Fastening device to reduce belt damage

Description

BACKGROUND

[0001] An imaging system includes, for example, a conveyance device that conveys a sheet, an image carrier on which an electrostatic latent image is to be formed, a developing device that develops the electrostatic latent image, a transfer device that secondarily transfers a toner image onto the sheet, a fixing device that fixes the toner image to the sheet, and an output device that outputs the sheet. EP2469346 discloses in its Figures 2 and 4 a restraint wall 162 to prevent longitudinal movement of the fusing belt 140 and a side belt guide 170 to support an inner surface of the end of the fusing belt 140. The restraint wall 162 includes two legs 162a arranged side by side with a distance therebetween and a connector 162b to connect the two legs 162a to each other. The side belt guide 170 protrudes from the restraint wall 162 and is inserted into the fusing belt 140. The side belt guide 170 has an arcuate shape and extends throughout the two legs 162a and the connector 162b. An outer circumference of the side belt guide 170 supports the inner surface of the end of the fusing belt 140 to guide rotation of the fusing belt 140.SUMMARY

[0002] The invention is set out in the appended set of claims.BRIEF DESCRIPTION OF DRAWINGS

[0003] FIG. 1 is a schematic view illustrating a configuration of an example imaging apparatus. FIG. 2 is a perspective view illustrating a fixing device according to one example. FIG. 3 is a schematic cross-sectional view of the fixing device illustrated in FIG. 2, taken along line III-III. FIG. 6 is a schematic cross-sectional view of an example fixing device, illustrated in an example operational state. FIG. 7 is a schematic cross-sectional view of the fixing device of FIG. 6, illustrated in another example operational state. FIG. 8 is a schematic cross-sectional view of an example fixing device, illustrated in an example operational state. FIG. 9 is a schematic cross-sectional view of the fixing device of FIG. 8, illustrated in another example operational state. FIG. 10 is a schematic cross-sectional view of an example fixing device, illustrated in an example operational state. FIG. 11 is a schematic cross-sectional view of the fixing device of FIG. 10, illustrated in another example operational state. FIG. 12 is a schematic cross-sectional view of an example fixing device, illustrated in an example operational state. FIG. 13 is a schematic cross-sectional view of the fixing device of FIG. 12, illustrated in another example operational state. FIG. 14 is a schematic cross-sectional view of an example fixing device, illustrated in an example operational state. FIG. 15 is a schematic cross-sectional view of the fixing device of FIG. 14, illustrated in another example operational state. DETAILED DESCRIPTION

[0004] In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted.

[0005] With reference to FIG. 1, an example imaging apparatus 1 uses yellow, magenta, cyan, and black colors of toner to form a color image. The imaging apparatus 1 includes, for example, a conveyance unit (conveyance device) 10 that conveys a sheet 3 which is a print medium, a transfer unit (or transfer device) 20 that transfers a developed toner image onto the sheet 3, a photoconductor unit (or photoconductor device) 30 having a surface (peripheral surface) to form an electrostatic latent image, a developing unit (or developing device) 40 that develops the electrostatic latent image with the toner, and a fixing device 100 that fixes the toner to the sheet 3. The photoconductor device 30 may include photoconductor devices 30Y, 30M, 30C, and 30K that correspond to yellow, magenta, cyan, and black colors, respectively. In addition, the developing device 40 may include developing devices 40Y, 40M, 40C, and 40K that correspond to yellow, magenta, cyan, and black colors, respectively.

[0006] The conveyance device 10 contains the sheet 3 on which an image is to be formed. In addition, the conveyance device 10 conveys the sheet 3 onto a conveyance path 4. The sheets 3 are stacked inside a cassette. The conveyance device 10 conveys the sheet 3 to reach a secondary transfer region 5 when the toner image conveyed by the transfer device 20 reaches the secondary transfer region 5.

[0007] The transfer device 20 conveys the toner images, which are formed by the respective photoconductor devices 30Y, 30M, 30C, and 30K and which are layered to form a single composite toner image, to the secondary transfer region 5. The transfer device 20 includes, for example, a transfer belt 21, a drive roller 21d, a tension roller 21a, guide rollers 21b and 21c, primary transfer rollers 22Y, 22M, 22C, and 22K, and a secondary transfer roller 24. The transfer belt 21 is suspended around the drive roller 21d, the tension roller 21a, and the guide rollers 21b and 21c. The transfer belt 21 is an endless belt that is driven by the drive roller 21d, to rotate. The primary transfer rollers 22Y, 22M, 22C, and 22K are provided on an inner peripheral side of the transfer belt 21 along a movement direction of the transfer belt 21. The secondary transfer roller 24 is provided to press the drive roller 21d from an outer peripheral side of the transfer belt 21 at the secondary transfer region 5, so as to transfer the composite toner image from the transfer belt 21 to the sheet 3. In addition, the transfer device 20 may include a belt cleaning device or the like that removes residual toner remaining on the transfer belt 21, after the composite toner image has been transferred to the sheet 3.

