JPH08114963A - Color image forming device - Google Patents

Abstract

PURPOSE: To provide a color image forming device capable of preventing color slurring without improving dimension and attachment accuracy in an image carrying belt and a driving roll, even if thermal expansion and shrinkage occur, with suppression of increase in the cost. CONSTITUTION: The color image forming device is composed of a belt reference position detecting sensor 22 detecting the reference position of an intermediate transfer belt 15, an encoder 17A detecting the reference position of the driving roll 17, a phase shift detecting part 36 detecting a phase shift in the rotational positions of the intermediate transfer belt 15 and the driving roll 17, based on detection timing at both detected reference positions, a belt tensile force correcting value calculating part 37 calculating the tensile force correcting value of the transfer belt 15 based on the phase shift and a belt tensile force imparting device control part 38 actuating the belt tensile force imparting device 27 in accordance with the calculated tensile force correcting value.

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, and more particularly, to reducing a color shift by reducing a phase shift of a rotational position between an image carrying belt on which a color toner image is formed and a driving roll for driving the belt. The present invention relates to a prevented color image forming apparatus.

[0002]

2. Description of the Related Art A conventional color image forming apparatus includes, for example, an intermediate transfer belt driven by a driving roll. In this color image forming apparatus, R (red), G (green), and B (blue) color image signals sequentially obtained by scanning a document are transferred to IPS (Ima).
image processing, image data is processed, color image signals are read from the IPS one by one, and exposure and development are performed on the photoconductor drum to perform Y (yellow), M (magenta), and C (cyan). ),
A corresponding color toner image of BK (black) is formed.

Each color toner image is transferred to the intermediate transfer belt one by one, and a color image is formed on the intermediate transfer belt by transferring four times. The color image is transferred onto the recording medium and then fixed, whereby the color image is recorded on the recording medium.

In this color image forming apparatus, for example, as disclosed in Japanese Patent Application Laid-Open No. 2-12271, the outer diameter of a drive roll for driving the intermediate transfer belt is adjusted to adjust the circumference of the intermediate transfer belt and the drive roll. The ratio of the perimeters is set to an integral multiple so that color misregistration does not occur in each color during transfer.

In such a color image forming apparatus, when the intermediate transfer belt is driven by the drive roll, the shaft portion of the drive roll is driven by the angular velocity fluctuation frequency in terms of forming accuracy, specifically, non-roundness, eccentricity and the like. When an eccentric frequency of one rotation and one cycle occurs, and such a frequency is superimposed on the intermediate transfer belt, the peripheral speed of the intermediate transfer belt fluctuates. In particular, the eccentric frequency in the low frequency band has a great influence on the positional error between the intermediate transfer belt and the driving roll.

FIG. 11 shows the position error of the driving roll due to the above-mentioned eccentricity by curves R ₁ and R ₂ so as to correspond to the color images of the respective colors, and the driving roll causes a speed fluctuation on the intermediate transfer belt. And it depends on 2
00 to 600 μm, pp (peak to peak)
Position error k) occurs (amplitude of the curves R ₁ and R ₂ ).

The belt position detection signal B in FIG. 11 is
This is a reference position signal output every time the intermediate transfer belt makes one rotation. As is clear from the comparison between the belt position detection signal B of the 2nd (N) th rotation and the position signal R ₂ of the drive roll, there is a phase shift in the rotational position of the drive roll at the detection timing of the intermediate transfer belt.

FIG. 12 shows the image front ends P of the first color image and the second (N) th color image in conformity with each other based on the curves R ₁ and R ₂ of FIG.

The difference e (x) between the curves R ₁ and R ₂ is the color shift amount. This color shift amount e (x) is obtained by comparing the curve R ₁ with Asin.
Assuming that (x + γ) -Asin ωγ, the following formula (1)
Indicated by

[Equation 1] Furthermore, when the equation (1) is approximated,

[Equation 2] Next, based on the formula (2), the belt surface position error A =
Assuming that the phase difference between the belt circumference and the roll circumference is 0.2 mm, the driving roll diameter is 30 mm, the belt circumference is 2 mm, and the belt angular velocity is ω, the image formation is performed by four belt rotations.

(Equation 3) Therefore, the maximum value of color misregistration | e (x) | max is

[Equation 4] Becomes

Normally, it is possible to recognize that the color shift is about 0.1 mm, and therefore it is necessary to set it to 0.05 mm or less in order to obtain a high image quality.

