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 Art

[0002] Conventionally, an image forming apparatus has been proposed that includes a cartridge support member capable of supporting a plurality of cartridges and being pulled out from the apparatus main body, 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 separates from the drums of the respective cartridges 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 a toner patch and a tension roller that applies tension to the intermediate transfer belt, and a sensor unit that detects the toner patch (see Patent Document 2). The sensor unit is swingably supported with respect to a sensor unit support shaft provided on the apparatus main body of the image forming apparatus.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems 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 able to move up and down so as to be able to move toward and away from the cartridge drum, similar to the intermediate transfer belt unit described in Patent Document 1. In this case, since the sensor unit pivot shaft extends in a substantially horizontal direction, when the intermediate transfer belt unit moves up and down, a large load is placed on the sensor unit pivot shaft, the sensor unit, and the intermediate transfer belt unit. This may cause deformation or damage to the sensor unit pivot shaft, the sensor unit, and the intermediate transfer belt unit.

[0006] Therefore, the present invention aims to provide an image forming apparatus capable of reducing deformation and damage to belt units and detection units. [Means for solving the problem]

[0007] The present invention relates to an image forming apparatus comprising an apparatus body having a main frame, an image carrier for carrying a toner image, and a rotatable At the same time, the toner image supported on the image carrier is transferred in a primary transfer. Endless belt and ,before The device comprises a tensioning member for tensioning the belt, and has a first position where the belt and the image carrier are in contact, and a second position where the belt is separated from the image carrier. , rotates around the first drive axis A belt unit capable of transferring the toner image carried on the belt to a sheet. ru ten The device comprises a printing section and a detection unit that is movably supported on the main frame and detects the toner image transferred to the belt, wherein the detection unit is Engaged with the aforementioned belt unit, The belt unit moves from the first position to the second position. Rotation do Rotation In operation Following suit, With respect to the main frame Rotates around a second pivot axis, which is different from the first pivot axis. It is characterized by doing so. Furthermore, the present invention relates to an image forming apparatus, comprising: an apparatus body having a main frame; an image carrier for carrying a toner image; an endless belt that is rotatable and onto which the toner image carried on the image carrier is first transferred; a first tensioning member and a second tensioning member for tensioning the belt; a belt tension adjustment mechanism for adjusting the belt's hull by tilting the first tensioning member relative to the second tensioning member; a belt unit that is movable between a first position where the belt and the image carrier are in contact and a second position where the belt is separated from the image carrier; a transfer unit for transferring the toner image carried on the belt to a sheet; and a detection unit that is movably supported by the main frame and detects the toner image transferred to the belt, wherein the detection unit engages with the first tensioning member when the belt unit is in the first position and moves relative to the main frame to follow the movement of the belt unit from the first position to the second position. [Effects of the Invention]

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

[0009] [Figure 1] A schematic diagram showing the printer according to the first embodiment. [Figure 2] A perspective view showing the intermediate transfer belt unit. [Figure 3] (a) is a cross-sectional view showing the front door and its surrounding components, and (b) is a perspective view showing the front door and its surrounding components. [Figure 4] (a) is a cross-sectional view showing the interlocking configuration of the front door and the sliding member, and (b) is a perspective view showing the interlocking configuration of the front door and the sliding member. [Figure 5] A perspective view showing the configuration for biasing the tension roller. [Figure 6] A diagram showing the positioning configuration of the intermediate transfer belt unit relative to the main body of the printer, located on the rear and left side. [Figure 7] (a) is a diagram showing the intermediate transfer belt unit in the first position with the front door closed, and (b) is a diagram showing the intermediate transfer belt unit in the second position with the front door open. [Figure 8] A diagram showing the printer's operation during image formation. [Figure 9] (a) is a diagram showing the printer with the front door open, and (b) is a diagram showing the cartridge support pulled out. [Figure 10] A perspective view showing the sensor unit. [Figure 11] (a) is a perspective view showing the support configuration of the sensor unit to the beam, and (b) is a front view showing the support configuration of the sensor unit to the beam. [Figure 12] (a) is a cross-sectional view showing the orientation of the sensor unit when the intermediate transfer belt unit is in the first position, and (b) is a cross-sectional view showing the orientation of the sensor unit when the intermediate transfer belt unit is in the second position. [Figure 13] (a) is a perspective view showing an intermediate transfer belt unit according to the second embodiment, and (b) is a perspective view showing the tension unit covered with a frame cover. [Figure 14] An exploded perspective view showing the tension unit and belt-side adjustment mechanism. [Figure 15] Cross-sectional view showing a tension unit and a belt proximity adjustment mechanism. [Figure 16] (a) is a cross-sectional view showing the posture of the sensor unit when the intermediate transfer belt unit is in the first position, and (b) is a cross-sectional view showing the posture of the sensor unit when the intermediate transfer belt unit is in the second position.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated, the scope of the present invention is not intended to be limited only to those. Also, in each drawing, peripheral components that are unnecessary for the description 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 the image forming apparatus include an electrophotographic copying machine, an electrophotographic printer, a facsimile apparatus, and a word processor. Also, the image forming apparatus includes both monochrome and color.

[0012] Also, a cartridge is, for example, a process cartridge or a developing cartridge, which is detachable from the apparatus main body of the image forming apparatus. And this cartridge contributes to the image forming process of forming an image on the recording material in a state of being mounted on the apparatus main body of the image forming apparatus. Here, a process cartridge is one in which at least one of charging means, developing means, and cleaning means as process means and a photosensitive drum are integrally formed into a cartridge and detachably mounted on the apparatus main body of the image forming apparatus.

[0013] Therefore, a process cartridge also includes one in which a developing means and a photosensitive drum are integrated into a single cartridge and detachably mounted on the main body of an image forming apparatus. Furthermore, a process cartridge also includes one in which a charging means, developing means, or cleaning means as process means, and a photosensitive drum are integrated into a single cartridge and detachably mounted on the main body of the apparatus. A process cartridge that has the photosensitive drum and developing means integrated together is called a so-called integrated type. A process cartridge that has the photosensitive drum and process means other than the developing means integrated together is called a so-called separate type.

