JP2002137450A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an image color shift inconspicuous in an imaging apparatus for forming four-color images. SOLUTION: The imaging apparatus includes one or more polygon mirrors 110 for deflecting a plurality of light beams modulated in accordance with image signals of each color into a horizontal scanning direction, a light beam scanning means for making at least light beams of two colors among the plurality of light beams deflected in the horizontal scanning direction by the polygon mirrors 110 opposite in a scanning direction with respect to light beams of the other colors, an imaging means for forming images of each color, and a control means for controlling optical writing of the light beam scanning means. The light beam scanning means scans light beams LM and LC for forming images of magenta and cyan in the same scanning direction. The control means corrects a horizontal scanning/writing start position of the other colors based on the magenta image or the cyan image when the writing start position in the horizontal scanning direction is to be corrected.

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 printer, a copying machine, a facsimile, and a printing machine using a light beam scanning device having a plurality of light beams.

[0002]

2. Description of the Related Art In recent years, an image forming apparatus for forming an image of a plurality of colors has been required to have an improved recording speed. In the case of forming an image of a plurality of colors, in an image forming apparatus using an electrophotographic method, a series of electrophotographic processes of charging, exposure, development, transfer, and cleaning needs to be performed a plurality of times. There is a problem that printing time is longer. For this reason, the color image forming apparatus described in JP-A-6-171157 is provided with the same number of photosensitive drums for a plurality of image signals and has a one-to-one correspondence with each color image signal. A latent image is formed on the photoreceptor drum, visualized and developed using developers of different colors, and the visualized images are sequentially transferred to recording paper. With this method, it is possible to improve the recording speed when forming a plurality of color images. In the above publication, a light beam scanning device for forming a latent image on a photosensitive drum is constituted by one unit, and a rotary polygon mirror (hereinafter, referred to as a scanning polygon mirror) for scanning a light beam of each color on the photosensitive member. Providing only one polygon mirror makes it possible to reduce the size and cost of the apparatus.

Further, the light beam scanning device is provided with an fθ lens or the like. Particularly, when a plastic lens is used, a change in the environmental temperature or a change in the temperature inside the device may cause the change.
The shape and refractive index of the plastic lens change. For this reason, the scanning position on the image plane of the photoconductor changes, and a magnification error occurs in the main scanning direction, so that a high-quality image cannot be obtained. Further, in an apparatus that forms an image of a plurality of colors using a plurality of laser beams and lenses, a color misregistration occurs due to a magnification error, and a high-quality image cannot be obtained.
In particular, in the color image forming apparatus described in JP-A-6-171157, four color light beams are scanned on the photoreceptor by using one polygon mirror. The opposite of the two colors. Therefore, when the magnification of each color in the main scanning direction fluctuates, a position shift (color deviation) in the main scanning direction occurs by an amount corresponding to the magnification fluctuation for the color whose scanning direction is opposite.

[0004] On the other hand, there is also known a technique for correcting a magnification error and a color shift of an image caused by a change in an environmental temperature, a change in an in-machine temperature or the like. As an example of this, see, for example, JP-A-9-5
The invention described in 8053 is known. According to the invention described in Japanese Patent Application Laid-Open No. 9-58053, laser beams are detected at at least two places in one main scan of each of a plurality of laser beams, and each laser beam is detected by one laser beam detecting means. From a predetermined clock until detection by another laser beam detecting means, and the write modulation frequency of each laser beam is corrected in accordance with the count number. The timing from the synchronous position to the image writing is corrected. This makes it possible to always obtain a high-quality image with the same magnification without being affected by a change in scanning speed due to a change in temperature, and to maintain the same magnification of an image by each laser beam. It is said that high-quality images without color shift can be obtained.

[0005]

However, when such a magnification correction is performed, a slight error in the magnification directly results in color misregistration, depending on the degree of accuracy of the magnification correction. This color shift is visually inconspicuous in a yellow image, but is noticeable in a magenta image and a cyan image even with a slight color shift.

