JP2002072115A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that the accompanying variation of a side magnification rate occurs and causes image quality to become poor in the case that the deviation of a write position in a sub scanning direction is adjusted in an exposure device performing a writing process using a laser light. SOLUTION: Each angle of incidence into a photoreceptor and a light- deflecting member that deflects the light beam is established so that the fluctuation of an optical path length falls within limits set by a conditional expression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus that forms an image by performing exposure using a laser beam.

[0002]

2. Description of the Related Art In digital copiers and laser printers, a laser light source such as a semiconductor laser is used as a light source.
An image is formed by exposing the photoconductor.

Many image forming apparatuses that form an image using a laser light source are provided with adjustment means for adjusting the position at which a laser beam is incident on a photosensitive member, ie, the writing position. For example, in Japanese Patent Application Laid-Open No. H11-23778, a “F” -shaped mark (hereinafter referred to as a “registration mark”) is formed on a photoreceptor, the position of the formed registration mark is detected, and a semiconductor is formed based on a detection signal. The laser drive timing is controlled to adjust the writing position.

In a color image forming apparatus, since it is important to accurately match the positions of the respective color images to eliminate color misregistration, the above-described adjustment of the writing position is a very important technique. ing.

The adjustment of the writing position generally comprises adjustment in the main scanning direction and adjustment in the sub-scanning direction. Adjustment in the main scanning direction is performed by so-called magnification adjustment. This magnification adjustment is performed by adjusting the clock frequency of the pulse for driving the semiconductor laser, and the adjustment in the sub-scanning direction is performed by adjusting the optical system, particularly, a mirror that bends the light beam so that the light beam is incident on the photoconductor. In many cases, the optical bending is performed optically using an optical bending member.

[0006]

The adjusting means for adjusting the sub-scanning direction by adjusting the optical bending member can use the optical bending member used to make the exposure optical system compact for adjusting the exposure position. This is an effective means for reducing the size of an apparatus having four exposure apparatuses while maintaining the accuracy, such as a full-color image forming apparatus.

In such a compact image forming apparatus, a small-diameter drum-shaped photoconductor as a photoconductor is often used in combination with an optical bending member.

However, the combination of the optical bending member and the small-diameter photosensitive member has a problem that the adjustment of the writing position in the sub-scanning direction involves a variation in lateral magnification as described below. Next, FIG. 1 and FIG.
This will be described with reference to FIG.

The adjustment of the writing position in the sub-scanning direction is to displace the scanning line SL1 in FIG. 1 to the reference scanning line SL0. The adjustment of the scanning line SL1 before the adjustment to the scanning line SL2 by moving in parallel in the sub-scanning direction Y is performed by controlling the timing of the driving pulse for driving the semiconductor laser. It is difficult to adjust the scanning line SL2 adjusted in this manner to the reference line scanning line SL0 by the above-described timing control, and this adjustment is performed optically using an optical bending member. As shown in FIG. 2, one end MRA of a mirror MR as a light bending member is fixed, and the mirror MR is rotated by displacing the other end MRB as shown by an arrow with this as an axis. Due to the rotation of the mirror MR, the optical path changes from RB1 to RB2 at the other end MRB.
As a result, the incident position on the photoconductor is displaced from p1 to p2, and the scanning line SL2 matches the reference line SL0, so that the writing position in the sub-scanning direction is corrected.

However, the above correction makes the lateral magnification, that is, the magnification in the main scanning direction non-uniform at each position in the main scanning direction. In the design of the scanning optical system, the length of the optical path at the maximum image height, that is, the optical paths RA1 and RB1 in FIG.
Are designed to have the same length. However, FIG.
As a result of the correction in the sub-scanning direction as shown in (b), the optical path at one maximum image height changes from RB1 to RB2, and this change causes variation in the lateral magnification. The deviation of the change of the optical path length from the image height from the reference value is not a change in proportion to the image height but a non-linear change because the photoconductor PC has a drum shape. Therefore, the variation in the lateral magnification becomes complicated, and it is difficult to correct the variation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problem of the lateral magnification variation accompanying the correction of the positional deviation in the sub-scanning direction.

