Image forming device

Abstract

To prevent stick slip occurring between an endless belt and a slide sheet.SOLUTION: An image forming apparatus comprises: a rotating member; an endless belt; a heater; a pressure pad; a slide sheet; and a control unit. The endless belt is in contact with an outer peripheral surface of the rotating member and is rotated following the rotation of the rotating member. A substrate of the endless belt is formed of heat-resistant resin that does not include fluorine and has a glass-transition temperature of 140°C or more. The pressure pad sandwiches the endless belt with the rotating member to form a nip part. The slide sheet is sandwiched between an inner peripheral surface of the endless belt and the pressure pad. A substrate of the slide sheet is formed of heat-resistant resin that does not include fluorine and has a glass-transition temperature of 140°C or more. When executing a fixing operation, the control unit controls a nip pressure and the peripheral speed of the endless belt so as to satisfy V / P≥200, wherein V [mm / sec] is the peripheral speed of the endless belt, and P [MPa] is the maximum nip pressure of nip pressures at the nip part.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus including a fixing device that fixes a developer image onto a sheet. [Background technology]

[0002] Conventionally, a fixing device that is used in an image forming apparatus and fixes a developer image onto a sheet is known (see Patent Document 1). In the fixing device, an endless belt is sandwiched between a rotating member and a pressure pad to form a nip portion. A sliding sheet for reducing friction is disposed between the endless belt and the pressure pad. The endless belt and the sliding sheet are made of heat-resistant resin. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-198655 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when heat-resistant resin is used for both the endless belt and the sliding sheet, the resins tend to adhere to each other, which may cause stick-slip, a phenomenon in which the endless belt and the sliding sheet alternate between sticking and slipping. When stick-slip occurs, it may cause abnormal noise and increased wear on the endless belt and the sliding sheet.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS In view of the above, an object of the present invention is to suppress the stick-slip that occurs between the endless belt and the sliding sheet. [Means for solving the problem]

[0006] The image forming apparatus according to the present invention for solving the above-mentioned problems includes a rotating member, an endless belt, a heater, a pressure pad, a sliding sheet, and a control unit. The endless belt contacts the outer peripheral surface of the rotating member and rotates in accordance with the rotation of the rotating member. The endless belt is made of a heat-resistant resin having a base material that does not contain fluorine and a glass transition temperature of 140°C or higher. The heater heats at least one of the rotating member and the endless belt. The pressure pad sandwiches the endless belt between the rotating member and the pressure pad to form a nip portion. The sliding sheet is sandwiched between the inner peripheral surface of the endless belt and the pressure pad. The sliding sheet is made of a heat-resistant resin having a base material that does not contain fluorine and a glass transition temperature of 140°C or higher. When performing a fixing operation in which a sheet on which a developer image has been formed is sandwiched between a rotating member and an endless belt to fix the developer image, the control unit controls the circumferential speed of the endless belt to be V [mm / sec] and the maximum nip pressure of the nip pressure in the nip portion to be P [MPa], and controls the nip pressure and the circumferential speed of the endless belt to satisfy V / P≧200.

[0007] According to this configuration, the control unit performs control so as to satisfy V / P≧200, so that stick-slip occurring between the endless belt and the sliding sheet can be suppressed.

[0008] In addition, in the above-mentioned image forming apparatus, the control unit may be configured, when receiving a print command, to start rotation of the rotating member at a nip pressure smaller than that when performing the fixing operation, and after the peripheral speed of the endless belt reaches a predetermined speed, to change the nip pressure to the nip pressure when performing the fixing operation.

[0009] According to this, the control section reduces the nip pressure when the rotation speed of the fixing device is low at the start, so that the occurrence of stick-slip can be suppressed.

[0010] In the image forming apparatus, the predetermined speed may be a speed at which fixing is performed.

[0011] In addition, in the above-mentioned image forming apparatus, when the control unit completes the fixing operation and stops the endless belt, the control unit may be configured to maintain the circumferential speed of the endless belt at the speed when the fixing operation is performed, reduce the nip pressure to a pressure lower than that when the fixing operation is performed, and then stop the rotating member.

[0012] According to this, the nip pressure is lowered to a pressure lower than that during the fixing operation, and then the rotating members are stopped, thereby making it possible to suppress the occurrence of stick-slip.

[0013] In the image forming apparatus described above, the maximum nip pressure of the nip portion when performing a fixing operation can be changed between a first nip pressure P1 [MPa] and a second nip pressure P2 [MPa] that is greater than the first nip pressure, and the peripheral speed of the endless belt can be rotated at a first speed V1 [mm / s] and a second speed V2 [mm / s] that is greater than the first speed V1 to perform image formation, and V1, V2, P1, and P2 are such that V2 / P2≧200, V2 / P1≧200, and V1 / P1 ≧200, V1 / P2<200, and the control unit is capable of executing a first fixing process in which the peripheral speed of the endless belt is rotated at a second speed V2 and fixing is performed at a second nip pressure P2, a second fixing process in which the peripheral speed of the endless belt is rotated at the second speed V2 and fixing is performed at a first nip pressure P1, and a third fixing process in which the peripheral speed of the endless belt is rotated at the first speed V1 and fixing is performed at the first nip pressure P1, but the control unit may be configured not to execute the process in which the peripheral speed of the endless belt is rotated at the first speed V1 and fixing is performed at the second nip pressure P2.

[0014] According to this, the peripheral speed of the endless belt is rotated at the first speed V1, and the process of fixing with the second nip pressure P2 that is greater than the first nip pressure is not performed, so that the occurrence of stick-slip can be suppressed.

[0015] In addition, in the above-mentioned image forming apparatus, the maximum nip pressure of the nip portion during fixing can be changed between a first nip pressure P1 and a second nip pressure P2 greater than the first nip pressure P1, and the pressure pad includes a first pressure pad that sandwiches the endless belt between itself and the rotating member, and a second pressure pad that is arranged downstream of the first pressure pad in the sheet transport direction and sandwiches the endless belt between itself and the rotating member, and when the maximum nip pressure is the first nip pressure P1, the endless belt is sandwiched between the first pressure pad and the rotating member, and the endless belt is not sandwiched between the second pressure pad and the rotating member, and when the maximum nip pressure is the second nip pressure P2, the endless belt is sandwiched between the first pressure pad and the rotating member and the second pressure pad.

[0016] In the image forming apparatus described above, when the rotation of the rotating member starts, the maximum nip pressure of the nip portion may be set to the first nip pressure P1.

[0017] According to this, since the nip pressure is low at the start of the fixing operation, the occurrence of stick-slip can be suppressed.

[0018] In addition, in the above-mentioned image forming apparatus, the second pressure pad may have a durometer hardness higher than that of the first pressure pad, and when the maximum nip pressure is the second nip pressure P2, the area in the nip portion where the maximum nip pressure is reached may be located in the range where the second pressure pad and the rotating member are nipped.

