur.

Japanese Patent Application Laid-Open No. 7-128603 is an example in which a scanning optical system of a scanning optical device used in a color image forming apparatus is composed of a glass lens and a glass cylinder mirror. However, in this publication, since all optical elements of all the scanning optical systems are made of glass, the aberration change due to the wavelength fluctuation of the semiconductor laser remains, and the aberration cannot be corrected by the aspherical surface, so that the optical path length is long and the cost is high. There is a problem that.

According to the present invention, in a color image forming apparatus having a plurality of scanning optical devices, a change in aberration caused by an environmental change (temperature change) of each scanning optical device is caused by a refracting portion of a scanning optical element of each scanning optical device. By correcting the power change between the laser and the diffraction part and the wavelength fluctuation of the semiconductor laser, it is possible to suppress the registration deviation between the colors and the image density unevenness between the colors with a simple structure, and to achieve high-definition printing. It is an object of the present invention to provide a compact color image forming apparatus suitable for a computer.

[0013]

The color image forming apparatus according to the present invention comprises: (1) a plurality of scanning optical devices each having light source means including a semiconductor laser, and optical elements including a refraction section and a diffraction section; Color image forming for guiding a plurality of light beams emitted from each scanning optical device to different regions on a single image carrier surface, and scanning the image carrier surface with the plurality of light beams to form a color image Wherein the plurality of scanning optical devices each have an aberration change in the main scanning direction on the image carrier surface due to an environmental change of the scanning optical device, and a power change between a refraction portion and a diffraction portion of the optical element. The correction is made by the wavelength fluctuation of the semiconductor laser.

In particular, (1-1) the aberration change in the main scanning direction is a magnification change, and (1-2) the aberration change in the main scanning direction is a focus change.

(2) A plurality of scanning optical devices having a light source means including a semiconductor laser and an optical element including a refraction unit and a diffraction unit are provided, and a plurality of light beams emitted from each scanning optical device are converted into a single light beam. A color image forming apparatus that guides light to different regions on the surface of the image carrier and forms a color image by scanning the surface of the image carrier with the plurality of light fluxes; Aberration changes in the main scanning direction and the sub-scanning direction on the surface of the image carrier due to environmental fluctuations of the optical device are corrected by a power change between a refraction section and a diffraction section of the optical element and a wavelength fluctuation of the semiconductor laser. It is characterized by doing so.

In particular, (2-1) the aberration change in the main scanning direction is a magnification change and / or a focus change, and the aberration change in the sub-scanning direction is a focus change.

In the above (1) and (2), the refracting portion of the optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction. Having a diffractive optical element having different powers in the scanning direction and the sub-scanning direction,
In (1) and (2), the refracting portion of the optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction. The diffractive portion of the optical element has a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and the cylinder lens and the diffractive optical element are composed of a combined optical element combined with each other, In (1) and (2), the refracting portion of the optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction. The diffractive portion of the optical element includes a first diffractive optical element having power in the main scanning direction and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction. Wherein the first diffractive optical element is disposed in the vicinity of the toric lens, and the cylinder lens and the second diffractive optical element comprise a composite optical element combined with each other.

(3) A plurality of scanning optical devices having a light source means including a semiconductor laser and an optical element including a refraction section and a diffraction section are provided, and a plurality of light beams emitted from each scanning optical apparatus correspond to each other. A color image forming apparatus that guides light onto a plurality of image bearing member surfaces and scans the plurality of image bearing member surfaces with the plurality of light beams to form a color image. The aberration change in the main scanning direction on the surface of the image carrier due to the environmental change of the scanning optical device is corrected by the power change between the refraction portion and the diffraction portion of the optical element and the wavelength change of the semiconductor laser. It is characterized by having.

In particular, (3-1) the aberration change in the main scanning direction is a magnification change, and (3-2) the aberration change in the main scanning direction is a focus change.

(4) A plurality of scanning optical devices having a light source means including a semiconductor laser and an optical element including a refraction portion and a diffraction portion are provided, and a plurality of light beams emitted from each scanning optical device correspond to each other. A color image forming apparatus that guides light onto a plurality of image bearing member surfaces and scans the plurality of image bearing member surfaces with the plurality of light beams to form a color image. Aberration changes in the main scanning direction and sub-scanning direction on the surface of the image carrier due to environmental fluctuations of the scanning optical device are corrected by a power change between a refraction portion and a diffraction portion of the optical element and a wavelength change of the semiconductor laser. It is characterized by the fact that.

In particular, (4-1) the aberration change in the main scanning direction is a magnification change and / or a focus change, and the aberration change in the sub-scanning direction is a focus change.

In the above (3) and (4), the refracting portion of the optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction. Having a diffractive optical element having different powers in the scanning direction and the sub-scanning direction,
In (3) and (4), the refracting portion of the optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction. The diffractive portion of the optical element has a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and the cylinder lens and the diffractive optical element are composed of a combined optical element combined with each other, In (3) and (4), the refracting portion of the optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction. The diffractive portion of the optical element includes a first diffractive optical element having power in the main scanning direction and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction. Wherein the first diffractive optical element is disposed in the vicinity of the toric lens, and the cylinder lens and the second diffractive optical element comprise a composite optical element combined with each other.

