Image forming apparatus

Abstract

To provide an image forming apparatus that prevents the occurrence of deformation of a belt in a stopped state.SOLUTION: When a fixing belt 301 is stopped, a steering mechanism is actuated to rotate a steering roller 308 from a home position by a predetermined angle or more. A steering base 317 is rotated to rotate the steering roller 308 from the home position. When the steering base 317 is rotated by a predetermined angle or more, steering rollers 315 of the steering base 317 are fitted into a fitting groove 318b of a steering stay 318. The fitting of the steering rollers 315 into the fitting groove 318b reduces the amount of compression of a tension spring 314, and reduces a tension applied to the fixing belt 301 compared to that in a state in which the fixing belt is stretched. In this manner, the belt tension when the fixing belt 301 is not rotated can be reduced, and consequently compressive residual strain hardly occurs in the fixing belt 301.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine. [Background technology]

[0002] Image forming apparatuses are equipped with a fixing device that applies heat and pressure to a recording material on which a toner image has been formed, thereby fixing the toner image to the recording material. One example of a fixing device proposed is a belt heating type fixing device using a heated belt (see Patent Document 1). In the belt heating type, the belt is pressurized by a pressure roller while being tensioned with a certain amount of tension. As a result, a stationary belt can develop deformation over time in the nip area where the recording material is nipped and conveyed and heat and pressure are applied, or in the bent area where the tension roller bends (known as residual compression strain). If the belt is rotated while such deformation occurs, it becomes difficult to apply uniform heat and pressure to the recording material in the nip area, which can result in poor fixing of the toner image or noise from the belt.

[0003] Therefore, it has been proposed in the past to perform control to eliminate belt deformation by heating the belt to a predetermined temperature and rotating it for a predetermined period of time when rotating a stopped belt (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-140135 [Patent Document 2] Japanese Patent Application Publication No. 2018-101086 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the belt is deformed while the image forming apparatus is stopped as described above, it takes time to correct the deformation of the belt, and image formation cannot be performed during that time, which reduces the operational efficiency of the image forming apparatus.

[0006] SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide an image forming apparatus in which deformation of the belt is unlikely to occur when the apparatus is stopped. [Means for solving the problem]

[0007] An image forming apparatus according to one embodiment of the present invention includes an image forming unit that forms a toner image on a recording material, a fixing device that applies heat and pressure to the recording material on which the toner image has been formed by the image forming unit to fix the toner image to the recording material, and a control unit that controls the fixing device, wherein the fixing device includes an endless belt that applies heat to the recording material, a first roller that stretches the belt, a second roller that stretches the belt together with the first roller, a pressure rotating body that contacts the outer peripheral surface of the belt and nip-conveys the recording material on which the toner image has been formed together with the belt to form a nip portion where the toner image is fixed to the recording material, a holding member that holds the second roller, a bearing portion that supports the rotation shaft of the second roller, and a biasing member that is provided on the holding member and biases the bearing portion so as to press the second roller against the inner peripheral surface of the belt, The image forming apparatus includes a support member that rotatably supports a holding member, and a steering unit that rotates the holding member relative to the support member at a first rotational angle within a predetermined range, thereby tilting the second roller relative to the first roller and moving the rotating belt in the direction of the rotation axis of the second roller, wherein the support member has a region that abuts the rotating holding member, and has a step in the biasing direction of the belt between a first region that applies a first tension to the belt when the holding member is rotated at the first rotational angle, and a second region that applies a second tension that is smaller than the first tension to the belt when the holding member is rotated to a second rotational angle that is larger than the predetermined range, and when the image forming apparatus transitions from power on to power off, the control unit rotates the holding member to the second rotational angle using the steering unit. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an image forming apparatus in which deformation of the belt is unlikely to occur when the apparatus is stopped. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] (a) Schematic diagram showing the belt in tension, (b) Schematic diagram showing the belt in slack. [Figure 8] FIG. 2 is a control block diagram showing a control system for a steering mechanism. [Figure 9] 10 is a flowchart showing a belt tension change process. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Image forming device> The present embodiment will be described. First, the configuration of the image forming apparatus of this embodiment will be described with reference to FIG. 1. The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd provided corresponding to the four colors of yellow, magenta, cyan, and black. This embodiment is a tandem-type image forming apparatus 1 in which the image forming units Pa, Pb, Pc, and Pd are arranged along the rotation direction of an intermediate transfer belt 204. The image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an original reading device 2 connected to the device main body 3 of the image forming apparatus 1 or an external host device such as a print server connected to the device main body 3 so as to be able to communicate with the device main body 3. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0011] As shown in FIG. 1, the image forming apparatus 1 includes a document reading device 2 and a device main body 3. The document reading device 2 reads a document placed on a document table glass 21. Light emitted from a light source 22 is reflected by the document and forms an image on a CCD sensor 24 via optical components 23, such as a lens. When this optical unit is scanned in the direction indicated by the arrow under the control of a reader control unit, it reads the document line by line and converts it into an electrical signal data stream. The image signal obtained by the CCD sensor 24 is sent to the device main body 3, where it is processed by a control unit 30 in accordance with the image forming units described below. The control unit 30 also receives external inputs as image signals from external host devices, such as a print server. The control unit 30 controls the entire image forming apparatus 1.