[0019] In the image forming apparatus described above, at least one of the base material of the endless belt and the base material of the sliding sheet may be made of polyimide.

[0020] In the image forming apparatus described above, the base material of the endless belt and the base material of the sliding sheet may both be made of polyimide.

[0021] In the image forming apparatus described above, grease may be disposed between the endless belt and the sliding sheet.

[0022] According to this, since the grease is disposed between the endless belt and the sliding sheet, the occurrence of stick-slip can be suppressed.

[0023] In addition, in the above-mentioned image forming apparatus, the opposing surface of the sliding sheet that faces the inner surface of the endless belt may be configured to have a contact portion that contacts the endless belt and a plurality of recesses that are recessed from the contact portion and do not contact the endless belt.

[0024] According to this, the opposing surface of the sliding sheet has a plurality of recesses that do not come into contact with the endless belt, so that the occurrence of stick-slip can be suppressed. Effect of the Invention

[0025] According to the present invention, stick-slip occurring between the endless belt and the sliding sheet can be suppressed. [Brief description of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view showing a color printer according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing the fixing device. [Diagram 3] FIG. 2 is an exploded perspective view showing each member disposed inside an endless belt in a fixing device. [Figure 4] 3A is an enlarged view of a portion of the endless belt and the sliding sheet in FIG. 2, and FIG. 3B is an enlarged perspective view of the opposing surface of the sliding sheet. [Diagram 5] FIG. 2 is a perspective view showing a pressure changing mechanism in the fixing device. [Figure 6] 1A is a cross-sectional view showing the pressure changing mechanism when the nip pressure is the second nip pressure, and FIG. 1B is a cross-sectional view showing the structure around the nip portion. [Figure 7] 1A is a cross-sectional view showing a pressure changing mechanism when the nip pressure is a first nip pressure, and FIG. 1B is a cross-sectional view showing a structure around the nip portion. [Figure 8] FIG. 2 is a diagram showing the relationship between a control unit and an object controlled by the control unit. [Figure 9]5 is a time chart showing an example of the operation of the control unit before and after fixing. [Figure 10] 11 is a table showing the V / P value and the abnormal noise judgment results when the maximum nip pressure of the nip portion and the peripheral speed of the endless belt are changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. As shown in FIG. 1, a color printer 1, as an example of an image forming device, includes within a main body housing 2 a supply section 20 that supplies a sheet S, an image forming section 30 that forms a toner image on the sheet S, a fixing device 80 that fixes the toner image to the sheet S, a discharge section 90 that discharges the sheet S on which the image has been formed, and a control section 100.

[0028] An opening 2A is formed in the upper part of the main body housing 2, and this opening 2A is opened and closed by an upper cover 3 that is rotatably supported by the main body housing 2. The upper surface of the upper cover 3 serves as a discharge tray 4 that accumulates the sheets S discharged from the main body housing 2, and a plurality of LED mounting members 5 that hold the LED units 40 are provided on the lower surface.

[0029] The supply unit 20 is provided in the lower part of the main body housing 2, and includes a supply tray 21 that is detachable from the main body housing 2, and a supply mechanism 22 that conveys the sheet S from the supply tray 21 to the image forming unit 30. The supply mechanism 22 includes a pickup roller 23, a separation roller 24, a separation pad 25, and a registration roller 26.

[0030] In the supply unit 20, the sheets S in the supply tray 21 are sent out by the pickup roller 23. Next, the sheets S are separated one by one by the separation roller 24 and the separation pad 25. Thereafter, the registration roller 26 aligns the leading edge of the sheet S, and then conveys the sheet S toward the image forming unit 30. In detail, the registration roller 26 comes into contact with the conveyed sheet S in a stationary state, aligns the leading edge of the sheet S, and starts rotating to send out the sheet S.

[0031] The image forming section 30 includes four LED units 40, four process cartridges 50, a transfer unit 70, and a belt cleaner 10.

[0032] The LED unit 40 is pivotably connected to the LED mounting member 5, and is appropriately positioned and supported by a positioning member provided in the main body housing 2.

[0033] The process cartridges 50 are arranged side by side in the front-rear direction between the upper cover 3 and the supply unit 20. The process cartridge 50 is configured to include a photosensitive drum 51 as an example of a photosensitive member, a charger 52, a developing roller 53, a toner storage chamber 54 that stores toner as an example of a developer, a cleaning roller 55, and the like.

[0034] The process cartridges 50 are indicated by the reference characters 50K, 50Y, 50M, and 50C containing toner of each color, black, yellow, magenta, and cyan, and are arranged in that order from the upstream in the conveying direction of the sheet S. In this specification and drawings, when identifying the photosensitive drum 51, developing roller 53, cleaning roller 55, etc. corresponding to the color of toner, the reference characters K, Y, M, and C are attached to correspond to black, yellow, magenta, and cyan, respectively.

[0035] The photosensitive drum 51 is a member capable of carrying toner. More specifically, a portion of the surface of the photosensitive drum 51 exposed to the LED unit 40 carries the toner. The photosensitive drum 51 is provided in each of the multiple process cartridges 50. The photosensitive drums 51 are arranged in a line along the transport direction of the sheet S.

[0036] The developing roller 53 is a roller that carries toner and is configured to come into contact with the photosensitive drum 51 and supply the toner to the electrostatic latent image on the photosensitive drum 51.

[0037] The cleaning roller 55 is a member capable of collecting toner on the photosensitive drum 51. The cleaning roller 55 is provided adjacent to each photosensitive drum 51 so as to correspond to each photosensitive drum 51.

[0038] The transfer unit 70 is provided between the supply section 20 and each process cartridge 50 , and includes a drive roller 71 , a driven roller 72 , a belt 73 , and a transfer roller 74 .

[0039] The driving roller 71 and the driven roller 72 are arranged in parallel and spaced apart in the front-rear direction, and an endless belt 73 is stretched between them. The belt 73 is a member for conveying the sheet S. The outer circumferential surface of the belt 73 is in contact with the photosensitive drum 51. Four transfer rollers 74 are arranged inside the belt 73, facing the respective photosensitive drums 51.

[0040] The transfer roller 74 sandwiches the belt 73 between itself and the photosensitive drum 51. The sheet S is transported by the belt 73 and the photosensitive drum 51.

[0041] The belt cleaner 10 is a device that comes into sliding contact with the belt 73 to collect toner and the like adhering to the belt 73, and is disposed below the belt 73. Specifically, the belt cleaner 10 includes a sliding roller 11, a collection roller 12, a blade 13, and a waste toner container 14.

