JP2015114637A - Fixing device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably rotate a fixing belt by suppressing occurrence of slip between an auxiliary drive member and the fixing belt.SOLUTION: A fixing device 18 includes a fixing belt 21 provided rotatably around a rotational axis A, a pressurizing member 22 which press-contacts to the fixing belt 21 to form a fixing nip 31, being rotatably provided, a drive source 35 for rotating the pressurizing member 22, an auxiliary drive member 27 which press-contacts to the fixing belt 21, being rotatably provided, and an auxiliary drive source 39 for rotating the auxiliary drive member 27. The fixing belt 21 includes a sheet pass region R1 through which a recording medium passes, and a non sheet pass region R2 provided outside along the rotational axis A direction in the sheet pass region R1. The auxiliary driving member 27 does not contact to the sheet pass region R1, and press-contacts to the non sheet pass region R2.

Description

  The present invention relates to a fixing device that fixes a toner image on a recording medium, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as a printer or a copying machine forms a toner image on the surface of a recording medium such as paper, and then heats and pressurizes the recording medium and the toner image by a fixing device. Is fixed on the recording medium.

  In recent years, with increasing demands for power saving and shortening of warm-up time, reduction of heat capacity of fixing devices has been actively studied. As a specific method for realizing a low heat capacity of the fixing device, for example, there is a sliding belt method. The sliding belt type fixing device includes a flexible fixing belt, a pressing member that presses against the fixing belt to form a fixing nip, a pressing member that presses the fixing belt toward the pressing member, It has. In general, the pressure member is rotated by a driving source connected to the pressure member so that the fixing belt is rotated following the rotation of the pressure member, and the fixing belt is slid with respect to the pressing member. It is.

  For example, in Patent Document 1, as a fixing device of a sliding belt type, a fixing belt (see “Heating Belt 6” in Patent Document 1) and a pressure member that presses against the fixing belt to form a fixing nip (Patent Document) 1 (refer to “Pressure roller 5”), a drive source for rotating the pressure member (see “Motor 13” in Patent Document 1), and an auxiliary drive member (see Patent Document 1) that is rotatably provided in contact with the fixing belt. 1, and an auxiliary drive source that rotates an auxiliary drive member (see “auxiliary motor 23” of Patent Document 1).

JP 2007-156276 A

  In Patent Document 1, the auxiliary drive member is in contact with the entire region of the fixing belt in the rotation axis direction (see FIG. 2 of Patent Document 1). For this reason, the toner that has moved from the recording medium passing through the fixing nip to the fixing belt may move from the fixing belt to the auxiliary driving member, and the auxiliary driving member may be soiled by the toner. If the auxiliary drive member is contaminated with toner in this manner, slip may occur between the auxiliary drive member and the fixing belt, and the fixing belt may not be stably rotated.

  In view of the above-described circumstances, an object of the present invention is to suppress the occurrence of slip between the auxiliary driving member and the fixing belt and to stably rotate the fixing belt.

  The fixing device of the present invention includes a fixing belt that is rotatably provided around a rotation shaft, a fixing nip that is in pressure contact with the fixing belt, a pressure member that is rotatably provided, and the pressure member that rotates. A driving source that is in contact with the fixing belt and rotatably provided, and an auxiliary driving source that rotates the auxiliary driving member, and the fixing belt has a sheet passing area through which a recording medium passes. And a non-sheet passing area provided outside the sheet passing area in the rotation axis direction, and the auxiliary driving member is not in contact with the sheet passing area and is in pressure contact with the non-sheet passing area. It is characterized by.

  By adopting such a configuration, even if the toner moves from the recording medium passing through the fixing nip to the sheet passing area of the fixing belt, it becomes difficult for the toner to move from the sheet passing area of the fixing belt to the auxiliary driving member. The auxiliary drive member is less likely to be soiled with toner. Therefore, it is possible to suppress the occurrence of slip between the auxiliary driving member and the fixing belt, and it is possible to rotate the fixing belt stably. Further, the auxiliary driving member is pressed against the non-sheet passing region of the fixing belt, so that the fixing belt is not easily biased to one side in the rotation axis direction.

