Fixing device

Abstract

To reduce an amount by which a pressure arm protrudes outward of a pressure spring in a direction orthogonal to the biasing direction of the pressure spring.SOLUTION: A fixing device 1 comprises: a pressure arm 60 and a pressure spring 70 that press a first member (heating unit 2) against a second member (pressure roller 3); a cam 80 that presses the pressure arm 60 resisting against the biasing force of the pressure spring 70; and a frame 4. The frame 4 includes a rail that supports the first member in such a way as to be movable in a prescribed direction, and a first spring hook 41E which one end of the pressure spring 70 is hooked on. The pressure arm 60 includes a body part 61, a supported part 62 that is located at one end of the body part 61, and a first and a second tip part 63, 64 that are located at the other end of the body part 61. The supported part 62 is rotatably supported to the frame 4. The first tip part 63 has a pressed surface F2 that is pressed by the cam 80. The second tip part 64 extends in a direction different from the first tip part 63, and has a second spring hook 64A which the other end of the pressure spring 70 is hooked on.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a sheet. [Background technology]

[0002] A known fixing device includes a pressure arm that presses a heat unit against a pressure roller, a pressure spring that urges the pressure arm toward the pressure roller, and a cam that urges the pressure arm against the urging force of the pressure spring (see Patent Document 1). In this technology, the base end of the pressure arm is rotatably supported by a frame.

[0003] The tip of the pressure arm has a spring hook on which one end of the pressure spring is hooked and a pressed surface that is pressed by the cam. The spring hook and the pressed surface are aligned in a direction perpendicular to the biasing direction of the pressure spring. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-194541 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional technology, the pressed surface and the spring hook are aligned in a direction perpendicular to the biasing direction of the pressure spring, which creates the problem that the pressure arm protrudes farther outward than the pressure spring in a direction perpendicular to the biasing direction of the pressure spring.

[0006] Therefore, an object of the present invention is to reduce the amount by which the pressure arm protrudes outward beyond the pressure spring in a direction perpendicular to the biasing direction of the pressure spring. [Means for solving the problem]

[0007] In order to solve the above problem, the fixing device of the present invention includes a first member having a belt, a second member that sandwiches a sheet between the first member and the second member, a pressure arm that presses the first member toward the second member, a pressure spring that urges the pressure arm toward the second member, a cam that presses the pressure arm against the urging force of the pressure spring, and a frame. The frame supports the first member, the second member, and the pressure spring, and rotatably supports the pressure arm and the cam. The frame has a rail that supports the first member movably in a predetermined direction, a first support part that supports the pressure arm rotatably about a first axis, a second support part that supports the cam rotatably about a second axis different from the first axis, and a first spring hook on which one end of the pressure spring is hooked. The pressure arm has a main body portion, a supported portion, a first tip portion, and a second tip portion. The main body has a first end and a second end, and a pressure surface between the first end and the second end that presses the first member. The supported portion is supported by the first supporting portion and is located at the first end of the main body portion. The first tip is located at the second end of the main body and has a pressed surface that is pressed by the cam. The second tip is located at the second end of the main body, extends in a different direction from the first tip, and has a second spring hook on which the other end of the pressure spring is hooked.

[0008] With this configuration, the pressure arm has a first tip end portion having a pressure-receiving surface and a second tip end portion having a second spring hook, so the pressure-receiving surface and the second spring hook can be aligned in a direction substantially parallel to the biasing direction of the pressure spring, thereby reducing the amount by which the pressure arm protrudes outward from the pressure spring in a direction perpendicular to the biasing direction of the pressure spring.

[0009] The first member may have a heater that heats the sheet.

[0010] The second member may also be a rotatable roller.

[0011] Furthermore, the frame may have a base that supports the second member, and the rail may have a first extension extending from the base to one side in the specified direction, and a second extension extending from the base to one side in the specified direction, the second extension being spaced apart from the first extension in a direction along the first axis and a direction perpendicular to the specified direction, and the distance from the first axis to the base end of the first extension in the specified direction may be smaller than the distance from the first axis to the tip of the first extension.

