JP2002072700A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent image having no image defect by preventing a belt member from being damaged in a stabilizing mode at image non-forming time. SOLUTION: In the stabilizing mode in which photoreceptors 7Y, 7M, 7C and 7K or an intermediate transfer belt (belt member) 2 is rotated in a state where the photoreceptors 7Y, 7M, 7C and 7K are separated from the belt 2, the belt 2 is rotated when the photoreceptors 7Y, 7M, 7C and 7K are rotated, and the photoreceptors 7Y, 7M, 7C and 7K are stopped when the belt 2 is rotated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus using a belt member such as an intermediate transfer belt or a sheet conveying belt used in a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, four photoconductors and an intermediate transfer belt are opposed to each other, and the intermediate transfer belt is pressed against the photoconductors by four primary transfer rollers to form cyan (C) and magenta (C) on each photoconductor. M), yellow (Y), and black (K) toner images are formed, and the respective toner images are sequentially superimposed on the intermediate transfer belt and primary-transferred, and then the intermediate transfer belt and a secondary transfer that is pressed against the intermediate transfer belt 2. Description of the Related Art A tandem type color image forming apparatus has been known in which a color toner image is secondarily transferred to a sheet passing between rollers to obtain a color image.

[0003] This image forming apparatus, besides a color image,
Monochrome images can also be formed. When forming a monochrome image, the primary transfer roller is retracted so that the intermediate transfer belt is separated from the cyan, magenta, and yellow photoconductors to contact only the black photoconductor, and these three photoconductors are stopped. Thus, a toner image is formed only on the black photoconductor, and only the black toner image is transferred to the intermediate transfer belt to form a monochrome image. In the stabilization mode during non-image formation, the intermediate transfer belt is separated from all four photoconductors, and the intermediate transfer belt is rotated to clean the secondary transfer roller that is in pressure contact with the intermediate transfer belt. The measurement is performed, and the toner concentration is measured and the toner is replenished by rotating the photosensitive member.

[0004]

However, the intermediate transfer belt sometimes has some slack such as wrinkles or undulations due to belt meandering or distortion during forming of the belt. Even if the intermediate transfer belt is separated from the photoreceptor, if any of the intermediate transfer belts is rotated, the slack of the intermediate transfer belt comes into contact with the photoreceptor, and contact damage occurs on both the intermediate transfer belt and the photoreceptor. Then, each time the slack portion of the intermediate transfer belt comes into contact with the photoreceptor, the contact flaw of the slack portion becomes deep, and an image defect occurs. Conversely, even if the intermediate transfer belt comes into contact with the photoreceptor and damages it, if the photoreceptor rotates during image formation, the next contact will be a different part, so the intermediate transfer generated on the photoreceptor Contact flaws with the belt are dispersed rather than at one location. Further, since the surface of the photoreceptor is always shaved by the cleaning blade to a small amount and the contact flaw is also erased, the contact flaw on the photoreceptor does not matter.

In order to prevent such contact between the photosensitive member and the intermediate transfer belt, it is conceivable to set a large distance between the two members. However, in this case, the pressing force of the primary transfer roller against the photosensitive member during image formation is not sufficient. It becomes uniform and image defects occur. In addition, by rotating the photoconductor and the intermediate transfer belt together in the stabilization mode at the time of non-image formation, the occurrence of contact scratches can be prevented, but the photoconductor and the intermediate transfer belt are rotated more than necessary. As a result, there is a problem that the life is shortened.

On the other hand, when a monochrome image is formed, the intermediate transfer belt is separated from the cyan, magenta and yellow photoconductors and is brought into contact with only the black photoconductor, so that the intermediate transfer belt is located upstream from the contact portion with the black photoconductor. The side is inclined. For this reason, before the toner image on the black photoconductor is transferred to the intermediate transfer belt, a discharge occurs and an image defect occurs.

The above problem also occurs in an image forming apparatus of a type in which a toner image is directly transferred to a sheet conveyed on a sheet conveying belt having the same configuration as the intermediate transfer belt. Hereinafter, the belt member described in the present specification is a concept including an intermediate transfer belt and a paper transport belt. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and prevents damage to a belt member in a stabilization mode during non-image formation and discharge before transfer during monochrome image formation, thereby preventing image defects. It is an object to provide an image forming apparatus capable of forming a simple image.

