JPH09184991A - Optical scanning device and image forming device utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multi-beam optical scanning device which suppresses the curvature of main scanning lines and increases the picture quality of a print image by providing an image forming means or the like which image-forms plural light beams scanned by a scanning means at specified positions on an object to be scanned, etc. SOLUTION: An after-deflection optical system 21 gives specified aberrational characteristics to four laser beams L deflected by respective surfaces of an optical deflection device 5 over the entire area of the length direction of the horizontal scanning direction of a laser beam L (Y, M, C, and B) deflected by the optical deflection device 5 to a photoreceptor drum 58. Further, this device has 1st-3rd image forming lenses 27, 29, and 31 as optical means for suppressing variation of the image of formation plane of the laser beam L within a certain range. Further, dustproof glass parts 39Y, 39M, 39C, and 39B are arranged where the four laser beams L are emitted from the multi-beam optical scanning device 1. Consequently, the horizontal scanning line curvature of the laser beam L is suppressed and the laser beam is guided to the photoreceptor drum 58.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam optical scanning apparatus for scanning a plurality of beams, which can be used in a multi-drum type color printer, a multi-drum type color copier, a high-speed laser printer or a digital copier. The present invention relates to an image forming apparatus using a multi-beam optical scanning device.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as a multi-drum type color printer or a multi-drum type color copier, a plurality of image forming sections corresponding to color separated color components and a color image forming section A laser exposure device or optical scanning device is used which provides image data corresponding to the component, that is, a plurality of laser beams.

In this type of image forming apparatus, there are an example in which a plurality of optical scanning devices are arranged corresponding to each image forming section, and a multi-beam optical scanning device formed so as to be able to provide a plurality of laser beams. It is known that they are arranged.

In general, an optical scanning device includes a semiconductor laser element as a light source, a first lens group for narrowing a beam diameter of a laser beam emitted from the laser element to a predetermined size,
An optical deflecting device that continuously reflects the laser beam narrowed down by the first lens group in a direction orthogonal to the direction in which the recording medium is conveyed; and a laser beam deflected by the optical deflecting device at a predetermined position on the recording medium. It has a second lens group to form an image. In many cases, the direction in which the laser beam is deflected by the optical deflecting device is referred to as the main scanning direction, and the direction in which the recording medium is transported, that is, the direction orthogonal to the main scanning direction is referred to as the sub-scanning direction.

The multi-beam optical scanning device includes a semiconductor laser element which is a light source, a cylinder lens, an fθ lens, etc., where N is the number of multi-beams, as disclosed in Japanese Patent Laid-Open No. 5-83485. There is an example in which N sets of lens groups and N / 2 sets of optical deflectors are used. That is, in the example disclosed in JP-A-5-83485, in the case of four laser beams, four sets of laser elements and lens groups and two sets of optical deflectors are used.

Separately from this, two groups of fθ lenses are prepared,
All the laser beams deflected by the optical deflector are made incident while only one set of the first fθ lens group close to the optical deflector is made incident, while the second fθ lens group distant from the optical deflector makes all the laser beams. An example in which a plurality of sheets corresponding to each of the above is used is also proposed. That is, in this example, in the case of 4 laser beams, only 4 sets of the second fθ lens are used.

Japanese Patent Application No. 62-232344 discloses f
A method is disclosed in which only one set of θ lens groups is provided, a toric surface is arranged on at least one lens surface of the fθ lens group, and all the laser beams are incident on the same fθ lens.

Further, Japanese Patent Laid-Open No. 5-34612 discloses that
A method of utilizing a plurality of half mirrors to sequentially superimpose four laser beams as a laser beam that can be regarded as one laser beam and guide the laser beams to an optical deflector is shown.

[0009]

[Patent Document 1] Japanese Patent Application Laid-Open No. 5-83485
When the multi-beam optical scanning device seen in the publication is used, compared with the case where a plurality of optical scanning devices are used,
Although the size of the space occupied by the optical scanning device is reduced, as the optical scanning device alone, the cost of parts and assembly increases due to the increase in the number of lenses or mirrors, or the optical scanning device alone. There is an increase in size and weight. Also, due to the shape error of the fθ lens, the individual error, the mounting error, or the like, the bending of the main scanning line of the laser beam for each color component, or fθ
It is known that the deviation of the aberration characteristic represented by the characteristic and the like on the image plane becomes non-uniform.

In an example in which only the first fθ lens is commonly used, the above-mentioned JP-A-5-8348 may be caused by a shape error, a solid error or a mounting error of the second fθ lens.
There is a problem that the same inconvenience as in the example seen in Japanese Patent Publication No. 5 occurs.

Further, in the example disclosed in Japanese Patent Application No. 62-232344, since only the toric surface whose shape is not optimized is arranged, it is mainly applied to any one of a plurality of laser beams. There is a problem that scan line bending occurs. An example in which a part of the laser beam directed to the scanning device is controlled in the optical axis direction has been proposed in connection with the above-mentioned Japanese Patent Laid-Open No. 62-232344, but the aberration characteristics are sufficiently sufficient in all the imaging regions. Is difficult to correct.

Further, in the example disclosed in Japanese Patent Application No. 62-232344, since the amount of change in the refractive index of the lens formed of plastic due to the temperature change is relatively large, a wide range of environmental conditions, especially Under the temperature condition, there is a problem that characteristics such as field curvature, main scanning line curvature, or fθ characteristic vary greatly. In this example, however, various conditions such as achromaticity, field curvature, field distortion, and lateral magnification must be satisfied, especially in the entire area in the sub-scanning direction, so that there is a problem that the number of lenses is increased. At the same time, in order to ensure the parallelism of the main scanning lines of each laser beam, the accuracy of the housing must be made extremely high, which increases the cost.

In addition, as shown in some of the above-mentioned publications, in order to guide the main scanning lines of the laser beam from the laser element in parallel to each other in each of the plurality of image forming sections. Must be adjusted with certainty because the angle error of each mirror is multiplied each time the number of mirrors is increased, or the accuracy of the housing must be very high. It is known that it must be.

This not only increases the cost for the adjustment work, but also causes the main scanning due to factors other than the positional deviation of the mirror, which is represented by the inclination of the rotation axis of the deflecting device or the inclination of the toric lens around the optical axis. Since the inclinations of the lines cannot be separated, the inclinations of the main scanning lines due to these causes are also adjusted at the mirror position, so that their mutual positions are increasingly displaced from the designed values, causing deterioration such as field curvature. Is also known.

In view of these proposals, in order to reduce the size and cost of the multi-beam optical scanning device,
Only one set of the imaging lens, that is, the fθ lens is arranged for all the laser beams, and further, the optical path of the laser beam that passes through the fθ lens and goes to the photosensitive drum, that is, the laser beam, is formed by a plurality of reflection mirrors. It will be appreciated that folding is beneficial.

However, when the plurality of reflecting mirrors are arranged so as to be movable only in one of the rotation direction and the parallel movement direction, the parallelism of the respective laser beams which have passed through the fθ lens and are directed toward the photosensitive drum is increased. It is known that it is substantially difficult to adjust both the defocus amount and the defocus amount at the same time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-beam optical scanning device capable of suppressing the bending of the main scanning line and improving the quality of a printed image, and an image forming apparatus to which the optical scanning device is applied. .

[0018]

According to the present invention, in order to achieve the above object, a scanning means for scanning a plurality of light beams toward an object to be scanned, and a scanning means for each of the plurality of light beams are provided. Optical means for giving a predetermined optical characteristic, reflecting means arranged between the optical means and the scanning object corresponding to each of the plurality of light beams, and by the reflecting means, heading for the scanning object. Optical path correction means for correcting the scanning position shifts of the plurality of light beams toward the scanning object with respect to the optical paths of the plurality of light beams and tilted at an angle such that the transmittance is within a predetermined range. And an image forming unit that forms an image of the plurality of light beams scanned by the scanning unit on a predetermined position of the object to be scanned, and an optical scanning device.

Further, according to the present invention, the scanning means for scanning the plurality of light beams toward the object to be scanned, the optical means for giving a predetermined optical characteristic to each of the plurality of light beams, and the optical means. A reflecting means disposed between the means and the scanning object corresponding to each of the plurality of light beams, and an incident surface for an optical path of the plurality of light beams toward the scanning object by the reflecting means. An optical path correcting means fixed non-vertically, and an image forming means for forming an image of the plurality of light beams scanned by the scanning means on a predetermined position of the scanning object. The means is tan {θ-sin ^-1 (sin θ / n)} / tan {where n is the refractive index of the optical path correcting means and θ is the incident angle of the light beam with respect to the normal to the incident surface of the optical path correcting means. θ + sin ^-1 (s
in θ / n)} = 0.1, where θ is Θ, the optical scanning is characterized in that the angle is fixed at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg). A device is provided.

