JP2005115075A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To bring an endless belt into contact with an image carrier or separate the endless belt from the image carrier in response to an image formation content without generating large size of an apparatus and the meander of the endless belt. <P>SOLUTION: The image forming apparatus arranges eccentric cams 212 and 222 rotated at a rotation angle in response to a content of image forming operation, cam followers 214 and 224 contacted on the peripheral face of the eccentric cams 212 and 222, transmission members 215a-215d holding transfer rollers 13a-13d by interlocking with each of the cam followers 214 and 224, and a tension member 230 pushing up an upper side range to the outside in a moving route of an intermediate transfer belt 11 by interlocking with the cam follower 224 in the inside of a loop-like moving route formed by the intermediate transfer belt 11 stretched between a drive roller 11a and a driven roller 11b. The pushing-up amount of the intermediate transfer belt 11 by the tension member 230 changes in response to the vertical positions of transfer rollers 13a-13d, and the moving route of the intermediate transfer belt 11 changes in response to the content of the image forming operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention forms a full-color image on a recording medium such as paper via an endless belt by arranging a plurality of image forming portions that form images of different hues by electrophotographic image formation in one direction. In particular, the present invention relates to an image forming apparatus in which an endless belt is selectively brought into contact with or separated from an image carrier provided in each image forming unit.

  In recent years, there has been an increasing demand not only for monochrome image formation but also full-color image formation for electrophotographic image forming apparatuses, and development of electrophotographic full-color image forming apparatuses has been promoted. Usually, a full-color image forming apparatus forms an image using toner of a corresponding hue for each of image data of a plurality of hues obtained by color-separating a color image. For example, the same color image is read through a filter for each of the three primary colors (red, green, and blue) of additive mixed colors, and at least the three primary colors (cyan, magenta, yellow) of the subtractive mixed colors are read from the read data. Image data is created, a visualized image is created using toner of a corresponding hue based on the image data of each hue, and a full color image is formed by superimposing the visualized images of each hue.

  In such a full-color image forming apparatus, an exposure process, a development process, and a transfer process are necessary for each hue, and the alignment of the visualized image of each hue becomes a problem, and the image formation speed of a full-color image is a monochrome image formation. The impression that it is slow compared to the speed is strong.

  For this reason, conventionally, a semiconductive endless belt is rotatably provided, and a plurality of image forming portions that individually form visualized images of different hues are arranged in a line along the moving direction of the outer peripheral surface of the endless belt. There has been proposed a tandem-type full-color image forming apparatus that is arranged and forms one full-color image while the endless belt rotates at least once.

  In the tandem full-color image forming apparatus, the visualized image of each hue formed by each image forming unit is superimposed on the outer peripheral surface of the endless belt and then transferred onto the paper, or the outer peripheral surface of the endless belt. A transfer conveyance system that sequentially transfers the visualized image of each hue formed by each image forming unit onto the surface of the recording medium that is sucked and conveyed is used to increase the speed of full-color image formation. During full-color image formation, the outer peripheral surface of the endless belt in the intermediate transfer system and the surface of the recording medium transported by the endless belt in the transfer transport system are applied to the image carrier individually provided in each image forming unit with a predetermined pressure contact force. Abut.

  The transfer conveyance method has an advantage that the transfer process is performed only once for each hue because the visualized image formed in each image forming unit is directly transferred to the surface of the recording medium. Since the medium is adsorbed and transported, not only the configuration for charging the recording medium is required, but also the disadvantage that the charged charge of the recording medium affects the transfer state of the visualized image and deteriorates the image forming state. is there. On the other hand, in the intermediate transfer method, although the transfer process is performed twice for each hue, it is notable that the recording medium need not be charged for conveyance and the image forming state can be improved.

  On the other hand, even though the demand for full-color image formation has increased, black-and-white monochrome image formation is still the mainstream, and a further increase in monochrome image formation is desired. For this reason, in a full-color image forming apparatus, it is necessary to eliminate the slowdown of monochrome image formation caused by going through a plurality of image forming units arranged for full-color image formation.

  When a monochrome image is formed in a tandem full-color image forming apparatus, image formation is performed only in a single image forming unit among the plurality of image forming units, and image formation is not performed in the remaining image forming units. As described above, in an image forming unit that is not used for monochrome image formation, it is also necessary to prevent deterioration of the image carrier and color mixing of toner due to the image carrier contacting the endless belt or the recording medium.

  Furthermore, if the endless belt remains in contact with each image carrier during standby when neither monochrome image formation nor full color image formation is performed, the endless belt is deformed. Further, the recording medium remaining between the image carrier and the endless belt cannot be removed during jam processing, and parts cannot be replaced or cleaned during maintenance work.

  Therefore, a conventional tandem full-color image forming apparatus includes an image forming unit that forms a black image in addition to an image forming unit that forms images of the three primary colors of subtractive color mixing, and these image forming units A configuration is disclosed in which the position of the endless belt is changed between when a monochrome image is formed and when a full-color image is formed to increase the speed of monochrome image formation (see, for example, Patent Documents 1 to 3).

In these conventional configurations, at least one of the driving roller and the driven roller that stretches the endless belt and supplies the rotational force to the endless belt is moved with respect to the image forming unit. In these configurations, when the endless belt moves, the axial distance between the driving roller and the driven roller that stretches the endless belt is always kept constant, and the endless belt is moved without considering the change in the circumference of the endless belt. be able to.
Japanese Patent Laid-Open No. 10-039651 Japanese Patent Laid-Open No. 10-293437 Japanese Patent No. 2574804

  However, in the above-described conventional configuration, the position of the endless belt is clearly displaced during monochrome image formation and full-color image formation so as not to adversely affect the image carrier provided in the image forming unit that is not used during monochrome image formation. For this purpose, it is necessary to increase the amount of movement of the driving roller or the driven roller, which causes a problem of increasing the size of the apparatus.

  In addition, the image carrier and the endless belt included in each image forming unit are in contact with each other in a transfer region having a predetermined width called a transfer nip. In this transfer region, the endless belt bends according to the curvature of the surface of the image carrier. Therefore, in the configuration in which the distance between the shafts of the driving roller and the driven roller is always kept constant, the endless belt separated from the image carrier provided in the image forming unit not used at the time of monochrome image formation causes a tarmi, There is a problem of causing meandering.