[0006] The present invention has been made in view of such a situation of the prior art, and its object is to provide yellow, magenta,
An image forming apparatus for forming images of four colors of cyan and black, comprising one or a plurality of deflecting means for deflecting a plurality of light beams modulated in accordance with image signals of respective colors in a main scanning direction. An image forming apparatus provided with a light beam scanning device in which at least two color light beams of a plurality of light beams deflected in the main scanning direction by the means have a scanning direction opposite to that of the other color light beams. Another object of the present invention is to make the color shift of an image inconspicuous.

Another object is to make the color shift of an image less noticeable when the user corrects the color shift of the image.

[0008]

In order to achieve the above-mentioned object, the present invention provides a method for deflecting a plurality of light beams modulated in accordance with image signals of yellow, magenta, cyan and black in a main scanning direction. A light beam having at least two colors of a plurality of light beams deflected in the main scanning direction by the deflecting device, the light beam having a scanning direction opposite to that of another color light beam; An image forming apparatus comprising: a beam scanning unit; an image forming unit that forms the image of each color; and a control unit that controls light writing of the light beam scanning unit, wherein the light beam scanning device includes magenta and cyan images. Are scanned in the same scanning direction with a light beam for forming the light beam. Note that the control means corrects the writing position in the main scanning direction when correcting the main scanning writing position of another color based on the magenta image or the cyan image and corrects the image magnification in the main scanning direction. Also, the image magnification of another color is corrected based on the magenta image or the cyan image. For this correction, a reference pattern for image registration formed on the transfer medium is provided, and a detecting means for detecting the reference pattern for image registration is provided. The control means changes the write clock for each color based on the time difference between the detected reference patterns. In addition, a correction value for the correction can be input from an external input device.
As the external input device, an operation panel is used for a copying machine or a facsimile, and a personal computer is used for a printer.

With this configuration, the color shift between the magenta image and the cyan image can be made inconspicuous.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In the following description,
Equivalent parts are given the same reference numerals, and BK, Y, C,
The configuration corresponding to each color is distinguished by adding M to the reference numerals.

1. First Embodiment FIG. 1 is a schematic configuration diagram showing a four-drum type image forming apparatus according to a first embodiment of the present invention. This image forming apparatus includes four sets of image forming units 100BK, 100Y, 100C, and 100M in order to form a color image in which images of four colors (magenta, cyan, yellow, and black) are superimposed.
And one laser beam scanning device (optical unit) 1. For each color, photoconductors 101BK, 101Y, 1
01C and 101M, the chargers 102BK and 10
2Y, 102C, 102M, developing unit 103BK,
103Y, 103C, 103M, transfer device 104BK, 1
04Y, 104C, 104M, cleaning unit 1
05BK, 105Y, 105C, 105M, static eliminator 10
6BK, 106Y, 106C, 106M are provided, and charge, exposure, development,
An image is formed on the recording paper P by the transfer. The first color image was formed on the recording paper P conveyed by the transfer belt B in the direction of the arrow, and then the images of the second color, the third color, and the fourth color were transferred in this order, whereby the four color images were superimposed. A color image can be formed on the recording paper P. Then, although not shown, the image on the recording paper P is fixed by the fixing device.

Laser beam scanning device 1 according to this embodiment
Are laser beams L of different colors above and below the surface of the polygon mirror 110 using one polygon mirror 110.
By deflecting and scanning BK, LY, LC, and LM, and further performing counter-distribution scanning around the polygon mirror 110,
The laser beams for four colors are applied to the respective photoconductors 101BK,
Scan on 101Y, 101C, and 101M. The laser beams LBK, LY, LC, and LM of each color are deflected by the polygon mirror 110, and the fθ lenses 112YBK,
After passing through 112CK, the first mirrors 113BK, 113Y,
113C, 113M, second mirror 114BK, 114
Y, 114C and 114M are folded back and BTL115B
After passing through K, 115Y, 115C, and 115M, they are turned back by the third mirrors 116BK, 116Y, 116C, and 116M, and the photoconductors 101BK and 101 corresponding to the respective colors.
Scan on Y, 101C and 101M. The BTL is an abbreviation of Barrel Toroidal Lens, and performs focusing in the sub-scanning direction (light-condensing function and position correction in the sub-scanning direction (surface tilt, etc.)).

