JP2003050365A - Image forming apparatus using multi-beam system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To approximate the writing start positions of a plurality of laser beams by separately setting the writing start timing of each scan line. SOLUTION: A first and second sensors 251, 252 detect a first laser beam 103a to determine the time interval Ta of each detection timing. The first sensor 251 detects the first laser beam 103a, turns the first laser beam 103a OFF, and turns a second laser beam 103b ON, then the second sensor 252 detects the second laser beam 103b to determine the time interval Tb of each detection timing. Then, respective time intervals Ta and Tb are compared, the writing start timing by the second laser beam 103b is set according to a comparison result, and the writing start positions of the first and second laser beams 103a and 103b are made to coincide with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital copying machine,
The present invention relates to an electrophotographic image forming apparatus such as a laser printer or a facsimile machine, and more particularly to an image forming apparatus using a multi-beam method for writing an image with a plurality of laser beams.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a photoconductor is charged and modulated with a laser beam, and the photoconductor is repeatedly scanned by the laser beam to form an electrostatic latent image on the photoconductor. The electrostatic latent image is developed with toner, the toner image is transferred from the photoconductor to the recording paper, and the toner image on the recording paper is fixed.

Further, in a laser beam scanning device, the laser beam is reflected by a rotary polygon mirror, the laser beam is made incident on the photoconductor, and the photoconductor is repeatedly scanned by the laser beam. Further, in order to control the writing start position of the laser beam on the photoconductor, an optical sensor is installed at a predetermined position, the writing start timing of the laser beam is derived from the detection timing of the laser beam by the optical sensor, and this writing is performed. Writing from the start timing to the photosensitive member by the laser beam was started.

On the other hand, there is known a multi-beam type scanning device in which a plurality of laser beams simultaneously scan respective scanning lines on a photosensitive member in order to realize a high recording speed or a high recording density. Has been.

Also in this type of scanning apparatus, a plurality of laser beams are reflected by a rotating polygon mirror, each laser beam is made incident on a photoconductor, and the photoconductor is repeatedly scanned by each laser beam. Further, when changing the recording density, it is necessary to change the interval of each scanning line on the photoconductor, so that the interval of each scanning line is adjusted by inclining the emitting direction of each laser beam from each laser light source. is doing.

[0006]

By the way, when the scanning lines on the photoconductor are simultaneously scanned by a plurality of laser beams, the positions of the scanning lines in the scanning direction are deviated from each other at the same time point. . Therefore, if the writing start timing of each scanning line is matched, the writing start position of each laser beam on the photoconductor is displaced in the scanning direction, and the image quality is deteriorated. For example, as shown in FIG. 13, each of the scanning lines A1 and B1 is formed by two laser beams.
, A2, B2, A3, B3, ... When scanning two lines at a time, one scanning line A1 by one laser beam,
The writing start position Wa of A2, A3, ... And the writing start position Wb of each scanning line B1, B2, B3 ,.

Therefore, the present invention has been made in view of the above problems of the prior art, and it is possible to set the writing start timing of each scanning line separately to bring the writing start positions of a plurality of laser beams close to each other. An object of the present invention is to provide an image forming apparatus using a simple multi-beam method.

[0008]

In order to solve the above-mentioned problems, the present invention detects a scanning deviation of each laser beam in an image forming apparatus using a multi-beam method for writing an image with a plurality of laser beams. Scanning deviation detecting means and a writing control means for setting respective writing start timing by each laser beam based on the scanning deviation of each laser beam detected by the scanning deviation detecting means, the scanning deviation detecting means, Each laser beam includes a plurality of sensors that are arranged at predetermined intervals in the scanning direction of each laser beam and that detects each laser beam, and an on-off unit that turns each laser beam on and off, and the detection timing of each laser beam by each sensor Depending on, while selectively turning on and off each laser beam by the on-off means,
The scanning deviation of each laser beam is derived from the detection timing of each laser beam by each sensor.

According to the present invention having such a configuration, the respective laser beams are detected by the respective sensors arranged at a constant interval in the scanning direction of the respective laser beams. Then, the scanning deviation of each laser beam is derived from the detection timing of each laser beam by each sensor while selectively turning on and off each laser beam according to the detection timing of each laser beam by each sensor. For example, one laser beam is detected by two sensors, and the time interval of each detection timing is calculated. Further, when one of the sensors detects the laser beam, the laser beam is turned off, the other one laser beam is turned on, and the other sensor detects the other laser beam. The time interval of the detection timing of is calculated. When the time intervals of the two coincide, there is no scanning deviation of each laser beam. When the latter time interval is longer than the former time interval, scanning with another laser beam is delayed. Furthermore, when the latter time interval is shorter than the former time interval, scanning with another laser beam is in progress. If the writing start timing of each laser beam is set based on the scanning deviation of each laser beam thus obtained, the writing start position of each laser beam can be made closer.

Further, in the present invention, the writing control means sets each writing start timing by each laser beam by controlling each image writing signal which modulates each laser beam.

Here, the write start timing of each laser beam is set by adjusting the start timing of each image write signal that modulates each laser beam.