[0008] The photoconductor device 30 includes a photoconductor drum 31, a charging roller 32, an exposure unit (or exposure device) 34, and a cleaning unit (cleaning device) 38. The photoconductor drum 31 has a peripheral surface forming an electrostatic latent image carrier to form an image. The photoconductor drum 31 may be, for example, an organic photoconductor (OPC). Each of the photoconductor devices 30Y, 30M, 30C, and 30K include the same components so as to form respective toner images with the respective colors of toner. The photoconductor drums 31 of the photoconductor devices 30Y, 30M, 30C, and 30K are provided along the movement direction of the transfer belt 21, and face the primary transfer rollers 22Y, 22M, 22C, and 22K, so as to interpose the transfer belt 21 therebetween, in order to transfer the toner images to the transfer belt 21. As illustrated in FIG. 1, the charging roller 32 and the cleaning device 38 are provided around the photoconductor drum 31.

[0009] The charging roller 32 uniformly charges the surface of the photoconductor drum 31 to a predetermined potential. The exposure device 34 exposes the surface of the photoconductor drum 31 to light, the surface being charged by the charging roller 32, according to an image (electrostatic latent image) to be formed. The exposure device 34 in one example irradiates the surface of the photoconductor drum 31 with a laser light to change the potential of a portion of the surface of the photoconductor drum 31 that is exposed to the light. The change in potential forms the electrostatic latent image on the surface of the photoconductor drum 31.

[0010] The cleaning device 38 recovers toner that remains on the photoconductor drum 31 after the toner image on the photoconductor drum 31 is primarily transferred onto the transfer belt 21. The cleaning device 38 may be configured to cause a cleaning blade to come into contact with the peripheral surface of the photoconductor drum 31 to remove the toner remaining on the photoconductor drum 31. A charge eliminating lamp that resets the potential of the photoconductor drum 31 may be disposed on the periphery of the photoconductor drum 31 between the cleaning device 38 and the charging roller 32 in a rotational direction of the photoconductor drum 31.

[0011] Toner is supplied to four developing devices 40 from four toner tanks 36 corresponding to the four developing devices 40. The toner tank 36 includes toner tanks 36Y, 36M, 36C, and 36K that correspond to yellow, magenta, cyan, and black colors, respectively. The four toner tanks 36Y, 36M, 36C, and 36K are respectively filled with, for example, a first replenishment developer in which yellow toner and a carrier are mixed, a second replenishment developer in which magenta toner and a carrier are mixed, a third replenishment developer in which cyan toner and a carrier are mixed, and a fourth replenishment developer in which black toner and a carrier are mixed. The developing devices 40Y, 40M, 40C, and 40K develop the electrostatic latent images formed on the respective photoconductor drums 31 with the toner from the respective toner tanks 36Y, 36M, 36C, and 36K. The electrostatic latent image is developed, thereby generating the toner images on the photoconductor drums 31.

[0012] Each of the developing devices 40Y, 40M, 40C, and 40K may include, for example, a developing roller 41, a supply auger 42, and a stirring auger 43. The developing roller 41 is a developer carrier that supplies toner to the electrostatic latent image formed on the peripheral surface of the photoconductor drum 31. The developing roller 41 receives the developer from the supply auger 42 due to magnetic force to convey the developer to the photoconductor drum 31.

[0013] The supply auger 42 and the stirring auger 43 stir the magnetic carrier and the non-magnetic toner forming the developer, to tribocharge the carrier and the toner. The stirring auger 43 conveys the charged developer to the supply auger 42. The supply auger 42 supplies the mixed and stirred developer to the developing roller 41. Each of the supply auger 42 and the stirring auger 43 has a helical conveyance surface disposed along a longitudinal direction (direction orthogonal to the view of FIG. 1).

[0014] The fixing device 100 fixes the toner image, which is secondarily transferred onto the sheet 3 from the transfer belt 21, to the sheet 3. The fixing device 100 includes, for example, a heating belt 120 and a drive roller 140. The heating belt 120 is, for example, a member that has a tubular shape and is rotatable around the rotational axis thereof. For example, a heat source such as a halogen lamp may be provided inside the heating belt 120. The drive roller 140 is, for example, a cylindrical member that is rotatable around the rotational axis thereof. The drive roller 140 is provided to press the heating belt 120. A heat-resistant elastic layer made of, for example, silicone rubber or the like is provided on outer peripheral surfaces of the heating belt 120 and the drive roller 140. The sheet 3 is caused to pass through a fixing nip portion that is a contact region between the heating belt 120 and the drive roller 140, so that the toner image is fused and fixed to the sheet 3.

[0015] In addition, the imaging apparatus 1 may be provided with output rollers 52 and 54 that output the sheet 3, to which the toner image is fixed by the fixing device 100, outside the apparatus.

[0016] A fixing device for an imaging apparatus will be described, according to various examples.

[0017] A fixing device 90 illustrated in FIG. 2 may replace the fixing device 100 in FIG. 1. The fixing device 90 includes a heating belt 91 having flexibility, a drive roller 93, and a support device 95. The heating belt 91 is a belt that has a tubular shape and is rotatable around the rotational axis thereof, and extends in a longitudinal direction that is a rotational axis direction. For example, a heat source such as a halogen lamp is provided inside the heating belt 91. In addition, a plate 92 is disposed inside the heating belt 91, as illustrated in FIG. 3. The plate 92 is slidable relative to an inner peripheral surface of the heating belt 91. For example, the plate 92 has a substantially U-shaped cross section, and a surface of the plate 92 toward the drive roller 93 is formed flat.

