JP2002214943A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing abnormality from occurring in an image transferred to transfer-paper due to the kind and the thickness of the transfer-paper carried to a transfer part being a contact part between an image carrier and a transfer member. SOLUTION: In the case of carrying transfer-paper P consisting of cardboard to the transfer part, the cam follower piece 650b of a pressure switching plate 650 is pushed up by the cam edge 660a of a pressure switching cam 660. A pressure switching spring 670 laid over between the locking part 650a of the plate 650 and a supporting body 620 is elongated. By the elongation of the spring 670, rotational force in the clockwise direction with a supporting shaft 621 as center is applied to the supporting body 620. Thus, pressing force by the pressing spring 641 of a pressing member 640 for pressing the pressing piece 620a of the supporting body 620 so as to rock the supporting body 620 in the counterclockwise direction is reduced, and the contact pressure of a secondary transfer bias roller 605 to an intermediate transfer belt 501 by a contacting/separating mechanism is made low, and the contact pressure becomes optimal to the transfer-paper P consisting of the cardboard.

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 copying machine, a facsimile, and a printer.
A transfer member configured to be able to freely contact and separate from the surface of the image carrier, and a transfer member conveyed toward a transfer section between the transfer member and the image carrier; The image forming apparatus is configured to transfer the toner image formed on the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, an image carrier such as a photosensitive drum, a photosensitive belt, or an intermediate transfer belt is used, and a toner image formed on the image carrier is transferred. There is known an image forming apparatus which transfers an image to a transfer material such as a sheet or an OHP sheet by means to form an image.

For example, in an "image forming apparatus" disclosed in JP-A-11-231667, a toner image formed on the photosensitive drum is transferred by a primary transfer bias roller which is a primary transfer member of the transfer means. The primary transfer is performed on the intermediate transfer belt. Then, a transfer bias having a polarity opposite to the charging polarity of the toner image is applied to a secondary transfer bias roller serving as a secondary transfer member, and a transfer unit where the intermediate transfer belt and the secondary transfer bias roller contact each other,
The toner image primary-transferred onto the intermediate transfer belt is electrically attracted to the transfer material conveyed toward the transfer unit, and is secondary-transferred.

The transfer member is usually configured to be able to freely contact and separate from the surface of the image carrier by means of a contact and separation means. This prevents the transfer member or the image carrier from being deformed over time due to the transfer member being constantly in contact with the surface of the image carrier, or continuously transferring a plurality of toner images on the image carrier. This is to prevent contact between the toner image on the image carrier and the transfer member when an image is formed on the image carrier. In particular, in an image forming apparatus of an intermediate transfer system in which toner images of a plurality of colors which are sequentially superimposed and primary transferred on the intermediate transfer belt are collectively transferred by the secondary transfer bias roller,
When forming two or more color images, the intermediate transfer belt and the secondary transfer bias roller must be in contact with or separated from each other.

[0005] Further, the contact and separation between the intermediate transfer belt and the secondary transfer bias roller can be performed by disposing a plurality of photosensitive drums along the intermediate transfer belt and forming the respective colors formed on the respective photosensitive drums. After the toner image is superimposed on the intermediate transfer belt and primary-transferred, the primary-transferred toner image is transferred by a nip between the intermediate transfer belt and a secondary transfer bias roller.
This is also essential in a tandem-type image forming apparatus for performing the next transfer.

As described above, in an image forming apparatus in which the transfer member comes into contact with or separates from the surface of the image carrier, the transfer portion is contacted when the image carrier comes into contact with the transfer member. The transfer member is pressed against the image carrier at a predetermined pressure so that a transfer nip having a predetermined width is formed by the contact between the image carrier and the transfer member.

That is, the transfer nip is generally
When a toner image carried on the image carrier is transferred by the transfer member onto a transfer material weighing about 90 kg to 220 kg, which is called plain paper, an optimal image can be formed on the transfer material. Nip width is set. Further, the contact pressure of the transfer member with respect to the image carrier in the transfer section is such that the transfer nip having the nip width as described above is formed in the transfer section which is a contact section between the image carrier and the transfer member. It is set to such a pressure.

[0008]

However, in this type of conventional image forming apparatus, a transfer material having a thickness greater than that of the plain paper, for example, a transfer material called "thick paper" weighing 220 kg or more is used. Is transferred to the transfer unit, and the toner image formed on the image carrier is transferred by the transfer member to form an image.If the transfer is not performed properly, an abnormal image called a print may occur. there were. This is because the thick paper is conveyed to the transfer section, and the stiffness (bending strength) of the thick paper causes the transfer member to move away from the image carrier against the contact pressure. It is considered that the displacement is caused by a decrease in the nip width of the transfer nip of the transfer portion.

Further, when the above-described thick paper is conveyed to the transfer section, the resistance when the thick paper enters the transfer nip of the transfer section becomes large. For this reason, when the thick paper enters the transfer nip, a shock (shock) is applied to the image carrier and the transfer member, and the thick paper flaps,
This shock and flapping is transmitted to the transfer nip,
The transferred image transferred to the cardboard sometimes became an abnormal image that was locally displaced.

