JP2019066507A - Fixing apparatus - Google Patents

Abstract

To provide a fixing apparatus configured to improve convenience while preventing abnormal noise.SOLUTION: A cam member 150 has a cam surface 155 whose distance from a rotation center X150 is made shorter toward a second direction R2. A control unit C1 displaces a second fixing member 102 to a pressure-contact position by rotating the cam member 150 in a first direction R1 by means of a driving source M1, and displaces the second fixing member 102 to a separation position by rotating the cam member 150 in the second direction R2 by means of the driving source M1. When a position where a part 151 of the cam surface 155 is in contact with a holding member 130 with the second fixing member 102 displaced at the separation position is defined as a first position PS1 and a position where the part 151 of the cam surface 155 is separated from the holding member 130 with the second fixing member 102 displaced at the pressure-contact position is defined as a second position PS2, the first direction R1 is opposite to a direction R3 in which a distance from the first position PS1 to the second position PS2 around the rotation center X150 is minimum.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing device.

  Patent Document 1 discloses an example of a conventional fixing device. In this fixing device, a recording sheet is sandwiched and heated by a pressure roller, a nip plate and a fixing belt, and a developer image is thermally fixed on the recording sheet. The fixing device includes a second frame, a cam and a tension coil spring.

  The second frame has a pressure contact position (first position) at which the nip plate and the fixing belt are in pressure contact with the pressure roller, and a separated position (third position) at which the nip plate and the fixing belt are separated from the pressure roller. And nipping plate and fixing belt. The cam can be rotated in a narrow angle range of about 90 ° or so in one direction and the other direction around the axis of the shaft by the user operating the operation unit. The cam has a first release surface and a full release surface. The tension coil spring biases the nip plate and the fixing belt in a biasing direction approaching the pressure roller via an arm member connected to the second frame.

  The cam is rotated by about 90 ° in one direction from the first direction and turned to the third direction by the user to bring the first release surface into contact with the arm member and nip it against the tension coil spring. The plate and the fixing belt are displaced to the separated position. On the other hand, the cam causes the first release surface and the complete release surface to be separated from the arm member by being operated by the user and rotating about 90 degrees in the other direction from the third direction to about the first direction. The nip plate and the fixing belt biased by the tension coil spring are displaced to the pressing position.

JP, 2013-68660, A

  By the way, in order to improve the convenience of the fixing device, it is conceivable to automatically displace the second fixing member between the pressure contact position and the separated position. However, in this case, noise such as collision noise between components may be generated.

  When the fixing device described in Patent Document 1 is specifically described as an example, a drive source and a transmission portion are newly provided to rotate the cam, and the nip plate and the fixing belt are automatically displaced between the pressure contact position and the separation position. It is possible to do it. However, the transmission part generally includes meshing gears, mating shaft holes and shafts, and the like, and has a gap or the like between the components thereof. Then, when the cam rotates, the position at which the arm member and the first release surface or the full release surface contact is displaced relative to the axis of the cam. Thereby, the direction in which the biasing force of the tension coil spring tries to rotate the cam about the axis of the shaft may be suddenly changed from one direction to the other direction or from the other direction to the one direction by the change in the rotation posture of the cam. There is sex. In such a case, the gap between the components of the transmission unit may be rapidly eliminated, and noise such as collision noise between components may be generated.

  The present invention has been made in view of the above-described conventional circumstances, and an object of the present invention is to provide a fixing device capable of improving convenience while suppressing the generation of abnormal noise.

The fixing device according to the present invention is a fixing device that heats a recording sheet with a first fixing member and a second fixing member, and thermally fixes the developer image on the recording sheet,
The second fixing member is displaceable between a pressing position where the second fixing member presses against the first fixing member and a separating position where the second fixing member separates from the first fixing member. A holding member for holding the
A cam member rotatable about a rotation center in a first direction and in a second direction opposite to the first direction, and having a cam surface whose distance from the rotation center is shortened in the second direction;
A biasing member for biasing the second fixing member in a biasing direction approaching the first fixing member;
A driving source generating a driving force for rotating the cam member in the first direction and the second direction;
A transmission unit for transmitting the driving force to the cam member;
A control unit that controls the drive source;
The control unit
By rotating the cam member in the first direction by the drive source, the cam surface is separated from the holding member, and the second fixing member biased by the biasing member is displaced to the pressure contact position. ,
By rotating the cam member in the second direction by the drive source, the cam surface is brought into contact with the holding member, and the second fixing member is displaced to the separated position against the biasing member.
With the second fixing member displaced to the separated position, a position where a part of the cam surface contacts the holding member is a first position, and the second fixing member is displaced to the pressure contact position. Assuming that the position at which the part of the surface separates from the holding member is a second position, the first direction is opposite to the direction in which the second position is reached at the shortest distance from the first position around the rotation center. It is characterized by being oriented.

  In the fixing device of the present invention, the cam member is rotated in the first direction and the second direction by the drive source and the transmission unit, and the second fixing member is automatically displaced between the pressure contact position and the separated position. Thereby, the position where the holding member and the cam surface are in contact with each other is the center of rotation, as compared with the case where the second fixing member is displaced between the pressure contact position and the separated position by rotating the cam member in the same direction all the time. The range of relative displacement can be narrowed.

  Further, in this fixing device, the first direction is set opposite to the direction in which the second position is reached at the shortest distance from the first position around the rotation center. That is, in the above-described conventional fixing device, the cam is rotated by the shortest distance to displace the nip plate and the fixing belt between the pressure contact position and the separated position, whereas in the fixing device of the present invention The second fixing member can be displaced between the press-contacting position and the separating position by rotating by a long distance. As a result, the range in which the position at which the holding member and the cam surface are in contact with each other relative to the center of rotation can be further narrowed.

  As a result, in this fixing device, the direction in which the urging force of the urging member causes the cam member to rotate about the rotation center is from the first direction to the second direction or the second direction depending on the change in the rotation posture of the cam member. Can be suppressed from being suddenly changed in the first direction. Thereby, the collision of the component parts of a transmission part can be suppressed.

  Therefore, in the fixing device of the present invention, the convenience can be improved while suppressing the generation of abnormal noise.

