JPH09325622A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the shortening of the lives of a photoreceptor drum unit and a transfer unit caused by their damage due to their rubbing at the time of exchanging the photoreceptor drum unit. SOLUTION: Rollers 5b, 5c and 5d are attached to a side plate 5A and an intermediate transfer belt 5a is extended on these rollers 5b, 5c and 5d, to constitute the transfer unit 5. The transfer unit 5 is supported to freely rock on the driving shaft of the driving roller 5b. A contact/uncontact rocking plate 5g attached to the lower part of the side plate 5A is raised and lowered by the rotation of a cam 5h on an image forming device main body side, to rock the whole of the transfer unit. When a toner image is secondarily transferred, the cam 5h is arranged on a double dotted chain line, to bring the intermediate transfer belt 5a into contact with the drum 1. On the other hand, when the unit for the drum 1 is exchanged, the cam 5h is arranged on a full line position, to separate the intermediate transfer belt 5a from the drum 1. Thus, the damage of the drum 1 and the intermediate transfer belt caused by their rubbing is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic color image forming apparatus, toner images of respective colors are formed on an image bearing member such as a photosensitive drum, and finally these toner images of plural colors are transferred onto paper or the like. It is transferred onto a material to obtain a color image. Several methods are known for transferring the toner image at this time.

For example, the image forming apparatus shown in FIG. 4 has an intermediate transfer drum 55 which carries a recording material S on the surface thereof, and the toner image formed on the photosensitive drum 51 is transferred to the intermediate transfer drum 5.
A method is known in which the step of directly transferring to the recording material S on 5 is carried out for a plurality of color toners, and the toner images of a plurality of colors are directly superposed on the transfer material S carried on the surface of the intermediate transfer drum 55. In the figure, 52 is a charging roller for uniformly charging the surface of the photosensitive drum 51, 53 is an exposing means for irradiating a laser beam to form an electrostatic latent image on the photosensitive drum 51, and 54 is a developing device, which is rotatable. The rotary member 54 and four developing devices mounted on the rotating member 54, that is, developing devices 54Y, 54M, 54C, and 54Bk that store toners of yellow, magenta, cyan, and black, respectively. Further, 55 is an intermediate transfer drum on which a sheet S such as paper is carried (adsorbed) on the surface, and 56 is residual toner remaining on the photosensitive drum 51.
A cleaning device 57 for removing from the surface is a transfer material feeding portion, and has a paper feeding cassette 57a, a transport roller 57b, and the like. Further, 58 is a fixing device for fixing the toner image transferred onto the transfer material S, 59 is a discharge roller, and 60 is a paper discharge tray. In the transfer method according to this configuration, since the transfer material S needs to be wound around the surface of the intermediate transfer drum 55, there are large restrictions on the thickness and size of the transfer material S, and the transfer path for the transfer material S is also large. It gets complicated.

In contrast to the above method, a primary transfer step of transferring a toner image formed on a photosensitive drum to an intermediate transfer belt is performed for each color toner, and a plurality of color toner images are once superposed on the intermediate transfer belt. A method is known in which the toner images are combined, and then the toner images are collectively secondarily transferred onto a transfer material. This method is suitable for downsizing the device and lowering the cost because there are many types of transfer materials that can be used because the transfer material transport path is similar to black and white, and there are many technologies that can be diverted from the mechanical aspect. is there.

[0005]

By the way, in the latter image forming apparatus using the intermediate transfer belt described above, in order to improve the maintainability and extend the life of the apparatus, the photosensitive drum is made into a cartridge and the intermediate transfer is performed. The unitization of the intermediate transfer body including the belt has been promoted, and the photosensitive drum and the intermediate transfer body can be easily replaced by the user. Therefore, conversely, for example, when the photosensitive drum or the intermediate transfer member is replaced, the two may be inadvertently rubbed with each other, and the part that does not need to be replaced may be damaged and the life may be shortened. .

Therefore, according to the present invention, when the first image bearing member such as the photosensitive drum or the second image bearing member such as the intermediate transfer member is replaced, scratches or the like are generated due to the rubbing of the two, and the like. An object of the present invention is to provide an image forming apparatus that prevents the life of parts from being shortened.

