JP2011053722A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which is excellent in manual operability for changing the relative position between a pressure roller and a heating roller, and to provide an image forming apparatus equipped with the fixing device. <P>SOLUTION: The pressure roller 32 comes in contact with the heating roller 31, while being pressed by a pressing member. The pressed state can be released by a releasing member 82. At least, when the pressed state is released, the facing position of the pressure roller 32 with respect to the heating roller 31 can be changed in the circumferential direction of the heating roller 31. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus such as a laser printer including the same.

  An image forming apparatus such as a laser printer is provided with a fixing device that fixes toner transferred onto a sheet to the sheet. The fixing device includes a heating roller and a pressure roller arranged in a pressed state on the heating roller. The sheet onto which the toner has been transferred is conveyed between the heating roller and the pressure roller. Then, while the sheet passes between the heating roller and the pressure roller, the toner is fixed to the sheet by heating and pressing.

In this type of fixing device, it is known that the paper curls along the peripheral surface of the heating roller or the pressure roller, so-called paper curling. The paper curl causes a paper jam (conveyance failure) and a paper stack state on the paper discharge tray.
Accordingly, the pressure roller is provided so as to be movable (position changeable) with respect to the heating roller, and the pressure roller for the heating roller according to the state of the paper curl (the toner transfer surface of the paper is concavely or convexly curved). There has been proposed a paper curl that is corrected by changing the position (see, for example, Patent Document 1).
JP-A 64-9484

  However, the configuration according to the above proposal is provided with a motor and a mechanism (such as a rack and pinion mechanism) for converting the driving force of the motor into the moving force of the pressure roller, which increases the size of the device. End up. In order to reduce the size of the apparatus, it may be possible to omit the motor for moving the pressure roller and move the pressure roller by hand. A large force exceeding the sliding resistance must be applied, and the operability is not good.

  Accordingly, an object of the present invention is to provide a fixing device excellent in manual operability when changing the relative position between a pressure member and a heating roller, and an image forming apparatus including the same.

  In order to achieve the above object, according to the first aspect of the present invention, in the fixing device, the heating roller, a pressure member disposed to face the heating roller, the pressure member is pressed, and the pressure member A pressing member that presses the pressing roller against the heating roller, and a release member that releases the pressing of the pressing member by the pressing member, and the pressing member releases at least the pressing member by the pressing member. In this state, in the circumferential direction of the heating roller, it can be displaced so that the position facing the heating roller changes.

  According to a second aspect of the present invention, in the first aspect of the present invention, the first frame that holds the heating roller and the pressing member are held, and at least the pressing of the pressing member by the pressing member is released. A second frame configured to be displaceable so that an opposing position of the pressure member with respect to the heating roller changes in the circumferential direction in the circumferential direction; and the pressing member provided in the second frame, And a positioning member for positioning the second frame with respect to the first frame.

According to a third aspect of the present invention, in the second aspect of the present invention, the positioning member includes a plurality of positioning portions arranged in the circumferential direction for positioning the second frame in the circumferential direction. It is characterized by being.
According to a fourth aspect of the present invention, in the invention of the third aspect, the positioning member is formed with a plurality of concave portions and convex portions alternately in the circumferential direction, and the positioning portion is the concave portion. In addition, the pressing member includes an engagement piece that engages with the concave portion.

According to a fifth aspect of the invention, in the invention of the fourth aspect, the engagement piece is configured to engage with the concave portion in a non-contact state with the bottom surface of the concave portion. .
The invention according to claim 6 is the invention according to any one of claims 2 to 5, wherein the positioning members are provided at both ends of the second frame in the axial direction of the heating roller. It is characterized by.

  According to a seventh aspect of the present invention, in the invention according to any one of the second to sixth aspects, the positioning member is provided so as to be movable with respect to the second frame. A first urging member for urging the pressing member and pressing the pressing member against the second frame, and a first urging member for urging the positioning member in a direction opposite to the urging direction by the first urging member. 2 urging members.

