JP3434502B2 - Optical scanning device - Google Patents

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 device for scanning a plurality of beams, which is applicable to a multi-drum type color printer, a multi-drum type color copying machine, a high-speed laser printer, a digital copying machine and the like. 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 An optical scanning device (laser exposure device) that provides image data corresponding to the component, that is, a plurality of laser beams is used.

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.

Generally, an optical scanning device includes a semiconductor laser element as a light source, a first lens group for narrowing the 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 to a predetermined position on the recording medium. It has a second lens group for forming an image. In many cases, the direction in which the laser beam is deflected by the optical deflector is referred to as the main scanning direction, and the direction in which the recording medium is conveyed, that is, the direction orthogonal to the main scanning direction is referred to as the sub-scanning direction.

By the way, it is known that the number of rotations of the rotary mirror of the optical deflector is proportional to the resolution and the image forming speed required for the image forming apparatus, that is, the process speed. Also, the image frequency is proportional to the square of the resolution and the process speed. From this, it is known that in order to improve the resolution or the process speed, it is necessary to increase the number of rotations of the rotating mirror of the optical deflector and to secure a sufficient image frequency.

However, increasing the rotational speed of the rotary mirror of the optical deflector increases the time required until the rotational speed of the rotary mirror stabilizes. Therefore, the image is actually output after the print request signal is input. However, there is a problem of increasing the time until printed. Further, as the number of rotations of the rotating mirror is increased, there is a problem that the cost is significantly increased due to factors such as the material of the bearing, durability, and assembly accuracy. Separately from this, since the windage of the rotating mirror is increased by increasing the number of rotations of the rotating mirror, it is required to improve the output of the motor used for rotating the rotating mirror.

On the other hand, in order to increase the image frequency, not only the length of the signal line needs to be shortened but also the line width needs to be narrowed, and the influence of stray capacitance or noise is increased at an accelerating rate. Therefore, there is a problem that the cost is increased.

[0008]

By the way, if image information can be recorded on a recording medium by N laser beams, for example, the number of rotations of the rotating mirror and the image frequency are reduced to 1 / N, respectively. To be done. Therefore, many multi-beam optical scanning devices have been proposed so far.

For example, in Japanese Patent Laid-Open No. 59-188616, when the number of multi-beams is N, N sets of semiconductor lasers, cylinder lenses and glass f.theta. An example of using two sheets is disclosed.

However, JP-A-59-188616
In the example disclosed in Japanese Patent Publication, as a single optical scanning device,
The increase in the number of lenses or mirrors increases the cost of parts and assembly cost, or increases the size and weight of the optical scanning device alone. Also, f
The deviation of the main scanning line of the laser beam for each color component or the deviation of the aberration characteristic represented by the fθ characteristic on the image plane due to the shape error, individual error, or mounting error of the θ lens becomes uneven. It has been known. The main scanning line curve indicates that the trajectory of the laser beam scanned toward the image plane is curved, and the non-uniformity of the fθ characteristics means that the beam position on the image plane relative to the angle θ of the scanned laser beam is mutual. It shows that it shifts to.

The bending of the main scanning line or the non-uniformity of the fθ characteristic causes various problems in the color image forming apparatus, such as color misregistration, image density unevenness or image bleeding.

Japanese Unexamined Patent Publication (Kokai) No. 2-58014 discloses an example in which two laser beams pass through one of the two fθ lenses, and the remaining lenses use two sets for each laser beam. Has been done. However, even with this method, the main scanning line bending and the fθ characteristic cannot be made uniform, and there is a problem that, for example, color misregistration or image density unevenness occurs.

In the examples shown in JP-A-59-188616 and JP-A-2-58014, although M multi-beams can be passed,
It does not correspond when each of the M beams includes Ni (2 or more) beams. Therefore, in order to improve the resolution or the process speed, it is required to increase the rotation speed of the rotating mirror and the image frequency.

Japanese Patent Laid-Open No. 4-50908 discloses a lens in which the radius of curvature of the lens in the sub-scanning direction can be defined regardless of the shape in the main scanning direction. However, the lens disclosed in Japanese Patent Application Laid-Open No. 4-50908 has symmetry in the plane in the main scanning direction and the plane in the sub scanning direction including the optical axis. There is a problem of deterioration. Further, in the example shown in this publication, since the cross section in the sub-scanning direction is an arc, there is a problem that the beam spacing in the sub-scanning direction is not constant when a plurality of beams are passed. Further, in the example shown in this publication, since the light transmittance in the peripheral portion is greatly reduced as compared with the vicinity of the center, there is a problem that color unevenness is likely to occur in a halftone image or a color image. .

Japanese Unexamined Patent Publication No. 57-67375 discloses a method of detecting horizontal synchronization provided by a plurality of beams with the same detector. However, in the example disclosed in JP-A-57-67375, in order to guide each of the plurality of beams to the distributor, it is required to separate each beam in the main scanning direction. Therefore, there is a problem that it is difficult to match the image writing timing for each beam.

JP-A-59-26005 and 260
In Japanese Patent Publication No. 06, one of a plurality of laser elements is made to emit light to detect horizontal synchronization, and when the horizontal synchronization is detected, the emission of the corresponding laser element is stopped and the other laser elements are made to emit light. An example is shown. However, it is required to separate each beam in the main scanning direction. Therefore, there is a problem that it is difficult to match the image writing timing for each beam.

Japanese Patent Application Laid-Open No. 64-73369 shows an example in which the writing timing of another beam is set based on the horizontal synchronizing signal of one beam. However, this method has a problem that the timing reproducibility is likely to change due to temperature rise and the like.

Japanese Unexamined Patent Publication No. 61-25366 discloses a laser power based on a signal from the resolution switching means.
An example of controlling each of the scanning speed and the image frequency is shown. However, in the example disclosed in Japanese Patent Laid-Open No. 61-25366, there is a problem that it cannot be used when there are two or more beams.

In many color image forming apparatuses, the frequency of outputting a black image tends to be higher than the frequency of outputting a color image. Further, the black image is required to have sharpness or sharpness as compared with the color image. However, since an optical device suitable for a laser beam corresponding to a color image does not require resolution as compared with an optical device suitable for a laser beam corresponding to a black image, an optical device suitable for a laser beam corresponding to a black image is required. Utilizing the device adds cost.

An object of the present invention is to provide a multi-beam optical scanning device suitable for an image forming apparatus capable of providing a color image without color shift at low cost.

[0021]

The present invention has been made on the basis of the above-mentioned problems. ΣN _i (N ₁ + N ₂ + ...
N _M ), M is an integer of 2 or more, and at least one of N _i is an integer of 2 or more, and a light source having a reflecting surface rotatably formed is arranged in the main scanning direction. One polarizing means for deflecting and ΣN _i lights deflected by the deflecting means are imaged so as to scan a predetermined image plane at a constant speed, and the influence of surface tilt of the reflecting surface of the deflecting means is corrected. Possibly, an optical means including a lens whose curvature changes smoothly, an optical path changing means for changing a reflection / emission angle in the main scanning direction depending on a height in a sub scanning direction which is a direction perpendicular to the main scanning direction, The light of the M group is made incident on the optical path changing means with different heights in the sub-scanning direction, passes through a predetermined position of the optical means, and then the reflection / emission angle in the main scanning direction is changed by the optical path changing means. Of the light spacing where N _i of the light is 2 or more And a detection unit that detects a relative position, wherein each of the light beams of the M group is incident on the detection unit at different timings.

[0022] In addition, the inventions _{are, ΣN i (N 1 + N} 2 +
In · · · _{N M)} present, M is a light source is at least one integer of 2 or more of the two or more integer, and _{N i,} the N
M sets of optical members provided with positive power in the sub-scanning direction for converging the ΣN _i emitted lights from each of the _i light sources in the sub-scanning direction orthogonal to the main scanning direction, and rotatably One polarization unit having a reflection surface formed and configured to deflect light in the main scanning direction, and Σ deflected by the deflection unit.
The N _i of optical with imaged to scan at a constant speed in a predetermined image surface, to be corrected tilt effect of the reflecting surface of the deflection means, and optical means including a lens smoothly changing curvature An optical path changing means for changing the reflection / emission angle in the main scanning direction depending on the height in the sub-scanning direction which is a direction perpendicular to the main scanning direction, and the light of the M group by changing the height in the sub-scanning direction. After being incident on the optical path changing means and passing through a predetermined position of the optical means, N _{i of the} light whose reflection and emission angle in the main scanning direction is changed by the optical path changing means is 2
A detection means for detecting the relative position of the light interval as described above,
And light of each of the M groups is incident on the detection means at different timings.

[0023]

The optical scanning device according to the present invention, with respect to a plurality of laser beams, applies each of the N _i incident beams to the main scanning direction before the incidence on the M optical members having a positive power only in the sub scanning direction. in synthesized by generally superimposed beams each N _i book between the most deflecting means side of the lens and the image plane of the second optical means, for guiding to intersect with respect to the sub-scanning direction. The lens having a positive power only in the sub-scanning direction is a cylinder lens having a negative power in the sub-scanning direction, which is formed of a material substantially the same as that of the lens of the second optical means, and the second optical means. The lens is made of a material having a smaller change in the refractive index with respect to temperature and humidity than the above lens, and has a positive power in the sub-scanning direction.

[0024] Therefore, with respect to the beam distance of the N _i present, the refractive index due to the effects of temperature and humidity, the influence of the variation due to the shape change is reduced. It also works similarly for the M group beams. Further, since the influence of the fluctuation of the temperature and humidity of the beam waist position near the image plane is suppressed, the fluctuation of the beam diameter is reduced.

[0025] Thus, variations in the inter-beam distance N _i present, bending the main scanning line or fθ characteristic can be prevented from being uneven. Therefore, various defects such as color misregistration, uneven image density, and image bleeding are eliminated.

Further, according to the optical scanning device of the present invention, in the second optical means, at least one surface of the lens of the second optical means includes a scanning surface including the optical axis and a lens surface extending in the main scanning direction. The shape of the intersecting line is asymmetric with respect to the optical axis of the lens surface, does not have a rotational symmetry axis, and the plane symmetry plane to which the relationship of plane symmetry is given is one or less.

A surface having one or less plane-symmetrical surface has a radius of curvature in the sub-scanning direction at each position in the main scanning direction, which extends in the main scanning direction including the optical axis of the second optical means. It can be set independently of the shape of the line where the surfaces intersect. Further, a surface having one or less plane-symmetrical surface is a line that intersects the scanning surface and the lens surface, which has a coefficient of at least a quaternary or more in the sub-scanning direction and includes the optical axis of the second optical means and spreads in the main scanning direction. It can be set independently of the shape of. The second optical means preferably has a positive power in the vicinity of the optical axis in the sub-scanning direction. When the second optical means includes a doublet lens, the optical axis vicinity power is defined to be approximately 0 in the main scanning direction by the lens on the deflecting means side and negative in the lens on the image plane side 2.
By being composed of a single lens, variations in various characteristics due to changes in temperature and humidity are suppressed.

With these, incident light can be made incident on the deflecting means from a direction other than the front direction, so that various characteristics in the main scanning direction due to the asymmetry of the rotating mirror of the deflecting means can be improved. Further, the effective swing angle or the scanning width can be improved. Further, the correction rate of the surface tilt of the rotating mirror is increased, so that the beam intervals in the sub-scanning direction are made uniform. Furthermore, the spherical aberration and the coma aberration distortion in the sub-scanning direction are also improved by the terms of the fourth or higher order. Furthermore, fluctuations in the beam position in the sub-scanning direction are reduced. It is possible to support both single beam and multiple beams.

Therefore, it is possible to suppress color unevenness in a halftone image or a color image.

Further, according to the optical scanning device of the present invention,
Only one detection means is arranged for a plurality of beams,
The relative position of the N _i beams that have passed the predetermined position of the second optical means is detected. Accordingly, the relative position in the sub-scanning direction for writing an image for each beam can be kept constant by the N _i −1 or N _i position control means in the sub-scanning direction. With respect to the main scanning direction, it can be used as a horizontal synchronization generation detecting means. These prevent the writing relative position of the image from changing due to temperature rise or the like. Further, even if the housing or the like is deformed, the relative positions of the N _i beams can be accurately detected.

Furthermore, according to the optical scanning device of the present invention, the power in the main scanning direction of one lens of the second optical means is formed to be negative near the optical axis and positive at the lens end. Therefore, the laser beams from the first and second laser elements can be imaged on the image plane with good characteristics while suppressing the fluctuation of the value of f in the fθ characteristic due to the change in temperature and humidity.

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a transfer type color image forming apparatus using a multi-beam optical scanning device according to a first embodiment of the present invention. In this type of color image forming apparatus, normally, Y or yellow, M or magenta, C or cyan, and B or black.
Four types of image data that are color-separated for each color component of (black) and four sets of various devices that form an image for each color component corresponding to Y, M, C, and B are used. Therefore, by adding Y, M, C, and B to each reference code, the image data for each color component and the device corresponding to each are identified.

As shown in FIG. 1, the image forming apparatus 10
0 is a color component obtained by color separation, that is, Y = yellow, M =
First to fourth image forming units 50Y and 50M that form an image for each of magenta, C = cyan, and B = black.
It has 50C and 50B.

Each image forming section 50 (Y, M, C and B)
Is a third folding mirror 37Y, 37M, 3 of the multi-beam optical scanning device 1 described later with reference to FIGS. 2 to 64.
7Y and 50Y, 50M 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 the first folding mirror 33B. , 50C and 50B are arranged in series in this order.

Each image forming section 50 (Y, M, C and B)
Below each of the image forming units 50 (Y, M, C and B)
A conveyor belt 52 that conveys the image formed by is disposed.

The conveyor belt 52 is stretched 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)
Respectively have photosensitive drums 58Y, 58M, 58C and 58B each having a cylindrical drum shape and formed so as to be rotatable in the direction of the arrow and on which an electrostatic latent image corresponding to an image is formed.

Each photosensitive drum 58 (Y, M, C
And B) around the photosensitive drum 58 (Y, M, C
And a charging device 60 for providing a predetermined electric potential to the surface of B).
Y, 60M, 60C and 60B, photoconductor drum 58
(Y, M, C and B) developing devices 62Y, 62M, 62C and 62B for developing by supplying toner provided with a color corresponding to the electrostatic latent image formed on the surface of (Y, M, C and B),
With the conveyor belt 52 interposed between the photoconductor drums 58 (Y, M, C and B), the photoconductor drums 58 (Y,
M, C and B), and transfer for transferring the toner image of the photoconductor drum 58 (Y, M, C and B) to the recording medium P, that is, the recording medium P that is conveyed by the conveyance belt 52 or the conveyance belt 52. After the toner image is transferred through the devices 64Y, 64M, 64C and 64B and the transfer device 64 (Y, M, C and B), the photosensitive drum 58 (Y,
M, C and B) cleaners 66Y, 66M, 66C and 66B for removing the residual toner remaining on the M, C and B), and a photosensitive member after the toner image is transferred through the transfer device 64 (Y, M, C and B). Static eliminator 68Y, 6 for removing the residual potential remaining on the body drum 58 (Y, M, C and B)
8M, 68C and 68B are the respective photosensitive drums 58
They are arranged in order along the rotation direction of (Y, M, C and B).

The mirrors 37Y and 3Y of the optical scanning device 1 are
The laser beams LY, LM, LC, and LB, which are two beams combined into two beams in the sub-scanning direction on the photoconductor drum 58 guided by 7M, 37C, and 33B, are respectively charged by the charging devices 60. (Y, M, C and B) and each developing device 62 (Y, M, C and B) are irradiated.

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, which is close to the tension roller 54, the paper P, which is formed in a substantially half-moon shape and is stored in the paper cassette 70, is
A delivery roller 72 is arranged to take out the sheets one by one from the top. Sending roller 72 and tension roller 5
4 and the photosensitive drum 5 of the image forming unit 50B (black) between the front end of one sheet of paper P taken out from the cassette 70
A registration roller 74 for aligning the tip of the toner image formed on 8B 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, substantially on the outer periphery of the belt drive roller 56 with the conveyor belt 52 sandwiched, 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 of the paper P is arranged.

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

FIG. 2 shows a multi-beam optical scanning device used in the color image forming apparatus shown in FIG. Note that in the color image forming apparatus shown in FIG. 1, four types of image data, which are usually Y, yellow, M, magenta, C, cyan, and B, black (black), are color-separated. , M, C
Since four sets of various devices that form an image for each color component corresponding to B and B are used, similarly, by adding Y, M, C, and B to each reference symbol, The image data for each and the corresponding device are identified.

As shown in FIG. 2, in the multi-beam optical scanning device 1, a laser beam emitted from a laser element as a light source is arranged on an image plane arranged at a predetermined position, that is, the first to the third shown in FIG. Fourth image forming unit 50Y, 50
M, 50C and 50B photoconductor drums 58Y and 58
It has a single optical deflecting device 5 as a deflecting means for deflecting each of M, 58C and 58B toward a predetermined position at a predetermined linear velocity. Note that, hereinafter, the direction in which the laser beam is deflected by the optical deflector 5 is referred to as the main scanning direction.

The optical deflecting device 5 includes a polygon mirror body 5a having a plurality of, for example, eight plane reflecting mirrors (planes) arranged in a regular polygonal shape, and the polygon mirror body 5a at a predetermined speed in the main scanning direction. It has a motor (not shown) for rotating. The polygon mirror body 5a is made of, for example, aluminum.
Further, each reflecting surface of the polygon mirror 5a is a surface including a direction in which the polygon mirror body 5a is rotated, that is, a surface orthogonal to the main scanning direction,
That is, after being cut along the sub-scanning direction, the cut surface, for example, is provided by a surface protective layer such as S _i O ₂ is deposited.

Between the light deflecting device 5 and the image plane, the first and second imaging lenses 30a for giving a predetermined optical characteristic to the laser beam deflected in a predetermined direction by the reflecting surface of the light deflecting device 5. And a pair of post-deflection optical systems 30 composed of 30b and the combined laser beams L (Y, Y, emitted from the second imaging lens 30b of the post-deflection optical system 30).
M, C and B) individual beams to reach a predetermined position before the area in which the image is written, and only one horizontal sync detector 23 and post-deflection optics 21 and horizontal 4 × 2 combined laser beams L (Y, M, which are arranged between the synchronous detector 23 and passed through at least one lens described later in the post-deflection optical system 21).
Only one set of the folding mirror 25 for horizontal synchronization is provided which reflects a part of C and B) toward the horizontal synchronization detector 23 in different directions in the main and sub-scanning directions.

