JP2000199868A - Multibeam image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make scanning magnification on a photoreceptor in terms of each beam constant, to realize scanning in an unmagnified state and to form a high- quality image by providing plural write CLK generation means for adjusting the write modulation speed of a multibeam scanning optical system and constituting the write CLK generation means so that CLK frequency can be set independently of every scanning beam. SOLUTION: A 1st LD array modulation part 220 is constituted of an LD modulation part A221, an LD modulation part B222, and write CLK generation parts A227 and B228. A 2nd LD array modulation part 230 is constituted of an LD modulation part C231, an LD modulation part D232, write CLK generation parts C239 and D240, a line memory 237 and an image inverting means 238. The plural write CLK generation parts A to D (227, 228, 239 and 240) for adjusting the write modulation speed of the multibeam scanning optical system are constituted so that the CLK frequency can be set independently of every scanning beam.

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 which forms an image by forming an electrostatic latent image by scanning a laser beam on a photoreceptor by electrophotography using a laser light source. More specifically, the present invention relates to a multi-beam image forming apparatus having functions of a digital copying machine, a facsimile, a laser printer, and the like that form an image using electrophotography.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. Hei 5-29711 discloses an invention of "multi-beam semiconductor laser ray and multi-beam laser printer". JP-A-5-530
No. 68 discloses an invention of “multi-beam scanning optical system”,
JP-A-5-66354 discloses an invention of an "information recording device", JP-A-5-294003 discloses an invention of an "image recording device", and JP-A-6-216559 discloses a disclosure of the invention.
Invention of "multi-beam laser light source", JP-A-8-292
No. 384 discloses an invention of an "image writing device",
In the specification of US Pat. No. 5,088,871, the invention of "multi-beam scanning optical system" is described. However,
Neither of these publications describes an invention having a plurality of multi-beam scanning optical systems.

Conventionally, a laser beam is scanned on a photoreceptor using a laser scanning optical system to form an electrostatic image (electrostatic latent image), and an image is formed on a recording medium using electrophotography. In the forming apparatus, the rotation speed of the polygon mirror motor is used as a parameter for the scanning speed of the photosensitive member in the main scanning direction, and the limit of the scanning speed is limited by the rotation speed of the polygon motor.

In recent years, due to the 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 photosensitive member, and the laser scanning speed is reduced by 1 / (number of laser elements). A multi-beam scanning optical system to be controlled has been proposed, and a two-beam scanning optical system using two lasers as a multi-beam has been realized.

[0005] However, a multi-beam scanning optical system exceeding two beams has not been realized, and development of a lens optical system that stably scans a photoconductor with three or more laser beams in parallel has been desired.

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. In order to increase the copying speed and printing speed of a digital copying machine and a laser printer, two or more beams, for example, three beams may be simultaneously scanned on the photoconductor to increase the number of scanning lines. As described above, a multi-beam scanning optical system having three or more beams has not yet been put to practical use.

When two or more beams are scanned in parallel on the photoconductor at the same time, the scanning interval (scanning pitch) of each beam in the sub-scanning direction (rotation direction of the photoconductor) on the photoconductor.
It is necessary to bring the beams sufficiently close using an optical stop.

At present, a method of manufacturing a plurality of semiconductor lasers in close proximity to each other is being developed. However, an LD array of 3 LDs (semiconductor laser diodes, hereinafter referred to as LD) or more has at present been put to practical use. There are few things, and it is very difficult in terms of the manufacturing method, and the cost is high.

By using a plurality of two-beam scanning optical systems that have already been put to practical use, it is possible to increase the copying speed and printing speed of digital copiers, laser printers, and the like as compared with the current ones.

[0010] Further, with the practical use of a multi-beam scanning optical system having three or more beams in the future, the use of a plurality of such multi-beam scanning optical systems will make it possible to realize a higher copying speed and printing speed.

[0011]

According to the present invention, when each multi-beam optical system scans a photosensitive member with a laser beam, each multi-beam passes through a scanning optical system (each optical element). L for determining the main scanning magnification by correcting the mismatch of the main scanning equal magnification caused by the variation in the element manufacturing method.
The purpose is to be able to form a higher quality image by enabling the D modulation speed to be adjusted independently by each LD and allowing the scanning magnification on the photoreceptor for each beam to be constant and equal. And

Further, according to the present invention, the time at which each multi-beam arrives at the synchronization detecting means is shifted to the main scanning so that the writing position of each beam in the main scanning can be detected with high accuracy. It is an object of the present invention to be able to form a high quality image.