[0008]

According to a first aspect of the present invention, there is provided a photoconductor, a belt member disposed to face the photoconductor, and a photoconductor provided via the belt member. In an image forming apparatus including a transfer member that presses and a switching unit that switches the transfer member between a state where the belt member is in contact with the photosensitive member and a state where the belt member is separated from the photosensitive member, the image forming apparatus includes a transfer member that is separated from the photosensitive member and the belt member. In the stabilization mode in which the photoconductor or the belt member is rotated, the belt member is rotated when the photoconductor is rotated, and the photoconductor is stopped when the belt member is rotated.

In the first aspect, when the photosensitive member is rotated in the stabilizing mode, the belt member is also rotated. Therefore, even if the belt member is slack, no contact scratch is generated on the slack portion, and an image defect is generated. Does not occur. In addition, when the belt member is rotated, the photoconductor is stopped. However, even if the belt member has a slack and the slack portion contacts the photoconductor to cause a damage, as described above, the photoconductor is not formed during image formation. If rotated, the next contact portion will be another portion, so the contact flaws on the photoreceptor will be dispersed instead of one place. Further, since the surface of the photoreceptor is always shaved by the cleaning blade to a small amount and the contact flaw is also erased, the contact flaw on the photoreceptor does not matter.

It is preferable that the peripheral speed of the photoreceptor and the belt member satisfies the peripheral speed of the photoreceptor ≧ the peripheral speed of the belt member. Here, if the peripheral speed of the photoconductor is the same as the peripheral speed of the belt member, no contact flaw occurs. Further, by making the peripheral speed of the belt member slower than that of the photoconductor, the belt member is not rotated more than necessary, and the life is not shortened.

[0011] The belt member may be formed of a flexible belt, and may be located above the photosensitive member. in this way,
When the belt member is above the photoreceptor, since the slack of the belt member is sagged by gravity, contact flaws may be generated. However, according to the invention, no contact flaw is generated.

According to a second aspect of the present invention, there is provided a photoreceptor comprising: a plurality of photoreceptors arranged at regular intervals on one plane; a belt member disposed to face the photoreceptors; A plurality of transfer members that press against each photoconductor via the belt member; a first state in which the belt member contacts the plurality of photoconductors; a second state in which the belt member contacts one photoconductor;
And a switching means for switching to a third state separated from all the photoconductors, wherein in the second state, the belt member is moved near a position where the belt member contacts the photoconductor. A pressing member for pressing the photosensitive member is provided.

In the second aspect of the present invention, when the belt member is in the second state of contact with one photosensitive member, the belt member is pressed toward the photosensitive member by the pressing member in the vicinity of the position where the belt member contacts the photosensitive member. Therefore, the inclination on the upstream side from the contact portion between the belt member and the photoconductor is eliminated, and discharge before transfer does not occur, and image defects do not occur.

The pressing member may be configured to press the belt member against the photosensitive member in conjunction with a switching operation of the switching means. By doing so, there is no need to provide a separate drive mechanism for the pressing member, and the structure is simplified.

[0015] The pressing member may be formed of a thin plate having elasticity against bending, and a tip of the pressing member may be pressed against the belt member in a bent state. By doing so, the thin plate is deformed following slack such as wrinkles and undulations of the belt member, and a flat surface of the belt member can be secured.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a tandem digital color printer (hereinafter, simply referred to as a “printer”) 10 according to an embodiment of the present invention.

First, a schematic configuration of the printer 1 will be described.
The printer 1 includes an intermediate transfer belt 2 as a belt member at a substantially central portion inside the printer. Intermediate transfer belt 2
Is rotatably driven in the direction of arrow A while being supported by the outer peripheral portions of the three rollers 3, 4, and 5. The roller 3 is a tension roller that applies tension to the intermediate transfer belt 2. The roller 5 is connected to a drive motor (not shown), and the rollers 3 and 4 are driven to rotate as the roller 5 rotates.

Below the lower horizontal portion of the intermediate transfer belt 2,
Four image forming units 6Y, 6M, 6C, and 6K corresponding to respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged side by side along the intermediate transfer belt 2. I have.