[0012]

The object of the present invention described above is achieved by the following invention. 1. A photoconductor, a laser light source, a deflecting means for deflecting a light beam from the laser light source to form a light beam for performing main scanning, and bending the light beam from the deflecting means;
An exposure device, comprising: an optical bending member that causes a light beam to be incident on the photoconductor, and an adjustment device that can adjust at least an incident position of the light beam on the photoconductor in the sub-scanning direction by adjusting the optical bending member. Wherein the angle of incidence of the light beam on the bending member and the photoconductor satisfies the following expression.

| D ｛cos (2γ−π / 2) tan α +
sin (2γ−π / 2) −1｝ | ≦ 0.2 mm The sign in the above expression has the following meaning: d (mm): displacement of the optical bending member from a reference position along the optical path at the maximum image height Amount, α (rad): Incident angle at the maximum image height in the direction perpendicular to the scanning surface on the photoconductor (+ is defined as being counterclockwise with respect to the normal direction of the surface of the photoconductor), γ ( rad): Angle of incidence of the light beam on the light bending member at the maximum image height.

2. 2. The image forming apparatus according to claim 1, wherein the photoconductor is a drum-shaped photoconductor.

3. An image forming apparatus having a plurality of sets of the photoreceptor and the exposure device, and capable of forming a color image, wherein the position shift between the images of each color is adjusted by adjusting the incident position in each of the exposure devices. 3. The image forming apparatus according to 1 or 2, wherein the image is corrected.

[0016]

FIG. 3 shows an image forming apparatus according to an embodiment of the present invention. FIG. 3 shows an overall image of the image forming apparatus according to the embodiment of the present invention.

The image forming apparatus shown in FIG. 3 includes a yellow image forming section 9Y for forming a yellow toner image, a magenta image forming section 9M for forming a magenta toner image, a cyan image forming section 9C for forming a cyan toner image, and a black toner. A full-color toner image is formed on the intermediate transfer body 6 by the black image forming unit 9K that forms an image, and a full-color toner image is transferred from the intermediate transfer body 6 to the recording paper P to form a full-color toner image on the recording paper P. Is what you do.

The yellow image forming section 9Y comprises a drum-shaped photosensitive member 1Y, a scorotron charger, a charging device 2Y for applying a uniform charging potential to the photosensitive member 1Y, and a dot formed on the photosensitive member 1Y by a light beam from a laser light source. Exposure device 3 for exposure
Y, a developing device 4 for developing an electrostatic latent image formed on the photoreceptor 1Y by charging and exposure to form a yellow toner image
Y, a charging device 7Y including a scotron charger for transferring the toner image on the photoconductor 1Y to the intermediate transfer member 6, and the photoconductor 1Y
And a cleaning device 8Y for cleaning.

The magenta image forming section 9M includes a photoreceptor 1M, a charging device 2M, an exposing device 3M, a developing device 4M, a transfer device 7M, and a cleaning device 8M having the same functions as those described above in the yellow image forming portion 9Y. The cyan image forming section 9C includes a photoconductor 1K and a charging device 2CL having the same functions as those described above in the yellow image forming section 9Y.
2. An image forming unit 9K includes a photoconductor 1K, a charging device 2K, and an exposure device having the same functions as those described above in the yellow image forming unit 9Y, including an exposure device 3C, a developing device 4C, a transfer device 7C, and a cleaning device 8C. 3K, developing device 4
K, a transfer device 7K and a cleaning device 8K.

The intermediate transfer member 6 is stretched around a driving roller 6A, a driven roller 6B, and a driven roller 6C, and rotates in a direction indicated by an arrow. Around the intermediate transfer member 6, a yellow image forming portion 9Y, a magenta image forming portion 9M, a cyan image forming portion 9C, a black image forming portion 9K, and corotron charging for transferring the toner image on the intermediate transfer member 6 to the recording paper P A transfer device 7A, which is a transfer device, a separation device 7B, which is a corotron charger for separating the recording paper P from the intermediate transfer member 6, and a cleaning device 8A for cleaning the intermediate transfer member 6, are provided.

The recording paper P is stored in a paper feed cassette 20, carried out of the paper feed cassette 20 by a paper feed roller 21, and transferred by a registration roller 22 in synchronism with the formation of a toner image on the intermediate transfer body 6. Paper is fed to the position 7A. Reference numeral 10 denotes a fixing device having a belt as a heating source and a pressing roller, and fixes the toner image on the recording paper P while conveying the recording paper P. Recording paper P that has passed through fixing device 10
Is discharged to a discharge tray 26 via transport rollers 23, 24, and 25.

Reference numerals 5Y, 5M, 5C, and 5K denote toner containers for storing yellow toner, magenta toner, cyan toner, and black toner, respectively, and developing devices 4Y, 4K, 4M, and 4K from which toners of respective colors correspond. Will be replenished.