[0012] According to this configuration, the first support portion is disposed at the base of the rail where strength can be more easily ensured than at the tip, so distortion of the frame due to the spring force of the pressure spring acting on the pressure arm can be suppressed.

[0013] Furthermore, in the predetermined direction, the distance from the second spring hook to the second shaft may be smaller than the distance from the first spring hook to the second spring hook.

[0014] Furthermore, in the predetermined direction, the distance from the second spring hook to the second shaft may be smaller than the distance from the second spring hook to the first shaft.

[0015] Furthermore, the second spring hook and the pressed surface may face each other in the predetermined direction.

[0016] Furthermore, the pressure arm may not have a portion located on a line segment that is along the predetermined direction and that connects the second spring hook and the pressed surface.

[0017] Furthermore, in the specified direction, the second spring hook may be located between the second axis and the first axis, and in the specified direction, the first axis may be located between the first spring hook and the second spring hook, and the first spring hook and the second spring hook may be aligned in the specified direction.

[0018] The pressed surface may be substantially parallel to a normal to a circle having the first axis as its center at an intersection of the pressed surface and the circle.

[0019] The second member may be a roller that is rotatable around a third axis, and the first axis may be located between the third axis and the second axis in the predetermined direction.

[0020] Furthermore, the distance from the first shaft to the pressure surface may be smaller than the distance from the first shaft to the second spring hook.

[0021] Furthermore, the pressure surface may be located between the first axis and the second spring hook in a direction perpendicular to the direction along the first axis and the predetermined direction. [Effects of the Invention]

[0022] According to the present invention, the amount by which the pressure arm protrudes outward beyond the pressure spring in the direction perpendicular to the biasing direction of the pressure spring can be reduced. [Brief explanation of the drawings]

[0023] [Figure 1] 1A is a cross-sectional view showing a fixing device according to an embodiment, and FIG. 1B is an enlarged cross-sectional view showing the periphery of a heater. [Figure 2] (a) is a diagram showing the surface on which the heater's resistance heating element is arranged, (b) is a diagram of the heater and heat conduction member seen from the back side of the heater, and (c) is a cross-sectional view of the heater etc. cut longitudinally. [Figure 3] FIG. 2 is a cross-sectional view showing the nip pressure changing mechanism, illustrating a state in which the nip pressure becomes a first nip pressure. [Figure 4] FIG. 10 is a cross-sectional view showing the nip pressure changing mechanism, illustrating a state in which the nip pressure becomes a second nip pressure. [Figure 5] FIG. 2 is an exploded perspective view showing a frame and a part of a nip pressure change mechanism. [Figure 6] FIG. 2 is a perspective view showing a first frame. [Figure 7] FIG. 2 is a side view showing the first frame. [Figure 8] FIG. 2(a) is a diagram showing the positional relationship of each member, and FIG. 2(b) is a diagram showing an enlarged view of the first tip portion and the second tip portion. DETAILED DESCRIPTION OF THE INVENTION

[0024] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. As shown in Fig. 1(a), the fixing device 1 is a device that fixes a toner image on a sheet S. The fixing device 1 is installed in an image forming apparatus such as a printer. The fixing device 1 includes a heating unit 2 as an example of a first member, a pressure roller 3 as an example of a second member, and a frame 4.

[0025] The pressure roller 3 is rotatable about a third axis X3, and is capable of sandwiching the sheet S between itself and the heating unit 2. The pressure roller 3 has a cylindrical shaft 3A and a cylindrical roller portion 3B. The shaft 3A is made of, for example, metal. The roller portion 3B is made of, for example, rubber. The roller portion 3B covers a portion of the shaft 3A.

[0026] The heating unit 2 includes a heater 10, a holder 20, a heat conductive member 30, a stay ST, and a belt BL. The heater 10 heats the sheet S via the belt BL.