Further, in the present invention, the writing start position in the scanning direction of each laser beam is set according to the detection timing by one of the sensors of the scanning deviation detecting means.

As described above, if the writing start position in the scanning direction of each laser beam is set in accordance with the detection timing by one of the sensors of the scanning deviation detecting means,
That is, if the synchronization of the scanning of each laser beam is set, it is possible to reduce the size and cost of the device without providing a special synchronization sensor.

Further, in the present invention, the respective sensors of the scanning deviation detecting means are arranged in parallel in the scanning direction of each laser beam with a preset interval.

In this case, the scanning time of each sensor by each laser beam can be accurately obtained.

Further, in the present invention, a synchronization lens for converging each laser beam to each sensor of the scanning deviation detecting means is provided, and the distance between the sensors on both outsides of the scanning deviation detecting means is the scanning deviation detecting means. Compared with the scanning distance of each laser beam on each sensor, the scanning distance is shorter than the scanning distance limited by the size of the synchronous lens and is longer than the scanning distance in one cycle of the image writing signal that modulates the laser beam. Has been done.

If the distance between the sensors on both outer sides of the scanning deviation detecting means is shorter than the scanning distance limited by the size of the synchronizing lens, the laser beam is detected by the respective sensors on the outer sides through the synchronizing lens. can do. Further, if the distance between the sensors is longer than the scanning distance in one cycle of the image writing signal that modulates the laser beam, the writing start timing of each laser beam is changed in the cycle unit of the image writing signal, The writing start positions of the respective laser beams can be brought close to each other.

Further, in the present invention, each laser beam is incident on the rotary polygonal mirror, is reflected, passes through the synchronous lens, and scans each sensor of the scanning deviation detecting means.

With this synchronous lens, the laser beams can be brought close to and focused on each sensor.

Further, in the present invention, each sensor of the scanning deviation detecting means is arranged on the same substrate.

By arranging the respective sensors on the same substrate in this way, the positions of the respective sensors do not deviate from each other.

Further, in the present invention, a light shielding plate for shielding ambient light is provided between the respective sensors of the scanning deviation detecting means.

If the light shielding plate for shielding the ambient light is provided between the sensors as described above, it is possible to prevent erroneous detection of each sensor.

Further, in the present invention, the installation area of each sensor of the scanning deviation detecting means is isolated from the installation areas of other electronic parts.

In this case, it is difficult for reflected light from other electronic components to enter each sensor, and it is possible to prevent erroneous detection by each sensor.

Further, in the present invention, each sensor of the scanning deviation detecting means is composed of one package in which a two-chip sensor is mounted.

1 equipped with a two-chip sensor in this way
If the package is used, the distance between the sensors of the two chips becomes constant, and the scanning deviation of each laser beam can be accurately obtained.

Further, in the present invention, the lead terminals of the respective sensors of the scanning deviation detecting means are arranged substantially orthogonal to the scanning direction of each laser beam.

In this case, even if the sensors are arranged side by side, the lead terminals of the sensors are not obstructive and the sensors can be brought close to each other.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a side view schematically showing an embodiment of an image forming apparatus using the multi-beam method of the present invention. Further, FIG. 2 is an enlarged view showing a part of the image forming apparatus.

The image forming apparatus 1 of this embodiment is of a multi-functional type and functions as a copying machine, a printing machine, a facsimile machine and the like. The image forming apparatus 1 includes a printer 2
A scanner 3, an automatic document feeder 4, a paper discharge processor 5, and a multi-stage paper feeder 6.

In the automatic document feeder 4, when the document is placed on the document set tray 40, the document is conveyed and positioned on the platen glass 30, and after the image of the document is read by the scanner 3, the document is read. Are transported and discharged. Further, one side of the automatic document feeder 4 is pivotally supported so that an original that cannot be conveyed can be placed on the platen glass 30, and the entire apparatus 4 can be opened and closed.

In the scanner 3, either an automatic reading mode or a manual operation reading mode can be selected and set. When the former automatic reading mode is selected, the image of the original is read in conjunction with the conveyance of the original onto the platen glass 30 by the original conveying device 4. When the latter manual operation reading mode is selected, the image of the document placed on the platen glass 30 is read in response to the manual operation. In either mode, the first and second scanning units 31, 32
While maintaining a predetermined speed relationship with each other, the first scanning unit 31 exposes the image of the original document placed on the platen glass 30, and the first and second scanning units 3
1 and 32 guide reflected light from the document to a lens 33, and the lens 33 converts the image of the document into a photoelectric conversion element (C
The image is formed on the CD 34. The CCD 34 repeatedly scans and reads the image of the document in the main scanning direction, and outputs image data representing the image of the document.

In the printer 2, the image data from the scanner 3 and the image data from an external device (for example, a personal computer) are input and an image represented by the image data is recorded on a recording sheet.

The printer control section 24 functions as an interface for controlling the electrophotographic process section 20 and receiving image data from an external device. The image control unit 25 performs predetermined image processing on image data from an external device, or according to the image data, the optical scanning unit 22.
Drive control.