Further, according to the present invention, scanning means for scanning the plurality of light beams toward the object to be scanned, and at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams. A reflecting means disposed between the optical means and the scanning object corresponding to each of the plurality of light beams, and an optical path of the plurality of light beams toward the scanning object by the reflecting means. A plurality of light beams directed toward the object to be scanned are offset, and a parallel plate that is inclined at an angle such that the transmittance is within a predetermined range is scanned by the scanning unit. An optical scanning device comprising: an image forming unit that forms an image of a plurality of light beams on a predetermined position of the scanning object; and a housing unit that houses the scanning unit and the image forming unit. Provided That.

Further, according to the present invention, scanning means for scanning the plurality of light beams toward the object to be scanned, and at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams. A reflecting means disposed between the optical means and the scanning object corresponding to each of the plurality of light beams, and an optical path of the plurality of light beams toward the scanning object by the reflecting means. And a parallel flat plate whose incident surface is non-perpendicularly arranged, and which forms an image of the plurality of light beams scanned by the scanning device at a predetermined position of the scanning object; and the scanning. Means and an accommodating means for accommodating the image forming means, wherein the parallel plate has a refractive index of the parallel plate of n, and an incident angle of the light beam with respect to a normal to an incident surface of the parallel plate is θ, tan {θ-sin ^-1 (sin θ / n)} / tan {θ + sin ^-1 (s
In θ / n)} = 0.1, when θ is Θ, it is fixed to the accommodating means at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg). An optical scanning device is provided.

Further, according to the present invention, a plurality of light sources, each of which is intensity-modulated according to image data and corresponds to a plurality of color components respectively, and a light beam emitted from each of the plurality of light sources, First optical means including: a first optical member that gives a predetermined optical characteristic; and a second optical member that focuses each of the plurality of light beams given the optical characteristic by the first optical member in a first direction. Scanning means for scanning a plurality of light beams that have passed through the first optical means toward an object to be scanned, and at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams, With respect to the optical means and the optical path of the plurality of light beams toward the scanning object by the reflection means, which is arranged corresponding to each of the plurality of light beams between the object to be scanned, Before The plurality of light beams scanned by the scanning means include a parallel flat plate that corrects scanning position deviations of a plurality of light beams toward a scanning object and is inclined at an angle such that the transmittance is within a predetermined range. A second optical means for forming an image of the beam at a predetermined position on the scanning object; an accommodating means for accommodating the scanning means and the image forming means; and a first optical means, a scanning means, and a second optical means. A plurality of image carriers for holding respective images corresponding to the respective light beams emitted from the plurality of light sources guided through the image carriers, and the image carriers arranged corresponding to the plurality of image carriers, respectively. A plurality of developing means for visualizing the image held on,
An image forming apparatus comprising:

Further, according to the present invention, a plurality of light sources which are intensity-modulated according to image data and respectively correspond to a plurality of color components, and a light beam emitted from each of the plurality of light sources are provided. First optical means including: a first optical member that gives a predetermined optical characteristic; and a second optical member that focuses each of the plurality of light beams given the optical characteristic by the first optical member in a first direction. Scanning means for scanning a plurality of light beams that have passed through the first optical means toward an object to be scanned, and at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams, Reflecting means arranged between the optical means and the scanning object corresponding to each of the plurality of light beams, and incident on the optical paths of the plurality of light beams toward the scanning object by the reflecting means. surface Parallel flat plate disposed so non-perpendicular,
Second optical means for forming an image of the plurality of light beams scanned by the scanning means on a predetermined position of the object to be scanned, an accommodating means for accommodating the scanning means and the imaging means, and A plurality of image carriers for holding respective images corresponding to the respective light beams emitted from the plurality of light sources guided through the first optical means, the scanning means, and the second optical means, and the plurality of images. A plurality of developing means arranged corresponding to each of the carriers and visualizing an image held on the image carrier, wherein the parallel plate has a refractive index n of the parallel plate, Letting θ be the incident angle of the light beam with respect to the normal to the incident surface, tan {θ−sin ⁻¹ (sin θ / n)} / tan {θ + sin ⁻¹ (s
In θ / n)} = 0.1, when θ is Θ, it is fixed to the accommodating means at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg). An image forming apparatus is provided.

According to the optical scanning device of the present invention, the light beams emitted from the plurality of light sources are directed to the predetermined scanning object by the scanning means after the predetermined optical characteristics are given by the first optical means. Be scanned. The plurality of light beams scanned by the scanning means are guided to the object to be scanned by the reflecting means after given predetermined optical characteristics by at least one set of optical means. The plurality of light sources, the first optical means, the scanning means, the pair of optical means, and the reflecting means are housed in one housing means.

At the position between the reflecting means and the object to be scanned, that is, the position at which the light beam reflected by the reflecting means is emitted from the accommodating means, a parallel plate for dust-proofing the inside of the optical scanning device is provided. It is arranged, tilted at a predetermined angle, and fixed to the accommodating means. The parallel flat plate is capable of correcting the scanning position shifts of the plurality of light beams toward the scanning target with respect to the optical paths of the plurality of light beams toward the scanning target by the reflecting means, and within a range where a predetermined transmittance can be secured. It is tilted and fixed at an angle of.

According to the present invention, the deviation of the scanning position of the light beam can be corrected by inclining the parallel plate by 0.3 deg or more. However, the light beam which substantially passes through the parallel plate as the tilt angle increases. The optical path length also increases, and the transmittance is lost due to internal absorption or scattering. The permissible range of the loss of transmittance is within 10%.

Therefore, letting n be the refractive index of the parallel plate and θ be the incident angle of the light beam with respect to the normal to the plane of incidence of the parallel plate, the incident angle of the light beam at which the transmittance is lost by 10%,
That is, the inclination angle θ of the parallel plate is tan {θ−sin ⁻¹ (sin θ / n)} / tan {θ + sin ⁻¹ (s
in θ / n)} = 0.1. When θ that satisfies this expression is Θ, by tilting the parallel plate at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg) and fixing it to the accommodating means, the light beam is effectively scanned. Positional deviation can be corrected.

Further, according to the image forming apparatus equipped with this optical scanning device, the light beam emitted from the optical scanning device is guided to a predetermined scanning object while suppressing the main scanning line bending, so The deviation of each dot position of the print image due to the deviation of the scanning position of the beam is suppressed, and the quality of the print image can be improved.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an optical scanning device of the present invention and an image forming apparatus using the optical scanning device will be described in detail below with reference to the drawings.

FIG. 1 is a front sectional view of a four-drum type color image forming apparatus incorporating a multi-color optical scanning device according to an embodiment of the present invention. Incidentally, in this type of color image forming apparatus, four types of image data separated into color components of Y or yellow, M or magenta, C or cyan and B or black (black), and Y or M are usually used. , C and B, four sets of various devices for forming an image for each color component are used. Therefore, by adding Y, M, C and B to each reference symbol, It is assumed that each image data and the corresponding device are identified.

As shown in FIG. 1, the image forming apparatus 100.
Is a first to fourth image forming section 50Y, 50M, 5 that forms an image for each color separated color component, that is, Y = yellow, M = magenta, C = cyan, and B = black.
It has 0C and 50B.

Each image forming section 50 (Y, M, C and B)
Is the third folding mirror 37Y, 37 of the optical scanning device 1.
50Y below the optical scanning device 1 corresponding to the position where the laser beam L (Y, M, C and B) corresponding to each color component image is emitted via M, 37C and the first folding mirror 33B. , 50M, 50C and 50B are arranged in series in this order.

Below the respective image forming sections 50 (Y, M, C and B), a transfer material on which the images formed by the respective image forming sections 50 (Y, M, C and B) are transferred is conveyed. A conveyor belt 52 is disposed.

The conveyor belt 52 is wound around a belt drive roller 56 and a tension roller 54 which are rotated in the direction of the arrow by a motor (not shown), and is rotated at a predetermined speed in the direction in which the belt drive roller 56 is rotated.

Each image forming section 50 (Y, M, C and B)
Are photosensitive drums 58 each having a cylindrical drum shape and formed so as to be rotatable in the direction of the arrow, and functioning as an image carrier on which an electrostatic latent image corresponding to image information to be printed is formed.
It has Y, 58M, 58C and 58B.

