JP2000162845A - Tandem-type color image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device capable of obtaining an outputted image of high quality with inconspicuous color slippage at a low cost. SOLUTION: Photoreceptor drums 3Y and 3M are driven by the same motor M3 via a timing belt B3. Thus, the number of motors and timing belts in use is reduced. Then, the rotating speed of the photoreceptor drum 3M is detected by an encoder 11M, and the feedback control of the output of the motor M3 is executed based on the detected speed signal. Additionally, the rotating speed of the photoreceptor drums 3K and 3C are detected separately by encoders 11K and 11C, and the feedback control of the outputs of the motors M1 and M2 is executed based on the respective detected speed signals. Thus, color slippages other than yellow one is reduced, since the color slippages other than the yellow is inconspicuous, so that a full color image of high quality with inconspicuous color slippages as a whole is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used in an electrophotographic copying machine, a printer, and the like.
More specifically, the present invention relates to a tandem-type color image forming apparatus capable of obtaining an output image with inconspicuous color misregistration even when the drive transmission system to the photosensitive member is eccentric.

[0002]

2. Description of the Related Art As one type of color image forming apparatus, a tandem system in which an image forming system (photoconductor, developing device, transfer device, etc.) provided independently for each developing color is arranged along a paper path. There are types. In such an image forming apparatus, toner images of respective developing colors are simultaneously formed by the respective image forming systems, and these toner images are successively transferred onto a sheet during a series of sheet passing operations. This has the advantage that the image forming process can be speeded up as compared with a method in which toner images of each development color are sequentially formed on one photosensitive member. (Shift) must be prevented.

Therefore, in order to prevent this displacement,
For example, in Japanese Patent Application Laid-Open No. Sho 62-145262, a plurality of photoconductors are driven by a single drive motor via a timing belt or the like so as to prevent misalignment between colors. However, in such a configuration, the pulley of the photoconductor is eccentric (the eccentricity of the gear),
If the timing belt has uneven thickness, the rotation of the photoconductor is fluctuated, and a positional shift between the colors occurs. Then, due to the positional deviation, there is a possibility that the toner images of the respective colors do not overlap with each other accurately, a color deviation occurs, and the quality of the output image is deteriorated.

In order to prevent the occurrence of color misregistration,
The following image forming apparatus is used. FIG. 19 shows a schematic configuration of a photoconductor drive system in the image forming apparatus. In this image forming apparatus, individual motors MM, MC, MY, MK are provided for each of the photoconductors of magenta (M), cyan (C), yellow (Y), and black (K), and pulleys PM, PC, PY, PK and motor MM, M
Separate timing belts B for C, MY and MK
M, BC, BY, and BK are multiplied. And the motor M
By driving M, MC, MY, and MK, each photoconductor is rotated. Also, encoders EM attached to pulleys PM, PC, PY, and PK of each photoconductor,
The rotation speed of each photoconductor is read using EC, EY, and EK, and the outputs of motors MM, MC, MY, and MK that drive each photoconductor are feedback-controlled based on the speed signal. Thus, by suppressing the rotation fluctuation of the photoconductor, even if the pulley is eccentric, etc.
The position shift on the surface of each photoconductor is prevented, and an output image with less noticeable color shift is obtained.

[0005]

However, in the above-described image forming apparatus, the motors MM, MC, MY, MK, the timing belts BM, B
C, BY, BK, and encoders EM, EC, EY,
EK is provided and each motor MM, MC, MY, MK
Needs to be feedback-controlled based on speed signals from the encoders EM, EC, EY, and EK. For this reason, there is a problem that the number of components constituting the device increases, which not only complicates the device but also increases the cost.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-described problems, and provides a tandem-type color image forming apparatus capable of obtaining a high-quality output image with less noticeable color shift at a low cost. That is the task.

[0007]

According to a tandem type color image forming apparatus of the present invention, a plurality of photoconductors, a first photoconductor among the photoconductors, and a second photoconductor are provided. A drive unit for driving the color unit; and a control unit for performing feedback control of the drive unit based on the rotation speed of the photoconductor for the second color.

In this image forming apparatus, the photosensitive member for the first color and the photosensitive member for the second color are rotationally driven by the same driving means. Therefore, the number of driving means used is reduced. Then, a signal of the rotation speed of the photoconductor for the second color, which is rotationally driven by the driving unit, is transmitted to the control unit. The output of the driving unit is controlled by the control unit that has received the signal based on the rotation speed of the photoconductor for the second color.

