Fixing apparatus and image forming apparatus

Abstract

To provide a fixing device that can prevent damage to the ends in an axial direction of a fixing member.SOLUTION: A fixing device comprises: a fixing belt that applies heat to a toner image on a sheet while rotating around an axis; a pressure roller that forms a pressure area with the fixing belt while rotating around an axis, and applies pressure to toner on the sheet passing through the pressure area; a pair of holding members 24 having shaft support parts 25 that rotatably guide both ends in an axial direction of the fixing belt around the axis, and regulation surfaces that are in contact with the ends in the axial direction of the fixing belt to regulate a movement in the axial direction of the fixing belt; and a frame 23 having a pair of side plates 30 that support the fixing belt with the pair of holding members 24 therebetween and rotatably support both ends in the axial direction of the pressure roller around the axis. The positions of attachment of the pair of holding members 24 to the pair of side plates 30 are provided so that the interval between the side plates on the upstream side becomes larger than the interval on the downstream side in a sheet passage direction across the pressure area.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] A fixing device including a film and a pressure roller that forms a nip portion in contact with the film is known (Patent Document 1). A regulating member having a regulating surface that restricts the movement of the film in the longitudinal direction and a guiding surface that guides the inner peripheral surface of the film is attached to the longitudinal end portion of the film. For example, when a rotational speed difference occurs between both ends in the longitudinal direction of the film, the side with a higher rotational speed of the film tilts downstream in the conveyance direction of the recording material, and the inner peripheral surface on the downstream side of the film may separate from the guiding surface. When the longitudinal end portion of the film contacts the regulating surface in a state where the inner peripheral surface of the film has separated from the guiding surface, the longitudinal end portion of the film may break or the like. In the fixing device described in Patent Document 1, the downstream side of the regulating surface is inclined so as to be away from the longitudinal end portion of the film, making it difficult for the longitudinal end portion of the film to contact the downstream side of the regulating surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the fixing device described above did not take into account the inclination of the regulating members at all. That is, if the regulating members on both sides in the longitudinal direction (axial direction) were mounted in an inclined position so that they approached each other from upstream to downstream in the direction of transport of the recording material, the longitudinal end of the film would be more likely to come into contact with the regulating surface, even if an inclination was formed on the downstream side of the regulating surface. Therefore, the inclination formed on the downstream side of the regulating surface was sometimes insufficient to prevent damage to the longitudinal end of the film.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can suppress damage to the axial end of the fixing member. [Means for solving the problem]

[0006] The fixing device of the present invention comprises: a fixing member formed in a flexible cylindrical shape and heating a toner image on a medium while rotating around an axis; a pressurizing member that rotates around an axis and forms a pressurizing region between itself and the fixing member, pressurizing the toner on the medium as it passes through the pressurizing region; a pair of holding members having shaft support portions that guide both axial ends of the fixing member so as to be rotatable around an axis, and restricting surfaces that restrict the axial movement of the fixing member by contacting the axial ends of the fixing member; and a frame having a pair of side plates that support the fixing member via the pair of holding members and rotatably support both axial ends of the pressurizing member, wherein the mounting positions of at least one pair of the holding members on the pair of side plates are arranged such that the spacing is wider downstream of the pressurizing region than upstream in the direction of passage of the medium.

[0007] In this case, the frame may have a first stay that is installed between a pair of side plates on the upstream side in the direction of passage, and a second stay that is longer in the axial direction than the first stay and is installed between the pair of side plates on the downstream side in the direction of passage than the first stay.

[0008] In this case, each of the side plates has a fitting groove cut from one end in the vertical direction perpendicular to the axial direction and the direction of passage toward the other, into which the retaining member is fitted. The first stay may be provided upstream of the fitting groove in the direction of passage, and the second stay may be provided downstream of the fitting groove in the direction of passage.

