JP5629651B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for improving color misregistration when toner images transferred from a plurality of photosensitive drums are superimposed.

  2. Description of the Related Art Conventionally, for example, there is a tandem type image forming apparatus that forms a color image by superimposing toner images of each color formed by a photosensitive drum for each color on an intermediate transfer belt or recording paper (see Patent Document 1 below). . In this image forming apparatus, when the toner images of the respective colors are overlapped, the toner images of the respective colors are transferred to a position different from the original position to prevent a position shift (color shift). Sometimes, a position detection toner pattern for each color is formed on the intermediate transfer belt, and the position of each color toner pattern is detected by a photosensor to perform alignment, thereby correcting color misregistration.

  Here, in the case where images are continuously formed on a plurality of recording sheets, the temperature inside the apparatus changes during image formation and the running speed of the intermediate transfer belt changes. In the sub-scanning direction, the color misregistration may occur again during the image forming operation even if the color misregistration is corrected as described above in the initial operation of the apparatus. Therefore, in the image forming apparatus, during the image forming operation, the rotational speed of the drive roller that drives the intermediate transfer belt is detected, and the rotational speed of the drive source (drive motor) of the drive roller is determined according to the detected value. Control to correct color misregistration.

  Further, when the temperature of the driving roller expands due to a temperature rise due to continuous image forming operation and the diameter thereof increases, and the traveling speed of the intermediate transfer belt changes, a relative displacement between the intermediate transfer belt and the exposure device occurs. Cause color misregistration. For this reason, as shown in Patent Document 2 below, the material of the driving roller of the belt and the material of the holding unit that fixes and positions the exposure device inside the image forming apparatus are the same material, and the thermal expansion component of the driving roller In response to this, an image forming apparatus has also been proposed in which the holding unit is also thermally expanded to change the position of the exposure apparatus to cancel the relative positional deviation between the two members.

Japanese Patent Laid-Open No. 2005-3920 JP 2000-77772 A

  However, as in the image forming apparatus disclosed in Patent Document 1, if the color misregistration at the time of continuous printing is to be eliminated by detecting the position of each color toner image by a photosensor, the image forming operation is interrupted and intermediate Since it is necessary to change the rotation speed of the driving roller of the transfer belt, productivity is lowered. Further, the color misregistration correction by controlling the rotational speed of the driving roller requires a special mechanism for detecting the rotational speed of the driving roller, which increases the cost of the apparatus.

  In addition, the drive roller of the intermediate transfer belt should be made of an alumite-treated high-hardness material in order to prevent toner or its additive from entering between the intermediate transfer belt and the drive roller and scraping the surface of the drive roller. Therefore, as in the image forming apparatus disclosed in Patent Document 2, it is actually difficult to configure the holding portion with a material having high hardness. Further, it is desired to develop an image forming apparatus that can superimpose toner images of each color with higher accuracy than the image forming apparatus disclosed in Patent Document 2.

  The present invention has been made to solve the above-described problem, and forms a color image by superimposing toner images formed by a plurality of photosensitive drums arranged side by side in the running direction of the intermediate transfer belt. Another object of the present invention is to make it possible to superimpose toner images of each color with higher accuracy than before without causing an increase in cost or a decrease in productivity.

The invention according to claim 1 of the present invention includes an intermediate transfer belt stretched around a plurality of rollers so as to be able to run endlessly,
A plurality of photosensitive drums arranged side by side in the running direction of the intermediate transfer belt;
An exposure unit which is provided in plural for each predetermined number of photosensitive drums among the plurality of photosensitive drums, and forms an electrostatic latent image based on image data on the peripheral surface of the corresponding photosensitive drum;
A developing unit that is provided for each of the photosensitive drums, supplies toner to a peripheral surface of the photosensitive drum, and uses the electrostatic latent image as a toner image;
A transfer unit for transferring toner images on the peripheral surfaces of the plurality of photosensitive drums from the plurality of photosensitive drums to the surface of the intermediate transfer belt;
A drive roller that forms part of the plurality of rollers and drives the intermediate transfer belt;
A guide unit attached to the apparatus main body of the image forming apparatus, and a holding unit provided at a position corresponding to an exposure unit other than a predetermined exposure unit fixed to the apparatus main body so as not to move; The other exposure unit is fitted, and a guide unit having a guide rail that guides the other exposure unit to be movable in the traveling direction of the intermediate transfer belt;
The has a shape extending in the traveling direction of the intermediate transfer belt, provided to connecting the said holding portion other exposed portion, and fixing the other exposure unit to the apparatus main body, guided by the guide rail A fixing member that positions the other exposure unit to be moved in the traveling direction of the intermediate transfer belt,
The fixing member is exposed by an exposure unit to which the fixing member is attached from a photosensitive drum that is exposed by an exposure unit that is immovably fixed to the apparatus main body in the traveling direction of the intermediate transfer belt. The image forming apparatus expands in the running direction of the intermediate transfer belt according to a temperature change in the apparatus main body by a predetermined length according to the distance to the photosensitive drum.

  When a color image is formed by superimposing the color toner images formed by the plurality of photosensitive drums, the driving roller of the intermediate transfer belt is thermally expanded due to a temperature rise inside the apparatus due to, for example, continuous image forming operation. In some cases, the diameter increases and the traveling speed of the intermediate transfer belt stretched around the diameter increases. According to the present invention, even in such a case, each fixing member is attached to the fixing member from the photosensitive drum that is exposed by the exposure unit that is immovably fixed to the mounting body. Expands in the intermediate transfer belt traveling direction (upstream or downstream in the traveling direction) by a predetermined length according to the distance of the photosensitive drum exposed by the exposure unit according to the temperature change in the apparatus main body. Therefore, as described above, the intermediate transfer belt traveling speed is increased during the image forming operation, and the toner images formed on the photosensitive drums are shifted from the originally superposed positions of the toner images. Even if it exists, it is possible to cancel the deviation amount.

  For example, when the toner image formed on the photosensitive drum exposed by the exposure unit fixed by the fixing member reaches the reference photosensitive drum, the predetermined length of the fixing member By setting the value to match the amount of misalignment that occurs in each image, it is possible to reduce misalignment of each color toner image caused by factors such as thermal expansion of the drive roller during continuous image forming operations. The toner images can be superimposed.