In particular, when the image carrier is an endless belt such as the above-mentioned intermediate transfer belt, the thick paper is transported to a contact portion between the intermediate transfer belt and the transfer member. At this time, the occurrence of the abnormal image due to the shock or the flutter becomes remarkable. That is, the intermediate transfer belt has some slack even in a stretched state. Therefore, when the transfer member comes into contact with the intermediate transfer belt, the belt portion on the downstream side in the moving direction from the contact portion between the intermediate transfer belt and the transfer member is sharply tensioned. As a result, the progress of the belt portion on the upstream side in the moving direction from the contact portion of the intermediate transfer belt is temporarily stopped. Then, the tension and the stop of the movement of the intermediate transfer belt are repeated until the movement speed of the intermediate transfer belt at the contact portion is stabilized. For this reason, when the contact member comes into contact with the intermediate transfer belt, the flapping in the moving direction of the intermediate transfer belt (shock or vibration due to jitter) is a relatively rigid rigid drum-shaped image carrier. Larger than. As described above, in the image forming apparatus using the intermediate transfer belt, an abnormal image is significantly generated when the thick paper is conveyed to the contact portion between the intermediate transfer belt and the transfer member.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a method for transferring and transferring a transfer material to a transfer section which is a contact section between an image carrier and a transfer member. Accordingly, it is an object of the present invention to provide an image forming apparatus capable of preventing an image transferred to the transfer material from causing an image abnormality.

[0012]

In order to achieve the above object, the present invention is directed to an image carrier that carries a toner image formed on a surface thereof and moves, and a method for moving the image carrier relative to the surface of the image carrier. The toner image formed on the surface of the image carrier is transferred onto a transfer material conveyed toward a transfer portion between the transfer member and the image carrier by a transfer member configured to be freely contactable and detachable. An image forming apparatus, comprising: a transfer unit that performs transfer and a contact / separation unit that causes the transfer member to contact / separate from the surface of the image carrier; and the contact unit that contacts the surface of the image carrier by the contact / separation unit. It is characterized by having contact pressure switching means for switching the contact pressure of the transfer member in at least two stages.

In this image forming apparatus, the contact pressure of the transfer member contacting the surface of the image carrier by the contact / separation means is switched in at least two stages by the contact pressure switching means. Thereby, the contact pressure of the transfer member that contacts the surface of the image carrier is switched to a contact pressure suitable for the transfer material conveyed to the transfer unit, and the image of the image transferred to the transfer material is changed. It is possible to prevent the occurrence of a difference.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the contact pressure switching means is configured to control the image bearing member according to the type and thickness of the transfer material conveyed to the transfer section. The contact pressure of the transfer member contacting the surface of the transfer member is switched.

In this image forming apparatus, the contact pressure switching means reduces the contact pressure of the transfer member contacting the surface of the image carrier with the type and thickness of the transfer material conveyed to the transfer section. According to this, it is possible to switch in stages. Therefore, in this image forming apparatus, the contact pressure of the transfer member that comes into contact with the surface of the image carrier is switched to a contact pressure suitable for the type and thickness of the transfer material conveyed to the transfer section. It is possible to prevent the occurrence of a difference in the image transferred to the transfer material.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, there is provided a transfer material selection button for selecting a type of a transfer material to be conveyed to the transfer section. When the type of the transfer material is selected by the transfer material selection button, the contact pressure of the transfer member that contacts the surface of the image carrier is switched. is there.

In this image forming apparatus, when the type of the transfer material is selected by the transfer material selection button,
The contact pressure switching means switches the contact pressure of the transfer member that contacts the surface of the image carrier in at least two stages. Thereby, the contact pressure of the transfer member that contacts the surface of the image carrier according to the type of the transfer material selected by the transfer material selection button, for example, the paper quality and thickness of the transfer material. It is possible to switch. Therefore, in this image forming apparatus, for example, by arranging the transfer material selection button on the operation panel of the apparatus main body, the operator can easily switch the contact pressure of the transfer member that contacts the surface of the image carrier. Will be able to do it.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second, or third aspect, the contact pressure switching means is configured to control the image forming apparatus according to a transport speed of a transfer material transported to the transfer section. It is characterized in that the contact pressure of the transfer member that contacts the surface of the carrier is switched.

As described above, the abnormal image is generated by changing the nip width of the transfer nip of the transfer section depending on the thickness of the transfer material. The degree of occurrence of such an abnormal image is as follows. And the transfer speed of the transfer material. That is, when the linear velocity of the transfer section of the image carrier and the transfer member is high, the passage time of the transfer material passing through the transfer nip of the transfer section becomes short. This is the same as reducing the nip width of the transfer nip. For this reason, in this case, the transfer condition to the transfer material in the transfer unit is likely to cause an abnormality in the image on the transfer material as in the case where the above-described thick paper is conveyed to the transfer unit. Therefore, when the transfer material is thick, it is desirable to reduce the linear velocity of the transfer portion of the image carrier and the transfer member so as to shorten the passage time of the transfer material passing through the transfer nip of the transfer portion. In this image forming apparatus, by the contact pressure switching means, the contact pressure of the transfer member contacting the surface of the image carrier, according to the transport speed of the transfer material transported to the transfer unit, It is possible to switch step by step. Therefore, in this image forming apparatus, the contact pressure of the transfer member that contacts the surface of the image carrier is switched to a contact pressure suitable for the transfer speed of the transfer material conveyed to the transfer section, and It is possible to prevent the occurrence of a difference in the image transferred to the image.

Further, the invention of claim 5 is based on claims 1, 2,
In the image forming apparatus of (3) or (4), after the toner image is primarily transferred from a latent image bearing member on which the toner image is formed by a primary transfer unit, the toner image is transferred to a secondary transfer member. And an intermediate transfer member which is secondarily transferred to the transfer material by means.