  The pressure member may increase in diameter from the inner side toward the outer side in the rotation axis direction, and the auxiliary drive member may increase in diameter from the outer side in the rotation axis direction toward the inner side.

  As described above, the diameter of the pressure member increases from the inner side toward the outer side in the rotation axis direction, so that the recording medium passing through the fixing nip can be expanded from the inner side toward the outer side in the rotation axis direction. Is less likely to occur. On the other hand, when the diameter of the pressure member increases from the inner side to the outer side in the rotation axis direction as described above, the fixing belt tends to be biased to the outer side in the rotation axis direction. By increasing the diameter toward the inner side, the fixing belt can be moved from the outer side to the inner side in the rotation axis direction. Therefore, the fixing belt is less likely to be biased outward in the rotation axis direction, and the rotation of the fixing belt can be stabilized.

  The auxiliary drive member is provided on the outer side in the rotational axis direction of the first inclined part, the first inclined part having a diameter increasing from the inner side to the outer side in the rotational axis direction, and from the outer side in the rotational axis direction to the inner side. A second inclined portion that expands in diameter, and a top portion provided between the first inclined portion and the second inclined portion, and the rotation of the auxiliary drive member in a circumferential region of the auxiliary drive member The apex is positioned on the outer side in the rotational axis direction than the central portion in the axial direction. The top may be located.

  By adopting such a configuration, it is possible to repeatedly bring the fixing belt toward the inner side and the outer side in the rotation axis direction as the auxiliary driving member rotates. Therefore, it is possible to suppress the fixing belt from being biased to the inner side or the outer side in the rotation axis direction, and to stabilize the rotation of the fixing belt.

  The auxiliary drive member is provided movably along the rotation axis direction between a first position and a second position located on the inner side in the rotation axis direction than the first position. When the size recording medium passes through the fixing nip, the auxiliary driving member is held in the first position, and the second size recording medium having a width in the rotation axis direction narrower than that of the first size recording medium. The auxiliary drive member may be held in the second position when passing through the fixing nip.

  By adopting such a configuration, it is possible to effectively bias the fixing belt toward the outer side in the rotation axis direction regardless of which of the first size recording medium and the second size recording medium passes through the fixing nip. It is possible to suppress and stabilize the rotation of the fixing belt.

  The fixing device further includes a pressing member that presses the fixing belt toward the pressing member, and a support member that supports the pressing member. When the fixing belt rotates, the fixing belt rotates the pressing belt. You may slide with respect to a member.

  By adopting such a configuration, it is possible to reduce the heat capacity of the fixing device and to quickly raise the temperature of the fixing belt.

  The image forming apparatus of the present invention includes any one of the fixing devices described above.

  According to the present invention, it is possible to suppress the occurrence of slip between the auxiliary driving member and the fixing belt, and to stably rotate the fixing belt.

1 is a schematic diagram illustrating an outline of a configuration of a printer according to a first embodiment of the present invention. FIG. 3 is a side sectional view showing a state where each auxiliary driving roller is in a first position in the fixing device of the printer according to the first embodiment of the present invention. FIG. 5 is a side cross-sectional view illustrating a state where each auxiliary driving roller is in a second position in the printer fixing device according to the first embodiment of the present invention. FIG. 5 is a side sectional view showing a fixing device of a printer according to a second embodiment of the present invention. FIG. 6 is a schematic development view in which an auxiliary drive roller is developed along a circumferential direction in a printer fixing device according to a second embodiment of the present invention. In the fixing device of the printer according to the second embodiment of the present invention, (a) is a side view showing a state in which each auxiliary drive roller is at a rotation reference position. (B) is a side view showing a state in which each auxiliary drive roller is rotated 90 degrees from the rotation reference position. (C) is a side view showing a state in which each auxiliary drive roller is rotated 180 degrees from the rotation reference position. (D) is a side view showing a state where each auxiliary drive roller is rotated 270 degrees from the rotation reference position. (E) is a side view showing a state where each auxiliary drive roller is rotated 360 degrees from the rotation reference position (a state where each auxiliary drive roller is restored to the rotation reference position).

