JP2002023455A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate any turbulence in an image by preventing a generation of a scar to a photoreceptor. SOLUTION: In the device, primary transfer means 30Y, M, C and K are brought into a pressurized contact with the photoreceptors 22Y, M, C and K through an intermediate recording medium 12 in a color image formation, a multi layer image is formed by transferring images of different colors that are formed at the multiple number of image forming means 20Y, M, C and K and the primary transfer means are separated from the photoreceptors 22Y, M and C of the image forming means 20Y, M and C that are other than the image forming means 20K for black color when forming a black-and-white image. When the black-and-white image is formed, the photoreceptors 22Y, M and C of the 20Y, M and C that are other than the image forming means 20K for the black color are rotated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called tandem type color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a so-called tandem type color image forming apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-28294, in which a plurality of image forming units each containing a toner of a different color are arranged side by side along an intermediate transfer belt. It has been known.

In this type of image forming apparatus, the intermediate transfer belt is pressed against the photoreceptor of each image forming unit by a primary transfer roller, while the secondary transfer roller is pressed against the intermediate transfer belt, and the intermediate transfer belt is in contact with the intermediate transfer belt. A sheet as a recording medium is supplied between the secondary transfer rollers. Images of different colors formed by the respective image forming units are primary-transferred onto the intermediate transfer belt in a superimposed manner, and the overlapped images are secondary-transferred to paper. Then, when the sheet passes through the fixing unit, the image is heated and fixed on the sheet, and is then discharged onto a discharge tray. When forming a black and white image, the primary transfer roller is retracted from the photoconductors of the image forming units other than the black image forming unit.

[0004]

However, there are cases where the intermediate transfer belt is in contact with the photosensitive member even when the primary transfer roller is retracted. In such a case, if the intermediate transfer belt is run to form a black-and-white image, the photosensitive member may be damaged, which may cause image disturbance.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide an image forming apparatus which prevents damage to a photoreceptor and has no image disturbance.

[0006]

In order to solve the above-mentioned problems, the present invention provides a plurality of image forming means for forming images of different colors including a photoreceptor, and a photoreceptor of the plurality of image forming means. An intermediate recording medium that is driven so as to be sequentially contacted, and a color image formed by the plurality of image forming units that is pressed against the photoconductor via the intermediate recording medium during color image formation. The image is transferred to the upper side to form a multiplex image, and when a black-and-white image is formed, the primary transfer means is separated from the photosensitive member of the image forming means other than the black image forming means, and is pressed against the intermediate recording medium via a sheet to perform intermediate recording. In the image forming apparatus provided with a secondary transfer unit for transferring a multiplex image on a medium to a sheet, a photosensitive member of an image forming unit other than a black image forming unit is rotated during black and white image formation. .

According to the configuration of the present invention, when forming a black-and-white image, not only the primary transfer unit is separated from the photosensitive member but also the photosensitive member of the image forming unit other than the black image forming unit is rotated. In addition, even if the intermediate recording medium is in contact with the photoreceptor, the occurrence of scratches on the photoreceptor is prevented, and image disturbance is eliminated.

Preferably, the photosensitive member is rotated at a low speed in synchronization with the running of the intermediate recording medium.

[0009]

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 10 will be described. The printer 10 includes an intermediate transfer belt 12 at a substantially central portion inside the printer. The intermediate transfer belt 12 is supported by the outer peripheral portions of the three rollers
It is designed to be driven to rotate in the direction.

Below the lower horizontal portion of the intermediate transfer belt 12, yellow (Y), magenta (M), cyan (C),
Four image forming units 20 </ b> Y, 20 </ b> M, 20 </ b> C, and 20 </ b> K corresponding to each color of black (K) are arranged along the intermediate transfer belt 12.

Each of the image forming units 20Y, 20M, 20C,
20K is a photosensitive drum 22Y, 22M, 22C, 22
K. Each photoconductor drum 22Y, 22
Around the M, 22C, and 22K, the chargers 24Y, 24M, 24C, and 24K, the print head units 26Y, 26M, 26C, and 26K, and the developing units 28Y, 28M, 28C, and 28K are sequentially arranged along the rotation direction. And each of the photosensitive drums 22Y, 22M, 22C,
Primary transfer rollers 30Y, 30M, 30 facing 22K
C, 30K and cleaners 32Y, 32M, 32C, 32
And K are arranged respectively. Print head unit 26
Y, 26M, 26C, and 26K are composed of a large number of LEDs arranged in the main scanning direction parallel to the axial direction of the photosensitive drum.