[0018] As illustrated in FIG. 3, the drive roller 93 is disposed adjacent to the heating belt 91 so as to be parallel to the heating belt 91. The drive roller 93 is rotated around the rotational axis thereof by a motor or the like, and drives the heating belt 91 to rotate. The sheet 3 is conveyed through a nip region to be formed between the drive roller 93 and the heating belt 91 along the conveyance path 4.

[0019] The support device 95 rotatably supports the heating belt 91.

[0020] FIGS. 6 and 7 illustrate an example fixing device 100 as viewed from a direction orthogonal to the conveyance direction of the sheet 3 and to a rotational axis 120L direction of the heating belt 120 (e.g. from a direction orthogonal to a plane extending along the conveyance direction of the sheet 3 and along a rotational axis 120L direction of the heating belt 120). Incidentally, in FIG. 6, the drive roller 140 is undepicted. The drive roller 140 of the fixing device 100 may include a drive roller 140 having a similar configuration as that of the drive roller 93 of the fixing device 90 illustrated in FIG. 2.

[0021] As illustrated in FIG. 6, the example fixing device 100 includes the heating belt 120, a bushing 150, and a guide wall 160. The heating belt 120 may have a similar configuration as that of the heating belt 91 illustrated in FIG. 2. Namely, the heating belt 120 has a tubular shape and is rotatable around a rotational axis 120L thereof, and extends longitudinally in the rotational axis 120L direction. In some examples, a heat source and a plate are disposed inside the heating belt 120. The heating belt 120 is driven to rotate by the drive roller 140.

[0022] The bushings 150 are located at opposite longitudinal ends of the heating belt 120. Each of the bushings 150 includes a shoulder 151, a stem 152, and a protrusion portion 153. The shoulder 151 is disposed adjacent to an edge 121 in the longitudinal direction of the heating belt 120. The shoulder 151 may have, for example, a plate shape that extends substantially orthogonally to the rotational axis 120L of the belt 120, such that a thickness of the plate extends in the longitudinal direction of the heating belt 120. The shoulder 151 has a wall surface that can contact the edge 121 of the heating belt 120. The distance between the shoulders 151 of the bushings 150 is greater than the length of the heating belt 120, such that the heating belt 120 is displaceable in the longitudinal direction relative to the bushing 150. Similarly to the configuration of the fixing device 90, the bushing 150 may be pressed toward a heating belt 120 by a biasing force of a spring or the like.

[0023] The stem 152 protrudes from the shoulder 151 toward the heating belt 120, and to the inside of the heating belt 120 to support the heating belt 120. The stem 152 has a substantially cylindrical shape and includes a convex portion 152a that comes into contact with an inner surface 123 of the heating belt 120 when the heating belt 120 is displaced in the longitudinal direction. The stem 152 in one example may have a so-called barrel shape. Namely, the diameter taken at an axial center of the stem 152 is greater than the diameter taken at an axial end portion of the stem 152. The stem 152 has an outer peripheral surface 152b which is smoothly curved such that the axial center of the stem 152 is outwardly convex. The outer peripheral surface 152b may be curved (e.g., in an arcuate shape) from a proximal end (located adjacent the shoulder 151) to a distal end (located inside the heating belt 120) along an axial direction.

[0024] The protrusion portion 153 protrudes from a side of the shoulder 151 that is opposite to the stem 152. A distal end side of the protrusion portion 153 forms an inclined portion 153a that extends in an oblique direction relative to the longitudinal direction of the heating belt 120, away from the shoulder 151 and toward the upstream side in the conveyance direction of the conveyance path 4.

[0025] When the heating belt 120 moves toward the bushing 150, the guide wall 160 guides the bushing 150 such that the bushing 150 moves toward the upstream side of the conveyance direction in the conveyance path 4. The guide wall 160 is disposed adjacent to the bushing 150. Namely, the guide wall 160 is disposed opposite to the heating belt 120 relative to the bushing 150. In one example, the guide wall 160 has an inclined surface 161 facing the inclined portion 153a of the protrusion portion 153. The inclined surface 161 extends straight in the oblique direction relative to the longitudinal direction of the heating belt 120, away from the heating belt 120 and toward the upstream side in the conveyance direction.

[0026] In the example fixing device 100, when the heating belt 120 moves in the longitudinal direction to come into contact with the shoulder 151, an edge 121a of the heating belt 120 presses against the bushing 150. The inclined portion 153a of the protrusion portion 153 slides along the inclined surface 161 of the guide wall 160, so that the bushing 150 pressed toward the guide wall 160 moves along the guide wall 160 toward the upstream side of the conveyance direction as illustrated in FIG. 7. In this case, the inner surface 123 of an end portion 122 on a movement direction side in the heating belt 120 (e.g., the end portion 122 corresponding to the direction of the longitudinal movement of the heating belt 120), is pressed by the stem 152 of the bushing 150 moving toward the upstream side of the conveyance direction. As described above, the force toward the upstream side is applied to the end portion 122 on the movement direction side in the heating belt 120, thereby changing the alignment of the heating belt 120 relative to the drive roller 140. Consequently, the heating belt 120 moves in a direction away from the shoulder 151, thereby correcting the posture (or alignment) of the heating belt 120.

