Belt device and image forming apparatus

Abstract

Even if the belt member's alignment is corrected, the relative positions of the multiple roller members that tension and support the belt member are less likely to shift. [Solution] A main frame 81 is provided that rotatably holds only one end in the width direction of the secondary transfer roller 72 among a plurality of roller members 72 to 77 on which the secondary transfer belt 71 is stretched, while rotatably holding all of the other ends in the width direction of the plurality of roller members 72 to 77. A faceplate 82 is provided that rotatably holds all of the one end in the width direction of the plurality of roller members 72 to 77, and drive mechanisms 86 to 88 are provided that are configured to rotate the faceplate 82 relative to the main frame 81 at one end in the width direction about the rotation axis of the secondary transfer roller 72. Based on the detection result detected by the belt position detection sensor 89, the drive mechanisms 86 to 88 are driven so that the position in the width direction of the secondary transfer belt 71 matches a predetermined reference position.

Description

[Technical Field]

[0001] This invention relates to a belt device equipped with belt members such as a secondary transfer belt, an intermediate transfer belt, and a transfer belt, and to an image forming apparatus such as a copier, printer, facsimile, or a multifunction device thereof that is equipped with the same. [Background technology]

[0002] Conventionally, image forming apparatuses such as copiers and printers are known to be equipped with a belt alignment correction mechanism that corrects the belt alignment of belt members such as intermediate transfer belts and secondary transfer belts (see, for example, Patent Document 1).

[0003] More specifically, the belt deviation correction mechanism tilts one or two of the three or more roller members that tension and support the belt member so that any deviation in the belt member is corrected. [Overview of the project] [Problems that the invention aims to solve]

[0004] In conventional belt systems, when the belt member's alignment was corrected, the relative positions (alignment) of the multiple roller members that tension and support the belt member would sometimes shift significantly.

[0005] This invention was made to solve the above-mentioned problems, and aims to provide a belt device and an image forming apparatus in which the relative positional relationship of the multiple roller members that tension and support the belt member is less likely to shift even when the belt member is corrected to be closer to the belt. [Means for solving the problem]

[0006] The belt device in this invention comprises a plurality of roller members, a belt member stretched over the plurality of roller members, a main roller member as one of the plurality of roller members, a first holding member that rotatably holds only one end of the main roller member in the width direction and rotatably holds all of the other ends of the plurality of roller members in the width direction, a second holding member that rotatably holds all of the one end of the plurality of roller members in the width direction, a drive mechanism configured to allow the second holding member to rotate around the rotation axis of the main roller member relative to the first holding member at one end in the width direction, and a detection means for detecting the position of the belt member in the width direction, wherein the drive mechanism is driven so that the position of the belt member in the width direction coincides with a predetermined reference position based on the detection result detected by the detection means. [Effects of the Invention]

[0007] According to the present invention, even if the belt member's alignment is corrected, the relative positions of the multiple roller members that tension and support the belt member are less likely to shift. This makes it possible to provide a belt device and an image forming apparatus. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a diagram showing a magnified view of a portion of the image-making section. [Figure 3] This is a schematic diagram showing the vicinity of the intermediate transfer belt device and the secondary transfer belt device. [Figure 4] This is a diagram showing the configuration of the secondary transfer belt device. [Figure 5] This is a front view showing the main frame and faceplate of the secondary transfer belt device. [Figure 6] This diagram shows the secondary transfer belt unit installed on the base stand, in the width direction. [Figure 7] This diagram shows the main parts of the secondary transfer belt device in the width direction. [Figure 8]This is a front view showing the rotation of the faceplate relative to the main frame. [Figure 9] (A) A diagram showing the positional relationship of multiple roller members when belt alignment correction is performed in this embodiment, (B) A diagram showing the positional relationship of multiple roller members when belt alignment correction is performed as Comparative Example 1, and (C) A diagram showing the positional relationship of multiple roller members when belt alignment correction is performed as Comparative Example 2. [Figure 10] This figure shows the intermediate transfer belt device and the secondary transfer belt device, respectively, being held within the main body of the image forming apparatus. [Figure 11] This figure shows a secondary transfer belt device as a comparative example. [Figure 12] (A) A diagram showing a secondary transfer belt stretched and supported on multiple roller members arranged in parallel, and (B) A diagram showing a secondary transfer belt stretched and supported on multiple roller members that are not arranged in parallel. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for carrying out this invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations will be simplified or omitted as appropriate.

[0010] First, the overall configuration and operation of the image forming apparatus 100 will be explained using Figures 1 and 2. Figure 1 is a schematic diagram showing a printer as an image forming apparatus, and Figure 2 is an enlarged view showing a part of its image-forming section. As shown in Figure 1, an intermediate transfer belt 8 (intermediate transfer body) is installed in the center of the image forming apparatus 100 as a second belt member. Opposite the intermediate transfer belt 8, image forming units 6Y, 6M, 6C, and 6K corresponding to each color (yellow, magenta, cyan, and black) are arranged side by side. The intermediate transfer belt 8, as a second belt member, contacts the secondary transfer belt 71, which is a belt member, to form a nip (secondary transfer nip) through which the sheet P is conveyed. Also, an operation display panel (operation display unit) for displaying information related to the printing operation (image forming operation) and performing operations is installed on the upper part of the image forming apparatus 100.

[0011] Referring to FIG. 2, the image forming unit 6Y corresponding to yellow is composed of a photosensitive drum 1Y as a photoreceptor, a charging unit 4Y, a developing unit 5Y, a cleaning unit 2Y, a lubricant supply device 3, a charge removing unit, etc. disposed around the photosensitive drum 1Y. And on the photosensitive drum 1Y, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge removing process) is performed, and a yellow image is formed on the photosensitive drum 1Y.

[0012] Note that the other three image forming units 6M, 6C, and 6K have substantially the same configuration as the image forming unit 6Y corresponding to yellow except that the color of the toner used is different, and images corresponding to their respective toner colors are formed. Hereinafter, the description of the other three image forming units 6M, 6C, and 6K will be appropriately omitted, and only the description of the image forming unit 6Y corresponding to yellow will be made.

[0013] Referring to FIG. 2, the photosensitive drum 1Y is rotationally driven counterclockwise by a drive motor. And at the position of the charging unit 4Y, the surface of the photosensitive drum 1Y is uniformly charged (this is the charging process). Thereafter, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure unit 7, and an electrostatic latent image corresponding to yellow is formed by exposure scanning in the width direction (the direction perpendicular to the paper surface of FIGS. 1 and 2, which is the main scanning direction) at this position (this is the exposure process).

