Image forming apparatus

Abstract

In an image forming apparatus, a first fixing member includes a roller. A second fixing member includes a belt to form a clamping portion together with the first fixing member. A pressure modification mechanism modifies a clamping pressure at the clamping portion to a selected one of a first clamping pressure and a second clamping pressure that is smaller than the first clamping pressure. A controller drives a first motor to drive the roller, and fixes a developer image on a sheet while the clamping pressure is the first clamping pressure. When a final sheet of one or more sheets to be fixed according to a print job has passed through the clamping portion, the controller modifies the clamping pressure from the first clamping pressure to the second clamping pressure while driving the first motor, and stops the first motor after the clamping pressure is modified to the second clamping pressure.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus including a fixing device that fixes a developer image on a sheet. Background Art

[0002] A fixing device known in the art includes a heater and a pressure roller. The heater comprises a belt formed into a loop, a heater, and a nip plate disposed within the belt loop. The pressure roller presses the belt against the nip plate. The heater can be switched between a pressure contact position, where the heater contacts the pressure roller, and a separation position, where the heater and pressure roller are separated.

[0003] However, there is no technology that can reduce damage to the belt, especially after printing is completed. Summary of the Invention

[0004] In view of the foregoing, the present disclosure provides a technique for reducing damage to a tape when printing is complete.

[0005] To achieve the above-mentioned and other purposes, the present disclosure provides an image forming device. The image forming device includes a first fixing member, a second fixing member, a first motor, a pressure modification mechanism, and a controller. The first fixing member has a roller. The second fixing member has a belt to form a clamping portion together with the first fixing member. The first motor is configured to drive the roller. The pressure modification mechanism is configured to modify the clamping pressure at the clamping portion to a selected one of a first clamping pressure and a second clamping pressure that is less than the first clamping pressure. The controller is configured to: drive the first motor to drive the roller; fix the developer image on the sheet while the clamping pressure is the first clamping pressure; when the final sheet of one or more sheets to be fixed according to a print job has passed through the clamping portion, while driving the first motor, modify the clamping pressure from the first clamping pressure to the second clamping pressure; and stop the first motor after the clamping pressure is modified to the second clamping pressure.

[0006] Preferably, the image forming apparatus further includes a fixed sheet sensor disposed downstream of the nip portion, the fixed sheet sensor configured to detect a sheet passing through the nip portion. The controller modifies the clamping pressure from the first clamping pressure to the second clamping pressure after a first time has elapsed from a moment when the fixed sheet sensor detects that a trailing edge of a final sheet has passed through the nip portion.

[0007] Preferably, the image forming apparatus further includes a second motor and a first clutch. The second motor is configured to drive the pressure modifying mechanism. The first clutch is configured to switch between a first transmission state in which the driving force of the second motor is transmitted to the pressure modifying mechanism and a first disconnection state in which the driving force of the second motor is not transmitted to the pressure modifying mechanism.

[0008] Preferably, the pressure modification mechanism includes a cam configured to pivotally move between a first position where the clamping pressure becomes a first clamping pressure and a second position where the clamping pressure becomes a second clamping pressure. Modifying the clamping pressure includes controlling the second motor to switch the first clutch to a first transmission state, thereby pivotally moving the cam from the first position to the second position.

[0009] Preferably, the image forming apparatus further includes a photosensitive member and a developing roller. The developing roller is configured to supply developer to the photosensitive member. The second motor further drives the developing roller.

[0010] Preferably, the image forming apparatus further includes a photosensitive member, a developing roller, a switching mechanism, and a second clutch. The developing roller is configured to supply developer to the photosensitive member. The switching mechanism is configured to switch the state of the developing roller between a contact state in which the developing roller contacts the photosensitive member and a separation state in which the developing roller is separated from the photosensitive member. The second clutch is configured to switch between a second transmission state in which the driving force of the second motor is transmitted to the switching mechanism and a second separation state in which the driving force of the second motor is not transmitted to the switching mechanism.

[0011] Preferably, the pressure modification mechanism includes a cam configured to pivotally move between a first position in which the clamping pressure becomes a first clamping pressure and a second position in which the clamping pressure becomes a second clamping pressure. Modifying the clamping pressure includes controlling the second motor to rotate while the second clutch is in the second disconnecting state, and then controlling the second motor to switch the first clutch to the first transmitting state, thereby pivotally moving the cam from the first position to the second position.

[0012] Preferably, the cam is pivotally moved from the second position to the first position by forward rotation of the second motor, and the cam is pivotally moved from the first position to the second position by reverse rotation of the second roller. The controller is configured to further drive the second motor in the forward direction while printing is being performed. Modifying the clamping pressure includes controlling the second motor to rotate in the reverse direction.

[0013] Preferably, when the clamping pressure is modified from the first clamping pressure to the second clamping pressure, the second motor rotates at a slower rotation speed than when printing is performed.

[0014] Preferably, the modification is performed after the second motor starts driving and rotating at a constant rotation speed.

[0015] Preferably, stopping the first motor is performed after a second time has elapsed from the moment when the modification is completed.

[0016] Preferably, the second fixing member includes an upstream pad and a downstream pad. The upstream pad is configured to clamp the belt together with the first fixing member. The downstream pad is located downstream of the upstream pad in the direction of sheet conveyance. The downstream pad is configured to clamp the belt together with the first fixing member. When the clamping pressure is a first clamping pressure, both the upstream pad and the downstream pad clamp the belt together with the first fixing member. When the clamping pressure is a second clamping pressure, the upstream pad clamps the belt together with the first fixing member, while the downstream pad does not clamp the belt together with the first fixing member.

[0017] Preferably, the second clamping pressure is a minimum clamping pressure within a range in which the pressure modification mechanism can set the clamping pressure.

[0018] Preferably, the image forming apparatus further includes a heater configured to heat the first fixing member.

[0019] Preferably, the pressure modifying mechanism includes a cam configured to pivotally move between a first position at which the nip pressure becomes a first nip pressure and a second position at which the nip pressure becomes a second nip pressure. The second fixing member moves between the first nip position at which a nip portion is formed between the first fixing member and the second fixing member, and a second nip position at which a distance from the first fixing member to the second fixing member is greater than a distance at the first nip position.

[0020] According to another aspect, the present disclosure provides an image forming device. The image forming device includes a first fixing member, a second fixing member, and a pressure modification mechanism. The first fixing member has a roller. The second fixing member has a belt to form a clamping portion together with the first fixing member. The pressure modification mechanism is configured to modify the clamping pressure at the clamping portion to a selected one of a first clamping pressure and a second clamping pressure that is smaller than the first clamping pressure. The image forming device is configured to: drive the roller; fix the developer image on the sheet in a state where the clamping pressure is the first clamping pressure; when the final sheet of one or more sheets fixed according to the print job has passed through the clamping portion, while driving the roller, modify the clamping pressure from the first clamping pressure to the second clamping pressure; and stop the roller after the clamping pressure is modified to the second clamping pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specific features and advantages of the present disclosure and other objects will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0022] Figure 1 is a sectional view showing a color printer according to an embodiment;

[0023] Figure 2 is a cross-sectional view showing a fixing device of a color printer;

[0024] Figure 3 is an exploded perspective view showing components located in an internal space defined by the belt in the fixing device;

[0025] Figure 4 is a perspective view showing a pressure modifying mechanism of a color printer;

[0026] FIG5( a) is a cross-sectional view showing the pressure modification mechanism when the clamping pressure is the maximum clamping pressure;

[0027] FIG5( b) is a cross-sectional view showing the periphery of the configuration of the clamping region when the clamping pressure is the maximum clamping pressure;

[0028] FIG6( a) is a sectional view showing the pressure modification mechanism when the clamping pressure is a second clamping pressure;

[0029] FIG6( b) is a cross-sectional view showing the periphery of the configuration of the clamping region when the clamping pressure is a second clamping pressure;

[0030] Figure 7 is an explanatory diagram showing a relationship between a controller and components controlled by the controller; and

[0031] Figure 8 is a timing diagram illustrating operations performed by the controller. DETAILED DESCRIPTION

[0032] Next, embodiments of the present disclosure will be described while referring to the accompanying drawings. Figure 1 A color printer 1 is shown as an example of an image forming apparatus. The color printer 1 is provided with a main housing 2, and within the main housing 2 are provided: a sheet feeding section 20 for supplying a sheet S to be printed; an image forming section 30 for forming a toner image on the sheet S supplied by the sheet feeding section 20; a fixing device 80 for fixing the toner image on the sheet S; a paper discharge section 90 for discharging the sheet S from the main housing 2 after the image has been formed and fixed on the sheet S; and a controller 100.

