Fixing apparatus and image forming apparatus

Abstract

To provide a fixing device that can suppress damage to the axial end of the fixing member. [Solution] The fixing device comprises a flexible fixing member, a pressing member, a pair of holding members 47 that hold both axial ends of the fixing member, and a pair of side plates 31 arranged parallel to the transport direction, each having a recess into which the pair of holding members 47 are mounted. The holding member 47 has a pivot support 53 that guides one axial end of the fixing member, a restricting surface 51 that restricts the axial movement of the fixing member 41, and an upstream groove 59 and a downstream groove 61 provided on the upstream and downstream sides of the pivot support 53 in the transport direction, into which the side plates 31 are fitted. When the side plates 31 are fitted into the upstream groove 59 and the downstream groove 61 and the pair of holding members 47 are mounted in the recess, the distance between the restricting surfaces 51 widens from the upstream side to the downstream side in the transport direction.

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image on a sheet and an image forming apparatus including the fixing device.

Background Art

[0002] In a fixing device using a flexible fixing belt, both ends of the fixing belt are held by a pair of holding members. The pair of holding members are supported by a pair of side plates of a fixing housing. The pair of holding members are provided with regulating surfaces for regulating movement of the fixing belt in the axial direction (a direction intersecting the conveyance direction). When the fixing belt is rotating normally, a force for moving the fixing belt in the axial direction does not occur, and both end faces of the fixing belt do not contact the regulating surfaces. <>

[0003] However, when a difference in rotational speed occurs at both ends of the fixing belt, the fixing belt inclines with respect to the conveyance direction such that the end on the side with the higher rotational speed is on the downstream side in the conveyance direction. Then, a force for moving the fixing belt toward the end on the side with the higher rotational speed along the axial direction acts on the fixing belt. When the fixing belt moves in the axial direction in such an inclined posture, when the downstream end face of the fixing belt contacts the regulating surface, the fixing belt may be folded and damaged.

[0004] Therefore, in the fixing device described in Patent Document 1, a pair of side plates supporting a pair of holding members that hold both ends of the fixing belt are provided such that the distance between the side plates becomes wider from the upstream side toward the downstream side. When the pair of holding members are supported by such a pair of side plates, the distance between the regulating surfaces of both holding members becomes wider on the downstream side than on the upstream side. Thereby, even if the fixing belt moves in the axial direction, it becomes difficult for the downstream end face of the fixing belt to contact the regulating surface, and thus breakage of the end of the fixing belt can be prevented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In the above-described anchoring device, in order to widen the gap between the side plates from the upstream side to the downstream side, the length of the stay installed between the downstream side plates was made longer than the length of the stay installed between the upstream side plates, thereby twisting both side plates to widen the gap. When both side plates are twisted in this way, the anchoring housing becomes unstable. Therefore, depending on the rigidity of the anchoring housing, the gap between the side plates may not be stable, and there is a problem in that the damage to the ends of the anchoring belt cannot be reliably prevented.

[0007] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can reliably suppress damage to the axial end of the fixing member. [Means for solving the problem]

[0008] The fixing device of the present invention comprises: a fixing member formed in a flexible cylindrical shape and rotatable around an axis; a pressurizing member rotatable around an axis that forms a pressurizing region between itself and the fixing member for heating and pressurizing toner on a sheet while conveying the sheet in a predetermined conveying direction; a pair of holding members that hold both ends of the fixing member in the axial direction; and a pair of side plates arranged parallel to the conveying direction, each of the pair of holding members having a recess into which it is mounted along a mounting direction intersecting the conveying direction, wherein each of the pair of holding members holds one end of the fixing member in the axial direction in the rotational direction The pair of holding members is characterized in that, when the side plates are fitted into the recess by fitting the side plates into the upstream and downstream grooves, the distance between the regulating surfaces widens from the upstream side to the downstream side in the conveying direction.

[0009] In the present invention, each of the upstream groove and the downstream groove has an inner surface on the regulating surface side and an outer surface facing the inner surface with a gap wider than the thickness of the side plate, and the inner surface of the upstream groove has an inward protrusion that the side plate abuts against, and the inner surface of the downstream groove has an inward protrusion that the side plate abuts against, and the height of the inward protrusion of the upstream groove is higher than the height of the inward protrusion of the downstream groove.