[0014] Here, the process cartridge can be attached to and detached from the main body of the image forming apparatus by the user. Therefore, maintenance of the image forming apparatus can be easily performed. The process means acts on the photosensitive drum.

[0015] Furthermore, a developing cartridge has a developing roller and contains a developer (toner) used to develop the electrostatic latent image formed on the photoreceptor drum by the developing roller. It is removablely attached to the main body of the device. In the case of a developing cartridge, the photoreceptor drum is attached to the main body of the device or to a cartridge support member described later. Alternatively, the photoreceptor drum is provided in a separate process cartridge (in this case, the process cartridge does not have a developing mechanism). The developing cartridge can also be attached to and detached from the main body of the device by the user. Therefore, maintenance of the image forming apparatus can be easily performed.

[0016] Therefore, the cartridge includes integrated or separate process cartridges. Furthermore, the cartridge also includes cases where a separate process cartridge and a developer cartridge are used as a pair. In the cartridge, the photoreceptor drum is fixedly mounted to the main body of the device or to a cartridge support member described later. Furthermore, the developer cartridge is detachably mounted to the cartridge support member so as to be able to act on the photoreceptor drum. The recording material, a sheet, is one on which an image is formed by the image forming apparatus, and includes, for example, paper, an OHP sheet, etc.

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

[0018] Furthermore, the printer 100 includes a main body 100A, which includes an outer casing 101 and a main frame 102, and a front door 50 that is supported by the main frame 102 so as to be openable and closable. Inside the printer 100, there is a cartridge housing section 103 that houses a cartridge support 60 and 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), respectively. 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 formation process of process cartridge PY will be explained, and the descriptions of process cartridges PM, PC, and PK will be omitted.

[0020] The process cartridge PY comprises a photosensitive drum 1 as an image carrier for holding 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 circumference 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 having a photosensitive drum 1 and process means acting on the photosensitive drum 1, namely the charging roller 2, the developing roller 3, and the cleaning blade 4.

[0021] As shown in Figures 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, as a belt, is a rotatable, endless belt, stretched by the drive roller 12, the driven roller 13, and the tension roller 14, and rotated by the drive roller 12. The frame member 15 has a central frame 15C and side plate frames 15L and 15R, and the side plate frames 15L and 15R rotatably support the drive roller 12, the driven roller 13, and the tension roller 14. The primary transfer rollers 16Y, 16M, 16C, and 16K, as primary transfer sections, are provided inside the intermediate transfer belt 11.

[0022] The sensor unit 400 is positioned opposite the tensioning member and the tension roller 14, which is the first tensioning member, via the intermediate transfer belt 11. The sensor unit 400 is capable of detecting information about the toner patch, which is a toner image transferred to the intermediate transfer belt 11, and can, for example, detect the density of the toner patch. The control unit provided in the printer 100 can control the density of the toner image by controlling each process cartridge PY, PM, PC, PK and the laser scanner 5 according to the detection result of the sensor unit 400.

[0023] The fixing unit 33 includes a fixing film 33a that is heated by a heater, and a pressure roller 33b that presses against the fixing film 33a. The feeding unit 30 is located at the bottom of the printer 100 and houses the sheet S. The feeding unit 30 also has a pickup roller 31 for feeding the sheet S.

[0024] Next, the image formation operation of the printer 100 configured in this way will be described. When an image signal is input to the laser scanner 5 from a personal computer (not shown), the laser scanner 5 emits laser light corresponding to the image signal onto the photosensitive drum 1 of the process cartridge PY.

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

[0027] In parallel with this image formation process, the sheets S contained in the feeding unit 30 are fed out by the pickup roller 31 and then separated one by one by the separation roller pair 31a. The full-color toner image on the intermediate transfer belt 11 is then transferred to the sheets S, which have been transported by the separation roller pair 31a and the transport roller pair 31b, by a secondary transfer bias applied to the secondary transfer roller 32, which acts as a secondary transfer unit. Any toner remaining on the intermediate transfer belt 11 is removed by the 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, causing the toner to melt and solidify (fix) to the sheet. The sheet S that has passed through the fixing unit 33 is discharged into the discharge tray 34 by the discharge roller pair 34a.

[0029] In the following explanation, with respect to printer 100, the front side is the side on which the front door 50 is located. The rear side is the opposite side. The front-to-back direction is the direction from the rear of printer 100 to the front (forward direction) and the opposite direction (rear direction). Left and right are left or right when viewing printer 100 from the front. The left-to-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 upward direction is the direction from bottom to top, and the downward direction is the direction from top to bottom.

[0030] Furthermore, in the description of this embodiment, reference numerals ending in "L" or "R" basically refer to components that are provided in pairs on the left and right sides of the printer 100. Reference numerals ending in "L" indicate the left component of a pair, while reference numerals ending in "R" indicate the right component of a pair. In the following, regarding such reference numerals ending in "L" or "R", only one of them may be described, and the description of the other may be omitted.

[0031] [Front door surrounding 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 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. These left side plate 102L and right side plate 102R extend in the vertical and front-rear directions.

[0032] The left guide member 102dL is fixed to the front side of the left plate 102L, and the right guide member 102dR is fixed to the front side of the right plate 102R. These left guide members 102dL and right guide members 102dR extend vertically in a columnar shape. The beam section 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, which will be described below, is provided approximately symmetrically on the left and right sides of the printer 100. Therefore, only the left side of the printer 100 will be described, and the right side will be omitted.

[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 the first link member 56 has elongated holes 56a and 56b that extend vertically, respectively. In addition, an elongated hole 102hL that extends in the front-rear direction is formed on the left side plate 102L, and a slide member 51 is supported so as to be slidable in the front-rear direction. The slide member 51 has a shaft portion 51b that engages with the elongated hole 102hL, and a shaft portion 51a that is provided in front of the shaft portion 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 an elongated hole 57c that engages with the shaft portion 51a of the slide member 51, and is rotatably supported on the left side plate 102L about a pivot axis 57b.