[0033] An opening 2A is formed at the top of the main housing 2. An upper cover 3 is pivotally supported on the main housing 2 and opens and closes the opening 2A. The top surface of the upper cover 3 forms a paper discharge tray 4 that collects sheets S discharged from the main housing 2. A plurality of LED mounting members 5 are provided on the bottom surface of the upper cover 3. Each LED mounting member 5 holds an LED unit 40.

[0034] A sheet feeding section 20 is provided in the bottom portion of the main housing 2. The sheet feeding section 20 is provided with a paper tray 21 that is detachably mounted in the main housing 2, and a sheet feeding mechanism 22 that conveys a sheet S from the paper tray 21 toward the image forming section 30. The sheet feeding mechanism 22 includes a pickup roller 23, a separation roller 24, a separation pad 25, and registration rollers 26.

[0035] In the sheet feeding section 20, the pickup roller 23 feeds a sheet S from the paper tray 21. Subsequently, the separation roller 24 and the separation pad 25 separate the sheet S fed by the pickup roller 23, ensuring that each sheet is fed one at a time. Thereafter, the registration rollers 26 straighten the leading edge of the sheet S before conveying it toward the image forming section 30. Specifically, when the sheet S is conveyed to the registration rollers 26, the registration rollers 26 are stopped. When the sheet S contacts the stopped registration rollers 26, the leading edge of the sheet S is aligned with the registration rollers 26, thereby eliminating any skew in the sheet S. Subsequently, the registration rollers 26 begin rotating to convey the sheet S forward.

[0036] The image forming section 30 includes four LED units 40 , four process cartridges 50 , a transfer unit 70 , and a belt cleaner 10 .

[0037] The LED units 40 are coupled to the corresponding LED mounting members 5 so as to be pivotable relative to the LED mounting members 5. Positioning members provided in the main housing 2 support the LED units 40 in place.

[0038] The process cartridges 50 are arranged in parallel in the front-to-rear direction between the upper cover 3 and the sheet feeding portion 20. Each process cartridge 50 is composed of a photosensitive drum 51 as an example of a photosensitive member, a charger 52, a developing roller 53, a toner accommodating chamber 54 for accommodating toner (an example of a developer), and a cleaning roller 55.

[0039] The process cartridges 50 are denoted by symbols 50K, 50Y, 50M, and 50C to indicate the colors of the toners they contain. Thus, the process cartridge 50K contains black (K) toner, the process cartridge 50Y contains yellow (Y) toner, the process cartridge 50M contains magenta (M) toner, and the process cartridge 50C contains cyan (C) toner. The process cartridges 50K, 50Y, 50M, and 50C are arranged in the given order starting from the upstream side in the conveying direction of the sheet S. Note that in the specification and the drawings, the same symbols K, Y, M, and C are also attached to the photosensitive drum 51, the developing roller 53, and the cleaning roller 55 to identify the colors of the toners used with the corresponding components (i.e., black, yellow, magenta, and cyan).

[0040] The photosensitive drum 51 is a member capable of carrying toner. Specifically, each LED unit 40 exposes the surface of the corresponding photosensitive drum 51 so that an electrostatic latent image is formed thereon, and the area of the photosensitive drum 51 on which the electrostatic latent image is formed carries toner. One photosensitive drum 51 is provided in each process cartridge 50. The photosensitive drums 51 are arranged at intervals along the conveyance direction of the sheet S.

[0041] The developing roller 53 is a roller that carries toner and is configured to contact the corresponding photosensitive drum 51 so as to supply toner to the electrostatic latent image formed on the photosensitive drum 51 .

[0042] The developing roller 53 can be brought into contact with or separated from the corresponding photosensitive drum 51. The controller 100 controls the switching mechanism SW (see FIG. Figure 7 ) to switch the developing roller 53 between the pressure contact position and the separation position. Specifically, all of the developing rollers 53K, 53Y, 53M, and 53C are brought into contact with the corresponding photosensitive drums 51K, 51Y, 51M, and 51C in color mode to supply toner to the corresponding photosensitive drums 51K, 51Y, 51M, and 51C. However, only the black developing roller 53K is brought into contact with the photosensitive drum 51K in monochrome mode, while the developing rollers 53Y, 53M, and 53C for the remaining three colors are separated from their corresponding photosensitive drums 51Y, 51M, and 51C. In the cleaning process described later, all of the developing rollers 53K, 53Y, 53M, and 53C are separated from the corresponding photosensitive drums 51K, 51Y, 51M, and 51C.

[0043] The cleaning rollers 55 are members capable of recovering toner from the corresponding photosensitive drums 51. One cleaning roller 55 is provided adjacent to the corresponding photosensitive drum 51.

[0044] The transfer unit 70 is provided between the sheet feeding portion 20 and the process cartridge 50. The transfer unit 70 is provided with a driving roller 71, a driven roller 72, a belt 73, and a transfer roller 74.

[0045] The drive roller 71 and the driven roller 72 are arranged parallel to each other while being separated in the front-to-back direction. The belt 73 is an endless belt stretched around the drive roller 71 and the driven roller 72. The belt 73 is a member for conveying the sheet S. The outer surface of the belt 73 contacts the photosensitive drum 51. Four transfer rollers 74 are provided within the belt 73 at positions opposing the corresponding photosensitive drums 51.

[0046] The belt 73 is interposed between the photosensitive drum 51 and the corresponding transfer roller 74. The sheet S is conveyed by the belt 73 and the photosensitive drum 51.

[0047] The belt cleaner 10 is a device that slides against the belt 73 to recover toner and other substances that have been deposited on the belt 73. The belt cleaner 10 is provided below the belt 73. Specifically, the belt cleaner 10 is provided with a sliding contact roller 11, a recovery roller 12, a blade 13, and a waste toner container 14.

[0048] The sliding contact roller 11 is provided so as to contact the outer surface of the belt 73. The belt 73 is interposed between the sliding contact roller 11 and the backup roller 15 provided inside the belt 73. The sliding contact roller 11 recovers the substance deposited on the belt 73.

[0049] The recovery roller 12 is a roller that slides in contact with the sliding contact roller 11 to recover the material deposited on the sliding contact roller 11. The blade 13 is provided so as to slide against the recovery roller 12 and scrape off the recovered material on the recovery roller 12. The material scraped off from the recovery roller 12 falls into the waste toner container 14.

[0050] The fixing device 80 is provided with a first fixing member 81 and a second fixing member 82. The structure of the fixing device 80 will be described in more detail later.

[0051] In the image forming unit 30 having the above-described structure, the charger 52 applies a uniform charge to the surface of the photosensitive drum 51. Subsequently, the charged surface of the photosensitive drum 51 is exposed to light by the LED unit 40, forming an electrostatic latent image based on image data on the photosensitive drum 51. Thereafter, toner is supplied from the developing roller 53 to the electrostatic latent image, forming a toner image carried on the photosensitive drum 51.

[0052] As the sheet S passes between the photosensitive drum 51 and the corresponding transfer roller 74 provided inside the belt 73, the toner image formed on each photosensitive drum 51 is transferred to the sheet S carried on the belt 73. As the sheet S passes between the first fixing member 81 and the second fixing member 82, the toner image transferred to the sheet S is thermally fixed to the sheet S.

[0053] The paper discharge section 90 is provided with a discharge side conveying path 91 and a plurality of conveying rollers 92. After the toner image is thermally fixed to the sheet S, the conveying rollers 92 convey the sheet S along the discharge side conveying path 91 and discharge the sheet S from the main casing 2 to be collected in the paper discharge tray 4.

[0054] like Figure 2 As shown, the fixing device 80 is provided with a heater 110 and a pressure modifying mechanism 300 (see FIG. 1 ) described later, in addition to the first fixing member 81 and the second fixing member 82 described above. Figure 4). The pressure modifying mechanism 300 described later presses the second fixing member 82 against the first fixing member 81. In the following description, the direction in which the second fixing member 82 presses against the first fixing member 81 and the opposite direction thereof will be referred to as a "prescribed direction". In this embodiment, the prescribed direction is orthogonal to the width direction and the moving direction described later, and is a direction in which the first fixing member 81 and the second fixing member 82 face each other.