Next, the pre-deflection optical system between the laser element as the light source and the optical deflector 5 will be described in detail.

The optical scanning device 1 includes the first and second two (N ₁ = N ₂ = N ₃ = N ₄ ) satisfying N _i (i is a positive integer).
= 2) laser element, and generates a laser beam corresponding to image data color-separated into color components, the first to fourth light sources 3Y, 3M, 3C and 3B (M and M are positive integers, Here, it has 4).

The first to fourth light sources 3Y, 3M, 3C and 3B each emit a yellow first laser beam 3Ya which emits a laser beam corresponding to a yellow image.
And a yellow second laser 3Yb, M, that is, a magenta first laser 3Ma that emits a laser beam corresponding to a magenta image, and a magenta second laser 3Mb, C, that is, a cyan first laser 3Ca and cyan that emits a laser beam corresponding to a cyan image. It has a second laser 3Cb, and a black first laser 3Ba and a black second laser 3Bb for emitting a laser beam corresponding to B, that is, a black (black) image. It should be noted that the first to fourth laser beams L forming a pair are emitted from the respective laser elements.
Ya and LYb, LMa and LMb, LCa and LCb, and LBa and LBb are emitted.

Each laser element 3Ya, 3Ma, 3
Between the Ca and 3Ba and the light deflecting device 5, four sets of deflections for adjusting the cross-sectional beam spot shapes of the laser beams LYa, LMa, LCa and LBa from the respective light sources 3Ya, 3Ma, 3Ca and 3Ba to a predetermined shape are provided. The front optical system 7 (Y, M, C and B) is arranged.

Here, the laser beam LYa directed from the yellow first laser 3Ya toward the optical deflector 5 is represented as
The pre-deflection optical system 7 (Y) will be described.

The divergent laser beam emitted from the yellow first laser 3Ya is given a predetermined converging property by the finite focus lens 9Ya, and then the diaphragm 10Ya
The cross-sectional beam shape is adjusted to a predetermined shape. Aperture 10Y
The laser beam LYa that has passed through a is given a predetermined converging property only in the sub-scanning direction via the hybrid cylinder lens 11Y, and the optical deflecting device 5
Will be guided to.

A half mirror 12Y is provided between the finite focus lens 9Ya and the hybrid cylinder lens 11Y.
Finite focus lens 9Ya and hybrid cylinder lens 1
It is inserted at a predetermined angle with respect to the optical axis between 1Y.

On the surface of the half mirror 12Y opposite to the surface on which the laser beam LYa from the first yellow laser 3Ya is incident, a predetermined beam in the sub-scanning direction with respect to the laser beam LYa from the first yellow laser 3Ya. The laser beam LYb from the yellow second laser 3Yb arranged so as to be able to provide the space is
The laser beam LYa is incident on the laser beam LYa at predetermined beam intervals in the sub-scanning direction. The second yellow laser 3
Between the Yb and the half mirror 12Y, a finite focus lens 9Yb and a diaphragm 10Yb that give a predetermined convergence to the laser beam LYb from the second yellow laser 3Yb are arranged.

The respective laser beams LYa and L are combined into a substantially single laser beam having a predetermined beam interval in the sub-scanning direction via the half mirror 12Y.
Yb passes through a laser synthesizing mirror unit 13, which will be described later with reference to FIG. 8, and is guided to the optical deflecting device 5.

Similarly, in relation to M, that is, magenta, a finite focus lens 9Ma and a diaphragm 1 are provided between the magenta first laser 3Ma and the laser synthesizing mirror unit 13.
0 Ma, the hybrid cylinder lens 11M, the half mirror 12M, the magenta second laser 3Mb, the finite focus lens 9Mb and the diaphragm 10Mb, that is, C, ie, cyan, between the cyan first laser 3Ca and the laser synthesizing mirror unit 13, Finite focus lens 9Ca, diaphragm 10
Ca, hybrid cylinder lens 11C, half mirror 12C, cyan second laser 3Cb, finite focus lens 9
Cb and diaphragm 10Cb, and in relation to B, that is, black, a finite focus lens 9Ba and diaphragm 10B are provided between the black first laser 3Ba and the laser combining mirror unit 13.
a, the hybrid cylinder lens 11B, the half mirror 12B, the second black laser 3Bb, the finite focus lens 9Bb, and the diaphragm 10Bb are respectively arranged at predetermined positions. The light sources 3 (Y, M, C and B), the pre-deflection optical system 7 (Y, M, C and B), and the laser synthesizing mirror unit 13 are held by, for example, an aluminum alloy. It is held integrally by the member 15.

Finite focus lens 9 (Y, M, C and B)
a and 9 (Y, M, C and B) b are respectively
A single lens in which a UV-curing plastic aspherical lens (not shown) is bonded to the aspherical glass lens or the spherical glass lens is used.

FIG. 3 shows the half mirror 1 of the pre-deflection optical system 7.
2 is a partial cross-sectional view of an optical path between the reflection surface of the optical deflecting device 5 and the reflection surface of the optical deflecting device 5, as viewed from the sub-scanning direction with a folding mirror and the like omitted. In FIG. 3, one laser beam L
Only the optics for Y (LYa) are shown representatively.

Hybrid cylinder lens 11 (Y)
Is PM having substantially the same curvature in the sub-scanning direction.
It is formed by a cylinder lens 17 (Y) of MA and a cylinder lens 19 (Y) of glass. The surface of the PMMA cylinder lens 17 (Y) that contacts air is formed to be substantially flat.

Further, the hybrid cylinder lens 11
(Y) is cylinder lens 17 (Y) and cylinder lens 1
9 (Y) is due to adhesion between the exit surface of the cylinder lens 17 (Y) and the entrance surface of the cylinder lens 19 (Y),
Alternatively, they are integrally formed by being pressed from a predetermined direction toward a positioning member (not shown). In the hybrid cylinder lens 11 (Y), the cylinder lens 17 (Y) may be integrally formed on the entrance surface of the cylinder lens 19 (Y).

Plastic cylinder lens 17 (Y),
For example, it is formed of a material such as PMMA (polymethylmethacryl). Glass cylinder lens 19 (Y)
Is formed of a material such as TaSF21. Further, the respective cylinder lenses 17 (Y) and 19 (Y) are fixed to the finite focus lens 9 at accurate intervals by the positioning portion integrally formed with the holding member 15.

Table 1 below shows optical numerical data of the pre-deflection optical system 7.

[0067]

[Table 1]

As is clear from Table 1, the finite focus lens 9 and the hybrid cylinder lens 11 corresponding to the respective color components are the same lenses for all color components by themselves. In addition, Y (yellow)
The pre-deflection optical system 7Y and the pre-deflection optical system 7B corresponding to B (black) have substantially the same lens arrangement. Further, the pre-deflection optical system 7M corresponding to M (magenta) and the pre-deflection optical system 7C corresponding to C (cyan) are different from the pre-deflection optical systems 7Y and 7B in that they have a finite focus lens 9 and a hybrid cylinder. Lens 1
The distance from 1 is widened.

FIG. 4 shows each of the pre-deflection optical systems 7 (Y, M, C and B) shown in FIG. 3 and Table 1 in the direction orthogonal to the rotation axis of the reflecting surface of the optical deflector 5 (sub-axis). (Scanning direction)
Reflecting surfaces 13Y and 13M of the respective laser synthesizing mirrors
And the laser beam L from 13C to the optical deflector 5
Y, LM and LC are indicated. (LY is LYa and LYb, LM is LMa and LMb, LC is LCa and LCb
Made of).

As is apparent from FIG. 4, the respective laser beams LY, LM, LC and LB are transmitted by the optical deflector 5
Are guided to the optical deflecting device 5 at mutually different intervals in a direction parallel to the rotation axis of the reflecting surface of. Also, the laser beam L
M and LC are asymmetrical with respect to a surface that is orthogonal to the rotation axis of the reflection surface of the optical deflector 5 and that includes the center of the reflection surface in the sub-scanning direction, that is, a surface that includes the optical axis of the system of the optical scanning device 1. , Is guided to each reflecting surface of the light deflecting device 5. The laser beams LY, LM, L on the reflecting surfaces of the optical deflector 5 are
The distance between C and LB is 3.20 m between LY and LM.
m, 2.70 mm between LM and LC, and 2.30 mm between LC and LB.

FIG. 5 shows an optical member arranged between the optical deflecting device 5 of the optical scanning device 1 and each of the photosensitive drums 58, that is, the image plane, when the deflection angle of the optical deflecting device 5 is 0 °. The state viewed from the sub-scanning direction is shown.

As shown in FIG. 5, the post-deflection optical system 30
Between the second image-forming lens 30b of FIG.
4 × 2 laser beams L (Y, M,
C and B) to bend the first folding mirror 33 (Y, M, C and B) toward the image plane, and the laser beams LY, LM and LC folded by the first folding mirrors 33Y, 33M and 33C. Further, second and third folding mirrors 35Y, 35M and 35C and 37Y, 37M and 37C which are folded back are arranged. As is apparent from FIG. 5, the laser beam LB corresponding to the B (black) image is guided back to the image plane without being passed through other mirrors after being turned back by the first turning mirror 33B. .

The first and second image forming lenses 30a and 30b, the first folding mirror 33 (Y, M, C and B), and the second folding mirrors 35Y, 35M and 35C respectively perform optical scanning. Intermediate base 1a of device 1
For example, it is fixed to a plurality of fixing members (not shown) formed by integral molding by adhesion or the like.

Also, the third folding mirrors 37Y, 37
M and 37C are movably arranged in at least one direction related to the direction perpendicular to the mirror surface via a fixing rib and an inclination adjusting mechanism described later with reference to FIG.

Third folding mirrors 37Y, 37M, 3
7C and the first folding mirror 33B and the image plane, and 4 × 2 = 8 laser beams L (Y, M, C) reflected via the respective mirrors 33B, 37Y, 37M and 37C. Further, dust-proof glass 39 (Y, M, C and B) for dust-proofing the inside of the optical scanning device 1 is further arranged at a position where the optical scanning device 1 emits B and B).

Next, the optical characteristics between the hybrid cylinder lens 11 and the post-deflection optical system 30 will be described in detail.

Post-deflection optical system 30, that is, the first two-lens set
Since the second imaging lenses 30a and 30b are formed of plastic, for example, PMMA, the ambient temperature changes, for example, between 0 ° C and 50 ° C, so that the refractive index n becomes 1.4876 to 1.4
It is known to change up to 789. In this case, the imaging plane on which the laser beams that have passed through the first and second imaging lenses 30a and 30b are actually focused, that is, the imaging position in the sub-scanning direction fluctuates by about ± 12 mm. .

From this, by incorporating a lens of the same material as that of the lens used for the post-deflection optical system 30 in the pre-deflection optical system 7 shown in FIG. 3 in an optimized curvature state, The fluctuation of the image plane caused by the fluctuation of the refractive index n due to the temperature change is ± 0.5 mm (hereinafter, [m
m]). 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 30 is a plastic lens, the change in the refractive index due to the temperature change of the lens of the post-deflection optical system 30 causes It is possible to correct the chromatic aberration in the sub-scanning direction that occurs as a result.

FIG. 6 shows the first to fourth combined laser beams L (Y, M, C and B) passing between the optical deflector 5 shown in FIG. 5 and the image plane and the optical scanning. FIG. 6 is an optical path diagram showing a relationship with the optical axis of the system in the sub-scanning direction of the apparatus 1.

As shown in FIG. 6, the first to fourth combined laser beams L (Y, M, C and B) reflected by the reflecting surface of the optical deflector 5 are respectively reflected by the first Between the imaging lens 30a and the second imaging lens 30b, in the sub-scanning direction, the optical axis of the system is intersected and guided to the image plane.

FIG. 7 shows the arrangement of the laser elements used in the pre-deflection optical system shown in FIG. 2 in detail.

As already described with reference to FIG. 2, the first to fourth light sources 3 (Y, M, C and B) are each a set of two yellow first lasers 3Ya and yellow second lasers. 3Yb, a magenta first laser 3Ma and a magenta second laser 3Mb, a cyan first laser 3Ca and a cyan second laser 3Cb, and a black first laser 3Ba and a black second laser 3Bb. In addition,
The respective lasers forming a pair are arranged at a distance in the sub-scanning direction by a predetermined distance corresponding to the beam distance on the image plane described later. A pair corresponding to each pair, that is, a color component, is a sub-scanning direction distance that is defined in advance corresponding to each reflection area of the laser synthesizing mirror block 13 shown in FIG. They are arranged in four layers.

FIG. 8 shows a laser synthesizing mirror unit which guides the first to fourth synthesized laser beams LY, LM, LC and LB to each reflecting surface of the optical deflector 5 as a bundle of laser beams. 13 is shown.

The laser synthesizing mirror unit 13 includes first to third mirrors 13M, 13C and a plurality of mirrors 13M and 13C which are arranged by a number smaller by "1" than the number of color components capable of forming an image (the number of color-separated colors). 13B and the first to third holding mirrors 13M, 13C and 13B, respectively.
The mirror holding portions 13α, 13β and 13γ and the bases 13a that support the respective holding portions 13α, 13β and 13γ. The base 13a and the respective holding portions 13α, 13β and 13γ
Has a small coefficient of thermal expansion, and is integrally formed of, for example, an aluminum alloy.

At this time, the light source 3Y, that is, the yellow first
The laser beam LY from the laser 3Ya and the yellow second laser 3Yb is directly guided to each reflecting surface of the light deflecting device 5, as described above. In this case, the laser beam LY is located closer to the base 13a than the optical axis of the system of the optical scanning device 1.
The mirror 13 fixed to the side, that is, the first holding portion 13α
It is passed between M and the base 13a.

Here, the laser beams LM, LC and L which are reflected by the respective mirrors 13M, 13C and 13B of the synthesizing mirror 13 and are guided to the light deflecting device 5.
B and the intensity (light quantity) of the laser beam LY directly guided to the optical deflector 5 will be considered.

According to the laser synthesizing mirror unit 13 shown in FIG. 8, the respective laser beams LM and LC are
And LB are regions in which the laser beams LM, LC and LB of the preceding stage which are incident on the reflecting surfaces of the optical deflecting device 5 are separated in the sub-scanning direction, and are folded by ordinary mirrors (13M, 13C and 13B). . Therefore, each reflective surface
Each laser beam L (M, M, which is reflected by (13M, 13C and 13B) and then supplied toward the polygon mirror body 5a.
The amount of light of C and B) can be maintained at approximately 90% or more of the amount of light emitted from the finite focus lens 9. Not only can the output of each laser element be reduced, but aberration due to the inclined parallel plate does not occur, so that the aberration of the light reaching the image plane can be uniformly corrected. As a result, each laser beam can be narrowed down, and as a result, high definition can be dealt with. The laser element 3Y corresponding to Y (yellow) is directly guided to each reflecting surface of the optical deflecting device 5 without being involved in any one of the combining mirrors 13, so that the output capacitance of the laser is reduced. Not only can be reduced, but also the mirror (13M, 13M) that may occur in other laser beams reflected by the synthetic mirror
The error of the incident angle on each reflecting surface due to the reflection at C and 13B) is removed.

Next, referring to FIG. 2 and FIG. 5, the laser beam L (Y,
M, C and B) and the respective laser beams LY, LM, L emitted to the outside of the optical scanning device 1 through the post-deflection optical system 30.
Inclination of C and LB and folding mirrors 33B, 37Y,
The relationship with 37M and 37C will be described.

As already described, the polygon mirror 5a of the optical deflector 5 reflects the first and second imaging lenses 30a.
The laser beams LY, LM, LC and LB to which the predetermined aberration characteristics have been given by the first and the third folding mirrors 30b and 30b, respectively, are first folding mirrors 33Y, 33M, 33C and 33, respectively.
It is folded back in a predetermined direction via B.

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 58b through the dustproof glass 39B.
On the other hand, the remaining laser beams LY, LM and LC
Are guided to the second folding mirrors 35Y, 35M and 35C, respectively.
35M and 35C allow the third folding mirror 3
7Y, 37M and 37C, and further the third folding mirrors 37Y, 37M and 37C.
After being reflected by, the dustproof glass 39Y, 39, respectively
M and 39C form images on the respective photosensitive 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 imaged on the photoconductor drums 58B and 58C at substantially equal intervals.

By the way, the laser beam LB is applied to the polygon mirror 5.
After being deflected by a, it is emitted from the optical scanning device 1 toward the photoconductor drum 58 only by being reflected by the folding mirror 33B. From this, the folding mirror 33 is substantially formed.
It is possible to secure the laser beam LB guided by only one B sheet.

When a plurality of mirrors are present in the optical path, this laser beam LB is changed (varied) in various aberration characteristics of the image on the image plane on the image plane, which is increased (multiplied) according to the number of mirrors, or main scanning line bending, etc. , It is useful as a reference ray for relatively correcting the remaining laser beams L (Y, M and C).

When there are a plurality of mirrors in the optical path, it is preferable that the number of mirrors used for each of the laser beams LY, LM, LC and LB be made even or odd. That is, as shown in FIG. 5, the number of mirrors involved in the laser beam LB in the post-deflection optical system is one except for the polygon mirror 5 a of the optical deflector 5.
(Odd number), the number of mirrors in the post-deflection optical system involved in the laser beams LC, LM and LY is three (odd number) except for the polygon mirror 5a. Here, regarding any one of the laser beams LC, LM and LY, the second
Assuming that the second mirror 35 is omitted, the direction of the main scanning line bending due to the inclination of the lens of the laser beam passing through the optical path where the second mirror 35 is omitted (the number of mirrors is an even number) is different from that of other lasers. The number of beams, that is, the number of mirrors, is opposite to the direction of the main scanning line bending due to the tilt or the like of an odd number of lenses, which causes a color shift which is a harmful problem when reproducing a predetermined color.

Therefore, 4 × 2 laser beams LY, L
When reproducing a predetermined color by superimposing M, LC and LB, the number of mirrors arranged in the optical path of each laser beam LY, LM, LC and LB is substantially unified into an odd number or an even number. It

FIG. 9 shows the folding mirror for horizontal synchronization in detail.