[0014] Thereafter, the surface of the photosensitive drum 1Y reaches the position facing the developing unit 5Y, and the electrostatic latent image is developed at this position, and a yellow toner image is formed (this is the developing process). After that, the surface of the photosensitive drum 1Y reaches the position facing the intermediate transfer belt 8 and the primary transfer roller 9Y, and at this position, the toner image formed on the surface of the photosensitive drum 1 is primarily transferred to the surface of the intermediate transfer belt 8 (this is the primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

[0015] After that, the surface of the photosensitive drum 1Y reaches the position facing the cleaning unit 2Y, and at this position, the untransferred toner remaining on the photosensitive drum 1Y is collected into the cleaning unit 2Y by the cleaning blade 2a (this is the cleaning process). Here, inside the cleaning unit 2Y, a lubricant supply device 3 (a photosensitive drum lubricant supply device) including a lubricant supply roller 3a, a solid lubricant 3b, a compression spring 3c (biasing member), etc. is provided. Then, the lubricant is scraped off little by little from the solid lubricant 3b by the lubricant supply roller 3a that rotates in the clockwise direction in FIG. 2, and the lubricant is supplied to the surface of the photosensitive drum 1Y by the lubricant supply roller 3a. Finally, the surface of the photosensitive drum 1Y reaches the position facing the charge elimination unit, and at this position, the residual potential on the photosensitive drum 1 is removed. Thus, a series of imaging processes performed on the photosensitive drum 1Y ends. <>

[0016] Note that the above-described imaging process is also performed in the same manner in the other imaging units 6M, 6C, 6K as in the yellow imaging unit 6Y. That is, from the exposure unit 7 disposed above the imaging unit, the laser beam L based on the image information is irradiated onto the photosensitive drums 1M, 1C, 1K of each imaging unit 6M, 6C, 6K. Specifically, the exposure unit 7 emits the laser beam L from a light source and irradiates the photosensitive drum while scanning the laser beam L with a polygon mirror driven to rotate through a plurality of optical elements. Note that a plurality of LEDs arranged side by side in the width direction may be used as the exposure unit 7. Subsequently, after development processes by each developing unit 5M, 5C, and 5K, the toner images of each color formed on each photoreceptor drum 1M, 1C, and 1K are superimposed onto the intermediate transfer belt 8 for primary transfer. In this way, a color image is formed on the intermediate transfer belt 8.

[0017] Here, the intermediate transfer belt 8 is stretched and supported by multiple roller members 16-22, 80, and is endlessly moved in the direction of the arrow in Figure 3 by the rotational drive of one roller member (drive roller 16) by a drive motor. The four primary transfer rollers 9Y, 9M, 9C, and 9K each have an intermediate transfer belt 8 sandwiched between them and the photoreceptor drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. A transfer voltage (primary transfer bias) with the opposite polarity to the toner polarity is then applied to the primary transfer rollers 9Y, 9M, 9C, and 9K. The intermediate transfer belt 8 then travels in the direction of the arrow, sequentially passing through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of each color on the photoreceptor drums 1Y, 1M, 1C, and 1K are superimposed onto the surface of the intermediate transfer belt 8 and primary transferred (this is the primary transfer process).

[0018] Subsequently, the intermediate transfer belt 8, on which the toner images of each color have been superimposed and primary transferred, reaches a position opposite the secondary transfer belt 71, which is a belt member. At this position, the secondary transfer opposing roller 80 (opposing roller) sandwiches the intermediate transfer belt 8 (second belt member) and the secondary transfer belt 71 (belt member) between itself and the secondary transfer roller 72 (main roller member), forming a secondary transfer nip. The four toner images formed on the intermediate transfer belt 8 are then secondary transferred onto a sheet P of paper or the like, which has been transported to the position of this secondary transfer nip (this is the secondary transfer process). At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 8.

[0019] Subsequently, the intermediate transfer belt 8 reaches the intermediate transfer cleaning unit 10. At this position, any untransferred toner or other deposits adhering to the surface of the intermediate transfer belt 8 are removed. Furthermore, the intermediate transfer belt 8 reaches the position of the lubricant supply device 30, which acts as an intermediate transfer lubricant supply device. At this position, lubricant is supplied to the surface of the intermediate transfer belt 8. Thus, the series of transfer processes performed on the intermediate transfer belt 8 are completed.

[0020] Referring to Figure 1, the sheet P that is transported to the secondary transfer nip position is transported from the paper feeding section 26 located below the main body of the device 100, via the paper feeding roller 27 and the pair of registration rollers 28, etc. More specifically, the paper feeding unit 26 stores multiple sheets P, such as transfer paper, stacked on top of each other. When the paper feeding roller 27 is driven to rotate counterclockwise in Figure 1, the top sheet P is fed via the first transport path K1 towards the space between the register rollers 28.

[0021] The sheet P, transported by the register roller pair 28 (timing roller pair), temporarily stops at the position of the roller nip of the register roller pair 28, where the rotational drive has been stopped. Then, in time with the color image on the intermediate transfer belt 8, the register roller pair 28 is driven to rotate, and the sheet P is transported toward the secondary transfer nip. In this way, the desired color image is transferred onto the sheet P.

[0022] Subsequently, the sheet P onto which the color image has been transferred at the secondary transfer nip is transported by the secondary transfer belt 71, separated from the secondary transfer belt 71, and then transported to the fixing unit 50 by the transport belt 60. At this position, the color image transferred to the surface is fixed onto the sheet P by heat and pressure from the fixing belt and pressure rollers (this is the fixing process). Subsequently, the sheet P is discharged from the device via the second transport path K2 by the paper discharge roller pair. The sheet P discharged from the device by the paper discharge roller pair is sequentially stacked on the stacking section as output images. Thus, the series of image formation processes in the image forming apparatus are completed.

