Fixing apparatus and image forming apparatus

Abstract

This design suppresses belt misalignment during transportation and improves the ease of belt replacement. [Solution] The device comprises an endless belt, a pressing member that contacts the outer circumferential surface of the endless belt, a nip forming member that contacts the inner circumferential surface of the endless belt at a position opposite to the pressing member and forms a nip portion between the endless belt and the pressing member, a tension applying member that rotatably suspends the endless belt and applies tension to the endless belt by pressing it, and the tension applying member is supported so as to be able to move between a pressing position for pressing the endless belt and a release position for releasing the pressure on the endless belt, a first holding member that holds the tension applying member at the release position, which is moved a first distance from the pressing position in the opposite direction to the pressing direction, and a second holding member that holds the tension applying member at an intermediate position, which is moved a second distance shorter than the first distance from the pressing position in the opposite direction to the pressing direction.

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image formed on a recording material and an image forming apparatus including the same.

Background Art

[0002] Conventionally, an electrophotographic image forming apparatus has a fixing device for fixing an unfixed toner image formed on a recording material. As one of such fixing devices, a configuration is known in which a toner image is fixed between a fixing belt, which is an endless belt suspended by a plurality of suspension members, and a pressing member that contacts the outer peripheral surface of the fixing belt (Patent Document 1).

[0003] In Patent Document 1, a nip portion is formed between a pressure roller and a fixing belt by using a pad member that sandwiches the fixing belt between the pressure roller. By using the pad member, the nip portion can be formed widely without causing the apparatus to become large, and the toner image can be fixed to the recording material in a shorter time and at a lower temperature.

[0004] Also, in Patent Document 1, the position of the fixing belt is detected by a photosensor via a flag, and based on the result, the position in the width direction of the fixing belt is controlled by tilting a steering roller, which is one of the suspension members. In order to control the position by the steering roller, tension is applied to the fixing belt by pressing the steering roller against the fixing belt.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in Patent Document 1, pressing the steering roller against the fixing belt increases the holding force of the fixing belt by the steering roller, which may cause the fixing belt to shift in the width direction perpendicular to the rotation direction due to vibrations during the transportation of the device.

[0007] Therefore, Patent Document 2 provides a mechanism that moves the steering roller between a pressing position, where it presses against the inner circumferential surface of the anchoring belt, and a release position, where it releases that pressure. By keeping the steering roller in the release position during transport of the device, displacement of the anchoring belt due to the restraining force (holding force) received from the steering roller is suppressed.

[0008] On the other hand, if the pressure exerted by the steering roller on the anchoring belt is sufficiently small in the release position, the anchoring belt can be moved in the width direction, and the anchoring belt can be replaced. However, if the pressure exerted by the steering roller on the anchoring belt is too small in the release position, the force holding the anchoring belt will weaken too much, which may actually reduce the effectiveness of suppressing the positional displacement of the anchoring belt during equipment transport.

[0009] Therefore, the objective of the present invention is to suppress displacement of the endless belt due to vibration during transportation and to improve the ease of replacing the endless belt. [Means for solving the problem]

[0010] A typical configuration of the present invention is characterized by comprising: an endless belt rotatably suspended by a plurality of suspension members; a pressing member that abuts against the outer circumferential surface of the endless belt; a nip forming member that contacts the inner circumferential surface of the endless belt at a position opposite to the pressing member and forms a nip portion between the endless belt and the pressing member; a tension applying member that rotatably suspends the endless belt and applies tension to the endless belt by pressing it; and the tension applying member being supported so as to be movable between a pressing position for pressing the endless belt and a release position for releasing the pressure on the endless belt, a first holding member that holds the tension applying member at the release position, which is moved a first distance from the pressing position in the opposite direction to the pressing direction; and a second holding member that holds the tension applying member at an intermediate position, which is moved a second distance shorter than the first distance from the pressing position in the opposite direction to the pressing direction. [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress displacement of the endless belt due to vibration during transportation and to improve the ease of replacing the endless belt. [Brief explanation of the drawing]