[0036] A door guide 50a is fixed to the front door 50, which serves as the door section, 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 frame 102 so that it can be opened and closed 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 rotatably supported on the left guide member 102dL about the connecting arm shaft 55b.

[0038] As shown in Figures 3(a) to 4(b), when the front door 50 is opened, the shaft portion 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 Figure 4(a). As the connecting arm 55 rotates, the shaft portion 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 to the front of the printer 100 by the shaft portion 55c and slides forward. The rotation angle of the connecting arm 55 is limited to the range in which the shaft portion 55c can move along the elongated hole 56a, and this determines the opening and closing angle of the front door 50. That is, when the shaft portion 55c abuts against the upper end of the elongated hole 56a, the front door 50 is stably held in the open position.

[0039] As the first link member 56 slides forward, the engagement between the shaft portion 57a ​​and the elongated hole 56b causes the second link member 57 to rotate clockwise around the pivot axis 57b. When the second link member 57 rotates clockwise, the engagement between the shaft portion 51a and the elongated hole 57c causes the slide member 51 to slide to the rear side of the printer 100. The rotation angle of the second link member 57 is limited to the range in which the shaft portion 57a ​​can move within 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 operation, and the slide member 51 slides to 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 body 100A is called the first slide position (see Figure 3(a)), and the position of the slide member 51 when the front door 50 is open relative to the device body 100A is called the second slide position (see Figure 4(a)). As the slide member 51 moves in the front-rear direction, the intermediate transfer belt 11 moves between a first position where image formation is possible and a second position where image formation is not possible, as will be described later.

[0041] Furthermore, the first link member 56 (56L) on the left side of the printer 100 also serves as a mechanism that releases the electrical contacts of each process cartridge from the printer 100 side in conjunction with the opening operation of the front door 50. In addition, the first link member 56 (56R) on the right side of the printer 100 also serves as a mechanism that releases the connection between each process cartridge and the drive on the device body 100A side in conjunction with the opening operation of the front door 50.

[0042] [Intermediate Transfer Belt Unit] Next, the intermediate transfer belt unit 10 will be described in detail using Figures 5 to 7(b). Since the intermediate transfer belt unit 10 is arranged approximately symmetrically as shown in Figure 2, only the left side of the intermediate transfer belt unit 10 will be described, and the right side will be omitted.

[0043] As shown in Figure 5, an elongated 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 elongated hole 15aL so as to be movable in the longitudinal direction A of the elongated hole 15aL. The elongated hole 15aL extends in approximately the front-rear direction when the intermediate transfer belt unit 10 is in the first position (see Figure 1).

[0044] As shown in Figures 2 and 5, the tension roller 14 has 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 Figure 10). The tension roller bearing 17L has 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 is provided to rotate around the shaft portion 14aL and move along the elongated hole 15aL. A tension spring 18 is compressed between the side plate frame 15L and the tension roller bearing 17L, and the tension spring 18, as the first biasing part, biases the tension roller 14 toward the inner circumferential surface of the intermediate transfer belt 11. As a result, tension is applied to the intermediate transfer belt 11.

[0045] The shaft portion 14aL may be a solid shaft or a cylindrical shaft. In this 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 it may also have a hole portion that is rotatably supported by the solid shaft portion 14aL.

[0046] Figure 6 shows the positioning configuration of the intermediate transfer belt unit 10 relative to the main body 100A of the printer 100, located on the rear and left side. As shown in Figure 6, the drive roller 12 is rotatably supported on 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, acting as a second tensioning member, is positioned upstream of the tension roller 14 in the withdrawal direction DD, which will be described later. The drive roller bearing 19L engages vertically (up and down) with a groove 102a formed in the left side plate 102L. As a result, the intermediate transfer belt unit 10 is positioned vertically relative to the main body 100A.

[0047] Furthermore, the secondary transfer roller 32, which contacts the drive roller 12 via the intermediate transfer belt 11, is biased in the direction of arrow C, which is approximately in the rearward direction, by a spring (not shown). 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 102a. As a result, the intermediate transfer belt unit 10 is positioned in the front-rear direction relative to the main body 100A of the device.

[0048] In this state, the intermediate transfer belt unit 10 is rotatably mounted between a first position (see Figure 7(a)) and a second position (see Figure 7(b)) with respect to the rotation center 12a of the drive roller 12. As shown in Figures 7(a) and 7(b), a lever member 52 is provided on the slide member 51, which slides in conjunction with the opening and closing of the front door 50 (see Figure 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 positioned below the intermediate transfer belt unit 10 and is configured to contact the first lower surface 15a and the second lower surface 15c of the 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 sliding member 51 is located in a first sliding position as shown in Figure 7(a) when the front door 50 is closed, and in a second sliding position as shown in Figure 7(b) when the front door 50 is open. The sliding member 51 is provided with a lever member 52 that can move up and down relative to the sliding member 51. When the front door 50 is closed and the sliding member 51 is in the first sliding position as shown in Figure 7(a), the lever member 52 contacts the first lower surface 15a and biases the intermediate transfer belt unit 10 upward by the biasing force of the biasing 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 60, and the intermediate transfer belt unit 10 is positioned in the first position. When the intermediate transfer belt unit 10 is in the first position, the photosensitive drums 1 of each process cartridge PY, PM, PC, and PK come into contact with the intermediate transfer belt 11. Therefore, the printer 100 becomes ready to form an image.

[0051] When the front door 50 is opened and the slide member 51 is in the second slide position as shown in Figure 7(b), the lever member 52 comes into contact with the second lower surface 15c. The biasing force of the biasing spring 53 is relatively weak, and when the lever member 52 is in contact with the second lower surface 15c, the intermediate transfer belt unit 10 is positioned in 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 Figure 6). Note that when the slide member 51 is in the second slide position, the lever member 52 may be separated from the second lower surface 15c.

[0052] When the intermediate transfer belt unit 10 is in the second position, the photosensitive drums 1 of each process cartridge PY, PM, PC, and PK are separated from the intermediate transfer belt 11. As a result, the printer 100 is unable to form an image. Note that when the intermediate transfer belt unit 10 is in the second position, it is sufficient that at least one of the photosensitive drums 1 of each process cartridge PY, PM, PC, and PK is separated from the intermediate transfer belt 11. It is not necessary for all of the photosensitive drums 1 to be separated from the intermediate transfer belt 11.