[0007]

According to a first aspect of the present invention, there is provided a toner image forming step of forming a toner image on a first image carrier and the toner image is transferred onto a second image carrier. 1
The next transfer step is performed a plurality of times for the toners of a plurality of colors to form the toner images of the plurality of colors on the second image carrier, and then the toner images of the plurality of colors on the second image carrier are first formed. Three
In the image forming apparatus for secondarily transferring the image onto the image carrier at one time, the second image carrier has a plurality of shafts including drive shafts, an intermediate transfer belt stretched around these shafts, The transfer unit is integrally configured as a transfer unit having a shaft and a support member that supports the intermediate transfer belt, and the transfer unit is supported so as to be swingable about the drive shaft, It is characterized in that it has a transfer position in contact with the first image carrier and a retracted position in which it is separated from the first image carrier.

In the present invention according to claim 2, the transfer unit has a roller member for positioning the transfer position of the transfer unit by bringing it into contact with the non-image forming area of the first image carrier. It is characterized by

The present invention according to claim 3 is characterized in that the transfer unit is arranged at the retreat position when the rotational drive of the first image carrier and the intermediate transfer belt is started.

According to a fourth aspect of the present invention, there is provided density detecting means for detecting the density of the toner image on the first image carrier, and the transfer unit is retracted when the density is detected by the density detecting means. It is characterized in that it is placed in a position.

According to a fifth aspect of the present invention, the transfer unit is detachably attached to the main body of the image forming apparatus.

[Operation] The main operation (operation according to claim 1) of the above configuration is as follows.

When the transfer unit (second image carrier) is swung around the drive shaft and placed in the retracted position, the transfer unit is separated from the first image carrier. Therefore, for example, when the first image carrier and the transfer unit are replaced, it is possible to prevent the two from rubbing against each other.

Further, since the transfer unit swings around the drive shaft, the relative positional relationship between each member for transmitting power to the drive shaft and the drive shaft does not change. Therefore, for example, positioning when mounting the transfer unit becomes easy.

[0015]

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

FIG. 1 is a vertical sectional view showing a schematic structure of the entire image forming apparatus according to the present invention.

First, with reference to FIG. 1, an outline of the entire image forming apparatus M will be described. The image forming apparatus M shown in the figure is a four-color full-color laser beam printer.

The image forming apparatus M shown in FIG. 1 includes a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as a first image bearing member. The photosensitive drum 1 is rotationally driven counterclockwise in the figure by a driving unit (not shown). Around the photosensitive drum 1, a charging device 2 that uniformly charges the surface of the photosensitive drum 1 in order along the rotation direction thereof, and a laser beam is radiated based on image information to form an electrostatic latent image on the photosensitive drum 1. Exposure unit 3, a developing device 4 for developing a toner image by attaching toner to the electrostatic latent image, a transfer unit 5 as a second image carrier on which the toner image on the photosensitive drum 1 is primarily transferred, A cleaning device 6 for removing the transfer residual toner remaining on the surface of the photosensitive drum 1 after the next transfer is provided. In addition, transfer material (3rd
Feeding means 7, 2 for feeding the image carrier (S) toward the transfer unit 5 and carrying the transfer material after the secondary transfer.
A fixing device 8 for fixing the toner image on the transfer material S after the next transfer is provided.

The photosensitive drums 1 will be described in detail below.

The photosensitive drum 1 has, for example, a diameter of about 47 mm.
The organic photoconductor layer (OPC photoconductor) is applied to the outer peripheral surface of the aluminum cylinder. Both ends of the photosensitive drum 1 are rotatably supported by support members (not shown), and the driving force from a drive motor (not shown) is transmitted to one end of the photosensitive drum 1 so that the photosensitive drum 1 rotates in the direction of the arrow. Driven. The photosensitive drum 1 is unitized together with a supporting member, and is detachably attached to the main body of the image forming apparatus. Thereby, the photosensitive drum 1
Can be easily replaced with each unit according to its life.

The charging device 2 is, for example, Japanese Patent Laid-Open No. 63-63.
A so-called contact charging type as shown in Japanese Patent Publication No. 149669 can be used. The charging member is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1, and a charging bias voltage is applied to the roller by a power source (not shown), whereby the photosensitive drum 1 The surface is uniformly charged.

The exposing means 3 has a polygon mirror 3a, and the polygon mirror 3a is irradiated with image light corresponding to an image signal by a laser diode (not shown). The polygon mirror 10a is rotated at a high speed by a scanner motor (not shown), and the reflected image light is selectively exposed on the surface of the charged photosensitive drum 1 through the imaging lens 3b, the reflection mirror 3c, etc. It is configured to form a latent image.

