JP3325071B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, such as a color copying machine or a business color copying machine, for forming an image on a transfer material such as paper using a plurality of photosensitive members.
More specifically, the present invention relates to an image forming apparatus capable of forming a color image and a monochrome image.

[0002]

2. Description of the Related Art In recent years, in response to the color orientation of offices,
Color copiers have appeared.

One type of the color copying machine is a four-tandem photosensitive drum tandem system. In this method, four photosensitive drums are arranged in parallel, and on each photosensitive drum,
In this method, a toner image is formed using yellow, magenta, cyan, and black toners, and the toner images are sequentially transferred to one transfer material to obtain a color image.

In the four-tandem tandem system, a transfer material placed on a transport belt comes into contact with four photoconductors one after another to transfer a toner image. In the case other than the formation of a full-color image, for example, when only a black image is formed, the toner image is not formed on the three photosensitive drums of yellow, magenta, and cyan, and the toner image is formed by the black toner. Only do. Therefore, only the toner image of the black toner is transferred to the transfer material, and an image of only black is obtained.

As described above, in the conventional apparatus, even when only a single-color image is required, the transfer material comes into contact with the other three photoconductor drums as image carriers. Unnecessary color toner remaining on the transfer material adheres to the transfer material, deteriorating the image quality. Further, there is a problem that the life of the photosensitive member as the image carrier is shortened due to unnecessary contact of the transfer material conveying belt.

[0006]

The conventional apparatus has a structure in which the transfer material conveying belt is positioned so as to be in contact with all the image carriers in the same manner as in the case of forming a monochromatic image, as in the case of forming a color image. Thus, there have been problems such as deterioration of image quality due to mixing of toner of an unnecessary color and shortening of life of the image carrier.

SUMMARY OF THE INVENTION The present invention has been made based on the above circumstances, and it is an object of the present invention to prevent a contact between an image carrier of an image forming means and a transfer material conveying belt which are unnecessary for image formation at the time of monochrome image formation. Can avoid and improve image quality,
Another object of the present invention is to provide an image forming apparatus capable of extending the life of an image carrier.

[0008]

In order to achieve the above object, an image forming apparatus according to the present invention is capable of forming a color image and a single-color image, and includes a plurality of image carriers which are sequentially arranged. A plurality of image forming means which are provided corresponding to each other and form images of different colors on the respective image carriers, and each image carrier is stretched so that a halfway portion faces each image carrier; Transport means having a single transfer material transport belt for sequentially transporting the transfer material to the body, and a transfer means provided corresponding to each of the image carriers, for the transfer material transported by the transfer material transport belt A plurality of transfer means for transferring the images formed on the respective image carriers, and contacting the image carrier corresponding to the image forming means for forming an image of a color corresponding to the color image during color image formation And single color image The conveying direction of the transfer material at the time of
The transfer material transport belt so that it contacts only the image carrier for monochrome image formation that is disposed at the most downstream side along
The rotation axis of the image carrier for forming a monochrome image is a pivot point.
Means for displacing the belt without changing its shape.

The image forming apparatus according to the present invention is capable of forming a color image and a monochromatic image. The image forming apparatus is provided corresponding to a plurality of image carriers which are sequentially arranged. A plurality of image forming means for forming images of different colors on a body, and a transfer for extending a transfer material to each of the image carriers in such a manner that an intermediate portion is opposed to each of the image carriers. A transfer unit having a material transport belt, and an image formed on each of the image carriers on a transfer material transported by the transfer material transport belt, the image being provided for each of the image carriers. A plurality of transfer means, and a plurality of rollers for stretching the transfer material transport belt so that the intermediate portion faces each image carrier, and a rotating shaft of the image carrier for forming a monochromatic image. Can be displaced with the pivot as a pivot point A belt unit frame and a first position where the intermediate portion of the belt unit frame is brought into contact with an image carrier corresponding to image forming means for forming an image of a color corresponding to a color image Means for urging the belt unit frame constantly urged to the first position by the urging means to form an image of a color corresponding to a single-color image in a middle portion of the transfer material conveying belt. Frame displacing means for rotating and displacing against a biasing force of the biasing means at a second position contacting only the image carrier corresponding to the image forming means for performing the image forming means, and the belt for forming a color image unit frame - arm in the first position, the at the time of monochromatic image formation belt unit frame - arm second
Control means for switching and controlling the frame displacing means so as to be at the position shown in FIG.