The photoconductor drums 58 (Y, M, C and B) are provided at predetermined positions around the photoconductor drums 58 (Y, M, C and B).
Charging devices 60Y, 60M, 60C and 60B for providing a predetermined surface potential on the surface of (Y, M, C and B), and static electricity formed on the surface of each photoconductor drum 58 (Y, M, C and B). Developing devices 62Y, 6 functioning as developing means for developing the electrostatic latent image with toner given a corresponding color.
2M, 62C and 62B, and the conveying belt 52 is interposed between the photosensitive drum 58 (Y, M, C and B) and is opposed to the photosensitive drum 58 (Y, M, C and B) and conveyed. The recording paper P transported via the belt 52 or the transport belt 52 is attached to each of the photoconductor drums 58 (Y, M, C).
And B) transfer devices 64Y, 6 for transferring the toner image on
4M, 64C and 64B, transfer device 64 (Y, M, C
And cleaners 66Y, 66M, 66C and 66B for removing the residual toner remaining on the surface of the photosensitive drum 58 (Y, M, C and B) after the toner image is transferred through the transfer device 64 and the transfer device 64. (I, M, C and B), a static eliminator 68Y, 68M for removing residual potentials remaining on the respective photoconductor drums 58 (Y, M, C and B) after the toner image is transferred via (Y, M, C and B). 68C and 68B
Are sequentially arranged along the rotation direction of each photosensitive drum 58 (Y, M, C and B).

The respective mirrors 37Y, 3 of the optical scanning device 1 are
Laser beams LY, LM, LC and LB guided by 7M, 37C and 33B are respectively charged to respective charging devices 60 (Y, M, C and B) and developing devices 62 (Y,
Between M, C and B).

Below the conveyor belt 52, a paper cassette 70 for accommodating a recording medium, that is, a paper P for transferring an image formed by each image forming section 50 (Y, M, C and B) is arranged. ing.

At one end of the paper cassette 70 and in the vicinity of the tension roller 54, a half-moon roller (feeding roller) 72 for taking out the paper P stored in the paper cassette 70 one by one (from the top) is arranged. Has been done. Between the delivery roller 72 and the tension roller 54,
The leading edge of one sheet of paper P taken out from the cassette 70 and each image forming unit 50 (Y, M, C and B), especially 50B
Accordingly, a registration roller 74 for aligning each of the photoconductor drums 58 (Y, M, C and B), particularly, the tip of the toner image formed on 58B is arranged.

Registration roller 74 and first image forming section 5
0Y, in the vicinity of the tension roller 54, substantially with the conveyor belt 52 interposed therebetween.
A suction roller 76 that provides a predetermined electrostatic suction force to one sheet of paper P that is conveyed at a predetermined timing via the registration roller 72 is disposed on the outer circumference of the sheet. The axis of the suction roller 76 and the tension roller 54 are arranged in parallel.

At one end of the conveyor belt 52, in the vicinity of the belt drive roller 56, and substantially on the outer periphery of the belt drive roller 56 with the conveyor belt 52 interposed therebetween, the conveyor belt 52 is provided.
Alternatively, registration sensors 78 and 80 for detecting the position of the image formed on the sheet P conveyed by the conveyor belt are arranged at a predetermined distance in the axial direction of the belt drive roller 56 (FIG. 1). Is a front sectional view, so only the rear sensor 80 is shown).

On the conveyor belt 52 corresponding to the outer periphery of the belt drive roller 56, a conveyor belt cleaner 82 for removing toner adhering to the conveyor belt 52 or paper dust on the paper P is arranged.

Paper P conveyed through the conveyor belt 52
A fixing device 84 that fixes the toner image transferred to the sheet P to the sheet P is disposed in a direction in which the toner image is separated from the tension roller 56 and further conveyed.

FIG. 2 and FIG. 3 are a schematic plan view and a schematic sectional view of the multi-beam optical scanning device according to the embodiment of the present invention with the housing removed. As already described with reference to FIG. 1, in the color laser beam printer shown in FIG.
Y, magenta = M, cyan = C, and black = B, four types of color-separated image data for each color component;
Since four sets of various devices that form images for each color component corresponding to M, C, and B are used, similarly, by adding Y, M, C, and B to each reference numeral, , The image data for each color component and the corresponding device are identified.

As shown in FIG. 2, the multi-beam optical scanning device 1 includes first to fourth semiconductors as light sources for generating laser beams LY, LM, LC and LB corresponding to image data for each color component. Lasers (hereinafter referred to as laser elements) 3Y, 3M, 3C and 3B, and laser beams L (Y, M, C and B) emitted from the respective laser elements 3 (Y, M, C and B) , The object placed at a predetermined position, that is, the first of the image forming apparatus 100.
To the photosensitive drums 58Y, 58M and 58 of the fourth image forming units 50Y, 50M, 50C and 50B, respectively.
It is composed of an optical deflecting device 5 as scanning means for scanning or deflecting toward C and 58B at a predetermined linear velocity.

Each of the laser elements 3Y, 3M, 3C and 3B is set at a predetermined angle with respect to the optical deflector 5 and is set at 3 degrees.
They are arranged in the order of Y, 3M, 3C and 3B. The laser element 3B, that is, the laser element corresponding to the black (B) image is arranged so that it can be directly incident on the reflection surface of the optical deflector 5.

Between each laser element 3 (Y, M, C and B) and the optical deflector 5, the laser element 3 (Y,
Pre-deflection optical system 7Y, 7M functioning as a light source side optical system for adjusting the cross-sectional beam spot shape of the laser beam L (Y, M, C, B) from M, C and B) to a predetermined shape , 7C and 7B are arranged.

The light deflecting device 5 is, for example, a polygonal mirror body 5a in which eight plane reflecting mirrors (planes) are arranged in a regular polygonal shape.
And a polygonal mirror body 5a is constituted by a motor 5m for rotating the polygonal mirror body 5a in a predetermined direction at a constant speed. The polygon mirror body 5a is made of, for example, an aluminum alloy.

Pre-deflection optical system 7 (Y, M, C and B)
For each laser beam L (Y, M, C and B) emitted by each laser element 3 (Y, M, C and B)
A finite focus lens 9Y that provides a predetermined convergence in both the direction in which (Y, M, C, and B) is deflected (hereinafter referred to as the main scanning direction), the main scanning direction, and the sub scanning direction orthogonal to the main scanning direction. , 9M, 9C and 9B, and the respective laser beams L (Y, M, C and B) passed through the respective finite focus lenses 9 (Y, M, C and B).
, The hybrid cylinder lenses 11Y, 11M, 11C and 11B which further provide convergence only in the sub-scanning direction, and the four laser beams L passed through the respective hybrid cylinder lenses 11 (Y, M, C and B). It has a pre-deflection folding mirror block 13 for bending (Y, M, C and B) toward each deflection surface (reflection surface) of the optical deflector 5. The laser element 3
(Y, M, C and B), finite focus lens 9 (Y, M,
C and B), hybrid cylinder lens 11 (Y,
M, C and B) and the mirror block 13 are integrally arranged on a holding member 15 formed of, for example, an aluminum alloy.

Finite focus lens 9 (Y, M, C and B)
Are each formed by an aspherical glass lens or a spherical glass lens on which an aspherical surface is bonded with UV curable plastic. Further, each lens is fixed on the holding member 15 via a lens barrel or a lens holding ring (not shown) made of a material having substantially the same thermal expansion coefficient as the holding member 15.

Hybrid cylinder lens 11 (Y,
M, C and B) include plastic cylinder lenses 17Y, 17M, 17C and 17B and glass cylinder lenses 19Y, 19M, 19C and 19B, respectively.

Each plastic cylinder lens 1
7 (Y, M, C and B) and glass cylinder lens 19
(Y, M, C, and B) have substantially the same curvature in the sub-scanning direction. Each plastic cylinder lens 17 (Y, M, C and B) is made of a material such as PMMA (polymethylmethacryl). Glass cylinder lens 19 (Y, M,
C and B) are formed of a material such as SFS1. Further, each of the cylinder lenses 17 and 19 is fixed on the holding member 15 via a lens barrel (lens holding ring) (not shown) formed of a material having substantially the same coefficient of thermal expansion as the holding member 15. The finite focus lens 9 (Y, M, C and B) and the hybrid cylinder lens 11 (Y, M, C and B) may be held by the same lens barrel.

A laser beam L (Y, M, C and B) deflected by each reflecting surface of the light deflecting device 5 is provided between the light deflecting device 5 and the photosensitive drum 58. Each of the laser beams L () passing through the post-deflection optical system 21 and the post-deflection optical system 21 functioning as an image plane side optical system for forming a substantially linear image at a predetermined position of 58, that is, a second optical means. Y, M, C and B)
Of the four laser beams L (Y, Y, which are arranged between the post-deflection optical system 21 and the horizontal sync detector 23 and which pass through the post-deflection optical system 21.
A horizontal sync folding mirror 25 is arranged to reflect a part of M, C and B) toward the horizontal sync detector 23. The horizontal synchronization detector 23 and the horizontal synchronization folding mirror 25 are arranged in only one set for the four laser beams L (Y, M, C and B). Further, the folding mirror 25 for horizontal synchronization is formed so that each of the four laser beams can be sequentially incident on the horizontal synchronization detector 23, as described later with reference to FIG.

Next, the optical characteristics of the post-deflection optical system 21 will be described in detail.