The developing device 4 includes a rotatable body 4A,
4 developing devices mounted on this, namely, yellow,
The developing units 4Y, 4M, 4C, and 4Bk, which store toners of magenta, cyan, and black, respectively, are provided. When developing the electrostatic latent image on the photosensitive drum 1, a predetermined developing device for a color to be attached to the electrostatic latent image is arranged at the developing position. That is, the predetermined developing device is stopped at the developing position facing the photosensitive drum 1 by the rotation of the rotating body, and the developing sleeve 4b of the developing device is positioned so as to face the photosensitive drum 1 with a minute gap (about 300 μm). Then, the electrostatic latent image on the photosensitive drum 1 is developed. This development is performed as follows. The toner in the container of the developing device corresponding to the color to be developed is sent to the applying roller 4a by the sending mechanism, and the rotating applying roller 4a and the blade 4c apply a thin layer of toner to the outer circumference of the rotating sleeve 4b, and Charge is given (triboelectric charging). By applying a developing bias between the sleeve 4b and the photosensitive drum 1 on which the electrostatic latent image is formed, toner is attached to the electrostatic latent image and developed as a toner image. Further, the sleeve 4b of each developing device is connected to a high-voltage power source for developing each color provided in the main body of the image forming apparatus when each developing device is arranged at the developing position, and the developing device for each color is developed. A voltage is selectively applied every time. It should be noted that each of the developing devices is configured to be individually attachable to and detachable from the rotating body 4A, and the rotating body 4A can be attached to and detached from the apparatus main body.

Transfer unit 5 as second image carrier
Is a secondary transfer of a plurality of toner images sequentially primary-transferred from the photosensitive drum 1 and superposed to the transfer material S at once. The transfer unit 5 includes an intermediate transfer belt 5a that runs in the direction of arrow R5. The intermediate transfer belt 5a of the present embodiment is a belt having a circumferential length of about 440 mm,
The drive roller 5b, the secondary transfer counter roller 5c, and the driven roller 5d are wound around by three rollers. The conveyor belt 5a is configured to travel in the direction of arrow K5 by the rotation of the drive roller 3b. Further, at a predetermined position outside the intermediate transfer belt 5a, the intermediate transfer belt 5a is
A cleaning unit 5e which can be brought into contact with and separated from the surface of the recording medium is provided, and the transfer residual toner remaining after the secondary transfer is collectively removed on the recording material S described later. This cleaning unit 5
At e, the charging roller 5f is brought into contact with the intermediate transfer belt 5a to give the toner a charge opposite to that at the time of transfer. The toner to which the opposite charge is applied is electrostatically attached to the photosensitive drum 1 and then collected by a cleaning device 6 for the photosensitive drum 1 which will be described later. The cleaning method of the intermediate transfer belt 5a is not limited to the electrostatic cleaning described above, but may be a mechanical method such as a blade or a fur brush, or a combination thereof.

The cleaning device 6 is a so-called transfer residual toner that remains on the surface of the photosensitive drum 1 without being primarily transferred after the toner developed on the photosensitive drum 1 by the developing device 5 is primarily transferred to the intermediate transfer belt 5a. Is to be removed. In the cleaning device 4 of the same figure, the transfer residual toner is sent to a waste toner container attached to the side surface of the image forming apparatus main body by a waste toner carrying screw (not shown) passed through the waste toner container 6a. When the waste toner in the waste toner container becomes full, it is removed and replaced.

The feeding / conveying means 7 feeds the transfer material S to the image forming section, and accommodates a plurality of transfer materials S.
Paper feed cassette 7a loaded in the lower part of the image forming apparatus main body
It has. During image formation, the conveyance roller 7b is driven and rotated in accordance with the image forming operation to separate and feed the transfer materials S in the paper feed cassette 7a one by one, and are guided by the guide plate 7c to pass through the registration roller 7d and intermediate transfer. The sheet is fed to the belt 5a.

The fixing device 8 fixes a plurality of toner images secondarily transferred to the transfer material S. As shown in FIG. 1, the drive roller 8a is driven and rotated, and the transfer material is pressed against the drive roller 8a. The fixing roller 6b applies heat and pressure to S. That is, the transfer material S that has passed through the secondary transfer roller 5n that collectively transfers the toner on the intermediate transfer belt 5a is conveyed by the drive roller 8a when passing through the fixing device 8, and heat and pressure are applied by the fixing roller 8b. Is applied. As a result, the toner images of a plurality of colors are fixed on the surface of the transfer material S.