  An object of the present invention is to provide an image forming apparatus capable of bringing an endless belt into contact with or separating from an image carrier in accordance with image forming contents without causing an increase in the size of the apparatus or meandering of the endless belt.

  The present invention has the following configuration as means for solving the above-described problems.

(1) an endless belt that is looped between a driving roller and a driven roller whose positions in the apparatus are fixed to form a loop-shaped movement path;
A plurality of image carriers arranged in parallel within a predetermined range along the moving direction of the endless belt;
A plurality of transfer members disposed inside the movement path and facing each of the plurality of image carriers with a part of the endless belt interposed therebetween;
An eccentric cam that rotates at a rotation angle corresponding to the content of the image forming operation around a rotation axis parallel to the rotation axis of the drive roller and the driven roller;
A transfer member moving mechanism that converts a change in the radius of the eccentric cam at a specific rotation angle into a displacement in the contact / separation direction of the transfer member with respect to the image carrier;
And a tension member that is locked to the transfer member moving mechanism and deforms the moving path of the endless belt in conjunction with the operation of the transfer member moving mechanism.

  In this configuration, when the eccentric cam rotates at a rotation angle corresponding to the content of the image forming operation, a change in radius at a specific rotation angle of the eccentric cam is transmitted to the transfer member via the transfer member moving mechanism, and the transfer member is The moving path of the endless belt is deformed by the tension member that is displaced in the contact / separation direction with respect to the image carrier and is linked to the transfer member moving mechanism. Therefore, as the plurality of transfer members positioned inside the loop-shaped moving path formed by the endless belt approaches or separates from the plurality of image carriers with the endless belt interposed therebetween, the endless belt is The endless belt is brought into contact with or separated from each of the plurality of image carriers without being displaced by the driving roller and the driven roller that are stretched.

  (2) The endless belt is an intermediate transfer belt onto which toner images formed on the plurality of image carriers are sequentially transferred.

  In this configuration, when the eccentric cam rotates at a rotation angle corresponding to the content of the image forming operation, a change in radius at a specific rotation angle of the eccentric cam is transmitted to the transfer member via the transfer member moving mechanism, and the transfer member is The moving path of the intermediate transfer belt is deformed by a tension member that is displaced in the contact / separation direction with respect to the image bearing member and interlocked with the transfer member moving mechanism. Therefore, the intermediate transfer member is moved in accordance with the movement of each of the plurality of transfer members positioned inside the loop-shaped movement path formed by the endless belt toward or away from each of the plurality of image carriers with the intermediate transfer belt interposed therebetween. The intermediate transfer belt contacts or separates from each of the plurality of image carriers without being displaced by the driving roller and the driven roller on which the belt is stretched, and is formed on the image carrier according to the contents of the image forming operation. The transferred toner image is transferred to the intermediate transfer belt.

(3) The plurality of image carriers are formed with a plurality of color image image carriers on which subtractive three-color toner images are formed during full-color image formation, and a black toner image is formed during monochrome image formation. An image carrier for monochrome images
The transfer member moving mechanism includes a color image moving member that is locked to the tension member and that integrally moves all of the transfer members facing the image carrier for the color image.

  In this configuration, all of the plurality of transfer members facing each of the plurality of color image image carriers are integrally moved by the color image moving member, and according to the integral movement of the plurality of transfer members. The endless belt contacts or is separated from all of the image carriers for color images. Therefore, the endless belt is brought into contact with or separated from the image carrier for a plurality of color images in a single process.

  (4) The transfer member moving mechanism further includes a monochrome image moving member that moves a transfer member facing the image carrier for the monochrome image.

  In this configuration, the endless belt is brought into contact with or separated from all of the image carriers for color images in accordance with the integral movement of the plurality of transfer members facing each of the image carriers for color images. At the same time, the endless belt contacts or separates from the monochrome image carrier in accordance with the movement of the transfer member facing the monochrome image carrier. Therefore, the endless belt contacts or separates in each step for each of the plurality of color image carrier and monochrome image carrier.

  (5) The transfer member moving mechanism and the tension member are arranged inside the moving path.

  In this configuration, the endless belt is brought into contact with or separated from the plurality of image carriers by the transfer member moving mechanism and the tension member arranged inside the loop-shaped moving path formed by the endless belt. Therefore, a mechanism for bringing the endless belt into contact with or separating from the plurality of image carriers is not arranged outside the moving path of the endless belt.

  (6) The transfer member moving mechanism includes a contact portion that contacts the peripheral surface of the eccentric cam at the specific rotation angle position at the contact portion, and the peripheral surface of the tension member has one end portion on the inner periphery of the endless belt. It is characterized in that it abuts on the surface and is swingably supported at the other end, and is locked to the transfer member moving mechanism via an elastic member.

  In this configuration, when the radius at a specific rotation angle of the eccentric cam changes due to the rotation of the eccentric cam, the transfer member moves so that the contact portion contacts the peripheral surface of the eccentric cam at the specific rotation angle position. The mechanism moves, and this movement is transmitted to the tension member via the elastic member, and the tension member swings. Therefore, one end of the tension member abuts on the inner peripheral surface of the endless belt while being urged by the elastic force of the elastic member.

  (7) The tension member is a roller whose peripheral surface is in contact with the inner peripheral surface of the endless belt, and a roller having a larger diameter in the central portion in comparison with the diameters of both end portions in the axial direction. It is supported by a rotating shaft parallel to the rotating shaft.

  In this configuration, when the endless belt moves along the movement path, a force in the direction in which both end portions in the width direction are directed toward the center acts on the endless belt from the peripheral surface of the roller of the tension member. Therefore, even when the endless belt moves at a high speed, the endless belt does not meander.

  (8) The tension member makes the moving path of the endless belt one of the first to third paths according to the contents of the image forming operation in conjunction with the operation of the transfer member moving mechanism. To do.

  In this configuration, the movement path of the endless belt stretched around the driving roller and the driven roller whose positions are fixed changes into three types according to the contents of the image forming operation. Therefore, the approach or separation state of the plurality of transfer members with respect to the plurality of image carriers and the contact or separation state of the endless belt between the driving roller and the driven roller appropriately change according to the contents of the image forming operation. .

  (9) The first path is a path during standby of an image forming operation in which the endless belt is separated from all of the plurality of image carriers.

  In this configuration, the endless belt is separated from all of the plurality of image carriers when waiting for the image forming operation. Therefore, the endless belt does not come into contact with the plurality of image carriers in a state where the image forming operation is not performed, and the endless belt is not partially deformed.