In this image forming apparatus, a plurality of color toner images are superimposed on the intermediate transfer member and primary-transferred, and then the superposed plural color toner images are transferred to the transfer material by the secondary transfer means. By performing the secondary transfer, a color image can be formed on the transfer material. In the case where such a color image is formed, if the secondary transfer means comes into contact with the intermediate transfer body and the intermediate transfer body is fluttered, the flutter causes primary transfer onto the intermediate transfer body. The next image is disturbed. Such image disturbance during the formation of a color image causes a color shift of the image that is secondarily transferred onto the transfer material. In the image forming apparatus of the present invention, the contact pressure of the transfer member that comes into contact with the surface of the image carrier, which is one of the causes of the fluttering, is suitable for the transfer material conveyed to the transfer section. Can be switched to the contact pressure. This makes it possible to reduce the fluttering of the intermediate transfer member and form a color image without color misregistration.

According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the intermediate transfer body is such that the transfer material conveyed toward the transfer section is located in front of the transfer section. The inner peripheral surface in front of the transfer portion is constituted by an endless belt stretched by a fixed stretching member so as to be conveyed along the surface of the transfer portion.

In this image forming apparatus, for example, as shown in FIG. 9A, a transfer sheet P as a transfer material conveyed toward the transfer section is transferred by the fixed stretching member 900 to the transfer sheet. The inner peripheral surface of the intermediate transfer belt 501 before the transfer unit is stretched so that the intermediate transfer belt 501 is conveyed along the surface of the intermediate transfer belt 501 as an intermediate transfer body formed of the endless belt just before the unit. Have been. For this reason, when the transfer paper P made of thick paper is conveyed to the transfer portion of the secondary transfer bias roller 605 as the transfer member, which is the contact portion with the intermediate transfer belt 501, the transfer paper P is transferred to the intermediate transfer belt 501. An attempt is made to go straight along the surface of the belt 501. As a result, the stiffness (bending strength) of the transfer paper P made of the thick paper is obtained.
As a result, the secondary transfer bias roller 605
As shown in FIG. 2B, the position is changed from a position indicated by a dotted line to a position indicated by a solid line in a direction away from the intermediate transfer belt 501 against the contact pressure. As a result, the nip width of the transfer nip of the transfer portion decreases, and an abnormality occurs in an image transferred to the transfer sheet P. In the image forming apparatus of the present invention, as described above, the contact pressure of the transfer member that contacts the surface of the image carrier is switched to a contact pressure suitable for the transfer material conveyed to the transfer unit. Thus, it is possible to prevent occurrence of an abnormal image of the image transferred to the transfer material.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter, referred to as a color copying machine) as an image forming apparatus will be described. First, the schematic configuration and operation of the color copying machine according to the present embodiment will be described with reference to FIG. This color copier includes a color image reading device (hereinafter, referred to as a color scanner) 1,
Color image recording device (hereinafter referred to as color printer)
2, a paper feed bank 3 and the like.

The color scanner 1 converts the image of the original 4 on the contact glass 121 into an illumination lamp 122, mirror groups 123a, 123b, 123c, and a lens 124.
And form an image on the color sensor 125 via. Then, the color image information of the document 4 is stored in, for example, Red, Green.
The image data is read for each of n, Blue (hereinafter, R, G, B) color separation lights and converted into an electric image signal. The color sensor 125 of this example is composed of R, G, and B color separation means and a photoelectric conversion element such as a CCD, and photoelectrically converts a three-color image of the document 4 separated by the color separation means. Reading by the element at the same time. Then, based on the intensity levels of the R, G, B color separation image signals obtained by the color scanner 1, a color conversion process is performed by an image processing unit (not shown), and Black (hereinafter, referred to as Bk), Cyan
(Hereinafter, referred to as C), Magenta (hereinafter, referred to as M), and Yellow (hereinafter, referred to as Y) color image data are obtained.

The operation of the color scanner 1 for obtaining the color image data of Bk, C, M and Y is as follows. Upon receiving a scanner start signal that is timed with the operation of the color printer 2 described later, an optical system including an illumination lamp 122 and mirror groups 123a, 123b, 123c scans the document 4 in the left direction of the arrow, and performs once. To obtain four color image data. This is stored in a memory (not shown) and pulled out, thereby sequentially obtaining four color image data. Then, each time the color printer 2 sequentially visualizes and superimposes the images to form a final four-color full-color image.

The color printer 2 includes a photosensitive drum 200 as an image carrier, a writing optical unit 220,
Revolver developing unit 230, intermediate transfer unit 50
0, a secondary transfer unit 600, a fixing device 270, and the like. The photosensitive drum 200 rotates in the counterclockwise direction indicated by an arrow, and the photosensitive drum cleaning device 2 surrounds the photosensitive drum 200.
01, static elimination lamp 202, charger 203, potential sensor 2
04, a selected developing unit of the revolver developing unit 230, a developing density pattern detector 205, an intermediate transfer unit 500, a secondary transfer unit 600, and the like.

The writing optical unit 220
Converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the image of the document 4, and forms an electrostatic latent image on the photosensitive drum 200. The writing optical unit 220 includes a semiconductor laser 221 as a light source, a laser emission drive control unit (not shown), a polygon mirror 222 and a rotation motor 223, an f / θ lens 224, a reflection mirror 225, and the like.