According to FIG. 9, the folding mirror 25 for horizontal synchronization includes the respective combined laser beams LY and L.
In order to reflect M, LC and LB to the horizontal sync detector 23 at different timings in the main scanning direction and to provide substantially the same height on the horizontal sync detector 23 in the sub scanning direction, First to fourth folding mirror surfaces 25Y, 25M, 25C and 25B formed at different angles in the scanning direction and the sub-scanning direction, and respective mirrors 25 (Y, M, C and B) are integrally held. It has a mirror block 25a.

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

In this way, not only can the respective laser beams LY, LM, LC and LB deflected by the optical deflector 5 be made incident on the same detection position of one detector 23, For example, it is possible to eliminate the shift of the horizontal synchronizing signal due to the sensitivity or position shift of each detector, which is a problem when a plurality of detectors are arranged. The horizontal sync detector 23 includes laser beams LY and L per line in the main scanning direction by the horizontal sync folding mirror 25.
It goes without saying that M, LC and LB are incident four times in total and two horizontal synchronization signals are obtained for each beam. 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.

FIG. 10 shows a third folding mirror 37Y,
It is a schematic perspective view which shows the support mechanism of 37M and 37C.

According to FIG. 10, the third folding mirror 3
7 (Y, M and C) are fixed portions 41 (Y, M and C) integrally formed with the intermediate base 1a and fixed portions at predetermined positions of the intermediate base 1a of the optical scanning device 1, respectively. It is held by the mirror pressing leaf spring 43 (Y, M and C) which is opposed to the portion 41 (Y, M and C) with the corresponding mirror interposed therebetween.

A pair of fixed portions 41 (Y, M and C) are formed at both ends (main scanning direction) of each mirror 37 (Y, M and C). Two protrusions 45 (Y, M and C) for holding the mirror 37 (Y, M and C) at two points are formed on one of the fixed portions 41 (Y, M and C), respectively. . The two protrusions 45 (Y, M
And C) are ribs 46, as shown by the dotted lines in FIG.
(Y, M and C). The remaining fixed portion 41 (Y, M and C) supports the mirror held by the protrusion 45 (Y, M and C) so as to be movable in the direction perpendicular to the mirror surface or along the optical axis. Set screw 47
(Y, M and C) are arranged.

As shown in FIG. 10, each mirror 37 (Y, M and C) has a projection 45 when the set screw 47 (Y, M and C) is moved in a predetermined direction.
It is moved in the direction perpendicular to the mirror surface or in the optical axis direction with (Y, M and C) as the fulcrum. In this method, the inclination in the main scanning direction, that is, the bending of the main scanning line can be corrected, but the combined laser beams LY, LM,
Regarding the gap between the LC and LB in the sub-scanning direction,
I can not cope. Therefore, the deviation of the interval in the sub-scanning direction is dealt with by changing the horizontal writing timing, which will be described later with reference to FIGS. 11 to 14.

The registration correction (adjustment) mode will be described below.

FIG. 11 is a schematic perspective view showing the vicinity of the conveyor belt of the image forming apparatus shown in FIG. 1 for explaining the registration correction mode. As described above, the registration centers 78 and 80 are connected to the conveyor belt 52.
In the width direction, that is, in the main scanning direction H at predetermined intervals. The line (virtual) connecting the centers of the registration centers 78 and 80 is the image forming section 50 (Y, M, C).
And B) are defined substantially parallel to the axes of the photoconductors 58 (Y, M, C and B). The line connecting the centers of the resist centers 78 and 80 is preferably the image forming unit 5
It is placed exactly parallel to the 0B photoconductor 58B.

FIG. 12 shows registration sensors 78 and 80.
FIG. 7 is a schematic cross-sectional view of (the sensor 78 and 80 are substantially the same, and is represented by 78).

The sensor 78 (80) is connected to the housing 78a.
(80a) is arranged at a predetermined position of the housing 78a (80a) and has a predetermined wavelength in the image on the conveyor belt 52, at least wavelengths near 450, 550 and 600 nm,
The reference light source 78b (80b) for irradiating light including the light, the light generated from the reference light source 78b (80b) is focused on the image on the conveyor belt 52, and the light reflected by the image is detected by a photo sensor described later. 78d (80d) and a convex lens 78c (80c) for forming an image on the convex lens 7
Photosensor 78d (80) for detecting the reflected light from the image collected by 8c (80c) and converting it into an electric signal
d) etc. are included.

The photo sensor 78d (80d) is shown in FIG.
11, the first and second photodetection regions 78A and 78B (80A and 8B) are divided into two along the main scanning direction H orthogonal to the sub-scanning direction V shown in FIG.
0B) has a region division type pin diode.

The wavelength of the light used for the light source 78b (80b) is the peak wavelength of the absorption spectrum distribution of each toner of C, cyan, Y, yellow and M magenta, respectively, and the detection sensitivity for each toner is Reserved to maintain. Also, the convex lens 78
The lateral magnification of c (80c) is -1.

FIG. 13 shows the registration sensors 78 and 80.
It is a schematic diagram which shows the principle by which the position of an image can be detected via.

According to FIG. 13A, the registration sensor 7
In the photo sensor 78d of No. 8, the boundary portion 78C between the first and second detection areas 78A and 78B is the conveyor belt 52.
It is arranged so as to coincide with the reference position Ho related to the main scanning direction H of the image formed above. (Similarly, in the photo sensor 80d of the registration sensor 80, the boundary portion 80C of the first and second detection areas 80A and 80B is the reference position Hd related to the main scanning direction H of the image formed on the transport belt 52. The images are arranged so that they match.)
For example, the sensor passes through B, C, M, and Y in this order (the image Y is omitted).

According to FIG. 13B, the convex lens 78c
Since the lateral magnification of (80c) is -1, the output voltage output from each pin diode 78A (80A) and 78B (80B) is in the direction of deviation between the design center Ho (Hd) in the main scanning direction and the image. The pin diode on the opposite side is detected with the design center Ho (Hd) sandwiched between the reversed direction and the deviation center.

For example, since the image B is roughly line-symmetrical with respect to the reference position Ho (Hd) in the main scanning direction H, the outputs from the corresponding pin diodes 78A (80A) and 78B (80B) are Generally, they are the same. On the other hand, the image C has a reference position Ho (H
Since it is deviated to the area B side around d),
Corresponding pin diodes 78A (80A) and 78B
The output from (80B) is A> B.

Here, the sum of the outputs of the pin diodes corresponding to the respective images B and C, that is, A + B, and the difference, that is, A-B, are obtained, and each is thresholded at a predetermined threshold level TH to obtain each image. The centers of B and C in the sub scanning direction V and the center of the main scanning direction H can be detected. That is, by detecting a position (for example, TB and TC) at which the sum (A + B) of the outputs of the pin diodes exceeds the threshold level TH, the center of the corresponding image in the sub-scanning direction V and the output difference (A−B) The center of the main scanning direction H can be detected by detecting the value of the level Ps of).

FIG. 14 is a schematic block diagram of an image control unit for controlling the image forming operation of the 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
It includes multiple control units such as 5B. The image control CPU 111, the timing control unit 113, and each data control unit 115 (Y, M, C, and B) are connected to each other 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 a motor or a roller, 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 control unit 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 registration sensors 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 required by an adjustment mode described later are connected. There is.

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 the image data stored in (Y, M, C, and B), the image forming units 50 (Y, M, C, and B) are directed to the respective photosensitive drums 58 (Y, M, C, and B). Corresponding light source 3 (Ya, Y
b, Ma, Mb, Ca, Cb and Ba, Bb) based on the output signals from the laser drive unit 116 (Y, M, C and B) and the registration sensors 78 and 80.
Based on the signals from the registration correction calculation device 117 and the registration correction calculation device 117, which calculates the correction amount of the image writing timing by the combined laser beams LY, LM, LC and LB based on the signals from the registration sensors 78 and 80. The image forming units 50 (Y, M, C and B) and the lasers 3 (Y) of the light source 3 of the optical scanning device 1.
a, Yb, Ma, Mb, Ca, Cb and Ba, Bb)
Timing setting device 118 that defines various timings for operating the image forming apparatus, and each image forming unit 50.
Oscillation frequency variable circuit (voltage-controlled oscillator, that is, voltage-controlled oscillation circuit) that corrects the deviation due to the solid-state error for each (Y, M, C, and B) and the difference in the optical path length of each optical path in the optical scanning device 1. , Hereafter referred to as VCO) 119Y, 119M, 119C and 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 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 line memory, a plurality of latch circuits and an OR gate, respectively, and is similarly integrated in an ASIC or the like.

The registration correction arithmetic unit 117 is a microprocessor including at least four sets of comparators and OR gates, and is similarly integrated in an ASIC or the like.

VCO 119 (Y, M, C and B) is
Each of them is an oscillation circuit whose output frequency can be changed according to the applied voltage, and has a frequency variable range of about ± 3%. A harmonic oscillation circuit, an LC oscillation circuit, a simulated reactance variable LC oscillation circuit, or the like is used as this type of oscillation circuit. In addition, VCO1
Also known as 19 is a circuit element in which a converter for converting an output waveform from a sine wave to a rectangular wave is integrally incorporated.

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 output to the horizontal sync signal Hsyn via the horizontal sync signal generation circuit 121.
It is converted to c and input to each data control unit 115 (Y, M, C and B).

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

The image forming apparatus 100 has an image forming (normal) mode in which an image is formed on the sheet P conveyed through the conveyor belt 52 and a registration correction (adjustment) mode in which an image is directly formed on the conveyor belt 52. It is possible to operate in two modes.

In the registration correction mode, as shown in FIG. 11, two pairs of test images 178 (Y) are formed on the conveyor belt 52 with a predetermined distance in the main scanning direction H orthogonal to the sub scanning direction V. , M, C and B) and 180 (Y,
M, C and B) are formed.

A pair of test images 178 (Y, M, C and B) and 180 (Y, M, C and B) are stored in the ROM.
Are formed in correspondence with the resist adjustment image data stored in advance. Test images 178 and 180
Is moved in the sub-scanning direction V as the conveyor belt 52 moves, and passes through the registration sensors 78 and 80. As a result, the deviation between the test images 178 and 180 and the registration sensors 78 and 80 is detected.
In the registration correction mode, the feeding roller 72 for feeding the paper P from the cassette 70 and the fixing device 84.
Remains stopped.

Specifically, under the control of the main controller 101, the first to fourth image forming sections 50Y, 50M and 50 are formed.
C and 50B are energized, and each image forming unit 50 (Y,
A predetermined potential is applied to the surface of each photosensitive drum 58 (Y, M, C and B) of M, C and B). At the same time, the polygon mirror 5a of the optical deflector 5 of the optical scanning device 1 is rotated at a predetermined speed under the control of the image control CPU 111 of the image controller 110.

Subsequently, the image data corresponding to the test image loaded from the ROM is loaded into each image memory 114 (Y, M, C and B) under the control of the image control CPU 111. After that, the timing control unit 113 sets the timing data set by the timing setting device 118 and the internal RAM of the timing control unit 113.
Based on the registration correction data stored in (in this case, if the registration correction data is not stored in the internal RAM, the initial data stored in the ROM is used) from the timing control unit 113 to the vertical synchronization. The signal Vsync is output.

The vertical synchronizing signal Vsync generated by the timing controller 113 is supplied to each data controller 115.
(Y, M, C and B) and each VCO 119 (Y, M
M, C and B).

Each data control unit 115 (Y, M, C and B) corresponds to the optical scanning device 1 by the corresponding laser drive unit 116 (Y, M, C and B) based on the vertical synchronizing signal Vsync. Each laser 3Ya, 3Yb of the light source 3,
3Ma, 3Mb, 3Ca, 3Cb, 3Ba and 3Bb
The laser beams L (Y, M, C and B) emitted from the lasers 3 (Y, M, C and B) a and 3 (Y, M, C and B) b of the light source 3 are moved horizontally. The horizontal sync signal generating circuit 121 is detected by the sync detector 23.
After the horizontal synchronizing signal Hsync is output from the image memory 114, a predetermined clock (until the output from the registration sensors 78 and 80 is input, the initial data stored in the ROM is used) is counted, and then the image memory 114 is counted.
The image data stored in (Y, M, C and B) is output at a predetermined timing.

At this time, the oscillation frequency data which is the initial data stored in the ROM is supplied from each VCO 119 (Y, M, C and B) to each data control section 115 (Y, M, C and B). To be done.

Then, each data control unit 115 (Y, M,
By controlling C and B), each laser driving unit 116 is controlled.
A laser drive signal corresponding to the image data is output from (Y, M, C and B) to each laser 3 (Y, M, C and B) a and 3 (Y, M, C and B) b of the light source 3. ,
Laser beam L whose intensity is modulated based on image data
(Ya, Yb, Ma, Mb, Ca, Cb and Ba, B
b) is output.

As a result, the image forming sections 50Y, 50M, 50C and 5 which are corresponding to a predetermined potential in advance are provided.
0B photosensitive drums 58Y, 58M, 58C and 5
An electrostatic latent image corresponding to the test image data is formed on each of 8B. This electrostatic latent image is developed by the developing devices 62Y and 6Y.
2M, 62C, and 62B develop the toners corresponding to the corresponding colors, and convert the test toner images into four colors (two sets).

The two sets of test toner images on the photosensitive drums 58 (Y, M, C and B) are transferred to the transfer devices 64Y and 6Y.
It is directly transferred to the conveyor belt 52 via 4M, 64C and 64B and conveyed toward the registration sensors 78 and 80.

Two sets of test toner images are recorded on the registration sensor 7
When passing through 8 and 80, the registration sensors 78 and 80 output a predetermined output corresponding to the relative position of each test toner image based on the positions of the registration sensors 78 and 80, that is, the deviation of the test toner image. It

The outputs from the registration sensors 78 and 80 are input to the registration correction calculation device 117 and used to calculate the deviation of each test toner image.

The registration correction arithmetic unit 117 has a pair of test toner images for each color formed at a predetermined distance in the sub-scanning direction, that is, 178Y, 180Y and 178Y.
For each of M and 180M, 178C and 180C, and 178B and 180B, the deviation of the position in the sub-scanning direction is detected, and then the average value is calculated. From the deviation amount between this average value and the predetermined design value, The correction amount Vr of the timing of outputting the vertical synchronization signal Vsync is defined. As a result, each light source 3 (Ya, Yb, Ma, M of the optical scanning device 1 is
b, Ca, Cb and Ba, Bb) light emission timing,
That is, the intervals at which the image forming units 50 (Y, M, C and B) are arranged and the first light emitted from the optical scanning device 1.
To the fourth combined laser beams L (Y, M, C and B), the deviation in the sub-scanning direction depending on the distance in the sub-scanning direction from each other is aligned.

Further, the registration correction calculation device 117 is set to 1
A set of test toner images, such as 178Y, 178M,
After detecting the displacement of each of the 178C and 178B in the main scanning direction, the average value is calculated, and the image is output after the horizontal synchronization signal Hsync is output from the displacement amount between the average value and a predetermined design value. The correction amount Hr of the timing of outputting data is specified. Thus, the timing of intensity modulation of the laser beam L (Y, M, C and B) emitted from each laser 3 (Y, M, C and B) of each light source 3 of the optical scanning device 1, that is, , The writing positions in the main scanning direction of the image data recorded on the photosensitive drums 58 (Y, M, C and B) of the image forming sections 50 (Y, M, C and B) are aligned.

The registration correction calculation unit 117 further includes
A pair of test toner images, namely 178Y and 180Y,
178M and 180M, 178C and 180C, and 17
For each of 8B and 180B, the deviation of the position in the main scanning direction is detected, and then the average value is calculated, and the deviation amount between the calculated average value and a predetermined design value is calculated, and based on this deviation amount. , VCO119 (Y, M, C and B)
The amount of correction Fr of the oscillation frequency output from is specified. As a result, each laser 3 (Y, Y of each light source 3 of the optical scanning device 1
M, C and B) to photoconductor drums 58 (Y, M, C and B) of each image forming unit 50 (Y, M, C and B).
Length of each laser beam emitted toward the main scanning direction per clock, that is, each photoconductor 58 (Y,
The lengths of one line in the main scanning direction imaged in M, C and B) are matched.

Incidentally, the respective correction amounts Vr, Hr and Fr obtained by the registration correction calculation device 117 are
Each is temporarily stored in the RAM unit in the timing control unit 113. In this case, the respective correction amounts Vr,
Hr and Fr may be stored in the nonvolatile RAM 103. In addition, these correction operations are performed when a correction mode is instructed by a control panel (not shown), a power switch (not shown) of the image forming apparatus 100 is turned on, or the number of prints counted by a counter (not shown) or the like. Is executed at a predetermined timing such as when the number of sheets reaches a predetermined number.

The test toner image on the conveyor belt 52 used in the adjustment mode is further conveyed with the rotation of the conveyor belt 52 and removed by the belt cleaner 82.

Next, the image forming (normal) mode will be described.

When an image formation start signal is supplied from an operation panel or a host computer (not shown), each image forming section 50 (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 in 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 biased based on a predetermined timing, for example, the vertical synchronizing signal Vsync from the timing control unit 113, so that one sheet of paper is fed from the paper cassette 70. P is taken out. The taken-out sheet P is transferred to the image forming units 50 (Y, M, C) by the registration rollers 72.
And Y provided by the image forming operation according to B),
The timing is matched with the toner images of M, C and B,
The suction roller 74 is in close contact with the conveyor belt 52, and is guided toward each image forming unit 50 as the conveyor belt 52 rotates.

On the other hand, based on the data set by the timing setting device 118 and the registration data and 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.

When the vertical synchronization signal Vsync is output by the timing control unit 113, each data control unit 115
(Y, M, C and B), each laser drive unit 116
(Y, M, C, and B) are energized, and one line in the main scanning direction from each laser 3 (Y, M, C, and B) a and 3 (Y, M, C, and B) b of each light source 3 A minute laser beam is applied to each photoconductor 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 sync signal Hsync generated from the horizontal sync signal generation circuit 121 based on the laser beam for one line, each VCO 119 (Y, M,
C and B) clocks are counted and each VCO1
When the number of clocks of 19 (Y, M, C and B) reaches a predetermined value, the image data to be printed is read from each image memory 114 (Y, M, C and B).

Then, each data control unit 115 (Y, M,
By controlling C and B), each laser driving unit 116 is controlled.
Image data is transferred to (Y, M, C and B) in order to change the intensity of each laser beam L (Y, M, C and B) emitted from each light source 3, and each image forming unit 50 is transferred.
(Y, M, C and B) photoconductor drums 58 (Y, M
An image without deviation is formed on M, C and B).