According to the present invention, the write CLK generating means for determining the write modulation speed of the laser beam scanned by each multi-beam has a plurality of means independent for each scanning beam, and the CLK frequency can be set independently. It is intended to be.

The present invention also has a sufficient setting resolution so that each writing CLK generating means can correct a magnification error in the main scanning scanning direction, and on the photosensitive member for main scanning in each multi-beam. The setting value of each write CLK generating means for determining the scanning speed of the modulating means for each beam can be independently adjusted so that the scanning magnification of each beam becomes equal in accordance with the scanning magnification of Is controlled to be constant and equal.

According to the present invention, the scanning of the laser beam of each multi-beam can be performed by one synchronous detection unit by shifting the time for optically scanning the synchronous detection unit shared by the laser beams of each multi-beam scanning optical system. A synchronization detection pulse is generated with a time lag with the synchronization detection signal generated by the above-described method, and the scanning position of each multi-beam can be detected temporally. Divided into, for example, DETP1, DETP2,
By providing means for generating DETP3, DETP4,..., Etc., it is possible to generate each synchronization detection signal synchronized with the scanning of each laser beam, and accurately determine the writing start position of the main scanning of each laser beam. The purpose is to do.

[0016]

According to the present invention, there is provided an image forming apparatus by electrophotography in which an image is formed on a photosensitive member by scanning a laser beam with a scanning optical system. A plurality of multi-beam scanning optical systems capable of simultaneously scanning on, an image information input means, an image information processing means, and a plurality of laser modulation means for independently driving and modulating a plurality of laser light emitting elements according to the image information; A synchronization detecting unit for detecting a scanning position of the scanning optical system, and a plurality of write CLK generating units for adjusting each write modulation speed of the multi-beam scanning optical system, wherein the write CLK generating unit includes:
A multi-beam image forming apparatus characterized in that the CLK frequency can be set independently for each scanning beam.

The write CLK generating means has a setting resolution capable of correcting a magnification error in the main scanning direction, independently adjusts the set value of the write CLK generating means, and scans the photosensitive member. Control means for making the magnification constant and substantially equal may be further provided.

Further, the multi-beam scanning optical system adjusts an optical path of the multi-beams to the synchronous detection main scanning direction to change the time of arrival of the multi-beams at the synchronous detection means. A synchronization detection signal dividing unit that divides a synchronization detection signal for each beam from the detection signal and generates a plurality of synchronization detection signals synchronized with a plurality of laser beam scannings; May be adjusted in synchronization with the synchronization detection signal for each beam.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the configuration of the present invention will be described below with reference to the embodiments of the present invention. In the present embodiment, the case where the multi-beam scanning optical system is a two-beam scanning optical system and has two two-beam scanning optical systems will be described. (Description of the operation of the scanning optical system is omitted)

As shown in FIG. 1, a multi-beam image forming apparatus according to the present invention comprises a photosensitive drum 101 and a first
A beam writing unit 110, a second two-beam writing unit 120, and an exposure unit 102, a developing unit 103, a transfer unit 104,
Transfer / separation unit 105, cleaning unit 10
6 and the like.

The distance between the position a where the first two-beam writing unit 110 scans on the photoreceptor and the position b where the second two-beam writing unit 120 scans on the photoreceptor is, for example, Dmm. .

FIG. 2 shows the configuration of the multi-beam scanning optical system. As shown in FIG. 2, LD arrays 223 and 233 as laser light sources and collimating lenses 122 and 132
And a rotating polygon mirror 123 (hereinafter, referred to as a polygon mirror motor) that reflects a laser beam and scans the photosensitive member via an optical element such as a lens, and makes the laser scanning on the photosensitive member uniform. Lenses 124 and 134 and reflection mirrors 126 and 136. In addition, a photodetector 125 that detects the rotational position of the polygon mirror motor and generates an electrical timing signal is arranged as shown in FIG. 2, and each of the multi-beam scanning optical systems rotated and scanned by the polygon mirror motor 123. The laser light is reflected by the reflection mirror 127,
137, before reaching the photoconductor 101,
25 to be scanned.

Although a plurality of single beam scanning optical systems have been put to practical use, a plurality of synchronization detecting means are provided separately for each scanning optical system. In the present embodiment, the synchronization detecting means is arranged so as to be shared by the respective multi-beam scanning optical systems, and the optical path lengths of the respective scanning optical systems are made equal. Thereby, the light amounts of the laser beams scanned by the respective scanning optical systems are made substantially the same. In the present embodiment, the synchronization detecting means is disposed so as to be optically substantially flush with the photoconductor surface.