[0027] As shown in FIG. 1(b), the heater 10 has a substrate 11, a resistance heating element 12 supported by the substrate 11, and a cover 13. The substrate 11 is made of a long, narrow rectangular ceramic plate made of aluminum oxide. The heater 10 is a so-called ceramic heater. The resistance heating element 12 is formed by printing on one surface of the substrate 11. As shown in FIG. 2(a), in this embodiment, two resistance heating elements 12 are provided. The two resistance heating elements 12 are each elongated in the longitudinal direction of the heater 10 and arranged parallel to each other and spaced apart in the lateral direction perpendicular to the longitudinal direction. A conductor 19A is connected to one end 12A of each resistance heating element 12, and a power supply terminal 18 is provided at each end of the conductor 19A to supply power to the resistance heating element 12.

[0028] The power supply terminal 18 is electrically connected to the resistance heating element 12 via a conductor 19A. The power supply terminal 18 is located at one longitudinal end 11E of the substrate 11. As shown in FIG. 2(c), a connector C that supplies electricity to the heater 10 is connected to the power supply terminal 18. The connector C is detachable from one longitudinal end of the heater 10. For convenience, the resistance heating element 12, cover 13, and belt BL are not shown in FIG. 2(c).

[0029] The other ends 12B of the resistance heating elements 12 are connected to each other by conductive wires 19B. The number of resistance heating elements 12 is not particularly limited. Alternatively, a resistance heating element having a larger heat generation amount at the longitudinal center than at the longitudinal ends and a resistance heating element having a larger heat generation amount at the longitudinal ends than at the longitudinal center may be provided, and the heat generation distribution in the longitudinal direction may be adjusted by individually controlling each resistance heating element.

[0030] 1(b), the cover 13 covers the resistance heating element 12. The cover 13 is made of, for example, glass.

[0031] 1(a), the holder 20 has a function of supporting the heater 10 and guiding the belt BL. The holder 20 is made of, for example, resin.

[0032] The stay ST supports the holder 20. The stay ST is made of, for example, metal.

[0033] The belt BL is endless and made of metal or resin. The belt BL rotates around the heater 10 while being guided by the holder 20. The belt BL has an outer peripheral surface and an inner peripheral surface. The outer peripheral surface comes into contact with the pressure roller 3 or the sheet to be heated. The inner peripheral surface comes into contact with the heater 10.

[0034] The heat conducting member 30 is a member that conducts heat in the longitudinal direction of the heater 10 to make the temperature of the heater 10 uniform in the longitudinal direction. The heat conducting member 30 is a plate-shaped member that is located between the heater 10 and the holder 20. When the heating unit 2 sandwiches the sheet S between itself and the pressure roller 3, the heat conducting member 30 is sandwiched between the heater 10 and the holder 20. The heat conducting member 30 is made of, for example, aluminum.

[0035] 2(a) and 2(b), one end 12A and the other end 12B of the resistance heating element 12 are located, in the longitudinal direction, outside the maximum width W1 of the sheet that can be used in the heating unit 2 and inside one end 30A and the other end 30B of the heat conducting member 30. In other words, the length of the heat conducting member 30 is longer than the length of the resistance heating element 12 in the longitudinal direction.

[0036] In the longitudinal direction, the length of substrate 11 is longer than the length of heat conduction member 30. One end 30A of heat conduction member 30 is located inside one end 11A of substrate 11 in the longitudinal direction. The other end 30B of heat conduction member 30 is located outside the other end 11B of substrate 11 in the longitudinal direction.

[0037] 5, the frame 4 has a first frame 41 and a second frame 42. The first frame 41 supports the heating unit 2 and the pressure roller 3. The second frame 42 is attached to the first frame 41 so as to cover the heating unit 2 from the side opposite the pressure roller 3.

[0038] 6, the first frame 41 has a base 41A and rails 41B. The base 41A has recesses A1 that support the pressure roller 3 via bearings BR (see FIG. 5). The recesses A1 are located at both ends of the base 41A in the axial direction of the pressure roller 3.

[0039] The rail 41B supports the heating unit 2 so that it can move in a predetermined direction. In the following description, the axial direction of the pressure roller 3 will also be simply referred to as the "axial direction." The conveying direction of the sheet S at the nip portion will also be simply referred to as the "conveying direction." In this embodiment, the conveying direction of the sheet S at the nip portion is perpendicular to the axial direction and the predetermined direction. In addition, in the drawings, the arrow indicating the direction will point to one side. In particular, the arrow indicating the conveying direction will point to the downstream side of the conveying direction.