(10) The second path is a path during full-color image formation in which the endless belt is in contact with all of the image carrier,
The third path is a path for forming a monochrome image in which the endless belt is in contact with the image carrier for monochrome images and is separated from the image carrier for full-color images.

  In this configuration, the endless belt contacts all of the plurality of image carriers when forming a full-color image, and only contacts the image carrier for monochrome images when forming a monochrome image. Therefore, the endless belt contacts only the image carrier used for the image forming operation among the plurality of image carriers, and deterioration due to the contact of the image carrier not used for the image forming operation with the endless belt does not occur.

  (11) The tension member causes a predetermined tension to act on the endless belt in at least each of the second and third paths.

  In this configuration, the circumferential length of the endless belt does not change regardless of which of the second and third paths. Therefore, a constant tension always acts on the endless belt during the image forming operation, and the contact state of the endless belt with the image carrier during the image forming operation is maintained constant.

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

  (1) An endless belt as each of a plurality of transfer members positioned inside a loop-shaped moving path formed by the endless belt approaches or separates from each of the plurality of image carriers with the endless belt interposed therebetween. Since the endless belt can be brought into contact with or separated from each of the plurality of image carriers without any displacement of the driving roller and the driven roller, the movement path of the endless belt is included in the contents of the image forming operation. There is no need to use a complicated mechanism for displacing the driving roller or the driven roller in order to achieve the corresponding state, and the apparatus can be downsized.

  (2) As each of the plurality of transfer members positioned inside the loop-shaped movement path formed by the intermediate transfer belt approaches or separates from each of the plurality of image carriers with the intermediate transfer belt interposed therebetween, The intermediate transfer belt can be brought into contact with or separated from each of the plurality of image carriers without being displaced by the driving roller and the driven roller on which the intermediate transfer belt is stretched. It is not necessary to use a complicated mechanism for displacing the driving roller or the driven roller in order to transfer the toner image in an appropriate state to the intermediate transfer belt in a state corresponding to the content of the forming operation, and the apparatus can be downsized. .

  (3) The endless belt is brought into contact with or separated from all the image carriers for color images in accordance with the integral movement of the plurality of transfer members facing each of the image carriers for color images. Accordingly, the endless belt can be brought into contact with or separated from the image carrier for a plurality of color images in one step, and the moving path of the endless belt can be quickly changed to a state corresponding to the content of the image forming operation. be able to.

  (4) An image carrier for a plurality of color images by contacting or separating an endless belt in each step for each of the image carrier for a plurality of color images and the image carrier for a monochrome image. The endless belt can be brought into contact with or separated from each other in a single step, and the movement path of the endless belt can be quickly changed to a state corresponding to the contents of the image forming operation including the full color image forming operation and the monochrome image forming operation. Can be changed.

  (5) A mechanism for bringing the endless belt into contact with or separating from the plurality of image carriers is not disposed outside the moving path of the endless belt, and the apparatus can be downsized.

  (6) A predetermined tension is applied to the endless belt even if the movement path is changed by bringing the end of the tension member into contact with the inner peripheral surface of the endless belt while being urged by the elastic force of the elastic member. be able to.

  (7) To prevent the endless belt from meandering by applying a force in the direction in which both ends in the width direction are directed toward the center of the endless belt moving along the moving path from the peripheral surface of the roller of the tension member. Come.

  (8) The approach or separation state of the plurality of transfer members with respect to the plurality of image carriers and the contact or separation state of the endless belt between the driving roller and the driven roller are appropriately changed according to the contents of the image forming operation. Can be made.

  (9) It is possible to prevent partial deformation of the endless belt by preventing the endless belt from coming into contact with a plurality of image carriers in a state where no image forming operation is performed.

  (10) By bringing the endless belt into contact with only the image carrier used in the image forming operation among the plurality of image carriers, deterioration due to contact with the endless belt of the image carrier not used in the image forming operation is prevented. Can be prevented.

  (11) A constant tension is always applied to the endless belt during the image forming operation, and the contact state of the endless belt with the image carrier during the image forming operation can be maintained constant.

  Hereinafter, an image forming apparatus according to the best embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 forms multicolor and single color images on a recording medium such as paper according to image data transmitted from the outside. For this reason, the image forming apparatus 100 includes an exposure unit E, a photosensitive drum (corresponding to the image carrier of the present invention) 101 (101a to 101d), a developing unit 102 (102a to 102d), and a charging roller 103 (103a to 103a). 103d), a cleaning unit 104 (104a to 104d), an intermediate transfer belt (corresponding to an endless belt of the present invention) 11, an intermediate transfer roller (corresponding to a transfer member of the present invention, hereinafter simply referred to as a transfer roller) 13. (13a to 13d) A secondary transfer roller 14, a fixing device 15, paper transport paths P1, P2, and P3, a paper feed cassette 16, a manual paper feed tray 17, a paper discharge tray 18, and the like are provided.

  The image forming apparatus 100 converts each hue of four colors by adding black (K) to cyan (C), magenta (M), and yellow (Y), which are three subtractive primary colors obtained by color separation of a color image. Image formation is performed using corresponding image data. The photosensitive drum 101 (101a to 101d), the developing unit 102 (102a to 102d), the charging roller 103 (103a to 103d), the transfer roller 13 (13a to 13d), and the cleaning unit 104 (104a to 104d) are in each hue. Accordingly, four each are provided, and four image forming portions Pa to Pd are configured. The image forming portions Pa to Pd are arranged in a line in the moving direction (sub-scanning direction) of the intermediate transfer belt 11.

  The charging roller 103 is a contact-type charger that uniformly charges the surface of the photosensitive drum 101 to a predetermined potential. Instead of the charging roller 103, a contact-type charger using a charging brush or a contact-type charger using a charging charger can be used. The exposure unit E includes a semiconductor laser (not shown), a polygon mirror, a reflection mirror, and the like, and each of the laser beams modulated by the image data of each hue of black, cyan, magenta, and yellow is transferred to the photosensitive drums 101a to 101d. By irradiating each, a latent image corresponding to the image data is formed on the surfaces of the photosensitive drums 101a to 101d. On each of the photosensitive drums 101a to 101d, a latent image is formed by image data of each hue of black, cyan, magenta, and yellow.