(5) A plurality of light beams emitted from a plurality of scanning optical devices are respectively guided to different regions on a single image carrier surface, and the plurality of light beams scan the image carrier surface to color. In a color image forming apparatus for forming an image, the plurality of scanning optical devices each include a light source unit including a semiconductor laser, and a first unit that converts a light beam emitted from the light source unit into a substantially parallel light beam.
And a second element for forming the converted substantially parallel light beam into a line image elongated in the main scanning direction on the deflecting surface of the deflecting element.
And a third optical element having a refraction section and a diffraction section for forming a light beam deflected by the deflection element into a spot on the image carrier surface, and the plurality of scanning optical devices. The aberration change in the main scanning direction on the surface of the image carrier due to the environmental change of the scanning optical device is caused by the power change of the refraction portion and the diffraction portion of the third optical element and the wavelength change of the semiconductor laser. It is characterized by being corrected.

In particular, (5-1) the aberration change in the main scanning direction is a magnification change, and (5-2) the aberration change in the main scanning direction is a focus change.

(6) A plurality of light beams emitted from a plurality of scanning optical devices are respectively guided to different regions on a single image carrier surface, and the plurality of light beams scan the image carrier surface to perform color scanning. In a color image forming apparatus for forming an image, the plurality of scanning optical devices each include a light source unit including a semiconductor laser, and a first unit that converts a light beam emitted from the light source unit into a substantially parallel light beam.
And a second element for forming the converted substantially parallel light beam into a line image elongated in the main scanning direction on the deflecting surface of the deflecting element.
And a third optical element having a refraction section and a diffraction section for forming a light beam deflected by the deflection element into a spot on the image carrier surface, and the plurality of scanning optical devices. The aberration change in the main scanning direction and the sub-scanning direction on the surface of the image carrier due to the environmental change of the scanning optical device is caused by the power change between the refraction part and the diffraction part of the third optical element, and the semiconductor laser. A color image forming apparatus, wherein the correction is made by the wavelength variation of the color image.

In particular, (6-1) the aberration change in the main scanning direction is a magnification change and / or a focus change, and the aberration change in the sub-scanning direction is a focus change.

In the above (5) and (6), the refractive portion of the third optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction. The diffractive portion of the element may have a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and in (5) and (6), the refracting portion of the third optical element may be different from the main scanning direction. It has a plastic toric lens having different powers in the sub-scanning direction and a cylinder lens having power in the main scanning direction, and the diffractive portion of the third optical element is different from each other in the main scanning direction and the sub-scanning direction. It has a diffractive optical element having different powers, and the cylinder lens and the diffractive optical element are composed of a combined optical element combined with each other, and in the above (5) and (6), the refraction of the third optical element Department It has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction, and the diffractive portion of the third optical element supplies power in the main scanning direction. Having a first diffractive optical element and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, wherein the first diffractive optical element is disposed near the toric lens; The cylinder lens and the second
Is characterized by comprising a composite optical element combined with each other.

(7) guiding a plurality of light beams emitted from a plurality of scanning optical devices onto a plurality of corresponding image carrier surfaces,
In a color image forming apparatus for forming a color image by scanning each of the plurality of image carriers with the plurality of light beams, the plurality of scanning optical devices emit light from a light source unit including a semiconductor laser, respectively, and the light source unit. A first optical element for converting the light beam into a substantially parallel light beam, a second optical element for forming the converted substantially parallel light beam into a line image elongated in the main scanning direction on the deflecting surface of the deflecting element, and A third optical element having a refraction part and a diffraction part for forming a light beam deflected by the element in a spot shape on the surface of the image carrier, and the plurality of scanning optical devices are respectively provided by the scanning optical device. An aberration change in the main scanning direction on the surface of the image carrier due to an environmental change is corrected by a power change of the refraction portion and the diffraction portion of the third optical element and a wavelength change of the semiconductor laser. It is characterized by:

In particular, (7-1) the aberration change in the main scanning direction is a magnification change, and (7-2) the aberration change in the main scanning direction is a focus change.

(8) guiding a plurality of light beams emitted from a plurality of scanning optical devices onto a plurality of corresponding image carrier surfaces,
In a color image forming apparatus for forming a color image by scanning each of the plurality of image carriers with the plurality of light beams, the plurality of scanning optical devices emit light from a light source unit including a semiconductor laser, respectively, and the light source unit. A first optical element for converting the light beam into a substantially parallel light beam, a second optical element for forming the converted substantially parallel light beam into a line image elongated in the main scanning direction on the deflection surface of the deflection element, and A third optical element having a refraction part and a diffraction part for forming a light beam deflected by the element in a spot shape on the surface of the image carrier, and the plurality of scanning optical devices are respectively provided by the scanning optical device. Aberration changes in the main scanning direction and the sub-scanning direction on the surface of the image carrier due to environmental fluctuations are corrected by a power change between the refraction portion and the diffraction portion of the third optical element and a wavelength change of the semiconductor laser. Is characterized by the fact that There.

In particular, (8-1) the aberration change in the main scanning direction is a magnification change and / or a focus change, and the aberration change in the sub-scanning direction is a focus change.

In the above (7) and (8), the refractive portion of the third optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction. The diffractive portion of the element may have a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and in (7) and (8), the refraction portion of the third optical element may be different from the main scanning direction. It has a plastic toric lens having different powers in the sub-scanning direction and a cylinder lens having power in the main scanning direction, and the diffractive portion of the third optical element is different from each other in the main scanning direction and the sub-scanning direction. It has a diffractive optical element having different powers, and the cylinder lens and the diffractive optical element are composed of a composite optical element combined with each other, and in the above (7) and (8), the refraction of the third optical element Department It has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction, and the diffractive portion of the third optical element supplies power in the main scanning direction. Having a first diffractive optical element and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, wherein the first diffractive optical element is disposed near the toric lens; The cylinder lens and the second
Is characterized by comprising a composite optical element combined with each other.

[0033]

[First Embodiment] FIG. 1 is a schematic view of a main part of a color image forming apparatus according to a first embodiment of the present invention.