FIG. 2 is a plan view showing a schematic configuration of the laser beam scanning device, and is a view of the laser beam scanning device 1 of FIG. 1 as viewed from above. Laser beams from the LD unit 120M for M color and the LD unit 120BK for BK color are transmitted through cylinder lenses (hereinafter, referred to as CYL) 121M,
The laser beam (light beam) LBK, LM is deflected by the polygon mirror 110 being rotated by the polygon mirror 110 being rotated by the reflection mirror 122BK, 122M.
After passing through YBK, 112CM, the first mirror 113BK, 1
Folded by 13M. The laser beams LC and LY from the LD unit 120C for cyan C and the LD unit 120Y for yellow Y are CYL121C and 121Y.
Passes through the upper mirror of the polygon mirror 110,
The rotation of the polygon mirror 110 deflects the laser beams LC and LY, and the fθ lenses 112CM and 112
The light passes through YBK and is folded back by the first mirrors 113C and 113Y.

In the present embodiment, first ends are provided at both ends in the main scanning direction.
Cylinder mirror (hereinafter referred to as CYM1) CMY1_
YBK, CMY1_CM, second cylinder mirror (hereinafter referred to as CYM2) CMY2_YBK, CYM2_C
M, a first sensor (hereinafter, referred to as S1) S1_YBK,
S1_CM, second sensor (hereinafter, referred to as S2) S2_
YBK, S2_CM, fθ lens 112
The laser beam passing through YBK and 112CM is CYM1_
YBK, CMY1_CM, CYM2_YBK, CYM2
S1_YBK, S1_C reflected and condensed by _CM
M, S2_YBK, and S2_CM.

First sensors S1_YBK, S1_CM
Also plays a role of a synchronization detection sensor for detecting a laser beam scanning synchronization signal which becomes a synchronization detection signal.
The laser beam LY from the LD unit 120Y and the laser beam LBK from the LD unit 120BK use common CYM1_YBK, CYM2_YBK, and S1_YBK, S2_YBK. The same applies to the LD unit 120C and the LD unit 120M. Since two laser beams are incident on the same sensor, the incident timings are different so that each can be detected. However, two sensors may be provided for each laser beam.

As can be seen from FIG.
And the black BK laser beams LY and LBK are scanned in the opposite directions by the cyan C and magenta M laser beams LC and LM.

FIG. 3 is a block diagram showing details of the image writing control unit in the image forming apparatus of the present embodiment. Although the write control unit 300 is described only for cyan C and magenta M, the same configuration is used for yellow Y and black BK. In the present embodiment, it is assumed that the laser beam LC is scanning ahead of the laser beam LM.

When the laser beams LC and LM scan, a synchronization detection signal DETP1_CM from S1_CM is generated.
Is sent to the synchronization signal separation units 301M and 301C, and the synchronization signal DETP1_C of the LD unit 120C for cyan C
And the synchronization signal DE of the LD unit 120M for magenta M
It is separated into TP1_M. FIG. 4 shows a synchronization signal separation unit 301.
FIG. 5 is a block diagram showing details of M, and FIG.
5 is a timing chart showing the timing of an output signal from 1M.