[0027] The stem 152 of the fixing device 100 includes the convex portion 152a that comes into contact with the inner surface 123 of the heating belt 120 when the heating belt 120 is displaced in the longitudinal direction. For this reason, when the bushing 150 moves toward the upstream side of the conveyance direction, the inner surface 123 of the heating belt 120 is protected from being impacted by a corner edge 152c on a distal end side of the stem 152, as the contact area between the inner surface 123 of the heating belt 120 and the stem 152 is relatively large, and the force that is applied from the stem 152 to the heating belt 120 is unlikely to be concentrated at one location. Consequently, damage to the heating belt is inhibited.

[0028] FIGS. 8 and 9 illustrate another example fixing device 200 as viewed from a direction orthogonal to a conveyance direction 4 of the sheet 3 and to a rotational axis 220L direction of a heating belt 220, and shown without any drive roller. According to examples, the fixing device 200 may include a driving roller 93 similarly to the fixing device 90 illustrated in FIG. 2.

[0029] The example fixing device 200 includes the heating belt 220, a bushing 250, and a guide wall 260. The heating belt 220 may have a similar configuration as that of the heating belt 91 illustrated in FIG. 2. Namely, the heating belt 220 is a belt that has a tubular shape and is rotatable around a rotational axis 220L thereof, and extends in a longitudinal direction that is the rotational axis 220L direction. For example, a heat source and a plate are disposed inside the heating belt 220. The heating belt 220 is driven to rotate by the drive roller.

[0030] The bushings 250 are disposed at opposite ends of the heating belt 220. The bushing 250 includes a shoulder 251, a stem 252, and a protrusion portion 253. The shoulder 251 is disposed adjacent to an edge 221 in the longitudinal direction of the heating belt 220. The shoulder 251 may have, for example, a plate shape extending substantially orthogonally to the longitudinal axis of the heating belt 220. The shoulder 251 has a wall surface that can come into contact with the edge 221 of the heating belt 220. The distance between the shoulders 251 of the bushings 250 is greater than the length of the heating belt 220. For this reason, the heating belt 220 is displaceable in the longitudinal direction relative to the bushings 250. Similarly to the configuration of the fixing device 90, the bushings 250 may be pressed toward the heating belt 220 by the biasing force of a spring or the like.

[0031] The stem 252 protrudes from the shoulder 251 toward the heating belt 220, and to the inside of the heating belt 220 to support the heating belt 220. The stem 252 has a substantially cylindrical shape.

[0032] The protrusion portion 253 protrudes from the shoulder 251, on a side opposite to the stem 252. A distal end side of the protrusion portion 253 forms an inclined portion 253a that forms a surface extending in an oblique direction relative to the longitudinal direction of the heating belt 220, away from the shoulder 251 and toward the upstream side in the conveyance direction of the conveyance path 4. When viewed from the direction orthogonal to the conveyance direction of the sheet 3 and to the rotational axis 220L direction of the heating belt 220, the inclined portion 253a has a smoothly curved surface shape so as to be convex toward an inclined surface 261 to be described later. For example, the inclined portion 253a may be formed in an arcuate shape from a proximal end (located closer to the shoulder 251) to a distal end (located away from the shoulder 251) in an extending direction.

[0033] With reference to FIG. 9, when the heating belt 220 moves toward the bushing 250, the guide wall 260 guides the bushing 250 such that the bushing 250 moves along an arcuate path 259 toward the upstream side of the conveyance direction in the conveyance path 4. The guide wall 260 is disposed adjacent to the bushing 250, on a side of the bushing 250 that is opposite to the heating belt 220. In one example, the guide wall 260 forms the inclined surface 261 facing the inclined portion 253a of the protrusion portion 253. The inclined surface 261 extends substantially linearly in the oblique direction relative to the longitudinal direction of the heating belt 220, toward the upstream side in the conveyance direction.

[0034] When the heating belt 220 moves in the longitudinal direction to come into contact with the shoulder 251, an edge 221a of the heating belt 220 presses against the bushing 250. The inclined portion 253a of the protrusion portion 253 slides along the inclined surface 261 of the guide wall 260, so that the bushing 250 pressed toward the guide wall 260 moves along the guide wall 260 toward the upstream side of the conveyance direction as illustrated in FIG. 9. In this case, an inner surface 223 of an end portion 222 on a movement direction side in the heating belt 220 (e.g., the end portion 222 corresponding to the direction of the longitudinal movement of the heating belt 220), is pressed by the stem 252 of the bushing 250 moving toward the upstream side of the conveyance direction. As described above, the force toward the upstream side is applied to the end portion 222 on the movement direction side in the heating belt 220, which in turn changes the alignment of the heating belt 220 relative to the drive roller. Consequently, the heating belt 220 moves in a direction away from the shoulder 251, and the posture (or alignment) of the heating belt 220 is thereby corrected.

[0035] The bushing 250 of the fixing device 200 forms the inclined portion 253a including an end surface that comes into contact with the guide wall 260. The end surface of the inclined portion 253a is formed from the proximal end to the distal end in the extending direction so as to be convex toward the inclined surface 261. As one example, the end surface of the inclined portion 253a is formed in an arcuate shape from the proximal end to the distal end in the extending direction. Consequently, when the inclined portion 253a is engaged with the guide wall 260, the bushing 250 moves along the arcuate path 259. Here, the arcuate path 259 is illustrated to schematically represent the movement of the bushing 250 for ease of understanding, and does not necessarily illustrate the movement path of the bushing 250 with accuracy. When the bushing 250 is pressed against the heating belt 220, the inclined portion 253a can slide along the inclined surface 261 and the bushing 250 can rotate around a contact portion of the inclined portion 253a with the inclined surface 261. As described above, the arcuate path 259 depicts a state where the bushing 250 moves obliquely toward the upstream side of the conveyance direction and a state where the angle of the bushing 250 is changed such that the axial angle of the stem 252 is changed.