<First Embodiment>
First, the overall configuration of the printer 1 (image forming apparatus) will be described with reference to FIG.

  The printer 1 includes a box-shaped printer main body 2, and a paper feed cassette 3 that stores paper (recording medium) is accommodated in a lower portion of the printer main body 2. A paper discharge tray is disposed on the upper surface of the printer main body 2. 4 is provided. An upper cover 5 is attached to the upper surface of the printer main body 2 so as to be openable and closable on the side of the paper discharge tray 4, and a toner container 6 is accommodated below the upper cover 5.

  An exposure unit 7 composed of a laser scanning unit (LSU) is disposed below the paper discharge tray 4 above the printer body 2, and an image forming unit 8 is provided below the exposure unit 7. Yes. The image forming unit 8 is rotatably provided with a photosensitive drum 10 as an image carrier. Around the photosensitive drum 10, a charger 11, a developing device 12, a transfer roller 13, and a cleaning device are provided. The apparatus 14 is disposed along the rotation direction of the photosensitive drum 10 (see arrow X in FIG. 1).

  A paper transport path 15 is provided inside the printer main body 2. A paper feed unit 16 is provided at the upstream end of the conveyance path 15, and a transfer unit 17 configured by the photosensitive drum 10 and the transfer roller 13 is provided at a middle portion of the conveyance path 15. Is provided with a fixing device 18, and a paper discharge unit 19 is provided at the downstream end of the conveyance path 15. A reverse path 20 for double-sided printing is formed below the transport path 15.

  Next, an image forming operation of the printer 1 having such a configuration will be described.

  When the printer 1 is turned on, various parameters are initialized, and initial setting such as temperature setting of the fixing device 18 is executed. Then, when image data is input from a computer or the like connected to the printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 10 is charged by the charger 11, exposure corresponding to the image data is performed on the photosensitive drum 10 by laser light from the exposure device 7 (see the two-dot chain line P in FIG. 1). The electrostatic latent image is formed on the surface of the photosensitive drum 10. Next, the electrostatic latent image is developed by the developing device 12 into a toner image with toner.

  On the other hand, the sheet taken out from the sheet cassette 3 by the sheet feeding unit 16 is conveyed to the transfer unit 17 in synchronization with the above-described image forming operation, and the toner image on the photosensitive drum 10 is transferred to the sheet by the transfer unit 17. Is transferred to. The sheet on which the toner image has been transferred is conveyed downstream in the conveyance path 15 and enters the fixing device 18 where the toner image is fixed on the sheet. The paper on which the toner image is fixed is discharged from the paper discharge unit 19 to the paper discharge tray 4. The toner remaining on the photosensitive drum 10 is collected by the cleaning device 14.

  Next, the fixing device 18 will be described in more detail with reference to FIGS. Hereinafter, for convenience of explanation, the left side in FIGS. 2 and 3 is the front side (front side) of the fixing device 18. An arrow Fr in FIGS. 2 and 3 indicates the front side (front side) of the fixing device 18. 2 and 3 indicate the inner side in the front-rear direction, and the arrow O in FIGS. 2 and 3 indicates the outer side in the front-rear direction.

  The fixing device 18 includes a fixing belt 21, a pressure roller 22 (pressure member) disposed below the fixing belt 21, a support member 23 disposed at a lower portion inside the fixing belt 21, and the fixing belt 21. A pressing member 24 disposed on the inside of the fixing belt 23 and below the support member 23, a heater 25 (heat source) disposed on the inside of the fixing belt 21 and above the supporting member 23, and on the inside of the fixing belt 21 and above the heater 25. , A pair of auxiliary drive rollers 27 (auxiliary drive members) arranged above the front and rear ends of the fixing belt 21, and a moving mechanism arranged on the front upper side and the rear upper side of the fixing belt 21. 28.

  The fixing belt 21 is a flexible thin-walled belt and has a long cylindrical shape in the front-rear direction. The fixing belt 21 is provided to be rotatable about a rotation axis A extending in the front-rear direction. That is, in the present embodiment, the front-rear direction is the rotation axis direction of the fixing belt 21.