Each image forming unit 6Y, 6M, 6C, 6K
Have photoconductor drums 7Y, 7M, 7C and 7K, respectively. Around the photosensitive drums 7Y, 7M, 7C, and 7K, the photosensitive drums are sandwiched between the charger 8, the print head unit 9, the developing unit 10, and the intermediate transfer belt 2 in order along the rotation direction. Primary transfer rollers 11Y, 11M, 11C, 11K facing the drums 7Y, 7M, 7C, 7K;
Cleaners 12 are arranged respectively.

A secondary transfer roller 13 is pressed against a portion of the intermediate transfer belt 2 supported by the roller 5. A nip portion between the secondary transfer roller 13 and the intermediate transfer belt 2 forms a secondary transfer area 14.

A belt cleaner 15 for scraping the toner remaining on the intermediate transfer belt 2 after the secondary transfer and collecting it in a waste toner box 16 is pressed against a portion of the intermediate transfer belt 2 supported by the rollers 4. Have been.

At the lower part of the printer 1, a paper feed cassette 17 is provided.
Are removably arranged. The sheets S stacked and stored in the sheet cassette 17 are sent out one by one to the transport path 19 from the uppermost one by the rotation of the sheet feeding roller 18.

The transport path 19 is connected to the nip portion of the timing roller pair 20, the secondary transfer area 14,
It extends to the paper discharge tray 23 through the fixing roller 21 and the paper discharge roller 24.

An AIDC (image density) sensor 22 also serving as a registration sensor is provided between the image forming unit 6K on the most downstream side of the intermediate transfer belt 2 and the secondary transfer area 14. The registration sensor 22 measures an interval between patterns of each color formed on the intermediate transfer belt 2 and compares the interval with a predetermined reference value.
This is for adjusting the writing start timing of the image of each color.

The intermediate transfer belt 2 will be further described. Both ends of three rollers 3, 4, and 5 supporting the intermediate transfer belt 2 are rotatably supported on a frame 27 as shown in FIGS. Thus, the intermediate transfer belt unit 26 is formed. Inside the intermediate transfer belt 2, primary transfer rollers 11Y, 11M, 11C, 1
1K is provided.

These primary transfer rollers 11Y, 11M,
11C and 11K have a separating mechanism described below. Primary transfer rollers 11Y, 11M, 11C, 11K
As shown in FIG. 3, is rotatably supported at the tip of an arm 29 rotatably supported by a shaft 28 on both frames 27. A lever 30 extends upward near the shaft 28 of the arm 29. A spring 31 is mounted between each lever 30 and the frame 27.
By urging in the middle clockwise direction, the primary transfer rollers 11Y, 11M,
11C and 11K are pressed against the photosensitive drums 7Y, 7M, 7C and 7K via the intermediate transfer belt 2.

Between the primary transfer rollers 11Y and 11M,
A cam shaft 32 is supported between the frames 27 on both sides, and cams 33 are fixed near both ends of the cam shaft 32. As shown in FIG. 2, the cam shaft 32 protrudes outward from one frame 27, and a gear 34 is fixed to a tip of the cam shaft 32. The gear 34 is configured to be rotationally driven by meshing with a drive gear (not shown) on the apparatus main body side. Cam 3
3 has two cam surfaces 33A and 33B.

Outside the both ends of the primary transfer roller 11Y, a retract lever 35 is connected to the frame 2 via a shaft 36.
7 so as to be rotatable. The two retract levers 35 are urged counterclockwise by a torsion spring 37 as shown in FIG. One end of one retract lever 35 and the other retract lever 3
A pressing roller 38 is rotatably supported between one end of the pressing roller 5 and the other end. The other end of each retract lever 35 is in pressure contact with the cam surface 33B of the cam 33.

A support member 40 for supporting the pressing member 39 is arranged on the upstream side in the rotation direction of the intermediate transfer belt 2 with respect to the primary transfer roller 11K. This support member 40
Are rotatably supported on the shafts 41 by the frames 27 on both sides. At both ends of the support member 40, levers 42 are extended upward. A spring 43 is mounted between the lever 42 and the frame 27 so that the lever 42 is urged clockwise in FIG. 3 to press the pressing member 39 against the inner surface of the intermediate transfer belt 2. The pressing member 39 is formed of a thin plate-shaped material having elasticity against bending. In the present embodiment, the pressing member 39 is formed of a polyester film having a thickness of 0.125 mm.