[0042] The sliding contact roller 11 is disposed so as to be in contact with the outer circumferential surface of the belt 73. The sliding contact roller 11 sandwiches the belt 73 between itself and a backup roller 15. The sliding contact roller 11 collects deposits on the belt 73.

[0043] The recovery roller 12 is a roller that is in sliding contact with the sliding roller 11, and recovers the deposits that have adhered to the sliding roller 11. The deposits on the recovery roller 12 are scraped off by a blade 13 that is disposed in sliding contact with the recovery roller 12, and enter a waste toner container 14.

[0044] The fixing device 80 includes a rotating member 81 and a belt unit 82. The structure of the fixing device 80 will be described in detail later.

[0045] In the image forming unit 30 configured as above, first, the surface of the photosensitive drum 51 is uniformly charged by the charger 52 and then exposed to light by the LED unit 40. As a result, an electrostatic latent image based on image data is formed on the photosensitive drum 51. Thereafter, toner is supplied to the electrostatic latent image by the developing roller 53, so that a toner image is carried on the photosensitive drum 51.

[0046] When the sheet S supplied onto the belt 73 passes between the photosensitive drum 51 and a transfer roller 74 disposed inside the belt 73, the toner image formed on the photosensitive drum 51 is transferred onto the sheet S. Then, when the sheet S passes between a rotating member 81 and a belt unit 82, the toner image transferred onto the sheet S is thermally fixed.

[0047] The discharge section 90 includes a discharge-side transport path 91 and a plurality of transport rollers 92. The sheet S on which the toner image has been thermally fixed is transported along the discharge-side transport path 91 by the transport rollers 92, discharged to the outside of the main body housing 2, and accumulated in the discharge tray 4.

[0048] 2, the fixing device 80 includes a heater 110, a rotating member 81, a belt unit 82, and a pressure change mechanism 300 (see FIG. 5) described later. The belt unit 82 is urged toward the rotating member 81 by the pressure change mechanism 300 described later. In the following description, the direction in which the belt unit 82 is urged toward the rotating member 81 is referred to as a "predetermined direction." In this embodiment, the predetermined direction is a direction perpendicular to the width direction and movement direction described later, and is a direction in which the rotating member 81 and the belt unit 82 face each other.

[0049] The rotating member 81 has a rotatable roller 120. The belt unit 82 is a member that forms a nip portion NP between the rotating member 81 and itself. The belt unit 82 includes an endless belt 130, a pressure pad N, a holder 140, a stay 200, a belt guide G, and a sliding sheet 150. In the following description, the width direction of the endless belt 130 is simply referred to as the "width direction." The width direction is the direction in which the rotation axis of the roller 120 extends, that is, the axial direction of the roller 120. The width direction is perpendicular to a predetermined direction.

[0050] The heater 110 is a halogen lamp that emits light and generates heat when energized, and uses radiant heat to heat the roller 120. The heater 110 is disposed so as to pass through the inside of the roller 120 along the rotation axis of the roller 120. In this embodiment, the heater 110 is disposed inside the rotating member 81 and heats the rotating member 81.

[0051] Roller 120 is a cylindrical roller that is long in the width direction, and is heated by heater 110. Roller 120 has an element tube 121 made of metal or the like, and an elastic layer 122 that covers the outer peripheral surface of element tube 121. Elastic layer 122 is made of rubber such as silicone rubber. Roller 120 is rotatably supported by a side frame 83 (see FIG. 5), which will be described later, and is driven to rotate counterclockwise in FIG. 2 by inputting a driving force from a fixing motor M2 (see FIG. 8) provided in main body housing 2.

[0052] The endless belt 130 is a long, tubular member having flexibility. The endless belt 130 has a base material that is a film material constituting the main body of the endless belt 130, and a coating layer provided on the surface of the base material.

[0053] The base material of the endless belt 130 is made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher. In this embodiment, the base material of the endless belt 130 is made of polyimide (glass transition temperature 220° C.). The base material of the endless belt 130 is mainly made of polyimide and may contain fine particles such as carbon to provide conductivity. The coating layer of the endless belt 130 is made of a fluorine-based resin (PFA, PTFE, etc.) and is provided on the surface that contacts the roller 120.

[0054] The endless belt 130 forms a nip portion NP between itself and the rotating member 81, more specifically, the roller 120. The endless belt 130 contacts the outer peripheral surface of the rotating member 81, and is rotated in accordance with the rotation of the rotating member 81. A pressure pad N, a holder 140, a stay 200, a belt guide G, and a sliding sheet 150 are arranged inside the endless belt 130.

[0055] In other words, the pressure pad N, the holder 140, the stay 200, the belt guide G and the sliding sheet 150 are covered by the endless belt .

[0056] 2 and 3, the pressure pad N is a member that forms a nip portion NP by sandwiching the endless belt 130 between itself and the rotating member 81. The pressure pad N includes a first pressure pad N1 and a second pressure pad N2.

[0057] The first pressure pad N1 has a first pad PD1 and a first fixed plate B1. The first pad PD1 is a rectangular parallelepiped member. The first pad PD1 is made of rubber such as silicone rubber. The first pad PD1 and the rotating member 81 sandwich the endless belt 130 to form a first nip portion NP1.

[0058] In the following description, the movement direction of the endless belt 130 in the first nip portion NP1 and in the nip portion NP described later in detail will simply be referred to as the "movement direction." In this embodiment, the movement direction is along the outer circumferential surface of the roller 120, but since this direction is roughly along a direction perpendicular to the predetermined direction and the width direction, it will be illustrated as a direction perpendicular to the predetermined direction and the width direction. The movement direction is the same as the conveyance direction of the sheet S in the nip portion NP.

[0059] The first pad PD1 is fixed to the surface of the first fixed plate B1 on the side of the roller 120. The first fixed plate B1 is made of a material harder than the first pad PD1, such as a metal.

[0060] The second pressure pad N2 is disposed downstream in the transport direction with a gap therebetween from the first pressure pad N1. The second pressure pad N2 has a second pad PD2 and a second fixed plate B2.

[0061] The second pad PD2 is a rectangular parallelepiped member. The second pad PD2 is made of rubber such as silicone rubber. The second pad PD2 forms a second nip portion NP2 by sandwiching the endless belt 130 between the second pad PD2 and the rotating member 81. The second pad PD2 is separated from the first pad PD1 in the rotation direction of the endless belt 130.

[0062] Therefore, between the first nip portion NP1 and the second nip portion NP2, there is an intermediate nip portion NP3 where the pressure from the belt unit 82 does not directly act. In this intermediate nip portion NP3, the endless belt 130 contacts the roller 120, but there is no member that sandwiches the endless belt 130 between the roller 120 and the intermediate nip portion NP3, so almost no pressure is applied. Therefore, the sheet S passes through the intermediate nip portion NP3 while being heated by the roller 120 and almost without being pressurized. In this embodiment, the region from the upstream end of the first nip portion NP1 to the downstream end of the second nip portion NP2, that is, the entire region where the outer circumferential surface of the endless belt 130 and the roller 120 contact each other, is referred to as the nip portion NP. In other words, in this embodiment, the nip portion NP includes a portion to which the pressing force from the first pad PD1 and the second pad PD2 is not applied.