Generally, there are variations (tolerances) in the peripheral length of the intermediate transfer belt, and when the intermediate transfer belt is replaced in the market, due to the difference in the belt peripheral length, the belt peripheral length becomes different from the belt peripheral length at the time of superimposing each color. A phase shift occurs due to the difference in roll circumference. The occurrence of this phase shift hinders the matching of the image leading edge positions during the multiple transfer of color images, and as a result, causes the color shift.

Therefore, in the conventional color image forming apparatus, in order to reduce the color shift to 0.05 mm or less, the peripheral length of the intermediate transfer belt, the dimensional accuracy such as the outer diameter of the driving roll and the roundness, and these It is necessary to improve the mounting accuracy when assembling.

[0013]

However, according to the conventional color image forming apparatus, there is a limit to increase the above-described dimensional accuracy and mounting accuracy, and even if the accuracy is increased, thermal expansion based on temperature change is caused. It is difficult to compensate for the reduction in accuracy due to contraction. Naturally, the higher the precision, the higher the cost. These problems are common to other color image forming apparatuses, such as an apparatus that superimposes color toner images on a photosensitive belt without using an intermediate transfer belt. Therefore, an object of the present invention is to provide a color image forming apparatus that prevents color misregistration without increasing the dimensional accuracy and mounting accuracy of the image bearing belt and the drive roll.

Another object of the present invention is to provide a color image forming apparatus capable of preventing color misregistration even if there is an error in the belt circumference due to belt replacement.

Still another object of the present invention is to provide a color image forming apparatus capable of preventing color misregistration without increasing cost.

[0016]

SUMMARY OF THE INVENTION The present invention prevents color misregistration without increasing the dimensional accuracy and mounting accuracy of the image bearing belt and the drive roll, and prevents color misregistration even if there is an error in the belt circumference due to belt replacement. Further, in order to suppress the cost increase and prevent the color misregistration, the first position for detecting the reference position provided on the drive roll
Of the drive roll and the image bearing belt based on the detection of the reference positions of the first and second detecting means. There is provided a color image forming apparatus having a phase shift detecting unit that detects a shift and a belt period changing unit that advances or retards the phase of a belt rotation position by changing the tension of an image carrying belt.

[0017]

According to the color image forming apparatus of the present invention, when the first and second detecting means detect the reference positions of the driving roll and the image carrying belt, the phase shift detecting means detects the driving roll and the image based on the detection result. The phase shift of the rotation position of the carrier belt is detected. When the phase shift is detected, the belt period changing means changes the tension of the image bearing belt at the timing when the color toner image is not formed to reduce the phase shift. The circumference of the image bearing belt changes based on the change in belt tension, and the cycle changes based on the change in circumference.

[0018]

First Embodiment A color image forming apparatus of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of a color image forming apparatus using an intermediate transfer belt. This color image forming apparatus includes an image input apparatus 1 for scanning an original image, and an image output apparatus for printing on recording paper based on an image signal scanned by the image input apparatus 1 and processed by an image processing apparatus (not shown). It is composed of 8.

The image input device 1 includes a lamp 3 for irradiating a document (not shown) placed on a transparent document table 2 with light.
And the reflection mirrors 4 and 5 that reflect the reflected light from the original,
A lens 6 that focuses the reflected light from the mirror 5, and a lens 6
And an electric charge imaging device (CCD) 7 on which the light focused by the above is incident. The electric charge imaging device 7 simultaneously separates the incident light into R, G and B signals and reads them.

The image output device 8 separates the R, G and B signals obtained by the image input device 1 into Y (yellow), M (magenta), C (cyan) and BK (black) and stores them. IPS (Image Proses) not shown
9A of laser light source based on image data obtained by performing image processing with IPS
Oscillates the modulated laser light, and the polygon mirror 9B
An image writing device 9 which is deflected by a mirror, and a mirror 10 which reflects a laser beam emitted from the image writing device 9 in a scanning direction,
The photosensitive drum 11 to which the laser light reflected by the mirror 10 is irradiated and the developing materials of the toners of Y, M, C, and BK are arranged at intervals of 90 degrees in the circumferential direction, and are rotated at the time of development to obtain respective colors. And a developing unit 12 of a rotary type that supplies the corresponding toner to the surface of the photosensitive drum 11, and a charger 13 around the photosensitive drum 11 and a photosensitive member for removing the toner remaining on the photosensitive drum 11. A body cleaner 14 is arranged.

