JPH0980853A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of color slurring in an image by changing the speed of a transfer body, while reducing influence on the image to the minimum. SOLUTION: The device is provided with a traveling, or rotating image forming body 13, an image writing means 9 for scanning with an exposing beam L formed based on an image signal for every color at a prescribed cycle and writing a latent image on the image forming body 13, a transfer body 16 which travels, or rotates at the prescribed cycle in the same direction of the image forming body 13 in contact with the image forming body 13 so that a toner image formed on the image forming body is transferred to the transfer body plural times, and a driving means 123 for separately driving the image forming body 13 and the transfer body 16. Besides, the device is provided with detecting means 11 and 22 for detecting a phase difference between a scanning cycle and the traveling, or rotating cycle of the transfer body 16 and a correcting means 100 for increasing/decreasing the traveling, or rotating speed of the transfer body 16 when the toner image is not transferred to the transfer body 16, and correcting the phase difference.

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 used in a copying machine, a printer, a facsimile or the like, and more particularly to a technique for preventing color misregistration of an image.

[0002]

2. Description of the Related Art In recent years, as a color image forming apparatus such as a copying machine, an apparatus in which an image is written by a laser beam is being widely used. Conventionally, various methods and apparatuses for obtaining a color image using a laser beam have been proposed, which can be roughly classified into the following three methods.

Method 1 A latent image of the first color is formed by scanning a laser beam on the surface of a photosensitive drum or a photosensitive belt, which is an image carrier, and the latent image is developed to form a toner image of the first color. To do. Subsequently, a latent image of the second color is formed and developed, and thus, toner images of a plurality of colors are formed so as to be superposed on the surface of the image forming body, and thus the color formed on the image forming body is formed. The toner images are collectively transferred onto a recording paper which is an image carrier.

Method 2 A laser beam is scanned on the surface of the image forming body to form a latent image of the first color, and the latent image is developed to form a toner image of the first color. Is transferred to the intermediate transfer body. Subsequently, a latent image of the second color is formed on the surface of the image forming body, the toner image of the second color is developed, and this toner image is transferred to the intermediate transfer body. In this way, the toner images of a plurality of colors are superposed on the surface of the intermediate transfer body, and the color toner images thus formed on the intermediate transfer body are collectively transferred onto the recording paper.

Method 3 A laser beam is scanned on the surface of the image forming body to form a latent image of the first color, and the latent image is developed to form a toner image of the first color. Is transferred onto the recording paper. Then, a latent image of the second color is formed on the surface of the image forming body to develop the toner image, and the toner image is transferred onto the recording paper. In this way, the toner images of a plurality of colors are formed on the recording paper in a superimposed manner.

In any of the above methods, when the speed of the image forming member or the image bearing member fluctuates, a color shift occurs between the toner image transferred at that time and the toner image already transferred to the image bearing member. Will occur. Even if the speed of the image forming body does not fluctuate, if the rotation cycle of the image forming body is not an integral multiple of the scanning cycle of the laser beam, the toner image of each color is scanned up to 1 time in the sub-scanning direction. There is an inconvenience that a color shift of a minute occurs. Therefore, Japanese Patent Application Laid-Open No. 4-326374 proposes a technique for preventing the occurrence of such color shift. The color image forming apparatus according to this proposal is applied to the technique of the method 1 described above. A mark is provided on the surface of the photoconductor belt, and the mark is detected every time the laser beam is scanned to rotate the photoconductor belt. Is controlled. In particular,
By delaying the traveling of the photosensitive belt, the timing at which the tip of the image forming area reaches the scanning start position is matched with the scanning start timing of the laser beam.

[0007]

Now, let us consider a case where the above technique is applied to the above method. In the method, the color shift of the image occurs when the toner image formed on the image forming body is superposed on the toner image already transferred on the intermediate transfer body. Therefore, when the above technique is applied to the method, the traveling speed of the intermediate transfer member is adjusted when no image is being written to the image forming member so that there is no problem even if the speed of the image forming member fluctuates. It is possible to do it. However, during that time, the primary transfer is being performed from the image forming body to the intermediate transfer body, so that the speed fluctuation of the intermediate transfer body may adversely affect the primary transfer. Therefore, the present invention
To provide a color image forming apparatus using an intermediate transfer member, which can suppress the occurrence of color misregistration of the image by changing the speed of the intermediate transfer member while minimizing the influence on the image. It is an object.