[0012] The apparatus main body 3 includes multiple image forming units Pa, Pb, Pc, and Pd, and each of the image forming units Pa to Pd forms an image based on the image signal. The image signal is converted into a laser beam that is PWM (pulse width modulated) by a control unit 30. A polygon scanner 31 serving as an exposure device scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto photosensitive drums 200a to 200d serving as image carriers of each of the image forming units Pa to Pd.

[0013] Image forming unit Pa forms a toner image of yellow (Y), image forming unit Pb forms a toner image of magenta (M), image forming unit Pc forms a toner image of cyan (C), and image forming unit Pd forms a toner image of black (Bk), respectively. Since these image forming units Pa to Pd have approximately the same configuration, the following description will be given taking image forming unit Pa, which forms a toner image of yellow (Y), as an example, and descriptions of the other image forming units Pb to Pd will be omitted. In image forming unit Pa, a toner image is formed on the surface of photosensitive drum 200a based on an image signal.

[0014] The charging roller 201a charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from the polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. The developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back side of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0015] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming station, where the toner images of each color formed at image forming stations Pa to Pd are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through image forming station Pd, which is located at the most downstream position in the rotation direction of intermediate transfer belt 204, is conveyed to secondary transfer station T2, which is composed of a pair of secondary transfer rollers 205 and 206. At secondary transfer station T2, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image from intermediate transfer belt 204 to the recording material.

[0016] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208, which is made up of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the position of the paper, and the recording material is transported to a secondary transfer unit T2.

[0017] The recording material onto which the toner image has been transferred at secondary transfer section T2 is transported to fixing device 8, where heat and pressure are applied to fix the toner image to the recording material. The recording material that has passed through fixing device 8 is discharged onto discharge tray 7. When forming images on both sides of the recording material, after the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (back side) of the recording material, and the recording material is discharged onto discharge tray 7.

[0018] <Fixing device> Next, the fixing device 8 of this embodiment will be described with reference to FIG. 2. In this embodiment, a fixing device 8 employs a belt heating system using an endless fixing belt 301. As shown in FIG. 2, the fixing device 8 includes a belt unit 309, a pressure roller 305, and a recording material detection sensor 95. In FIG. 2, "X" indicates the conveyance direction of the recording material S, "Y" indicates the width direction, and "Z" indicates the pressure direction. In this specification, the width direction refers to the direction intersecting the conveyance direction of the recording material S in the fixing nip N (described later), in other words, the direction of the rotation axis of the pressure roller 305. Furthermore, the fixing device 8 viewed from the upstream side in the conveyance direction is referred to as the "front," the left side as viewed from the front is referred to as the "left," and the right side as viewed from the front is referred to as the "right." FIG. 2 shows the fixing device 8 viewed from the left.

[0019] <Pressure roller> Pressure roller 305, which serves as a pressure rotating body, is provided so as to be able to contact and apply pressure to fixing belt 301 of belt unit 309. Pressure roller 305 is a roller having a cylindrical core, an elastic layer on the outer periphery of the core, and a release layer on top of the elastic layer. As an example, the core is made of stainless steel (SUS) with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (PFA) with a thickness of 100 μm.

[0020] A gear (not shown) is fixed to one end of the pressure roller 305, and the pressure roller 305 is connected to a drive motor M1 via the gear and driven to rotate. When the pressure roller 305 rotates, frictional force generated in the fixing nip N transmits the rotational force of the pressure roller 305 to the fixing belt 301. In this way, the fixing belt 301 is rotated by the pressure roller 305.