The electrophotographic process section 20 includes a photosensitive drum 200, a charging roller 201, an optical scanning unit 22, a developing unit 202, a transfer unit 203, a cleaning unit 204, a charge eliminating unit (not shown) and the like. The surface of the photoconductor drum 200 is the charging roller 20.
1 to be uniformly charged. The optical scanning unit 22 forms a laser beam modulated according to image data, and repeatedly scans the surface of the photosensitive drum 200 in the main scanning direction by the laser beam to form an electrostatic latent image on the surface of the photosensitive drum 200. To do. The developing unit 202 supplies toner to the surface of the photoconductor 200. This toner is the photosensitive drum 2.
A toner image is formed by adhering to the electrostatic latent image on the surface of No. 00. The transfer unit 203 superposes the recording sheet conveyed from below and the photosensitive drum 200, and transfers the toner image from the photosensitive drum 200 to the recording sheet.

A fixing device 23 is arranged above the electrophotographic process section 20. The fixing device 23 heats and pressurizes the recording paper to fix the toner image on the recording paper.

Further, the recording paper is carried by each carrying roller 28 and delivered to the relay path unit 8 of the paper discharge processing device 5.

A paper feeding section 21 is arranged below the printer 2. The paper feeding unit 21 separates and takes out the recording papers one by one from the paper storage tray 210 and the paper storage tray 210 that store the recording papers in a stacked manner.
A separation supply unit 211 that supplies the recording paper to the electrophotographic process unit 20 is provided. The paper storage tray 210 can be pulled out from the main body of the image forming apparatus 1,
In the pulled-out state, the recording paper is supplied to the paper storage tray 210.

The multi-stage sheet feeding device 6 is an option,
It is detachable from the image forming apparatus 1. In the multi-stage sheet feeding device 6, a plurality of types of recording sheets are stored in their respective sheet storage trays 610. Each separate supply unit 6
A reference numeral 11 separates and takes out the recording paper from each paper storage tray 610, and the recording paper is taken out from the electrophotographic process unit 2.
Send to 0. It should be noted that each paper storage tray 610 can be pulled out from the main body of the multi-stage paper feeding device 6, and in the pulled-out state, recording paper is supplied to each paper storage tray 610. Further, the number and size of each sheet storage tray may be changed appropriately.

The paper discharge processing device 5 comprises a relay path unit 8 and a post-processing unit 9. Relay pass unit 8
Receives the recording paper from the printer 2, and guides the recording paper to the post-processing unit 9 by each of the transport rollers 85.

The post-processing unit 9 receives the recording paper from the relay path unit 8 and performs the post-processing on the recording paper. Post-processing includes stable processing and sorting processing. The post-processing unit 9 includes a plurality of paper discharge trays 51.
a, 51b, 51c, etc., and each gate plate 52,
The recording paper is ejected to the respective output trays 51a, 5a by swinging 53.
It leads to either 1b or 51c. For example, in the image forming apparatus 1, when the copy mode is set, the recording paper is discharged to the upper discharge tray 51a, and when the print mode is set, the recording paper is discharged to the middle discharge tray 51b. However, when the facsimile mode is set, the recording paper is discharged to the lower discharge tray 51c.
To discharge.

On the other hand, the printer 2 and the optional paper discharge processing device 5 are mounted on the multi-stage paper feeding device 6. The scanner 3 and the automatic document feeder 4 are mounted on the system rack 7. On the bottom of the multi-stage paper feeding device 6, each moving roller 63 and each fixed portion 64 are provided. If the fixing portions 64 are screwed into the bottom of the multi-stage sheet feeding device 6 to separate the fixing portions 64 from the floor surface and the multi-stage sheet feeding device 6 is supported by the moving rollers 63, the multi-stage sheet feeding device 6 is moved. be able to. In this state, the multi-stage paper feeding device 6, the printer 2, and the paper discharge processing device 5 are moved and arranged inside the system rack 7. After that, each fixing part 64 is rotated and projected to bring each fixing part 64 into contact with the floor surface, and the multi-stage sheet feeding device 6 is fixed by each fixing part 64.

FIG. 3 is a perspective view showing the optical scanning unit 22 in the image forming apparatus 1 shown in FIGS. In addition, FIG. 4 is a plan view showing the optical scanning unit 22.

Here, the first and second semiconductor lasers 11 are
2a and 112b are provided. The first and second semiconductor lasers 112a and 112b are connected to the first and second laser beams 1
03a and 103b are emitted. The first and second laser beams 103 a and 103 b are collimator lens 113, concave lens 114, rectangular diaphragm 115 a of aperture plate 115,
The light enters the reflecting surface 120a of the polygon mirror 120 through the beam splitter 117 including a half mirror and the like, and is reflected by the reflecting surface 120a. Furthermore, the first
And the second laser beams 103a and 103b are formed by the fθ lens 12 including the first lens 121 and the second lens 122.
3, the light is reflected by the emission folding mirror 124 and the cylindrical mirror 125, and the photosensitive drum 20
It is incident on 0. In addition, the first and second laser beams 103
The light beams a and 103b are incident on the main scanning lines adjacent to each other on the photosensitive drum 200. Therefore, the incident positions of the first and second laser beams 103a and 103b are separated in the sub-scanning direction.