[0008]

According to a first aspect of the present invention, there is provided a color image forming apparatus comprising: an image forming body which is run or rotated; and an exposure beam formed on the image forming body based on an image signal for each color. Image writing means for writing a latent image by scanning at a predetermined cycle, developing means for developing the latent image to form a toner image, and the same direction while contacting with the image forming body at a predetermined cycle. A transfer body on which the toner image formed on the image forming body is transferred a plurality of times to form a color image on the surface by being run or rotated to, and the image forming body and the transfer body, respectively. In a color image forming apparatus provided with a driving unit that is separately driven,
Detection means for detecting a phase difference between the scanning cycle and the traveling or rotating cycle of the transfer body, and the traveling or rotating speed of the transfer body when the toner image is not transferred to the transfer body. And a correction means for correcting the phase difference.

A color image forming apparatus according to a second aspect is
An image forming body that can be run or rotated, an image writing unit that writes a latent image by scanning the image forming body with an exposure beam formed based on an image signal for each color at a predetermined cycle, and the latent image. Formed on the image forming body by contacting with the developing means for developing a toner image to form a toner image and traveling or rotating in the same direction as the developing means while contacting the image forming body based on a predetermined periodic signal. A transfer body on which a toner image is transferred a plurality of times to form a color image on the surface, drive means for driving one of the image forming body and the transfer body, and a drive force of the drive means are transmitted. In a color image forming apparatus including the image forming body and a driving force transmitting means for driving the other of the transfer bodies, a detecting means for detecting a phase difference between the scanning cycle and the traveling or rotation cycle of the transfer body. And the above image When the writing of the latent image to an adult is not performed by increasing or decreasing the travel or rotational speed of the transfer member is characterized in that a correcting means for correcting the phase difference.

A color image forming apparatus according to a third aspect is
An image forming body that can be run or rotated, an image writing unit that writes a latent image by scanning the image forming body with an exposure beam formed based on an image signal for each color at a predetermined cycle, and the latent image. Formed on the image forming body by contacting with the developing means for developing a toner image to form a toner image and traveling or rotating in the same direction as the developing means while contacting the image forming body based on a predetermined periodic signal. A transfer body on which a toner image is transferred a plurality of times to form a color image on the surface, a plurality of drive sources for individually driving the image forming body and the transfer body, and the same drive signal for each drive source. In a color image forming apparatus having a driving unit for driving, a detecting unit that detects a phase difference between the scanning period and the traveling or rotation period of the transfer body, and writing of the latent image on the image forming body. Is not done To increase or decrease the travel or rotational speed of the transfer member is characterized in that a correcting means for correcting the phase difference.

(Operation) The operation of the present invention will be described below with reference to FIG. FIG. 4 is a diagram for explaining the timing from the writing of the latent image on the image forming body such as the photoconductor to the transfer of the toner image onto the transfer body. In the color image forming apparatus of the present invention, the latent image is written on the image forming body while the transfer body makes one round, and the writing is performed as shown in FIG. 4 during the writing of the latent image of each color. There are time zones that cannot be ignored. In addition,
The time zone (indicated by symbol A in the figure) from when the reference position of the transfer body reaches a predetermined position until writing of the latent image is called a "writing non-image area". Further, in the color image forming apparatus of the present invention, the toner image on the image forming body is transferred to the transfer body while the transfer body makes one round, and the time during which transfer is not performed between the toner images of the respective colors is transferred. There is a band, and its time zone (indicated by reference numeral B in the figure) is called a "transfer non-image area".

In the color image forming apparatus according to the first aspect of the present invention, since the running or rotation speed of the transfer body is changed in the transfer non-image area, there is no influence on the transferred toner image. Further, according to the first aspect of the present invention, since the driving unit that drives the image forming body and the transfer body separately is provided, the speed of the image forming body is hardly affected even if the speed of the transfer body is changed. Therefore, even if the speed of the transfer body is changed during the writing of the second color, the influence on the image written on the image forming body hardly occurs.