[0010]

According to the image forming apparatus of the present invention , the angle of the stretched transfer material conveying belt can be changed between the time of forming a color image and the time of forming a single color image without changing the state of the transfer material conveying belt. This makes it possible to avoid unnecessary contact between the image carrier of the image forming means and the transfer material transport belt during the formation of a single-color image, thereby preventing unnecessary contact of the transfer material with the photosensitive drum. In addition, it is possible to solve the problem that the toner of an unnecessary color adheres to the transfer material and degrades the quality of the image, and the problem that the life of the photoconductor is shortened by unnecessary contact with the transfer material transport belt. Further, since the stretched state of the transfer material conveying belt is not changed, there is no possibility that the transfer material conveying belt will be overloaded and its service life will not be shortened.

[0011]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 schematically shows the structure of a four-tandem color copying machine as an image forming apparatus.
In this color copying machine, photosensitive drums 2Y, 2M, 2C, and 2B as four image carriers sequentially arranged in parallel are provided.
K, and the respective photosensitive drums 2Y, 2M, 2C, 2BK
2Y, 2M, 2
A plurality of image forming means 150Y, 150M, 150C, 150BK for forming images on C, 2BK, respectively, and a conveying means for sequentially conveying a transfer material 8 made of paper to the photosensitive drums 2Y, 2M, 2C, 2BK. 200, and the photoconductor drums 2Y, 2M, 2C, and 2BK, respectively, and the photoconductor drums 2Y, 2M, 2C, and 2B with respect to the transfer material 8 conveyed by the conveyance unit 200.
Transfer rollers 5Y, 5M, 5C, 5BK as a plurality of transfer means for transferring toner images formed on K, respectively.
Having.

The four image forming means 150Y and 15
0M, 150C, 150BK are solid-state scanning heads 1Y, 1
M, 1C, 1BK, a recording unit composed of a 1 × image forming optical system, etc., charging devices 3Y, 3M, 3C, 3BK, and a developing device 4
Y, 4M, 4C, 4BK, cleaning devices 6Y, 6
M, 6C, 6BK, static eliminators 7Y, 7M, 7C, 7BK
And the like.

The yellow image forming means 150Y will be described. The solid scanning head 1Y outputs exposure light to the photosensitive drum 2Y according to yellow image data sent from a print control unit (not shown). The solid-state scanning head 1Y has a structure in which minute light-emitting portions are arranged at equal intervals on a line in the main scanning direction, and responds to an on-off signal sent from a print controller in accordance with a pattern to be printed. By controlling the lighting of the individual light emitting units in the main scanning direction line, the light from the light emitting units is imaged on the photosensitive drum 2Y by the same-magnification image forming optical system that forms the light one-to-one. Perform exposure. Note that, specifically, an LED head array having a resolution of 444 DPI was used for the solid-state scanning head 1Y, and a Selfoc lens array was used for the 1 × image forming optical system.

Around the photosensitive drum 2Y, a charging device 3Y for charging the surface of the photosensitive drum 2Y, a developing device 4Y,
Transfer roller 5Y as transfer device, cleaning device 6
Y, a static eliminator 7Y is provided.

The photosensitive drum 2Y is driven to rotate at a peripheral speed of V0 by a drive motor (not shown). The surface of the photosensitive drum 2Y is charged by a charging device 3Y including a conductive charging roller provided in contact with the surface of the photosensitive drum 2Y. The charging roller is rotated by contacting the surface of the photosensitive drum 2Y.

The surface of the photosensitive drum 2Y is formed of an organic photoconductor. This photoconductor generally has a high resistance, but has a property that when irradiated with light, the specific resistance of the light irradiated portion changes. Then, the charged yellow
By irradiating the surface of the photoconductor drum 2Y with light corresponding to the yellow print pattern from the solid-state scanning head 1Y through an equal-magnification imaging optical system, an electrostatic latent image of the yellow print pattern is formed on the photoconductor drum 2Y. Formed on the surface.

The electrostatic latent image is an image formed on the surface of the photosensitive drum 2Y by charging, and is a solid scanning head 1Y.
, The specific resistance of the irradiated surface of the photoconductor decreases, and the charged charge on the surface of the photosensitive drum 2Y flows,
On the other hand, it is a so-called negative latent image formed by remaining charges in a portion of the solid scanning head 1Y that has not been irradiated with light.