At the start of printing, first, an L for cyan C
Since only D unit 120C is turned on, DETP1
_CM passes directly through the separation unit 401 constituted by a gate circuit, and DETP1_CM = DETP1_C.
The signal DETP1_C is sent to a separation signal generator 402 composed of a counter and a comparator counted up by the write clock WCLK (C, M) to generate a separation signal MASK. The MASK signal is a signal that turns on at a predetermined timing from DETP1_C and turns off at a predetermined time. There is no problem as long as the timing is such that DETP1_C and DETP1_M can be reliably separated. By generating the MASK signal, the LD unit 12 is started from the next scan.
0C, the LD unit 120M is also turned on, and DETP1
By sending the _CM and MASK signals to the separation unit 401, D
ETP1_CM can be separated into DETP1_C and DETP1_M.

In the write control unit 300M, the separated DETP1_M is a phase synchronous clock generation unit 302M, a synchronous detection lighting control unit 303M, and a magnification correction unit 304M.
Sent to The magnification correction unit 304M has a function of determining a write clock frequency for modulating a laser and generating the write clock frequency. Using the fact that the image magnification in the main scanning direction changes depending on the write clock frequency, DETP1
It also has a magnification correction function of measuring the time difference between _M and DETP2_CM, and varying the write clock frequency from the result.

Clock WC generated by magnification correction
LK_M and the synchronization detection signal DETP1_M separated by the synchronization signal separation unit 301M
Clock VCL sent to 2M and synchronized with DETP1_M
LD drive unit 3 for generating K_M and controlling laser lighting
Send to 05M.

In the LD driving section 305M, the clock VCL
The laser is controlled to be turned on in accordance with an image signal synchronized with K_M. Then, the laser beam L is output from the LD unit 120M.
M is emitted, deflected by the polygon mirror 110, passes through the fθ lens 112CM, and scans the photoconductor 101M.

The DE separated by the synchronization signal separating unit 301M
TP1_C, DETP1_M, and WCLK_M generated by the magnification correction unit 304M are transmitted to the synchronization detection lighting control unit 30.
Send to 3M. The synchronization detection lighting control unit 303M includes a counter and a comparator. In this embodiment, since the laser beam LC for cyan C is ahead of the laser beam LM for magenta M, it detects DETP1_C. From ON after a preset time, and DETP1
A signal BD_M that is turned off after detecting the signal _M is generated,
By sending the signal to the LD driving unit 305M, BD_M = H
The laser lights up at the time. When the BD_M is turned on, the laser beam LM for magenta M is turned on by the sensor S1_
It must be before passing over the CM.

In the synchronization detection lighting control unit 303M, it is necessary to light the magenta M laser beam LM in order to output DETP2_CM from the sensor S2_CM by scanning the laser beam at the time of magnification correction. Control is performed so that BD_M is turned on not before detecting DETP1_C but before passing over S2_CM. For DETP2_CM, cyan C
Laser beam LC for magenta M and laser beam L for magenta M
Since M is not turned on at the same time, there is no need to separate them.

The polygon motor drive control section 310 receives the instruction from the printer control section 320,
11 is controlled to rotate at a specified number of rotations.

FIG. 6 is a block diagram showing details of the magnification correction section 304M. The magnification correction unit 304M sends the clock CLK from the reference clock generation unit 601 to the write clock generation unit 602, and generates a clock WCLK_M.
The time difference between DETP1_M and DETP2_CM is measured by the write clock WCLK_M, and the time difference T is sent to the comparison control unit 603. FIG. 7 shows a time difference counting unit 604.
FIG. 4 is a block diagram showing the details of. Time difference counting unit 60
4, the counter 6041 first sets the DETP1
_M clears the counter and the clock WCLK
Start counting _M. Then, the count value is sent to the latch 6042, and the counter value T is latched at the rising edge of DETP2_CM. The timing is shown in the timing chart of FIG. The time difference counting unit 604 sends the time difference (counter value) T to the comparison control unit 603, compares it with the reference time difference T0, determines clock setting data from the comparison result, and writes the clock setting data.
02, and a clock WCLK_M is generated.

