Image forming apparatus

Abstract

To provide an image forming apparatus that can reduce deformation of and damage to a belt unit and a detection unit.SOLUTION: An image forming apparatus comprises: an apparatus body that has a main body frame; a belt unit that is movable between a first position and a second position; and a detection unit that is movably supported by the main body frame and detects a toner image transferred to a belt. The detection unit moves relative to the main body frame in conjunction with a movement operation of the belt unit moving from the first position to the second position so as not to inhibit the movement of the belt unit.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] Conventionally, an image forming apparatus has been proposed that includes a cartridge support member that can support multiple cartridges and can be pulled out from the main body of the apparatus, and an intermediate transfer belt unit that moves in conjunction with the opening and closing of a door (see Patent Document 1). When the door is opened, the intermediate transfer belt unit moves so that the intermediate transfer belt is separated from the drum of each cartridge supported by the cartridge support member.

[0003] Also, an image forming apparatus has been proposed that includes an intermediate transfer belt unit having an intermediate transfer belt capable of carrying toner patches and a tension roller that applies tension to the intermediate transfer belt, and a sensor unit that detects the toner patches (see Patent Document 2). The sensor unit is supported so as to be swingable on a sensor unit support shaft provided in the main body of the image forming apparatus. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-81194 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-106483 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, consider an intermediate transfer belt unit described in Patent Document 2 that is configured to be movable up and down so as to be able to approach and separate from the cartridge drum, like the intermediate transfer belt unit described in Patent Document 1. In this case, because the sensor unit swing shaft extends in a substantially horizontal direction, when the intermediate transfer belt unit moves up and down, a large load is applied to the sensor unit swing shaft, the sensor unit, and the intermediate transfer belt unit. This could result in deformation or damage to the sensor unit swing shaft, the sensor unit, and the intermediate transfer belt unit.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that can reduce deformation and damage to the belt unit and the detection unit. [Means for solving the problem]

[0007] The present invention provides an image forming apparatus comprising: an apparatus main body having a main body frame; an image carrier carrying a toner image; a rotatable endless belt; a primary transfer unit that transfers the toner image carried on the image carrier to the belt; and a tension member that tensions the belt; a belt unit that is movable between a first position where the belt and the image carrier are in contact with each other and a second position where the belt is separated from the image carrier; a secondary transfer unit that transfers the toner image carried on the belt to a sheet; and a detection unit that is movably supported on the main body frame and detects the toner image transferred to the belt, wherein the detection unit moves relative to the main body frame in conjunction with the movement of the belt unit from the first position to the second position so as not to hinder the movement of the belt unit. [Effects of the Invention]

[0008] According to the present invention, deformation and damage to the belt unit and the detection unit can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic view showing an entire printer according to a first embodiment. [Figure 2] FIG. 2 is a perspective view showing an intermediate transfer belt unit. [Figure 3] FIG. 2A is a cross-sectional view showing the front door and its surrounding structure, and FIG. 2B is a perspective view showing the front door and its surrounding structure. [Figure 4] 1A is a cross-sectional view showing the interlocking structure between the front door and the sliding member, and FIG. 1B is a perspective view showing the interlocking structure between the front door and the sliding member. [Figure 5] FIG. 4 is a perspective view showing a configuration for biasing the tension roller. [Figure 6] 4 is a diagram showing a positioning configuration of an intermediate transfer belt unit relative to the printer main body on the rear and left side of the printer. FIG. [Figure 7] FIG. 1A is a diagram showing the intermediate transfer belt unit positioned at a first position when the front door is closed, and FIG. 1B is a diagram showing the intermediate transfer belt unit positioned at a second position when the front door is open. [Figure 8] FIG. 2 is a diagram showing the state of the printer during image formation. [Figure 9] FIG. 1A shows the printer with the front door open, and FIG. 1B shows the cartridge support member pulled out. [Figure 10] FIG. [Figure 11] 1A is a perspective view showing a support structure for a beam portion of a sensor unit, and FIG. 1B is a front view showing the support structure for a beam portion of a sensor unit. [Figure 12] 1A is a cross-sectional view showing the posture of the sensor unit when the intermediate transfer belt unit is located at a first position, and FIG. 1B is a cross-sectional view showing the posture of the sensor unit when the intermediate transfer belt unit is located at a second position. [Figure 13] 10A is a perspective view showing an intermediate transfer belt unit according to a second embodiment, and FIG. 10B is a perspective view showing a state in which a tension unit is covered with a frame cover. [Figure 14] FIG. 4 is an exploded perspective view showing a tension unit and a belt deviation adjustment mechanism. [Figure 15] FIG. 4 is a cross-sectional view showing a tension unit and a belt deviation adjustment mechanism. [Figure 16] 1A is a cross-sectional view showing the posture of the sensor unit when the intermediate transfer belt unit is located at a first position, and FIG. 1B is a cross-sectional view showing the posture of the sensor unit when the intermediate transfer belt unit is located at a second position. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions. Therefore, unless otherwise specified, the scope of the present invention is not intended to be limited to these. Furthermore, in each drawing, peripheral components not necessary for the explanation are not shown as appropriate.

[0011] Here, an electrophotographic image forming apparatus (hereinafter referred to as an image forming apparatus) forms an image on a recording material using an electrophotographic image forming process. Examples of image forming apparatuses include electrophotographic copiers, electrophotographic printers, facsimile machines, and word processors. Image forming apparatuses include both monochrome and color devices.

[0012] The term "cartridge" refers to, for example, a process cartridge or a developing cartridge that is detachably mounted in the main body of an image forming apparatus. When attached to the main body of an image forming apparatus, this cartridge contributes to the image forming process of forming an image on a recording material. Here, the term "process cartridge" refers to a cartridge that integrates at least one of a charging means, a developing means, and a cleaning means, as process means, with a photosensitive drum, and is detachably mounted in the main body of an image forming apparatus.

[0013] Therefore, the term "process cartridge" also includes a cartridge in which the developing means as the process means and the photosensitive drum are integrated into a cartridge that can be removably mounted in the main body of an image forming apparatus. The term "process cartridge" also includes a cartridge in which the charging means, the developing means, or the cleaning means as the process means and the photosensitive drum are integrated into a cartridge that can be removably mounted in the main body of an image forming apparatus. A process cartridge that has the photosensitive drum and the developing means integrated into it is called an integrated type. A process cartridge that has the photosensitive drum and the process means other than the developing means integrated into it is called a separate type.

[0014] The process cartridge can be attached to and detached from the main body of the image forming apparatus by the user, which makes it easy to perform maintenance on the image forming apparatus. The process means acts on the photosensitive drum.

[0015] A developer cartridge is a device that has a developing roller, stores developer (toner) used to develop an electrostatic latent image formed on a photosensitive drum by the developing roller, and is removably attached to the main body of the device. In the case of a developer cartridge, the photosensitive drum is attached to the main body of the device or to a cartridge support member described below. Alternatively, the photosensitive drum is provided in a separate process cartridge (in this case, the process cartridge does not have a developing means). The developer cartridge can also be attached to and detached from the main body of the device by the user. This makes it easy to perform maintenance on the image forming device.

[0016] Therefore, the term "cartridge" includes integrated and separate process cartridges. The term "cartridge" also includes a case where a separate process cartridge and a developer cartridge are used as a pair. The term "cartridge" also includes a case where a photosensitive drum is fixedly attached to the main body of the apparatus or a cartridge support member (described later). The term "cartridge" also includes a case where a developer cartridge is removably attached to the cartridge support member so as to be operable with the photosensitive drum. The term "sheet" as a recording material refers to a material on which an image is formed by an image forming apparatus, and includes, for example, paper, overhead projector sheets, etc.