[0036] When the bushing 250 moves along the arcuate path 259 toward the upstream side of the conveyance direction, a corner edge 252c on a distal end of the stem 252 (located distally from the shoulder 251) is inhibited from pressing against the inner surface 223 of the heating belt 220. As in the illustrated example, in a case where the inclined portion 253a has an arcuately curved surface, the magnitude of rotation of the bushing 250 can be changed steplessly (gradually). For this reason, the magnitude of rotation of the bushing 250 can be automatically adjusted while minimizing friction between the inner surface 223 of the heating belt 220 and an outer peripheral surface of the stem 252. Namely, the magnitude of rotation of the bushing 250 can be automatically adjusted such that an axial direction of the heating belt 220 coincides with an axial direction of the stem 252.

[0037] FIGS. 10 and 11 illustrate another example fixing device 300 as viewed from a direction orthogonal to a conveyance direction 4 of the sheet 3 and to a rotational axis 320L direction of a heating belt 320, and shown without any drive roller. According to examples, the fixing device 300 may include a driving roller 93 similarly to the fixing device 90 illustrated in FIG. 2.

[0038] The example fixing device 300 includes the heating belt 320, a bushing 350, and a guide wall 360. The heating belt 320 may have a similar configuration as that of the heating belt 91 illustrated in FIG. 2. Namely, the heating belt 320 is a belt that has a tubular shape and is rotatable around a rotational axis 320L thereof, and extends in a longitudinal direction that is the rotational axis 320L direction. For example, a heat source and a plate are disposed inside the heating belt 320. The heating belt 320 is driven to rotate by the drive roller.

[0039] The bushings 350 are disposed at opposite ends of the heating belt 320. The bushing 350 includes a shoulder 351, a stem 352, and a protrusion portion 353. The shoulder 351 is disposed adjacent to an edge 321 in the longitudinal direction of the heating belt 320. The shoulder 351 may have, for example, a plate shape extending substantially orthogonally to the longitudinal axis of the heating belt 320. The shoulder 351 has a wall surface that can come into contact with the edge 321 of the heating belt 320. The distance between the shoulders 351 of the bushings 350 is greater than the length of the heating belt 320. For this reason, the heating belt 320 is displaceable in the longitudinal direction relative to the bushings 350. Similarly to the configuration of the fixing device 90, the bushings 350 may be pressed toward the heating belt 320 by the biasing force of a spring or the like.

[0040] The stem 352 protrudes from the shoulder 351 toward the heating belt 320, and to the inside of the heating belt 320 to support the heating belt 320. The stem 352 has a substantially cylindrical shape.

[0041] The protrusion portion 353 protrudes from the shoulder 351, on a side opposite to the stem 352. A distal end of the protrusion portion 353 forms an inclined portion 353a that has a planar shape and extends in an oblique direction relative to the longitudinal direction of the heating belt 320, away from the shoulder 351 and toward the upstream side in the conveyance direction of the conveyance path 4.

[0042] With reference to FIG. 11, when the heating belt 320 moves toward the bushing 350, the guide wall 360 guides the bushing 350 such that the bushing 350 moves along an arcuate path 359 toward the upstream side of the conveyance direction in the conveyance path 4. The guide wall 360 is disposed adjacent to the bushing 350, on a side of the bushing 350 opposite to the heating belt 320. In one example, the guide wall 360 forms an inclined surface 361 facing the inclined portion 353a of the protrusion portion 353. The inclined surface 361 extends in the oblique direction relative to the longitudinal direction of the heating belt 320, away from the heating belt 320 and toward the upstream side in the conveyance direction. When viewed from the direction orthogonal to the conveyance direction of the sheet 3 and to the rotational axis 320L direction of the heating belt 320, the inclined surface 361 has a smoothly curved surface shape so as to be concave relative to the inclined portion 353a. For example, the inclined surface 361 may be formed in an arcuate shape from one end to the other end in an extending direction. In addition, the inclined surface 361 may be curved such that the curvature is continuously changed from the one end to the other end in the extending direction.

[0043] When the heating belt 320 moves in the longitudinal direction to come into contact with the shoulder 351, an edge 321a of the heating belt 320 presses against the bushing 350. The inclined portion 353a of the protrusion portion 353 slides along the inclined surface 361 of the guide wall 360, so that the bushing 350 pressed toward the guide wall 360 moves along the guide wall 360 toward the upstream side of the conveyance direction as illustrated in FIG. 11. In this case, an inner surface 323 of an end portion 322 on a movement direction side in the heating belt 320 (e.g., the end portion 322 corresponding to the direction of the longitudinal movement of the heating belt 320), is pressed by the stem 352 of the bushing 350 moving toward the upstream side of the conveyance direction. As described above, the force toward the upstream side is applied to the end portion 322 on the movement direction side in the heating belt 320, which in turn changes the alignment of the heating belt 320 relative to the drive roller. Consequently, the heating belt 320 moves in a direction away from the shoulder 351, and the posture (or alignment) of the heating belt 320 is thereby corrected.