  The fixing belt 21 includes, for example, a base material layer, an elastic layer provided around the base material layer, and a release layer that covers the elastic layer. The base material layer of the fixing belt 21 is formed of, for example, a metal such as Ni (nickel) or a resin such as polyimide. The elastic layer of the fixing belt 21 is made of, for example, silicon rubber. The release layer of the fixing belt 21 is formed of a fluorine resin such as PFA, for example. 2 and 3, the layers of the fixing belt 21 (base material layer, elastic layer, release layer) are displayed without being particularly distinguished.

  Formed on the outer peripheral surface of the fixing belt 21 are a sheet passing area R1 through which the sheet passes and a non-sheet passing area R2 that is provided on both front and rear sides (outside in the front-rear direction) of the sheet passing area R1 and through which the sheet does not pass. Yes. FIG. 2 shows a sheet passing area R1 and a non-sheet passing area R2 corresponding to a first size sheet (for example, A4 portrait size sheet), and FIG. 3 is more than the above described first size sheet. A paper passing area R1 and a non-paper passing area R2 corresponding to a second size paper (for example, B5 vertical size paper) having a narrow width in the front-rear direction are displayed.

  The pressure roller 22 is rotatably supported by a fixing frame (not shown). The pressure roller 22 has a long cylindrical shape in the front-rear direction. The pressure roller 22 is in pressure contact with the fixing belt 21, and a fixing nip 31 is formed between the fixing belt 21 and the pressure roller 22.

  The pressure roller 22 includes, for example, a cylindrical core member 32, an elastic layer 33 provided around the core member 32, and a release layer (not shown) that covers the elastic layer 33. ing. The core material 32 of the pressure roller 22 is formed of a metal such as stainless steel or aluminum. A drive gear 34 is fixed to the rear end portion of the core member 32 of the pressure roller 22. The drive gear 34 is connected to a drive source 35 configured by a motor or the like. The elastic layer 33 of the pressure roller 22 is formed of, for example, silicon rubber or silicon sponge. The release layer (not shown) of the pressure roller 22 is made of, for example, a fluorine resin such as PFA. The pressure roller 22 has a shape (so-called “reverse crown shape”) that gradually increases in diameter from the inner side to the outer side in the front-rear direction.

  The support member 23 extends in the front-rear direction. The support member 23 is made of, for example, a sheet metal. The support member 23 passes through the fixing belt 21. An end portion on the outer side in the front-rear direction of the support member 23 is fixed to a fixing frame (not shown).

  The pressing member 24 extends in the front-rear direction. The pressing member 24 is made of a heat resistant resin such as LCP (Liquid Crystal Polymer). The pressing member 24 faces the pressure roller 22 via the fixing belt 21, and the fixing belt 21 is sandwiched between the pressure member 22. The upper surface of the pressing member 24 is fixed to the lower surface of the support member 23. Thereby, the pressing member 24 is supported by the support member 23. The lower surface of the pressing member 24 presses the fixing belt 21 toward the lower side (pressure roller 22 side).

  The heater 25 has a long shape in the front-rear direction. The heater 25 is composed of, for example, a halogen heater or a ceramic heater.

  The guide member 26 has a long shape in the front-rear direction. The guide member 26 is made of a conductive metal such as aluminum.

  Each auxiliary drive roller 27 has a cylindrical shape. Each auxiliary drive roller 27 includes, for example, an elastic layer and a release layer that covers the elastic layer. The elastic layer of each auxiliary drive roller 27 is made of, for example, silicon rubber. The release layer of each auxiliary drive roller 27 is formed of a fluorine-based resin such as PFA, for example. 2 and 3, the layers (elastic layer, release layer) of each auxiliary drive roller 27 are displayed without being particularly distinguished. Each auxiliary drive roller 27 has a diameter that gradually increases from the outside in the front-rear direction toward the inside.

  The auxiliary drive rollers 27 are provided on the front end side (one end side in the rotation axis direction) and the rear end side (the other end side in the rotation axis direction) of the fixing belt 21. Each auxiliary drive roller 27 is not in contact with the sheet passing region R1 of the fixing belt 21, but is in pressure contact with each non-sheet passing region R2 of the fixing belt 21. Each auxiliary drive roller 27 faces the guide member 26 via each non-sheet passing region R2 of the fixing belt 21, and each non-sheet passing region R2 of the fixing belt 21 is sandwiched between the auxiliary driving roller 27 and the guide member 26. .