The polygon mirror 120 is a regular polygonal prism and has a reflecting surface 120a on each side wall.
Further, the polygon mirror 120 is driven to rotate,
Each reflecting surface 120a of the polygon mirror 120 is sequentially directed toward the photosensitive drum 200 side. The first and second laser beams 103a and 103b are reflected by the reflecting surface 120a facing the photoconductor drum 200 side, and the reflecting surface 120a
In the main scanning direction (Y-axis direction). Along with this, the spots of the first and second laser beams 103a and 103b move on the photoconductor drum 200 along respective main scanning lines adjacent to each other, and the photoconductor drum 200 is main-scanned. Each time each reflecting surface 120a of the polygon mirror 120 faces the photosensitive drum 200 side, the first
The second laser beams 103a and 103b move along the respective main scanning lines, and the main scanning of the photosensitive drum 200 is repeated. At the same time, the photoconductor drum 200 is rotated, and each main scanning line assumed on the photoconductor drum 200 is sequentially moved in the sub-scanning direction (Z-axis direction). As a result, an electrostatic latent image is formed on the photoconductor drum 200.

Further, the first and second laser beams 103
When the spots a and 103b move out of the main scanning range on the photosensitive drum 200, the first and second laser beams 103a and 103b emit the output folding mirror 12.
Cylindrical mirror 125 after being reflected by 4
Instead, it enters the sync detection mirror 126. And
The first and second laser beams 103a and 103b are reflected by the synchronization detection mirror 126, and the synchronization lens 128
The laser beam is incident on the laser beam detector 127 via. As will be described later, the detection output of the laser beam detector 127 is used to detect the first and second laser beams 103a and 103b.
Deviation in the main scanning direction or main scanning synchronization is detected.

FIG. 5A is a plan view conceptually showing the optical path in the optical scanning unit 22. In addition, FIG.
[Fig. 3] is a side view conceptually showing the same optical path. The first and second laser beams 103a and 103b are rotated by being reflected by the reflecting surface 120a of the polygon mirror 120, but in FIG. 5A, the fθ lens 123,
Output folding mirror 124, cylindrical mirror 12
5 and the first and second portions passing through the center of the photosensitive drum 200.
Only the laser beams 103a and 103b are shown.

Here, the first and second semiconductor lasers 112
a, 112b, collimator lens 113, concave lens 11
4, the aperture plate 115, the cylindrical lens 116, and the beam splitter 117 are the incident optical system 101.
Further, the polygon mirror 120, the fθ lens 123, the emission folding mirror 124, and the cylindrical mirror 12
5 is an emission optical system 102.

In the incident optical system 101, the first and second laser beams 103a and 103b are transmitted from the first and second semiconductor lasers 112a and 112b to the polygon mirror 120.
Of the first and second laser beams 103a and 103b on the reflecting surface 120a, the spot shape of the first and second laser beams 103a and 103b is formed into a linear shape having a width wider than that of the reflecting surface 120a.

In this incident optical system 101, the first and second laser beams 103a and 103b are the first and second laser beams.
When emitted from the semiconductor lasers 112a and 112b, they are converted into parallel light by the collimator lens 113 and diffused by the concave lens 114. Then, by the diaphragm 115 a of the aperture plate 115, the first and second laser beams 103
The cross-sectional shape of a and 103b is formed into a rectangular shape that is long in the main scanning direction (Y-axis direction) and short in the sub-scanning direction (Z-axis direction). Furthermore, the first and second laser beams 103a, 103
The beam b is converged in the Z-axis direction by the cylindrical lens 116, deflected by the beam splitter 117, and incident on the polygon mirror 120.

Here, the first and second laser beams 10 are
3a and 103b are diffused by the concave lens 114, and the cross-sectional shapes of the first and second laser beams 103a and 103b are shaped into a rectangular shape that is long in the main scanning direction and short in the sub scanning direction by the diaphragm 115a of the aperture plate 115. And the second laser beams 103a and 103b to the cylindrical lens 11
Since the beam is converged in the sub-scanning direction by 6, the first and second laser beams 103a and 10a on the polygon mirror 120 are formed.
The spot shape of 3b becomes a linear shape that is long in the main scanning direction, and its width is wider than the anti-slope surface 120a of the polygon mirror 120.

In the emission optical system 102, the polygon mirror 1 receives the first and second laser beams 103a and 103b.
While being repeatedly moved in the main scanning direction (Y-axis direction) by 20, the first and second laser beams 103a and 103b are guided to the photoconductor drum 200 to be incident thereon, and the photoconductor drum 20
0, the spots of the first and second laser beams 103a and 103b are moved at a constant speed in the main scanning direction to shape the spots of the first and second laser beams 103a and 103b into a preset shape and size. .