  Therefore, the photosensitive drum 101a is an image carrier for a monochrome image of the present invention on which a black toner image is formed when a monochrome image is formed. The photosensitive drums 101b to 101d are subtractive three-color toners when forming a full-color image. It is an image carrier for a color image of the present invention on which an image is formed.

  The developing unit 102 supplies a developer to the surface of the photosensitive drum 101 on which the latent image is formed, and visualizes the latent image into a toner image. Each of the developing units 102a to 102d contains developers of hues of black, cyan, magenta, and yellow, and latent images of the hues formed on the photosensitive drums 101a to 101d are respectively black, cyan, The toner images are visualized as magenta and yellow toner images. The cleaning unit 104 removes and collects toner remaining on the surface of the photosensitive drum 101 after development and image transfer.

  The intermediate transfer belt 11 disposed above the photosensitive drum 101 is stretched between the driving roller 11a and the driven roller 11b to form a loop-shaped movement path. The outer peripheral surface of the intermediate transfer belt 11 faces the photosensitive drum 101d, the photosensitive drum 101c, the photosensitive drum 101b, and the photosensitive drum 101a in this order. Transfer rollers 13a to 13d are arranged at positions facing the respective photosensitive drums 101a to 101d with the intermediate transfer belt 11 interposed therebetween. In order to transfer the toner images carried on the surfaces of the photosensitive drums 101a to 101d onto the intermediate transfer belt 11, a transfer bias having a polarity opposite to the charging polarity of the toner is applied to the transfer rollers 13a to 13d. As a result, the toner images of each hue formed on the photosensitive drum 101 (101a to 101d) are sequentially transferred to the outer peripheral surface of the intermediate transfer belt 11, and a full color toner image is formed on the outer peripheral surface of the intermediate transfer belt 11. Is done.

  However, when image data of only a part of the hues of cyan, magenta, yellow, and black is input, some of the four photosensitive drums 101a to 101d corresponding to the hue of the input image data. A latent image and a toner image are formed only on the photoreceptor 101. For example, when a monochrome image is formed, a latent image and a toner image are formed only on the photosensitive drum 101 a corresponding to the black hue, and only the black toner image is transferred to the outer peripheral surface of the intermediate transfer belt 11. .

  Each of the transfer rollers 103a to 103d is configured by covering the surface of a shaft made of a metal (for example, stainless steel) having a diameter of 8 to 10 mm with a conductive elastic material (for example, EPDM, urethane foam, etc.). A high voltage is uniformly applied to the intermediate transfer belt 11 by the elastic material. Instead of the transfer roller 103, a brush-like intermediate transfer member can be used.

  As described above, the toner image formed on the outer peripheral surface of the intermediate transfer belt 11 is conveyed to a position facing the secondary transfer roller 14 by the rotation of the intermediate transfer belt 11. The secondary transfer roller 14 is pressed against the outer peripheral surface of the intermediate transfer belt 11 with a predetermined nip pressure during image formation. When the paper fed from the paper feed cassette 16 or the manual paper feed tray 17 passes between the secondary transfer roller 14 and the intermediate transfer belt 11, the polarity of the toner charged on the secondary transfer roller 14 is opposite to that of the toner. The high voltage is applied. As a result, the toner image is transferred from the outer peripheral surface of the intermediate transfer belt 11 to the surface of the sheet.

  In order to maintain the nip pressure between the secondary transfer roller 14 and the intermediate transfer belt 11 at a predetermined value, either the secondary transfer roller 14 or the drive roller 11a is made of a hard material (metal or the like) and remains. The other is made of a soft material such as an elastic roller (such as an elastic rubber roller or a foaming resin roller).

  Further, of the toner adhering to the intermediate transfer belt 11 from the photosensitive drum 101, the toner remaining on the intermediate transfer belt 11 without being transferred onto the sheet is removed by the cleaning unit 12 in order to prevent color mixing in the next process. Collected.

  The sheet on which the toner image has been transferred is guided to the fixing device 15, and passes between the heating roller 15a and the pressure roller 15b to be heated and pressed. As a result, the toner image is firmly fixed on the surface of the paper. The paper on which the toner image is fixed is discharged onto the paper discharge tray 18 by the paper discharge roller 18a.

  In the image forming apparatus 100, a substantially vertical direction for feeding the paper stored in the paper cassette 16 to the paper discharge tray 18 between the secondary transfer roller 14 and the intermediate transfer belt 11 and via the fixing device 15. A paper transport path P1 is provided. In the paper transport path P1, a pickup roller 16a that feeds the paper in the paper cassette 16 one by one into the paper transport path P1, a transport roller r that transports the fed paper upward, and a transported paper to a predetermined level. A registration roller 19 that guides between the secondary secondary transfer roller 14 and the intermediate transfer belt 11 at a timing, and a paper discharge roller 18 a that discharges the paper to the paper discharge tray 18 are disposed.

  Further, inside the image forming apparatus 100, a paper conveyance path P2 in which a pickup roller 17a and a conveyance roller r are arranged is formed between the manual paper feed tray 17 and the registration roller 19. Further, a paper transport path P3 is formed between the paper discharge roller 18a and the upstream side of the registration roller 19 in the paper transport path P1.

  The paper discharge roller 18a is rotatable in both forward and reverse directions, and is used for forming a single-sided image for forming an image on one side of a sheet and for forming a second-side image in forming a double-sided image for forming an image on both sides of a sheet. Driven in the forward direction, the paper is discharged to the paper discharge tray 18. On the other hand, when the first side image is formed in the double-sided image formation, the discharge roller 18a is driven in the normal rotation direction until the rear end of the paper passes through the fixing device 15, and then reversely rotated with the rear end of the paper sandwiched. Driven in the direction, the sheet is guided into the sheet conveyance path P3. As a result, the paper on which the image is formed on only one side when the double-sided image is formed is guided to the paper transport path P1 with the front and back surfaces and the front and rear ends reversed.

  The registration roller 19 feeds a sheet fed from the sheet cassette 16 or the manual feed tray 17 or conveyed via the sheet conveying path P 3 at a timing synchronized with the rotation of the intermediate transfer belt 11. 14 and the intermediate transfer belt 11. For this reason, the registration roller 19 stops rotating when the operation of the photosensitive drum 101 and the intermediate transfer belt 11 is started, and the sheet fed or conveyed prior to the rotation of the intermediate transfer belt 11 has the front end at the registration roller 19. The movement in the sheet conveyance path P1 is stopped in a state where the sheet 19 is in contact with the sheet 19. Thereafter, the registration roller 19 is a position where the secondary transfer roller 14 and the intermediate transfer belt 11 are in pressure contact with each other, at a timing when the front end of the sheet and the front end of the toner image formed on the intermediate transfer belt 11 face each other. Start spinning.