In accordance with the rotation of the photoconductor 1Y as indicated by the arrow, charging by the charging device 2Y, exposure by the exposure device 3Y, and development by the developing device 4Y are performed, and a magenta toner image is formed on the photoconductor 1M, and a cyan image is formed on the photoconductor 1C. A toner image and a black toner image are formed on the photoconductor 1K. Timing is controlled so that these color toner images are superimposed on the intermediate transfer member 6 to form a full-color toner image.

The full-color toner image on the intermediate transfer member 6 is transferred to the recording paper P by the transfer device 7A. After the full-color toner image is fixed on the recording paper P by the fixing device 10, the recording paper P is discharged to the paper discharge tray 26.

After transfer, the photoreceptors 1Y, 1M, 1C and 1K are cleaned by the cleaning devices 8Y, 8M, 8C and 8K, respectively, so that the next image can be formed. After the transfer of the full-color toner image, the intermediate transfer member 6 is cleaned by the cleaning device 8A to be ready for the next image formation. The toner consumed by the development is supplied from the toner containers 5Y, 5M, 5C, and 5K to the corresponding developing devices 4Y, 4M, 4C, and 4K, respectively.

FIG. 4 shows an exposure optical system of the image forming apparatus according to the embodiment of the present invention. The exposure devices 3Y, 3M, 3C and 3K in FIG. 3 have the same exposure optical system, and FIG. 4 shows an exposure optical system common to these exposure devices 3Y, 3M, 3C and 3K.

A light beam from a semiconductor laser (not shown) as a laser light source that emits a light beam is scanned (scanned in the main scanning direction) within a range of an image width by a rotating polygon mirror 31 as a deflecting means. Is formed. Light beam R
After passing through the lens 32, the light is bent by mirrors 33 and 34, is passed through a cylindrical lens 35, is bent by a mirror 36 as an optical bending member so that the incident angle becomes almost 0 degree, and is incident on the photoconductor 1. Mirror 3
Reference numeral 6 denotes a mirror indicated by MR in FIG. 2, which is rotatably mounted around one end, and the writing position in the sub-scanning direction is corrected by the correction shown in FIGS.
Since the apparatus is configured such that the maximum value of the correction falls within the fixed values p1 and p2 in the design of the apparatus, the correction is performed within the range of p1 and p2.

FIG. 5 shows mirrors at both ends of the maximum correction range of the mirror 36 in the exposure optical system shown in FIG. 4, and R1 and R2 show optical paths formed by the mirrors 36A and 36B, respectively. Photoconductor 1 (Photoconductors 1Y, 1M,
1C and 1K are represented by a common photoreceptor 1) in a drum shape and its circumference is a circle, but in FIG. 5, it is close to a straight line 1S.

As shown in FIG. 5, the optical path length of the optical path R1 is d.
+ L, whereas the optical path length of the optical path R2 is L + L1 +
L2. The difference in optical path length between the optical paths R1 and R2 becomes non-linear, that is, changes in proportion to the image height as the distance from the optical axis of the exposure optical system increases.

As shown in FIG. 5, L1 = d sin θ = d
sin (2γ−π / 2), L2 = dcos (2γ−π /
2) becomes tan α, and the optical path length difference ΔR becomes the following (1)
Given by the formula. Equation (1) ΔR = d ｛cos (2γ−π / 2) tanα + sin
(2γ−π / 2) −1} The sign in the expression (1) has the following meaning.

D (mm): the displacement of the optical bending member from the reference position along the optical path at the maximum image height, α (rad): the direction perpendicular to the scanning surface of the photosensitive member at the maximum image height Γ (rad): the incident angle of the light beam to the light bending member at the maximum image height.

According to the experiment, it was found that the variation of the lateral magnification can be suppressed well by setting | ΔR | ≦ 0.2 mm by appropriately selecting the values of d, α and γ.

The parameters in the equation (1) are as shown in FIG. FIG. 6 shows the optical systems OP1 and OP2 in which the arrangement of the photoconductor 1 and the mirror 36 and the incident angle γ are changed. 7 (a), 7 (b), 7 (c), 7 (d)
Are the reflection portions S entering and leaving the mirror 36 of the optical system OP1.
1. Incident portion S2 of optical system OP1 to photoreceptor 1, optical system O
A portion S1 of the P2 entering the mirror 36 and a portion S2 of the optical system OP2 entering the photoconductor 1 are shown in an enlarged manner. Also, the optical path difference Δ
Table 1 shows the evaluation of the image when R is changed, and Table 2 shows the values of the parameters in the optical systems OP1 and OP2 in FIG.