In this emission optical system 102, the first and second laser beams 103a and 103b are moved in the main scanning direction at a constant angular velocity by the polygon mirror 120,
It passes through the fθ lens 123. The fθ lens 123 converges the first and second laser beams 103a and 103b in the main scanning direction. Further, the fθ lens 123 causes the first and second laser beams 103 a and 10 on the photoconductor drum 200.
The 1st and 2nd so that the spot of 3b moves at a constant speed.
The angular velocities of the laser beams 103a and 103b are converted.
The first and second laser beams 103a and 103b are
The light is reflected by the output folding mirror 124 and enters the cylindrical mirror 125. Cylindrical mirror 1
25 is the first and second laser beams 103a and 103b
Is converged in the sub-scanning direction (Z-axis direction), and the influence of the surface tilt of the polygon mirror 120 is reduced by the first and second laser beams 1.
A correction is made to exclude them from 03a and 103b. The first and second laser beams 103a and 103b are reflected by the cylindrical mirror 125 and enter the photosensitive drum 200.

Here, the first and second laser beams 10 are
3a and 103b are converged in the main scanning direction by the fθ lens 123, and the first and second laser beams 103a and 103b are converged.
Are converged in the sub-scanning direction by the cylindrical mirror 125, so that the spots of the first and second laser beams 103a and 103b on the photosensitive drum 200 are shaped into a preset shape and size.

As described above, the spots of the first and second laser beams 103a and 103b are the photosensitive drums 2.
When the laser beam 103 moves out of the main scanning range on 00, the first and second laser beams 103a and 103b enter the laser beam detection unit 127 via the emission folding mirror 124, the synchronization detection mirror 126, and the synchronization lens 128. . At this time, the first and second laser beams 103a, 1
03b is converged in the main scanning direction by the fθ lens 123, is converged in the sub scanning direction by the cylindrical lens 130, and is further converged in both the main scanning direction and the sub scanning direction by the synchronizing lens 128. As a result, the laser beam detection unit The first and second laser beams 103a and 103b on the light receiving surface 127 are shaped into a preset shape and size.

The detection output of the laser beam detector 127 is used to detect the shift between the first and second laser beams 103a and 103b and to detect the main scanning synchronization. Then, the first and second laser beams 103a, 103a,
The writing start position on the photosensitive drum 200 by 03b is set.

FIG. 6 shows the first and second semiconductor lasers 112.
3 is a block diagram showing a configuration around a, 112b and a laser beam detector 127. FIG. Laser beam detector 127
Is the first and second sensors 251, 25 arranged in parallel in the scanning direction of the first and second laser beams 103a, 103b.
Equipped with 2. The image control unit 25 and a detection data calculation unit 253 that detects a shift between the first and second laser beams 103a and 103b and main scanning synchronization based on the detection outputs of the first and second sensors 311 and 312. , The first and the second depending on the deviation between them and the main scanning synchronization.
An image writing control unit 254 that forms an image writing signal for the semiconductor lasers 112a and 112b is provided. The first and second semiconductor lasers 112a and 112b are the first and second laser beams 1 corresponding to the respective image writing signals.
03a and 103b are emitted.

Prior to writing an image, the deviation between the first and second laser beams 103a and 103b and main scanning synchronization are detected by the following procedure.

First, the image writing control section 254 forms an image writing signal for continuously emitting the first laser beam 103a and applies this image writing signal to the first semiconductor laser 112a. As a result, the first laser beam 103a is continuously emitted as shown by the solid line in FIG. Further, the second laser beam 103b is not emitted as shown by the dotted line in FIG.

At this time, as shown in FIG. 7A, the first and second sensors 251 and 252 arranged side by side in the scanning direction are
The first laser beam 103a is sequentially detected, and a detection output as shown in FIG. 7B is added to the detection data calculation unit 253.
The detection data calculation unit 253 includes the first and second sensors 25.
Based on the detection outputs of the first and second sensors 251, 252, the respective detection time points T1, T2 of the first laser beam 103a by the first and second sensors 251, 252 are detected, and the time interval Ta between these detection time points T1, T2 is obtained. .

Subsequently, the detection data calculation unit 253
Based on the rescanning of the first laser beam 103a as shown in FIG. 8A, based on the detection output of the first sensor 251 of the laser beam detection unit 127 as shown in FIG. 8B,
The time T3 at which the first sensor 251 detects the first laser beam 103a is detected. Then, the detection data calculation unit 2
When the 53 detects this detection time T3, the first and second
The image writing control unit 254 is instructed to switch between the laser beams 103a and 103b. In response to this, the image writing control unit 254 outputs an image writing signal for stopping the emission of the first laser beam 103a to the first semiconductor laser 112a.
In addition to the above, an image writing signal for emitting the second laser beam 103b is formed, and this image writing signal is applied to the second semiconductor laser 112b. This allows
As shown by the dotted line in FIG. 8A, the first laser beam 103a
Is stopped and the second laser beam 103b is started to be emitted as shown by the solid line in FIG. After this, the detection data calculation unit 253, based on the detection output of the second sensor 252 as shown in FIG. 8B, the second sensor 252.
The detection time T4 of the second laser beam 103b is detected. Then, the detection data calculation unit 253 detects the detection time T3 of the first laser beam 103a and the second laser beam 10a.
The time interval Tb between the detection points T4 of 3b is obtained.