  FIG. 2 is a diagram illustrating a configuration of a transfer member moving mechanism and a belt contacting / separating mechanism provided in the image forming apparatus. The intermediate transfer belt 11 is stretched between the driving roller 11a and the driven roller 11b to form a loop-shaped moving path including a substantially horizontal range above and below. Below the intermediate transfer belt 11, photosensitive drums 101a to 101d of the image forming stations Pa to Pd are arranged. The photosensitive drums 101a to 101d are arranged side by side along the lower range of the moving path of the intermediate transfer belt 11, and the outer peripheral surface of the intermediate transfer belt 11 is positioned below the moving path of the photosensitive drums 101a to 101d. Opposite to. The intermediate transfer belt 11 moves in the arrow B direction in the lower range of the movement path by the rotation of the driving roller 11a in the arrow A direction.

  Inside the loop-shaped movement path of the intermediate transfer belt 11, transfer rollers 13a to 13d included in the image forming stations Pa to Pd are arranged. Each of the transfer rollers 13a to 13d is pivotally supported so as to be movable in the vertical direction (Y-Y direction) at a position facing each of the photosensitive drums 101a to 101d with the intermediate transfer belt 11 interposed therebetween. Accordingly, the transfer rollers 13a to 13d are close to or separated from the photosensitive drums 101a to 101d. The transfer rollers 13a to 13d are urged upward by a predetermined elastic force.

  Eccentric cams 212 and 222, cam followers 214 and 224 as transfer member moving mechanisms of the present invention, transmission members 215a to 215d, and a tension member 230 are arranged inside the loop-shaped moving path of the intermediate transfer belt 11. Yes. The cam follower 214 and the transmission member 215a constitute the monochrome image moving member 210 of the present invention, and the cam follower 224 and the transmission members 215b to 215d constitute the color image moving member 220 of the present invention. The eccentric cam 212 rotates about the rotation shaft 213. The eccentric cam 222 rotates about the rotation shaft 223. The rotating shafts 213 and 223 are disposed in parallel with the rotating shafts of the driving roller 11a and the driven roller 11b.

  The tension member 230 includes a lever 231 that pivotally supports a roller 232 at one end and is swingable around a rotation shaft 233 at the other end. The other end portion of a coil spring (corresponding to the elastic member of the present invention) 234 whose one end portion is locked to the cam follower 224 is locked to the intermediate portion of the lever 231. Therefore, the lever 231 is locked to the cam follower via the coil spring 234. The peripheral surface of the roller 232 is in contact with the inner peripheral surface of the intermediate transfer belt 11 in the range above the movement path of the intermediate transfer belt 11.

  In the monochrome image moving member 210, the cam follower 214 is movable in the horizontal direction (X-X direction), and the contact portion of the cam follower 214 moves around the eccentric cam 212 at the horizontal rotation angle position of the eccentric cam 212. It is in contact with the surface. The cam follower 214 is biased toward the eccentric cam 212 by the elastic force of an elastic member (not shown). The transmission member 215a is supported by the cam follower 214 so as to be movable in the vertical direction, and is urged downward by the elastic force of the spring 216a. In the transmission member 215a, a concave portion 215aa and a concave portion 215ab for supporting the transfer roller 13a included in the black image forming station Pa from above are formed at different positions in the vertical direction and the horizontal direction.

  When the distance from the rotation shaft 213 to the circumferential surface of the eccentric cam 212 (the length of the radius on the cam follower 214 side at the horizontal rotation angle of the eccentric cam 212) changes due to the rotation of the eccentric cam 212, the cam follower 214 together with the transmission member 215a. It is displaced in the horizontal direction, and one of the recess 215aa or the recess 215ab of the transmission member 215a is selectively positioned above the transfer roller 13a. In the transmission member 215a, the recess 215aa and the recess 215ab are formed at different positions in the vertical direction. Further, the transfer roller 13a is biased upward. Accordingly, the vertical position of the transfer roller 13a is defined by the transmission member 215a, and the vertical position of the transfer roller 13a is determined depending on whether the concave portion 215aa or the concave portion 215ab is positioned above the transfer roller 13a by the rotation of the eccentric cam 212. As a result, the transfer roller 13a approaches or separates from the photosensitive drum 101a, which is an image carrier for monochrome images.

  In the color image moving member 220, the cam follower 224 is movable in the horizontal direction, and the contact portion of the cam follower 224 is in contact with the circumferential surface of the eccentric cam 222 at the horizontal rotation angle position of the eccentric cam 222. . The cam follower 224 is urged toward the eccentric cam 222 by the elastic force of an elastic member (not shown). The transmission members 215b to 215d are supported by the cam follower 224 so as to be movable in the vertical direction, and are urged downward by the elastic force of the springs 216b to 216d. On the transmission members 215b to 215d, concave portions 215ba, 215bb, 215bc to 215da, 215db, and 215dc for supporting the transfer rollers 13b to 13d included in the image forming stations Pb to Pd of cyan, magenta, and yellow from above are provided in the vertical direction. And are formed at different positions in the horizontal direction.

  When the distance from the rotation shaft 223 to the circumferential surface of the eccentric cam 222 (the length of the radius on the cam follower 224 side at the horizontal rotation angle of the eccentric cam 212) changes due to the rotation of the eccentric cam 222, the cam follower 224 is transmitted to the transmission member 215b. 215d is displaced in the horizontal direction, and the recesses 215ba to 215da, the recesses 215bb to 215db, or the recesses 215bc to 215dc of the transmission members 215b to 215d are selectively positioned above the transfer rollers 13b to 13d. In the transmission members 215b to 215d, the recesses 215ba to 215da and the recesses 215bc to 215dc and the recesses 215bb to 215db are formed at different positions in the vertical direction. Further, the transfer rollers 13b to 13d are biased upward. Accordingly, the vertical positions of the transfer rollers 13b to 13d are defined by the transmission members 215b to 215d, and the recesses 215ba to 215da or the recesses 215bc to 215dc are positioned above the transfer rollers 13b to da by the rotation of the eccentric cam 212 or the recesses 215bb to 215bb. The upper and lower positions of the transfer rollers 13b to 13d change depending on whether 215db is positioned, and the transfer rollers 13b to 13d are close to or separated from the photosensitive drums 101b to 101d, which are image carriers for color images.

