JPH10324019A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image density from being thin or thick by detecting an electrostatic latent image potential on a photosensitive body and adjusting an interval of a plurality of light beams on the basis of the detection result. SOLUTION: Two laser beams from laser light sources 21, 22 are passed through waveform-shaping lenses 25, 26. The laser beam passing the waveform- shaping lens 25 is reflected at a reflecting mirror 27. The laser beams are synthesized by an optical element 31, deflected and scanned by a polygon mirror 23 and projected on a photosensitive drum 11. An electrostatic latent image is formed on the photosensitive drum 11. A surface potentiometer 20 detects a first electrostatic latent image potential and a second electrostatic latent image potential shaped like a linear pair pattern on the photosensitive drum 11, and inputs to a control circuit 35. The control circuit 35 obtains an average value of the first and second electrostatic latent image potentials on the basis of potential detection signals. A piezoelectric element 29 is controlled so that a difference between the average value and a target value is within a predetermined value, whereby an emission interval of two laser beams is adjusted to be roughly ideal.

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 such as a laser beam printer, a digital copying machine, a laser facsimile and the like.

[0002]

2. Description of the Related Art In recent years, laser beam printers have become faster and faster.
It has been widely used to satisfy the demand for high image quality. In this laser beam printer, a photoconductor such as a photoconductor drum is moved in the sub-scanning direction and uniformly charged by a charger, and one laser beam from a laser is applied to the photoconductor by a rotating polygon mirror such as a polygon mirror. By exposing the photoreceptor by scanning in the main scanning direction, an image is written on the photoreceptor to form an electrostatic latent image, and the electrostatic latent image is developed by a developing device and transferred to transfer paper by a transfer device. doing. Here, the rotating polygon mirror is rotated at a predetermined rotation speed by a motor.

In order to further increase the speed of this type of laser beam printer, it is necessary to rotate a rotary polygon mirror for scanning the laser beam at a high speed. However, it is technically very difficult to rotate the rotating polygonal mirror at high speed, and as the rotating polygonal mirror becomes higher in speed, uneven rotation, reduced durability, increased noise, etc. occur, resulting in stable high-quality images. There is a problem that can not be obtained.

In order to solve this problem, a so-called multi-beam type laser beam is used in which a plurality of laser beams from a laser are simultaneously scanned in the main scanning direction on a photoreceptor by a rotating polygon mirror such as a polygon mirror. Printers have been proposed. Such a multi-beam type laser beam printer can be operated at high speed, and the rotation speed of the rotary polygon mirror can be reduced in accordance with the number of laser beams. For example, when the number of laser beams is two, In some cases, the rotation speed of the rotary polygon mirror is half that of a laser beam printer having one laser beam.
Therefore, the rotating polygon mirror can reduce uneven rotation, improve durability, and reduce noise.

Further, in an image forming apparatus such as a multi-beam type laser beam printer, various adjusting means for accurately adjusting the interval between a plurality of laser beams are disclosed in JP-A-61-15118 and JP-A-61-15118. JP-A-61-15119, JP-A-2-10212, JP-A-7-181
No. 410 publication.

[0006]

In an image forming apparatus such as a multi-beam type laser beam printer described above,
The interval between a plurality of laser beams needs to be accurately adjusted on the photoconductor to an interval corresponding to the writing density (resolution).
For example, in an image forming apparatus for writing an image by scanning a photosensitive member with two laser beams as described in Japanese Patent Application Laid-Open No.
In the case of 0 dpi, the interval between the two laser beams must be exactly 63.5 μm. For example, if the interval between the two laser beams is 50 μm, as shown in FIG. Two straight lines 1 and 2 written in the main scanning direction on the photoreceptor by the laser beams B1 and B2
Is 50 μm compared to the ideal spacing of 63.5 μm.
m, 77 μm. As a result, fine stripe-like shading occurs in the image density, and the image quality deteriorates.