[0021] The pressure roller 305 contacts the outer peripheral surface of the fixing belt 301 so as to sandwich the fixing belt 301 between itself and a pressure pad 303 of a belt unit 309, and forms a fixing nip N between itself and the fixing belt 301, where the recording material S is sandwiched and conveyed between itself and the fixing belt 301, and the toner image is fixed to the recording material S. To do this, the pressure roller 305 is provided so as to be movable toward the pressure pad 303 by a drive source (not shown). In the case of this embodiment, the pressure roller 305 presses the fixing belt 301 so that, for example, the pressure force of the fixing nip N during image formation is "1600 N," and the length of the fixing nip N in the conveyance direction is "24.5 mm" and the length in the width direction is "326 mm."

[0022] <Belt unit> Belt unit 309 has an endless fixing belt 301, a heating roller 307, a steering roller 308, and a fixing pad unit 300. Fixing belt 301 is stretched between two tension rollers, heating roller 307 and steering roller 308, and fixing pad unit 300. Fixing belt 301 has thermal conductivity, heat resistance, and the like, and is formed in a thin cylindrical shape. Fixing belt 301 has a three-layer structure in which, from the inner periphery, a base layer, an elastic layer, and a release layer are formed on a substrate such as rubber. As an example, the base layer is 80 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA.

[0023] If such a fixing belt 301 is left at room temperature with a certain tension applied while stopped, residual compression strain is likely to occur in the fixing nip N and in the bent portions bent by the heating roller 307 and steering roller 308. Residual compression strain is deformation that occurs mainly in the elastic layer due to compression, and a deformed elastic layer is difficult to return to its original state even when the compressed state is released. To return it to its original state, fixing belt 301 needs to be heated to a predetermined temperature or higher while rotating.

[0024] Heating roller 307 as a first roller is disposed inside fixing belt 301 and is rotatably supported on belt unit side plate 313 so as to stretch fixing belt 301 together with fixing pad unit 300. Heating roller 307 is a cylindrical metal roller made of metal such as aluminum or stainless steel with a thickness of, for example, 1 mm, and has a halogen heater 306 disposed inside for heating fixing belt 301. Heating roller 307 is heated by halogen heater 306, and fixing belt 301 is heated to a predetermined temperature by heating roller 307. The temperature of fixing belt 301 is detected by temperature sensor 650.

[0025] The fixing pad unit 300 has a holding stay 302 and a pressure pad 303, and is arranged inside the fixing belt 301. The holding stay 302 is a rigid member made of, for example, metal that extends in the width direction of the fixing belt 301, and holds the pressure pad 303. The pressure pad 303 is provided inside the fixing belt 301 in a non-rotating manner. The pressure pad 303 is a resin member that extends in the width direction, and the width direction length of the pressure pad 303 is longer than the width direction length of the maximum size recording material on which an image can be formed. The pressure pad 303 is made of a resin with good insulating properties and heat resistance, such as LCP (liquid crystal polymer resin).

[0026] In order to reduce the frictional force between the fixing belt 301 and the pressure pad 303, it is preferable to provide a sliding member (not shown) between the pressure pad 303 and the fixing belt 301. The sliding member is disposed at a position facing the pressure roller 305 with the fixing belt 301 sandwiched therebetween. It is also preferable to apply a lubricant such as silicone oil to the inner circumferential surface of the fixing belt 301 in order to allow the fixing belt 301 to slide smoothly against the sliding member.

[0027] In this embodiment, the fixing belt 301 is pressed from the outside by the pressure roller 305 against the pressure pad 303 held by the holding stay 302. This forms a wide fixing nip N between the pressure roller 305 and the fixing belt 301, ensuring the above-mentioned length in the conveying direction and width direction. Furthermore, by holding the resin pressure pad 303 on the metal holding stay 302, which has greater rigidity, the deflection that occurs in the pressure pad 303 when pressed is reduced, thereby achieving a fixing nip width that is uniform in the width direction. A recording material detection sensor 95 is located immediately before the fixing nip N and detects the timing when the recording material S enters the fixing device 8.