[0053] Furthermore, the lifting mechanism of the intermediate transfer belt unit 10 does not necessarily have to be a sliding member 51. For example, it could be a lifting mechanism using an eccentric cam or a linkage mechanism.

[0054] Furthermore, although this embodiment shows a configuration in which the intermediate transfer belt unit 10 rotates around the rotation center of the drive roller 12, the entire intermediate transfer belt unit 10 may also be configured to move linearly in the vertical direction. In that case, it is necessary to release the engagement between the input member that provides drive input to the drive roller 12 and the drive roller 12.

[0055] [Removing the process cartridge] Next, we will explain how to remove process cartridges PY, PM, PC, and PK using Figures 8 to 9(b). As process cartridges PY, PM, PC, and PK are used for image formation, the developer contained in each cartridge is consumed. The cartridge loses its commercial value when the developer is consumed to the point where it can no longer produce images of a quality satisfactory to the user who purchased it.

[0056] For example, the printer 100 is equipped with means for detecting the remaining amount of developer in each process cartridge (PY, PM, PC, PK). For process cartridges whose remaining amount falls below a preset threshold for cartridge life prediction or warning, the display unit displays a life prediction or warning for that process cartridge. 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] As shown in Figures 1 and 8, when the front door 50 is closed, the cartridge support 60 that supports the process cartridges PY, PM, PC, and PK is mounted on the main body 100A of the apparatus. At this time, the groove 60c formed on the rear of the cartridge support 60 engages with the positioning shaft 102e provided on the main body frame 102.

[0058] Furthermore, the positioning shaft 60b provided at the front of the cartridge support 60 engages with a groove 102f provided in the main frame 102. This determines the vertical and longitudinal position of the cartridge support 60. With this configuration, the cartridge support 60 does not shift position even when subjected to the biasing force of the biasing spring 53 (see Figure 7(a)) via the intermediate transfer belt unit 10.

[0059] As shown in Figure 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. This creates a gap between the intermediate transfer belt 11 of the intermediate transfer belt unit 10 in the second position and each photosensitive drum 1.

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

[0061] [Sensor unit configuration] Next, the configuration of the sensor unit 400 will be explained using Figures 10 to 11(b). As shown in Figure 10, the sensor unit 400, as a detection unit, has a holding part 410, a pair of density detection sensors 40c as detection parts, a sensor cable 40d, and a sensor spring 41 as a second biasing part. The holding part 410 has a holder 40 and a sensor unit support shaft 42 as a support part, and the holder 40 holds the pair of density detection sensors 40c. The pair of density detection sensors 40c detect the density of toner images such as toner patches on the intermediate transfer belt 11 by irradiating light onto the intermediate transfer belt 11 and receiving the reflected light. These density detection sensors 40c and an electrical circuit 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 roughly U-shape. A groove 40aL that can engage with the shaft portion 14aL of the tension roller bearing 17L is formed at one end of the holder 40, and a groove 40aR that can engage with the shaft portion 14aR of the tension roller bearing 17R is formed at the other end of the holder 40. The grooves 40aL and 40aR are formed in a roughly U-shape. A pair of concentration detection sensors 40c are fixed to the holder 40 such that, when viewed in the left-right direction, the direction of light irradiation passes through the center of the arcs of the grooves 40aL and 40aR.

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

[0064] As shown in Figures 11(a) and 11(b), the sensor unit support shaft 42 has a first engaging portion 42b, a second engaging portion 42c, and a third engaging portion 42d that are aligned vertically. These first engaging portion 42b, second engaging portion 42c, and third engaging portion 42d extend rearward from the abutment surface 42e that abuts against the holder 40. In addition, the beam portion 102c of the main frame 102 (see Figure 3(b)) has a first hole 102g, a second hole 102h, and a third hole 102i that are aligned vertically.

[0065] The first engaging portion 42b is formed in a hook shape, inserted into the first hole 102g, and fitted to the first hole 102g in the left-right direction. The second engaging portion 42c has a boss shape with a substantially T-shaped cross-section and is fitted to the second hole 102h in the left-right and vertical directions. A tapered surface 42f is formed on the upper surface of the second engaging portion 42c, and the tapered surface 42f slopes downward as it faces forward towards the printer 100. The third engaging 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 engaging portion 42b and the second engaging portion 42c engage with the first hole portion 102g and the second hole portion 102h, respectively, thereby positioning the sensor unit support shaft 42 vertically and horizontally with respect to the beam portion 102c of the main frame 102. The third engaging portion 42d is a temporary support claw portion to prevent the sensor unit support shaft 42 from falling off the beam portion 102c during assembly of the printer 100 or replacement of the intermediate transfer belt unit 10. Specifically, the third engaging portion 42d engages 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 mounted on the device body 100A.

[0067] As described above, the sensor unit support shaft 42 is supported by the beam portion 102c of the main frame 102, so the sensor spring 41 biases the sensor unit support shaft 42 toward the beam portion 102c and biases 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, as shown in Figure 12(a).

[0068] Furthermore, the holder 40 is biased by the 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 mounted on the main body 100A, the grooves 40aL and 40aR of the holder 40 stably engage with the shafts 14aL and 14aR. Therefore, the distance between the density detection sensor 40c held in the holder 40 and the intermediate transfer belt 11 is guaranteed, and the density detection sensor 40c can stably detect the density of the toner patch on the intermediate transfer belt 11. Note that the density detection sensor 40c is positioned downstream of the intermediate transfer belt 11 in the withdrawal direction DD, as shown in Figure 12(a).

[0069] As explained in Figure 5, the tension roller 14 is biased forward by the tension spring 18. That is, the biasing direction of the holder 40 by the sensor spring 41 and the biasing direction of the tension roller 14 by the tension spring 18 are in opposite directions. The holder 40 is movable in the front-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-rear direction, is inserted into the sensor unit pivot hole 40b of the holder 40.