[0009] In this case, each of the side plates has a fitting groove cut from one end in the vertical direction perpendicular to the axial direction and the direction of passage toward the other, into which the retaining member is fitted, and the frame preferably has a connecting plate installed between one end of the pair of side plates in the vertical direction such that the distance between the pair of side plates downstream of the fitting groove in the direction of passage is wider than the distance between the pair of side plates upstream of the fitting groove in the direction of passage.

[0010] The image forming apparatus of the present invention includes any of the fixing devices described above. [Effects of the Invention]

[0011] According to the present invention, damage to the axial end of the fixing member can be suppressed. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram (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 schematic cross-sectional view showing a fixing device according to one embodiment of the present invention. [Figure 4] This is a plan view (cross-sectional view) showing the fixing belt of a fixing device according to one embodiment of the present invention. [Figure 5] This is a side view showing a holding member of a fixing device according to one embodiment of the present invention. [Figure 6] This is a cross-sectional view taken from VI-VI in Figure 5. [Figure 7] This is a side view showing the side plate, etc., of a fixing device according to one embodiment of the present invention. [Figure 8] This is a plan view showing the frame of a fixing device according to one embodiment of the present invention. [Figure 9] This is a plan view showing an enlarged portion of the frame of a fixing device according to one embodiment of the present invention. [Figure 10] This is a plan view showing the frame of a fixing device according to a modified example of one embodiment of the present invention. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the attached drawings. In the drawings, Fr, Rr, L, R, U, and D indicate front, back, left, right, up, and down, respectively. Furthermore, the front-to-back direction (direction of passage), left-to-right direction (axial direction), and up-to-down direction are mutually orthogonal. While this specification uses terms indicating direction and position, these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Also, "upstream" and "downstream," and similar terms, refer to the "upstream" and "downstream" directions (conveyor direction) of the paper P, and similar concepts. Note that in each figure, the dimensions and angles of the components are not precise but are schematic for illustrative purposes.

[0014] An image forming apparatus 1 according to an embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram (side view) of the image forming apparatus 1.

[0015] Image forming apparatus 1 is an electrophotographic printer. Image forming apparatus 1 comprises a main body 2 that has a roughly rectangular parallelepiped shape. A paper feed cassette 3 for storing paper P (medium) is detachably provided at the bottom of the main body 2. A paper output tray 4 is provided on the top surface of the main body 2. Note that the paper P, as an example of a medium, is not limited to paper, but may be a resin sheet or the like.

[0016] The image forming apparatus 1 includes a paper feeding device 5, an image forming device 6, and a fixing device 7. The paper feeding device 5 is provided at the upstream end of a conveyance path 9A extending from a paper feed cassette 3 to a paper discharge tray 4, and feeds the sheets of paper P accommodated in the paper feed cassette 3 one by one into the conveyance path 9A. The image forming device 6 is provided in the middle of the conveyance path 9A, and forms a toner image on the sheet of paper P being conveyed. The fixing device 7 is provided on the downstream side of the conveyance path 9A, and thermally fixes the toner image on the sheet of paper P.

[0017] In the conveyance path 9A, there is provided a registration roller pair 10A that temporarily blocks the sheet of paper P being conveyed to correct the inclination (skew correction) of the sheet of paper P. Below the conveyance path 9A, there is provided a reverse conveyance path 9B that branches off on the downstream side of the conveyance path 9A and merges with the upstream side of the conveyance path 9A. In the reverse conveyance path 9B, there are provided a plurality of conveyance roller pairs 10B for conveying the sheet of paper P.

[0018] The image forming device 6 has a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is disposed at the front upper part of the apparatus main body 2, and accommodates, for example, black toner (developer). The drum unit 12 has a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape, and is rotationally driven around its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged in order of the image forming process around the photosensitive drum 14. The transfer roller 17 forms a transfer nip by contacting the photosensitive drum 14 from below. The optical scanning device 13 is provided above the photosensitive drum 14, and emits scanning light toward the surface of the photosensitive drum 14.

[0019] [Image Forming Process] The operation of the image forming apparatus 1 will be described. A control device (not shown) that comprehensively controls the image forming apparatus 1 executes an image forming process as follows based on the image data input from an external terminal.