FIG. 9 is a flowchart showing the processing procedure of the magnification correction unit 304M. Before executing this process, the write clock WCLK_M is set so that the time difference T becomes equal to the reference time difference T0, and the magnification of the image in the main scanning direction is in agreement. In such a state,
First, the time difference T between the sensors (S1_CM and S2_CM)
Is counted (step 901). Then, the time difference T is compared with the reference time difference T0 (step 902). If the time difference T is substantially equal to the reference time difference T0 (step 903), the process ends, and the write clock WCLK_M remains unchanged. Then, the image forming operation is started (Step 907).

On the other hand, if T ≠ T0, the comparison control unit 60
3 sends the setting data corresponding to the difference between the two to the write clock generator 602, and writes the write clock W whose frequency has been changed.
CLK_M is generated (steps 905 and 906), the image forming operation is started (step 907), and the image forming operation is repeated until the page to be written is completed (steps 907 and 908). Note that the time difference T and the reference time difference T
When comparing 0, it is originally determined whether or not they are completely equal. However, if the magnification error is within an allowable error range, it is determined to be normal. Therefore, when the time difference becomes longer, the write clock frequency is changed.

Regarding the write control unit 300C, the synchronization detection lighting control unit 303C determines that the laser beam LC for cyan C is ahead of the laser beam LM for magenta M in this embodiment, so that DETP1_C Is turned on after a preset time has elapsed since DETP1_C
Generates a signal BD_C that turns off after detecting the
This will be sent to the drive unit 305C. The timing at which BD_C is turned on is when the laser beam LC for cyan C is S1_
It must be before passing over the CM.

In the synchronization detection lighting control unit 303C, the laser beam LC for cyan C needs to be lit in order to output DETP2_CM from the sensor S2_CM by scanning the laser beam during magnification correction, and the lighting signal BD_C Is turned on before passing over the sensor S2_CM. The DETP2_CM does not need to be separated because the laser beam LC for cyan C and the laser beam LM for magenta M are not simultaneously turned on.

The write control unit Y includes a write control unit C,
Since the write control unit BK is the same as the write control unit M,
Description is omitted.

2. Second Embodiment FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a second embodiment. The image forming apparatus according to this embodiment differs from the image forming apparatus according to the first embodiment in that a third sensor S3 for detecting an image alignment pattern on the transfer belt B is provided. The third sensor S3 is a reflection type optical sensor that detects an image alignment pattern (oblique line pattern) formed on the transfer belt, and based on the detection result, determines the image position in the main scanning direction between the colors. Correct the misalignment.

FIG. 11 is a block diagram showing details of an image writing control unit of the image forming apparatus according to the second embodiment. The image writing control unit according to this embodiment includes main-scanning writing position control units 306C and 306C in writing control units 300C and 300M.
306M is provided, and a detection signal from the third sensor S3 is sent to the printer control unit 320. The printer control unit 320 calculates a shift amount of each color with respect to magenta M from the detection result of the third sensor S3. The third embodiment is different from the first embodiment in that the main scanning writing position correction data is sent from the printer control unit 320 to the main scanning writing position control unit 306C.
The main scanning write position control unit 306C includes a printer control unit 3
The write timing of the image signal C is changed in units of one cycle of the write clock VCLK_C according to the correction data from 20. The same applies to the write control units Y and BK, and a description thereof will be omitted.

FIG. 12 is a flowchart showing the processing procedure for image alignment correction in the second embodiment, and FIG. 16 is a diagram showing an example of an image alignment pattern written on the transfer belt B.

In this processing, first, an image alignment pattern PN (each color M, C, Y, BK) as shown in FIG.
Is formed on the transfer belt B (step 12).
01). The image pattern PN is detected by the third sensor S3 and sent to the printer control unit 320 (step 120).
2). The printer control unit 320 calculates an image position shift amount of each color with respect to magenta M (step 1203), and calculates a shift amount Xmc of yellow Y with respect to magenta M, a shift amount Xmc of cyan C with respect to magenta M, and a shift amount Xmk of black BK with respect to magenta M. Check if it is almost equal to 0 (Step 1
204). In this check, if it is almost equal to 0, that is, if it is 以下 or less of the correction resolution (21.2 μm or less for 600 dpi), the image forming operation is started with the main scanning write position of each color as it is. (Step 1
206). If any one of them has a correction resolution equal to or more than の of the correction resolution, the main scanning write position is corrected for the color by the shift amount (step 1205). Thereafter, the image forming operation is started (step 1206), and the image forming operation is repeated until the last page (steps 1206, 12).
07).