Below the photoconductor drum 11, a toner image formed on the surface of the drum is transferred to a thickness of 0.05 to
An intermediate transfer belt device 16 having a polyimide intermediate transfer belt 15 of 0.3 mm and a perimeter of 200 to 600 mm is provided. The intermediate transfer belt 15 is driven by a driving roll 17 having a diameter of 20 to 50 mm, and a supporting roll 18, 19
Supported by. An encoder 17A for detecting a reference position at the time of rotation is attached to the rotary shaft of the drive roll 17, and a belt tension applying device 2 for moving the support roll 18 in the horizontal direction in the drawing is provided outside the support roll 18.
7 are provided.

Here, the drive roll 17 and the support roll 1
The intermediate transfer belt 15 is configured to rotate once when 8 and 19 rotate an integral number.

The intermediate transfer belt device 16 includes a primary transfer corotron 20 provided at a primary transfer point of the intermediate transfer belt 15, a belt cleaner 21 provided adjacent to the driving roll 17, and a reference position of the intermediate transfer belt 15. A belt reference position detection sensor (hereinafter, referred to as a sensor) 22 that detects a mark 29 (described later) provided on the sheet transfer device (tray) 23 at a secondary transfer point where the support roll 19 is located. The toner image transferred to the intermediate transfer belt 15 is transferred to the recording paper by sandwiching the recording paper (not shown) supplied through the paper supply roll 24 with the secondary transfer roll 25. The recording paper on which the toner image is transferred is belted by the fixing device 26 to fix the toner image. Further, the rotation reference position of the drive roll 17 is detected by the output of the Z phase of the encoder 17A (a description of conventional technology is omitted).

As another method of detecting the rotation reference position of the drive roll, the reference position of the motor shaft is detected from the encoder of the motor shaft (not shown) that drives the drive roll, and the reference position of the drive roll shaft is calculated from the reduction ratio. Or a method of detecting the rotation reference position from the drive motor command frequency.

FIG. 2 shows the arrangement of the intermediate transfer belt 15 and the belt tension imparting device 27. The belt tension imparting device 27 is provided with a spring 28 mounted between the belt tension imparting device 27 and the rotating shaft 18A of the support roll 18, and the support roll 18 is provided. A predetermined tension is applied to the intermediate transfer belt 15 by applying an external force to the intermediate transfer belt 15. A mark 29 having a reflectance different from that of the belt is provided on the side of the non-image forming surface of the intermediate transfer belt 15 which is conveyed by the drive roll 17 and the support rolls 18 and 19.

The mark 29 may be formed by making a hole in the intermediate transfer belt 15 or may be a means such as sticking materials having different reflectances, as long as it can detect a specific position on the belt. It doesn't matter.

FIG. 3 shows the structure of the belt tension applying device 27, in which the transmission shaft 3 for transmitting the rotational force generated by the motor 30.
1 is a rotating roller 32 that is fixed to the transmission shaft 31 and rotates.
A link 33 supported by a pin 32A rotatable about a center of the rotating roller 32 and a link 3
Link 3 connected to pin 3 by a rotatable pin 33A
4 are arranged at both ends of the rotation shaft 18A of the support roll 18, and a spring 28 is attached between one end of the link 34 and the rotation shaft 18A. The motor 30 may be a stepping motor or a motor such as a DC / AC motor.

FIG. 4 shows the belt tension applying device 27 of FIG. 3 from the side, and the link 33 changes the rotational motion of the rotary roller 32 accompanying the rotation AB of the transmission shaft 31 into a movement amount based on the eccentricity l. It is converted and transmitted to the link 34 via the pin 33A. The link 34 is moved in the horizontal direction AB by a slide rail 35 provided in the belt tension applying device 27.
To change the tension of the spring 28 attached to one end.

FIG. 5 shows a cycle correction control device of the intermediate transfer belt 15 in the color image forming apparatus of the present invention. The rotation reference position detection signal of the encoder 17A provided on the drive roll 17 and the intermediate transfer belt 15 are provided. The phase shift detection unit 36 that detects the phase shift by comparing the measurement values obtained by measuring the belt reference position detection signal of the sensor 22 that detects the generated mark 29 with a common crystal clock, and the phase shift detection. A belt tension correction amount calculation unit 37 that calculates a tension correction amount of the intermediate transfer belt 15 based on the phase shift between the drive roll 17 and the intermediate transfer belt 15 detected by the unit 36, and a belt tension correction amount calculation unit 37. The belt tension applying device 27 according to the tension correction amount
And a belt tension control unit 38 for operating the.

The operation of the color image forming apparatus of the present invention having the above structure will be described below.