[0020] The charging device 15 charges the surface of the photoreceptor drum 14, and the light scanning device 13 emits scanning light based on the image data to form an electrostatic latent image on the photoreceptor drum 14. The developing device 16 develops a toner image on the photoreceptor drum 14 using toner supplied from the toner container 11. The paper feed device 5 feeds sheets of paper P one by one from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew corrected by the registration roller pair 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photoreceptor drum 14 to the surface of the paper P as it passes through the transfer nip. The fuser device 7 heat-fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fuser device 7 is discharged into the output tray 4.

[0021] In the case of double-sided printing, the paper P that has passed through the fuser unit 7 is switched back at the downstream end of the transport path 9A and sent to the reversal transport path 9B. The paper P is transported by the transport roller pair 10B, returned to the transport path 9A from the reversal transport path 9B, skew corrected by the registration roller pair 10A, and then sent to the transfer nip. After that, the toner image is transferred to the paper P, heat-fixed, and the double-sided printed paper P is discharged into the output tray 4.

[0022] [Fusing device] The fixing device 7 will be described with reference to Figures 2 to 7. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a schematic cross-sectional view showing the fixing device 7. Figure 4 is a plan view (cross-sectional view) showing the fixing belt 20. Figure 5 is a side view showing the holding member 24. Figure 6 is a cross-sectional view taken along line VI-VI in Figure 5. Figure 7 is a side view showing the side plate 30, etc.

[0023] As shown in Figures 2 and 3, the fixing device 7 comprises a fixing belt 20, a pressure roller 21, a heater 22, and a frame 23. The fixing belt 20 and the pressure roller 21 are supported by the frame 23, which is fixed to the device body 2. The heater 22 is located inside the fixing belt 20.

[0024] <Fixing belt> An example of a fixing member, the fixing belt 20, is an endless belt formed in a substantially cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of, for example, a synthetic resin that has heat resistance and flexibility (elasticity).

[0025] (Retaining member) As shown in Figure 4, a pair of retaining members 24 are attached to both the left and right ends of the anchoring belt 20. Each retaining member 24 has a pivot portion 25 and a flange portion 26, and is integrally molded from, for example, a synthetic resin having heat resistance and wear resistance. Since the pair of retaining members 24 are generally symmetrical in shape, the following description will mainly focus on one of the retaining members 24.

[0026] As shown in Figure 5, the pivot support portion 25 is formed in a roughly cylindrical shape with a roughly C-shaped cross-section, with the bottom (the side of the pressurized region N described later) open. The pivot support portion 25 is inserted inward from both ends of the anchoring belt 20 and holds the portion of the anchoring belt 20, excluding the lower surface which becomes the pressurized region N, in a roughly cylindrical shape (see also Figure 4). In addition, the pivot support portion 25 guides both axial ends of the anchoring belt 20 so that they can rotate around their axis.

[0027] As shown in Figures 5 and 6, the flange portion 26 is formed to extend radially from the axial outer end of the pivot support portion 25. An insulating wall 26A is formed on the outer edge of the flange portion 26, excluding the lower edge, so as to extend inward in the axial direction (see also Figure 4). The insulating wall 26A is formed in a roughly rectangular tubular shape with the bottom open. The insulating wall 26A is provided to increase the creepage distance from the substrate or the like placed near the retaining member 24 to the fixing belt 20. Insertion grooves 26B extending in the vertical direction are recessed on both the left and right end faces of the flange portion 26 of the retaining member 24 (see Figures 4 and 6). In addition, the axial inner end face of the flange portion 26 is a restricting surface 27 that the end of the fixing belt 20 can contact. As will be described in detail later, the restricting surface 27 restricts the axial movement of the fixing belt 20 by contacting the axial end of the fixing belt 20.