As a result, each photosensitive drum 58 (Y, M,
Each laser beam L (Y, M,
C and B) are deviations of optical paths from the lasers 3 (Y, M, C and B) of the light sources 3 to the photoconductor drums 58 (Y, M, C and B) or the photoconductor drums 58.
(Y, M, C and B) is accurately connected to each photoconductor drum 58 (Y, M, C and B) without being affected by the variation of the beam spot diameter on the image plane due to the deviation of the diameter of (Y, M, C and B). To be imaged.

The first to fourth image forming sections 50 (Y,
M, C and B) photoconductor drums 58 (Y,
The first to fourth laser beams L (Y, M, C and B) imaged on M, C and B) are respectively charged to the photosensitive drums 58 (Y, M) which are previously charged to a predetermined potential. , C and B) on the basis of the image data, an electrostatic latent image corresponding to the image data is formed on each photosensitive drum 58 (Y, M, C and B).

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 photosensitive 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 on the paper P that are exactly overlapped with each other are formed on the paper P. In addition,
After the toner image is transferred to the paper P, the residual toner remaining on the photosensitive drums 58 (Y, M, C and B) is removed by the cleaner 66 (Y, M, C and B), and The residual potential left on each of the photoconductor drums 58 (Y, M, C and B) is the static elimination lamp 68 (Y, M, C and B).
It is used for the 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, 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 for transporting the sheet P to be used.

Next, the post-deflection optical system between the optical deflector 5 and the image plane will be described in detail.

FIGS. 15 to 50 and Tables 2 to 6 show the first surface of the first imaging lens 30a of the post-deflection optical system 30, that is, the light incident surface, and the second surface of the first imaging lens 30a. That is, the light emitting surface, the first of the second imaging lens 30b
Surface or light incident surface (lens surface number in Table 5 is indicated by "3"), second surface of the second imaging lens 30b or light emitting surface (lens surface number in Table 6 is "4") Various optical properties (as shown) and lens data are shown.

[0160]

[Table 2]

[0161]

[Table 3]

[0162]

[Table 4]

[0163]

[Table 5]

[0164]

[Table 6]

In FIGS. 15 to 50, the axis x is aligned with the optical axis direction of the post-deflection optical system, "+" toward the optical deflector 5 and "to the image plane". -"Shall be given. The axis y is aligned with the main scanning direction and indicates that the direction of light deflected by the optical deflector 5, that is, the direction in which the polygon mirror 5a of the optical deflector is rotated is from "+" to "-". I shall. In addition,
The same is displayed in Tables 2 to 6. On the other hand, the axis z coincides with the sub-scanning direction, and for example, the side on which the laser beam LB shown in FIG. 4 is passed, that is, the upper side with respect to the optical axis of the system in the sub-scanning direction is indicated by "+". And

When a toric lens is used in a conventional optical scanning device, in order to optimize aberration characteristics such as spherical aberration, coma aberration, field curvature or magnification error in the image plane, It is known that three or more imaging lenses are required.

Here, the shapes of the entrance surface and the exit surface of the respective lens surfaces of the first and second plastic lenses 30a and 30b are represented by the polynomial equation (1) in Table 2 and simulated. The results obtained will be described.

In the equation (1), the spherical aberration in the sub-scanning direction is defined by the term of Amn n ≠ 0 and Amn ≠ 0.
Various aberration characteristics in the main scanning direction can be optimized by coma aberration, field curvature distortion aberration, magnification error, and the like, and by terms of Am of m ≠ 0 and Amn ≠ 0. Here, according to the result of simulating the shape of each lens surface of the first and second plastic lenses 30a and 30b, one of the four lens surfaces of lens surface numbers 1 to 4 is (2 In the equation, Am of n ≠ 0 and Amn ≠
Contains a term of 0 (that is, does not include a particular rotational symmetry axis)
In the case of a lens surface, it was found that the correction of coma aberration and spherical aberration was insufficient, and the cross-sectional beam spot diameter on the image plane was about 100 μm.
Also, when two or more lens surfaces including the terms of Amn n ≠ 0 and Amn ≠ 0 are arranged, it becomes clear that the cross-sectional beam spot diameter on the imaging plane can be narrowed down to about 40 μm. It was

For the lens surface of each lens, (1)
When the total number of Amn shown in the formula (contents of the sigma term) is simulated, as shown in Tables 3 to 6,
m ≧ 11 and n ≧ 2, where (m, n) = (0,
It has been confirmed that various aberration characteristics in the main scanning direction and the sub-scanning direction can be favorably set under the condition that 0), (2,0) and (0,1) are satisfied.

FIG. 15 shows the shape of the first surface of the first imaging lens 30a, that is, the light incident surface. That is, as shown in FIG. 15, the first imaging lens 30a
The first surface of is formed asymmetrically with respect to the optical axis, that is, (y = 0, z = 0). The target surface is only one of the surfaces defined by z = 0.

FIG. 16 shows the curvature of the first surface of the first imaging lens 30a in the sub-scanning direction at the intersection of the optical scanning surface and the lens surface with respect to the plane including the optical axis of the system and extending in the main scanning direction. It is shown. That is, FIG. 16 shows a characteristic of the shape of the first surface in the sub-scanning direction shown in FIG. 15, that is, the optical axis.
It is shown that the first surface of the first imaging lens 30a is asymmetric with respect to (y = 0, z = 0). As can be seen from this figure and the equations in Table 2, the shapes in the main scanning direction and the sub scanning direction can be set independently. As a result, the main scanning line bending, the beam diameter on the image plane (sub-scanning direction), and surface tilt correction can be sufficiently performed for a wide deflection angle, and the temperature and humidity can be adjusted in combination with other lenses. An optical system that is not easily affected by changes can be provided.

In FIG. 17, with respect to the first surface of the first imaging lens 30a, the main scanning direction coordinates of the curvature in the sub scanning direction at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction. The second derivative is shown. That is, FIG. 17 shows that the rate of change of the curvature of the first surface in the sub-scanning direction shown in FIG. 15 changes asymmetrically with respect to the point of intersection with the optical axis in the main scanning direction. Lens 30a according to FIG.
18 does not have a rotationally symmetric surface, and according to FIG. 18, the primary scanning direction primary differential value with respect to the system optical axis direction coordinate of the line of intersection between the main scanning plane including the optical axis of the system and the lens surface has two polarities. It turns out that it has a value. As a result, while maintaining the characteristics in the sub-scanning direction described in the description of FIG. 16, in the main scanning direction as well, without increasing the lens thickness for a wide deflection angle, f
The θ characteristic can be corrected. The thicker the lens, the longer the molding time, especially in the case of a plastic molded lens, leading to an increase in cost.

In FIG. 18, with respect to the first surface of the first imaging lens 30a, the optical axis direction coordinate at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction with respect to the main scanning direction coordinate. The differential value is shown. That is, in FIG.
Is the inclination of the curvature of the first surface in the main scanning direction shown in FIG.
It indicates that the (direction) changes at a position other than the point intersecting the optical axis.

FIG. 19 shows the radius of curvature in the main scanning direction at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction for the first surface of the first imaging lens 30a. . That is, FIG. 19 shows a characteristic of the shape of the first surface in the main scanning direction shown in FIG. 15, that is, the optical axis (y = 0, z =
0), the first surface of the first imaging lens 30a is asymmetric. In addition, this lens surface shows that the curvature in the main scanning direction changes its sign in the middle of the main scanning direction, which makes it possible to widen the lens without increasing the absolute value of the power in the main scanning direction. Various characteristics in the main scanning direction can be optimized with respect to the deflection angle. It is known that, on the lens surface, the larger the absolute value of the power, the more likely it is that aberration will occur. Therefore, in order to avoid this, the performance can be improved.

FIG. 20 shows the first surface of the first imaging lens 30a in the main scanning direction of the lens surface with reference to the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction. The position in the sub-scanning direction at each point, that is, the shape in the sub-scanning direction is shown. That is, FIG. 20 shows that the shape of the first surface in the sub-scanning direction shown in FIG. 15 is asymmetric with respect to the main scanning direction.

FIG. 21 shows the deviation of the shape of the first surface of the first imaging lens 30a from the shape of the circular arc having the curvature in the sub-scanning direction z = 0 of the shape in the sub-scanning direction. On the other hand, it is shown that the shape includes a higher order (fourth order or more) term. Further, FIG. 22 shows an asymmetrical component with respect to the shape of the first surface of the first imaging lens 30a in the main scanning direction with respect to the scanning surface spreading in the main scanning direction. That is, FIG.
1 and 22 show that the first surface of the first imaging lens 30a does not include a rotationally symmetric surface in either the main scanning direction or the sub scanning direction. Note that, as shown in FIG. 21, the coefficient of a term larger than at least a quartic term in the sub-scanning direction is set to the shape of a line where the scanning surface including the optical axis and extending in the main scanning direction intersects with the lens surface, and the sub-scanning direction. By controlling independently of the radius of curvature, various aberration characteristics in the main scanning direction and the sub scanning direction can be set well.

FIG. 23 shows the shape of the second surface of the first imaging lens 30a, that is, the light exit surface. As shown in FIG. 23, the second surface of the first imaging lens 30a is
It is formed asymmetrically with respect to the optical axis, that is, (y, z) = (0,0). The plane symmetry plane of this plane is only one plane defined by z = 0.

Hereinafter, similar to the first surface of the first imaging lens 30a shown in FIGS. 15 to 22, that is, the light incident surface,
24 to 30, regarding the second surface of the first imaging lens 30a, a plane including the optical axis of the system and extending in the main scanning direction, that is, a curvature in the sub-scanning direction at the intersection of the optical scanning surface and the lens surface, Second-order differential value of curvature in the sub-scanning direction at the intersection of a plane including the optical axis of the system in the main scanning direction and the lens surface, a plane including the optical axis of the system and extending in the main scanning direction, and the lens surface The differential value of the optical axis direction coordinate at the intersection point with respect to the main scanning direction coordinate, the main scanning direction curvature at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction, the main scanning direction including the optical axis of the system The position in the sub-scanning direction at each point in the main scanning direction of the lens surface based on the intersection of the expanding plane and the lens surface, that is, the shape in the sub-scanning direction, the curvature of the shape in the sub-scanning direction in the sub-scanning direction z = 0 Deviation of shape from the arc you have, along with , Asymmetric component for scanning plane extending in the main scanning direction, respectively, are shown.

As shown in FIGS. 23 to 30, the second surface of the first imaging lens 30a is scanned in the main scanning direction with respect to the optical axis (y = 0, z = 0), like the first surface. Direction and the sub-scanning direction are asymmetrical, and the inclination of the curvature in the sub-scanning direction and the inclination of the curvature in the main-scanning direction change asymmetrically with respect to the point intersecting the optical axis in the main-scanning direction. It is recognized that neither of the sub-scanning directions includes the rotational symmetry plane. From FIG. 23, it can be seen that the exit surface of the lens 30a does not have a rotationally symmetric surface, and the plane symmetric surface of this surface is only one surface made at z = 0. As a result, it is possible to improve various characteristics in the main and sub-scanning directions over the entire range for a wide deflection angle.

Further, FIG. 24 shows that the curvature of the lens surface in the sub-scanning direction changes its sign in the middle of the main scanning direction, which results in the absolute value of the power of the lens in the sub-scanning direction. It is possible to optimize various characteristics in the sub-scanning direction with respect to a wide deflection angle without increasing. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

FIG. 26 shows that the primary scanning direction primary differential value with respect to the system optical axis direction coordinates of the line of intersection between the main scanning plane including the optical axis of the system and the lens surface has two extreme values. As a result, the fθ characteristic can be corrected for the wide deflection angle in the main scanning direction without increasing the lens thickness. The thicker the lens, the longer the molding time, especially in the case of a plastic molded lens, leading to an increase in cost.

Further, FIG. 27 shows that the curvature of the lens surface in the main scanning direction changes its sign in the middle of the main scanning direction, which shows the absolute power of the lens in the main scanning direction. It is possible to optimize various characteristics in the main scanning direction for a wide deflection angle without increasing the value. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

FIG. 28 shows the shape in the sub-scanning direction when the coordinates of the intersection of the plane including the optical axis of the system and extending in the main scanning direction and the lens surface are set to 0. It is shown that the relative relationship of the sub scanning direction with respect to the optical axis part is reversed in the middle of the main scanning direction, which is very useful for improving various characteristics in the sub scanning direction over a wide width in the sub scanning direction. ing.

FIG. 29 shows the sub-scanning direction z of the shape in the sub-scanning direction.
It shows that there is a deviation of the shape from a circular arc having a curvature at = 0, and that it also includes a high-order (fourth order or more) term in the sub-scanning direction. It is possible to realize a shape in which the relative relationship between the peripheral portion and the optical axis portion in the sub-scanning direction is reversed in the middle of the main scanning direction.

As described above, both surfaces of the lens 30a do not have a rotational symmetry axis and the scanning direction 1 with respect to the optical axis coordinate of the line of intersection with the scanning plane.
It can be seen that the second derivative has two extreme values.

FIG. 31 shows the shape of the first surface of the second imaging lens 30b, that is, the light incident surface. As shown in FIG. 31, the first surface of the second imaging lens 30b is
It is formed asymmetrically with respect to the optical axis, that is, (y, z) = (0,0).

Hereinafter, similar to the first surface of the second imaging lens 30b shown in FIGS. 15 to 22, that is, the light incident surface,
32 to 38, with respect to the first surface of the second imaging lens 30b, a plane including the optical axis of the system and extending in the main scanning direction, that is, the curvature in the sub-scanning direction at the intersection of the optical scanning surface and the lens surface, Second-order differential value of curvature in the sub-scanning direction at the intersection of a plane including the optical axis of the system in the main scanning direction and the lens surface, a plane including the optical axis of the system and extending in the main scanning direction, and the lens surface The differential value of the optical axis direction coordinate at the intersection point with respect to the main scanning direction coordinate, the main scanning direction curvature at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction, the main scanning direction including the optical axis of the system The position in the sub-scanning direction at each point in the main scanning direction of the lens surface based on the intersection of the expanding plane and the lens surface, that is, the shape in the sub-scanning direction, the curvature of the shape in the sub-scanning direction in the sub-scanning direction z = 0 Deviation of shape from the arc you have, along with , Asymmetric component for scanning plane extending in the main scanning direction, respectively, are shown.

As shown in FIGS. 31 to 38, the first surface of the second imaging lens 30b has the first imaging lens 3
Similarly to the first surface of 0a, it is asymmetrical with respect to the optical axis (y = 0, z = 0) in the main scanning direction and the sub-scanning direction, and the inclination of the curvature in the sub-scanning direction and the main scanning direction It is recognized that each of the curvature inclinations changes asymmetrically with respect to the optical axis in the main scanning direction, and neither the main scanning direction nor the sub scanning direction includes a rotationally symmetric surface.

It can be seen from FIG. 31 that the incident surface of the lens 30b does not have a rotationally symmetric surface, and the plane symmetric surface of this surface is only one surface made at z = 0. As a result, it is possible to improve various characteristics in the main and sub-scanning directions over the entire range for a wide deflection angle.

Further, FIG. 32 shows that the curvature of the lens surface in the sub-scanning direction changes its sign midway in the main scanning direction (near y = 80). The characteristics in the sub-scanning direction can be optimized for a wide deflection angle without increasing the absolute value of the directional power. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

Further, FIG. 34 shows that the inclination of the lens surface in the main scanning direction changes the sign in the middle of the main scanning direction, which makes it possible to determine the depth of the lens in the optical axis direction. It can be made shallow, which is effective in facilitating the manufacture of the mold and suppressing the warpage of the lens during molding.

Further, FIG. 35 shows that the curvature of the lens surface in the main scanning direction changes its sign in the middle of the main scanning direction, which results in the absolute value of the power in the main scanning direction of the lens. It is possible to optimize various characteristics in the main scanning direction with respect to a wide deflection angle without increasing. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

FIG. 37 shows the sub-scanning direction z of the sub-scanning direction shape.
It shows that there is a deviation of the shape from an arc having a curvature at = 0, and that it also includes a high-order (fourth order or more) term in the sub-scanning direction, which is spread over a wide width in the sub-scanning direction. It is greatly useful for improving various characteristics in the sub-scanning direction.

FIG. 39 shows the shape of the second surface of the second imaging lens 30b, that is, the light exit surface. As shown in FIG. 39, the second surface of the second imaging lens 30b is
It is formed asymmetrically with respect to the optical axis, that is, (y, z) = (0,0).

Hereinafter, similar to the first surface of the first imaging lens 30a shown in FIGS. 15 to 22, that is, the light incident surface,
40 to 46, with respect to the second surface of the second imaging lens 30b, a plane extending in the main scanning direction including the optical axis of the system, that is, a curvature in the sub-scanning direction at the intersection of the optical scanning surface and the lens surface, Second-order differential value of curvature in the sub-scanning direction at the intersection of a plane including the optical axis of the system in the main scanning direction and the lens surface, a plane including the optical axis of the system and extending in the main scanning direction, and the lens surface The differential value of the optical axis direction coordinate at the intersection point with respect to the main scanning direction coordinate, the main scanning direction curvature at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction, the main scanning direction including the optical axis of the system The position in the sub-scanning direction at each point in the main scanning direction of the lens surface based on the intersection of the expanding plane and the lens surface, that is, the shape in the sub-scanning direction, the curvature of the shape in the sub-scanning direction in the sub-scanning direction z = 0 Deviation of shape from the arc you have, along with , Asymmetric component for scanning plane extending in the main scanning direction, respectively, are shown.

As shown in FIG. 39 to FIG. 46, the second surface of the second imaging lens 30b is the same as the first surface in the main scanning with respect to the optical axis (y = 0, z = 0). Direction and the sub-scanning direction are asymmetrical, and the inclination of the curvature in the sub-scanning direction and the inclination of the curvature in the main-scanning direction change asymmetrically with respect to the point intersecting the optical axis in the main-scanning direction. It is recognized that neither of the sub-scanning directions includes the rotational symmetry plane.

From FIG. 39, it can be seen that the exit surface of the lens 30b does not have a rotationally symmetric surface, and the plane symmetric surface of this surface is only one surface made at z = 0. As a result, it is possible to improve various characteristics in the main and sub-scanning directions over the entire range for a wide deflection angle.