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

[0071] [Sensor unit tracking operation] Next, using Figures 12(a) and 12(b), the tracking operation of the sensor unit 400 when the intermediate transfer belt unit 10 rotates between the first and second positions will be explained. In the following explanation, only the left side of the sensor unit 400 will be described, and the description of the right side will be omitted.

[0072] As described above, when the front door 50 is closed relative to the main body 100A, the intermediate transfer belt unit 10 is in the first position, as shown in Figure 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 due to the biasing force of the sensor spring 41.

[0073] At this time, as shown in Figures 11(a) and 11(b), the first engaging portion 42b is inserted into the first hole 102g, and there is a gap between it and the upper edge of the first hole 102g. Also, the third engaging portion 42d is gaped with the lower edge of the third hole 102i. Furthermore, a tapered surface 42f is formed on the upper part of the second engaging portion 42c. For this reason, the sensor unit support shaft 42 is configured to be rotatable in the Q direction around the contact point 42g, which will be described later.

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

[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. Also, a force G2 in the direction of gravity, based on the weight of the sensor unit 400, acts on the shaft portion 42a of the sensor unit support shaft 42 from the sensor unit pivot hole 40b. Then, a first moment acts on the sensor unit 400 in the Q direction (counterclockwise direction in Figure 12(a)) as a first direction centered on the contact point 42g at the lower end of the abutment surface 42e, due to forces G1 and G2. In addition, a second moment acts on the sensor unit 400 in the -Q direction (clockwise direction in Figure 12(a)) 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 the contact point 42g to force G1. Distance L2 is the distance in the front-rear direction from the contact point 42g to force G2. Distance L3 is the vertical distance from the contact point 42g to biasing force G3. G1 = 350 gf G2 = 50 gf G3 = 250 gf L1 = 2.85 cm L2 = 0.6 cm L3 = 0.6 cm The first moment in the Q direction = (G1 × L1) + (G2 × L2) = 1027.5 gf·cm - Second moment in the Q direction = G3 × L3 = 150 gf·cm

[0077] With the parameters set as described above, the first moment in the Q direction > 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 pivot point. 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 in accordance with the intermediate transfer belt unit 10.

[0078] As described above, when the front door 50 is opened relative to the main body 100A, the intermediate transfer belt unit 10 rotates downward from the first position to the second position around the rear rotation center 12a (see Figure 6) of the printer 100. The sensor unit 400 then rotates in the Q direction around the contact point 42g while engaged with the shafts 14aL and 14aR of the tension roller bearings 17L and 17R of the intermediate transfer belt unit 10. In other words, 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 rotatably mounted on the beam portion 102c of the main frame 102 around a contact point 42g, and the holder 40 is movably mounted on the sensor unit support shaft 42 in the axial direction of the shaft portion 42a. Furthermore, the holder 40 is biased by the sensor spring 41 so as to maintain the state in which the groove portions 40aL and 40aR are engaged with the shaft portions 14aL and 14aR.

[0080] Therefore, the sensor unit 400 follows the intermediate transfer belt unit 10 so that the grooves 40aL and 40aR do not detach from the shafts 14aL and 14aR, and do not obstruct the movement of the intermediate transfer belt unit 10. Thus, excessive load is not placed on the intermediate transfer belt unit 10 or the sensor unit 400, and deformation or damage to these intermediate transfer belt unit 10 and sensor unit 400 can be reduced.

[0081] Furthermore, the sensor unit 400 follows the intermediate transfer belt unit 10, rotating in the Q direction around the contact point 42g so as to move away from the cartridge support 60. Therefore, with the front door 50 open relative to the main body 100A, the sensor unit 400 does not interfere with the movement of the cartridge support 60 in the pulling direction DD (see Figure 9(b)). In addition, since the sensor unit 400 does not need to be replaced or removed when replacing process cartridges PY, PM, PC, PK or the intermediate transfer belt unit 10, costs can be reduced and maintainability can be improved.

[0082] <Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment is configured by providing a belt-adjustment mechanism 200 near the tension roller of the first embodiment. For this reason, the same configuration as in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0083] [Tension Unit] The intermediate transfer belt unit 70, as a belt unit according to this embodiment, has tension units 140L, 140R and a belt adjustment mechanism 200. Figure 13(a) is a perspective view showing the tension unit 140L that applies tension to the intermediate transfer belt 11. Figure 13(a) is shown with the frame cover 151L of Figure 13(b) removed. As shown in Figure 13(a), the tension unit 140L has a tension pivot member 144L, a tension stay 143L, a tension spring 145L, and a tension spring receiving member 146L. The tension pivot member 144L is supported on the frame member 150 so as to be rotatable about a pivot axis 144a. The tension spring receiving member 146L is fixed to the tension stay 143L, and a tension spring 145L is compressed between the tension pivot 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 biased 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 Figure 12(b), the frame cover 151L is fixed to the frame member 150 by fasteners such as screws, and the frame cover 151L is positioned outside the tension unit 140L in the left-right direction.

[0085] As shown in Figure 14, on the opposite side of the tension unit 140L, across the roller section 14b, is a tension unit 140R with the same configuration as the tension unit 140L. Specifically, the tension unit 140R includes a tension pivot member 144R, a tension stay 143R, a tension spring 145R, and a tension spring receiving member 146R. A frame cover 151R is positioned on the outer side of the tension unit 140R in the left-right direction.

[0086] [Belt-side adjustment mechanism] Next, the belt alignment adjustment mechanism 200 will be described using Figures 14 and 15. The belt alignment adjustment mechanism 200 includes adjustment members 210L and 210R positioned at both ends of the roller section 14b, and an interlocking member 220. The adjustment members 210L and 210R, which serve as the first and second adjustment members, are rotatably supported by tension roller bearings 17L and 17R, respectively, and each has a cam surface 210a that is eccentric from the tension roller bearings 17L and 17R, which are the centers of rotation. Furthermore, the adjustment members 210L and 210R are configured to contact the intermediate transfer belt 11 which is shifted in the left-right direction, and by contacting the intermediate transfer belt 11, they rotate in the same direction as the intermediate transfer belt 11 due to frictional force.