[0017] First Embodiment [Overall structure] First, a first embodiment of the present invention will be described. A printer 100 as an image forming apparatus according to the first embodiment is an electrophotographic laser beam printer. As shown in FIG. 1, the printer 100 has an intermediate transfer belt unit 10 as a belt unit, a cartridge support body 60 (see FIGS. 7(a) and 7(b)), four process cartridges PY, PM, PC, and PK, and a laser scanner 5. The printer 100 also has a feeding unit 30, a fixing unit 33, and a sensor unit 400 as a detection unit.

[0018] Furthermore, the printer 100 has an apparatus main body 100A including an exterior casing 101 and a main body frame 102, and a front door 50 that is supported so as to be openable and closable relative to the main body frame 102. Inside the printer 100, there are provided a cartridge support 60 and a cartridge housing section 103 that houses the process cartridges PY, PM, PC, and PK.

[0019] The four process cartridges PY, PM, PC, and PK are supported by a cartridge support 60 and form toner images of four colors: yellow (Y), magenta (M), cyan (C), and black (K). The four process cartridges PY, PM, PC, and PK have the same configuration except for the colors of the images they form. Therefore, only the configuration and image forming process of the process cartridge PY will be described, and descriptions of the process cartridges PM, PC, and PK will be omitted.

[0020] The process cartridge PY has a photosensitive drum 1 as an image carrier that carries a toner image, a charging roller 2, a developing roller 3, and a cleaning blade 4. The photosensitive drum 1 is constructed by coating the outer periphery of an aluminum cylinder with an organic photoconductive layer, and is rotated by a drive motor (not shown). In other words, each process cartridge is a so-called integrated process cartridge that has the photosensitive drum 1 and the charging roller 2, developing roller 3, and cleaning blade 4 as process means that act on the photosensitive drum 1.

[0021] As shown in FIGS. 1 and 2, the intermediate transfer belt unit 10 includes an intermediate transfer belt 11, a drive roller 12, a driven roller 13, a tension roller 14, a frame member 15, and primary transfer rollers 16Y, 16M, 16C, and 16K. The intermediate transfer belt 11 is a rotatable, endless belt that is stretched around the drive roller 12, the driven roller 13, and the tension roller 14 and rotated by the drive roller 12. The frame member 15 includes a center frame 15C and side plate frames 15L and 15R, which rotatably support the drive roller 12, the driven roller 13, and the tension roller 14. The primary transfer rollers 16Y, 16M, 16C, and 16K that serve as primary transfer sections are provided inside the intermediate transfer belt 11.

[0022] The sensor unit 400 is disposed at a position facing the tension roller 14, which serves as a tension member and a first tension member, across the intermediate transfer belt 11. The sensor unit 400 is capable of detecting information on the toner patch, which is a toner image transferred onto the intermediate transfer belt 11, and is capable of detecting, for example, the density of the toner patch. A control unit provided in the printer 100 controls the process cartridges PY, PM, PC, and PK and the laser scanner 5 according to the detection results of the sensor unit 400, thereby controlling the density of the toner image.

[0023] The fixing unit 33 has a fixing film 33a heated by a heater and a pressure roller 33b that is in pressure contact with the fixing film 33a. The feeding unit 30 is provided at the bottom of the printer 100 and stores the sheets S. The feeding unit 30 also has a pickup roller 31 that feeds the sheets S.

[0024] Next, we will explain the image forming operation of the printer 100 configured as above. When an image signal is input to the laser scanner 5 from a personal computer (not shown) or the like, the laser scanner 5 irradiates the photosensitive drum 1 of the process cartridge PY with a laser beam corresponding to the image signal.

[0025] At this time, the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2, and an electrostatic latent image is formed on the surface by irradiating it with laser light from the laser scanner 5. The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing roller 3, and a yellow (Y) toner image is formed on the photosensitive drum 1.

[0026] Similarly, the laser scanner 5 irradiates the photosensitive drums of the process cartridges PM, PC, and PK with laser light, forming magenta (M), cyan (C), and black (K) toner images on the respective photosensitive drums. The toner images of each color formed on each photosensitive drum are transferred to the intermediate transfer belt 11 by primary transfer rollers 16Y, 16M, 16C, and 16K, and are then transported to the secondary transfer roller 32 by the intermediate transfer belt 11, which is rotated by a drive roller 12. Any toner remaining on the photosensitive drum 1 after the toner image has been transferred to the intermediate transfer belt 11 is collected by a cleaning blade 4. The image formation process for each color is performed at a timing to overlap the upstream toner image that has been primarily transferred onto the intermediate transfer belt 11.

[0027] In parallel with this image forming process, the sheets S stored in the feeding unit 30 are sent out by a pickup roller 31, and then separated one by one by a separation roller pair 31a. Then, the full-color toner image on the intermediate transfer belt 11 is transferred onto the sheet S conveyed by the separation roller pair 31a and the conveying roller pair 31b by a secondary transfer bias applied to a secondary transfer roller 32 serving as a secondary transfer section. Any toner remaining on the intermediate transfer belt 11 is removed by a belt cleaning unit 35.

[0028] The sheet S onto which the toner image has been transferred is subjected to predetermined heat and pressure by the fixing film 33a and pressure roller 33b of the fixing unit 33, thereby melting and fixing (fixing) the toner. The sheet S that has passed through the fixing unit 33 is discharged onto the discharge tray 34 by a pair of discharge rollers 34a.

[0029] In the following description, the front side (front face) of the printer 100 is the side where the front door 50 is located. The rear side (rear face) is the opposite side. The front-to-rear direction is the direction from the rear side of the printer 100 to the front side (front direction) and the opposite direction (rear direction). The left and right are left and right when looking at the printer 100 from the front side. The left and right direction is the direction from right to left (left direction) and the opposite direction (right direction). Up and down are up and down in the direction of gravity. The up direction is the direction from bottom to top, and the down direction is the direction from top to bottom.

[0030] In the description of this embodiment, reference symbols with "L" or "R" at the end basically refer to left and right pairs of components provided on the left and right sides of the printer 100. Reference symbols with "L" at the end indicate the left-hand side of the pair of components, and reference symbols with "R" at the end indicate the right-hand side of the pair of components. In the following, with reference symbols with "L" or "R" at the end, only one of the components will be described, and the description of the other may be omitted.

[0031] [Front door peripheral configuration] Next, the front door 50 and its surrounding configuration will be described using Figures 3(a) to 4(b). More specifically, the configuration that operates in conjunction with opening and closing the front door 50 will be described. As shown in Figures 3(a) and 3(b), the main body frame 102 has a left side plate 102L, a right side plate 102R, a left guide member 102dL, a right guide member 102dR, and a beam portion 102c. The left side plate 102L is provided on the left side of the printer 100, and the right side plate 102R is provided on the right side of the printer 100. The left side plate 102L and the right side plate 102R extend vertically and in the front-to-rear direction.

[0032] The left guide member 102dL is fixed to the front side of the left side plate 102L, and the right guide member 102dR is fixed to the front side of the right side plate 102R. The left guide member 102dL and the right guide member 102dR extend vertically like pillars. The beam portion 102c extends in the left-right direction to connect the left guide member 102dL and the right guide member 102dR.

[0033] The configuration linked to the front door 50 described below is provided approximately symmetrically on the left and right sides of the printer 100, so only the left side of the printer 100 will be described, and the right side of the printer 100 will not be described.

[0034] A first link member 56 is supported on the left side plate 102L so as to be slidable in the front-rear direction, and elongated holes 56a and 56b extending vertically are formed in the first link member 56. Further, a elongated hole 102hL extending in the front-rear direction is formed in the left side plate 102L, and a slide member 51 is supported on the left side plate 102L so as to be slidable in the front-rear direction. The slide member 51 has a shaft 51b that engages with the elongated hole 102hL and a shaft 51a that is provided forward of the shaft 51b.

[0035] The first link member 56 and the slide member 51 are connected by a second link member 57. More specifically, the second link member 57 has a shaft portion 57a ​​that engages with the elongated hole 56b of the first link member 56 and a elongated hole 57c that engages with the shaft portion 51a of the slide member 51, and is supported on the left side plate 102L so as to be rotatable about the rotation shaft 57b.