The revolver developing unit 230
Is composed of a Bk developing unit 231K, a C developing unit 231C, an M developing unit 231M, a Y developing unit 231Y, and a revolver rotation drive unit which rotates each developing unit in a counterclockwise direction indicated by an arrow. A developing bias in which an AC voltage Vac is superimposed on a negative DC voltage Vdc is applied to each developing sleeve by a developing bias power supply (not shown), and the developing sleeve is set at a predetermined potential with respect to the metal base layer of the photosensitive drum 200. Biased.

When the copying machine main body is in a standby state, the revolver developing unit 230 moves the Bk developing unit 231K to the developing position 30K.
When the copy operation is started, reading of the Bk color image data is started from the color scanner 1 at a predetermined timing. Image formation starts (hereinafter, an electrostatic latent image based on Bk image data is converted to Bk image data).
It is called a latent image. The same applies to C, M, and Y). Before the front end of the electrostatic latent image reaches the Bk developing position, the Bk developing unit 231K is moved to the developing position and the rotation of the Bk developing sleeve is started before the front end of the electrostatic latent image reaches the Bk developing position so that development can be performed from the front end of the Bk electrostatic latent image. And B
The k electrostatic latent image is developed with Bk toner. And after that Bk
The developing operation of the electrostatic latent image area is continued, but when the trailing end of the electrostatic latent image passes the Bk developing position, the revolver developing unit 230 is immediately moved until the developing device for the next color comes to the developing position.
Rotates. This is completed at least before the leading end of the electrostatic latent image based on the next image data arrives.

As shown in FIG. 2, the intermediate transfer unit 500 includes an intermediate transfer belt 501 which is an intermediate transfer member stretched over a plurality of rollers. Around the intermediate transfer belt 501, the second transfer unit 600
Secondary transfer bias roller 60 as a secondary transfer charge applying means
5, a belt cleaning blade 504 serving as an intermediate transfer body cleaning unit, a lubricant applying brush 505 serving as a lubricant applying member of a lubricant applying unit, and the like are disposed so as to face each other.

A position detecting mark is provided on the outer peripheral surface or the inner peripheral surface of the intermediate transfer belt 501. However, on the outer peripheral surface side of the intermediate transfer belt 501, it is necessary to devise a method of providing a position detection mark so as to avoid the pass area of the belt cleaning blade 504, and it may be difficult to arrange the mark. A position detection mark is provided on the inner peripheral surface side of the intermediate transfer belt 501. An optical sensor 514 as a mark detecting sensor is provided with an intermediate transfer belt 501.
Are provided between the primary transfer bias roller 507 and the drive roller 508, which are bridged.

The intermediate transfer belt 501 includes a primary transfer bias applying roller 507, a belt driving roller 508, a belt tension roller 509, and a primary transfer charge applying means.
Secondary transfer opposed roller 510, cleaning opposed roller 5
11 and a feedback current detection roller 512. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded. A transfer bias controlled to a predetermined magnitude of current or voltage in accordance with the number of superimposed toner images is applied to the primary transfer bias roller 507 by a primary transfer power supply 801 controlled by a constant current or a constant voltage. ing.

The intermediate transfer belt 501 is driven in the direction of the arrow by a belt drive roller 508 that is driven to rotate in the direction of the arrow by a drive motor (not shown). The intermediate transfer belt 501 is made of a semiconductor or an insulator and has a single-layer or multilayer structure. Further, the intermediate transfer belt is set to be larger than the maximum paper-passable size in order to overlap the toner images formed on the photosensitive drum 200.

A secondary transfer bias roller 605, which is a secondary transfer unit, has a contact / separation mechanism as a contact / separation unit, which will be described later, with respect to the surface of the intermediate transfer belt 501 at a portion stretched by the secondary transfer opposed roller 510. , So as to be able to come and go. The secondary transfer bias roller 605 is a part of the intermediate transfer belt 50 that is stretched around the secondary transfer facing roller 510.
1 is provided so as to sandwich the recording paper P therebetween.
A transfer bias of a predetermined current is applied by a secondary transfer power supply 802 controlled by a constant current.

The registration roller 610 feeds the transfer paper P as a transfer material at a predetermined timing between the secondary transfer bias roller 605 and the intermediate transfer belt 501 stretched over the secondary transfer opposing roller 510. A cleaning blade 608, which is a cleaning unit, is in contact with the secondary transfer bias roller 605. The cleaning blade 608 is for removing the adhered matter attached to the surface of the secondary transfer bias roller 605 for cleaning.

In the color copying machine having such a configuration,
When the image forming cycle is started, the photosensitive drum 200
Is rotated in a counterclockwise direction indicated by an arrow by a drive motor (not shown), and Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed on the photosensitive drum 200. The intermediate transfer belt 501 is rotated clockwise by an arrow by a belt driving roller 508.
The Bk toner image, the C toner image, the M toner image, and the Y toner are transferred by a transfer bias caused by a voltage applied to the primary transfer bias roller 507 with the rotation of the intermediate transfer belt 501.
The primary transfer of the toner image is performed, and finally Bk, C, M,
The toner images are formed on the intermediate transfer belt 501 in the order of Y so as to overlap each other.

For example, the formation of the Bk toner image is performed as follows. In FIG. 2, the charging charger 203 includes:
The surface of the photosensitive drum 200 is uniformly charged to a predetermined potential with a negative charge by corona discharge. The timing is determined based on the belt mark detection signal, and a writing optical unit (not shown) performs raster exposure using laser light based on the Bk color image signal. When this raster image is exposed, in the exposed portion of the surface of the photosensitive drum 200 that is initially uniformly charged, the charge proportional to the amount of exposure light disappears, and a Bk electrostatic latent image is formed. In this Bk electrostatic latent image,
The negatively charged Bk on the developing roller of the Bk developing device 231K
Due to the contact of the toner, the toner does not adhere to the portion of the photosensitive drum 200 where the charge remains, and the toner is attracted to the portion having no charge, that is, the exposed portion, and Bk similar to the electrostatic latent image is obtained. A toner image is formed.

