JP2017044850A - Fixation device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent engagement between a first swing member and a traction spring from being accidentally released.SOLUTION: A fixation device 23 includes: a fixation member; a pressure member which forms a fixation nip by being brought into pressure-contact with the fixation member; and a pressure adjustment mechanism 34 which switches the pressure of the fixation nip. The pressure adjustment mechanism 34 includes: a first swing member 51; a cam 52 which is provided so as to be able to press the first swing member 51; a second swing member 53 which supports the pressure member; and a traction spring 54 which is interposed between the first swing member 51 and the second swing member 53. The traction spring 54 includes a first engagement part 81 which is engaged with the first swing member 51. The first engagement part 81 includes: a first linear part 84; a second linear part 85 which is bent from the first linear part 84; and a falling prevention part 86 which is bent from the second linear part 85.SELECTED DRAWING: Figure 10

Description

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

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines and printers include a fixing device that fixes a toner image on a sheet.

  For example, Patent Document 1 discloses a fixing member (see “Fixing Roller 1” in Patent Document 1) and a pressure member (see “Pressure Roller 2” in Patent Document 1) that presses against the fixing member to form a fixing nip. ) And a pressure adjusting mechanism for switching the pressure of the fixing nip (see “Pressure release means 3”, etc. in Patent Document 1).

  Various mechanisms have been developed as the pressure adjusting mechanism. For example, a first swing member, a cam provided to be able to press the first swing member, a second swing member that rotatably supports the pressure member, a first swing member, and a second swing member There is known a pressure adjusting mechanism including a traction spring interposed therebetween.

JP-A-11-65350

  In the fixing device as described above, when the pressure of the fixing nip is weakened by the pressure adjusting mechanism, the engagement between the first swing member and the traction spring is inadvertently released, and the pressure of the fixing nip may not be switched. is there.

  In view of the above circumstances, an object of the present invention is to prevent the first swinging member and the traction spring from being inadvertently released.

  The fixing device of the present invention includes a fixing member that is rotatably provided, a fixing nip that is in pressure contact with the fixing member, a pressure member that is rotatably provided, and a fixing device that rotatably supports the fixing member. A main body and a pressure adjusting mechanism for switching the pressure of the fixing nip, wherein the pressure adjusting mechanism includes a first swinging member that is swingably supported by the fixing device main body, and the first swinging member. A cam that can be pressed, a second swing member that is swingably supported by the fixing device body, and that rotatably supports the pressure member; the first swing member and the second swing member; A traction spring interposed between the members, wherein the traction spring engages with the first oscillating member, and a second engagement engages with the second oscillating member. And a spring body that connects the first engagement portion and the second engagement portion. The first engagement portion includes a first linear portion extending along the axial direction of the spring body, and a second line bent from an end portion of the first linear portion on the side away from the spring body. And a retaining portion bent from an end of the second linear portion on the side away from the first linear portion.

  By adopting such a configuration, it is possible to prevent the engagement between the first swing member and the traction spring from being inadvertently released, and avoid the situation where the pressure of the fixing nip cannot be switched. can do.

  The fixing member is provided so as to be rotatable about a rotation shaft, and the fixing device main body includes a rib provided on the inner side in the rotation shaft direction of the second swing member, and the second swing member is provided on the rib. , The falling of the second swing member may be regulated.

  By adopting such a configuration, even if the direction in which the traction spring pulls the second swing member varies somewhat, the second swing member is unlikely to fall down. Along with this, it is possible to suppress the tilt of the bearing interposed between the second swing member and the pressurizing member, and it is possible to suppress the generation of abnormal noise accompanying the tilt of the bearing.

  An abutting portion capable of abutting on the second oscillating member is provided at an outer edge of the rib in the rotation axis direction, and the traction spring pulls the second oscillating member on the abutting portion. It may be provided in parallel to the direction to do.

  By adopting such a configuration, the second rocking member is more unlikely to fall down.

  The first engagement portion further includes a connection portion that connects an end portion of the spring body on the first engagement portion side and an end portion of the first linear portion on the spring body side, and the connection portion includes The shaft center of the spring body may be passed.

  By adopting such a configuration, the first engaging portion can be easily engaged with the first swing member.