[0036] A door guide 50a is fixed to the front door 50 serving as a door portion, and an elongated hole 50b is formed in the door guide 50a. The door guide 50a is provided integrally with the front door 50 and is rotatably supported on the left guide member 102dL by a hinge shaft 54. In other words, the front door 50 is supported on the main body frame 102 so as to be able to open and close around the hinge shaft 54.

[0037] The door guide 50a and the first link member 56 are connected by a connecting arm 55. More specifically, the connecting arm 55 has a shaft portion 55c that engages with the elongated hole 56a of the first link member 56 and a shaft portion 55a that engages with the elongated hole 50b of the door guide 50a, and is supported by the left guide member 102dL so as to be rotatable about the connecting arm shaft 55b.

[0038] As shown in FIGS. 3A to 4B, when the front door 50 is opened, the shaft 55a of the connecting arm 55 moves along the elongated hole 50b of the door guide 50a fixed to the front door 50. As a result, the connecting arm 55 rotates clockwise around the connecting arm shaft 55b, as shown in FIG. 4A. As the connecting arm 55 rotates, the shaft 55c of the connecting arm 55 moves upward along the elongated hole 56a of the first link member 56. At this time, the first link member 56 is pulled toward the front of the printer 100 by the shaft 55c and slides forward. The rotation angle of the connecting arm 55 is limited to the range within which the shaft 55c can move through the elongated hole 56a, thereby determining the opening and closing angle of the front door 50. In other words, when the shaft 55c hits the upper end of the elongated hole 56a, the front door 50 is stably held in the open state.

[0039] As the first link member 56 slides forward, the second link member 57 rotates clockwise around the rotation shaft 57b due to the engagement between the shaft 57a and the elongated hole 56b. When the second link member 57 rotates clockwise, the engagement between the shaft 57a and the elongated hole 57c causes the slide member 51 to slide toward the rear of the printer 100. The rotation angle of the second link member 57 is limited to the range in which the shaft 57a can move in the elongated hole 56b, thereby determining the range in which the slide member 51 can slide.

[0040] When the front door 50 is closed from the open position to the closed position, the connecting arm 55, the first link member 56, and the second link member 57 move in the opposite direction to the above-described operations, and the slide member 51 slides toward the front of the printer 100. Here, the position of the slide member 51 when the front door 50 is closed relative to the device main body 100A is referred to as a first slide position (see FIG. 3(a)), and the position of the slide member 51 when the front door 50 is open relative to the device main body 100A is referred to as a second slide position (see FIG. 4(a)). As the slide member 51 moves in the front-to-rear direction, the intermediate transfer belt 11 moves between a first position where an image can be formed and a second position where an image cannot be formed, as will be described later.

[0041] The first link member 56 (56L) on the left side of the printer 100 also serves as a mechanism that disconnects the electrical contacts of each process cartridge on the printer 100 side in conjunction with the opening of the front door 50. The first link member 56 (56R) on the right side of the printer 100 also serves as a mechanism that disconnects each process cartridge from the drive of the apparatus main body 100A in conjunction with the opening of the front door 50.

[0042] [Intermediate transfer belt unit] Next, the intermediate transfer belt unit 10 will be described in detail with reference to Figures 5 to 7(b). Note that since the intermediate transfer belt unit 10 is provided in a substantially symmetrical manner as shown in Figure 2, only the left side of the intermediate transfer belt unit 10 will be described, and a description of the right side of the intermediate transfer belt unit 10 will be omitted.

[0043] 5, a long hole 15aL is formed in the side plate frame 15L of the intermediate transfer belt unit 10, and a tension roller bearing 17L is supported in the long hole 15aL so as to be movable in the longitudinal direction A of the long hole 15aL. The long hole 15aL extends substantially in the front-rear direction when the intermediate transfer belt unit 10 is located at the first position (see FIG. 1).

[0044] As shown in FIGS. 2 and 5, the tension roller 14 includes a roller portion 14b that contacts the inner circumferential surface of the intermediate transfer belt 11, a left tension roller bearing 17L, and a right tension roller bearing 17R (see FIG. 10). The tension roller bearing 17L includes a shaft portion 14aL that rotatably supports the roller portion 14b. That is, the shaft portion 14aL of the tension roller bearing 17L is movable in a direction perpendicular to the axial direction of the shaft portion 14aL, and the roller portion 14b rotates around the shaft portion 14aL and is movable along the elongated hole 15aL. A tension spring 18 is compressed between the side plate frame 15L and the tension roller bearing 17L. The tension spring 18, which serves as a first biasing portion, biases the tension roller 14 toward the inner circumferential surface of the intermediate transfer belt 11. This applies tension to the intermediate transfer belt 11.

[0045] The shaft portion 14aL may be a solid shaft or a cylindrical shaft. In the present embodiment, the roller portion 14b has a shaft portion extending in the left-right direction that is rotatably supported by the cylindrical shaft portion 14aL, but the roller portion 14b may have a hole that is rotatably supported by the solid shaft portion 14aL.

[0046] FIG. 6 is a diagram showing a positioning configuration of the intermediate transfer belt unit 10 relative to the device main body 100A on the rear and left side of the printer 100. As shown in FIG. 6, the drive roller 12 is rotatably supported by the frame member 15 (side plate frame 15L) of the intermediate transfer belt unit 10 via a drive roller bearing 19L. The drive roller 12, which serves as a second tension member, is disposed upstream of the tension roller 14 in the pull-out direction DD, which will be described later. The drive roller bearing 19L is engaged in the vertical direction (up and down direction) with a groove 102a formed in the left side plate 102L. This positions the intermediate transfer belt unit 10 vertically relative to the device main body 100A.

[0047] Furthermore, the secondary transfer roller 32, which contacts the drive roller 12 via the intermediate transfer belt 11, is biased by a spring (not shown) in the direction of arrow C, which faces approximately backward. The secondary transfer roller 32 presses the drive roller 12 in the direction of arrow C via the intermediate transfer belt 11, and the drive roller bearing 19L abuts against the groove portion 102a. This positions the intermediate transfer belt unit 10 in the front-rear direction relative to the apparatus main body 100A.

[0048] In this state, the intermediate transfer belt unit 10 is provided rotatably between a first position (see FIG. 7(a)) and a second position (see FIG. 7(b)) around the rotation center 12a of the drive roller 12. As shown in FIGS. 7(a) and 7(b), a lever member 52 is provided on a slide member 51 that slides in conjunction with the opening and closing of the front door 50 (see FIG. 4(a)) as described above. The lever member 52 is supported so as to be movable in the vertical direction relative to the slide member 51 and is biased upward by a biasing spring 53. The lever member 52 is disposed below the intermediate transfer belt unit 10 and configured to be able to abut against a first lower surface 15a and a second lower surface 15c of a side plate frame 15L of the intermediate transfer belt unit 10. The second lower surface 15c is located above the first lower surface 15a.

[0049] As described above, the slide member 51 is located at the first slide position as shown in Fig. 7(a) when the front door 50 is closed, and is located at the second slide position as shown in Fig. 7(b) when the front door 50 is open. The slide member 51 is provided with a lever member 52 that can move up and down relative to the slide member 51. When the front door 50 is closed and the slide member 51 is located at the first slide position as shown in Fig. 7(a), the lever member 52 abuts against the first lower surface 15a and urges the intermediate transfer belt unit 10 upward by the urging force of the urging spring 53.

[0050] As a result, the upper surface 15b of the side plate frame 15L abuts against the lower surface 60a of the cartridge support body 60, and the intermediate transfer belt unit 10 is positioned at the first position. When the intermediate transfer belt unit 10 is positioned at the first position, the photosensitive drums 1 of the process cartridges PY, PM, PC, and PK abut against the intermediate transfer belt 11. This puts the printer 100 in a state where it can form images.