A slide plate 44 is slidably mounted on the frames 27 on both sides. Slide plate 44
A rectangular hole 45 into which the upper end of the lever 30 of each of the primary transfer rollers 11Y, M, C, and K projects;
Opening 46 into which one end of the pressing member 39 protrudes, and the pressing member 39
And a notch 47 into which the upper end of the lever 42 protrudes. Lever 30 of primary transfer rollers 11Y, 11M, 11C in pressure contact with photoconductor drums 7Y, 7M, 7C
From the upper end of each of the holes 45 of the slide plate 44 into which the levers 30 protrude to the right edge in FIG.
Is set smaller than the dimension S2 from the upper end of the lever 30 of the primary transfer roller 11K in pressure contact with the photosensitive drum 11K to the right edge in FIG. 2 of the hole 45a of the slide plate 44 into which the lever 30 protrudes. ing. Also,
The dimension S3 from the upper end of the lever 42 of the pressing member 39 to the right edge in FIG. 2 of the notch 47 of the slide plate 44 into which the lever 42 protrudes is the dimension S3 of the hole 45a.
It is the same as 2. A protruding piece 4 with which the cam surface 33A of the cam 33 contacts the left edge of the opening 46 in FIG.
8 extends downward. Thereby, the cam 33
When the cam surface 33A rotates clockwise, it pushes the protruding piece 48 to move the slide plate 44 in the left direction a in FIG. 3, and when rotated counterclockwise, the slide plate 44 It moves in the right-side b direction as it rotates clockwise by the urging force of the spring 43.

The primary transfer rollers 11Y, 11M, 11C,
11K, as shown in FIG. 4B, the photosensitive drums 7Y and 7K.
When the intermediate transfer belt 2 is completely retracted from M, 7C, and 7K, the intermediate transfer belt 2 is inclined with respect to the plane where the outer peripheral surfaces of the photosensitive drums 7Y, 7M, 7C, and 7K are in contact. Here, the distance between the intermediate transfer belt 2 and the photosensitive drum 7K to which the intermediate transfer belt 2 is closest is determined in consideration of the droop of the intermediate transfer belt 2 and the drop of the primary transfer roller 11K due to gravity. It is set constant.

On the other hand, the secondary transfer roller 13 also has a separation mechanism described below. As shown in FIG. 6, the secondary transfer roller 13 is rotatably supported at the tip of an arm 52 rotatably supported by a shaft 51 at a fixed portion of the apparatus main body. The shaft 5 by the spring 53
By being urged counterclockwise around 1, it is in pressure contact with the roller 5 via the intermediate transfer belt 2. The spring 53
It is attached between the arm 52 and one end of a substantially L-shaped drive lever 55 rotatably supported by a shaft 54 at a fixed portion of the apparatus main body. A cam 56 is in contact with the other end of the drive lever 55. When the cam 56 is at the position shown in FIG. 6, the secondary transfer roller 13 is retracted from the roller 5 of the intermediate transfer belt 2, and the cam 56 is moved by about 180 °.
When rotated, the drive lever 55 rotates clockwise, the arm 52 rotates counterclockwise via the spring 53, and the secondary transfer roller 13 presses against the roller 5 of the intermediate transfer belt 2. The drive lever 55 is integrally provided with a lever 57 extending toward the AIDC sensor 22.