A secondary transfer roller 34 is pressed against a portion of the intermediate transfer belt 12 supported by the roller 18.
The nip between the secondary transfer roller 34 and the intermediate transfer belt is
A secondary transfer area 36 is provided.

A belt cleaner 38 is pressed against a portion of the intermediate transfer belt 12 supported by the rollers 16.
This belt cleaner 38 is for scraping off the toner remaining on the intermediate transfer belt 12 after the secondary transfer and collecting it in the waste toner box 40.

At the lower part of the printer 10, a paper feed cassette 4 is provided.
2 are removably arranged. The sheets S stacked and stored in the sheet cassette 42 are sent out one by one from the uppermost one to the transport path 46 by the rotation of the sheet feeding roller 44.

The transport path 46 is connected to the nip portion of the timing roller pair 48, the secondary transfer area 36,
The fixing unit 50 extends to the sheet discharge tray 11 through the fixing unit 50.

An AIDC (image density) sensor 52 also serving as a registration sensor is provided between the image forming unit 20K on the most downstream side of the intermediate transfer belt 12 and the secondary transfer area 36. Further, a timing sensor 54 for detecting whether or not the sheet S has arrived at the timing roller pair 48 is provided near the timing roller pair 48.

The fixing unit 50 includes a pair of rollers 56,
A fixing belt 60 supported by 58 and driven to rotate in the direction of arrow B, and a fixing roller 62 pressed against the roller 56 via the fixing belt 60 and driven to rotate in the direction of the arrow are provided. The nip portion between the fixing belt 60 and the fixing roller 62 through which the transferred paper passes forms a fixing area 64.

The intermediate transfer belt 12 will be further described. Both ends of three rollers 14, 16, and 18 for supporting the intermediate transfer belt 12 are rotatably supported by a frame 71 as shown in FIG. I have. Inside the intermediate transfer belt 12, primary transfer rollers 30Y, 30M, 30
C and 30K are provided.

These primary transfer rollers 30Y, 30M,
Each of 30C and 30K has a separating mechanism described below. Primary transfer rollers 30Y, 30M, 30C, 30K
As shown in FIGS. 2 and 4, the shaft 7 is attached to the frames 71 on both sides.
The arm 73 is rotatably supported by the tip of an arm 73 rotatably supported by the arm 2. A lever 74 extends upward near the axis of the arm 73. A spring 75 is mounted between each lever 74 and the frame 71, and the arm 73 is
By urging in the middle clockwise direction, the primary transfer rollers 30Y, 30M,
30C and 30K are pressed against the photosensitive drums 22Y, 22M, 22C and 22K via the intermediate transfer belt 12. Between the primary transfer rollers 30Y and 30M,
A cam shaft 76 is supported between the frames 71 on both sides, and two cams 77 are fixed near both ends of the cam shaft 76. The cam shaft 76 protrudes outward from one of the frames 71, and a gear 78 is fixed to the end thereof. The gear 78 meshes with a drive gear (not shown) on the apparatus main body side and is driven to rotate.

A slide plate 79 is slidably mounted on the frames 71 on both sides. Slide plate 79
A rectangular hole 80 into which the upper end of each lever 74 protrudes.
And an opening 81 into which one end of the cam 77 protrudes. From the upper ends of the levers 74 of the primary transfer rollers 30Y, 30M, 30C in pressure contact with the photosensitive drums 22Y, 22M, 22C, to the right edge in FIG. 2 of each hole 80 of the slide plate 79 into which those levers 74 protrude. The dimension S1 is smaller than the dimension S2 from the upper end of the lever 74 of the primary transfer roller 30K in pressure contact with the photosensitive drum 30K to the right edge in FIG. 2 of the hole 80a of the slide plate 79 into which the lever 74 protrudes. It is set small. The cam 7 is provided on the left edge of the opening 81 in FIG.
A protruding piece 82 with which abutment 7 contacts extends downward. Thus, when the cam 77 rotates clockwise, the projection 82
Is pressed to move the slide plate 79 in the direction a on the left side in FIG. 2 and rotate counterclockwise. As the slide plate 79 rotates clockwise by the urging force of the spring 75, To the right in the direction b.
A protruding piece 83 extends downward at the right end of the slide plate 79 in FIG. 2, and a solenoid 84 is arranged to face the protruding piece 83. When the solenoid 84 is turned on, the plunger 85 retreats against the urging force of the spring 86, and when turned off, the plunger 85 projects by the urging force of the spring 86 to move the slide plate 79 in the direction a in FIG. It is something to move.