The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the pressing member is in contact with the second frame at at least two positions in the circumferential direction. It is said.
According to a ninth aspect of the present invention, there is provided a fixing device for fixing a developer on a recording sheet conveyed in a predetermined direction, a heating member, a pressure member disposed to face the heating member, and the pressure member. A pressing member that presses the pressing member against the heating member, and a release member that releases the pressing of the pressing member by the pressing member, and the pressing member includes at least the pressing member It is characterized in that it can be displaced so that the position facing the heating roller changes in the predetermined direction when the pressure member is in a released state.

  According to a tenth aspect of the present invention, in the image forming apparatus, the fixing device according to any one of the first to ninth aspects is provided.

According to the first aspect of the present invention, the pressure member is configured to be displaceable with respect to the heating roller at least in a state where the pressing of the pressure member to the heating roller is released. The position of the member can be easily changed. Therefore, it is excellent in manual operability when the relative position between the pressure member and the heating roller is changed.
According to the second aspect of the present invention, the pressing member is positioned on the first frame (heating roller) when the second frame holding the pressing member is engaged with the pressing member. Therefore, the pressure member can be accurately positioned on the heating roller.

  According to the third aspect of the present invention, the positioning member is formed with a plurality of positioning portions arranged in the circumferential direction around the rotation axis of the heat roller. And in each positioning part, the 2nd frame is positioned. Therefore, the second frame can be positioned at a plurality of positions in the circumferential direction. As a result, the pressure member can be accurately arranged at a plurality of positions with respect to the heat roller.

According to invention of Claim 4, the recessed part currently formed in the positioning member makes a positioning part, and the engagement piece with which a press member is equipped engages with a recessed part, A 2nd frame is made into a 1st frame. Can be positioned with respect to each other.
According to the fifth aspect of the present invention, the engagement piece and the bottom surface of the recess are not in contact with each other with the engagement piece engaged with the recess. Therefore, no force is applied to the positioning member from the pressing member via the engagement piece. As a result, unnecessary force is prevented from being applied to the pressure member via the positioning member, so that the pressure member can be reliably pressed against the heating roller.

According to the sixth aspect of the present invention, since the positioning members are provided at both ends of the second frame in the axial direction of the heating roller, the second frame is positioned at both ends with respect to the first frame. Can do. Therefore, highly accurate positioning of the second frame with respect to the first frame can be achieved.
According to the invention of claim 7, the pressing member is urged by the first urging member. The positioning member is provided so as to be movable with respect to the second frame, and is biased by the second biasing member in a direction opposite to the biasing direction by the first biasing member. In other words, the pressing member and the positioning member are urged in the directions approaching each other by the first urging member and the second urging member, respectively. Therefore, the engagement between the pressing member and the positioning member is difficult to disengage, and the positioning state of the second frame with respect to the first frame by the positioning member can be favorably maintained.

According to the eighth aspect of the present invention, the pressing member can be brought into contact with the heating roller in a well-balanced pressing state in the circumferential direction of the heating roller.
According to the ninth aspect of the present invention, the pressurizing member is configured to be displaceable with respect to the heating member at least in a state where the pressing of the pressurizing member to the heating member is released. The position of the member can be easily changed. Therefore, it is excellent in manual operability when changing the relative position between the pressure member and the heating member.

  According to the tenth aspect of the present invention, it is possible to ensure excellent manual operability in the fixing device while reducing the size of the image forming apparatus.

1. 1 is a side sectional view of a laser printer according to an embodiment of the present invention.
A laser printer 1 as an example of an image forming apparatus includes a feeder unit 3 and an image forming unit 4 in a main body casing 2.
A front cover 5 is provided on the side wall on one side of the main casing 2 so as to be openable and closable with the lower end portion as a fulcrum. When the front cover 5 is opened, the internal space of the main casing 2 is opened. In this state, the process cartridge 13 (described later) can be attached to and detached from the internal space of the main casing 2. When the front cover 5 is closed, the internal space of the main casing 2 is closed.

In the following description, one side (the right side in FIG. 1) on which the front cover 5 is provided is the front side, and the opposite side (the left side in FIG. 1) is the rear side. Further, the left and right are defined with reference to the laser printer 1 as viewed from the front side. Further, with respect to the process cartridge 13 and the developing cartridge 19 (described later), the front, rear, left, right, top and bottom are defined based on the mounting state with respect to the main casing 2.
(1) Feeder Unit The feeder unit 3 includes a paper feed tray 6, a paper feed roller 7, a paper feed pad 8, a pickup roller 9, a pinch roller 10, and a pair of registration rollers 11.