[0087] The interlocking member 220 has a pivot shaft 220a that is rotatably supported by the frame member 150 and connects the adjustment members 210L and 210R. The pivot shaft 220a is positioned in the center between the adjustment members 210L and 210R in the left-right direction. That is, when the interlocking member 220 rotates around the pivot 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 shifts to the right, the adjustment member 210R contacts the end of the intermediate transfer belt 11 and rotates together with it. Here, the contact pressure between the adjustment members 210L, 210R and the end of the intermediate transfer belt 11 in the left-right direction is called the shifting force. As a result, the cam surface 210a of the adjustment member 210R rotates while sliding against the sliding surface 151a of the frame cover 151R. This causes one end of the roller portion 14b on the side where the intermediate transfer belt 11 has shifted, i.e., the right end, to descend. At the same time, the adjustment member 210L rotates in the opposite direction to the adjustment member 210R as the interlocking member 220 rotates around the pivot axis 220a. This causes the other end of the roller portion 14b, i.e., the left end, to rise.

[0089] In other words, the tension unit 140R rotates upward around the pivot axis 144a, and the tension unit 140L rotates downward around the pivot axis 144a, causing the tension roller 14 to tilt relative to the drive roller 12. To put it another way, the interlocking member 220, acting as an interlocking part, tilts the tension roller 14 relative to the drive roller 12 by interlocking the adjustment members 210L and 210R.

[0090] In this embodiment, the intermediate transfer belt unit 70 attempts to move the intermediate transfer belt 11 in the opposite direction (e.g., left) to the initial shift direction (e.g., right) by tilting the tension roller 14, thereby adjusting the shift of the intermediate transfer belt 11 and reducing the shifting force. Once the rotational moments of the adjustment members 210L and 210R are balanced, the adjustment members 210L and 210R stop, and no shifting force is generated on the intermediate transfer belt 11. In other words, the belt shift adjustment mechanism 200 adjusts the shift of the intermediate transfer belt 11 by tilting the tension roller 14 relative to the drive roller 12 when the intermediate transfer belt 11 is shifted to one end in the width direction W, which is perpendicular to the movement direction BD of the intermediate transfer belt 11 (see Figure 13(b)). Note that the width direction W is parallel to the left-right direction of the printer 100.

[0091] In this embodiment, as shown in Figure 15, the top surface 151b of the frame cover 151R (151L) contacts the bottom surface 60a of the cartridge support 60 during image formation. This determines the height position of the intermediate transfer belt unit 70, positioning it, for example, to a first position.

[0092] [Sensor unit tracking operation] Next, using Figures 16(a) and 16(b), we will explain the tracking operation of the sensor unit 400 when the intermediate transfer belt unit 70 rotates between the first and second positions. In the following explanation, we will mainly describe only the left side of the sensor unit 400, and omit the explanation of the right side.

[0093] As mentioned above, the belt alignment adjustment mechanism 200 is characterized in that once the rotational moments of the adjustment members 210L and 210R are balanced, no shifting force is generated on the intermediate transfer belt 11. As a condition for this, the cam surfaces 210a of the adjustment members 210L and 210R must be in contact with the sliding surfaces 151a of the frame covers 151L and 151R, respectively. If the cam surfaces 210a move away from the sliding surfaces 151a, the angular phase of the adjustment members 210L and 210R may change, which changes the alignment of the tension roller 14. This can then generate a shifting force on the intermediate transfer belt 11 again, potentially negatively affecting image quality until the adjustment of the intermediate transfer belt 11 is complete.

[0094] Whether the cam surfaces 210a of the adjustment members 210L and 210R come into contact with the sliding surface 150a is determined by the moment around the pivot axis 144a generated by the weight of the tension units 140L and 140R and the tension roller 14, and the tension of the intermediate transfer belt 11. In this embodiment, as shown in Figure 15, the tension vector of the intermediate transfer belt 11 is positioned to point towards the pivot axis 144a of the tension pivot axis 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 weight of the tension units 140L and 140R and the tension roller 14.

[0095] As described above, when the front door 50 is closed relative to the main body 100A, the intermediate transfer belt unit 70 is in the first position, as shown in Figure 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 due to the biasing force of the sensor spring 41.

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

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

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

[0099] As a result of the parameter settings described above, 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 pivot point. 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 in accordance with the intermediate transfer belt unit 70.

[0100] As described above, when the front door 50 is opened relative to the main body 100A, the intermediate transfer belt unit 70 rotates downward from the first position to the second position around the rear rotation center 12a (see Figure 6) of the printer 100. The sensor unit 400 then rotates in the Q direction around the contact point 42g while engaged with the shaft portions 14aL and 14aR of the tension roller bearings 17L and 17R of the intermediate transfer belt unit 70, which is equipped with a belt-adjustment mechanism 200. In other words, 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 so that the grooves 40aL and 40aR do not fall off the shafts 14aL and 14aR, and do not obstruct the movement of the intermediate transfer belt unit 70. Thus, excessive load is not placed on the intermediate transfer belt unit 70 or the sensor unit 400, and deformation or damage to these intermediate transfer belt unit 70 and 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 and 210R of the belt-side adjustment mechanism 200 maintain contact with the sliding surfaces 151a of the frame covers 151L and 151R. As a result, a toner image with stable image quality can be formed on the sheet.

[0103] [Other embodiments] In all of the embodiments described above, the holder 40 of the sensor unit 400 was engaged with the shaft portions 14aL and 14aR of the tension roller bearings 17L and 17R, but it is not limited to this. For example, the holder 40 may be engaged with other parts of the intermediate transfer belt unit. Alternatively, the holder 40 may be engaged with a link member or the like that is linked to the movement of the intermediate transfer belt unit.

[0104] Furthermore, in all of the embodiments described above, the holder 40 has grooves 40aL, 40aR that can engage with the shaft portions 14aL, 14aR of the tension roller bearings 17L, 17R, but is not limited to this. For example, the tension roller bearings 17L, 17R may be provided with grooves, and the holder 40 may be provided with shaft portions that engage with the grooves.