When an image is written in the area A of the photoreceptor with two laser beams whose interval is smaller than the ideal interval, the electrostatic latent images 1 and 2 formed in the area A on the photoreceptor by each laser beam.
, The overlap increases, the line becomes thicker, and the density increases. Conversely, when an image is written in the area B on the photoconductor with two laser beams whose intervals are wider than the ideal interval, the electrostatic latent images 1 and 2 formed on the photoconductor with each laser beam overlap. Respectively, the lines become thinner, and the density becomes lower.
For this reason, the image density varies. Originally,
If the interval between the two laser beams is accurately adjusted to the ideal interval, such density unevenness should not occur, and the interval between the laser beams is accurately adjusted to the ideal interval. There is a need to.

The present invention provides an image forming apparatus capable of accurately and easily adjusting the interval between a plurality of light beams, preventing image density from becoming uneven, and obtaining a high quality image. The purpose is to do.

[0009]

Means for Solving the Problems To achieve the above object, the invention according to claim 1 comprises a photosensitive member, a charging means for uniformly charging the photosensitive member, and a charging member for uniformly charging the photosensitive member. In an image forming apparatus having a plurality of light emitting elements that emit a plurality of light beams for scanning a surface to form an electrostatic latent image, the plurality of light emitting elements emit light with a pattern signal to at least light the photosensitive member. Pattern generating means for exposing in two predetermined patterns; potential detecting means for detecting an electrostatic latent image potential on the photoreceptor; and an interval between the plurality of light beams based on a detection result of the potential detecting means. Control means for adjusting the distance between a plurality of light beams, the distance between a plurality of light beams is accurately and easily adjusted, the density of image density is prevented, and a high-quality image is obtained.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the pattern generating means causes the plurality of light emitting elements to emit light by a first pattern signal, and causes the first static electricity on the photosensitive member. Forming a second electrostatic latent image on the photoreceptor by causing the plurality of light emitting elements to emit light with a second pattern signal and forming the second electrostatic latent image;
And adjusting the intervals between the plurality of light beams so that the detection result of the potential detection means for the electrostatic latent image of the above and the detection result of the potential detection means for the second electrostatic latent image substantially coincide with each other. The distance between the plurality of light beams can be adjusted accurately and easily, and the density of the image is prevented from becoming uneven, and a high-quality image can be obtained.

[0011]

FIG. 2 shows an embodiment of the present invention. This embodiment is an embodiment of the first aspect of the present invention. The photoreceptor 11 is, for example, a photoreceptor drum having a photoreceptor layer of amorphous silicon on its surface. The photoreceptor 11 is rotationally driven by a rotation drive unit and moves in the sub-scanning direction. The photosensitive drum 11 is uniformly charged by a charging means 13 composed of a charging charger after being entirely exposed by a pre-exposure lamp 12, and is exposed by an optical writing device 14 to write an image. An image is formed.

The electrostatic latent image on the photosensitive drum 11 is visualized by a developing unit 15 as a developing means to become a toner image, and the toner image on the photosensitive drum 11 is transferred from a paper feeding device. The image is transferred to a transfer material made of paper by a transfer means 16 consisting of a transfer charger. The transfer paper is separated from the photosensitive drum 11 by the separation charger 17, the toner image is fixed by the fixing device 18, and is discharged to the outside. The photosensitive drum 11 is cleaned by the cleaner 19 after the transfer paper is separated. A potential detecting means 20 composed of a surface electrometer is disposed between the optical writing device 14 and the developing device 15 and detects the potential of the electrostatic latent image on the photosensitive drum 11.

In the optical writing device 14, as light emitting elements for emitting a plurality of light beams, for example, laser light sources 21 and 22 composed of two semiconductor lasers are used, and two laser beams from the laser light sources 21 and 22 are used. Is deflected and scanned by a polygon mirror 23 as one rotating polygon mirror, is reflected by a return mirror 24, and is irradiated onto the photosensitive drum 11. Thus, the optical writing device 14
Is provided with optical means including laser light sources 21 and 22, a polygon mirror 23, a folding mirror 24, and the like. As shown in FIG. 3, two laser beams B1 and B2 from the laser light sources 21 and 22 are used on the photosensitive drum 11. Are simultaneously scanned in the main scanning direction over two rows.