In FIG. 1, reference numerals 11, 12, 13, and 14 denote scanning optical devices, 21, 22, 23, and 24 denote photosensitive drums as image carriers, 31, 32, 33, and 34 denote developing units, and 41 denotes a developing device. It is a conveyor belt. In the color image forming apparatus according to the present embodiment, four scanning optical devices (11, 12, 13, 14) each having a small aberration variation due to environmental variation (temperature variation) are arranged as described below, and each of them is C (cyan). ), M (magenta), Y (yellow), and B (black), respectively.
Image signals (image information) are recorded on 2, 23, 24 surfaces,
It prints color images at high speed.

Next, a description will be given of a method of satisfactorily correcting a change in aberration of the scanning optical apparatus, which is a feature of the present invention, due to an environmental change, and an optical element thereof. Incidentally, a plurality of scanning optical devices 11, 12, 13, and 14 constituting the color image forming apparatus.
Since the configuration and the optical function are the same, the scanning optical device 11 will be described below as a representative.

FIG. 2 is a schematic view of a main part showing the scanning optical device 11 and the corresponding image carrier 21. FIG. 3 is a sectional view of a main part of the optical system shown in FIG. 2 in the main scanning direction.

2 and 3, reference numeral 1 denotes a light source means,
For example, it consists of a semiconductor laser. Reference numeral 2 denotes a collimator lens as a first optical element, which converts a divergent light beam (light beam) emitted from the light source unit 1 into a substantially parallel light beam. Reference numeral 3 denotes an aperture stop, which restricts a passing light beam (light amount). Reference numeral 4 denotes a cylindrical lens (cylinder lens) serving as a second optical element, which has a predetermined refractive power only in the sub-scanning direction, and deflects a light beam passing through the aperture stop 3 in a sub-scanning cross section, as will be described later. An image is formed on the deflection surface 5a of the vessel 5 as a substantially linear image.

Reference numeral 5 denotes an optical deflector as a deflecting element, for example, a polygon mirror (rotating polygon mirror), which is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor.

Reference numeral 6 denotes a scanning optical element serving as a third optical element having fθ characteristics, and has a refracting portion and a diffractive portion. The refracting portion is composed of a single plastic toric lens 61 having different powers in the main scanning direction and the sub-scanning direction, and both lens surfaces of the toric lens 61 in the main scanning direction have an aspheric shape. The diffractive portion is composed of a long diffractive optical element 62 having different powers in the main scanning direction and the sub-scanning direction. In the present embodiment, the rotating shaft of the optical deflector 5 and the surface of the photosensitive drum 21 (scanned surface)
The toric lens 61 is arranged on the optical deflector 5 side from the middle point, and the diffractive optical element 62 is arranged on the photosensitive drum 21 surface side.
The scanning optical element 6 forms a light beam based on the image information deflected by the optical deflector 5 on the surface of the photosensitive drum 21 and corrects the tilt of the deflecting surface 5a of the optical deflector 5 in the sub-scan section. I have. Although the diffractive optical element 62 in the present embodiment is made of plastic manufactured by injection molding, the present invention is not limited to this. For example, the same effect can be obtained even if a replica diffraction grating is formed on a glass substrate. can get.

The color image forming apparatus according to the present embodiment has four scanning optical devices 11, 12, 13, and 14 as described above.
Thus, latent images are formed on the corresponding surfaces of the photosensitive drums 21, 22, 23, and 24 using light beams based on the respective modulation signals. For example, C (cyan), M (magenta), Y
(Yellow) and B (black) latent images are formed on the corresponding surfaces of the photosensitive drums 21, 22, 23, and 24, and then are multiplex-transferred onto a recording material to form one full-color image.

The divergent light beam emitted from the semiconductor laser 1 in the scanning optical device 11 in this embodiment is converted by the collimator lens 2 into a substantially parallel light beam,
The light flux (light quantity) is restricted by the light and enters the cylindrical lens 4. Of the substantially parallel light beam incident on the cylindrical lens 4, the light beam is emitted as it is in the main scanning section. In the sub-scanning section, the light converges and forms a substantially linear image (a linear image elongated in the main scanning direction) on the deflection surface 5a of the optical deflector 5. The light beam deflected by the deflecting surface 5a of the light deflector 5 is guided to the surface of the photosensitive drum 21 via the toric lens 61 and the diffractive optical element 62,
By rotating the light deflector 5 in the direction of arrow A,
The surface of the photosensitive drum 21 is optically scanned in the direction of arrow B.
As described above, for example, latent images of C (cyan), M (magenta), Y (yellow), and B (black) are formed on the corresponding photosensitive drums 21, 22, 23, and 24, and thereafter, are formed on a recording material. Multiple transfer is performed to form one full color image.

The shapes of the toric lens 61 and the diffractive optical element 62 constituting the third optical element 6 of the scanning optical device 11 in this embodiment are respectively the toric lens. . An aspherical shape in which the main scanning direction can be expressed by a function up to the tenth order, the origin is the intersection with the optical axis of the toric lens, the optical axis direction is the x axis, the axis perpendicular to the optical axis in the main scanning section is the y axis, When the axis orthogonal to the optical axis in the scanning section is the z-axis, the generatrix direction corresponding to the main scanning direction is

[0043]

(Equation 1) (However, R is the radius of curvature, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspherical coefficients) The sagittal direction corresponding to the sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction) But,

[0044]