[0028] As shown in Figure 3, a support member 28 is provided inside the fixing belt 20. The support member 28 is formed from a metal material such as stainless steel and is shaped like a roughly rectangular tube that is long in the left-right direction (axial direction). The support member 28 is installed between a pair of holding members 24 (axis support 25). A heater holder 29 is fixed to the lower part of the support member 28. The heater holder 29 is formed from a synthetic resin that has heat resistance and wear resistance and is shaped like a roughly semi-cylindrical shape that is long in the left-right direction. The heater holder 29 is in contact with the lower inner circumferential surface of the fixing belt 20 (the inner circumferential surface on the pressure roller 21 side).

[0029] <Pressure Roller> As shown in Figures 2 and 3, a pressure roller 21, as an example of a pressure member, is formed in a roughly cylindrical shape that is long in the left-right direction. The pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on its outer surface. A drive motor M is connected to the left end of the core 21A via a gear train (not shown). The pressure roller 21 contacts the fixing belt 20 from below, forming a pressure region N between it and the fixing belt 20. The pressure region N refers to the area from the upstream position where the pressure is 0 Pa, through the position where pressure is applied, to the downstream position where the pressure becomes 0 Pa again.

[0030] <Heater> As shown in Figure 3, the heater 22 is formed in a roughly rectangular plate shape that is elongated in the left-right direction and is fixed to the lower surface of the heater holder 29. The heater 22 has a heating resistor (not shown) that is laminated on the substrate and generates heat when energized. The heater 22 has the heating resistor in contact with the inner circumferential surface of the fixing belt 20 at a position corresponding to the pressurized area N.

[0031] <frame> The frame 23 is made of a metal material such as steel or stainless steel. As shown in Figure 2, the frame 23 is a box-shaped structure having a pair of side plates 30, first to third stays 31 to 33, and a connecting plate 34. Since the pair of side plates 30 are generally symmetrical, the following description will mainly focus on one side plate 30.

[0032] (Side panel) The pair of side plates 30 are formed, for example, by bending sheet metal to create a nearly upright plate shape. The pair of side plates 30 are arranged facing each other in the left-right direction, with the fixing belt 20 and the like in between. The fixing belt 20 and the pressure roller 21 are installed between the pair of side plates 30.

[0033] As shown in Figure 7, the side plate 30 has a fitting groove 35 cut from the upper end (one end in the vertical direction) downward (the other end). The fitting groove 35 is formed in the middle of the side plate 30 in the front-rear direction, and the side plate 30 is formed so that the rear side of the fitting groove 35 (downstream side in the direction of passage) is higher than the front side of the fitting groove 35 (upstream side in the direction of passage). A pair of left and right protrusions 36 are formed to protrude upward from the upper end of the side plate 30 separated by the fitting groove 35.

[0034] The fitting groove 35 is formed to have a downward slope from front to back (from upstream to downstream in the direction of passage). The core metal 21A of the pressure roller 21 and the retaining member 24 of the fixing belt 20 are fitted into the fitting groove 35. In detail, the end of the core metal 21A is inserted into the fitting groove 35 from above and is supported so as to be rotatable around its axis at the lower part of the fitting groove 35. After the end of the core metal 21A is inserted into the fitting groove 35, the retaining member 24 is inserted into the fitting groove 35. The side edges 35A and 35B of the fitting groove 35 are relatively inserted into the insertion groove 26B (see Figure 6) of the retaining member 24. The fixing belt 20 is supported by a pair of side plates 30 via a pair of retaining members 24 (see Figure 2). Each retaining member 24 is pressed downward by an elastic member (not shown), such as a compression spring, and the fixing belt 20 is held in contact with the pressure roller 21.