The primary transfer rollers 30Y, 30M, 30C,
30K is a photosensitive drum 22Y, 22K as shown in FIG.
M, 22C, 22K, the intermediate transfer belt 12 and the photosensitive drums 22Y, 22M, 22C,
The separation amount T of 22K is determined by the slack amount of the intermediate transfer belt 12 and the primary transfer rollers 30Y, 30M, 30C, 30K.
It is equal to or greater than the sum of the drop due to gravity.

More specifically, the separation amount T is set so as to satisfy the following relationship, where t is the thickness of the intermediate transfer belt 12.

3t <T <15t If not more than 3t, the slack of the intermediate transfer belt 12 contacts and damages the photosensitive drums 22Y, 22M, 22C, 22K during running. As shown in FIG. 6, the winding angle θ when the endmost primary transfer roller 30Y, for example, located on the upstream side is pressed against the photosensitive drum 22Y becomes large, and discharge occurs in the X portion in FIG. 6 other than the pressed region. This is because the toner on the photosensitive drum 22Y scatters on the intermediate transfer belt 12 before reaching the pressure contact area, thereby deteriorating transferability. In this embodiment, the separation amount T is 1.2 mm when t = 0.15, and the winding angle θ of the intermediate transfer belt 12, that is, the inclination angle θ ′ of the intermediate transfer belt 12, is 1 ° or less.

On the other hand, the secondary transfer roller 34 also has a separation mechanism described below. As shown in FIG. 2, the secondary transfer roller 34 is rotatably supported at the tip of an arm 88 rotatably supported by a shaft 87 at a fixed portion of the apparatus main body. Shaft 8 by spring 89
7 is pressed against the intermediate transfer belt 12 by being urged counterclockwise. A protruding piece 90 protrudes near the shaft 87 of the arm 88, and the protruding piece 90 has a solenoid 91.
Are arranged facing each other. When the solenoid 91 is turned on, the plunger 92 retreats against the urging force of the spring 93, and when turned off, the plunger 92 projects by the urging force of the spring 93 to press the projecting piece 90, and the arm 88. Is rotated clockwise in the figure.

Next, the general operation of the printer 10 having the above configuration will be described. When an image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the printer 10, the image signal processing unit converts the image signal into a yellow, cyan, magenta, and black digital image. A signal is generated, and the signal is transmitted to the LED drive circuit for the print head. The drive circuit performs exposure by causing the print head units 26Y, 26M, 26C, 26K of the respective image forming units 20Y, 20M, 20C, 20K to emit light based on the input digital signal. This exposure is performed by the print head units 26Y, 26M,
The processing is performed with a time difference in the order of 26C and 26K. Thereby, each of the photosensitive drums 22Y, 22M, 22
An electrostatic latent image for each color is formed on the surface of C, 22K.

Each of the photosensitive drums 22Y, 22M, 22C,
The electrostatic latent image formed on the image forming device 22K is stored in each of the developing devices 28Y and 28Y.
8M, 28C, and 28K are developed to form toner images of respective colors. Then, the toner images of the respective colors are primary-transferred by the respective primary transfer rollers 30 </ b> Y, 30 </ b> M, 30 </ b> C, and 30 </ b> K so as to be sequentially superimposed on the intermediate transfer belt 12 moving in the arrow A direction.

The superimposed toner image formed on the intermediate transfer belt 12 in this manner is
Reaches the secondary transfer area 36 with the movement of. In the secondary transfer area 36, the superimposed toner images of each color are sent out from the paper feed cassette 42 to the transport path 46 by the action of the secondary transfer roller 34 and are collectively collected on the sheet S supplied by the timing roller pair 48. Is secondarily transcribed. The toner remaining on the intermediate transfer belt 12 after the secondary transfer is collected by the belt cleaner 38.