[0010] In the present invention, the outer surface of the upstream groove has an outward projection that the side plate abuts against, the outer surface of the downstream groove has an outward projection that the side plate abuts against, and the height of the outward projection of the upstream groove and the height of the outward projection of the downstream groove are the same.

[0011] The present invention is characterized by comprising an image forming unit that forms a toner image on a sheet, and a fixing unit that fixes the toner image formed by the image forming unit to the sheet. [Effects of the Invention]

[0012] According to the present invention, damage to the axial end of the fixing member can be suppressed. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic side view showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] This is a perspective view showing a fixing device according to one embodiment of the present invention. [Figure 3] This is a side view showing the side plate of the fixing housing of a fixing device according to one embodiment of the present invention. [Figure 4] This is a cross-sectional view showing a belt assembly and a pressure roller of a fixing device according to one embodiment of the present invention. [Figure 5] This is a perspective view showing a holding member of a fixing device according to one embodiment of the present invention. [Figure 6] This is a plan view showing a holding member of a fixing device according to one embodiment of the present invention. [Figure 7] This is a side view of the holding member of a fixing device according to one embodiment of the present invention, as seen from the upstream side. [Figure 8] This is a side view of the holding member of a fixing device according to one embodiment of the present invention, as seen from the downstream side. [Figure 9] This is a plan view showing a retaining member attached to a fixing housing in a fixing device according to one embodiment of the present invention. [Modes for carrying out the invention]

[0014] The following describes an image forming apparatus and a fixing apparatus according to one embodiment of the present invention, with reference to the drawings.

[0015] First, referring to FIG. 1, the overall configuration of the image forming apparatus 1 will be described. FIG. 1 is a front view schematically showing the internal configuration of the image forming apparatus 1. The reference signs Fr, Rr, L, R, Up, and Lo attached to the subsequent drawings indicate the front, rear, left, right, top, and bottom, respectively.

[0016] In the apparatus main body 3 of the image forming apparatus 1, there are provided a paper feed cassette 5 for accommodating paper, a paper feed device 7 for feeding out the paper from the paper feed cassette 5, an image forming unit 9 for forming a toner image on the paper by an electrophotographic method, a fixing device 11 for fixing the toner image on the paper, a discharge device 13 for discharging the paper, and a discharge tray 15 on which the discharged paper is stacked. Further, a registration roller pair 17 is disposed between the paper feed device 7 and the image forming unit 9.

[0017] The paper feed cassette 5 is accommodated in a cassette accommodating portion 3a provided at the lower part inside the apparatus main body 3. The paper feed device 7 is disposed above the front end portion of the cassette accommodating portion 3a. The registration roller pair 17 is disposed above the paper feed device 7. The image forming unit 9 is disposed behind the registration roller pair 17. The fixing device 11 is disposed behind the image forming unit 9. The discharge device 13 is disposed above the fixing device 11. The discharge tray 15 is provided on the upper surface of the apparatus main body 3.

[0018] Furthermore, in the apparatus main body 3, a main conveyance path 19a and a duplex conveyance path 19b for conveying the paper are formed. The main conveyance path 19a is formed along the conveyance direction X from the paper feed device 7 toward the discharge device 13 through the image forming unit 9 and the fixing device 11. In the following description, the upstream side and the downstream side indicate the upstream side and the downstream side in the conveyance direction X. The duplex conveyance path 19b branches off from the main conveyance path 19a on the downstream side of the fixing device 11 and merges into the main conveyance path 19a on the upstream side of the registration roller pair 17.

[0019] Next, the image forming operation will be briefly described. In the case of single-sided printing, the paper fed from the paper feed cassette 5 by the paper feeding device 7 is conveyed along the main conveyance path 19a. After the skew is corrected by the registration roller pair 17, it is conveyed to the image forming unit 9. In the image forming unit 9, a toner image is formed on the paper. The paper on which the toner image is formed is conveyed to the fixing device 11 along the main conveyance path 19a, and the toner image is fixed on the paper in the fixing device 11. The paper on which the toner image is fixed is discharged to the discharge tray 15 by the discharge device 13.