The photosensitive drum 2 charged as described above
The light of the solid-state scanning head 1Y is focused on the exposure position on Y, and the photosensitive drum 2Y on which the latent image is formed rotates at the speed of V0 to the developing position. Then, at this developing position, the latent image on the photosensitive drum 2Y is converted into a visible toner image by the developing device 4Y.

A yellow toner formed of a resin containing a yellow dye is prepared in the developing device 4Y.
The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and has a charge having the same polarity as the charged band on the photosensitive drum 2Y. As the surface of the photosensitive drum 2Y passes through the developing device 4Y, the yellow toner is electrostatically attached only to the latent image portion from which the charge has been removed, and the latent image is developed by the yellow toner. (Reversal development).

The photosensitive drum 2Y on which the yellow toner image is formed continues to rotate around the outer periphery V0, and is conveyed by the transfer roller 5Y at a transfer position at a timing by a paper feeding system. Transfer material (paper) 8 on 12
The toner image is transferred onto the top.

The paper feeding system includes a pickup roller 9, a feed roller 10, and a registration roller 11.
The transfer roller 8 lifted from the sheet cassette 39 by the pickup roller 9 is conveyed by the feed roller 10 to the registration roller 11 by one sheet. The registration roller 11 feeds the transfer material 8 onto the transfer material transport belt 12 after adjusting the posture of the transfer material 8. The peripheral speed of the registration roller 11 and the peripheral speed of the transfer material conveying belt 12 are determined by the photosensitive drum 2Y.
Is set to be equal to the peripheral speed V0. The transfer material 8 is sent to the transfer position of the photosensitive drum 2Y together with the transfer material transport belt 12 at a constant speed V0 with the photosensitive material drum 2Y while a part of the transfer material 8 is held by the registration roller 11.

At the transfer position, the yellow toner image on the photosensitive drum 2Y in contact with the transfer material 8 is transferred to a transfer roller 5Y.
As a result, the toner image is separated from the photosensitive drum 2Y and transferred onto the transfer material 8, and as a result, a yellow toner image of a print pattern based on the yellow print signal is formed on the transfer material 8.

The transfer roller 5Y is constituted by a transfer roller having semi-conductivity. The transfer roller supplies an electric field having a polarity opposite to the potential of the yellow toner electrostatically attached to the photosensitive drum 2Y from the back side of the transfer material transport belt 12. This electric field is applied to the transfer material transport belt 1
2, and acts on the yellow toner image on the photosensitive drum 2Y through the transfer material 8, so that the photosensitive drum 2Y
To transfer the toner image to the transfer material 8.

The transfer material 8 onto which the yellow toner image has been transferred in this way is then supplied to the magenta image forming means 150M, further to the cyan image forming means 150C, and further to the black image forming means 150BK.

The magenta image forming means 150M, the cyan image forming means 150C, and the black image forming means 15
0BK is composed of the same components and functions in which the yellow (Y) in the yellow image forming means 150Y described above is replaced with magenta (M), cyan (C), and black (BK). For simplicity, a description of these image forming units will be omitted.

The transfer material 8 on which the color superimposed image has been formed is sequentially passed through the yellow transfer position, the magenta transfer position, the cyan transfer position, and the black transfer position, and is sent to the fixing device 13.

The fixing device 13 is composed of a heat roller incorporating a heater. The fixing device 13 heats only the toner image placed on the transfer material 8 by the electric charge.
The color-superposed toner image is melted and permanently fixed to the transfer material 8. The transfer material 8 on which the fixing is completed is carried out to the paper discharge tray 15 by the delivery roller 14.

On the other hand, the photosensitive drums 2Y, 2M, 2C, and 2BK of the respective colors that have passed the transfer position are kept at the outer peripheral speed V as they are.
0 and the cleaning devices 6Y, 6M, 6
C, 6BK cleans residual toner and paper dust, and further, the electric potential of the surface is made constant by the static elimination lamps of the static elimination devices 7Y, 7M, 7C, 7BK, and the charging devices 3Y, 3M, 3C, 3BK again as necessary. Enter a series of processes from.