As shown in FIG. 2, the 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 are α> β.
Each reflection mirror is configured so that 2
Alternatively, a system having three or more single beam scanning optical systems may be configured to share the synchronization detecting means.

As shown in FIG. 6, each LD array 223,
In the multi-beam 233, the angles α and β have a relationship of α> β, so that the synchronization detection signal of the photodetector 125 is temporally shifted by the scanning of each multi-beam, The scanning position can be determined.

As shown in FIGS. 5 and 6, in the conventional multi-beam scanning optical system, each LD array usually has a light emitting point of each LD so that the scanning time is shifted. They are mounted so that they line up diagonally straight. Thus, the scanning position of each LD can be detected by the photodetector.

As shown in FIG. 3 and FIG.
0, the synchronization detection signal of the photodetector is used as a detection signal of the scanning position of each laser,
These are separated into TP1, DETP3, DETP2, and DETP4, and input to the image information separation unit. As shown in FIG.
The main scanning direction on the photoconductor of each scanning optical system is reversed.

The rotation speed (RPM) of the polygon motor is determined from the printing speed requirement of the device. For the case of a single beam (s), the linear velocity of the photoconductor v (mm / s),
The printing pixel density (dpi: dot per inch) and the number n of mirror surfaces of the polygon mirror motor are determined by the following equation (1).

Rotational speed (s) = (v × dpi × 60) / (25.4 × n) (1) When a plurality of LDs are simultaneously scanned (m),
The rotation speed of the polygon motor is given by the following equation. Number of rotations (m) = (v × dpi × 60) / (25.4 × n × m) (2) (m: simultaneous scanning number of LD)

In this embodiment, since there are four LDs, m = 4, and the number of rotations of the polygon mirror motor is 1
This makes it possible to reduce the number of LDs to 1/4 as compared with the case of individual LDs.

Normally, it is difficult for the multi-beam scanning optical systems of the writing units 110 and 120 to completely match the optical characteristics due to variations in the manufacturing method of the optical elements and variations in the mounting positions of the optical elements. It is.

Among the optical characteristics, the scanning magnification, which is determined from the speed at which the laser beam scans the photosensitive member, varies depending on each multi-beam.

Conventionally, since the modulation speed of each LD is the same, the electrostatic latent image formed by each of the multi-beam scanning optical systems varies depending on the scanning magnification, causing a dot shift on the image. Was.

Conventionally, in order to maintain the same magnification of the scanning magnification of the single beam scanning optical system, the precision at the time of manufacturing each optical component, the precision of the mounting position, and the fine adjustment of the LD modulation speed have been improved. Was done by doing.

In the present invention, a write CLK generator is provided so that the fine adjustment of the LD modulation speed performed by the conventional single beam scanning optical system can be finely adjusted independently for each laser beam. ing.

The write CLK generating unit performs fine adjustment,
It is composed of a PLL (Phase Locked Loop) synthesizer circuit as shown in FIG. The output frequency of the write CLK is such that the reference CLK frequency is Fref and the write CLK is
If the frequency is Fwout, it is given by the following equation (3).

Fwout = Fref × Divf / Divr / Divo (3) In the equation (3), Divf is a division ratio of the feedback divider (306), and Divr is a division ratio of the input divider (301). Yes, Div is the frequency division ratio of the output divider (307).

The magnification error of the main scanning of each multi-beam scanning optical system is finely adjusted by changing each of the above-mentioned dividers. The adjustment value may be obtained by calculating backward from the inspection result of the scanning magnification after manufacturing the writing unit, or may be obtained from an actual formed image after manufacturing the image forming apparatus.

The output frequency of each write CLK generator is set and fine-tuned according to the adjustment value obtained by the above method for the magnification error of the main scanning of each beam. In the magnification error of each multi-beam, the adjustment value is set in advance to the write CLK generation units A to D (227, 2
28, 239, 240).

As shown in FIG. 3, the image information input to the image processing unit 160 by the image input unit 150 is processed by the image processing unit and transmitted to the writing unit 200. As a light source for writing on the photoconductor, for example, a semiconductor laser diode (LD) is used. (2LD array in this embodiment)

The writing section 200 includes an image information separating section 210,
As shown in FIG. 4, the first LD array modulator 220 includes a first LD array modulator 220, a second LD array modulator 230, and a synchronization signal separator 250.
Are the LD modulator A (221) and the LD modulator B (22)
2), LD array 1 (223), LD1 (224), L
D3 (225), a write CLK generator A (227) and a write CLK generator B (228), and the second LD array modulating section 230 includes an LD modulating section C (2).
31), LD modulator D (232), LD array 2 (23
3), LD2 (234), LD4 (235), write CL
K generator C (239), write CLK generator D (24
0), a line memory 237 and an image reversing means 238.