[0063] The second pad PD2 is fixed to the surface of the second fixed plate B2 on the side of the roller 120. The second fixed plate B2 is made of a material harder than the second pad PD2, such as a metal.

[0064] The durometer hardness of the first pad PD1 is higher than the durometer hardness of the elastic layer 122 of the roller 120. The durometer hardness of the second pad PD2 is higher than the durometer hardness of the first pad PD1.

[0065] Here, the durometer hardness is defined in ISO7619-1. The durometer hardness is a value obtained from the depth of a specified indenter when the indenter is pressed into a test piece under defined conditions. For example, when the durometer hardness of the elastic layer 122 is 5, it is preferable that the durometer hardness of the first pad PD1 is 6 to 10, and the durometer hardness of the second pad PD2 is 70 to 90.

[0066] The holder 140 is a member that holds the pressure pad N. The holder 140 is made of a heat-resistant resin or the like. The holder 140 has a holder main body 141 and two engagement portions 142 and 143.

[0067] The holder body 141 is a portion that holds the pressure pad N. Most of the holder body 141 is disposed within the range of the endless belt 130 in the width direction. The holder body 141 is supported by a stay 200.

[0068] The engaging portions 142, 143 extend from each end in the width direction of the holder body 141. The engaging portions 142, 143 are disposed outside the range of the endless belt 130 in the width direction. The engaging portions 142, 143 engage with each end in the width direction of the first stay 210 described later.

[0069] The stay 200 is a member that is located on the opposite side of the pressure pad N with respect to the holder 140 and supports the holder 140. The stay 200 includes a first stay 210 and a second stay 220 that is connected to the first stay 210 by a connecting member CM.

[0070] The first stay 210 is a member that supports the holder main body 141 of the holder 140. The first stay 210 is made of metal or the like. The first stay 210 has a base portion 211 and a hemming bent portion HB that is bent by hemming.

[0071] The base portion 211 has a contact surface Ft at one end on the holder 140 side, which contacts the holder main body 141 of the holder 140. The contact surface Ft is a flat surface perpendicular to a predetermined direction.

[0072] The base portion 211 has load input portions 211A at both ends in the width direction, which receive a force from a pressure change mechanism 300 (see FIG. 5) described later. The load input portions 211A are recesses that open to the side opposite the pressure pad N in a predetermined direction, and are formed at the end of the base portion 211 opposite the pressure pad N in the predetermined direction.

[0073] A buffer member BF made of resin or the like is attached to the load input portion 211A. The buffer member BF is a member for suppressing friction between the metal base portion 211 and a metal arm 310 (see FIG. 5), which will be described later.

[0074] The belt guide G is a member that guides an inner circumferential surface 131 of the endless belt 130. The belt guide G is made of a heat-resistant resin or the like. The belt guide G has an upstream guide G1 and a downstream guide G2.

[0075] As shown in FIG. 2, the upstream guide G1, the downstream guide G2 and the first stay 210 are fastened together by a screw SC.

[0076] The sliding sheet 150 is a rectangular sheet for reducing frictional resistance between the first pad PD1 and the second pad PD2 and the endless belt 130. The sliding sheet 150 is sandwiched between the inner circumferential surface 131 of the endless belt 130 and the first pad PD1 and the second pad PD2 at the nip portion NP. The sliding sheet 150 is made of an elastically deformable material. The base material of the sliding sheet 150 does not contain fluorine and is made of a heat-resistant resin having a glass transition temperature of 140° C. or higher. In this embodiment, the base material of the sliding sheet 150 is made of polyimide (glass transition temperature 220° C.). The sliding sheet 150 is made of a substrate that is a film material constituting the main body of the sliding sheet 150, and has no coating layer on its surface. Therefore, the substrates of the sliding sheet 150 and the endless belt 130 are in contact with each other. The substrate of the sliding sheet 150 is mainly made of polyimide, and may contain fine particles such as carbon to provide electrical conductivity.

[0077] As shown in FIGS. 4(a) and (b), the sliding sheet 150 has an opposing surface 151 that faces the inner circumferential surface 131 of the endless belt 130. The opposing surface 151 is formed in an uneven shape with multiple polygonal sides forming ridges. In this embodiment, the opposing surface 151 is formed in an uneven shape with multiple square sides forming ridges. The opposing surface 151 has a contact portion 152 that contacts the endless belt 130 and multiple recesses 153 that do not contact the endless belt 130.

[0078] The ratio of the area of ​​the contact portion 152 to the area of ​​the facing surface 151 having a predetermined area is 50% or less. The contact portion 152 is located on the side of a square formed on the facing surface 151. The contact portion 152 extends obliquely with respect to the rotation direction, i.e., the moving direction, of the endless belt 130. The contact portion 152 has a groove 154 formed therein, which extends in the direction in which the contact portion 152 extends.

[0079] The groove 154 extends obliquely with respect to the moving direction of the endless belt 130. The depth of the groove 154 is 0.1 to 0.005 times the depth of the recess 153. The groove 154 has a first groove 154A and a second groove 154B.

[0080] The recess 153 is a portion recessed from the contact portion 152 in a direction away from the endless belt 130. The recess 153 is surrounded by the contact portion 152. In this embodiment, since the contact portion 152 is formed in a square shape, the recess 153 is in the shape of a quadrangular pyramid with the base as the apex.

[0081] Grease GR is disposed between the endless belt 130 and the sliding sheet 150. The grease GR is intended to reduce friction between the endless belt 130 and the sliding sheet 150. The grease GR is located on the inner circumferential surface 131 of the endless belt 130, the contact portion 152, the recess 153, and the groove 154 of the sliding sheet 150.

[0082] Here, color printer 1 is capable of changing the maximum nip pressure of nip portion NP during fixing, by pressure change mechanism 300, between a first nip pressure P1 and a second nip pressure P2 that is higher than first nip pressure P1. The first nip pressure P1 is the minimum nip pressure within the range of nip pressures that can be changed by the pressure change mechanism 300, and is the nip pressure that is set when no printing is being performed or when fixing an envelope or the like. The second nip pressure P2 is the maximum nip pressure within the range of nip pressures that can be changed by the pressure change mechanism 300, and is the nip pressure that is set during normal printing, more specifically, when fixing a toner image on plain paper or the like.