[0020] In the case of double-sided printing, the paper on which the toner image is fixed on one side of the paper by the fixing device 11 is switched back after passing through the fixing device 11 and conveyed to the duplex conveyance path 19b. The paper is conveyed along the main conveyance path 19a via the duplex conveyance path 19b. Then, after the skew of the paper is corrected by the registration roller pair 17, the toner image is transferred to the other side of the paper by the image forming unit 9. The paper on which the toner image is transferred is conveyed to the fixing device 11 along the main conveyance path 19a, and the toner image is fixed on the other side of the paper in the fixing device 11. The paper on which the toner image is fixed is conveyed to the discharge device 13 along the main conveyance path 19a and discharged to the discharge tray 15 by the discharge device 13.

[0021] Next, the fixing device 11 will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing the internal structure of the fixing device 11. The fixing device 11 includes a fixing housing 21, a belt assembly 23, and a pressure roller 25.

[0022] First, the fixing housing 21 will be described. The fixing housing 21 includes left and right side plates 31 facing each other in the left-right direction, and upper and lower stays 33 and front and rear stays 35 disposed between the left and right side plates 31. The left and right side plates 31 are supported in parallel by the upper and lower stays 33 and the front and rear stays 35. That is, the distance between the left and right side plates 31 is constant in the conveyance direction X. The fixing housing 21 is made of sheet metal.

[0023] The left and right side plates 31 will be described with reference to Figure 3. Figure 3 is a side view showing the left side plate 31. The side plate 31 is roughly rectangular in shape and has recesses 37 into which the ends of the belt assembly 23 and the pressure roller 25 are mounted. The recesses 37 are slightly inclined downstream from the upper edge of the side plate 31 downwards. The recesses 37 have, in the depth direction, an upper part 37a into which the end of the belt assembly 23 is mounted and a lower part 37b into which the end of the pressure roller 25 is mounted. The upstream and downstream side edges of the upper part 37a are formed parallel to each other. The belt assembly 23 is mounted on the upper part 37a along the mounting direction parallel to both side edges of the upper part 37a.

[0024] Next, the belt assembly 23 will be described with reference to Figure 4. Figure 4 is a cross-sectional view showing the belt assembly 23 and the pressure roller 25. The belt assembly 23 comprises a fixing belt 41, a heater 43 for heating the fixing belt 41, a heater holder 45 in which the heater 43 is housed, and left and right holding members 47 (not shown in Figure 4, see Figure 5) that hold the heater holder 45.

[0025] First, the fixing belt 41 will be described. The fixing belt 41 is formed in a cylindrical shape having a predetermined inner diameter and a width longer than the width of the paper. The fixing belt 41 is made of a flexible material and has a base layer, an elastic layer provided on the outer surface of the base layer, and a release layer provided on the outer surface of the elastic layer. The base layer is made of resin. The elastic layer is made of silicone rubber or the like. The release layer is made of PFA tubing or the like.

[0026] Next, the heater 43 will be described. The heater 43 is a rectangular plate-shaped surface heater 43. The surface heater 43 comprises a base material, an insulating layer, a heat-retaining resistor layer, and a coating layer. When current is passed through the heat-retaining resistor layer, the heat-retaining resistor layer generates heat.

[0027] Next, the heater holder 45 will be described. The heater holder 45 is formed in a substantially semi-cylindrical shape along the circumferential direction of the inner surface of the fixing belt 41 and has a width wider than the width of the fixing belt 41. A flat surface is formed at the top of the outer surface of the heater holder 45. A recess is formed in the flat surface in which the planar heater 43 is housed. The heater holder 45 is made of a heat-resistant resin such as liquid crystal polymer. The heater holder 45 is supported by the stay 46.

[0028] Next, the left and right retaining members 47 will be described with reference to Figures 5 to 8. Figure 5 is a perspective view of the retaining member 47, Figure 6 is a plan view of the retaining member 47 viewed from the upstream side, Figure 7 is a side view of the retaining member 47 viewed from the downstream side, and Figure 8 is a side view of the retaining member 47. Here, the left retaining member 47 will be described. The right retaining member 47 has the same function as the left retaining member 47. The retaining members 47 are made of a resin that has heat resistance and wear resistance.