Here, it is preferable that the control means performs control for reducing fluctuations in the rotation speed of the photosensitive member for the second color. The second color is more preferably a color other than yellow. By performing such control, the displacement of the surface of the photoconductor for the second color can be suppressed to a small value. As a result, color shift in the photoconductor is prevented. However, the photoreceptor for the first color may have a large rotation fluctuation and a large positional deviation. Here, it is empirically known that the color misregistration of yellow is less noticeable. For this reason, if the first color is yellow, a high-quality image in which the color shift is inconspicuous as a whole can be obtained even if the position shift on the surface of the photoconductor for the first color becomes large. Therefore, with such a simple configuration, the occurrence of color misregistration is effectively prevented, and the number of driving means used is reduced, so that the cost is also excellent.
The colors other than yellow are cyan, magenta, and black.

Further, in the tandem type color image forming apparatus according to the present invention, the driving means also drives the photosensitive member for the third color among the photosensitive members, and the control means controls the photosensitive member for the second color. The driving unit may be feedback-controlled based on a representative value of the rotation speed of the photoconductor for the third color and the rotation speed of the photoconductor for the third color. In this case, it is desirable that the second color and the third color be colors other than yellow.

With such a configuration, the photoconductors for the first color, the second color, and the three colors are driven by the same driving means. Therefore, the number of driving units used can be further reduced. In this image forming apparatus, the control unit detects the rotational speeds of the photoconductor for the second color and the photoconductor for the third color, calculates their representative values, and drives based on the representative values. The output of the means is controlled. Here, an average value is mainly used as the representative value, but a median value or a weighted average value can also be used. Thereby, while the rotation fluctuation of the photoconductor for the second color and the photoconductor for the third color is suppressed to be small on average, the rotation fluctuation of the photoconductor for the first color may be large. For this reason, yellow, which is known to have less noticeable color misregistration,
By using the color, a high-quality image with less noticeable color shift as a whole can be obtained. Further, since the number of driving means used is reduced, the cost is excellent. The colors other than yellow include cyan,
Magenta and black.

Further, according to the tandem type color image forming apparatus of the present invention, a plurality of photoconductors, a driving unit for driving two or more of the photoconductors, and each photoconductor driven by the driving unit Control means for performing feedback control of the driving means based on the representative value of the rotation speed of the driving means.

In this image forming apparatus, two or more photosensitive members are rotationally driven by the same driving means. Therefore,
The number of driving means used is reduced. Then, the control means detects the rotational speed of each photoconductor being rotationally driven by the drive means, calculates a representative value of these rotational speeds, and outputs the output of the drive means based on the representative value. Controlled. As a result, the rotation fluctuation of the photoconductor can be suppressed on average. For this reason, the misregistration of each photoconductor is reduced, so that color misregistration is prevented, and a high-quality image is obtained. Therefore, with such a simple configuration, the occurrence of color misregistration is effectively prevented, and the number of driving means used is reduced, so that the cost is also excellent.

Further, in the tandem-type color image forming apparatus according to the present invention, it is preferable that the tandem type color image forming apparatus includes a timing belt for transmitting a drive from the driving means to each of the photosensitive members. Particularly, a toothed timing belt is preferable. This is because the responsiveness of the feedback control in the control means is improved because the timing belt has a small backlash.

Further, according to the tandem type color image forming apparatus of the present invention, a plurality of photoconductors, a driving unit for driving two or more of the photoconductors, and each photoconductor driven by the driving unit A pulley provided to the drive unit, a timing belt for transmitting drive from the drive unit to each of the pulleys, and a control unit for performing feedback control of the drive unit based on one rotation speed of each photoconductor driven by the drive unit. And the phases of the eccentricities of the respective pulleys are matched with each other.

In this image forming apparatus, two or more photosensitive members are driven to rotate by the same driving means. Therefore,
The number of driving means used is reduced. Further, the pulley is assembled in a state where the phases of the pulleys of the other photoconductors match the phases of the pulleys of the photoconductors whose rotational speeds are detected. Then, based on the rotation speed of the photoconductor on which the speed detection is being performed, the output of the driving unit is feedback-controlled by the control unit. For this reason, the rotation accuracy of the photoconductor on which the speed detection is performed is improved. As for the rotation accuracy of the photoconductor other than that, since the phase of each pulley is matched with the phase of the pulley of the photoconductor whose speed is being detected, the difference in the amount of deflection of the pulley and the accuracy of the drive transmission means are different. Only remains as displacement. Accordingly, the displacement of each photoconductor is reduced, so that a high-quality image with small color displacement can be obtained. Therefore, with such a simple configuration, the occurrence of color misregistration is effectively prevented, and the number of driving units used is reduced, so that the cost is also excellent.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an image forming apparatus according to the present invention. The tandem-type color image forming apparatus according to the present embodiment is used in a tandem-type digital copying machine that prints a full-color image on printing paper based on a digital image signal.