[0044] When viewed from the direction orthogonal to the conveyance direction of the sheet 3 and to the rotational axis 320L direction of the heating belt 320, the inclined surface 361 of the guide wall 360 is formed to be concave relative to the inclined portion 353a from a proximal end to a distal end in the extending direction. Consequently, when the inclined portion 353a is engaged with the guide wall 360, the bushing 350 moves along the arcuate path 359. Here, the arcuate path 359 is illustrated to schematically represent the movement of the bushing 350 for ease of understanding, and does not necessarily illustrate the actual movement path of the bushing 350 with accuracy. When the bushing 350 is pressed against the heating belt 320, the inclined portion 353a can slide along the inclined surface 361 and the bushing 350 can rotate due to a concave shape of the inclined surface 361. As described above, the arcuate path 359 depicts a state where the bushing 350 moves obliquely toward the upstream side of the conveyance direction and a state where the angle of the bushing 350 is changed such that the axial angle of the stem 352 is changed.

[0045] When the bushing 350 moves along the arcuate path 359 toward the upstream side of the conveyance direction, a corner edge 352c on a distal end side of the stem 352 is inhibited from pressing the inner surface 323 of the heating belt 320. As in the illustrated example, in a case where the inclined surface 361 is an arcuately curved surface, the magnitude of rotation of the bushing 350 is determined by the position of the bushing 350 relative to the inclined surface 361 in the conveyance direction. In addition, the axial inclination of the heating belt 320 is also determined by the position of the bushing 350 relative to the inclined surface 361 in the conveyance direction. Therefore, in one example, the inclined surface 361 may be formed such that an axial direction of the heating belt 320 coincides with an axial direction of the stem 352. In this case, an outer peripheral surface of the stem 352 and the inner surface 323 of the heating belt 320 are parallel to each other, and thus damage to the heating belt 320 is inhibited.

[0046] FIGS. 12 and 13 illustrate another example fixing device 400 as viewed from a direction orthogonal to the conveyance direction of the sheet 3 and to a rotational axis 420L direction of a heating belt 420, and shown without any drive roller. According to examples, the fixing device 400 may include a driving roller 93 similarly to the fixing device 90 illustrated in FIG. 2.

[0047] The example fixing device 400 includes the heating belt 420, a bushing 450, and a guide wall 460. The heating belt 420 may have a similar configuration as that of the heating belt 91 illustrated in FIG. 2. Namely, the heating belt 420 is a belt that has a tubular shape and is rotatable around a rotational axis 420L thereof, and extends in a longitudinal direction that is the rotational axis 420L direction. For example, a heat source and a plate are disposed inside the heating belt 420. The heating belt 420 is driven to rotate by the drive roller.

[0048] In addition, the heating belt 420 is displaceable in the longitudinal direction away from a shoulder 451 to avoid contact between an edge 421 of the heating belt 420 and the shoulder 451 to be described later. In one example, the heating belt 420 includes an inner surface 423 and a rib 425 that extends on the inner surface 423 in an end portion of the heating belt 420. The rib 425 is formed all around the inner surface 423 in a circumferential direction to form a ring shape. The edge 421 of the heating belt 420 is located more outwardly than the rib 425 in the longitudinal direction. Namely, the rib 425 is spaced away from the edge 421 inside the heating belt 420.

[0049] The bushings 450 are disposed at opposite ends of the heating belt 420. The bushing 450 includes the shoulder 451, a stem 452, and a protrusion portion 453. The shoulder 451 is disposed adjacent to the edge 421 in the longitudinal direction of the heating belt 420. The shoulder 451 may have, for example, a plate shape extending substantially orthogonally to the longitudinal axis of the heating belt 420. The distance between the shoulders 451 of the bushings 450 is greater than the length of the heating belt 420. Similarly to the configuration of the fixing device 90, the bushings 450 may be pressed toward the heating belt 420 by the biasing force of a spring or the like.

[0050] The stem 452 protrudes from the shoulder 451 toward the heating belt 420. The distance between the stems 452 of the bushings 450 is shorter than the longitudinal length of the heating belt 420. The stems 452 extend to the inside of the heating belt 420 to support the heating belt 420, and have a substantially cylindrical shape. The axial length of the stem 452 is longer than the length of a segment of the heating belt 420 taken from the rib 425 to the edge 421 in the longitudinal direction. The segment of the heating belt 420 is the portion of the heating belt 420 which extends outwardly from the rib 425 in the longitudinal direction. In addition, the diameter of the stem 452 is larger than the inner diameter of the rib 425.

[0051] The protrusion portion 453 protrudes from the shoulder 451, on a side opposite to the stem 452. A distal end side of the protrusion portion 453 forms an inclined portion 453a that forms a surface extending in an oblique direction relative to the longitudinal direction of the heating belt 420, away from the shoulder 451 and toward the upstream side in the conveyance direction of the conveyance path 4.