Further, in the color image forming apparatus according to the second and third aspects, the running or rotating speed of the transfer body is changed when the latent image is not written on the image forming body.
Changing the speed of the transfer member has no effect on the image written on the image forming member. Further, in claim 2, the image forming body and the transfer body are made to travel or rotate by one driving means,
In the third aspect, since the plurality of drive sources that individually drive the image forming body and the transfer body are driven by the same drive signal, when the drive speed of the drive means is changed, the traveling or rotation speeds of the two become the same. , There is almost no speed difference between the two. Therefore, even if the speed of the transfer body is changed during transfer,
There is almost no effect on the transferred toner image.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) First Embodiment A. Overall Configuration of Color Image Forming Apparatus An embodiment of the present invention will be described below with reference to FIGS. 1 to 7. FIG. 1 is a side sectional view showing the entire color image forming apparatus of the embodiment. The color image forming apparatus according to the embodiment is roughly configured by an image input unit 1 that scans a document and outputs an image signal, and an image output unit 8 that forms an image on a sheet based on the image signal. In the image input section 1, a document placed on the upper surface of the transparent document table 2 (not shown)
The lamp 3 is irradiated with light, and the reflected light from the document is incident on the lens 6 via the reflection mirrors 4 and 5. Lens 6
Of the incident light is converged and made incident on the charge coupled device 7 such as CCD, and the charge coupled device 7 simultaneously decomposes the incident light into each color of red (R), green (G) and blue (B). R, B,
Output G signal.

The image output unit 8 supplies the R, B, and G signals supplied from the image input unit 1 to the complementary colors yellow (Y), magenta (M), cyan (C), and black (K). ), An image processing unit (Image Processi) that decomposes and stores the image signal of each color (also referred to as Y, M, C, K signals)
ng System, indicated by reference numeral 8a only in FIG. 3). Then, the image signal supplied from the image processing unit 8a is modulated into the laser beam L by the image writing unit 9. The laser beam L is deflected by the polygon mirror 10a provided in the image writing unit 9, and main scanning for writing the image is performed at a constant cycle. Note that reference numeral 1
Reference numeral 0b is a motor for rotating the polygon mirror 10a.

On the optical path of the laser beam L, there is arranged an SOS sensor (detection means) 11 which detects the start of main scanning based on the transmission of the laser beam L and outputs a scanning start (SOS) signal. Further, the laser beam L that has passed through the SOS sensor 11 is reflected by the reflection mirror 12, is irradiated onto the outer peripheral surface of the photoconductor drum (image forming body) 13, and is main-scanned in the axial direction of the photoconductor drum 13. .
Then, by repeating this main scanning at a constant cycle, an electrostatic latent image of a predetermined color (for example, yellow) is written on the outer peripheral surface of the photosensitive drum 13. In FIG. 1, reference numeral 14a is a charger for uniformly charging the outer peripheral surface of the photosensitive drum 13 prior to writing of the electrostatic latent image, and 14b is a cleaner for removing toner remaining on the photosensitive drum 13. Is.

When the electrostatic latent image is written on the photosensitive drum 13, the developing device (developing means) 15 immediately develops the latent image. The developing device 15 has yellow, magenta, cyan, and black developing sleeves 15 a to 15 d, and supplies toner of a color corresponding to the written electrostatic latent image to the photosensitive drum 13. Then, the toner image thus formed is primarily transferred onto the intermediate transfer belt (transfer member) 16 which is always in contact with the outer periphery of the photosensitive drum 13. Then, the yellow to black toner images are sequentially transferred onto the intermediate transfer belt 16 to form a color toner image. In the figure, reference numerals 18 and 19 are support rollers for movably supporting the intermediate transfer belt 16, and 20 is a corotron for charging the intermediate transfer belt 16 with electric charges having a polarity opposite to that of the toner.

The intermediate transfer belt 16 is run by the driving roller 17 in the same direction as the rotation direction of the photosensitive drum 13 at the same speed. The belt drive motor 123 (only shown in FIG. 3) that rotates the drive roller 17 is provided separately from the motor (not shown) that rotates the photosensitive drum 13. Therefore, even if the running speed of the intermediate transfer belt 16 is increased or decreased to be different from the rotation speed of the photoconductor drum 13, the rotation speed of the photoconductor drum 13 is almost unaffected and remains substantially constant.