[0029] The retaining member 47 has a substantially rectangular, flat end face 51, as shown in Figure 6. In the present invention, the end face 51 is an example of a restricting surface that restricts the axial movement of the fixing belt 41. Hereafter, the end face 51 will be referred to as the restricting surface 51. The restricting surface 51 has a substantially 3 / 4 arc-shaped opening (not shown) that is open at the bottom. A pivot support 53 is erected along the periphery of the opening. The pivot support 53 is formed in a substantially cylindrical shape with a substantially C-shaped cross-section that is open at the bottom. The axial direction of the pivot support 53 is perpendicular to the restricting surface 51. An insulating wall 55 is erected along the edges of the restricting surface 51, except for the bottom edge.

[0030] The left and right ends of the fixing belt 41 are inserted into the pivot portions 53 of the left and right holding members 47. The pivot portions 53 hold the fixing belt 41 in a substantially cylindrical shape and guide the fixing belt 41 so that it can rotate along the circumferential direction (rotational direction).

[0031] The holding member 47 has an upstream groove 59 and a downstream groove 61 formed on the side opposite the pivot support 53, with the regulating surface 51 in between, oriented in the vertical direction. As shown in Figure 6, the upstream groove 59 and the downstream groove 61 are arranged side by side in the conveying direction X, on the upstream and downstream sides of the pivot support 53. The openings of the upstream groove 59 and the downstream groove 61 face in opposite directions. That is, the opening of the upstream groove 59 faces the upstream side in the conveying direction X, and the opening of the downstream groove 61 faces the downstream side in the conveying direction X.

[0032] As shown in Figures 7 and 8, the upstream groove 59 and the downstream groove 61 have inner surfaces 59a and 61a on the side of the regulating surface 51, and outer surfaces 59b and 61b facing the inner surfaces 59a and 61a. The inner surfaces 59a and 61a and the outer surfaces 59b and 61b are parallel, and the distance between the two sides is wider than the thickness of the side plate 31 of the anchoring housing 21.

[0033] As shown in Figure 7, an inward projection 63 is formed at the upper end of the inner surface 59a of the upstream groove 59. The inward projection 63 is approximately rectangular in shape, and its end face is formed flat and parallel to the regulating surface 51. The lower surface of the inward projection 63 is inclined upward. The height H1 of the inward projection 63 is 0.25 mm in one example. In addition, an outward projection 65 is formed at the lower end of the outer surface 59b of the upstream groove 59. The outward projection 65 is also approximately rectangular in shape, and its end face is formed flat and parallel to the regulating surface 51. The lower surface of the outward projection 65 is inclined upward. The distance G1 between the end face of the outward projection 65 and the inner surface 59a is approximately equal to the thickness of the side plate 31 of the anchoring housing 21. A predetermined distance is maintained between the end face of the inward projection 63 and the end face of the outward projection 65.

[0034] As shown in Figure 8, an inward projection 67 is formed at the upper end of the inner surface 61a of the downstream groove 61. The inward projection 67 is approximately rectangular in shape, and its end face is formed flat and parallel to the regulating surface 51. The lower surface of the inward projection 67 is inclined upward. The height H2 of the inward projection 67 is 0.05 mm in one example, which is lower than the height H1 of the inward projection 63 of the upstream groove 59. In addition, an outward projection 69 is formed at the lower end of the outer surface 61b of the downstream groove 61. The outward projection 69 is also approximately rectangular in shape, and its end face is formed flat and parallel to the regulating surface 51. The lower surface of the outward projection 69 is inclined upward. The height of the outward projection 69 is equal to the height of the outward projection 65 of the upstream groove 59. The distance G1 between the end face of the outward projection 69 and the inner surface 61a is approximately equal to the thickness of the side plate 31 of the anchoring housing 21. A predetermined gap is maintained between the end face of the inward projection 67 and the end face of the outward projection 69.

[0035] Next, the pressure roller 25 will be described with reference to Figure 4. The pressure roller 25 has a rotating shaft, an elastic layer provided on the outer surface of the rotating shaft, and a release layer provided on the outer surface of the elastic layer.

[0036] Referring again to Figures 2 and 3, both ends of the rotating shaft of the pressure roller 25 are supported by the lower part 37b of the recesses 37 in the left and right side plates 31 of the fixing housing 21. A drive gear (not shown) is fixed to one end of the rotating shaft of the pressure roller 25. The drive gear is connected to a motor M (see Figure 2) via a gear train (not shown).

