Fixing device

Abstract

To appropriately control the deviation of a fixing belt when a pressure rotating body is in a separation state.SOLUTION: A fixing device has a pressure rotating body separation and contact mechanism, and steering control to reciprocate a fixing belt in a width direction. In a non-paper feed state in which paper is not fed through a nip part of the fixing device, when a pressure rotating body is in a separation state, the steering control performed by a steering mechanism reciprocates the fixing belt within a narrower range in the width direction than in a contact state.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image on a recording material to the recording material.

Background Art

[0002] An image forming apparatus has a fixing device for fixing an unfixed toner image on a recording material to the recording material.

[0003] The fixing device includes a fixing belt that is rotationally driven and applies heat to the unfixed toner, and a pair of rotators including a pressure rotating body that is rotationally driven and forms a nip portion between the fixing belt by pressing the fixing belt. When a recording material on which unfixed toner has been placed is conveyed through the nip portion, the heat of the fixing belt and the pressure applied by the pressure rotating body are applied to the recording material, and the unfixed toner is fixed to the recording material.

[0004] The fixing device also has a contact / separation mechanism that is movable between a position where the pressure rotating body is in contact with the fixing belt and a position where they are separated from each other.

[0005] Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2015-59964) discloses steering control for reciprocating the fixing belt in the width direction. By repeatedly reciprocating the fixing belt within a predetermined area, it is possible to prevent the fixing belt from coming off the steering roller. Also, it is possible to prevent the edge portion of the recording material from repeatedly passing through the same area of the fixing belt. Therefore, deterioration of the surface of the fixing belt can be suppressed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] During image formation, the pressure rotating body presses the fixing pad via the fixing belt with a force of 170 kg, applying the pressure necessary for fixing to the recording material.

[0008] When the recording material is not passed through the fixing nip portion for several seconds, in order to prevent the temperature rise of the pressure rotating body, the pressure rotating body is separated from the fixing belt (separated state). When the fixing belt is reciprocally moved in the width direction by steering control in the separated state, the reciprocating speed of the fixing belt increases by 2 to 3 times compared to the contacting state.

[0009] Conventionally, the conditions of the steering control in the contacting state were also applied in the separated state. Therefore, appropriate steering control was not performed in the separated state.

[0010] As a result, in the separated state, the steering control was not in time, and there was a risk of a deviation error occurring.

[0011] Therefore, an object of the present invention is to appropriately perform the steering control in the separated state.

Means for Solving the Problem

[0012] In order to solve the above problems, a fixing device according to the present invention forms a nip portion by a rotatable endless fixing belt, a heating roller that contacts the inner peripheral surface of the fixing belt and gives heat to the fixing belt, a steering roller that contacts the inner peripheral surface of the fixing belt together with the heating roller, and a pressure rotating body that presses the fixing belt, and sandwiches and conveys a recording material carrying unfixed toner in the nip portion to fix an unfixed toner image on the recording material. The fixing device includes a contact / separation mechanism that makes the pressure rotating body movable between a position in contact with the fixing belt and a position separated from the fixing belt, a belt position detection unit that detects the position of the fixing belt in the width direction of the fixing belt, and a control unit that performs control to swing the steering roller so as to move the fixing belt to a predetermined position in the width direction based on the detection result of the belt position detection unit. The steering roller is movable to a position inclined at a first inclination angle and a position inclined at a second inclination angle smaller than the first inclination angle with respect to a position where the steering roller is parallel to the heating roller. The belt position detection unit can detect that the fixing belt is at a first predetermined position and a second predetermined position in the width direction. The first predetermined position and the second predetermined position are such that the center of the fixing belt is located on the end side of the steering roller with respect to the center of the steering roller in the width direction, and the center position of the fixing belt at the first predetermined position is located on the end side of the steering roller with respect to the center position of the fixing belt at the second predetermined position. When it is detected that the pressure rotating body is in the contact state and the fixing belt is at the first predetermined position, an operation of inclining the steering roller is performed, and the steering roller is inclined at the first inclination angle so as to be inclined in a first direction. When it is detected that the pressure rotating body is in the contact state and the fixing belt is at the second predetermined position, the operation of inclining the steering roller is not performed. When it is detected that the pressure rotating body is in the separated state and the fixing belt is at the second predetermined position, the operation of inclining the steering roller is performed, and the steering roller is inclined at the second inclination angle so as to be inclined in a first direction which is a predetermined direction. This is the gist of the invention.

Effects of the Invention

[0013] In the separated state, steering control can be appropriately performed.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Mode for Carrying Out the Invention

[0015] <Image forming apparatus> FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus 100. As shown in FIG. 1, four types of image forming units, namely yellow, magenta, cyan, and black, are arranged along the moving direction of the intermediate transfer belt 6 in the image forming apparatus 100. First, the process of forming a toner image on the intermediate transfer belt 6 will be described by taking the yellow image forming unit PY as an example.

[0016] The surface of the photosensitive drum 3 that is rotationally driven by the charger 2 is uniformly charged (charging). Thereafter, the surface of the photosensitive drum 3 is irradiated with a laser according to the image data input by the exposure device 5, and an electrostatic latent image is formed on the surface of the photosensitive drum 3 (exposure). Thereafter, a yellow toner image is formed on the photosensitive drum by the developing device 1 (development). The primary transfer roller 24 applies a voltage having a polarity opposite to the potential polarity of the yellow toner image to the intermediate transfer belt 6. As a result, the yellow toner on the photosensitive drum 3 is transferred to the intermediate transfer belt 6 (primary transfer). Note that the yellow toner remaining on the surface of the photosensitive drum without being transferred is scraped off by the toner cleaner 4 and removed from the surface of the photosensitive drum 3. This series of processes is similarly performed for magenta, cyan, and black. As a result, a full-color toner image is formed on the intermediate transfer belt 6.

[0017] The toner image on the intermediate transfer belt 6 is conveyed to the secondary transfer portion n2 formed by the secondary transfer roller pair 11 and 14. The recording material A is taken out one by one from the recording material cassette 10 and fed to the secondary transfer portion n2 in accordance with the timing at which the toner image is conveyed. Then, the toner image on the intermediate transfer belt 6 is transferred to the recording material A (secondary transfer). Specific examples of the recording material A include plain paper, resin sheet, coated paper, thick paper, and overhead projector sheet.

[0018] The recording material A onto which the toner image has been transferred is conveyed to the fixing device 30 and is fixed by receiving heat and pressure in the fixing device 30 (fixing). The recording material A onto which the toner image has been fixed is discharged to the paper discharge tray 8.

[0019] The image forming apparatus 100 can also perform monochrome image formation. During monochrome image formation, only the black image forming unit PK among the plurality of image forming units is driven.

[0020] Double-sided printing, in which images are formed on both sides of a recording material, will be described. After the recording material A on which an image has been formed on one side is discharged from the fixing device 30, it is guided to the paper path 18 by the flapper 7. When the recording material A is conveyed from the paper path 18 to the reverse path 19, it is conveyed in a switchback manner on the reverse path 19. Thereafter, the recording material A passes through the double-sided path 20 and is conveyed to the paper path 21. At this time, the recording material A is in a state of being reversed front to back. Thereafter, the recording material A is conveyed to the secondary transfer unit n2 again, and when the toner image is transferred, the toner image is fixed by the fixing device 30. Then, the recording material A on which double-sided printing has been performed is discharged to the discharge tray 8.

[0021] This process from charging to the recording material A on which the toner image has been fixed being discharged to the discharge tray 8 is defined as an image forming process (print job). Also, the period during which image formation is being performed is defined as during the image forming process (during the print job).

[0022] <Fixing device> Next, the fixing device 30 of the present embodiment will be described with reference to FIG. 2.