First, a first embodiment will be described. As shown in FIG. 1, the image forming apparatus mainly includes photosensitive drums 3Y, 3M, 3C, and 3K that are continuously arranged in parallel. Around the photosensitive drums 3Y, 3M, 3C, and 3K, the photosensitive drums 3
Charging brushes 5Y, 5M, 5C and 5K for uniformly charging the surfaces of Y, 3M, 3C and 3K, and photosensitive drums 3Y and 3
Laser heads 7Y, 7M, 7C, 7K for writing required electrostatic latent images on M, 3C, 3K in accordance with image information, and developing units 2Y, which apply toner to the electrostatic latent images for development.
2M, 2C, and 2K, and the photosensitive drums 3Y and 3 after development.
Cleaning brushes 4Y, 4M, 4C, 4K for removing toner remaining on M, 3C, 3K, and transfer rollers 6Y, 6M, 6C, 6 for transferring toner images to copy paper P.
K and the like are arranged.

When an image is formed by such a color image forming apparatus, the surfaces of the photosensitive drums 3Y, 3M, 3C and 3K are uniformly charged by the charging brushes 5Y, 5M, 5C and 5K. Next, the laser heads 7Y, 7M, 7
By C and 7K, exposure scanning is performed by laser light corresponding to each reproduced color. By such exposure, an electrostatic latent image corresponding to each reproduced color is written on each of the photosensitive drums 3Y, 3M, 3C, and 3K. Subsequently, the electrostatic latent images are developed by the developing devices 2Y, 2M, 2C, and 2 containing the toner of each reproduction color.
By K, each is developed to be a toner image of each color. These toner images are transferred to the transfer rollers 6Y and 6Y.
By M, 6C, and 6K, the images are sequentially transferred onto the copy paper P in an overlapping manner. Thereafter, the transfer paper P on which the toner images are superimposed and transferred is conveyed to the fixing roller 10, where it is heated to melt the toner images of each color to form a full-color image, and the toner is fixed on the copy paper P. Is done.

Here, the drive system of each photosensitive drum in the image forming apparatus will be described in detail with reference to FIG. FIG. 2 schematically shows the outline of the drive system of each photosensitive drum. Photoconductor drums 3K, 3C, 3M, 3
Pulleys 13K, 13C, 13M, 13Y are provided on the Y rotation shaft.
Is provided. Further, the photosensitive drums 3K, 3C,
Encoders 11K, 11C, and 11M are attached to the 3M rotation shaft. This encoder detects the rotation speed of the photosensitive drum. Further, a motor M1 for rotationally driving the photosensitive drum 3K, a motor M for rotationally driving the photosensitive drum 3C, and a motor M3 for rotationally driving the photosensitive drums 3M and 3Y are provided. Then, a timing belt is hung on these pulleys and the motor. Specifically, the timing belt B1 is hung on the motor M1 and the pulley 13K, the timing belt B2 is hung on the motor M2 and the pulley 13C, and the timing belt B3 is hung on the motor M3 and the pulleys 13M and 13Y. . By these,
When each motor rotates, each pulley, that is, each photosensitive drum rotates via each timing belt. In particular, the photosensitive drums 3M and 3Y rotate by driving the same motor M3.

The operation of the driving system of the image forming apparatus thus configured will be described. When the motor M1 is driven, the pulley 13K is rotated via the timing belt B1. As a result, the photosensitive drum 3K is also rotated. Similarly, when the motor M2 is driven, the photosensitive drum 3C is rotated. When the motor M3 is driven, the pulleys 13M and 13Y are rotated via the timing belt B3. As a result, the photosensitive drums 3M and 3Y are rotated. When the respective photoconductor drums rotate, the rotation speeds of the photoconductor drums 3K, 3C, 3M are detected by the encoders 11K, 11C, 11M. These detected speed signals are sent to a control unit that controls the entire image forming apparatus. The control unit transmits an output signal to each motor based on the speed signal. The output of each motor is controlled based on this output signal.

That is, the output of the motor M1 is controlled based on the speed signal detected by the encoder 11K, the output of the motor M2 is controlled based on the speed signal detected by the encoder 11C, and the motor M3 is controlled based on the speed signal detected by the encoder 11M. Is controlled. Specifically, when the rotation speed of each of the photosensitive drums 3K, 3C, 3M is higher than a specified speed, each of the photosensitive drums 3K, 3C, 3M
The output of the motors M1, M2, M3 for driving the motors is reduced to slow down the rotation. Conversely, the photosensitive drums 3K,
When the rotation speed of 3C, 3M is lower than the specified speed,
Motors M1, which drive the photosensitive drums 3K, 3C, 3M
The output of M2 and M3 is increased to speed up the rotation. That is, the output control of each of the motors M1, M2, M3 is performed so as to reduce the rotation fluctuation of each of the photosensitive drums 3K, 3C, 3M.

