JP2000075228A - Multi-beam image forming device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To synchronously detect laser scanning of each multi-beam by shifting the optical scanning time of the synchronous detection means shared by the laser beams of each multi-beam scanning optical system. Provided is a multi-beam image forming apparatus that generates a synchronization detection pulse with a time lag by a synchronization detection signal generated by a means. SOLUTION: The synchronization detecting means is disposed so as to be optically substantially flush with the photosensitive facing surface. As shown in FIG. 2, each of the reflecting mirrors such that angles α and β between the reflecting surface of the polygon mirror motor 123 and the optical paths reaching the reflecting mirrors 127 and 137 and the photodetector 125 satisfy α> β. Is configured. Each LD array 223, 233
Since the above angles α> β in the multi-beams from FIG. 6, as shown in FIG. 6, the synchronization detection signal of the detector has a time lag due to each multi-beam scanning, and Can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam image forming apparatus having a multi-beam scanning optical system for simultaneously scanning two or more lines in one scan using a plurality of laser light sources.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus for forming an image on a recording medium by using an electrophotographic technique, a laser beam is scanned on a photoreceptor using a laser scanning optical system to form an electrostatic image (electrostatic image). (Latent image) is used. In this image forming apparatus, the polygon mirror is rotated by a polygon motor. The scanning speed on the photosensitive member in the main scanning direction is a polygon mirror motor rotation speed as a parameter, and the scanning speed limit is the polygon motor rotation speed. Limited by rotational speed limits. In recent years, due to the above-mentioned limit of the scanning speed in the main scanning direction, a plurality of laser beams are simultaneously scanned in parallel in a single scan on the photoconductor, and the laser scanning speed is controlled by 1 / (number of laser elements). A multi-beam scanning optical system that forms an image on a photoconductor by
Particularly, a two-beam scanning optical system using two lasers has been realized.

A multi-beam scanning optical system and an image forming apparatus having the multi-beam scanning optical system are disclosed in, for example,
-29711, JP-A-5-53068, JP-A-5-66354, JP-A-5-294003, JP-A-6-216559, JP-A-8-29
No. 2,384, and Japanese Patent No. 2,508,871. These multi-beam scanning optical systems and image forming apparatuses having the multi-beam scanning optical system are configured so that the positions where the respective multi-beam scanning optical systems scan the photoconductors coincide. In the image forming apparatus equipped with this multi-beam scanning optical system, a multi-beam scanning optical system of three or more beams has not yet been realized, and a lens that stably scans a photoconductor with three or more laser beams in parallel. Optical systems need to be developed.

On the other hand, a digital copying machine is required to have a copying speed equivalent to that of a conventional high-speed analog copying machine. To increase the copying speed and printing speed of digital copiers and laser printers, two beams,
It is sufficient to simply increase the number of scanning lines for simultaneously scanning the three beams and the photosensitive member. However, as described above, a multi-beam scanning optical system having three or more beams has not been put to practical use yet.

[0005]

When two or more beams are scanned in parallel on the photoconductor at the same time, the scanning interval (scanning pitch) of each beam on the photoconductor in the sub-scanning direction (rotation direction of the photoconductor). Must be sufficiently close using an optical stop. At present, the development of a method of manufacturing a plurality of semiconductor lasers in close proximity is progressing. However, at present, few LD arrays of 3 LD or more have been put to practical use, and the production method is very difficult, and the cost is low. Will be higher. By using a plurality of two-beam scanning optical systems that have already been put into practical use, it becomes possible to increase the copying speed and printing speed of digital copiers, laser printers, and the like as compared with the current products. Further, if a multi-beam scanning optical system with three or more beams is put to practical use in the future, a higher copying speed and printing speed can be realized by using a plurality of such multi-beam scanning optical systems.

Accordingly, a first object of the present invention is to shift the time for optically scanning the synchronous detection means shared by the laser beams of the respective multi-beam scanning optical systems by sharing the synchronous detection means. The multi-beam laser scanning of each multi-beam is time-shifted by a synchronizing detection signal generated by one synchronizing detection means to generate a synchronizing detection pulse, so that the scanning position of each multi-beam can be detected temporally. A beam image forming apparatus is provided.

A second object of the present invention is to divide a synchronization detection signal generated by the synchronization detection means into laser beams, and to divide the synchronization detection signal into DETP1, DETP2, DETP3, and DETP.
The means for generating... Can generate respective synchronization detection signals synchronized with the scanning of each laser beam, and can accurately determine the writing start position of the main scanning of each laser beam. It is an object of the present invention to provide a multi-beam image forming apparatus capable of performing the above.