A sensor cover 58 extending in the width direction of the intermediate transfer belt 2 is disposed between the AIDC sensor 22 and the intermediate transfer belt 2. The sensor cover 58 includes
As shown in FIG. 7, a window 59 is formed, through which a resist pattern formed on the intermediate transfer belt 2 can be detected. Holes 60 formed at both ends of the sensor cover 58 are provided with shafts 61 at fixed portions of the apparatus main body.
The shutter lever 62 is rotatably supported by the projection 63 at the tip of the shutter lever 62. The shutter lever 62
An inclined surface 64 on which the tip of the lever 57 slides is formed. As a result, when the drive lever 55 rotates clockwise in FIG. 6 to press the secondary transfer roller 13 against it, the tip of the lever 57 slides down the inclined surface 64 of the shutter lever 62 and the shutter lever 62 Rotates clockwise in FIG. 7 against the urging force of the return spring 65,
The window 59 is shifted from the AIDC sensor 22, and the AIDC sensor 22 is covered with the sensor cover 58. As a result, the AIDC sensor 2
2 is prevented from becoming dirty. Conversely, the secondary transfer roller 13
When the drive lever 55 rotates counterclockwise in the figure to separate the shutter lever 62, the tip of the lever 57 slides upward on the slope of the shutter lever 62, and the shutter lever 62 is biased by the return spring 65 in FIG. , The window 59 coincides with the AIDC sensor 22. As a result, the resist detection by the AIDC sensor 22 can be performed during non-image formation.

The belt cleaner 15 will be further described. The belt cleaner 15 is attached to a cleaner unit 71. Cleaner unit 71
Is integrated with the intermediate transfer belt unit 26, and has therein a groove 72 for receiving the waste toner scraped off by the belt cleaner 15, as shown in FIG.
And a transport coil 73 that transports the waste toner in the groove 72 toward a discharge port (not shown) provided at one end of the groove 72.
Are provided. A hook 74 protrudes from the bottom surface of the cleaner unit 71.

The waste toner box 16 has a concave portion 75 on its upper surface.
Is formed, and the concave portion 75 is provided in the cleaner unit 71.
Of the waste toner box 16
Can be attached to and detached from the cleaner unit 71. At one end of the upper surface of the waste toner box 16, an inlet (not shown) for receiving waste toner discharged from the discharge port of the cleaner unit 71 is formed. Inside the waste toner box 16, a transport coil 76 that transports the waste toner received from the entrance located at one end to the other end is accommodated.

When the waste toner box 16 is removed, FIG.
As shown in (B), the intermediate transfer belt unit 26
The hook 74 of the cleaner unit 71 and the two protrusions 77 provided on the roller 5 side of the frame 27 of the intermediate transfer belt unit 26 can be mounted on the floor as tripods.
Thereby, it is possible to prevent the intermediate transfer belt 2 from directly contacting the floor and being damaged.

Next, the general operation of the printer 1 having the above configuration will be described. External device (eg personal computer)
When an image signal is input to the image signal processing unit (not shown) of the printer 1 from the printer, the image signal processing unit creates a digital image signal by converting the image signal into yellow, cyan, magenta, and black. The signal is transmitted to the print head LED drive circuit. This drive circuit is
Based on the input digital signal, each image forming unit 6
The Y, 6M, 6C, and 6K print heads 9 emit light to perform exposure. Thereby, each of the photosensitive drums 7Y, 7
Electrostatic latent images for each color are formed on the surfaces of M, 7C, and 7K, respectively.

The electrostatic latent images formed on the respective photosensitive drums 7Y, 7M, 7C, 7K are developed by the respective developing units 10 to become toner images of respective colors. The toner images of the respective colors are transferred to the respective primary transfer rollers 11Y, 11M, 11M.
By the action of C and 11K, primary transfer is performed on the intermediate transfer belt 2 moving in the direction of the arrow A in such a manner that the intermediate transfer belt 2 is sequentially superimposed.

The superimposed toner image thus formed on the intermediate transfer belt 2 reaches the secondary transfer area 14 as the intermediate transfer belt 2 moves. In the secondary transfer area 14, the superposed toner images of the respective colors are transferred to the sheet cassette 1 by the action of the secondary transfer roller 13.
7 to the transport path 19 and the timing roller pair 2
The secondary transfer is collectively performed on the sheet S supplied by the number 0.
The toner remaining on the intermediate transfer belt 2 after the secondary transfer is collected by the belt cleaner 15.

The sheet S on which the toner image has been secondarily transferred is sent to the fixing roller 21 through the transport path 19, where the toner image is fixed on the sheet S. Then, the paper S is discharged to the paper discharge tray 23 via the paper discharge rollers 24.