[0083] 5, the fixing device 80 further includes a frame FL and a pressure change mechanism 300. The frame FL is a frame that supports the rotating member 81 and the belt unit 82, and is made of metal or the like. The frame FL includes side frames 83 and brackets 84 that are disposed on both sides in the width direction of the rotating member 81 and the belt unit 82, and connection frames 85 that are connected to each side frame 83.

[0084] The side frame 83 is a frame that supports the rotating member 81 and the belt unit 82. The side frame 83 has a spring engagement portion 83A that engages with one end of a first spring 320, which will be described later.

[0085] The bracket 84 is a member that supports the belt unit 82 movably in a predetermined direction, and is fixed to the side frame 83. More specifically, the bracket 84 has a first elongated hole 84A that supports the end of the first stay 210 movably in the predetermined direction via the engagement portion 143 of the holder 140. The first elongated hole 84A is an elongated hole that is long in the predetermined direction.

[0086] Pressure change mechanism 300 is a mechanism that changes the nip pressure of nip portion NP. As shown in Figures 5 and 6(a), pressure change mechanism 300 includes arm 310, first spring 320, second spring 330, and cam 340. Arm 310, first spring 320, second spring 330, and cam 340 are provided at one end side and the other end side in the width direction of frame FL, respectively.

[0087] The arm 310 is a member for pressing the first stay 210 via the buffer member BF. The arm 310 supports the belt unit 82, and is supported by the side frame 83 so as to be rotatable.

[0088] The arm 310 has an arm body 311 and a cam follower 350. The arm body 311 is an L-shaped plate-like member made of metal or the like.

[0089] The arm body 311 has one end 311A ​​rotatably supported by the side frame 83, the other end 311B to which the first spring 320 is connected, and an engagement hole 311C that supports the belt unit 82. The engagement hole 311C is disposed between the one end 311A ​​and the other end 311B, and engages with the buffer member BF.

[0090] Moreover, the arm body 311 further has a guide protrusion 312 extending towards the cam 340. The guide protrusion 312 is disposed between the other end 311B and the engagement hole 311C in the direction from the other end 311B towards the engagement hole 311C.

[0091] Cam follower 350 is attached movably relative to guide protrusion 312 of arm body 311, and is capable of contacting cam 340. Cam follower 350 is made of resin or the like, and has a cylindrical portion 351 that fits into guide protrusion 312, a contact portion 352 provided at one end of cylindrical portion 351, and a flange portion 353 provided at the other end of cylindrical portion 351.

[0092] Cylindrical portion 351 is supported by guide protrusion 312 so as to be movable in the extending direction of guide protrusion 312. Contact portion 352 is a wall that closes an opening at the end portion of cylindrical portion 351 on the cam 340 side, and is disposed between cam 340 and the tip of guide protrusion 312. Flange portion 353 protrudes from the other end of cylindrical portion 351 in a direction perpendicular to the moving direction of cam follower 350.

[0093] In addition, a second spring 330 is disposed between the cylindrical portion 351 and the arm body 311. This allows the arm body 311 to be biased by the first spring 320 and also biased by the second spring 330.

[0094] The first spring 320 is a spring that applies a first biasing force to the belt unit 82. In detail, the first spring 320 applies the first biasing force to the belt unit 82 via the arm main body 311.

[0095] More specifically, the first spring 320 biases the first pad PD1 and the second pad PD2 toward the roller 120 via the arm body 311, the buffer member BF, the first stay 210, and the holder 140. The first spring 320 is a tension coil spring made of metal or the like, and has one end connected to the spring engagement portion 83A of the side frame 83 and the other end connected to the other end portion 311B of the arm body 311.

[0096] The second spring 330 is a spring capable of applying a second biasing force to the belt unit 82 in a direction opposite to the first biasing force. More specifically, the second spring 330 is capable of applying the second biasing force to the belt unit 82 via the arm main body 311. The second spring 330 is a compression coil spring made of metal or the like, and is disposed between the tubular portion 351 and the arm main body 311 with the guide protrusion 312 inserted in the space surrounded by the compression coil spring.

[0097] The cam 340 is a member that switches the arm body 311 between a first position and a second position. The cam 340 is supported by the side frame 83 so as to be rotatable between a first cam position shown in Fig. 6(a) and a second cam position shown in Fig. 7(a).

[0098] Cam 340 is made of resin or the like, and has first portion 341, second portion 342, and third portion 343. First portion 341, second portion 342, and third portion 343 are located on the outer circumferential surface of cam 340.

[0099] The first portion 341 is the portion closest to the cam follower 350 when the cam 340 is located at the first cam position. As shown in Fig. 6(a) , when the cam 340 is located at the first cam position, the first portion 341 is separated from the cam follower 350.

[0100] The second portion 342 is a portion that comes into contact with the cam follower 350 when the cam 340 rotates approximately 90 degrees clockwise from the first cam position. The distance from the second portion 342 to the rotation center of the cam 340 is greater than the distance from the first portion 341 to the rotation center of the cam 340.

[0101] The third portion 343 is a portion that comes into contact with the cam follower 350 when the cam 340 is located at the second cam position. More specifically, the third portion 343 is a portion that comes into contact with the cam follower 350 when the cam 340 rotates approximately 270 degrees clockwise from the first cam position as shown in Fig. 7(a). The distance from the third portion 343 to the rotation center of the cam 340 is greater than the distance from the second portion 342 to the rotation center of the cam 340.

[0102] When the cam 340 is located at the first cam position, the cam 340 is separated from the cam follower 350. When the cam 340 is separated from the cam follower 350 in this manner, the arm main body 311 is in the first position shown in Figure 6(a).

[0103] Specifically, when the cam 340 is located at the first cam position, the first biasing force of the first spring 320 is applied to the belt unit 82 via the arm body 311. When the first biasing force is applied to the belt unit 82 by the first spring 320 in this manner, the nip pressure becomes the second nip pressure P2.

[0104] When the maximum nip pressure is the second nip pressure P2, the endless belt 130 is sandwiched between the first pressure pad N1 and the second pressure pad N2 and the rotating member 81. When the maximum nip pressure is the second nip pressure P2, the area in the nip portion where the maximum nip pressure occurs is located in the range where the second pressure pad N2 and the rotating member 81 nip the endless belt 130.

[0105] Moreover, the first cam position is a position where the second nip pressure is P2, and the second cam position is a position where the first nip pressure is P1.

[0106] 7(a) from the first cam position shown in Fig. 6(a) to the second cam position shown in Fig. 7(a), the cam 340 moves the cam follower 350 relative to the arm body 311, and then presses the arm body 311 via the cam follower 350. This causes the arm body 311 to rotate from the first posture to a second posture different from the first posture.

[0107] As a result, when the arm body 311 is in the second posture, the belt unit 82 is positioned at a position (position in FIG. 7(b)) farther from the roller 120 than when the arm body 311 is in the first posture (position in FIG. 6(b)).