  Further, in this fixing device, since the cam surface is separated from the holding member with the second fixing member in the pressure contact position, the pressing force of the second fixing member against the first fixing member is only the biasing force of the biasing member. Determined by As a result, it can be easily realized that the pressing force of the second fixing member is set to a desired magnitude.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus provided with a fixing device according to an embodiment. FIG. 2 is a perspective view of the fixing device of the embodiment. FIG. 2 is a side view of the fixing device of the embodiment. FIG. 7 is a schematic cross-sectional view showing a state in which the second fixing member is in the separated position. FIG. 7 is a schematic cross-sectional view showing a state in which the second fixing member is in the weak pressure contact position. FIG. 7 is a schematic cross-sectional view showing a state in which the second fixing member is in a pressure contact position. It is a perspective view of a cam member. It is a side view of a cam member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a fragmentary side view explaining an operation of a cam member to a holding member. It is a partial side view explaining the 1st direction of a cam member. It is a graph which shows the relationship between the rotation angle of a cam member, and the moment which acts on a cam member from a holding member.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Example)
As shown in FIG. 1, the fixing device 100 of the embodiment is an example of a specific aspect of the fixing device of the present invention. The fixing device 100 is provided in the image forming apparatus 1. The image forming apparatus 1 is a laser printer that forms an image on a sheet SH by an electrophotographic method.

  In FIG. 1, the right side of the drawing is defined as the front of the image forming apparatus 1, and the side coming to the left when the image forming apparatus 1 is viewed from the front, that is, the front side of the drawing is defined as the left of the image forming apparatus 1. , Displays the left, right, upper and lower directions. And each direction shown in each figure after FIG. 2 is made to correspond to each direction shown in FIG. 1, and is displayed. In the following, the fixing device 100 will be described in detail after the schematic configuration of each component included in the image forming apparatus 1 is described based on FIG. 1 and the like.

<Schematic Configuration of Image Forming Apparatus>
As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 2, a supply unit 20, a process cartridge 7, a scanner unit 8, a fixing device 100, and a discharge unit 29.

  The device body 2 is configured to include a housing and a frame member (not shown) provided in the housing. A sheet cassette 2C is detachably provided at a lower portion in the apparatus main body 2. Inside the sheet cassette 2C, recording sheets SH on which an image is to be formed are accommodated in a stacked state. The recording sheet SH is a sheet, an OHP sheet, or the like. Further, in the present embodiment, an envelope is also included in the recording sheet SH.

  A discharge tray 2D is provided on the upper surface of the apparatus body 2. The recording sheet SH on which the image formation has been completed is discharged to the discharge tray 2D.

  The supply unit 20, the process cartridge 7, the scanner unit 8, the fixing device 100 and the discharge unit 29 are assembled to a frame member (not shown) at a position above the sheet cassette 2 C in the apparatus main body 2.

  In the apparatus body 2, a transport path P1 is provided. The conveyance path P1 passes through the supply unit 20 while making a U-turn upward from the front end of the sheet cassette 2C, then proceeds substantially horizontally backward, and further U-turns upward through the process cartridge 7 and the fixing device 100. While it is a path leading to the discharge tray 2D via the discharge unit 29.

  The supply unit 20 feeds the recording sheet SH accommodated in the sheet cassette 2C to the conveyance path P1 sheet by sheet by the supply roller 21, the separation roller 22 and the separation pad 22A. Then, the supply unit 20 conveys the recording sheet SH toward the process cartridge 7 by the conveyance roller 23A and the pinch roller 23P disposed along the conveyance path P1, and the registration roller 24A and the pinch roller 24P.

  The process cartridge 7 includes a toner storage unit 7A, a photosensitive drum 7B, a developing roller 7C, a charger 7D, and the like, which have a known configuration.

  The scanner unit 8 is provided above the process cartridge 7. The scanner unit 8 is configured to include a laser light source, a polygon mirror, an fθ lens, a reflecting mirror, and the like, which are known configurations. The scanner unit 8 irradiates the photosensitive drum 7B in the process cartridge 7 with a laser beam from above.

  The surface of the photosensitive drum 7B is uniformly positively charged by the charger 7D with the rotation thereof, and then exposed by high-speed scanning of a laser beam emitted from the scanner unit 8. Thereby, an electrostatic latent image corresponding to the image to be formed on the recording sheet SH is formed on the surface of the photosensitive drum 7B. The developing roller 7C supplies the developer from the toner storage unit 7A to the surface of the photosensitive drum 7B in correspondence to the electrostatic latent image. Thus, the developer image is carried on the surface of the photosensitive drum 7B. The developer image is transferred onto the recording sheet SH passing through the process cartridge 7.

  The fixing device 100 is provided behind the process cartridge 7. The fixing device 100 includes a heating belt unit 102 positioned on the upper side with respect to the conveyance path P1, and a pressure roller 101 opposed to the heating belt unit 102 from below with the conveyance path P1 interposed therebetween. The fixing device 100 heats and presses the recording sheet SH with the pressure roller 101 and the heating belt unit 102 to thermally fix the developer image on the recording sheet SH.

  The discharge unit 29 discharges the recording sheet SH on which the developer image is fixed to the discharge tray 2D by the discharge roller 29A and the discharge pinch roller 29P.

<Detailed Configuration of Fixing Device>
As shown in FIGS. 2 and 3, the fixing device 100 includes a fixing frame 120, a pressure roller 101, a heating belt unit 102, a pair of left and right holding members 130, a pair of left and right cam members 150, and a pair of left and right tension coil springs 109. Have.

  The pressure roller 101 is an example of the “first fixing member” in the present invention. The heating belt unit 102 is an example of the “second fixing member” in the present invention. The tension coil spring 109 is an example of the “biasing member” in the present invention.

  The right holding member 130 has the same shape as the left holding member 130. For this reason, the illustration of the right holding member 130 is simplified. The right cam member 150 has the same shape as the left cam member 150. For this reason, the illustration of the right cam member 150 is simplified.

  Further, as shown in FIG. 2, the fixing device 100 includes a control unit C1, a motor M1, and a transmission unit G1. The control unit C1 is configured as a microcomputer mainly composed of a CPU, a ROM, and a RAM (not shown). The ROM stores a program for the CPU to control various operations of the image forming apparatus 1 and a program for executing identification processing. The RAM is used as a storage area for temporarily recording data and signals used when the CPU executes the above program, or as a work area for data processing. The control unit C1 not only controls the fixing device 100, but also controls the entire image forming apparatus 1 including the supply unit 20, the process cartridge 7, the scanner unit 8 and the discharge unit 29. The motor M1 is an example of the "drive source" in the present invention. The motor M1 may be dedicated to the fixing device 100, or may also serve as a drive source of the supply unit 20, the process cartridge 7, and the discharge unit 29. In the present embodiment, the motor M1 is a stepping motor, and is controlled by the control unit C1 to rotate forward and backward.

  As shown in FIGS. 2 and 3, the fixing frame 120 has a base portion 121 and a pair of left and right side wall portions 122. The base portion 121 extends long in the left-right direction, and is supported by a frame member (not shown) of the apparatus main body 2.

  The left side wall 122 is connected to the left end of the base 121. The left side wall 122 projects upward and extends in the front-rear direction. As shown in FIG. 2, the right side wall 122 is connected to the right end of the base 121. The right sidewall 122 projects upward and extends in the front-rear direction. The right side wall portion 122 has the same shape as the left side wall portion 122. For this reason, illustration of the right side wall part 122 is simplified.