The transfer material transport belt 12 that has transported the transfer material 8 has an endless structure, and has a fixing device 13.
Drive roller 16 and driven roller 17 on the transfer material supply port side
And is held by. The driving roller 16 receives a driving force from a driving motor (not shown), and is driven such that the outer peripheral speed V0 of the photosensitive drum and the outer peripheral speed of the belt are equal as described above.

On the other hand, the driven roller 17 has a mechanism that can move in a direction parallel to the transfer material transfer direction on the shafts on both sides of the roller. The driven roller 17 is driven by a compression spring 18 in a direction opposite to the transfer material transfer direction. Is pressed to apply a tensile load to the substrate. The mechanism that enables the driven roller 17 to move in a direction parallel to the transfer material transport direction includes a long hole (not shown) provided in the frame, a driven hole that slides on the long hole and rotates the driven roller 17. It is composed of a roller holding member 21.

After transferring the transfer material 8 to the fixing device 13, the transfer material transport belt 12 removes residual toner and paper dust adhering to the belt surface by a belt cleaning device 22. Is transported.
In the case of monochromatic printing by the image forming unit 150B,
As described above, the recording unit / image forming unit other than the color selected does not operate.

The conveying means 200 is stretched between a belt driving roller 16 provided in parallel and a driven roller 17 which also serves as a non-stop roller, and the intermediate portion of the conveying means 200 is
The transfer belt 12 has an endless transfer material transport belt 12 stretched to face Y, 2M, 2C, and 2BK.
The driven roller 17 is a driven roller compression spring 1.
8, the transport belt 12 is tensioned.

First, the transfer material transport belt 12 that transports the transfer material 8 has an endless endless structure.
And the driven roller 1 on the transfer material supply port side
7. The driving roller 16 receives a driving force from a driving motor (not shown) and is driven so that the outer peripheral speed V0 of the photosensitive drum and the outer peripheral speed of the belt become equal.

On the other hand, the driven roller 17 has a mechanism which can be moved in a direction parallel to the transfer material transport direction on the shafts on both sides of the roller, and is driven by a compression spring 18 in a direction opposite to the transfer material transport direction. Is pressed to apply a tensile load to the. The mechanism that enables the driven roller 17 to move in a direction parallel to the transfer material transport direction includes an elongated hole 50 (see FIG. 4) provided in the belt unit frame 24 described later, and a sliding member that slides through the elongated hole 50. Is constituted by a driven roller holding member 21 which can rotate. Next, the conveying means 200 having the transfer material conveying belt 12 will be described in detail with reference to FIGS.

In the drawing, reference numeral 24 denotes a belt unit frame, on which the transfer material transport belt 12 is arranged so that the intermediate portion thereof faces each of the photosensitive drums 2Y, 2M, 2C, 2BK. Drive roller 16 for stretching
And a driven roller 17 are incorporated. Further, the transfer rollers 5Y, 5M, 5C, and 5BK as transfer devices are in a built-in state. The belt unit frame 24 is configured to be rotatable and displaceable with the rotation shaft 26 of the photosensitive drum 2BK for forming a single color image as a rotation fulcrum.

On the lower surface side of the belt unit frame 24, two feed-side compression springs 27 and discharge-side compression springs 28 are respectively provided as biasing means, and are always biased upward. As shown in FIG. 2 and FIG. 3, image forming means 150Y and 15 for forming an image of a color corresponding to a color image in the middle of the transfer material conveying belt 12 are provided.
Photoconductor drum 2 corresponding to 0M, 150C, 150BK
Y, 2M, 2C, and 2BK are urged to the first position in contact with them.

Further, the belt unit frame 24 constantly biased to the first position by the feed-side compression spring 27 and the discharge-side compression spring 28 as biasing means.
On the free end side, that is, on the lower surface of the driven roller 17 side, an arm 30 formed of a cut and raised tongue piece is provided. A solenoid 29 as a frame displacement means is connected to the arm 30.

A second position where the intermediate portion of the transfer material transport belt 12 contacts only the photosensitive drum 2BK corresponding to the image forming means 150B for forming an image of a color corresponding to a single color image, that is, FIG. Can be rotated and displaced to the position shown in FIG. 3 against the urging force of the compression springs 27 and 28.