[0008]

According to the first aspect of the present invention, there are provided a plurality of multi-beam scanning optical systems for simultaneously scanning laser beams from a plurality of laser light-emitting elements on a photosensitive member in parallel. In a multi-beam image forming apparatus for forming an image by using image information, image information input means for inputting image information, image information processing means for performing predetermined processing on image information input from the image information input means, Independently drives multiple laser light emitting elements,
With a plurality of laser modulation means to modulate, the plurality of multi-beam scanning optical system, the scanning speed in the main scanning direction,
To control the scanning speed of the main scanning, which is calculated backward from the rotation speed of the photoconductor, which is the scanning speed in the sub-scanning direction, by the value obtained by dividing the scanning speed by the number of laser light emitting elements held in the device, in order to keep the writing start position of the main scanning constant. Synchronization detecting means for detecting the scanning position,
The first object is achieved by arranging the light-emitting elements of each multi-beam at positions where the times at which each multi-beam arrives at the synchronous detection means are shared by a plurality of multi-beam scanning optical systems. .

According to a second aspect of the present invention, in the first aspect of the present invention, a synchronization detection signal for each beam is divided from the synchronization detection signal generated by the synchronization detection means, and scanning is performed by a plurality of laser beams. A synchronous detection signal dividing unit that generates a plurality of synchronous detection signals; and determines a write start position of main scanning of each laser beam in synchronization with each of the divided synchronization detection signals. Achieve the objectives.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to FIGS. FIG.
FIG. 2 is a diagram illustrating a configuration of a multi-beam image forming apparatus according to the embodiment. As shown in this figure, the photosensitive drum 101, the first two-beam writing unit 110, and the second
Two-beam writing unit 120 and photosensitive drum 110
, The exposure unit 102 and the developing unit 10
3, transfer unit 104, transfer and separation unit 105,
It is composed of a cleaning unit 106 and the like. It is assumed that the distance between the position a where the first two-beam writing unit 110 scans the photoconductor and the position b where the second two-beam writing unit 120 scans the photoconductor is Dmm.

FIG. 2 shows the configuration of a multi-beam scanning optical system. As shown in this figure, the multi-beam scanning optical system includes LD arrays 223 and 233 as laser light sources.
Polygon mirror 123 (hereinafter, polygon mirror motor) that reflects laser light and scans the photosensitive member via an optical element such as a lens.
And f for making the scanning of the laser on the photoconductor uniform.
θ lenses 124 and 134 and reflection mirrors 126 and 136
And Further, a photodetector 125 for detecting the rotational position of the polygon mirror motor 123 and generating an electrical timing signal is provided.
The laser light of each multi-beam scanning optical system rotated and scanned by 3 is arranged to scan the photodetector 125 before reaching the photoconductor 101 by the reflection mirrors 127 and 137.

In the prior art, a scanning optical system having a plurality of single-beam scanning optical systems has been put to practical use. However, a plurality of synchronization detecting means are provided, one for each scanning optical system. In the embodiment, the synchronization detecting means is arranged so as to be shared by each of the multi-beam scanning optical systems, and the scanning optical systems have the same optical path length so that the scanning can be performed by the respective scanning optical systems. The amount of laser light to be emitted is the same. In the present embodiment, the synchronization detecting means is disposed so as to be optically substantially the same as the photosensitive facing surface. As shown in FIG. 2, each of the reflecting mirrors such that angles α and β between the reflecting surface of the polygon mirror motor 123 and the optical paths reaching the reflecting mirrors 127 and 137 and the photodetector 125 satisfy α> β. Is configured. A system having a plurality of single-beam scanning optical systems may be configured to share the synchronization detecting means.

Since the angles of the multi-beams from each of the LD arrays 223 and 233 satisfy α> β, as shown in FIG. As a result, a time shift occurs, and the scanning position of each multi-beam can be determined. As shown in FIGS. 5 and 6, in the conventional multi-beam scanning optical system, each LD array is
Is usually mounted so that the light emitting points of the LDs are obliquely arranged on a straight line so that the scanning of the LDs is shifted in time, so that the photodetector 125 can detect the scanning position of each LD. I have.

The synchronization detection signal, which is the output of the photodetector 125 shown in FIG. 3, is supplied to the synchronization signal division unit 250 of the writing unit 200 as a detection signal of the scanning position of each laser as shown in FIG. , DETP3, DETP2,
It is separated into DETP4 and input to the image information separation unit 210. As shown in FIG. 2, the scanning directions of the main scanning on the photosensitive members of the respective scanning optical systems are reversed.