  In addition, according to the present invention, it is not necessary to add a special mechanism for detecting the rotational speed of the driving roller of the intermediate transfer belt, and it is sufficient to provide the fixing member, and the image forming operation is interrupted. Since the transfer position of the toner image formed on each photosensitive drum to the intermediate transfer belt is adjusted while continuing, the productivity is not reduced.

The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the holding portion includes an extension portion extending from an upper edge of the side portion of the guide rail and the extension. A first hole formed in the portion,
A second hole is formed in a side surface of the casing of the exposure unit,
A third hole is formed at both ends of the fixing member,
The exposure unit fixed to the apparatus main body so as not to move is fixed to the apparatus main body by screwing using the first hole and the second hole,
The other exposure section includes screwing using the first hole and a third hole formed at one end of the fixing member, and other than the second hole and the fixing member. It is fixed to the apparatus main body via the fixing member by screwing using a third hole formed at the end.

The invention according to claim 3 is the image forming apparatus according to claim 1 or 2 , wherein
At least one of the exposure units is provided as an integral unit for each of the two or more photosensitive drums,
The fixing member is integrally provided for each of the two or more photosensitive drums and is attached to each exposure unit serving as the other exposure unit,
A fixing member provided integrally with each of the two or more photosensitive drums and attached to the exposure unit serving as the other exposure unit is exposed by an exposure unit fixed to the apparatus main body so as not to move. In accordance with the temperature change in the apparatus main body, only an average value of lengths determined in advance according to the distance from the photosensitive drum to each photosensitive drum exposed by the exposure unit to which the fixing member is attached. The intermediate transfer belt expands in the running direction.

  According to this invention, since the fixing member is attached to each exposure unit provided integrally for each of the two or more photosensitive drums, the setting of the initial arrangement position of each exposure unit and the fixing member are used. It is not necessary to attach the exposed exposure unit to the apparatus main body for each photosensitive drum corresponding to the exposure unit.

The invention according to claim 4 is the image forming apparatus according to claim 1 or 2 , wherein
The exposure unit is individually provided for each of the plurality of photosensitive drums,
The fixing member is separately attached to each of the exposure units provided individually for each of the photosensitive drums.

  According to the present invention, since the fixing member is separately attached to each of the exposure units individually provided for each photosensitive drum, each exposure is performed by the fixing member in accordance with the temperature change in the apparatus main body. It is possible to eliminate the color misregistration with high accuracy by moving the parts individually.

  According to the present invention, in an image forming apparatus that forms a color image by superimposing each color toner image formed by a plurality of photosensitive drums arranged in parallel in the running direction of the intermediate transfer belt, an increase in cost and a decrease in productivity are achieved. Without incurring, it is possible to superimpose toner images of each color with higher accuracy than in the past.

1 is a front sectional view showing a structure of an image forming apparatus according to an embodiment of the present invention. It is a schematic perspective view which shows the structure which fixes each exposure apparatus to a lower main body. FIG. 4 is a diagram illustrating superposition of toner images formed by image forming units. FIG. 4 is a diagram illustrating a positional deviation of a toner image formed by each image forming unit. FIG. 4 is a diagram illustrating superposition of toner images of respective colors by the image forming apparatus when a driving roller is thermally expanded. It is a schematic side view which shows other embodiment of the structure which fixes each exposure apparatus to a lower main body. It is a schematic side view which shows other embodiment of the structure which fixes each exposure apparatus to a lower main body. It is a schematic side view which shows other embodiment of the structure which fixes each exposure apparatus to a lower main body.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be applied to an image forming apparatus that employs an electrophotographic system and includes an intermediate transfer belt, such as a copier, a printer, a facsimile machine, and a multifunction machine having these functions.

  FIG. 1 is a front sectional view showing the structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 includes an apparatus main body 11 including an image forming unit 12, a fixing device 13, a paper feeding unit 14, a paper discharging unit 15, a document reading unit 16, and the like.

  The apparatus main body 11 includes a lower main body 111, an upper main body 112 disposed so as to face the lower main body 111, and a connecting portion 113 provided between the upper main body 112 and the lower main body 111. The connecting portion 113 is a structure for connecting the paper discharge portion 15 between the lower main body 111 and the upper main body 112 to each other. In FIG. And is L-shaped in a plan view. The upper body 112 is supported on the upper end portion of the connecting portion 113.

  The lower main body 111 includes an image forming unit 12, a fixing device 13, and a paper feeding unit 14. The upper body 112 is provided with a document reading unit 16. The paper feed unit 14 has a paper feed cassette 142 that can be inserted into and removed from the apparatus main body 11. In this paper feed cassette 142, a paper bundle P1 formed by stacking recording papers P is accommodated. In this embodiment, the paper feed cassette 142 is provided in one stage, but it may be provided in two or more stages.

  The image forming unit 12 performs an image forming operation for forming a toner image on the recording paper P fed from the paper feeding unit 14. The image forming unit 12 is arranged in order from the upstream side to the downstream side in the traveling direction of the intermediate transfer belt 125, the magenta image forming unit 12M using magenta toner, and the cyan toner using cyan toner. Image forming unit 12C, yellow image forming unit 12Y using yellow toner, and black image forming unit 12B using black toner (hereinafter, each image forming unit is described without distinction. And an intermediate transfer belt 125 stretched between a plurality of rollers such as a driving roller 125a (secondary transfer opposing roller) so as to be capable of endless running in the sub-scanning direction in image formation. The intermediate transfer belt 125 is stretched around the drive roller 125a. The peripheral surface and a contact with the secondary transfer roller 210.

  Each image forming unit 120 includes a photosensitive drum 121, a developing device 122 that supplies toner to the photosensitive drum 121, a toner cartridge (not shown) that contains toner, a charging device 123, an exposure device 124, a primary device. A transfer roller 126 and a drum cleaning device 127 are integrally provided.

  The photosensitive drum 121 forms an electrostatic latent image and a toner image along the electrostatic latent image on the peripheral surface thereof. The developing device (developing unit) 122 supplies toner to the photosensitive drum 121. Each developing device 122 is appropriately supplied with toner from the toner cartridge.

  The charging device 123 is provided immediately below the photosensitive drum 121. The charging device 123 uniformly charges the peripheral surface of each photosensitive drum 121.