[0051] When the front door 50 is opened and the slide member 51 is located at the second slide position as shown in FIG. 7(b), the lever member 52 abuts against the second lower surface 15c. The biasing force of the biasing spring 53 is relatively weak, and when the lever member 52 abuts against the second lower surface 15c, the intermediate transfer belt unit 10 is located at the second position, which is lower than the first position, due to its own weight. More specifically, the intermediate transfer belt unit 10 rotates downward from the first position to the second position around the rotation center 12a of the drive roller 12 (see FIG. 6). Note that when the slide member 51 is located at the second slide position, the lever member 52 may be spaced apart from the second lower surface 15c.

[0052] When the intermediate transfer belt unit 10 is located at the second position, the photosensitive drums 1 of the process cartridges PY, PM, PC, and PK are spaced apart from the intermediate transfer belt 11. This puts the printer 100 in a state where it is unable to form images. Note that when the intermediate transfer belt unit 10 is located at the second position, it is sufficient that at least one of the photosensitive drums 1 of the process cartridges PY, PM, PC, and PK is spaced apart from the intermediate transfer belt 11. However, it is not necessary that all of the photosensitive drums 1 are spaced apart from the intermediate transfer belt 11.

[0053] The lifting mechanism of the intermediate transfer belt unit 10 does not necessarily have to be the slide member 51. For example, it may be an eccentric cam lifting mechanism or a link mechanism.

[0054] Furthermore, in this embodiment, the intermediate transfer belt unit 10 is configured to rotate around the center of rotation of the drive roller 12, but the entire intermediate transfer belt unit 10 may be configured to move linearly in the vertical direction. In this case, it is necessary to disengage the drive roller 12 from the input member that inputs the driving force to the drive roller 12.

[0055] [Removing the process cartridge] Next, a method for removing the process cartridges PY, PM, PC, and PK will be described with reference to Figures 8 to 9(b). As the process cartridges PY, PM, PC, and PK are used for image formation, the developer contained in each developing device is consumed. When the developer is consumed to the extent that the cartridge is no longer able to form images of a quality that satisfies the user who purchased the cartridge, the commercial value of the cartridge is lost.

[0056] Therefore, for example, the printer 100 is equipped with a means for detecting the amount of developer remaining in each of the process cartridges PY, PM, PC, and PK. When a process cartridge has a detected remaining amount lower than a preset threshold for a cartridge lifespan notification or warning, a lifespan notification or warning for that process cartridge is displayed on the display unit. This prompts the user to prepare a replacement process cartridge or to replace the process cartridge, thereby maintaining the quality of the output image.

[0057] 1 and 8, when the front door 50 is closed, the cartridge support body 60 that supports the process cartridges PY, PM, PC, and PK is attached to the apparatus main body 100A. At this time, a groove 60c formed in the rear part of the cartridge support body 60 is engaged with a positioning shaft 102e provided on the main body frame 102.

[0058] Furthermore, the positioning shaft 60b provided at the front of the cartridge support member 60 engages with a groove 102f provided in the main body frame 102. This determines the vertical and front-rear position of the cartridge support member 60. With the above configuration, the cartridge support member 60 does not shift position even when it receives the urging force of the urging spring 53 (see FIG. 7(a)) via the intermediate transfer belt unit 10.

[0059] 9(a), when the front door 50 is opened, the intermediate transfer belt unit 10 moves from the first position to the second position as described above, which creates a gap between the intermediate transfer belt 11 of the intermediate transfer belt unit 10 located at the second position and each photosensitive drum 1.

[0060] 9(b), the user pulls out the cartridge support member 60, which serves as a drawer, in a pull-out direction DD relative to the apparatus main body 100A. The pull-out direction DD is the direction from the rear side of the printer 100 to the front side. At this time, because there is a gap between the intermediate transfer belt 11 and each photosensitive drum 1, even if the cartridge support member 60 is pulled out, damage to the intermediate transfer belt 11 and each photosensitive drum 1 can be reduced. With the cartridge support member 60 pulled out from the apparatus main body 100A, the process cartridges PY, PM, PC, and PK can be removed upward from the cartridge support member 60.

[0061] [Sensor unit configuration] Next, the configuration of the sensor unit 400 will be described with reference to FIGS. 10 to 11(b). As shown in FIG. 10, the sensor unit 400 as a detection unit includes a holding portion 410, a pair of density detection sensors 40c as detection portions, a sensor cable 40d, and a sensor spring 41 as a second biasing portion. The holding portion 410 includes a holder 40 and a sensor unit support shaft 42 as a support portion, and the holder 40 holds the pair of density detection sensors 40c. The pair of density detection sensors 40c detect the density of a toner image, such as a toner patch, on the intermediate transfer belt 11 by irradiating light onto the intermediate transfer belt 11 and receiving the reflected light. The density detection sensors 40c and an electric board (not shown) are connected by a sensor cable 40d.

[0062] The holder 40 extends in the left-right direction and is formed in a generally U-shape. One end of the holder 40 is formed with a groove 40aL that can engage with the shaft 14aL of the tension roller bearing 17L, and the other end of the holder 40 is formed with a groove 40aR that can engage with the shaft 14aR of the tension roller bearing 17R. The grooves 40aL and 40aR are formed in a generally U-shape. The pair of concentration detection sensors 40c are fixed to the holder 40 so that the direction of light irradiation passes through the center of the arc of the grooves 40aL and 40aR when viewed in the left-right direction.

[0063] A sensor unit fulcrum hole 40b is formed in the center of the holder 40 in the left-right direction, and the sensor unit fulcrum hole 40b is engaged with the shaft portion 42a of the sensor unit support shaft 42. The shaft portion 42a is inserted into the sensor spring 41, which is made up of a coil spring, and the sensor spring 41 is compressed between the sensor unit support shaft 42 and the holder 40.

[0064] 11(a) and 11(b), the sensor unit support shaft 42 has a first engagement portion 42b, a second engagement portion 42c, and a third engagement portion 42d aligned in the vertical direction. The first engagement portion 42b, the second engagement portion 42c, and the third engagement portion 42d extend rearward from an abutment surface 42e that abuts against the holder 40. In addition, a first hole 102g, a second hole 102h, and a third hole 102i aligned in the vertical direction are formed in the beam portion 102c of the main body frame 102 (see FIG. 3(b)).

[0065] The first engagement portion 42b is formed in a hook shape and is inserted into the first hole 102g, fitting in the left-right direction relative to the first hole 102g. The second engagement portion 42c has a boss shape with a roughly T-shaped cross section and fits in the second hole 102h in the left-right direction and vertical direction. A tapered surface 42f is formed on the upper surface of the second engagement portion 42c, and the tapered surface 42f slopes downward toward the front of the printer 100. The third engagement portion 42d is inserted into the third hole 102i and has a claw shape that engages with the upper edge of the third hole 102i.

[0066] The first engagement portion 42b and the second engagement portion 42c engage with the first hole portion 102g and the second hole portion 102h, respectively, so that the sensor unit support shaft 42 is positioned vertically and left-right with respect to the beam portion 102c of the main body frame 102. The third engagement portion 42d is a claw portion for temporary support to prevent the sensor unit support shaft 42 from falling off the beam portion 102c when assembling the printer 100 or replacing the intermediate transfer belt unit 10. In other words, the third engagement portion 42d is configured to engage with the third hole portion 102i, so that the sensor unit support shaft 42 does not separate from the intermediate transfer belt unit 10 when the intermediate transfer belt unit 10 is not attached to the apparatus main body 100A.

[0067] In this way, because the sensor unit support shaft 42 is supported by the beam portion 102c of the main body frame 102, the sensor spring 41 urges the sensor unit support shaft 42 toward the beam portion 102c, and urges the holder 40 toward the rear of the printer 100. As a result, the abutment surface 42e of the sensor unit support shaft 42 is pressed against the beam portion 102c, and the sensor unit support shaft 42 is held in a position where the abutment surface 42e and the beam portion 102c are in surface contact with each other, as shown in FIG.