[0037] The left and right retaining members 47 of the belt assembly 23 are mounted on the upper part 37a of the recesses 37 of the left and right side plates 31 of the fixing housing 21, along the mounting direction. Specifically, the upstream side plate 31 (referred to as the upstream side plate 31U) and the downstream side plate 31 (referred to as the downstream side plate 31D) of the recess 37 are inserted into the upstream groove 59 and the downstream groove 61 of the retaining member 47. The upstream side plate 31U is inserted through the gap between the outward protrusion 65 and the inner surface 59a of the upstream groove 59 (see Figure 7), and the downstream side plate 31D is inserted through the gap between the outward protrusion 69 and the inner surface 61a of the downstream groove 61 (see Figure 8). Since the lower surfaces of the outward protrusions 65 and 69 are inclined upward, the upstream side plate 31U and the downstream side plate 31D are guided into the gap along their lower surfaces. Furthermore, the upstream side plate 31U is inserted through the gap between the inner protrusion 63 and the outer surface 59b of the upstream groove 59 (see Figure 7), and the downstream side plate 31D is inserted through the gap between the inner protrusion 67 and the outer surface 61b of the downstream groove 61 (see Figure 8). Since the lower surfaces of the inner protrusions 63 and 67 are also inclined upward, the upstream side plate 31U and the downstream side plate 31D are guided into the gap along their lower surfaces.

[0038] As shown in Figure 9, when the retaining member 47 is fully inserted into the upper part 37a of the recess 37, the upstream side plate 31U is fixed in place by being sandwiched between the outer protrusion 65 and the inner surface 59a of the upstream groove 59, and is pushed outward (away from the regulating surface 51) by the inner protrusion 63. In other words, the inner protrusion 63 is pushed inward (towards the regulating surface 51) relative to the side plate 31. Similarly, the downstream side plate 31D is fixed in place by being sandwiched between the outer protrusion 69 and the inner surface 61a of the downstream groove 61, and is pushed outward by the inner protrusion 67. In other words, the inner protrusion 67 is pushed inward relative to the side plate 31.

[0039] As mentioned above, the height H1 of the inner protrusion 63 of the upstream groove 59 is higher than the height H2 of the inner protrusion 67 of the downstream groove 61. Therefore, the distance over which the inner protrusion 63 of the upstream groove 59 is pushed inward is longer than the distance over which the inner protrusion 67 of the downstream groove 61 is pushed inward. As a result, the left and right retaining members 47 are mounted on the side plate 31 in a position where the regulating surface 51 is inclined outward in the axial direction of the pivot support 53, from the upstream side to the downstream side. In other words, as shown in Figure 9, the distance D1 between the regulating surfaces 51 downstream of the pivot support 53 is longer than the distance D2 between the regulating surfaces 51 upstream of the pivot support 53.

[0040] Furthermore, the stays 46 of the belt assembly 23 protrude through the openings of the left and right holding members 47 and are supported by the left and right side plates 31 of the fixing housing 21. The heater 43 held in the heater holder 45 faces the pressure roller 25 with the fixing belt 41 in between. As a result, a pressurized area is formed between the fixing belt 41 and the pressure roller 25.

[0041] The fixing operation of the fixing device 11 having the above configuration will now be described. When the motor M is driven and the pressure roller 25 rotates, the fixing belt 41 follows the pressure roller 25 and rotates in the opposite direction to the rotation of the pressure roller 25. Also, the heater 43 is driven and the fixing belt 41 is heated. When the sheet on which the toner image has been transferred is conveyed to the pressure area, the toner image is heated and fixed to the sheet.

[0042] While the fixing operation is being performed normally, both end faces of the fixing belt 41 do not contact the restricting surfaces 51 of the left and right holding members 47. However, differences in rotational speed may occur at both ends of the fixing belt 41 due to dimensional inaccuracies of the pressure rollers 25 and the fixing housing 21, or misalignment of the left and right holding members 47. In this case, the fixing belt 41 tilts with respect to the transport direction X such that the end with the faster rotational speed is on the downstream side in the transport direction. Specifically, at the end with the faster rotational speed, the downstream inner surface is guided along the pivot support 53, but the upstream inner surface lifts away from the pivot support 53. In addition, a force acts on the fixing belt 41 that moves it axially towards the end with the faster rotational speed. If the fixing belt 41 moves in the aforementioned position and comes into contact with the restricting surface 51, the end of the fixing belt 41 may break.