[0023] Here, as shown in Figure 1, the image forming apparatus 100 in this embodiment is equipped with a double-sided transport device 40 that transports the sheet P toward the secondary transfer nip in order to transfer the toner image on the intermediate transfer belt 8 to the back side of the sheet P after the toner image has been transferred to the front side by the secondary transfer nip (transfer nip). Specifically, when the "double-sided printing mode," which prints on both sides of sheet P (the front and back sides), is selected, sheet P, after the fixing process on the front side is completed, is not ejected as is, as when the "single-sided printing mode" is selected. Instead, it is guided to the third transport path K3 in the double-sided transport device 40, where its transport direction is reversed, and then transported again via the fourth transport path K4 towards the position of the secondary transfer nip (secondary transfer belt device 69). At the position of the secondary transfer nip, an image is formed on the back side of sheet P (secondary transfer) by the same image forming process (image forming operation) as described above. After that, it undergoes a fixing process in the fixing unit 50 and is discharged from the image forming device main body 100 via the second transport path K2.

[0024] Next, Figure 2 will provide a more detailed explanation of the configuration and operation of the developing unit 5Y (developing device) in the image-making section. The developing unit 5Y consists of a developing roller 51Y facing the photoreceptor drum 1Y, a doctor blade 52Y facing the developing roller 51Y, two transport screws 55Y disposed within the developer storage unit, a density detection sensor 56Y for detecting the toner concentration in the developer, and the like. The developing roller 51Y consists of a magnet fixed inside and a sleeve that rotates around the magnet. A two-component developer G, consisting of a carrier and toner, is stored within the developer storage unit.

[0025] The developing unit 5Y, configured in this way, operates as follows: The sleeve of the developing roller 51Y rotates in the direction of the arrow in Figure 2. The developer G, which is supported on the developing roller 51Y by the magnetic field formed by the magnet, moves along the developing roller 51Y as the sleeve rotates. Here, the developer G in the developing unit 5Y is adjusted so that the proportion of toner in the developer G (toner concentration) is within a predetermined range. Specifically, when a low toner concentration is detected by the toner concentration sensor installed in the developing unit 5Y, new toner is supplied to the developing unit 5Y from the toner container 58 so that the toner concentration is within the predetermined range. Subsequently, the toner supplied from the toner container 58 into the developer container is mixed and agitated with the developer G by two transport screws 55Y, circulating between the two isolated developer containers (movement in the direction perpendicular to the paper plane in Figure 2). The toner in the developer G is then attracted to the carrier by triboelectric charging and, together with the carrier, is supported on the developer roller 51Y by the magnetic force formed on the roller 51Y.

[0026] The developer G supported on the developing roller 51Y is transported in the direction of the arrow in Figure 2 to the position of the doctor blade 52Y. At this position, the amount of developer G on the developing roller 51Y is adjusted to the appropriate level, and then it is transported to the position opposite the photoreceptor drum 1Y (the developing area). Then, the toner is attracted to the latent image formed on the photoreceptor drum 1Y by the electric field formed in the developing area. After that, the developer G remaining on the developing roller 51Y reaches above the developer storage section as the sleeve rotates, and at this position it is detached from the developing roller 51Y. The toner container 58 is detachably (replaceable) installed in the developing unit 5Y (image forming apparatus 100). When the new toner contained inside the toner container 58 is depleted, it is removed from the developing unit 5Y (image forming apparatus 100) and replaced with a new one.

[0027] Next, the intermediate transfer belt device 15 in this embodiment will be described in detail using Figure 3 and other figures. Referring to Figure 3, the intermediate transfer belt device 15 consists of an intermediate transfer belt 8 as a second belt member, four primary transfer rollers 9Y, 9M, 9C, and 9K, a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, a lubricant opposing roller 21, a backup roller 22, an intermediate transfer cleaning section 10, a lubricant supply device 30 as an intermediate transfer lubricant supply device, a secondary transfer opposing roller 80 as an opposing roller, and the like.

[0028] The intermediate transfer belt 8 contacts four photoreceptor drums 1Y, 1M, 1C, and 1K, each carrying a toner image of a different color, to form a primary transfer nip. The intermediate transfer belt 8 is stretched and supported primarily by eight roller members (a drive roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning opposing roller 20, a lubricant opposing roller 21, a backup roller 22, and a secondary transfer opposing roller 80).

[0029] In this embodiment, the intermediate transfer belt 8 is constructed by dispersing a conductive material such as carbon black in a single or multiple layer of PVDF (vinyldenine fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. The intermediate transfer belt 8 has a volume resistivity of 10 6 ~10 13 Ωcm, surface resistivity of the back side of the belt is 10 7 ~10 13 It is adjusted to be in the range of Ωcm. Also, the intermediate transfer belt 8 is set to have a thickness in the range of 20 to 200 μm. In this embodiment, the thickness of the intermediate transfer belt 8 is about 60 μm, and the volume resistivity is 10 9 It is set to approximately Ωcm. Furthermore, a release layer can be coated onto the surface of the intermediate transfer belt 8 if necessary. In this case, fluororesins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinyldenine fluoride), PEA (perfluoroalkoxy fluoropolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PVF (vinyl fluoride) can be used as the coating material, but are not limited to these.

[0030] The primary transfer rollers 9Y, 9M, 9C, and 9K are in contact with their respective photoreceptor drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 8. Specifically, the yellow transfer roller 9Y is in contact with the yellow photoreceptor drum 1Y via the intermediate transfer belt 8, the magenta transfer roller 9M is in contact with the magenta photoreceptor drum 1M via the intermediate transfer belt 8, the cyan transfer roller 9C is in contact with the cyan photoreceptor drum 1C via the intermediate transfer belt 8, and the black transfer roller 9K is in contact with the black photoreceptor drum 1K via the intermediate transfer belt 8.

[0031] The drive roller 16 is positioned downstream of the intermediate transfer belt in the direction of travel relative to the four photoreceptor drums, and is positioned so as to contact the inner surface of the intermediate transfer belt 8 when the intermediate transfer belt 8 is wrapped around it at a winding angle of approximately 120 degrees. The drive roller 16 is rotated clockwise in Figure 3 by a drive motor Mt1 controlled by the control unit 90. As a result, the intermediate transfer belt 8 travels in a predetermined direction (clockwise in Figure 3).

[0032] The driven roller 17 is positioned upstream of the intermediate transfer belt 8 in the direction of travel relative to the four photoreceptor drums, and is positioned so as to contact the inner surface of the intermediate transfer belt 8 when the intermediate transfer belt 8 is wrapped around it at a winding angle of approximately 180 degrees. The portion of the intermediate transfer belt 8 from the driven roller 17 to the drive roller 16 is set to be approximately horizontal. The driven roller 17 rotates in a clockwise direction as the intermediate transfer belt 8 travels, as shown in Figure 3.