[0105] Furthermore, in all of the embodiments described above, the intermediate transfer belt units 10 and 70 were configured to move between a first position and a second position in conjunction with the opening and closing of the front door 50, but are not limited to this. For example, the intermediate transfer belt units 10 and 70 may be moved manually by the user after the front door 50 has been opened by the user.

[0106] Furthermore, in all of the above-described configurations, the process cartridges PY, PM, PC, and PK were configured to be pulled out collectively in the withdrawal direction DD by the cartridge support 60, but this is not limited to this configuration. For example, the process cartridges PY, PM, PC, and PK may be configured to be individually detachable from the main body 100A of the apparatus.

[0107] Furthermore, the disclosure of this embodiment includes the following configurations and methods. (Composition 1) A device body having a main frame, An image carrier that holds the toner image, A belt unit comprising a rotatable endless belt, a primary transfer unit for transferring the toner image carried on the image carrier to the belt, and a tensioning member for tensioning the belt, wherein the belt unit is movable between a first position where the belt and the image carrier are in contact and a second position where the belt is separated from the image carrier, A secondary transfer unit that transfers the toner image supported on the belt to a sheet, The system includes a detection unit that is movably supported by the main frame and detects the toner image transferred to the belt, The detection unit moves relative to the main frame in conjunction with the movement of the belt unit from the first position to the second position, so as not to obstruct the movement of the belt unit. An image forming apparatus characterized by the following: (Configuration 2) The detection unit includes a detection unit for detecting the toner image transferred to the belt, and a holding unit that holds the detection unit and engages with the tensioning member, and follows the movement of the tensioning member when the belt unit performs the movement operation. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) The holding portion has a support portion that is rotatably supported with respect to the main frame, The support portion has a contact point that contacts the main frame, The detection unit rotates around the contact point so as not to obstruct the movement of the belt unit when the belt unit performs the movement operation. The image forming apparatus according to configuration 2, characterized in that... (Composition 4) The belt unit has a frame member, The tensioning member has a roller portion that contacts the inner circumferential surface of the belt, and a shaft portion that is supported by the frame member and rotatably supports the roller portion. The holding portion is movably supported with respect to the support portion and has a holder for holding the detection portion. The holder has a groove that engages with the shaft portion. The image forming apparatus according to configuration 3, characterized in that it is a picture forming apparatus. (Composition 5) The shaft portion is supported on the frame member so as to be movable in a direction perpendicular to the axial direction of the shaft portion. The image forming apparatus according to configuration 4, characterized in that... (Composition 6) The belt unit has a first biasing portion that biases the tensioning member toward the inner circumferential surface of the belt, The detection unit has a second biasing unit that biases the holder so that the groove engages with the shaft, The biasing force of the second biasing unit is smaller than the biasing force of the first biasing unit. The image forming apparatus according to configuration 5, characterized by the features described herein. (Composition 7) The moment in the first direction around the contact point, based on the weight of the belt unit and the detection unit, is greater than the moment in the second direction opposite to the first direction around the contact point, based on the biasing force of the second biasing unit. The image forming apparatus according to configuration 6, characterized by the features described therein. (Composition 8) The device includes a door section that is supported in a manner that allows it to be opened and closed relative to the main body of the device, The belt unit performs the movement operation in conjunction with the opening of the door portion relative to the main body of the device. An image forming apparatus according to any one of configurations 2 to 6, characterized by the above. (Composition 9) A cartridge including the image carrier, The device includes a pull-out section that supports the cartridge and can be pulled out in the pull-out direction relative to the main body of the device, The detection unit of the detection unit is located downstream of the belt in the pulling direction. An image forming apparatus according to any one of configurations 2 to 8, characterized by the above. (Composition 10) The tensioning member is the first tensioning member, The belt unit has a second tensioning member positioned upstream of the first tensioning member in the pulling direction, the second tensioning member tensions the belt together with the first tensioning member, and is rotatable between the first position and the second position about the rotation center of the second tensioning member. The image forming apparatus according to configuration 9, characterized by the features described therein. (Composition 11) The belt is provided with a belt alignment adjustment mechanism that adjusts the belt's alignment by tilting the first tensioning member relative to the second tensioning member when the belt is aligned to one end in the width direction perpendicular to the belt's direction of movement. The image forming apparatus according to configuration 10, characterized in that... (Composition 12) The belt adjustment mechanism includes a first adjustment member that moves by receiving force from one end of the belt in the width direction, a second adjustment member that moves by receiving 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 causes the first adjustment member and the second adjustment member to move in conjunction, thereby tilting the first tensioning member relative to the second tensioning member. The image forming apparatus according to configuration 11, characterized by the features described above. [Explanation of Symbols]

[0108] 1: Image carrier (photosensitive drum) / 10: Belt unit (intermediate transfer belt unit) / 11: Belt (intermediate transfer belt) / 12: Second tensioning member (drive roller) / 12a: Rotation center / 14: Tensioning member, first tensioning member (tension roller) / 14aL: Shaft part / 14b: Roller part / 15: Frame member / 16Y, 16M, 16C, 16K: Primary transfer part (primary transfer roller) / 18: First biasing part (tension spring) / 32: Secondary transfer part (secondary transfer roller) / 40: Holding part (holder) / 40aL: Groove part / 40c: Detection part (density detection sensor) / 41: Second biasing part (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:Device body / 102:Main frame / 200:Belt 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. A device body having a main frame, An image carrier that holds the toner image, A belt unit comprising: an endless belt that is rotatable and onto which the toner image supported on the image carrier is first transferred; and a tensioning member that tensions the belt, wherein the belt unit is rotatable around a first pivot axis between a first position where the belt and the image carrier are in contact and a second position where the belt is separated from the image carrier, A transfer unit that transfers the toner image carried on the belt to a sheet, The system includes a detection unit that is movably supported by the main frame and detects the toner image transferred to the belt, The detection unit engages with the belt unit and rotates around a second pivot axis, which is different from the first pivot axis, relative to the main frame, so as to follow the rotational movement of the belt unit from the first position to the second position. An image forming apparatus characterized by the following:

2. The detection unit includes a detection unit for detecting the toner image transferred to the belt, and a holding unit that holds the detection unit and engages with the tensioning member, and follows the movement of the tensioning member when the belt unit performs the rotational operation. The image forming apparatus according to feature 1.