  As shown in FIGS. 2 and 3, the left and right side wall portions 122 are formed with concave portions 122 </ b> A that are recessed rearward and downward from the upper end edge.

  A pressure roller support portion 123 is provided below the concave portion 122A in the left and right side wall portions 122. Linear motion guide portions 124A and 124B are provided on upper portions of the concave portions 122A in the left and right side wall portions 122.

  A holding member support portion 125 is provided at the upper front corner of the left and right side wall portions 122. A hook 126 is provided so as to project downward at a position shifted upward from the lower and rear corners of the left and right side wall portions 122.

  The pressure roller 101 is a roller that integrally rotates with a rotating shaft 101S extending in the left-right direction. The rotary shaft 101S is rotatably supported by the pressure roller support portions 123 of the left and right side wall portions 122 via bearings (not shown).

  As shown in FIG. 2, the left end portion of the rotating shaft 101S is connected to the motor M1 via a planetary gear type one-way clutch 101C. Although not shown, the planetary gear type one-way clutch 101C includes an input gear to which the driving force of the motor M1 is transmitted, an output gear disposed apart from the input gear and connected to the rotation shaft 101S, and a rotation of the input gear. This is a known configuration having an arm pivotable around the center and a planetary gear supported rotatably at the tip of the arm and constantly meshing with the input gear. When the motor M1 rotates forward, the planetary gear is displaced to a position where it meshes with the output gear, so the driving force of the motor M1 is transmitted to the rotating shaft 101S. As a result, the pressure roller 101 rotates counterclockwise in FIG. On the other hand, when the motor M1 reversely rotates, the planetary gear is displaced to a position separating from the output gear, so the driving force of the motor M1 is not transmitted to the rotating shaft 101S. As a result, the pressure roller 101 does not rotate.

  The heating belt unit 102 includes the fixing belt 105 and the heater 102H shown in FIG. 4, the nip plate 103 shown in FIGS. 2 to 4, the reflecting plate 104 and the stay 106, and the pair of left and right guide members 110 shown in FIGS. And is included. The right guide member 110 has the same shape as the left guide member 110. For this reason, the illustration of the right guide member 110 is simplified.

  As shown in FIG. 4, the fixing belt 105 is an endless belt having heat resistance and flexibility. The fixing belt 105 has a tubular shape and extends long in the left-right direction. The fixing belt 105 is made of, for example, stainless steel, and the outer peripheral surface thereof is coated with a fluorine resin or the like.

  Although illustration is omitted, the fixing belt 105 is rotatable by being guided by the left and right guide members 110 at both end portions in the left-right direction. Inside the fixing belt 105, a heater 102H, a nip plate 103, a reflection plate 104 and a stay 106 are provided.

  The heater 102H is, for example, a halogen heater, and is a member that emits radiant heat to heat the nip plate 103.

  As shown in FIGS. 2 to 4, the nip plate 103 is disposed to be in sliding contact with the inner peripheral surface of the fixing belt 105 at a position facing the pressure roller 101 from above. The nip plate 103 is a plate-like member that receives the radiant heat from the heater 102H and transfers the heat to the fixing belt 105 and further to the developer image on the recording sheet SH. The nip plate 103 is formed by bending a plate material having a high thermal conductivity, for example, aluminum.

  The reflective plate 104 is disposed at a predetermined distance from the heater 102H so as to surround the heater 102H. The reflection plate 104 is a member that reflects radiation heat emitted from the heater 102H toward the nip plate 103 so as to be away from the nip plate 103. The reflection plate 104 is formed by bending a plate material made of, for example, aluminum having a large reflectance of infrared rays and far infrared rays into a substantially U-shaped cross section.

  The stay 106 has a substantially U-shaped cross section along the outer surface of the reflecting plate 104 and is arranged to cover the reflecting plate 104. The stay 106 is a member that secures the rigidity of the nip plate 103 by holding both end portions of the nip plate 103 in the front-rear direction via the reflection plate 104. The stay 106 is formed by, for example, bending a plate material made of, for example, steel, which has a rigidity higher than that of the nip plate 103.

  As shown in FIGS. 2 and 3, the left and right guide members 110 integrally support the heater 102H, the nip plate 103, the reflection plate 104, and both ends of the stay 160 in the left-right direction. The guide member 110 is made of an insulating material such as resin.

  The left and right guide members 110 are sandwiched by the linear motion guide portions 124A and 124B in a state where they enter into the recessed portions 122A of the left and right side wall portions 122. The left and right guide members 110 are vertically linearly movable along the recessed portions 122A of the left and right side wall portions 122 by being guided by the linear motion guide portions 124A and 124B. As shown in FIGS. 4 to 6, the fixing belt 105, the heater 102H, the nip plate 103, the reflecting plate 104 and the stay 160 also approach the pressure roller 101 as the left and right guide members 110 move linearly. The linear movement is possible to be separated.

  When the heating belt unit 102 is in the position shown in FIG. 4, the nip plate 103 and the fixing belt 105 are separated from the pressure roller 101. When the heating belt unit 102 is in the position shown in FIG. 5, the nip plate 103 and the fixing belt 105 are in contact so as to crush a part of the outer peripheral surface of the pressure roller 101. When the heating belt unit 102 is in the position shown in FIG. 6, the nip plate 103 and the fixing belt 105 are in contact such that a part of the outer peripheral surface of the pressure roller 101 is crushed more than in the state of FIG.

  The position of the heating belt unit 102 shown in FIG. 4 is a separated position where the heating belt unit 102 is separated from the pressure roller 101. The position of the heating belt unit 102 shown in FIG. 6 is a pressure contact position where the heating belt unit 102 is in pressure contact with the pressure roller 101. The pressure contact position is a position corresponding to the recording sheet SH having a general thickness such as a sheet or an OHP sheet. The position of the heating belt unit 102 shown in FIG. 5 is a weak pressure contact position where the heating belt unit 102 is in pressure contact with the pressure roller 101 with a pressure smaller than the pressure in the pressure contact position shown in FIG. The weak pressure contact position is a position corresponding to the case where the recording sheet SH is an envelope SH1 or the like thicker than a general sheet.

  When the pressure roller 101 rotates while the heating belt unit 102 is in the pressure contact position shown in FIG. 6 or the weak pressure contact position shown in FIG. 5, the fixing belt 105 in contact with the pressure roller 101 is rotated accordingly. It has become.

  As shown in FIGS. 2 and 3, the left holding member 130 has the front end portion projecting downward and enters the holding member support portion 125 of the left side wall portion 122. The front end portion of the right holding member 130 protrudes downward and enters the holding member support portion 125 of the right side wall portion 122. The left and right holding members 130 are swingably supported around the swing axis X130 by the left and right holding member support portions 125.