[0043] As described above, according to the present invention, since the spacing between the regulating surfaces 51 widens from the upstream side to the downstream side, even if the anchoring belt 41 moves in the axial direction, the end face of the anchoring belt 41 is less likely to come into contact with the downstream regulating surface 51. Therefore, damage to the end of the anchoring belt 41 can be suppressed.

[0044] Furthermore, the left and right side plates 31 of the fixing housing 21 are arranged parallel to each other along the transport direction X. In this way, no twisting force is applied to the left and right side plates 31, making it easy to assemble the fixing housing 21 and allowing the left and right holding members 47 and pressure rollers 25 to be stably supported by the fixing housing 21.

[0045] Furthermore, by simply changing the height of the internal protrusions 63 and 67 formed in the upstream groove 59 and downstream groove 61 of the retaining member 47, the distance between the regulating surfaces 51 of the left and right retaining members 47 can be widened from the upstream side to the downstream side.

[0046] In the above embodiment, the left and right holding members 47 were configured to be mounted on the side plate 31 in a position inclined outward in the axial direction of the pivot support 53, thereby making the distance D1 between the restricting surfaces 51 downstream of the pivot support 53 longer than the distance D2 between the restricting surfaces 51 upstream of the pivot support 53. However, instead of configuring the left and right holding members 47 to be mounted on the side plate 31 in such an inclined position, the restricting surfaces 51 may be formed to be inclined outward in the axial direction of the pivot support 53 from upstream to downstream. In this case, the axial direction of the pivot support 53 is not perpendicular to the restricting surfaces 51. In this example, the left and right holding members 47 are mounted on the side plate 31 in a position where the pivot support 53 is perpendicular to the conveying direction X, and the distance between the restricting surfaces 51 widens from upstream to downstream.

[0047] Although the present invention has been described in terms of specific embodiments, the present invention is not limited to the above embodiments. Those skilled in the art can modify the above embodiments without departing from the scope and spirit of the present invention. [Explanation of Symbols]

[0048] 1. Image forming apparatus 9 Image forming unit 11 Fixing device 25 Pressure Rollers 31 Side panel 41 Fixing member 47 Retaining member 51 Regulatory aspects 53 axis branch 59 Upstream ditch 59a Inside surface 59b External surface 61 Downstream groove 61a Inside surface 61b External surface 63, 67 Inward protrusion 65, 69 External convex part

Claims

1. A flexible, cylindrical fixing member that can rotate around its axis, A pressurizing member, which is rotatable around an axis, is provided between the fixing member and the sheet, and which forms a pressurizing region for heating and pressurizing the toner on the sheet while conveying the sheet in a predetermined conveying direction. A pair of holding members that hold both ends of the fixing member in the axial direction, Each of the pair of holding members has a recess into which it is mounted along a mounting direction intersecting the transport direction, and comprises a pair of side plates arranged parallel to the transport direction, Each of the pair of retaining members is A pivot support that guides one end of the fixing member in the axial direction along the rotational direction, A restricting surface that restricts the axial movement of the fixing member by contacting one end face of the fixing member in the axial direction, The shaft support is provided along the mounting direction on the upstream and downstream sides in the conveying direction, and the recess has an upstream groove and a downstream groove into which the side plate is fitted, The fixing device is characterized in that, when the pair of holding members are fitted into the upstream groove and the downstream groove and mounted in the recess, the distance between the regulating surfaces widens from the upstream side to the downstream side in the conveying direction.

2. Each of the upstream groove and the downstream groove has an inner surface on the regulating surface side and an outer surface that faces the inner surface with a gap wider than the thickness of the side plate. An inward protrusion is formed on the inner surface of the upstream groove, with which the side plate abuts. An inward protrusion is formed on the inner surface of the downstream groove, with which the side plate abuts. The fixing device according to claim 1, characterized in that the height of the internal protrusion of the upstream groove is higher than the height of the internal protrusion of the downstream groove.

3. The outer surface of the upstream groove has an outward protrusion that the side plate abuts against. The outer surface of the downstream groove has an outward protrusion that the side plate abuts against. The fixing device according to claim 2, characterized in that the height of the outward projection of the upstream groove and the height of the outward projection of the downstream groove are the same.

4. An image forming unit that forms a toner image on a sheet, An image forming apparatus characterized by comprising: a fixing device according to claim 1 for fixing a toner image formed in the image forming unit onto a sheet;

Images