[0055] The first fixing member 81 includes a rotatable roller 120. When the second fixing member 82 is positioned against the first fixing member 81, a nip region NP is formed therebetween. The second fixing member 82 includes a belt 130, a nip-forming member N, a retainer 140, a support 200, a belt guide G, and a sliding sheet 150. The belt 130 and the sliding sheet 150 are made of a heat-resistant resin, such as polyimide, having a glass transition temperature greater than or equal to 140 degrees Celsius. In the following description, the width direction of the belt 130 will be referred to simply as the "width direction." The width direction is the direction in which the rotation axis of the rotatable roller 120 extends. Therefore, the width direction is the same as the axial direction of the rotatable roller 120. The width direction is orthogonal to the specified direction.

[0056] The heater 110 is a halogen lamp. When powered, the heater 110 emits light and generates heat. The radiant heat generated by the heater 110 heats the rotatable roller 120. The heater 110 extends through the interior of the rotatable roller 120 along the rotation axis of the rotatable roller 120.

[0057] The rotatable roller 120 is a cylindrical roller elongated in the width direction. The rotatable roller 120 is heated by the heater 110. The rotatable roller 120 has a tubular body 121 formed of metal or the like, and an elastic layer 122 covering the outer surface of the tubular body 121. The elastic layer 122 is formed of rubber (such as silicone rubber). The rotatable roller 120 is rotatably supported on the side frame 83 (see FIG. 1 ) described later. Figure 4 ). The first motor M1 (refer to Figure 7 Description) is provided in the main housing 2. The first motor M1 is an input for driving the rotatable roller 120 in Figure 2 The fixing motor rotates counterclockwise.

[0058] The belt 130 is a long cylindrical member having flexibility. The belt 130 forms a nip region NP together with the first fixing member 81, particularly the rotatable roller 120. Although not shown in the figure, the belt 130 has a base formed of metal, resin, etc., and a release layer covering the outer surface of the base. Due to the friction between the belt 130 and the rotatable roller 120 or the sheet S interposed between the belt 130 and the rotatable roller 120, the belt 130 follows the rotation of the rotatable roller 120. Figure 2Grease or other lubricant is applied to the inner peripheral surface 131 of the belt 130. The clamp forming member N, the retainer 140, the support 200, the belt guide G and the sliding sheet 150 are all arranged in the inner space defined by the cylindrical belt 130.

[0059] Thus, the nip forming member N, the holder 140 , the stay 200 , the belt guide G, and the sliding sheet 150 are surrounded by the belt 130 .

[0060] like Figure 2 and Figure 3 As shown, the nip forming member N, together with the rotatable roller 120, clamps a portion of the belt 130 to form a nip region NP. The nip forming member N includes an upstream nip forming member N1 and a downstream nip forming member N2.

[0061] The upstream nip forming member N1 includes an upstream pad P1 and an upstream fixing plate B1. The upstream pad P1 is a rectangular parallelepiped member. The upstream pad P1 is formed of rubber (such as silicone rubber). The upstream pad P1 and the rotatable roller 120 sandwich a portion of the belt 130 to form an upstream nip region NP1.

[0062] In the following description, the direction in which the belt 130 moves within the upstream nip region NP1 and the nip region NP will be referred to simply as the "movement direction." In this embodiment, the movement direction is the direction following the outer peripheral surface of the rotatable roller 120. However, since this direction is substantially orthogonal to the specified direction and the width direction within the nip region NP, the movement direction is illustrated in the figures as being orthogonal to both. Note that within the nip region NP, the movement direction is the same as the conveyance direction of the sheet S.

[0063] The upstream pad P1 is fixed to a surface of the upstream fixing plate B1 that is opposite to the rotatable roller 120. The upstream fixing plate B1 is a member formed of metal or other material that is harder than the upstream pad P1.

[0064] The downstream nip forming member N2 is arranged on the downstream side of the upstream nip forming member N1 in the moving direction and is spaced apart from the upstream nip forming member N1. The downstream nip forming member N2 has a downstream pad P2 and a downstream fixing board B2.

[0065] The downstream pad P2 is a rectangular parallelepiped member. It is formed of rubber (such as silicone rubber). Together with the rotatable roller 120, the downstream pad P2 clamps a portion of the belt 130 to form a downstream clamping area NP2. The downstream pad P2 is separated from the upstream pad P1 in the direction of belt 130 rotation.

[0066] Therefore, an intermediate nip region NP3 exists between the upstream nip region NP1 and the downstream nip region NP2, where the second fixing member 82 does not directly apply pressure to the first fixing member 81. Although the belt 130 contacts the rotatable roller 120 in the intermediate nip region NP3, since no members exist on the opposite side of the rotatable roller 120 from the belt 130 in this region, the belt 130 applies little pressure to the rotatable roller 120. Therefore, the sheet S passing through the intermediate nip region NP3 is heated by the rotatable roller 120 but receives little pressure. In this embodiment, the area from the upstream side of the upstream nip region NP1 to the downstream side of the downstream nip region NP2—that is, the entire area on the outer surface of the belt 130 that is in contact with the rotatable roller 120—is referred to as the nip region NP. Therefore, the nip region NP in this embodiment includes an area that receives no pressure from the upstream pad P1 or the downstream pad P2. In other words, the clamping area NP is an area from the upstream end point where the belt 130 is in pressure contact with the rotatable roller 120 in the moving direction to the downstream end point where the belt 130 is in pressure contact with the rotatable roller 120 in the moving direction. The belt 130 and the rotatable roller 120 can be in pressure contact with each other at a single point. In this case, the clamping area is a single clamping point. In addition, actions such as "clamping", "clamping" and "nipping" indicate that two components (such as the first fixing member 81 and the second fixing member 82) are in contact with each other and generate pressure between them. Therefore, the clamping area is an area or point where two components are in contact with each other and at least includes a clamping portion for clamping a sheet by the two components.

[0067] The downstream pad P2 is fixed to the surface of the downstream fixing plate B2 that is opposite to the rotatable roller 120. The downstream fixing plate B2 is a member formed of a metal or the like that is harder than the downstream pad P2.

[0068] Note that the hardness of the upstream pad P1 is greater than the hardness of the elastic layer 122 provided on the rotatable roller 120. Furthermore, the hardness of the downstream pad P2 is greater than the hardness of the upstream pad P1.

[0069] The term "hardness" in this specification refers to the Shore hardness measured using a durometer according to the method specified in ISO 7619-1. Shore hardness is a value based on the depth of indentation when a specified presser foot is pressed into a test piece under specified conditions. For example, in this embodiment, if the Shore hardness of the elastic layer 122 is 5, the Shore hardness of the upstream pad P1 is preferably between 6 and 10, while the Shore hardness of the downstream pad P2 is preferably between 70 and 90.

[0070] The retainer 140 is a member that holds the clamp forming member N. The retainer 140 is formed of a heat-resistant resin or the like. The retainer 140 has a retainer body 141 and two engaging portions 142 and 143 ( Figure 3 ).

[0071] The holder body 141 is a member that holds the nip forming member N. Most of the holder body 141 is provided within the range of the belt 130 in the width direction. The holder body 141 is supported by the support column 200 .

[0072] The engaging portions 142 and 143 extend outward in the width direction from respective ends of the holder body 141. The engaging portions 142 and 143 are located outside the range of the belt 130 in the width direction. The engaging portions 142 and 143 engage with respective width direction ends of the first support 210 described later.

[0073] The support 200 is a member that supports the holder 140. The support 200 is located on the opposite side of the clamp forming member N relative to the holder 140. The support 200 is provided with a first support 210 and a second support 220. The second support 220 is connected to the retainer 140 by a connecting member CM ( Figure 3 ) is connected to the first pillar 210.

[0074] The first support column 210 is a member that supports the holder body 141 of the holder 140. The first support column 210 is formed of metal, etc. The first support column 210 has a base portion 211 and a hem HB that has been bent in a hemming process.

[0075] The base portion 211 has a contact surface Ft along an edge facing the holder 140 for contacting the holder body 141 of the holder 140. The contact surface Ft is a flat surface perpendicular to a prescribed direction.

[0076] The base portion 211 has a load input portion 211A provided on each widthwise end. The load input portion 211A is connected to the pressure modification mechanism 300 (see FIG. Figure 4 ) receives force. A load input portion 211A is formed in an edge of the base portion 211 on the side opposite to the grip forming member N in a prescribed direction. The load input portion 211A is a recessed portion that opens toward the side opposite to the grip forming member N in a prescribed direction.