  The rear end portion side of the holding member 130 is bent into a substantially L-shaped cross section, and the lower surface of the bent portion is a contact surface 131A. A hook 132 is formed on the rear end side of the holding member 130.

  An engagement portion 133 is formed between the contact surface 131A of the holding member 130 and the pivot axis X130. The engagement portion 133 is engaged with the upper end portion 111 of the guide member 110. In the vicinity of the upper end portion 111 of the guide member 110, a pressed portion 112 which protrudes in a block shape is formed. The lower end edge of the engaging portion 133 is in contact with the pressed portion 112.

  As the holding member 130 swings clockwise in FIG. 3, the engaging portion 133 of the holding member 130 pulls the upper end portion 111 of the guide member 110 upward. Thus, the heating belt unit 102 is displaced toward the separated position shown in FIG.

  On the other hand, when the holding member 130 swings counterclockwise in FIG. 3, the lower end edge of the engaging portion 133 of the holding member 130 pushes the pressed portion 112 downward. As a result, the heating belt unit 102 is displaced toward the weak pressure contact position shown in FIG. 5 and further displaced toward the pressure contact position shown in FIG. That is, the holding member 130 holds the heating belt unit 102 so as to be displaceable between the separated position shown in FIG. 4 and the pressure contact position shown in FIG.

  As shown in FIGS. 2 and 3, the upper end of the left tension coil spring 109 is engaged with the hook 132 of the left holding member 130, and the lower end thereof is engaged with the hook 126 of the left side wall 122. It is locked. Although the drawing is simplified, the right side tension coil spring 109 is similarly engaged at its upper end with the hook 132 of the right holding member 130 and its lower end is engaged with the hook 126 of the right side wall 122 It has been stopped.

  The tension coil spring 109 biases the heating belt unit 102 in a biasing direction DF1 in which it approaches the pressure roller 101. Further, the biasing direction DF1 is a direction in which the holding member 130 approaches the cam surface 155 of the cam member 150. The biasing direction DF1 extends substantially in parallel with the direction in which the recess 122A of the side wall 122 is recessed, and is inclined downward and rearward.

  A transmission shaft 190 is provided at a position above the rear and upper corner portions of the left and right side wall portions 122 and below the contact surface 131A of the left and right holding members 130. The transmission shaft 190 is rotatably supported by a frame member (not shown) of the device body 2 around a rotational axis X150 extending in the left-right direction. The transmission shaft 190 is an axial member having high strength and rigidity, for example, made of steel. Shaft portions 191 are formed at both end portions of the transmission shaft 190 in the left-right direction. As shown in FIG. 2, the transmission gear 199 is fitted to the tip end of the shaft portion 191 on the left end side of the transmission shaft 190 so as to be integrally rotatable.

  As shown in FIGS. 2 and 3, the cam member 150 on the left side is the shaft portion 191 on the left end side of the transmission shaft 190 and is located directly below the contact surface 131A of the holding member 130 on the left side. It is fitted integrally rotatably. The cam member 150 on the right side is the shaft portion 191 on the right end side of the transmission shaft 190, and is integrally rotatably fitted in a portion located immediately below the contact surface 131A of the holding member 130 on the right side.

  As shown in FIG. 2, the transmission unit G1 includes an electromagnetic clutch GC1, a gear group (not shown) connecting the motor M1 and the input side of the electromagnetic clutch GC1, a transmission gear 199 connected to the output side of the electromagnetic clutch GC1, and a transmission shaft 190 and a fitting portion between the shaft portion 191 of the transmission shaft 190 and the shaft hole 160 of the cam member 150 are mainly included. The electromagnetic clutch GC1 is connected to the control unit C1, and is controlled by the control unit C1 to switch between the connected state and the disconnected state.

  Transmission unit G1 transmits the driving force of motor M1 to cam member 150 when motor M1 is controlled by control unit C1 to rotate forward and electromagnetic clutch GC1 is controlled by control unit C1 and switched to the connected state. The cam member 150 is rotated in the first direction R1 about the rotation center X150.

  On the other hand, in the transmission unit G1, when the motor M1 is controlled by the control unit C1 to be reversely rotated and the electromagnetic clutch GC1 is controlled by the control unit C1 to be switched to the connected state, the driving force of the motor M1 is transferred to the cam member 150. By transmitting, the cam member 150 is rotated about the rotation center X150 in the second direction R2 opposite to the first direction R1.

  The first direction R1 is the clockwise direction of FIG. The second direction R2 is a counterclockwise direction in FIG.

  As shown in FIGS. 7 to 15, the cam member 150 has a cam surface 155 that can contact the contact surface 131 A of the holding member 130. When viewed along the rotation center X150, the contact surface 131A in contact with the cam surface 155 of the holding member 130 extends linearly so as to incline rearward and upward.

  The cam surface 155 has a distance from the rotation center X150 that is shorter in the second direction R2. Here, in the configuration in which “the distance from the rotation center X150 becomes shorter in the second direction R2”, the cam surface 155 has a constant distance from the rotation center X150 and extends a predetermined length around the rotation center X150. Includes the configuration formed in part of In other words, in a configuration in which a portion where the distance from the rotation center X150 is longer in the second direction R2 is formed in a part of the cam surface 155, “the distance from the rotation center X150 is in the second direction R2 It does not correspond to the "shortened" configuration.

  The cam member 150 also has a nonuse surface 159 adjacent to one end and the other end of the cam surface 155. The non-use surface 159 connects one end and the other end of the cam surface 155 in a substantially linear manner. The control unit C1 controls the motor M1 and the electromagnetic clutch GC1 to rotate the cam member 150 in the first direction R1 and the second direction R2 in a range where the non-use surface 159 does not contact the contact surface 131A of the holding member 130. It is supposed to be.

  As shown in FIG. 8, the cam surface 155 has a first circumferential surface 151, a second circumferential surface 152, a third circumferential surface 153, and a fourth circumferential surface 154.

  The first circumferential surface 151 is set to a first distance L 1 at which the distance from the rotation center X 150 is the longest on the cam surface 155. The first circumferential surface 151 extends around the rotation center X150 with a predetermined length L151 while maintaining the first distance L1. The connection between the first circumferential surface 151 and the unused surface 159 is rounded.

  The second circumferential surface 152 is provided at a predetermined interval in the second direction R2 around the rotation center X150 with respect to the first circumferential surface 151. The second circumferential surface 152 is set to a second distance L2 in which the distance from the rotation center X150 is shorter than the first distance L1. The second circumferential surface 152 extends around the rotation center X150 by a predetermined length L152 while maintaining the second distance L2.