As shown in FIG. 5, a solenoid 29 as a frame displacement means is connected to a solenoid power supply 35 controlled by a CPU 31 as a control means, as shown in FIG. Further, the CPU 31 includes the image forming units 150Y, 150M, 150C, 150B.
K and input means 36 for designating whether to form a color image or a monochromatic image, and for inputting other necessary information such as the number of copies and the magnification.

When the input means 36 specifies that a color image is to be formed, the CPU 31 sends a signal that the solenoid power supply 35 is turned off. Sends a signal that the solenoid power supply 35 is turned on. The switching control is performed so that the belt unit frame 24 is at the first position during color image formation, and the belt unit frame 24 is at the second position during monochrome image formation. .

When forming a color image, the belt unit frame 24 is provided with the compression springs 27 and 28.
The transfer belt 12 is pushed up by the transfer rollers 5Y, 5M, 5C,
Photoconductor drums 2Y, 2M, 2C corresponding to 5Bk
-It is pressed by 2Bk.

At this time, the power of the solenoid 29 is controlled to be OFF by the CPU 31 in accordance with a control flowchart described later, and only the force of the compression springs 27 and 28 applied to the belt unit frame 24. By starting image formation in this state, the transfer material 8 is transferred to each of the photosensitive drums 2Y, 2M, 2C,
The images formed on 2Bk are sequentially transferred to the transfer material 8, and a color image can be obtained.

On the other hand, when a monochrome image is formed, the state changes to the state shown in FIG. In the case of monochrome image formation, the power supply 35 of the solenoid 29 is turned on by the CPU 31 according to a control flowchart described later.

As a result, the solenoid 29 pulls the plunger 29A and pulls the arm 30 provided on the belt unit frame 24 connected thereto. As a result, the downward force by the solenoid 29 and the paper-side compression spring 2
7 upward force will be applied. The pulling force of the solenoid 29 is designed to be greater than the pressing force of the feed-side compression spring 27, whereby a downward force is applied to the feed side of the belt unit frame 24.

On the other hand, on the discharge side of the same belt unit frame 24, the discharge side compression spring 2 described above is provided.
8, a force for pressing upward is acting. That is, at this time, a pulling force acts on the belt unit frame 24 on the sheet feeding side and a pushing force on the sheet discharging side. With this force, the belt unit frame 24
The photoconductor is inclined around the black photoconductor rotation shaft 26.

Even if the belt unit frame 24 is inclined,
The black transfer roller 5BK is maintained in a state where the transfer material transport belt 12 is pressed firmly against the black photosensitive drum 2BK. On the other hand, the yellow, magenta, and cyan photosensitive drums 2Y, 2M, and 2C do not contact the transfer belt 12.

By starting image formation in this state, the transfer material 8 transfers only the image formed on the black photosensitive drum 2BK to the transfer material 8, and a black monochromatic image can be obtained. At this time, since the transfer material transport belt 12 is in a non-contact state with the yellow, magenta, and cyan photosensitive drums 2Y, 2M, and 2C, the residual toner on the yellow, magenta, and cyan photosensitive drums 2Y, 2M, and 2C is removed. It does not move to the transfer material 8. Further, the transfer material transport belt 12
Are photosensitive drums 2Y and 2 of yellow, magenta and cyan
Since there is no contact with M, 2C, no mechanical stress is applied to the photosensitive drums 2Y, 2M, 2C due to contact sliding.

When a color image formation is designated and an OFF signal is given to the solenoid 29, the suction force of the plunger 29A is released to the solenoid 29, so that there is no force in the direction of pulling down the belt unit frame 24. . If the suction force of the solenoid 29 is lost, there is no longer any force for suppressing the pressing force of the feed unit side compression spring 27 against the belt unit frame 24, so that the feed side compression spring 2
7, the belt unit frame 24 rotates counterclockwise.

However, since there are three other photosensitive drums 2Y, 2M, 2C upstream of the black photosensitive drum 2Bk, the four photosensitive drums 2Y, 2M, 2C and the transfer paper transport belt 12 is maintained in contact. Thus, the OFF signal given to the solenoid 29 causes
The belt unit frame 24 rotates, and the four photosensitive drums 2Y, 2M, 2C, 2BK and the transfer paper transport belt 12
Is obtained in a state of contact with.