[0023] In the present embodiment, a fixing device using an endless fixing belt 310 is employed. In FIG. 2, the recording material is conveyed in the direction indicated by the arrow α. The fixing device 30 includes a heating rotating body 300 having the fixing belt 310, and a pressurizing rotating body 330 that forms a nip portion N with the fixing belt 310 by contacting and applying pressure to the fixing belt 310.

[0024] The heating rotating body 300 includes the fixing belt 310, a steering roller 350, a fixing pad 380 that is a pad member, and a heating roller 340. The fixing pad 380 and the heating roller 340 are in contact with the inner peripheral surface of the fixing belt. Also, the fixing belt 310 is stretched by the fixing pad 380 and the heating roller 340.

[0025] The heating roller 340 is formed in a cylindrical shape from a metal such as aluminum or stainless steel. In the present embodiment, it is formed from an aluminum pipe with an outer diameter of 80 mm. Inside the heating roller 340, a halogen heater 341 is installed as a means for heating the fixing belt 310. By the halogen heater 341, the heating roller 340 is heated to a predetermined temperature. The fixing belt 310 is heated by the heating roller 340 heated by the heat of the halogen heater 341. The fixing belt 310 is controlled to a predetermined target temperature according to the basis weight of the recording material to be fixed, based on the temperature detection result by a fixing temperature detection sensor (not shown). Note that the heating means is not limited to a halogen heater, and for example, a configuration in which the heating roller 340 generates heat by electromagnetic induction heating (IH) may be used. Further, the heating roller 340 is rotationally driven in the direction of arrow R1 by receiving drive from the drive motor M1.

[0026] The fixing belt 310 is excellent in heat conductivity and heat resistance, and its shape is, for example, an endless belt with a thin wall and an inner diameter of 120 mm. In the present embodiment, the fixing belt 310 has a three-layer structure in which a base layer, an elastic layer on the outside of the base layer, and a release layer on the outside of the elastic layer are provided. The base layer has a thickness of 60 μm and is made of polyimide resin (PI), the elastic layer has a thickness of 300 μm and is made of silicone rubber, and the release layer has a thickness of 30 μm and is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 310 is rotationally driven passively when the pressurizing rotating body 330 described later comes into contact with and rotates the fixing belt 310. Further, since the heating roller 340 is rotationally driven by receiving drive from the drive motor M1, the fixing belt 310 is also rotationally driven passively by the rotational drive of the heating roller 340.

[0027] The fixing pad 380 is disposed on the inner peripheral surface of the fixing belt 310 so as to face the pressurizing rotating body 330 with the fixing belt 310 interposed therebetween.

[0028] The pressure rotating body 330 has a cylindrical core made of aluminum, an elastic layer with a thickness of 1 mm on the outside of the core, and a release layer on the outside of the elastic layer to enhance the separability from the toner.

[0029] The pressure rotating body 330 is movable by a contact / separation mechanism that moves it into contact with or away from the fixing belt 310. The contact / separation mechanism has a frame 385 and a drive motor (not shown). The frame 385 is supported by the image forming apparatus 100. The frame 385 supports the pressure rotating body 330. The frame 385 is rotated about the rotation axis 332 by receiving drive from a drive motor (not shown). When the frame 385 is rotated about the rotation axis 332 by a drive motor (not shown), the pressure rotating body 330 is moved in the direction of arrow P. As a result, the pressure rotating body 330 is brought into contact (contact state) with the fixing pad 380 across the fixing belt 310 in a direction perpendicular to the conveyance direction α of the recording material. Thereby, the nip portion N is formed. In this embodiment, it is pressed with a total pressure of 2000 N, and the width of the nip portion N is 24 mm. When the frame 385 is rotated in the direction opposite to the contact direction about the rotation axis 332, the pressure rotating body 330 is in a separated state from the fixing belt 310 (separated state).

[0030] Also, the pressure rotating body 330 is rotationally driven in the direction of arrow R2. Therefore, the fixing belt 310 sandwiched between the pressure rotating body 330 and the fixing pad 380 is rotationally driven following the rotational drive of the pressure rotating body 330.

[0031] From the above description, the recording material carrying the unfixed toner image by the heating rotating body 300 and the pressure rotating body 330 is nipped and conveyed at the nip portion N, heat and pressure are applied, and fixing is performed.

[0032] <Steering roller> Next, the steering roller 350 in this embodiment will be described with reference to FIGS. 2 and 3.

[0033] In the contact state of this embodiment, a force of 2000 N is applied to the fixing belt. Therefore, the surface of the fixing belt 310 may be damaged by the edge portion of the recording material, resulting in uneven gloss. The details will be described later.

[0034] <Gloss unevenness due to paper edge damage> Paper edge damage refers to the damage to the surface of the fixing belt caused by the cut end portion (edge portion) of the recording material. When fixing unfixed toner to the recording material, the portion of the fixing belt 310 that comes into contact with the edge portion (edge contact portion) is subjected to a greater stress than the portion that does not come into contact with the edge portion (non-edge contact portion). The area damaged by the edge portion of the recording material may have a concave shape compared to the non-edge contact portion. The dent generated on the surface of the fixing belt 310 by the edge portion of the recording material is called paper edge damage.

[0035] When fixing unfixed toner to the recording material, the fixing device 30 applies pressure and heat to the recording material. At this time, the surface state of the fixing belt 310 is reflected in the gloss of the surface of the image after fixing. If there are irregularities on the surface of the fixing belt 310, the state of the irregularities will be reflected in the gloss of the image surface, resulting in uneven gloss (gloss unevenness) on the image surface.

[0036] Therefore, when unfixed toner is fixed to the recording material with paper edge damage on the surface of the fixing belt, gloss unevenness like a straight line is drawn on the image surface.

[0037] In this embodiment, in order to suppress paper edge damage on the surface of the fixing belt 310, steering control by the steering mechanism 400 that reciprocates the fixing belt 310 in the width direction is used.

[0038] The steering control will be described with reference to FIG. 3.

[0039] As shown in FIG. 3, the steering mechanism 400 has a steering roller 350, a steering motor 401, a worm 402, a worm wheel 403, and a fork plate 404. The steering motor 401 is rotatable in the forward rotation direction and the reverse rotation direction. When the steering motor 401 receives a signal from the control unit 600 and is rotationally driven, the worm 402 attached to the steering motor 401 is rotated.

[0040] The rotation of the worm 402 is converted by a drive conversion unit 410 in which the worm wheel 403 and the fork plate 404 are integrally formed into a swing in the axial direction of the rotation axis of the steering motor 401 with the rotation shaft portion 405 as the swing center. That is, the worm wheel 403 is meshed with the worm 402 and is provided so as to be reciprocally movable in the axial direction of the rotation axis of the steering motor 401 according to the rotation of the worm 402. For this purpose, the meshing surface of the worm wheel 403 is formed in an arc shape so as to mesh with the worm 402 at the central portion in the rotation axis direction. In this way, according to the rotation of the steering motor 401, the drive conversion unit 410 can swing the rotation shaft portion 405 with the swing center via the worm 402 and the worm wheel 403.

[0041] Further, the steering mechanism 400 has a steering operation shaft 406, a steering roller support arm 351, and a bearing portion 352. The steering operation shaft 406, the steering roller support arm 351, and the bearing portion 352 are integrally formed and attached to the steering roller 350. The bearing portion 352 rotatably supports the rotation shaft of the steering roller 350. The steering roller support arm 351 is provided so as to be rotatable and supports the steering roller 350 so as to be rotatable by holding the bearing portion 352.

[0042] A steering operation shaft 406 that fits into the above-described drive conversion unit 410 is fixed to the steering roller support arm 351. The steering operation shaft 406 is fitted into the fork plate 404 of the drive conversion unit 410 and can move together with the drive conversion unit 410 while remaining fitted to the drive conversion unit 410. In this way, the inclination of the steering roller 350 changes in conjunction with the swing of the drive conversion unit 410. That is, by driving the steering motor 401, the arrangement angle of the steering roller 350 with respect to the heating roller 340 (see FIG. 2) can be continuously changed. Thus, when the steering angle of the steering roller 350 is adjusted, the fixing belt 310 stretched between the steering roller 350 and the heating roller 340 is reciprocally moved in the width direction. Therefore, it is possible to realize steering control of the fixing belt 310 that reciprocates within a predetermined region in the width direction. The fixing belt 310 reciprocates such that the moving direction is exactly opposite when the steering motor 401 is rotated forward to tilt the steering roller 350 and when the steering motor 401 is rotated backward to tilt the steering roller 350.