The post-deflection optical system 21 has a wide deflection width, that is, the length of the laser beam L (Y, M, C and B) deflected by the optical deflector 5 to the photosensitive drum 58 in the main scanning direction. Four laser beams L (Y, M, C and B) deflected by each reflecting surface of the optical deflector 5 in the entire region
In addition to the above, the first to third connection means as optical means for giving a predetermined aberration characteristic and suppressing the fluctuation of the image plane of each laser beam L (Y, M, C and B) within a certain range. It has image lenses 27, 29 and 31.

The first imaging lens 27 is a double-sided toric lens in which both the entrance surface 27in and the exit surface 27ra are toric surfaces. The combined power of the entrance surface 27in and the exit surface 27ra in the sub-scanning direction is positive, and the direction of the toric rotational symmetry axis of each surface is the entrance surface 2
7 in is defined in the main scanning direction, and the emission surface 27ra is defined in the sub scanning direction. Second imaging lens 29
Is a single-sided toric lens in which the incident surface 29in is a rotationally symmetrical surface and the exit surface 29ra is a toric surface.
The combined power of the entrance surface 29in and the exit surface 29ra in the sub scanning direction is negative, and the direction of the toric rotational symmetry axis of the exit surface 29ra is defined as the main scanning direction.

The third imaging lens 31 is a one-sided toric lens in which the entrance surface 31in is a toric surface and the exit surface 31ra is a rotationally symmetrical surface. The incident surface 31in
The combined power of the exit surface 31ra in the sub-scanning direction is positive, and the direction of the toric rotational symmetry axis of the entrance surface 31in is defined as the main scanning direction.

Between the third imaging lens of the post-deflection optical system 21, that is, the lens 31 closest to the photosensitive drum 58 and the photosensitive drum 58, the four laser beams LY and LM having passed through the lens 31 are provided. , LC and LB are bent toward the photoconductor drum 58 to form a first folding mirror 33Y,
33M, 33C and 33B, and the second folding mirrors 35Y, 35M and 35 which further fold the laser beams LY, LM and LC bent by the first folding mirrors 33Y, 33M and 33C as the reflecting means.
C and the third folding mirrors 37Y, 37M and 3
7C is arranged. As shown in FIG. 3 (and FIG. 1), the laser beam LB corresponding to B, that is, the black image is folded back by the first folding mirror 33B and then passes through the photosensitive drum without passing through other mirrors. You will be guided to 58. That is, the second folding mirrors 35Y and 35M
And 35C and the third folding mirrors 37Y, 37.
Three M and 37C are arranged for each of the four laser beams.

The first, second and third imaging lenses 27,
29 and 31, and the first folding mirror 33B,
Each of a plurality of fixing members (not shown) formed on the intermediate base 1a of the optical scanning device 1 by integral molding,
It is fixed by adhesion. The first folding mirror 33B is brought into contact with the surface of the mirror, that is, the surface of a supporting member such as glass on which metal or the like as a reflecting member is deposited. As a result, the laser beam incident on each mirror is not affected by the thickness of the supporting member of the mirror, refraction by the supporting member, and internal reflection,
The optical path length can be set accurately. On the other hand, the rest of the first folding mirror 33, namely the mirror 33 (Y, M and C), the second folding mirror 35 (Y, M and C) and the third folding mirror 35 (Y, M and C). ) Are, as will be described later with reference to FIG. 13, respectively, a fixed member formed to be changeable in angle and position, a reflecting surface, that is, a main body member such as glass, or a reflective member such as aluminum applied or vapor-deposited. The side of the reflecting surface is brought into contact with the fixing member with a predetermined pressure from the back surface, that is, the body member side, so that the position of the reflecting surface is fixed so as not to change.

Between the third folding mirrors 37Y, 37M and 37C, and between the first folding mirror 33B and the photosensitive drum 58, the respective mirrors 33B and 37 are provided.
At the position where the four laser beams L (Y, M, C and B) reflected via Y, 37M and 37C are emitted from the optical scanning device 1, the inside of the optical scanning device 1 is further protected from dust. Dust-proof glasses 39Y, 39M, 39C and 39B are arranged for this purpose.

The dustproof glasses 39Y, 39M, 39C and 39B are formed in a parallel flat plate shape, and are respectively shown in FIG.
, The corresponding mirrors 33B, 37Y, 3
At a predetermined angle, that is, in the optical simulation of the design stage described in detail later, so as to non-perpendicularly intersect with the respective chief rays of the four laser beams LY, LM, LC, and LB reflected via 7M and 37C. It is fixed to the housing 1 as the accommodating means at an angle within a prescribed allowable range.

Each laser beam LY, LM, LC
And LB by the third folding mirrors 37Y, 37M and 37C, and the first folding mirror 33B,
The light is emitted to the outside of the optical scanning device 1 at approximately equal intervals. Here, the laser beam LB (black) is emitted from the optical scanning device 1 toward the photosensitive drum 58 via the optical path including the first folding mirror 33B and only one sheet. The number of mirrors in each optical path is one and three, so they are unified into odd numbers. This means that the first to third imaging lenses 27, 29 and 3 of the post-deflection optical system are used.
The main scanning line bending direction (phase of main scanning line bending) of each laser beam L (Y, M, and C) that reaches the image plane due to the inclination of each lens 1 can be made the same direction. Further, as will be described later with reference to FIG. 4, the laser beam LB passes through the passage area 13B of the mirror block 13, and therefore, in the optical path as compared with the remaining laser beams L (Y, M and C). The error included is small and can be used as a reference when adjusting the parallelism of the remaining laser beams L (Y, M and C).

Next, the hybrid cylinder lens 11Y
The optical characteristics of will be described in detail.

Post-deflection optical system 21, that is, first to third
The imaging lenses 27, 29 and 31 of
For example, the refractive index n changes from 1.4876 to 1.4789 when the ambient temperature of the optical scanning device changes, for example, between 0 ° C. and 50 ° C. because it is formed of PMMA. It is known. In this case, the first to third imaging lenses 27, 29 and 31
The image plane on which the laser beam L (Y, M, C and B) that has passed through is actually focused, that is, the image forming position in the sub-scanning direction fluctuates by about ± 12 mm. Here, a lens made of the same material as that of the lens used for the post-deflection optical system 21 is incorporated in the pre-deflection optical system 7 in a state in which the curvature is optimized, so that a change in the refractive index n due to a temperature change is caused. It is possible to suppress the fluctuation of the image plane caused by the above-mentioned change to about ± 0.5 mm. That is, as compared with the conventional optical system in which the pre-deflection optical system 7 is a glass lens and the post-deflection optical system 21 is a lens formed of PMMA, the refractive index of the post-deflection optical system 21 due to the temperature change of the lens. It is possible to correct the chromatic aberration in the sub-scanning direction caused by the change in

As shown in FIG. 3 (and FIG. 1), the respective laser beams LY, LM, LC and L
B is incident symmetrically with respect to the optical axis of the optical scanning device 1 (optical axis of the system) in the sub-scanning direction. That is, the laser beams LY and LB are incident on the polygon mirror 5a symmetrically with respect to the optical axis O. Also, the laser beams LM and L
Similarly, C is guided to the polygon mirror 5a symmetrically with respect to the optical axis O and on the optical axis O side with respect to the laser beams LY and LB. This means that each laser beam L
For (Y, M, C and B), the post-deflection optical system 21 is
It shows that optimization can be performed at two locations in the sub-scanning direction.
Therefore, characteristics such as field curvature and astigmatism of each laser beam L (Y, M, C and B) can be further improved,
The number of lenses of the post-deflection optical system 21 can be reduced.

The mirror block 13 is shown in detail in FIG.

As shown in FIG. 4, the mirror block 1
Reference numeral 3 denotes a block body 13a formed of a material having a small coefficient of thermal expansion, for example, an aluminum alloy, and the number of image-forming color components formed on a predetermined surface of the block body 13a, that is, the number of color-separated colors. A plurality of reflecting surfaces 13Y, 13M arranged by "1" less than
And 13C.

According to FIG. 4, the mirror block 13 has the first to fourth laser beams LY, LM, LC and L.
B as a laser beam Lo of one bundle
It is used to guide each reflective surface of. In detail, the mirror block 13 has the laser element 3Y for making it enter.
The first reflection surface 13Y for returning the laser beam LY emitted from the optical path to the respective reflection surfaces of the optical deflecting device 5, the laser beam LM from the laser element 3M, and the laser beam LC from the laser element 3C are respectively emitted. Second and third reflecting surfaces 13 that are folded back toward the respective reflecting surfaces of the deflecting device 5.
M and 13C and a passage area 13B for guiding the laser beam LB from the laser element 3B to the respective reflecting surfaces of the optical deflector 5 as they are.