[0040] The rails 41B are disposed at one end and the other end of the base 41A in the axial direction. The rails 41B have a first extending portion B1 and a second extending portion B2. The first extending portion B1 extends from the base 41A to one side in a predetermined direction. The second extending portion B2 extends from the base 41A to one side in the predetermined direction. The second extending portion B2 is spaced apart from the first extending portion B1 in the conveying direction. The recess A1 is located between the first extending portion B1 and the second extending portion B2 in the conveying direction.

[0041] 3, fixing device 1 further includes a nip pressure changing mechanism NM for changing the nip pressure between heating unit 2 and pressure roller 3. Nip pressure changing mechanism NM includes a shaft SF, a pressure arm 60, a pressure spring 70, and a cam 80. First frame 41 supports pressure spring 70 and rotatably supports pressure arm 60 and cam 80.

[0042] 5, the pressure arm 60 and the cam 80 are respectively disposed at one end and the other end of the first frame 41 in the axial direction. Although not shown, the pressure spring 70 is also respectively disposed at one end and the other end of the first frame 41 in the axial direction. Since the structure of one side of the nip pressure change mechanism NM in the axial direction is substantially the same as the structure of the other side, the structure of one side in the axial direction will be mainly described below as a representative.

[0043] The shaft SF extends in the axial direction. The shaft SF is made of, for example, metal. Cams 80 are fixed to each axial end of the shaft SF. The first frame 41 has second support portions 41C that rotatably support the shaft SF. The second support portions 41C are disposed at one end and the other end of the first frame 41 in the axial direction. The second support portions 41C have holes H1 that rotatably support the shaft SF.

[0044] As shown in FIG. 3, the second support portion 41C rotatably supports the shaft SF, thereby supporting the cam 80 rotatably about the second axis X2.

[0045] The pressure arm 60 is an arm that presses the heating unit 2 toward the pressure roller 3. The first frame 41 has a first support portion 41D that supports the pressure arm 60 rotatably around a first axis X1. The first support portion 41D is a substantially cylindrical protrusion. The first axis X1, the second axis X2, and the third axis X3 are located at different positions. The first axis X1, the second axis X2, and the third axis X3 are parallel to each other. In other words, the direction along the first axis X1 is parallel to the axial direction.

[0046] The pressure spring 70 is a tension coil spring that biases the pressure arm 60 toward the pressure roller 3. The biasing direction of the pressure spring 70 is approximately parallel to a predetermined direction. The first frame 41 has a first spring catch 41E on which one end of the pressure spring 70 is hooked.

[0047] The cam 80 is capable of pressing the pressure applying arm 60 against the biasing force of the pressure applying spring 70. Specifically, the cam 80 is capable of rotating between a first position shown in Fig. 3 and a second position shown in Fig. 4.

[0048] When the cam 80 is in the first position, the nip pressure is a first nip pressure, and when the cam 80 is in the second position, the nip pressure is a second nip pressure that is smaller than the first nip pressure.

[0049] The pressure arm 60 has a main body portion 61, a supported portion 62, a first tip portion 63, and a second tip portion 64. The first tip portion 63 has a base portion 63A made of metal and a cam follower 63B (see also FIG. 5) made of resin. The main body portion 61, the supported portion 62, the base portion 63A, and the second tip portion 64 are made of metal and are integrally formed. The cam follower 63B is fitted into the base portion 63A.

[0050] The main body 61 has a first end E1 and a second end E2. The main body 61 extends from the first end E1 to one side in a predetermined direction and then extends downstream in the conveyance direction, with the second end E2 being the downstream end in the conveyance direction. The main body 61 has a pressure surface F1 between the first end E1 and the second end E2 that presses the heating unit 2 against the pressure roller 3.

[0051] Here, the heating unit 2 has side guides SG at each end in the axial direction. The side guides SG support the axial ends of the stay ST. The side guides SG are movably supported on the rails 41B. The pressure surface F1 presses the side guides SG toward the pressure roller 3.