[0043] In this way, by the steering mechanism 400, the fixing belt 310 reciprocates within the region of the steering roller 350 in the width direction. By reciprocating the fixing belt 310, it is possible to prevent the edge portion of the recording material from repeatedly passing through the same region on the surface of the fixing belt 310. Thereby, it is possible to suppress paper edge scratches generated on the surface of the fixing belt 310.

[0044] <Fixing Belt Position Detection> Using FIGS. 2, 3, and 4, a belt position detection unit for detecting the position of the fixing belt 310 in the width direction will be described.

[0045] In this embodiment, a sensor unit 390 for detecting the position of the end of the fixing belt 310 in the width direction is provided. Based on the output signal of this sensor unit 390, the position of the end of the fixing belt 310 is detected. By operating the steering mechanism 400 described above based on the detected position of the end of the fixing belt 310, the inclination angle of the steering roller 350 is changed. The configuration of the sensor unit 390 will be described with reference to FIG. 4.

[0046] As shown in FIG. 4, the sensor unit 390 of this embodiment includes a contact member 391 that contacts the end of the fixing belt 310, an arm member 392 for supporting the contact member 391, a belt position detection unit 393 as a moving member, and three sensors 394, 395, and 396 for detecting the position of the end of the fixing belt 310. As the sensors 394, 395, and 396 serving as the belt position detection unit, for example, optical sensors are used. The contact member 391 is disposed on one end side of the arm member 392 so as to contact the end in the width direction.

[0047] The arm member 392 is biased by a coil spring (not shown) from the end of the fixing belt 310 toward the center in the width direction. The arm member 392 is rotatably provided so as to follow the movement in the width direction via the contact member 391. A belt position detection unit 393 as a moving member is provided on the other end side of the arm member 392. The belt position detection unit 393 is, for example, a fan-shaped column member, and a plurality of openings 393a and a plurality of detected portions 393b are formed on the arc-shaped outer peripheral surface. Three sensors 394, 395, and 396 are arranged side by side at a predetermined interval along the rotational movement direction of the belt position detection unit 393 so as to face the outer peripheral surface on which the openings 393a and the detected portions 393b are formed with respect to this belt position detection unit 393.

[0048] In this embodiment, when the fixing belt 310 moves from one end side to the other end side in the width direction, the belt position detection unit 393 rotates in accordance with the movement of the fixing belt 310. In response to the rotation of the belt position detection unit 393, the positional relationship between the sensors 394, 395, 396 and the detected portion 393b (or the opening 393a) changes. Specifically, switching is performed between a detection state in which the sensors 394, 395, 396 detect the detected portion 393b and a non-detection state in which the sensors 394, 395, 396 face the opening 393a and thus do not detect the detected portion 393b.

[0049] In this embodiment, optical sensors are used for the sensors 394, 395, 396. The sensors 394, 395, 396 include a light emitting unit that irradiates light and a light receiving unit that receives the reflected light of the light irradiated from the light emitting unit. The sensors 394, 395, 396 irradiate a predetermined amount of light toward the belt position detection unit 393 by the light emitting unit. When the irradiated light is blocked by the detected portion 393b of the belt position detection unit 393, the light receiving units included in the sensors 394, 395, 396 do not receive the light irradiated from the light emitting unit. On the other hand, when the irradiated light is not blocked by the opening 393a of the belt position detection unit 393, the light receiving unit receives the light irradiated from the light emitting unit. Thus, the presence or absence of light reception in each of the sensors 394, 395, 396 is determined in accordance with the movement of the belt position detection unit 393.

[0050] <Control Unit> As shown in FIG. 1, the image forming apparatus 100 includes a control unit 600. The control unit 600 will be described with reference to FIG. 5 while referring to FIGS. 2 to 4. However, in addition to those shown in the figures, various devices such as motors and power supplies for operating the image forming apparatus 100 are connected to the control unit 600, but since they are not essential to the gist of the invention, their illustration and description are omitted here.

[0051] The control unit 600 as the control means performs various controls such as image forming operations, and has, for example, a CPU 601 (Central Processing Unit) and a memory 602. The memory 602 is composed of a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The memory 602 stores various programs and various data for controlling the image forming apparatus 100. The CPU 601 can execute various programs stored in the memory 602, and can operate the image forming apparatus 100 by executing the various programs.

[0052] In the case of this embodiment, the CPU 601 can execute the "image forming job process (program)" stored in the memory 602 and the "steering control" described later.

[0053] In the memory 602, for example, during the belt-side control process, a "sensor value table" (see FIG. 9 described later) that is referred to for specifying the end position of the fixing belt 310 that reciprocates by steering control and for determining the presence or absence of a failure in the sensor unit 390 is stored. Note that the memory 602 can also temporarily store calculation processing results and the like accompanying the execution of various programs.

[0054] The operation unit 40 is connected to the control unit 600 via an input / output interface. The operation unit 40 is capable of, for example, starting instructions for various programs such as image forming job processing by the user, and inputting various data such as the size of the recording material (A3, B4, etc.), and has, for example, a touch panel type liquid crystal screen (display unit). Various screens including software keys can be displayed on this liquid crystal screen, and various functions such as starting instructions for various programs pre-assigned according to the touch operation of the software keys by the user can be executed. Further, the liquid crystal screen can display various information such as the operation status and error information of the image forming apparatus to notify the user. That is, in the case of this embodiment, the operation unit 40 can function as a notification means. Note that the notification of various information such as error information is not limited to the notification method by display as described above, and may be an appropriate method such as a notification method by sound using a sound generation means such as a speaker.

[0055] Furthermore, a drive motor M1, a steering motor 401, a temperature sensor 370, a halogen heater 341, a sensor unit 390, a position sensor 407, and a motor for driving the pressure rotating body 330 are connected to the control unit 600 via an input / output interface. When a start instruction for an image forming job is given from the operation unit 40, the control unit 600 (specifically, the CPU 601) executes the "image forming job" stored in the memory 602. The control unit 600 controls the image forming apparatus 100 based on the execution of the "image forming job". Accordingly, the control unit 600 drives the drive motor M1 to rotate the heating roller 340, thereby rotating the fixing belt 310. Further, the control unit 600 controls the halogen heater 341 so that the surface temperature of the fixing belt 310 becomes a desired target temperature (180°C in this embodiment) based on the detection result of the temperature sensor 370. Since the control unit 600 controls the motor for driving the pressure rotating body 330, it is also possible to determine whether the pressure rotating body 330 is in contact with or separated from the fixing belt 310.

[0056] In the case of this embodiment, the control unit 600 controls the steering motor 401 based on the detection result of the sensor unit 390, specifically, based on the combination of the output signals of the three sensors 394, 395, and 396 (see FIG. 6(b) described later). That is, the control unit 600 detects the end position of the fixing belt 310 based on the detection result of the sensor unit 390, and rotates the steering motor 401 forward or backward according to the required rotation amount accordingly. In this way, the control unit 600 can operate the above-described steering mechanism 400 by the steering motor 401 to perform steering control on the fixing belt 310.