The Bk toner image formed on the photosensitive drum 200 in this manner is primarily transferred onto the surface of the intermediate transfer belt 501 which is rotating at a constant speed while being in contact with the photosensitive drum 200. The photosensitive drum 20 after this primary transfer
A small amount of untransferred residual toner remaining on the surface of
The photoconductor drum 200 is cleaned by the photoconductor cleaning device 201 in preparation for reuse. This photosensitive drum 200
On the side, the process proceeds to the Y image forming process after the Bk image forming process, and the reading of the Y image data by the color scanner starts at a predetermined timing.
An electrostatic latent image is formed.

After the trailing end of the previous Bk electrostatic latent image has passed and before the leading end of the T electrostatic latent image has arrived, the rotating operation of the revolver developing unit 230 is performed, and the Y developing device 231Y is set at the development position, and the Y electrostatic latent image is developed with the Y toner. Thereafter, the development of the Y electrostatic latent image area is continued, but when the rear end of the Y electrostatic latent image passes, the revolver developing unit rotates as in the case of the Bk developing machine 231K, and the next operation is performed. Is moved to the developing position. This is also completed before the leading end of the next C electrostatic latent image reaches the developing position. In the image forming processes of C and M, the operations of reading the color image data, forming the electrostatic latent image, and developing are the same as those in the processes of Bk and Y described above, and thus the description is omitted.

The toner images of Bk, Y, C, and M sequentially formed on the photosensitive drum 200 in this manner are sequentially aligned on the same surface of the intermediate transfer belt 501 and primary-transferred. As a result, a toner image in which a maximum of four colors are superimposed on the intermediate transfer belt 501 is formed. on the other hand,
At the time when the image forming operation is started, the transfer paper P is fed from a paper feed unit such as a transfer paper cassette or a manual feed tray, and stands by at the nip of the registration roller 610.

The leading end of the toner image on the intermediate transfer belt 501 is applied to a secondary transfer portion where a nip is formed by the intermediate transfer belt 501 stretched around the secondary transfer opposing roller 510 and the secondary transfer bias roller 605. When the transfer paper P is moved, the registration roller 610 is driven so that the leading end of the transfer paper P coincides with the leading end of the toner image.
And the toner image are registered.

As described above, when the transfer paper P passes through the secondary transfer section, four colors on the intermediate transfer belt 501 are generated by the transfer bias by the voltage applied to the secondary transfer bias roller 605 by the secondary transfer power supply 802. The superimposed toner image is collectively transferred (secondarily transferred) onto the transfer paper P. The transfer paper P is neutralized by passing through a portion facing a transfer paper neutralization charger 606 disposed on the downstream side of the secondary transfer unit.
0 (see FIG. 1). Then, the transfer paper P is melted and fixed at the nip portion between the fixing rollers 271 and 272 of the fixing device 270,
The paper is sent out of the apparatus main body 2 and is stacked face up on a copy tray (not shown).

On the other hand, the photosensitive drum 2 after the belt transfer
The surface of the cleaning member 201 is cleaned by the photoconductor cleaning device 201, and is uniformly discharged by the discharging lamp 202. Further, the residual toner remaining on the surface of the intermediate transfer belt 501 after the secondary transfer of the toner image onto the transfer paper P is cleaned by the belt cleaning blade 504. The belt cleaning blade 504 is configured to be brought into and out of contact with the surface of the intermediate transfer belt 501 at a predetermined timing by a cleaning member separation / contact mechanism (not shown). On the upstream side of the belt cleaning blade 504 in the moving direction of the intermediate transfer belt 501, a toner seal member 503 that comes into contact with and separates from the surface of the intermediate transfer belt 501 is provided. The toner seal member 503 receives the dropped toner dropped from the belt cleaning blade 504 during the cleaning of the residual toner, and prevents the dropped toner from scattering on the transfer path of the transfer paper P. The toner seal member 503 is brought into and out of contact with the surface of the intermediate transfer belt 501 together with the belt cleaning blade 504 by the cleaning member separation / contact mechanism.

The lubricant 506 shaved off by the lubricant application brush 505 is applied to the surface of the intermediate transfer belt 501 from which the residual toner has been removed.
The lubricant 506 is made of, for example, a solid such as zinc stearate, and is provided so as to be in contact with the lubricant applying brush 505. Also, the intermediate transfer belt 501
Remaining on the surface of the intermediate transfer belt 501
The toner is removed by the charge removing bias applied by the belt charge removing brush 502 in contact with the surface of the sheet. Here, the lubricant applying brush 505 and the belt neutralizing brush 502
Are brought into contact with and separated from the surface of the intermediate transfer belt 501 at a predetermined timing by respective contact / separation mechanisms (not shown).

Here, at the time of a repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 200 are performed as follows.
After the fourth sheet (M) image forming step of the first sheet, the process proceeds to the second sheet first color (Bk) image forming step at a predetermined timing. Further, after the batch transfer process of the first four-color superimposed toner image onto the transfer paper, the second Bk toner image is formed on the surface of the intermediate transfer belt 501 by the belt cleaning blade 504. The primary transfer is performed. Thereafter, the operation is the same as that of the first sheet.
The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. In the case of the single color copy mode,
Until the predetermined number of sheets is completed, the revolver developing unit 2
The copying operation is performed with only the 30 color developing machines in the developing operation state and the belt cleaning blade 504 kept in contact with the intermediate transfer belt 501.