[0068] Furthermore, the holder 40 is biased by a sensor spring 41 so that the grooves 40aL and 40aR engage with the shafts 14aL and 14aR, respectively. As a result, when the intermediate transfer belt unit 10 is attached to the apparatus main body 100A, the grooves 40aL and 40aR of the holder 40 stably engage with the shafts 14aL and 14aR. This ensures a constant distance between the concentration detection sensor 40c held by the holder 40 and the intermediate transfer belt 11, allowing the concentration detection sensor 40c to stably detect the density of the toner patch on the intermediate transfer belt 11. As shown in FIG. 12(a), the concentration detection sensor 40c is disposed downstream of the intermediate transfer belt 11 in the pull-out direction DD.

[0069] 5, the tension roller 14 is biased forward by the tension spring 18. That is, the direction in which the sensor spring 41 biases the holder 40 and the direction in which the tension spring 18 biases the tension roller 14 are opposite to each other. The holder 40 is movable in the front-to-rear direction relative to the sensor unit support shaft 42 because the shaft portion 42a of the sensor unit support shaft 42, which extends in the front-to-rear direction, is inserted into the sensor unit fulcrum hole 40b of the holder 40.

[0070] Therefore, the holder 40 can follow the tension roller 14 as the intermediate transfer belt 11 shrinks (changes in circumference). The biasing force of the sensor spring 41 is set to be sufficiently smaller than the biasing force of the tension spring 18, so that the sensor spring 41 does not hinder the positional fluctuation of the tension roller 14 as the intermediate transfer belt 11 shrinks (changes in circumference).

[0071] [Sensor unit tracking operation] 12(a) and 12(b), the following describes the movement of the sensor unit 400 when the intermediate transfer belt unit 10 rotates between the first position and the second position. Note that the following mainly describes only the left side of the sensor unit 400, and the description of the right side is omitted.

[0072] As described above, when the front door 50 is closed relative to the apparatus main body 100A, the intermediate transfer belt unit 10 is located at the first position as shown in Fig. 12(a). The sensor unit 400 is held in a position where the abutment surface 42e and the beam portion 102c are in surface contact with each other by the biasing force of the sensor spring 41.

[0073] 11(a) and 11(b), when the first engagement portion 42b is inserted into the first hole 102g, there is a gap between the first engagement portion 42b and the upper edge of the first hole 102g. Also, there is a gap between the third engagement portion 42d and the lower edge of the third hole 102i. Furthermore, a tapered surface 42f is formed on the upper part of the second engagement portion 42c. Therefore, the sensor unit support shaft 42 is configured to be rotatable in the Q direction around a contact point 42g, which will be described later.

[0074] Next, when the front door 50 is opened relative to the apparatus main body 100A, as shown in FIG. 12(b), the intermediate transfer belt unit 10 rotates from the first position to the second position around the rotation center 12a (see FIG. 6).

[0075] At this time, a force G1 in the direction of gravity based on the weight of the intermediate transfer belt unit 10 acts on the grooves 40aL and 40aR of the holder 40 of the sensor unit 400. A force G2 in the direction of gravity based on the weight of the sensor unit 400 acts on the shaft 42a of the sensor unit support shaft 42 from the sensor unit fulcrum hole 40b. A first moment acts on the sensor unit 400 in the Q direction (counterclockwise in FIG. 12A) as a first direction centered on the contact point 42g at the lower end of the abutment surface 42e due to the forces G1 and G2. A second moment acts on the sensor unit 400 in the −Q direction (clockwise in FIG. 12A) as a second direction centered on the contact point 42g based on the biasing force G3 of the sensor spring 41. The −Q direction is the opposite direction to the Q direction.

[0076] The parameters in this embodiment are as follows: Distance L1 is the distance in the front-rear direction from contact point 42g to force G1; distance L2 is the distance in the front-rear direction from contact point 42g to force G2; and distance L3 is the distance in the vertical direction from contact point 42g to biasing force G3. G1=350gf G2=50gf G3=250gf L1=2.85cm L2=0.6cm L3=0.6cm First moment in Q direction = (G1 × L1) + (G2 × L2) = 1027.5 gf cm Second moment in the -Q direction = G3 × L3 = 150 gf cm

[0077] With the above parameter settings, the first moment in the Q direction is greater than the second moment in the -Q direction, so the sensor unit support shaft 42 rotates in the Q direction with the contact point 42g as the fulcrum. The holder 40 is movable in the axial direction of the shaft portion 42a relative to the sensor unit support shaft 42, and is biased by the sensor spring 41, so it moves following the intermediate transfer belt unit 10.

[0078] As described above, when the front door 50 is opened relative to the apparatus main body 100A, the intermediate transfer belt unit 10 rotates downward from the first position to the second position around the rotation center 12a (see FIG. 6) on the rear side of the printer 100. Then, the sensor unit 400 rotates in the Q direction around the contact point 42g while engaging with the shafts 14aL, 14aR of the tension roller bearings 17L, 17R of the intermediate transfer belt unit 10. That is, the sensor unit 400 moves relative to the main body frame 102 in conjunction with the movement of the intermediate transfer belt unit 10 from the first position to the second position so as not to obstruct the movement of the intermediate transfer belt unit 10.

[0079] At this time, the sensor unit support shaft 42 of the sensor unit 400 is provided so as to be rotatable about a contact point 42g relative to the beam portion 102c of the main body frame 102, and the holder 40 is provided so as to be movable in the axial direction of the shaft portion 42a relative to the sensor unit support shaft 42. Furthermore, the holder 40 is biased by a sensor spring 41 so as to maintain the state in which the grooves 40aL, 40aR are engaged with the shaft portions 14aL, 14aR.

[0080] Therefore, the sensor unit 400 follows the intermediate transfer belt unit 10 without the grooves 40aL, 40aR falling off the shafts 14aL, 14aR and without interfering with the movement of the intermediate transfer belt unit 10. Therefore, excessive load is not applied to the intermediate transfer belt unit 10 or the sensor unit 400, and deformation or damage to the intermediate transfer belt unit 10 and the sensor unit 400 can be reduced.

[0081] Furthermore, the sensor unit 400 rotates in the direction Q about the contact point 42g so as to move away from the cartridge support body 60 by following the intermediate transfer belt unit 10. Therefore, when the front door 50 is open relative to the apparatus main body 100A, the sensor unit 400 does not interfere with the movement of the cartridge support body 60 in the pull-out direction DD (see FIG. 9(b)). Furthermore, when replacing the process cartridges PY, PM, PC, PK or the intermediate transfer belt unit 10, there is no need to replace or remove the sensor unit 400, which reduces costs and improves maintainability.

[0082] <Second embodiment> Next, a second embodiment of the present invention will be described, which is configured by providing a belt deviation adjustment mechanism 200 near the tension roller of the first embodiment. Therefore, the same components as those in the first embodiment will be omitted from the illustrations or will be described by using the same reference numerals in the drawings.

[0083] [Tension unit] The intermediate transfer belt unit 70, which serves as a belt unit according to this embodiment, includes tension units 140L and 140R and a belt deviation adjustment mechanism 200. FIG. 13(a) is a perspective view showing the tension unit 140L that applies tension to the intermediate transfer belt 11. FIG. 13(a) is a view showing a state in which the frame cover 151L shown in FIG. 13(b) is removed. As shown in FIG. 13(a), the tension unit 140L includes a tension fulcrum member 144L, a tension stay 143L, a tension spring 145L, and a tension spring receiving member 146L. The tension fulcrum member 144L is supported by the frame member 150 so as to be rotatable about a fulcrum shaft 144a. The tension spring receiving member 146L is fixed to the tension stay 143L, and a tension spring 145L is compressed between the tension fulcrum member 144L and the tension spring receiving member 146L.