(Equation 2) Where _{r '= r 0 (1 +} D 2 Y 2 + D 4 Y 4 + D 6 Y 6 + D 8 Y 8 + D
₁₀ Y ¹⁰ ) (where r ₀ is the sagittal radius of curvature on the optical axis, D ₂ , D ₄ , D
₆ , D ₈ and D ₁₀ are aspheric coefficients) Diffractive optical element. . A diffraction surface represented by a second-order phase function in which the main scanning direction is up to the sixth order and the sub-scanning direction is different depending on the position in the main scanning direction is φ = mλ = b ₂ Y ² + b ₄ Y ⁴ + b ₆ Y ⁶ + (d ₀ + d ₁
Y + d ₂ Y ² + d ₃ Y ³ + d ₄ Y ⁴ ) Z ² (where φ is a phase function, m is the diffraction order, λ is the wavelength used,
Y is the height from the lens optical axis, b ₂ , b ₄ , b ₆ , d ₀ ,
d ₁ , d ₂ , d ₃ , and d ₄ are represented by the following expressions: phase coefficients, and in Embodiments 1 to 3, + 1st-order diffracted light is used.

Table 1 shows the optical arrangement, the aspheric coefficient of the toric lens 61, and the diffractive optical element 62 in this embodiment.
Is shown.

[0046]

[Table 1] In the present embodiment, the aberration change in the main scanning direction and the sub-scanning direction on the surface of the photosensitive drum 21 due to the environmental fluctuation (temperature fluctuation) of the scanning optical device 11 is determined by the power change between the toric lens 61 and the diffractive optical element 62 and the semiconductor laser. Correction is made by the wavelength variation of 1. The aberration change in the main scanning direction is a magnification change and / or a focus change, and the aberration change in the sub-scanning direction is a focus change.

FIG. 4 is an explanatory diagram showing paraxial aberrations (field curvature in the main scanning direction and the sub-scanning direction and a shift in magnification (position), etc.) before and after the environmental change in the present embodiment. (Design value), and the broken line indicates that the scanning optical device is +
This is a characteristic (effective value) when the temperature is raised by 25 ° C.

In general, when image information for each color is recorded on a plurality of photosensitive drum surfaces from a plurality of scanning optical devices and a color image is formed, registration deviation between the colors and image density unevenness between the colors are visually noticeable. In order to eliminate this, it is necessary for each scanning optical device to have a magnification shift due to environmental fluctuation (temperature fluctuation) of 40 μm or less and a focus shift in the main scanning direction and the sub-scanning direction of ± 1.0 mm or less.

In this embodiment, as shown in FIG.
The magnification (position) deviation in the main scanning direction due to the temperature rise is 31 μm, which can be suppressed to a pixel (position) deviation of about 3/4 pixel or less in the case of a printer with a resolution of 600 dpi, for example. The defocus in the main scanning direction is +0.
7 mm, and the defocus in the sub-scanning direction is -0.5 mm, both of which can be suppressed to a level causing no visual problem.

In this embodiment, the behavior at the time of raising the temperature has been mainly described. However, the same effects as described above can be obtained also in other environmental changes such as a temperature decrease.

In the present embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding, and shortening the optical path length by correcting a high angle of view aberration using an aspherical surface. Can be achieved at the same time.

As described above, in this embodiment, as described above, the toric lens 61 and the diffractive optical element 62 are used as the scanning optical element 6 of the scanning optical apparatus 11, and the plurality of scanning optical apparatuses 11, 12, 13, and 14 use the plurality of scanning optical apparatuses. Photosensitive drums 21 and
By performing image recording on the 2, 23, and 24 surfaces, a color image forming apparatus with less registration deviation between respective colors due to environmental fluctuations such as temperature rise and less image density unevenness between respective colors can be easily configured. It can be realized at low cost.

Although the color image forming apparatus in this embodiment is constituted by a plurality of scanning optical devices and a plurality of photosensitive drums corresponding to the scanning optical devices, the photosensitive drum may be constituted by a single photosensitive drum. In this case, a plurality of light beams emitted from a plurality of scanning optical devices are respectively guided to different regions on a single photosensitive drum surface, and the plurality of light beams scan the photosensitive drum surface to form a color image. You should do it. Further, in the present embodiment, the aberration change on the photosensitive drum surface caused by the environmental fluctuation is compensated for in both the main scanning direction and the sub-scanning direction. However, a satisfactory color image can be obtained by compensating only in the main scanning direction.

[Embodiment 2] FIG. 5 shows Embodiment 2 of the present invention.
FIG. 3 is a cross-sectional view of a main scanning direction main part of an optical system extracted from a plurality of scanning optical devices constituting a color image forming apparatus and a corresponding photosensitive drum. In the figure, the same elements as those shown in FIG. 3 are denoted by the same reference numerals.

The present embodiment is different from the first embodiment in that a cylindrical lens (cylindrical lens) 63a having power in the main scanning direction, instead of the long diffractive optical element 62, That is, a composite optical element 63 is used in which a diffractive optical element 63b having different powers in different directions is combined. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

That is, in the figure, reference numeral 16 denotes a scanning optical element as a third optical element having fθ characteristics, and a first optical element 16 having different powers in the main scanning direction and the sub-scanning direction.
A single plastic toric lens 61 as a refraction portion, a single plastic cylinder lens 63a as a second refraction portion having power in the main scanning direction,
The cylindrical lens 63a and the diffractive optical element 63b have a diffractive optical element 63b as a diffractive portion having different powers in the main scanning direction and the sub-scanning direction. Element) 63
Consists of

Table 2 shows the optical arrangement, the aspherical coefficients of the toric lens 61 and the cylinder lens 63a, and the phase terms of the diffractive optical element 63b in this embodiment.