In the configuration of each LD array, two LDs and one PD (photodiode) 226 are incorporated in one package, and these are connected as shown in FIG. Normally, the image information transmitted to the writing unit 200 is sequentially transmitted for each scanning line in the main scanning direction. The image information of the even lines is sequentially transmitted to the unit 220, and is transmitted to the second LD array modulation unit 230.

The first LD array modulating section 220 is connected with DETP1 and DETP3 as synchronization signals.
Similarly, the second LD array modulating section 230 receives DETP
2. DETP4 is connected.

Each first LD array modulator (220)
For example, the image information of the first, fifth,..., 4m + 1, and the 〜 lines is converted to the falling edge of the synchronization pulse of the DETP1 signal and the write CLK frequency A ｛MHz generated by the write CLK generation unit A (227). Synchronize with｝, LD
The signal is transmitted to the modulation unit A (221) and 3, 7, to 4m + 3,
The image information of the first to third lines is written to the falling edge of the synchronization pulse of the DETP3 signal and the write CLK generator B (22).
The data is transmitted to the LD modulator B (222) in synchronization with the write CLK frequency B {MHz} generated in 8).

Similarly, the second LD array modulator (2
In 30), the image information of the even lines is stored in the line memory 237 for a time given by the following equation (4).
The image information of the second, sixth, ..., 4m + 2, ... lines is
The LD modulator C (231) is synchronized with the falling edge of the synchronization pulse of the TP2 signal and the write CLK frequency C {MHz} generated by the write CLK generator C (239).
And the image information of the fourth, eighth, fourth, fourth, and fourth lines is written to the falling edge of the synchronization pulse of the DETP4 signal and the write C generated by the write CLK generator D (240).
Synchronizing with the LK frequency D {MHz}, the LD modulator D
(232). (M = 1, 2, 3, ...)

Here, the line image information temporarily stored in the line memory 237 is inverted by the image inverting means 238, and the second LD array modulator (23)
0). Here, the temporary storage time T is given by the following equation (4). Temporary storage time T (s) = D (mm) / v (mm / s) (4) In the above equation (4), D and v are the same as described above.

The first LD array modulating section 220 is included in the first two-beam writing unit 110 and has the second L
D array modulation section 230 is included in the second two-beam writing unit.

In this embodiment, the control unit of the second LD array modulation unit 230 has the line memory 237 and the image inversion means 238.
The line memory and the like may be provided between the 0 and the second LD array modulation section 230 or in the image information separation section 210.

The LD modulators A and B respectively output signals (DETP1, DET) synchronized with the rotation of the polygon mirror motor.
According to the line image information transmitted in synchronization with P3),
LD1 (224) and LD3 (225) are modulated and controlled.
The LD emits light, and an odd-numbered line is scanned in parallel on the photoconductor at the same time by a multi-beam scanning optical system to form an electrostatic latent image.

Similarly, the LD modulating sections C and D respectively output signals (DETP2, DETP2,
In response to the line information transmitted in synchronization with the DETP 4), the LD 2 (234) and the LD 4 (235) are modulated and the LDs are made to emit light by the multi-beam scanning optical system. Are scanned in parallel to form an electrostatic latent image.

As shown in FIG. 5, the electrostatic latent image on the photosensitive member is converted by the first two-beam writing unit 110
The odd-numbered lines are scanned every two lines, and after the temporary storage time T (s), the photosensitive member is rotated and moved by D (mm) from the position where it was written to the first two-beam writing unit. The second two-beam writing unit 120 is located at the center of the scanning interval of the odd-numbered line formed on the photosensitive member.
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 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, the main scanning synchronization and the main scanning are performed based on the image information input by the image input unit 150.
In addition, a high-quality electrostatic latent image corrected for the magnification error is formed on the photoconductor.

Hereinafter, a final image is formed on a recording medium such as paper by a known 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 embodiment, an LD array is used. However, a plurality of single LDs are installed in parallel, and light is condensed on the photosensitive member at a desired beam pitch using optical elements such as prisms and lenses. May be.

Further, a plurality of multi-beam scanning optical systems each having three or more beams may be provided. By realizing a scanning optical system having three or more beams, the printing speed can be easily increased by the configuration disclosed in the present invention. become able to do.