[0012] [Figure 1] Main cross-sectional view of the image forming apparatus [Figure 2] Schematic cross-sectional view of the fixing device in an image forming apparatus. [Figure 3] Perspective view of the fixing device [Figure 4] Perspective view of the fixing device [Figure 5] Perspective view of the fixing device in Example 1 [Figure 6] Perspective view of the fixing device in Example 1 [Figure 7] Cross-sectional view of the fixing device in Example 1 [Figure 8] Cross-sectional view of the fixing device in Example 1 [Figure 9] Cross-sectional view of the fixing device in Example 1 [Figure 10] Perspective view of the fixing device in Example 2 [Figure 11] Cross-sectional view of the fixing device in Example 2

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that the dimensions, materials, shapes, relative arrangements, etc. of the components described below are merely examples and are not intended to limit the scope of the present invention thereto.

[0014] 〔Example 1〕 An image forming apparatus including a fixing device according to Example 1 will be described. In the following description, as the image forming apparatus, a full-color copier including a plurality of photosensitive drums will be exemplified and described, but the present invention is not limited thereto. The present invention can also be applied to other image forming apparatuses such as a monochrome copier including one photosensitive drum, a monochrome printer, or a full-color laser beam printer. Further, the present invention can also be applied to a fixing device used in such an image forming apparatus.

[0015] [[ID=2 | 0]]First, the image forming apparatus will be described using FIG. 1. FIG. 1 is a main cross-sectional view showing the overall configuration of the image forming apparatus 100.

[0016] <Image forming apparatus> The image forming apparatus 100 includes an image forming unit 110 that forms an image on a recording material P, a fixing device 200 that fixes the image formed on the recording material P, an operation unit 180, and a control board 150.

[0017] The image forming apparatus 100 conveys the recording material P conveyed from the recording material storage unit 103 to the image forming unit 110 and forms a toner image on the recording material P. Thereafter, the image forming apparatus 100 conveys the recording material P on which the toner image has been formed by the image forming unit 110 to the fixing device 200 and applies heat and pressure to fix the unfixed toner on the recording material P to the recording material P. The recording material P is, for example, a sheet such as paper or OHP. <00000 | 9>

[0018] The image forming apparatus 100 has an image forming section 110, which includes stations 120a, 120b, 120c, and 120d as image forming sections. The image forming apparatus 100 also includes an intermediate transfer belt 115 and a transfer roller 116. Stations 120a, 120b, 120c, and 120d each form yellow, magenta, cyan, and black toner images on the intermediate transfer belt 115.

[0019] Each station 120a to 120d has a photosensitive drum 111 as an image carrier and a primary charger 112, a developer 114, and other process means that act on it. Each station 120a to 120d has a different toner color but is configured similarly.

[0020] In station 120a, the photosensitive drum 111, acting as the image carrier, rotates counterclockwise in the direction shown in Figure 1. The primary charger 112 charges the photosensitive drum 111 to a uniform surface potential. The laser unit 113 has a light source that emits laser light and forms a latent image on the photosensitive drum 111. The developer 114 uses a developer containing toner to develop the latent image formed on the photosensitive drum 111 and form a toner image. The configurations of stations 120b, 120c, and 120d are the same as those of station 120a, so their description is omitted.

[0021] The toner images formed by stations 120a, 120b, 120c, and 120d are transferred onto the intermediate transfer belt 115. The transfer roller 116 transfers the toner image on the intermediate transfer belt 115 onto the recording material P being transported from the recording material storage unit 103.

[0022] The fixing device 200 fixes the toner image transferred to the recording material P to the recording material P by applying heat and pressure to the recording material P. The fixing device 200 includes a fixing belt 201, a pressure roller 202, etc.

[0023] In the case of single-sided printing, the image forming apparatus 100 guides the recording material P, which has completed image formation via the image forming unit 110 and the fixing unit 200, to the discharge path 139 using the flapper 132, and discharges it to the outside of the apparatus using the discharge roller. The flapper 132 is a guide member (guide member) that guides the recording material P, which has passed through the image forming unit 110 and the fixing unit 200, to the transport path 134, or to the outside of the image forming apparatus 100.