In the sheet feed tray 6, sheets P as an example of recording sheets are stacked. The uppermost sheet P in the sheet feed tray 6 is sent out between the sheet feed roller 7 and the sheet feed pad 8 by the pickup roller 9. The fed paper P passes through the paper feed roller 7 and the paper feed pad 8 and between the paper feed roller 7 and the pinch roller 10 in order, and is conveyed to the registration roller 11. Then, the sheet P is conveyed by the registration roller 11 toward the transfer position (described later) of the image forming unit 4 after registration.
(2) Image Forming Unit The image forming unit 4 includes a scanner unit 12, a process cartridge 13, and a fixing unit 14 as an example of a fixing device.
(2-1) Scanner Unit The scanner unit 12 is disposed in the upper part in the main body casing 2. The scanner unit 12 includes a laser (not shown), a polygon mirror 15, a plurality of lenses 16, and a plurality of reflecting mirrors 17, and is directed toward a photosensitive drum 20 (described later) of the process cartridge 13 as indicated by a chain line. A laser beam is emitted.
(2-2) Process Cartridge The process cartridge 13 is disposed below the scanner unit 12. The process cartridge 13 includes a drum cartridge 18 and a developing cartridge 19 that is detachably attached to the drum cartridge 18.

A photosensitive drum 20 is rotatably provided on the drum cartridge 18. In the drum cartridge 18, a scorotron charger 21 and a transfer roller 22 are disposed around the photosensitive drum 20.
The developing cartridge 19 includes an agitator 24, a supply roller 25, a developing roller 26, and a layer thickness regulating blade 27 in a housing 23.

In the casing 23, a toner storage chamber 28 and a developing chamber 29 are formed side by side. The toner storage chamber 28 and the developing chamber 29 are communicated with each other through a communication port 30.
The toner storage chamber 28 stores a non-magnetic one-component positively charged polymerized toner.
The agitator 24 is provided in the toner storage chamber 28.
The supply roller 25 is provided behind the communication port 30 in the developing chamber 29.

The developing roller 26 is provided in the developing chamber 29 and is in pressure contact with the supply roller 25 from the rear side.
The layer thickness regulating blade 27 is formed in a plate shape extending in the left-right direction. The base end portion of the layer thickness regulating blade 27 is fixed to the housing 23, and the free end portion is in pressure contact with the peripheral surface of the developing roller 26.
(2-3) Development / Transfer Operation While the toner in the toner storage chamber 28 is agitated in the toner storage chamber 28 by the rotation of the agitator 24, a part of the supply roller in the development chamber 29 is connected through the communication port. 25. The toner supplied to the supply roller 25 is supplied to the developing roller 26 by the rotation of the supply roller 25. At this time, the toner is triboelectrically charged between the supply roller 25 and the developing roller 26 to which a developing bias is applied. The toner thus supplied to the developing roller 26 is regulated in thickness by the layer thickness regulating blade 27 as the developing roller 26 rotates, and is carried on the peripheral surface of the developing roller 26 as a thin layer having a constant thickness. .

On the other hand, the surface of the photosensitive drum 20 is uniformly positively charged by the scorotron charger 21 as the photosensitive drum 20 rotates. Then, the surface of the positively charged photosensitive drum 20 is selectively irradiated with a laser beam from the scanner unit 12 to form an electrostatic latent image based on image data.
When the electrostatic latent image formed on the surface of the photosensitive drum 20 faces the developing roller 26 by the rotation of the photosensitive drum 20, the positively charged toner carried on the surface of the developing roller 26 becomes the electrostatic latent image. Supplied. As a result, the electrostatic latent image is visualized and a toner image is carried on the surface of the photosensitive drum 20. The toner image is transferred between the photosensitive drum 20 and the transfer roller 22 (
The image is transferred onto the paper P conveyed to the transfer position.
(3) Fixing Unit The fixing unit 14 is provided behind the process cartridge 13. The fixing unit 14 includes a heating roller 31 as an example of a heating member, and a pressure roller 32 as an example of a pressure member that is pressed against the heating roller 31 from below. The heating roller 31 includes a metal tube whose surface is coated with a fluororesin, and a halogen lamp for heating inserted into the metal tube. The pressure roller 32 has a configuration in which a metal roller shaft 31A is covered with a rubber material.