In the above-described image formation, when forming a color image, the secondary transfer roller 13 is in pressure contact with the roller 5 via the intermediate transfer belt 2 as shown in FIG. The cam surface 33A of the cam 33 is in contact with the projection 48 of the slide plate 44 at the α position. As a result, the primary transfer rollers 11Y, 11M, 11C, and 11K are
9 rotates clockwise by the urging force of the spring 31, so that the photosensitive drums 7 </ b> Y and 7 </ b>
M, 7C, 7K. Further, as shown in FIG. 5A, the cam surface 33B is at the x position and the retract lever 3 is at the position x.
5 is in contact. As a result, the pressing roller 38 presses the intermediate transfer belt 2, and the intermediate transfer belt 2 from the pressure contact portion between the photosensitive drum 7 </ b> Y and the primary transfer roller 11 </ b> Y to the roller 4 is inclined, as indicated by the two-dot chain line. Can be prevented. Assuming that the retract roller 38 is not provided, as shown by a two-dot chain line, the primary transfer roller 11
As the winding angle of the intermediate transfer belt 2 with respect to Y increases, a discharge occurs upstream of the pressure contact area, and the photosensitive drum 7Y
The upper toner scatters on the intermediate transfer belt 2 before reaching the pressure contact area, and deteriorates transferability. However, in the present embodiment, the photosensitive drum 7 is
The inclination of the intermediate transfer belt 2 on the upstream side of the pressure contact portion between Y and the primary transfer roller 11Y is eliminated, toner does not scatter, and good transferability is obtained.

In the case of forming a black and white image, FIG.
As shown in (3), the cam surface 33A of the cam 33 rotates clockwise until it comes into contact with the projection 48 of the slide plate 44 at the β position. Accordingly, the slide plate 44 is pressed by the cam 33 and moves in the left a direction, and the edge of the hole 45 of the slide plate 44 is moved to the lever 30 of the primary transfer rollers 11Y, 11M, and 11C.
As a result, the arm 29 rotates counterclockwise against the urging force of the spring 31, and the primary transfer rollers 11Y and 11Y
M and 11C are separated from the photosensitive drums 7Y, 7M and 7C. Also, as shown in FIG. 5B, the cam surface 33B
At the y position, it comes into contact with the retract lever 35 and the pressing roller 3
Reference numeral 8 retreats from the intermediate transfer belt 2. On the other hand, the edge of the hole 45a of the slide plate 44 is the lever 3 of the primary transfer roller 11K.
Since 0 is not pressed, the primary transfer roller 11K remains pressed against the photosensitive drum 7K via the intermediate transfer belt 2. Thereby, only the transfer from the photosensitive drum 7K of the black image forming unit 6K to the intermediate transfer belt 2 becomes possible,
A black and white image is formed.

When forming the black and white image, the slide plate 44
The edge of the notch 47 does not press the lever 42 of the pressing member 39, so that the pressing member 39 keeps pressing the intermediate transfer belt 2 toward the photosensitive drum 7K.
Therefore, as shown by the one-dot chain line in FIG. 9, the intermediate transfer belt 2 on the upstream side from the pressure contact portion between the photosensitive drum 7K and the primary transfer roller 11K can be prevented from being inclined. Assuming that the pressing member 39 is not provided, the winding angle of the intermediate transfer belt 2 with respect to the primary transfer roller 11K increases, as indicated by the one-dot chain line, and a discharge occurs upstream of the pressure contact area, and the photosensitive drum 7K The upper toner scatters on the intermediate transfer belt 2 before reaching the pressure contact area, and deteriorates transferability. However, in the present embodiment, the pressing roller 3
8, the pressing member 39 eliminates the inclination of the intermediate transfer belt 2 on the upstream side of the pressure contact portion between the photosensitive drum 7 </ b> K and the primary transfer roller 11 </ b> K, so that toner does not scatter and good transferability is obtained. can get.

During non-image formation, as shown in FIG. 4B, the cam 77 rotates clockwise at the γ position until it comes into contact with the projection 48 of the slide plate 44. As a result, the slide plate 44 is pressed by the cam 33 and moves further in the left a direction, and the edges of the holes 45 and 45a of the slide plate 44 press the levers 30 of the primary transfer rollers 11Y, 11M, 11C and 11K. , The arm 29 further rotates counterclockwise against the urging force of the spring 31, and all the primary transfer rollers 11
Y, 11M, 11C and 11K are photosensitive drums 7Y and 7
Separate from M, 7C, 7K. Further, as shown in FIG. 5C, the cam surface 33B moves the retract lever 3 at the z position.
5, the pressing roller 38 is further retracted from the intermediate transfer belt 2. At the same time, as shown in FIG. 4B, the edge of the notch 47 of the slide plate 44 presses the lever 42 of the pressing member 39, so that the pressing member 39 retreats from the intermediate transfer belt 2. On the other hand, the secondary transfer roller 13 is separated from the intermediate transfer belt 2.