The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Become. In the case of the single color copy mode, only the developing device of the predetermined color of the revolver developing unit 230 is in the developing operation state until the predetermined number of copies are completed, and the belt cleaning blade 504 is brought into contact with the intermediate transfer belt 501. The copy operation is performed in the state in which the copy operation is performed.

As described above, in a color copying machine in which the secondary transfer bias roller 605 comes into contact with and separates from the surface of the intermediate transfer belt 501, the intermediate transfer belt 501 and the secondary transfer bias Roller 605
And the intermediate transfer belt 50
1 and the secondary transfer bias roller 605
The secondary transfer bias roller 605 is attached to the intermediate transfer belt 501 so that a transfer nip having a predetermined width is formed.
At a predetermined pressure.

That is, the transfer nip is generally
Suitable for the transfer paper P when the toner image carried on the intermediate transfer belt 501 is transferred by the secondary transfer bias roller 605 onto the transfer paper P weighing about 90 kg to 220 kg called plain paper. The nip width is set so as to perform an accurate image formation. The contact pressure of the secondary transfer bias roller 605 with respect to the intermediate transfer belt 501 in the transfer unit is such that the transfer nip having the nip width as described above causes the intermediate transfer belt 501 and the secondary transfer bias roller 605 to contact each other. The pressure is set so as to be formed in the transfer portion, which is the contact portion.

However, in this type of conventional image forming apparatus, transfer paper having a thickness greater than that of the plain paper, for example, transfer paper P called "thick paper" weighing 220 kg or more is conveyed to the transfer unit. And the intermediate transfer belt 501
The toner image formed on the secondary transfer bias roller 60
When the image is formed by transferring the image by using No. 5, an abnormal image called a print may be generated without performing appropriate transfer. This is because when the thick paper as described above is conveyed to the transfer section, as shown in FIGS. 9A and 9B, the stiffness (bending strength) of the transfer paper P made of the thick paper causes
It is considered that the transfer paper P is displaced in a direction away from the intermediate transfer belt 501 against the contact pressure and the nip width of the transfer nip of the transfer portion is reduced.

Further, when the above-described thick paper is conveyed to the transfer section, the resistance when the thick paper enters the transfer nip of the transfer section becomes large. For this reason, when the thick paper enters the transfer nip, a shock is applied to the intermediate transfer belt 501 and the secondary transfer bias roller 605.
Or the flutter occurs on the cardboard, and the shock or flutter is transmitted to the transfer nip, and the transferred image transferred on the cardboard becomes an abnormal image that is locally displaced.

Accordingly, in the color copying machine according to the present embodiment, the surface of the image carrier is brought into contact with the intermediate transfer belt 501 by a contacting / separating means for bringing the secondary transfer bias roller 605 into and out of contact therewith. And a contact pressure switching means for switching the contact pressure of the transfer member to at least two stages.

In this image forming apparatus, the contact pressure of the secondary transfer bias roller 604 contacting the surface of the intermediate transfer belt 501 by the contact / separation means by the contact pressure switching means in at least two stages. Can be switched. As a result, the contact pressure of the secondary transfer bias roller 604 that contacts the surface of the intermediate transfer belt 501 is switched to a contact pressure suitable for the transfer paper P conveyed to the transfer section, and It is possible to prevent the occurrence of an image difference in the transferred image.

FIGS. 10 and 11 show an example of a mechanism for contacting and separating the secondary transfer bias roller 605 in the secondary transfer unit 600. FIG. FIG. 10 shows a state in which the secondary transfer bias roller 605 is separated from the intermediate transfer belt 501 (hereinafter, this state is referred to as “during separation”).
FIG. 11 shows a state in which the secondary transfer bias roller 605 is in contact with the intermediate transfer belt 501 (hereinafter, this state is referred to as “at the time of contact”).

The contact / separation mechanism includes a support 620 for supporting the secondary transfer bias roller 605 so as to be capable of moving toward and away from the surface of the intermediate transfer belt 501, and a support 62.
And an eccentric cam 630 for displacing the secondary transfer roller 0 in the direction of movement of the secondary transfer bias roller 605. The support 620 is swingably supported by a support shaft 621 provided at a position near the belt transport device 210. The secondary transfer bias roller 605 is rotatably supported by a portion of the support 620 that faces the secondary transfer opposing roller 510 with the intermediate transfer belt 501 interposed therebetween.

A pressing piece 620a provided at a free end of the support 620 near the registration roller includes:
The pressing member 640 is pressed against the elastic force of the pressing spring 641. When the pressing member 640 is pressed against the support 620, the support member 620 is pivoted about its support shaft 621 as shown in FIG.
At 0, a swinging behavior of swinging in the counterclockwise direction is provided. The swing of the support 620 due to the swing behavior is such that the driven piece 620b of the support 620 is moved away from the cam edge 630 of the eccentric cam 630 at the time of separation shown in FIG.
a.