The toner image transferred onto the paper P is fixed on the paper P by being heated and pressed while the paper P passes between the heating roller 31 and the pressure roller 32 in the fixing unit 14.
(4) Paper Discharge The paper P on which the toner image has been fixed is conveyed toward the paper discharge roller 33 and is discharged onto the paper discharge tray 34 formed on the upper surface of the main body casing 2 by the paper discharge roller 33.
2. Details of Fixing Unit FIGS. 2 (a), 2 (b), 3 (a), 3 (b), 4 (a), and 4 (b) are obtained by cutting the fixing unit 14 partially. It is a right view shown. 5 and 6 are rear views of the fixing unit 14 (viewed from the rear side).
(1) Frame The fixing unit 14 includes an upper frame 41 as an example of a first frame that rotatably holds the heating roller 31 and a lower frame 42 as an example of a second frame that rotatably holds the pressure roller 32. And. The upper frame 41 and the lower frame 42 are not connected to each other, and the lower frame 42 is provided so as to be movable in the circumferential direction of the heating roller 31 with respect to the upper frame 41.
(1-1) Upper Frame The upper frame 41 is made of resin, and integrally includes a pair of left and right side walls 43, an upper wall 44, a front wall 45, and a rear wall 46.

As shown in FIG. 5 and FIG. 6, the pair of side walls 43 are opposed to each other with an interval in the left-right direction. For example, as shown in FIG. 2A, each side wall 43 is formed with a notch 47 that receives the end of the heating roller 31.
A pressing member support portion 48 for supporting a pressing member 72 (described later) is provided at the front portion of each side wall 43. In addition, a square cylindrical spring accommodating portion 49 that accommodates a coil spring 77 (described later) is provided at the rear end portion of each side wall 43.

The upper wall 44 is constructed between the upper ends of the side walls 43.
The front wall 45 is constructed between the front portions of the side walls 43. On the front surface of the front wall 45, a plurality of paper guide ribs 50 for guiding the paper P between the heating roller 31 and the pressure roller 32 are provided side by side at appropriate intervals. Each of the paper guide ribs 50 is formed in a triangular plate shape that protrudes toward the front and decreases in the downward direction.

The rear wall 46 is constructed between the rear ends of the side walls 43. A roller holding portion 51 is provided on the rear wall 46. The roller holding portion 51 protrudes rearward from substantially the entire width of the rear wall 46. As shown in FIGS. 5 and 6, rollers 52 for guiding the conveyance of the paper P after the fixing process are disposed at a plurality of positions at appropriate intervals in the left-right direction at the tip of the roller holding portion 51. Each is held rotatably. Further, on the lower surface of the roller holding portion 51, a sheet peeling claw 84 having a substantially triangular shape in a side view for peeling the sheet P from the peripheral surface of the heating roller 31 is provided at a position corresponding to each roller 52.
(1-2) Lower Frame The lower frame 42 is formed by bending a metal plate. As shown in FIGS. 2 to 4, the front wall 53, the bottom wall 54, the rear wall 55, and a pair of left and right side walls. 56 are integrally provided.

The front wall 53 faces the pressure roller 32 from the front side.
The bottom wall 54 is formed in a substantially rectangular shape extending rearward from the lower end edge of the front wall 53. As shown in FIGS. 5 and 6, the bottom wall 54 is formed so that the width in the left-right direction is shorter than the width in the left-right direction of the front wall 53, and between the left and right end edges of the bottom wall 54 and the left and right side walls 56. A space 57 is formed.