  The exposure device (exposure unit) 124 is provided below the photosensitive drum 121 and further below the charging device 123. The exposure device 124 irradiates the peripheral surface of the charged photosensitive drum 121 with laser light corresponding to each color based on image data input from a computer or the like or image data acquired by the document reading unit 16, and each photosensitive member. An electrostatic latent image is formed on the peripheral surface of the drum 121. The exposure device 124 is a so-called laser exposure device, which is a laser light source that outputs a laser beam, a polygon mirror that reflects the laser beam toward the surface of the photosensitive drum 121, and a laser beam reflected by the polygon mirror. Optical components such as a lens and a mirror for guiding the drum 121 are provided.

  The exposure device 124 includes an exposure device 124M for the image forming unit 12M for magenta, an exposure device 124C for the image forming unit 12C for cyan, an exposure device 124Y for the image forming unit 12Y for yellow, and an image formation for black. An exposure device 124B is separately provided for each unit 12B. In the present embodiment, the exposure device 124B located on the most downstream side in the traveling direction of the intermediate transfer belt 125 is fixedly attached to the lower main body 111 so as not to move. On the other hand, individual fixing members (not shown in FIG. 1) are attached to the exposure devices 124Y, 124C, and 124M for other colors, respectively, and the bottom surface portion of the lower main body 111 responds to expansion and contraction due to thermal expansion of the fixing members. It is fixed to the lower main body 111 so as to be slidable. However, the exposure devices 124Y, 124C, and 124M are fixed to the lower main body 111 so as to be movable in the traveling direction of the intermediate transfer belt 125. Details of fixing the exposure devices 124B, 124Y, 124C, and 124M to the lower main body 111 will be described later.

  The developing device 122 supplies toner to the electrostatic latent image on the peripheral surface of the photoconductive drum 121 rotating in the direction of the arrow and stacks the toner, and the toner corresponding to the image data is formed on the peripheral surface of the photoconductive drum 121. Form an image.

  The intermediate transfer belt 125 is disposed above the photosensitive drums 121. The intermediate transfer belt 125 is stretched between the driving roller 125a on the left side in FIG. 1 and the driven roller 125b on the right side in FIG. It is in contact. The driven roller 125b is provided at a position facing the driving roller 125a, and is driven to rotate as the intermediate transfer belt 125 travels endlessly. The intermediate transfer belt 125 is driven by a driving roller 125 a in a state where an image carrying surface on which a toner image is transferred is set on the outer circumferential surface thereof and in contact with the circumferential surface of the photosensitive drum 121. The intermediate transfer belt 125 travels endlessly between the driving roller 125a and the driven roller 125b while synchronizing with each photosensitive drum 121.

  A primary transfer roller (transfer unit) 126 is provided at a position facing each photosensitive drum 121 with the intermediate transfer belt 125 interposed therebetween. A transfer bias is applied to the primary transfer roller 126 by a transfer bias application mechanism (not shown). The primary transfer roller 126 transfers the toner image formed on the outer peripheral surface of each photosensitive drum 121 to the intermediate transfer belt 125. Transfer to the surface.

  The drive roller 125a causes the intermediate transfer belt 125 to run endlessly by a rotational driving force applied from a drive motor (not shown) driven under the control of a control unit (not shown). In this embodiment, in order to prevent the toner and its additive from entering between the intermediate transfer belt 125 and the drive roller 125a and scraping the surface of the drive roller 125a, the drive roller 125a is a high hardness material that has been anodized. (For example, AL (aluminum) or the like).

  The control unit (not shown) drives and controls the primary transfer roller 126 and the image forming unit 120 for each color, and the magenta toner image formed on the surface of the intermediate transfer belt 125 by the magenta image forming unit 12M. The cyan toner image formed by the cyan image forming unit 12C is then transferred to the same position on the intermediate transfer belt 125, and then the yellow image forming unit 12Y is formed at the same position on the intermediate transfer belt 125. The transfer of the yellow toner image and the transfer of the black toner image formed by the final black image forming unit 12B are performed so that the toner images of the respective colors overlap each other. It is formed on the surface of the transfer belt 125 (intermediate transfer (primary transfer)).

  A transfer bias is applied to the secondary transfer roller 210 by a transfer bias applying mechanism (not shown). The secondary transfer roller 210 transfers the color toner image formed on the surface of the intermediate transfer belt 125 onto the recording paper P conveyed from the paper supply unit 14. The secondary transfer roller 210 is provided in contact with the outer peripheral surface of the intermediate transfer belt 125 in a sheet conveyance path 190 where the intermediate transfer belt 125 is stretched around the driving roller 125a. The secondary transfer roller 210 forms a nip portion N where the toner image is secondarily transferred onto the recording paper P, between the intermediate transfer belt 125 and the drive roller 125a. The recording paper P being conveyed through the paper conveyance path 190 is pressed and sandwiched between the intermediate transfer belt 125 and the secondary transfer roller 210 at the nip portion N, where the toner image on the intermediate transfer belt 125 is transferred to the recording paper P two times. Next transferred.

  The drum cleaning device 127 is provided on the left side of each photoconductive drum 121 in FIG. 1, and removes residual toner on the peripheral surface of the photoconductive drum 121 for cleaning. The peripheral surface of the photosensitive drum 121 cleaned by the drum cleaning device 127 goes to the charging device 123 again for a new charging process.

  A sheet conveyance path 190 extending in the vertical direction is formed at the left position in FIG. 1 with respect to the image forming unit 12. A pair of conveyance rollers 192 is provided at an appropriate position on the sheet conveyance path 190. The conveyance roller pair 192 conveys the recording paper P fed from the paper supply unit 14 toward the nip N and the fixing device 13.

  The fixing device 13 includes a heating roller 132 provided with an energization heating element as a heating source therein, and a pressure roller 134 disposed to face the heating roller 132. The fixing device 13 heats the toner image on the recording paper P transferred by the image forming unit 12 while the recording paper P passes through the fixing nip portion between the heating roller 132 and the pressure roller 134. The fixing process is performed by applying heat from 132. The recording paper P on which the color image has been formed and has undergone the fixing process passes through a paper discharge conveyance path 194 extending from the upper part of the fixing device 13, toward a paper discharge tray 151 provided on the top of the lower main body 111. Discharged.

  The sheet feeding unit 14 includes a manual feed tray 141 that can be freely opened and closed on the right side wall in FIG. 1 of the apparatus main body 11, and a sheet feeding cassette 142 that is detachably mounted at a position below the exposure apparatus 124 in the lower body 111. And.