[0077] The buffer member BF is installed in the load input portion 211A. The buffer member BF is formed of a resin or the like. The buffer member BF suppresses the metal base portion 211 from contacting the metal arm 310 (see FIG. 1 ) described later. Figure 4 Each buffer member BF has a fitting portion BF1 that fits into the corresponding load input portion 211A, and a pair of leg portions BF2 that are respectively provided on the upstream and downstream sides of the outer width direction end of the corresponding base portion 211 in the moving direction.

[0078] The belt guide G is a member that guides the inner peripheral surface 131 of the belt 130. The belt guide G is formed of a heat-resistant resin, etc. The belt guide G has an upstream guide G1 and a downstream guide G2.

[0079] Sliding sheet 150 is a rectangular sheet designed to reduce frictional resistance between belt 130 and pads P1 and P2. Sliding sheet 150 is interposed between inner circumferential surface 131 of belt 130 and pads P1 and P2 within nip region NP. Sliding sheet 150 is formed from an elastically deformable material. While any suitable material may be used for sliding sheet 150, a resin sheet containing polyimide is employed in this embodiment.

[0080] like Figure 2 As shown, the upstream guide G1 , the downstream guide G2 and the first support 210 are fastened together by screws SC.

[0081] like Figure 4 As shown, the fixing device 80 is further provided with a frame FL and a pressure modifying mechanism 300. The frame FL is formed of metal or the like and supports the first fixing member 81 and the second fixing member 82. The frame FL includes two side frames 83, two brackets 84, and a connecting frame 85. The side frames 83 and the brackets 84 are provided at the widthwise ends of the first fixing member 81 and the second fixing member 82. The connecting frame 85 connects the two side frames 83.

[0082] The side frames 83 are frame members that support the first fixing member 81 and the second fixing member 82. Each side frame 83 has a spring engaging portion 83A. One end of a first spring 320 described later is engaged in each spring engaging portion 83A.

[0083] The brackets 84 are fixed to the corresponding side frames 83. The brackets 84 are members that support the second fixing member 82 so that the second fixing member 82 can move in a specified direction. Specifically, each bracket 84 has a first elongated hole 84A that extends in the specified direction. The elongated holes 84A guide the corresponding ends of the first support posts 210 via the engaging portions 142 and 143 of the retainer 140, allowing the first support posts 210 to move in the specified direction.

[0084] The pressure modification mechanism 300 modifies the clamping pressure at the clamping area NP. Figure 4 and 5(a) As shown, the pressure modification mechanism 300 is provided with a pair of arms 310, a first spring 320, a second spring 330 and a cam 340. Each of the arms 310, the first spring 320, the second spring 330 and the cam 340 is provided on the first and second widthwise sides of the frame FL.

[0085] The arm 310 is a member for pressing the first stay 210 via the buffer member BF. The arm 310 supports the second fixing member 82 and is supported by the side frame 83 so as to be pivotally movable.

[0086] Each arm 310 has an arm body 311 and a cam follower 350. The arm body 311 is an L-shaped plate-like member formed of metal or the like.

[0087] Each arm body 311 has a first end 311A pivotally supported on the corresponding side frame 83, a second end 311B coupled to one end of the corresponding first spring 320, and an engagement hole 311C supporting the second fixing member 82. The engagement hole 311C is formed at a position between the first end 311A and the second end 311B and engages with the corresponding buffer member BF.

[0088] The arm body 311 also has a guide protrusion 312 extending toward the cam 340. The guide protrusion 312 is provided between the second end 311B and the engagement hole 311C in a direction from the second end 311B to the engagement hole 311C.

[0089] The cam follower 350 is mounted above the guide protrusion 312 of the arm 311 and is movable relative to the guide protrusion 312 and is capable of contacting the cam 340. The cam follower 350 is formed of a resin or the like. The cam follower 350 includes a cylindrical portion 351 mounted above the guide protrusion 312, a contact portion 352 provided at one end of the cylindrical portion 351, and a flange portion 353 provided at the other end of the cylindrical portion 351.

[0090] The cylindrical portion 351 is supported by the guide protrusion 312 and is movable in the direction in which the guide protrusion 312 extends. The contact portion 352 is a wall that closes an opening formed in the end portion of the cylindrical portion 351 on the cam 340 side. The contact portion 352 is arranged between the cam 340 and the end portion of the guide protrusion 312. A flange portion 353 protrudes from the other end of the cylindrical portion 351 in a direction orthogonal to the moving direction of the cam follower 350.

[0091] The second spring 330 is provided between the cylindrical portion 351 and the arm body 311. With this configuration, the arm body 311 can be pushed by the first spring 320 and the second spring 330.

[0092] The first spring 320 applies a first urging force to the second fixing member 82 , and specifically, applies the first urging force to the second fixing member 82 through the arm body 311 .

[0093] More specifically, the first springs 320 push the upstream pad P1 and the downstream pad P2 toward the rotatable roller 120 via the arm body 311, the buffer member BF, the first support column 210, and the retainer 140. The first springs 320 are tension coil springs formed of metal, etc. One end of each first spring 320 is coupled to the spring engagement portion 83A of the corresponding side frame 83, while the other end is coupled to the second end 311B of the corresponding arm body 311.

[0094] The second spring 330 can apply a second urging force to the second fixing member 82 in a direction opposite to the first urging force, and specifically, can apply the second urging force to the second fixing member 82 through the arm body 311. The second spring 330 is a compression coil spring formed of metal, etc. The second spring 330 is disposed between the corresponding cylindrical portion 351 and the arm body 311, wherein the guide protrusion 312 is inserted into an internal space formed in the compression coil spring 330.

[0095] The cam 340 is a member capable of changing the compression state of the second spring 330 between a first compressed state (in which no second thrust is applied to the second fixing member 82), a second compressed state (in which the second thrust is applied to the second fixing member 82), and a third compressed state (in which the second spring 330 is further compressed from the second compressed state). The cam 340 is supported on the corresponding side frame 83 so as to be pivotally movable (or rotatable) between a first cam position (shown in FIG. 5( a) ), an intermediate cam position (not shown), and a second cam position (see FIG. 6( a) ). The intermediate cam position is pivotally movable (or rotated) approximately 90 degrees clockwise from the first cam position in FIG. 5( a) , and the second cam position is pivotally movable (or rotated) approximately 270 degrees clockwise from the first cam position in FIG. 5( a) .

[0096] The cams 340 are formed of resin, etc. Each cam 340 has a first region 341 , a second region 342 , and a third region 343 . The first region 341 , the second region 342 , and the third region 343 are located along the circumferential surface of the cam 340 .

[0097] The first region 341 is a region located closest to the cam follower 350 when the cam 340 is in the first cam position. When the cam 340 is in the first cam position shown in FIG. 5( a ), the first region 341 is separated from the cam follower 350 .

[0098] The second area 342 is an area on the cam 340 that contacts the cam follower 350 when the cam 340 is in the intermediate cam position. More specifically, when the cam 340 has pivotally moved (or rotated) approximately 90 degrees clockwise in FIG. 5( a) from the first cam position, the second area 342 contacts the cam follower 350. The distance from the second area 342 to the rotation center of the cam 340 is greater than the distance from the first area 341 to the rotation center of the cam 340.

[0099] The third region 343 is the region that contacts the cam follower 350 when the cam 340 is in the second cam position. More specifically, the third region 343 is the region of the cam 340 that contacts the cam follower 350 after the cam 340 has pivotally moved (or rotated) approximately 270 degrees clockwise in FIG. 5( a ) from the first cam position, as shown in FIG. 6( a ), or when the cam 340 has pivotally moved (or rotated) approximately 180 degrees clockwise in FIG. 5( a ) from the intermediate cam position. The distance from the third region 343 to the rotational center of the cam 340 is greater than the distance from the second region 342 to the rotational center of the cam 340.

[0100] When the cam 340 is in the first cam position, the second spring 330 is in the first compressed state because the cam 340 is separated from the cam follower 350. When the cam 340 causes the second spring 330 to be in the first compressed state in this manner, the arm 311 is in the first orientation shown in Figure 5(a).

[0101] Specifically, when the cam 340 has placed the second spring 330 in the first compressed state, the cam 340 is separated from the cam follower 350, so that the second urging force of the second spring 330 is not applied to the second fixing member 82 via the arm body 311, and only the first urging force of the first spring 320 is applied to the second fixing member 82 via the arm body 311. When the first spring 320 applies the first urging force to the second fixing member 82 and the second spring 330 does not apply the second urging force to the second fixing member 82 in this orientation, the clamping pressure is the maximum clamping pressure.