Further, FIG. 40 shows that the curvature of the lens surface in the sub-scanning direction changes its sign in the middle of the main scanning direction, which results in the absolute value of the power of the lens in the sub-scanning direction. It is possible to optimize various characteristics in the sub-scanning direction with respect to a wide deflection angle without increasing. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

Further, FIG. 42 shows that the inclination of the lens surface in the main scanning direction changes its sign in the middle of the main scanning direction, which makes it possible to determine the depth of the lens in the optical axis direction. It can be made shallow, which is effective in facilitating the manufacture of the mold and suppressing the warpage of the lens during molding.

Further, FIG. 43 shows that the curvature of the lens surface in the main scanning direction changes its sign in the middle of the main scanning direction, which results in the absolute value of the power in the main scanning direction of the lens. It is possible to optimize various characteristics in the main scanning direction with respect to a wide deflection angle without increasing. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

FIG. 45 shows the sub-scanning direction z of the shape in the sub-scanning direction.
It shows that there is a deviation of the shape from an arc having a curvature at = 0, and that it also includes a high-order (fourth order or more) term in the sub-scanning direction, which is spread over a wide width in the sub-scanning direction. It is greatly useful for improving various characteristics in the sub-scanning direction.

FIG. 47 relates to the first imaging lens 30a, from the curvature in the sub-scanning direction corresponding to each position in the main scanning direction on the light exit surface to the sub-scanning direction corresponding to each position in the main scanning direction on the light incident surface. The curvature is removed, and the refractive index n of PMMA, which is the material of the first imaging lens 30a, is 1 to 1 (refractive index in air).
The continuous power distribution in the sub-scanning direction in the state where the first imaging lens 30a is regarded as a thin lens is obtained by taking the product with the numerical value excluding. Further, FIG. 48 shows the distribution of the power in the main scanning direction of the lens when the first imaging lens 30a is regarded as a thin lens, which is obtained by the same method as in FIG. 47 using the curvature in the main scanning direction. It is shown.

FIG. 49 shows the second imaging lens 30b in the sub-scanning direction corresponding to each position in the main scanning direction of the light incident surface from the radius of curvature in the sub-scanning direction corresponding to each position in the main scanning direction of the light emitting surface. Is subtracted from the refractive index n of PMMA, which is the material of the second imaging lens 30b, to be 1 (refractive index in air).
The continuous power distribution in the sub-scanning direction in the state where the second imaging lens 30b is regarded as a thin lens is obtained by taking the product with the numerical value excluding. Further, FIG. 50 shows the power in the main scanning direction of the lens when the second imaging lens 30b is regarded as a thin lens, which is obtained by the same method as in FIG.

As shown in FIGS. 47 and 49, the first and second imaging lenses 30a and 30b are in the sub scanning direction over the entire area including the vicinity of the optical axis in the main scanning direction and the peripheral portion, respectively. , With positive power.

As shown in FIG. 48, it is recognized that the power of the first imaging lens 30a in the main scanning direction becomes "0" near the optical axis in the main scanning direction. Further, as shown in FIG. 50, the power of the second imaging lens 30b in the main scanning direction may be “negative” near the optical axis in the main scanning direction and “positive” in the peripheral portion. Is recognized.

FIG. 51 shows a light source 3 (Y, M, C and B).
Respectively, that is, the yellow first laser 3Ya, the yellow second laser 3Yb, and the magenta first laser 3M.
a and magenta second laser 3Mb, cyan first laser 3Ca and cyan second laser 3Cb, and two paired laser beams LYa emitted from each of black first laser 3Ba and black second laser 3Bb.
And LYb, LMa and LMb, LCa and LC
b, and the relative positions of LBa and LBb in the sub-scanning direction are shown. As shown in FIG. 51, two laser beams paired with each other, that is, Ni.
The laser beam of (i is a positive integer, i = 2) in the sub-scanning direction is already between the light incident surface of the first imaging lens 30a, that is, the first surface and the image surface, particularly in FIG. As described above, the characteristics of each lens are defined so that the first surface of the first imaging lens 30a and the second surface of the second imaging lens 30b intersect each other. As a result, Ni (i
= 2) The beam intervals of the two laser beams can be kept constant regardless of changes in temperature and humidity.

52 to 64, various characteristics provided by the first and second imaging lenses 30a and 30b whose lens surface shapes are defined by the equation (1) will be described below in the main scanning direction. A detailed description will be given with the image plane beam position as the horizontal axis.

FIG. 52 shows the defocus amounts of the laser beam LMa emitted from the first magenta laser 3Ma in the main scanning direction and the sub scanning direction on the image plane including the state where the refractive index is changed. Ie x
It shows the variation in the axial direction. Reference numeral FSY indicates the main scanning direction, FSZ indicates the sub scanning direction, and subscripts 1, 2 and 3 indicate refractive indices n = 1.4855, n = 1.4, respectively.
821 and n = 1.4889. Further, FIG. 53 shows the laser beam LCa from the first cyan laser 3Ca, in the same manner as the example shown in FIG. 52, in the main scanning direction and the sub-scanning direction of the laser beam on the image plane including the state in which the refractive index is changed. The defocus amount in each direction, that is, the variation in the x-axis direction is shown. Note that the symbol FSY
Is the main scanning direction, FSZ is the sub scanning direction, and the subscripts 1,
2 and 3 have a refractive index n = 1.4855, n, respectively.
= 1.4821 and n = 1.4889. On the other hand, FIG. 54 shows a laser beam L from each of the black first laser 3Ba and the yellow first laser 3Ya.
Regarding Ba and LYa (as also shown in Table 1, LBa and LYa are symmetrical with respect to the optical axis of the system in the sub-scanning direction), the refractive index was changed as in the example shown in FIG. The defocus amounts of the laser beam in the main scanning direction and the sub scanning direction, that is, variations in the x-axis direction on the image plane including the state are shown. Reference numeral FSY is the main scanning direction, FSZ is the sub scanning direction, and subscripts 1, 2 and 3 are refractive indices n = 1.4855, n = 1.
It corresponds to the condition of 4821 and n = 1.4889.
As shown in FIGS. 52 to 54, each defocus amount is ± 1.5 [m] with the maximum laser beam.
m].

FIG. 55 shows the magnitude of the scanning line bending in the main scanning direction of the laser beam on the image plane, including the state where the refractive index is changed, for the laser beam LMa emitted from the first magenta laser 3Ma. ing. The subscripts 1, 2 and 3 respectively have a refractive index n = 1.4855, n =
Corresponds to 1.4821 and n = 1.4889. Further, FIG. 56 relates to the laser beam LCa from the first cyan laser 3Ca, and scans the image plane in the main scanning direction including the state in which the refractive index is changed, as in the example shown in FIG. The state of line bending is shown. The subscripts 1, 2 and 3 respectively have a refractive index n = 1.485.
5, n = 1.4821 and n = 1.4889. On the other hand, FIG. 57 shows a laser beam L from each of the black first laser 3Ba and the yellow first laser 3Ya.
Regarding Ba and LYa, similarly to the example shown in FIG.
It shows the size of the scanning line curve of the laser beam in the main scanning direction on the image plane, including the state where the refractive index is changed. Note that the subscripts 1, 2 and 3 respectively have a refractive index n = 1.
4855, n = 1.4821, and n = 1.4889. As shown in FIGS. 55 to 57, the size of each scanning line bend is suppressed within the range of ± 0.015 [mm] with the maximum laser beam.

FIG. 58 shows the laser beams LMa and LMb emitted from the first magenta laser 3Ma and the second magenta laser 3Mb, respectively, in the main scanning direction in the image plane including the state where the refractive index is changed. It indicates the degree of deviation (variation in spacing). The subscripts 1, 2 and 3
Respectively have a refractive index n = 1.48555, n = 1.48.
21 and the condition of n = 1.4889. Further, FIG. 59 shows laser beams LCa and LCb from the cyan first laser 3Ca and the cyan second laser 3Cb.
With respect to the above, similarly to the example shown in FIG. 58, the deviation of the mutual spacing in the main scanning direction on the image plane including the state in which the refractive index is changed.
It indicates the degree of (variation of interval). Subscripts 1 and 2
And 3 have a refractive index n = 1.4855, n =
This corresponds to the conditions 1.4821 and n = 1.4889. On the other hand, FIG. 60 shows the black first laser 3Ba and the black second laser 3Ba.
As to the laser beams LBa and LBb and LYa and LYb from the laser 3Bb and the yellow first laser 3Ya and the yellow second laser 3Yb, respectively, an image plane including a state in which the refractive index is changed, as in the example shown in FIG. Shows the degree of mutual deviation (interval fluctuation) of the laser beams in the main scanning direction. The subscripts 1, 2 and 3 respectively have a refractive index n = 1.485.
5, n = 1.4821 and n = 1.4889. As shown in FIGS. 58 to 57, the defocus amount of the fluctuation of each beam interval is suppressed within the range of 0.0002 [mm] for the maximum laser beam.

FIG. 61 shows the first to fourth laser beams LYa and LYb, LMa and LMb, LCa and LCb, and the main and sub-scanning directions of the laser beam on the respective image planes of LBa and LBb. The fluctuation rate of the beam diameter, that is, the fluctuation rate of the reciprocal of the light collection angle is shown. The symbol YANG indicates the main scanning direction, ZYAG.
Indicates the sub-scanning direction, and subscripts 1 and 2 correspond to the first laser a and the second laser b. As shown in FIG. 61, the fluctuation rate of the beam diameter is 7% from peak to peak.
It is suppressed to some extent.

FIG. 62 shows the fluctuation rate of the fθ characteristic of the first to fourth laser beams LYa, LMa, LCa and LBa in the main scanning direction of the laser beam on the respective image planes. As shown in FIG. 62, the fθ characteristic is suppressed to about 0.65% regardless of the type of laser beam.

FIG. 63 shows the first to fourth laser beams LMa, LCa, LYa and L in a state in which the plane tilt of each reflecting surface of the polygon mirror of the optical deflector is accommodated within 1 minute.
The variation of the beam position of the laser beam in the sub-scanning direction on each image plane of Ba is shown. The subscripts 1 and 2 are laser beams LMa and LCa, and the subscript 3 is LBa and LYa, as shown in Table 1.
Since it is symmetrical with respect to the optical axis of the system in the sub-scanning direction, it corresponds to both the laser beams LYa and LBa. As shown in FIG. 63, the variation of the beam position is 0.0 at the maximum.
03 [mm] It is suppressed. If there is no tumble correction,
This is 0.186, and it can be said that the imaging lens system including the lenses 30a and 30b has a surface tilt correction rate of 1/62.

FIG. 64 shows the variation rate of the transmittance with respect to the image plane beam position of the laser beam in the main scanning direction on the respective image planes of the first to fourth laser beams LYa, LMa, LCa and LBa. . The subscripts 1 and 2 correspond to the laser beams LMa and LCa, respectively, and the subscript 3 corresponds to both the laser beams LYa and LBa. As shown in FIG. 64, the variation of the transmittance is suppressed to about 3.5% regardless of the type of laser beam.

As described above, the light incident surface and the light emitting surface of the first imaging lens 30a and the light incident surface and the light emitting surface of the second imaging lens 30b are respectively calculated by the equation (1). By optimizing the shape of, the aberration characteristics such as spherical aberration in the image plane, coma aberration, field curvature or magnification error can be kept within a predetermined range by using only two imaging lenses. .

That is, by making the shape of the line intersecting the scanning surface and the lens surface extending in the main scanning direction asymmetric with respect to the optical axis of the system penetrating the lens surface, the image forming surface in the main scanning direction is larger than the image surface. It is possible to prevent the deviation and the fθ characteristic from deviating across the optical axis in the main scanning direction. Further, it is possible to reduce flare in the main scanning direction and the sub-scanning direction even for a laser beam that is largely deviated from the optical axis. Further, the fluctuation amount of the intensity distribution of the beam passing through which position in the main scanning direction can be kept within a predetermined range. Furthermore, the bending of the main scanning line can be reduced, and the laser beam emitted from the light source is Ni.
When i is a positive integer, it is possible to suppress the variation of the beam interval in the sub-scanning direction of each beam. Furthermore, the movement of the image plane in the sub-scanning direction due to the surface tilt of each reflecting surface of the polygon mirror of the optical deflector can be reduced.

Next, a modification of the first embodiment shown in FIGS. 1 to 64 will be described.

69 and 70, the laser beams LYa and LYb, LMa and LMb, LCa are directed toward the horizontal sync detector 23 and the horizontal sync detector 23 incorporated in the optical scanning device 1 shown in FIG. And LCb
And the horizontal synchronization folding mirror 25 that reflects LBa and LBb, and the relationship in which the respective laser beams emitted from the second imaging lens 30b are incident on the horizontal synchronization detector 23 and the horizontal synchronization signal is output. Has been done.

FIG. 69 is a schematic plan view of the optical scanning device 1 with the mirrors and the like removed, and FIG. 70 is a schematic plan view showing only the optical elements, and FIG. 70 is the synchronous detectors 23 and 1 shown in FIG.
FIG. 6 is a partial side view showing a horizontal synchronization folding mirror 25 having only one plane (reflection surface) and a laser beam traveling from the horizontal synchronization folding mirror 25 toward the sync detector 23 in the sub-scanning direction.

As shown in FIGS. 69 and 70, M
Group laser beams LYa and LYb, LMa and L
Mb, LCa and LCb and LBa and LBb
Are shifted in timing with respect to the main scanning direction via the folding mirror for horizontal synchronization 25, and are sequentially incident on predetermined positions of the synchronization detector 23. The synchronization detector 23 is a known position sensor capable of detecting a position in the z direction, and detects the position of each laser beam in the sub-scanning direction. Also, the folding mirror 2 for horizontal synchronization
Reference numeral 5 folds back the laser beam that has passed through the second imaging lens 30b. Therefore, when the synchronization detector 23 detects that the laser beam is deviated in the sub-scanning direction due to some reason, for example, it will be described later. With respect to the light source having the beam interval changing mechanism of the second embodiment shown in FIG. 68, feedback for correcting the deviation of the beam interval in the sub-scanning direction is possible.

The detection of horizontal synchronization of each laser beam will be described in detail below.

First, the yellow first laser 3Ya of the first light source 3Y is made to emit light. As a result, the synchronization detector 23
The laser beam LYa, which is folded back by the horizontal synchronization folding mirror 25 and is separated from the optical axis of the system by a predetermined distance in the sub-scanning direction, is incident on the predetermined position. Therefore,
The horizontal synchronization signal of the laser beam LYa is obtained from the slope signal of the sum signal of the synchronization detector 23 when the laser beam LYa reaches the synchronization detector 23. Then, the position of the laser beam LYa in the z-axis direction is measured from the difference signal of the synchronization detector 23.

After this, the yellow first laser 3Ya is stopped and the yellow second laser 3Yb is caused to emit light. Here, this time, the position of the laser beam LYb in the z-axis direction is measured from the difference signal of the synchronous detector 23, and the slope signal of the sum signal of the synchronous detector 23 when the laser beam LYb deviates from the synchronous detector 23. The horizontal synchronizing signal of the laser beam LYb is obtained from the.

Hereinafter, LMa and LMb, LCa and LCb, and LBa and LBb, respectively,
Similarly, the horizontal synchronizing signal and the position information in the z direction are obtained.

Accordingly, the first to fourth light sources 3 (Y
a, Yb, Ma, Mb, Ca, Cb and Ba, Bb)
The timing for emitting light, that is, the writing timing in the main scanning direction is defined. Further, if necessary, in order to correct the deviation of the beam interval in the sub-scanning direction, the two laser beams LYa and LYb, LMa of the M group which make a pair with each other.
And the beam spacings of LMb, LCa and LCb and LBa and LBb are fed back to the beam spacing changing mechanism.

FIG. 65 shows a transfer type color image forming apparatus using a multi-beam optical scanning device according to the second embodiment of the present invention. Note that the same reference numerals are given to configurations that are substantially the same as the configurations already described with reference to FIGS. 1 to 64, and detailed description thereof will be omitted.

As shown in FIG. 65, the image forming apparatus 1
00 is the color component obtained by color separation, that is, Y = yellow, M
= First to fourth image forming units 50Y and 50 that form an image for each of magenta, C = cyan, and B = black
It has M, 50C and 50B.

Each image forming section 50 (Y, M, C and B)
Are third folding mirrors 37Y, 37 of a multi-beam optical scanning device 151, which will be described later with reference to FIGS. 66 to 71.
The optical scanning device 15 corresponds 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.
1 is arranged in series below 1 in the order of 50Y, 50M, 50C and 50B.

FIG. 66 shows a multi-beam optical scanning device used in the color image forming apparatus shown in FIG. As in the first embodiment, Y, M, C, and B are added to the reference symbols to identify the image data for each color component and the corresponding device.

As shown in FIG. 66, the multi-beam optical scanning device 151 directs a laser beam emitted from a laser element as a light source toward a predetermined position on an image plane arranged at a predetermined position. It has only one optical deflecting device 5 as a deflecting means for deflecting at a linear velocity. Note that, hereinafter, the direction in which the laser beam is deflected by the optical deflector 5 is referred to as the main scanning direction.

Between the light deflecting device 5 and the image plane, the first and second imaging lenses 30a for giving a predetermined optical characteristic to the laser beam deflected in a predetermined direction by the reflecting surface of the light deflecting device 5. And a post-deflection optical system 30 composed of a pair of optical elements 30b.

Next, the pre-deflection optical system between the laser element as the light source and the optical deflector 5 will be described in detail.

The optical scanning device 1 has N_i (i is a positive integer N
_Four= 2, N₁= N_Two= N_Three= 1, N _Four= 2 is a black beam
(Indicating that there are two),
Laser bee corresponding to image data separated into color components
The first to fourth light sources 3Y, 3M, 3C that generate
And 3B (M is a positive integer, where 4)
It

First to third light sources 3Y, 3M and 3
C is a yellow laser 3Y that emits a laser beam corresponding to Y, that is, a yellow image, a magenta laser 3M that emits a laser beam that corresponds to M, that is, a magenta image, and C, that is, cyan that emits a laser beam that corresponds to a cyan image. Laser 3C and B
That is, the black first laser 3Ba and the black second laser 3Bb that emit a laser beam corresponding to a black image.
have. That is, the first to third light sources 3Y,
3M and 3C satisfy N ₁ = N ₂ = N ₃ = 1 and the fourth light source 3B satisfies N ₄ = 2. Therefore, from the first to third light sources 3Y, 3M and 3C, respectively,
One laser beam LY, LM, and LC is emitted, and two laser beams LBa and LBb that form a pair and have a beam interval of a predetermined distance in the sub-scanning direction are emitted from the fourth light source 3B. To be done.