3. The holding portion has a support portion that is rotatably supported with respect to the main frame, The support portion has a contact point that contacts the main frame, The detection unit rotates around the contact point, which serves as the second pivot axis, so as not to obstruct the rotation of the belt unit when the belt unit performs the rotational operation. The image forming apparatus according to feature 2.

4. The belt unit has a frame member, The tensioning member has a roller portion that contacts the inner circumferential surface of the belt, and a shaft portion that is supported by the frame member and rotatably supports the roller portion. The holding portion is movably supported with respect to the support portion and has a holder for holding the detection portion. The holder has a groove that engages with the shaft portion. The image forming apparatus according to feature 3.

5. The shaft portion is supported on the frame member so as to be movable in a direction perpendicular to the axial direction of the shaft portion. The image forming apparatus according to feature 4.

6. The belt unit has a first biasing portion that biases the tensioning member toward the inner circumferential surface of the belt, The detection unit has a second biasing unit that biases the holder so that the groove engages with the shaft, The biasing force of the second biasing unit is smaller than the biasing force of the first biasing unit. The image forming apparatus according to feature 5.

7. The moment in the first direction around the contact point, based on the weight of the belt unit and the detection unit, is greater than the moment in the second direction opposite to the first direction around the contact point, based on the biasing force of the second biasing unit. The image forming apparatus according to feature 6.

8. A door portion is supported on the main body of the device so as to be openable and closable, The device includes an interlocking mechanism that causes the belt unit to perform the rotational movement in conjunction with the opening of the door portion relative to the main body of the device. The image forming apparatus according to any one of claims 1 to 7.

9. The holding portion has a first engaging portion that engages with one end of the tensioning member and a second engaging portion that engages with the other end of the tensioning member. The detection unit is supported by the main frame such that the first engaging portion and the second engaging portion follow the movement of the tensioning member when the belt unit performs the rotational operation. The image forming apparatus according to any one of claims 2 to 7.

10. A cartridge including the image carrier, The device includes a pull-out section that supports the cartridge and can be pulled out in the pull-out direction relative to the main body of the device, The detection unit of the detection unit is located downstream of the belt in the pulling direction. The image forming apparatus according to any one of claims 2 to 7.

11. The tensioning member is the first tensioning member, The belt unit has a second tensioning member positioned upstream of the first tensioning member in the pulling direction, the second tensioning member tensions the belt together with the first tensioning member, and is rotatable between the first position and the second position about the rotation center which serves as the first pivot axis of the second tensioning member. The image forming apparatus according to feature 10.

12. The belt is provided with a belt alignment adjustment mechanism that adjusts the belt's alignment by tilting the first tensioning member relative to the second tensioning member when the belt is aligned to one end in the width direction perpendicular to the belt's direction of movement. The image forming apparatus according to feature 11.

13. The belt adjustment mechanism includes a first adjustment member that moves by receiving force from one end of the belt in the width direction, 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 causes the first adjustment member and the second adjustment member to move in opposite directions. The image forming apparatus according to feature 12.

14. A device body having a main frame, An image carrier that holds the toner image, A belt unit comprising: an endless belt that is rotatable and onto which the toner image supported on the image carrier is first transferred; a first tensioning member and a second tensioning member that tension the belt; and a belt tension adjustment mechanism that adjusts the belt's position by tilting the first tensioning member relative to the second tensioning member, wherein the belt unit is movable between a first position where the belt and the image carrier are in contact and a second position where the belt is separated from the image carrier. A transfer unit that transfers the toner image carried on the belt to a sheet, The system includes a detection unit that is movably supported by the main frame and detects the toner image transferred to the belt, The detection unit engages with the first tensioning member when the belt unit is in the first position, and moves relative to the main frame to follow the movement of the belt unit from the first position to the second position. An image forming apparatus characterized by the following:

15. The belt adjustment mechanism includes a first adjustment member that moves by receiving force from one end of the belt in the width direction perpendicular to the direction of movement 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 causes the first adjustment member and the second adjustment member to move in opposite directions. The image forming apparatus according to feature 14.

16. When the belt is moved towards one end in the width direction, the first adjusting member rises due to receiving force from the one end of the belt, and the second adjusting member descends due to receiving force from the other end of the belt. The image forming apparatus according to feature 15.

17. The detection unit includes a detection unit for detecting the toner image transferred to the belt, and a holding unit that holds the detection unit and engages with the first tensioning member, and follows the movement of the first tensioning member when the belt unit performs the movement operation. The image forming apparatus according to feature 14.

18. A cartridge including the image carrier, The device includes a pull-out section that supports the cartridge and can be pulled out in the pull-out direction relative to the main body of the device, The detection unit of the detection unit is located downstream of the belt in the pulling direction. The image forming apparatus according to feature 17.

19. The second tensioning member is positioned upstream of the first tensioning member in the pulling direction. The image forming apparatus according to feature 18.

20. The holding portion has a first engaging portion that engages with one end of the first tensioning member and a second engaging portion that engages with the other end of the first tensioning member. The detection unit is supported by the main frame such that the first engaging portion and the second engaging portion follow the movement of the first tensioning member when the belt unit performs the movement operation. The image forming apparatus according to feature 17.

21. The belt unit is rotatable between the first position and the second position about the rotation center of the second tensioning member. The detection unit rotates around the point of contact with the main frame in conjunction with the movement of the belt unit. The image forming apparatus according to any one of claims 15 to 20.

22. A door portion is supported on the main body of the device so as to be openable and closable, The device includes an interlocking mechanism that causes the belt unit to perform the movement operation in conjunction with the opening of the door portion relative to the main body of the device. The image forming apparatus according to any one of claims 15 to 20.

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