In this embodiment, step 1
As can be seen from 204 and 1205, the determination as to whether or not to perform the correction is determined by the correction resolution, but may be set to a level that does not cause any problem on the image. In this embodiment, magenta M is used as a reference.
May be used as a reference.

Here, the pattern PN and the shift amount thereof will be supplemented. That is, the MCY on the transfer belt B
The pattern PN is formed by forming an oblique line image at a preset timing for each of the BK colors.
When N is formed, the transfer belt B moves to detect the diagonal line of each color by the sensor S3, and the shift of each color of CYBK with respect to magenta M which is the first color is measured using time as a parameter. Therefore, the time is compared with a preset time (diagonal line writing timing) to calculate a shift amount with respect to magenta M, and a main scanning writing position control unit main scanning writing position control unit 306C (other colors are also used). Feedback). When the pattern PN is formed as an oblique line as described above, if the image shifts in the main scanning direction, the detection timing shifts accordingly, so that it is possible to correct the detection timing shift.

Other parts not particularly described are the same as those described in the first embodiment.
And functions similarly.

3. Third Embodiment FIG. 13 is a block diagram showing details of an image writing control unit according to a third embodiment, and FIG. 17 is a pattern for image alignment written on a transfer belt B similarly to FIG. It is a figure showing the example of. This third embodiment is similar to the second embodiment described above.
A fourth sensor S4 is provided in addition to the third sensor S3 with respect to the third embodiment, and the first and second image alignment patterns PN1 written on both ends of the transfer belt B by the two sensors S3 and S4. , PN2, and corrects the image position shift between the colors in the main scanning direction and the image magnification in the main scanning direction based on the detection results. Thus, by writing the same patterns PN1 and PN2 on both sides of the transfer belt B and detecting the patterns, it is possible to detect not only a shift in the main scanning direction but also a magnification error. In the third embodiment, in the image forming apparatus shown in FIG. 10, in addition to the third sensor S3, fourth sensors S4 (indicated by reference numerals in parentheses in FIG. 10) are provided at both ends in the main scanning direction. , The fourth sensor S4 as shown in FIG.
Is also input to the printer control unit 320. The other components are configured in the same manner as in the third embodiment and function in the same manner. Therefore, the same components are denoted by the same reference numerals, and duplicate description will be omitted.

In this embodiment, a third sensor S3 for detecting the first and second patterns PN1 and PN2,
The detection signal from the fourth sensor S4 is sent to the printer controller 32.
0, and the printer control unit 320
Calculate the shift amount and magnification error of each color with respect to magenta M,
From the printer control unit 320 to the main scanning writing position control unit 306
C, the main-scanning writing position correction data and the magnification correction unit 304C.
Is different from the third embodiment in that the magnification correction data is sent to the third embodiment. The main scanning writing position control unit 306C changes the writing timing of the image signal C in units of one cycle of the writing clock VCLK_C according to the correction data from the printer control unit 320. Further, the magnification correction unit 304C uses the correction data from the printer control unit 320 to output the clock WCLK
Change the frequency of _C. The same applies to the write control units Y and BK.

FIG. 14 is a flowchart showing the processing procedure of image magnification correction in the third embodiment. The processing procedure of the image alignment correction is the same as that of the second embodiment described in the flowchart of FIG. However, in the present embodiment, the two sensors S3 and S4
After the magnification correction, the average value of the image shift amounts calculated from the two sensor outputs may be sent to the main scanning writing position control unit 306C.