Next, the image forming operation of the image forming apparatus M having the above structure will be described.

In synchronism with the rotation of the intermediate transfer belt 5a, the photosensitive drum 1 is rotated in the direction of the arrow (counterclockwise) in FIG.
The surface of the photosensitive drum 1 is uniformly charged by the charging device 2, and the exposure unit 3 irradiates a yellow image with light to form a yellow electrostatic latent image on the photosensitive drum 1. Simultaneously with the formation of the electrostatic latent image, the developing device 4 is driven to dispose the yellow developing device 4Y at the developing position, and the charging polarity of the photosensitive drum 1 is set so that the yellow toner adheres to the electrostatic latent image on the photosensitive drum 1. By applying a voltage having the same polarity and substantially the same potential as the above, yellow toner is attached to the electrostatic latent image for development. A voltage having a polarity opposite to that of the toner is applied to the primary transfer roller (driven roller) 5d to primarily transfer the yellow toner image on the photosensitive drum 1 onto the intermediate transfer belt 5a.

When the primary transfer of the yellow toner image is completed as described above, the next developing device is rotationally moved and positioned at the developing position facing the photosensitive drum 1, and magenta and cyan are used in the same manner as in the case of yellow. Then, for each color of black, electrostatic latent image formation, development, and primary transfer are sequentially performed, and four color toner images are superimposed on the intermediate transfer belt 5a. These toner images are collectively secondarily transferred onto the transfer material S supplied from the feeding / conveying unit 7.

Then, the transfer material S after the secondary transfer is conveyed to the fixing device 8, where the toner image is fixed, and then discharged by the discharge roller 9 onto the discharge tray 10 outside the main body of the image forming apparatus. Then, the image formation is completed.

Next, the transfer unit 5 will be described in more detail with reference to FIGS.

FIG. 2 is a view showing a state in which the transfer unit 5 is arranged at a transfer position where it comes into contact with the photosensitive drum 1, and FIG. 3 is shown in FIG. 3 where the transfer unit 5 is arranged at a retracted position separated from the photosensitive drum 1. FIG.

The intermediate transfer belt 5a includes a driving roller 5b,
It is stretched between the secondary transfer counter roller 5c and the driven roller 5d with a tension capable of driving rotation. Each roller 5
b, 5c, and 5d are rotatably supported by bearings between two side plates (support members) 5A and 5A joined by stays, and the intermediate transfer belt 5a is driven by the drive roller 5a.
The rotation of d rotates in the direction of arrow K5. That is, each of the rollers 5b, 5c, 5d and the intermediate transfer belt 5a stretched over the rollers are integrally supported by the side plate 5A, and constitute the transfer unit 5 as a whole.

In the transfer unit 5, a bearing (not shown) that axially supports the drive roller 5b is positioned with respect to a semicircular bearing receiver (not shown) that protrudes inside the frame of the image forming apparatus main body. As a result, it is supported by the frame described above. Therefore, the transfer unit 5 can swing about the drive roller 5b. In the transfer unit 5, the contact / separation oscillating plate 5g attached to the lower portion of the side plate 5A is arranged on the image forming apparatus main body side, and is a cam 5h integrated with a rotation-controllable shaft.
By receiving a force in the vertical direction due to the rotation of, the entire transfer unit 5 is swung about the drive shaft of the drive roller 5b, and the roller (roller member) 5j on the side plate 5A side forms a non-image on the photosensitive drum 1. By hitting the area, it is positioned at the transfer position shown in FIG. In addition, contact / separation swing plate
Is urged counterclockwise in FIG. 2 by a tension spring 5k interposed between the side plate 5A and the protrusion 5m.

The swinging operation of the transfer unit 5 is performed as follows. That is, the transfer unit 5 is pushed up by the cam 5h so that the roller 3j comes into contact with a part of the photosensitive drum 1, thereby disposing the intermediate transfer belt 5a at the transfer position (FIG. 2) where the intermediate transfer belt 5a contacts the photosensitive drum 1. On the other hand, the transfer unit 5 is rotated by the rotation of the cam 5h (see FIG.
Solid line), and is pushed down in the direction of arrow R5.
The intermediate transfer belt 5a is arranged at a retracted position (see FIG. 3) for separating it from the photosensitive drum 1.