[0028] In the belt unit 309, due to component precision, an alignment error may occur between the tension rollers that tension the fixing belt 301, where the rotation axes of the rollers are not parallel but misaligned. In such a case, the rotating fixing belt 301 is likely to shift toward one of the edges in the width direction, which may damage the fixing belt 301 or other components. Therefore, in this embodiment, to prevent belt shift, one of the tension rollers that tension the fixing belt 301 is used as a steering roller 308. The steering roller 308 is a member in which a rubber material is provided on the surface of a hollow metal shaft (e.g., a stainless steel shaft) formed with a diameter of, for example, 20 mm, to increase the grip force on the fixing belt 301.

[0029] In this embodiment, the steering roller 308 serving as the second roller is disposed downstream of the heating roller 307 and upstream of the pressure pad 303 in the rotation direction of the fixing belt 301. The steering roller 308 controls the position of the fixing belt 301 in the width direction while rotating in accordance with the fixing belt 301. The steering roller 308 is rotated relative to the fixing belt 301 around the center (or one end) in the width direction via a steering unit 600 that operates in accordance with the forward and reverse rotation of a steering motor 350. As the steering roller 308 rotates, a tension difference is generated between both ends of the fixing belt 301, causing the fixing belt 301 to move in the width direction. This prevents the fixing belt 301 from shifting toward the center.

[0030] A position sensor 390 (see FIG. 8 described later) for detecting the end position of the fixing belt 301 is disposed at one point on the rotation path of the fixing belt 301. The end position of the fixing belt 301 is detected based on the output signal of the position sensor 390, and the steering motor 350 is rotated forward or backward in accordance with the detected end position, thereby rotating the steering roller 308 via the steering unit 600.

[0031] <Discharge unit> A discharge unit 500 is disposed downstream in the conveying direction of the fixing nip N for discharging the recording material S that has passed through the fixing nip N to the outside of the fixing device 8. The discharge unit 500 has an air nozzle 501 that blows compressed air to peel the recording material S that has passed through the fixing nip N from the fixing belt 301, a lower separation guide 502 that peels the recording material S from the pressure roller 305, and a pair of conveying rollers 503 that convey the peeled recording material S. A recording material detection sensor 700 is disposed downstream in the conveying direction of the discharge unit 500 for detecting the recording material S that has passed through the fixing nip N and is conveyed by the discharge unit 500.

[0032] In this embodiment, although not shown, both ends of the heating roller 307 and the pressure roller 305 in the width direction are rotatably supported via bearing members on side plates arranged on one end and the other end of the fixing frame (fixing unit frame body). Similarly to the heating roller 307 and the pressure roller 305, both ends of the holding stay 302 are supported by the same side plates on one end and the other end, respectively.

[0033] <Steering mechanism> Next, the steering mechanism of this embodiment will be described with reference to FIGS. 3 to 7(b). Note that, for convenience of illustration, the steering stay 318 is omitted in FIG. 3. As shown in FIGS. 3 and 4, the steering unit 600 has a steering base 317 and a steering arm 320. The steering base 317 as a holding member is a rigid member made of, for example, metal that extends in the width direction and holds the steering roller 308. Specifically, steering holders 316 as bearings are provided at both ends of the steering base 317 in the width direction, and a rotation shaft 308a of the steering roller 308 is supported by the steering holders 316. Furthermore, a base tilting shaft 317a is provided at one end of the steering base 317 so as to protrude outward from the side surface.

[0034] The steering arm 320 is mounted on a side plate of the fixing frame that supports one end of the heating roller 307, etc., so as to be rotatable up and down about an arm rotation shaft 320a. For example, when the steering motor 350 (see FIG. 2) rotates forward, the steering arm 320 is rotated upward via a drive gear unit (not shown), and when the steering motor 350 rotates reversely, the steering arm 320 is rotated downward via the drive gear unit. A steering arm link 321 is provided on the steering arm 320. A base tilting shaft 317a of the steering base 317 is fitted into the steering arm link 321.

[0035] As shown in FIG. 4 , the steering unit 600 also includes a steering stay 318. The steering base 317 is supported by the steering stay 318 as a support member so as to be rotatable about the base rotation shaft 317b. Therefore, when the steering arm 320 is rotated, the steering base 317 rotates about the base rotation shaft 317b relative to the steering stay 318 via the steering arm link 321 and the base tilting shaft 317a. As described above, the steering roller 308 is supported by the steering base 317 and therefore rotates integrally with the steering base 317. This changes the angle of contact between the steering roller 308 and the fixing belt 301, causing the fixing belt 301 to reciprocate in the width direction. The fixing belt 301 reciprocates in the opposite direction when the steering motor 350 is rotated forward to tilt the steering roller 308 and when the steering motor 350 is rotated backward to tilt the steering roller 308.