  The horizontal displacement of the cam follower 224 due to the rotation of the eccentric cam 222 is transmitted to the lever 231 via the coil spring 234, and the lever 231 swings about the rotation shaft 233 when the eccentric cam 222 rotates. When the lever 231 swings about the rotation shaft 233, the vertical position of the roller 232 changes according to the swing angle of the lever 231. Since the peripheral surface of the roller 232 is in contact with the inner peripheral surface of the intermediate transfer belt 11 in the upper range in the movement path of the intermediate transfer belt 11, the movement path of the intermediate transfer belt 11 is deformed when the vertical position of the roller 232 changes. To do.

  Accordingly, when the cam follower 224 is displaced in the horizontal direction together with the transmission members 215b to 215d by the rotation of the eccentric cam 222, any of the recesses 215ba to 215da, the recesses 215bc to 215dc, or the recesses 215bb to 215db is positioned above the transfer rollers 13b to 13d. Accordingly, the swing angle of the lever 231 changes, and the movement path of the intermediate transfer belt 11 is deformed.

  FIG. 3 is a diagram showing a moving path of the intermediate transfer belt in the image forming apparatus. FIG. 3A shows a first path which is a movement path during standby of the image forming operation of the intermediate transfer belt 11 in the image forming apparatus 100. When waiting for the image forming operation, the cam follower 214 is in contact with a portion of the peripheral surface of the eccentric cam 212 that is farthest from the rotation shaft 213 (portion having the longest radius) in the monochrome image moving member 210, and the upper side of the transmission member 215a. The recess 215aa is located above the transfer roller 13a, and the transfer roller 13a is separated from the photosensitive drum 101a and the intermediate transfer belt 11.

  In the standby state of the image forming operation, the cam follower 224 comes into contact with the portion of the color image moving member 220 farthest from the rotation shaft 223 (the portion with the longest radius) on the circumferential surface of the eccentric cam 222, and the cam follower 224 is horizontal. Since the upper concave portions 215ba to 215da of the transmission members 215b to 215d are positioned above the transfer rollers 13b to 13d, the transfer rollers 13b to 13d are the photosensitive drums 101b to 101d. And the intermediate transfer belt 11. At the same time, the inclination angle of the tension member 230 from the vertical direction of the lever 231 is the smallest, the roller 232 is located at the uppermost position, and a part of the upper range in the moving path of the intermediate transfer belt 11 protrudes upward. .

  As a result, when waiting for the image forming operation, the intermediate transfer belt 11 is pushed up most by the roller 232 of the tension member 230 in the upper range in the movement path, and the transfer roller 13a with respect to the lower range in the movement path. ˜13d are spaced apart upward, the intermediate transfer belt 11 is horizontally in the lower range in the movement path until it leaves the peripheral surface of the driven roller 11b and then contacts the peripheral surface of the drive roller 11a. Thus, the intermediate transfer belt 11 does not contact any of the photosensitive drums 101a to 101d and the transfer rollers 13a to 13d.

  FIG. 3B shows a third path that is a movement path when the intermediate transfer belt 11 in the image forming apparatus 100 is formed. At the time of monochrome image formation, the cam follower 214 comes into contact with the portion of the peripheral surface of the eccentric cam 212 that is closest to the rotation shaft 213 (the portion with the shortest radius) in the monochrome image moving member 210, and the concave portion 215ab below the transmission member 215a. Is positioned above the transfer roller 13a, and the transfer roller 13a is close to the photosensitive drum 101a, and actually contacts the photosensitive drum 101a with the intermediate transfer belt 11 interposed therebetween.

  Further, when forming a monochrome image, the cam follower 224 is provided in a portion where the distance from the rotation shaft 223 on the peripheral surface of the eccentric cam 222 is an intermediate portion (a portion having an intermediate radius between the maximum radius and the minimum radius). The upper concave portions 215 bc to 215 dc of the transmission members 215 b to 215 d are positioned above the transfer rollers 13 b to 13 d, and the transfer rollers 13 b to 13 d are separated from the photosensitive drums 101 b to 101 d and the intermediate transfer belt 11. At the same time, the inclination angle of the tension member 230 from the vertical direction of the lever 231 of the tension member 230 is larger than that during standby, and the roller 232 is positioned below. As a result, a part of the upper range in the moving path of the intermediate transfer belt 11 protrudes upward by a small amount compared to the standby time of the image forming operation.

  As a result, during monochrome image formation, the intermediate transfer belt 11 is slightly pushed up by the roller 232 of the tension member 230 in the upper range in the movement path of the intermediate transfer belt 11, and the lower side in the movement path of the intermediate transfer belt 11. In the range, the intermediate transfer belt 11 contacts the photosensitive drum 101a via the transfer roller 13a, and the transfer rollers 13b to 13d are separated upward from the intermediate transfer belt 11. Therefore, when the intermediate transfer belt 11 leaves the peripheral surface of the driven roller 11b in the lower range in the moving path, the photosensitive drum 101a and the transfer roller 13a do not come into contact with the photosensitive drums 101b to 101d and the transfer rollers 13b to 13d. After coming into contact with the peripheral surface of the drive roller 11a, it comes into contact with the peripheral surface of the drive roller 11a.

  FIG. 3C shows a second path that is a movement path of the intermediate transfer belt 11 in the image forming apparatus 100 when a full-color image is formed. At the time of full-color image formation, the cam follower 214 is in contact with the portion closest to the rotation shaft 213 (the portion with the shortest radius) on the peripheral surface of the eccentric cam 212 in the monochrome image moving member 210, and the concave portion 215ab below the transmission member 215a. Is positioned above the transfer roller 13a, and the transfer roller 13a is close to the photosensitive drum 101a, and actually contacts the photosensitive drum 101a with the intermediate transfer belt 11 interposed therebetween.