FIG. 6 is a control flowchart of the present invention. First, when a copy start signal is received, it is determined whether the designated copy is a full-color image or a black monochrome image. When a full-color image is designated, the power of the solenoid 29 fitted to the belt unit frame 24 is turned off. As a result, the belt unit frame 24 is in a horizontal state, and the photoconductors 2Y, 2M, 2C, and 2BK and the transfer rollers 5Y, 5M, 5C, and 5BK are in a state of firmly sandwiching the transfer material transport belt 12. Next, each process speed is set to the color mode. This is because, in the case of a color image, a maximum of four color toners are accumulated on the transfer material 8, and in order to sufficiently dissolve and fix the four layers of color toners, the toner is passed slowly through the fixing device 13. This is because sufficient heating is required.

Then, according to the yellow image data,
As described above, a yellow toner image is formed on the photosensitive drum 2Y of the yellow image forming means 150Y, and is transferred onto the transfer material 8 on the transfer material transport belt 12 supplied at a proper timing.

The transfer material 8 on which the yellow toner image has been transferred is
Next, the magenta image forming unit 150M, the cyan image forming unit 150C, and the black image forming unit 1
50BK, and a magenta toner image on the transfer material 8
The cyan toner image and the black toner image are sequentially transferred.
Then, the toner is sent to the fixing device 13. Then, the color image formation is continuously executed while maintaining this state until the designated number of copies is completed.

On the other hand, when the black single-color image is designated, the power supply 31 of the solenoid 29 is turned on as described above, whereby the belt unit frame 24 is turned on.
1 is inclined about the black photosensitive drum rotating shaft 26 as shown in FIG. The photosensitive drums 2Y, 2M, 2C, and 2BK of the photoconductor drums and the transfer material transport belt 12 are in a non-contact state.

Next, each process speed is set to the black monochrome mode. As described above, in the case of a color image, up to four color toners are accumulated on the transfer material 8,
In order to sufficiently dissolve and fix the four-layered color toners, it is necessary to slowly pass through the fixing device 13 and sufficiently heat them. However, in the case of a black monochrome image, one color toner layer is used. Heating and fixing do not require as much heating time as color images.

Therefore, the process speed can be set as a speed higher than that at the time of color image formation. By switching the process speed, particularly in the case of a black monochrome image, the number of copies per unit time can be increased by increasing the process speed. Next, the image formation on the photosensitive drum 2BK is started, and the transfer material 8 is conveyed to form a black toner image on the transfer material 8 as described above. Until the designated number of copies is completed, the black-and-white image is continuously formed while maintaining this state.

As described above, by using very simple control and structure, the state of the stretched transfer material transport belt 12 is not changed between when forming a color image and when forming a single-color image. The angle can be changed. This allows
At the time of monochrome image formation, the photosensitive drums 2Y, 2C of the image forming units 150Y, 150M, 150C that are unnecessary for image formation.
M, 2C and the transfer material transport belt 12 can be prevented from contacting with each other, so that the transfer material 8 does not need to contact the unnecessary photosensitive drums 2Y, 2M, 2C. To solve the problem of deteriorating the quality of the image by adhering to the transfer belt 12 and shortening the service life due to the mechanical stress of the photosensitive drums 2Y, 2M, 2C due to unnecessary contact sliding with the transfer material transport belt 12. it can. Further, since the stretched state of the transfer material transport belt 12 is not changed, the transfer material transport belt 12 is not overwhelmed and its life is not shortened.

[0058]

According to the present invention, the following effects can be obtained.

According to the image forming apparatus of the present invention , the angle of the stretched transfer material conveying belt can be changed between the time of forming a color image and the time of forming a single color image without changing the state of the transfer material conveying belt. This makes it possible to avoid unnecessary contact between the image carrier of the image forming means and the transfer material transport belt during the formation of a single-color image, thereby preventing unnecessary contact of the transfer material with the photosensitive drum. In addition, it is possible to solve the problem that the toner of an unnecessary color adheres to the transfer material and degrades the quality of the image, and the problem that the life of the photoconductor is shortened by unnecessary contact with the transfer material transport belt. Further, since the stretched state of the transfer material transport belt is not changed, there is an effect that the transfer material transport belt is not overloaded and its life is not shortened.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a positional relationship between a photosensitive drum and a transfer material conveyance belt during black monochromatic image formation according to an embodiment of the present invention.