[0058]

[Table 2] In the present embodiment, the aberration change in the main scanning direction and the sub-scanning direction on the surface of the photosensitive drum 21 due to the environmental change (temperature change) of the scanning optical device 11 is determined by the power change between the toric lens 61 and the composite optical element 63 and the semiconductor laser. Correction is made by the wavelength variation of 1.

FIG. 6 is an explanatory diagram showing paraxial aberrations (field curvature in the main scanning direction and the sub-scanning direction and a shift in magnification (position), etc.) before and after the environmental change in the present embodiment. (Design value), and the broken line indicates that the scanning optical device is +
This is a characteristic (effective value) when the temperature is raised by 25 ° C.

In this embodiment, a long diffractive optical element 63b is used.
Cylinder lens 63a having power in the main scanning direction
Are combined, it is possible to perform highly accurate compensation especially for a magnification (position) shift in the main scanning direction.

In the present embodiment, as shown in FIG.
The magnification (position) deviation in the main scanning direction due to the temperature rise is 4 μm, which can be suppressed to a pixel (position) deviation of about 1/10 pixel or less in the case of a printer with a resolution of 600 dpi, for example. The defocus in the main scanning direction is +0.
6 mm, and the defocus in the sub-scanning direction is -0.4 mm, which can be suppressed to a level causing no visual problem.

In the present embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding, and shortening the optical path length by correcting a high angle of view aberration using an aspherical surface. Can be achieved at the same time.

As described above, in this embodiment, as described above, the scanning optical element 16 of the scanning optical device 11 uses the toric lens 61 and the composite optical element 63 composed of the cylinder lens 63a and the diffractive optical element 63b. By performing image recording on the plurality of photosensitive drums 21, 22, 23, and 24 by the plurality of scanning optical devices 11, 12, 13, and 14, registration deviation between respective colors due to environmental fluctuations such as temperature rise is particularly high. A color image forming apparatus that is accurately compensated for and has less image density unevenness between colors can be realized at a low cost with a simple configuration.

[Embodiment 3] FIG. 7 shows Embodiment 3 of the present invention.
FIG. 3 is a cross-sectional view of a main scanning direction main part of an optical system extracted from a plurality of scanning optical devices constituting a color image forming apparatus and a corresponding photosensitive drum. In the figure, the same elements as those shown in FIG. 5 are denoted by the same reference numerals.

This embodiment is different from the second embodiment in that a diffractive optical element 64 having power in the main scanning direction is arranged near the toric lens 61.
Other configurations and optical functions are substantially the same as those of the second embodiment, and thus, similar effects are obtained.

That is, in the figure, reference numeral 26 denotes a scanning optical element as a third optical element having fθ characteristics, and a first optical element 26 having different powers in the main scanning direction and the sub-scanning direction.
, A single plastic toric lens 61 as a refracting portion, a first diffractive optical element 64 as a first diffractive portion having power in the main scanning direction disposed near the toric lens 61, and A single plastic cylinder lens 63a as a second refracting portion having power, and a second diffractive optical element 63b as a second diffracting portion having different powers in the main scanning direction and the sub-scanning direction. The cylinder lens 63a and the second
Is composed of a composite optical element (long diffraction element) 63 combined with each other.

Table 3 shows the optical arrangement, the aspheric coefficients of the toric lens 61 and the cylinder lens 63a, and the phase terms of the first and second diffractive optical elements 64 and 63b in this embodiment.

[0068]

[Table 3] In the present embodiment, the toric lens 61, the first diffractive optical element 64, and the composite optical element 63 determine the change in aberration in the main scanning direction and the sub-scanning direction on the surface of the photosensitive drum 21 due to environmental fluctuation (temperature fluctuation) of the scanning optical device 11. And the wavelength change of the semiconductor laser 1 is used for correction.

FIG. 8 is an explanatory view showing paraxial aberrations (field curvature in the main scanning direction and the sub-scanning direction and a shift in magnification (position), etc.) before and after the environmental change in the present embodiment. (Design value), and the broken line indicates that the scanning optical device is +
This is a characteristic (effective value) when the temperature is raised by 25 ° C.

In the present embodiment, in addition to the composite optical element 63, the first diffractive optical element 64 having power in the main scanning direction is arranged near the toric lens 61, so that the magnification (position) shift in the main scanning direction. Can be compensated with high accuracy,
Further, the configuration is such that almost no field curvature and distortion of the design value itself remain.

In the present embodiment, as shown in FIG.
The magnification (position) deviation in the main scanning direction due to the temperature rise is 2 μm, which can be suppressed to a pixel (position) deviation of about 1/20 pixel or less in the case of a printer with a resolution of 600 dpi, for example. The defocus in the main scanning direction is +0.
6 mm, and the defocus in the sub-scanning direction is -0.2 mm, both of which can be suppressed to a level causing no visual problem. Also, it can be seen that the aberration of the design value (before the environmental change) is well corrected as shown in FIG.

In this embodiment, all of these environmental fluctuations are compensated for by plastic optical elements, thereby reducing the manufacturing cost by molding, and shortening the optical path length by correcting the high angle of view aberration using an aspheric surface. Can be achieved at the same time.

As described above, in this embodiment, the toric lens 61, the first diffractive optical element 64, and the cylinder lens 63a and the second diffractive optical element 63b are combined as the scanning optical element 26 of the scanning optical device 11 as described above. Scanning optical devices 1 using the composite optical element 63
A plurality of photosensitive drums 21, 22, 22
By performing image recording on the surfaces 23 and 24, it is possible to easily realize a color image forming apparatus in which registration deviation between respective colors due to environmental fluctuations such as temperature rise is compensated for with high accuracy and image density unevenness between the colors is small. With the configuration, it can be realized at low cost.

