JP2004184449A - Transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device capable of preventing the occurrence of an abnormal image due to curling or the like while suppressing the increase of cost due to the increase of the number of parts. <P>SOLUTION: The transfer device is provided with: a belt 3 which is laid around rolls 3A and 3C installed side by side to form a horizontally spread surface H; a plurality of transfer members 8 and 8' which are arranged along the spread surface H inside a circumferential range of the belt 3; a plurality of photoreceptors 4 and 4' which face respectively the transfer member 8 and 8' with the spread surface H between; and a supporting means 100 which supports rockably the roll 3C positioned in the upstream side in the moving direction of the spread surface H and the transfer member 8' other than the transfer member 8 being the closest to the roll 3A positioned in the downstream side in the moving direction of the spread surface H among the rolls forming the spread surface H. The supporting means 100 is constituted so that the belt 3 is made nearer to and away from the photoreceptor 4' remaining the transfer member 8 which is in the closest position to the roll 3A in the downstream side in the moving direction of the spread surface H in a state where the roll 3C positioned in the upstream side in the moving direction of the spread surface H is installed on a rocking end. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transfer device and an image forming apparatus, and more particularly, to a configuration in which a belt is used as a transfer member when forming a multicolor image including a full-color image.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a printing machine, a configuration capable of forming not only a single color but also a multicolor image including a full color is known.
As a method of forming a full-color image, a plurality of developing devices are arranged so as to be in contact with a photoconductor as one latent image carrier, and a toner image of each color is created for each rotation of the photoconductor, and the image is formed. There is a method called a tandem method, which is different from a so-called one-drum method in which a photoreceptor is sequentially transferred to a sheet held on an intermediate transfer member or a transfer drum to form a color toner image (for example, a tandem method). Patent Document 1).
[0003]
In the tandem system, the number of photoconductors is increased by the number of colors (usually three or four), and corresponding developing devices are arranged so that the paper continuously contacts the photoconductor to obtain a color image. It has the following configuration. Unlike the one-drum system, this system does not require the photosensitive member to be rotated the number of times of image formation, and has the advantage of high productivity.
[0004]
In the tandem system, a belt is used as a transfer / transport member that moves paper while facing each photoconductor.
When the belt is in constant contact with each photoconductor, the developing device that performs image forming processing accompanying the photoconductor also works in conjunction with it. Therefore, even when the photoconductor is not used, the operation is performed, which is disadvantageous in the running cost.
[0005]
Therefore, in order to selectively use each photoconductor in accordance with the color image forming mode, the transfer / conveying belt is always in contact with only the photoconductor capable of forming a specific color image, and the other color image is formed. A configuration has been proposed in which a photosensitive member that can be formed can be selectively contacted and separated (for example, Patent Document 1).
[0006]
FIG. 6 is a schematic diagram showing a transfer / conveyance belt contact / separation mechanism including the above-mentioned Patent Document 1. In FIG. 6, photosensitive members D1, D2, D3, and D4 arranged in a horizontal direction in FIG. The transfer members A1 to A4 provided so as to face the body except for those facing the photoreceptor D1 capable of forming a color image other than black are provided inside the orbiting area of the belt B. It is supported by a swingable support arm C with the swinging fulcrum C1 as a fulcrum, and can be moved toward and away from the photoconductors D2 to D4 according to the swinging position of the support arm C.
The belt B is maintained at a predetermined tension by a tension roller E provided on a side opposite to a position facing the photoconductor in the orbiting area. Note that, in the drawing, reference numeral K indicates a cleaning unit.
[0007]
[Patent Document 1]
JP-A-2002-139887 (Claim 1, FIG. 4)
[0008]
[Problems to be solved by the invention]
However, the conventional belt contact / separation structure including the configuration disclosed in Patent Document 1 has the following problems.
As is clear from the configuration shown in FIG. 6, the support arms C for moving the belt toward and away from the photoconductor are transfer members A <b> 2 to A Since A4 is supported as a target, the swing angle must be increased when the belt is separated from each photoconductor. In particular, the pair of rollers R1 and R2 for forming the belt expanding surface have a small diameter due to a tendency to miniaturize the apparatus, and it may be difficult to set the swing angle of the support arm C in the vertical direction. As a result, the belt may not be reliably separated from the photoconductor.