In the contact / separation mechanism having such a structure, the toner image on the intermediate transfer belt 501 is
At the time of the next transfer, the eccentric cam 6 shown in FIG.
The 30 camshafts 630b are rotated 180 degrees clockwise (in the direction of the arrow) by a cam drive source (not shown). Accordingly, the eccentric cam 630 rotates 180 degrees, and the rotation of the eccentric cam 630 causes the support 620 to swing counterclockwise by the elastic force of the pressing spring 641 via the pressing member 640. And, this support 62
As a result, the driven piece 620b in contact with the cam edge 630a of the eccentric cam 630 rises so as to follow the cam edge 630a, and as shown in FIG. The roller 605 is connected to the intermediate transfer belt 5
Touch 01. At the time of this contact, the eccentric cam 6
A gap G is formed between the cam edge 630a of the No. 30 and the driven piece 620b, so that the secondary transfer bias roller 605 and the intermediate transfer belt 501 are surely in contact with each other.

Next, the contact pressure of the secondary transfer bias roller 605 contacted / separated by the contact / separation mechanism with the intermediate transfer belt 501 is switched to a contact pressure suitable for the transfer paper P conveyed to the transfer section. An example of the configuration of the contact pressure switching means will be described. This contact pressure switching means is, for example, as shown in FIGS.
50, pressure switching cam 660, pressure switching spring 6
70. The pressure switching plate 650 is swingably supported by a cam shaft 630b of the contact / separation mechanism.

Here, when the transfer paper P made of thick paper is conveyed to the transfer section, the pressure switching cam 660 is rotated in a predetermined direction by a cam driving source (not shown), and the pressure is switched by a cam edge 660a. As shown in FIG. 3, the cam follower 650b of the pressure switching plate 650 is pushed up.

Thus, the pressure switching spring 670 spanned between the locking portion 650a of the pressure switching plate 650 and the support 620 is extended. Due to the extension of the pressure switching spring 670, a clockwise rotational force is applied to the support 620 about the support shaft 621. Thereby, the pressing piece 620 of the support 620 is swung so as to swing the support 620 counterclockwise.
The pressing force of the pressing spring 641 of the pressing member 640 pressing a is reduced. As a result, the contact pressure of the secondary transfer bias roller 605 against the intermediate transfer belt 501 by the contact / separation mechanism decreases. In this state, the contact pressure of the secondary transfer bias roller 605 with respect to the intermediate transfer belt 501 is set in advance so as to be an optimal contact pressure for the transfer paper P made of the thick paper.

On the other hand, when the transfer paper P made of plain paper is conveyed to the transfer section, the pressure switching cam 660 is rotated in a predetermined direction by a cam drive source (not shown), and the cam edge 660a is moved as shown in FIG. As shown in FIG.
50 are separated from the cam follower 650b.

As a result, the pressure switching spring 670 bridged between the locking portion 650 a of the pressure switching plate 650 and the support 620 is contracted. Due to the contraction of the pressure switching spring 670, the clockwise rotational force about the support shaft 621 urged against the support 620 is released. Thereby, the support 62
The pressing force of the pressing spring 641 of the pressing member 640 pressing the pressing piece 620a of the support 620 is increased so that 0 is swung counterclockwise. As a result, the secondary transfer bias roller 6 by the contact / separation mechanism is used.
05, the contact pressure against the intermediate transfer belt 501 increases. The secondary transfer bias roller 605 in this state
The contact pressure with respect to the intermediate transfer belt 501 is set in advance so as to be an optimal contact pressure for the transfer paper P made of upper plain paper.

In the color copying machine according to the present embodiment, the secondary transfer bias roller 6
05, the contact pressure on the intermediate transfer belt 501 is
The state where the contact pressure is optimal for the transfer paper P made of the upper plain paper, that is, the state shown in FIG. 4 is the home position of the contact / separation mechanism. FIG. 6 shows a process corresponding operation for determining the home position. The switching process in the thick paper mode for transporting the thick paper to the transfer unit is performed according to the flow shown in FIG. Further, the processing operation when returning from the cardboard mode to the home position is described below.
This is shown in the flow of FIG.

Here, the secondary transfer bias roller 60
The contact pressure of the fifth transfer roller 501 with the intermediate transfer belt 501 may be changed by switching the swing position of the support 620 with a solenoid.

In this embodiment, the case where the intermediate transfer belt 501 is the intermediate transfer belt 501 has been described. However, the present invention is also applied to an image forming apparatus in which the image carrier is a drum-shaped intermediate transfer member. be able to. further,
The present embodiment is an example in which the present invention is applied to an image forming apparatus including the intermediate transfer unit 500. For example, the image forming apparatus does not include the intermediate transfer unit and directly transfers the transfer material conveyed from the image carrier by the transfer material conveyance belt. The present invention can be similarly applied to an image forming apparatus configured to perform transfer. In this case, the transfer material transport belt serves as an image carrier. Further, the deceleration means includes:
This is also effective in a tandem type image forming apparatus.

[0066]

According to the present invention, the contact pressure of the transfer member which contacts the surface of the image carrier is switched to a contact pressure suitable for the transfer material conveyed to the transfer section. Thus, there is an excellent effect that it is possible to prevent the occurrence of image difference of the image transferred to the transfer material.

In particular, according to the second aspect of the present invention, the contact pressure of the transfer member contacting the surface of the image carrier is adjusted to a contact pressure suitable for the type and thickness of the transfer material conveyed to the transfer section. In this case, there is an excellent effect that it is possible to prevent the occurrence of image difference of the image transferred to the transfer material.

According to the third aspect of the present invention, by arranging the transfer material selection button on the operation panel of the apparatus main body, the operator can reduce the contact pressure of the transfer member that contacts the surface of the image carrier. There is an excellent effect that switching can be easily performed.