[0057] <Belt position detection unit> The above-described belt position detection unit 393 will be described with reference to FIGS. 6(a) and 6(b). FIG. 6(a) is a top view for explaining the belt position detection unit 393, and FIG. 6(b) shows the combination of the output signals of the respective sensors 394, 395, and 396 when the belt position detection unit 393 is used. The 27 regions in FIG. 6(a) are a configuration used when detecting nine positions of the fixing belt 310 in the width direction with three sensors (394, 395, and 396). For example, when each of the sensors 394, 395, and 396 is in a detection state of detecting the detected portions 393b1 to 393b5, in other words, when in a shielding state shielded by the detected portions 393b1 to 393b5, an output signal "0" is output. On the other hand, when each of the sensors 394, 395, and 396 is in a non-detection state of not detecting the detected portions 393b1 to 393b5, in other words, when in an open state (also referred to as a non-shielding state) facing the openings 393a1 to 393a4, an output signal "1" is output.

[0058] In FIG. 6(b), "first sensor" indicates sensor 394, "second sensor" indicates sensor 395, "third sensor" indicates sensor 396, and the belt position is a value determined by the combination of the output signals of the respective sensors 394, 395, and 396. In the case of this embodiment, the control unit 600 can detect the end position of the fixing belt 310 at nine finely divided positions according to the above-described belt position determined according to the combination of the output signals (0 or 1) of the sensors 394, 395, and 396.

[0059] An explanation of the positions obtained by dividing the end position of the fixing belt 310 into nine parts will be given with reference to FIG. 7. FIG. 7 is a view showing one end side of the fixing belt 310 such that the pressing rotating body 330 is positioned on the lower side from the conveying direction α. The detectable positions are the "first close" position where the fixing belt 310 has moved to the maximum on one end side, the "second close" position where it has moved to the maximum on the other end side, and seven positions obtained by equally dividing the interval between these "first close" and "second close" positions. The seven positions are, in order from the one closer to the "first close" position, the "front 3" position, the "front 2" position, the "front 1" position, the "center" position, the "rear 1" position, the "rear 2" position, and the "rear 3" position. Here, the "front" and "rear" positions mean the positions with reference to the operation unit 40.

[0060] In the case of this embodiment, the detected portions 393b1 to 393b5 are arranged such that two or more of the sensors 394, 395, and 396 are in the detected state (0) or the non-detected state (1) according to the above-described moving positions of the sensor flag 393. Further, the detected portions 393b1 to 393b5 are arranged such that all of the sensors 394, 395, and 396 are in the detected state (or non-detected state) when the fixing belt 310 is in the "first close" position or the "second close" position.

[0061] In this embodiment, the "front 3" position is set as the first predetermined position, and the "front 1" position is set as the second predetermined position. The "front 1" position is located on the "center" position side with respect to the "front 3" position.

[0062] When the fixing belt 310 is positioned at the "center" position, it indicates that the center position of the fixing belt 310 in the width direction is at the center position of the steering roller 350. When the fixing belt 310 is positioned at the "front 1-3" positions, it indicates that the center position of the fixing belt 310 in the width direction is located on one end side of the center position of the steering roller 350. Conversely, when the fixing belt 310 is positioned at the "rear 1-3" positions, it indicates that the center position of the fixing belt 310 in the width direction is located on the other end side of the center position of the steering roller 350. Therefore, when the belt position detection unit 393 detects that the fixing belt 310 is positioned at the second predetermined position in the width direction, it indicates that the fixing belt 310 is located closer to the center position of the steering roller 350 than when it is positioned at the first predetermined position.

[0063] Also, the center position of the fixing belt 310 and the center position of the steering roller 350 may deviate slightly due to variations in assembly accuracy.

[0064] Figure 7 shows nine positions from the first closer position to the second closer position. The nine positions are arranged at equal intervals, and each interval in this embodiment is 3 mm (see Figure 7). Also, in this embodiment, the first closer position is on one end side of the steering roller 350. The "center" position is the center position of the nine positions arranged at equal intervals. Therefore, when the belt position detection unit 393 detects that the end of the fixing belt 310 is positioned at the "center" position, it means that the fixing belt is located at the center position of the steering roller 350 in the width direction.

[0065] As shown in Fig. 6(a), the sensor flag 393 is a sector-column member, and five detected portions 393b1 to 393b5 are formed on the outer peripheral surface where the sensors 394, 395, and 396 are arranged opposite to each other. In other words, four openings 393a1 to 393a4 are formed on the outer peripheral surface so that the five detected portions 393b1 to 393b5 are formed. In the present embodiment, the three sensors 394, 395, and 396 are arranged side by side at a predetermined interval along the moving direction (arrow X direction) of the sensor flag 393. Note that four or more detected portions 393b1 to 393b5 may be formed as long as the number is more than the number of sensors.

[0066] As the sensor flag 393 moves, the five detected portions 393b1 to 393b5 are formed so that the detection state and the non-detection state are switched by any one of the sensors 394, 395, and 396. That is, when the fixing belt 310 moves in the width direction, as shown in Fig. 6(b), the detected portions 393b1 to 393b5 are formed so that only one of the output signals of the sensors 394, 395, and 396 changes. The detected portions 393b1 to 393b5 are formed with a width as shown in Fig. 6(a) when, for example, the sensor flag 393 is divided into 27 regions at equal angles in the circumferential direction with the rotation center O of the sensor flag 393 as the starting point. Specifically, the detected portions 393b1 and 393b2 occupy two regions, the detected portions 393b3 and 393b5 occupy four regions, and the detected portion 393b4 occupies three regions.

[0067] As shown in FIG. 6(b), when the sensor flag 393 shown in FIG. 6(a) is used, when the fixing belt 310 (specifically, the end position) is in the "second closest cut" position, the output signals of the three sensors 394, 395, and 396 are all "0". That is, the three sensors 394, 395, and 396 are in a detection state where they detect the detected parts 393b1, 393b3, and 393b4, respectively. When the fixing belt 310 moves from the "second closest cut" position to the "back 3" position, the output signal of the sensor 396 changes from "0" to "1", and the output signals of the other sensors 394 and 395 remain unchanged at "0". That is, only the output signal of the sensor 396 changes. At this time, the sensor 396 faces the opening 393a4.

[0068] When the fixing belt 310 moves from the "back 3" position to the "back 2" position, only the output signal of the sensor 394 changes from "0" to "1". At this time, the sensor 394 faces the opening 393a1. When the fixing belt 310 moves from the "back 2" position to the "back 1" position, only the output signal of the sensor 395 changes from "0" to "1". At this time, the sensor 395 faces the opening 393a3. That is, all three sensors 394, 395, and 396 face the openings 393a1, 393a3, and 393a4, respectively, and are in a non-detection state where none of the detected parts 393b1 to 393b5 are detected. Therefore, the output signals of the three sensors 394, 395, and 396 all become "1".

[0069] When the fixing belt 310 moves from the "back 1" position to the "middle" position, only the output signal of the sensor 394 changes from "1" to "0". At this time, the sensor 394 is detecting the detected part 393b2. When the fixing belt 310 moves from the "middle" position to the "front 1" position, only the output signal of the sensor 396 changes from "1" to "0". At this time, the sensor 396 is detecting the detected part 393b5. When the fixing belt 310 moves from the "front 1" position to the "front 2" position, only the output signal of the sensor 394 changes from "0" to "1". At this time, the sensor 394 faces the opening 393a2. When the fixing belt 310 moves from the "front 2" position to the "front 3" position, only the output signal of the sensor 395 changes from "1" to "0". At this time, the sensor 395 is detecting the detected part 393b4. Further, when the fixing belt 310 moves from the "front 3" position to the "first near cut" position, only the output signal of the sensor 394 changes from "1" to "0". At this time, the sensor 394 is detecting the detected part 393b3. When the fixing belt 310 is in the "first near cut" position, the output signals of all the sensors are "0". That is, all of the three sensors 394, 395, and 396 are in a detection state where they are respectively detecting the detected parts 393b3, 393b4, and 393b5. When the fixing belt 310 moves from the "first near cut" position to the "second near cut" position, since it is only necessary to reverse the change in the output signals of the above-described sensors 394, 395, and 396, the description here is omitted.