At the time of non-image formation, a stabilization mode such as toner concentration detection and cleaning of the secondary transfer roller 13 is executed.

In detecting the toner density, the photosensitive drums 7Y, 7Y
By rotating the developing devices 10 by rotating 7M, 7C and 7K, the toner and the carrier in the developing devices 10 are stirred, and the toner concentration is detected. In this toner density detection, only the photosensitive drums 7Y, 7M, 7C, and 7K need be rotated, and the intermediate transfer belt 2 does not need to be rotated. But,
For example, if the intermediate transfer belt 2 is moved to the photosensitive drums 7Y, 7M, 7
C, 7K, the photosensitive drums 7Y, 7K
When M, 7C, and 7K are rotated, slack such as wrinkles and undulations of the intermediate transfer belt 2 cause the photosensitive drums 7Y, 7M, 7
C, 7K, the intermediate transfer belt 2 and the photosensitive drum 7
Contact flaws occur in both Y, 7M, 7C and 7K. Then, the slack portion of the intermediate transfer belt 2 is
Each time it comes into contact with 7M, 7C, 7K, the contact flaw in the slack portion becomes deep, and an image defect occurs. Therefore, in the present embodiment, the intermediate transfer belt 2 is also rotated while rotating the photosensitive drums 7Y, 7M, 7C, 7K. As a result, even if the intermediate transfer belt 2 has a slack, no contact scratch occurs at the slack portion, and no image defect occurs. At this time, if the peripheral speed of the intermediate transfer belt 2 is the same as the peripheral speed of the photosensitive drums 7Y, 7M, 7C, and 7K as in image formation, no contact flaw occurs. However, the peripheral speed of the photosensitive drums 7Y, 7M, 7C, 7K does not necessarily have to be the same as that of the photosensitive drums 7Y, 7M, 7K.
It is sufficient that the peripheral speed of C, 7K ≧ the peripheral speed of the intermediate transfer belt 2 is satisfied. Thus, by making the peripheral speed of the intermediate transfer belt 2 slower than that of the photoconductors 7Y, 7M, 7C, 7K,
The intermediate transfer belt 2 is not rotated more than necessary, and the life is not shortened. Also, the intermediate transfer belt 2
Since the photosensitive drum 7K closest to the intermediate transfer belt 2 comes into contact with the intermediate transfer belt 2, the intermediate transfer belt 2 may be rotated in synchronization with the photosensitive drum 7K.

The cleaning of the secondary transfer roller 13 is performed as a pretreatment of the intermediate transfer belt 2 when the power is turned on.
This is performed after image formation for every 200 sheets. In the cleaning of the secondary transfer roller 13, the secondary transfer roller 1
The secondary transfer roller 13 is rotated by rotating the intermediate transfer belt 2 by pressing the intermediate transfer belt 3 against the intermediate transfer belt 2. At this time, the photosensitive drums 7Y, 7M, 7C, 7K are stopped. As described above, even if the intermediate transfer belt 2 has a slack and the slack portion comes into contact with the photosensitive drums 7Y, 7M, 7C, and 7K and is damaged, as described above, the photosensitive drums 7Y, 7M, 7C, When 7K rotates, the next contacting part becomes another part, so that the photosensitive drums 7Y, 7M, 7
Contact flaws on C, 7K are dispersed rather than at one location.
Further, since the surfaces of the photosensitive drums 7Y, 7M, 7C, and 7K are constantly scraped by the cleaner 12 to a small extent, and the contact flaws are eliminated, the contact flaws on the photosensitive drums 7Y, 7M, 7C, and 7K do not matter.