[0033] The tension roller 19 is in contact with the outer circumferential surface of the intermediate transfer belt 8. The pre-transfer roller 18, cleaning opposing roller 20, lubricant opposing roller 21, backup roller 22, and secondary transfer opposing roller 80 are in contact with the inner circumferential surface of the intermediate transfer belt 8. Between the secondary transfer opposing roller 80 and the lubricant opposing roller 21, an intermediate transfer cleaning section 10 (cleaning blade) is installed so as to contact the cleaning opposing roller 20 via an intermediate transfer belt 8. Between the cleaning opposing roller 20 and the tension roller 19, a lubricant supply device 30 (intermediate transfer lubricant supply device) is installed so as to contact the lubricant opposing roller 21 via an intermediate transfer belt 8. The lubricant supply device 30 consists of a lubricant supply roller, solid lubricant, and a compression spring (biasing member), similar to the lubricant supply device 3 for the photoreceptor drum. The lubricant supply roller, which rotates counterclockwise as shown in Figure 3, scrapes off small amounts of lubricant from the solid lubricant, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supply roller. The roller members 17-22 and 80, excluding the drive roller 16, all rotate in conjunction with the movement of the intermediate transfer belt 8.

[0034] Referring to Figures 3 and 4, the secondary transfer opposing roller 80 is in contact with the secondary transfer roller 72 (secondary transfer belt device 69) via the intermediate transfer belt 8 and the secondary transfer belt 71. The secondary transfer opposing roller 80 has a cylindrical core made of stainless steel or the like, with a volume resistance of 10 on its outer surface. 7 ~10 8 An elastic layer (with a thickness of approximately 5 mm) is formed from NBR rubber with a hardness of approximately Ω and a hardness (JIS-A hardness) of approximately 48 to 58 degrees.

[0035] Furthermore, in this embodiment, the secondary transfer opposing roller 80 is electrically connected to the power supply unit 99 (bias output means), and a secondary transfer bias of approximately -5kV is applied from the power supply unit 99. This secondary transfer bias applied to the secondary transfer opposing roller 80 is for secondary transfer of the toner image primary transferred to the surface of the intermediate transfer belt 8 onto the sheet P that is transported to the secondary transfer nip, and is a secondary transfer bias (DC voltage) with the same polarity as the toner (negative polarity in this embodiment). As a result, the toner carried on the toner-carrying surface (outer peripheral surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer opposing roller 80 side toward the secondary transfer belt device 69 side by the secondary transfer electric field.

[0036] The secondary transfer belt device 69, which functions as a belt device, will be described below with reference to Figure 4. Referring to Figure 4, the secondary transfer belt device 69, which is a belt device, is installed opposite the intermediate transfer belt device 15, which is a second belt device. The secondary transfer belt device 69 consists of a secondary transfer belt unit 70 as a belt unit, moving mechanisms 92 and 93 (pressure mechanisms), a base 83 (support member), and the like. The secondary transfer belt unit 70 consists of a secondary transfer belt 71 as a belt member, a plurality of roller members 72 to 77 (a secondary transfer roller 72 as a main roller member, and first to fifth tension rollers 73 to 77), and the like.

[0037] The secondary transfer belt 71, as a belt member, is an endless belt stretched and supported by six roller members 72 to 77, and is made of almost the same material as the intermediate transfer belt 8. The secondary transfer belt 71 (belt member) contacts the intermediate transfer belt 8 (second belt member) to form a secondary transfer nip (transfer nip), and also conveys the sheet P that is sent out from the secondary transfer nip.

[0038] The secondary transfer roller 72 as the main roller member forms a secondary transfer nip by sandwiching the intermediate transfer belt 8 and the secondary transfer belt 71 between itself and the secondary transfer counter roller 80. The secondary transfer roller 72 is formed (coated) with an elastic layer having a hardness (Asker C hardness) of about 40 to 50 degrees on a hollow core made of stainless steel, aluminum, etc. The elastic layer of the secondary transfer roller 72 can be formed into a solid or foamed sponge shape by dispersing a conductive filler such as carbon or containing an ionic conductive material in a rubber material such as polyurethane, EPDM, or silicone. In the present embodiment, the elastic layer has a volume resistance of 10 6.5 ~10 7.5 Ω or so in order to suppress the concentration of the transfer current. Note that in the present embodiment, the secondary transfer roller 72 is grounded. Also, the secondary transfer roller 72 is rotationally driven counterclockwise in FIG. 4 by a drive motor (not shown) controlled by the control unit 90, and rotates (runs) the secondary transfer belt 71 counterclockwise in FIGS. 3 and 4. Along with this, a plurality of roller members 73 to 77 that contact the inner peripheral surface (or outer peripheral surface) of the secondary transfer belt 71 rotate idly.

[0039] The first tension roller 73 is disposed at a position on the downstream side in the conveyance direction of the sheet P with respect to the secondary transfer nip. The sheet P sent out from the secondary transfer nip is conveyed along the secondary transfer belt 71 that runs counterclockwise in FIG. 4, and then is separated (separated by curvature) from the secondary transfer belt 71 by the secondary transfer belt 71 having a curved surface formed along the outer periphery of the first tension roller 73 at the position of the first tension roller 73. Note that in the present embodiment, out of the plurality of roller members 72 to 77, two roller members (the secondary transfer roller 72 as the main roller member and the second tension roller 74 as the supported roller member) are rotatably supported by a base 83 as a support member. Also, the base 83 is configured to be moved up and down by the moving mechanisms 92 and 93 so that the pressure (nip pressure) in the secondary transfer nip is increased or decreased. These will be described in detail later. Furthermore, in this embodiment, the secondary transfer belt 71 is tensioned and supported by six roller members 72 to 77, and only the fourth tension roller 76 is configured to contact the outer circumferential surface of the secondary transfer belt 71. However, the number of roller members that tension and support the secondary transfer belt 71, and the number and position of roller members that contact the outer circumferential surface of the belt, are not limited to those of this embodiment.