[0070] In order to prevent the fixing belt 310 from coming off the steering roller 350, when the belt position detection unit 393 detects that the fixing belt 310 is located at the "first side cut-off" position or the "second side cut-off" position, the control unit 600 determines that it is a side cut-off error via the sensor unit 390. When the control unit 600 determines that it is a side cut-off error, the image forming process is stopped, and the pressure rotating body 330 is in a separated state. Also, in order to notify the user that it is a side cut-off error, the operation unit 40 may be caused to display that it is a side cut-off error. By making it in a separated state, it becomes easier for the service technician to perform the work for returning the image forming apparatus 100 from the side cut-off error to a state where image formation is possible, that is, to restore it. In the present embodiment, it is the work of moving the fixing belt 310 to the "center" position side rather than the "first side cut-off" position or the "second side cut-off" position.

[0071] In the present embodiment, the method of detecting the width direction position by the belt position detection unit 393 and the sensors 394, 395, 396 has been described, but the means for detecting the belt width direction position is not limited to this, and a line sensor, an eddy current type sensor, or the like may be used.

[0072] <When the pressure rotating body is in contact> When fixing is performed by the fixing device 30 by applying heat and pressure to the recording material carrying the unfixed toner image, the pressure rotating body 330 comes into contact with the fixing belt 310 to form a fixing nip N, and is in a contact state. In the contact state, the pressure rotating body 330 presses the fixing pad 380 with a force of 2000 N via the fixing belt 310. Therefore, paper edge scratches are generated on the surface of the fixing belt 310. When paper edge scratches are formed on the surface of the fixing belt 310, gloss unevenness occurs as if a line is drawn on the image surface. Therefore, when the pressure rotating body 330 is in the contact state, the steering mechanism 400 performs steering control on the fixing belt 310 in order to suppress the deterioration of the surface of the fixing belt 310 due to paper edge scratches.

[0073] In order to suppress the edge damage of the paper, the edge portion of the recording material is prevented from repeatedly passing through the same area on the surface of the fixing belt 310. To achieve this, when the pressure rotating body 330 is in the contact state, a configuration is used in which the position of the fixing belt 310 where the operation of tilting the steering roller 350 is performed is reduced compared to the separated state.

[0074] In this embodiment, the number of positions of the fixing belt 310 where the operation of tilting the steering roller 350 is performed is two. Also, by increasing the tilt angle of the steering roller 350, it leads to suppressing the edge portion of the recording material from repeatedly passing through the same area on the surface of the fixing belt 310. Therefore, it is possible to suppress the deterioration of the surface of the fixing belt 310 due to paper edge damage.

[0075] The details of the steering control by the steering mechanism 400 when the pressure rotating body 330 is in the contact state will be described later with reference to FIGS. 8, 9, and 10.

[0076] When performing the image forming process, the pressure rotating body 330 is in the contact state.

[0077] When the control unit 600 determines that the pressure rotating body 330 is in the contact state, as shown in FIG. 8, the steering roller 350 is tilted according to the position of the fixing belt 310, and steering control is performed.

[0078] An explanation will be given along the flowchart of FIG. 8.

[0079] First, the control unit 600 determines that the pressure rotating body 330 is in the contact state.

[0080] S001 In the contact state, the first detection of the position of the fixing belt 310 by the belt position detection unit 393 is performed. When the belt position detection unit 393 detects that the fixing belt 310 is located at the first near-cut position or the second near-cut position (near-cut position), the control unit 600 issues a near-cut error. If it is detected that the fixing belt 310 is not located at the near-cut position, the process proceeds to S002.

[0081] S002 When, in the first detection by the belt position detector 393, it is detected that the fixing belt 310 is located at the "front 1", "front 2", or "front 3" positions, the process proceeds to S003. When, in the first detection by the belt position detector 393, it is detected that the fixing belt 310 is located at the "center", "rear 1", "rear 2", or "rear 3" positions, the process proceeds to S006.

[0082] S003 By the steering control, the steering roller 350 is tilted at the first tilt angle. As a result, in the width direction, the fixing belt 310 can be widely used, and deterioration of the surface of the fixing belt 310 can be prevented.

[0083] The first tilt angle will be described with reference to FIG. 10. FIG. 10 is a view seen from the direction of arrow α in FIG. 2, and the fixing belt 310 is not shown in order to explain the tilt angle of the steering roller 350. The pressure rotating body 330 is located below the paper surface. 350a in FIG. 10 indicates the state when the steering roller is parallel to the heating roller 340. The first tilt angle is the angle at which the steering roller 350 is tilted with respect to the steering roller 350a for the purpose of moving the fixing belt 310 to the other end side of the steering roller 350 in the contact state. In the present embodiment, an operation is performed to tilt the steering roller 350a counterclockwise on the paper surface of FIG. 10 to the position of 350b. The direction in which the steering roller 350a is tilted counterclockwise on the paper surface is defined as the first direction. Then, the fixing belt 310 is moved to the other end side of the steering roller 350. The tilt angle from 350a to 350b of the steering roller 350 at this time is defined as the first tilt angle (angle A). Although 350a in the present embodiment indicates the state when it is parallel to the heating roller 340, it may be slightly deviated due to variations in assembly accuracy.

[0084] As a result of the operation of tilting the steering roller 350a to the position of 350b, the steering roller 350 is in a state of being tilted at the first tilt angle.

[0085] It takes about 1.5 seconds to change the tilt angle of the steering roller 350. Therefore, there is a case where the fixing belt 310 may exceed the "front 3" position beyond the first near-cut position side (overshoot). When the fixing belt 310 reaches the first near-cut position and the belt position detection unit 393 detects that the fixing belt 310 is located at the first near-cut position, the control unit 600 issues a near-cut error.

[0086] On the other hand, it is also conceivable that the fixing belt 310 is at a position beyond the "front 3" position toward the first near-cut position side and has not reached the first near-cut position. In this case, when the steering roller 350 is tilted to the first tilt angle, the fixing belt 310 is moved from between the "front 3" position and the first near-cut position to the one-end side of the steering roller 350. As a result, the belt position detection unit 393 detects that the fixing belt 310 is located at the "front 3" position, but the tilt angle of the steering roller 350 is tilted at the first tilt angle A in the first direction.

[0087] Since the steering roller 350 is tilted to the first tilt angle, the fixing belt 310 is moved in the order of the "front 2", "front 1" (second predetermined position), "middle", "rear 1", and "rear 2" positions. While the fixing belt 310 is being moved to the other-end side, the belt position detection unit 393 detects the position of the fixing belt 310 at the "front 2", "front 1" (second predetermined position), "middle", "rear 1", and "rear 2" positions, but the operation of changing the tilt angle of the steering roller 350 by steering control is not performed. The steering roller 350 is in a state of being tilted at the first tilt angle.

[0088] Still, a configuration may be adopted in which the belt position detection unit 393 does not detect that the fixing belt 310 is located at the "front 2", "front 1" (second predetermined position), "middle", "rear 1", and "rear 2" positions, and the operation of tilting the steering roller 350 by steering control is not performed.

[0089] S004 When the fixing belt 310 is moved to the other end side of the steering roller 350 and the belt position detection unit 393 detects that the fixing belt 310 is located at the "back 3" position, the process proceeds to S006. If the belt position detection unit 393 does not detect that the fixing belt 310 is located at the "back 3" position, the process proceeds to S005.

[0090] S005 When it is detected that the fixing belt 310 is located at the close position, a close error is issued. If it is not detected that the fixing belt 310 is located at the close position, the process returns to S003.

[0091] S006 An operation is performed to tilt the steering roller 350 at an angle -A so that the fixing belt 310 is moved to one end side by the steering control of the steering mechanism 400.