FIG. 1 shows a control system for adjusting the interval between the laser beams B1 and B2 and an optical writing device 14. In the optical writing device 14, specifically, the laser light sources 21, 2
Two laser beams from 2 pass through waveform shaping lenses 25 and 26 including a collimator lens and an aperture member, and the laser beam from the waveform shaping lens 25 is reflected by a reflection mirror 27. The movable portion 28 has a reflection mirror 27 fixed to one surface side and a piezoelectric element 29 fixed to the other surface side,
It is rotatably supported by the rotating shaft 30.

The laser beam B from the waveform shaping lens 26
2 and the laser beam B1 reflected by the reflection mirror 27 are combined by an optical element 31 as a beam combining element, are deflected and scanned by a polygon mirror 23, and are scanned via an fθ optical system 32 and a return mirror 24.
Irradiated on 1 The laser modulator 33 is a laser light source 2 composed of a semiconductor laser according to image data during image formation.
1 and 22 are modulated and the photosensitive drum 11 is scanned by the laser beams B1 and B2, whereby an image is written and an electrostatic latent image is formed.

The pattern generating means 34 generates a plurality of pattern signals at a predetermined timing during non-image formation.
For example, a first pattern signal to be written by the laser beams B1 and B2 (a pattern signal of a line pair pattern in which the density becomes high like the area A on the photosensitive drum 11 as shown in FIG. 4) and the laser beams B2 and B1 , A second pattern signal to be written (as shown in FIG.
1 and a pattern signal in the form of a line pair pattern in which the density is low as in the region B on the first line. The laser modulator 33 modulates and drives the laser light sources 21 and 22 according to the respective pattern signals from the pattern generator 34, and the photosensitive drum 11 is exposed entirely by the pre-exposure lamp 12 and then has a constant potential by the charging charger 13. It is charged to Vo.

Therefore, the first photosensitive drum 11 has a first pattern signal to be written by the laser beams B1 and B2, which is written by the laser beams B1 and B2, and has a line pair pattern corresponding to the first pattern signal. An electrostatic latent image is formed, and a second pattern signal to be written by the laser beams B2, B1 is written by the laser beams B1, B2, and a second electrostatic latent image in a line pair pattern corresponding to the second pattern signal. An image is formed. A surface voltmeter 20 detects the potential of the first electrostatic latent image in the form of a line pair pattern and the potential of the second electrostatic latent image in the form of a line pair pattern on the photosensitive drum 11, and controls the control circuit as control means. Input to 35.

The control circuit 35 controls the potential of the first electrostatic latent image on the photosensitive drum 11 detected by the surface voltmeter 20 at one time based on the potential detection signal from the surface voltmeter 20 and the second potential. The average value of the potential of the electrostatic latent image and the piezoelectric element 2 are determined so that the difference between the average value and the target value Vtd1 is within a predetermined value (so that the average value is substantially equal to the target value Vtd1).
9 to adjust the light emission interval (interval in the sub-scanning direction) of the laser beams B1 and B2 to a substantially ideal interval, or to control the piezoelectric element 29 to change the interval between the laser beams B1 and B2 in the sub-scanning direction. While the first electrostatic latent image having the line pair pattern and the second electrostatic latent image having the line pair pattern are repeatedly formed on the photosensitive drum 11 twice or more, the surface potential with respect to these electrostatic latent images is changed. The surface potential meter 20 detects the potential of the first electrostatic latent image on the photosensitive drum 11 and the second electrostatic latent image detected two or more times based on the potential detection signal from the meter 20. An average value of the potential of the image and the potential of the first electrostatic latent image is obtained each time the potential of the first electrostatic latent image and the potential of the second electrostatic latent image are detected, and the difference between the average value and the target value Vtd1 is equal to or less than a predetermined value. So that the average value is substantially equal to the target value Vtd1. ) To adjust the emission interval of the laser beam B1, B2 (sub-scanning direction interval) by controlling the piezoelectric element 29.

It is technically very difficult to directly measure the laser beam emission intervals (intervals in the sub-scanning direction), and a dedicated jig is required. It is almost impossible to adjust the interval (interval in the sub-scanning direction) (necessary when the laser light source is damaged at the user's site). In the present embodiment, the light emission interval (sub-scanning direction interval) of the laser beam is not measured directly but by using the electrostatic latent image as a substitute value. It can be adjusted to the extent that it does not appear as final image density unevenness,
An image having a desired density can be obtained uniformly.

