JPH10197810A - Color image forming equipment - Google Patents

Abstract

[PROBLEMS] To be able to correct pitch fluctuations in the sub-scanning direction and suppress fluctuations in line length in the main scanning direction due to the fluctuations, so that a high-quality image can be obtained. I do. SOLUTION: A detection value of a dynamic pitch change in a sub-scanning direction is input to a deflection mirror control circuit 36, and the position of the deflection mirror 23 is adjusted according to the pitch change. The deflecting mirror control circuit 36 obtains an image frequency corresponding to the amount of movement of the deflecting mirror 23, and sends a setting signal SET to the image frequency control circuit 35. The image frequency control circuit 35 based on the setting signal SET
The output clock signal WCLK is input to an LD drive circuit 37, which outputs the clock signal WCLK.
Light modulation of the laser light 30 is performed using CLK as a reference clock. The modulation of the reference clock suppresses fluctuations in the line length in the main scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly, to a color image forming apparatus of a type in which toner images of a plurality of colors are superimposed.

[0002]

2. Description of the Related Art First, the overall structure of a color image forming apparatus of this type will be described based on two types. FIG.
1 shows an overall configuration of a color image forming apparatus of a type in which colors are superimposed on a photosensitive drum. As shown in FIG. 1, a charger 2, exposure units 9, 4 are provided around a rotating photosensitive drum 1.
A developing unit 3, a transfer unit 4, and a photoreceptor cleaner 5 holding two different color toners (black Bk, yellow Y, magenta M, and cyan C) are arranged. The photosensitive drum 1 rotates clockwise, and is uniformly charged by the charger 2. The exposure device 9 outputs the laser modulated light 10 according to the image writing signal, and causes the photosensitive drum 1 to scan. An electrostatic latent image is formed on the photosensitive drum 1 exposed by the laser light. Here, the image pattern to be exposed is a single-color image pattern obtained by color-separating a color image into yellow, magenta, cyan, and black.

The formed first-color electrostatic latent image is developed by a first-color developing unit, whereby a first-color toner image is obtained. Next, the photosensitive drum 1 charged by the charger 2 is irradiated with a laser beam to perform exposure of the second color. The formed second-color electrostatic latent image is developed by the second-color developing device, and the second-color electrostatic latent image is formed on the photosensitive drum 1.
A color toner image is obtained. Hereinafter, the same processing is performed for the third color and the fourth color, and a toner image of four colors superimposed on the photosensitive drum 1 is obtained. Thereafter, the toner image is transferred onto the transfer paper 8 by the transfer device 4, and a full-color image of four colors is obtained via the fixing device 7.

FIG. 4 shows the overall configuration of a so-called tandem type color image forming apparatus in which image forming units are arranged side by side along a conveyor belt. The image forming units 50Y, 50M, 50C, and 50K that form images of different colors (yellow, magenta, cyan, and black) respectively include transfer paper 5
8 are arranged in a line along a conveyor belt 61 that conveys the sheet 8. The transport belt 61 is bridged by transport rollers 62 and 63, one of which is a driving roller that rotates and the other is a driven roller that is driven and rotated.
Due to the rotation of 2, 63, it is driven to rotate in the direction of the arrow. A paper feed tray 64 in which the transfer paper 58 is stored is provided below the transport belt 61. The transfer paper at the uppermost position among the stored transfer papers 58 is fed during image formation,
It is attracted onto the conveyor belt 61 by electrostatic attraction. The attracted transfer paper 58 is conveyed to the first image forming unit 50Y (yellow), where a yellow image is formed. The first image forming unit 50Y includes a photosensitive drum 51Y.
And a charger 52 disposed around the photosensitive drum 51Y.
Y, exposure unit 59Y, developing unit 53Y, photoconductor cleaner 55
Y. The surface of the photosensitive drum 51Y is
After being uniformly charged by the charger 52Y, it is exposed to laser light 60Y corresponding to a yellow image by the exposure device 59Y, and an electrostatic latent image is formed. The formed electrostatic latent image is developed by the developing device 53Y, and a toner image is formed on the photosensitive drum 51Y. This toner image is transferred to the photosensitive drum 51Y.
Is transferred by the transfer unit 54Y at a position (transfer position) in contact with the transfer paper 58 on the transfer belt 61, and a monochromatic (yellow) image is formed on the transfer paper 58. The photoreceptor drum 51Y after the transfer is cleaned of the toner remaining on the drum surface by the photoreceptor cleaner 55Y, and is ready for the next image formation.