When the image forming start is instructed, the laser light source 9A of the image writing device 9 outputs laser light corresponding to the color image of the first color. This laser light is deflected in the scanning direction by the polygon mirror 9B, then reflected by the mirror 10 and irradiated on the photoconductor drum 11 charged by the charger 13, thereby forming an electrostatic latent image. This electrostatic latent image is developed with the corresponding color toner in the developing device unit 12 located in the rotation direction of the photosensitive drum 11. Next, the developed color toner image is conveyed to the primary transfer point where the primary transfer corotron 20 is provided and transferred to the intermediate transfer belt 15.

The intermediate transfer belt 15 is a photosensitive drum 11.
It is driven by the drive roll 17 so as to rotate in synchronism with
Image writing is started on the photosensitive drum 11 by laser light scanning. The full-color image formed by repeating the above-described operation for each color to transfer the color toner images multiple times forms the support rolls 19 and 2 at the secondary transfer point.
The recording paper guide chute 39 is moved by the next transfer roll 25.
Is transferred to the recording paper 24A supplied by the paper transport roll 24 via the.

In the image forming process described above, the rotation reference position detection signal of the encoder 17A provided on the drive roll 17 and the belt reference position detection signal of the sensor 22 are output to the phase shift detector 36. Since the driving roll 17 has an outer diameter that makes an integer rotation when the intermediate transfer belt 15 makes one rotation, a rotation reference position detection signal is output an integral number of times in one belt cycle. The phase shift detection unit 36 uses the sensor 22.
The capture counts obtained by capturing the belt reference position detection signal and the rotation reference position detection signal of the encoder 17A with a crystal clock of several MHz are compared. Here, when there is no phase difference between the cycles of the intermediate transfer belt 15 and the drive roll 17, the capture count 0 (zero) is output to the belt tension correction amount calculation unit 37. Therefore, since the correction amount of the belt tension is also 0, the belt tension control unit 38 causes the belt tension applying device 2 to
No control signal is output to 7, and the belt tension applying device 27 does not operate.

In the above-described color image forming apparatus, for example, when the intermediate transfer belt 15 is replaced, the drive roll 17 based on the difference in the circumferential length from the intermediate transfer belt 15 before the replacement.
There may be a phase difference with the cycle of 6 rotations. Alternatively, the synchronization between the intermediate transfer belt 15 and the drive roll 17 may be deviated due to environmental changes such as temperature and humidity. Next, a case where there is a phase difference between one cycle of the intermediate transfer belt 15 and a cycle of an integral rotation of the drive roll 17 will be described.

The intermediate transfer belt 15 was replaced when the color image forming apparatus was maintained. It is assumed that the increase in belt circumference after replacement was 0.5 mm.

In this state, image formation is started and the sensor 22
The phase shift detection unit 36 captured the detection signal of 1) and the reference position detection signal of the encoder 17A with the crystal clock, and compared the periods.

FIG. 6 is a timing chart showing the detection signal a of the mark 29 by the sensor 22 and the detection signal b of the rotation reference position by the encoder 17A. IT _BK is the cycle of the detection signal a at the time of black toner transfer, IT _Y , I
T _M and IT _C are the periods of the detection signal a at the time of yellow, magenta, and cyan toner transfer. (A) shows a synchronized state, that is, a state in which an integer number of detection signals b are output in IT _BK , IT _Y , IT _M , and IT _C of each cycle IT. If not performed, the rotation reference position detection signal b becomes the period IT as shown in (B).
After the color toner image of the first color has been transferred onto the belt in _BK, occurs a detection error t to the detection signal a to start the transfer of the color toner image of the second color in the periodic IT _Y. This detection error t is due to the breaking of the relationship between the belt circumference and the circumference of the drive roll, which is an integral multiple, that is, the phase difference between the reference positions. After that, this phase difference is 2t, 3t. ． ． And accumulate.

Here, the period of n rotations of the drive roll 17 is

L / V-[(D + a) × π] / V × n = [L-{(D + a) × π} × n] /V=0.5/100=0.005 (s) --- -(6) V is the belt speed, L is the peripheral length of the intermediate transfer belt, D is the diameter of the driving roll, and a is the thickness of the intermediate transfer belt. Therefore, the detection error t is 0.005 (s). . If this detection error t is captured by a crystal clock of 1 MHz, for example,

## EQU00006 ## A capture count of 1 M (Hz) .times.0.005 (s) = 5K (Clocks)-(7) is obtained. Since this detection error t is added for each cycle of the belt, the third color IT
2t = 0.01 at the transfer start timing of _M
(S), 3t = 0.015 (s) at the transfer start timing of the fourth color IT _C.