[0035] (Stages 1-3) The first to third stays 31 to 33 are formed, for example, by bending sheet metal. As shown in Figures 2 and 7, the first to third stays 31 to 33 connect a pair of side plates 30 and maintain a constant distance between the pair of side plates 30. The first stay 31 is installed between the pair of side plates 30 at the front (upstream side). The second stay 32 is installed between the pair of side plates 30 at the rear (downstream side) of the first stay 31. The third stay 33 is installed between the pair of side plates 30 midway between the first stay 31 and the second stay 32. In detail, the first stay 31 is located in front of the fitting groove 35 (upstream side) and below the side plate 30. The second stay 32 is located behind the fitting groove 35 (downstream side) and above the side plate 30. The third stay 33 is located diagonally forward and downward from the lower end of the fitting groove 35. The left and right ends of the first to third stays 31 to 33 are fixed to a pair of side plates 30 with screws (not shown).

[0036] (Connection plate) As shown in Figure 2, the connecting plate 34 is formed, for example, by bending sheet metal, and when viewed from the side, it is shaped like a crank with a pair of horizontal surfaces of different heights connected by a vertical surface. Each horizontal surface of the connecting plate 34 has four engagement holes 37 on both the left and right sides. The connecting plate 34 is installed between the upper ends of a pair of side plates 30 (between one end in the vertical direction) by passing each projection 36 of the pair of side plates 30 through the respective engagement holes 37. Each engagement hole 37 is sized to allow the projection 36 to be loosely inserted. The connecting plate 34 is then fixed to the pair of side plates 30 with screws (not shown).

[0037] Furthermore, the frame 23 (for example, the second stay 32) is provided with a temperature sensor (not shown) for detecting the surface temperature of the fixing belt 20. The drive motor M, heater 22, and temperature sensor, etc., are electrically connected to the control device of the image forming apparatus 1 via various drive circuits (not shown) and controlled as appropriate.

[0038] [Function of the fixing device] Here, the operation of the fixing device 7 (fixing process) will be explained. The pressure roller 21 rotates under the driving force of the drive motor M, and the fixing belt 20 rotates in accordance with the pressure roller 21 (see arrow in Figure 3). The heater 22 heats the fixing belt 20. The control device receives a detection signal from the temperature sensor and starts executing the image forming process described earlier while controlling the heater 22 to maintain a preset temperature.

[0039] The paper P onto which the toner image has been transferred enters the frame 23. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressurized area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressurized area N while rotating around its axis. As a result, the toner image is fixed to the paper P. The paper P with the fixed toner image is then sent out of the frame 23 and discharged into the output tray 4.

[0040] [Pulling force and damage to the fixing belt] Incidentally, when the anchoring belt 20 rotates under a uniform force in the left-right direction (axial direction), no force is generated that moves the anchoring belt 20 in the axial direction (hereinafter referred to as "pushing force"). The axial ends of the anchoring belt 20 do not come into contact with the restricting surfaces 27 of the pair of holding members 24 (see solid lines in Figure 4).

[0041] However, if the outer diameter of the pressure roller 21 is not uniform, or if the biasing force of the pair of elastic members that bias the pair of holding members 24 is not uniform, a difference in rotational speed will occur between the left and right sides of the fixing belt 20, causing an uneven force to act on the fixing belt 20. For example, if the rotational speed on the left side is faster than on the right side (greater conveying force) (see the white arrow (solid line) in Figure 4), the fixing belt 20 will be tilted more downstream on the left side than on the right side (see the dashed line in Figure 4). As a result, the inner circumferential surface on the left side of the fixing belt 20 is guided upstream of the pivot support 25, and the inner circumferential surface on the right side of the fixing belt 20 is guided downstream of the pivot support 25. When the rotational direction (F1) of the fixing belt 20 is tilted with respect to the passage direction (F0) of the paper P, a component force (F2) acts on the fixing belt 20, attempting to move it to the left (towards the faster rotational speed). This component force (F2) is the pulling force, which moves the anchoring belt 20 to the left (see the white arrow (dotted line) in Figure 4). The left end of the anchoring belt 20 comes into contact with the restricting surface 27 of the holding member 24, restricting its movement to the left (see the dotted line in Figure 4).