The transfer paper 58 on which the monochromatic (yellow) image has been transferred by the first image forming unit 50Y is conveyed to the second image forming unit 50M (magenta) by the conveying belt 61. Here, similarly, the photosensitive drum 5
The toner image (magenta) formed on the 1M
8 and transferred. The transfer paper 58 further includes a third image forming unit 50C (cyan) and a fourth image forming unit 50K.
(Black), and the similarly formed toner image is transferred. The transfer paper 58 on which the color image has been formed after passing through the fourth image forming unit 50K is peeled off from the transport belt 61, is fixed by the fixing device 57, and is discharged to the discharge tray 65.

In the above two types of color image forming apparatuses, laser light is emitted by the photosensitive drum due to a rotational speed variation of a drive motor (not shown) for driving the photosensitive drum, or a speed variation of the photosensitive drum due to an eccentricity of a rotating shaft. When scanning is performed, unevenness may occur in the interval in the sub-scanning direction. At this time, since the writing line interval in the sub-scanning direction is not constant due to the speed fluctuation of the scanning position (writing position), the density of the image density such as image pitch unevenness may occur, and the image quality may be remarkably deteriorated.

In a tandem-type color image forming apparatus, pitch fluctuations in the sub-scanning direction and positional deviations in the sub-scanning direction also occur due to fluctuations in the speed of the conveying belt in addition to the fluctuations in the speed of the photosensitive drum. Sometimes fell.

Therefore, in this type of color image forming apparatus, in order to further eliminate the dot position deviation and obtain a high quality color image, not only the stationary (static) registration position deviation is corrected but also A method of positively correcting the position of a dynamic position shift in the sub-scanning direction is being adopted. Specific correction methods include a method of controlling the rotation speed of the polygon motor and a method of controlling the position of a deflecting mirror in the exposure device.

Here, a countermeasure for obtaining an image having no pitch unevenness in the sub-scanning direction with respect to the speed fluctuation of the photosensitive drum or the conveyance belt, that is, a countermeasure against the problem in the tandem type will be described. FIG. 5, FIG.
A part of the color image forming apparatus described in FIG.
FIG. 2 is a diagram schematically illustrating a photosensitive drum, an exposure device, and a peripheral portion thereof. Although there are four photosensitive drums in FIG. 4, only one of the photosensitive drums is shown. In FIG. 5, laser light 30 is output from a laser diode (LD) 20 provided inside the exposure device 19, which is displayed as a region surrounded by a broken line. This laser light 30 is used to operate L based on an input image signal.
The latent image is modulated by the D drive circuit 32 and forms an electrostatic latent image on the photosensitive drum 31 by scanning and exposing the photosensitive drum 31. The laser light 30 is emitted from the polygon motor 2
Polygon mirror 22 as rotating polygon mirror supported by 1
Is reflected by the deflection mirror 23 via the fθ lens 25, and scans the periphery of the photosensitive drum 31 in the main scanning direction.

At one end of the deflecting mirror 23, a synchronization detection sensor 24 is placed. The synchronization detection sensor 24 receives a laser beam 30 for each surface of the polygon mirror 22, and writes the laser beam 30 in the main scanning direction. Generate signal DET.
The write reference signal DET is input to the LD drive circuit 32 and determines the write start timing of the laser beam 30 in the main scanning direction line in the LD drive circuit 32. The rotating shaft 31a of the photosensitive drum 31 has a rotation speed V1.
Is provided. The encoder 26 generates an encoder signal ENC as a pulse signal in accordance with the rotation of the photosensitive drum 31. The encoder 26 detects the frequency of the encoder signal ENC to obtain the rotation speed of the photosensitive drum 31. Can be. The encoder signal ENC is input to the frequency / speed converter 27, and the frequency / speed converter 27 outputs a speed signal V1.

The obtained speed signal V1 is input to the deflection mirror control circuit 33, and the deflection mirror control circuit 33 outputs pulse signals PLS-1 and PLS-2 according to the detected speed fluctuation. The pulse signals PLS-1 and PLS-2 are sent to the corresponding pulse motor drivers 34a and 34b, respectively, and the pulse motor drivers 34a and 34b drive the corresponding pulse motors 28a and 28b to rotate. Pulse motor 28
Corresponding eccentric cams 29a and 29b are attached to a and 28b, and deflecting mirror holders 38a and 38b are provided so as to press the eccentric cams 29a and 29b. The deflecting mirror holders 38a and 38b
Holding.