The sheet S on which the toner image has been secondarily transferred is sent to the fixing unit 50 through the transport path 46, where it passes through the fixing area 64, where the toner image is fixed on the sheet S. Then, the paper S is discharged to the paper discharge tray 11.

During the image forming job described above, when forming a color image, as shown in FIG. 2, the solenoid 84 of the intermediate transfer belt 12 and the solenoid 91 of the secondary transfer roller 34 are turned on and Plunger 8
5, 92 are retracted against the urging force of the springs 86, 93. Further, the cam 77 is at the α position,
Is in contact with 2. Each primary transfer roller 30Y, 30M,
30C and 30K are in pressure contact with the photosensitive drums 22Y, 22M, 22C and 22K via the intermediate transfer belt 12 when the arm 73 rotates clockwise by the urging force of the spring 75.

In the case of forming a black and white image, FIG.
As shown in FIG. 7, the cam 77 rotates clockwise at the β position until it comes into contact with the projection 82 of the slide plate 79. As a result, the slide plate 79 is pressed by the cam 77 and moves in the left a direction, and the edge of the hole 80 of the slide plate 79 presses the lever 74 of the primary transfer rollers 30Y, 30M, and 30C. Rotating counterclockwise against the urging force of 75, the primary transfer rollers 30Y, 30M, and 30C separate from the photosensitive drums 22Y, 22M, and 22C. On the other hand, the edge of the hole 80a of the slide plate 79 is
Since the 0K lever 74 is not pressed, the primary transfer roller 3
0K is a photosensitive drum 22K via the intermediate transfer belt 12.
It remains pressed against. As a result, only the transfer from the photosensitive drum 22K of the black image forming unit 20K to the intermediate transfer belt 12 becomes possible, and a black and white image is formed.

During the black and white image formation, the photosensitive drums 22Y, 22M, 22C of the image forming units 20Y, 20M, 20C in the non-image forming state continue to rotate without stopping. Accordingly, even if the intermediate transfer belt 12 comes into contact with the photosensitive drums 22Y, 22M, and 22C, it is possible to prevent image damage without damaging the photosensitive drums 22Y, 22M, and 22C. In addition,
When forming a monochrome image, the photosensitive drum 22 in the image forming state
K is rotated at a lower speed than at the time of color image formation, and the intermediate transfer belt 12 is also driven to run at a low speed accordingly. Therefore, if the photosensitive drums 22Y, 22M, and 22C in the non-image forming state are rotated at a low speed in synchronization with the traveling drive of the intermediate transfer belt 12, the photosensitive drums 22Y, 22M, and 22C are further damaged. Therefore, it is possible to prevent image disturbance.

During a non-job for image formation, as shown in FIG.
Rotate clockwise until it comes into contact with 2. As a result, the slide plate 79 is pressed by the cam 77 and further moves in the left a direction, and the edges of the holes 80, 80a of the slide plate 79 press the levers of the primary transfer rollers 30Y, 30M, 30C, 30K. The arm 73 further rotates counterclockwise against the urging force of the spring 75, and all the primary transfer rollers 3
0Y, 30M, 30C, and 30K are the photosensitive drums 22Y,
Separated from 22M, 22C, 22K. Further, the solenoid 91 of the secondary transfer roller 34 is turned off, and the plunger 92 protrudes by the urging force of the spring 93, and the arm 88
Is pressed. Thus, the arm 88 rotates clockwise against the urging force of the spring 89, and the secondary transfer roller 34 is separated from the intermediate transfer belt 12. As described above, during the non-job, all the primary transfer rollers 30Y, 30Y
0M, 30C, and 30K are photosensitive drums 22Y, 22M,
22C and 22K, and the secondary transfer roller 34 is separated from the intermediate transfer belt 12, so that the intermediate transfer belt 12 and the photosensitive drums 22Y, 22M,
Even if the intermediate transfer belt 12 is extracted, the intermediate transfer belt 12 is not damaged. Further, the primary transfer rollers 30Y, 30Y
Since 0M, 30C, 30K and the secondary transfer roller 34 do not press against the intermediate transfer belt 12, the intermediate transfer belt 12 is not deformed. As a result, the intermediate transfer belt 12
Disorder of the image due to scratches and deformation of the image is eliminated.