[0052] With reference to FIG. 13, when the heating belt 420 moves toward the bushing 450, the guide wall 460 guides the bushing 450 such that the bushing 450 moves toward the upstream side of the conveyance direction in the conveyance path 4. The guide wall 460 is disposed adjacent to the bushing 450, on a side of the bushing 450 that is opposite to the heating belt 420. In one example, the guide wall 460 forms an inclined surface 461 facing the inclined portion 453a of the protrusion portion 453. The inclined surface 461 extends substantially linearly in the oblique direction relative to the longitudinal direction of the heating belt 420, toward the upstream side in the conveyance direction.

[0053] When the heating belt 420 moves in the longitudinal direction to come into contact with the bushing 450, the heating belt 420 presses against the bushing 450. The inclined portion 453a of the protrusion portion 453 slides along the inclined surface 461 of the guide wall 460, so that the bushing 450 pressed toward the guide wall 460 moves along the guide wall 460 toward the upstream side of the conveyance direction as illustrated in FIG. 13. In this case, the inner surface 423 of an end portion 422 on a movement direction side in the heating belt 420 (e.g., the end portion 422 corresponding to the direction of the longitudinal movement of the heating belt 420), is pressed by the stem 452 of the bushing 450 moving toward the upstream side of the conveyance direction. As described above, the force toward the upstream side is applied to the end portion 422 on the movement direction side in the heating belt 420, which in turn changes the alignment of the heating belt 420 relative to the drive roller. Consequently, the heating belt 420 moves in a direction away from the bushing 450, and the posture (or alignment) of the heating belt 420 is thereby corrected.

[0054] The heating belt 420 of the fixing device 400 includes a pair of the ribs 425 on the right and left in an axial direction. When the heating belt 420 moves toward the bushing 450, the rib 425 comes into contact with an end portion of the bushing 450, namely, the distal end of the stem 452. The stem 452 is pressed against the rib 425, and thus the bushing 450 is pressed toward the guide wall. As illustrated in FIG. 13, the rib 425 is spaced away from an edge 421a of the heating belt 420 such that a gap is maintained between the edge 421a of the heating belt 420 and the shoulder 451 of the bushing 450 when the rib 425 comes into contact with the distal end of the stem 452. Consequently, when the bushing 450 is pressed by the heating belt 420, the shoulder 451 is prevented from causing damage to the edge 421a of the heating belt 420.

[0055] FIGS. 14 and 15 illustrate another example fixing device 500 as viewed from a direction orthogonal to a conveyance direction of the sheet 3 and to a rotational axis 520L direction of a heating belt 520, shown without any drive roller. According to examples, the fixing device 500 may include a driving roller 93 similarly to the fixing device 90 illustrated in FIG. 2.

[0056] The example fixing device 500 includes the heating belt 520, a bushing 550, and a guide wall 560. The heating belt 520 may have a similar configuration as that of the heating belt 91 illustrated in FIG. 2. Namely, the heating belt 520 is a belt that has a tubular shape and is rotatable around a rotational axis 520L thereof, and extends in a longitudinal direction that is the rotational axis 520L direction. For example, a heat source and a plate are disposed inside the heating belt 520. The heating belt 520 is driven to rotate by the drive roller.

[0057] The bushings 550 are disposed at opposite ends of the heating belt 520. The bushing 550 includes a shoulder 551, a stem 552, and a protrusion portion 553. The shoulder 551 is disposed adjacent to an edge 521 in the longitudinal direction of the heating belt 520. The shoulder 551 may have, for example, a plate shape extending substantially orthogonally to the longitudinal axis of the heating belt 520. The shoulder 551 has a wall surface 551a that can come into contact with the edge 521 of the heating belt 520. The distance between the shoulders 551 of the bushings 550 is greater than the length of the heating belt 520. For this reason, the heating belt 520 is displaceable in the longitudinal direction relative to the bushings 550. Similarly to the configuration of the fixing device 90, the bushings 550 may be pressed toward the heating belt 520 by the biasing force of a spring or the like.

[0058] The stem 552 protrudes from the shoulder 551 toward the heating belt 520, and to the inside of the heating belt 520 to support the heating belt 520. The stem 552 has a substantially cylindrical shape. A groove portion 552a that is recessed inward in a radial direction is formed in an end portion on a shoulder 551 side in the stem 552. The groove portion 552a is formed all around the stem 552 in a circumferential direction to have a ring shape. The groove portion 552a is provided with a flange 555 having a ring shape. As described above, the bushing 550 further includes the flange 555 mounted around the stem 552. The flange 555 is located between the shoulder 551 and the heating belt 520 in the longitudinal direction. The inner diameter of the flange 555 is larger than the outer diameter of the groove portion 552a. Namely, the flange 555 is rotatably supported in the groove portion 552a. In addition, the outer diameter of the flange 555 is larger than the outer diameter of a portion of the stem 552, the portion being closer to a distal end side than the groove portion 552a. The friction coefficient between the heating belt 520 and the flange 555 is greater than the friction coefficient between the heating belt 520 and the stem 552.

[0059] The protrusion portion 553 protrudes from the shoulder 551, on a side opposite to the stem 552. A distal end side of the protrusion portion 553 forms an inclined portion 553a that has a surface shape and extends in an oblique direction relative to the longitudinal direction of the heating belt 520, away from the shoulder 551 and toward the upstream side in the conveyance direction of the conveyance path 4.