The support arm C is a specially provided member, and the increase in cost due to the addition of such a configuration cannot be denied. In particular, Patent Document 1 discloses a configuration for setting the swinging position of the support arm, in which a special side plate member is provided at the swing end of the support arm and the side plate member is displaced by a cam. Comes with an increase in scores. Regarding the increase in the number of parts, there is an auxiliary roller P provided on the support arm C. The auxiliary roller P is a member for providing a transfer nip portion of the belt B between the auxiliary roller P and the photoconductor D4. Therefore, the support arm C requires a member that is not related to each transfer member.
[0009]
On the other hand, the belt maintains the stretched state by the application of tension. However, as described above, if the rollers R1 and R2 are constantly applied with high pressure, the radius of curvature of the rollers is small. Has a curl, and the belt may be wavy. As a result, an abnormal image in which a color shift or the like due to a shift in an image transfer position when forming a multicolor image is easily caused is likely to occur. In particular, when the use frequency of black images, that is, so-called monochrome images, is greater than that of full-color images, the state in which the same portion is wrapped around by the rollers R1 and R2 in a state of contacting only one photoconductor and being separated from the other photoconductor is considered. When maintained, a curling tendency, that is, a so-called curl, is likely to occur in a portion wound around the roller.
[0010]
Further, the belt B is a member that needs to be replaced due to its life or the like, and it is desired that the workability of removal at the time of replacement be improved.
[0011]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in the conventional transfer device, particularly in a transfer device having a structure capable of coming in contact with and separating from a photoreceptor. It is an object of the present invention to provide a transfer device and an image forming apparatus having a configuration that can prevent the occurrence of an image and that can easily perform maintenance and replacement work.
[0012]
[Means for Solving the Problems]
The invention according to claim 1 is a belt capable of forming a horizontal expansion surface by being wound around juxtaposed rollers, and a plurality of transfer members arranged along the expansion surface inside the orbital area of the belt. A plurality of photoconductors respectively facing the transfer members with the extended surface interposed therebetween, and a roller that is located on the upstream side in the moving direction of the extended surface among the rollers that form the extended surface of the belt; Supporting means for swingably supporting a transfer member excluding a transfer member closest to a roller positioned downstream of the movement direction, wherein the support means is a roller positioned upstream of the expansion surface in the movement direction. In the state where the belt is arranged at the swinging end, the belt is moved toward and away from the photosensitive member while leaving the transfer member closest to the roller on the downstream side in the moving direction of the expanding surface. I have.
[0013]
According to a second aspect of the present invention, in addition to the first aspect, among the rollers located on both sides of the expanding surface of the belt, the roller located on the downstream side in the moving direction of the expanding surface is configured to swing the support means. A roller is used as a moving fulcrum, and a roller on the upstream side in the moving direction of the expanding surface is located at the oscillating fulcrum and a swing end as a reference.
[0014]
According to a third aspect of the present invention, in addition to the first or second aspect, the roller on the downstream side in the moving direction of the spreading surface is used as a driving member for the belt, and the roller on the upstream side in the moving direction is used for expanding the belt. It is characterized in that it is used as a tension roller for applying tension in a direction parallel to the surface.
[0015]
According to a fourth aspect of the present invention, in addition to the first or second aspect, the belt is wound around a roller having a fixed arrangement position separately from the juxtaposed rollers, and the transfer member is provided with the photosensitive member. It is characterized in that the tension at the time of moving toward and away from the body changes.
[0016]
According to a fifth aspect of the present invention, in addition to the fourth aspect, a change in the tension of the belt is set within 50%.
[0017]
According to a sixth aspect of the present invention, in addition to the fourth or fifth aspect, a state in which the tension of the belt is reduced is set to a standby state.
[0018]
According to a seventh aspect of the present invention, in addition to the fourth or fifth aspect, the tension of the belt is different depending on whether only one of the plurality of photoconductors is used or when all the photoconductors are used. It is characterized by changing.
[0019]
The invention of claim 8 is characterized in that, in addition to the invention of claim 7, the belt tension is lower when only one of the photoconductors is used than when all of the photoconductors are used. I have.