[0084] The tension stay 143L is rotatably engaged with the tension roller bearing 17L. Therefore, the roller portion 14b is urged toward the inner circumferential surface of the intermediate transfer belt 11 by the tension spring 145L via the tension spring receiving member 146L, the tension stay 143L, and the tension roller bearing 17L. Also, as shown in FIG. 12(b), a frame cover 151L is fixed to the frame member 150 with fasteners such as screws, and the frame cover 151L is disposed outside the tension unit 140L in the left-right direction.

[0085] 14, on the opposite side of the roller portion 14b from the tension unit 140L, there is disposed a tension unit 140R having a similar configuration to the tension unit 140L. That is, the tension unit 140R has a tension fulcrum member 144R, a tension stay 143R, a tension spring 145R, and a tension spring receiving member 146R. A frame cover 151R is disposed on the outer side in the left-right direction of the tension unit 140R.

[0086] [Belt offset adjustment mechanism] Next, the belt offset adjustment mechanism 200 will be described with reference to Figures 14 and 15. The belt offset adjustment mechanism 200 has adjustment members 210L and 210R arranged on both ends of the roller portion 14b, and an interlocking member 220. The adjustment members 210L and 210R, serving as the first and second adjustment members, are rotatably supported by the tension roller bearings 17L and 17R, respectively, and each have a cam surface 210a that is eccentric from the tension roller bearings 17L and 17R, which are the centers of rotation. The adjustment members 210L and 210R are configured to be able to come into contact with the intermediate transfer belt 11 that is offset in the left-right direction, and by coming into contact with the intermediate transfer belt 11, frictional force causes them to rotate in the same direction as the intermediate transfer belt 11.

[0087] The interlocking member 220 has a fulcrum shaft 220a rotatably supported by the frame member 150, and connects the adjustment members 210L and 210R. The fulcrum shaft 220a is disposed in the center between the adjustment members 210L and 210R in the left-right direction. In other words, when the interlocking member 220 rotates around the fulcrum shaft 220a, the adjustment members 210L and 210R rotate in opposite directions around the tension roller bearings 17L and 17R. In addition, the frame covers 151L and 151R are provided with sliding surfaces 151a that can slide against the cam surfaces 210a of the adjustment members 210L and 210R, respectively.

[0088] For example, if the intermediate transfer belt 11 is shifted to the right, the adjustment member 210R comes into contact with the end of the intermediate transfer belt 11 and rotates together with the intermediate transfer belt 11. Here, the contact pressure between the adjustment members 210L and 210R and the left-right ends of the intermediate transfer belt 11 is referred to as a shift force. Then, the cam surface 210a of the adjustment member 210R rotates while rubbing against the sliding surface 151a of the frame cover 151R. As a result, one end of the roller portion 14b on the side where the intermediate transfer belt 11 is shifted, i.e., the right end, descends. At the same time, the interlocking member 220 rotates around the fulcrum shaft 220a, causing the adjustment member 210L to rotate in the opposite direction to the adjustment member 210R. As a result, the other end of the roller portion 14b, i.e., the left end, ascends.

[0089] That is, tension unit 140R rotates upward about fulcrum shaft 144a, and tension unit 140L rotates downward about fulcrum shaft 144a, causing tension roller 14 to tilt with respect to drive roller 12. In other words, interlocking member 220, which functions as an interlocking portion, interlocks adjustment members 210L and 210R, thereby tilting tension roller 14 with respect to drive roller 12.

[0090] The intermediate transfer belt unit 70 of this embodiment attempts to move the intermediate transfer belt 11 in the opposite direction (e.g., leftward) from the initial deviation direction (e.g., rightward) by tilting the tension roller 14, thereby adjusting the deviation of the intermediate transfer belt 11 and reducing the deviation force. Once the rotational moments of the adjustment members 210L and 210R are balanced, the adjustment members 210L and 210R stop, and the deviation force of the intermediate transfer belt 11 is no longer generated. In other words, the belt deviation adjustment mechanism 200 adjusts the deviation of the intermediate transfer belt 11 by tilting the tension roller 14 with respect to the drive roller 12 when the intermediate transfer belt 11 deviates to one end in the width direction W perpendicular to the movement direction BD (see FIG. 13(b)). The width direction W is parallel to the left-right direction of the printer 100.

[0091] 15, in this embodiment, the top surface 151b of the frame cover 151R (151L) comes into contact with the bottom surface 60a of the cartridge support body 60 during image formation. This determines the position of the intermediate transfer belt unit 70 in the height direction, and the intermediate transfer belt unit 70 is positioned at, for example, the first position.

[0092] [Sensor unit tracking operation] 16(a) and 16(b), the following describes the movement of the sensor unit 400 when the intermediate transfer belt unit 70 rotates between the first position and the second position. Note that the following mainly describes only the left side of the sensor unit 400, and the description of the right side is omitted.

[0093] As mentioned above, the belt deviation adjustment mechanism 200 is characterized in that once the rotational moments of the adjustment members 210L and 210R are balanced, no deviation force is generated in the intermediate transfer belt 11. This condition requires that the cam surfaces 210a of the adjustment members 210L and 210R be in contact with the sliding surfaces 151a of the frame covers 151L and 151R, respectively. If the cam surfaces 210a separate from the sliding surfaces 151a, the angular phase of the adjustment members 210L and 210R may change, changing the alignment of the tension roller 14. This may again generate deviation force in the intermediate transfer belt 11, potentially adversely affecting image quality until deviation adjustment of the intermediate transfer belt 11 is complete.

[0094] Whether the cam surfaces 210a of the adjustment members 210L, 210R come into contact with the sliding surface 150a is determined by the moment around the fulcrum shaft 144a generated by the weights of the tension units 140L, 140R and the tension roller 14, and the tension of the intermediate transfer belt 11. In this embodiment, as shown in FIG. 15, the vector of the tension of the intermediate transfer belt 11 is arranged to face the fulcrum shaft 144a of the tension fulcrum shaft 144 so that the moment generated by the tension of the intermediate transfer belt 11 can be ignored. Therefore, the contact state between the cam surfaces 210a and the sliding surface 150a is maintained by the moment generated by the weights of the tension units 140L, 140R and the tension roller 14.

[0095] As described above, when the front door 50 is closed relative to the apparatus main body 100A, the intermediate transfer belt unit 70 is located at the first position as shown in Fig. 16(a). The sensor unit 400 is held in a position where the abutment surface 42e and the beam portion 102c are in surface contact with each other by the biasing force of the sensor spring 41.

[0096] When the front door 50 is opened relative to the apparatus main body 100A, the intermediate transfer belt unit 70 rotates from the first position to the second position around the rotation center 12a (see FIG. 6) as shown in FIG. 16(b).

[0097] At this time, a force G10 in the direction of gravity, which is based on the weight of the tension units 140L, 140R and the tension roller 14, acts on the grooves 40aL, 40aR of the holder 40 of the sensor unit 400. That is, the force G10 is a force in the direction of gravity, which is based on the weight of the intermediate transfer belt unit 70. Furthermore, a force G20 in the direction of gravity, which is based on the weight of the sensor unit 400, acts on the shaft portion 42a of the sensor unit support shaft 42 through the sensor unit fulcrum hole 40b. The forces G10 and G20 act on the sensor unit 400 in the Q direction (counterclockwise in FIG. 16A), which is a first direction centered on the contact point 42g at the lower end of the abutment surface 42e. Furthermore, a second moment in the −Q direction (clockwise in FIG. 16A), which is a second direction centered on the contact point 42g, acts on the sensor unit 400 based on the biasing force G30 of the sensor spring 41. The −Q direction is the direction opposite to the Q direction.