  The retaining portion includes an end portion of the first linear portion on the spring body side, an end portion of the first linear portion on a side away from the spring body, and the second linear portion of the first linear portion. It may be provided so as to protrude from a plane passing through the end portion on the side separated from the one linear portion.

  By adopting such a configuration, it is possible to more reliably prevent the first swing member and the traction spring from being inadvertently released.

  The first swing member includes a swing plate that is swingably supported by the fixing device body, and a roller that is rotatably supported by the swing plate, and the cam presses the roller. The first engagement portion may be engaged with the swing plate.

  By adopting such a configuration, the first engagement portion can be reliably engaged with the first swing member while reducing the frictional force between the cam and the first swing member.

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

  According to the present invention, it is possible to prevent the first swing member and the traction spring from being inadvertently released.

1 is a schematic diagram illustrating an outline of a color printer according to an embodiment of the present invention. 1 is a cross-sectional view showing a fixing device and its peripheral part in a color printer according to an embodiment of the present invention. 1 is a perspective view showing a fixing device according to an embodiment of the present invention as viewed from below. FIG. 2 is a perspective view showing an internal structure of a fixing device according to an embodiment of the present invention. FIG. 3 is a perspective view showing a state where the nip pressure is a first pressure in the fixing device according to the embodiment of the present disclosure. FIG. 4 is a cross-sectional view illustrating a state where the nip pressure is a first pressure in the fixing device according to the embodiment of the present disclosure. FIG. 6 is a perspective view showing a second swinging member and its peripheral part in the fixing device according to the embodiment of the present invention. In the fixing device according to an embodiment of the present invention, FIG. In the fixing device according to an embodiment of the present invention, FIG. FIG. 3 is a perspective view showing a traction spring and its peripheral portion in the fixing device according to the embodiment of the present invention. 1 is a block diagram illustrating a control system for a fixing device according to an embodiment of the present invention. FIG. 5 is a cross-sectional view illustrating a state where the nip pressure is a second pressure in the fixing device according to the embodiment of the present disclosure. FIG. 9 is a perspective view showing a state where the nip pressure is a first pressure in a fixing device according to another different embodiment of the present invention.

  Hereinafter, the configuration of the color printer 1 (image forming apparatus) will be described with reference to the drawings. Hereinafter, the front side of the sheet in FIG. 1 is the front side of the color printer 1. Arrows Fr, Rr, L, R, U, Lo attached to the respective drawings respectively indicate the front side, the rear side, the left side, the right side, the upper side, and the lower side of the color printer 1.

  As shown in FIG. 1, the color printer 1 includes a box-shaped printer main body 2. A paper feed cassette 3 for storing paper is provided at the lower part of the printer main body 2. A first paper discharge tray 4 is provided above the printer main body 2, and a second paper discharge tray 5 is provided above the first paper discharge tray 4. A cover 6 that can be opened and closed is provided at the right end of the printer body 2.

  Inside the printer main body 2, an intermediate transfer belt 7 (image carrier) is provided between a plurality of rollers. Below the intermediate transfer belt 7, four image forming units 8 are provided for the toner colors (for example, four colors of magenta, cyan, yellow, and black) along the lower portion of the intermediate transfer belt 7. Each image forming unit 8 is rotatably provided with a photosensitive drum 9, and around the photosensitive drum 9, a charger 10, a developing unit 11, a primary transfer unit 12, and a cleaning device 13 are provided. The static eliminator 14 is arranged in the order of the primary transfer process. Four containers 18 are provided above the developing unit 11. Each container 18 contains toner of a color corresponding to each image forming unit 8. An exposure device 19 is provided below the four image forming units 8.

  A paper transport path 20 (hereinafter simply referred to as “transport path 20”) is provided on the right side of the printer body 2. A paper feeding unit 21 is provided at the upstream end of the conveyance path 20, a secondary transfer unit 22 is provided at the right end side of the intermediate transfer belt 7 at a middle portion of the conveyance path 20, and fixing is performed at a downstream part of the conveyance path 20. A device 23 is provided.

  The conveyance path 20 branches into a first branch path 24 that is a lower branch path and a second branch path 26 that is an upper branch path in a portion downstream of the fixing device 23. The second branch path 26 is connected to a portion upstream of the secondary transfer unit 22 of the transport path 20 via a double-sided transport path 28 provided on the right side of the transport path 20.