This embodiment is an embodiment of the first aspect of the present invention, in which a photosensitive member 11, a charging means 13 for uniformly charging the photosensitive member 11, and a uniform charging of the photosensitive member 11 An image forming apparatus including a plurality of laser light sources as light emitting elements for emitting a plurality of light beams for scanning a charged surface to form an electrostatic latent image; A pattern generator 34 for emitting light by a pattern signal to expose the photoconductor 11 in at least two predetermined patterns; a potential detector 20 for detecting an electrostatic latent image potential on the photoconductor 11; Since the control circuit 35 is provided as control means for adjusting the interval between the plurality of light beams based on the detection result of the potential detecting means 20, the interval between the plurality of light beams can be adjusted accurately and easily. It can be capable of preventing the density of the image density obtaining a high quality image.

Although this embodiment uses two types of patterns, the types of patterns are not limited to these, and three or more types of patterns may be used. Further, the pattern may be not only a modulation pattern but also a plurality of patterns obtained by combining a light emission amount pattern with a modulation pattern. Also,
In the above embodiment, the interval between the laser beams in the sub-scanning direction is controlled so that the average value of the potentials of the two electrostatic latent images based on the two pattern signals is substantially equal to the target value. Needless to say, this is not the case. In the above embodiment, the light beam is 2
In the case of a book, the number of light beams is not limited to this. When there are more than two light beams, the number of patterns may be increased so that the interval between each light beam can be detected.

Another embodiment of the present invention is an embodiment of the second aspect of the present invention. In the above embodiment, the light emission interval (interval in the sub-scanning direction) of the laser beams B1 and B2 is adjusted as follows. . That is, the pattern generating means 34 outputs the laser beams B1, B
2 generates a first pattern signal to be written (a pattern signal of a line pair pattern in which the density increases as in the area A on the photosensitive drum 11 as shown in FIG. 4). The laser modulator 33 modulates and drives the laser light sources 21 and 22 with the first pattern signal from the pattern generator 34, and the photosensitive drum 11 is entirely exposed by the pre-exposure lamp 12 and then fixed by the charging charger 13. Is charged to the potential Vo.

Therefore, the first photosensitive drum 11 has a first pattern signal to be written by the laser beams B1 and B2, which is written by the laser beams B1 and B2 and has a first line-pair pattern corresponding to the first pattern signal. An electrostatic latent image is formed. The surface voltmeter 20 detects the potential of the line-pattern first electrostatic latent image on the photosensitive drum 11,
The detected value Vtd2 is input to the control circuit 35.

Next, a second pattern signal to be written by the pattern generating means 34 with the laser beams B2 and B1 (FIG. 4)
As shown in FIG. 5, a pattern signal in the form of a line pair pattern in which the density decreases as in the region B on the photosensitive drum 11 is generated. The laser modulator 33 modulates and drives the laser light sources 21 and 22 in response to the second pattern signal from the pattern generator 34, and the photosensitive drum 11
After the entire surface has been exposed by the charging device 2, it is charged to a constant potential Vo by the charging charger 13.

Therefore, the photosensitive drum 11 has the second pattern signal to be written by the laser beams B2 and B1 written by the laser beams B1 and B2, and the second pattern signal of the line pair pattern corresponding to the second pattern signal. An electrostatic latent image is formed. The surface voltmeter 20 detects the potential of the second electrostatic latent image in a line pair pattern on the photosensitive drum 11,
The detected value Vtd3 is input to the control circuit 35.

The control circuit 35 determines the difference between the detection values Vtd2 and Vtd3 of the surface electrometer 20 and determines whether or not the difference is equal to or less than a predetermined value and the detection values Vtd2 and Vtd3 are substantially equal. It is determined whether or not the light emission intervals (intervals in the sub-scanning direction) of the laser beams B1 and B2 are substantially equal to a target value. If the difference between the detection values Vtd2 and Vtd3 is not smaller than a predetermined value, the piezoelectric element 29 is controlled. To change the light emission intervals (intervals in the sub-scanning direction) of the laser beams B1 and B2 again to form the first electrostatic latent image and the second electrostatic latent image in the line pair pattern as described above, and a surface voltmeter. Then, it is determined whether the difference between the detection values Vtd2 and Vtd3 is equal to or less than a predetermined value.