[0098] The parameters in this embodiment are as follows: Distance L1 is the distance in the front-rear direction from contact point 42g to force G10; distance L2 is the distance in the front-rear direction from contact point 42g to force G20; and distance L3 is the distance in the vertical direction from contact point 42g to biasing force G30. G10=80gf G20=50gf G30=250gf L1=2.85cm L2=0.6cm L3=0.6cm First moment in Q direction = (G10 × L1) + (G20 × L2) = 258 gf cm Second moment in the -Q direction = G30 × L3 = 150 gf cm

[0099] With the above parameter settings, the first moment in the Q direction is greater than the second moment in the -Q direction, so the sensor unit support shaft 42 rotates in the Q direction with the contact point 42g as the fulcrum. The holder 40 is movable in the axial direction of the shaft portion 42a relative to the sensor unit support shaft 42, and is biased by the sensor spring 41, so it moves following the intermediate transfer belt unit 70.

[0100] As described above, when the front door 50 is opened relative to the apparatus main body 100A, the intermediate transfer belt unit 70 rotates downward from the first position to the second position around the rotation center 12a (see FIG. 6) on the rear side of the printer 100. Then, the sensor unit 400 rotates in the Q direction around the contact point 42g while engaging with the shafts 14aL, 14aR of the tension roller bearings 17L, 17R of the intermediate transfer belt unit 70 equipped with the belt deviation adjustment mechanism 200. That is, the sensor unit 400 moves relative to the main body frame 102 in conjunction with the movement of the intermediate transfer belt unit 70 from the first position to the second position so as not to obstruct the movement of the intermediate transfer belt unit 70.

[0101] Therefore, the sensor unit 400 follows the intermediate transfer belt unit 70 without the grooves 40aL, 40aR falling off the shafts 14aL, 14aR and without interfering with the movement of the intermediate transfer belt unit 70. Therefore, excessive load is not applied to the intermediate transfer belt unit 70 or the sensor unit 400, and deformation or damage to the intermediate transfer belt unit 70 and the sensor unit 400 can be reduced.

[0102] Furthermore, the sensor unit 400 follows the intermediate transfer belt unit 70 while the cam surfaces 210a of the adjustment members 210L, 210R of the belt deviation adjustment mechanism 200 maintain contact with the sliding surfaces 151a of the frame covers 151L, 151R, respectively. This allows a toner image of stable image quality to be formed on the sheet.

[0103] [Other embodiments] In all of the above-described embodiments, the holder 40 of the sensor unit 400 is engaged with the shafts 14aL and 14aR of the tension roller bearings 17L and 17R, but this is not limiting. For example, the holder 40 may be engaged with another part of the intermediate transfer belt unit. Furthermore, the holder 40 may be engaged with a link member or the like that moves in conjunction with the movement of the intermediate transfer belt unit.

[0104] In addition, in all of the embodiments described above, the holder 40 is formed with grooves 40aL, 40aR that can engage with the shafts 14aL, 14aR of the tension roller bearings 17L, 17R, but this is not limiting. For example, grooves may be provided in the tension roller bearings 17L, 17R, and the holder 40 may be provided with shafts that engage with the grooves.

[0105] In addition, in any of the above-described embodiments, the intermediate transfer belt units 10, 70 are configured to move between the first position and the second position in conjunction with the opening and closing of the front door 50, but this is not limiting. For example, the intermediate transfer belt units 10, 70 may be manually moved by the user after the front door 50 is opened by the user.

[0106] In addition, in all of the above-described embodiments, the process cartridges PY, PM, PC, and PK are configured to be pulled out collectively in the pulling-out direction DD by the cartridge support body 60, but this is not limiting. For example, the process cartridges PY, PM, PC, and PK may be configured to be individually detachable from the apparatus main body 100A.

[0107] The disclosure of the present embodiment also includes the following configurations and methods. (Configuration 1) a device main body having a main body frame; an image carrier that carries a toner image; a belt unit including a rotatable endless belt, a primary transfer unit that transfers the toner image carried on the image carrier onto the belt, and a tension member that tensions the belt, the belt unit being movable between a first position where the belt and the image carrier contact each other and a second position where the belt is spaced apart from the image carrier; a secondary transfer unit that transfers the toner image carried on the belt onto a sheet; a detection unit that is movably supported on the main body frame and detects the toner image transferred onto the belt, the detection unit moves relative to the main body frame in conjunction with the movement of the belt unit from the first position to the second position so as not to hinder the movement of the belt unit. An image forming apparatus characterized by: (Configuration 2) The detection unit includes a detection portion that detects the toner image transferred to the belt, and a holding portion that holds the detection portion and engages with the tension member, and follows the movement of the tension member when the belt unit performs the moving operation. 2. The image forming apparatus according to claim 1, (Configuration 3) the holding portion has a support portion that is rotatably supported by the main body frame, the support portion has a contact point that comes into contact with the main body frame, the detection unit rotates around the contact point so as not to hinder the movement of the belt unit when the belt unit performs the moving operation; 3. The image forming apparatus according to configuration 2. (Configuration 4) the belt unit has a frame member; the tension member has a roller portion that contacts the inner peripheral surface of the belt, and a shaft portion that is supported by the frame member and rotatably supports the roller portion, the holding portion has a holder that is movably supported by the support portion and holds the detection portion, The holder has a groove that engages with the shaft. 4. The image forming apparatus according to configuration 3. (Configuration 5) The shaft portion is supported movably relative to the frame member in a direction perpendicular to the axial direction of the shaft portion. 5. The image forming apparatus according to configuration 4. (Configuration 6) the belt unit has a first biasing portion that biases the tension member toward the inner circumferential surface of the belt, the detection unit has a second biasing portion that biases the holder so that the groove portion engages with the shaft portion; The biasing force of the second biasing portion is smaller than the biasing force of the first biasing portion. 6. The image forming apparatus according to configuration 5. (Configuration 7) a moment in a first direction about the contact point, which is based on the weights of the belt unit and the detection unit, is greater than a moment in a second direction, which is opposite to the first direction and is based on the biasing force of the second biasing portion, about the contact point; 7. The image forming apparatus according to configuration 6, (Configuration 8) a door portion supported on the device body so as to be openable and closable; the belt unit performs the moving operation in conjunction with the door being opened relative to the apparatus body. 7. The image forming apparatus according to any one of configurations 2 to 6. (Configuration 9) a cartridge including the image carrier; a drawer section that supports the cartridge and is capable of being drawn out in a drawing direction relative to the main body of the apparatus, the detection portion of the detection unit is disposed downstream of the belt in the pull-out direction. 9. The image forming apparatus according to any one of configurations 2 to 8. (Configuration 10) the tension member is a first tension member, the belt unit has a second tension member disposed upstream of the first tension member in the pull-out direction, tensioning the belt together with the first tension member, and is rotatable between the first position and the second position around a rotation center of the second tension member; 10. The image forming apparatus according to configuration 9, (Configuration 11) a belt deviation adjustment mechanism that adjusts the deviation of the belt by tilting the first tension member relative to the second tension member when the belt deviates toward one end in a width direction perpendicular to the moving direction of the belt; 11. The image forming apparatus according to claim 10, (Configuration 12) The belt deviation adjustment mechanism includes a first adjustment member that moves when it receives a force from one end of the belt in the width direction, a second adjustment member that moves when it receives a force from one end of the belt in the width direction, and an interlocking part that connects the first adjustment member and the second adjustment member and interlocks the first adjustment member and the second adjustment member, thereby tilting the first tension member relative to the second tension member. 12. The image forming apparatus according to claim 11, [Explanation of symbols]