  Next, the printing operation of the color printer 1 will be described.

  When the color printer 1 is turned on, various parameters are initialized, and initial settings such as temperature setting of the fixing device 23 are executed. When image data is input from a computer or the like connected to the color printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photoconductor drum 9 is charged by the charger 10, the photoconductor drum 9 is exposed in accordance with the image data by the laser light (see arrow P) from the exposure device 19, and the photoconductor is exposed. An electrostatic latent image is formed on the surface of the drum 9. Next, the electrostatic latent image is developed into a toner image of a corresponding color by the developing device 11 with the toner supplied from the container 18. This toner image is primarily transferred to the surface of the intermediate transfer belt 7 in the primary transfer portion 12. Each image forming unit 8 sequentially repeats the above operation, whereby a full-color toner image is formed on the intermediate transfer belt 7. Note that the toner and charge remaining on the photosensitive drum 9 are removed by the cleaning device 13 and the static eliminator 14.

  On the other hand, the paper taken out from the paper feed cassette 3 by the paper feed unit 21 is conveyed to the secondary transfer unit 22 in synchronism with the above-described image forming operation. The full-color toner image is secondarily transferred to the paper. The sheet on which the toner image is secondarily transferred is conveyed downstream in the conveyance path 20 and enters the fixing device 23, and the toner image is fixed on the sheet in the fixing device 23. The sheet on which the toner image is fixed enters either the first branch path 24 or the second branch path 26. The paper that has entered the first branch path 24 is discharged onto the first paper discharge tray 4. The sheet that has entered the second branch path 26 is discharged onto the second sheet discharge tray 5 or is transported to the duplex transport path 28 for duplex printing.

  Next, the fixing device 23 will be described in detail. An arrow Y attached to FIG. 2 indicates the sheet conveyance direction. An arrow I appropriately attached to each figure indicates an inner side in the front-rear direction, and an arrow O appropriately attached to each figure indicates an outer side in the front-rear direction.

  As shown in FIG. 2, the right surface (outer surface) of the fixing device 23 is covered with the cover 6 described above. The fixing device 23 includes a fixing device main body 31, a heating roller 32 (fixing member) accommodated in the left side portion of the fixing device main body 31, and a pressure roller 33 (pressure member) accommodated in the right side portion of the fixing device main body 31. ), A pressure adjusting mechanism 34 provided on each of the front end side and the rear end side of the fixing device main body 31, and a guide member 35 covering the upper side of the fixing device main body 31.

  As shown in FIG. 3, the fixing device main body 31 has a box shape that is long in the front-rear direction. A driving gear 41 is provided at the rear end of the fixing device main body 31. As shown in FIG. 4, side plates 42 are provided at the front and rear portions of the fixing device main body 31. Each side plate 42 is provided substantially perpendicular to the front-rear direction. Each side plate 42 is provided outside the heating roller 32 and the pressure roller 33 in the front-rear direction. A first spring receiving portion 43 is provided at the lower right portion of each side plate 42.

  As shown in FIG. 5, the fixing device main body 31 is provided with ribs 44 on the inner side in the front-rear direction of the right side portion of each side plate 42. Abutting portions 45 are provided along the left and right direction (vertical direction in the drawing of FIG. 5) at the outer edge of each rib 44 in the front-rear direction.

  As shown in FIG. 2, the heating roller 32 has a cylindrical shape. The heating roller 32 includes, for example, a cylindrical core material made of a metal such as aluminum or iron, and a release layer that covers the core material and is made of a fluorine resin such as PFA.

  A pair of upper and lower heaters 46 are accommodated inside the heating roller 32, and the heating roller 32 is heated by each heater 46. Each heater 46 is constituted by, for example, a halogen heater or a ceramic heater. A separation member 47 is provided on the upper side of the heating roller 32 (downstream side in the sheet conveyance direction), and the separation member 47 separates the sheet from the surface of the heating roller 32.