[0040] The characteristic configuration and operation of the secondary transfer belt device 69 as a belt device in this embodiment will be described in detail below with reference to Figures 4 to 10, etc. As explained earlier using Figure 4, the secondary transfer belt device 69, which functions as a belt device, is equipped with a plurality of roller members 72-77, a secondary transfer belt 71 which is a belt member stretched over the plurality of roller members 72-77, and so on. The secondary transfer roller 72 functions as a main roller member, one of the roller members 72-77. The secondary transfer belt 71 is a belt member that presses against the secondary transfer opposing roller 80, which is an opposing roller, via the intermediate transfer belt 8, which is a second belt member. The secondary transfer roller 72, acting as the main roller member, is pressed against the intermediate transfer belt 8 via the secondary transfer belt 71. The secondary transfer roller 72 (main roller member) contacts the secondary transfer opposing roller 80 (opposing roller) via the secondary transfer belt 71 (belt member) and the intermediate transfer belt 8 (second belt member), forming a nip (secondary transfer nip) on which the sheet P is conveyed.

[0041] Referring to Figures 4 to 7, the secondary transfer belt device 69 (belt device) in this embodiment is further provided with a main frame 81 (main structure) as a first support member, a faceplate 82 as a second holding member, drive mechanisms 86 to 88, a belt-edge detection sensor 89 as a detection means, a base stand 83 as a support member, and moving mechanisms 92, 93. In this embodiment, the secondary transfer belt unit 70 is composed of a secondary transfer belt 71, a plurality of roller members 72-77, a main frame 81, a faceplate 82, drive mechanisms 86-88, a belt position detection sensor 89, etc. This secondary transfer belt unit 70 is supported by a base stand 83 which serves as a support member, to constitute the secondary transfer belt device 69.

[0042] Referring to Figures 6 and 7, the main frame 81 functions as a first holding member that rotatably holds only one end in the width direction of the secondary transfer roller 72 (main roller member) among the multiple roller members 72 to 77 (the left-hand shaft portion in Figures 6 and 7), while rotatably holding the other end in the width direction of all the multiple roller members 72 to 77 (the secondary transfer roller 72 and the first to fifth tension rollers 73 to 77) (the right-hand shaft portion in Figures 6 and 7). The main frame 81, as the first holding member, is a structure that has a roughly U-shaped cross-section and is mainly composed of a front plate 81b located on the front side of the image forming apparatus body 100 (the front side on which the user operates the operation display panel 95), a rear plate 81a located on the opposite rear side, and a stay 81c bridging the rear plate 81a and the front plate 81b.

[0043] Referring to Figures 6 and 7, the faceplate 82 functions as a second holding member that rotatably holds one end in the width direction (the left-hand shaft portion in Figures 6 and 7) of the multiple roller members 72 to 77 (the secondary transfer roller 72 and the first to fifth tension rollers 73 to 77). The second retaining member, the faceplate 82, is a plate-shaped member and is positioned along the rear side (one end in the width direction) of the rear plate 81a of the main frame 81.

[0044] Referring to Figures 7 and 8, the drive mechanisms 86 to 88 are configured such that the faceplate 82 (second holding member) can rotate around the rotation axis of the secondary transfer roller 72 (main roller member) relative to the main frame 81 (first holding member) at one end in the width direction (the left side in Figure 7). Specifically, while the main frame 81 is fixed in a non-rotating state, the faceplate 82 is rotated by the drive mechanisms 86-88 around the rotation axis of the secondary transfer roller 72 in the direction of the double arrows in Figure 5. Referring to Figures 7 and 8, the drive mechanism mainly consists of a drive motor 87, a drive cam 88, and a tension spring 86. The drive motor 87 is a motor that can rotate in both forward and reverse directions and is fixedly held in place on the faceplate 82. The drive cam 88 is mounted on the motor shaft of the drive motor 87 and is an eccentric cam formed to be able to contact a contact portion 81d (contact plate) that is formed to protrude from the stay 81c of the main frame 81. The tension spring 86 (biasing member) has a hook at one end connected to a shaft portion that protrudes from the rear plate 81a (main frame 81), and a hook at the other end connected to a shaft portion that protrudes from the faceplate 82. With this configuration, the spring force of the tension spring 86 biases the faceplate 82 so that the drive cam 88 is always in contact with the contact portion 81d (main frame 81). Then, the control unit 90 controls the drive motor 87 so that the faceplate 82 rotates in forward and reverse directions relative to the main frame 81 (rear side plate 81a) around the rotation axis of the secondary transfer roller 72.

[0045] Referring to Figures 6 and 7, the belt offset detection sensor 89 functions as a detection means for detecting the position of the secondary transfer belt 71 as a belt member in the width direction (the direction perpendicular to the plane of the paper in Figures 4 and 5, and the left-right direction in Figures 6 and 7). In other words, the belt offset detection sensor 89 as a detection means detects whether or not the secondary transfer belt 71 is offset, as well as its direction and magnitude (amount of offset). Specifically, referring to Figure 7, etc., the belt-edge detection sensor 89 in this embodiment is configured such that its contacted portion is always in contact with the end face (one end face in the width direction) of the secondary transfer belt 71 by a biasing means (not shown). The amount and direction of movement of the contacted portion of the belt-edge detection sensor 89 in the width direction are optically detected, and the belt-edge (direction and amount of edge) of the secondary transfer belt 71 is determined by the control unit 90. Furthermore, the configuration of the belt-side detection sensor 89 (detection means) is not limited to that of this embodiment, and other known configurations can be adopted.

[0046] In this embodiment, based on the detection result detected by the belt deviation detection sensor 89 (detection means), the drive mechanisms 86-88 (drive motors 87) are driven so that the position of the secondary transfer belt 71 (belt member) in the width direction matches a predetermined reference position (the central position where no belt deviation occurs). More specifically, if the belt-edge detection sensor 89 (detection means) detects that the secondary transfer belt 71 (belt member) is positioned shifted to one end in the width direction (left side in Figure 7) from the reference position (center position), the control unit 90 controls the drive motor 87 so that the drive mechanisms 86-88 rotate the faceplate 82 (second holding member) in the positive direction (for example, counterclockwise in Figure 5) so that the secondary transfer belt 71 moves to the other end in the width direction (right side in Figure 7). In response to this, if the belt-edge detection sensor 89 detects that the secondary transfer belt 71 is positioned further to the other end in the width direction (right side in Figure 7) than the reference position (center position), the control unit 90 controls the drive motor 87 so that the drive mechanisms 86-88 rotate the faceplate 82 in the opposite direction (the opposite direction to the "forward direction" mentioned above, for example, clockwise in Figure 5) so that the secondary transfer belt 71 moves to one end in the width direction (left side in Figure 7). By correcting (correcting) the belt bias of the secondary transfer belt 71 in real time in this way, problems such as the secondary transfer belt 71 falling off or wear at the ends can be reduced.