  Each auxiliary drive roller 27 is provided around the front end portion and the rear portion of the shaft member 36 extending along the front-rear direction, and is provided to be rotatable integrally with the shaft member 36. Each auxiliary drive roller 27 is movable in the front-rear direction between a first position (see FIG. 2) and a second position (see FIG. 3) located on the inner side in the front-rear direction than the first position. Is provided. A contact member 37 is fixed to the shaft member 36 on the inner side in the front-rear direction than the auxiliary drive rollers 27. An auxiliary drive gear 38 is fixed to the rear end portion of the shaft member 36. The auxiliary drive gear 38 is connected to an auxiliary drive source 39 configured by a motor or the like.

  Each moving mechanism 28 includes a cam 41 disposed on the outer side in the front-rear direction of each auxiliary drive roller 27, and a coil spring 42 (biasing member) disposed on the inner side in the front-rear direction of each auxiliary drive roller 27.

  The cam 41 of each moving mechanism 28 is provided to be rotatable about the cam shaft 43. The outer peripheral portion of the cam 41 is in contact with the outer surface in the front-rear direction of each auxiliary drive roller 27. A small-diameter portion 44 and a large-diameter portion 45 whose distance from the cam shaft 43 is longer than that of the small-diameter portion 44 are provided on the outer peripheral portion of the cam 41. The cam 41 is connected to a drive unit 46 constituted by a motor or the like.

  An end portion on the outer side in the front-rear direction of the coil spring 42 of each moving mechanism 28 is in contact with a surface on the inner side in the front-rear direction of each auxiliary drive roller 27. The end portion on the inner side in the front-rear direction of the coil spring 42 is in contact with the outer surface in the front-rear direction of each contact member 37. Each coil spring 42 urges each auxiliary drive roller 27 to the first position (see FIG. 2).

  In the fixing device 18 configured as described above, when the toner image is fixed on the paper, the driving gear 34 is rotated by the driving source 35. When the drive gear 34 rotates in this way, the pressure roller 22 rotates integrally with the drive gear 34. In addition, when the toner image is fixed on the paper, the auxiliary drive gear 38 is rotated by the auxiliary drive source 39. When the auxiliary drive gear 38 rotates in this way, the shaft member 36 and each auxiliary drive roller 27 rotate integrally with the auxiliary drive gear 38. When the pressure roller 22 and each auxiliary drive roller 27 rotate as described above, the fixing belt 21 that presses against the pressure roller 22 and each auxiliary drive roller 27 rotates. When the fixing belt 21 rotates in this way, the fixing belt 21 slides with respect to the pressing member 24.

  Further, when the toner image is fixed on the paper, the heater 25 is operated (lit). When the heater 25 is thus operated, the fixing belt 21 is heated by the heater 25. In this state, when the sheet is conveyed to the fixing nip 31, the sheet and the toner image are heated and pressurized, and the toner image is fixed on the sheet.

  When the first size paper (for example, A4 vertical size paper) passes through the fixing nip 31, as shown in FIG. 2, the small diameter portion 44 of the cam 41 of each moving mechanism 28 is connected to each auxiliary driving roller 27. The auxiliary drive rollers 27 are held at the first position by the urging force of the coil spring 42. On the other hand, when the second size paper (for example, B5 vertical size paper) whose width in the front-rear direction is narrower than the first size paper passes through the fixing nip 31, the cam 41 is rotated 180 degrees by the drive unit 46. . Accordingly, as shown in FIG. 3, the large-diameter portion 45 of the cam 41 abuts on the outer surface in the front-rear direction of each auxiliary drive roller 27, and the cam 41 resists the urging force of the coil spring 42. The driving roller 27 is pressed from the first position to the second position, and each auxiliary driving roller 27 is held at the second position.