Between the respective laser elements 3Y, 3M, 3C and 3Ba and the optical deflecting device 5, laser beams L from the corresponding light sources 3Y, 3M, 3C and 3Ba are provided.
Four sets of pre-deflection optical systems 7 (Y, LM, LC and LBa for adjusting the cross-sectional beam spot shapes to predetermined shapes)
M, C and B) are arranged.

Here, the pre-deflection optical system 7Y will be described by representing the laser beam LY directed from the yellow laser 3Y to the optical deflector 5.

The divergent laser beam emitted from the yellow laser 3Y is given a predetermined convergence by the finite focus lens 9Y, and then the cross-sectional beam shape is adjusted to a predetermined shape by the diaphragm 10Y. The laser beam LY that has passed through the diaphragm 10Y receives the hybrid cylinder lens 1
Predetermined converging property is given to only the sub-scanning direction via 1Y, and the light is emitted toward the optical deflector 5.

Similarly, in relation to M, that is, magenta, the magenta laser 3M passes through the finite focus lens 9M, the diaphragm 10M and the hybrid cylinder lens 11M and is directed to the light deflector 5. Further, with respect to C, that is, cyan, the cyan laser 3C is passed through the finite focus lens 9C, the diaphragm 10C, and the hybrid cylinder lens 11C, and is directed to the light deflecting device 5.

On the other hand, the divergent laser beam emitted from the first black laser 3Ba is finite focus lens 9B.
After a given convergence is given by a, the aperture 10Ba
Thereby, the cross-sectional beam shape is adjusted to a predetermined shape. The laser beam LBa that has passed through the diaphragm 10Ba is guided to the optical deflecting device 5 via the hybrid cylinder lens 11B, with a predetermined converging property only in the sub-scanning direction. A half mirror 12B is inserted between the finite focus lens 9Ba and the hybrid cylinder lens 11B at a predetermined angle with respect to the optical axis between the finite focus lens 9Ba and the hybrid cylinder lens 11B. On the other hand, in the half mirror 12B,
A surface opposite to the surface on which the laser beam LBa from the first black laser 3Ba is incident is arranged so as to be able to provide a predetermined beam interval in the sub-scanning direction with respect to the laser beam LBa from the first black laser 3Ba. The laser beam LBb from the second black laser 3Bb is incident on the laser beam LBa from the first black laser 3Ba at a predetermined beam interval and angle in the sub-scanning direction. A finite focus lens 9Bb and a diaphragm 10Bb that give a predetermined convergence to the laser beam LBb from the second black laser 3Bb are arranged between the second black laser 3Bb and the half mirror 12B.

The laser beam LY passed through the hybrid cylinder lens 11Y, the laser beam LM passed through the hybrid cylinder lens 11M, the laser beam LC passed through the hybrid cylinder lens 11C, and the pair passed through the hybrid cylinder lens 11B. The laser beams LBa and LBb forming the laser beam are combined with other laser beams by the laser synthesizing mirror unit (not described) which is substantially the same as the laser synthesizing mirror unit 13 shown in FIG. 8 in the first embodiment. It is guided to the optical deflector 5. The optical elements used in each of the pre-deflection optical systems 7 (Y, M, C and B) are the respective optical elements alone, and are the same as in FIG.
Since it is substantially the same as the optical element used in the first embodiment shown in FIG. 4, detailed description thereof will be omitted.

FIG. 67 shows a cross section in the sub-scanning direction of the laser beam directed from the optical deflecting device 5 to the image plane in the state where the deflection angle of the laser beam by each reflecting surface of the polygonal mirror of the optical deflecting device 5 is 0 °. ing.

As shown in FIG. 67, the first to fourth laser beams L reflected by the reflecting surface of the optical deflector 5 are shown.
The laser beams LB in which Y, LM and LC, and the pair of two laser beams LBa and LBb are collected together are respectively the first imaging lens 30a.
Between the second imaging lens 30b and the second imaging lens 30b, the light is guided to the image surface (photosensitive drum 58) in the sub scanning direction, intersecting the optical axis of the system.

By the way, as described in the section of the prior art, in the color image forming apparatus, when the frequency of outputting the color image and the frequency of outputting the black image are compared, the frequency of outputting the black image is high. There is a tendency. Further, the black image is required to have sharpness or sharpness as compared with the color image. However, since an optical device suitable for a laser beam corresponding to a color image does not require resolution as compared with an optical device suitable for a laser beam corresponding to a black image, an optical device suitable for a laser beam corresponding to a black image is required. Utilizing the device adds cost.

From this, N ₄ (= 2) is equal to other N ₁ =
As a value different from N ₂ = N ₃ = 1, 600 DPI for black,
Yellow, magenta, and cyan are set to 300 DPI. The image forming apparatus shown in FIG. 65 is formed so as to provide at least two resolutions of 600 dots per inch (hereinafter referred to as [dpi]) and 400 [dpi] for a black image. There is. A fixed 300 [dpi] is given to each of the color images, that is, the first to third light sources 3Y, 3M, and 3C.

The resolution changing mode of the image forming apparatus shown in FIG. 65 will be described below.

Generally, the effective energy diameter of the beam diameter of the laser beam is represented by 1 / e ² as is well known. At this time, the 1 / e ² diameter Do in the sub-scanning direction is a beam interval (hereinafter, referred to as a beam interval defined based on the resolution of an image to be recorded).
(Denoted as GP), AMP x GP = Do, (1.2 ≤ AMP
It is desired that ≦ 1.6) (the optimum value of AMP varies depending on the process).

That is, G defined depending on the resolution
It is known that setting the effective energy diameter Do to be slightly larger than P reduces density unevenness due to, for example, jitter caused by driving of the photosensitive drum. The line interval when writing with a single beam and resolution DPI is LGP.

From this fact, as shown in FIG.
In order to record an image with Ni = 2 laser beams with a resolution of 600 [dpi], the effective energy diameter Do of each laser beam is 1.2 times GP or more.
In addition to setting 1.6 times, in order to reduce the density unevenness more effectively, the distance between the laser beams is set to about 1.2 to 1.6 for the AMP prescribed depending on the resolution, and the beam distance is set. It is beneficial to change to GP '.

Therefore, for example, when GP ′ is obtained for various resolutions, GP ′ = (25.4AMP / DPI−25.4AMP / DPIo) / (Pi−1) = AMP × LGP × {1- (DPI / DPIo)} / (Pi-1) Here, DPIo represents the maximum resolution that the image forming apparatus can form an image, and DPI represents the resolution to be changed ... (2) As shown in FIG. It is only necessary to change the beam interval in the sub-scanning direction of the two laser beams forming a pair by using the resolution changing mechanism described later using.

The optical scanning device 151 of the image forming apparatus shown in FIG. 65 has a maximum resolution of DPIo = 600 [dp.
i], the changeable resolution DPI is DPI ≧ 1 /
It is defined in Pi x DPIo.

Here, the DPI is set to 400 [dpi] AMP
= 1.2, the beam spacing on the image plane for Ni = 2 is narrowed from 42.3 micrometers (hereinafter referred to as [μm]) to 25.4 [μm], and a plurality of Pi
(Pi is an integer of 2 or more, and here, Pi = 2) beams to form an image for one pixel.

In this case, in order to keep the process speed constant, the image frequency is DPI ² × Pi / DPI ² = 0.8888.
It goes without saying that the deflection speed of the optical deflector is changed to double the DPI × Pi / DPIo = 1.3333 times.

For reference, the DPI is 300 [dpi].
Then, the beam interval is 50.8 [μm], the deflection speed of the optical deflector is the same as that at DPIo (the first laser and the second laser are simultaneously emitted), and the image frequency is 1 /
Changed to 2.

FIG. 68 shows the optical scanning device 1 shown in FIG.
The second black laser 3Bb of the fourth light source 3B used for the light source 51
A holding unit for holding, that is, a resolution changing mechanism is shown.

As shown in FIG. 68, the black second laser 3
Bb is a laser holding unit 2 that holds the black second laser 3Bb
It is inserted into a laser holder part formed at a predetermined position of Bb and fixed to the laser holder part with an adhesive (not shown). In the lateral direction of the laser holding portion 2Bb, that is, in the direction in which the laser beam LBb from the second black laser 3Bb held via the laser holder portion is emitted, an adhesive agent (not shown) or an illustration provided from the holding portion 2Bb side is shown. The lens holding portion 4Bb holding the finite focus lens 9Bb is fixed by a screw or the like. The finite focus lens 9Bb has a lens housing integrally formed therein and has a cylindrical outer shape. Thereby, the finite focus lens 9Bb is, for example, by the leaf spring 6Bb,
The lens holding portion 4Bb is pressed in a predetermined direction. Further, the diaphragm 10Bb is inserted into a groove formed in a predetermined position of the lens holding portion 4Bb in advance, and is fixed to the lens holding portion 4Bb with an adhesive (not shown). In addition,
The finite focus lens 9Bb is a laser beam LB emitted from the laser element 3Bb by a positioning protrusion (not shown) or the like formed in advance on the lens holding portion 4Bb.
After the optical axis is adjusted with respect to b, the lens holding unit 4B ₂
It is fixed with adhesive or the like.

Lens holder 4Bb and laser holder 2
Bb is arranged at a predetermined position of the housing 151a of the optical scanning device 151, with the electromagnetic actuator 14Bb whose thickness is changed according to the applied voltage interposed between the housing 151a and each holding portion. Has been done.

The electromagnetic actuator 14Bb changes the beam interval in the sub-scanning direction between the laser beam LBa emitted from the first black laser 3Ba and the laser beam LBb emitted from the second black laser 3Bb in response to the above-mentioned change in resolution. In order to change, for example, 600 [dpi], 400
It is possible to provide a predetermined thickness corresponding to a resolution of [dpi] and 300 [dpi], and the thickness is changed to a thickness corresponding to the resolution supplied through a voltage supply unit (not shown). These amounts are LBa and LBb at the positions in the Z direction that have produced the difference signal of the synchronization detector 23 described above.
Receive feedback from the difference. As the electromagnetic actuator 14Bb, for example, a known piezo element is used.

Further, in the optical scanning device 151 shown in FIG. 65, the black second laser 3Bb includes the hybrid cylinder lens 11B and the first and second imaging lenses 30.
Although it is guided to a predetermined position on the image surface by a and 30b, if the distance that the lens holding portion 4Bb and the laser holding portion 2Bb are moved by the displacement of the electromagnetic actuator 14Bb is dx, −0 on the image surface. .636
It becomes dx. Incidentally, in the second embodiment shown in FIGS. 65 to 68, M = 4 and Ni = 1 (Y), Ni = 1.
(M), Ni = 1 (C) and Ni = 2 (B) have been described as an example only when the beam spacing adjusting mechanism is N4 -1 = 2-1 -1. The beam spacing adjustment mechanism shown may be arranged. Further, although the beam incident position is adjusted in this embodiment, the incident angle and the incident position can be adjusted by arranging the piezo at the end of 4Bb so as to generate an inclination and pressing the other with a spring or the like. It is possible.

FIG. 72 shows a monochromatic image forming apparatus in which the two-beam optical scanning device according to the third embodiment of the present invention is used. It should be noted that 200 is assigned to the configuration substantially the same as the configuration of the first embodiment already described with reference to FIGS. 1 to 64 and the configuration of the second embodiment shown in FIGS. 65 to 68. The added symbols are printed and detailed description is omitted.

As shown in FIG. 72, the image forming apparatus 2
00 has an image forming unit 250 of a known laser beam printer system.

The image forming section 250 is shown in FIGS.
The folding mirror 2 of the optical scanning device 201 described later using
It is arranged at a position where the laser beams L1 and L2 are emitted via 33.

The image forming section 250 has a cylindrical drum shape and is formed so as to be rotatable in a predetermined direction, and has a photosensitive drum 258 on which an electrostatic latent image corresponding to the image is formed. Around the photoconductor drum 258, a charging device 260 for providing a predetermined potential on the surface of the photoconductor drum 258, and a toner having a color corresponding to the electrostatic latent image formed on the surface of the photoconductor drum 258 are provided. Developing device 2 that develops by supplying
62, the recording medium P, that is, the recording paper P, which is opposed to the photoconductor drum 258 with the conveyance belt 252 interposed between the photoconductor drum 258 and the conveyance belt 252, and which is conveyed by the conveyance belt 252. Transfer device 264 for transferring the toner image on 258, transfer device 264
After the toner image is transferred through the photoconductor drum 25
8 is a charge removing device 268 for removing the residual potential remaining on the photoconductor drum 258 after the toner image is transferred through the cleaner 266 for removing the residual toner remaining on the photoconductor drum 258. They are arranged in order along the rotation direction.

The laser beams L1 and L2 guided by the mirror 233 of the optical scanning device 201 are applied between the charging device 260 and the developing device 262.

Below the photoconductor 258, the image forming section 25 is formed.
A sheet cassette 270 for accommodating a recording medium, that is, a sheet P for transferring an image formed by 0 is arranged.

On one side of the paper cassette 270, which is close to the tension roller 254, a delivery roller 272 which is formed in a substantially half-moon shape and takes out the papers P stored in the paper cassette 270 from the uppermost one by one.
Are arranged. Between the delivery roller 272 and the photosensitive drum 258, the registration roller 2 for aligning the leading end of one sheet of paper P taken out from the cassette 270 and the leading end of the toner image formed on the photosensitive drum 258.
76 are arranged.

The photoconductor drum 258 is transferred by the transfer device 264.
A fixing device 284 that fixes the toner image transferred onto the paper P to the paper P is arranged in the direction in which the paper P onto which the image formed on the paper P is transferred is conveyed.

FIG. 73 shows a two-beam optical scanning device used in the image forming apparatus shown in FIG.

As shown in FIG. 73, the optical scanning device 20
1 is a first and a second laser element 203 as a light source
a and 203b A single optical deflecting device 205 as a deflecting means for deflecting the Ni = 2 laser beams emitted at a predetermined linear velocity toward a predetermined position on the image plane arranged at a predetermined position is provided. Have Note that, hereinafter, the direction in which the laser beam is deflected by the optical deflector 5 is referred to as the main scanning direction.

Between the optical deflector 5 and the image plane, there is only one sheet which gives the first and second laser beams deflected in the predetermined direction by the reflecting surface of the optical deflector 205 a predetermined optical characteristic. The imaging lens 230 is arranged. A dustproof glass 239 is arranged between the imaging lens 230 and the image plane.

Next, the pre-deflection optical system between the laser element as the light source and the optical deflector 5 will be described in detail.

In the optical scanning device 201, 2 satisfying Ni = 2 is satisfied.
It includes one laser element and has M (M is a positive integer, here 1) groups of light sources 203.

A finite focus lens 209a as a pre-deflection optical system, a diaphragm 210a, a half mirror 212, and a hybrid cylinder lens 211 are arranged between the first laser 203a of the light source 203 and the optical deflector 5. There is. In addition, the first laser 203a of the half mirror 212
A second laser 203b, a finite focus lens 209b, and a diaphragm 210b are arranged on the surface opposite to the surface on which the laser beam L1 from the laser beam is incident. The optical characteristics, shapes, materials, etc. of the optical elements used in the pre-deflection optical system are substantially the same as those of the first and second embodiments already described, and thus detailed description thereof will be omitted.

Next, 1 between the optical deflector 205 and the image plane is set.
The post-deflection lens optical system will be described in detail.

73 to 98 and Tables 7 and 8 show that only one imaging lens 2 of the post-deflection optical system 230 is used.
Various optical properties and lens data for 30 first or light entrance and second or light exit surfaces are shown.

[0275]

[Table 7]

[0276]

[Table 8]

FIG. 74 shows the shape of the first surface of the imaging lens 230, that is, the light incident surface. That is, FIG.
As shown in FIG. 4, the first surface of the imaging lens 230 is formed asymmetrically with respect to the optical axis, that is, (y = 0, z = 0).

FIG. 75 shows the curvature of the first surface of the imaging lens 230 in the sub-scanning direction at the intersection of the optical scanning surface and the lens surface, that is, a plane including the optical axis of the system and extending in the main scanning direction. There is. That is, FIG. 75 shows a characteristic of the shape of the first surface in the sub-scanning direction shown in FIG. 74, that is, the optical axis (y =
0, z = 0), the first surface of the imaging lens 230 is asymmetrical. Further, FIG. 75 shows that the curvature of the lens surface in the sub-scanning direction changes sign in the middle of the main scanning direction, which increases the absolute value of the power in the sub-scanning direction of the lens. It is possible to optimize various characteristics in the sub-scanning direction for a wide deflection angle. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

In FIG. 76, with respect to the first surface of the imaging lens 230, the secondary differential of the curvature in the sub-scanning direction at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction is shown. Values are shown. That is, FIG.
Is the inclination of the curvature of the first surface in the sub-scanning direction shown in FIG.
It shows that the (directionality) changes asymmetrically with respect to the point intersecting the optical axis in the main scanning direction.

In FIG. 77, with respect to the first surface of the imaging lens 230, the differential value of the coordinate in the optical axis direction at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction is shown. It is shown. That is, it can be seen that the primary scanning direction first-order differential value with respect to the system optical axis direction coordinates of the line of intersection between the main scanning plane including the optical axis of the system and the lens surface has two extreme values. As a result, while maintaining the characteristics in the sub-scanning direction described in the description of FIG. 75, fθ in the main scanning direction without increasing the lens thickness for a wide deflection angle.
The characteristics can be corrected. The thicker the lens, the longer the molding time, especially in the case of a plastic molded lens, leading to an increase in cost.

FIG. 78 shows the curvature in the main scanning direction at the intersection of the lens surface and the plane that extends in the main scanning direction and includes the optical axis of the system for the first surface of the imaging lens 230. That is, FIG. 78 shows that the first surface of the imaging lens 230 is asymmetric with respect to the feature of the shape of the first surface in the main scanning direction shown in FIG. 74, that is, the optical axis (y = 0, z = 0). Is shown. Also, this lens surface shows that the curvature in the main scanning direction changes its sign in the middle of the main scanning direction,
As a result, various characteristics in the main scanning direction can be optimized for a wide deflection angle without increasing the absolute value of the power in the main scanning direction of the lens. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

In FIG. 79, regarding the first surface of the imaging lens 230, at each point in the main scanning direction of the lens surface with reference to the intersection point of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction. Is shown in the sub-scanning direction. That is, FIG.
Indicates that the shape of the first surface in the sub scanning direction shown in FIG. 74 is asymmetric with respect to the main scanning direction.