[0042] In this case, as shown by the dashed line in Figure 5, the inner surface on the left side of the anchoring belt 20 is guided upstream of the pivot support 25 and is lifted (separated) from the downstream side of the pivot support 25. If the left end of the anchoring belt 20 comes into contact with the regulating surface 27 while the inner surface of the anchoring belt 20 is lifted from the pivot support 25, the left side of the anchoring belt 20 may break, such as by bending.

[0043] [Position of the retaining member] Therefore, in the fixing device 7 according to this embodiment, the mounting positions (fitting grooves 35) of the pair of retaining members 24 on the pair of side plates 30 are arranged such that the spacing between them is wider downstream than upstream in the direction of passage of the paper P, with the pressurized area N in between. As a result, the pair of retaining members 24 are in an inclined position such that, when viewed from a planar perspective, they move away from each other from the upstream side to the downstream side.

[0044] The structure for positioning the pair of holding members 24 in an inclined position will be described in detail below with reference to Figures 8 and 9. Figure 8 is a plan view showing the frame 23. Figure 9 is a plan view showing an enlarged portion of the frame 23.

[0045] As shown in Figure 8, in the fixing device 7 according to this embodiment, the second stay 32 of the frame 23 is formed to be longer in the left-right direction (axial direction) than the first stay 31. The length L2 of the second stay 32 is, for example, about 0.5 to 2.0 mm longer than the length L1 of the first stay 31. The third stay 33 is formed to be the same length as the second stay 32.

[0046] When the pair of side plates 30 are fixed to the axial ends of the first to third stays 31 to 33, the pair of side plates 30 are inclined to move away from each other from the first stay 31 to the third stay 33 when viewed from a planar (or bottom) surface, and are approximately parallel from the third stay 33 to the second stay 32. In other words, the pair of side plates 30 are spaced apart gradually from the left end (upstream end) to the fitting groove 35 (upstream side edge 35A), and are spaced at a constant distance from the fitting groove 35 (downstream side edge 35B) to the right end (downstream end). That is, the spacing on the downstream side of the pair of side plates 30 is wider than the spacing on the upstream side. Also, as shown in Figure 9, the downstream side edge 35B of each fitting groove 35 is shifted outward in the axial direction compared to the upstream side edge 35A. The displacement G between the downstream side edge 35B and the upstream side edge 35A is, for example, about 0.5 to 1.0 mm. Furthermore, the inclination angle of each holding member 24 is, for example, about 0.5 to 2 degrees, which is an angle that does not hinder the rotation of the fixing belt 20.

[0047] In the fixing device 7 according to the embodiment described above, a pair of retaining members 24 are fitted into a pair of fitting grooves 35 whose downstream edges 35B are shifted outward, so that they are positioned in an inclined position so that they move away from each other from the upstream side to the downstream side (see Figures 8 and 9). With this configuration, the distance between both ends of the fixing belt 20 in the axial direction and the pair of restricting surfaces 27 can be made wider on the downstream side than on the upstream side. As a result, even if the fixing belt 20 moves in the axial direction, the ends of the fixing belt 20 are less likely to come into contact with the downstream side of the restricting surfaces 27 of the retaining members 24, thereby suppressing damage to the ends of the fixing belt 20.

[0048] Furthermore, in the anchoring device 7 according to this embodiment, the first to third stays 31 to 33 are installed between a pair of side plates 30 at intervals in the direction of passage, connecting the pair of side plates 30. With this configuration, the frame 23 forms a generally box-shaped structure, and the rigidity (strength) of the frame 23 can be increased compared to when the frame 23 is composed only of a pair of side plates 30. As a result, the pair of side plates 30 (holding members 24) can be held in a position where they are spread out more on the downstream side than on the upstream side.

[0049] In the fixing device 7 according to this embodiment, when viewed from above, the pair of side plates 30 are inclined upstream of the fitting groove 35 and substantially parallel downstream of the fitting groove 35. However, the present invention is not limited to this. For example, only the vicinity of the fitting groove 35 of the pair of side plates 30, which is the mounting position for the pair of retaining members 24, may be inclined, and the upstream and downstream sides of the pair of side plates 30 may be substantially parallel (not shown). Alternatively, for example, the entire pair of side plates 30 may be inclined so that they move away from each other from the upstream side to the downstream side (not shown). In other words, the mounting positions of at least one pair of retaining members 24 on the pair of side plates 30 should be spaced further apart downstream than upstream in the direction of passage.