[0102] When the cam 340 pivotally moves (or rotates) from the first cam position shown in FIG5(a) to the intermediate cam position, the cam 340 contacts the cam follower 350 and moves the cam follower 350 a predetermined amount relative to the arm 311. When the cam 340 moves to the intermediate cam position, the compressed state of the second spring 330 is deformed into a second compressed state that is more compressed than the first compressed state.

[0103] Since the cam follower 350 is pressed by the cam 340 when the cam 340 is in the intermediate cam position, the second urging force of the second spring 330 is applied to the second fixing member 82 in the opposite direction to the first urging force via the arm body 311. Therefore, when the first spring 320 applies the first urging force to the second fixing member 82 and the second spring 330 applies the second urging force to the second fixing member 82, the nip pressure becomes an intermediate nip pressure that is smaller than the maximum nip pressure.

[0104] Note that when the cam 340 places the second spring 330 in the second compressed state, the arm 311 maintains the aforementioned first orientation. Here, the downstream pad P2 remains pressed against the rotatable roller 120, so that a load is applied to the downstream pad P2. While the downstream pad P2 is pressed against the rotatable roller 120, i.e., while a load is applied to the downstream pad P2, the shape of the downstream pad P2 remains substantially unchanged, regardless of the magnitude of the load. Because the shape of the downstream pad P2 remains substantially unchanged, the support 200 supporting the downstream pad P2 and the arm 310 supporting the support 200 remain in a substantially fixed position, regardless of the magnitude of the load. Furthermore, since the position of the upstream pad P1 is determined by the position of the downstream pad P2, the position of the upstream pad P1 remains unchanged while the shape and position of the downstream pad P2 remain substantially unchanged. Therefore, the total clamping width (the length from the entrance of the upstream clamping area NP1 to the exit of the downstream clamping area NP2) does not differ between strong clamping (maximum clamping pressure) and weak clamping (intermediate clamping pressure), and thus, the position of the arm 310 remains substantially constant.

[0105] Here, the downstream pad P2 does not deform under these circumstances because it has a sufficiently greater hardness than the upstream pad P1 and the elastic layer 122 of the rotatable roller 120. More specifically, the downstream pad P2 has sufficient hardness to be substantially nondeformed under the clamping pressure required in the downstream nip region NP2, which is within a range from the maximum clamping pressure (downstream clamping pressure in strong clamping) to the intermediate clamping pressure (downstream clamping pressure in weak clamping). In other words, the maximum clamping pressure and the intermediate minimum clamping pressure required for downstream clamping are set to a level within which the downstream pad P2 is substantially nondeformed.

[0106] Here, “the downstream pad P2 hardly undergoes deformation change” allows the downstream pad P2 to undergo some deformation, as long as the amount of change in the clamping width (the clamping length and position in the moving direction of the belt 130) of the downstream clamping area NP2 formed by the downstream pad P2 does not affect the conveying of the sheet and the image quality (that is, the amount of change in the downstream clamping width does not have to be zero).

[0107] In this manner, since the arm body 311 is in the first orientation regardless of whether the compressed state of the second spring 330 is the first compressed state or the second compressed state, the upstream pad P1 and the downstream pad P2 press the belt 130 against the rotatable roller 120 regardless of whether the nip position is the maximum nip pressure or the intermediate nip pressure. Specifically, since the position of the second fixing member 82 relative to the rotatable roller 120 is substantially the same in the maximum and intermediate nip pressure states, the width (length in the moving direction) of the nip area NP is substantially the same for both states.

[0108] Here, the maximum nip pressure or the intermediate nip pressure is a first nip pressure set for printing, particularly for fixing a toner image onto a sheet S. For example, the maximum nip pressure is used when the sheet S has a first thickness, while the intermediate nip pressure is used when the sheet S has a second thickness greater than the first thickness. That is, the first nip pressure is set between the maximum nip pressure and the intermediate nip pressure according to the thickness of the sheet S.

[0109] In addition, the first cam position or the intermediate cam position is a first position where the clamping pressure is the maximum clamping pressure or the intermediate clamping pressure (ie, the first clamping pressure). In addition, the second cam position is a second position where the clamping pressure is the minimum clamping pressure (ie, the second clamping pressure).

[0110] When pivotally moving (or rotating) from the intermediate cam position to the second cam position shown in FIG6( a), the cam 340 first moves the cam follower 350 further toward the arm 311, and then presses the arm 311 through the cam follower 350. As a result, the second spring 330 is deformed to a third compressed state, which is more compressed than the second compressed state, and the arm 311 is pivotally moved from the first orientation to a second orientation different from the first orientation.

[0111] Specifically, in the initial stage of the process for pivotally moving (or rotating) the cam 340 from the intermediate cam position to the second cam position, the cam follower 350 moves relative to the arm 311, causing the contact portion 352 of the cam follower 350 to approach the distal end of the guide protrusion 312. When the contact portion 352 contacts the distal end of the guide protrusion 312, the compressed state of the second spring 330 is in the third compressed state. When the cam 340 thus causes the second spring 330 to be in the third compressed state, the contact portion 352, which constitutes a portion of the cam follower 350, is interposed between the cam 340 and the guide protrusion 312. In other words, the contact portion 352 contacts both the cam 340 and the guide protrusion 312. Thereafter, as the cam 340 further pivotally moves (or rotates), the cam 340 presses against the guide protrusion 312 via the contact portion 352, causing the arm 311 to pivotally move from the first orientation to the second orientation against the urging force of the first spring 320.

[0112] When the arm body 311 is placed in the second orientation by this operation, the second fixing member 82 is positioned farther away from the rotatable roller 120 (the position in Figure 6 (b)) than when the arm body 311 is in the first orientation (the position in Figure 5 (b)). The position of the second fixing member 82 when the arm body 311 is in the first orientation will be referred to as the "first clamping position", and the position of the second fixing member 82 when the arm body 311 is in the second orientation will be referred to as the "second clamping position". In the second clamping position, the distance between the first fixing member 81 and the second fixing member 82 is greater than the distance in the first clamping position. As the cam 340 pivotally moves (or rotates), the second fixing member 82 moves between the first clamping position and the second clamping position, in which the second fixing member 82 is farther away from the rotatable roller 120 than in the first clamping position. When the second fixing member 81 is in the second clamping position shown in Figure 6 (b), the rotatable roller 120 is in pressure contact with the belt 130 corresponding to the downstream portion of the upstream pad P1. Therefore, in this case, the nip region NP is the area between the rotatable roller 120 and the belt 130 corresponding to the downstream portion of the upstream pad P1. In this case, although the rotatable roller 120 is in contact with the belt 130 in the area downstream of the upstream pad P1, little nip pressure is generated in this area. Therefore, the nip region NP does not include the area downstream of the upstream pad P1. Although in this example, the rotatable roller 120 is in contact with a portion of the belt 130 in the area downstream of the upstream pad P1, when the second fixing member 81 is in the second nip position, the rotatable roller 120 can separate from the portion of the belt 130 in the area downstream of the upstream pad P1.

[0113] When the cam 340 moves to the second cam position, causing the arm 311 to switch to the second orientation, the position of the second fixing member 82 relative to the rotatable roller 120 changes so that the width of the clamping area NP is smaller than the width when the arm 311 is in the first orientation, and the clamping pressure is a minimum clamping pressure that is smaller than the intermediate clamping pressure. In other words, by changing the orientation of the arm 310 and the cam 340, the clamping pressure and the clamping width can be modified. Specifically, when the arm 310 is in the second orientation, the belt 130 is only clamped between the upstream pad P1 and the rotatable roller 120, and not between the downstream pad P2 and the rotatable roller 120. Therefore, when the arm 310 is in the second orientation, the upstream clamping pressure and the upstream clamping width generated in the upstream clamping area NP1 are both reduced, while the downstream clamping pressure generated in the upstream clamping area NP2 is eliminated. In other words, when the arm 310 is in the second orientation, the upstream clamping region NP1 is the only region that generates clamping pressure, whereas when the arm 310 is in the first orientation, both the upstream clamping region NP1 and the downstream clamping region NP2 are regions that generate clamping pressure. Therefore, when the arm 310 is in the second orientation, the size of all regions that generate clamping pressure is smaller than when the arm is in the first orientation.