According to the fourth aspect of the present invention, the contact pressure of the transfer member contacting the surface of the image carrier is switched to a contact pressure suitable for the transfer speed of the transfer material transferred to the transfer section. Thus, there is an excellent effect that it is possible to prevent the occurrence of image difference of the image transferred to the transfer material.

According to the fifth aspect of the present invention, the contact pressure of the transfer member that comes into contact with the surface of the image carrier, which is one of the causes of fluttering, is conveyed to the transfer section. Since the contact pressure can be switched to a contact pressure suitable for the transfer material, there is an excellent effect that the flutter of the intermediate transfer body can be reduced and a color image without color shift can be formed.

According to the sixth aspect of the present invention, the contact pressure of the transfer member contacting the surface of the image carrier is switched to a contact pressure suitable for the transfer material conveyed to the transfer section, There is an excellent effect that the occurrence of an abnormal image of the image transferred to the transfer material can be prevented.

[Brief description of the drawings]

FIG. 1 is a front view showing a schematic configuration of a color copying machine according to an embodiment of the present invention.

FIG. 2 is a front view showing a schematic configuration of a main part of the color copying machine.

FIG. 3 is a schematic configuration diagram of a main part for describing a configuration of a contact pressure switching unit in a secondary transfer unit of the color copying machine.

FIG. 4 is a schematic diagram of a main part showing a configuration of the contact pressure switching means at a home position.

FIG. 5 is a schematic perspective view of the contact pressure switching means.

FIG. 6 is a flowchart showing a processing corresponding operation for determining a home position of the contact pressure switching means.

FIG. 7 is a flowchart showing a process corresponding operation of a switching process in a thick paper mode in which a thick paper is transported to a transfer unit by the contact pressure switching means.

FIG. 8 is a flowchart showing a processing operation when returning from the thick paper mode to the home position.

FIGS. 9A and 9B are schematic configuration diagrams illustrating a configuration of a secondary transfer unit in a conventional color copying machine.

FIG. 10 is a schematic configuration diagram showing a configuration when a contact / separation mechanism of a secondary transfer bias roller is separated in a color copying machine according to an embodiment of the present invention.

FIG. 11 is a schematic configuration diagram showing a configuration at the time of contact of a contact / separation mechanism of a secondary transfer bias roller in the color copying machine according to the embodiment of the present invention.

[Explanation of symbols]

 200 Photoconductor drum 203 Charging charger 220 Writing optical unit 230 Revolver developing unit 500 Intermediate transfer unit 501 Intermediate transfer belt 502 Belt discharging brush 503 Toner seal member 504 Belt cleaning blade 505 Lubricant application brush 506 Lubricant 507 Primary transfer bias roller 508 Belt drive roller 510 Secondary transfer opposing roller 600 Secondary transfer unit 605 Secondary transfer bias roller 606 Transfer paper discharging charger 610 Registration roller 620 Support 620a Pressing piece 620b Follower piece 621 Support shaft 630 Eccentric cam 630a Cam edge 630b Cam shaft 640 Pressing member 641 Pressing spring 650 Pressure switching plate 650a Locking piece 650b Cam driven piece 660 Pressure switching cam 660a Pressure switching cam Kamuen 670 pressure switching spring P transfer paper

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shin Chihara 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H027 DA20 DC02 EA18 ED24 EF09 FA30 FA35 2H032 AA05 AA15 BA09 BA13 BA19 BA23 BA30 CA02 CA04 CA11

Claims (6)

[Claims] An image carrier that carries a toner image formed on the surface and moves, and a transfer member that is configured to be able to come into contact with and separate from the surface of the image carrier, and is formed on the surface of the image carrier. Transfer means for transferring the toner image thus transferred onto a transfer material conveyed toward a transfer section between the transfer member and the image carrier, and contacting the transfer member with the surface of the image carrier. An image forming apparatus comprising: a contact pressure switching unit configured to switch a contact pressure of the transfer member in contact with a surface of the image carrier by at least two stages by the contact / separation unit. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the contact pressure switching unit contacts the surface of the image carrier according to a type and a thickness of a transfer material conveyed to the transfer unit. An image forming apparatus configured to switch a contact pressure of the transfer member. 3. The image forming apparatus according to claim 2, further comprising a transfer material selection button for selecting a type of transfer material to be conveyed toward said transfer section, wherein said contact pressure switching means includes a transfer material selection button. An image forming apparatus configured to switch the contact pressure of the transfer member that contacts the surface of the image carrier when the type of the transfer material is selected. 4. The image forming apparatus according to claim 1, wherein said contact pressure switching means is adapted to move the contact pressure switching means with respect to a surface of said image carrier in accordance with a transfer speed of a transfer material transferred to said transfer unit. An image forming apparatus configured to switch a contact pressure of the transfer member that comes into contact with the transfer member. 5. The image forming apparatus according to claim 1, wherein said image carrier is primary-transferred from said latent image carrier on which said toner image is formed by primary transfer means. An image forming apparatus, wherein the toner image is an intermediate transfer member that is secondarily transferred to the transfer material by a secondary transfer unit after the toner image is formed. 6. The image forming apparatus according to claim 5, wherein the transfer material conveyed toward the transfer section is conveyed along the surface of the intermediate transfer body before the transfer section. As described above, the image forming apparatus is characterized in that the inner peripheral surface in front of the transfer section is constituted by an endless belt stretched by a fixed stretching member.