[0050] Furthermore, in the fixing device 7 according to this embodiment, the connecting plate 34 was installed between the upper ends of a pair of side plates 30, but the present invention is not limited thereto. For example, each projection 36 may be formed on the lower end of the side plate 30, and the connecting plate 34 may be installed between the lower ends of a pair of side plates 30 (not shown). Note that the connecting plate 34 may be omitted (not shown).

[0051] Furthermore, in the fixing device 7 according to this embodiment, the second stay 32 is formed to be longer than the first stay 31, and the third stay 33 is formed to be the same length as the second stay 32, but the present invention is not limited thereto. For example, the stays may be formed to be longer in the order of the first stay 31, the third stay 33, and the second stay 32 (not shown).

[0052] [Differentiation] Referring to Figure 10, the modified fixing device 7 will be described. Figure 10 is a plan view showing the frame 23 of the modified fixing device 7. Note that the same explanation as that given for the fixing device 7 above will be omitted in the following description.

[0053] In the modified fixing device 7, the second and third stays 32 and 33 are formed to the same length as the first stay 31, and the opening positions of the engagement holes 38 of the connecting plate 34 are different. Specifically, the pair of left and right engagement holes 38 that open on the downstream side are formed to be shifted outward in the left-right direction (axial direction) than the pair of left and right engagement holes 38 that open on the upstream side. In other words, the distance S2 between the pair of engagement holes 38 on the downstream side is wider than the distance S1 between the pair of engagement holes 38 on the upstream side (S2 > S1). The connecting plate 34 is installed between the upper ends of a pair of side plates 30 by passing each projection 36 through each engagement hole 38 while opening the downstream side of the pair of side plates 30 outward in the left-right direction (or narrowing the upstream side inward in the left-right direction). Each engagement hole 38 is formed to a size that prevents the inserted projection 36 from rattling.

[0054] According to the modified fixing device 7 of this embodiment, the connecting plate 34 is installed between the upper ends of the pair of side plates 30, which allows the distance between the pair of side plates 30 downstream of the fitting groove 35 to be wider than the distance between the pair of side plates 30 upstream of the fitting groove 35. This allows the pair of holding members 24 to be arranged in an inclined position so that they move away from each other from upstream to downstream in the direction of passage. As a result, the ends of the fixing belt 20 are less likely to come into contact with the downstream side of the restricting surface 27 of the holding member 24, thus suppressing damage to the ends of the fixing belt 20, and other effects similar to those of the fixing device 7 described above can be obtained.

[0055] In the modified fixing device 7, the first to third stays 31 to 33 were all formed to the same length. However, this is not limited to this configuration, and the second to third stays 32 to 33 may be formed to be longer than the first stay 31, similar to the fixing device 7 described earlier (not shown). Also, the third stay 33 may be omitted (not shown).

[0056] In this embodiment (including modified versions; the same applies hereinafter), the fixing device 7 had a fitting groove 35 cut downward from the upper end of the side plate 30, but the present invention is not limited to this. The fitting groove 35 may also be cut upward from the lower end of the side plate 30 (not shown).

[0057] Furthermore, in the fixing device 7 according to this embodiment, the connecting plate 34 was connected to the side plate 30 by screwing the projection 36 through the engagement holes 37 and 38, but the present invention is not limited thereto. For example, the projection 36 and engagement holes 37 and 38 may be omitted, and the connecting plate 34 may be connected to the side plate 30 by means of adhesive or welding (not shown).

[0058] Furthermore, in the fixing device 7 according to this embodiment, the fixing belt 20 and the pressure roller 21 were supported in the fitting groove 35, but the device is not limited to this, and for example, the pressure roller 21 may be rotatably supported on the side plate 30 at a position different from the fitting groove 35 (not shown).