[0114] The minimum clamping pressure is when printing is not performed, especially when the first motor M1 (see Figure 7 ) is set for the non-printing time when the printing is stopped. The minimum clamping pressure is also the minimum clamping pressure within the range of clamping pressures that can be modified by the pressure modification mechanism 300. The maximum clamping pressure is the maximum clamping pressure within the same range.

[0115] In this embodiment, when the clamping pressure is set to the minimum clamping pressure, the belt 130 is clamped between the upstream pad P1 and the rotatable roller 120, but the present disclosure is not limited to this configuration. For example, when the clamping pressure is the minimum clamping pressure, the belt 130 does not need to be clamped between the upstream pad P1 and the rotatable roller 120. In this case, the minimum clamping pressure is 0.

[0116] like Figure 7 As shown, the color printer 1 is provided with a first motor M1, a second motor M2, a first clutch C1, a switching mechanism SW, a second clutch C2, a sheet sensor SE1, a fixed sheet sensor SE2, and a position sensor SE3.

[0117] The second motor M2 is a developing motor or a pressure modifying motor. The second motor M2 is configured to rotate in both the forward and reverse directions and is primarily configured to drive each developing roller 53 to rotate. In this embodiment, the rotation direction of the second motor M2 during printing will be referred to as the forward direction. The second motor M2 is coupled to the developing roller 53 via a gear and a clutch (not shown) to rotate the developing roller 53. The second motor M2 is also coupled to the switching mechanism SW via a second clutch C2 and a gear (not shown). The second motor M2 is also coupled to the cam 340 of the pressure modifying mechanism 300 via a first clutch C1 and a gear (not shown).

[0118] The first motor M1 is provided to drive the rotatable roller 120 to rotate.

[0119] The second clutch C2 is, for example, an electromagnetic clutch and is a developing clutch that can be switched between a second transmission state in which the driving force of the second motor M2 is transmitted to the switching mechanism SW and a second disconnection state in which the driving force of the second motor M2 is not transmitted to the switching mechanism SW.

[0120] The switching mechanism SW is configured to switch the state of the developing roller 53 between a pressure-contact state in which the developing roller 53 is pressed against the photosensitive drum 51 and a separated state in which the developing roller 53 is separated from the photosensitive drum 51. When the second clutch C2 is set to the second transmission state under the conditions that the developing roller 53 is in the separated state and the second motor M2 is rotating in the forward direction, the switching mechanism SW switches the developing roller 53 from the separated state to the pressure-contact state. When the second clutch C2 is set to the second transmission state under the conditions that the developing roller 53 is in the pressure-contact state and the second motor M2 is rotating in the forward direction, the switching mechanism SW switches the developing roller 53 from the pressure-contact state to the separated state.

[0121] For example, the first clutch C1 is an electromagnetic clutch. The first clutch C1 is a pressure modification clutch capable of switching between a first transmission state, in which the driving force of the second motor M2 is transmitted to the cam 340 of the pressure modification mechanism 300, and a first disconnection state, in which the driving force of the second motor M2 is not transmitted to the cam 340. When the first clutch C1 is placed in the first transmission state, with the cam 340 in the second cam position and the second motor M2 rotating in the forward direction, the cam 340 pivotally moves (or rotates) counterclockwise from the second cam position shown in FIG. 6( a ) to the first cam position shown in FIG. 5( a ) in the accompanying drawings. When the first clutch C1 is placed in the first transmission state, with the cam 340 in the first cam position and the second motor M2 rotating in the reverse direction, the cam 340 pivotally moves (or rotates) clockwise from the first cam position shown in FIG. 5 toward the second cam position shown in FIG. 6( a ) in the accompanying drawings.

[0122] The sheet sensor SE1 and the fixed sheet sensor SE2 function to detect the presence or absence of a sheet S. Each of the sheet sensors SE1 and SE2 is provided with a pivot lever that pivots when pressed by a sheet S being conveyed in the conveying direction, and a photosensor that detects the pivoting of the pivot lever. In this embodiment, the sheet sensors SE1 and SE2 are set to ON when a sheet S passes (i.e., when the pivot lever is pushed past by the sheet S), and are set to OFF when a sheet S does not pass (i.e., when the pivot lever is not pushed past by the sheet S). However, the relationship between the orientation of the pivot lever and the ON / OFF signals from the sheet sensors SE1 and SE2 may be reversed.

[0123] In this specification, the expression "sensor for detecting a prescribed event" refers to a sensor for outputting a signal that enables the controller 100 to determine whether a prescribed event has occurred. For example, the above-mentioned "sensor for detecting the presence or absence of a sheet S" refers to a sensor that outputs a signal by which the controller 100 can determine the presence or absence of the sheet S.

[0124] In this embodiment, when the sheet sensor SE1 or SE2 is ON, the controller 100 determines that a sheet S exists at the position of the sheet sensor SE1 or SE2. When the sheet sensor SE1 or SE2 is OFF, the controller 100 determines that a sheet S does not exist at the corresponding position of the sheet sensor SE1 or SE2.

[0125] The sheet sensor SE1 is provided upstream of the fixing device 80 in the conveying direction of the sheet S. Specifically, the sheet sensor SE1 is provided downstream of the registration roller 26 and upstream of the image forming section 30 in the conveying direction of the sheet S.

[0126] The fixing sheet sensor SE2 is provided to detect when the trailing edge of the sheet S has passed through the nip region NP. By determining whether the fixing sheet sensor SE2 has been switched from ON to OFF, the controller 100 can determine whether the trailing edge of the sheet S has passed through the nip region NP. The fixing sheet sensor SE2 is provided in the fixing device 80. The fixing sheet sensor SE2 is provided downstream of the nip region NP in the conveying direction of the sheet S.

[0127] The position sensor SE3 is provided to detect the position of the second fixing member 82. Specifically, the position sensor SE3 is provided near the second clamping position and detects the second fixing member 82 when the second fixing member 82 approaches the second clamping position. FIG5(a) shows an example in which the position sensor SE3 is provided at a position capable of detecting the pivoting of the arm body 311. However, the position sensor SE3 may be provided at any position capable of detecting a member that moves in association with the movement of the second fixing member 82.

[0128] For example, the position sensor SE3 can be constructed by a photoelectric sensor having a light-emitting unit and a light-receiving unit. As shown in FIG5( a), when the second fixing member 82 is in the first clamping position (when the arm body 311 is in the first orientation), the light emitted from the light-emitting unit is not blocked by the arm body 311 and is received by the light-receiving unit. As shown in FIG6( a), when the second fixing member 82 is in the second clamping position (when the arm body 311 is in the second orientation), the light emitted from the light-emitting unit is blocked by the arm body 311 and is therefore not received by the light-receiving unit. The position sensor SE3 constructed in this manner can detect when the second fixing member 82 approaches the second clamping position.

[0129] Figure 7 The controller 100 shown is provided with a CPU, RAM, ROM, nonvolatile memory, ASIC, input / output circuits, etc. The controller 100 executes various processes by performing calculation operations based on print commands output from an external computer, signals output from sensors SE1-SE3, and programs and data stored in the ROM, etc.

[0130] When the trailing edge of the final sheet S in one or more sheets printed according to a print job passes through the nip region NP, the controller 100 changes the nip pressure from the first nip pressure to the second nip pressure while the first motor M1 continues to be driven, and then stops driving the first motor M1. Specifically, based on the signal received from the fixed sheet sensor SE2, the controller 100 waits until a first time T1 has elapsed after determining that the trailing edge of the final sheet S in the print job has passed through the nip region NP. Once the first time T1 has elapsed, the controller 100 changes the nip pressure from the first nip pressure to the second nip pressure.

[0131] In this embodiment, a print job is considered to be a set of pages that can be printed continuously on a sheet without returning to a standby state. Here, assuming that a (previous) page and its next page can be printed continuously on a (previous) sheet and its next sheet, the image data of the next page can be analyzed and prepared so that the feeding of the next sheet for printing the next page can be started when the sheet of the previous sheet for the previous page has passed a specified point on the conveyance path.

[0132] During printing, the controller 100 rotates the developing roller 53 by rotating the second motor M2 in the forward direction. After printing is complete, the controller 100 places the second clutch C2 in the second disconnected state and, while the second clutch C2 is in the second disconnected state, rotates the second motor M2 in the reverse direction. The controller 100 then rotates the cam 340 from the first cam position or the intermediate cam position to the second cam position by placing the first clutch C1 in the first transmitting state. The controller 100 rotates the second motor M2 in the reverse direction at a rotational speed slower than that used during printing.