That is, the peripheral length of the intermediate transfer belt 15 is L ±
If it fluctuates within a range of 0.5 mm, the capture count fluctuates within a range of ± 0 to 5K. Needless to say, this variation in the capture count may occur due to the thickness of the intermediate transfer belt and the variation (tolerance) in the diameter of each roll.

FIG. 7 shows a flow chart of the cycle correction of the intermediate transfer belt 15 in the color image forming apparatus of the present invention shown in FIGS. First, the phase shift detector 3
Based on the capture count output from 6, the increase or decrease of the tension of the intermediate transfer belt 15 is determined. In the case of this embodiment, the belt tension is increased. Then, the correction amount of the belt tension required for the period correction is calculated. When the correction amount of the belt tension is calculated, the adjustment amount of the spring 28 of the belt tension applying device 27 that applies the belt tension to the intermediate transfer belt 15 is calculated. When the adjustment amount of the spring 28 is calculated, the belt tension control unit 38 outputs a command pulse according to the adjustment amount of the spring 28 to the motor 30 of the belt tension imparting device 27, the motor 30 rotates, and the spring 28 is desired. Set to be the adjustment amount of. When the spring 28 is set to a desired adjustment amount, the rotary shaft 18A of the support roll 18 is displaced according to the adjustment amount of the spring 28, whereby the tension of the intermediate transfer belt 15 changes, and the tension of the intermediate transfer belt 15 changes. The cycle of the intermediate transfer belt 15 is corrected. This is because the adjustment amount of the spring is proportional to the tension of the intermediate transfer belt, and the tension of the intermediate transfer belt is proportional to the cycle.

FIG. 8 shows an LUT (Look Up Tab) showing the correlation between the cycle TR ₀ of the intermediate transfer belt 15 and the belt tension T and the tension adjustment amount P of the spring 28.
le). Intermediate transfer belt 15 measured before correction
Based on the capture count ΔTR ₀ of the detection error between the cycle A of the intermediate transfer belt 15 and the cycle A ′ of the intermediate transfer belt 15 which is the target value to be controlled, the belt tension T to be corrected corresponding to the section BB ′ of the LUT. A correction amount ΔT of is obtained. Further, based on the correction amount ΔT of the belt tension T, the adjustment amount ΔP of the spring 28 corresponding to the section DD ′ of the LUT is obtained.

The spring 28 thus obtained
Is output to the belt tension control unit 38, and the belt tension control unit 38 supplies a command pulse based on the adjustment amount ΔP of the spring 28 to the motor 30 of the belt tension applying device 27.

The motor 30 of the belt tension imparting device 27 is rotated based on the supply of the command pulse, and the tension of the spring 28 is set to be higher than the tension at the cycle A of the intermediate transfer belt 15 before correction. By increasing the tension of the spring 28, the phase shift between the roll circumference and the belt circumference is eliminated.

[0045]

Second Embodiment FIG. 9 shows a photosensitive drum 1 according to the first embodiment.
1 shows a color image forming apparatus in which the photosensitive belt 40 is driven by a driving roll 41 and a tension roll 42 instead of 1. Overlapping description of parts having the same configurations and functions as those of the first embodiment will be omitted. In this image forming apparatus, a belt reference position detection sensor 40A for detecting a belt reference position provided on the photosensitive belt 40, a roll reference position detection sensor 41A for detecting a rotation reference position of the drive roll 41, and a tension roll 42 are provided. A belt tension applying device 43 that displaces to adjust the tension of the photosensitive belt 40 is provided.

According to the color image forming apparatus having the above-mentioned structure, the belt peripheral length of the photosensitive belt 40, the driving roll 41 and the tension roll 42 and the phase difference due to the roll peripheral length can be eliminated. It is possible to prevent the occurrence of color misregistration of the color image together with the synchronism of. Further, the same effect can be obtained even when applied to a photoconductor belt of a color image forming apparatus that uses a transfer drum that holds a sheet and transfers a toner image.

[0047]

[Third Embodiment] FIG. 10 shows a multi-color toner image formed by superposing toner images of respective colors on a photosensitive belt 40 driven by a driving roll 41 and a tension roll 42, and collectively transferring the toner images onto a recording sheet. A belt tension imparting device 43 for displacing the tension roll 42 to adjust the tension of the photosensitive belt 40 is provided. Descriptions of portions having the same configurations as those of the first and second embodiments in other configurations will be omitted.