[0060] With reference to FIG. 15, when the heating belt 520 moves toward the bushing 550, the guide wall 560 guides the bushing 550 such that the bushing 550 moves toward the upstream side of the conveyance direction in the conveyance path 4. The guide wall 560 is disposed adjacent to the bushing 550, on a side of the bushing 550 that is opposite to the heating belt 520. In one example, the guide wall 560 forms an inclined surface 561 facing the inclined portion 553a of the protrusion portion 553. The inclined surface 561 extends substantially linearly in the oblique direction relative to the longitudinal direction of the heating belt 520, toward the upstream side in the conveyance direction.

[0061] When the heating belt 520 moves in the longitudinal direction, the heating belt 520 presses against the bushing 550. The inclined portion 553a of the protrusion portion 553 slides along the inclined surface 561 of the guide wall 560, so that the bushing 550 pressed toward the guide wall 560 moves along the guide wall 560 toward the upstream side of the conveyance direction as illustrated in FIG. 15. In this case, an inner surface 523 of an end portion 522 on a movement direction side in the heating belt 520 (e.g., the end portion 522 corresponding to the direction of the longitudinal movement of the heating belt 520), is pressed by the stem 552 of the bushing 550 moving toward the upstream side of the conveyance direction. As described above, the force toward the upstream side is applied to the end portion 522 on the movement direction side in the heating belt 520, which in turn changes the alignment of the heating belt 520 relative to the drive roller. Consequently, the heating belt 520 moves in a direction away from the bushing 550, and the posture (or alignment) of the heating belt 520 is thereby corrected.

[0062] In the bushing 550 of the fixing device 500, the stem 552 includes the flange 555. When the heating belt 520 moves toward the bushing 550, an edge 521a of the heating belt 520 comes into contact with the flange 555, as illustrated in FIG. 15. The flange 555 is pressed against the heating belt 520, and thus the bushing 550 is pressed toward the guide wall 560 via the flange 555. In this case, the heating belt 520 is displaceable in the longitudinal direction away from the shoulder 551. As described above, in one example, the flange 555 transmits force from the heating belt 520 to the bushing 550 such that a gap is maintained between the edge 521 of the heating belt 520 and the shoulder 551 when the heating belt 520 moves toward the shoulder 551. Namely, since contact between the edge 521 of the heating belt 520 and the shoulder 551 is avoided, the shoulder 551 is prevented from causing damage to the edge 521a of the heating belt 520. Since the friction coefficient between the heating belt 520 and the flange 555 is greater than the friction coefficient between the heating belt 520 and the stem 552, the heating belt 520 moving along an axial direction can slide on a distal end side of the stem 552 to come into contact with the flange 555.

[0063] It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted.

Claims

1. A fixing device (90, 100, 200, 300, 400, 500) comprising: a belt (91, 120, 220, 320, 420, 520) having a tubular shape and extending in a longitudinal direction, the belt having a longitudinal end forming an edge of the belt; a drive roller (93, 140) to rotate the belt, to convey a print medium between the drive roller and the belt; and a bushing (96, 150, 250, 350, 450, 550) located at the longitudinal end of the belt, the bushing including a shoulder (151, 251, 351, 451, 551) separated from the longitudinal end of the belt and a stem (152, 252, 352, 452, 552) extending from the shoulder to an inside of the belt to support the belt, wherein the belt is displaceable in the longitudinal direction away from the shoulder of the bushing so as to prevent contact between the edge of the belt and the shoulder; and a guide wall (160, 260, 360, 460, 560) adjacent to the bushing to guide the bushing to move along an arcuate path (259, 359) in a direction opposite to a conveyance direction of the print medium, when the belt moves toward the bushing.

2. The fixing device according to claim 1, wherein the stem of the bushing includes a convex portion that is in contact with an inner surface of the belt when the belt is displaced in the longitudinal direction.

3. The fixing device according to claim 2, wherein the convex portion has a barrel shape.

4. The fixing device according to claim 1, whereby an axial direction of the stem of the bushing is to coincide with an axial direction of the belt when the bushing moves along the guide wall in the direction opposite to the conveyance direction.

5. The fixing device according to claim 1 or to claim 4, wherein the bushing has an end surface that is in contact with a surface of the guide wall, and wherein the end surface of the bushing or the surface of the guide wall is curved to guide the bushing along the arcuate path when the bushing is moved by the belt.

6. The fixing device according to claim 1, wherein the belt includes an inner peripheral surface and a rib (425) extending from the inner peripheral surface in a longitudinal end portion to contact an end portion of the bushing when the belt moves toward the shoulder of the bushing, and wherein the rib is separated from the edge of the belt by a distance to form a gap between the edge of the belt and the shoulder of the bushing when the rib contacts the end portion of the bushing.

7. The fixing device according to claim 1, comprising: a flange (555) mounted around the stem of the bushing, between the shoulder and the belt in the longitudinal direction of the belt, the flange to transmit a force from the belt to the shoulder while maintaining a gap between the edge of the belt and the shoulder, when the belt moves toward the shoulder.

8. The fixing device according to claim 7, wherein a groove having a ring shape is formed around the stem, and wherein the flange is rotatably supported in the groove of the stem.

9. The fixing device according to claim 7 or to claim 8, wherein a friction coefficient between the belt and the flange is greater than a friction coefficient between the belt and the stem.