As the configuration of the diffractive optical element used in each of the embodiments, for example, a single-layer kinoform-shaped single-layer configuration shown in FIG. 9 or a different grating thickness as shown in FIG. Alternatively, a two-layer structure in which two layers (the same) are stacked can be applied.

FIG. 10 shows the wavelength dependence of the diffraction efficiency of the first-order diffracted light of the diffractive optical element 101 shown in FIG. The actual configuration of the diffractive optical element 101 is such that an ultraviolet-curing resin is applied to the surface of the base material 102, and a layer 10 having a grating thickness d such that the diffraction efficiency of the first-order diffracted light at a wavelength of 530 nm becomes 100% at the resin portion.
3 is formed.

As is apparent from FIG. 10, the diffraction efficiency of the design order decreases as the distance from the optimized wavelength of 530 nm increases, while the diffraction efficiencies of the zero-order diffraction light and the second-order diffraction light of the orders near the design order increase. An increase in diffracted light other than the design order causes a flare, leading to a decrease in the resolution of the optical system.

FIG. 12 shows the wavelength dependence of the diffraction efficiency of the first-order diffracted light of the laminated diffractive optical element in which the two layers 104 and 105 shown in FIG. 11 are laminated.

In FIG. 11, a first layer 10 made of an ultraviolet curable resin (nd = 1.499, νd = 54) is formed on a base material 102.
4 is formed thereon, and another ultraviolet curable resin (nd = 1.
598, νd = 28). In this combination of materials, the lattice thickness d1 of the first layer 104 is d1 = 13.8 μm, and the lattice thickness d2 of the second layer 105 is
Is d2 = 10.5 μm.

As can be seen from FIG. 12, the diffraction efficiency of the design order has a high diffraction efficiency of 95% or more over the entire use wavelength range by using a diffractive optical element having a laminated structure.

The material of the diffractive optical element having the above-mentioned laminated structure is not limited to the ultraviolet curable resin, but other plastic materials can be used. Depending on the base material, the first layer 104 may be directly applied to the base material. It may be formed. Further, the lattice thicknesses do not necessarily have to be different, and depending on the combination of materials, the lattice thicknesses of the two layers 104 and 105 may be equal as shown in FIG.

In this case, since the lattice shape is not formed on the surface of the diffractive optical element, it is excellent in dust resistance and the workability of assembling the diffractive optical element can be improved.

[0082]

As described above, according to the present invention, in a color image forming apparatus having a plurality of scanning optical devices as described above, the change in aberration caused by the environmental fluctuation of each scanning optical device is refracted by the scanning optical element of each device. By compensating for the power change between the part and the diffraction part and the wavelength fluctuation of the semiconductor laser, respectively,
It is possible to achieve a compact color image forming apparatus suitable for high-definition printing, with a simple configuration, capable of suppressing the registration deviation between the colors and the image density unevenness between the colors.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of a color image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part showing the scanning optical device shown in FIG. 1 and an image carrier corresponding thereto.

3 is a sectional view of a main part of the optical system shown in FIG. 2 in a main scanning direction.

FIG. 4 is a paraxial aberration diagram of the scanning optical device according to the first embodiment of the present invention.

FIG. 5 is a sectional view of a main part of an optical system of a scanning optical device constituting a color image forming apparatus according to a second embodiment of the present invention in a main scanning direction.

FIG. 6 is a paraxial aberration diagram of the scanning optical device according to the second embodiment of the present invention.

FIG. 7 is a sectional view of a main part of an optical system of a scanning optical device constituting a color image forming apparatus according to a third embodiment of the present invention in a main scanning direction.

FIG. 8 is a paraxial aberration diagram of the scanning optical device according to the third embodiment of the present invention.

FIG. 9 is an explanatory diagram of a diffractive optical element according to the present invention.

FIG. 10 is an explanatory diagram of a wavelength dependence characteristic of the diffractive optical element according to the present invention.

FIG. 11 is an explanatory diagram of a diffractive optical element according to the present invention.

FIG. 12 is an explanatory diagram of a wavelength dependence characteristic of the diffractive optical element according to the present invention.

FIG. 13 is an explanatory view of a diffractive optical element according to the present invention.

FIG. 14 is a sectional view of a main portion of a conventional scanning optical device in a main scanning direction.

FIG. 15 is a schematic view of a main part of a conventional color image forming apparatus.

[Explanation of symbols]

Reference Signs List 1 light source means (semiconductor laser) 2 first optical element (collimator lens) 3 aperture stop 4 second optical element (cylinder lens) 5 deflection element (optical deflector) 6, 16, 26 third optical element ( Scanning optical element 61 Toric lens 62 Diffractive optical element 63 Composite optical element (cylinder lens + diffractive optical element) 64 Diffractive optical element 11, 12, 13, 14 Scanning optical device 21, 22, 23, 24 Image carrier (photosensitive drum) ) 31, 32, 33, 34 Developing device 41 Conveyor belt

Claims (32)