Respective reflecting surfaces 13Y, 13M and 1
3C is provided by cutting out a position corresponding to each reflecting surface of the block body 13a at a predetermined angle, and then coating or vapor depositing a material having a high reflectance such as aluminum on the cutting surface. . The positions corresponding to the respective reflection surfaces of the block body 13a may be mirror-finished by polishing after cutting.

According to the mirror block shown in FIG. 4, the reflecting surfaces 13Y, 13M and 13C are cut out from one block body 13a, so that the relative tilt error for each mirror is reduced. Also, the block body 1
By manufacturing 3a by die casting, for example,
A highly accurate mirror block can be provided.

As described above, the laser beam LB from the laser element 3B does not intersect with the mirror block 13 and passes through the passing region 13 on the block body 13a.
After passing through B, it is directly guided to each reflecting surface of the light deflecting device 5.

Here, each laser beam L (Y, Y which is reflected by the mirror block 13 and guided to the optical deflector 5 is shown.
M and C) and the intensity (light quantity) of the laser beam LB directly guided to the light deflector 5 will be considered.

As already described in the section of the prior art, Japanese Patent Application Laid-Open No. 5-34612 discloses a method of making two or more laser beams into a bundle of laser beams to enter the reflecting surface of the optical deflector. The method of stacking laser beams in order is shown by the half mirror. However, since a plurality of half mirrors are used, the amount of light of the laser beam emitted from each laser is reduced to 5 times for each reflection and transmission (every time passing through the half mirror).
It is known that 0% is wasted. In this case, even if the transmittances and reflectances of the half mirrors are optimized for each laser beam, the intensity of one laser beam that passes through all the half mirrors
(Light intensity) is about 25% of the light intensity output from the laser element
Will be reduced to. Further, due to the fact that the half mirror exists in the optical path in a tilted manner in the optical path, and the number of the half mirrors through which each laser beam passes is different, etc. It is known that the characteristics differ for each laser beam. The characteristics such as curvature of field and astigmatism that are different for each laser beam make it difficult to form all the laser beams on the respective photoconductor drums using only the same finite focus lens and cylinder lens. .

On the other hand, according to the mirror block 13 shown in FIG. 4, the respective laser beams LY,
LM and LC are the former stages of incidence on the polygonal mirror 5a of the optical deflector 5, and are laser beams LY, LM and LC.
Is a region separated in the sub-scanning direction (shown by shading in FIG. 6) and is folded by a normal mirror. Therefore, the light amount of each laser beam L (Y, M, C, and B) supplied (reflected) toward the photoconductor drum 58 by the polygon mirror 5a can be maintained at about 90% or more of the emitted light amount. This not only can reduce the output of each laser, but also can uniformly correct the aberration of the light reaching the photosensitive drum 58, so that the laser beam can be narrowed down and high definition can be dealt with. The laser element 3B corresponding to B (black) has a passing area 13B of the mirror block 13.
Since it is guided through the polygonal mirror 5a after passing through, the output capacity of the laser can be reduced and an error in the incident angle on the polygonal mirror 5a due to the reflection on the reflecting surface can be eliminated.

FIG. 5 shows the folding mirror for horizontal synchronization in detail.

According to FIG. 5, the folding mirror 2 for horizontal synchronization is used.
5 is the respective laser beam LYLM, LC and L
In order to reflect B in the main scanning direction to the horizontal synchronization detector 23 at different timings, it is possible to provide substantially the same height on the horizontal synchronization detector 23 in the sub scanning direction.
First to fourth folding mirror surfaces 25Y, 25M, which are formed at different angles in the main scanning direction and the sub scanning direction,
25C and 25B and respective mirrors 25
It has a mirror block 25a which holds (Y, M, C and B) together.

The mirror block 25a is formed of, for example, PC (polycarbonate) containing glass. Each mirror 25 (Y, M, C, and B) is formed by depositing a metal such as aluminum at a position corresponding to the block 25a molded at a predetermined angle.

In this way, not only can each laser beam LY, LM, LC and LB deflected by the optical deflector 5 be made incident on one detector 23, but, for example, the detector It is possible to eliminate the deviation of the horizontal synchronizing signal due to the sensitivity or the positional deviation of each detector, which is a problem when a plurality of detectors are arranged. It is needless to say that the horizontal synchronization detector 23 receives the laser beams LY, LM, LC and LB per line in the main scanning direction four times in total by the horizontal synchronization folding mirror 25. Further, the mirror block 25a is designed so that one mirror surface of the mold can be created by cutting from the block, and is devised so that it can be removed from the mold without requiring an undercut.

Next, referring again to FIG. 3 (and FIG. 1), the respective laser beams L (Y, M, C and B) reflected by the polygon mirror 5a of the optical deflecting device 5 and the post-deflection optics are shown. The relationship between the inclinations of the laser beams LY, LM, LC and LB emitted to the outside of the optical scanning device 1 through the system 21 and the folding mirrors 33B, 37Y, 37M and 37C will be described.

As described above, the laser beams LY, LM, which are reflected by the polygonal mirror 5a of the optical deflector 5 and are given predetermined aberration characteristics by the first to third plastic lenses 27, 29 and 31. LC and LB are folded back in a predetermined direction via the first folding mirrors 33Y, 33M, 33C and 33B, respectively.

At this time, the laser beam LB is reflected by the first folding mirror 33B and then guided as it is to the photosensitive drum 58 through the dustproof glass 39B. On the other hand, the remaining laser beams LY, LM, and LC have second folding mirrors 35Y, 35M, and 35C, respectively.
And is reflected by the second folding mirrors 35Y, 35M and 35C toward the third folding mirrors 37Y, 37M and 37C, and further reflected by the third folding mirrors 37Y, 37M and 37C,
The dustproof glasses 39Y, 39M and 39C respectively form images on the respective photoconductor drums at substantially equal intervals. In this case, the laser beam LB emitted from the first folding mirror 33B and the laser beam LC adjacent to the laser beam LB are also substantially evenly spaced apart from each other on the photosensitive drum 58B.
And 58C.

By the way, as shown in FIGS. 3 and 6, the dustproof glasses 39Y, 39M, 39C and 39B.
Are respectively reflected by the mirrors 33B, 37Y, 37M and 37C and directed to the respective photosensitive drums 58 (Y, M, C and B), and the respective laser beams L (Y, M, C and B).
Are arranged at a predetermined angle, that is, at a right angle with respect to the chief ray. From this, each laser beam L
(Y, M, C and B) are dustproof glass 39 (Y, M, C
By passing through C and B), it is guided to an emission position different from the extension line of the incident position when the dust-proof glass 39 is incident. Here, each laser beam L (Y, Y, M passed through the dustproof glass 39 (Y, M, C and B)
The deviation between the incident position and the outgoing position of M, C, and B) is minimized when the deflection angle of the polygonal mirror 5a of the optical deflecting device 5 is 0 °, and gradually increases as the deflection angle is increased. It As a result, each laser beam L
Y, LM, LC and LB and dustproof glass 39 of each
The angles formed by Y, 39M, 39C, and 39B are optimally set for each laser beam, as described later with reference to FIGS. 7 and 8, so that the first to third imaging lenses 27, 29 are formed. It is possible to correct the deviation in the magnitude of the bending of the main scanning line given to each laser beam L (Y, M, C, and B) when passing through and 31. Therefore, in the color image forming apparatus 100, color misregistration caused by superimposing four laser beams is reduced.

7 and 8 show the laser beams LY,
FIG. 6 is an optical path diagram showing a relationship between an angle formed by LM, LC and LB and dust-proof glasses 39Y, 39M, 39C and 39B corresponding thereto and a main scanning line bend of each laser beam LY, LM, LC and LB.

FIG. 7 shows a dustproof glass 39 (here, Y,
One of M, C, and B will be described as a representative) That is, the parallel plate is formed on the photosensitive drum by the reflection point of the mirror of the laser beam directed from the mirror arranged in the preceding stage to the corresponding photosensitive drum and the photosensitive drum. FIG. 6 is a cross-sectional view of a state inclining by an angle θ with respect to the optical path of the laser beam when there is no parallel plate between the line and the position, that is, between the mirror and the photoconductor drum, as seen from the sub-scanning direction.

As shown in FIG. 7, a parallel plate (39)
Let d be the thickness of, and n be the refractive index of the parallel plate (39).
Since the incident angle of the laser beam incident on the parallel plate is represented by θ, the refraction angle θ ′ at the incident surface of the laser beam is
According to Snell's law, θ ′ = sin ⁻¹ (sin θ / n) (1) can be written. Further, the laser beam is emitted from the parallel flat plate at the refraction angle θ. That is, the laser beam incident on the parallel plate is emitted in parallel with the incident laser beam through the parallel plate.