[0092] In FIG. 10, 350a of the steering roller indicates the state when it is parallel to the heating roller 340. The angle -A is the angle by which the steering roller 350 is tilted with respect to the steering roller 350a for the purpose of moving the fixing belt 310 to one end side of the steering roller 350. In the present embodiment, an operation is performed to tilt the steering roller 350a to the position of 350c in the clockwise direction on the paper surface of FIG. 10. The direction of tilting the steering roller 350a in the clockwise direction on the paper surface is defined as the second direction. That is, the second direction is the direction opposite to the first direction of tilting counterclockwise on the paper surface, which is the clockwise direction of tilting. Then, the fixing belt 310 is moved to one end side of the steering roller 350. The tilting angle from the steering roller 350a to the steering roller 350c at this time is defined as the angle -A.

[0093] As a result of performing the operation of tilting the steering roller 350a to the position of 350c, the steering roller 350 is in a state tilted at an angle -A.

[0094] It takes about 1.5 seconds to change the tilt angle of the steering roller 350. Therefore, there is a case where the fixing belt 310 may exceed the "back 3" position to the side closer to the second cut-off position (overshoot). When the fixing belt 310 reaches the second cut-off position and the belt position detection unit 393 detects that the fixing belt 310 is located at the second cut-off position, the control unit 600 issues a cut-off error.

[0095] On the other hand, it is also conceivable that the fixing belt 310 is at a position beyond the "back 3" position to the side closer to the second cut-off position and has not reached the second cut-off position. In this case, when the steering roller 350 is tilted at an angle of -A, the fixing belt 310 is moved from between the "back 3" position and the second cut-off position to the side of one end of the steering roller 350. As a result, the belt position detection unit 393 detects that the fixing belt 310 is located at the "back 3" position, but the tilt angle of the steering roller 350 is in a tilted state at -A.

[0096] Since the angle of the steering roller 350 is tilted at -A, the fixing belt 310 is moved in the order of the "back 2", "back 1", "center", "front 1" (second predetermined position), "front 2" positions. While the fixing belt 310 is being moved to the side of one end, the belt position detection unit 393 detects the position of the fixing belt 310 at the "front 2", "front 1" (second predetermined position), "center", "back 1", "back 2" positions, but the operation of tilting the steering roller 350 by steering control is not performed. The steering roller 350 is in a tilted state at an angle of -A.

[0097] It may also be configured such that the belt position detection unit 393 does not detect that the fixing belt 310 is located at the positions of "back 2", "back 1", "center", "front 1" (second predetermined position), "front 2", and the operation of tilting the steering roller 350 by steering control is not performed.

[0098] S007 When the fixing belt 310 is moved to one end side of the steering roller 350 and the belt position detection unit 393 detects that the fixing belt 310 is located at the front 3 (first predetermined position), the process proceeds to S003. If the belt position detection unit 393 does not detect that the fixing belt 310 is located at the "front 3" position (first predetermined position), the process proceeds to S008.

[0099] S008 If it is detected that the fixing belt 310 is located at the offset position, an offset error is issued. If it is not detected that the fixing belt 310 is located at the offset position, the process returns to S006.

[0100] As shown in FIG. 9, when the pressing rotating body 330 is in the contact state, the steering roller 350 is inclined at an angle A or an angle -A. Also, the fixing belt 310 is at the "front 1", "front 2", "rear 1", "rear 2" positions, and the operation of inclining the steering roller 350 is not performed. At the "front 3" and "rear 3" positions, the operation of inclining the steering roller 350 is performed. Therefore, the fixing belt 310 will reciprocate between the "front 3" (first predetermined position) and the "rear 3" positions. That is, in the width direction, within the range where no offset error occurs, the fixing belt 310 can be reciprocated in a wider range compared to the separated state described later. Therefore, deterioration of the surface of the fixing belt 310 due to paper edge damage can be suppressed.

[0101] It should be noted that although it is described that steering control is performed at the "front 3" position and the "rear 3" position, steering control may also be performed at the "front 2" and "rear 2" positions. In this case, when the belt position detection unit 393 detects that the fixing belt 310 is located at the front 2 position, the operation of inclining the steering roller 350 is performed. At this time, the position of the steering roller 350 is inclined toward the 350a side with respect to 350b. Similarly, when the belt position detection unit 393 detects that the fixing belt 310 is located at the "rear 2" position, the operation of inclining the steering roller 350 is performed. At this time, the position of the steering roller 350 is inclined toward the 350a side with respect to 350c.

[0102] Furthermore, when the pressure rotating body 330 is in the contact state, it is not necessarily configured to perform the above-described steering control. For example, the range in which the fixing belt 310 reciprocates may be changed according to the type of recording material used. Also, although the inclination angle of the steering roller 350 is set to A or -A, the present invention is not limited thereto, and the inclination angle may be changed according to the type of recording material used.

[0103] <When the pressure rotating body is in the separated state> During a print job, the recording material is continuously conveyed to the nip portion N and fixing is performed. Therefore, during the print job, the pressure rotating body 330 is in the contact state. However, even during the print job, the pressure rotating body 330 may be in the separated state. For example, it is conceivable that different print jobs are continuously printed and the image formation signal is delayed. Also conceivable is a case where time is required for post-processing such as a stapling operation with an accessory. In addition, when fixing is performed from a recording material with a large basis weight to a recording material with a small basis weight, the pressure rotating body 330 may be separated from the fixing belt to lower the temperature of the fixing belt 310 in order to lower the fixing temperature. In such cases, the paper is not conveyed to the nip portion N, and a non-paper-passing state occurs.

[0104] When the non-paper-passing state occurs, the surface temperature of the pressure rotating body 330 rises excessively due to the heat of the fixing belt 310. When fixing is performed on the recording material in a state where the temperature of the pressure rotating body 330 has risen excessively, the toner is excessively dissolved. The excessively dissolved toner may adhere to the surface of the pressure rotating body 330 or the fixing belt 310 and may re-adhere to a subsequent recording material. The area of the recording material to which the toner has re-adhered may result in image defects.

[0105] In order to suppress image defects caused by the temperature rise of the pressure rotating body 330, the pressure rotating body 330 is separated in the non-paper-passing state.

[0106] When the pressure rotating body 330 is in the separated state, the pressing force of 2000 N on the fixing belt 310 is released. Then, due to the steering control, the reciprocating movement speed of the fixing belt 310 in the width direction increases by about 2 to 3 times compared with the state where the pressure rotating body 330 is in contact. When the steering control is performed to change the inclination angle of the steering roller 350 at the "front 3" (first predetermined position) and the "back 3" positions, which are the same conditions as when the pressure rotating body 330 is in contact, there is a risk of overshooting to the side of the approaching position and an approaching error occurring. Also, there is a risk that the fixing belt 310 will exceed the approaching position and derail from the steering roller 350.

[0107] It is possible to suppress the approaching error by reducing the rotation speed of the fixing belt 310. However, the non-paper-passing state considered here is the paper interval for several seconds (about 4 seconds). Therefore, if the rotation speed of the fixing belt 310 is sufficiently decelerated so that no approaching error occurs, it takes time to return to the original speed immediately before the non-paper-passing state. If the rotation speed of the fixing belt 310 cannot be restored in time before the subsequent recording material is conveyed to the nip portion N, the productivity has to be reduced. Therefore, it was desired to suppress the occurrence of approaching errors while maintaining the productivity.

[0108] When the pressure rotating body 330 is in the separated state, the nip portion N is not formed, and the surface of the fixing belt 310 is not deteriorated by the recording material flange portion. Therefore, in the width direction, when the pressure rotating body 330 is in the separated state, it is not necessary to reciprocate the fixing belt 310 in a wide range like the steering control in the contact state. That is, it may be reciprocated in a range narrower than the reciprocating movement of the fixing belt 310 in the contact state of the pressure rotating body 330.