In this way, the phase shift between the intermediate transfer belt and the drive roll is detected, and the belt tension is changed based on the detected phase shift, whereby thermal expansion of the belt based on dimensional accuracy, mounting accuracy, and temperature change. It is possible to correct the deviation of the reference position due to contraction or the like. Therefore, since it is possible to correct the phase shift without increasing the belt circumference precision, the drive roll diameter precision, and the drive precision more than necessary, the color shift of the color image can be performed without increasing the cost required for manufacturing the device. Can be eliminated and high image quality can be obtained.

[0049]

As described above, according to the color image forming apparatus of the present invention, the tension of the image carrying belt is changed according to the phase shift amount between the reference position of the driving roll and the reference position of the image carrying belt. It is possible to prevent color misregistration without increasing the dimensional accuracy and mounting accuracy of the image bearing belt and the drive roll. Further, it is possible to prevent color shift regardless of thermal expansion and contraction due to temperature change, and it is also possible to suppress an increase in manufacturing cost.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a perspective view showing an intermediate transfer belt and a belt tension applying device in the color image forming apparatus of the present invention.

FIG. 3 is a plan view showing a belt tension applying device in the color image forming apparatus of the present invention.

FIG. 4 is a side view showing a belt tension applying device in the color image forming apparatus of the present invention.

FIG. 5 is an explanatory diagram showing a belt cycle correction control device in the color image forming apparatus of the present invention.

FIG. 6 is a sensor 2 in the color image forming apparatus of the present invention.
2 is a timing chart showing the detection timing of the reference position detection signal of 2 and the encoder 17A.

FIG. 7 is a flowchart showing a process of correcting a phase shift between the intermediate transfer belt and the drive roll.

FIG. 8 is a LUT in the color image forming apparatus of the present invention.
It is explanatory drawing which shows (Look Up Table).

FIG. 9 is an explanatory diagram showing another embodiment of the color image forming apparatus of the present invention.

FIG. 10 is an explanatory diagram showing another embodiment of the color image forming apparatus of the present invention.

FIG. 11 is an explanatory diagram showing a position error due to a speed variation of a belt surface due to a driving roll.

FIG. 12 is an explanatory diagram of a phase shift between a belt and a drive roll.

[Explanation of symbols]

1 image input device, 2 document table, 3 lamps, 4
5 reflection mirror 6 lens, 7 charge imaging device, 8 image output device, 9 image writing device 9A laser light source, 9B polygon mirror 10 reflection mirror, 11 photoconductor drum 12 developing device unit, 13 charger 14 photoconductor cleaner, 15 intermediate transfer belt 16 intermediate transfer belt device, 17 drive roll 18, 19 support roll, 20 primary transfer corotron 21 belt cleaner, 22 belt reference position detection sensor 23 paper transport device, 24 paper supply roll, 25
Secondary transfer roll 26 Fixing device, 27 Belt tension applying device, 28
Spring 29 mark, 30 motor 31 transmission shaft, 32 rotation roller, 32A / 33A
Pin 33/34 Link, 35 Slide rail, 36
Phase shift detection unit 37 Belt tension correction amount calculation unit, 38 Belt tension control unit 40 Photosensitive belt, 40A Belt reference position detection sensor 41 Drive roll, 41A Drive roll reference position detection sensor 42 Tension roll, 43 Belt tension applying device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masakazu Kobayashi Masakazu Kobayashi 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Business Office (72) Kimito Omori 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. On-site (72) Inventor Junichi Murakami 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A color image forming apparatus for forming a color image by superposing a plurality of color toner images on an image bearing belt rotatably driven by a drive roll, wherein a first position for detecting a reference position of the drive roll is provided. Detection means, second detection means for detecting the reference position of the image carrying belt, and rotational positions of the drive roll and the image carrying belt based on the detection of the reference position by the first and second detecting means. And a belt tension varying means for adjusting the tension of the image bearing belt according to the phase shift amount. 2. The belt tension varying means comprises a calculating means for calculating the belt tension applied according to the phase shift amount, and a tension applying means for applying the tension calculated by the calculating means to the image bearing belt. The color image forming apparatus according to claim 1, which is configured. 3. The tension calculating means calculates the belt tension based on a look-up table showing a rotation cycle of the image bearing belt and a tension applied to the image bearing belt by the tension applying means. 3. The color image forming apparatus according to claim 2, wherein the applying unit is constituted by a link that cams and an elastic member that is provided between the link and a rotation shaft of a support roll that supports the image carrying belt.