  The third circumferential surface 153 is provided at a position spaced apart from the second circumferential surface 152 in the first direction R1 around the rotation center X150. The third circumferential surface 153 is set to a third distance L3 in which the distance from the rotation center X150 is longer than the second distance L2.

  The fourth circumferential surface 154 is provided at a position spaced apart from the second circumferential surface 152 in the second direction R2 around the rotation center X150. The fourth circumferential surface 154 is set to a fourth distance L4 in which the distance from the rotation center X150 is shorter than the second distance L2.

  The range between the first circumferential surface 151 and the second circumferential surface 152 in the cam surface 155 is a gentle curved surface in which the distance from the rotation center X150 is gradually shortened in the second direction R2. Further, the range between the fourth circumferential surface 154 and the second circumferential surface 152 in the cam surface 155 is also a gentle curved surface in which the distance from the rotation center X150 is gradually shortened in the second direction R2.

  In the cam surface 155, the length LW1 between the first circumferential surface 151 and the second circumferential surface 152 is set larger than the length LW2 between the second circumferential surface 152 and the fourth circumferential surface 154. .

  As shown in FIGS. 7 and 8, the cam member 150 has an axial hole 160 centered on the rotation center X150. The axial hole 160 has a substantially D-shaped cross section in which a part of the cylindrical surface 163 is cut away by the first flat surface 161.

  As shown in FIGS. 2 and 3, the shaft portion 191 of the transmission shaft 190 is inserted into the shaft hole 160 of the cam member 150. The shaft portion 191 of the transmission shaft 190 has a substantially D-shaped cross section that matches the shaft hole 160 of the cam member 150. The shaft portion 191 of the transmission shaft 190 has a second flat surface 192 that abuts on the first flat surface 161. As shown in FIG. 8, the first flat surface 161 is disposed so as to overlap the direction DD1 from the rotation center X150 toward the first circumferential surface 151.

  As shown in FIGS. 7 and 8, the shaft hole 160 has rib-shaped first and second protrusions 165 and 166 extending parallel to the rotation center X 150. The first protrusion 165 and the second protrusion 166 are examples of the “pair of protrusions” in the present invention. As shown in FIG. 8, the first protrusion 165 and the second protrusion 166 sandwich a perpendicular line PL 1 orthogonal to the first flat surface 161 and passing through the rotation center X 150 when viewed along the rotation center X 150 direction. It projects from the cylindrical surface 163 toward the first flat surface 161 at mutually opposing positions.

  As described in detail below, the control unit C1 separates the cam surface 155 from the contact surface 131A of the holding member 130 by rotating the cam member 150 in the first direction R1 by the motor M1, and biases the tension coil spring 109. The heating belt unit 102 is displaced to the pressing position shown in FIG. On the other hand, the control unit C1 rotates the cam member 150 in the second direction R2 by the motor M1 to bring the cam surface 155 into contact with the contact surface 131A of the holding member 130 and against the tension coil spring 109 against the heating belt unit 102. Is displaced to the separated position shown in FIG.

  As shown in FIG. 2, a photo interrupter S1 is connected to the control unit C1. The controller C1 detects whether the cam member 150 is in the position shown in FIG. 9 by detecting the rotational attitude of the transmission gear 199 by the photo interrupter S1, ie, the heating belt unit 102 is in the separated position shown in FIG. Detect if there is. Then, with the position of the cam member 150 shown in FIG. 9 as the origin position, the control unit C1 accurately rotates the motor M1, which is a stepping motor, forwardly and reversely with pulse signal control or the like to accurately rotate the cam member 150. Change well. When displacing the cam member 150 from the origin position shown in FIG. 9 toward the position shown in FIG. 15, the control unit C1 rotates the cam member 150 in the first direction R1. The control unit C1 rotates the cam member 150 in the second direction R2 when returning the cam member 150 to the home position shown in FIG.

  As shown in FIG. 2, FIG. 3 and FIG. 9, the first distance L 1 is the cam surface 155 in a state where the first circumferential surface 151 of the cam surface 155 is in contact with the contact surface 131 A of the holding member 130. The heating belt unit 102 is displaced to the separated position shown in FIG.

  As shown in FIGS. 10 and 11, when the control unit C1 starts rotating the cam member 150 in the first direction R1 by the motor M1, the cam member 150 forms the first circumferential surface 151 and the second circumferential surface of the cam surface 155. The range between the position 152 and 152 is brought into contact with the contact surface 131 A of the holding member 130. Since the range is a gentle curved surface in which the distance from the rotation center X150 gradually decreases in the second direction R2, the holding member 130 gradually swings in the biasing direction DF1, and the heating belt unit 102 Approaches the pressure roller 101. Then, as shown in FIG. 11, when the third circumferential surface 153 contacts the contact surface 131 A of the holding member 130, the heating belt unit 102 contacts the pressure roller 101.

  As shown in FIG. 12, when the control unit C1 further rotates the cam member 150 in the first direction R1, the cam member 150 brings the second circumferential surface 152 of the cam surface 155 into contact with the contact surface 131A of the holding member 130. . In this state, the holding member 130 further swings in the biasing direction DF1, and the heating belt unit 102 squeezes a part of the outer peripheral surface of the pressure roller 101 and is displaced to the weak pressure contact position shown in FIG.

  As shown in FIGS. 13 and 14, when the control unit C1 further rotates the cam member 150 in the first direction R1, the cam member 150 forms the fourth circumferential surface 154 and the second circumferential surface 152 on the cam surface 155. The area between them is brought into contact with the contact surface 131A of the holding member 130. Since the range is a gentle curved surface in which the distance from the rotation center X150 gradually decreases in the second direction R2, the holding member 130 gradually swings in the biasing direction DF1, and the heating belt unit 102 Further crushes a part of the outer peripheral surface of the pressure roller 101. Then, as shown in FIG. 14, when the fourth circumferential surface 154 faces the contact surface 131A of the holding member 130, the cam surface 155 is separated from the contact surface 131A. In other words, the heating belt unit 102 contacts the pressure roller 101 before the cam surface 155 of the cam member 150 rotating in the first direction R1 separates from the contact surface 131A of the holding member 130. In the state shown in FIG. 14, the gap between the fourth circumferential surface 154 and the contact surface 131A is very small, and the cam member 150 is further rotated in the first direction R1, whereby the cam surface 155 and the contact surface 131A are separated. The gap widens.

  As shown in FIG. 15, when the control unit C1 further rotates the cam member 150 in the first direction R1, the cam member 150 causes the non-use surface 159 to face the contact surface 131A of the holding member 130 with a gap. . As a result, only the biasing force of the tension coil spring 109 acts on the holding member 130, and the heating belt unit 102 is displaced to the pressing position shown in FIG.

  When the control unit C1 causes the motor M1 to rotate the cam member 150 in the second direction R2, the cam member 150 and the holding member 130 operate reversely to the above description, and the heating belt unit 102 is moved from the pressing position shown in FIG. It is displaced to the separated position shown in FIG.