[0020]
According to a ninth aspect of the present invention, in addition to the first aspect of the present invention, the supporting means may be configured such that the swing fulcrum when swinging while leaving the one transfer member is extended. It is characterized in that it is set between the transfer member and the transfer member located closest to the roller, including the roller on the downstream side in the surface movement direction.
[0021]
An image forming apparatus according to a tenth aspect of the present invention uses the transfer device according to any one of the first to ninth aspects as an image forming apparatus.
[0022]
According to an eleventh aspect of the present invention, in addition to the tenth aspect, the plurality of photoconductors are capable of forming images of different colors, and among them, a position closest to the downstream side in the moving direction of the expanding surface. Is used for forming a black image.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 illustrated in FIG. 1 is a color printer that can form a full-color image. The present invention can be applied not only to a color printer but also to a facsimile machine, a copying machine or a printing machine which can use an electrostatic recording system or an electrophotographic system.
[0024]
In FIG. 1, the image forming apparatus 1 is provided with a paper feeding unit B below and a paper discharging unit C above the image forming processing unit PA installed at the center in the vertical direction.
In the image forming processing unit PA, a plurality of image forming units 2A, 2B, 2C, and 2D are juxtaposed in the horizontal direction, and each of the image forming units 2A to 2D abuts and abuts on a photosensitive member of the image forming unit. It faces a primary transfer belt 3 which is a primary transfer body having a possible extending surface.
[0025]
The image forming units 2A to 2D are units capable of forming images of yellow, magenta, cyan, and black used to form a full-color image, and a detailed configuration will be described with reference to one of them. It is as follows. It is needless to say that the other image forming units have the same configuration.
[0026]
In the image forming unit 2A, a photoconductor 4 as a latent image carrier using a drum that can rotate while being in contact with the primary transfer belt 3 is arranged. A charging device 5, a writing device 6, a developing device 7, a primary transfer device 8, and a cleaning device 9 including a blade 9A and a neutralization lamp 9B for executing an image forming process in the rotation process of FIG.
[0027]
The photoreceptor 4 has a structure in which an organic photosensitive layer as a photoconductive substance is provided on the surface of an aluminum cylinder having a diameter of about 30 to 100 mm. The photosensitive member 4 may have an amorphous silicon layer formed on the surface. In the present embodiment, as will be described later, the photoconductor 4 at a position closest to the roller 3A located on the downstream side in the movement direction (the direction indicated by the symbol F in FIG. 1) of the primary transfer belt 3 in the horizontal direction. However, it is designed to be used as a photoreceptor for forming a frequently used black image regardless of whether a full-color image or a monochrome image is formed.
[0028]
The writing device 6 is provided for the photoconductors included in each of the image forming units 2A to 2D, and is provided with a laser light source, a deflecting member using a rotating polygon mirror, and an image forming optical system, although not denoted by reference numerals. Scanning light is radiated to the photosensitive member by a signal from an image forming control unit (not shown) based on the image forming timing between the image forming units.
[0029]
In the image forming units 2A to 2D, a charging process, a writing process, and a developing process for the photoconductor are executed at a preset image forming timing, and the electrostatic latent image formed in the writing process is converted into a visible image in the developing process. When the image is processed and processed, the image is sequentially transferred to the primary transfer belt 3. At the time of transfer, the image is electrostatically transferred by a primary transfer device 8 which is provided inside the orbital area of the primary transfer belt 3 and faces the photoconductor 4 with the primary transfer belt 3 interposed therebetween.
The primary transfer device 8 uses a roller that generates a small amount of ozone, such as at the time of electric discharge, by contacting the back surface of the primary transfer belt 3. The primary transfer device 8 has a polarity opposite to that of the toner used in the developing process and is relatively low. By applying a voltage transfer bias, the toner carried on the photoconductor 4 is electrostatically transferred to the primary transfer belt 3.
[0030]
The photoreceptor 4 after the primary transfer removes residual toner and residual charge on the photoreceptor by a blade 9A and a discharging lamp 9B included in the cleaning device 9, and is prepared for the next image forming process.