  The manual feed tray 141 is a tray that is provided at a position below the right surface of the lower main body 111 and feeds the recording paper P toward the image forming unit 12 by a manual feed operation. The paper feed cassette 142 accommodates a paper bundle P1 formed by stacking a plurality of recording papers P. A pickup roller 143 is provided above the sheet feeding cassette 142, and the pickup roller 143 feeds the uppermost recording sheet P of the sheet bundle P 1 stored in the sheet feeding cassette 142 toward the sheet conveyance path 190.

  The paper discharge unit 15 is formed between the lower main body 111 and the upper main body 112. The paper discharge unit 15 includes a paper discharge tray 151 formed on the upper surface of the lower main body 111. The paper discharge tray 151 is a tray from which the recording paper P on which the toner image is formed by the image forming unit 12 is discharged after the fixing process is performed by the fixing device 13.

  The document reading unit 16 includes a contact glass 161 mounted on the upper surface opening of the upper main body 112 for placing a document, an openable / closable document pressing cover 162 for pressing the document placed on the contact glass 161, And a reading mechanism 163 that reads an image of a document placed on the contact glass 161. The reading mechanism 163 optically reads an image of a document using an image sensor such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and generates image data.

  Next, a configuration for fixing the exposure devices 124B, 124Y, 124C, and 124M to the lower main body 111 will be described. FIG. 2 is a schematic side view showing a configuration for fixing the exposure apparatuses 124B, 124Y, 124C, and 124M to the lower main body 111. As shown in FIG. In FIG. 2, only the attachment portions of the exposure devices 124B, 124Y, 124C, and 124M with respect to the lower main body 111 of the image forming apparatus 1 are shown.

  A guide portion 20 that slides the exposure device 124 in the running direction of the intermediate transfer belt 125 is attached to the bottom of the lower main body (an example of the apparatus main body in the claims) 111. Exposure units 124B, 124Y, 124C, and 124M for the respective colors are positioned at the bottom of the lower main body 111 facing the peripheral surface of the intermediate transfer belt 125 and below the photosensitive drum 121 of each image forming unit 120. Is disposed via the guide portion 20.

  The guide unit 20 includes a guide rail 21 that holds the exposure apparatuses 124B, 124Y, 124C, and 124M, and a fixing member 22 that fixes the exposure apparatuses 124B, 124Y, 124C, and 124M to the guide rail 21.

  As shown in FIG. 2, the guide rail 21 is in surface contact with the lower surfaces of the exposure apparatuses 124B, 124Y, 124C, and 124M, and a bottom surface portion 211 on which these exposure devices are placed, and both side ends of the bottom surface portion 211. And is formed at the upper edge portion of the side surface portion 212 and further intermediate from the upper edge portion. And a holding portion 213 protruding to the transfer belt 125 side. The holding unit 213 is provided with holding units 213B, 213Y, 213C, and 213M corresponding to the exposure apparatuses 124B, 124Y, 124C, and 124M, respectively.

  In each of the exposure devices 124B, 124Y, 124C, and 124M, the apparatus bottom surface comes into surface contact with the bottom surface portion 211 and the apparatus side surface faces the side surface portion 212 in the accommodation region surrounded by the bottom surface portion 211 and the side surface portion 212 in the guide rail 21. It is stored in a state of surface contact.

As described above, the exposure devices 124B, 124Y, 124C, and 124M accommodated in the guide rail 21 are arranged so that the position of the intermediate transfer belt 125 on the guide rail 21 in the traveling direction is the circumference on the peripheral surface of the corresponding photosensitive drum 121. It is set so that the laser beam for exposure is irradiated to a predetermined position in the direction. In the present embodiment, of the exposure devices 124B, 124Y, 124C, and 124M arranged as described above, the side surface of the exposure device 124B arranged at the most downstream position in the traveling direction of the intermediate transfer belt 125 is It is fixed to the holding portion 213B provided at the position where the exposure device 124B is provided, so that it cannot be moved by screws or screws. As described above, the position at which the exposure device 124B is fixed by the holding unit 213B is a position at which exposure can be performed at a predetermined position on the peripheral surface of the photosensitive drum 121 of the black image forming unit 12B. The holding unit 213B is provided with a screw hole or a screw hole (hereinafter referred to as a screw hole or the like) that can be screwed or screwed to fix the exposure apparatus 124B and the holding unit 213B, for example. ing. Further, a screw hole or the like is also provided on the side surface of the exposure apparatus 124B at a position facing the screw hole or the like of the holding unit 213B. This fixation, the exposure apparatus 124B, the position in the running direction of the intermediate transfer belt 125 in the guide rail 21 is fixed.

  On the other hand, the exposure devices 124Y, 124C, and 124M for other colors are stored in advance on the peripheral surface of the photosensitive drum 121 of the corresponding color image forming unit while being accommodated in the guide rail 21 in the same manner as the exposure device 124B. It is arranged at a position where exposure is possible at a predetermined position. Similar to the holding portion 213B, the holding portions 213Y, 213C, and 213M provided for fixing these color exposure apparatuses are provided with screw holes and the like. In addition, screw holes and the like are provided in the side portions of the exposure apparatuses of the respective colors.

  Each of these exposure apparatuses 124Y, 124C, and 124M is separately attached to the corresponding holding portion 213 by the fixing member 22 at the arrangement position. The fixing member 22 has, for example, a long shape, and is provided with screw holes or the like in the vicinity of both end portions in the length direction. Here, the fixing members 22 for the exposure apparatuses 124Y, 124C, and 124M are referred to as fixing members 22Y, 22C, and 22M, respectively. Each fixing member 22Y, 22C, 22M is formed of the same material (for example, SECC-C). Each fixing member 22 </ b> Y, 22 </ b> C, 22 </ b> M is attached to a corresponding exposure apparatus so that its length direction extends in the traveling direction of the intermediate transfer belt 125, and fixes the corresponding exposure apparatus to the holding unit 213.

  In this embodiment, each of the fixing members 22Y, 22C, and 22M has a length (dimension in the length direction) in the traveling direction of the intermediate transfer belt 125 that is set separately. For example, the distance between the screw holes and the like that the fixing members 22Y, 22C, and 22M have at both ends in the length direction is such that when the fixing members 22Y, 22C, and 22M are thermally expanded, the intermediate transfer belt 125 The length is set such that a predetermined extension amount can be obtained in the traveling direction. The length at which the predetermined extension amount is obtained has a different value for each of the fixing members 22Y, 22C, and 22M (details will be described later).