In this embodiment, a case will be described in which each of the multi-beam scanning optical systems is a two-beam scanning optical system and has two two-beam scanning optical systems. The description of the operation of the scanning optical system is omitted. The rotation speed (RPM) of the polygon motor is determined from the printing speed requirement of the device,
Photoconductor linear velocity v (mm / s), print pixel density (dpi: dot pe)
r inch) and the number n of mirror surfaces of the polygon mirror motor are determined by the following equation.

[0016]

## EQU00001 ## RPM = (v.times.dpi.times.60) / (25.4.times.n) (1)

The above equation (1) is the number of revolutions of the polygon mirror motor when a single laser is scanned on the photosensitive member, and when a plurality of LDs are scanned simultaneously, the number of revolutions of the polygon motor is given by the following equation. Can be

[0018]

## EQU2 ## RPM (m) = (v × dpi × 60) / (25.4 × n × m) (2)

In this example, since there are four LDs, m =
4 and the number of rotations of the polygon mirror motor can be suppressed to 1/4 as compared with the case of 1LD. As shown in FIG. 3, the image processing unit 16 is
The image information input to 0 is processed in the image processing unit 160, and then transmitted to the writing unit 200. A semiconductor laser diode (hereinafter, LD) is used as a light source for writing to the photoconductor. In this example, it is a 2LD array.

The writing section 200 includes an image information separating section 210,
It comprises a first LD array modulator 220, a second LD array modulator 230, and a synchronization signal divider 250.
Further, as shown in FIG. 4, the first LD array modulator 220
Are LD modulator A (221) and LD modulator B (22)
2), LD array 1 (223), LD1 (224), L
D3 (225), and the second LD array modulator 230 includes an LD modulator C (231) and an LD modulator D.
(232), LD array 2 (233), LD2 (23
4), an LD 4 (235), a line memory 237, and an image inverting unit 238.

In the configuration of each LD array, two LDs and one PD (photodiode) 226 are incorporated in one package, and are internally connected as shown in FIG. The image information transmitted to the writing unit 200 is usually
Since the information is sequentially transmitted as information for each scanning line in the main scanning direction, the image information of the odd lines is sequentially transmitted to the first LD array modulation unit 220 in the image information separation unit 210, and the image information of the even lines is sequentially transmitted to the first LD array modulation unit 220. The signal is transmitted to the second LD array modulator 230. DETP1 and DETP3 are connected to the first LD array modulating section 220 as synchronization signals. Similarly, DTP is supplied to the second LD array modulating section 230.
ETP2 and DETP4 are connected.

In each of the first LD array modulating sections 220, the image information of the 1, 5,..., 4m + 1,.
In synchronization with the falling edge of the synchronization pulse of the ETP1 signal, the signal is transmitted to the LD modulation unit A (221), and 3, 7,.
4m + 3, the image information of the 〜th line is transmitted to the LD modulation section B (222) in synchronization with the falling edge of the synchronization pulse of the DETP3 signal.

Similarly, the second LD array modulator 23
0, the image information of the even line is temporarily stored in the line memory 237 for a time given by the following equation (3).
The image information of the second, sixth, ..., 4m + 2, ... line is DET
In synchronization with the falling edge of the synchronization pulse of the P2 signal, the signal is transmitted to the LD modulation section C (231),
The image information of the m-th to th lines is synchronized with the falling edge of the synchronization pulse of the DETP4 signal, and the LD modulation unit D (2
32). (M = 1, 2, 3, ...)

Here, the line image information temporarily stored in the line memory 237 is inverted by the image inverting section 238, and is sent to the second LD array modulating section 230 from the rear end of the main scanning.

[0025]

[Equation 3] Temporary storage time T (s) = D (mm) / V (mm / s) Equation (3)

The first LD array modulation section 220 has a first 2
The second LD included in the beam writing unit 110
The array modulating unit 230 includes the second two-beam writing unit 12
0 is included. In this example, the second LD array modulator 2
A line memory 237 and an image reversing unit 238
However, between the image information separating unit 210 and the second LD array modulating unit 230 and the image information separating unit 2
10 may be provided. LD modulator A, B
Respectively correspond to LD1 (224) and LD3 (22) according to the line image information transmitted in synchronization with the signals (DETP1, DETP3) synchronized with the rotation of the polygon mirror motor.
5) Modulation control is performed to cause the LD to emit light, and an odd-numbered line is simultaneously scanned in parallel on the photoreceptor by a multi-beam scanning optical system to form an electrostatic latent image.