[0036] In this embodiment, a "home position" is set at a position where the steering roller 308 is approximately horizontal with respect to the heating roller 307. A position flag is provided on the rotating steering arm 320, and the steering unit 600 has a position sensor (see FIG. 8 described later) for detecting the position flag. That is, on the steering arm 320, the position flag is formed at a position that can be detected by the position sensor when the steering roller 308 is located at the "home position."

[0037] As described above, both ends of the rotation shaft 308a of the steering roller 308 are supported by the steering holder 316 of the steering base 317. As shown in FIG. 5, one end of the tension spring 314 is fixed to the steering holder 316, and the other end of the tension spring 314 is fixed to the steering base 317.

[0038] In order to apply tension to the fixing belt 301, the steering roller 308 needs to press the fixing belt 301 from the inside to the outside. Therefore, a steering holder 316 that supports the steering roller 308 is biased toward the fixing belt 301 by a tension spring 314. The tension spring 314 as a biasing member is, for example, a compression spring, and biases the steering holder 316 in a compressed state. In this way, the steering roller 308 is biased by the tension spring 314 via the steering holder 316. Therefore, when the compression amount of the tension spring 314 changes, the magnitude of the tension applied to the fixing belt 301 (belt tension) changes. In this way, in this embodiment, the steering roller 308 also functions as a tension roller that applies tension to the fixing belt 310.

[0039] Furthermore, at both widthwise ends of the steering base 317, on the two sides opposite the one side to which the tension spring 314 is fixed, steering rollers 315 are provided as protrusions protruding toward the steering stay 318. The steering rollers 315 are formed to be rotatable and are constantly in contact with the steering stay 318 by the tension spring 314. As a rotating body, the steering rollers 315 rotate on the steering stay 318 in conjunction with the rotation of the steering roller 308. Therefore, the steering rollers 315 disposed at both ends rotate in opposite directions and move in an arc along the rotational trajectory of both ends of the rotating steering roller 308. This allows the steering base 317 to rotate smoothly relative to the steering stay 318.

[0040] 6, in this embodiment, a fitting groove 318b is formed in the steering stay 318. The fitting groove 318b is a concave groove formed in the steering stay 318. The fitting groove 318b is formed to a size that allows the steering roller 315 to be loosely fitted onto the trajectory of the rotation of the steering roller 315 in the steering stay 318.

[0041] The fitting groove 318b is formed in a region (second region) into which the steering roller 315 can fit when the steering base 317 rotates a predetermined angle or more (second rotation angle) with respect to the home position. The fitting groove 318b is formed so that the steering roller 315 can fit when the steering base 317 rotates a predetermined angle, for example, +6° or more, with the home position as the reference angle of 0°. In this embodiment, to distinguish from the fitting groove 318b, the position of the steering stay 318 with which the steering roller 315 abuts when the steering base 317 rotates within a range smaller than the predetermined angle is conveniently referred to as the "reference region 318a." The reference region 318a is a first region within a predetermined range smaller than +6° with respect to a reference line (HP) passing through the steering roller rotation center 318c, and the fitting groove 318b is a second region that is farther from the reference line (HP) than the reference region 318a. When the steering base 317 is in the home position, the direction of the rotation axis of the steering roller 308 substantially coincides with the reference line (HP). In this specification, the angle when the steering base 317 (which can also be called the steering roller 308) is rotated counterclockwise relative to the steering stay 318 in Figure 6 is indicated by "+".

[0042] In this embodiment, the fitting grooves 318b are formed only at positions (upper right, lower left) where the steering rollers 315 fit when the steering base 317 is rotated counterclockwise, but this is not limitative. The fitting grooves 318b may be formed both at positions (upper right, lower left) where the steering rollers 315 fit when the steering base 317 is rotated counterclockwise and at positions (lower right, upper left) where the steering rollers 315 fit when the steering base 317 is rotated clockwise. Furthermore, the positions where the fitting grooves 318b are formed are not limited to positions at or above the predetermined angle of ±6° as described above, and may be formed at appropriate positions according to product specifications. Furthermore, the fitting grooves 318b may have an inclined surface 3181 that continues from the reference region 318a so that the depth of the groove increases with increasing distance from the reference region 318a. When the steering roller 315 rotates in contact with the inclined surface 3181, the steering base 317 can rotate smoothly between the fitting groove 318b and the reference area 318a.