[0052] The supported portion 62 is located at the first end E1 of the main body portion 61. The supported portion 62 is supported by the first support portion 41D of the first frame 41.

[0053] The first tip portion 63 is located at the second end E2 of the main body portion 61. The first tip portion 63 has a pressed surface F2 that is pressed by the cam 80. More specifically, the base portion 63A extends in a direction inclined with respect to the conveying direction so as to be positioned on one side of a predetermined direction as it moves from the second end E2 of the main body portion 61 toward the downstream side in the conveying direction. The cam follower 63B attached to the base portion 63A has the pressed surface F2.

[0054] The second tip portion 64 is located at the second end E2 of the main body portion 61. The second tip portion 64 extends in a different direction from the first tip portion 63. The second tip portion 64 has a second spring hook 64A on which the other end of the pressure spring 70 is hooked.

[0055] 8(a), in the predetermined direction, the distance D1 from the second spring hook 64A to the second axis X2 is smaller than the distance D2 from the first spring hook 41E to the second spring hook 64A. In the predetermined direction, the distance D1 from the second spring hook 64A to the second axis X2 is smaller than the distance D3 from the second spring hook 64A to the first axis X1.

[0056] The second spring hook 64A is located between the second axis X2 and the first axis X1 in the predetermined direction. The first axis X1 is located between the first spring hook 41E and the second spring hook 64A in the predetermined direction. The first spring hook 41E and the second spring hook 64A are aligned in the predetermined direction.

[0057] The first axis X1 is located between the third axis X3 and the second axis X2 in the predetermined direction. A distance D4 from the first axis X1 to the pressure surface F1 is smaller than a distance D5 from the first axis X1 to the second spring hook 64A. The pressure surface F1 is located between the first axis X1 and the second spring hook 64A in the conveying direction.

[0058] The pressed surface F2 is substantially parallel to a normal line LN to a circle CC at an intersection P between the circle CC and the pressed surface F2, the circle CC being centered on the first axis X1. The second spring hook 64A and the pressed surface F2 face each other in a predetermined direction. As shown in Fig. 8(b), the pressure arm 60 does not have a portion located on a line segment LS that is aligned in the predetermined direction and connects the second spring hook 64A and the pressed surface F2.

[0059] 7, the first support portion 41D is located near the base of the rail 41B. More specifically, the first support portion 41D is located at the base portion 41A. In the predetermined direction, a distance D6 from the first axis X1 to the base end B11 of the first extension portion B1 is smaller than a distance D7 from the first axis X1 to the tip end B12 of the first extension portion B1.

[0060] As described above, the following effects can be obtained in this embodiment. Since the pressure arm 60 has a first tip 63 having a pressed surface F2 and a second tip 64 having a second spring hook 64A, the pressed surface F2 and the second spring hook 64A can be aligned in a direction substantially parallel to the biasing direction of the pressure spring 70. This makes it possible to reduce the amount by which the pressure arm 60 protrudes outward from the pressure spring 70 in a direction perpendicular to the biasing direction of the pressure spring 70. In other words, it is possible to reduce the amount by which the pressure arm 60 protrudes in the direction away from the heating unit 2 in the conveyance direction from the pressure spring 70.

[0061] Since the first support portion 41D is disposed at the base of the rail 41B where strength can be more easily ensured than at the tip, distortion of the first frame 41 due to the spring force of the pressure spring 70 applied to the pressure arm 60 can be suppressed.

[0062] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below.

[0063] The first member is not limited to a heating unit, but may be, for example, a pressure unit having a pressure pad and a belt, in which case the second member may be a heating roller that sandwiches the belt between the pressure pad and the heating roller.

[0064] The pressure spring is not limited to a tension coil spring, but may be, for example, a torsion spring. The first support portion may be a portion having a hole for rotatably supporting the pressure arm, and the second support portion may be a protrusion for rotatably supporting the cam.

[0065] The pressure arm does not have to have a cam follower. That is, the first tip portion may be made of metal only. In this case, the first tip portion made of metal only may have the pressed surface.