The swinging operation of the transfer unit 5 is utilized in the following cases.

The first is the case where the photosensitive drum 1 is detached as a unit, and this is to prevent the surface of the photosensitive drum from sliding against the intermediate transfer belt 5a and being damaged.

Second, after the unit of the photosensitive drum 1 is replaced and mounted, when the first attempt is made to move the unit, the intermediate transfer belt 5a can be securely connected until the drive coupling (not shown) on the photosensitive drum 1 side is securely coupled. This is to prevent a large slip between the and. That is, both the photosensitive drum 1 and the intermediate transfer belt 5a are driven to rotate for a predetermined period of time, and then they are brought into contact with each other, thereby preventing the surfaces of both from being damaged.

Thirdly, when the developing density of each color developing device is measured on the photosensitive drum 1 by the density detecting means, the intermediate transfer belt 5a is separated from the surface of the photosensitive drum 1. This is because the density detection sensor (density detection means) 11 for detecting the density of the toner image on the photosensitive drum 1 is arranged on the downstream side of the contact point between the intermediate transfer belt 5a and the photosensitive drum 1. This is for avoiding the influence of the contact of the intermediate transfer belt 5a and improving the detection accuracy.

[0041]

As described above, according to the present invention,
By making the second image carrier (transfer unit) swingable about the drive shaft, the first image carrier (photosensitive drum)
The intermediate transfer belt can be brought into and out of contact with, for example,
When the first image bearing member is replaced as a unit, the intermediate transfer belt is separated from the first image bearing member, so that the life of these members is shortened due to scratches or the like caused by rubbing of the two. This can be effectively prevented.

Further, since the first image carrier and the intermediate transfer belt are in contact with each other at the time of starting rotation after the replacement, it is possible to avoid damage on the surfaces of the both, and further, on the first image carrier. It is possible to improve the accuracy of detecting the density of the toner image.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the configuration of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a state in which an intermediate transfer belt of a transfer unit is arranged at a transfer position.

FIG. 3 is a diagram showing a state in which an intermediate transfer belt of a transfer unit is arranged at a retracted position.

FIG. 4 is a vertical cross-sectional view showing the configuration of a conventional image forming apparatus.

[Explanation of symbols]

 1 First Image Carrier (Photosensitive Drum) 2 Charging Device 3 Exposure Means 4 Developing Device 4A Rotating Body 4Bk Black Developing Device 4C Cyan Developing Device 4M Magenta Developing Device 4Y Yellow Developing Device 5 Second Image Carrier (Transfer unit) 5A Support member (side plate) 5a Intermediate transfer belt 5b Drive roller 5g Contact / separation oscillating plate 5h Cam 5i Roller member (roller) 6 Cleaning device 7 Feeding / conveying member 8 Fixing device S Third image carrier (recording) Material)

Claims (5)

[Claims] 1. A toner image forming step of forming a toner image on a first image carrier and a primary transfer step of transferring the toner image onto a second image carrier are carried out for a plurality of color toners. After the toner image of a plurality of colors is formed on the second image bearing member by repeating the above-mentioned process, the toner images of a plurality of colors on the second image bearing member are collectively secondary-printed on the third image bearing member. In an image forming apparatus for transferring, the second image carrier has a plurality of shafts including drive shafts, an intermediate transfer belt stretched around these shafts, and a support member supporting the shafts and the intermediate transfer belt. A transfer unit that is integrally configured as a transfer unit and that is swingably supported about the drive shaft to bring the intermediate transfer belt into contact with the first image carrier. Position and a retracted position for separating from the first image carrier An image forming apparatus characterized by: 2. The transfer unit includes a roller member that positions the transfer position of the transfer unit by contacting with a non-image forming area of the first image carrier. 1. The image forming apparatus according to 1. 3. The transfer unit according to claim 1, wherein the transfer unit is arranged at the retracted position at the start of rotational driving of the first image carrier and the intermediate transfer belt. Image forming apparatus. 4. A density detecting unit for detecting the density of the toner image on the first image carrier, wherein the transfer unit is arranged at the retreat position when the density is detected by the density detecting unit. Any one of claims 1 to 3 characterized in that
An image forming apparatus according to any one of the preceding claims. 5. The transfer unit is detachably attached to the main body of the image forming apparatus, according to claim 1.
An image forming apparatus according to any one of the preceding claims.