The rear wall 55 extends upward from the rear edge of the bottom wall 54. A pair of extending portions 58 extending to the left side and the right side are formed at the upper end portion of the rear wall 55.
Each side wall 56 is bent forward from the front end edge of the extending portion 58 of the rear wall 55 and extends in the front-rear direction. For example, as shown in FIG. 2A, a bearing housing portion 59 is formed in each side wall 56 by being cut out in a substantially U shape downward from the upper end edge thereof. A resin bearing member 60 is fitted and fixed to the bearing housing portion 59. The pressure roller 32 is rotatably held between the side walls 56 by the rotation shaft 32 a of the pressure roller 32 being rotatably inserted into the bearing member 60.
(2) Positioning member On the outside of each side wall 56 of the lower frame 42 (left side of the left side wall 56, right side of the right side wall 56), for example, a metal plate is bent as shown in FIG. A positioning member 61 to be formed is provided. Each positioning member 61 includes a main body 62 that faces the side wall 56 from the outside in the axial direction of the pressure roller 32, and a portion between the bottom wall 54 and the side wall 56 of the lower frame 42 from the central portion of the lower end edge of the main body 62. An operation portion 63 extending toward the space 57 is integrally provided.

  As shown in FIG. 2B, a long hole 64 is formed in the main body 62 at the center in the front-rear direction in the direction opposite to the heating roller 31 and the pressure roller 32 (substantially in the vertical direction). . A boss 65 protruding from the side wall 56 of the lower frame 42 is inserted into the elongated hole 64 in a loosely fitted state. A substantially C-shaped resin stopper 66 is fixed to the tip of the boss 65. In addition, a long hole 67 is formed in the main body 62 at a position spaced apart before and after the long hole 64 in the facing direction of the heating roller 31 and the pressure roller 32 (the long diameter direction of the long hole 64). ing. A boss 68 protruding from the side wall 56 of the lower frame 42 is inserted into each elongated hole 67 in a loosely fitted state. Accordingly, the positioning member 61 is provided so as not to be detached from the side wall 56 of the lower frame 42 and to be movable in the direction in which the heating roller 31 and the pressure roller 32 face each other.

  The lower end edge of the main body 62 is formed in an arc shape around the rotation axis of the heating roller 31 on both the front and rear sides of the operation unit 63. Then, a plurality of convex portions 69 projecting downward from the lower end edge of the main body portion 62 are formed at intervals from each other, so that the main body portion 62 has a positioning portion 70 including a concave portion adjacent to each convex portion 69. Are formed side by side along the circumferential direction of the heating roller 31 (hereinafter sometimes simply referred to as “circumferential direction”). Each positioning portion 70 has a bottom surface positioned above the lower end portion 56a of the side wall 56 of the lower frame 42, and is formed to a depth such that engagement pieces 80 and 81 to be described later do not contact the bottom surface.

Each operation part 63 is formed in a substantially rectangular shape. One end portion of a leaf spring 71 as an example of a second urging member is fixed to the surface of each operation portion 63 facing the pressure roller 32. The other end of the leaf spring 71 is fixed to the front wall 53 of the lower frame 42. Accordingly, the positioning member 61 is biased downward (in a direction opposite to a biasing direction of a coil spring 77 described later) by the plate spring 71. Further, one end portion of the leaf spring 71 may only be in contact with the surface of the operation portion 63 facing the pressure roller 32.
(3) Pressing member A pressing member 72 formed by bending a metal plate is provided outside each positioning member 61. Each pressing member 72 is integrally provided with a substantially V-shaped main body portion 73 and two engaging portions 74 and 75 in side view.

  The main body 73 faces the side wall 56 of the lower frame 42 from the outside in the rotational axis direction of the pressure roller 32. The substantially V-shaped one end of the main body 73 enters the pressing member support 48 of the upper frame 41. The pressing member support portion 48 is provided with a support shaft (not shown) extending in the left-right direction, and one end portion of the main body portion 73 is rotatably supported by the support shaft. On the other hand, for example, as shown in FIG. 3A, a flange portion 76 is formed at the other V-shaped other end portion of the main body portion 73. One end of a coil spring 77 as an example of a first biasing member accommodated in the spring accommodating portion 49 of the upper frame 41 is locked to the flange portion 76. The other end of the coil spring 77 is locked to the spring accommodating portion 49, and the coil spring 77 has an elastic force in a direction in which both ends approach each other, that is, in a direction in which the flange portion 76 approaches the upper frame 41. .