In the processing procedure of FIG. 14, first, the first and second two image alignment patterns (oblique lines) PN
1, PN2 are formed at both ends on the transfer belt B (step 1401). The image patterns PN1 and PN2 are detected by the sensors S3 and S4 and sent to the printer control unit (step 1402). The printer control unit 320 calculates an image magnification error of each color with respect to magenta M (step 140).
3), magnification error Mm of yellow Y with respect to magenta M
y, it is checked whether the magnification error Mmc of cyan C with respect to magenta M and the magnification error Mmk of black BK with respect to magenta M are substantially equal to 0 (step 140).
4). If these three are almost equal to 0, that is, if they are equal to or less than the correction resolution, the image alignment operation is started with the write clocks of the respective colors as they are (step 1406). If any one has a resolution higher than the correction resolution, the magnification of the color is corrected by the error (change the frequency of the write clock) (step 140).
5). Thereafter, an image positioning operation is started (step 1406), and the image forming operation is executed until all pages are completed (steps 1406, 1407).

In this embodiment, the determination as to whether or not to perform correction is determined by the correction resolution.
The level may be set to a level that does not cause any problem on the image. Also,
In this embodiment, an example based on magenta M is shown, but cyan C may be used as a reference.

Other parts which are not particularly described are the same as those of the first embodiment.
And functions similarly.

4. Fourth Embodiment FIG. 15 is a block diagram illustrating details of an image writing control unit according to a third embodiment. This embodiment is different from the third embodiment in that an operation panel 330 that allows a user to input an instruction is connected to the printer control unit 320, and the operation panel 33
The difference is that the image magnification in the main scanning direction and the image position deviation in the main scanning direction can be corrected by an instruction from 0. The user inputs the image position shift amount of each color with respect to magenta M or cyan C and the magnification error from the operation panel 330. Other components are configured in the same manner as in the first to third embodiments, and function similarly.

If the image forming apparatus to which the present invention is applied is a printer, input may be made from a personal computer instead of the operation panel 330.

[0047]

As described above, according to the first aspect of the present invention, the light beam scanning device scans the light beams for forming the magenta and cyan images in the same scanning direction. It can be less noticeable.

According to the second aspect of the invention, when the write position in the main scanning direction is corrected, the main scan write position of another color is corrected based on the magenta image or the cyan image. The deviation can be made inconspicuous.

According to the third aspect of the invention, when correcting the image magnification in the main scanning direction, the image magnification of another color is corrected based on the magenta image or the cyan image.
Further, the color shift of the image can be made inconspicuous.

According to the fourth aspect of the present invention, since the reference pattern for image alignment formed on the transfer medium is provided and the correction is performed based on the reference pattern, the color shift of the image is made inconspicuous. Correction can be performed reliably.

According to the fifth aspect of the present invention, there is further provided detecting means for detecting a reference pattern for image alignment, and the control means changes the write clock for each color based on the time difference between the detected reference patterns. In addition, the correction for making the color shift of the image inconspicuous can be performed with high accuracy.

According to the sixth aspect of the present invention, since the correction value is input from the external input device, the color shift of the image can be corrected according to the user's will.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a four-drum type image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view illustrating a schematic configuration of a laser beam scanning device used in the image forming apparatus of FIG.

FIG. 3 is a block diagram illustrating details of an image writing control unit in the image forming apparatus according to the first embodiment.

FIG. 4 is a block diagram illustrating details of a synchronization signal separation unit in FIG. 3;

FIG. 5 is a timing chart showing the timing of an output signal from a synchronization signal separation unit in FIG. 3;

FIG. 6 is a block diagram illustrating details of a magnification correction unit in FIG. 3;

FIG. 7 is a block diagram illustrating details of a time difference counting unit in FIG. 6;

8 is a timing chart showing the timing of an output signal from a time difference counting unit in FIG.