When the eccentric cams 29a and 29b rotate, the rotating shafts of the eccentric cams 29a and 29b and the deflecting mirror holder 3
Since the distance of the outer peripheral portion in contact with the deflection mirrors 8a and 38b changes, the deflection mirror 23 held by the deflection mirror holders 38a and 38b moves. These eccentric cams 29a, 29
By moving the deflecting mirror 23 by the same amount by the same amount at both ends of the deflecting mirror 23 at the same time, the deflecting mirror 23 moves in parallel in the direction shown by the arrow. The translation amount of the deflecting mirror 23 is determined by the frequency / speed converter 27.
Is determined in the deflection mirror control circuit 33 based on the speed fluctuation of the low-frequency component of the speed fluctuation V1 detected by the above.

As described above, conventionally, the deflection mirror inside the exposure device is moved in parallel with respect to the pitch fluctuation in the sub-scanning direction caused by the speed fluctuation of the photosensitive drum (or the conveyance belt). The position at which the photosensitive drum is exposed is changed to correct the pitch fluctuation.

[0014]

However, the above-mentioned method of correcting the pitch fluctuation in the sub-scanning direction by moving the deflection mirror inside the exposure unit in parallel as described above has the following problems. That is, when the position of the deflecting mirror is moved in parallel according to the speed fluctuation of the photosensitive drum or the like, the distance (optical path length) until the laser light reflected from the polygon mirror is irradiated on the photosensitive drum due to the movement. Changes. FIG. 6 shows this state. In FIG. 6, when the deflection mirror 23 is moved in parallel by ΔM, the irradiation position P of the laser beam 30 on the photosensitive drum 31 also moves by ΔL, and the optical path length of the laser beam 30 also changes by ΔM. . Such a change in the optical path length causes a problem that the line length in the main scanning direction changes. FIG. 7 is a diagram illustrating this problem.
Actually, the course of the laser light 30 is changed by the deflecting mirror 23, but is shown in a plan view for easy understanding. From FIG. 7, the optical path length becomes Δ by the parallel movement of the deflecting mirror 23.
It can be seen that when the length is changed by M, the length in the main scanning direction (main scanning line length) on the photosensitive drum 31 is changed by ΔL.

This will be described with a specific example. As shown in FIG. 7, the distance from the fθ lens 25 to the irradiation position P of the photosensitive drum 31 is 300 mm, and the spread width of the beam is 80 mm.
Think of it as mm. When the deflecting mirror 23 is translated by ΔM = 0.1 mm, the optical path length is 300.1 mm, and the main scanning line length is also 80/300 × 300.1 = 80.027 mm. That is, the length of the main scanning line is increased by about ΔL = 27 μm. As can be seen from FIG. 7, since this line length variation occurs at both ends of the main scanning line, 2 × Δ
A line length variation corresponding to L, that is, a line length equivalent to 54 μm occurs. For example, in the case of an image having a pixel density of 600 (dpi), one dot is about 42 μm, and the amount of the fluctuation is a displacement of one dot or more.

The deflection mirror control circuit 33 detects the detection speed V1
, A speed variation ΔV1 is obtained from the above, and a pitch variation of the sub-scanning line resulting from the speed variation is calculated. Further, a pulse signal is output to the pulse motor drivers 34a and 34b so that the position of the deflecting mirror 23 is translated in accordance with the pitch fluctuation. FIG. 8 shows the mirror translation amount ΔM with respect to the speed fluctuation V1 of the deflecting mirror 23.
Further, the variation (2 × ΔL) of the line length of the main scanning line when the parallel movement of the deflection mirror 23 is performed is also shown.

According to the present invention, when correcting the pitch fluctuation in the sub-scanning direction caused by the speed fluctuation of the photosensitive drum or the like by moving the deflection mirror in parallel, it is possible to suppress the fluctuation of the line length in the main scanning direction. Accordingly, it is an object of the present invention to provide a color image forming apparatus capable of obtaining a high-quality color image free from a pitch shift in the sub-scanning direction and a position shift in the main scanning direction.

[0018]

Means for correcting the position of the deflecting mirror with respect to the pitch fluctuation in the sub-scanning direction and, at the same time, controlling the modulation of the writing reference clock in accordance with the correction amount,
That is the gist of the present invention. Specifically, claim 1
In the described invention, the operation of deflecting the exposure beam reflected by the rotating polygon mirror and irradiating the exposure beam on the photosensitive drum with a deflecting mirror, forming an electrostatic latent image and developing the image is repeated a plurality of times, and a plurality of color toners are formed. In a color image forming apparatus that obtains a color image by superimposing an image on a photosensitive drum, a pitch fluctuation detecting unit that detects a dynamic pitch fluctuation in a sub-scanning direction that periodically fluctuates in an output image; Deflecting mirror correcting means for steadily correcting the position of the deflecting mirror that deflects the exposure beam in accordance with the amount of light, thereby correcting the pitch fluctuation in the sub-scanning direction of the output image, and according to the amount of correction of the deflecting mirror. And a reference clock correcting means for correcting the frequency of the reference clock that determines the writing timing of the exposure beam.