As shown in FIG. 2, a mark M having a light reflectance different from that of the intermediate transfer belt 16 is formed on a side portion of the surface of the intermediate transfer belt 16. The mark M is detected by a mark sensor (detection means) 22 arranged so as to face the intermediate transfer belt 16, and at that time, the mark sensor 22 is detected.
Outputs the belt reference signal TR0. The position of the intermediate transfer belt 16 at that time is the reference position (Home Positio
n). In FIG. 1, reference numeral 23 is a cleaner for removing the residual toner on the intermediate transfer belt 16, and 25 is a cleaner.
Is a secondary transfer roller which is arranged so as to be capable of coming into contact with and separating from the supporting roller 19. The sheets stacked on the sheet feed tray 26 are taken out one by one by the sheet feed roller 27 and supplied to the nip portion between the secondary transfer roller 25 and the support roller 19. At that time, the paper is charged to the opposite polarity to the toner by a charger (not shown). As a result, the toner on the intermediate transfer belt 16 is secondarily transferred to the paper at the nip portion. In this way, the sheet on which the color toner image is secondarily transferred from the intermediate transfer belt 16 is sent to the fixing device 28 and the toner image is fixed.

B. Control Mechanism of Color Image Forming Apparatus FIG. 3 is a control block diagram of the color image forming apparatus. In the figure, reference numeral 102 is a main controller. The main controller 102 generates various control signals for controlling each unit of this color image forming apparatus. Also, reference numeral 10
Reference numeral 0 is a control unit that controls the traveling speed of the intermediate transfer belt 16 in order to correct the traveling speed, and 101 is an image writing timing control unit. The image writing timing control unit 101 inputs the belt reference signal TRO output from the mark sensor 22 and then counts a predetermined number of SOS signals input from the SOS sensor 11 to write start signal.
Activate Page Sync. Then, triggered by this, the Y, M, C, and K signals stored in the image processing unit 8a are output to the image writing unit 9.

The control unit 100 includes an SOS signal output from the SOS sensor 11 and a belt reference signal TR.
0 is input. Then, the control unit 100 calculates the phase difference between the running cycle of the intermediate transfer belt 16 and the scanning cycle of the polygon mirror 10a from these signals, and the correction signal for increasing or decreasing the running speed of the intermediate transfer belt 16 from the result of this operation. Is output to the reference clock generator 120. The reference clock generator 120 includes a PLL (Phase Locked L
A VCC (Voltage Control Oscilater) using oop) is used, and a reference clock having a frequency proportional to the input voltage is output to the drive motor control unit 121. The drive motor controller 121 supplies the belt drive motor 123 with an exciting current having a frequency corresponding to the supplied reference clock. As the belt drive motor 123, a stepping motor, a DC brushless motor, or the like is used.

Further, a transfer start signal BTR indicating the transfer start timing output from the main controller 102 is input to the control section 100, and the output of the correction signal and the output stop timing are controlled. . That is, in this embodiment, as will be described later, in the primary transfer non-image area, the intermediate transfer belt 16
In order to change the traveling speed of No. 1, the timing of starting the speed change and the timing of stopping the speed change are controlled based on the transfer start signal BTR. In the second embodiment of the present invention, since the traveling speed of the intermediate transfer belt 16 is changed in the writing non-image area, the control unit 100 has
A write start signal Page Sync output from the image write timing control unit 101 is also input.

C. Operation of Color Image Forming Apparatus FIG. 5 shows the timing from the detection of the belt reference signal TR0 by the image writing timing control unit 101 to the start of image writing in the first and second colors. . As shown in this figure, the scanning by the laser beam L is always performed, and the signal from the SOS sensor 11 is always generated at a constant cycle.
Only when c is output, the Y, M, C and K signals are converted into the laser beam L. Therefore, image write signal Page Sync
The image is not written even if scanning is performed by the laser beam L until is output. Further, the laser beam L reaches the image forming area of the photosensitive drum 13 at the same time when it has finished passing through the SOS sensor 11. For this reason, as shown in FIG.
It starts at the timing of the fall of the signal from the S sensor 11. Therefore, in this embodiment, the falling edge of the signal from the SOS sensor 11 is used as the SOS signal indicating the start of scanning.

Now, the image writing timing control unit 101
As shown in FIG. 5, when the first SOS signal is detected after detecting the belt reference signal TR0 of the first color (yellow), after that, N SOS signals are counted and then the image writing signal Page Sync is set. Activate. As a result, the image of the first color is written and subsequently developed with the toner of the first color. Similarly, after detecting the belt reference TR0 of the second color (magenta), the first S
When the OS signal is detected, N SOS signals are counted after that, and the image writing signal Page Sync is activated. As a result, the image of the second color is written and subsequently developed with the toner of the second color.