[0034]

[Table 1]

[0035]

[Table 2]

As is clear from Table 1, when the optical path difference ΔR was 0.2 mm, it was determined that the color misregistration was good by visual color shift evaluation.
In the case of m, the color shift was remarkable. A satisfactory color image was obtained because the optical path difference ΔR was 0.2 m.
m, and when it exceeds 0.2 mm, color misregistration of a color image due to variation in lateral magnification tends to occur. As is clear from this, the optical systems OP1 and OP1 in FIG.
That is, the optical system under the conditions shown in Table 2 can form a good image, but the optical system OP2 cannot form a satisfactory image.

8 and 9 show an optical path difference ΔR of 0.2 mm,
This is a simulation of the incident position of the light beam on the photosensitive member 1 of the optical system set to 0.8 mm. FIG.
, The horizontal axis represents the image height from the optical axis (image height = 0 mm) to the maximum image height, and the vertical axis represents the deviation of the incident position of the light beam on the photosensitive member 1 from the reference position in the sub-scanning direction in mm. Represent. In FIG. 9, the maximum displacement is about 0.05 mm,
Although the color image was in a range where color shift did not occur, in the optical system in which the optical path difference ΔR was set to 0.8 mm, the maximum position shift was 0.2 mm, and the color shift of the color image was remarkable.

[0038]

According to the first aspect of the invention, even when the writing position is corrected in the sub-scanning direction, the variation in the lateral magnification is suppressed well, and a clear and high-quality image can be formed. become.

According to the second aspect of the present invention, the variation in the lateral magnification caused when a drum-shaped photosensitive member is used is effectively suppressed.

According to the third aspect of the invention, the color shift due to the variation in the lateral magnification is effectively suppressed, and a clear and high-quality color image can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining adjustment of a writing position by a beam.

FIG. 2 is a diagram for explaining adjustment of a writing position by a beam.

FIG. 3 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating an optical system of the image forming apparatus according to the embodiment of the present invention.

FIG. 5 is a partially enlarged view of the optical system of FIG. 4;

FIG. 6 is a diagram illustrating an optical path when parameters of an optical system are changed.

FIG. 7 is a partially enlarged view of an optical path in FIG. 6;

FIG. 8 is a diagram simulating the incident position of a light beam on a photosensitive member.

FIG. 9 is a diagram simulating the incident position of a light beam on a photosensitive member.

[Explanation of symbols]

Reference Signs List 1 photoreceptor 36 mirror d displacement amount of optical bending member from reference position along optical path at maximum image height α incident angle of light beam on photoconductor at maximum image height γ Incident angle of light beam ΔR Optical path difference R, R1, R2 Optical path

Claims (3)

[Claims] 1. A photosensitive member, a laser light source, a deflecting unit for deflecting a light beam from the laser light source to form a light beam for performing main scanning, and bending the light beam from the deflecting unit to form the photosensitive member An image forming apparatus, comprising: a light bending member that causes a light beam to be incident on the photosensitive member; and an adjusting device that can adjust at least an incident position of the light beam to the photoconductor in the sub-scanning direction by adjusting the light bending member. An image forming apparatus, wherein an angle of incidence of a light beam on the bending member and the photoconductor satisfies the following expression. | D ｛cos (2γ−π / 2) tanα + sin (2γ
−π / 2) -1｝ | ≦ 0.2 mm [The symbols in the above expression have the following meanings. D (mm): displacement of the optical bending member from a reference position along the optical path at the maximum image height; α (rad): Incident angle at a maximum image height in a direction perpendicular to the scanning surface of the photosensitive member (+ is defined in a counterclockwise direction with respect to a normal direction of the surface of the photosensitive member), γ (rad) : Angle of incidence of the light beam on the light bending member at the maximum image height. ] 2. The image forming apparatus according to claim 1, wherein the photoconductor is a drum-shaped photoconductor. 3. An image forming apparatus having a plurality of sets of the photoconductor and the exposure device and capable of forming a color image, wherein each color image is adjusted by adjusting the incident position in each of the exposure devices. The image forming apparatus according to claim 1, wherein a positional shift between the image forming apparatuses is corrected.