[0066] The heater is not limited to a ceramic heater, and may be, for example, a halogen lamp, etc. In this case, the heating unit may be configured to include a belt, a nip plate that sandwiches the belt between the belt and the pressure roller, and a heater that heats the nip plate.

[0067] The elements described in the above-described embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0068] 1 Fixing device 2 heating units 3 Pressure roller 4 frames 41 First Frame 41B Rail 41C 2nd support part 41D 1st support part 41E First spring holder BL Belt 60 Pressure Arm 61 Main body 62 Supported part 63 1st tip 64 2nd tip 64A Second spring holder 70 Pressure spring 80 Cam E1 1st end E2 2nd end F1 pressure surface F2 Pressed surface S seat X1 1st axis X2 2nd axis

Claims

1. a first member having a belt; a second member that sandwiches the sheet between itself and the first member; a pressure arm that presses the first member toward the second member; a pressure spring that biases the pressure arm toward the second member; a cam that presses the pressure arm against the biasing force of the pressure spring; a frame that supports the first member, the second member, and the pressure spring, and rotatably supports the pressure arm and the cam, a rail that supports the first member so that the first member can move in a predetermined direction; a first support portion that supports the pressure arm so that the pressure arm can rotate about a first axis; a second support portion that supports the cam rotatably around a second axis different from the first axis; a first spring hook on which one end of the pressure spring is hooked; and a frame having the first spring hook. The pressure arm is a main body having a first end and a second end, the main body having a pressure surface between the first end and the second end that presses the first member; a supported portion supported by the first support portion, the supported portion being located at the first end of the main body portion; a first tip portion located at the second end of the main body portion, the first tip portion having a pressed surface that is pressed by the cam; a second tip portion located at the second end of the main body portion, extending in a direction different from the first tip portion, and having a second spring hook onto which the other end of the pressure spring is hooked.

2. 2. The fixing device according to claim 1, wherein the first member has a heater for heating the sheet.

3. 3. The fixing device according to claim 1, wherein the second member is a rotatable roller.

4. the frame has a base that supports the second member; The rail is a first extension portion extending from the base portion to one side in the predetermined direction; a second extension portion extending from the base portion to one side in the predetermined direction, the second extension portion being spaced apart from the first extension portion in a direction perpendicular to the first axis and the predetermined direction; 4. The fixing device according to claim 1, wherein a distance from the first axis to a base end of the first extension portion in the predetermined direction is smaller than a distance from the first axis to a tip end of the first extension portion.

5. 5. The fixing device according to claim 1, wherein a distance from the second spring hook to the second shaft in the predetermined direction is smaller than a distance from the first spring hook to the second spring hook.

6. 6. The fixing device according to claim 1, wherein a distance from the second spring hook to the second shaft in the predetermined direction is smaller than a distance from the second spring hook to the first shaft.

7. 7. The fixing device according to claim 1, wherein the second spring hook and the pressed surface face each other in the predetermined direction.

8. 8. The fixing device according to claim 1, wherein the pressure arm does not have a portion located on a line segment that is along the predetermined direction and that connects the second spring hook and the pressed surface.

9. In the predetermined direction, the second spring holder is located between the second shaft and the first shaft, In the predetermined direction, the first shaft is located between the first spring hook and the second spring hook, 9. The fixing device according to claim 1, wherein the first spring hook and the second spring hook are aligned in the predetermined direction.

10. 10. The fixing device according to claim 1, wherein the pressed surface is substantially parallel to a normal to a circle having the first axis as its center at an intersection of the pressed surface and the circle.

11. the second member is a roller rotatable about a third axis, 11. The fixing device according to claim 1, wherein the first shaft is located between the third shaft and the second shaft in the predetermined direction.

12. 12. The fixing device according to claim 1, wherein a distance from the first shaft to the pressure surface is smaller than a distance from the first shaft to the second spring hook.

13. 13. The fixing device according to claim 1, wherein the pressure surface is located between the first axis and the second spring hook in a direction perpendicular to the first axis and the predetermined direction.

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