  By adopting such a configuration, it is possible to effectively suppress the bias of the fixing belt 21 outward in the front-rear direction regardless of whether the first size paper or the second size paper passes through the fixing nip 31. As a result, the rotation of the fixing belt 21 can be stabilized.

  In the present embodiment, as described above, each auxiliary driving roller 27 does not contact the sheet passing area R1 of the fixing belt 21, but presses the non-sheet passing area R2 of the fixing belt 21. By adopting such a configuration, even if the toner moves from the sheet passing through the fixing nip 31 to the sheet passing area R1 of the fixing belt 21, the toner is transferred from the sheet passing area R1 of the fixing belt 21 to each auxiliary driving roller 27. Therefore, the auxiliary driving rollers 27 are not easily contaminated with toner. Therefore, it is possible to suppress the occurrence of slip between each auxiliary drive roller 27 and the fixing belt 21, and the fixing belt 21 can be stably rotated. Along with this, it is possible to avoid a situation in which a part of the fixing belt 21 is locally heated by the heater 25 and excessively heated.

  Further, the auxiliary driving rollers 27 are pressed against the non-sheet passing regions R2 of the fixing belt 21, so that the fixing belt 21 is not easily biased to one side in the front-rear direction. Therefore, the front and rear ends of the fixing belt 21 are less likely to come into contact with a member provided on the outer side in the front and rear direction of the fixing belt 21 (for example, a pulley for regulating the bias of the fixing belt 21). Damage can be suppressed and the durability of the fixing belt 21 can be improved.

  The pressure roller 22 has a diameter that increases from the inner side in the front-rear direction toward the outer side, and each auxiliary drive roller 27 has a diameter that increases from the outer side in the front-rear direction toward the inner side. As described above, the diameter of the pressure roller 22 increases from the inner side to the outer side in the front-rear direction, so that the paper passing through the fixing nip 31 can be expanded from the inner side to the outer side in the front-rear direction. It becomes difficult to do. On the other hand, when the pressure roller 22 increases in diameter from the inner side in the front-rear direction as described above, the fixing belt 21 tends to be biased outward in the front-rear direction. By increasing the diameter from the inner side toward the inner side, the fixing belt 21 can be moved inward from the outer side in the front-rear direction. Therefore, the fixing belt 21 is not easily biased outward in the front-rear direction, and the rotation of the fixing belt 21 can be stabilized.

  The fixing device 18 is provided with a pressing member 24 that presses the fixing belt 21 downward (on the pressure roller 22 side) and a support member 23 that supports the pressing member 24. When the belt 21 rotates, the fixing belt 21 slides with respect to the pressing member 24. By adopting such a configuration, it is possible to reduce the heat capacity of the fixing device 18 and to quickly raise the temperature of the fixing belt 21.

  In the present embodiment, a case has been described in which the pressure roller 22 has a shape (so-called “reverse crown shape”) that gradually increases in diameter from the inner side to the outer side in the front-rear direction. On the other hand, in another different embodiment, the fixing belt 21 may have a shape (so-called “reverse crown shape”) in which the diameter of the fixing belt 21 gradually increases from the inner side to the outer side.

  In the present embodiment, the case where each auxiliary drive roller 27 is increased in diameter from the outer side in the front-rear direction has been described. However, in another different embodiment, each auxiliary drive roller 27 is expanded from the inner side in the front-rear direction toward the outer side. You may make it diameter.

  In the present embodiment, the case where the moving mechanism 28 including the cam 41 and the coil spring 42 is used has been described. However, in other different embodiments, other moving mechanisms having different configurations may be used.

  In the present exemplary embodiment, the case where the configuration of the present invention is applied to the fixing device 18 that slides the fixing belt 21 with respect to the pressing member 24 has been described. On the other hand, in other different embodiments, the configuration of the present invention is applied to a fixing device in which a fixing belt is stretched around a plurality of rollers and a fixing device in which a fixing belt is provided around one roller. May be.

  In the present embodiment, the case where the heater 25 is used as a heat source has been described. However, in another different embodiment, an IH coil provided outside or inside the fixing belt 21 may be used as a heat source.