[0043] As shown in FIG. 7A, when the steering roller 315 is in the reference area 318a of the steering stay 318, the fixing belt 301 is in a stretched state with a constant tension applied thereto. At this time, the length of the tension spring 314 is "L1" and the belt tension is "F." As the steering roller 308 rotates while the fixing belt 301 is rotating, the steering roller 315 rotates on the reference area 318a of the steering stay 318 while receiving a reaction force of the belt tension "F." Therefore, the fixing belt 301 is moved back and forth in the width direction with a constant tension applied thereto, and belt deviation is suppressed.

[0044] On the other hand, as shown in Fig. 7(b), when the steering roller 315 is fitted into the fitting groove 318b, the fixing belt 301 is in a slack state rather than a taut state. At this time, the length of the tension spring 314 is "L2 (L1 < L2)". That is, when the steering roller 315 is fitted into the fitting groove 318b, the steering base 317 moves to the side opposite to the steering holder 316. Accordingly, the tension spring 314 extends, and the length of the tension spring 314 increases by the amount of movement of the steering base 317 corresponding to the fitting of the steering roller 315 into the fitting groove 318b of the steering stay 318, so the amount of compression of the tension spring 314 decreases. Since the amount of compression of the tension spring 314 decreases, the tension (second tension) applied to the fixing belt 301 becomes lower than the tension (first tension) in the taut state. Thus, compared with the case where the steering roller 315 is in the reference region 318a of the steering stay 318, the fixing belt 301 is stretched in a slack state. In the present embodiment, as will be described later, when the rotation of the fixing belt 301 is stopped, the steering roller 315 is fitted into the fitting groove 318b so that the fixing belt 301 is slackened.

[0045] As described above, in the present embodiment, when the steering base 317 is rotated at a first rotation angle within a predetermined range, a first tension is applied to the fixing belt 301 in the reference region 318a that contacts the steering stay 318. Then, when the steering base 317 is rotated to a second angle larger than the predetermined range, in the region outside the reference region 318a of the steering stay 318 where the steering base 317 (specifically, the steering roller 315) contacts, when the steering roller 315 is fitted into the fitting groove 318b, a second tension smaller than the first tension is applied to the fixing belt 301. To achieve this, the fitting groove 318b is formed in the region outside the reference region 318a, and a step is provided in the biasing direction of the fixing belt 301 between the reference region 318a.

[0046] Note that the present invention is not limited to forming the fitting groove 318b in the area outside the reference area 318a, and a protruding portion may be provided in the steering stay 318 so that the reference area 318a protrudes further toward the steering base 317 than the area outside the reference area 318a. On the other hand, the steering base 317 does not need to be provided with a protruding portion such as the steering roller 315 described above. In this case, the surface of the steering base 317 facing the steering stay 318 slides against the protruding portion of the steering stay 318 as it rotates.

[0047] <Steering mechanism control system> Next, the control system of the steering unit 600 by the control unit 900 will be described using Fig. 8 with reference to Fig. 2 and Fig. 4. Note that various devices other than those shown in the figure are connected to the control unit 900, but illustration and description of these devices will be omitted here as they are not the main focus of the invention.

[0048] The control unit 30 has a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each unit by reading a program corresponding to the control procedure stored in the ROM. The RAM stores work data and input data, and the CPU performs control by referring to the data stored in the RAM based on the program, etc. An operation unit 4 is connected to the control unit 30, and the control unit 30 can perform various settings related to image formation based on input from the operation unit 4. The operation unit 4 may be, for example, a touch panel, and accepts inputs such as the start of various programs such as an "image formation job" and various data inputs in response to a user's touch operation.