  Both front and rear ends of the heating roller 32 are attached to the side plates 42 of the fixing device main body 31 via first bearings 48, respectively. As a result, the heating roller 32 is rotatably supported by the fixing device main body 31. The heating roller 32 is rotatable about a rotation axis A extending in the front-rear direction. That is, in this embodiment, the front-rear direction is the rotation axis direction of the heating roller 32.

  The pressure roller 33 has a cylindrical shape. The pressure roller 33 is, for example, a cylindrical core material made of a metal such as aluminum or iron, an elastic layer formed around the core material and made of silicon rubber, and the elastic layer. And a release layer made of a fluorine resin. The pressure roller 33 is in pressure contact with the heating roller 32, and a fixing nip N is formed between the heating roller 32 and the pressure roller 33.

  As shown in FIGS. 5 and 6, each pressure adjusting mechanism 34 includes a first swing member 51, a cam 52 provided on the right side of the first swing member 51, and a second provided on the right side of the cam 52. A swing member 53, a traction spring 54 interposed between the first swing member 51 and the second swing member 53, and a pressing spring 55 provided on the right side of the second swing member 53 are provided. Yes.

  The first rocking member 51 of each pressure adjusting mechanism 34 includes a rocking plate 57 and a roller 58 attached to a substantially central portion in the vertical direction of the rocking plate 57.

  The swing plate 57 of the first swing member 51 of each pressure adjusting mechanism 34 is swingably supported by the fixing device body 31 via a first swing shaft 61 provided on the upper end side thereof. The swing plate 57 has a substantially U-shaped cross section, and includes a base plate 62 and a pair of guide plates 63 bent toward the left from both front and rear end portions of the base plate 62. A through hole 64 is provided at a substantially central portion in the vertical direction of the base plate 62. An engagement hole 65 is provided at the lower end of each guide plate 63.

  The roller 58 of the first swing member 51 of each pressure adjusting mechanism 34 is rotatably supported by the swing plate 57 via a roller shaft 67 installed on the pair of guide plates 63 of the swing plate 57. . The left side portion and the center portion in the left-right direction of the roller 58 are disposed on the left side (the side away from the cam 52) of the base plate 62 of the swing plate 57. The right side portion of the roller 58 protrudes to the right side (cam 52 side) of the base plate 62 of the swing plate 57 through the through hole 64.

  The cam 52 of each pressure adjusting mechanism 34 is fixed to a camshaft 69 extending along the front-rear direction. The camshaft 69 is rotatably supported on each side plate 42 of the fixing device main body 31, and the cam 52 rotates with the rotation of the camshaft 69. The cam 52 includes a large diameter portion 70 having a long distance from the center of the cam shaft 69 (rotation center of the cam 52) and a small diameter portion 71 having a distance from the center of the cam shaft 69 shorter than the large diameter portion 70. ing. The small diameter portion 71 is configured by a flat surface and does not have a curvature.

  The second swing member 53 of each pressure adjustment mechanism 34 has a plate shape that is long in the vertical direction. The second swing member 53 is provided substantially perpendicular to the front-rear direction. The second swing member 53 is swingably supported by the fixing device main body 31 via a second swing shaft 73 provided on the upper end side thereof. A pressure roller 33 is rotatably supported on the upper part of the second swing member 53 via a second bearing 74. A second spring receiving portion 75 is provided below the second swing member 53. An engagement groove 76 is provided at the lower end of the second swing member 53.

  As shown in FIG. 7, the ribs 44 of the fixing device main body 31 are provided on the inner side in the front-rear direction of the second swing member 53 of each pressure adjustment mechanism 34. The upper part of the second swing member 53 is in contact with the contact portion 45 of each rib 44. As a result, the second rocking member 53 is restricted from falling inward in the front-rear direction.

  As shown in FIG. 8, the traction spring 54 of each pressure adjustment mechanism 34 includes a first engagement portion 81 provided at the left end portion (one end portion) and a second engagement portion provided at the right end portion (the other end portion). An engaging portion 82 and a spring body 83 that connects the first engaging portion 81 and the second engaging portion 82 are provided.

  The first engaging portion 81 of the traction spring 54 of each pressure adjusting mechanism 34 includes a first linear portion 84 and a left end portion of the first linear portion 84 (an end portion on the side away from the spring body 83) in the front-rear direction. The second linear portion 85 that is bent inward and the end portion on the inner side in the front-rear direction of the second linear portion 85 (the end portion on the side away from the first linear portion 84) are bent upward. And a connecting portion 87 that connects the left end portion (end portion on the first engagement portion 81 side) of the spring body 83 and the right end portion (end portion on the spring body 83 side) of the first linear portion 84. And.