  Control unit C1 displaces heating belt unit 102 between the separated position shown in FIG. 4, the weak pressure-contacted position shown in FIG. 5, and the pressure-contacted position shown in FIG. Let

  For example, when the type of the recording sheet SH is a sheet or the like, the control unit C1 displaces the heating belt unit 102 to the pressure contact position shown in FIG. If the type of the recording sheet SH is an envelope or the like, the control unit C1 displaces the heating belt unit 102 to the weak pressure contact position shown in FIG. Thus, the fixing device 100 can perform a suitable heat fixing process according to the thickness of the recording sheet SH.

  Also, for example, when the image forming apparatus 1 shifts to the sleep mode, the heating belt unit 102 is displaced to the separated position shown in FIG. 4 and the heating belt unit 102 is shown in FIG. 5 just before the image forming operation is started. It is displaced to a weak pressure contact position or a pressure contact position shown in FIG. As a result, the period in which the pressure roller 101 is pressed and heated locally can be reduced, and quality maintenance and durability improvement of the heat fixing process of the fixing device 100 can be realized.

  The postures of the cam member 150 and the holding member 130 shown by solid lines in FIG. 16 are the same as in FIG. 9, and correspond to the heating belt unit 102 displaced to the separated position shown in FIG. The attitude of the cam member 150 shown by the two-dot chain line in FIG. 16 is the same as that in FIG. 15, and corresponds to the state in which the heating belt unit 102 is displaced to the pressing position shown in FIG.

  As shown in FIG. 16, with the heating belt unit 102 displaced to the separated position shown in FIG. 4, the position at which the first circumferential surface 151 of the cam member 150 contacts the contact surface 131A of the holding member 130 is the first position PS1. Do. The first circumferential surface 151 is an example of the “part of the cam surface contacting the holding member in a state where the second fixing member is displaced to the separated position” according to the present invention.

  A position at which the first circumferential surface 151 of the cam member 150 is separated from the contact surface 131A of the holding member 130 in a state in which the heating belt unit 102 is displaced to the pressure contact position shown in FIG.

  The direction R3 of reaching the second position PS2 at the shortest distance from the first position PS1 around the rotation center X150 is the same direction as the second direction R2. The first direction R1 is opposite to the direction R3 of reaching the second position PS2 at the shortest distance from the first position PS1 around the rotation center X150.

  In the graph shown in FIG. 17, the state where the rotation angle of the cam member 150 is near the origin corresponds to the state where the heating belt unit 102 is displaced to the pressure contact position shown in FIG. The state in which the rotational angle of the cam member 150 approaches the broken line DL1 corresponds to the state in which the heating belt unit 102 is displaced to the separated position shown in FIG. Note that, in this graph, the reaction force acting from the pressure roller 101 in which a part of the outer peripheral surface of the heating belt unit 102 is crushed is not taken into consideration.

  When the cam member 150 rotates in the first direction R1, a reaction force acts on the cam surface 155 from the contact surface 131A of the holding member 130 biased by the tension coil spring 109, and the moment M150 around the rotation center X150 is applied to the cam member 150. Works. When the rotation angle of the cam member 150 exceeds the broken line DL1, the moment M150 rapidly reverses. In this embodiment, the cam member 150 is rotated in the first direction R1 and the second direction R2 within the range in which the non-use surface 159 does not contact the contact surface 131A of the holding member 130. It does not exceed. That is, under the control of the control unit C1, the direction in which the biasing force of the tension coil spring 109 tries to rotate the cam member 150 around the rotation center X150 changes from the first direction R1 to the second direction R2 Or the sudden change from the second direction R2 to the first direction R1 is suppressed.

<Function effect>
In the fixing device 100 of the embodiment, as shown in FIGS. 9 to 15, the cam member 150 is rotated in the first direction R1 and the second direction R2 by the motor M1 and the transmission portion G1 shown in FIG. The unit 102 is automatically displaced between the pressing position shown in FIG. 6 and the separated position shown in FIG. Thereby, temporarily, the cam member 150 is always rotated in the same direction, and not only the cam surface 155 but also the non-use surface 159 is used to use the heating belt unit 102 in the pressure contact position shown in FIG. 6 and the separated position shown in FIG. The range in which the position at which the contact surface 131A of the holding member 130 and the cam surface 155 contact with each other is relatively displaced with respect to the rotation center X150 can be narrowed as compared with the case of displacement between the two.

  Further, in this fixing device 100, as shown in FIG. 16, the first direction R1 is set opposite to the direction R3 of reaching the second position PS2 at the shortest distance from the first position PS1 around the rotation center X150. ing. That is, in the above-described conventional fixing device, the cam rotates with the shortest distance to displace the nip plate and the fixing belt between the pressure contact position and the separated position. However, the heating belt unit 102 can be displaced between the press-contacting position shown in FIG. 6 and the separated position shown in FIG. Thereby, the range in which the position at which the contact surface 131A of the holding member 130 and the cam surface 155 contact with each other is relatively displaced with respect to the rotation center X150 can be further narrowed.

  As a result, in the fixing device 100, the direction in which the biasing force of the tension coil spring 109 causes the cam member 150 to rotate about the rotation center X150 is a change from the first posture R1 to the second direction R2. Or sudden change from the second direction R2 to the first direction R1 can be suppressed. Thereby, the collision of the component parts of the transmission part G1 can be suppressed. Specifically, as shown in FIG. 2, the fitting portion between the shaft portion 191 of the transmission shaft 190 and the shaft hole 160 of the cam member 150, and the fitting portion between the shaft portion 191 of the transmission shaft 190 and the transmission gear 199 In and the like, the gap between the fitting pieces disappears rapidly, and it is possible to suppress that the fitting pieces collide with each other.

  Therefore, in the fixing device 100 of the embodiment, the convenience can be improved while suppressing the generation of the abnormal noise.

  Further, in the fixing device 100, with the heating belt unit 102 in the pressure contact position shown in FIG. 6, the cam surface 155 of the cam member 150 is separated from the contact surface 131A of the holding member 130, as shown in FIG. Since the non-use surface 159 faces the contact surface 131 A with a gap, the pressure contact force of the heating belt unit 102 against the pressure roller 101 is determined only by the biasing force of the tension coil spring 109. As a result, it can be easily realized that the pressing force of the heating belt unit 102 is set to a desired magnitude.