[0047] Furthermore, by configuring it in this way, even if the belt-side of the secondary transfer belt 71 (belt member) is corrected, the relative positional relationship (alignment) of the multiple roller members 72 to 77 that tension and support the secondary transfer belt 71 becomes less likely to shift.

[0048] The reasons for this will be explained in detail below. In the secondary transfer belt device 169 shown in Figure 11 as a comparative example, multiple roller members 72-77 that tension and support the secondary transfer belt 71 are all rotatably held by two side plates 181a and 181b (face plates). That is, one end in the width direction of the multiple roller members 72-77 (the left shaft portion in Figure 11(B)) is rotatably held by the rear side plate 181a, and the other end in the width direction (the right shaft portion in Figure 11(B)) is rotatably held by the front side plate 181b. The secondary transfer belt unit (composed of a secondary transfer belt 71, multiple roller members 72-77, side plates 181a, 181b, etc.) is configured as a secondary transfer belt device 169 with the secondary transfer roller 72 and the second tension roller 74 held (positioned) on the base stand 83, and this secondary transfer belt device 169 (base stand 83) is positioned on the image forming apparatus body 100. As shown in Figure 12(A), the secondary transfer belt 71, which is stretched and supported by multiple roller members 72-77, does not experience belt deviation when the parallelism of the multiple roller members 72-77 is maintained. However, as shown in Figure 12(B), if the parallelism between the roller members is disrupted due to variations in parts or assembly, belt deviation of the secondary transfer belt 71 will occur. In such cases, as shown in Figure 9(B) as a comparative example, if one attempts to correct the belt bias by tilting one end of a roller member (the fourth tension roller 76 in the example of Figure 9(B)) in the width direction to cause belt bias in the opposite direction to the direction in which the belt bias occurred, the positional relationship between the fourth tension roller 76 and the other roller members 72-75 and 77 will be misaligned. In such cases, secondary transfer defects are more likely to occur due to misalignment in the positional relationship of the multiple roller members 72-77 (especially the distance between the first to fifth tension rollers 73-77 and the secondary transfer roller 72). Furthermore, as shown in Figure 9(C) as another comparative example, if the rear plate 181a is rotated relative to the front plate 181b around the rotation center R in order to eliminate the misalignment between such roller members 72-77, the secondary transfer belt unit will twist. In such a case, the center of the rotation axis of the secondary transfer roller 72 will be misaligned with respect to the secondary transfer opposing roller 80 (opposing roller), and the nip pressure of the secondary transfer nip will not be uniform across the width direction, resulting in an unsuccessful secondary transfer process. In contrast, in this embodiment, as shown in Figure 9(A), the faceplate 82 that rotatably holds all the roller members 72 to 77 around the rotation axis of the secondary transfer roller 72 which is rotatably fixed (positioned) on the main frame 81 is configured to be rotatable. As a result, the secondary transfer belt unit 70 does not twist, and the positional relationship of the multiple roller members 72 to 77 (especially the distance between the first to fifth tension rollers 73 to 77 and the secondary transfer roller 72) does not shift, allowing for a good secondary transfer process to be maintained while correcting the belt-like position of the secondary transfer belt 71.

[0049] In this embodiment, the secondary transfer belt device 69 (belt device) and the secondary transfer opposing roller 80 (opposing roller) are each held (positioned) separately by the image forming apparatus body 100. More specifically, as explained earlier, the intermediate transfer belt 8 as the second belt member and the secondary transfer opposing roller 80 as the opposing roller are held (positioned) by the intermediate transfer belt device 15 as the second belt device. As shown in Figure 10, the secondary transfer belt device 69 (belt device) and the intermediate transfer belt device 15 (second belt device) are each held (positioned) separately by the main body 100 of the image forming apparatus.

[0050] More specifically, the secondary transfer belt unit 70 (composed of a secondary transfer belt 71, a plurality of roller members 72-77, a main frame 81, a faceplate 82, drive mechanisms 86-88, a belt position detection sensor 89, etc.) constitutes the secondary transfer belt device 169 with the secondary transfer roller 72 and the second tension roller 74 supported (positioned) on a base stand 83 (support member), and the secondary transfer belt device 169 (base stand 83) is held (positioned) on the image forming apparatus body 100.

[0051] As shown in Figure 6, the base stand 83 functions as a support member that rotatably supports both ends in the width direction of the secondary transfer roller 72 (main roller member) and both ends in the width direction of the second tension roller 74, which is a supported roller member among the multiple roller members 72-77 excluding the secondary transfer roller 72 (main roller member). Then, as shown in Figure 10, the positioning pins 83a and 83b of the base stand 83 (secondary transfer belt device 69) are fitted into the rear side plate 110 and the front side plate 111 of the image forming apparatus body 100, respectively, thereby positioning the secondary transfer belt device 69 relative to the image forming apparatus body 100. On the other hand, as shown in Figure 10, the positioning pins 15a and 15b of the intermediate transfer belt device 15 are fitted to the rear side plate 110 and the front side plate 111 of the image forming apparatus body 100, respectively, thereby positioning the intermediate transfer belt device 15 relative to the image forming apparatus body 100. Thus, in this embodiment, the secondary transfer roller 72 is positioned on the image forming apparatus body 100 via the base 83 together with another roller member (in this embodiment, the second tension roller 74), and the secondary transfer opposing roller 80 is also positioned on the image forming apparatus body 100 as a component of the intermediate transfer belt device 15. Therefore, even if belt-alignment correction of the secondary transfer belt 71 is performed as described above, the positional relationship between the secondary transfer roller 72 and the secondary transfer opposing roller 80 can be maintained, and a good secondary transfer process can be performed with a stable secondary transfer nip.

[0052] Referring to Figure 7, in this embodiment, the secondary transfer roller 72 (main roller member) is rotatably held by the main frame 81 (first holding member) and the faceplate 82 (second holding member) via self-aligning ball bearings 85. More specifically, the shaft portion at one end in the width direction of the secondary transfer roller 72 is held by the rear plate 81a via a first self-aligning ball bearing 85, and is also held by the faceplate 82 via a second self-aligning ball bearing 85. The shaft portion at the other end in the width direction of the secondary transfer roller 72 is held by the front plate 81b via a third self-aligning ball bearing 85. This configuration reduces the problem of the faceplate 82 interfering with the secondary transfer roller 72 when the faceplate 82 is rotated around the rotation axis of the secondary transfer roller 72 relative to the main frame 81 (rear side plate 81a). Although not shown in the diagram, the first to fifth tension rollers 73 to 77 are rotatably held on the faceplate 82 via bearings (such as ordinary ball bearings or sliding bearings) at one end in the width direction, and the shafts at the other end in the width direction are rotatably held on the front plate 81b via bearings (such as ordinary ball bearings or sliding bearings).