  In the present embodiment, the case where the configuration of the present invention is applied to the printer 1 has been described. However, in another different embodiment, the configuration of the present invention is applied to other image forming apparatuses such as a copying machine, a facsimile, and a multifunction peripheral. May be.

<Second Embodiment>
Next, a fixing device 18 according to a second embodiment of the present invention will be described with reference to FIGS. Since the configuration of the members other than the auxiliary drive roller 51 (auxiliary drive member) is the same as that of the first embodiment, the description thereof is omitted.

  As shown in FIG. 4, the outer peripheral surface of each auxiliary drive roller 51 has a V-shaped cross section. Each auxiliary drive roller 51 includes a first inclined portion 52, a second inclined portion 53 provided outside the first inclined portion 52 in the front-rear direction, and a top portion provided between the first inclined portion 52 and the second inclined portion 53. 54. The 1st inclination part 52 is gradually diameter-expanded toward the outer side from the front-back direction inner side. The 2nd inclination part 53 is gradually expanded in diameter toward the inner side from the front-back direction outer side.

  As shown in FIG. 5 and the like, the position of the top 54 in the front-rear direction continuously changes along the circumferential direction of each auxiliary drive roller 51 (up and down in the drawing of FIG. 5). Assuming that the circumferential position of each auxiliary drive roller 51 is θ (0 ° ≦ θ <360 °), a region of 0 ° ≦ θ <90 ° and a region of 270 ° <θ <360 ° (hereinafter “region S1”). ), The apex portion 54 is located on the outer side in the front-rear direction than the center portion in the front-rear direction of each auxiliary drive roller 51. Therefore, the width of the first inclined portion 52 in the front-rear direction is wider than the width of the second inclined portion 53 in the front-rear direction. Note that the area S1 is displayed as two separate areas in the drawing of FIG. 5, but is actually one continuous area.

  On the other hand, in the region of 90 ° <θ <270 ° (hereinafter referred to as “region S <b> 2”), the top portion 54 is located on the inner side in the front-rear direction than the center portion in the front-rear direction of each auxiliary drive roller 51. Therefore, the width of the second inclined portion 53 in the front-rear direction is wider than the width of the first inclined portion 52 in the front-rear direction.

  Further, at the θ = 90 ° and θ = 270 ° portions, that is, at the boundary between the region S1 and the region S2, the top portion 54 is located at the center in the front-rear direction of each auxiliary drive roller 51. Therefore, the width in the front-rear direction of the first inclined portion 52 and the width in the front-rear direction of the second inclined portion 53 are the same.

  In the configuration as described above, as shown in FIG. 6A, in the state where each auxiliary drive roller 51 is at the rotation reference position, the center portion in the circumferential direction of the region S1 of each auxiliary drive roller 51 (FIG. 5 at 0 °) contacts the non-sheet passing region R2 of the fixing belt 21. In the region S1, since the width in the front-rear direction of the first inclined portion 52 is wider than the width in the front-rear direction of the second inclined portion 53, the fixing belt 21 is brought closer to the outer side in the front-rear direction.

  Next, as shown in FIG. 6B, when each auxiliary drive roller 51 rotates 90 degrees from the rotation reference position, the boundary between the region S1 and the region S2 of each auxiliary drive roller 51 (the 90 ° position in FIG. 5). ) Contacts the non-sheet passing region R2 of the fixing belt 21. Since the width in the front-rear direction of the first inclined portion 52 and the width in the front-rear direction of the second inclined portion 53 are the same at the boundary between the region S1 and the region S2, the fixing belt 21 cannot be moved inward or outward in the front-rear direction. .

  Next, as shown in FIG. 6C, when each auxiliary drive roller 51 is rotated 180 degrees from the rotation reference position, the circumferential center of the region S2 of each auxiliary drive roller 51 (the position of 180 ° in FIG. 5). ) Contacts the non-sheet passing region R2 of the fixing belt 21. In the region S2, since the width of the second inclined portion 53 in the front-rear direction is wider than the width of the first inclined portion 52 in the front-rear direction, the fixing belt 21 is brought inward in the front-rear direction.