  Further, at the time of full-color image formation, the cam follower 224 is in contact with the portion of the color image moving member 220 closest to the rotation shaft 223 on the peripheral surface of the eccentric cam 222, and the concave portions 215bb to 215db below the transmission members 215b to 215d are formed. Located above the transfer rollers 13b to 13d, the transfer rollers 13b to 13d are close to the photosensitive drum 101a, and actually contact the photosensitive drum 101a with the intermediate transfer belt 11 interposed therebetween. At the same time, the inclination angle of the tension member 230 from the vertical direction of the lever 231 is the largest, and the roller 232 is positioned at the lowest position. As a result, a part of the upper range in the movement path of the intermediate transfer belt 11 does not protrude upward.

  As a result, during full-color image formation, the intermediate transfer belt 11 moves substantially horizontally in the upper range of the moving path of the intermediate transfer belt 11 until it reaches the peripheral surface of the driven roller 11b after leaving the peripheral surface of the drive roller 11a. Further, the intermediate transfer belt 11 contacts all of the photosensitive drums 101a to 101d by the transfer rollers 13a to 13d in the lower range in the movement path of the intermediate transfer belt 11. For this reason, when the intermediate transfer belt 11 leaves the peripheral surface of the driven roller 11b in the lower range in the movement path, the intermediate transfer belt 11 comes into contact with the peripheral surfaces of the photosensitive drums 101a to 101d and the transfer rollers 13a to 13d and then rotates around the drive roller 11a. Touch the surface.

  As described above, in the image forming apparatus 100, the movement path of the intermediate transfer belt 11 is selectively set to the first to third paths based on the rotation state of the eccentric cams 212 and 222 corresponding to the contents of the image forming operation. Change. Since the intermediate transfer belt 11 hardly expands or contracts in the movement direction, the shape of the eccentric cam 222 and the length of the movement path of the intermediate transfer belt 11 are always maintained constant in any of the first to third paths. The shape and arrangement position of the tension member 230 are determined.

  FIG. 4 is a block diagram illustrating a configuration of a control unit of the image forming apparatus. The control unit 300 of the image forming apparatus 100 includes an interface 304, an image memory 305, a paper feeding / conveying unit load device 306, an image forming unit load device 307, a temperature sensor 308, a motor driver 309, and a display. The input / output device such as the unit 310 is connected. The CPU 301 controls these input / output devices in accordance with a program written in the ROM 302 in advance, and stores data input / output during this time in a predetermined memory area of the RAM 303. The CPU 301 is connected to an external image output device such as a personal computer via an interface 304, and stores image data input from the interface 304 in the image memory 305.

  The sheet feeding / conveying section load device 305 includes a motor, a clutch, and a sensor for feeding and conveying sheets one by one from the sheet feeding tray 16 or the manual feed tray 17. The image forming unit load device 307 includes a motor, a clutch, and a sensor for forming an image on a sheet by the image forming stations Pa to Pd and the fixing device 15. The temperature sensor 308 detects the temperature of the heating roller 15 a in the fixing device 15. The motor driver 309 drives motors M1 and M2 that supply a rotational force to the rotation shafts 213 and 223 disposed in the intermediate transfer belt 11, respectively. The display unit 310 displays an operation state and the like on the display based on the display data supplied from the CPU 301.

  5 and 6 are flowcharts showing a processing procedure of the control unit of the image forming apparatus. FIG. 5 shows a processing procedure at the start of energization of the apparatus. FIG. 6 shows an image forming request from an external image output apparatus. The processing procedure at the time of input is shown.

  As shown in FIG. 5, when the power is turned on in the image forming apparatus 100, the CPU 301 detects the state of the intermediate transfer belt 11 (S1), and the movement path of the intermediate transfer belt 11 is shown in FIG. The motors M1 and M2 are driven so as to be the second path (S2). Next, the CPU 301 determines whether or not the sheet stays in the sheet transport path (S3). If the sheet stays in the sheet transport path, the CPU 301 prompts the user to remove the sheet via the display unit 310. Display is performed (S4). When the sheet does not stay in the sheet conveyance path, the CPU 301 performs a warm-up process and an initialization process (S5, S6). The warm-up process is a process for raising the heating roller 15a in the fixing device 15 to a set temperature. The initialization processing includes removal of the residual potential of the photosensitive drums 101a to 101d, preliminary charging of the developer in the developing units 102a to 102d, optimization of the developer concentration, initialization of each sensor and timer, and the like.

  When the warm-up process and the initialization process are completed, the CPU 301 displays that the image forming operation is possible via the display unit 310 (S7), and activates the timer assigned to the memory area MA1 of the RAM 303. Then, it is determined whether or not an image formation request has been input (S8, S9). When the timer counts a predetermined time without inputting an image formation request (S10), the CPU 301 sets the control temperature of the fixing device 15 to an energy saving temperature lower than the set temperature (S11), and the motor via the motor driver 309. M1 and M2 are driven to change the movement path of the intermediate transfer belt 11 to the first path shown in FIG. 3A (S12).

  With the above processing, the CPU 301 executes the warm-up process and the initialization process in a state where the movement path of the intermediate transfer belt 11 is set to the second path, and the warm-up process and the initialization process are completed and image formation is possible. When a predetermined time elapses without an image formation request being input, the image forming apparatus 100 is set in the energy saving mode to reduce power consumption. At this time, since the CPU 301 sets the movement path of the intermediate transfer belt 11 as the first path, the intermediate transfer belt 11 is in contact with the photosensitive drums 101a to 101d and the transfer rollers 13a to 13d when the image forming operation is not executed. Therefore, the intermediate transfer belt 11 is not partially deformed and the peripheral surfaces of the photosensitive drums 101a to 101d are not partially deteriorated.

  When an image formation request is input from the external image output device in S9 or S13 in FIG. 5, the CPU 301 determines whether or not the energy saving mode is set (S21), and the energy saving mode is set. If it is, the energized state of the image forming apparatus 100 is returned to the normal state, and the control temperature of the fixing device 15 is changed to the set temperature (S22). When the fixing device 15 reaches the set temperature (s23), the CPU 301 determines whether or not the movement path of the intermediate transfer belt 11 is the first path (S24), and the movement path of the intermediate transfer belt 11 is the first. If the first path is set, the movement path of the intermediate transfer belt 11 is changed to the second path (S25).

  Next, when the input image formation request relates to a full-color image, the CPU 301 executes full-color image formation while keeping the movement path of the intermediate transfer belt 11 as the second path (S26 → S27 → S30). If the input image formation request relates to a monochrome image, the CPU 301 changes the movement path of the intermediate transfer belt 11 to the third path, and then executes monochrome image formation (S26 → S28 to S30). ).