  The first linear portion 84 of the first engaging portion 81 of the traction spring 54 of each pressure adjusting mechanism 34 extends linearly along the left-right direction. The second linear portion 85 of the first engaging portion 81 is curved in an arc shape toward the left (in the direction away from the spring main body 83), and before and after the swing plate 57 of the first swing member 51. It engages with an engagement hole 65 provided in the guide plate 63 on the outer side in the direction. As shown in FIGS. 9 and 10, the retaining portion 86 of the first engagement portion 81 includes a right end portion f1 (end portion on the spring body 83 side) of the first linear portion 84 and a first linear portion. 84, a left end portion f2 (end portion on the side away from the spring main body 83), an end portion f3 on the inner side in the front-rear direction of the second linear portion 85 (end portion on the side away from the first linear portion 84), It protrudes from the plane S that passes through. As shown in FIG. 9, the connecting portion 87 of the first engaging portion 81 extends linearly along the front-rear direction and passes through the axis D of the spring body 83.

  As shown in FIGS. 5 and 6, the second engaging portion 82 of the traction spring 54 of each pressure adjusting mechanism 34 has an annular shape, and is engaged with the engaging groove 76 of the second swinging member 53. Match. The spring body 83 of the traction spring 54 of each pressure adjusting mechanism 34 is configured by an extendable coil spring, and the left-right direction is the axial direction.

  The pressing spring 55 of each pressure adjusting mechanism 34 is configured by a compressible coil spring, and the left-right direction is the axial direction. The right end portion (one end portion) of the pressing spring 55 is engaged with the first spring receiving portion 43 of each side plate 42 of the fixing device main body 31. The left end portion (the other end portion) of the pressing spring 55 is engaged with the second spring receiving portion 75 of the second swing member 53. That is, the pressing spring 55 is interposed between the fixing device main body 31 and the second swing member 53.

  The guide member 35 (see FIG. 2) has a long shape in the front-rear direction. A large number of conveying ribs 91 are arranged in the guide member 35 at intervals in the front-rear direction. The left side of each conveyance rib 91 faces the conveyance path 20 and the second branch path 26, and the upper part of each conveyance rib 91 faces the double-side conveyance path 28. Thus, each conveyance rib 91 constitutes a part of the conveyance path 20, the second branch path 26, and the double-sided conveyance path 28.

  Next, the control system of the fixing device 23 will be described with reference to FIG.

  The fixing device 23 is provided with a control unit 111. The control unit 111 is connected to a storage unit 112 configured by a storage device such as a ROM and a RAM, and the control unit 111 controls the fixing device 23 based on a control program and control data stored in the storage unit 112. It is configured to control each part.

  The control unit 111 is connected to each heater 46, and each heater 46 is energized based on a signal from the control unit 111, and the heating roller 32 is heated by each heater 46.

  The control unit 111 is connected to a drive source 113 configured by a motor or the like and capable of rotating in the forward and reverse directions. The drive source 113 is connected to the heating roller 32 via the drive gear 41 and the first one-way clutch 114 (first connection portion). The drive source 113 is connected to the cam 52 of each pressure adjusting mechanism 34 via the drive gear 41, the second one-way clutch 115 (second connection portion), and the camshaft 69.

  An operation of fixing a toner image on a sheet in the fixing device 23 configured as described above will be described.

  When the toner image is fixed on the paper, the drive source 113 is rotated forward. Thus, when the drive source 113 rotates forward, the rotation of the drive source 113 is transmitted to the heating roller 32 via the drive gear 41 and the first one-way clutch 114, and the heating roller 32 rotates (see arrow B in FIG. 2). . When the heating roller 32 rotates in this way, the pressure roller 33 that is in pressure contact with the heating roller 32 rotates in the opposite direction to the heating roller 32 (see arrow C in FIG. 2).