Here, a test for color misregistration in the photosensitive drums 3M and 3Y driven by the motor M3 was performed, and the results are shown in FIGS. 3 and 4. FIG. 3 shows a case where the feedback control is not performed, and FIG. 4 shows a case where the feedback control is performed. FIG.
As is clear from FIG. 7, when the feedback control is not performed, color misregistration occurs in both magenta (M) and yellow (Y). Then, when the feedback control is executed, the color shift of magenta (M) is improved as is apparent from FIG. This is because the rotation speed of the photosensitive drum 3M is detected by the encoder 11M, and the output of the motor M3 is feedback-controlled to reduce the rotation fluctuation of the photosensitive drum 3M based on the rotation speed. Although not shown, of course, cyan (C),
The color shift of black (K) is also improved. On the other hand,
It has been empirically known that although the color shift of yellow has not changed, yellow is not very noticeable even if there is a color shift. For this reason, a high-quality full-color output image in which color shift is not conspicuous as a whole is obtained.

As described above, the photosensitive drum 3Y for yellow and the photosensitive drum 3M for magenta, in which color misregistration is inconspicuous,
Are driven by the same motor M3 via the timing belt B3, the rotation speed of the photosensitive drum 3M is detected by the encoder 11M, and the output of the motor M3 is feedback-controlled based on the speed signal, so that the motor and the timing are controlled. After reducing the number of belts and encoders used, a high-quality full-color output image with less noticeable color shift can be obtained.

As described above in detail, according to the image forming apparatus of the first embodiment, the photosensitive drums 3Y and 3M are driven by the motor M3, which is the same drive source, via the timing belt B3. Is done. The photosensitive drums 3K and 3C are driven by motors M1 and M2, respectively. Thus, the number of motors and timing belts used can be reduced. Further, since no encoder is provided on the rotating shaft of the photosensitive drum 3Y, the number of encoders used can be reduced. Then, the rotation speed of the photosensitive drum 3M is detected by the encoder 11M,
The output of the motor M3 is feedback-controlled based on the detected speed signal. Also, the photosensitive drums 3K, 3
The rotation speed of C is detected by encoders 11K and 11C, respectively, and the outputs of motors M1 and M2 are feedback-controlled based on the detected speed signals. As a result, color shifts other than yellow are improved. Although the color shift of yellow is not improved, the color shift of yellow is inconspicuous. For this reason, a high-quality full-color output image with less noticeable color shift as a whole can be obtained. Therefore, an image forming apparatus capable of obtaining a high-quality full-color output image with less noticeable color shift is provided at low cost.

The present embodiment is merely an example, and does not limit the present invention. Therefore, of course, the present invention provides various improvements without departing from the gist thereof.
Deformation is possible. For example, in the first embodiment,
Although the photoconductor drums 3M and 3Y are driven by the motor M3, as shown in FIG. 5, the photoconductor drums 3Y and 3C are driven by the motor M3 by changing the arrangement order of the photoconductors. The same effect can be obtained.

Next, a second embodiment will be described. The image forming apparatus according to the second embodiment has the same basic configuration as the image forming apparatus according to the first embodiment, but has a different drive system for the photosensitive drum. That is, in this image forming apparatus, as shown in FIG. 6, the timing belt B1 is hung on the motor M1 and the pulley 13K, and the timing belt B is hung on the motor M4 and the pulley 13Y.
4, the motor M4 and the pulleys 13M and 13C
And the timing belt B5 is hung. As a result, when each motor rotates, each pulley, that is, each photoconductor drum rotates via each timing belt. In particular, the photosensitive drums 3M, 3C, and 3
Y rotates by driving the same motor M4. Encoders 11K, 11M, and 11C for detecting the rotational speeds of the photosensitive drums 3K, 3M, and 3C are attached to the rotating shafts of the photosensitive drums 3K, 3M, and 3C.

In this image forming apparatus, when the motor M1 is driven, the pulley 13K is driven via the timing belt B1.
Is rotated. As a result, the photosensitive drum 3K is also rotated. When the motor M4 is driven, the pulley 13Y is rotated via the timing belt B4,
The pulleys 13M and 13C are rotated via the timing belt B5. As a result, the photosensitive drums 3Y, 3M,
3C is rotated by driving the motor M4. When each photosensitive drum rotates, the photosensitive drums 3K, 3K
The rotation speeds of the M and 3C are the encoders 11K, 11M and 11
Detected by C. These detected speed signals are sent to a control unit that controls the entire image forming apparatus.
The control unit transmits an output signal to each motor based on the speed signal. The output of each motor is controlled based on this output signal.