  With the above processing, when an image formation request for a full-color image is input, the CPU 301 changes the movement path of the intermediate transfer belt 11 to the second path shown in FIG. 3C, and makes the intermediate transfer belt 11 the photosensitive drum 101a. ˜101d and transfer rollers 13a˜13d are brought into contact with each other to form a full color image. In addition, when an image formation request for a monochrome image is input, the CPU 301 changes the movement path of the intermediate transfer belt 11 to the third path shown in FIG. 3B, and the intermediate transfer belt 11 is moved to the photosensitive drum 101a and the transfer roller. Monochrome image formation is executed by contacting only 13a. At the time of monochrome image formation, the intermediate transfer belt 11 does not come into contact with the photosensitive drums 101b to 101d and the transfer rollers 13b to 13d that are not used in the image forming operation, so that the photosensitive drums 101b to 101d and the transfer rollers 13b to 13d Deterioration and mixing of toners of different colors in the developing devices 102a to 102d can be prevented. Therefore, the moving path of the intermediate transfer belt 11 can be in an appropriate state according to each of the plurality of image formation contents.

  FIG. 7 is a side view of a roller included in a tension member in the image forming apparatus. A rotating shaft 232 a protrudes from both ends of the roller 232 in the axial direction, and both ends of the rotating shaft 232 a are pivotally supported on one end side of the pair of levers 231. The pair of levers 231 is pivotally supported by the rotation shaft 233. The length in the axial direction of the roller 232 that makes the peripheral surface contact a part of the inner surface of the intermediate transfer belt 11 is substantially equal to the width of the intermediate transfer belt 11. Further, the diameter Dc of the central portion in the axial direction of the roller 232 is larger than the diameter De of both end portions, and is symmetrical with respect to the center line Lm in the axial direction.

  A contact force can be applied to the entire width of the intermediate transfer belt 11 from the peripheral surface of the roller 232, and the force is applied to the intermediate transfer belt 11 from both ends in the width direction (the axial direction of the roller 232) toward the center when rotating. Works. Thus, even when the intermediate transfer belt 11 rotates at high speed, the intermediate transfer belt 11 can be stably rotated without causing meandering in the intermediate transfer belt 11.

1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the transfer member moving mechanism with which the said image forming apparatus is equipped, and a belt contact-separation mechanism. FIG. 4 is a diagram illustrating a moving path of an intermediate transfer belt in the image forming apparatus. 2 is a block diagram illustrating a configuration of a control unit of the image forming apparatus. FIG. 4 is a flowchart illustrating a processing procedure of a control unit at the start of energization of the image forming apparatus. 6 is a flowchart illustrating a processing procedure of a control unit when an image formation request is input from an external image output apparatus. FIG. 3 is a front view and a side view of a first eccentric cam and a second eccentric cam in the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Intermediate transfer belt 11a Drive roller 12b Driven roller 13a-13d Transfer roller 100 Image forming apparatus 101a-101d Photosensitive drum 210 Monochrome image moving member 212, 222 Eccentric cam 214, 224 Cam follower 215a-215d Transmission member 220 Color image movement Member 230 Tension member 231 Lever 232 Roller 233 Rotating shaft

Claims (11)

An endless belt that is looped between a driving roller and a driven roller whose positions in the apparatus are fixed, and forms a loop-shaped movement path;
A plurality of image carriers arranged in parallel within a predetermined range along the moving direction of the endless belt;
A plurality of transfer members disposed inside the movement path and facing each of the plurality of image carriers with a part of the endless belt interposed therebetween;
An eccentric cam that rotates at a rotation angle corresponding to the content of the image forming operation around a rotation axis parallel to the rotation axis of the drive roller and the driven roller;
A transfer member moving mechanism that converts a change in the radius of the eccentric cam at a specific rotation angle into a displacement in the contact / separation direction of the transfer member with respect to the image carrier;
An image forming apparatus comprising: a tension member that is locked to the transfer member moving mechanism and deforms the moving path of the endless belt in conjunction with the operation of the transfer member moving mechanism.   The image forming apparatus according to claim 1, wherein the endless belt is an intermediate transfer belt onto which toner images formed on the plurality of image carriers are sequentially transferred. The plurality of image carriers include a plurality of color image image carriers on which subtractive three-color toner images are formed during full-color image formation, and a monochrome image on which black toner images are formed during monochrome image formation. And an image carrier for
2. The color image moving member according to claim 1, wherein the transfer member moving mechanism includes a color image moving member that is locked to the tension member and that integrally moves all of the transfer members facing the color image image bearing member. Image forming apparatus.   The image forming apparatus according to claim 3, wherein the transfer member moving mechanism further includes a monochrome image moving member that moves a transfer member facing the image carrier for the monochrome image.   The image forming apparatus according to claim 1, wherein the transfer member moving mechanism and the tension member are arranged inside the moving path.   The transfer member moving mechanism includes a contact portion that contacts the peripheral surface of the eccentric cam at the specific rotational angle position at the contact portion, and one end portion of the peripheral surface of the tension member abuts against the inner peripheral surface of the endless belt. The image forming apparatus according to claim 5, wherein the image forming apparatus is in contact with and supported by the other end so as to be swingable, and is engaged with the transfer member moving mechanism via an elastic member.   The tension member is a roller whose circumferential surface is in contact with the inner circumferential surface of the endless belt, and a roller having a larger central diameter than the diameter of both end portions in the axial direction is a rotation shaft of the driving roller and the driven roller. The image forming apparatus according to claim 5, wherein the image forming apparatus is supported by a rotation axis parallel to the axis.   4. The image according to claim 3, wherein the tension member makes the moving path of the endless belt one of the first to third paths according to the content of the image forming operation in conjunction with the operation of the transfer member moving mechanism. Forming equipment.   The image forming apparatus according to claim 8, wherein the first path is a standby path for an image forming operation in which the endless belt is separated from all of the plurality of image carriers. The second path is a path during full-color image formation in which the endless belt is in contact with all of the image carrier,
9. The image forming apparatus according to claim 8, wherein the third path is a path for forming a monochrome image in which the endless belt is in contact with the image carrier for monochrome images and is separated from the image carrier for full color images. .   The image forming apparatus according to claim 8, wherein the tension member applies a predetermined tension to the endless belt in at least each of the second and third paths.

Images