According to the second aspect of the present invention, the image forming means for deflecting the exposure beam reflected by the rotating polygon mirror, irradiating the exposure beam on the photosensitive drum, forming an electrostatic latent image on the photosensitive drum, and developing the image is provided by a conveyor belt. A plurality of toner images of a plurality of colors formed by the respective image forming means are respectively transferred to transfer paper on a conveyor belt to form a color image. Pitch fluctuation detecting means for detecting a dynamic pitch fluctuation in the sub-scanning direction that fluctuates periodically, and steadily correcting the position of a deflecting mirror that deflects the exposure beam according to the detected pitch fluctuation amount. Deflecting mirror correction means for correcting the pitch fluctuation of the output image in the sub-scanning direction, and a reference clock for determining the writing timing of the exposure beam according to the correction amount of the deflecting mirror. And a reference clock correction means for correcting the frequency of the click, and employs a configuration that.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. Since the present invention is applicable to the two types shown in FIG. 3 or FIG. 4 in the conventional example, the overall configuration is omitted. Further, the same parts as those of the conventional example are denoted by the same reference numerals, and the description of the operation and function is omitted unless it is necessary to perform the same operation. In FIG. 1, an encoder 26 and a frequency / speed converter 27 constitute a unit for detecting a dynamic pitch fluctuation in the sub-scanning direction. An image frequency control circuit 35 is provided between the deflecting mirror control circuit 36, which is a main part of the deflecting mirror correction means, and the LD driving circuit 37.
6 is input to the image frequency control circuit 35. The image frequency control circuit 35 is a circuit composed of a commercially available frequency synthesizer or the like, and has a function of changing the frequency (image frequency) of the output clock signal WCLK in accordance with the input setting signal SET. The deflecting mirror correction means includes, in addition to the deflecting mirror control circuit 36 described above,
Pulse motor drivers 34a and 34b, pulse motor 2
8a, 28b and eccentric cams 29a, 29b.

The clock signal WCLK output from the image frequency control circuit 35 is input to an LD driving circuit 37,
The drive circuit 37 performs optical modulation of the laser light 30 using the clock signal WCLK as a reference clock. In this way, by controlling the modulation of the writing reference clock, the pitch of the dots in the main scanning direction fluctuates by a small amount according to the set image frequency, and the main scanning line length also fluctuates. The deflection mirror control circuit 36 and the image frequency control circuit 35 constitute a reference clock correction unit. The deflecting mirror control circuit 36 translates the position of the deflecting mirror 23, modulates the image frequency of the reference clock that determines the writing timing, corrects the pitch fluctuation in the sub-scanning direction, and changes the line length in the main scanning direction. Also suppress. The fact that there is no variation in the line length in the main scanning direction is the same as the fact that there is no displacement of dots in the main scanning direction.

By such a modulation control of the reference clock, it is possible to correct the positional deviation in the sub-scanning direction and the positional deviation in the main scanning direction, so that a high quality image can be obtained.

Next, the operation performed by the deflection mirror control circuit 33 will be described. As shown in FIG. 2, the position of the deflecting mirror 23 is moved in parallel to the speed fluctuation ΔV1 of the photosensitive drum 31 as ΔM as in the prior art. At this time, the main scanning line length fluctuates by 2 × ΔL. To suppress the fluctuation of the line length, if the main scanning line length becomes longer than an ideal value, the image frequency is set higher. If the main scanning line length becomes shorter than the ideal value, the image frequency is set lower. This will be described with a specific example. In an ideal case, the number of dots in the main scanning direction is 7010 (
Dot), the speed at which the laser light 30 scans in the main scanning direction.
The image frequency is 1 × 10 ⁶ (mm / sec) and the image frequency is 23.60 (MHz). The main scanning line length L at this time is L = 7010 × (1 × 10 ⁶ ) / (23.60
× 10 ⁶ ) = 297.034 (mm). Set the deflection mirror 23 to 100 (μ
m) In the case of parallel movement, the main scanning line becomes longer by 54 (μm).
If the image frequency is set so as to be shorter (μm), the main scanning line length matches the ideal. At this time, the image frequency = 7010 × (1 × 10 ⁶ ) / (297.037-0.054) = 23.6040 (MHz).