When the power is cut off due to a power failure or forced power-off during an image forming job, the solenoid 84 of the intermediate transfer belt 12 and the solenoid 91 of the secondary transfer roller 34 are turned off and their plungers 85, The projection 92 projects by the biasing force of the springs 86 and 93. Thus, the plunger 85 of the solenoid 84 of the intermediate transfer belt 12
The slide plate 79 is pressed and moved in the direction a in FIG. As a result, the edges of the holes 80 and 80a of the slide plate 79 press the levers 74 of the primary transfer rollers 30Y, 30M, 30C and 30K, and the arm 73 further rotates counterclockwise against the urging force of the spring 75. And all the primary transfer rollers 30Y, 30M, 30C, 30K are moved to the photosensitive drum 22.
Separate from Y, 22M, 22C, 22K. On the other hand, the plunger 92 of the solenoid 91 of the secondary transfer roller 34
The projecting piece 90 of the arm 88 is pressed, and the arm 88 is
9 in a clockwise direction against the urging force of No. 9. As a result, the secondary transfer roller 34 is separated from the intermediate transfer belt 12. As described above, even if the power is cut off during a job, all the primary transfer rollers 30Y, 30M, 30C, and 30K are separated from the photosensitive drums 22Y, 22M, 22C, and 22K, and the secondary transfer roller 34 is also an intermediate transfer belt. Since the intermediate transfer belt 12 is separated from the intermediate transfer belt 12, even if the intermediate transfer belt 12 and the photosensitive drums 22Y, 22M, 22C, and 22K are pulled out for maintenance or the like, the intermediate transfer belt 12 is not damaged. Further, since the primary transfer rollers 30Y, 30M, 30C, 30K and the secondary transfer roller 34 do not press against the intermediate transfer belt 12, the intermediate transfer belt 12 is not deformed.
As a result, the image is not disturbed due to the scratch or deformation of the intermediate transfer belt 12.

[0034]

As is apparent from the above description, according to the present invention, in forming a black and white image, not only the primary transfer means is separated from the photoreceptor but also the light of the image forming means other than the black image forming means. Since the body is rotated, even if the intermediate recording medium is in contact with the photoreceptor, the photoreceptor is prevented from being damaged, and has the effect of eliminating image disturbance.

[Brief description of the drawings]

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

FIG. 2 is an enlarged view of the printer shown in FIG. 1 when a color image is formed on an intermediate transfer belt.

3A is an enlarged view of the intermediate transfer belt of FIG. 2 when a black and white image is formed, and FIG. 3B is an enlarged view of the intermediate transfer belt of FIG.

FIG. 4 is a plan view of FIG. 2;

FIG. 5 is a schematic diagram illustrating a separation amount between an intermediate transfer belt and a photosensitive drum.

FIG. 6 is a schematic diagram illustrating a winding angle of an intermediate transfer belt when a primary transfer roller and a photosensitive drum are pressed against each other.

[Explanation of symbols]

 Reference Signs List 10 Printer (image forming apparatus) 12 Intermediate transfer belt (intermediate recording medium) 20Y, M, C, K Image forming unit (image forming means) 22Y, M, C, K Photoconductor drum 30Y, M, C, K Primary transfer Roller (primary transfer means) 34 Secondary transfer roller (secondary transfer means) 73, 88 Arm (separation mechanism) 74 Lever (separation mechanism) 79 Slide plate (separation mechanism) 84, 91 Solenoid (separation mechanism)

Claims (2)

[Claims] 1. A plurality of image forming means for forming images of different colors including a photoreceptor, an intermediate recording medium running and driven to sequentially contact the photoreceptors of the plurality of image forming means, and a color image At the time of formation, the image is pressed against the photoreceptor via the intermediate recording medium, and images of different colors formed by the plurality of image forming means are transferred onto the intermediate recording medium to form a multiplexed image. A primary transfer unit that is separated from the photoreceptor of the image forming unit other than the image forming unit; and a secondary transfer unit that presses against the intermediate recording medium via a sheet and transfers a multiplex image on the intermediate recording medium to the sheet. An image forming apparatus comprising: a photosensitive member of an image forming unit other than a black image forming unit when a black and white image is formed; 2. The image forming apparatus according to claim 1, wherein the photoconductor is rotated at a low speed in synchronization with the running of the intermediate recording medium.