Here, as shown in FIG. 7, assuming that the distance between the incident laser beam and the emitted laser beam is Δx, Δx = d (tan θ-tan θ ′) cos θ (2)

FIG. 8 is a line connecting the dust-proof glass 39, that is, the parallel plate, between the reflection point of the mirror of the laser beam directed from the mirror arranged in the preceding stage to the corresponding photosensitive drum and the image forming position on the photosensitive drum. That is, it is a cross-sectional view seen from the main scanning direction in a state tilted by an angle φ with respect to the optical path of the laser beam when there is no parallel plate between the mirror and the photosensitive drum. The angle φ is equivalent to the amount by which the parallel plate is inclined with respect to the laser beam, but the amount by which the laser beam is deflected by the polygon mirror 5a of the optical deflector 5, that is, the swing angle (scanning angle) of the laser beam. ) Is shown.

As shown in FIG. 8, a parallel plate (39)
Let d be the thickness of, and n be the refractive index of the parallel plate (39).
Since the incident angle of the laser beam incident on the parallel plate is represented by φ, the refraction angle φ ′ at the incident surface of the laser beam is
According to Snell's law, φ ′ = sin ⁻¹ (sin φ / n) (3) can be written. Further, the laser beam is emitted from the parallel plate with a refraction angle φ. That is, the laser beam incident on the parallel plate is emitted in parallel with the incident laser beam through the parallel plate.

At this time, the distance d'where the laser beam incident on the parallel plate at the angle φ travels in the parallel plate is represented by d '= d / cosφ' (4). Needless to say, d '> d.

Now, replace d in FIG. 7 with d '.
When formulas (1) to (4) are rearranged, Δx = d [tanθ−tan {sin ⁻¹ (sinθ / n)}] cosθ / cos [sin ⁻¹ (sinφ / n)]… (5) is derived. Be issued.

FIG. 9 is a graph showing the relationship between the distance Δx shown in equation (5) and the tilt angle θ of the parallel plate in the sub-scanning direction. In FIG. 9, the maximum value of the swing angle of the laser beam, that is, the angle φ is 25 °, and the refractive index n of the parallel plate is n =
1.47 (the material of the glass is BK7), and the thickness d of the parallel plate is 2 millimeters.

As shown in FIG. 9, it is recognized that the parallel distance Δx between the incident laser beam and the emitted laser beam is increased substantially in proportion to the angle θ by inclining the parallel plate in the sub-scanning direction. To be By optimizing the amount and direction of tilting the parallel plate in the sub-scanning direction,
The possibility that the bending of the main scanning line imparted to each laser beam can be canceled by the first to third imaging lenses 27, 29 and 31 is shown.

FIG. 10 shows that in the optical scanning device 1 shown in FIG. 3, the parallel flat plate, that is, the dustproof glass 39 (Y, M, C and B) is used for each laser beam L (Y, M, C and B). 9 is a graph showing a state in which the amount of main scanning line bending changes when tilted in a range of ± 15 ° in the sub scanning direction.

As shown in FIG. 10, for each laser beam L (Y, M, C and B), it is recognized that there is an inclination angle θ that minimizes the main scanning line bending. Since the laser beam LY (yellow) and the laser beam LB (black) are symmetrical with respect to the optical axis O of the system with respect to the sub scanning direction, only the laser beam LY is displayed.
In this case, the laser beam LY and the laser beam LB are
Since the polarities (directions) are opposite, the directions in which the dustproof glass 39Y and the dustproof glass 39B are tilted in the optical scanning device 1 are opposite, but in the present embodiment, the polarities are substantially negligible. Be improved.

FIG. 11 relates to the main scanning line curve shown in FIG. 10, and the parallel flat plate, that is, the dustproof glass 39 (Y, M, C and B), with respect to each laser beam L (Y, M, C and B). Tilt within ± 3 ° in the sub-scanning direction,
6 is a graph in which an optimum tilt angle θ is obtained. Note that FIG.
Is substantially the same as when the graph shown in FIG. 10 is enlarged, and a detailed description thereof will be omitted.

As shown in FIGS. 11 and 10, the main scanning line bending amount of each of the laser beams LY, LM, LC and LB is obtained, and the corresponding dustproof glass 39Y,
Each of the laser beams LY, LM, LC and LB is tilted by a predetermined amount with respect to the optical path of the laser beam when there is no parallel plate between the mirror and the photosensitive drum. The main scanning line curve of can be minimized. That is, by arranging the parallel flat plates at an optimum angle, it is possible to provide an optical scanning device having an optical system in which the bending of the main scanning line is suppressed.

Next, in order to obtain the optimum tilt angle of the parallel plate, the relationship between the tilt angle θ of the parallel plate and the scanning line bending correction effect was measured. The measurement result is shown in FIG.

In designing the optical system of the optical scanning device, when the pitch between dots of the dots included in the print image is D, it is preferable if the allowable amount of main scanning line bending can be set within D / 4. It is known that various printed images can be obtained. In this embodiment, taking an optical scanning device having a performance of 600 DPI (dots / inch) as an example,
The allowable amount of bending of the main scanning line is about 10.6 μm or less.

Therefore, in the optical scanning device having the performance of 600 DPI, as shown in FIG. 12, the parallel plate is set to | 0.3 so that the main scanning line bend becomes 10 μm or less.
Inclination of | deg or more, that is, laser beam | 0.3 |
It was confirmed that the tilt of the main scanning line can be effectively corrected by making the light incident at an angle of not less than deg or not more than -0.3 deg.

On the other hand, by inclining the parallel plate, the optical path length of the laser beam that travels in the parallel plate is substantially increased,
The transmittance decreases due to the loss of the parallel plate itself, such as internal absorption and scattering.

The incident angle of the laser beam incident on the parallel plate is θ, and the emission angle of the laser beam emitted from the parallel plate is θ.
When t, the transmittance rp of the parallel plate can be expressed as rp = tan (θ−θt) / tan (θ + θt) (6). Here, assuming that the refractive index of the parallel plate is n, the emission angle θt can be written as θt = sin ⁻¹ (sin θ / n) (7) according to Snell's law. Therefore, the equation (6) is transformed from the equation (7) into rp = tan {θ−sin ⁻¹ (sin θ / n)} / tan {θ + sin ⁻¹ (sin θ / n)} (8). Here, the transmittance of the glass forming the parallel plate is about 90%, and the transmittance of at least about 80% is required for the parallel plate. Therefore, the parallel plate should be inclined. The loss amount of the transmittance due to 10% can be allowed up to 10%. Therefore, the incident angle θ of the laser beam at which the transmittance is lost by 10% is tan {θ−sin ⁻¹ (sin θ / n)} / tan {θ + sin ⁻¹ (sin θ / n)} = 0.1 (9 ) Can be calculated. Therefore, assuming that the incident angle θ that satisfies the expression (9) is Θ, if the incident angle θ of the laser beam incident on the parallel plate is within the range of θ ≦ θ, the transmittance of the laser beam transmitted through the parallel plate is Can secure 80% or more.

Therefore, the dustproof glass provided in the optical scanning device, that is, the parallel plate, is inclined by 0.3 deg or more at which the bending of the main scanning line is significantly suppressed, and the transmittance of the parallel plate is 80% or more. It is fixed to the housing of the optical scanning device by inclining within the following range. That is, by fixing the parallel plate to the housing at an inclination angle within the range of 0.3 ≦ θ ≦ θ (deg) (10), the bending of the main scanning line is effectively corrected, and the parallel plate has the minimum The required transmittance can be secured.

As described above, the dust-proof glass, that is, the parallel plate is tilted within the range satisfying the expression (10) and fixed to the housing of the optical scanning device, so that the inside of the optical scanning device is protected from dust and the optical scanning is performed. The main scanning line curve of the laser beam emitted from the device can be remarkably corrected.

FIG. 13 is a schematic block diagram of an image control unit for controlling the image forming operation of the color image forming apparatus shown in FIG.

The image forming apparatus 100 includes an image controller 110.
have.

The image control unit 110 includes the image control CPU 11
1. Timing control unit 113 and data control units 115Y, 115M, 115C and 11 corresponding to respective color components
5B and the like. Note that the image control CPU 111, the timing control unit 113, and the data control units 115 (Y, M, C, and B) are mutually connected via a bus line 112.

Further, the image control CPU 111 uses the bus line 112 to operate mechanical elements of the image forming apparatus 100, such as motors or rollers, and electrical elements, such as the charging device 60 (Y, M, C, and so on). B), the developing device 62 (Y, M, C and B) or the transfer device 64 (Y, M, C and B) and the main controller 101 for controlling the voltage value or the amount of current applied thereto. . The main controller 101 includes a ROM (read only memory) (not shown) in which initial data or a test pattern for initializing the apparatus 100 is stored, input image data or a register sensor 78 and 80. A RAM 102 (random access memory) for temporarily storing correction data and the like calculated according to the output, and a non-volatile memory 103 for storing various correction data obtained in an adjustment mode described later are connected. I have.