That is, the output of the motor M1 is controlled based on the speed signal detected by the encoder 11K, and the output of the motor M4 is controlled based on the average value of the speed signals detected by the encoders 11M and 11C. Specifically, the rotation speed of the photosensitive drum 3K and the photosensitive drums 3M and 3C
If the average speed is higher than the specified speed, the motor M
1 and M4 are reduced to slow down the rotation. Conversely, when the rotation speed of the photosensitive drum 3K and the average speed of the photosensitive drums 3M and 3C are lower than the specified speed, the output of the motors M1 and M4 is increased to increase the rotation. That is, the output control of each motor is performed so as to reduce the rotation fluctuation of each photosensitive drum.

Here, a test was conducted for color misregistration of the photosensitive drums 3Y, 3M, 3C driven by the motor M4, and the results are shown in FIGS. 7 and 8. FIG. 7 shows a case where the feedback control is not performed, and FIG. 8 shows a case where the feedback control is performed. FIG.
As is clear from FIG. 7, when the feedback control is not performed, color misregistration occurs in all of cyan (C), magenta (M), and yellow (Y). Then, when the feedback control is executed, the color misregistration of cyan (C) and magenta (M) is improved as is clear from FIG. This is because the rotation speeds of the photosensitive drums 3C and 3M are detected by the encoders 11C and 11M, and the motors are driven so as to averagely reduce the rotation fluctuation of the photosensitive drums 3C and 3M based on the average value of these rotation speeds. This is because the output of M2 is feedback-controlled. Although not shown, the color misregistration of black (K) is of course also improved. On the other hand, although the color shift of yellow is rather large, it has been empirically known that yellow does not stand out even if there is a color shift. For this reason, a high-quality full-color output image in which color shift is not conspicuous as a whole is obtained.

As described in detail above, according to the image forming apparatus of the second embodiment, the photosensitive drums 3M,
3C and 3Y are driven by a motor M4, which is the same drive source, via timing belts B5 and B4.
The photosensitive drum 3K is driven by a motor M1. Thus, the number of motors and timing belts used can be reduced. Further, since no encoder is provided on the rotating shaft of the photosensitive drum 3Y, the number of encoders used can be reduced. And the photosensitive drum 3
The rotation speeds of M and 3C are detected by encoders 11M and 11C, and the output of motor M4 is feedback-controlled based on the average value of the detected speed signals. Also,
The rotation speed of the photosensitive drum 3K is detected by the encoder 11K, and the motor M1 is detected based on the detected speed signal.
Is feedback-controlled. As a result, a color shift other than yellow is improved. Although the color shift of yellow is not improved, the color shift of yellow is inconspicuous.
For this reason, a high-quality full-color output image with less noticeable color shift as a whole can be obtained. Therefore, an image forming apparatus capable of obtaining a high-quality full-color output image with less noticeable color shift is provided at low cost.

The present embodiment is merely an example, and does not limit the present invention. Therefore, of course, the present invention provides various improvements without departing from the gist thereof.
Deformation is possible. For example, as shown in FIG. 9, the same effect can be obtained even if the arrangement order of the photoconductors is changed. Further, as shown in FIG. 10, the photosensitive drums 3M, 3C, 3
Y can be driven by a motor M4 via one timing belt B6. This further reduces the number of timing belts used, which is more advantageous in terms of cost.

Next, a third embodiment will be described. The image forming apparatus according to the third embodiment has the same basic configuration as the image forming apparatus according to the first embodiment, but has a different drive system for the photosensitive drum. That is, in this image forming apparatus, as shown in FIG. 11, the timing belt B1 is hung on the motor M1 and the pulley 13K, the timing belt B4 is hung on the motor M4 and the pulley 13M, and the motor M4 and the pulleys 13C and 13C.
The timing belt B5 is hanged on Y. As a result, when each motor rotates, each pulley, that is, each photoconductor drum rotates via each timing belt. In particular, the photosensitive drums 3M, 3C, 3Y
Are rotated by driving the same motor M4. Further, encoders 11K, 11M, 11C and 11Y for detecting the rotational speeds of the photosensitive drums 3K, 3M, 3C and 3Y are provided on the rotating shafts of the photosensitive drums 3K, 3M, 3C and 3Y.