Here, the first and second laser beams 103
The polygon mirror 120 scans a and 103b at exactly the same speed. Therefore, the first laser beam 1
If there is no advance or delay in the scanning of the second laser beam 103b with respect to the scanning of 03a, the time interval Tb coincides with the time interval Ta (Tb = Ta). In addition, the first laser beam 10
When the scanning of the second laser beam 103b is delayed with respect to the scanning of 3a, the time interval Tb becomes longer than the time interval Ta (Tb> Ta). Further, the second laser beam 103b
When the scanning of is progressing, the time interval Tb becomes shorter than the time interval Ta (Tb <Ta).

The detection data calculation unit 253 uses the time interval Tb.
Is longer than the time interval Ta, the time difference (Tb-Ta)
Only, the image writing control unit 254 is instructed to advance the writing timing by the second laser beam 103b.
In response to this, the image writing control unit 254 causes the time difference (T
An image writing signal whose writing timing is advanced by b-Ta) is formed, this image writing signal is applied to the second semiconductor laser 112b, and the second laser beam 103b is emitted from the second semiconductor laser 112b. If the time interval Tb is shorter than the time interval Ta, the detection data calculation unit 253 detects the second laser beam 1 by the time difference (Tb-Ta).
It is instructed to delay the write timing by 03b. In response to this, the image writing control unit 254 applies an image writing signal whose writing timing is delayed by the time difference (Tb-Ta) to the second semiconductor laser 112b, and causes the second semiconductor laser 112b to emit the second laser beam 103b. . As a result, the writing start position by the first laser beam 103a and the writing start position by the second laser beam 103b coincide with each other even if the scanning of the second laser beam 103b is advanced or delayed with respect to the scanning of the first laser beam 103a. , Deterioration of image quality is prevented.

For example, when the scanning of the second laser beam 103b is progressing and the time interval Tb is shorter than the time interval Ta, the first semiconductor laser 112 as shown in FIG. 9B is used.
An image writing signal whose writing timing is delayed by the time difference (Tb-Ta) as shown in FIG. 9C with respect to the image writing signal of a is formed, and this image writing signal is applied to the second semiconductor laser 112b. As a result, in terms of timing, the image writing signal of the first semiconductor laser 112a and the second
Although the image writing signal of the semiconductor laser 112b is deviated, each scanning line A1 by the first laser beam 103a is formed on the photosensitive drum 200 as shown in FIG.
, A2, A3, ... Writing start position Wa and each scanning line B1, B2, B3 by the second laser beam 103b.
The writing start positions Wb of, ...

On the other hand, the main scanning synchronization is based on the scanning of the first laser beam 103a.
First sensor 2 when detecting the laser beam 103a
Based on the detection output of 51, a main scanning synchronization signal as shown in FIG. 9A is formed. At this time, the second laser beam 1
0b depending on whether the scan of 03b is advanced or delayed.
The sensor 251 detects the first laser beam 103a after the second laser beam 103b or detects the first laser beam 103a before the second laser beam 103b. Therefore, the detection output of the first sensor 251 is selected at the detection timing of the first laser beam 103a,
A main scanning synchronization signal is formed based on the selected detection output.

As described above, in the present embodiment, the first and second sensors 251 and 252 are used for the first laser beam 103a.
Is detected and the time interval Ta of each detection timing is obtained. Then, when the first laser beam 103a is detected by the first sensor 251, the first laser beam 103a is turned off and the second laser beam 10a is turned off.
3b is turned on, the second laser beam 103b is detected by the second sensor 252, and the time interval Tb of each detection timing is obtained. After this, each time interval Ta
, Tb are compared, and the writing start timing by the second laser beam 103b is set according to the comparison result,
The writing start positions of the first and second laser beams 103a and 103b are matched. In addition, the first and second sensors 251 and 252 are connected to the first and second laser beams 103.
Since the a and 103b are arranged in parallel in the scanning direction, the time intervals Ta and Tb can be accurately obtained and the scanning deviation can be corrected with high accuracy. Furthermore, since the synchronization lens 128 is provided in front of the first and second sensors 251, 252,
The first and second laser beams 103a, 103b can be brought closer together and focused on the first and second sensors 251, 252.

By the way, as shown in FIG. 11, the first and second
When the distance between the sensors 251 and 252 is Ls, the scanning distance limited by the width of the synchronous lens 128 in the scanning direction is Lb, and the scanning distance in one cycle of the image writing signal is Lc, Ls <La <Lb is set. To do. If the separation distance Ls is shorter than the scanning distance Lb, the synchronization lens 128
The laser beam can be detected by the first and second sensors 251 and 252. In addition, the separation distance L
If s is longer than the scanning distance Lc, the writing start timing of each of the first and second laser beams 103a and 103b is changed in the cycle unit of the image writing signal to write the first and second laser beams 103a and 103b. The starting positions can be close to each other.

Further, the first and second sensors 251, 25
If the two are mounted in one package, the distance between the first and second sensors 251 and 252 can be adjusted to a constant distance in advance, and the first and second laser beams 103
It is possible to accurately obtain the scanning deviation between a and 103b.