[Claims] 1. A plurality of scanning optical devices each having a light source means including a semiconductor laser and an optical element including a refraction unit and a diffraction unit are provided, and a plurality of light beams emitted from each scanning optical device are converted into a single image. A color image forming apparatus that guides light to different regions on a surface of a carrier and forms a color image by scanning the surface of the image carrier with the plurality of light beams, wherein the plurality of scanning optical devices each include the scanning optical device. Aberration changes in the main scanning direction on the surface of the image carrier due to fluctuations in the environment of the apparatus are corrected by a power change between a refraction portion and a diffraction portion of the optical element and a wavelength change of the semiconductor laser. A color image forming apparatus. 2. The color image forming apparatus according to claim 1, wherein the change in aberration in the main scanning direction is a change in magnification. 3. The color image forming apparatus according to claim 1, wherein the change in aberration in the main scanning direction is a change in focus. 4. A plurality of scanning optical devices each having light source means including a semiconductor laser and an optical element including a refraction unit and a diffraction unit, and a plurality of light beams emitted from each scanning optical device are converted into a single image. A color image forming apparatus that guides light to different regions on a surface of a carrier and forms a color image by scanning the surface of the image carrier with the plurality of light beams, wherein the plurality of scanning optical devices each include the scanning optical device. Aberration changes in the main scanning direction and sub-scanning direction on the surface of the image carrier due to environmental fluctuations of the apparatus are corrected by power changes in the refraction and diffraction portions of the optical element and wavelength fluctuations of the semiconductor laser. A color image forming apparatus comprising: 5. The color image forming apparatus according to claim 4, wherein the change in aberration in the main scanning direction is a change in magnification and / or a change in focus, and the change in aberration in the sub-scanning direction is a change in focus. 6. The refracting portion of the optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and the diffractive portion of the optical element has a main scanning direction and a sub-scanning direction. 5. The apparatus according to claim 1, further comprising a diffractive optical element having different powers.
Color image forming apparatus. 7. A refracting portion of the optical element includes a plastic toric lens having different powers in a main scanning direction and a sub-scanning direction and a cylinder lens having power in a main scanning direction. The diffractive portion has a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and the cylinder lens and the diffractive optical element are composed of a composite optical element combined with each other. 1 or 4 color image forming apparatus. 8. A refracting portion of the optical element includes a plastic toric lens having different powers in a main scanning direction and a sub-scanning direction and a cylinder lens having power in a main scanning direction. The diffraction section has a first diffractive optical element having power in the main scanning direction and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction. 5. The color image forming apparatus according to claim 1, wherein the cylinder lens and the second diffractive optical element are arranged in the vicinity of the toric lens, and are composed of a composite optical element combined with each other. 9. A plurality of scanning optical devices each having a light source unit including a semiconductor laser and an optical element including a refraction unit and a diffraction unit, and a plurality of light beams emitted from the respective scanning optical devices are respectively associated with the plurality of scanning optical devices. A color image forming apparatus that guides light onto the surface of the image carrier and scans each of the plurality of image carriers with the plurality of light beams to form a color image, wherein the plurality of scanning optical devices each perform the scanning. An aberration change in the main scanning direction on the surface of the image carrier due to an environment change of the optical device is corrected by a power change between a refraction portion and a diffraction portion of the optical element and a wavelength change of the semiconductor laser. A color image forming apparatus, comprising: 10. The color image forming apparatus according to claim 9, wherein the change in aberration in the main scanning direction is a change in magnification. 11. The color image forming apparatus according to claim 9, wherein the change in aberration in the main scanning direction is a change in focus. 12. A plurality of scanning optical devices each having a light source means including a semiconductor laser, and an optical element including a refraction unit and a diffraction unit, and a plurality of light beams emitted from the respective scanning optical devices respectively corresponding to the plurality of scanning optical devices. A color image forming apparatus that guides light onto the surface of the image carrier and scans each of the plurality of image carriers with the plurality of light beams to form a color image, wherein the plurality of scanning optical devices each perform the scanning. Aberration changes in the main scanning direction and the sub-scanning direction on the surface of the image carrier due to environmental fluctuations of the optical device are corrected by a power change between a refraction section and a diffraction section of the optical element and a wavelength fluctuation of the semiconductor laser. A color image forming apparatus. 13. The color image forming apparatus according to claim 12, wherein the change in aberration in the main scanning direction is a change in magnification and / or a change in focus, and the change in aberration in the sub-scanning direction is a change in focus. 14. The refracting portion of the optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and the diffractive portion of the optical element has a main scanning direction and a sub-scanning direction. 13. The color image forming apparatus according to claim 9, further comprising a diffractive optical element having different powers. 15. The refracting portion of the optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction. The diffractive portion has a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and the cylinder lens and the diffractive optical element are composed of a composite optical element combined with each other. 9 or 12 color image forming apparatus. 16. The refracting portion of the optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction and a cylinder lens having power in the main scanning direction. The diffraction section has a first diffractive optical element having power in the main scanning direction and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction. 13. The color image forming apparatus according to claim 9, wherein the cylinder lens and the second diffractive optical element are arranged in the vicinity of the toric lens, and comprise a composite optical element combined with each other. 17. A color image by guiding a plurality of light beams emitted from a plurality of scanning optical devices to different regions on a single image carrier surface and scanning the image carrier surface with the plurality of light beams. A plurality of scanning optical devices, wherein each of the plurality of scanning optical devices includes a light source unit including a semiconductor laser, a first optical element that converts a light beam emitted from the light source unit into a substantially parallel light beam, A second optical element for forming a substantially parallel light beam into a line image elongated in the main scanning direction on the deflection surface of the deflection element, and a refraction for forming the light beam deflected by the deflection element into a spot on the image carrier surface; A third optical element having a portion and a diffractive portion, wherein each of the plurality of scanning optical devices has an aberration change in the main scanning direction on the image carrier surface due to an environmental change of the scanning optical device. The path between the refraction part and the diffraction part of the third optical element A color image forming apparatus, wherein the color image forming apparatus is adapted to be corrected by a power change and a wavelength fluctuation of the semiconductor laser. 