[0049] As shown in FIG. 8 , in addition to the operation unit 4, the control unit 30 is connected to the drive motor M1, the halogen heater 306, the steering motor 350, the position sensor 360, the position sensor 390, and the recording material detection sensor 700. As described above, the control unit 30 controls the drive motor M1 to start and stop the rotation of the fixing belt 301 via the pressure roller 305. The control unit 30 stops the rotating fixing belt 301, for example, when the image forming apparatus 1 is turned off, when the image forming apparatus 1 is in sleep mode, which consumes less power than when it is waiting for image formation, or when a jam occurs in which the recording material S gets stuck in the conveyance path during image formation. The control unit 30 also controls the heating of the fixing belt 301 by the halogen heater 306. The recording material detection sensor 700 is provided to detect delays and premature arrival of the recording material S in the fixing device 8, and the control unit 30 can determine whether a jam of the recording material S has occurred based on the detection result of the recording material detection sensor 700. Furthermore, the control unit 30 can control the steering motor 350 based on the detection result of the position sensor 360 so as to position the steering roller 308 at the "home position."

[0050] The control unit 30 can then control the steering motor 350 to rotate the steering roller 308. As described above, the rotation of the steering roller 308 causes the rotating fixing belt 301 to move back and forth in the width direction, thereby realizing steering control to position the fixing belt 301 within a predetermined range in the width direction. To do so, the control unit 30 detects the end position of the rotating fixing belt 301 based on the output signal of the position sensor 390, and controls the forward and reverse rotation of the steering motor 350 in accordance with the detected end position. When performing steering control, the control unit 30 controls the steering motor 350 so that the steering base 317 is rotated within an angle range of, for example, less than "+6°" and more than "-6°." This causes the steering roller 315 to rotate on the reference area 318a without engaging with the engaging groove 318b.

[0051] <Belt tension change processing> As described above, the control unit 30 stops the rotating fixing belt 301 when the image forming apparatus 1 is powered off, in sleep mode, or when a recording material S jams. However, as already mentioned, if the stopped fixing belt 301 remains tensioned, there is a risk of residual compressive strain developing in the fixing belt 301 over time. Therefore, in this embodiment, when the image forming apparatus 1 transitions from power-on to power-off, or in sleep mode or when a recording material S jams, the steering unit 600 is operated to transition the fixing belt 301 from a tensioned state (see FIG. 7A) to a slack state (see FIG. 7B) when the image forming apparatus 1 transitions from power-on to power-off, or when a recording material S jams. The "belt tension change process" that achieves this will be described below with reference to FIG. 9 along with FIGS. 2 and 8. FIG. 9 is a flowchart showing the belt tension change process. This belt tension change process is executed by the control unit 30, for example, when the image forming apparatus 1 is powered off, when the image forming apparatus 1 transitions to a power-saving standby mode, or when a recording material S jam is detected.

[0052] The control unit 30 stops the halogen heater 306 to stop heating the fixing belt 301 via the heating roller 307 (S1). The control unit 30 also stops the drive motor M1 to stop the rotation of the fixing belt 301 via the pressure roller 305 (S2). After a predetermined time has elapsed since the drive motor M1 was stopped, the control unit 30 determines whether the steering roller 308 is located at the home position based on the detection result of the position sensor 360 (S3). The predetermined time here may be at least the time from when the drive motor M1 is stopped until the rotation of the fixing belt 301 stops.

[0053] If the steering roller 308 is not located at the home position (NO in S3), the control unit 30 controls the steering motor 350 to operate the steering unit 600, thereby moving the steering roller 308 to the home position (S5). Once the steering roller 308 has moved to the home position, the control unit 30 proceeds to the process of step S4. If the steering roller 308 is already located at the home position (YES in S3), the control unit 30 proceeds to the process of step S4 without performing the process of step S5. When the steering roller 308 is located at the home position, as shown in FIG. 7(a), the steering roller 315 is not engaged with the engagement groove 318b, and therefore the fixing belt 301 is in a tensioned state.

[0054] In step S4, the control unit 30 controls the steering motor 350 to operate the steering unit 600, thereby rotating the steering roller 308 by a predetermined angle or more from the home position. The predetermined angle here is the angle (e.g., +6°) at which the steering roller 315 fits into the fitting groove 318b. When the steering roller 308 is located at a position rotated by the predetermined angle or more from the home position, the steering roller 315 fits into the fitting groove 318b, as shown in FIG. 7(b), and therefore the fixing belt 301 is in a slack state.