[0059] Furthermore, while the above description of the embodiments shows the application of the present invention to a monochrome image forming apparatus 1 as an example, the invention is not limited to this, and may also be applied to, for example, a color printer, copier, facsimile, or multifunction device.

[0060] The above description of the embodiments illustrates one aspect of the fixing apparatus and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiments. The present invention may be modified, substituted, or transformed in various ways without departing from the spirit of the technical idea, and the claims include all embodiments that may fall within the scope of the technical idea. [Explanation of symbols]

[0061] 1. Image forming apparatus 7. Fixing device 20 Fixing belt (fixing member) 21 Pressure roller (pressure component) 24 Retaining member 35 Fitting groove 25 axis branch 27. Regulatory aspects 23 frames 30 Side panels 31 First Stage 32 Second Stage 34 Connecting plate P Paper (medium)

Claims

1. A fixing member formed in a flexible cylindrical shape, which heats the toner image on the medium while rotating around its axis, A pressurizing member that rotates around an axis, forming a pressurized region between itself and the fixing member, and pressurizing the toner on the medium as it passes through the pressurized region, A pair of holding members having shaft support portions that guide both axial ends of the fixing member so as to be rotatable around an axis, and regulating surfaces that restrict the axial movement of the fixing member by contacting the axial ends of the fixing member, The device comprises a frame having a pair of side plates that support the fixing member via a pair of holding members and that rotatably support both axial ends of the pressing member around an axis, The mounting positions of at least one pair of the retaining members on the pair of side plates are arranged such that the spacing between them is wider downstream of the medium passage direction, with respect to the pressurized region in between. The aforementioned frame is A first stay is installed between a pair of side plates on the upstream side in the direction of passage, An anchoring device characterized by having a second stay that is longer in the axial direction than the first stay and is installed between a pair of side plates downstream of the first stay in the direction of passage.

2. Each of the aforementioned side plates has a fitting groove cut from one end toward the other in the vertical direction perpendicular to the axial direction and the direction of passage, into which the retaining member is fitted. The first stay is provided upstream of the fitting groove in the direction of passage, The fixing device according to claim 1, characterized in that the second stay is provided downstream of the fitting groove in the direction of passage.

3. Each of the aforementioned side plates has a fitting groove cut from one end toward the other in the vertical direction perpendicular to the axial direction and the direction of passage, into which the retaining member is fitted. The fixing device according to claim 1 or 2, characterized in that the frame has a connecting plate installed between one of the vertical ends of the pair of side plates such that the distance between the pair of side plates downstream of the fitting groove is wider than the distance between the pair of side plates upstream of the fitting groove in the direction of passage.

4. A fixing member formed in a flexible cylindrical shape, which heats the toner image on the medium while rotating around an axis, A pressurizing member that rotates around an axis, forming a pressurized region between itself and the fixing member, and pressurizing the toner on the medium as it passes through the pressurized region, A pair of holding members having shaft support portions that guide both axial ends of the fixing member so as to be rotatable around an axis, and regulating surfaces that restrict the axial movement of the fixing member by contacting the axial ends of the fixing member, The device comprises a frame having a pair of side plates that support the fixing member via a pair of holding members and that rotatably support both axial ends of the pressing member around an axis, The mounting positions of at least one pair of the retaining members on the pair of side plates are such that the spacing between them is wider downstream of the medium passage direction, with respect to the pressurized area. Each of the aforementioned side plates has a fitting groove cut from one end toward the other in the vertical direction perpendicular to the axial direction and the direction of passage, into which the retaining member is fitted. The anchoring device is characterized in that the frame has a connecting plate installed between one of the vertical ends of a pair of side plates such that the distance between the pair of side plates downstream of the fitting groove in the direction of passage is wider than the distance between the pair of side plates upstream of the fitting groove in the direction of passage.

5. An image forming apparatus characterized by comprising a fixing device according to any one of claims 1 to 4.

Images