[0108] In this manner, as a result of the position of the belt unit 82 relative to the roller 120 changing, when the cam 340 is located at the second cam position and the arm body 311 is in the second posture, the width of the nip portion NP becomes smaller than in the first posture, as shown in FIG. 7(b), and the nip pressure becomes the first nip pressure P1, which is the minimum nip pressure.

[0109] When the maximum nip pressure is the first nip pressure P1, the endless belt 130 is sandwiched between the first pressure pad N1 and the rotating member 81, and the endless belt is not sandwiched between the second pressure pad N2 and the rotating member 81. When the maximum nip pressure is the first nip pressure P1, the area in the nip portion where the maximum nip pressure occurs is located in the range where the first pressure pad N1 and the rotating member 81 are nipped.

[0110] As shown in FIG. 8, the color printer 1 further includes a developing motor M1, a fixing motor M2, and a pressure changing clutch C2.

[0111] The developing motor M1 is a motor that mainly drives and rotates each developing roller 53, and is configured to be capable of forward and reverse rotation. The developing motor M1 is connected to a cam 340 of the pressure change mechanism 300 via a pressure change clutch C2 and a gear (not shown).

[0112] The fixing motor M2 is a motor for driving the roller 120 to rotate.

[0113] The pressure change clutch C2 is, for example, an electromagnetic clutch. The pressure change clutch C2 is switchable between a second transmission state in which the driving force of the developing motor M1 is transmitted to the cam 340 of the pressure change mechanism 300 and a second disconnection state in which the driving force of the developing motor M1 is not transmitted to the cam 340 of the pressure change mechanism 300. When the cam 340 is located at the second cam position and the developing motor M1 is rotating forward, the pressure change clutch C2 turns in the second transmission state, counterclockwise from the second cam position shown in FIG. 7(a) to the first cam position shown in FIG. 6(a). When the cam 340 is located at the first cam position and the developing motor M1 is rotating backward, the pressure change clutch C2 turns in the second transmission state, clockwise from the first cam position shown in FIG. 6(a) to the second cam position shown in FIG. 7(a).

[0114] 8, the control unit 100 includes a CPU, RAM, ROM, non-volatile memory, ASIC, an input / output circuit, etc. The control unit 100 executes various processes by performing various arithmetic operations based on print commands output from an external computer and programs and data stored in the ROM, etc.

[0115] Next, the process performed by the control unit 100 when performing the fixing operation will be described. When starting rotation of rotating member 81, control unit 100 sets the maximum nip pressure of nip portion NP to first nip pressure P1. When printing on an envelope or special sheet, control unit 100 executes the fixing operation at first nip pressure P1, but when printing on plain paper, control unit 100 executes the fixing operation at second nip pressure P2. Here, the processing of the control unit when printing on plain paper will be described.

[0116] When the control unit 100 receives a print command, it starts rotating the rotating member 81 at a first nip pressure P1, which is a nip pressure smaller than that when performing the fixing operation, and after the peripheral speed of the endless belt 130 reaches a predetermined speed, it changes the nip pressure to a second nip pressure P2, which is the nip pressure when performing the fixing operation. Note that the predetermined speed is the speed when performing the fixing.

[0117] 9, when control unit 100 receives a print command, with the nip pressure set to first nip pressure P1 (time t0), it starts driving development motor M1 (time t1) and then starts driving fixing motor M2 (time t2). Then, after the circumferential speed of endless belt 130 becomes constant (time t3), control unit 100 drives pressure change clutch C2 for a predetermined time (times t4 to t5) to change the nip pressure from first nip pressure P1 to second nip pressure P2.

[0118] In addition, when the control unit 100 ends the fixing operation and stops the endless belt 130, it reduces the nip pressure from the second nip pressure P2 to the first nip pressure P1, which is a lower pressure than when the fixing operation is performed, while maintaining the circumferential speed of the endless belt 130 at the speed when the fixing operation is performed, and then stops the rotating member 81.

[0119] For example, when fixing is completed, the control unit 100 drives the pressure change clutch C2 for a predetermined time (time t11 to t12) to change the nip pressure from the second nip pressure P2 to the first nip pressure P1, turns off the fixing motor M2 (time t13), and after the endless belt 130 stops (time t14), turns off the developing motor M1 (time t15).

[0120] As described above, color printer 1 is capable of changing the maximum nip pressure of nip portion NP when performing a fixing operation between first nip pressure P1 and second nip pressure P2 that is greater than first nip pressure P1. Furthermore, the color printer 1 is capable of forming images by rotating the endless belt 130 at a first speed V1 and a second speed V2 that is faster than the first speed V1.

[0121] The control unit 100 performs image formation at a first speed V1 when printing on, for example, thick paper, glossy paper, label paper, etc. The control unit 100 also performs image formation at a second speed V2 when printing on, for example, plain paper, thin paper, etc.

[0122] In this embodiment, the first speed V1 [mm / sec], the second speed V2 [mm / sec], the first nip pressure P1 [MPa], and the second nip pressure P2 [MPa] satisfy V2 / P2≧200, V2 / P1≧200, V1 / P1≧200, and V1 / P2<200.

[0123] The control unit 100 is capable of executing a first fixing process in which the endless belt 130 is rotated at a second speed V2 and fixing is performed with a second nip pressure P2. The control unit 100 is capable of executing a second fixing process in which the endless belt 130 is rotated at a second speed V2 and the toner is fixed at a first nip pressure P1. The control unit 100 is capable of executing a third fixing process in which the endless belt 130 is rotated at a first speed V1 and fixing is performed with a first nip pressure P1. On the other hand, the control unit 100 rotates the endless belt 130 at the first speed V1, and does not execute the process of fixing with the second nip pressure P2.

[0124] In this way, when the control unit 100 performs a fixing operation of fixing the developer image by sandwiching the sheet S on which the developer image is formed between the rotating member 81 and the endless belt 130, the control unit 100 controls the nip pressure and the circumferential speed of the endless belt 130 to satisfy V [mm / sec], the maximum nip pressure of the nip pressure at the nip portion NP to be P [MPa], and the nip pressure and the circumferential speed of the endless belt 130 to satisfy V / P≧200.

[0125] Next, FIG. 10 shows the value of V / P [mm / (MPa·sec)] actually measured in the color printer 1 and the result of the abnormal noise judgment. The abnormal noise is a sound that is heard when stick-slip occurs between the endless belt 130 and the sliding sheet 150. The peripheral speed of the endless belt 130 was changed to five stages, namely, 30, 60, 79.2, 120, and 240 [mm / sec]. The maximum nip pressure of the nip portion NP was changed to three stages, namely, 0.29, 0.38, and 0.43 [MPa]. The endless belt 130 and the sliding sheet 150 are both made of polyimide, and grease GR is disposed between the endless belt 130 and the sliding sheet 150.