  Next, as shown in FIG. 6D, when each auxiliary drive roller 51 rotates 270 degrees from the rotation reference position, the boundary between the region S1 and the region S2 of each auxiliary drive roller 51 (position of 270 ° in FIG. 5). ) Contacts the non-sheet passing region R2 of the fixing belt 21. Since the width in the front-rear direction of the first inclined portion 52 and the width in the front-rear direction of the second inclined portion 53 are the same at the boundary between the region S1 and the region S2, the fixing belt 21 cannot be moved inward or outward in the front-rear direction. .

  Next, as shown in FIG. 6E, when each auxiliary drive roller 51 is rotated 360 degrees from the rotation reference position and restored to the rotation reference position, the center (in the circumferential direction) of the region S1 of each auxiliary drive roller 51 ( The position of 360 ° (0 °) in FIG. 5 contacts the non-sheet passing region R2 of the fixing belt 21. In the region S1, since the width in the front-rear direction of the first inclined portion 52 is wider than the width in the front-rear direction of the second inclined portion 53, the fixing belt 21 is brought closer to the outer side in the front-rear direction.

  By repeating the operation as described above as each auxiliary driving roller 51 rotates, the fixing belt 21 can be repeatedly moved toward the inside and outside in the front-rear direction. Therefore, it is possible to suppress the fixing belt 21 from being biased to the inner side or the outer side in the front-rear direction, and to stabilize the rotation of the fixing belt 21.

1 Printer (image forming device)
18 Fixing Device 21 Fixing Belt 22 Pressure Roller (Pressure Member)
23 support member 24 pressing member 27 auxiliary drive roller (auxiliary drive member)
31 Fixing nip 35 Drive source 39 Auxiliary drive source 51 Auxiliary drive roller (auxiliary drive member)
52 1st inclined part 53 2nd inclined part 54 Top part A Rotating shaft R1 Paper passing area R2 Non-paper passing area S1 One area in the circumferential direction (of the auxiliary driving roller) S2 Other area in the circumferential direction (in the auxiliary driving roller)

Claims (6)

A fixing belt provided rotatably around a rotation axis;
A pressure member provided in a rotatable manner to form a fixing nip by pressing against the fixing belt;
A drive source for rotating the pressure member;
An auxiliary drive member that is pressed against the fixing belt and rotatably provided;
An auxiliary drive source for rotating the auxiliary drive member,
The fixing belt is
A paper passing area through which the recording medium passes, and
A non-sheet passing region provided outside the sheet passing region in the rotational axis direction,
The fixing device is characterized in that the auxiliary driving member is not in contact with the sheet passing area and is in pressure contact with the non-sheet passing area. The pressure member expands from the inner side to the outer side in the rotation axis direction,
The fixing device according to claim 1, wherein the auxiliary driving member has a diameter that increases from the outer side toward the inner side in the rotation axis direction. The auxiliary drive member is
A first inclined portion whose diameter increases from the inner side toward the outer side in the rotational axis direction;
A second inclined portion that is provided on the outer side in the rotational axis direction of the first inclined portion and expands from the outer side in the rotational axis direction toward the inner side;
A top portion provided between the first inclined portion and the second inclined portion,
The top portion is located on the outer side in the rotational axis direction of the auxiliary drive member in one region in the circumferential direction of the auxiliary drive member, and the other region in the circumferential direction of the auxiliary drive member in the circumferential direction of the auxiliary drive member. The fixing device according to claim 1, wherein the top portion is located on the inner side in the rotation axis direction than the central portion in the rotation axis direction of the auxiliary driving member. The auxiliary drive member is provided movably along the rotation axis direction between a first position and a second position located on the inner side in the rotation axis direction than the first position,
When the first size recording medium passes through the fixing nip, the auxiliary drive member is held in the first position, and the second size recording is narrower in the rotation axis direction than the first size recording medium. The fixing device according to claim 1, wherein the auxiliary driving member is held in the second position when the medium passes through the fixing nip. A pressing member that presses the fixing belt toward the pressing member;
A support member that supports the pressing member;
The fixing device according to claim 1, wherein when the fixing belt rotates, the fixing belt slides with respect to the pressing member.   An image forming apparatus comprising the fixing device according to claim 1.

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