  Further, for example, in each of the exposure apparatuses 124Y, 124C, and 124M arranged at the above-described arrangement position, the position of the screw hole provided in each side surface portion is one end portion of the screw hole of the corresponding holding portion 213. These screw holes are positioned so as to be opposed to the screw holes at the other end of the corresponding fixing member 22 in which the screw holes are screwed.

  As described above, the fixing member 22 having one end screwed to the holding portion 213 is screwed into the screw hole at the other end of the fixing member 22 and the screw hole of the exposure apparatus corresponding to the fixing member 22. By being stopped, the exposure apparatuses 124Y, 124C, and 124M are separately fixed to the guide rail 21 by the fixing members 22Y, 22C, and 22M, respectively. That is, the exposure devices 124Y, 124C, and 124M are positioned in the traveling direction of the intermediate transfer belt 125 by the fixing members 22Y, 22C, and 22M. However, the contact portion between the bottom surface and the bottom surface portion 211 of the exposure apparatuses 124Y, 124C, and 124M and the contact portion between the side surface and the side surface portion 212 of the exposure apparatuses 124Y, 124C, and 124M are not fixed to the guide rail 21.

  Next, setting of the lengths of the fixing members 22Y, 22C, and 22M will be described. FIG. 3 is a diagram illustrating the superposition of toner images formed by the image forming units 120. FIG. 4 is a diagram illustrating the positional deviation of the toner images formed by the image forming units 120. FIG. 5 is a diagram illustrating the superposition of the color toner images by the image forming apparatus 1 when the driving roller 125a is thermally expanded. 2 to 5 conceptually show the positions and misalignment states of the color toner images for the sake of clarity.

  The lengths of the fixing members 22Y, 22C, and 22M in the above length direction correspond to the arrangement positions of the exposure devices 124Y, 124C, and 124M, and the change in the traveling speed of the intermediate transfer belt 125 based on the thermal expansion of the driving roller 125a. First, the color image formation by the image forming units 12M, 12C, 12Y, and 12B, that is, the superposition of the respective color toner images will be described.

  As described above, the image forming units 12M, 12C, 12Y, and 12B of the respective colors are provided at the above-described arrangement positions in the traveling direction of the intermediate transfer belt 125. When the driving roller 125a is rotationally driven by the driving motor and the intermediate transfer belt 125 starts to travel along with the driving roller 125a, the photosensitive drums 121 of the image forming units 12M, 12C, 12Y, and 12B are also driven in synchronization with each other. The motor starts rotating at the same peripheral speed. As shown in FIG. 3, in the image forming unit 12M on the most upstream side in the running direction of the intermediate transfer belt 125, the exposure device 124M has a laser at the predetermined position in the circumferential direction of the circumferential surface of the photosensitive drum 121. Exposure is performed by irradiating light (FIG. 3). When the circumferential surface of the photosensitive drum 121 rotates and the electrostatic latent image generated by the exposure becomes a toner image through the toner application by the developing device 122, the primary transfer is performed when the toner image reaches the surface of the intermediate transfer belt 125. The image is transferred onto the surface of the intermediate transfer belt 125 by the roller 126.

  As the intermediate transfer belt 125 travels, the transferred toner image is transferred next to the photosensitive drum 121 and the primary transfer roller 126 of the image forming unit 12C located downstream in the traveling direction of the intermediate transfer belt 125. Head to the transfer position. The image forming unit M disposed on the upstream side in the running direction of the intermediate transfer belt 125 with respect to the image forming unit 12C has the exposure position by the exposure device 124M on the circumferential surface of the photosensitive drum 121 transferred by the image forming unit 12M. The toner image thus set is set in accordance with the timing at which the intermediate transfer belt 125 conveys the toner image onto the intermediate transfer belt 125 by the image forming unit 12C. That is, the toner image formed at the predetermined position on the peripheral surface of the photosensitive drum 121 by the exposure device 124C and the developing device 122 is transferred to the intermediate transfer belt 125 by the rotation of the photosensitive drum 121. The timing at which the toner image transferred to the intermediate transfer belt 125 by the image forming unit 12M coincides with the timing at which the toner image transferred to the toner image transfer position to the intermediate transfer belt 125 by the image forming unit 12C matches. ing. As a result, as shown in FIG. 3, the toner images of the respective colors formed on the peripheral surface of the intermediate transfer belt 125 by the image forming units 12M and 12C overlap with each other on the peripheral surface of the intermediate transfer belt 125 without misalignment.

  Similarly, as shown in FIG. 3, in the image forming units 12 </ b> Y and 12 </ b> B, the toner images formed on the peripheral surface of the photosensitive drum 121 by the exposure devices 124 </ b> Y and 124 </ b> B and the developing device 122 The toner image transferred to the intermediate transfer belt 125 by the image forming unit 120 disposed at the upstream side in the running direction of the intermediate transfer belt 125 from the timing at which the rotation reaches the transfer position to the intermediate transfer belt 125 is intermediate. The timing at which the transfer belt 125 transports the toner to the transfer position is set to coincide.

  In this embodiment, the same photosensitive drum 121 is used for each of the image forming units 12M, 12C, 12Y, and 12B, and the exposure position in the circumferential direction of each photosensitive drum 121 is also set to the same position. In order to employ, the distance between the adjacent image forming units 120 is the same.

  As a result, as shown in FIG. 3, all color toner images formed on the peripheral surface of the intermediate transfer belt 125 by the image forming units 12M, 12C, 12Y, and 12B are rotated around the intermediate transfer belt 125 by the image forming unit 12B. A color image is formed by superimposing the toner image transfer position on the surface without any positional deviation.

  At this time, assuming that the rotational speed of the driving roller 125a is R (rpm) = (rotational speed / second), the belt linear velocity (traveling speed) V1 (mm / second) = drive roller diameter L (mm) × π × R is there. Each of the image forming units 12M, 12C, 12Y, and 12B transfers the toner image to the intermediate transfer belt 125 so that the toner images can be superimposed based on the belt linear velocity V1 (mm / second). The position and the exposure position in the circumferential direction of the peripheral surface of the photosensitive drum 121 by the exposure device 124 are determined.