[0031]
The primary transfer belt 3 is a seamless belt based on a resin film or rubber having a thickness of about 50 μm to 600 μm, and a horizontal extending surface H is formed by juxtaposed rollers 3A and 3C. In addition to the rollers 3A and 3C, the extended surface H is also wrapped around the roller 3B whose arrangement position is fixed, and moves in the direction indicated by the arrow F.
[0032]
The image forming processing unit PA is provided with a secondary transfer belt 12 forming a secondary transfer body facing the primary transfer belt 3.
The secondary transfer belt 12 is wound around a plurality of rollers 12A to 12D so as to be movable in the direction of the arrow shown in the figure.
[0033]
On the inner side of the secondary transfer belt 12, a secondary transfer roller 13 is provided so as to face the vicinity of the roller 3A on the primary transfer belt 3 side, and the toner image carried on the primary transfer belt 3 is electrostatically charged. A transfer bias for transfer is applied.
A transfer nip portion is formed between the roller 12B and the transfer roller 13 of the secondary transfer belt 12 while pressing the secondary transfer belt 13 against a roller 3A disposed inside the primary transfer belt 3. ing.
[0034]
The cleaning device 14 removes residual toner from the secondary transfer belt 12. The cleaning device 14 includes a cleaning roller 14A, a blade 14B, and a collection member 14C having the same functions as those of the cleaning device 11 for the primary transfer belt 3, and a unit accommodating these members is a fulcrum shaft. 14D allows the cleaning roller 14A to contact and separate from the secondary transfer belt 12.
[0035]
On the other hand, in the paper feed unit CB, paper feed cassettes 15 and 15 ′ accommodating sheets as recording media of a plurality of sizes, and feed rollers 16 and 15 disposed on the sheet feed side in each paper feed cassette. 16 ′ and a registration roller 17 provided at a position where the sheets extracted from each paper feed cassette merge.
[0036]
The paper discharge unit EC includes a fixing device 17 and a paper discharge tray 18 arranged on an extension of the extended surface of the secondary transfer belt 12.
The fixing device 17 includes a pair of heating rollers 17A and 17B opposed to each other with a sheet conveyance path extending on an extension of the extended surface of the secondary transfer belt 12 interposed therebetween.
[0037]
The sheet that has passed through the fixing device 17 is discharged to a discharge tray 18 via a pair of discharge rollers 18A.
[0038]
In the present embodiment, the sheet is discharged so that the image transferred from the primary transfer belt 3 is on the lower side. That is, the sheets stacked on the sheet discharge tray 18 are arranged in such a manner that the pages are arranged in order from the lower side. No post-processing is required. An image forming method for the primary transfer belt 3 and the secondary transfer belt 12 is also set so as to obtain such a discharge mode in which the pages can be aligned. The image forming order on the primary transfer belt 3 is set so that the transferred toner image is an erect image and the toner image transferred from the secondary transfer belt 12 to the sheet is a mirror image. When the first page faces downward, the toner image is directly transferred from the primary transfer belt 3 to the sheet.
[0039]
In the image forming apparatus 1 having the above-described configuration, the image forming units 12A to 12D perform the image forming in accordance with the image forming order set by the image forming control unit (not shown), and the image forming unit 12 </ b> A The carried toner images are sequentially transferred to the primary transfer belt 3 and are superimposed and transferred.
The transfer state of the superimposed transfer image carried on the primary transfer belt 3 with respect to the secondary transfer belt 12 is set according to the mode of single-sided printing or double-sided printing of the sheet.
[0040]
In the image forming mode on both sides of the sheet, the image superimposedly transferred on the primary transfer belt 3 is transferred to the secondary transfer belt 12. In this case, electrostatic transfer is performed by a transfer bias from the secondary transfer roller 13 at a position where the primary transfer belt 3 and the secondary transfer belt 12 are in contact with each other to form a transfer nip.
[0041]
When the transfer to the secondary transfer belt 12 is completed, the primary transfer belt 3 can perform the image transfer by superimposition again after the toner is removed by the cleaning device 11, and the superimposed transfer image is subjected to the primary transfer. The toner image carried on the secondary transfer belt 12 is collectively transferred onto the sheet fed from the paper feeding unit C while being carried on the belt 3.