FIG. 2 is a schematic view of a four-tandem tandem type color image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a positional relationship between a photosensitive drum and a transfer material conveying belt during color image formation in the embodiment.

FIG. 4 is a perspective view showing a configuration of a main part in the embodiment.

FIG. 5 is a block diagram showing a control system in the embodiment.

FIG. 6 is a flowchart in the embodiment.

[Explanation of symbols]

1Y, 1M, 1C, 1BK ... solid scanning head, 2Y, 2
M, 2C, 2BK: photosensitive drum (image carrier), 3Y,
3M, 3C, 3BK: Charging device, 4Y, 4M, 4C, 4
BK: developing device, 5Y, 5M, 5C, 5BK: transfer roller
La (transfer means), 6Y, 6M, 6C, 6BK ... cleaning device, 7Y, 7M, 7C, 7BK ... static eliminator, 8 ...
Transfer material, 9: pick-up roller, 10: feed roller, 11: registration roller, 12: transfer material transport belt,
13: fixing device, 14: delivery roller, 15: discharge tray, 16: drive roller, 17: driven roller, 18: driven roller compression spring, 21: driven roller holding member,
22: belt cleaning device, 23: paper cassette,
Reference numeral 24: Belt unit frame, 25: Black photoreceptor bearing, 26: Black photoreceptor rotating shaft, 27: Feed-side compression spring (biasing means), 28: Discharge-side compression spring (biasing means), 29: Solenoid (Frame displacement means), 29
A: plunger, 30: arm, 31: CPU (control means), 35: solenoid power supply, 36: input means, 50:
Slots, 150Y, 150M, 150C, 150BK: image forming means, 200: transport means.

Continuation of the front page (56) References JP-A-4-341873 (JP, A) JP-A-5-19641 (JP, A) JP-A-62-257181 (JP, A) JP-A-60-130764 (JP) , A) Hikaru 1-67664 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/01-15/01 117 G03G 15/16

Claims (2)

(57) [Claims] An image forming apparatus capable of forming a color image and a monochromatic image is provided corresponding to a plurality of image carriers sequentially arranged, and different colors are provided on each of the image carriers. A plurality of image forming means for forming an image, and a single transfer material transport belt stretched so that the intermediate portion faces each of the image carriers, and transports the transfer material sequentially to each of the image carriers. And a plurality of transfer means provided corresponding to each of the image carriers, and each of which transfers an image formed on each of the image carriers to a transfer material conveyed by the transfer material transport belt. The transfer means contacts the image carrier corresponding to the image forming means for forming an image of a color corresponding to the color image when forming a color image, and the transfer direction of the transfer material when forming a single color image.
The transfer material conveying belt is rotated around the rotation axis of the image carrier for monochromatic image formation so as to contact only the image carrier for monochromatic image formation arranged at the most downstream side along the line. Fulcrum and
Means for displacing the belt without changing its shape. 2. An image forming apparatus capable of forming a color image and a single-color image, provided in correspondence with a plurality of image carriers sequentially arranged, and having different colors on each image carrier. A plurality of image forming means for forming an image, and a transfer member having a transfer material transfer belt which is stretched so that a middle portion faces each of the image carriers and sequentially transfers a transfer material to each of the image carriers. Means, and a plurality of transfer means provided corresponding to each of the image carriers, respectively, to transfer an image formed on each of the image carriers to a transfer material transported by the transfer material transport belt; A plurality of rollers for extending the transfer material conveying belt so that a halfway portion faces each image carrier; and a rotation shaft around a rotation axis of the image carrier for forming a monochrome image. Dynamically displaceable belt unit Biasing the belt unit frame to a first position where an intermediate portion of the transfer material conveying belt comes into contact with an image carrier corresponding to an image forming means for forming an image of a color corresponding to a color image. And an image in which an intermediate portion of the belt unit frame constantly urged to the first position by the urging means forms an image of a color corresponding to a monochrome image in the transfer material conveying belt. Frame displacing means for rotating and displacing a second position in contact with only the image carrier corresponding to the forming means against the urging force of the urging means;
The arm is a first position, at the time of monochromatic image forming the belt unit frame - by comprising anda control means for controlling switching of the beam displacement means - the frame so arm is in the second position Characteristic image forming apparatus.