In this image forming apparatus, when the motor M1 is driven, the pulley 13K is driven via the timing belt B1.
Is rotated. As a result, the photosensitive drum 3K is rotated. When the motor M4 is driven, the pulley 13M is rotated via the timing belt B4,
The pulleys 13C and 13Y are rotated via the timing belt B5. As a result, the photosensitive drums 3M, 3C,
3Y is rotated by driving the motor M4. When each photosensitive drum rotates, the photosensitive drums 3K, 3K
The rotation speeds of M, 3C and 3Y are equal to those of encoders 11K and 11
M, 11C, 11Y. These detected speed signals are sent to a control unit that controls the entire image forming apparatus. The control unit transmits an output signal to each motor based on the speed signal. The output of each motor is controlled based on this output signal.

That is, the output of the motor M1 is controlled based on the speed signal detected by the encoder 11K, and the output of the motor M4 is controlled based on the average value of the speed signals detected by the encoders 11M, 11C and 11Y. Specifically, when the rotation speed of the photoconductor drum 3K and the average speed of the photoconductor drums 3M, 3C, and 3Y are higher than the specified speed, the output of the motors M1 and M4 is reduced to reduce the rotation. To Conversely, if the rotation speed of the photosensitive drum 3K and the average speed of the photosensitive drums 3M, 3C, 3Y are lower than the specified speed, the rotation of the motors M1 and M4 is increased by increasing the output of the motors M1 and M4. . That is,
The output control of each motor is performed so that the rotation fluctuation of each photosensitive drum is reduced.

Here, a test was conducted for color misregistration in the photosensitive drums 3M, 3C, 3Y driven by the motor M4, and the results are shown in FIGS. 12 and 13. FIG. 12 shows a case where the feedback control is not performed, and FIG. 13 shows a case where the feedback control is performed. As is apparent from FIG. 12, when the feedback control is not performed, color misregistration occurs in all of cyan (C), magenta (M), and yellow (Y). When the feedback control is executed, FIG.
As shown in the figure, although the color misregistration of yellow (Y) is slightly large, the color misregistration of cyan (C) and magenta (M) is greatly improved. I have. This is because the rotational speeds of the photosensitive drums 3M, 3C, 3Y are detected by the encoders 11M, 11C, 11Y, and the photosensitive drums 3M, 3C, 3Y are detected based on the average of these rotational speeds.
This is because the output of the motor M4 is feedback-controlled so that the rotational fluctuations of M, 3C, and 3Y are reduced on average. Although not shown, the color misregistration of black (K) is of course also improved. For this reason, a high-quality full-color output image in which color shift is not conspicuous as a whole is obtained.

As described above in detail, according to the image forming apparatus of the third embodiment, the photosensitive drums 3Y, 3Y
3C and 3M are driven by a motor M4 which is the same drive source via timing belts B5 and B4.
The photosensitive drum 3K is driven by a motor M1. Thus, the number of motors and timing belts used can be reduced. Then, the photosensitive drums 3M, 3
The rotation speeds of C and 3Y are determined by encoders 11M, 11C and 11
Y is detected, and the output of the motor M4 is feedback-controlled based on the average value of the detected speed signals. The rotation speed of the photosensitive drum 3K is
1K, and the output of the motor M1 is feedback-controlled based on the detected speed signal. Thereby, since the color shift is improved, a high-quality full-color output image in which the color shift is not conspicuous as a whole can be obtained. Therefore, an image forming apparatus capable of obtaining a high-quality full-color output image with less noticeable color shift is provided at low cost.

The present embodiment is merely an example, and does not limit the present invention. Therefore, of course, the present invention provides various improvements without departing from the gist thereof.
Deformation is possible. For example, as shown in FIG. 14, a higher quality output image can be obtained by independently driving the photosensitive drum 3M (or 3C or 3Y) by the motor M2.

Finally, a fourth embodiment will be described. The image forming apparatus according to the fourth embodiment has the same basic configuration as the image forming apparatus according to the first embodiment, but has a different drive system for the photosensitive drum. That is, in this image forming apparatus, as shown in FIG. 15, the timing belt B1 is hung on the motor M1 and the pulley 13K, the timing belt B4 is hung on the motor M4 and the pulley 13Y, and the motor M4 and the pulleys 13M and 13
C and a timing belt B5 are hung. As a result, when each motor rotates, each pulley, that is, each photoconductor drum rotates via each timing belt. In particular, the photosensitive drums 3Y, 3M, 3C
Are rotated by driving the same motor M4. Also, the rotating shafts of the photosensitive drums 3K and 3M include:
An encoder 11K for detecting these rotational speeds,
11M are provided. Furthermore, pulleys 13Y, 13
M, 13C are engraved with alignment marks 14Y, 14M, 14C for adjusting their phases. Then, with the alignment marks 14Y, 14M, and 14C aligned at the top position as shown in FIG.
Y, 13M, and 13C are assembled. Thus, the pulleys 13Y, 13M, and 13C rotate in a state in which the phases of the eccentricities match.