The first and second sensors 251, 252
Instead of the first to fourth sensors 2 as shown in FIG.
61 to 264 may be provided. In this case, the first to fourth sensors 261 to 264 appropriately detect the first and second laser beams 103a and 103b to detect the scanning deviation between the first and second laser beams 103a and 103b. Furthermore, by mounting and arranging the first to fourth sensors 261 to 264 on the same substrate 265, it is possible to prevent the first to fourth sensors 261 to 264 from being displaced from each other, and to detect a detection error. No need to give birth.

The first to fourth sensors 261 to 26 are also provided.
If each of the light-shielding plates 266 is provided between the four sensors, it is possible to prevent ambient light to the first to fourth sensors 261 to 264.
Further, on the substrate 265, the first to fourth sensors 261 to
The mounting area of H.264 is separated from the mounting areas of other electronic components, and other electronic components are not placed in the vicinity of the first to fourth sensors 261 to 264. This makes it difficult for reflected light from other electronic components to enter the first to fourth sensors 261 to 264, and prevents erroneous detection of the first to fourth sensors 261 to 264.

The first to fourth sensors 261 to 26 are also provided.
4 lead terminals 267 to the first and second laser beams 1
03a and 103b are arranged substantially orthogonal to the scanning direction. As a result, the lead terminals 267 do not get in the way, and the first to fourth sensors 261 to 264 can be brought close to each other. Then, the width of the synchronization lens 128 can be narrowed to reduce the size of the synchronization lens 128.

[0074]

As described above, according to the present invention, the respective laser beams are detected by the respective sensors arranged at regular intervals in the scanning direction of the respective laser beams. Then, the scanning deviation of each laser beam is derived from the detection timing of each laser beam by each sensor while selectively turning on and off each laser beam according to the detection timing of each laser beam by each sensor.
For example, one laser beam is detected by two sensors, and the time interval of each detection timing is calculated. Further, when one of the sensors detects the laser beam, the laser beam is turned off, the other one laser beam is turned on, and the other sensor detects the other laser beam. The time interval of the detection timing of is calculated. When the time intervals of the two coincide, there is no scanning deviation of each laser beam. When the latter time interval is longer than the former time interval, scanning with another laser beam is delayed. Furthermore, when the latter time interval is shorter than the former time interval, scanning with another laser beam is in progress. If the writing start timing of each laser beam is set based on the scanning deviation of each laser beam thus obtained, the writing start position of each laser beam can be made closer.

Further, according to the present invention, the write start timing of each laser beam is set by adjusting the start timing of each image write signal that modulates each laser beam.

Further, according to the present invention, the writing start position in the scanning direction of each laser beam is set according to the detection timing by one of the sensors, so that the synchronization sensor is not provided specially. It is possible to reduce the size and cost of the device.

Further, according to the present invention, since each sensor is arranged in parallel in the scanning direction of each laser beam with a preset interval, the scanning time of each sensor by each laser beam can be accurately obtained. You can

Further, according to the present invention, since the separation distance between the sensors on both outsides is shorter than the scanning distance limited by the size of the synchronizing lens, the laser beam is detected by the sensors on both outsides through the synchronizing lens. be able to.
Further, since the distance between the respective sensors is longer than the scanning distance in one cycle of the image writing signal that modulates the laser beam, the writing start timing of each laser beam is changed in units of the period of the image writing signal. The writing start positions of the laser beams can be brought close to each other.

Further, according to the present invention, since the synchronization lens is provided in front of each sensor, the laser beams can be brought close to and focused on each sensor by this synchronization lens.

Further, according to the present invention, since the sensors are arranged on the same substrate, the positions of the sensors do not deviate from each other.

Further, according to the present invention, since the light shielding plate for shielding the ambient light is provided between the respective sensors, the erroneous detection of the respective sensors can be prevented.

Furthermore, according to the present invention, since the installation area of each sensor of the scanning deviation detecting means is isolated from the installation area of the other electronic component, the reflected light from the other electronic component is input to each sensor. It is difficult to prevent erroneous detection of each sensor.

Further, according to the present invention, since one package in which the two-chip sensor is mounted is used, the distance between the two-chip sensors becomes constant, and the scanning deviation of each laser beam can be accurately obtained. .

Further, according to the present invention, since the lead terminals of the respective sensors of the scanning deviation detecting means are arranged substantially orthogonal to the scanning direction of the respective laser beams, even if the respective sensors are arranged in parallel, The lead terminals of each sensor do not get in the way, and each sensor can be brought closer.

[Brief description of drawings]

FIG. 1 is a side view schematically showing an embodiment of an image forming apparatus using a multi-beam method of the present invention.

FIG. 2 is an enlarged view showing a part of the image forming apparatus of FIG.

3 is a perspective view showing an optical scanning unit in the image forming apparatus of FIG.

FIG. 4 is a plan view showing the optical scanning unit of FIG.

5A is a plan view conceptually showing an optical path in the optical scanning unit of FIG. 3, and FIG. 5B is a side view conceptually showing the optical path.