  Next, a description will be given of the positional deviation that occurs in the superposed embodiment of the color toner images. When the temperature of the driving roller 125a is increased by the continuous image forming operation, the driving roller 125a is made of the above-described material such as AL. Therefore, as shown in FIG. 4, the diameter of the driving roller 125a is indicated by a broken line due to thermal expansion. It increases from the initial size to the size indicated by the solid line (L [mm] ⇒L + ΔL [mm]). Therefore, the peripheral speed of the outer peripheral surface of the drive roller 125a is increased (peripheral speed V2 (mm / second) of the outer peripheral surface of the drive roller 125a) = drive roller diameter (L (mm) + ΔL [mm]) × π × R ), The traveling speed V1 of the intermediate transfer belt 125 also increases (V1 [mm / s] ⇒V1 + ΔV [mm / s]). In particular, in the case of a structure in which a resin layer is provided on the surface of the driving roller 125a (alumite treatment) in order to improve the conveyance force of the intermediate transfer belt 125, a change in the running speed of the intermediate transfer belt 125 due to the influence of the thermal expansion is significant. become.

  As described above, when the traveling speed of the intermediate transfer belt 125 increases due to the increase in the diameter of the driving roller 125a due to thermal expansion, the toner image transferred to the peripheral surface of the intermediate transfer belt 125 by the image forming unit 120 of each color is The time required to reach the toner image transfer position by the next image forming unit 120 for transferring the toner image in an overlapping manner is shortened. For this reason, as shown in FIG. 4, the toner image previously transferred to the peripheral surface of the intermediate transfer belt 125 by the image forming unit 120 disposed on the upstream side in the running direction of the intermediate transfer belt 125 is the next intermediate image. When the toner image is transferred to the circumferential surface of the intermediate transfer belt 125 by the image forming unit 120 located on the downstream side in the running direction of the transfer belt 125, the toner transfer position by the downstream image forming unit 120 has already passed. become. For this reason, each time the toner image is transferred onto the circumferential surface of the intermediate transfer belt 125 by the image forming unit 120, a positional deviation occurs between the toner images. As a result, the toner images of the respective colors formed by the image forming units 12M, 12C, 12Y, and 12B are not accurately superimposed.

  Next, the superposition of the respective color toner images by the image forming apparatus 1 when the drive roller 125a is thermally expanded will be described. As described above, the image forming apparatus 1 uses the black image forming unit 12B fixed to the guide unit 20 so as not to be movable in the traveling direction of the intermediate transfer belt 125 as a reference, and the intermediate between the image forming units 120 for other colors. By changing the timing of toner image transfer onto the peripheral surface of the transfer belt 125, alignment is performed when the color toner images formed by the image forming units 12M, 12C, 12Y, and 12B are superimposed.

  For example, assuming that the distance between adjacent image forming units 120 is Ld (mm), the toner image transferred onto the peripheral surface of the intermediate transfer belt 125 by the image forming unit 12M is used as an image forming reference for toner image alignment. While the distance of Ld × 3 [mm] is moved to the toner image transfer position by the unit 12B, the movement distance of the toner image transferred onto the peripheral surface of the intermediate transfer belt 125 by the image forming unit 12C is Ld ×. 2 [mm], the moving distance of the toner image transferred onto the peripheral surface of the intermediate transfer belt 125 by the image forming unit 12Y is Ld × 1 [mm]. The longer the time required for the toner image transferred by each image forming unit 120 to reach the toner image transfer position by the reference image forming unit 12B, the more the image forming unit 12B is proportional to the time required for the arrival. As a result, the amount of deviation from the transferred toner image increases. For this reason, the color misregistration shown in FIG. 4 is such that the toner image transferred by the image forming unit 120 on the upstream side in the running direction of the intermediate transfer belt 125 is transferred by the image forming unit 120 on the downstream side in the same direction. The amount of deviation from the toner image transferred by the image forming unit 12B is larger than that of the image.

  For this reason, each toner image transferred by the image forming units 12M, 12C, and 12Y as the temperature rises and the running speed of the intermediate transfer belt 125 is increased with respect to the toner image transferred by the reference image forming unit 12B. In accordance with the change in the amount of deviation that occurs (for example, the change in the amount of deviation is measured in advance during the manufacturing process of the image forming apparatus 1), the exposure by the exposure devices of the image forming units 12M, 12C, and 12Y. Each exposure device 124M, 124C, 124Y is moved to the guide rail 21 so that the exposure position on the circumferential surface of the body drum 121 moves to the upstream side in the circumferential surface rotation direction of the photoreceptor drum 121 by the above-described deviation amount. The fixing members 22M, 22C, and 22Y are slid along the downstream side of the intermediate transfer belt 125 in the running direction. Thermal expansion coefficient and the length dimension is set.

  That is, assuming that the amount of deviation generated by the image forming unit 12M with respect to the image forming unit 12B when the temperature in the lower main body 111 changes by a constant temperature from the initial operation is dm (mm), the fixing member 22M The exposure position on the peripheral surface of the photosensitive drum 121 by the exposure device 124M of each image forming unit 12M is rotated by the peripheral surface of the photosensitive drum 121 by the amount of deviation dm (mm) generated by the unit 12M with respect to the image forming unit 12B. It is set to the raw material which has a thermal expansion coefficient which performs the thermal expansion moved to the upstream of a direction, and a length direction dimension. As a result, the fixing member 22M slides the exposure position by the exposure device 124M from the position indicated by the broken line in FIG. 5 to the position indicated by the solid line to the downstream side in the running direction of the intermediate transfer belt 125. As a result, the toner image on the circumferential surface of the intermediate transfer belt 125 by the image forming unit 12M is transferred from the position indicated by the broken line in FIG. Move upstream in the direction of travel. 5 virtually shows the transfer position of the toner image (the same applies to FIGS. 6 and 8).

  Similarly, the dimension in the length direction of the fixing member 22C is that the amount of deviation generated by the image forming unit 12C with respect to the image forming unit 12B is dc (mm) by the exposure device 124C on the peripheral surface of the photosensitive drum 121. The fixing member 22C is exposed to the exposure device 124C so that the position moves to the upstream side in the rotation direction of the peripheral surface of the photosensitive drum 121 (in FIG. 5, an example is shown by movement from the position indicated by the broken line to the position indicated by the solid line). Is set to a material having a coefficient of thermal expansion that slides the intermediate transfer belt 125 to the downstream side in the traveling direction of the intermediate transfer belt 125, and a length dimension. Accordingly, the toner image on the peripheral surface of the intermediate transfer belt 125 by the image forming unit 12C is transferred from the position indicated by the broken line in FIG. 5 to the position indicated by the solid line (the traveling direction of the intermediate transfer belt 125). Move upstream).