Here, the belt reference signal TR0 of the first color
Assuming that the time until the first SOS signal is detected after detection of T is T ₁ and the cycle of the SOS signal is T _SOS , the time from the detection of the belt reference signal TR0 of the first color to the start of image writing is “ T ₁ + T _SOS × N ”. In contrast, the time to detect the first SOS signal after the detection of the second color of the belt reference signal TR0 When T _2, until the image write start from the detection of the second color of the belt reference signal TR0 Is "T ₂ + T _SOS × N". Therefore, the time lag T _E from the detection of the belt reference signal TR0 to the writing of the first color and the second color is “T ₂ −T ₁ ]”
(However, T ₁ <T ₂ ). As described above, the writing start timing of the latent image of the second color is delayed from the writing timing of the latent image of the first color by “T ₂ −T ₁ ”, and this time shift T _E is indicated by an arrow in FIG. As indicated by A and B, it is expressed as a distance shift from the mark M provided on the intermediate transfer belt 16 to the transfer start position.

The positional deviation L _E between the writing start positions of the first and second colors on the photosensitive drum 13 is zero speed fluctuation from the belt reference position to the writing start, and the laser beam resolution is 400 dpi (scan line pitch). : 25.4m
When m / 400 = 63.5μm) to become _{L E = (T 1 -T 2} ) / T SOS × 64.5μm. Therefore, if this state is left as it is and the second color toner image is transferred onto the first color toner image and superimposed, a maximum color shift of 64.5 μm occurs.

A specific example will be described with reference to FIG. Traveling cycle T _TR0 of the intermediate transfer belt 16
Is 3300 ms, the count number N of the SOS signal is 625,
The time T _A from the first SOS signal detection after the detection of the belt reference signal TR0 to the start of writing the latent image is 250 ms, and 1 from the first SOS signal detection after the detection of the belt reference signal TR0.
The time T _{B ′} until the start of the next transfer is 890 ms, the time T _PS for writing the latent image on the photosensitive drum 13 is 2620 ms, and the time T _BTR for the primary transfer on the intermediate transfer belt 16 is 2930 m.
Let s. In this case, the time of the writing non-image area is T _A
(250 ms), the time T of the non-image area of the primary transfer
_{Since B} is “T _TR0 −T _BTR ”, it is 320 ms.

The time from the detection of the belt reference signal TR0 to the first SOS signal detection (hereinafter referred to as "blank time") is T ₁ , T ₂ , T ₃ and T ₄ from the first color to the fourth color. And 200μm, 70μm, 360μ respectively
m and 200 μm. Then, when this state is left and the transfer of the second and subsequent colors is performed, the positional deviation amount L _E for the toner image of the first color becomes the following value. The resolution of the writing scan is 400 dpi (1 line = 63.5 m).
m). Color deviation amount L _E of second color: (T ₂ −T ₁ ) / T _SOS × 63.
5 = (70-200) /400*63.5=-20.6
μm Third color misregistration amount L _E : (T ₃ −T ₁ ) / T _SOS × 63.
5 = (360-200) /400×63.5=25.4
μm fourth color of the color shift amount _{L E: (T 4 -T 1} ) / T SOS × 63.
5 = (200-200) /400×63.5=0 μm

Therefore, in this embodiment, the running speed of the intermediate transfer belt 16 is changed at a constant speed variation rate within a predetermined time before the second color toner image is overlaid on the first color toner image. Thus, the positional deviation of the toner image on the intermediate transfer belt 16 caused by the deviation of the writing start position corresponding to L _E is corrected. Of course, the third color, the fourth
The writing start position is similarly corrected before the colors are overlapped. In the present embodiment, the correction is performed by the photosensitive drum 1.
Since the motor 3 and the intermediate transfer belt 16 are rotated or run by separate motors, they are performed in the above-mentioned primary transfer non-image area.

The operation of correcting the writing position will be described with reference to the flowchart of FIG. First, the timer built in the control mechanism of the color image forming apparatus is reset, and then the timer starts counting after the first belt reference signal TR0 is detected (steps S1 to S3). Then, when the first SOS signal is detected, the counting by the timer is ended, and the count value T ₁ at that time is stored in the memory (steps S4 to S6). Next, the count value T _n from the detection of the second belt reference signal TR0 to the detection of the first SOS signal (in this case, n =
2) is stored in the memory (steps S7 to S12).