[0133] After rotating the second motor M2 in the reverse direction and switching the first clutch C1 to the first transmission state, the controller 100 determines whether the second fixing member 82 has moved to the vicinity of the second clamping position based on the signal received from the position sensor SE3. When the controller 100 determines that the second fixing member 82 has approached the second clamping position, it fixes the second fixing member 82 at the second clamping position by placing the first clutch C1 in the first disconnection state. This operation changes the clamping pressure from the first clamping pressure to the second clamping pressure.

[0134] Furthermore, when the controller 100 changes the clamping pressure from the first clamping pressure to the second clamping pressure, the controller 100 first begins reverse rotation of the second motor M2 and, after the rotational speed of the second motor M2 stabilizes, sets the first clutch C1 to the first transmission state. In other words, the first time T1 is set to the time required for the reverse rotational speed of the second motor M2 to stabilize after the trailing edge of the final sheet S of one or more sheets printed according to the print job passes through the clamping area NP. This process ensures that the movement speed of the second fixing member 82 is constant, allowing the second fixing member 82 to be more accurately positioned in the second clamping position.

[0135] During printing, the controller 100 rotates the first fixing member 81 and the second fixing member 82 by driving the first motor M1. When the trailing edge of the final sheet S among one or more sheets printed according to the print job has passed through the nip region NP and the nip pressure has changed from the first nip pressure to the second nip pressure, the controller 100 waits for a second time T2 to elapse. After the second time T2 has elapsed, the controller 100 stops driving the first motor M1, thereby stopping the rotation of the first fixing member 81 and the like.

[0136] The second time T2 is the length of time the first fixing member 81 continues to rotate while the second fixing member 82 is in the second nip position, and was set to a sufficiently long time through experiments, simulations, and the like. After printing according to the print job is completed, the controller 100 turns off the heater 111. For example, after the trailing edge of the final sheet of one or more sheets printed according to the print job has passed through the nip area NP, the controller 100 turns off the heater 111. In the conceivable case of stopping the first motor M1 immediately after the nip pressure has changed from the first to the second nip pressure, a portion of the belt 130 would be inserted between the upstream pad P1 and the stopped first fixing member 81, which would be at a high temperature. Therefore, heat from the first fixing member 81 would be concentrated on this portion of the belt 130. However, by continuing to rotate the first fixing member 81 for a sufficiently long second time T2 after the nip pressure has changed from the first to the second nip pressure, the belt 130, interposed between the rotating first fixing member 81 and the upstream pad P1, continues to rotate, following the rotation of the first fixing member 81. This configuration prevents heat in the first fixing member 81 from being concentrated on any portion of the belt 130 .

[0137] At this time, the first fixing member 81 continues to rotate to avoid overshooting the design temperature of the fixing device 80. Therefore, the second time T2 is set to the length of time required for the temperature of the fixing device 80 to stop rising and begin to fall after the nip pressure has changed from the first nip pressure to the second nip pressure. The second time T2 can be appropriately set through experiments, simulations, etc. to achieve a time sufficient for the worst-case scenario.

[0138] Next, the operation of the controller 100 will be described in detail. Figure 8 The timing diagrams shown execute various processes. Figure 8 The example in FIG. 1 shows a state where printing in color mode has ended. Therefore, during printing (e.g., at time t0), all developing rollers 53 are in a pressure-contact state, and the cam 340 is in the first position (the first cam position or the intermediate cam position). In the following description, placing clutches C1 and C2 in a transmitting state will be referred to as simply "engaging clutches C1 and C2," while placing clutches C1 and C2 in a disconnected state will be referred to as simply "closing clutches C1 and C2." The heater 111 is turned on while printing is in progress.

[0139] like Figure 8 As shown, the controller 100 drives the second motor M2 and the first motor M1 during printing (e.g., at time t0). Note that the second motor M2 is driven at a predetermined rotational speed (high speed) so that the rotational speed of the developing roller 53 is suitable for printing. When the final sheet S in the printing process has been conveyed to a position that straddles the sheet sensor SE1 and the fixed sheet sensor SE2, both the sheet sensor SE1 and the fixed sheet sensor SE2 are turned on (time t0).

[0140] When the trailing edge of the sheet S passes the sheet sensor SE1, the sheet sensor SE1 switches from ON to OFF (time t1). At time t1, the controller turns off the heater 111. After the sheet sensor SE1 has switched from ON to OFF, the controller 100 turns ON the second clutch C2 (time t2).

[0141] Through this action, each developing roller 53 sequentially switches from the pressure-contact state to the separation state (times t3, t4, t5, and t6). Once all developing rollers 53 are in the separation state, the controller 100 turns off the second clutch C2 and the second motor M2 (time t8). If the trailing edge of the sheet S passes the fixed sheet sensor SE2 while the developing rollers 53 sequentially switch from the pressure-contact state to the separation state, the fixed sheet sensor SE2 switches from on to off (time t7).

[0142] After the fixed sheet material sensor SE2 has switched from ON to OFF, the controller 100 waits for the third time T3 to pass. Once the third time T3 has passed, the controller 100 starts to reversely rotate the second motor M2 at a speed (low speed) slower than the rotation speed used in printing (time t9). When the first time T1, which is a time longer than the third time T3, has passed after the fixed sheet material sensor SE2 has switched from ON to OFF, the controller 100 turns the first clutch C1 to ON (time t10). The third time T3 is the length of time that passes from time t7 to time t9. In other words, the third time T3 is the length of time that the controller 100 waits before starting to reversely rotate the second motor M2 after the trailing edge of the sheet S has passed the fixed sheet material sensor SE2.

[0143] Here, the time obtained by subtracting the third time T3 from the first time T1 is a length of time required for the rotation speed of the second motor M2 to stabilize after reverse rotation of the second motor M2 starts, and is set through experiments, simulations, or the like.

[0144] After the first clutch C1 is turned on at time t10, the cam 340 rotates from the first position to the second position, whereby the clamping pressure gradually changes from the first clamping pressure to the second clamping pressure. When the cam 340 approaches the second position, the position sensor SE3 detects the second fixing member 82 (time t11).

[0145] After a prescribed time has passed from time t11 when the position sensor SE3 detects the second fixing member 82 , the controller 100 turns OFF the first clutch C1 (time t12 ). After this operation, the cam 340 is at the second position, and the nip pressure is the second nip pressure.

[0146] After turning OFF the first clutch C1, the controller 100 turns OFF the second motor M2 (time t13). After a second time T2 has passed from time t12 when the clamping pressure changes to the second clamping pressure, the controller 100 turns off the first motor M1 (time t14).

[0147] In the case where printing in the monochrome mode ends, the controller 100 performs processing similar to that described above. Figure 8 The examples in the example are different, but the timing of the steps performed on the various components is the same Figure 8 The examples are essentially the same as those in .

[0148] Through the above-described process, the following effects can be achieved in this embodiment. It is conceivable that after the printing operation is completed, the clamping pressure is changed to the second clamping pressure after the rotation of the first fixing member 81 is stopped. That is, in this conceivable situation, the clamping pressure is maintained at the first clamping pressure until the first fixing member 81 stops. Compared to this conceivable configuration, the configuration of this embodiment can better prevent the belt 130, which rotates as the first fixing member 81 rotates, from sliding unnecessarily under high clamping pressure against the clamping forming member N that supports the belt 130 from the side opposite to the first fixing member 81 after the printing process. In addition, in this embodiment, delaying the moment when the rotation of the first fixing member 81 stops can shorten the length of the period during which the belt 130 is clamped between the stopped first fixing member 81 and the clamping forming member N, thereby preventing heat from the stopped first fixing member 81 from concentrating in a portion of the belt 130. Therefore, this embodiment can prevent the belt 130 from causing damage after the printing operation.

[0149] Since the driving force of the second motor M2 is used both for switching the developing roller 53 between the press-contact state and the separated state and for modifying the nip pressure, this embodiment can reduce costs.

[0150] When the nip pressure is modified, the rotation speed of the second motor M2 is set to a slower speed than the rotation speed used during printing, thereby reducing noise that may occur when the cam 340 is driven.