[0109] When the pressing rotating body 330 is in a separated state, the reciprocating movement speed of the fixing belt 310 is 2 to 3 times faster than that in the contacting state. Further, when the pressing rotating body 330 is in a separated state, the surface of the fixing belt 310 is not deteriorated by the edge portion of the recording material. For these reasons, when the pressing rotating body 330 is in a separated state, steering control is performed so that the center position of the fixing belt 310 is maintained at the center position of the steering roller. Thereby, when the pressing rotating body 330 is in a separated state, it is possible to suppress the deviation error that occurs when the fixing belt 310 reaches the deviation position. In the present embodiment, a configuration is used in which the number of positions of the fixing belt 310 where the operation of tilting the steering roller 350 is performed is larger than two when the pressing rotating body 330 is in the contacting state, as compared with two positions.

[0110] Also, in the present embodiment, the rotation speed of the fixing belt 310 when the pressing rotating body 330 is in a separated state is equal to the rotation speed of the fixing belt 310 when in the contacting state. Moreover, in order to suppress the deviation error, the fixing belt 310 is reciprocally moved in a region narrower than the contacting state. Here, the term "equal" may be a configuration in which the rotation speed of the fixing belt 310 is decelerated to such an extent that productivity is not reduced.

[0111] Details of the control when the control unit 600 determines that the pressing rotating body 330 is in a separated state will be described later.

[0112] <Example 1> The belt position detection unit 393 detects the position of the fixing belt 310. An operation of tilting the steering roller 350 is performed according to the position of the fixing belt 310 in the width direction.

[0113] The method for determining the tilt angle in the present embodiment will be described in detail below.

[0114] In this embodiment, the target position of the fixing belt 310 is set (the target position in this embodiment is the "center" position), and an operation is performed to tilt the steering roller 350 so that the fixing belt 310 is moved to the target position. A specific method for determining the tilt angle in the separated state will be described using the flowchart of FIG. 13.

[0115] S30 First, the belt position detection unit 393 detects the position of the fixing belt 310.

[0116] S31 If the position of the fixing belt 310 is the near-side position, the process proceeds to S35, and a near-side error is output.

[0117] If the position of the fixing belt 310 is not the near-side position, the process proceeds to S32.

[0118] S32 Based on the detection result (B.Pnow) of the belt position detection unit 393, the difference B.Pdif from the target position "center" position is obtained.

[0119] Numbers from 1 to 7 are substituted into B.Pnow. The relationship between the position of the fixing belt 310 and the numbers substituted into B.Pnow is as shown in FIG. 15. For example, when the fixing belt 310 is at the front 3 (the first predetermined position), 1 is substituted, and when the fixing belt 310 is at the rear 3, 7 is substituted. B.Pdif = 4 - B.Pnow ··· Equation 1 S33 The integral gain I is added to the difference B.P.dif, and the cumulative value Itotal of the integral from the previous 1STEP is added. Here, the initial value of Itotal is 0. Itotal(n) = I × B.P.dif + Itotal(n - 1) ··· Equation 2 S34 The sum of the product of the difference B.P.dif and the proportional gain P and the cumulative value Itotal(n) of the integral is taken as the rudder angle. Rudder angle = P × B.P.dif + Itotal(n) ··· Equation 3 In this embodiment, the proportional gain P is 100, the integral gain I is 1, and the calculation is performed every 0.2 seconds. For example, when the detection result of the belt position detection unit 393 is the back 1, 5 is substituted into B.Pnow. The rudder angle in this case is as follows.

[0120] Rudder angle = 100×(4 - 5)+ 1×(4 - 5)= -101 The tilt angle of the steering roller 350 is determined by the value of the rudder angle obtained from the above calculation.

[0121] The tilt angle has positive and negative tilt angles with respect to the steering roller 350a. When the value obtained from Equations 1 to 3 is positive, an operation is performed to tilt the steering roller 350 for the purpose of moving the fixing belt 310 to the other end side of the steering roller 350. The steering roller 350 is tilted counterclockwise on the paper surface of FIG. 10. Similarly, when the value of the rudder angle is negative, an operation is performed to tilt the steering roller 350 for the purpose of moving the fixing belt 310 to one end side of the steering roller 350. The steering roller 350 is tilted clockwise on the paper surface of FIG. 10.

[0122] In FIG. 10, the case where the steering roller 350a is set as the rudder angle 0 and the steering roller 350a is parallel to the heating roller 340 is shown, but it is not limited thereto. Due to variations in assembly accuracy, the steering roller 350a may not be parallel to the heating roller 340, so it may be slightly displaced.

[0123] The larger the absolute value of the obtained rudder angle, the larger the amount of movement of 350a shown in FIG. 14 clockwise or counterclockwise.

[0124] That is, in the width direction, the farther the position of the fixing belt 310 is from the target position "center" position, the greater the inclination angle of the steering roller 350. From Equations 1, 2, and 3, when the position of the fixing belt 310 is at the target position "center" position, in this embodiment, the steering angle is 0. At this time, the steering roller 350 is inclined so that the fixing belt 310 is maintained at the "center" position. Thereby, when the position of the fixing belt 310 is at the target position "center" position, it is suppressed that the fixing belt 310 is moved from the target position to the other end side or one end side of the steering roller 350.

[0125] The above-described steering control means that in the width direction, an operation of inclining the steering roller 350 is performed according to the position of the fixing belt 310. That is, an operation of inclining the steering roller 350 is performed so that the fixing belt 310 is maintained at the "center" position in the width direction.

[0126] In the width direction, the position of the fixing belt 310 where the operation of inclining the steering roller 350 is performed is compared with the contact state, and is characterized in that it is on the "center" position side or also at the "center" position with respect to the position in the contact state. Thereby, in the width direction, the position of the fixing belt where the operation of inclining the steering roller 350 is performed indicates that there are more cases in the separated state than in the case where the pressing rotating body 330 is in the contact state.

[0127] In the contact state of this embodiment, the operation of inclining the steering roller 350 is not performed at the "front 1" (second predetermined position) position, and in the separated state, the operation of inclining the inclination angle of the steering roller 350 to the second inclination angle (B in the figure) is performed at the "front 1" (second predetermined position) position.

[0128] On the plane of FIG. 11, the second inclination angle is the angle at which the steering roller 350 is inclined with respect to the steering roller 350a for the purpose of moving the fixing belt 310 to the other end side of the steering roller 350. When the steering roller 350 is inclined counterclockwise on the plane of the paper which is the first direction, the fixing belt 310 is moved to the other end side of the steering roller 350. When the belt position detection unit 393 detects that the fixing belt 310 is located at the position of "front 1" (the second predetermined position), the steering roller 350a is inclined to the position on the 350a side with respect to the position of 350b and the position of 350d. The inclination angle at this time is defined as the second inclination angle (angle B). That is, the relationship is such that the first inclination angle > the second inclination angle.

[0129] Similarly, when the belt position detection unit 393 detects that the fixing belt 310 is located at the position of "rear 1", the steering roller 350 is inclined clockwise on the plane of the paper which is the second direction, and the fixing belt 310 is moved to the one end side of the steering roller 350. In this case, compared with the case where the steering roller 350 is inclined at an angle of -A, it is in a state of being inclined to the position inclined to the 350a side and the position of 350e (angle -B).

[0130] Also, in the separated state, at the position of "front 2" (the third predetermined position), an operation of inclining the inclination angle of the steering roller 350 to the third inclination angle is performed.

[0131] On the plane of FIG. 12, the third inclination angle is the angle at which the steering roller 350 is inclined for the purpose of moving the fixing belt 310 to the other end side of the steering roller 350 with respect to the steering roller 350a. When the steering roller 350 is inclined counterclockwise on the plane of the paper, the fixing belt 310 is moved to the other end side of the steering roller 350. When the belt position detection unit 393 detects that the fixing belt 310 is located at the position of "front 2" (the third predetermined position), the steering roller 350 is inclined to the position inclined to the 350b side and the position inclined to the 350f as compared with the case where the steering roller 350 is inclined at the second inclination angle. The inclination angle at this time is defined as the third inclination angle (C). That is, the relationship is such that the third inclination angle > the second inclination angle.