[0053] Referring to Figure 4, the secondary transfer belt device 69 (belt device) in this embodiment is provided with moving mechanisms 92 and 93 (pressure mechanisms) that move the secondary transfer belt device 69 so as to adjust the nip pressure (pressure) at the secondary transfer nip (nip). More specifically, this moving mechanism moves the base platform 83, which serves as a support member, up and down, and is mainly composed of a cam motor 92 and a cam 93. Then, the control unit 90 controls the cam motor 92, causing the cam 93 to rotate to the desired position (the position in the rotational direction), thereby adjusting the contact pressure (nip pressure of the secondary transfer nip) of the secondary transfer belt 71 (secondary transfer roller 72) against the intermediate transfer belt 8 (secondary transfer opposing roller 80). Specifically, in this embodiment, when the thickness of the sheet P being transported (passed through) to the secondary transfer nip is thick, the movement mechanisms 92 and 93 (cam motor 92) are controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is lower compared to when the sheet is thin. This ensures good transportability of the sheet P in the secondary transfer nip, regardless of the thickness of the sheet P. Furthermore, if the type of sheet P (paper type) being transported (passed through) to the secondary transfer nip is of low transferability, the movement mechanisms 92 and 93 (cam motor 92) are controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is greater than when the sheet P is of high transferability. This ensures good transferability in the secondary transfer nip regardless of the type of sheet P. Furthermore, when the image area ratio (the percentage of the effective image area occupied by the image portion) of the toner image (image) to be secondarily transferred to the sheet P is low, the movement mechanisms 92 and 93 (cam motor 92) are controlled by the control unit 90 so that the nip pressure of the secondary transfer nip is lower compared to when the image area ratio is high. This ensures stable transfer performance at the secondary transfer nip regardless of the size of the image area ratio. Furthermore, information regarding the thickness and type of sheet P can be acquired by the control unit 90 based on information about sheet P entered by the user through the operation display panel 95. In addition, information regarding the image area ratio can be acquired by the control unit 90 based on information written by the exposure unit 7.

[0054] Furthermore, in this embodiment, the moving mechanisms 92 and 93 are configured to completely separate the secondary transfer belt 71 from the intermediate transfer belt 8. The primary reason for controlling the system to be in this state is when the image forming apparatus 100 is not performing any printing operations (image forming process), such as when the device is stopped or after printing is completed. By implementing this control, it is possible to mitigate problems such as elastic strain caused by the intermediate transfer belt 8 and the secondary transfer belt 71 constantly being in contact.

[0055] As described above, the secondary transfer belt device 69 (belt device) in this embodiment includes a plurality of roller members 72 to 77, a secondary transfer belt 71 (belt member) stretched over the plurality of roller members 72 to 77, and a secondary transfer roller 72 (main roller member) as one of the plurality of roller members 72 to 77. A main frame 81 (first holding member) is provided that rotatably holds only one end of the plurality of roller members 72 to 77 in the width direction, while rotatably holding all of the other ends of the plurality of roller members 72 to 77 in the width direction. A faceplate 82 (second holding member) is provided that rotatably holds all of the plurality of roller members 72 to 77 in the width direction, a drive mechanism 86 to 88 is provided that is configured to allow the faceplate 82 to rotate around the rotation axis of the secondary transfer roller 72 relative to the main frame 81 at one end in the width direction, and a belt position detection sensor 89 (detection means) is provided that detects the position of the secondary transfer belt 71 in the width direction. Then, based on the detection result detected by the belt-edge detection sensor 89, the drive mechanisms 86 to 88 are driven so that the widthwise position of the secondary transfer belt 71 matches a predetermined reference position. This makes it less likely for the relative positions of the multiple roller members 72-77 that tension and support the secondary transfer belt 71 to shift, even if the belt-side of the secondary transfer belt 71 is corrected.

[0056] In this embodiment, the present invention was applied to an image forming apparatus 100 using a repulsive transfer method, in which the power supply unit 99 is configured to apply a secondary transfer bias to the secondary transfer opposing roller 80. However, the present invention can also be applied to an image forming apparatus using an attractive transfer method, in which the power supply unit is configured to apply a secondary transfer bias to the secondary transfer roller 72. In that case, the secondary transfer bias will have the opposite polarity to that of the repulsive transfer method. Furthermore, the present invention can also be applied to an image forming apparatus that uses both repulsive and attractive transfer methods. Furthermore, in this embodiment, the present invention was applied to a belt device 69 using a secondary transfer belt 71 as the belt member. However, the present invention is not limited to this, and can also be applied to belt devices using, for example, an intermediate transfer belt 8 or a transfer belt as the belt member. In that case, the main roller member among the plurality of roller members that tension the belt member will contact the opposing roller via the belt member to form a nip on which the sheet is conveyed. In addition, the belt device and the opposing roller will each be held separately in the main body of the image forming apparatus. Furthermore, in this embodiment, a structure having a substantially U-shaped cross-section was used as the first retaining member and a faceplate was used as the second retaining member, but the first and second retaining members are not limited to these forms. Furthermore, in this embodiment, the present invention was applied to an image forming apparatus 100 that forms a color image. However, the present invention can also be applied to an image forming apparatus that forms only a monochrome image. Furthermore, even in such cases, the same effects as those of this embodiment can be obtained.

[0057] It is clear that the present invention is not limited to this embodiment, and that this embodiment can be modified as appropriate within the scope of the technical concept of the present invention, in addition to what is suggested here. Furthermore, the number, position, shape, etc. of the constituent members are not limited to this embodiment, and can be set to a number, position, shape, etc. that is suitable for carrying out the present invention. [Explanation of symbols]

[0058] 1Y, 1M, 1C, 1K Photoconductor drum (photoconductor), 8. Intermediate transfer belt (second belt member), 15 Intermediate transfer belt device (second belt device), 69 Secondary transfer belt device (belt device), 70 Secondary transfer belt unit (belt unit), 71 Secondary transfer belt (belt component), 72 Secondary transfer roller (main roller member, roller member), 73 First tension roller (roller member), 74 Second tension roller (supported roller member, roller member), 75 Third tension roller (roller member), 76. Fourth tension roller (roller member), 77. Fifth tension roller (roller member), 80 Secondary transfer opposing roller (opposing roller), 81 Main frame (first retaining member), 81a Posterior plate; 81b Front side panel, 81c stay, 81d Contact part, 82 Face plate (second holding member), 83 Base stand (support member), 85 Self-aligning ball bearings, 86. Tension spring (drive mechanism), 87. Drive motor (drive mechanism), 88 Drive cam (drive mechanism), 89 Belt-side detection sensor (detection means), 92 Cam motor (movement mechanism), 93 Cam (moving mechanism), 100 Image forming apparatus (image forming apparatus main unit).