[0055] As described above, in this embodiment, when the fixing belt 301 is stopped, the steering unit 600 is operated to rotate the steering roller 308 from the home position by a predetermined angle or more. To rotate the steering roller 308 from the home position, the steering unit 600 rotates the steering base 317 that holds the steering roller 308. When the steering base 317 is rotated by a predetermined angle or more, the steering roller 315 provided on the steering base 317 fits into the fitting groove 318b formed in the steering stay 318. As described above, when the steering roller 315 fits into the fitting groove 318b, the tension applied to the fixing belt 301 is reduced compared to when the fixing belt 301 is tensioned. In this way, the belt tension when the fixing belt 301 is not rotating can be reduced compared to the belt tension when the fixing belt 301 is rotating, thereby loosening the fixing belt 301. This makes it less likely that residual compressive strain will occur in the fixing belt 301. Therefore, it is not necessary to perform control to eliminate deformation of fixing belt 301, and image formation can be performed by rotating fixing belt 301, thereby improving the operational efficiency of the image forming apparatus. Also, since fixing belt 301 can be loosened using steering unit 600, a simple configuration is sufficient.

[0056] The image forming apparatus 1 is shipped from a factory or the like with the fixing belt 301 in a loose state. This is to prevent residual compressive strain from occurring in the fixing belt 301 in the image forming apparatus 1 before it is shipped from the factory. Then, when the image forming apparatus 1 is installed at an installation location and the power of the image forming apparatus 1 is turned on, the control unit 30 operates the steering unit 600 to move the steering roller 308 to the home position. This causes the fixing belt 301 to transition from a loose state to a tensioned state. The control unit 30 then rotates the fixing belt 301. Alternatively, an installer may manually transition the fixing belt 301 from a loose state to a tensioned state before the power of the image forming apparatus 1 is turned on.

[0057] [Other embodiments] In the above-described embodiment, the heating roller 307 heated by the halogen heater 306 is used to heat the fixing belt 301, but this is not limiting. For example, the fixing belt 301 may be heated from the outside using an induction heating method, or an external heating method may be used in which a heating member is brought into contact with the outer peripheral surface of the fixing belt 301 to heat it. [Explanation of symbols]

[0058] 1...image forming apparatus, 8...fixing device, 30...control section, 301...belt (fixing belt), 305...pressure rotating body (pressure roller), 307...first roller (heating roller), 308...second roller (steering roller), 314...urging member (compression spring, tension spring), 315...protruding portion (rotating body, steering roller), 316...bearing portion (steering holder), 317...holding member (steering base), 318...support member (steering stay), 318b...engagement groove, 600...steering section, Pa, Pb, Pc, Pd...image forming section, S...recording material

Claims

1. In the image forming apparatus, an image forming unit that forms a toner image on a recording material; a fixing device that applies heat and pressure to a recording material on which a toner image has been formed by the image forming unit to fix the toner image to the recording material; a control unit that controls the fixing device, The fixing device an endless belt that applies heat to the recording material; a first roller over which the belt is stretched; a second roller that stretches the belt together with the first roller; a pressure rotating body that contacts the outer peripheral surface of the belt, sandwiches and conveys a recording material on which a toner image is formed together with the belt, and forms a nip portion where the toner image is fixed to the recording material; a holding member that holds the second roller; a bearing portion that supports a rotation shaft of the second roller; a biasing member provided on the holding member and biasing the bearing portion so as to press the second roller toward an inner circumferential surface of the belt; a support member that rotatably supports the holding member; a steering unit that rotates the holding member relative to the support member at a first rotation angle within a predetermined range to tilt the second roller relative to the first roller and move the rotating belt in the direction of the rotation axis of the second roller, the support member has a step in the urging direction of the belt between a first region that is in contact with the rotating holding member and that applies a first tension to the belt when the holding member is rotated at the first rotation angle, and a second region that applies a second tension that is smaller than the first tension to the belt when the holding member is rotated to a second rotation angle that is larger than the predetermined range, When the image forming apparatus transitions from a power-on state to a power-off state, the control unit causes the steering unit to rotate the holding member to the second rotation angle. An image forming apparatus characterized by:

2. the holding member has protruding portions at both ends in the direction of the rotation axis that protrude so as to come into contact with the support member, The support member has a fitting groove in the second region into which the protrusion fits.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The protrusion is a rotating body that rotates in contact with the support member.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. The biasing member is a compression spring.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. the control unit causes the steering unit to rotate the holding member to the second rotation angle during a sleep state in which power consumption is lower than during a standby state for image formation.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. the fixing device rotates the holding member to the second rotation angle by the steering portion when a jam of the recording material occurs; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images