In this image forming apparatus, when the motor M1 is driven, the pulley 13K is driven via the timing belt B1.
Is rotated. As a result, the photosensitive drum 3K is rotated. When the motor M4 is driven, the pulley 13Y is rotated via the timing belt B4,
The pulleys 13M and 13C are rotated via the timing belt B5. As a result, the photosensitive drums 3Y, 3M,
3C is rotated by driving the motor M4. When each photosensitive drum rotates, the photosensitive drums 3K, 3M
Are detected by the encoders 11K and 11M. These detected speed signals are sent to a control unit that controls the entire image forming apparatus. The control unit transmits an output signal to each motor based on the speed signal. The output of each motor is controlled based on this output signal.

That is, the output of the motor M1 is controlled based on the speed signal detected by the encoder 11K, and the output of the motor M4 is controlled based on the speed signal detected by the encoder 11M. Specifically, the photosensitive drums 3K and 3K
If the rotation speed of M is higher than the specified speed, the motor M
1 and M4 are reduced to slow down the rotation. Conversely, when the rotation speeds of the photosensitive drums 3K and 3M are lower than the specified speed, the outputs of the motors M1 and M4 are increased to increase the rotation speed. That is,
The output control of each motor is performed so that the rotation fluctuation of each photosensitive drum is reduced.

Here, a test for color misregistration on the photosensitive drums 3Y, 3M, 3C driven by the motor M4 was performed, and the results are shown in FIGS. 16 and 17. FIG. 16 shows a case where the feedback control is not performed, and FIG. 17 shows a case where the feedback control is performed. As is clear from FIG. 16, when the feedback control is not performed, color misregistration occurs in all of cyan (C), magenta (M), and yellow (Y). In addition, it can be seen that the phases of the waveforms of the respective color shifts, that is, the phases of the pulleys 13Y, 13M, and 13C match. Then, when the feedback control is executed, the color misregistration of cyan (C) and magenta (M) is improved as shown in FIG. That is, the rotation speed of the photosensitive drum 3M is detected by the encoder 11M, and based on the rotation speed, the output of the motor M4 is feedback-controlled so as to reduce the rotation fluctuation of the photosensitive drum 3M. This is because they are in phase with each other. Although not shown, the color misregistration of black (K) is of course also improved. On the other hand, it has been empirically known that the yellow color shift is not changed, but the yellow color shift is inconspicuous. For this reason, a high-quality full-color output image in which color shift is not conspicuous as a whole is obtained.

As described in detail above, according to the image forming apparatus of the fourth embodiment, the photosensitive drums 3M,
3C and 3Y are driven by a motor M4, which is the same drive source, via timing belts B5 and B4.
The photosensitive drum 3K is driven by a motor M1. Thus, the number of motors and timing belts used can be reduced. Then, the rotation speed of the photosensitive drum 3M is detected by the encoder 11M, and the output of the motor M4 is feedback-controlled based on the detected speed signal. The rotation speed of the photosensitive drum 3K is detected by the encoder 11K, and the output of the motor M1 is feedback-controlled based on the detected speed signal. Further, the pulleys 13Y, 13M, 13C are assembled so that their phases match. By these,
Since the color shift of each color is improved, a high-quality full-color output image in which the color shift is inconspicuous as a whole can be obtained. Therefore, an image forming apparatus capable of obtaining a high-quality full-color output image with less noticeable color shift is provided at low cost.

Note that the present embodiment is merely an example, and does not limit the present invention in any way. Therefore, of course, the present invention provides various improvements without departing from the gist thereof.
Deformation is possible. For example, as shown in FIG. 18, the same effect can be obtained only by assembling only the phases of the pulleys 13M and 13C.

As an embodiment of the present invention, an example in which the toner images on the respective photosensitive drums are directly superimposed and transferred directly on the copy paper P has been exemplified, but the toner images on the respective photosensitive drums are transferred on a transfer belt or the like. And may transfer the laminated toner image on the intermediate transfer member to the copy sheet P. Further, a gear can be used instead of the timing belt. The order in which the photosensitive drums are arranged is merely an example, and it is needless to say that the present invention is not limited to these.