[0042]
The sheet on which the toner images are collectively transferred is separated from the secondary transfer belt 12 by curvature separation when passing through the roller 12C located on the side of the fixing device 17 among the rollers around which the secondary transfer belt 12 is wound. Then, the toner advances to the fixing device 17, and the toner is melted and permeated by the heating and pressurization by the fixing device 17 to be fixed and discharged to the paper discharge tray 18. When the images transferred on both sides of the sheet are in page order, as described above, the toner image transferred by the primary transfer belt 3 is directed downward in the discharge tray 18 so that the toner image is discharged in the page order. Will be done.
[0043]
On the other hand, in the single-sided printing mode of the sheet, the image transferred to the primary transfer belt 3 only is transferred to the sheet, and the image transferred to the secondary transfer belt 12 is transferred to one side of the sheet. However, in the case of transferring the image on the primary transfer belt 3 side, the image transferred from the photosensitive member of each image forming unit to the primary transfer belt 3 is heated by a roller 3A to the sheet. Is thermally transferred. When the sheet carrying the image by the thermal transfer is discharged to the discharge tray 18, the image surface faces downward, and is discharged in a so-called face-down state.
[0044]
The primary transfer belt 3 on which the horizontal extension surface H is formed by the juxtaposed rollers 3A and 3C is arranged on the primary transfer device 8 with respect to the photosensitive member 4 juxtaposed in parallel with the extension surface H. The other primary transfer device 8 comes in contact with and separates from the other primary transfer devices. This configuration will be described below with reference to FIGS.
FIG. 2 is a schematic diagram illustrating a state of the primary transfer belt 3 when a full-color image is formed. In FIG. 2, the primary transfer belt 3 is a roller that can be juxtaposed to form a horizontal extending surface H. 3A and 3C, and at the same time apart from the rollers, the roller 3B whose position is fixed at a position distant from the expanding surface H so that the horizontal expanding surface H moves in the direction indicated by the arrow F. It is designed to move.
The movement of the primary transfer belt 3 is executed by using a roller 3A located downstream of the horizontal expanding surface H in the moving direction as a driving roller (hereinafter, referred to as a driving roller 3A).
[0045]
The roller 3 </ b> B functions as a backing member for the primary transfer belt 3 when cleaning the primary transfer belt 3, and when the rubbing pressure from the cleaning device 14 acts on the primary transfer belt 3, the primary transfer belt 3 The transfer belt 3 is prevented from loosening.
[0046]
A roller 3C located on the upstream side in the movement direction of the extension surface H of the primary transfer belt 3 is a tension roller that applies tension to the primary transfer belt 3 in a direction parallel to the extension surface H (hereinafter, this roller is referred to as a tensioner). Roller 3C). Therefore, the tension roller 3C is provided with an elastic body 101 such as a compression spring as tension applying means.
[0047]
In the primary transfer device 8 as a transfer member provided inside the orbiting area of the primary transfer belt 3 and facing each photoconductor, on the downstream side in the moving direction of the horizontal extending surface H of the primary transfer belt 3 in the movement direction. Other primary transfer devices (for convenience, indicated by reference numeral 8 'in FIG. 2) except for the primary transfer device 8 closest to the driving roller 3A, which is a positioned roller, are supported by common support means 100.
[0048]
The support means 100 includes a swing member having a swing fulcrum in a range where the primary transfer device 8 'is installed, including the drive roller 3A located on the downstream side in the movement direction of the horizontal expansion surface H. In this embodiment, the position of the drive roller 3A is used as a pivot point.
[0049]
The support means 100 has a primary transfer device 8 'located closest to the drive roller 3A, the other primary transfer device 8', and a tension roller 3C located on the upstream side in the moving direction of the expansion surface H at the swing end. The position of the tension roller 3C, which is an oscillating member and is located on the upstream side in the direction of movement of the spread surface with respect to the photosensitive member (indicated by reference numeral 4 'in FIG. 2 for convenience) facing the other primary transfer device 8'. The primary transfer device 8 ′ can be brought into contact with or separated from the primary transfer device 8 ′ by setting the swing radius to the swing radius.