FIG. 80 shows the shape of the first surface of the imaging lens 230 in the sub-scanning direction.
Deviation of the shape from an arc having a curvature at = 0, and FIG.
1 shows an asymmetrical component with respect to the shape of the first surface of the imaging lens 230 in the main scanning direction with respect to the scanning surface spreading in the main scanning direction. That is, FIGS. 80 and 81 show that the first surface of the imaging lens 230 does not include a rotationally symmetric surface in either the main scanning direction or the sub scanning direction. The plane symmetry plane of this plane is only one plane defined by z = 0. As shown in FIG. 80, coefficients of terms larger than at least a quaternary term in the sub-scanning direction are added to the shape of a line at which the scanning surface extending along the main scanning direction including the optical axis and the lens surface intersect, and the sub-scanning direction. By controlling independently of the radius of curvature, various aberration characteristics in the main scanning direction and the sub scanning direction can be set well.

FIG. 82 shows the shape of the second surface of the imaging lens 230, that is, the light exit surface. As shown in FIG. 82, the second surface of the imaging lens 230 has an optical axis (y,
z) = (0,0).

Hereinafter, similar to the first surface of the imaging lens 230 shown in FIGS. 74 to 81, that is, the light incident surface, FIG.
89 to 89, regarding the second surface of the imaging lens 230,
Curvature in the sub-scanning direction at the intersection of the optical scanning plane and the lens surface, including the optical axis of the system and extending in the main scanning direction, sub-scanning at the intersection of the lens surface and the plane extending in the main scanning direction, including the optical axis of the system Second derivative of the directional curvature with respect to the main scanning direction coordinate, the differential value with respect to the main scanning direction coordinate of the optical axis direction coordinate at the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction, and the optical axis of the system Main scanning direction curvature at the intersection of the plane extending in the main scanning direction and the lens surface, each point in the main scanning direction of the lens surface based on the intersection of the plane extending in the main scanning direction including the optical axis of the system and the lens surface At the position in the sub-scanning direction, that is, the shape in the sub-scanning direction, the deviation between the shape of the sub-scanning direction and the arc having the curvature in the sub-scanning direction z = 0, and the asymmetric component with respect to the scanning surface spreading in the main scanning direction, Each shown

As shown in FIGS. 83 to 89, the second surface of the imaging lens 230 is similar to the first surface in the optical axis (y
= 0, z = 0) in the main scanning direction and the sub-scanning direction, respectively, and the inclination of the curvature in the sub-scanning direction and the inclination of the curvature in the main scanning direction are respectively the optical axis in the main scanning direction. It is recognized that the crossing point changes asymmetrically, and neither the main scanning direction nor the sub scanning direction includes a rotational symmetry plane.

By the way, from the already explained FIG. 23, the lens 3
It can be seen that the exit surface of 0a does not have a rotationally symmetric surface, and the surface symmetric surface of this surface is only one surface made at z = 0. As a result, it is possible to improve various characteristics in the main and sub-scanning directions over the entire range for a wide deflection angle.

Further, FIG. 24 shows that the curvature of the lens surface in the sub-scanning direction changes its sign in the middle of the main scanning direction, which results in the absolute value of the power of the lens in the sub-scanning direction. It is possible to optimize various characteristics in the sub-scanning direction with respect to a wide deflection angle without increasing. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

On the other hand, FIG. 26 shows that the primary scanning direction primary differential value with respect to the system optical axis direction coordinate of the line of intersection between the main scanning plane including the optical axis of the system and the lens surface has two extreme values. Therefore, in the main scanning direction, the fθ characteristic can be corrected without increasing the lens thickness for a wide deflection angle. When the lens becomes thicker,
Particularly in the case of a plastic molded lens, the molding time becomes long, which leads to an increase in cost.

Further, FIG. 27 shows that the curvature of the lens surface in the main scanning direction changes its sign in the middle of the main scanning direction, which shows the absolute power of the lens in the main scanning direction. It is possible to optimize various characteristics in the main scanning direction for a wide deflection angle without increasing the value. It is known that, on the lens surface, a surface having a larger absolute value of power is more likely to cause aberration, and in order to avoid this, the performance can be improved.

FIG. 28 shows a shape with respect to the shape in the sub-scanning direction when the coordinates of the intersection of the plane including the optical axis of the system and extending in the main scanning direction and the lens surface are set to 0. It is shown that the relative relationship of the sub scanning direction with respect to the optical axis part is reversed in the middle of the main scanning direction, which is very useful for improving various characteristics in the sub scanning direction over a wide width in the sub scanning direction. ing.

FIG. 29 shows the sub-scanning direction z of the shape in the sub-scanning direction.
It shows that there is a deviation of the shape from a circular arc having a curvature at = 0, and that it also includes a high-order (fourth order or more) term in the sub-scanning direction. It is possible to realize a shape in which the relative relationship between the peripheral portion and the optical axis portion in the sub-scanning direction is reversed in the middle of the main scanning direction.

As described above, both surfaces of the lens 30a do not have a rotational symmetry axis and the scanning direction 1 with respect to the optical axis coordinate of the line of intersection with the scanning plane
It can be seen that the second derivative has two extreme values.

On the other hand, FIG. 86 shows that the curvature of the lens surface in the main scanning direction changes its sign in the middle of the main scanning direction. The characteristics in the main scanning direction can be optimized for a wide deflection angle without increasing the absolute value of. It is known that a lens surface is more likely to generate aberrations on a surface having a larger maximum power value, and in order to avoid this, the performance can be improved.

FIG. 87 shows the shape in the sub-scanning shape when the coordinates of the intersection of the lens surface and the plane including the optical axis of the system and extending in the main scanning direction are set to 0. It shows that the relative position with respect to the optical axis portion in the sub-scanning direction is reversed in the middle of the main scanning direction, which is very useful for improving various characteristics in the sub-scanning direction over a wide width in the sub-scanning direction. There is.

FIG. 88 is a sub-scanning direction z of the sub-scanning direction shape.
It shows that there is a deviation of the shape from a circular arc having a curvature at = 0, and that it also includes a high-order (fourth order or more) term in the sub-scanning direction. It is possible to realize a shape in which the relative position of the peripheral portion with respect to the sub-scanning direction optical axis portion is reversed in the middle of the main scanning direction.

From the above, it can be seen that both surfaces of the lens 230 do not have a rotational symmetry axis, and the primary differential value in the main scanning direction with respect to the optical axis coordinates of the intersection with the scanning plane has two extreme values.

FIG. 90 relates to the imaging lens 230, and removes the curvature in the sub-scanning direction of the light incident surface from the curvature of the sub-scanning direction in the main scanning direction. , The PMM which is the material of the imaging lens 230
The product of the refractive index n of A and the value obtained by subtracting 1 (refractive index in air) from the product of the continuous power in the sub-scanning direction when the imaging lens 230 is regarded as a thin lens. The distribution is shown.

FIG. 91 shows the image forming lens 230, in which the radius of curvature in the main scanning direction corresponds to each position in the main scanning direction of the light exit surface to the radius of curvature in the main scanning direction corresponding to each position in the main scanning direction of the light incident surface. Of the PMMA, which is the material of the imaging lens 230, and the product thereof is obtained by subtracting 1 (the refractive index in the air) from the refractive index n of the material of the imaging lens 230.
2 shows a continuous power distribution in the main scanning direction in the state where is regarded as a thin lens.

FIG. 92 shows the first laser 203 of the light source 203.
a shows the relative position in the sub-scanning direction of each of the two laser beams L1 and L2 emitted from the second laser 203b and paired with each other. As shown in FIG. 92, two laser beams paired with each other, that is, a laser beam of Ni = 2,
The characteristics of the imaging lens 230 are defined so that they intersect the optical axis of the system between the light incident surface of the imaging lens 230, that is, the first surface and the image surface. As a result, the beam interval between Ni = 2 laser beams can be kept constant regardless of changes in temperature and humidity.

Various characteristics provided by the imaging lens 230 will be described in detail below with reference to the image plane beam position in the main scanning direction as an axis, with reference to FIGS.

FIG. 93 shows the defocus amount of the laser beam in the main scanning direction and the sub scanning direction, that is, the variation in the z-axis direction on the image plane including the state where the refractive index is changed. The subscripts 1, 2 and 3 are respectively
Refractive index n = 1.4855, n = 1.4821 and n =
It corresponds to the condition of 1.4889. As shown in FIG. 93, the maximum defocus amount is ± 1.1.
It is suppressed within the range of [mm].

FIG. 94 shows the deviation of the interval (variation of the interval) in the main scanning direction on the image plane including the state where the refractive index is changed.
Indicates the degree of. The subscripts 1, 2 and 3 correspond to the conditions of refractive index n = 1.4855, n = 1.4821 and n = 1.4889, respectively. As shown in FIG. 94, the magnitude of variation in each beam interval is suppressed within the range of 0.0009 [mm] with the maximum laser beam.

FIG. 95 shows the fluctuation rate of the beam diameter in the main scanning direction and the sub-scanning direction, that is, the fluctuation rate of the reciprocal of the light collecting angle. The symbol YANG indicates the main scanning direction, ZYAG.
Correspond to the sub-scanning direction. As shown in FIG. 95, the fluctuation rate of the beam diameter is 8% from peak to peak.
It is suppressed to some extent.

FIG. 96 shows the variation rate of the fθ characteristic of the laser beam in the main scanning direction on the image plane. As shown in FIG. 96, the fθ characteristic is independent of the type of laser beam.
Generally, it is suppressed to the range of 0.3%.

FIG. 97 shows the fluctuation of the beam position of the laser beam in the sub-scanning direction when the surface tilt of each reflecting surface of the polygon mirror of the optical deflector is contained within 1 minute. As shown in FIG. 97, the variation of the beam position is maximum,
It is suppressed to 0.001 [mm]. When there is no face tilt correction, this value is 0.186, and it can be said that the lens 230 has a face tilt correction rate of 1/186.

FIG. 98 shows the change in transmittance with respect to the image plane beam position in the main scanning direction. As shown in FIG. 98, the variation in the transmittance depends on the type of laser beam,
Generally, it is suppressed to the range of 4%.

As described above, by optimizing the shapes of the first surface, that is, the entrance surface and the second surface, that is, the exit surface, at the respective positions in the main scanning direction and the sub scanning direction, only one imaging lens is formed. Only by doing so, it becomes possible to keep the aberration characteristics such as spherical aberration, coma aberration, field curvature or magnification error in the image plane within a predetermined range.

That is, by making the shape of the line intersecting the scanning surface extending in the main scanning direction and the lens surface asymmetric with respect to the optical axis of the system penetrating the lens surface, the image forming surface in the main scanning direction is made larger than the image surface. It is possible to prevent the deviation and the fθ characteristic from deviating across the optical axis in the main scanning direction. Further, it is possible to reduce flare in the main scanning direction and the sub-scanning direction even for a laser beam that is largely deviated from the optical axis. Further, the fluctuation amount of the intensity distribution of the beam passing through which position in the main scanning direction can be kept within a predetermined range.

[0310]

As described above, according to the optical scanning device of the present invention, the influence of the change in the refractive index due to the influence of temperature and humidity and the change due to the shape change on the inter-beam distance of N _i is reduced. It also works similarly for the M group beams. Further, since the influence of the fluctuation of the temperature and humidity of the beam waist position near the image plane is suppressed, the fluctuation of the beam diameter is reduced.

Furthermore, since the incident light can be made incident on the deflecting means from a direction other than the front direction, various characteristics in the main scanning direction due to the asymmetry of the rotating mirror of the deflecting means can be improved. Further, the effective swing angle or the scanning width can be improved. Further, the correction rate of the surface tilt of the rotating mirror is increased, so that the beam intervals in the sub-scanning direction are made uniform. Furthermore, the spherical aberration and coma in the sub-scanning direction are improved by the terms of the fourth and higher orders. Furthermore, fluctuations in the beam position in the sub-scanning direction are reduced.

Furthermore, the writing timing of the image for each beam can be matched. Further, it is possible to prevent the timing reproducibility from changing due to a temperature rise or the like. Further, even if the housing or the like is deformed, the positions of the N _i beams can be accurately detected.

Therefore, it is possible to prevent bending of the main scanning line or non-uniformity of the fθ characteristic. Further, various defects such as color shift, uneven image density, and image bleeding are eliminated.

Furthermore, it is possible to suppress color unevenness in a halftone image or a color image. Furthermore, an image forming apparatus with less line width change or color shift and color unevenness is provided.

With these, a color image can be provided at low cost.

When the M group is 1, the number of imaging lenses can be reduced to only one.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an image forming apparatus using a multi-beam optical scanning device that is an embodiment of the present invention.

FIG. 2 is a schematic plan view showing the arrangement of optical members of an optical scanning device incorporated in the image forming apparatus shown in FIG.

3 is a partial cross-sectional view of the optical scanning device shown in FIG. 2 taken along the optical axis of a system between a first light source and a light deflecting device.

4 is a partial cross-sectional view in the sub-scanning direction of the optical scanning device shown in FIG. 2, showing a schematic view of states of first to fourth laser beams directed to the optical deflecting device.

5 is a schematic cross-sectional view of the optical scanning device shown in FIG. 2 taken at a position where the deflection angle of the optical deflector is 0 °.

6 is a development view of an optical path obtained by removing a mirror and the like of an optical scanning device cut at a position where a deflection angle of the optical deflecting device shown in FIG. 5 is 0 °.

7 is a schematic plan view showing a state in which each optical member of the pre-deflection optical system of the optical scanning device shown in FIG. 2 is arranged.

8 is a plan view and a side view showing a laser synthesizing mirror unit of the optical scanning device shown in FIG.

9 is a schematic perspective view of a folding mirror for horizontal synchronization detection of the optical scanning device shown in FIG.

10 is a schematic perspective view showing an adjusting mechanism of an emission mirror of the optical scanning device shown in FIG.

11 is a schematic diagram showing the principle of registration correction in the image forming apparatus shown in FIG.

12 is a schematic cross-sectional view of the resist sensor shown in FIG.

13 is a schematic diagram showing a resist detection output of the resist sensor shown in FIG.

14 is a block diagram of an image controller of the image forming apparatus shown in FIG.

15 is a perspective view showing a shape of an incident surface of a first fθ lens of the optical scanning device shown in FIG.

16 is a graph showing a curvature in the sub-scanning direction of a portion where the scanning surface spreads in the main scanning direction of the incident surface of the first fθ lens of the optical scanning device shown in FIG. 2 and the lens surface intersects each other.

FIG. 17 is a main-scanning direction of curvature in the sub-scanning direction at an intersection of a lens surface and a plane that extends in the main-scanning direction and includes the optical axis of the system, with respect to the incident surface of the first fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the secondary differential value with respect to a coordinate.

FIG. 18 is a main scanning direction of optical axis direction coordinates at an intersection point of a lens surface with a plane including the optical axis of the system and extending in the main scanning direction with respect to the incident surface of the first fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the differential value with respect to coordinates.

FIG. 19 is a graph showing the curvature in the main scanning direction of a portion where the scanning surface spreading on the entrance surface of the first fθ lens of the optical scanning device shown in FIG.

20 is a diagram showing a sub-scanning shape of the incident surface of the first fθ lens of the optical scanning device shown in FIG. 2, which is based on the intersection of a plane that includes the optical axis of the system and extends in the main scanning direction and the lens surface. The graph which shows the position in the sub-scanning direction at each point in the main scanning direction of the surface.

21 is a schematic diagram showing a deviation of a shape of an incident surface of the first fθ lens of the optical scanning device shown in FIG. 2 from a circular arc having a curvature in the sub-scanning direction z = 0.

22 is a schematic diagram showing an asymmetrical component (sum of values of terms including odd-order terms of y) with respect to the scanning surface that spreads in the main scanning direction of the incident surface of the first fθ lens of the optical scanning device shown in FIG. 2;

23 is a perspective view showing the shape of the exit surface of the first fθ lens of the optical scanning device shown in FIG. 2. FIG.

24 is a graph showing a curvature in the sub-scanning direction of a portion where the scanning surface spreading in the main scanning direction and the lens surface of the emission surface of the first fθ lens of the optical scanning device shown in FIG. 2 intersect.

FIG. 25 is a main scanning direction of curvature in the sub-scanning direction at an intersection of a lens surface and a plane that extends in the main scanning direction and includes the optical axis of the system with respect to the exit surface of the first fθ lens of the optical scanning device illustrated in FIG. 2; The graph which shows the secondary differential value with respect to a coordinate.

FIG. 26 is a main scanning direction of optical axis direction coordinates at an intersection of a lens surface and a plane extending in the main scanning direction including the optical axis of the system with respect to the exit surface of the first fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the differential value with respect to coordinates.

27 is a graph showing the curvature in the main scanning direction of a portion where the scanning surface spreading on the emission surface of the first fθ lens of the optical scanning device shown in FIG.

FIG. 28 is a diagram showing a sub-scanning shape of the exit surface of the first fθ lens of the optical scanning device shown in FIG. 2, in which the lens is based on the intersection of a plane including the optical axis of the system and extending in the main scanning direction; The graph which shows the position in the sub-scanning direction at each point in the main scanning direction of the surface.

29 is a schematic diagram showing a deviation of the shape of the exit surface of the first fθ lens of the optical scanning device shown in FIG. 2 from the shape of an arc having a curvature in the sub-scanning direction z = 0.

30 is a schematic diagram showing an asymmetrical component (sum of values of terms including odd-order terms of y) with respect to a scanning plane that spreads in the main scanning direction on the exit surface of the first fθ lens of the optical scanning device shown in FIG. 2;

31 is a perspective view showing a shape of an incident surface of a second fθ lens of the optical scanning device shown in FIG.

32 is a graph showing the sub-scanning direction curvature of the portion where the scanning surface spreads in the main scanning direction of the incident surface of the second fθ lens of the optical scanning device shown in FIG. 2 and the lens surface intersects.