A substantially U-shaped notch 78 in side view is formed between one end and the other end of the main body 73. The bearing member 60 is inserted into the notch 78, thereby restricting the amount of movement of the lower frame 42 in the circumferential direction.
Claw portions 79 extending toward the side wall 56 of the lower frame 42 are formed on both front and rear sides of the notch 78. Each claw portion 79 faces the bearing member 60 from above. Thus, the lower frame 42 is provided between the four claw portions 79 and the engaging portions 74 and 75 described below so as not to fall off in a state having play.

  The engaging portion 74 is formed in a substantially L shape in bottom view, extending downward from the front portion of the lower end portion of the main body portion 73 and bending so as to face the operation portion 63 of the positioning member 61 from the front side. A distal end portion (a portion facing the operation portion 63) 80 of the engaging portion 74 is opposed to the lower end edge of the main body portion 62 of the positioning member 61 from below by being cut out in a rectangular shape from the upper end thereof. The distal end portion 80 enters the positioning portion 70 of the positioning member 61 and engages with the positioning portion (concave portion) 70 in a state where no force other than the urging force of the leaf spring 71 is applied to the positioning member 61. It is a piece.

  The engaging portion 75 extends downward from the rear portion of the lower end portion of the main body portion 73. The engagement portion 75 includes an engagement piece 81 extending from the front end edge of the lower end portion toward the positioning member 61. The engaging piece 81 faces the lower end edge of the main body 62 of the positioning member 61 from below, and the positioning member 70 of the positioning member 61 is not subjected to any force other than the urging force of the leaf spring 71. I'm stuck in.

Each pressing member 72 is urged by the elastic force of the coil spring 77 in the direction in which the other end of the main body 73 comes close to one end of the main body 73 as a fulcrum. By this urging, the engagement pieces 80 and 81 of each pressing member 72 abut against the lower end portion 56 a of the side wall 56 of the lower frame 42 and press the lower frame 42 in the direction approaching the upper frame 41. As a result, the pressure roller 32 held by the lower frame 42 comes into contact with the heating roller 31 held by the upper frame 41 in a pressed state, thereby forming a so-called nip state.
(4) Release member A release member 82 for releasing the pressing state of the pressure roller 32 against the heating roller 31 is attached to each pressing member 72. The release member 82 is made of resin and has a substantially L shape in side view. A support shaft 83 extending outward from the pressing member 72 is inserted into the bent portion of the release member 82. The release member 82 is in a first state in which the long piece portion extends downward from the support shaft 83 and the short piece portion faces the side wall 43 of the upper frame 41 with a space therebetween (FIGS. 2A and 2B). And a second state in which the long piece portion extends rearward and the tip of the short piece portion abuts against the side wall 43 of the upper frame 41 (FIGS. 3A, 3B, 4A, and 4). (Refer to (b))
And is swingably supported.
(5) Contact position changing operation of the pressure roller 32 with respect to the heating roller 31 As shown in FIG. 2A, when each release member 82 is in the first state, each release member 82 is placed on the side wall 43 of the upper frame 41. Since there is no contact, only the elastic force of the coil spring 77 acts on each pressing member 72. Therefore, the lower frame 42 is pressed by each pressing member 72, and the pressure roller 32 contacts the heating roller 31 in a pressed state.

  As shown in FIG. 3A, when each release member 82 is displaced from the first state to the second state, each release member 82 comes into contact with the side wall 43 of the upper frame 41, and each release member 82 causes the upper frame 41 to move. Is pressed, the upper frame 41 and each pressing member 72 are separated from each other against the elastic force of the coil spring 82. As a result, the pressure roller 32 slightly moves in a direction away from the heating roller 31, the pressing state of the pressure roller 32 against the heating roller 31 is released, and the pressure roller 32 is separated or weakly applied to the heating roller 31. It will be in the release state where it touches.

  As shown in FIG. 4A, when the operating portion 63 of each positioning member 61 is pressed against the urging force of the leaf spring 71 (pressed toward the pressure roller 32) in the released state, each positioning member 61 is pressed. Moves upward, and the engagement pieces 80, 81 of each pressing member 72 are disengaged from the positioning portion 70. Thus, the positioning state of the lower frame 42 due to the engagement pieces 80 and 81 engaging with the positioning portion 70 is released (stopper release), and the lower frame 42 is moved around the heating roller 31 with respect to the upper frame 41. Can be moved in the direction.