[0050]
When forming a full-color image, the support means 100 causes the primary transfer belt 8 so that all the primary transfer devices 8, 8 'including the position closest to the drive roller 3A face the photoconductors 4, 4'. 3 is brought into contact with the photoconductors 4 and 4 'to form a monochrome image using black, while leaving the primary transfer device 8 closest to the drive roller 3A side, other primary transfer devices 8'. And a swinging position for separating the tension roller 3C from the photoconductor 4 '.
[0051]
The support means 100 has a structure for swinging at the swing fulcrum side or the swing end side, and FIG. 3 shows the structure.
In FIG. 3, an operating portion 100A is provided in a part of the support means 100, and the peripheral surface of an eccentric cam 102, which is a swing drive member, is in contact with the operating portion 100A.
As shown in FIG. 4, the eccentric cam 102 is rotatably driven by a drive motor 104 provided on an output shaft of a worm 104A meshing with a worm wheel 103 provided on a support shaft 102A, and has a rotational position provided on the support shaft 102A. The contact / separation detection filler 105 and the position detection sensor 106 capable of detecting the phase of the contact / separation detection filler 105 are set. That is, by setting the phase relationship between the cam profile of the eccentric cam 102 and the contact / separation detection filler 105 in advance, the rotational phase of the drive motor 104 is controlled, so that the rocking position of the support means 100 by the eccentric cam 102 is changed. It can be set. As the swing fulcrum of the supporting means 100, a position between the position of the driving roller 3A and the position where the primary transfer member 8 closest to the driving roller 3A is installed, or the position of the driving roller 3A is set. When the roller 3A is used as a swing fulcrum, the base end of the support means 100 is supported by the rotation shaft of the drive roller 3A.
[0052]
In the present embodiment, in the above-described configuration, when forming a full-color image, the support unit 100 is in the state shown in FIG. The primary transfer belt 3 comes into contact with each of the photoconductors 4 and 4 ′ such that they face each other. At this time, the eccentric cam 102 makes the peripheral surface of the minimum diameter abut on the operating piece 100A of the support means 100.
In this state, the elastic body 101 provided on the tension roller 3C is in the most contracted state, and the high repulsive force is accumulated.
[0053]
The high repulsion force of the elastic body on the tension roller 3C side makes the tension of the primary transfer belt 3 the maximum value, and the wrapping force on the drive roller 3A also increases, thereby preventing the primary transfer belt 3 from slipping. The drive transmission accuracy is also improved, so that a transfer position shift and a color shift at the time of the superimposed transfer of the color images for the respective photoconductors 4 and 4 ′ can be prevented.
[0054]
On the other hand, when a monochrome image is formed, the supporting unit 100 is set to the state shown in FIG. 2B, and the other primary transfer device 8 'is left except for the primary transfer device 8 closest to the driving roller 3A. And the tension roller 3C swings in the direction away from the photoconductor 4 '. At this time, since the support means 100 swings by the swing radius including the position of the tension roller 3C, the swing amount for separating the primary transfer device 8 'from the photoconductor 4' is increased even if the swing angle is small. be able to.
[0055]
In this state, the distance (the distance indicated by reference numeral G1 in FIG. 2) between the roller 3B whose arrangement position is fixed and the support means 100 is the state shown in FIG. 2A (FIG. 2A). The distance between the roller 3B and the extended surface H (indicated by reference numeral H1 in FIG. 2) is changed from that of the time indicated by reference numeral G0 in FIG. It becomes smaller than the state (the distance indicated by the symbol H0 in FIG. 2A). For this reason, the primary transfer belt 3 is slackened by the above-described difference in the distance, and the elastic body 101 of the tension roller 3C for absorbing the slack also has a long length in the state shown in FIG. 3 (A), and extends to a length indicated by a symbol L1 in FIG. 3 (B). As a result, the repulsion force of the elastic body 101 is lower than in the state shown in FIG. 2A, and the wrapping force of the tension roller 3C is weaker than in the state shown in FIG. . At this time, the tension roller 3C is also pushed out from the original position by the extension of the elastic body 101, so that the nip width with respect to the primary transfer belt 3 is secured, and the slack on the drive roller 3A side can be eliminated.