[0126] As shown in Figure 10, when V / P was 184 or less, abnormal noise occurred, and when V / P was 207 or more, abnormal noise did not occur. From these results, it was determined that when V / P≧200 was satisfied, abnormal noise did not occur, and stick-slip did not occur. On the other hand, when V / P<200 was satisfied, abnormal noise occurred, and it was determined that stick-slip had occurred.

[0127] As described above, the following effects can be obtained in this embodiment. When performing a fixing operation between the rotating member 81 and the endless belt 130, the control unit 100 of the color printer 1 controls the nip pressure and the circumferential speed of the endless belt 130 to satisfy V / P≧200, where V is the circumferential speed of the endless belt 130 [mm / sec] and P is the maximum nip pressure among the nip pressures at the nip portion NP [MPa]. Therefore, stick-slip occurring between the endless belt 130 and the sliding sheet 150 can be suppressed.

[0128] Furthermore, when the control unit 100 receives a print command, it starts the rotation of the rotating member 81 with a nip pressure smaller than that when performing the fixing operation, and after the circumferential speed of the endless belt 130 reaches the speed when performing the fixing operation, it changes the nip pressure to the nip pressure when performing the fixing operation. Therefore, when the rotation speed of the endless belt 130 is low at the start of the rotation, the nip pressure is lowered to suppress the occurrence of stick-slip. In this case, although V / P≧200 is not satisfied immediately after the endless belt 130 starts to rotate, the maximum value of the nip pressure is lower than that during printing, so that it is possible to suppress the occurrence of stick-slip between the endless belt 130 and the sliding sheet 150.

[0129] Furthermore, when the control unit 100 ends the fixing operation and stops the endless belt 130, it reduces the nip pressure to a pressure lower than that when the fixing operation is performed while maintaining the circumferential speed of the endless belt 130 at the speed when the fixing operation is performed, and then stops the rotating member 81. This makes it possible to suppress the occurrence of stick-slip.

[0130] The control unit 100 rotates the endless belt 130 at the first speed V1, which is slower than the second speed V2, and does not perform the process of fixing at the second nip pressure P2, which is higher than the first nip pressure P1. This makes it possible to suppress the occurrence of stick-slip.

[0131] Furthermore, control unit 100 sets the maximum nip pressure of nip portion NP to first nip pressure P1 when starting rotation of rotating member 81. Therefore, since the nip pressure is low at the start of the fixing operation, the occurrence of stick-slip can be suppressed.

[0132] Furthermore, by disposing grease GR between the endless belt 130 and the sliding sheet 150, the occurrence of stick-slip can be suppressed.

[0133] Furthermore, since the opposing surface 151 of the sliding sheet 150 has a plurality of recesses 153 that do not come into contact with the endless belt 130, the occurrence of stick-slip can be suppressed.

[0134] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below.

[0135] In the above embodiment, the photosensitive drum 51 is exemplified as the photosensitive member, but the present invention is not limited to this, and for example, a belt-shaped photosensitive member may also be used.

[0136] In the above embodiment, the pressure change mechanism 300 was configured to change the nip pressure of the nip portion NP between a first nip pressure P1 and a second nip pressure P2, but the present invention is not limited to this and may be configured to be able to change the nip pressure between three or more pressure values, or steplessly.

[0137] In the above embodiment, the present invention is applied to a color printer 1, but the present invention is not limited to this and may be applied to other image forming devices, such as monochrome printers, copiers, and multifunction machines.

[0138] In the above embodiment, a halogen lamp is used as the heater, but the heater may be, for example, a carbon heater.

[0139] In the above embodiment, the heater is located inside the rotating member, but the present invention is not limited thereto, and the heater may be located inside the belt unit. For example, the belt unit may include an endless belt, a heater and a nip member located inside the endless belt, and the rotating member may be a pressure roller that sandwiches the endless belt between the nip member and the belt unit. Alternatively, the heater may be located outside the rotating member, and an external heating method may be used in which the heater is located outside the rotating member and the outer circumferential surface of the rotating member is heated, or an IH (Induction Heating) method may be used. Alternatively, the rotating member and the belt unit may each have a built-in heater. That is, the heater may be configured to heat at least one of the rotating member and the endless belt.

[0140] The rotating member may be a belt including a drive roller therein, that is, a nip may be formed between the belt of the rotating member and the belt of the belt unit.

[0141] In the above embodiment, the base material of the endless belt 130 and the base material of the sliding sheet 150 are both polyimide, but the present invention is not limited to this, and at least one of the base material of the endless belt 130 and the base material of the sliding sheet 150 may be configured to be polyimide. For example, the base material of the endless belt 130 may be made of polyimide, and the base material of the sliding sheet 150 may be made of another heat-resistant resin having a glass transition temperature of 140° C. or higher. Alternatively, the base material of the endless belt 130 may be made of another heat-resistant resin having a glass transition temperature of 140° C. or higher, and the base material of the sliding sheet 150 may be made of polyimide.

[0142] Furthermore, the base material of the endless belt 130 and the base material of the sliding sheet 150 may not be polyimide. For example, the base material of the endless belt 130 and the base material of the sliding sheet 150 may be polyetheretherketone (glass transition temperature 143° C.), polyetherimide (glass transition temperature 216° C.), polyamideimide (glass transition temperature 275° C.), or the like.

[0143] In the above embodiment, the first speed V1 [mm / sec], the second speed V2 [mm / sec], the first nip pressure P1 [MPa], and the second nip pressure P2 [MPa] were configured to satisfy V2 / P2≧200, V2 / P1≧200, V1 / P1≧200, and V1 / P2<200, but the present invention is not limited to this configuration. For example, in the case where V1 / P2≧200 is satisfied, the control unit 100 may rotate the endless belt 130 at the first speed V1 and perform the fixing process with the second nip pressure P2.

[0144] In the above embodiment, the fixing device 80 is configured to include a pressure change mechanism 300, but the present invention is not limited to this, and the main body housing may be equipped with the pressure change device, or a part of the pressure change mechanism may be provided in the fixing device and the other part may be provided in the main body housing.