  When the drive source 113 rotates forward as described above, the rotation of the drive source 113 is transmitted to the second one-way clutch 115 via the drive gear 41, but the second one-way clutch 115 transmits the rotation to the camshaft 69. do not do. That is, the transmission of rotation is blocked by the second one-way clutch 115. Therefore, the cam shaft 69 and the cam 52 of each pressure adjusting mechanism 34 do not rotate.

  Further, when fixing the toner image on the paper, each heater 46 is energized. When each heater 46 is energized in this way, the heating roller 32 is heated by each heater 46. When the sheet passes through the fixing nip N in this state, the sheet and the toner image are heated and pressurized, and the toner image is fixed on the sheet.

  Next, an operation of switching the pressure of the fixing nip N (hereinafter referred to as “nip pressure”) in the fixing device 23 configured as described above will be described.

  FIG. 6 shows a state where the large diameter portion 70 of the cam 52 presses the right side portion of the roller 58 of the first swing member 51. The posture of the cam 52 at this time is referred to as a “pressing posture”. Thus, in the state where the cam 52 is in the pressing posture, the spring body 83 of the traction spring 54 is extended beyond the natural length, and the traction spring 54 follows the second swing member 53 along the left-right direction. Tow left. On the other hand, the pressing spring 55 has a natural length and does not press the second swing member 53. The nip pressure at this time is referred to as “first pressure”. The first pressure is, for example, a nip pressure when performing single-sided printing on plain paper.

  Thus, when switching the nip pressure from the state where the nip pressure is the first pressure, the drive source 113 is rotated in the reverse direction. When the drive source 113 rotates in the reverse direction in this way, the rotation of the drive source 113 is transmitted to the cam 52 via the drive gear 41, the second one-way clutch 115, and the cam shaft 69, and the cam 52 rotates 180 degrees. When the cam 52 rotates 180 degrees in this way, as shown in FIG. 12, the pressure on the right side portion of the roller 58 of the first swinging member 51 by the large-diameter portion 70 of the cam 52 is released, and the small-diameter portion of the cam 52 71 faces the right side of the roller 58 of the first swing member 51. The posture of the cam 52 at this time is referred to as a “press release posture”.

  Thus, when the cam 52 rotates from the pressing posture to the pressing release posture, the first swing member 51 swings to the right and the spring body 83 of the traction spring 54 is restored to its natural length, and the second swing by the traction spring 54 is restored. Pulling on the moving member 53 is released. For this reason, the second swing member 53 swings to the right, and the pressure roller 33 rotatably supported by the second swing member 53 moves to the right (in the direction away from the heating roller 32). Accordingly, the pressing spring 55 is compressed more than the natural length, and presses the second swing member 53. The nip pressure at this time is referred to as “second pressure”. The second pressure is, for example, a nip pressure when printing is performed on the envelope, and is lower than the first pressure.

  When the drive source 113 rotates in the reverse direction as described above, the rotation of the drive source 113 is transmitted to the first one-way clutch 114 via the drive gear 41, but the first one-way clutch 114 transmits the rotation to the heating roller 32. do not do. That is, rotation transmission is blocked by the first one-way clutch 114. Therefore, the heating roller 32 and the pressure roller 33 do not rotate.

  In this way, when the nip pressure is switched from the state where the nip pressure is the second pressure, the drive source 113 is reversely rotated again. When the drive source 113 rotates in the reverse direction in this way, the rotation of the drive source 113 is transmitted to the cam 52 via the drive gear 41, the second one-way clutch 115, and the cam shaft 69, and the cam 52 rotates 180 degrees. When the cam 52 rotates 180 degrees in this way, the large diameter portion 70 of the cam 52 presses the right side portion of the roller 58 of the first swing member 51 as shown in FIG. Accordingly, the first swing member 51 swings to the left and pulls the traction spring 54, and the spring body 83 of the traction spring 54 extends beyond the natural length. Accordingly, the traction spring 54 pulls the second swinging member 53 leftward along the left-right direction, and the second swinging member 53 swings to the left and can rotate to the second swinging member 53. The pressure roller 33 supported on the left side moves to the left (direction approaching the heating roller 32). Along with this, the pressing spring 55 is restored to its natural length, and the pressing of the pressing spring 55 against the second swing member 53 is released. As described above, the nip pressure is switched from the second pressure to the first pressure.