FIG. 6 is a block diagram showing a configuration around first and second semiconductor lasers and a laser beam detector in the image forming apparatus of FIG.

7A is a diagram showing the emission states of the first and second laser beams with respect to the first and second sensors in the image forming apparatus of FIG. 1, and FIG. 7B is the detection of the first and second sensors. It is a figure which shows an output.

8A is a diagram showing another emission state of the first and second laser beams with respect to the first and second sensors in the image forming apparatus of FIG. 1, and FIGS. 8B and 8C are first and second diagrams, respectively. It is a figure which shows the detection output of a 2nd sensor.

9A is a diagram showing a main scanning synchronization signal, and FIGS. 9B and 9C are diagrams showing image writing signals of the first and second semiconductor lasers in the image forming apparatus of FIG.

10 is a diagram showing a writing start position of each scanning line on the photosensitive drum in the image forming apparatus of FIG.

11 is a diagram showing a scanning distance limited by a separation distance between the first and second sensors and a width of a synchronous lens in a scanning direction in the image forming apparatus of FIG.

12 is a plan view showing a modified example of a laser beam detection unit in the image forming apparatus of FIG.

FIG. 13 is a diagram showing a writing start position of each scanning line on a photosensitive drum in a conventional image forming apparatus.

[Explanation of symbols]

1 Image forming device 2 printer 3 scanner 4 Automatic document feeder 5 Paper ejection processing device 6 Multi-stage paper feeder 22 Optical scanning unit 112a First semiconductor laser 112b Second semiconductor laser 117 Beam splitter 120 polygon mirror 123 fθ lens 124 Output folding mirror 125 cylindrical mirror 126 Sync Detection Mirror 127 Laser beam detector 128 sync lens 251 1st sensor 252 second sensor 253 Detection data calculator 254 Image writing control unit 200 photoconductor drum

Continued front page    (72) Inventor Yasuhiro Ono             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Tetsuya Nishiguchi             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Hisashi Yamanaka             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company (72) Inventor Tetsuji Ito             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 2C362 BA69 BA70 BA89 BB30 BB31                       BB32 BB37 BB38                 2H045 AA01 BA02 BA22 BA33 CA88                       CA98 CB65                 5C072 AA03 BA04 HA02 HA06 HA09                       HA13 HB08 HB11 UA16 XA05

Claims (11)

[Claims] 1. An image forming apparatus using a multi-beam method for writing an image with a plurality of laser beams, wherein a scanning deviation detecting means for detecting a scanning deviation of each laser beam and each of the scanning deviation detecting means detect the deviation. Write control means for setting the write start timing of each laser beam based on the laser beam scanning deviation, and the scanning deviation detection means is arranged with a preset interval in the scanning direction of each laser beam. And a plurality of sensors for detecting each laser beam and an on / off means for turning on / off each laser beam. Meanwhile, each laser beam runs from the detection timing of each laser beam by each sensor. An image forming apparatus using a multi-beam method, which is characterized by deriving a deviation. 2. The writing control means sets each writing start timing by each laser beam by controlling each image writing signal which modulates each laser beam. Image forming apparatus using multi-beam method. 3. The multi-beam according to claim 1, wherein the writing start position in the scanning direction of each laser beam is set according to the detection timing by one of the sensors of the scanning deviation detecting means. Image forming apparatus using the method. 4. The image formation using the multi-beam method according to claim 1, wherein the respective sensors of the scanning deviation detecting means are arranged in parallel in the scanning direction of each laser beam with a preset interval. apparatus. 5. A synchronous lens for converging each laser beam to each sensor of the scanning deviation detecting means, wherein the distance between the sensors on both outsides of the scanning deviation detecting means is
Compared with the scanning distance of each laser beam on each sensor of the scanning deviation detecting means, the scanning distance is shorter than the scanning distance limited by the size of the synchronous lens, and the scanning is performed in one cycle of the image writing signal for modulating the laser beam. The image forming apparatus using the multi-beam method according to claim 1, wherein the image forming apparatus is longer than the distance. 6. The multi-beam according to claim 1, wherein each laser beam is incident on a rotary polygon mirror, is reflected by the rotary polygon mirror, passes through a synchronous lens, and is scanned by each sensor of the scanning deviation detecting means. Image forming apparatus using the method. 7. The image forming apparatus using the multi-beam method according to claim 1, wherein each sensor of the scanning deviation detecting means is arranged on the same substrate. 8. The image forming apparatus using the multi-beam method according to claim 1, wherein a light shielding plate for shielding ambient light is provided between each sensor of the scanning deviation detecting means. 9. The image forming apparatus using the multi-beam method according to claim 1, wherein an installation area of each sensor of the scanning deviation detecting means is isolated from an installation area of another electronic component. 10. Each sensor of the scanning deviation detecting means has two sensors.
The image forming apparatus using the multi-beam method according to claim 1, wherein the image forming apparatus is configured by one package in which a chip sensor is mounted. 11. The image forming method using the multi-beam method according to claim 1, wherein the lead terminals of each sensor of the scanning deviation detecting means are arranged substantially orthogonal to the scanning direction of each laser beam. apparatus.