Similarly, the LD modulators C and D respectively output signals (DETP2, DETP2) synchronized with the rotation of the polygon mirror motor.
According to the line information transmitted in synchronization with TP4), L
D2 (234) and LD4 (235) are modulated and LD
And an even number line is simultaneously scanned in parallel on the photosensitive member by a multi-beam scanning optical system to form an electrostatic latent image. As shown in FIG. 5, the electrostatic latent image on the photoreceptor is scanned by the first two-beam writing unit 110 every two odd-numbered lines.
The photoconductor rotates and moves by D (mm) from the position where the two-beam writing unit has written, and the second two-beam writing unit 120 is located at the center of the scanning interval of the odd-numbered line formed on the photoconductor. The even lines are scanned every two lines. As shown in FIG. 5, the scanning direction of the even lines is opposite to the scanning direction of the odd lines.

In order to be able to absorb variations in the mounting position of the writing unit and the writing position on the photoreceptor for each device, the time T until scanning of the even-numbered line is performed.
(S) can be adjusted for each device. By the above operation, an electrostatic latent image is formed on the photoconductor based on the image information input by the image input unit 150. Hereinafter, a final image is formed on a recording medium such as paper by an electrophotographic process. The method of transporting the recording medium, the operation of the electrophotographic process, and the like are the same as in the related art. In the above example, an LD array is used, but a plurality of single LDs may be installed in parallel and condensed at a desired beam pitch on the photoconductor using optical elements such as prisms and lenses.

A plurality of multi-beam scanning optical systems of three or more beams may be provided, and if a scanning optical system of three or more beams is put into practical use, the printing speed can be easily reduced by the configuration of this embodiment. Be able to speed up. As the image input means, a personal computer, transmission image data of a facsimile, data read by an image reading scanner of a copying machine, and, via a personal computer,
Although image data and the like transmitted from a scanner connected to the device are conceivable, in the present invention, all image information can be realized.

[0030]

According to the first aspect of the present invention, the scanning of the laser beam of each multi-beam is performed by shifting the time for optically scanning the synchronous detection means shared by the laser beams of the respective multi-beam scanning optical systems. Synchronous detection pulses are generated at a time lag with a synchronous detection signal generated by one synchronous detection means, and it becomes possible to temporally detect the scanning position of each multi-beam.

According to the second aspect of the present invention, the synchronization detection signal generated by the synchronization detection means is divided for each laser beam, and is divided into DETP1, DETP2, DETP3, and DETP.
.. Having the means for generating TP4,... Enables the generation of each synchronization detection signal synchronized with the scanning of each laser beam, thereby accurately determining the writing start position of the main scanning of each laser beam. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a multi-beam image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a multi-beam scanning optical system.

FIG. 3 is a block diagram illustrating a configuration of an image signal processing system.

FIG. 4 is a block diagram showing a configuration of a first LD array modulator and a second LD array modulator.

FIG. 5 is a diagram illustrating an electrostatic latent image forming operation in the present embodiment.

FIG. 6 is a diagram for explaining that the synchronization detection signal of the detector has a time lag due to each multi-beam scanning.

[Explanation of symbols]

 Reference Signs List 101 photoconductor drum 110 first two-beam writing unit 102 exposure unit 103 developing unit 104 transfer unit 105 transfer / separation unit 106 cleaning unit 120 second two-beam writing unit 122, 132 collimating lens 123 rotating polygon mirror (polygon) (Mirror motor) 125 Photodetector 200 Writing unit 210 Image information separation unit 223, 233 LD array 250 Synchronization signal division unit

Claims (2)

[Claims] 1. A multi-beam image forming apparatus having a plurality of multi-beam scanning optical systems for simultaneously scanning laser beams from a plurality of laser light-emitting elements on a photosensitive member in parallel, and forming an image using electrophotography. , Image information input means for inputting image information, image information processing means for performing predetermined processing on the image information input from the image information input means, independently driving a plurality of laser light emitting elements according to the image information, A plurality of laser modulation means for modulating, the plurality of multi-beam scanning optical system, the scanning speed in the main scanning direction, the scanning speed of the main scanning back calculated from the photoconductor rotation speed is a scanning speed in the sub-scanning direction. In order to keep the writing start position of the main scanning constant by controlling the value divided by the number of laser light emitting elements held in the device, there are multiple synchronous detection means for detecting the scanning position. Multi-beam scanning is shared by the optical system, the multi-beam image forming apparatus, each of the multi-beam is characterized in that a light-emitting element of each of the multi-beam in this position the time to reach are shifted to the synchronous detection means. 2. A synchronization detection signal for dividing a synchronization detection signal for each beam from a synchronization detection signal generated by the synchronization detection means and generating a plurality of synchronization detection signals synchronized with scanning of a plurality of laser beams. 2. The multi-beam image forming apparatus according to claim 1, further comprising a dividing unit, wherein a writing start position of the main scanning of each laser beam is determined in synchronization with each of the divided synchronization detection signals.