  Further, in the fixing device 100, as shown in FIG. 14, heating is performed before the fourth peripheral surface 154 of the cam surface 155 of the cam member 150 rotating in the first direction R1 separates from the contact surface 131A of the holding member 130. The belt unit 102 contacts the pressure roller 101. Thus, when the heating belt unit 102 is displaced from the separated position shown in FIG. 4 to the pressure contact position shown in FIG. 6, the heating belt unit is heated by the cam surface 155 at least until the heating belt unit 102 contacts the pressure roller 101. Since the displacement of the belt 102 can be restricted, the collision of the heating belt unit 102 biased by the tension coil spring 109 with the pressure roller 101 can be suppressed. Also, the biasing force of the tension coil spring 109 and the heating belt unit from when the heating belt unit 102 contacts the pressure roller 101 until the fourth circumferential surface 154 of the cam surface 155 separates from the contact surface 131A of the holding member 130. Since the reaction force received from the pressure roller 101 is offset by 102, sudden rotation of the cam member 150 can be suppressed. As a result, the generation of abnormal noise can be further suppressed.

  Further, in the fixing device 100, a part of the cam surface 155 contacting the holding member 130 in a state where the heating belt unit 102 is displaced to the separated position shown in FIG. 4 is the first circumferential surface 151 shown in FIG. . The first circumferential surface 151 is an arc surface extending a predetermined length around the rotation center X150 while maintaining the first distance L1. When a part of the cam surface 155 contacting the contact surface 131A of the holding member 130 with the heating belt unit 102 displaced to the separated position shown in FIG. 4 is, for example, the apex of the inclined surface, the reaction force from the holding member 130 Tends to rotate the cam member 150. In this respect, as shown in FIG. 9, since the first circumferential surface 151 extending in an arc shape around the rotation center X150 can stably receive the reaction force from the holding member 130, the reaction force from the holding member 130 The rotation of the cam member 150 can be suppressed.

  Further, in the fixing device 100, as shown in FIG. 12, the second peripheral surface 152 of the cam surface 155 contacts the contact surface 131A of the holding member 130, whereby the heating belt unit 102 is in the weak pressure contact position shown in FIG. Displace. With such a second circumferential surface 152, the heating belt unit 102 has a pressing force smaller than the pressing force at the pressing position between the pressing position shown in FIG. 6 and the separated position shown in FIG. 4 of the heating belt unit 102. The weak pressure-contacting position (for example, the envelope mode) shown in FIG. 5 to be in pressure-contacting with the pressure roller 101 can be easily set.

  Further, in the fixing device 100, as shown in FIG. 11, when the heating belt unit 102 contacts the pressure roller 101, the third circumferential surface 153 contacts the holding member 130 before the second circumferential surface 152. Contact surface 131A. Assuming that the weak pressing position shown in FIG. 5 is the position at the moment when the heating belt unit 102 contacts the pressure roller 101, the cam member 150 slightly rotates due to a product error of the cam surface 155 of the cam member 150 or the like. The weak pressure welding position may be shifted, and the pressure welding force at the weak pressure welding position may be easily dispersed. In this point, when the heating belt unit 102 contacts the pressure roller 101, the cam member 150 has a configuration in which the third circumferential surface 153 contacts the contact surface 131A of the holding member 130 earlier than the second circumferential surface 152. Even in the case of slight rotation, the weak pressure welding position shown in FIG. 5 is hard to shift, and the variation in pressure welding force at the weak pressure welding position can be suppressed.

  Further, in the fixing device 100, as shown in FIG. 8, in the range between the first circumferential surface 151 and the second circumferential surface 152 on the cam surface 155, the distance from the rotation center X150 is in the second direction R2. It is a gentle curved surface that is gradually shortened. Thus, when the cam member 150 is rotated between the separated position shown in FIG. 4 and the weak pressure contact position shown in FIG. 5, as shown in FIGS. 10 and 11, the smooth curved surface of the cam surface 155 130 can be displaced little by little. As a result, the generation of abnormal noise can be further suppressed.

  Further, in the fixing device 100, as shown in FIG. 8, in the range between the fourth circumferential surface 154 and the second circumferential surface 152 on the cam surface 155, the distance from the rotation center X150 is in the second direction R2. It is a gentle curved surface that is gradually shortened. Thus, when the cam member 150 is rotated between the pressure contact position shown in FIG. 6 and the weak pressure contact position shown in FIG. 5, the holding member 130 can be displaced little by little by the gentle curved surface of the cam surface 155. As a result, the generation of abnormal noise can be further suppressed.

  Further, in the fixing device 100, as shown in FIG. 8, on the cam surface 155, the length LW1 between the first circumferential surface 151 and the second circumferential surface 152 is the second circumferential surface 152 and the fourth circumferential surface. The length LW2 between 154 and 154 is set larger. Between the second circumferential surface 152 and the fourth circumferential surface 154 of the cam surface 155, a large reaction force acts on the cam surface 155 when the heating belt unit 102 presses the pressure roller 101. Thus, the influence of the biasing force of the tension coil spring 109 on the cam member 150 is suppressed. On the other hand, between the first circumferential surface 151 and the second circumferential surface 152 in the cam surface 155, the reaction force acting on the cam surface 155 becomes smaller when the heating belt unit 102 presses the pressure roller 101, and further The heating belt unit 102 separates from the pressure roller 101 and the reaction force disappears. Thus, the cam member 150 is susceptible to the biasing force of the tension coil spring 109. For this reason, the holding member 130 can be displaced little by little by the cam surface 155 of the setting described above in a range susceptible to the influence of the biasing force of the tension coil spring 109.

  Further, in the fixing device 100, as shown in FIGS. 2 and 3, the shaft hole 160 of the cam member 150 is substantially D-shaped in cross section, and the shaft portion 191 of the transmission shaft 190 is also aligned with the shaft hole 160. It is D-shaped. The second flat surface 192 of the shaft portion 191 is in contact with the first flat surface 161 of the shaft hole 160. As shown in FIG. 8, the first flat surface 161 is disposed so as to overlap the direction DD1 from the rotation center X150 toward the first circumferential surface 151. When the heating belt unit 102 is displaced to the separated position shown in FIG. 4, as shown in FIG. 9, the reaction force of the holding member 130 is most against the first circumferential surface 151 contacting the contact surface 131A of the holding member 130. Works great. In this respect, since the reaction force is transmitted to the transmission shaft 190 by the first flat surface 161 of the shaft hole 160 and the second flat surface 192 of the shaft portion 191 having the above configuration, the transmission shaft 190 having high strength The reaction can be received reliably.

  Further, in the fixing device 100, the second flat surface 192 is reliably brought into contact with the first flat surface 161 by the first projection 165 and the second projection 166 of the shaft hole 160 shown in FIGS. 7 and 8. As a result, the play between the shaft hole 161 and the shaft portion 191 can be reliably reduced.