By moving the lower frame 42 relative to the upper frame 41, the pressure roller 32 can be moved in the circumferential direction of the heating roller 31 in the released state. For example, as shown in FIG. 4B, the pressure roller 32 can be moved to the rear side in the circumferential direction with respect to the heating roller 31 rather than the state shown in FIG.
When each release member 82 is displaced from the second state to the first state from the release state shown in FIG. 4B, the pressure roller 32 is pressed by the heating roller 31 as shown in FIG. The pressure roller 32 and the heating roller 31 are in contact with each other. In FIG. 4B, the pressure roller 32 is in contact with the heating roller 31 on the rear side along the circumferential direction from the state shown in FIG.

Even when the pressure roller 32 is moved forward along the circumferential direction with respect to the heating roller 31, the same operation as described above can be performed.
3. As described above, since the pressure roller 32 is configured to be displaceable with respect to the heating roller 31 at least in a state where the pressure roller 32 is not pressed against the heating roller 31, the pressure to the heating roller 31 is increased. The position of the roller 32 can be easily changed. Therefore, it is excellent in manual operability when the relative position between the pressure roller 32 and the heating roller 31 is changed. Since the position of the pressure roller 32 with respect to the heating roller 31 can be easily changed, the curl can be easily corrected according to the curled state of the paper P.

  Further, by releasing the pressed state, the upper frame 41 and the lower frame 42 can be relatively moved with a small force. Therefore, a motor or the like for moving the upper frame 41 and the lower frame 42 relative to each other is unnecessary, and the size of the fixing unit 14 can be reduced, and the pressure roller 32 and the heating roller 31 can be reduced. Excellent manual operability for changing the relative position can be ensured. Then, by reducing the size of the fixing unit 14, the size of the laser printer 1 can be reduced.

Further, since the lower frame 42 holding the pressure roller 32 is engaged with the pressing member 72, the pressure roller 32 is positioned on the upper frame 41 (heating roller 31). 32 can be accurately positioned on the heating roller 31.
In the positioning member 61, a plurality of positioning portions 70 are formed side by side along the circumferential direction of the heating roller 31. Then, the lower frame 42 is positioned in each positioning portion 70. Therefore, the lower frame 42 can be positioned at a plurality of positions along the circumferential direction. As a result, the pressure roller 32 can be accurately arranged at a plurality of positions with respect to the heating roller 31.

In the fixing unit 14, the concave portion formed in the positioning member 61 forms the positioning portion 70, and the engagement pieces 80 and 81 provided in the pressing member 72 engage with the concave portion, so that the lower frame 42 becomes the upper frame 41. Can be positioned with respect to each other.
And in the state which the engagement pieces 80 and 81 engaged with the recessed part (positioning part 70), the engagement pieces 80 and 81 and the bottom face of a recessed part are not contacting. Therefore, no force is applied to the positioning member 61 from the pressing member 72 via the engagement pieces 80 and 81. As a result, unnecessary force is prevented from being applied to the pressure roller 32 via the positioning member 61, so that the pressure roller 32 can be reliably pressed against the heating roller 31.

In addition, since the positioning members 61 are provided at both ends of the lower frame 42 in the axial direction of the pressure roller 32, the lower frame 42 can be positioned at both ends of the upper frame 41. Therefore, highly accurate positioning of the lower frame 42 with respect to the upper frame 41 can be achieved.
The pressing member 72 is biased by a coil spring 77. The positioning member 61 is provided so as to be movable with respect to the lower frame 42, and is urged by a leaf spring 71 in a direction opposite to the urging direction by the coil spring 77. That is, the pressing member 72 and the positioning member 61 are urged by the coil spring 77 and the leaf spring 71 in the directions approaching each other. Therefore, the engagement between the pressing member 72 and the positioning member 61 is unlikely to be released, and the positioning state of the lower frame 42 with respect to the upper frame 41 by the positioning member 61 can be favorably maintained.