  Thus, in the present embodiment, the nip pressure can be switched between the first pressure and the second pressure by each pressure adjusting mechanism 34. For example, when fixing a toner image on a relatively weak sheet such as an envelope or thin paper, the nip pressure is reduced from a first pressure to a second pressure. Thereby, it is possible to suppress the generation of wrinkles on the paper.

  By the way, when switching the nip pressure as described above, if the direction in which the traction spring 54 pulls the second swing member 53 is slightly tilted from the normal direction, the second swing member 53 may fall. . When the second rocking member 53 is tilted in this way, the second bearing 74 interposed between the second rocking member 53 and the pressure roller 33 is tilted, which may cause abnormal noise. There is.

  Therefore, in the present embodiment, the second swinging member 53 is prevented from falling by contacting the second swinging member 53 to the contact portion 45 of each rib 44 of the fixing device main body 31. By adopting such a configuration, even if the direction in which the traction spring 54 pulls the second swing member 53 varies somewhat, the second swing member 53 is unlikely to fall down. Along with this, it is possible to suppress the tilting of the second bearing 74 interposed between the second swing member 53 and the pressure roller 33, and the generation of abnormal noise associated with the tilting of the second bearing 74. Can be suppressed.

  Further, the abutting portion 45 of each rib 44 is provided in parallel to the direction (left-right direction) in which the traction spring 54 pulls the second swing member 53. By adopting such a configuration, the second swing member 53 is more unlikely to fall down.

  Further, when the nip pressure is reduced from the first pressure to the second pressure by the pressure adjusting mechanisms 34 as described above, the spring body 83 of the stretched traction spring 54 is restored to the natural length, so The second linear portion 85 of the first engagement portion 81 of the traction spring 54 is easily detached from the engagement hole 65 of the swing plate 57 of the moving member 51. If the second linear portion 85 of the first engagement portion 81 is inadvertently removed from the engagement hole 65, the nip pressure may not be switched.

  Therefore, in the present embodiment, the second linear portion 85 of the first engagement portion 81 is bent upward from the front end in the front-rear direction (the end on the side away from the first linear portion 84). A retaining portion 86 is provided. By adopting such a configuration, it is possible to prevent the second linear portion 85 of the first engagement portion 81 from being inadvertently detached from the engagement hole 65, and the nip pressure cannot be switched. Such a situation can be avoided.

  Further, the retaining portion 86 of the first engaging portion 81 of the traction spring 54 includes a right end portion f1 (end portion on the spring body 83 side) of the first linear portion 84 and a left end portion f2 of the first linear portion 84. A plane S that passes through (the end portion on the side away from the spring body 83) and the end portion f3 on the inner side in the front-rear direction of the second linear portion 85 (the end portion on the side away from the first linear portion 84). It is provided so as to protrude from. By adopting such a configuration, it is possible to more reliably prevent the second linear portion 85 of the first engagement portion 81 from being inadvertently detached from the engagement hole 65.

  Further, the connecting portion 87 of the first engaging portion 81 of the traction spring 54 passes through the axis D of the spring main body 83. By adopting such a configuration, the second linear portion 85 of the first engagement portion 81 can be easily engaged with the engagement hole 65 of the swing plate 57 of the first swing member 51.

  The cam 52 is provided so that the roller 58 of the first swing member 51 can be pressed, and the second linear portion 85 of the first engagement portion 81 of the traction spring 54 swings the first swing member 51. The plate 57 is engaged with the engagement hole 65 of the plate 57. By adopting such a configuration, the first engagement portion 81 can be reliably engaged with the first swing member 51 while reducing the frictional force between the cam 52 and the first swing member 51. it can.

  In addition, since the pressure adjusting mechanism 34 is realized by a simple configuration using the traction spring 54 and the pressing spring 55, the manufacturing cost of the fixing device 23 can be reduced.

  Moreover, in this embodiment, as FIG. 6 shows, the small diameter part 71 of the cam 52 is comprised by the flat surface, and does not have a curvature. By adopting such a configuration, it becomes possible to increase the switching speed of the nip pressure, and it becomes easy to cope with a high-speed machine (a model having a high printing speed).