The timing control unit 113 has image memories 114Y and 11Y for storing image data for each color component.
4M, 114C and 114B, each image memory 114
Based on (Y, M, C and B), each image forming unit 50
(Y, M, C, and B)
A laser driver 116 (Y, M, C and B) for energizing the corresponding laser element 3 (Y, M, C and B) to irradiate a laser beam toward M, C and B), a resist sensor Based on the outputs from 78 and 80, the registration sensors 78 and 8 calculate the correction amount of the timing of writing the image by the laser beams LY, LM, LC and LB.
Registration correction calculation device 117 that calculates based on the signal from 0, each image forming unit 50 (Y, M, C and B) and the laser element 3 (of the optical scanning device 1 based on the signal from the registration correction calculation device 117). Y, M, C, and B), and a timing setting device 118 that defines various timings for operating the Y, M, C, and B), and each image forming unit 50 (Y,
M, C and B) and an oscillation frequency variable circuit (voltage controlled oscillator, that is, voltage controlled oscillation circuit, hereinafter) for correcting a deviation caused by a difference in optical path length of each optical path in the optical scanning device 1 VCO) 1
19Y, 119M, 119C, 119B, etc. are connected.

The timing control device 113 is a microprocessor which internally includes a RAM section capable of storing correction data. For example, a dedicated IC is based on individual specifications.
(Application Specific Integrated Circuit, hereinafter referred to as ASIC). The data control unit 115 (Y, M, C, and B) is a microprocessor including a plurality of latch circuits, an OR gate, and the like.
It is integrated in IC etc. Registration correction calculation device 11
7 is a microprocessor including at least four pairs of comparators and OR gates, and
It is integrated in IC etc. VCO119 (Y, M, C
And B) are oscillation circuits in which the output frequency can be changed according to the applied voltage, and have a frequency variable range of about ± 3%. As this kind of oscillation circuit, a harmonic oscillation circuit, an LC oscillation circuit or a simulated reactance variable LC oscillation circuit is used.
As an element that can be used as the VCO 119, a circuit element in which a converter that converts an output waveform from a sine wave to a rectangular wave is integrally incorporated is also known.

Image data from an external storage device (not shown) or a host computer is stored in each image memory 114 (Y, M, C and B). The output of the horizontal sync detector 23 of the optical scanning device 1 is converted into a horizontal sync signal Hsync via the horizontal sync signal generation circuit 121, and each data control unit 115 (Y, M, C and B).
Is input to

Next, the operation of the image forming apparatus 100 will be described with reference to FIGS.

First, when an image formation start signal is supplied from an operation panel or a host computer (not shown), each image forming section 50 is controlled by the main controller 101.
(Y, M, C and B) are warmed up, and the polygon mirror 5a of the optical deflecting device 5 of the optical scanning device 1 is rotated at a predetermined rotation speed under the control of the image control CPU 111.

Then, under the control of the main controller 101,
Image data to be printed is loaded into the RAM 102 from an external storage device, a host computer, or a scanner (image reading device). Part (or all) of the image data taken into the RAM 102 is stored in each image memory 114 (Y, M, C and B) under the control of the image control CPU 111 of the image control unit 110. Further, under the control of the main controller 101, the feed roller 72 is based on a predetermined timing, for example, the vertical synchronization signal Vsync from the timing control unit 113.
Then, one sheet of paper P is taken out from the paper cassette 70. The taken-out sheet P is provided by the registration rollers 72 by the image forming operations of the image forming units 50 (Y, M, C and B), Y, M, C and B.
The toner images are aligned in timing with each other, and are brought into close contact with the conveyance belt 52 by the suction roller 74, and are guided toward each image forming unit 50 as the conveyance belt 52 rotates.

On the other hand, based on the data set by the timing setting device 118 and the registration data and the clock data read from the internal RAM of the timing control unit 113 in parallel with or at the same time as the feeding and conveying operations of the paper P. The timing control unit 113 outputs the vertical synchronization signal Vsync.

The vertical synchronization signal Vsync is output by the timing control unit 113, whereby each data control unit 11
The laser drive units 116 (Y, M, C and B) are energized by the control of 5 (Y, M, C and B), and the laser drive units 116 (Y, M, C and B) move in the main scanning direction. A laser beam for one line is applied to each photosensitive drum 58 (Y, M, C and B) of each image forming section 50 (Y, M, C and B). Immediately after the input of the horizontal synchronization signal Hsync generated from the horizontal synchronization signal generation circuit 121 based on the laser beam for one line, each VCO 119 (Y, M,
C and B) are counted, and each VCO 1
When the number of clocks of 19 (Y, M, C and B) reaches a predetermined value, image data to be printed is read from each image memory 114 (Y, M, C and B). Then, under the control of each data control unit 115 (Y, M, C and B), each laser drive unit 116 (Y, M, C and B) is controlled by each laser element 3 (Y, M, C and B). ) Each laser beam L (Y, M, C and B) emitted from
Image data is transferred to change the intensity of each of the photoconductor drums 5 of each image forming unit 50 (Y, M, C and B).
8 (Y, M, C and B), an image without deviation is formed. As a result, each photosensitive drum 58 (Y,
M, C and B) each laser beam L (Y,
M, C and B) from each laser element 3 (Y, M, C and B) to each photosensitive drum 58 (Y, M, C and B).
Deviation of the optical path between or until each photosensitive drum 58
Accurately image on each photoconductor drum 58 (Y, M, C and B) without being affected by the fluctuation of the beam spot diameter on the image plane due to the deviation of the diameter of (Y, M, C and B). To be done.

The laser beams L (Y, M, and Y) focused on the photoconductor drums 58 (Y, M, C, and B), respectively.
C and B) change the electric potentials of the photosensitive drums 58 (Y, M, C and B), which are charged in advance to a predetermined electric potential, based on the image data.
8 (Y, M, C and B), an electrostatic latent image corresponding to the image data is formed. This electrostatic latent image is transferred to each developing device 62.
(Y, M, C and B) are developed with toner having a corresponding color and converted into a toner image.

Each toner image corresponds to each photoconductor drum 5
8 (Y, M, C, and B) is rotated toward the paper P being conveyed by the conveyor belt 52, and the transfer device 64 causes the paper P on the conveyor belt 52 to be conveyed at a predetermined timing. Is transferred at a predetermined timing. As a result, four color toner images that have exactly overlapped with each other on the paper P are formed on the paper P. It should be noted that each photoconductor drum 58 (Y, M, C and B) after the toner image is transferred onto the paper P has a corresponding cleaner 6
6 (Y, M, C and B) and the static elimination lamp 68 (Y, M
After the residual toner and residual potential are removed by M, C and B), they are used for subsequent image formation.

Paper P holding electrostatically four color toner images
Are further conveyed as the conveyor belt 52 rotates, and are separated from the conveyor belt 52 by the difference between the curvature of the belt drive roller 56 and the straightness of the paper P, and the fixing device 8
You will be guided to 4. The toner image as a color image is fixed on the sheet P guided to the fixing device 84 by melting the respective toners by the fixing device 84,
The sheet is discharged to a discharge tray (not shown).

On the other hand, after the paper P is supplied to the fixing device 84, the conveyor belt 52 is further rotated, and the belt cleaner 82 removes the undesired toner remaining on the surface and the paper is again fed from the cassette 70. It is used to convey the paper P that is used.

As described above, in this optical scanning device, the dust-proof glass, that is, the parallel flat plate, is arranged at the position where the laser beam is emitted, inclined at an angle within the predetermined allowable range defined by the equation (10). The optical scanning device main body is fixed to the housing. The angle at which the parallel flat plate is tilted is set within an allowable range defined based on the measurement result and the calculation result of the theoretical formula so that the bending of the main scanning line can be corrected and the predetermined transmittance can be maintained. . Therefore, the parallel flat plate applied to this optical scanning device can protect the inside of the optical scanning device from dust and can correct the main scanning line bending without requiring complicated adjustment, and the deviation of the scanning position of the laser beam can be suppressed. .

Further, in the image forming apparatus to which this optical scanning device is applied, the laser beam emitted from the optical scanning device is guided to the photosensitive drum with the main scanning line bending suppressed, so that a monochrome image is formed. When printing, the deviation of each dot position of the print image due to the deviation of the scanning position of the laser beam is suppressed, and the high quality of the print image can be achieved. Further, when a color image is printed, color misregistration is prevented, and the quality of the printed image can be improved.

This optical scanning device is a color copying machine,
Not only can it be applied to a color image forming apparatus such as a color printer, but it can also be applied to other image forming apparatuses such as a digital multi-function peripheral having a FAX function, a printer function, and a copying function, and a monochrome image forming apparatus. is there.