Next, the count values T ₁ and T _n are subtracted from each other, and the positional deviation amount L _E between the writing start positions of the first color and the nth color (n = 2 in this case) on the intermediate transfer belt 16 is subtracted.
Is calculated, and the intermediate transfer belt 1 is calculated based on the positional deviation amount L _E.
The correction amount P of the speed of the motor that drives 6 is set (steps S12 to S14). The correction amount P is a coefficient for changing the frequency of the reference clock generated from the reference clock generation unit 120. For example, 0.999900,0.
999905, 0.999910, ..., 1,1.00
The coefficient is set at intervals of 5 ppm, such as 0005, 1.000010, ..., And the coefficient corresponding to the deviation L _E obtained by the calculation is selected as the correction amount P.
Then, this correction amount P is multiplied by the initial frequency of the reference clock, and the result of this calculation is used as the frequency of the reference clock output from the reference clock generator 120. As a result, the running speed of the intermediate transfer belt 16 increases or decreases with respect to the initial steady speed.

The writing position is corrected by increasing or decreasing the traveling speed of the intermediate transfer belt 16 in the primary transfer non-image area (S15 to S20). In this case, if the correction amount of the traveling speed is large, there is a concern that slippage may occur between the intermediate transfer belt 16 and the driving roller 17, so the correction amount is made as small as possible. Therefore, the traveling speed is increased or decreased by making maximum use of the time T _B of the primary transfer non-image area. For example, in this embodiment, the time T _B is 3
Since the time is 20 ms, the speed is increased / decreased during 300 ms of that time (hereinafter, this time is referred to as correction time T _{B ′} ). If the steady speed of the intermediate transfer belt 16 is V _B ,
The relationship between the speed correction amount P and the positional deviation amount L _E is expressed by the following equation. _{P = (L E [μm]} × 10 -3) / (V B [mm / s] × T
_{B '} [ms] × 10 ^-3 )

The positional deviation amount L _E of the second color is −20.6 μ
m, which means that the latent image writing start position for the second color is delayed by 20.6 μm from the latent image writing start position for the first color. To correct this positional deviation, Intermediate transfer belt 16 on which the toner image of the first color is placed
It is necessary to slow down the running speed of. In the above equation, V _B = 16
By substituting 0, the second color misregistration amount L _E = −20.6 μm, and the correction time T _{B ′} = 300 ms, the correction amount P becomes approximately −430 PPM. That is, in order to correct the misregistration amount L _E of the second color, it suffices to run the correction time T _{B ′} of 300 ms with the running speed of the intermediate transfer belt 16 reduced by 430 PPM. Steps S17 to S20 of FIG.
Indicates processing for such correction. First, the traveling speed of the intermediate transfer belt 16 is reduced by 430 PPM (step S17), and the timer count is started (step S18). Then, when the count value of the timer reaches 300 ms, the traveling speed of the intermediate transfer belt 16 is returned to the steady speed (steps S19 and S20).

Next, the process proceeds to step S21, and the process returns to step S7 to correct the color misregistration of the next third color, and the same process as above is performed. The positional deviation amount L _E of the third color is 2
5.4 μm, which means that the latent image writing start position for the third color precedes the latent image writing position for the first color by 20.6 μm, and it is necessary to correct this positional deviation. Need to increase the traveling speed of the intermediate transfer belt 16. Then, in the above equation, the positional deviation amount L _E = 25.4 μm
The correction amount P obtained by substituting is about 530PPM,
The running speed of the intermediate transfer belt 16 is increased by 530 PPM in the primary transfer non-image area. Since the positional deviation amount L _E of the fourth color is 0, the running speed is not increased or decreased in this case. Then, when the processing of the fourth color is completed, the processing routine of the entire positional deviation correction is completed.

In the color image forming apparatus having the above structure, the intermediate transfer belt 16 is provided in the primary transfer non-image area.
Since the running speed of is changed, there is no influence on the transferred toner image. Further, since the photosensitive drum 13 and the intermediate transfer belt 16 are driven by separate motors, the speed of the photosensitive drum 13 is hardly affected even if the speed of the intermediate transfer belt 16 is changed. Therefore, even if the speed of the intermediate transfer belt 16 is changed during writing of the latent images of the second and subsequent colors, the latent images written on the photosensitive drum 13 are hardly affected. As described above, in the color image forming apparatus, it is possible to prevent the color shift of the transferred toner image without affecting the transferred toner image or the written latent image.

Particularly, in the above embodiment, the time of the primary transfer non-image area is maximally used and the intermediate transfer belt 16 is run at the correction speed during that time.
Can be reduced. As a result, slippage between the intermediate transfer belt 16 and the driving roller 17 can be prevented, and color shift of the toner image can be reliably prevented.