[0108] 1: image carrier (photosensitive drum) / 10: belt unit (intermediate transfer belt unit) / 11: belt (intermediate transfer belt) / 12: second tension member (drive roller) / 12a: rotation center / 14: tension member, first tension member (tension roller) / 14aL: shaft portion / 14b: roller portion / 15: frame member / 16Y, 16M, 16C, 16K: primary transfer portion (primary transfer roller) / 18: first urging portion (tension spring) / 32: secondary transfer portion (secondary transfer roller) / 40: holding portion (holder) / 40aL: groove portion / 40c: detection portion (density detection sensor) / 41: second urging portion (sensor spring) / 42 : Support part (sensor unit support shaft) / 42g: Contact point / 50: Door part (front door) / 60: Drawer part (cartridge support) / 100: Image forming apparatus (printer) / 100A: Apparatus main body / 102: Main body frame / 200: Belt deviation adjustment mechanism / 210L: First adjustment member (adjustment member) / 210R: Second adjustment member (adjustment member) / 220: Interlocking part (interlocking member) / 400: Detection unit (sensor unit) / 410: Holding part / BD: Movement direction / DD: Drawer direction / PY, PM, PC, PK: Cartridge (process cartridge) / Q: First direction / -Q: Second direction / WD: Width direction

Claims

1. an apparatus main body having a main body frame; an image carrier that carries a toner image; a belt unit including an endless belt that is rotatable and onto which the toner image carried on the image carrier is primarily transferred, and a tension member that tensions the belt, the belt unit being rotatable about a first rotation shaft between a first position where the belt contacts the image carrier and a second position where the belt is spaced apart from the image carrier; a transfer section that transfers the toner image carried on the belt onto a sheet; a detection unit that is movably supported on the main body frame and detects the toner image transferred onto the belt, the detection unit engages with the belt unit and rotates about a second rotation axis different from the first rotation axis with respect to the main body frame so as to follow a rotational movement of the belt unit from the first position to the second position; 1. An image forming apparatus comprising:

2. the detection unit includes a detection portion that detects the toner image transferred to the belt, and a holding portion that holds the detection portion and engages with the tension member and follows the movement of the tension member when the belt unit performs the rotational operation.

2. The image forming apparatus according to claim 1,

3. the holding portion has a support portion that is rotatably supported by the main body frame, The support portion has a contact point that comes into contact with the main body frame, the detection unit rotates around the contact point as the second rotation shaft so as not to hinder the rotation of the belt unit when the belt unit performs the rotational operation.

3. The image forming apparatus according to claim 2,

4. The belt unit has a frame member, the tension member has a roller portion that contacts an inner peripheral surface of the belt, and a shaft portion that is supported by the frame member and rotatably supports the roller portion, the holding portion has a holder that is movably supported by the support portion and holds the detection portion, The holder has a groove that engages with the shaft portion.

4. The image forming apparatus according to claim 3.

5. The shaft portion is supported movably relative to the frame member in a direction perpendicular to the axial direction of the shaft portion.

5. The image forming apparatus according to claim 4.

6. the belt unit has a first biasing portion that biases the tension member toward the inner circumferential surface of the belt, the detection unit has a second biasing portion that biases the holder so that the groove engages with the shaft portion, The biasing force of the second biasing portion is smaller than the biasing force of the first biasing portion.

6. The image forming apparatus according to claim 5,

7. a moment in a first direction about the contact point, which is based on the weights of the belt unit and the detection unit, is larger than a moment in a second direction, which is opposite to the first direction and is based on the biasing force of the second biasing portion, about the contact point; 7. The image forming apparatus according to claim 6,

8. a door portion supported so as to be openable and closable relative to the device body; a linking portion that causes the belt unit to perform the rotational movement in association with the door portion being opened relative to the device body, 8. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

9. The second rotation axis extends along the first rotation axis.

8. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

10. The retaining portion has a first engaging portion that engages with one end of the tension member and a second engaging portion that engages with the other end of the tension member, the detection unit is supported by the main body frame such that the first engagement portion and the second engagement portion follow the movement of the tension member when the belt unit performs the rotational movement.

8. The image forming apparatus according to claim 2, wherein the first and second electrodes are arranged in a first direction.

11. a cartridge including the image carrier; a drawer section that supports the cartridge and is capable of being drawn out in a drawing direction relative to the main body of the apparatus, The detection portion of the detection unit is disposed downstream of the belt in the pull-out direction.

8. The image forming apparatus according to claim 2, wherein the first and second electrodes are arranged in a first direction.

12. the tension member is a first tension member, the belt unit has a second tension member disposed upstream of the first tension member in the pull-out direction, tensioning the belt together with the first tension member, and is rotatable between the first position and the second position around a rotation center serving as the first rotation axis of the second tension member; 12. The image forming apparatus according to claim 11.

13. a belt deviation adjustment mechanism that adjusts the deviation of the belt by tilting the first tension member relative to the second tension member when the belt deviates to one end side in a width direction perpendicular to the moving direction of the belt; 13. The image forming apparatus according to claim 12.

14. The belt deviation adjustment mechanism includes a first adjustment member that moves when it receives a force from one end of the belt in the width direction, a second adjustment member that moves when it receives a force from the other end of the belt in the width direction, and an interlocking member that connects the first adjustment member and the second adjustment member and interlocks the first adjustment member and the second adjustment member in opposite directions.

14. The image forming apparatus according to claim 13.

15. An apparatus body having a body frame; an image carrier that carries a toner image; a belt unit including: an endless belt that is rotatable and onto which the toner image carried on the image carrier is primarily transferred; a first tension member and a second tension member that tension the belt; and a belt deviation adjustment mechanism that adjusts deviation of the belt by tilting the first tension member with respect to the second tension member, the belt unit being movable between a first position where the belt and the image carrier are in contact with each other and a second position where the belt is separated from the image carrier; a transfer section that transfers the toner image carried on the belt onto a sheet; a detection unit that is movably supported on the main body frame and detects the toner image transferred onto the belt, the detection unit engages with the first tension member when the belt unit is located at the first position, and moves with respect to the main body frame so as to follow the movement of the belt unit from the first position to the second position.

1. An image forming apparatus comprising:

16. The belt offset adjustment mechanism has a first adjustment member that moves by receiving force from one end of the belt in a width direction perpendicular to the moving direction of the belt, a second adjustment member that moves by receiving force from the other end of the belt in the width direction, and an interlocking member that connects the first adjustment member and the second adjustment member and interlocks the first adjustment member and the second adjustment member in opposite directions to each other.

16. The image forming apparatus according to claim 15.

17. When the belt moves toward one end in the width direction, the first adjustment member rises by receiving a force from the one end of the belt, and the second adjustment member descends by receiving a force from the other end of the belt.

17. The image forming apparatus according to claim 16.

18. The detection unit has a detection portion that detects the toner image transferred to the belt, and a holding portion that holds the detection portion and engages with the first tension member, and follows the movement of the first tension member when the belt unit performs the moving operation.

16. The image forming apparatus according to claim 15.

19. A cartridge including the image carrier; a drawer section that supports the cartridge and is capable of being drawn out in a drawing direction relative to the main body of the apparatus, The detection portion of the detection unit is disposed downstream of the belt in the pull-out direction.

20. The image forming apparatus according to claim 18,

20. The second tension member is disposed upstream of the first tension member in the pull-out direction.

20. The image forming apparatus according to claim 19,

21. The retaining portion has a first engaging portion that engages with one end of the first tension member and a second engaging portion that engages with the other end of the first tension member, the detection unit is supported by the main body frame such that the first engagement portion and the second engagement portion follow the movement of the first tension member when the belt unit performs the moving operation.

20. The image forming apparatus according to claim 18,

22. The belt unit is rotatable between the first position and the second position around a rotation center of the second tension member, the detection unit rotates about a contact point with the main body frame in association with the moving operation of the belt unit; 22. The image forming apparatus according to claim 15,

23. A door portion supported so as to be openable and closable relative to the device body; and a linking unit that causes the belt unit to perform the moving operation in linkage with the door unit being opened relative to the device body.

22. The image forming apparatus according to claim 15,

24. The belt unit is rotatable between the first position and the second position about a first rotation axis; The detection unit is rotatable with respect to the main body frame about a second rotation axis that is different from the first rotation axis and extends along the first rotation axis.

22. The image forming apparatus according to claim 15,

Images