[0145] The elements described in the above-mentioned embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0146] 1. Color printer 80 Fixing device 81 Rotating members 82 Belt unit 100 Control section 110 Heater 130 Endless Belt 131 Inner surface 150 Sliding Sheet 151 Opposite Surface 152 Contact part 153 Recess 300 Pressure change mechanism GR Grease M1 Development motor M2 Fuser motor N Pressure Pad N1 First pressure pad N2 2nd pressure pad NP Nip P1 1st nip pressure P2 Second nip pressure PD1 1st pad PD2 2nd Pad S Seat V1 1st speed V2 2nd speed

Claims

1. A rotating member; an endless belt that contacts an outer circumferential surface of the rotating member and rotates in accordance with the rotation of the rotating member, the endless belt having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; a heater for heating at least one of the rotating member and the endless belt; a pressure pad that sandwiches the endless belt between itself and the rotating member to form a nip portion; a sliding sheet sandwiched between an inner peripheral surface of the endless belt and the pressure pad, the sliding sheet having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; A control unit, When a fixing operation is performed to fix a developer image formed on a sheet by sandwiching the developer image between the rotating member and the endless belt, the control unit The peripheral speed of the endless belt is V [mm / sec], and the maximum nip pressure of the nip portion is P [MPa]. V / P≧200 and controlling the nip pressure and the peripheral speed of the endless belt so as to satisfy The control unit is when a print command is received, the rotation member is started with a nip pressure smaller than that when the fixing operation is performed; an image forming apparatus including: changing the nip pressure to a nip pressure for performing the fixing operation after the peripheral speed of the endless belt reaches a predetermined speed;

2. 2. The image forming apparatus according to claim 1, wherein the predetermined speed is a speed at which fixing is performed.

3. A rotating member; an endless belt that contacts an outer circumferential surface of the rotating member and rotates in accordance with the rotation of the rotating member, the endless belt having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; a heater for heating at least one of the rotating member and the endless belt; a pressure pad that sandwiches the endless belt between itself and the rotating member to form a nip portion; a sliding sheet sandwiched between an inner peripheral surface of the endless belt and the pressure pad, the sliding sheet having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; A control unit, When a fixing operation is performed to fix a developer image formed on a sheet by sandwiching the developer image between the rotating member and the endless belt, the control unit The peripheral speed of the endless belt is V [mm / sec], and the maximum nip pressure of the nip portion is P [MPa]. V / P≧200 and controlling the nip pressure and the peripheral speed of the endless belt so as to satisfy When the control unit stops the endless belt after completing the fixing operation, an image forming apparatus characterized in that, while maintaining the peripheral speed of the endless belt at the speed when the fixing operation is performed, the nip pressure is reduced to a pressure lower than that when the fixing operation is performed, and then the rotating member is stopped.

4. A rotating member; an endless belt that contacts an outer circumferential surface of the rotating member and rotates in accordance with the rotation of the rotating member, the endless belt having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; a heater for heating at least one of the rotating member and the endless belt; a pressure pad that sandwiches the endless belt between itself and the rotating member to form a nip portion; a sliding sheet sandwiched between an inner peripheral surface of the endless belt and the pressure pad, the sliding sheet having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; A control unit and an image forming apparatus comprising: When a fixing operation is performed to fix a developer image formed on a sheet by sandwiching the developer image between the rotating member and the endless belt, the control unit The peripheral speed of the endless belt is V [mm / sec], and the maximum nip pressure of the nip portion is P [MPa]. V / P≧200 and controlling the nip pressure and the peripheral speed of the endless belt so as to satisfy The image forming apparatus includes: a maximum nip pressure of the nip portion when performing the fixing operation can be changed between a first nip pressure P1 [MPa] and a second nip pressure P2 [MPa] that is greater than the first nip pressure, The endless belt is rotated at a circumferential speed of a first speed V1 [mm / s] and a second speed V2 [mm / s] that is faster than the first speed V1 to perform image formation. V1, V2, P1, and P2 are V2 / P2≧200 V2 / P1≧200 V1 / P1≧200 V1 / P2<200 Fulfilling The control unit is a first fixing process in which the peripheral speed of the endless belt is rotated at a second speed V2 and fixing is performed with the second nip pressure P2; a second fixing process in which the peripheral speed of the endless belt is changed to a second speed V2 and fixing is performed with the first nip pressure P1; a third fixing process in which the peripheral speed of the endless belt is rotated at a first speed V1 and fixing is performed at the first nip pressure P1; an image forming apparatus in which the peripheral speed of the endless belt is made to rotate at a first speed V1, and a process of fixing with the second nip pressure P2 is not performed.

5. A rotating member; an endless belt that contacts an outer circumferential surface of the rotating member and rotates in accordance with the rotation of the rotating member, the endless belt having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; a heater for heating at least one of the rotating member and the endless belt; a pressure pad that sandwiches the endless belt between itself and the rotating member to form a nip portion; a sliding sheet sandwiched between an inner peripheral surface of the endless belt and the pressure pad, the sliding sheet having a base material made of a heat-resistant resin that does not contain fluorine and has a glass transition temperature of 140° C. or higher; A control unit and an image forming apparatus comprising: The image forming apparatus includes: The maximum nip pressure of the nip portion during fixing can be changed between a first nip pressure P1 and a second nip pressure P2 that is greater than the first nip pressure P1, When a fixing operation is performed to fix a developer image formed on a sheet by sandwiching the developer image between the rotating member and the endless belt, the control unit The peripheral speed of the endless belt is V [mm / sec], and the maximum nip pressure of the nip portion is P [MPa]. V / P≧200 and controlling the nip pressure and the peripheral speed of the endless belt so as to satisfy The pressure pad is a first pressure pad that sandwiches the endless belt between the first pressure pad and the rotating member; a second pressure pad disposed downstream of the first pressure pad in a sheet conveying direction and sandwiching the endless belt between the first pressure pad and the rotating member, When the maximum nip pressure is the first nip pressure P1, the endless belt is sandwiched between the first pressure pad and the rotating member, and the endless belt is not sandwiched between the second pressure pad and the rotating member, When the maximum nip pressure is the second nip pressure P2, the endless belt is sandwiched between the first pressure pad and the rotating member and between the second pressure pad and the rotating member.

6. 6. The image forming apparatus according to claim 5, wherein when the rotation of the rotary member starts, the maximum nip pressure of the nip portion is set to the first nip pressure P1.

7. The second pressure pad has a durometer hardness higher than that of the first pressure pad, 7. An image forming apparatus according to claim 5, wherein when the maximum nip pressure is the second nip pressure P2, the area in the nip portion where the maximum nip pressure is achieved is located in a range where the second pressure pad and the rotating member are nipped.

8. 8. The image forming apparatus according to claim 1, wherein at least one of a base material of the endless belt and a base material of the sliding sheet is made of polyimide.

9. 9. The image forming apparatus according to claim 1, wherein a base material of the endless belt and a base material of the sliding sheet are both made of polyimide.

10. 10. The image forming apparatus according to claim 1, further comprising a grease disposed between the endless belt and the sliding sheet.

11. The image forming apparatus according to any one of claims 1 to 10, characterized in that the opposing surface of the sliding sheet facing the inner surface of the endless belt has a contact portion that contacts the endless belt and a plurality of recesses that are recessed from the contact portion and do not contact the endless belt.

Images