[0056]
In the present embodiment, the swing amount of the support unit 100 is defined so that the decrease in the tension of the primary transfer belt 3 is within 50%, thereby preventing the primary transfer belt 3 from being excessively slackened. Slip is prevented when the slack occurs. Thus, unlike the case of a full-color image, even when a monochrome image that does not require transfer position alignment is formed, slip that may occur on the roller, particularly the drive roller 3A side, is eliminated, and image expansion due to the slip is prevented. In addition, by reducing the winding force on the roller, it is possible to suppress the occurrence of curl, that is, the occurrence of curl. When the curl is generated, the mark is attached, and this becomes a horizontal band-like white spot, and an abnormal image is generated.
[0057]
In the present embodiment, the state shown in FIG. 2B, that is, the support unit 100 swings in a direction to separate the primary transfer device 8 ′ from the photoconductor 4 ′, and the tension of the primary transfer belt 3 is reduced. The standby state is set as a standby state, thereby preventing an image transfer failure due to a waving phenomenon due to curl on the primary transfer belt 3 during full-color image formation.
[0058]
The primary transfer belt 3 may be removed due to replacement due to its life or maintenance and inspection. In this case, the swinging fulcrum of the supporting means 100 is set between the primary transfer device 8 and the driving roller 3A including the driving roller 3A located on the downstream side in the moving direction of the expanding surface H in the belt orbiting area, In addition, the primary transfer device 8 'located on the drive roller 3A side can have a large contact / separation distance depending on the magnitude of the swing radius, so that the primary transfer belt 3 located outside thereof can be easily removed without increasing the tension. be able to.
[0059]
【The invention's effect】
According to the first, second and fourth aspects of the present invention, one of the rollers that are arranged side by side to form a horizontal expanding surface and one of the transfer member and the transfer member that is located on the upstream side in the movement direction of the expanding surface is left. Since the supporting means for bringing the transfer member into and out of contact with the photosensitive member is provided, the swing radius can be set to a length substantially along the extended surface. Thereby, the contact / separation operation between the photosensitive member and the transfer member can be enabled with a small swing angle. In particular, in the invention according to claim 4, since the distance between the roller whose arrangement is fixed and the spread surface can be changed, the winding around the roller due to the tension of the belt is suppressed, and the occurrence of an abnormal image is simplified. This can be achieved by a configuration.
[0060]
According to the third and fifth aspects of the present invention, the roller located on the downstream side in the moving direction of the expansion surface is used as a driving roller, and the roller on the upstream side in the moving direction is used as a tension roller for applying tension. It is possible to prevent slack on the drive roller side by absorbing slack at the swing end side where the belt is likely to loosen when the support means swings, and to prevent the occurrence of winding habits due to an increase in winding force. It becomes possible.
[0061]
According to the sixth aspect of the present invention, by setting the state in which the tension of the belt is reduced to the standby state, when the belt comes into contact with all of the photoconductors again, the state in which the belt has no curl or so-called curl is handled. be able to. As a result, image defects caused by curling can be reliably prevented.
[0062]
According to the seventh and eighth aspects of the present invention, the tension of the belt changes depending on the use mode of the photoconductor, and particularly when only one of the photoconductors is used, the tension is reduced as compared with when all the photoconductors are used. Therefore, it is possible to prevent the belt from deforming when forming a full-color image that is used less frequently than the monochrome image, and in particular, to prevent an abnormal image due to the occurrence of curling.
[0063]
According to the ninth aspect of the present invention, since the swinging fulcrum of the supporting means is provided between the transfer member disposed closest to the roller including the roller on the downstream side in the moving direction of the expansion surface and the transfer member. In addition, since the roller located downstream of the swinging fulcrum and the roller on the downstream side in the movement direction does not cause any obstacle and does not cause an increase in tension, the belt can be easily removed and replaced.