(2) Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the intermediate transfer belt 16 and the photoconductor drum 13 are driven by one motor. Specifically, the rotational force of the rotary shaft of one motor is branched and transmitted in two directions of the drive roller 17 of the intermediate transfer belt 16 and the photosensitive drum 13. Alternatively, the drive roller of the intermediate transfer belt 16 may be driven by a motor to press the surface of the photosensitive drum 13 against the intermediate transfer belt 16 so that the photosensitive drum 13 is rotated together.

In the structure in which the intermediate transfer belt 16 and the photoconductor drum 13 are rotated by one motor, when the rotation speed of the motor is changed, the traveling or rotation speed of the both changes similarly, and the difference between the traveling speed and the rotation speed is changed. Does not happen. Therefore,
Even if the rotation speed of the motor is changed during the primary transfer of the toner image, the transferred toner image is not affected, but if the rotation speed of the motor is changed during writing of the latent image, a latent image is formed. Disturbance occurs. Therefore, in the present embodiment, the traveling speed of the intermediate transfer belt 16 is changed in the writing non-image area where the latent image is not written. FIG. 8 is a flowchart showing such an operation.

In step S16 'of FIG. 8, the belt writing signal TR0 is detected before the image writing signal Page Syn.
It is determined whether or not it is a writing non-image area until c is output. Then, in the case of the writing non-image area, the traveling speed of the intermediate transfer belt 16 is changed to the writing non-image area in the same manner as described above, and then is returned to the steady speed, whereby the primary transfer of the second and subsequent colors is performed. Correct the start position of. In this way, since the running speed of the intermediate transfer belt 16 is changed when the latent image is not written on the photoconductor drum 13, there is no influence on the latent image written on the photoconductor drum 13. Further, the traveling speed of the intermediate transfer belt 16 is changed during the primary transfer to the intermediate transfer belt 16, but the rotation speed of the photosensitive drum 13 also changes in the same manner as the speed change of the intermediate transfer belt 16. Since there is no difference in peripheral speed between the two, there is almost no effect on the transferred toner image.

[0040] (3) Modification In each of the above embodiments with reference to the idle time T ₁ of the first color, blank time T ₂ of the second or subsequent color, ... and the difference between the idle time T ₁ of the first color Although the correction value P is calculated based on this, a predetermined reference time is stored in the memory, and the reference time and each blank time T _{1 to} T _{4 of} the first to fourth colors are stored.
The correction value P can also be calculated from the difference between and. As shown in FIG. 6, the blank time is shorter than the cycle of the SOS signal. Therefore, if the reference time is set to, for example, half the cycle of the SOS signal, the falling timing of the SOS signal is distributed before and after the ending timing of the reference time. Therefore, the difference between the reference time and the blank times T _{1 to} T _{4 of} the first to fourth colors becomes small, and the value of the correction amount P becomes small. As a result, slippage between the intermediate transfer belt 16 and the photoconductor drum 13 can be prevented. In each of the above embodiments, the traveling speed of the intermediate transfer belt 16 is changed at once, but it can be changed gradually. For example, the traveling speed is 5 for each pulse of the reference clock.
The intermediate transfer 16 can be advanced or delayed by a length corresponding to the color shift amount L _E by increasing or decreasing by PPM. Although the intermediate transfer belt 16 is used in each of the above-described embodiments, a drum-shaped transfer body can also be used. Although the photoconductor drum 13 is used in each of the above-described embodiments, a belt-shaped image forming body may be used. In each of the above-mentioned embodiments, the sensor 22 detects the mark M to output the belt reference signal TR0. However, a rotary encoder is connected to the drive roller 17 or the support roller 18 or 19 of the intermediate transfer belt 16,
It may be configured to extract the belt reference signal from the output of the rotary encoder. In each of the above-described embodiments, the toner image is superposed on the intermediate transfer belt 16 and primary-transferred to form a color toner image, and the toner image is secondarily transferred onto a sheet collectively.
For example, the above method 3 in which transfer is performed directly from a photosensitive drum onto paper.
The present invention can be applied to the color image forming apparatus. In the second embodiment, the photosensitive drum 13, the intermediate transfer belt 16 and one motor are driven, but they may be driven by separate motors and the control signals for driving may be the same. .