  Further, in the fixing device 100, as shown in FIGS. 9 to 15, the contact surface 131A in contact with the cam surface 155 of the holding member 130 extends linearly when viewed along the direction of the rotation center X150. Thereby, the position where the contact surface 131A and the cam surface 155 contact can be easily adjusted by the setting of the shape of the cam surface 155 as compared with the case where a contact surface extending in a curved shape is adopted instead of the contact surface 131A. .

  Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-described embodiments, and it goes without saying that the present invention can be appropriately modified and applied without departing from the scope of the present invention.

  The drive source and the transmission unit are not limited to the configuration of the embodiment. For example, the fixing device may include a motor for driving the cam member separately from the motor for driving the pressure roller. In addition, even if the drive source rotates only in the forward direction or stops and does not reverse rotation, the rotation direction transmitted to the cam member is switched in the middle of the transmission part, and the cam member is rotated in the first direction and the second direction. Good.

  The first fixing member and the second fixing member are not limited to the configuration of the embodiment. For example, the first fixing member may be a heating roller, the second fixing member may be a pressure roller, and the pressure roller may be in pressure contact with and separated from the heating roller.

  The holding member is not limited to the configuration that is pivotally supported, and may be, for example, linearly movable. The weak pressure welding position shown in FIG. 5 is not essential and can be omitted.

  The present invention is applicable to, for example, an image forming apparatus or a multifunction peripheral.

DESCRIPTION OF SYMBOLS 1 ... image forming apparatus, 100 ... fixing device, SH ... recording sheet 101 ... 1st fixing member (pressure roller), 102 ... 2nd fixing member (heating belt unit)
130: holding member, X150: center of rotation R1: first direction, R2: second direction, 155: cam surface, 150: cam member 109: biasing member (tension coil spring), DF1: biasing direction M1: drive source (: Motor), G1 ... Transmission part, C1 ... Control part 151 ... Part of the cam surface (first circumferential surface) contacting the holding member with the second fixing member displaced to the separated position
R3: direction from the first position to reach the second position at the shortest distance around the rotation center PS1: first position, PS2: second position L1: first distance, L2: second distance, 152: second circumferential surface, 153 third circumferential surface L3 third distance 154 fourth circumferential surface L4 fourth distance LW1 length between first circumferential surface and second circumferential surface on cam surface LW2 third on cam surface Length between two circumferential surfaces and fourth circumferential surface 160: shaft hole of cam member, 190: transmission shaft, 191: shaft portion of transmission shaft 163: cylindrical surface of shaft hole, 161: first flat surface, 192 ... second flat surface DD1 ... direction from the center of rotation toward the first circumferential surface PL1 ... perpendicular 165 perpendicular to the first flat surface, 165 ... a pair of protrusions (165 ... first protrusion, 166 ... 2nd projection part)
131A: Contact surface of holding member

Claims (11)

A fixing device that heats a recording sheet by a first fixing member and a second fixing member, and thermally fixes a developer image on the recording sheet,
The second fixing member is displaceable between a pressing position where the second fixing member presses against the first fixing member and a separating position where the second fixing member separates from the first fixing member. A holding member for holding the
A cam member rotatable about a rotation center in a first direction and in a second direction opposite to the first direction, and having a cam surface whose distance from the rotation center is shortened in the second direction;
A biasing member for biasing the second fixing member in a biasing direction approaching the first fixing member;
A driving source generating a driving force for rotating the cam member in the first direction and the second direction;
A transmission unit for transmitting the driving force to the cam member;
A control unit that controls the drive source;
The control unit
By rotating the cam member in the first direction by the drive source, the cam surface is separated from the holding member, and the second fixing member biased by the biasing member is displaced to the pressure contact position. ,
By rotating the cam member in the second direction by the drive source, the cam surface is brought into contact with the holding member, and the second fixing member is displaced to the separated position against the biasing member.
With the second fixing member displaced to the separated position, a position where a part of the cam surface contacts the holding member is a first position, and the second fixing member is displaced to the pressure contact position. Assuming that the position at which the part of the surface separates from the holding member is a second position, the first direction is opposite to the direction in which the second position is reached at the shortest distance from the first position around the rotation center. A fixing device characterized in that it is oriented.   The fixing device according to claim 1, wherein the second fixing member contacts the first fixing member before the cam surface of the cam member rotating in the first direction is separated from the holding member. The part of the cam surface is a first circumferential surface in which a distance from the rotation center is set to a longest first distance on the cam surface,
The fixing device according to claim 2, wherein the first circumferential surface extends a predetermined length around the rotation center while maintaining the first distance. The cam surface is provided at a predetermined interval in the second direction around the rotation center with respect to the first circumferential surface, and the second distance from the rotation center is shorter than the first distance. Have a second perimeter set to
The fixing device according to claim 3, wherein the second circumferential surface extends a predetermined length around the rotation center while maintaining the second distance. The cam surface has a third circumferential surface that contacts the holding member when the second fixing member contacts the first fixing member.
The third peripheral surface is provided at a position separated in the first direction around the rotation center with respect to the second peripheral surface, and the distance from the rotation center is a third distance longer than the second distance. The fixing device according to claim 4, wherein the fixing device is set.   The range between the first circumferential surface and the second circumferential surface in the cam surface is a gentle curved surface in which the distance from the rotation center is gradually shortened in the second direction. Or the fixing device according to 5. The cam surface has a fourth circumferential surface separated from the holding member in the range from the contact of the second fixing member to the first fixing member to the displacement to the pressure contact position,
The fourth circumferential surface is provided at a position separated in the second direction around the rotation center with respect to the second circumferential surface, and the distance from the rotation center is a fourth distance shorter than the second distance. Is set
The range between the fourth circumferential surface and the second circumferential surface in the cam surface is a gentle curved surface in which the distance from the rotation center is gradually shortened in the second direction. Fixing device as described.   In the cam surface, the length between the first circumferential surface and the second circumferential surface is set to be larger than the length between the second circumferential surface and the fourth circumferential surface. Fixing device as described. The cam member has an axial hole centered on the rotation center,
The transmission unit is rotatable around the rotation center, and has a transmission shaft having a shaft portion fitted in the shaft hole.
The shaft hole has a substantially D-shaped cross section in which a portion of the cylindrical surface is cut away by the first flat surface,
The shaft portion is substantially D-shaped in cross section aligned with the shaft hole, and has a second flat surface that contacts the first flat surface.
The fixing device according to any one of claims 3 to 8, wherein the first flat surface is arranged to overlap in a direction from the rotation center toward the first circumferential surface.   The axial holes are arranged from the cylindrical surface to the first flat surface at positions facing each other across a vertical line passing through the rotation center orthogonal to the first flat surface when viewed along the rotation center direction. 10. The fixing device according to claim 9, further comprising a pair of projecting portions that project toward the other.   The fixing device according to any one of claims 1 to 10, wherein a contact surface of the holding member in contact with the cam surface when viewed along the rotation center direction extends in a straight line.

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