[0132] Similarly, when the belt position detection unit 393 detects that the fixing belt 310 is located at the "rear 2" position, the steering roller 350 is inclined clockwise on the plane of the paper, which is the second direction, and the fixing belt 310 is moved to the one end side of the steering roller 350. In this case, as compared with the case where the steering roller 350 is inclined at the -B angle, the steering roller 350 is inclined to the position inclined to the 350c side and the position inclined to the 350g (angle -C).

[0133] The steering roller 350 is inclined at angles B, -B, C, and -C. The change amount of one inclination operation of the steering roller 350 in the contact state was from angle A to angle -A, whereas the change amount of one inclination operation of the steering roller 350 in the separated state is at most from angle C to angle -C. Therefore, the change amount of one inclination operation of the steering roller 350 in the separated state is smaller than that in the contact state. As a result, the fixing belt 310 is likely to be kept at the center of the steering roller 350.

[0134] When the pressing rotator 330 is in the contact state, the operation of inclining the steering roller 350 is not performed at the positions of "front 1", "front 2", "rear 1", and "rear 2". On the other hand, when the pressing rotator 330 is in the separated state, the operation of inclining the steering roller 350 is performed at the positions of "front 1", "front 2", "rear 1", and "rear 2".

[0135] By performing the above-described steering control, as shown in FIG. 14, it becomes possible to reciprocate the fixing belt 310 within a narrow range as compared with the case where the pressing rotating body 330 is in the contact state.

[0136] Specifically, in the present embodiment, when the pressing rotating body 330 is in the separated state, the range between the "front 1" position and the "rear 1" position is the moving range of the fixing belt 310 in the width direction. On the other hand, when the pressing rotating body 330 is in the contact state, the range between the "front 3" position and the "rear 3" position is the moving range of the fixing belt 310 in the width direction.

[0137] In the width direction, the distance between the center position of the moving range of the fixing belt 310 and the center position of the fixing belt 310 increases as the fixing belt 310 moves from the "rear 1" position to the "rear 3" position. Similarly, it increases as the fixing belt 310 moves from the "front 1" position to the "front 3" position. After the fixing belt 310 moves from the "center" position, the first operation of tilting the steering roller is performed at the "front 1" position or the "rear 1" position of the fixing belt in the case of the separated state. On the other hand, in the case of the contact state, it is performed at the "front 3" position or the "rear 3" position of the fixing belt. Therefore, in the width direction, after the center position of the fixing belt 310 moves away from the center of the moving range of the fixing belt 310, the distance between the center position of the fixing belt that first performs the operation of tilting the steering roller and the center position of the moving range of the fixing belt is smaller in the case where the pressing rotating body is in the separated state than in the case of the contact state.

[0138] <Example 2> A modification will be described with reference to the flowchart of FIG. 13.

[0139] FIG. 13 is obtained by changing "Is the belt position at the front 3?" in the flowchart S007 in the contact state of FIG. 8 to "Is the belt position at the front 1?", and changing "Is the belt position at the rear 3?" in S004 to "Is the belt position at the rear 1?".

[0140] Descriptions of overlapping parts with Example 1 are omitted.

[0141] S014 Since the steering roller 350 is inclined at the first inclination angle, the fixing belt 310 passes through the middle position and is moved to the other end side. While the fixing belt 310 is being moved to the other end side, the belt position detection unit 393 detects the position of the fixing belt 310. However, at the central position, control to change the inclination angle of the steering roller 350 by steering control is not performed. The steering roller 350 maintains the first inclination angle. When the belt position detection unit 393 detects that the fixing belt 310 has been moved to the other end side of the steering roller 350 and the fixing belt 310 is located at the back 1 position, the process proceeds to S006. If the belt position detection unit 393 does not detect that the fixing belt 310 is located at the back 1 position, the process proceeds to S005.

[0142] S017 When the belt position detection unit 393 detects that the fixing belt 310 has been moved to one end side of the steering roller 350 and the fixing belt 310 is located at the front 1 position, the process proceeds to S003. If the belt position detection unit 393 does not detect that the fixing belt 310 is located at the front 1 position, the process proceeds to S008.

[0143] It takes about 1.5 seconds to change the inclination angle of the steering roller 350. Therefore, as shown in FIG. 11, there may be a case where "overshoot" occurs in which the fixing belt 310 moves to the first-leaning cut position side because the steering control is not in time. However, by performing the steering control also at the front 1 and back 1 positions, it is possible to suppress the movement of the fixing belt 310 to the leaning cut position.

[0144] By performing the above-described steering control, as shown in FIG. 16, it is possible to reciprocate the fixing belt 310 within a narrow range as compared with the case where the pressing and rotating body 330 is in the contact state.

Description of Reference Numerals

[0145] 30 Fixing device 100 Image forming apparatus 300 Heating rotating body 310 Fixing belt 330 Pressing rotating body 340 Heating roller 350 Steering roller 350a Steering roller when parallel to the heating roller 350b Steering roller when inclined at the inclination angle A 350c Steering roller when inclined at the inclination angle -A 350d Steering roller when inclined at the inclination angle B 350e Steering roller when inclined at the inclination angle -B 390 Detection unit 393 Belt position detection unit 400 Steering mechanism N Nip portion Arrow α Conveying direction of the recording material

Claims

1. A rotatable endless fixing belt having a width including a first width direction and a second width direction; A heating roller that abuts on the inner peripheral surface of the fixing belt and applies heat to the fixing belt; A steering roller that abuts on the inner peripheral surface of the fixing belt together with the heating roller; A pressure rotating body that presses the fixing belt, forming a nip portion therewith, and sandwiching and conveying a recording material carrying unfixed toner in the nip portion to fix an unfixed toner image on the recording material. In the fixing device, An abutting and separating mechanism that makes the pressure rotating body movable between a position in contact with the fixing belt and a position separated from the fixing belt; A belt position detection unit that detects the position of the fixing belt in the width direction of the fixing belt; A control unit that performs control to swing the steering roller so as to move the fixing belt in the first width direction and the second width direction in the width direction based on the detection result of the belt position detection unit; and The steering roller forms a first angle when the fixing belt is at a predetermined position during a period in which the fixing belt is moved in either one of the first width direction and the second width direction in the contact state. The steering roller forms a second angle smaller than the first angle when the fixing belt is at the predetermined position during a period in which the fixing belt is moved in either one of the first width direction and the second width direction in the separated state. A fixing device characterized by the above.

2. In a predetermined job, the rotation speed of the fixing belt when the pressure rotating body is in a separated state is the same as the rotation speed of the fixing belt when the pressure rotating body is in a contact state. The fixing device according to claim 1, characterized by the above.

3. In one tilting operation of the steering roller based on the detection result of the belt position detection unit, the amount of change in the tilting angle of the steering roller in the contact state is larger than the amount of change in the tilting angle of the steering roller in the separated state. The fixing device according to claim 1, characterized by the above.

4. Further comprising a fixing pad that abuts on the inner peripheral surface of the fixing belt and forms a nip portion together with the pressure rotating body via the fixing belt. The fixing device according to claim 1, characterized by the above.

5. Comprising a drive motor that rotationally drives the heating roller. The fixing device according to claim 1, characterized by the above.

6. The steering roller is disposed on the downstream side in the rotation direction of the fixing belt from the heating roller. The fixing device according to claim 1, characterized in that.

7. The belt position detection unit is disposed between the steering roller and the heating roller in the rotation direction of the fixing belt. The fixing device according to claim 6, characterized in that.

8. When the distance between the center position of the fixing belt when the operation of tilting the steering roller is first performed after the center position of the fixing belt is separated from the center position of the movement range of the fixing belt and the center position of the movement range in the width direction of the fixing belt is defined as the center position distance, the center position distance in the separated state is smaller than that in the contact state. The fixing device according to claim 6, characterized in that.

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