The pressing member 72 contacts the lower frame 42 at two positions (engaging pieces 80 and 81) in the circumferential direction of the heating roller 31. Therefore, in the circumferential direction of the heating roller 31, the pressure roller 32 can be brought into contact with the heating roller 31 in a well-balanced pressing state.
4). Other Embodiments As an example of the image forming apparatus, a monochrome color laser printer has been described. However, the image forming apparatus according to the present invention may be configured as a color laser printer (including a tandem type and an intermediate transfer type).

Further, although the heating roller 31 is taken up as an example of the heating member, the heating member may be a film used in a film fixing method, or may be configured such that a film is stretched on the heating roller. .
Further, the pressure member is not limited to the pressure roller 32, and may be configured such that a belt is stretched around the roller.

1 is a side sectional view of a laser printer according to an embodiment of the present invention. FIG. 4 is a right side view of the fixing unit in a nip state, partly cut away, where (a) shows a state in which the pressure roller is relatively disposed on the front side, and (b) shows a state in which the pressure roller is relatively rearward. The state arranged on the side is shown. FIG. 4A is a right side view showing a partially cut fixing unit in a released state, in which FIG. 4A shows a state in which the pressure roller is relatively disposed on the front side, and FIG. The state arranged on the side is shown. FIG. 7 is a right side view of the fixing unit that has been stopper-released in a released state, in which (a) shows a state in which the pressure roller is relatively disposed on the front side, and (b) shows a state in which the pressure roller is The state arrange | positioned relatively rear side is shown. FIG. 6 is a rear view of the fixing unit in a nip state (viewed from the rear side). FIG. 6 is a rear view of the fixing unit in a released state.

DESCRIPTION OF SYMBOLS 1 Laser printer 31 Heat roller 32 Pressure roller 41 Upper frame 42 Lower frame 61 Positioning member 69 Convex part 70 Positioning part 72 Press member 80 Engagement piece 81 Engagement piece 82 Release member P Paper

Claims (10)

A heating roller;
A pressure member disposed opposite to the heating roller;
A pressing member that presses the pressing member and presses the pressing member against the heating roller;
A release member for releasing the pressing of the pressing member by the pressing member,
The pressure member is configured to be displaceable so that a position facing the heating roller is changed in a circumferential direction of the heating roller when at least the pressing of the pressing member by the pressing member is released. A fixing device characterized by that. A first frame for holding the heating roller;
When the pressure member is held and at least pressed by the pressure member, the pressure member is displaced so that the position of the pressure member facing the heating roller changes in the circumferential direction. A second frame configured to be capable;
The positioning device according to claim 1, further comprising a positioning member provided on the second frame for engaging the pressing member to position the second frame with respect to the first frame. The fixing device described.   The fixing device according to claim 2, wherein a plurality of positioning portions for positioning the second frame in the circumferential direction are arranged in the circumferential direction on the positioning member. In the positioning member, a plurality of concave portions and convex portions are alternately formed in the circumferential direction,
The positioning portion is the concave portion,
The fixing device according to claim 3, wherein the pressing member includes an engagement piece that engages with the concave portion.   The fixing device according to claim 4, wherein the engagement piece is configured to engage with the recess in a state of non-contact with a bottom surface of the recess.   The fixing device according to claim 2, wherein the positioning member is provided at both ends of the second frame in the axial direction of the heating roller. The positioning member is provided to be movable with respect to the second frame;
A first urging member for urging the pressing member and causing the second frame to press the pressing member;
The second urging member that urges the positioning member in a direction opposite to the urging direction by the first urging member is provided. Fixing device.   The fixing device according to claim 1, wherein the pressing member is in contact with the second frame at at least two positions in the circumferential direction. In a fixing device for fixing a developer on a recording sheet conveyed in a predetermined direction,
A heating member;
A pressure member disposed opposite to the heating member;
A pressing member that presses the pressing member and presses the pressing member against the heating member;
A release member for releasing the pressing of the pressing member by the pressing member,
The pressure member is configured to be displaceable so that a position facing the heating roller is changed in the predetermined direction at least when the pressure member is released from being pressed by the pressure member. A fixing device that is characterized.   An image forming apparatus comprising the fixing device according to claim 1.

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