[0151] After starting the reverse rotation of the second motor M2, the controller 100 in this embodiment waits for the rotation speed of the second motor M2 to stabilize and then places the first clutch C1 in the first transmission state. This method ensures that the rotation speed of the cam 340 is constant, so that the cam 340 can be placed in the second position more accurately.

[0152] By continuing to rotate the first fixing member 81 for a sufficiently long second time T2 after the nip pressure has been changed to the second nip pressure, the present embodiment can suppress wear on the belt 130 while cooling the first fixing member 81 more quickly.

[0153] The second clamping pressure is set to a second clamping pressure that is the minimum clamping pressure within the modification range of the pressure modification mechanism 300, thereby suppressing wear caused by sliding friction between the belt 130 and the clamping forming member N, which rotates by following the rotation of the first fixing member 81 and supports the belt 130 from the side opposite to the first fixing member 81.

[0154] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that many changes and modifications can be made therein without departing from the scope of the invention.

[0155] Although the photosensitive member of the present disclosure is described as the photosensitive drum 51 in the present embodiment, for example, a belt-shaped photosensitive member may be used instead.

[0156] In this embodiment, the pressure modifying mechanism 300 is configured to modify the clamping pressure in the clamping region NP between a maximum clamping pressure, an intermediate clamping pressure, and a minimum clamping pressure. However, the pressure modifying mechanism should be capable of modifying the clamping pressure in the clamping region between at least a first clamping pressure and a second clamping pressure. Thus, the pressure modifying mechanism may be configured to modify the clamping pressure between two, four, or more pressure values.

[0157] The pressure modification mechanism is not limited to the configuration described in the embodiment. For example, the pressure modification mechanism may be configured similarly to that shown in FIG5(a), but, for example, without the cam follower 350 and the second spring 330. In other words, the cam 340 may be configured to contact the arm body 311.

[0158] In this embodiment, the fixed film sensor SE2 ( Figure 7 ) is provided downstream of the nip region NP, but for example the fixed web sensor may instead be provided upstream of the nip region.

[0159] Although the present disclosure is applied to the color printer 1 in the present embodiment, the present disclosure may instead be applied to another image forming apparatus such as a monochrome printer, a copier, or a multifunction peripheral.

[0160] Although a halogen lamp is used as an example of the heater in this embodiment, the heater may be a carbon heater or the like.

[0161] Although the first fixing member in this embodiment is configured with a built-in heater, the second fixing member may alternatively be configured with a built-in heater. For example, the second fixing member may be provided with a belt, and a heater and a clamping forming member disposed in a space defined by the belt, while the first fixing member may be a pressure roller that clamps the belt and the clamping forming member of the second fixing member together. In this case, the first fixing member does not have a heater. Alternatively, the heater may be disposed outside the first fixing member, and an external heating system or an induction heating system may be employed to heat the circumferential surface of the first fixing member. Alternatively, both the first and second fixing members may be provided with a built-in heater.

[0162] Furthermore, the first fixing member may be formed of a belt wrapped around the heater, that is, a nip region may be formed between the belt of the first fixing member and the belt of the second fixing member.

[0163] Although the pressure modifying mechanism 300 is provided in the fixing device 80 in this embodiment, the pressure modifying mechanism may be provided in the main housing instead. Alternatively, a portion of the pressure modifying mechanism may be provided in the fixing device and the remaining portion may be provided in the main housing.

[0164] In the above example, the controller 100 turns off the heater at time t1. However, the controller 100 may turn off the heater at a time between the time period from time t1 to time t13.

[0165] The technical elements and variations thereof described above in this embodiment may be used in any suitable combination.

Claims

1. An image forming apparatus, characterized in that: include: a first fixing member having a roller; a second fixing member having a belt to form a nip portion with the first fixing member; photosensitive member; a developing roller configured to supply a developer to the photosensitive member; a switching mechanism configured to switch a state of the developing roller between a contact state in which the developing roller is in contact with the photosensitive member and a separation state in which the developing roller is separated from the photosensitive member; a first motor configured to drive the roller; a pressure modifying mechanism configured to modify a clamping pressure at the clamping portion to a selected one of a first clamping pressure and a second clamping pressure that is smaller than the first clamping pressure; a second motor configured to drive the pressure modifying mechanism and the developing roller; a first clutch configured to change between a first transmission state in which the driving force of the second motor is transmitted to the pressure modification mechanism and a first disconnection state in which the driving force of the second motor is not transmitted to the pressure modification mechanism; a second clutch configured to change between a second transmission state in which the driving force of the second motor is transmitted to the switching mechanism and a second disconnection state in which the driving force of the second motor is not transmitted to the switching mechanism; and A controller configured to: driving the first motor to drive the roller; fixing the developer image on the sheet in a state where the clamping pressure is the first clamping pressure; modifying the nip pressure from the first nip pressure to the second nip pressure while driving the first motor when a final sheet of one or more sheets fixed according to a print job has passed through the nip portion; and After modifying the clamping pressure to the second clamping pressure, the first motor is stopped.

2. The image forming apparatus according to claim 1, wherein Further including: a fixed sheet sensor disposed downstream of the clamping portion, the fixed sheet sensor being configured to detect the sheet passing through the clamping portion; wherein the controller modifies the clamping pressure from the first clamping pressure to the second clamping pressure after a first time has passed since the fixed sheet sensor detected that the trailing edge of the final sheet has passed through the clamping portion.

3. The image forming apparatus according to claim 1, wherein in, The pressure modification mechanism includes a cam configured to pivotally move between a first position where the clamping pressure becomes the first clamping pressure and a second position where the clamping pressure becomes the second clamping pressure, Wherein, modifying the clamping pressure includes controlling the second motor to switch the first clutch to the first transmitting state, thereby pivotally moving the cam from the first position to the second position.

4. The image forming apparatus according to claim 1, wherein in, The pressure modification mechanism includes a cam configured to pivotally move between a first position where the clamping pressure becomes the first clamping pressure and a second position where the clamping pressure becomes the second clamping pressure, Wherein, modifying the clamping pressure includes controlling the second motor to rotate while the second clutch is in the second disconnected state, and then controlling the second motor to switch the first clutch to the first transmission state, thereby pivotally moving the cam from the first position to the second position.

5. The image forming apparatus according to claim 3, wherein in, The cam is pivotally moved from the second position to the first position by forward rotation of the second motor, and the cam is pivotally moved from the first position to the second position by reverse rotation of the second motor. The controller is configured to further drive the second motor in a forward direction during printing. Wherein, modifying the clamping pressure includes controlling the second motor to rotate in the reverse direction.

6. The image forming apparatus according to claim 1, wherein in, When the clamping pressure is modified from the first clamping pressure to the second clamping pressure, the second motor rotates at a slower rotation speed than when printing is performed.

7. The image forming apparatus according to claim 4, wherein: in, The modification of the clamping pressure from the second clamping pressure to the first clamping pressure is performed after the second motor starts driving and rotating at a constant rotation speed.

8. The image forming apparatus according to any one of claims 1 to 6, wherein: in, Stopping the first motor is performed after a second time has elapsed from a time when the modification of the clamping pressure from the second clamping pressure to the first clamping pressure is completed.

9. The image forming apparatus according to any one of claims 1 to 6, wherein: in, The second fixing member includes: an upstream pad configured to clamp the belt together with the first fixing member; and a downstream pad located downstream of the upstream pad in the conveying direction of the sheet, the downstream pad being configured to nip the belt together with the first fixing member, wherein, when the clamping pressure is the first clamping pressure, the upstream pad and the downstream pad both clamp the belt together with the first fixing member, Here, when the nip pressure is the second nip pressure, the upstream pad and the first fixing member nip the belt together, while the downstream pad and the first fixing member do not nip the belt together.

10. The image forming apparatus according to any one of claims 1 to 6, wherein: in, The second clamping pressure is a minimum clamping pressure within a range in which the pressure modification mechanism can set the clamping pressure.

11. The image forming apparatus according to any one of claims 1 to 6, wherein: Further including: a heater configured to heat the first fixing member.

12. The image forming apparatus according to claim 1, wherein in, The pressure modification mechanism includes a cam configured to pivotally move between a first position where the clamping pressure becomes the first clamping pressure and a second position where the clamping pressure becomes the second clamping pressure, Wherein, the second fixing member moves between a first clamping position and a second clamping position, in which at the first clamping position, the clamping portion is formed between the first fixing member and the second fixing member, and in the second clamping position, the distance from the first fixing member to the second fixing member is greater than the distance at the first clamping position.

Images