[0064]
According to the tenth and eleventh aspects of the invention, the transfer member always faces the photosensitive member for forming a monochrome image, and the transfer member can contact and separate from the photosensitive member for forming images of other colors. Therefore, it is possible to reduce the running cost by switching the drive state of the less frequently used photoreceptor by causing the transfer member to face the frequently used photoreceptor. In addition, when switching from the monochrome image forming state to the full color image forming state, the state in which the belt tension has been reduced during the monochrome image forming is suppressed, and the occurrence of curling is suppressed. It is possible to eliminate the occurrence of positional deviation and color deviation.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a main configuration of an image forming apparatus according to an embodiment of the present invention.
FIGS. 2A and 2B are schematic diagrams for explaining a configuration of a transfer device used in the image forming apparatus shown in FIG. 1, wherein FIG. 2A shows a state during full-color image formation, and FIG. Each state during standby is shown.
FIG. 3 is a view for explaining a configuration of a swing drive unit of a support means used in the transfer device shown in FIG. 2;
FIG. 4 is a view showing a structure for swinging a support means used in the transfer device shown in FIG. 2;
5A and 5B are diagrams for explaining the action of a roller located on the upstream side in the movement direction of the belt expansion surface in the transfer device, and FIG. 5A illustrates a state in which the elastic body is accumulating a high repulsion force. , (B) show the state where the repulsive force is reduced.
FIG. 6 is a schematic diagram for explaining a conventional example regarding a contact / separation mechanism between a photosensitive member and a transfer member.
[Explanation of symbols]
1 Image forming apparatus
2 Imaging unit
3 Primary transfer belt
3A drive roller
3C tension roller
4,4 'photoreceptor
8,8 'primary transfer device as transfer member
100 support means
101 elastic body
H Expansion surface

Claims (11)

A belt that can be wrapped around juxtaposed rollers to form a horizontal extending surface,
A plurality of transfer members arranged along the spread surface inside the orbiting area of the belt,
A plurality of photoconductors facing each of the transfer members with the extending surface interposed therebetween,
Of the rollers forming the expansion surface of the belt, the transfer member excluding the transfer member closest to the roller located on the upstream side in the movement direction of the expansion surface and the roller located on the downstream side in the movement direction of the expansion surface Supporting means for swingably supporting,
The support means is configured such that a roller located on the upstream side in the moving direction of the expansion surface is arranged at the swing end, and the transfer member at a position closest to the roller on the downstream side in the movement direction of the expansion surface is left on the photoconductor. A transfer device, wherein the transfer belt is configured to contact and separate the belt. The transfer device according to claim 1,
Of the rollers located on both sides of the belt on the extending surface, the roller located on the downstream side in the moving direction of the extending surface is used as a swinging fulcrum of the support means, and the swinging fulcrum and the swinging end used as a reference are A transfer device, wherein a roller on the upstream side in the movement direction of the expansion surface is located. The transfer device according to claim 1, wherein
The roller on the downstream side in the moving direction of the expanding surface is used as a driving member of the belt, and the roller on the upstream side in the moving direction is used as a tension roller that applies tension in a direction parallel to the expanding surface of the belt. Transfer device. The transfer device according to claim 1, wherein
In addition to the rollers arranged side by side, the belt is wrapped around a roller having a fixed arrangement position, and the tension at which the transfer member moves the belt toward and away from the photoconductor changes. Transfer device. The transfer device according to claim 4,
The transfer device according to claim 1, wherein a change in the tension of the belt is set within 50%. The transfer device according to claim 4, wherein
A transfer device wherein a state in which the tension of the belt is reduced is a standby state. The transfer device according to claim 4, wherein
The transfer device according to claim 1, wherein the tension of the belt is changed when only one of the plurality of photoconductors is used and when all the photoconductors are used. The transfer device according to claim 7,
The transfer device according to claim 1, wherein the tension of the belt is lower when only one of the photoconductors is used than when all of the photoconductors are used. The transfer device according to claim 1, wherein
The supporting means may be configured such that the pivot point at which the one transfer member is swung remains between the disposition position of the transfer member closest to the roller including the roller on the downstream side in the movement direction of the spread surface. A transfer device set to: An image forming apparatus using the transfer device according to claim 1. The image forming apparatus according to claim 10,
The plurality of photoconductors are capable of forming images of different colors, and among them, the photoconductor closest to the downstream side in the moving direction of the expansion surface is used for forming a black image. apparatus.

Images