FIG. 9 is a flowchart illustrating a processing procedure of a magnification correction unit in FIG. 3;

FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIG. 11 is a block diagram illustrating details of an image writing control unit of the image forming apparatus according to the second embodiment.

FIG. 12 is a flowchart illustrating a processing procedure of image alignment correction according to the second embodiment.

FIG. 13 is a block diagram illustrating details of an image writing control unit according to a third embodiment.

FIG. 14 is a flowchart illustrating a processing procedure of image magnification correction according to the third embodiment.

FIG. 15 is a block diagram illustrating details of an image writing control unit according to a third embodiment.

FIG. 16 is a diagram illustrating an example of one alignment pattern written in the center of the transfer belt according to the second embodiment.

FIG. 17 is a diagram illustrating an example of two alignment patterns written in both end portions of the transfer belt according to the third embodiment.

[Explanation of symbols]

100BK, 100Y, 100C, 100M Image forming unit 110 Polygon mirror 111 Polygon motor 112YBK, 112CM fθ lens 115BK, 115Y, 115C, 115M BTL 120BK, 120Y, 120C, 120M LD unit 121BK, 121Y, 121C, 121M Cylinder lens (CYL) 122BK, 122M Reflection mirror CYM1 First cylinder mirror CYM2 Second cylinder mirror 300M, 300C Write control unit 301M, 301C Synchronization signal separation unit 302M, 302C Phase synchronization clock generation unit 303M, 303C Synchronization detection lighting control unit 304M, 304C Magnification correction unit 305M, 305C LD drive unit 306M, 306C Main scan writing position control unit 310 Polygon motor drive control unit 320 Printer control unit 330 an operation panel 401 separating section 402 separates the signal generating unit 601 reference clock generator 602 write clock generating unit 603 compares the control unit 604 time difference counting section PN, PN1, PN2 alignment patterns S1, S2, S3, S4 sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/04 111 B41J 3/00 M 5C079 H04N 1/04 H04N 1/04 D 1/113 104A 1/46 1/46 Z F term (reference) 2C362 BA51 BA52 BA66 BA68 BA70 CA18 CA22 CA23 CA39 CB35 2H030 AA01 AB02 AD17 BB02 BB16 BB44 BB56 BB63 2H045 AA01 BA22 BA34 CA88 CA98 DA11 DA26 2H076 AB05 AB06 AB12 AB16 AB18 AB22 AB33 AB67 AA03 HA02 HA06 HA13 HB08 HB11 QA14 QA17 XA05 5C079 HB03 KA03 KA08 LA01 LA24 LA37 NA01 PA01 PA02 PA03

Claims (6)

[Claims] A plurality of light beams that are modulated in accordance with image signals of yellow, magenta, cyan, and black in one or more main scanning directions, and are deflected in the main scanning direction by the deflecting units. A light beam scanning unit in which the light beams of at least two colors of the plurality of light beams have scanning directions opposite to light beams of other colors; an image forming unit for forming images of the respective colors; An image forming apparatus comprising: a light beam scanning unit that controls light writing by the light beam scanning unit, wherein the light beam scanning unit scans light beams for forming magenta and cyan images in the same scanning direction. Image forming apparatus. 2. The method according to claim 1, wherein the control unit corrects a main-scanning start position of another color based on a magenta image or a cyan image when correcting the start position in the main-scanning direction. Image forming apparatus. 3. The image processing apparatus according to claim 1, wherein the control unit corrects an image magnification of another color based on a magenta image or a cyan image when correcting the image magnification in the main scanning direction. Image forming apparatus. 4. The image forming apparatus according to claim 2, further comprising a reference pattern for image alignment formed on the transfer medium. 5. The image processing apparatus according to claim 1, further comprising detecting means for detecting the reference pattern for image alignment, wherein the control means changes a write clock for each color based on a time difference between the detected reference patterns. 5. The image forming apparatus according to 4. 6. The image forming apparatus according to claim 2, wherein a correction value for the correction is input from an external input device.