In the above embodiment, the present invention has been described by taking as an example an apparatus of the type in which a toner image is primarily transferred onto an intermediate transfer belt and this toner image is further secondary-transferred onto paper. The present invention is not limited to this, and can be applied to an apparatus of a type in which a toner image is directly transferred to a sheet conveyed on a sheet conveyance belt having the same configuration as the intermediate transfer belt.

[0049]

As is apparent from the above description, according to the first aspect, in the stabilization mode in which the photoconductor or the belt member is rotated while the photoconductor and the belt member are separated from each other,
When rotating the photoreceptor, the belt member is also rotated, and when the belt member is rotated, the photoreceptor is stopped, so even if the belt member has slack, no contact scratch occurs on the slack portion, A good image without image defects can be formed.

According to the second aspect of the present invention, when the belt member is in the second state of contact with one photosensitive member, the belt member is pressed against the photosensitive member near the position where the belt member contacts the photosensitive member. Since the pressing member is provided, the inclination of the belt member is eliminated, no discharge occurs before transfer, and a good image without image defects can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a printer according to the present invention.

FIG. 2 is a partial plan view of an intermediate transfer belt of the printer of FIG.

FIG. 3 is a front view of the intermediate transfer belt of the printer of FIG. 1 when a color image is formed.

4 is a front view of the intermediate transfer belt shown in FIG. 3 when a black-and-white image is formed (A) and when no image is formed (B).

5 is a partially enlarged front view of the intermediate transfer belt shown in FIG. 3 when a color image is formed (A), when a black and white image is formed (B), and when no image is formed (C).

FIG. 6 is a rear view showing a separation mechanism of a secondary transfer roller.

FIG. 7 is a side view showing a shutter mechanism of the AIDC sensor.

FIG. 8A is a front view showing an intermediate transfer belt unit, a cleaner unit and a waste toner box, and FIG. 8B is a front view showing a state where the intermediate transfer belt unit and the cleaner unit are placed on the floor.

FIG. 9 is an explanatory view showing the operation of the pressing member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printer (image forming apparatus) 2 Intermediate transfer belt (belt member) 6Y, M, C, K Image forming unit 7Y, M, C, K Photoconductor drum 11Y, M, C, K Primary transfer roller (transfer means) 33 Cam (switching means) 39 Pressing member 44 Slide plate (switching means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AB02 AD03 BB42 BB44 BB46 BB63 2H032 AA05 AA15 BA09 BA18 BA23 BA30 CA04 CA12 CA13

Claims (6)

[Claims] A photoreceptor, a belt member disposed to face the photoreceptor, a transfer member pressed against the photoreceptor via the belt member, and the belt member contacting the transfer member with the photoreceptor. An image forming apparatus provided with a switching means for switching between a state and a state separated from the photosensitive member, wherein the photosensitive member is rotated in a stabilizing mode in which the photosensitive member or the belt member is rotated in a state where the photosensitive member and the belt member are separated from each other. An image forming apparatus wherein the belt member is rotated at the time, and the photoreceptor is stopped at the time of rotating the belt member. 2. The image forming apparatus according to claim 1, wherein the peripheral speed of the photoconductor and the belt member satisfies a relation of a peripheral speed of the photoconductor ≧ a peripheral speed of the belt member. 3. The apparatus according to claim 1, wherein said belt member is formed of a flexible belt, and is located above the photosensitive member.
Or the image forming apparatus according to 2. 4. A plurality of photoreceptors arranged at regular intervals on one plane, a belt member disposed opposite to the photoreceptors, and a plurality of photoreceptors pressed against the respective photoreceptors via the belt members. A transfer member, and switching means for switching the transfer member to a first state in which the belt member is in contact with the plurality of photoconductors, a second state in which the belt member is in contact with one of the photoconductors, and a third state in which the belt member is separated from all the photoconductors. An image forming apparatus comprising: a pressing member that presses the belt member toward the photoconductor near the position where the belt member comes into contact with the photoconductor in the second state. apparatus. 5. The image forming apparatus according to claim 4, wherein the pressing member presses the belt member toward the photosensitive member in conjunction with a switching operation of the switching unit. 6. The pressing member according to claim 4, wherein the pressing member is formed of a thin plate having elasticity with respect to bending, and a tip of the pressing member is pressed against the belt member in a bent state. Image forming device.