  In the present embodiment, the case where the small diameter portion 71 of the cam 52 is configured by a flat surface and has no curvature has been described. On the other hand, in another different embodiment, as shown in FIG. 13, the small-diameter portion 71 of the cam 52 is configured by a curved surface and may have a curvature. By adopting such a configuration, the nip pressure can be switched gently.

  Although the case where the pressure adjustment mechanism 34 includes the cam 52 has been described in the present embodiment, the pressure adjustment mechanism 34 may not include the cam 52 in other different embodiments. That is, the pressure adjusting mechanism 34 may be any mechanism as long as the nip pressure can be switched.

  In the present embodiment, the case where the rotation of the drive source 113 is transmitted to the heating roller 32 and the heating roller 32 and the pressure roller 33 in pressure contact with the heating roller 32 rotates has been described. On the other hand, in another different embodiment, the rotation of the drive source 113 may be transmitted to the pressure roller 33 and the pressure roller 33 and the heating roller 32 in pressure contact with the pressure roller 33 may rotate.

  In the present embodiment, the case where the heating roller 32 is used as a fixing member has been described. On the other hand, in other different embodiments, a fixing belt may be used as a fixing member.

  In the present embodiment, the case where the configuration of the present invention is applied to the color printer 1 has been described. On the other hand, in other different embodiments, the configuration of the present invention can be applied to other image forming apparatuses such as a monochrome printer, a copying machine, a facsimile machine, and a multifunction machine.

1 Color printer (image forming device)
23 Fixing device 31 Fixing device body 32 Heating roller (fixing member)
33 Pressure roller (Pressure member)
34 Pressure adjusting mechanism 44 Rib 45 Contact portion 51 First swing member 52 Cam 53 Second swing member 54 Traction spring 57 Swing plate 58 Roller 81 First engagement portion 82 Second engagement portion 83 Spring body 84 First 1 linear portion 85 second linear portion 86 retaining portion 87 connecting portion N fixing nip

Claims (7)

A fixing member provided rotatably;
A pressure member provided in a rotatable manner to form a fixing nip by pressing against the fixing member;
A fixing device main body rotatably supporting the fixing member;
A pressure adjusting mechanism for switching the pressure of the fixing nip,
The pressure adjustment mechanism is
A first swinging member that is swingably supported by the fixing device body;
A cam provided to be able to press the first swing member;
A second swinging member supported by the fixing device main body so as to be swingable and rotatably supporting the pressure member;
A traction spring interposed between the first swing member and the second swing member,
The traction spring is
A first engagement portion that engages with the first swing member;
A second engagement portion that engages with the second swing member;
A spring body connecting the first engagement portion and the second engagement portion,
The first engaging portion is
A first linear portion extending along the axial direction of the spring body;
A second linear portion bent from an end portion of the first linear portion on a side away from the spring body;
A fixing device comprising: a retaining portion bent from an end portion of the second linear portion on a side away from the first linear portion. The fixing member is provided to be rotatable around a rotation axis,
The fixing device main body includes a rib provided on the inner side in the rotation axis direction of the second swing member, and the second swing member is brought into contact with the rib, thereby restricting the tilt of the second swing member. The fixing device according to claim 1, wherein:   An abutting portion capable of abutting on the second oscillating member is provided at an outer edge of the rib in the rotation axis direction, and the traction spring pulls the second oscillating member on the abutting portion. The fixing device according to claim 2, wherein the fixing device is provided in parallel to the direction of the fixing. The first engagement portion further includes a connecting portion that connects an end portion of the spring body on the first engagement portion side and an end portion of the first linear portion on the spring body side,
The fixing device according to claim 1, wherein the connecting portion passes through an axis of the spring body.   The retaining portion includes an end portion of the first linear portion on the spring body side, an end portion of the first linear portion on a side away from the spring body, and the second linear portion of the first linear portion. 5. The fixing device according to claim 1, wherein the fixing device is provided so as to protrude from a plane passing through an end portion on a side separated from the one linear portion. The first swing member is
A swing plate supported swingably on the fixing device body;
A roller rotatably supported by the swing plate,
The cam is provided to be able to press the roller,
The fixing device according to claim 1, wherein the first engagement portion engages with the swing plate.   An image forming apparatus comprising the fixing device according to claim 1.

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