The image input means includes a personal computer, facsimile transmission image data, data read by an image reading scanner of a copying machine, and image data transmitted from a scanner connected to a device via a personal computer. Although it can be used, in the present invention, any image information can be realized.

[0058]

The write CLK generating means for determining the write modulation speed of the laser beam scanned by each multi-beam has a plurality of means independent for each scanning beam, and the CLK frequency can be set independently. I do.

Each writing CLK generating means has a sufficient setting resolution so as to be able to correct a magnification error in the scanning direction of the main scanning, and according to the scanning magnification of the main beam of each multi-beam on the photosensitive member. Thus, the setting value of each write CLK generating means for determining the scanning speed of the modulating means of each beam so as to be the same magnification can be adjusted independently, the scanning magnification of each beam on the photoconductor is constant, and Control can be performed so as to be the same magnification.

By shifting the time for optically scanning the synchronous detection means shared by the laser beams of each multi-beam scanning optical system, the scanning of each multi-beam laser can be performed by one.
A synchronization detection pulse is generated at a time lag with the synchronization detection signal generated by the two synchronization detection means, and the scanning position of each multi-beam can be detected in time, and the synchronization detection signal generated by the synchronization detection means is Each of the laser beams is divided into DETP1, DETP2, DETP3, DETP
The means for generating .4,... 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 becomes possible.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing a configuration of a unit of the multi-beam image forming apparatus according to the present invention.

FIG. 4 is a diagram showing a configuration of a multi-beam scanning optical system.

FIG. 5 is a diagram showing a conventional multi-beam scanning.

FIG. 6 is a diagram showing a synchronization signal in the multi-beam image forming apparatus of the present invention.

FIG. 7 is a diagram showing a configuration of a write CLK generation unit (PLL synthesizer).

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 electrophotographic image forming system 101 photoreceptor drum 110 first two-beam writing unit 120 second writing unit 223 LD array 233 LD array 123 polygon mirror motor 122 collimating lens 132 collimating lens 124 fθ lens 125 photodetector 134 fθ lens 127 reflection mirror 137 reflection mirror 200 writing unit 210 image information separation unit 220 first LD array modulation unit 221 LD modulation unit A 222 LD modulation unit B 223 LD array 224 LD 225 LD 227 write CLK generation unit A 228 Write CLK generator B 230 Second LD array modulator 231 LD modulator C 232 LD modulator D 233 LD array 234 LD 235 LD 239 Write CLK generator C 240 Write CLK generator D 250 Synchronous signal Separation unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/113 F term (Reference) 2C362 AA16 BA48 BA53 BA69 BA70 BB32 BB34 BB37 2H045 AA01 BA23 CA82 CA92 CA98 2H076 AB06 AB33 AB67 CA17 DA42 5C051 AA02 CA07 DA02 DB02 DB08 DB22 DB24 DB30 DC07 DE02 DE29 FA01 5C072 AA03 BA03 CA06 CA11 DA02 DA04 HA02 HA06 HA13 HB13 XA01 XA05

Claims (3)

[Claims] 1. An image forming apparatus according to an electrophotographic technique for forming an image on a photosensitive member by scanning a laser beam with a scanning optical system, wherein a plurality of laser beams can be simultaneously scanned on the photosensitive member. Scanning optical system, image information input means, image information processing means, and independently driving a plurality of laser light emitting elements according to the image information.
A plurality of laser modulation means for modulating; a synchronization detection means for detecting a scanning position of the scanning optical system; and a plurality of write CLK generating means for adjusting each write modulation speed of the multi-beam scanning optical system. The multi-beam image forming apparatus according to claim 1, wherein said write CLK generating means can set a CLK frequency independently for each scanning beam. 2. The writing CLK generating means has a setting resolution capable of correcting a magnification error in the main scanning direction, independently adjusts a setting value of the writing CLK generating means, and 2. The multi-beam image forming apparatus according to claim 1, further comprising control means for making the scanning magnification constant and substantially equal. 3. The multi-beam scanning optical system adjusts the optical path of the multi-beam to the synchronous detection main scanning direction to change the time of arrival of the multi-beam at the synchronous detection means. A synchronization detection signal dividing unit that divides a synchronization detection signal for each beam from the detection signal and generates a plurality of synchronization detection signals synchronized with a plurality of laser beam scannings; 3. The multi-beam image forming apparatus according to claim 1, wherein the multi-beam image forming apparatus is capable of adjusting the distance in synchronization with the synchronization detection signal for each beam.