18. The color image forming apparatus according to claim 17, wherein the change in aberration in the main scanning direction is a change in magnification. 19. The color image forming apparatus according to claim 17, wherein the change in aberration in the main scanning direction is a change in focus. 20. A plurality of light beams emitted from a plurality of scanning optical devices are respectively guided to different areas on a single image carrier surface, and the plurality of light beams scan the image carrier surface to form a color image. A plurality of scanning optical devices, wherein each of the plurality of scanning optical devices includes a light source unit including a semiconductor laser, a first optical element that converts a light beam emitted from the light source unit into a substantially parallel light beam, A second optical element for forming a substantially parallel light beam into a line image elongated in the main scanning direction on the deflection surface of the deflection element, and a refraction for forming the light beam deflected by the deflection element into a spot on the image carrier surface; A third optical element having a portion and a diffractive portion, wherein each of the plurality of scanning optical devices has an aberration in a main scanning direction and a sub-scanning direction on the image carrier surface due to an environmental change of the scanning optical device. The change is the refractive portion of the third optical element. A power variation of the diffraction portion, a color image forming apparatus, characterized in that so as to be corrected by the wavelength variation of the semiconductor laser. 21. The color image forming apparatus according to claim 20, wherein the change in aberration in the main scanning direction is a change in magnification and / or a change in focus, and the change in aberration in the sub-scanning direction is a change in focus. 22. The refracting portion of the third optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and the diffractive portion of the third optical element has a main scanning direction. 2. The color image forming apparatus according to claim 1, further comprising a diffractive optical element having different powers in the direction and the sub-scanning direction. 23. The refracting portion of the third optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and a cylinder lens having power in the main scanning direction. The diffractive portion of the third optical element has a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and the cylinder lens and the diffractive optical element are composed of a composite optical element combined with each other. 21. The color image forming apparatus according to claim 17, wherein: 24. The refracting portion of the third optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and a cylinder lens having power in the main scanning direction. The diffractive portion of the third optical element includes a first diffractive optical element having power in the main scanning direction and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction. 18. The diffractive optical element according to claim 17, wherein the first diffractive optical element is disposed near the toric lens, and the cylinder lens and the second diffractive optical element are combined optical elements.
Or 20 color image forming apparatuses. 25. A plurality of light beams emitted from a plurality of scanning optical devices are guided on a plurality of corresponding image carrier surfaces, respectively.
In a color image forming apparatus for forming a color image by scanning each of the plurality of light beams on the surface of the plurality of image carriers, the plurality of scanning optical devices each include light source means including a semiconductor laser, and light emitted from the light source means. A first optical element that converts the light beam into a substantially parallel light beam, a second optical element that forms the converted substantially parallel light beam into a line image that is long in the main scanning direction on the deflection surface of the deflection element, A third optical element having a refraction part and a diffraction part for forming a light beam deflected by the element in a spot shape on the surface of the image carrier, wherein the plurality of scanning optical devices are respectively provided by the scanning optical device. An aberration change in the main scanning direction on the surface of the image carrier due to an environmental change is corrected by a power change of the refraction portion and the diffraction portion of the third optical element and a wavelength change of the semiconductor laser. A color image characterized by Forming apparatus. 26. The color image forming apparatus according to claim 25, wherein the change in aberration in the main scanning direction is a change in magnification. 27. The color image forming apparatus according to claim 25, wherein the change in aberration in the main scanning direction is a change in focus. 28. A plurality of light beams emitted from a plurality of scanning optical devices are guided on a plurality of corresponding image carrier surfaces, respectively.
In a color image forming apparatus for forming a color image by scanning each of the plurality of light beams on the surface of the plurality of image carriers, the plurality of scanning optical devices each include light source means including a semiconductor laser, and light emitted from the light source means. A first optical element that converts the light beam into a substantially parallel light beam, a second optical element that forms the converted substantially parallel light beam into a line image that is long in the main scanning direction on the deflection surface of the deflection element, A third optical element having a refraction part and a diffraction part for forming a light beam deflected by the element in a spot shape on the surface of the image carrier, wherein the plurality of scanning optical devices are respectively provided by the scanning optical device. Aberration changes in the main scanning direction and the sub-scanning direction on the surface of the image carrier due to environmental fluctuations are corrected by a power change between the refraction portion and the diffraction portion of the third optical element and a wavelength change of the semiconductor laser. It is characterized by Color image forming apparatus. 29. The color image forming apparatus according to claim 25, wherein the change in aberration in the main scanning direction is a change in magnification and / or a change in focus, and the change in aberration in the sub-scanning direction is a change in focus. . 30. The refracting portion of the third optical element has a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and the diffractive portion of the third optical element has a main scanning direction. 30. The color image forming apparatus according to claim 29, further comprising a diffractive optical element having different powers in the direction and the sub-scanning direction. 31. A refracting portion of the third optical element includes a plastic toric lens having different powers in a main scanning direction and a sub-scanning direction, and a cylinder lens having power in a main scanning direction. The diffractive portion of the third optical element has a diffractive optical element having different powers in the main scanning direction and the sub-scanning direction, and the cylinder lens and the diffractive optical element are composed of a composite optical element combined with each other. 29. The color image forming apparatus according to claim 25, wherein: 32. The refracting portion of the third optical element includes a plastic toric lens having different powers in the main scanning direction and the sub-scanning direction, and a cylinder lens having power in the main scanning direction. The diffractive portion of the third optical element includes a first diffractive optical element having power in the main scanning direction and a second diffractive optical element having different powers in the main scanning direction and the sub-scanning direction. 26. The diffractive optical element according to claim 25, wherein the first diffractive optical element is disposed near the toric lens, and the cylinder lens and the second diffractive optical element comprise a combined optical element.
Or 28 color image forming apparatus.