FIG. 33 is a main scanning direction of curvature in the sub-scanning direction at an intersection of a lens surface and a plane including the optical axis of the system and extending in the main scanning direction with respect to the incident surface of the second fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the secondary differential value with respect to a coordinate.

34 is a main scanning direction of optical axis direction coordinates at an intersection of a lens surface and a plane including the optical axis of the system and extending in the main scanning direction with respect to the incident surface of the second fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the differential value with respect to coordinates.

35 is a graph showing the curvature in the main scanning direction of a portion where the scanning surface spreading in the main scanning direction of the incident surface of the second fθ lens of the optical scanning device shown in FIG. 2 intersects with the lens surface.

FIG. 36 shows a lens with respect to the sub-scanning shape of the incident surface of the second fθ lens of the optical scanning device shown in FIG. 2, which is based on the intersection of a plane including the optical axis of the system and extending in the main scanning direction and the lens surface. The graph which shows the position in the sub-scanning direction at each point in the main scanning direction of the surface.

37 is a schematic diagram showing a deviation of a shape of an incident surface of the second fθ lens of the optical scanning device shown in FIG. 2 from a shape of an arc having a curvature in the sub-scanning direction z = 0.

38 is a schematic diagram showing an asymmetrical component (sum of values of terms including odd-order terms of y) with respect to the scanning surface that spreads in the main scanning direction on the incident surface of the second fθ lens of the optical scanning device shown in FIG. 2;

39 is a perspective view showing the shape of the exit surface of the second fθ lens of the optical scanning device shown in FIG. 2. FIG.

40 is a graph showing a curvature in the sub-scanning direction of a portion where the scanning surface that spreads in the main scanning direction on the exit surface of the second fθ lens of the optical scanning device shown in FIG. 2 intersects with the lens surface.

41 is a main scanning direction of curvature in the sub-scanning direction at an intersection of a lens surface and a plane extending in the main scanning direction including the optical axis of the system with respect to the exit surface of the second fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the secondary differential value with respect to a coordinate.

42 is a main scanning direction of optical axis direction coordinates at an intersection of a lens surface and a plane including the optical axis of the system and extending in the main scanning direction with respect to the exit surface of the second fθ lens of the optical scanning device shown in FIG. 2; The graph which shows the differential value with respect to coordinates.

43 is a graph showing the curvature in the main scanning direction of a portion where the scanning surface spreading on the emission surface of the second fθ lens of the optical scanning device shown in FIG.

FIG. 44 shows a lens with respect to the sub-scanning shape of the exit surface of the second fθ lens of the optical scanning device shown in FIG. 2, which is based on the intersection of a plane including the optical axis of the system and extending in the main scanning direction and the lens surface. The graph which shows the position in the sub-scanning direction at each point in the main scanning direction of the surface.

45 is a schematic diagram showing a deviation of a shape of an emission surface of the second fθ lens of the optical scanning device shown in FIG. 2 from a circular arc having a curvature in the sub-scanning direction z = 0.

FIG. 46 is a schematic diagram showing an asymmetrical component (sum of values of terms including odd-order terms of y) with respect to the scanning surface that spreads in the main scanning direction of the exit surface of the second fθ lens of the optical scanning device shown in FIG. 2;

47 is a graph showing the power over the entire area of the first fθ lens in the sub-scanning direction of the optical scanning device shown in FIG.

48 is a graph showing the overall power of the first fθ lens in the main scanning direction of the optical scanning device shown in FIG.

49 is a graph showing the power over the entire area of the second fθ lens in the sub-scanning direction of the optical scanning device shown in FIG.

50 is a graph showing the power in the entire main scanning direction of the second fθ lens of the optical scanning device shown in FIG. 2.

51 is a schematic diagram showing the relative position of each laser beam in the sub-scanning direction with respect to the optical axis of the hybrid cylinder lens after passing through the hybrid cylinder lens of the optical scanning device shown in FIG.

52 is a graph showing defocus amounts in the main scanning direction and the sub scanning direction with respect to the main scanning direction image plane beam position of the laser beam from the magenta first laser element of the optical scanning device shown in FIG.

53 is a graph showing the focus amount in each of the main scanning direction and the sub scanning direction with respect to the main scanning direction image plane beam position of the laser beam from the cyan first laser element of the optical scanning device shown in FIG. 2.

54 is a main scanning direction and a sub-scanning direction with respect to the image plane beam position of the main scanning direction of the laser beam from each of the black first laser element and the yellow first laser element of the optical scanning device shown in FIG. 2; So a graph showing the amount of focus.

55 is a graph showing the degree of main scanning line bending with respect to the image plane beam position in the main scanning direction of the laser beam from the first magenta laser element of the optical scanning device shown in FIG. 2.

56 is a graph showing the degree of main scanning line bending with respect to the image plane beam position in the main scanning direction of the laser beam from the cyan first laser element of the optical scanning device shown in FIG. 2.

57 shows the degree of main scanning line bending with respect to the image plane beam position in the main scanning direction of the laser beam from each of the first black laser element and the first yellow laser element cyan for the optical scanning device shown in FIG. The graph that shows.

58 is a graph showing the degree of variation in beam spacing with respect to the image plane beam position in the main scanning direction between the laser beams emitted from the first and second magenta laser elements of the optical scanning device shown in FIG.

59 is a graph showing the degree of variation in beam spacing with respect to the image plane beam position in the main scanning direction between the laser beams from the first laser and the second laser for cyan of the optical scanning device shown in FIG.

FIG. 60 is a beam interval with respect to a main scanning direction image plane beam position of laser beams from each of the first and second lasers for black and the first and second lasers for yellow of the optical scanning device shown in FIG. A graph showing the degree of variation of.

FIG. 61 is a main scanning direction image plane beam position of a laser beam from each of the magenta first laser, the cyan first laser, the black first laser and the yellow first laser of the optical scanning device shown in FIG. 6 is a graph showing the reciprocal of the angle of collection of light, that is, the variation rate of the beam diameter.

62 is a main scanning direction of a laser beam from each of a magenta first laser element, a cyan first laser element, a black first laser element, and a yellow first laser element of the optical scanning device shown in FIG. 2; The graph which shows the variation rate of f (theta) characteristic with respect to an image plane beam position.

63 is a main scanning direction of a laser beam from each of the magenta first laser element, the cyan first laser element, the black first laser element, and the yellow first laser element of the optical scanning device shown in FIG. 6 is a graph showing the degree of deviation of the beam position in the sub-scanning direction in which the plane tilt is corrected with respect to the image plane beam position.

64 is a main scanning direction of a laser beam from each of the magenta first laser element, the cyan first laser element, the black first laser element, and the yellow first laser element of the optical scanning device shown in FIG. 6 is a graph showing the degree of change in transmittance with respect to the image plane beam position.

65 is a schematic cross-sectional view showing another image forming apparatus different from the image forming apparatus shown in FIG.

66 is a schematic plan view showing the arrangement of optical members of the optical scanning device incorporated in the image forming apparatus shown in FIG.

67 is a partial cross-sectional view of the optical scanning device shown in FIG. 65 taken in a state where the deflection angle of the optical deflecting device is 0 °.

68 is a schematic diagram showing an example of a light source, that is, a light emitting unit of the optical scanning device shown in FIG.

69 is a schematic plan view showing a state in which the laser beam interval of the optical scanning device shown in FIG. 2 is detected.

70 is a schematic cross-sectional view showing a state in which the laser beam interval of the optical scanning device shown in FIG. 2 is detected.

71 is a schematic diagram showing an example of changing the laser beam interval for switching the resolution in the image forming apparatus shown in FIG.

72 is a schematic cross-sectional view showing an image forming apparatus different from the image forming apparatus shown in FIGS. 1 and 65. FIG.

73 is a schematic plan view showing the arrangement of optical members of an optical scanning device incorporated in the image forming apparatus shown in FIG. 72.

74 is a perspective view showing the shape of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73.

75 is a graph showing the curvature in the sub-scanning direction of the portion where the scanning surface spreading in the main scanning direction of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73 intersects with the lens surface.

76 is 2 with respect to the main scanning direction coordinate of the curvature in the sub scanning direction at the intersection of the lens surface and the plane that extends in the main scanning direction and includes the optical axis of the system with respect to the incident surface of the fθ lens of the optical scanning device shown in FIG. 73; Graph showing the second derivative.

77 is a graph showing a first-order differential value in the main scanning direction of a portion where the scanning surface spreading in the main scanning direction of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73 intersects with the lens surface.

78 is a graph showing the curvature in the main scanning direction of a portion where the scanning surface spreading in the main scanning direction of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73 intersects with the lens surface.

79 is a diagram showing the sub-scanning shape of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73, showing the main part of the lens surface based on the intersection of the flat surface including the optical axis of the system and extending in the main scanning direction; The graph which shows the position in the sub-scanning direction at each point in the scanning direction.

80 is a graph showing the deviation of the shape of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73 from the shape of a circular arc having a curvature in the sub-scanning direction z = 0.

81 is a schematic diagram showing an asymmetrical component with respect to the scanning plane that spreads in the main scanning direction regarding the main scanning shape of the incident surface of the fθ lens of the optical scanning device shown in FIG. 73.

82 is a perspective view showing the shape of the emission surface of the fθ lens of the optical scanning device shown in FIG. 73.

83 is a graph showing the curvature in the sub-scanning direction of the portion of the exit surface of the fθ lens of the optical scanning device shown in FIG. 73, which intersects the scanning surface spreading in the main scanning direction and the lens surface.

84 is 2 with respect to the main scanning direction coordinates of the curvature in the sub scanning direction at the intersection of the lens surface and the plane that extends in the main scanning direction and includes the optical axis of the system with respect to the exit surface of the fθ lens of the optical scanning device shown in FIG. 73; Graph showing the second derivative.

85 is a graph showing a first-order differential value in the main scanning direction of a portion where the exit surface of the fθ lens of the optical scanning device shown in FIG. 73 intersects with the scanning surface spreading in the main scanning direction and the lens surface.

86 is a graph showing the curvature in the main scanning direction of a portion where the scanning surface spreading in the main scanning direction of the exit surface of the fθ lens of the optical scanning device shown in FIG. 73 intersects with the lens surface.

87 is a diagram showing the sub-scanning shape of the exit surface of the fθ lens of the optical scanning device shown in FIG. 73, showing the main part of the lens surface based on the intersection of the lens surface and the flat surface including the optical axis of the system and extending in the main scanning direction; The graph which shows the position in the sub-scanning direction at each point in the scanning direction.

FIG. 88 is a graph showing the deviation of the shape of the exit surface of the fθ lens of the optical scanning device shown in FIG. 73 from the shape of an arc having a curvature in the sub-scanning direction z = 0.

89 is a schematic diagram showing an asymmetrical component with respect to the main scanning shape of the exit surface of the fθ lens of the optical scanning device shown in FIG. 73 with respect to the scanning surface spreading in the main scanning direction.

90 is a graph showing the power over the entire area of the fθ lens in the sub-scanning direction of the optical scanning device shown in FIG. 73.

91 is a graph showing the power over the entire area of the fθ lens in the main scanning direction of the optical scanning device shown in FIG. 73.

92 shows the relative position in the sub-scanning direction of the laser beams from the first and second laser elements with respect to the optical axis of the hybrid cylinder lens after passing through the hybrid cylinder lens of the optical scanning device shown in FIG. 73. Schematic.

FIG. 93 is a graph showing defocus amounts in the main scanning direction and the sub scanning direction with respect to the image plane beam position in the main scanning direction of the laser beam of the first laser element of the optical scanning device shown in FIG. 73.

94 is a graph showing the degree of variation in the beam interval of the second laser with respect to the image plane beam position in the main scanning direction of the first laser of the optical scanning device shown in FIG. 73.

95 is a graph showing the reciprocal of the light collecting angle, that is, the variation rate of the beam diameter with respect to the image plane beam position in the main scanning direction of the first laser element of the optical scanning device shown in FIG. 73.

96 is a graph showing the variation rate of the fθ characteristic with respect to the image plane beam position in the main scanning direction of the first laser element of the optical scanning device shown in FIG. 73.

97 is a graph showing the degree of deviation, that is, deviation, of the beam position in the sub-scanning direction in which the plane tilt is corrected with respect to the image plane beam position in the main scanning direction of the first laser element of the optical scanning device shown in FIG. 73.

98 is a graph showing the degree of change in transmittance with respect to the image plane beam position in the main scanning direction of the first laser element of the optical scanning device shown in FIG. 73.

[Explanation of symbols]

1 ... Multi-beam optical scanning device, 1a ... Intermediate base, 3Y, 3M, 3C and 3B ... Light source (first optical means), 3Ya ... Yellow first laser, 3Yb ...
Yellow second laser, 3Ma ... Magenta first laser,
3Mb ... Magenta second laser, 3Ca ... Cyan first laser, 3Cb ... Cyan second laser, 3B
a: black first laser, 3Bb ... black second laser, 5 ... optical deflecting device, 5a ... polygon mirror body, 7Y, 7M, 7C and 7B ... pre-deflection optical system
(First Optical Means), 9Y, 9M, 9C and 9B ... Finite Focus Lens (First Optical Means), 11Y, 11M, 1
1C and 11B ... Hybrid cylinder lens, 13
... Laser synthesizing mirror unit, 13M ... Magenta reflecting surface, 13Y ... Cyan reflecting surface, 13B ...
Black reflective surface, 13α ... Base, 15
... Holding member, 17Y, 17M, 17C and 17B ... Plastic cylinder lens, 19Y, 19M, 19C and 19B ... Glass cylinder lens, 23 ... Horizontal sync detector, 25 ... Folding mirror 30 for horizontal sync ... Post-deflection optical system (first 2 optical means), 30a ... 1st
Imaging lens, 30b ... second imaging lens,
33Y, 33M, 33C and 33B ... First folding mirror, 35Y, 35M and 35C ... Second folding mirror, 37Y, 37M and 37C ... Third folding mirror, 39Y, 39M, 39C and 39B ... Dust-proof glass, 41Y , 41M and 41C ... Fixed part, 43Y,
43M and 43C ... Mirror pressing leaf spring, 45Y, 4
5M and 45C ... Protrusion, 47Y, 47M and 47C
... Set screws, 50Y, 50M, 50C and 50B ... Image forming unit, 52 ... Conveyor belt, 54
... Belt drive roller, 56 ... Tension roller, 58
Y, 58M, 58C and 58B ... Photosensitive drum, 60
Y, 60M, 60C and 60B ... Charging device, 62Y,
62M, 62C and 62B ... Developing device, 64Y, 64
M, 64C and 64B ... Transfer device, 66Y, 66M,
66C and 66B ... Cleaner, 68Y, 68M, 68
C and 68B ... static eliminator, 70 ... paper cassette,
72 ... Sending roller, 74 ... Registration roller, 76 ... Adsorption roller, 78 ... Registration sensor, 80 ... Registration sensor, 82
... conveyor belt cleaner, 84 ... fixing device, 1
00 ... Image forming device, 101 ... Main control device, 102 ... RAM, 103 ... Non-volatile memory, 110 ... Image control unit,
111 ... Image control CPU, 112 ... Bus line,
113 ... Timing control unit, 114Y, 11
4M, 114C and 114 ... Image memory, 115Y,
115M, 115C and 115 ... Data control unit, 11
6Y, 116M, 116C and 116 ... Laser driver, 117Y, 117M, 117C and 117 ... Registration correction calculation device, 118Y, 118M, 118C and 118 ... Timing setting device, 119Y, 119M,
119C and 119 ... Oscillation frequency variable circuit, 121 ...
R> Horizontal sync signal generation circuit, P ... Paper.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G02B 13/18 H04N 1/036 Z H04N 1/036 B41J 3/00 D 1/113 H04N 1/04 104Z (56) References Kaihei 5-199372 (JP, A) JP 5-66650 (JP, A) JP 4-35453 (JP, A) JP 57-102609 (JP, A) JP 6-214174 ( (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 26/10 B41J 2/44 H04N 1/113

Claims (4)

(57) [Claims] 1. ΣN _i (N ₁ + N ₂ + ... N _M ) lines,
M is an integer of 2 or more, and at least one of N _i is an integer of 2 or more; and one polarizing means for deflecting the light in the main scanning direction, having a rotatably formed reflecting surface. And a ΣN _i light beam deflected by the deflecting means is imaged so as to scan a predetermined image surface at a constant speed, and the influence of the surface tilt of the reflecting surface of the deflecting means can be corrected, so that a smooth curvature can be obtained. Optical means including a lens for changing the optical axis, optical path changing means for changing the reflection / emission angle in the main scanning direction depending on the height in the sub scanning direction which is a direction perpendicular to the main scanning direction, Of the light whose reflection and emission angles in the main scanning direction have been converted by the optical path conversion means after being incident on the optical path conversion means with different heights in the scanning direction and having passed through a predetermined position of the optical means, N _i Is the relative position of the interval of the light is 2 or more A detection means for exiting, and each of the light of said group M, the optical scanning device characterized in that it is incident on the detecting means at different timings. 2. ΣN _i (N ₁ + N ₂ + ... N _M ) lines,
M is an integer of 2 or more, and at least one of N _i is an integer of 2 or more, and ΣN _i emitted light from each of the N _i light sources is a sub-direction orthogonal to the main scanning direction. M sets of optical members to which a positive power is applied in the sub-scanning direction for converging in the scanning direction, and one polarizing means having a reflecting surface rotatably formed and deflecting light in the main scanning direction , ΣN _i light beams deflected by the deflecting means are imaged so as to scan a predetermined image surface at a constant speed, and the influence of surface inclination of the reflecting surface of the deflecting means can be corrected, and the smooth curvature can be obtained. Optical means including a variable lens, optical path changing means for changing the reflection / emission angle in the main scanning direction depending on the height in the sub scanning direction which is a direction perpendicular to the main scanning direction, and sub scanning for the light of the M group. The light beams are incident on the optical path changing means with different directional heights. Was, after passing through the predetermined position of said optical means, for detecting the relative position of the light interval N _i is 2 or more of the light converted reflecting emission angle in the main scanning direction by the optical path changing means An optical scanning device comprising: a detection unit, wherein each of the light beams of the M group is incident on the detection unit at a different timing. 3. The writing timing is controlled based on the output of the detecting means.
The optical scanning device described. 4. The optical scanning apparatus according to any one of claims 1 to 3, characterized by further comprising a control means for controlling the interval in the sub-scanning direction of the light based on an output of said detecting means.