[0046]

As described above, according to the dandem type color image forming apparatus of the present invention, the color misregistration of the photoconductor of each color can be effectively suppressed with a simple structure. For this reason, a high-quality full-color output image with less noticeable color shift as a whole can be obtained. Accordingly, a tandem-type color image forming apparatus capable of obtaining a high-quality full-color output image with less noticeable color shift is provided at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram schematically illustrating a schematic configuration of a drive system of a photosensitive drum in the image forming apparatus of FIG. 1;

FIG. 3 is a diagram illustrating a color shift in each photosensitive drum before executing feedback control in the image forming apparatus of FIG. 1;

FIG. 4 is a diagram showing a color shift in each photosensitive drum after performing feedback control in the image forming apparatus of FIG. 1;

FIG. 5 is a diagram illustrating a modification of the image forming apparatus according to the first embodiment.

FIG. 6 is a diagram schematically illustrating a schematic configuration of a drive system of a photosensitive drum in an image forming apparatus according to a second embodiment.

FIG. 7 is a diagram illustrating a color shift in each photosensitive drum before executing feedback control in the image forming apparatus of FIG. 6;

FIG. 8 is a diagram illustrating a color shift in each photosensitive drum after performing feedback control in the image forming apparatus of FIG. 6;

FIG. 9 is a diagram illustrating a first modification of the image forming apparatus according to the second embodiment.

FIG. 10 illustrates a second example of the image forming apparatus according to the second embodiment.
It is a figure showing a modification of.

FIG. 11 is a diagram schematically illustrating a schematic configuration of a drive system of a photosensitive drum in an image forming apparatus according to a third embodiment.

FIG. 12 is a diagram illustrating a color shift in each photosensitive drum before executing feedback control in the image forming apparatus of FIG. 11;

13 is a diagram illustrating a color shift in each photosensitive drum after executing feedback control in the image forming apparatus of FIG. 11;

FIG. 14 is a diagram illustrating a modification of the image forming apparatus according to the third embodiment.

FIG. 15 is a diagram schematically illustrating a schematic configuration of a drive system of a photosensitive drum in an image forming apparatus according to a fourth embodiment.

FIG. 16 is a diagram illustrating a color shift in each photosensitive drum before performing feedback control in the image forming apparatus of FIG. 15;

FIG. 17 is a diagram illustrating a color shift in each photosensitive drum after performing feedback control in the image forming apparatus of FIG. 15;

FIG. 18 is a diagram illustrating a modification of the image forming apparatus according to the fourth embodiment.

FIG. 19 is a diagram schematically showing a schematic configuration of a drive system of a photosensitive drum in a conventional image forming apparatus.

[Explanation of symbols]

3Y, 3M, 3C, 3K Photosensitive drum 11Y, 11M, 11C, 11K Encoder 13Y, 13M, 13C, 13K Pulley 14Y, 14M, 14C Alignment mark B1, B2, B3, B4, B5, B6 Timing belt M1, M2 M3, M4 motor

Claims (8)

[Claims] A plurality of photoconductors; a driving unit for driving a first color photoconductor and a second color photoconductor; and a rotation speed of the second color photoconductor. A tandem-type color image forming apparatus, comprising: a control unit that performs feedback control of the driving unit. 2. The tandem-type color image forming apparatus according to claim 1, wherein the control unit performs control to reduce a fluctuation in a rotation speed of the photoconductor for the second color. Color image forming apparatus. 3. The tandem type color image forming apparatus according to claim 1, wherein the second color is a color other than yellow. 4. The tandem-type color image forming apparatus according to claim 1, wherein the driving unit also drives a third one of the photoconductors, and the control unit controls the second one of the photoconductors. A tandem-type color image forming apparatus, wherein feedback control of the driving unit is performed based on a representative value of a rotation speed of a photoconductor and a rotation speed of a photoconductor for the third color. 5. The tandem type color image forming apparatus according to claim 4, wherein the second color and the third color are colors other than yellow. 6. A plurality of photoconductors, a driving unit for driving two or more of the photoconductors, and a feedback control of the driving unit based on a representative value of a rotation speed of each photoconductor driven by the driving unit. A tandem-type color image forming apparatus. 7. A tandem-type color image forming apparatus according to claim 1, further comprising a timing belt for transmitting a drive from said drive unit to each of said photoconductors. Tandem type color image forming apparatus. 8. A plurality of photoconductors, a driving unit for driving two or more of the photoconductors, a pulley provided on each photoconductor driven by the driving unit, and each of the pulleys from the driving unit. A timing belt for transmitting drive to the drive unit, and a control unit for performing feedback control of the drive unit based on one rotation speed of each photoconductor driven by the drive unit, wherein the phases of the eccentricities of the pulleys match each other. A tandem-type color image forming apparatus.