  Similarly, the dimension of the fixing member 22Y in the length direction is such that the amount of deviation generated by the image forming unit 12Y with respect to the image forming unit 12B is dy (mm) by the exposure device 124Y on the peripheral surface of the photosensitive drum 121. The fixing member 22Y is exposed to the exposure device 124Y so that the position moves to the upstream side in the rotation direction of the circumferential surface of the photosensitive drum 121 (in FIG. 5, an example is shown by movement from a position indicated by a broken line to a position indicated by a solid line). Is set to a material having a coefficient of thermal expansion that slides the intermediate transfer belt 125 to the downstream side in the traveling direction of the intermediate transfer belt 125, and a length dimension. Accordingly, the toner image on the circumferential surface of the intermediate transfer belt 125 by the image forming unit 12Y is transferred from the position indicated by the broken line in FIG. 5 to the position indicated by the solid line (the traveling direction of the intermediate transfer belt 125). Move upstream).

  In addition, since each fixing member 22M, 22C, 22Y consists of the same raw material, the expansion / contraction amount by thermal expansion increases, so that a dimension is large. Therefore, in the present embodiment, the fixing member 22M of the image forming unit 12M has the largest dimension in the length direction according to the distance from the reference image forming unit 12B, and the length of the fixing member 22C of the image forming unit 12C. The direction dimension is the next largest, and the dimension in the Nagasawa direction of the fixing member 22Y of the image forming unit 12Y is set to the smallest.

  By setting the lengthwise dimensions of the fixing members 22M, 22C, and 22Y in this way, when the temperature in the lower main body 111 rises, the fixing members 22M, 22C, and 22Y are moved in the length direction by the amount corresponding to the temperature rise. By extending the toner image transfer positions on the peripheral surface of the intermediate transfer belt 125 by the image forming units 12M, 12C, and 12Y in the initial operation start state indicated by the broken line in FIG. 5, the deviation amounts dm (mm), Only dc (mm) and dy (mm) are moved to the upstream side in the running direction of the intermediate transfer belt 125.

  Thus, as shown in the toner image transfer position to the intermediate transfer belt 125 by the image forming unit 12B in FIG. 5, each color toner generated according to the speed increase of the intermediate transfer belt 125 generated according to the temperature rise in the lower main body 111. Misalignment during image superposition is eliminated.

  Since the fixing members 22M, 22C, and 22Y contract in the length direction in accordance with the temperature decrease when the temperature in the lower main body 111 decreases, the circumferential surface of the intermediate transfer belt 125 by the image forming units 12M, 12C, and 12Y. Each upward toner image transfer position moves to the downstream side in the running direction of the intermediate transfer belt 125 by the amount of deviation caused by the temperature drop. Therefore, the image forming apparatus 1 can prevent the occurrence of misalignment when the color toner images are superimposed, both when the temperature is rising and when the temperature is falling.

  Note that the fixing members 22M, 22C, and 22Y are replaced with the above-described configuration, for example, by an amount of deviation dm (mm), dc (mm), or dy (mm) according to a temperature change in the lower main body 111. It is also possible to employ a material having a coefficient of thermal expansion that is moved to the upstream side or the downstream side in the traveling direction of 125 separately. In this case, as shown in FIG. 6, it may be possible to align the fixing members 22M, 22C, and 22Y to the same lengthwise dimension. The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, a separate exposure device 124M, 124C, 124Y, 124B is provided for each of the image forming units 12M, 12C, 12Y, 12B, and the fixing members 22M, 22C, 22Y and guide rails are provided on the lower main body 111, respectively. However, as shown in FIG. 7, one exposure apparatus is used for each of the two image forming units 120, and exposure is performed for exposing two photosensitive drums 121 by one exposure apparatus. A configuration in which the apparatus 124YB and the exposure apparatus 124MC are provided can also be adopted. In this case, the exposure device 124YB is fixed to the lower main body 111 in a state in which the intermediate transfer belt 125 cannot be moved in the running direction in the same manner as the exposure device 124B described above. The exposure device 124MC is fixed to the lower main body 111 via the guide rail 22 in a state in which the intermediate transfer belt 125 can be slid in the traveling direction using the fixing member 22MC. That is, based on the position at which the toner image formed by exposure by the exposure device 124YB is transferred to the peripheral surface of the intermediate transfer belt 125, the expansion and contraction of the fixing member 22MC accompanying the temperature change causes the temperature change in the lower main body 111. The exposure position on the peripheral surface of each photosensitive drum 121 by the exposure device 124MC is moved upstream in the peripheral surface rotation direction of the photosensitive drum 121 by an amount of deviation dmc (mm) (as illustrated in FIG. 7). The exposure device 124MC on the other side is moved to the upstream side or the downstream side in the running direction of the intermediate transfer belt 125) (indicated by the movement from the position indicated by the broken line to the position indicated by the solid line). In FIG. 7, the position of the exposure device 124MC is slid from the position indicated by the broken line to the position indicated by the solid line on the downstream side in the running direction of the intermediate transfer belt 125 by the fixing member 22MC.

  That is, in the image forming apparatus 1 in the form shown in FIG. 7, a plurality of exposure apparatuses are provided integrally for each of a predetermined number of photosensitive drums out of a plurality of photosensitive drums, and one of the exposure apparatuses is provided. The intermediate transfer belt 125 is fixed to the lower main body 111 in a state where the intermediate transfer belt 125 cannot move in the traveling direction, and a toner image formed by exposure by the exposure device fixed so as not to move is transferred onto the circumferential surface of the intermediate transfer belt 125. The other side exposure apparatus is moved upstream or downstream in the traveling direction of the intermediate transfer belt 125 by the amount corresponding to the above-described necessary shift amount according to the temperature change in the lower main body 111. Let

  In this case, (1) onto the peripheral surface of the intermediate transfer belt 125 by the photosensitive drum 121M of the image forming unit 12M with respect to the toner image transfer position on the peripheral surface of the intermediate transfer belt 125 by the photosensitive drum 121B of the image forming unit 12B. (2) Toner image transfer position on the peripheral surface of the intermediate transfer belt 125 by the photosensitive drum 121C with respect to the transfer position of the toner image on the peripheral surface of the intermediate transfer belt 125 by the photosensitive drum 121B (3) The toner image transfer position on the peripheral surface of the intermediate transfer belt 125 by the photosensitive drum 121M and the photosensitive drum 121C with respect to the toner image transfer position on the peripheral surface of the intermediate transfer belt 125 by the photosensitive drum 121B. Any one of the average values of the deviation amounts is adopted.