[0123]

As described above, according to the present invention, it is possible to suppress the main scanning line bending and improve the quality of a printed image, and a multi-beam optical scanning device and an image to which the optical scanning device is applied. To provide a forming apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a color image forming apparatus that is an embodiment of the present invention.

FIG. 2 is an optical path diagram of the optical scanning device used in the color image forming apparatus shown in FIG. 1 when viewed from the main scanning direction with the first to third imaging lenses as a center.

FIG. 3 is a schematic cross-sectional view of the optical scanning device used in the color image forming apparatus shown in FIG. 1 cut at a position where a minimum value is present between a reflecting surface of an optical deflecting device and a photosensitive drum.

4 is a schematic perspective view of a folding mirror block used in the optical scanning device shown in FIGS. 2 and 3. FIG.

5 is a schematic perspective view of a folding mirror for horizontal synchronization detection used in the optical scanning device shown in FIGS. 2 and 3. FIG.

6 is a schematic cross-sectional view showing the position of a laser beam passing through each lens of the optical scanning device shown in FIGS. 2 and 3 in the sub-scanning direction.

7 is a schematic cross-sectional view showing the inclination of the parallel flat plate glass member of the optical scanning device shown in FIGS. 2 and 3 in the sub-scanning direction and the position of the laser beam passing through the parallel flat plate glass member in the sub-scanning direction.

8 is a schematic cross-sectional view showing the inclination of the parallel flat plate glass member shown in FIG. 7 in the sub-scanning direction and the distance in the main scan direction of the laser beam passing through the parallel flat plate glass member.

9 is a graph showing the relationship between the inclination of the parallel plate glass member shown in FIG. 7 in the sub-scanning direction and the bending of the main scanning line of the laser beam that has passed through the first to third imaging lenses.

10 is a graph showing the relationship between the inclination of the parallel plate glass member shown in FIG. 7 in the sub-scanning direction and the bending of the main scanning line of the laser beam that has passed through the first to third imaging lenses.

11 is a graph showing the relationship between the inclination of the parallel plate glass member shown in FIG. 7 in the sub-scanning direction and the bending of the main scanning line of the laser beam that has passed through the first to third imaging lenses.

FIG. 12 is a graph showing the relationship between the tilt angle of the parallel flat plate glass member shown in FIG. 7 and the main scanning line bending correction effect.

13 is a schematic block diagram showing a control unit of the image forming apparatus shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Multi-beam optical scanning device 3 ... Semiconductor laser element 5 ... Optical deflection device 7 ... Pre-deflection optical system 9 ... Finite focus lens 11 ... Hybrid cylinder lens 13 ... Mirror block 15 ... Holding member 17 ... Plastic cylinder lens 19 ... Glass cylinder Lens 21 ... Post-deflection optical system 23 ... Horizontal synchronization detector 25 ... Horizontal synchronization folding mirror 27 ... First imaging lens 29 ... Second imaging lens 31 ... Third imaging lens 33 ... First folding Mirror 35 ... Second folding mirror 37 ... Third folding mirror 39 ... Dust-proof glass 50 ... Image forming part 58 ... Photosensitive drum 62 ... Developing device

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area G03G 15/04

Claims (6)

[Claims] 1. A scanning means for scanning a plurality of light beams toward a scanning object, an optical means for giving a predetermined optical characteristic to each of the plurality of light beams, the optical means and the scanning object. A plurality of light beams directed toward the scanning target object with respect to the optical path of the plurality of light beams directed toward the scanning target object by the reflecting device disposed corresponding to each of the plurality of light beams between An optical path correcting unit that corrects the scanning position shift of the light beams and is inclined at an angle such that the transmittance is within a predetermined range, and scans the plurality of light beams by the scanning unit. And an image forming unit for forming an image on a predetermined position of the optical scanning device. 2. A scanning means for scanning a plurality of light beams toward a scanning object, an optical means for giving a predetermined optical characteristic to each of the plurality of light beams, and the optical means and the scanning object. And a reflection means arranged corresponding to each of the plurality of light beams, and the incidence surface is non-perpendicularly fixed to the optical paths of the plurality of light beams toward the scanning object by the reflection means. An optical path correcting means, and an image forming means for forming an image of the plurality of light beams scanned by the scanning means on a predetermined position of the scanning object, wherein the optical path correcting means comprises the optical path correcting means. The refractive index of the means is n,
Letting θ be the incident angle of the light beam with respect to the normal to the incident surface of the optical path correcting means, tan {θ−sin ⁻¹ (sin θ / n)} / tan {θ + sin ⁻¹ (s
in θ / n)} = 0.1, where θ is Θ, the optical scanning is characterized in that the angle is fixed at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg). apparatus. 3. A scanning means for scanning a plurality of light beams toward an object to be scanned, at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams, and the optical means. The scanning object is provided with respect to the reflecting means arranged between the scanning object and the plurality of light beams respectively, and the optical paths of the plurality of light beams toward the scanning object by the reflecting means. A plurality of light beams that are scanned by the scanning means, the parallel light plates that correct the scanning position deviations of the plurality of light beams toward each other and that are inclined at an angle such that the transmittance is within a predetermined range. An optical scanning device comprising: an image forming unit that forms an image on a predetermined position of an object to be scanned; and a housing unit that houses the scanning unit and the image forming unit. 4. A scanning means for scanning a plurality of light beams toward an object to be scanned, at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams, and the optical means. Reflecting means arranged between the object to be scanned and corresponding to the plurality of light beams respectively, and an incident surface being non-perpendicular to an optical path of the plurality of light beams directed to the object to be scanned by the reflecting means. An image forming means for forming an image of the plurality of light beams scanned by the scanning means on a predetermined position of the object to be scanned, and the scanning means and the image forming means. Storage means for storing
The parallel plate has a refractive index n of the parallel plate and an incident angle of the light beam with respect to a normal line of the incident surface of the parallel plate θ, and tan {θ-sin ^-1 (sin θ / n)} / Tan {θ ＋ sin ^-1 (s
In θ / n)} = 0.1, when θ is Θ, it is fixed to the accommodating means at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg). Optical scanning device. 5. A plurality of light sources that are intensity-modulated according to image data and correspond to a plurality of color components respectively, and give predetermined optical characteristics to the light beams emitted from the plurality of light sources, respectively. A first optical member including a first optical member and a second optical member that focuses a plurality of light beams given optical characteristics by the first optical member in a first direction; and the first optical member. Scanning means for scanning a plurality of light beams passing through the object toward a scanning object, at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams, the optical means and the scanning Reflecting means arranged between the object and the plurality of light beams corresponding to each of the plurality of light beams, and optical paths of the plurality of light beams toward the scanning object by the reflecting means are directed toward the scanning object. Multiple A plurality of light beams that are scanned by the scanning means and that include a parallel plate that corrects the scanning position deviation of the light beams and that is inclined at an angle such that the transmittance is within a predetermined range. Second optical means for forming an image at a predetermined position, accommodating means for accommodating the scanning means and the imaging means, and the plurality of parts guided through the first optical means, the scanning means, and the second optical means. A plurality of image carriers for holding respective images corresponding to the respective light beams emitted from the light sources, and the images held on the image carriers are arranged corresponding to the plurality of image carriers, respectively. An image forming apparatus comprising: a plurality of developing means for visualization. 6. A plurality of light sources which are intensity-modulated according to image data and respectively correspond to a plurality of color components, and a predetermined optical characteristic is given to a light beam emitted from each of the plurality of light sources. A first optical member including a first optical member and a second optical member that focuses a plurality of light beams given optical characteristics by the first optical member in a first direction; and the first optical member. Scanning means for scanning a plurality of light beams passing through the object toward a scanning object, at least one set of optical means for giving a predetermined optical characteristic to each of the plurality of light beams, the optical means and the scanning Reflecting means arranged between the object and the plurality of light beams corresponding to each of the plurality of light beams, and an incident surface non-perpendicular to the optical paths of the plurality of light beams toward the scanning object by the reflecting means. Flat Second optical means including a flat plate for forming an image of the plurality of light beams scanned by the scanning means on a predetermined position of the object to be scanned, and an accommodating means for accommodating the scanning means and the imaging means A plurality of image carriers that hold respective images corresponding to the respective light beams emitted from the plurality of light sources guided through the first optical unit, the scanning unit, and the second optical unit; A plurality of developing means disposed corresponding to each of the plurality of image carriers and visualizing an image held on the image carrier, wherein the parallel plate has a refractive index n of the parallel plate, Letting θ be the incident angle of the light beam with respect to the normal to the plane of incidence of the parallel plate, tan {θ−sin ⁻¹ (sin θ / n)} / tan {θ + sin ⁻¹ (s
In θ / n)} = 0.1, when θ is Θ, it is fixed to the accommodating means at an angle corresponding to θ that satisfies 0.3 ≦ θ ≦ Θ (deg). Image forming apparatus.