[0059] Furthermore, embodiments of the present invention can also be, for example, combinations of appendices 1 to 11 as follows. (Note 1) Multiple roller members, A belt member stretched over the aforementioned plurality of roller members, A main roller member as one of the plurality of roller members, A first holding member that rotatably holds only one end of the main roller member in the width direction among the plurality of roller members, and rotatably holds all of the other ends of the plurality of roller members in the width direction, A second holding member that rotatably holds one end of each of the aforementioned multiple roller members in the width direction, A drive mechanism is configured such that the second retaining member can be rotated relative to the first retaining member at one end in the width direction, with respect to the rotation axis of the main roller member, A detection means for detecting the position of the belt member in the width direction, Equipped with, A belt device characterized in that, based on the detection result detected by the detection means, the drive mechanism is driven so that the position of the belt member in the width direction coincides with a predetermined reference position. (Note 2) The belt device according to Appendix 1, characterized in that the main roller member contacts the opposing roller via the belt member, or the belt member and the second belt member, to form a nip on which the sheet is conveyed. (Note 3) The belt device according to Appendix 2, characterized in that the belt device and the opposing roller are each held separately by the main body of the image forming apparatus. (Note 4) The second belt member and the opposing roller are held by the second belt device, The belt device according to Appendix 2, characterized in that the aforementioned belt device and the second belt device are each separately held in the main body of the image forming apparatus. (Note 5) The belt device according to any one of the appendices 2 to 4, characterized by comprising a moving mechanism for moving the belt device so that the pressure at the nip can be adjusted. (Note 6) The belt device according to any one of the appendices 1 to 5, characterized in that it comprises support members that rotatably support both ends in the width direction of the main roller member and both ends in the width direction of the supported roller members among the plurality of roller members, excluding the main roller member. (Note 7) The belt device according to Appendix 6, characterized by comprising a moving mechanism for moving the support member up and down. (Note 8) The belt device according to any one of the appendices 1 to 7, characterized in that the main roller member is rotatably held by the first holding member and the second holding member, respectively, via self-aligning ball bearings. (Note 9) If the detection means detects that the belt member is positioned shifted to one end in the width direction from the reference position, the drive mechanism rotates the second holding member in the forward direction so that the belt member moves to the other end in the width direction. The belt device according to any one of the appendices 1 to 8, characterized in that, when the detection means detects that the belt member is positioned at a location shifted to the other end in the width direction from the reference position, the drive mechanism rotates the second holding member in the reverse direction so that the belt member moves to one end in the width direction. (Note 10) The belt member is a secondary transfer belt that presses against a secondary transfer opposing roller, which is an opposing roller, via an intermediate transfer belt, which is a second belt member. The belt device according to any one of the appendices 1 to 9, characterized in that the main roller member is a secondary transfer roller that presses against the intermediate transfer belt via the secondary transfer belt. (Note 11) An image forming apparatus characterized by being equipped with a belt device as described in any of Appendix 1 to Appendix 10. [Prior art documents] [Patent Documents]

[0060] [Patent Document 1] Japanese Patent Publication No. 2015-1732

Claims

1. Multiple roller members, A belt member stretched over the aforementioned plurality of roller members, A main roller member as one of the plurality of roller members, A first holding member that rotatably holds only one end of the main roller member in the width direction among the plurality of roller members, and rotatably holds all of the other ends of the plurality of roller members in the width direction, A second holding member that rotatably holds one end of each of the aforementioned multiple roller members in the width direction, A drive mechanism is configured such that the second retaining member can be rotated relative to the first retaining member at one end in the width direction, with respect to the rotation axis of the main roller member, A detection means for detecting the position of the belt member in the width direction, Equipped with, A belt device characterized in that, based on the detection result detected by the detection means, the drive mechanism is driven so that the position of the belt member in the width direction coincides with a predetermined reference position.

2. The belt device according to claim 1, characterized in that the main roller member contacts the opposing roller via the belt member, or the belt member and the second belt member, to form a nip on which the sheet is conveyed.

3. The belt device according to claim 2, characterized in that the belt device and the opposing roller are each held separately by the main body of the image forming apparatus.

4. The second belt member and the opposing roller are held by the second belt device. The belt device according to claim 2, characterized in that the aforementioned belt device and the second belt device are each separately held in the main body of the image forming apparatus.

5. The belt device according to claim 2, further comprising a moving mechanism for moving the belt device so that the pressure at the nip can be adjusted.

6. The belt device according to claim 1 or 2, further comprising support members that rotatably support both ends in the width direction of the main roller member and both ends in the width direction of the supported roller members among the plurality of roller members, excluding the main roller member.

7. The belt device according to claim 6, further comprising a moving mechanism for moving the support member up and down.

8. The belt device according to claim 1 or 2, characterized in that the main roller member is rotatably held by the first holding member and the second holding member, respectively, via self-aligning ball bearings.

9. If the detection means detects that the belt member is positioned shifted to one end in the width direction from the reference position, the drive mechanism rotates the second holding member in the forward direction so that the belt member moves to the other end in the width direction. The belt device according to claim 1 or 2, characterized in that, if the detection means detects that the belt member is positioned at a location shifted to the other end in the width direction from the reference position, the drive mechanism rotates the second holding member in the reverse direction so that the belt member moves to one end in the width direction.

10. The belt member is a secondary transfer belt that presses against a secondary transfer opposing roller, which is an opposing roller, via an intermediate transfer belt, which is a second belt member. The belt device according to claim 1 or 2, characterized in that the main roller member is a secondary transfer roller that presses against the intermediate transfer belt via the secondary transfer belt.

11. An image forming apparatus characterized by comprising the belt device described in claim 1 or claim 2.

Images