[0041]

As described above, according to the present invention, the positional deviation of the transferred toner image can be corrected without affecting the transferred toner image or the image written on the image forming body. It is possible (claims 1 to 3). Further, since it is possible to reduce the correction amount of the positional deviation of the transferred toner image, it is possible to solve various problems caused by the increase and decrease in the speed of the transfer body (claim 4). Furthermore, since the speed of the transfer member is gradually increased and decreased, various problems caused by the increase and decrease in speed can be eliminated (claim 5).

[Brief description of drawings]

FIG. 1 is a side sectional view showing a color image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing an intermediate transfer belt.

FIG. 3 is a control block diagram of the first embodiment.

FIG. 4 is a time chart showing timings of writing and transferring a latent image.

FIG. 5 is a time chart showing the timing from the detection of the belt reference signal to the start of writing the latent image.

FIG. 6 is a time chart showing timings of writing and transferring latent images of respective colors.

FIG. 7 is a flowchart showing the operation of the first embodiment.

FIG. 8 is a flowchart showing the operation of the second embodiment.

[Explanation of symbols]

9 ... Image writing section (image writing means), 11 ... SOS sensor (detection means), 13 ... Photosensitive drum (image forming body), 1
5 ... Developing device (developing means), 16 ... Intermediate transfer belt (transfer body), 22 ... Mark sensor (detection means), 100 ... Control section (correction means), 123 ... Belt drive motor (drive means, drive source).

Claims (5)

[Claims] 1. An image forming body which is driven or rotated,
Image writing means for writing a latent image on the image forming body by scanning an exposure beam formed on the basis of an image signal for each color in a predetermined cycle; and developing for developing the latent image to form a toner image. Means and the image forming body in contact with the image forming body in a predetermined cycle, and is run or rotated in the same direction as the image forming body, so that the toner image formed on the image forming body is transferred plural times to form a color image on the surface. A transfer body on which is formed,
In a color image forming apparatus including a driving unit that separately drives the image forming body and the transfer body, a detection unit that detects a phase difference between the scanning cycle and the traveling or rotation cycle of the transfer body. And a correction unit that corrects the phase difference by increasing or decreasing the traveling or rotation speed of the transfer body when the toner image is not transferred to the transfer body. Forming equipment. 2. An image forming body which is driven or rotated,
Image writing means for writing a latent image on the image forming body by scanning an exposure beam formed on the basis of an image signal for each color in a predetermined cycle; and developing for developing the latent image to form a toner image. And a toner image formed on the image forming body is transferred a plurality of times by contacting the image forming body based on a predetermined periodic signal and traveling or rotating in the same direction as the image forming body. A transfer body on which a color image is formed, driving means for driving one of the image forming body and the transfer body, and the driving force of the driving means is transmitted to the other of the image forming body and the transfer body. In a color image forming apparatus provided with a driving force transmitting means for driving the image forming body, a detecting means for detecting a phase difference between the scanning cycle and the traveling or rotation cycle of the transfer body, and the latent image on the image forming body. Image writing is done A color image forming apparatus comprising: a correction unit that corrects the phase difference by increasing or decreasing the traveling or rotation speed of the transfer member when not in use. 3. An image forming body that is driven or rotated,
Image writing means for writing a latent image on the image forming body by scanning an exposure beam formed on the basis of an image signal for each color in a predetermined cycle; and developing for developing the latent image to form a toner image. And a toner image formed on the image forming body is transferred a plurality of times by contacting the image forming body based on a predetermined periodic signal and traveling or rotating in the same direction as the image forming body. Color image including a transfer body on which a color image is formed, a plurality of drive sources that individually drive the image forming body and the transfer body, and drive means that drives each drive source with the same drive signal In the forming apparatus, a detection unit that detects a phase difference between the scanning cycle and the traveling or rotation cycle of the transfer member, and the transfer member when the latent image is not written to the image forming member. Traveling or rotation speed A color image forming apparatus comprising: a correction unit that increases and decreases to correct the phase difference. 4. A reference signal is output each time the transfer body makes one revolution, and a scanning start signal is output each time the scanning is started, and the first timing after the output timing of the reference signal is output. 2. The difference between the time until the timing of outputting the scanning start signal and a preset reference time is calculated, and the running or rotation speed of the transfer member is increased or decreased based on the calculation result. 4. The color image forming apparatus according to any one of 3 above. 5. The running or rotating speed of the transfer member is gradually increased or gradually decreased.
5. The color image forming apparatus according to any one of 4 to 4.