  In each of the above embodiments, the toner image transfer position onto the circumferential surface of the intermediate transfer belt 125 by the image forming unit 12B is used as a reference for alignment when the color toner images are overlaid. The toner image transfer position on the circumferential surface of the belt 125 is changed, but instead, the toner image transfer position used as a reference for the alignment is set as an intermediate transfer belt 125 by any one of the image forming units 12M, 12C, and 12Y. The toner image transfer position on the peripheral surface may be changed, and the toner image transfer position on the peripheral surface of the intermediate transfer belt 125 by another image forming unit may be changed. For example, the reference image forming unit is fixed to the guide rail 21 so that the intermediate transfer belt 125 is not slidable in the running direction in the same manner as described above, and the other image forming units are fixed to the fixing member as described above. The intermediate transfer belt 125 is fixed to the guide rail 21 so that the intermediate transfer belt 125 can be slid in the traveling direction by expansion and contraction due to thermal expansion of the fixing member.

  In this case, when the reference image forming unit (image form unit 12M) is located upstream in the traveling direction of the intermediate transfer belt 125 relative to the other image forming units, as shown in FIG. The holding portions 213C, 213Y, and 213B used for fixing the forming unit to the guide rail 21 are provided on the downstream side in the traveling direction of the intermediate transfer belt 125 from the exposure devices of the respective colors, and the exposure devices are respectively fixed members. It fixes to the corresponding holding | maintenance part 213C, 213Y, 213B by 22C, 22Y, 22B. As a result, the toner image transfer position on the circumferential surface of the intermediate transfer belt 125 by the reference image forming unit 120 is moved downstream in the running direction of the intermediate transfer belt 125 due to the increase in the running speed of the intermediate transfer belt 125 due to the temperature change. Even in the case of movement, the exposure position by the exposure device of the other image forming unit 120 can be moved downstream in the circumferential direction on the circumferential surface of the photosensitive drum 121 (see FIG. 8). An example of this is indicated by the movement from the position indicated by the broken line to the position indicated by the solid line), and the toner image transfer position on the peripheral surface of the intermediate transfer belt 125 by the other image forming unit 120 is moved downstream. Can do.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 111 Lower main body 12M, 12C, 12Y, 12B Image forming unit 121,121B, 121M, 121C, 121Y Photosensitive drum 122 Developing device 123 Charging device 124,124M, 124C, 124Y, 124B Exposure device 124MC, 124YB Exposure Device 125a Drive roller 125 Intermediate transfer belt 126 Primary transfer roller 20 Guide part 21 Guide rail 211 Bottom face part 212 Side face parts 213, 213B, 213C, 213M, 213Y Holding parts 22, 22Y, 22M, 22C, 22MC Fixing member

Claims (4)

An intermediate transfer belt stretched between a plurality of rollers so as to be able to run endlessly;
A plurality of photosensitive drums arranged side by side in the running direction of the intermediate transfer belt;
An exposure unit which is provided in plural for each predetermined number of photosensitive drums among the plurality of photosensitive drums, and forms an electrostatic latent image based on image data on the peripheral surface of the corresponding photosensitive drum;
A developing unit that is provided for each of the photosensitive drums, supplies toner to a peripheral surface of the photosensitive drum, and uses the electrostatic latent image as a toner image;
A transfer unit for transferring toner images on the peripheral surfaces of the plurality of photosensitive drums from the plurality of photosensitive drums to the surface of the intermediate transfer belt;
A drive roller that forms part of the plurality of rollers and drives the intermediate transfer belt;
A guide unit attached to the apparatus main body of the image forming apparatus, the position corresponding to at least one of the exposure units other than a predetermined exposure unit fixed to the apparatus main body so as not to move. A guide portion having a holding portion provided in the guide portion, and a guide rail that fits the other exposure portion and guides the other exposure portion to be movable in the traveling direction of the intermediate transfer belt,
The has a shape extending in the traveling direction of the intermediate transfer belt, provided to connecting the said holding portion other exposed portion, and fixing the other exposure unit to the apparatus main body, guided by the guide rail A fixing member that positions the other exposure unit to be moved in the traveling direction of the intermediate transfer belt,
The fixing member is exposed by an exposure unit to which the fixing member is attached from a photosensitive drum that is exposed by an exposure unit that is immovably fixed to the apparatus main body in the traveling direction of the intermediate transfer belt. An image forming apparatus that expands in the running direction of the intermediate transfer belt according to a temperature change in the apparatus main body by a predetermined length according to a distance to the photosensitive drum. The holding part has an extension part extended from the upper edge of the side part of the guide rail and a first hole formed in the extension part,
A second hole is formed in a side surface of the casing of the exposure unit,
A third hole is formed at both ends of the fixing member,
The exposure unit fixed to the apparatus main body so as not to move is fixed to the apparatus main body by screwing using the first hole and the second hole,
The other exposure section includes screwing using the first hole and a third hole formed at one end of the fixing member, and other than the second hole and the fixing member. The image forming apparatus according to claim 1, wherein the image forming apparatus is fixed to the apparatus main body via the fixing member by screwing using a third hole formed at an end. At least one of the exposure units is provided as an integral unit for each of the two or more photosensitive drums,
The fixing member is integrally provided for each of the two or more photosensitive drums and is attached to each exposure unit serving as the other exposure unit,
A fixing member provided integrally with each of the two or more photosensitive drums and attached to the exposure unit serving as the other exposure unit is exposed by an exposure unit fixed to the apparatus main body so as not to move. In accordance with the temperature change in the apparatus main body, only an average value of lengths determined in advance according to the distance from the photosensitive drum to each photosensitive drum exposed by the exposure unit to which the fixing member is attached. The image forming apparatus according to claim 1 , wherein the image forming apparatus expands in a running direction of the intermediate transfer belt . The exposure unit is individually provided for each of the plurality of photosensitive drums,
The image forming apparatus according to claim 1 , wherein the fixing member is separately attached to each of the exposure units provided individually for each of the photosensitive drums.