The control circuit 35 detects the detected values Vtd2, Vtd
The above operation is repeatedly performed until the difference between the detected values Vtd3 and Vtd3 becomes equal to or smaller than a predetermined value. It is determined that the values have become substantially equal to the values, and the adjustment of the light emission intervals (intervals in the sub-scanning direction) of the laser beams B1 and B2 ends.

This embodiment is an embodiment of the second aspect of the present invention, and in the image forming apparatus according to the first aspect, the pattern generating means 34 is configured to control the plurality of light emitting elements 21 by a first pattern signal. , 22 to emit light to form a first electrostatic latent image on the photoconductor 11, and to cause the plurality of light-emitting elements 21, 22 to emit light by a second pattern signal, so that a second electrostatic latent image is formed on the photoconductor 11. An electrostatic latent image is formed, and the control unit 35 compares the detection result of the potential detection unit 20 with respect to the first electrostatic latent image and the detection result of the potential detection unit 20 with respect to the second electrostatic latent image. Since the intervals between the plurality of light beams are adjusted so as to substantially match each other, the intervals between the plurality of light beams can be adjusted accurately and easily. Can be obtained. In this embodiment, the photosensitive member is scanned by using two laser beams. However, the photosensitive member may be scanned by using three or more light beams.

[0029]

As described above, according to the first aspect of the present invention, the photosensitive member, the charging means for uniformly charging the photosensitive member, and the uniformly charged surface of the photosensitive member are scanned. An image forming apparatus having a plurality of light emitting elements for emitting a plurality of light beams for forming an electrostatic latent image, wherein the plurality of light emitting elements emit light by a pattern signal to cause the photosensitive member to emit at least two predetermined patterns. A pattern generating means for exposing the light, a potential detecting means for detecting an electrostatic latent image potential on the photoconductor, and a control means for adjusting an interval between the plurality of light beams based on a detection result of the potential detecting means. Therefore, the interval between a plurality of light beams can be adjusted accurately and easily, and a high-quality image can be obtained in which the density of the image is prevented.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the pattern generating means causes the plurality of light emitting elements to emit light by a first pattern signal, thereby causing the first light emitting element to emit light on the photosensitive member. And causing the plurality of light-emitting elements to emit light with a second pattern signal to form a second electrostatic latent image on the photoconductor, wherein the control unit controls the first electrostatic latent image. Since the interval between the plurality of light beams is adjusted so that the detection result of the potential detection means for the latent image and the detection result of the potential detection means for the second electrostatic latent image substantially match, the plurality of light beams Can be adjusted accurately and easily, and the density of the image can be prevented from becoming uneven, so that a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a control system for adjusting a laser beam interval and an optical writing device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the same embodiment.

FIG. 3 is a perspective view showing a part of the embodiment.

FIG. 4 is a diagram illustrating a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Photoconductor 13 Charging means 15 Developing device 20 Potential detecting means 21, 22 Laser light source 23 Polygon mirror 34 Pattern generating means 35 Control circuit

Claims (2)

[Claims] A photoconductor, a charging unit for uniformly charging the photoconductor, and a plurality of light beams for forming an electrostatic latent image by scanning a uniformly charged surface of the photoconductor. An image forming apparatus having a plurality of light-emitting elements that emit light, a pattern generating means for causing the plurality of light-emitting elements to emit light by a pattern signal and exposing the photoconductor to at least two predetermined patterns; An image forming apparatus, comprising: a potential detecting means for detecting the potential of the electrostatic latent image; and a control means for adjusting an interval between the plurality of light beams based on a detection result of the potential detecting means. 2. An image forming apparatus according to claim 1, wherein said pattern generating means causes said plurality of light emitting elements to emit light by a first pattern signal to form a first electrostatic latent image on said photosensitive member. And causing the plurality of light-emitting elements to emit light by a second pattern signal to form a second electrostatic latent image on the photoconductor, wherein the control unit controls the potential detection unit for the first electrostatic latent image. An image forming apparatus, wherein an interval between the plurality of light beams is adjusted such that a detection result substantially matches a detection result of the potential detection unit with respect to the second electrostatic latent image.