The deflecting mirror control circuit 36 includes a deflecting mirror 2
Such an operation is performed together with the parallel movement of No. 3 to obtain an image frequency corresponding to the amount of movement of the deflection mirror 23, and a setting signal SET is sent to the image frequency control circuit 35. When a synthesizer is used as the image frequency control circuit 35, the setting resolution is 23.6040-23.6 = 0.004 (MHz) =
It is necessary to make it sufficiently smaller than 4 (kHz).

In the above embodiment, the speed fluctuation of the photosensitive drum is detected, the position of the deflecting mirror in the exposure device is corrected in accordance with the speed fluctuation, the line pitch fluctuation in the sub-scanning direction is corrected, and the main scanning is performed. Although the method of controlling the image frequency to suppress the line length fluctuation in the direction has been described, the same can be applied to the fluctuation of the speed of the conveyor belt, and the fluctuation of the speed of the photosensitive drum and the conveyor belt may occur in combination. It can also be implemented in the same case. According to such a method, a pitch variation in the sub-scanning direction and a dot position deviation in the main scanning direction are eliminated, and a high-quality color image can be obtained. In the above embodiment, the position of the deflecting mirror is corrected based on the speed fluctuation data of the photosensitive drum (or the conveyance belt). However, as a method of detecting the pitch fluctuation in the sub-scanning direction, an actual output image is used. May be directly detected, or data of pitch fluctuation may be obtained from an image formed on a photosensitive drum or a conveyance belt.

[0026]

According to the present invention, the pitch fluctuation in the sub-scanning direction is corrected by correcting the position of the deflecting mirror.
Since the configuration is such that the frequency of the reference clock that determines the write timing is corrected in accordance with this correction amount, fluctuations in the main scanning line length can be suppressed, positional deviation in the sub-scanning direction can be corrected, and The dot displacement can also be corrected, and a high quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an exposure device and a peripheral portion thereof according to an embodiment of the present invention.

FIG. 2 is a graph for explaining a function of a deflection mirror control circuit.

FIG. 3 is an overall configuration diagram of a conventional color image forming apparatus.

FIG. 4 is an overall configuration diagram of another conventional color image forming apparatus.

FIG. 5 is a schematic view of a conventional exposure device and its peripheral portion.

FIG. 6 is a schematic side view showing a shift of a photosensitive drum irradiation position due to parallel movement of a deflecting mirror in the related art.

FIG. 7 is a plan view showing a variation in a main scanning line length in the related art.

FIG. 8 is a graph for explaining the function of a conventional deflection mirror control circuit.

[Explanation of symbols]

Reference Signs List 22 polygon mirror as rotating polygon mirror 23 deflection mirror 30 laser beam as exposure beam 31 photosensitive drum 35 image frequency control circuit as part of reference clock correction means 36 as deflection mirror correction means or reference clock correction means Deflection mirror control circuit as part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Shinohara 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Tomonori Yabuta 10-3 Kitamura, Tottori City, Tottori Prefecture, Ricoh Microelectronics Co., Ltd.

Claims (2)

[Claims] An operation of deflecting an exposure beam reflected by a rotary polygon mirror, irradiating the exposure beam on a photosensitive drum with a deflecting mirror, forming an electrostatic latent image and developing the image is repeated a plurality of times, and a plurality of color toners are formed. In a color image forming apparatus for obtaining a color image by superimposing an image on a photosensitive drum, a pitch fluctuation detecting means for detecting a dynamic pitch fluctuation in a sub-scanning direction that periodically fluctuates in an output image; Deflecting mirror correcting means for correcting the pitch variation in the sub-scanning direction of the output image by constantly correcting the position of the deflecting mirror that is deflecting the exposure beam in accordance with the amount,
A color image forming apparatus comprising: a reference clock correction unit that corrects a frequency of a reference clock that determines a writing timing of an exposure beam according to a correction amount of the deflection mirror. 2. A plurality of image forming means for deflecting an exposure beam reflected by a rotary polygon mirror and irradiating the exposure beam onto a photosensitive drum to form an electrostatic latent image and developing the same, along a transport belt. A color image forming apparatus for forming a color image by transferring toner images of a plurality of colors formed by the respective image forming means onto transfer paper on a conveyor belt. Sub-scanning of an output image by constantly correcting the position of a deflecting mirror that deflects an exposure beam in accordance with a detected pitch fluctuation amount and a pitch fluctuation detecting unit that detects a dynamic pitch fluctuation in the scanning direction. Deflection mirror correction means for correcting pitch fluctuations in the direction,
A color image forming apparatus comprising: a reference clock correction unit that corrects a frequency of a reference clock that determines a writing timing of an exposure beam according to a correction amount of the deflection mirror.