[0024] On the other hand, in the case of double-sided printing, the image forming apparatus 100 inverts the recording material P after one side has been printed and transports it back to the image forming unit 110. Specifically, the flapper 132 guides the fixed recording material P to the transport path 134 and then to the inversion unit 136. When the inversion sensor 135 detects the rear end of the recording material P, the flapper 133 switches the transport direction of the recording material P to the transport path 137. The image forming apparatus 100 transports the recording material P, which has been inverted in the inversion unit 136, back to the image forming unit 110 via the flapper 133 and the transport path 137, and then to the fixing device 200. The recording material P, which has finished printing on both sides, is guided by the flapper 132 to the discharge path 139 and discharged outside the apparatus.

[0025] The control unit 180 includes a display screen and selection keys. The control unit 180 displays the status of the image forming apparatus 100 on the display screen and accepts operation instructions from the operator (user) via the selection keys.

[0026] Here, the operation unit 180 is exemplified as having a display screen and selection keys, but it is not limited to this configuration. The display screen of the operation unit 180 may be a touch-panel type LCD screen. In this case, for example, a numeric keypad for entering the number of copies or the recipient's telephone number when sending a fax will be displayed as soft keys in a predetermined area on the display screen. Furthermore, in the case of a touch-panel type display screen (LCD screen), it is also possible to accept information input by the operator through touch operations such as flicking, swiping, and scrolling.

[0027] The control board 150 has a control unit 151 and a memory 152, and controls each unit in the image forming apparatus 100. Based on detection signals input from various sensors and information stored in the memory 152, the control unit 151 outputs output signals to each electrical component to operate it at the desired timing and with the required control amount. Therefore, it is the control unit 151 that actually controls the electrical components. The memory 152 stores information data necessary for controlling each unit, and the control unit 151 reads and writes the information data stored in the memory 152.

[0028] Next, the configuration of the fixing device in this embodiment will be described using Figures 2 and 3. Figure 2 is a cross-sectional view of the fixing device in this embodiment, and Figure 3 is a partial perspective view of the fixing device 200.

[0029] <Fusing device> Figure 2 shows a schematic diagram of the overall configuration of the belt heating type fixing device 200 according to this embodiment. In the fixing device 200 shown in Figure 2, the recording material P is conveyed from right to left in Figure 2. The fixing device 200 includes a heating unit 210 and a pressure roller 202 as a pressure member that contacts the heating unit 210. The heating unit 210 and the pressure roller 202 are supported by the housing frame 300 of the fixing device 200. The heating unit 210 includes a fixing belt (hereinafter referred to as the belt) 201 as a rotatable endless belt, a pressure pad (hereinafter referred to as the pad) 203 as a nip forming member, and a heating roller 204 and a steer roller 205 as suspension members. The pressure roller 202 faces the belt 201 and contacts the outer circumferential surface of the belt 201 to form a nip portion N together with the belt 201.

[0030] The belt 201 is heated by a heating roller 204 which has a heating source, and therefore possesses thermal conductivity and heat resistance. The belt 201 is also a thin-walled cylindrical shape. In this embodiment, the belt 201 has a three-layer structure consisting of a base layer, an elastic layer on the outer circumference of the base layer, and a release layer on the outer circumference of the release layer. The base layer is 60 μm thick and made of polyimide resin (PI). The elastic layer is 300 μm thick and made of silicone rubber. The release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 201 is rotatably suspended by multiple suspension members. Specifically, the belt 201 is rotatably tensioned by a pad 203, a heating roller 204, and a steer roller 205.

[0031] The pad 203 is in contact with the inner circumferential surface of the belt 201 at a position opposite the pressure roller 202. The pad 203 is a nip-forming member that presses against the pressure roller 202 via the belt 201, forming a nip portion N of a predetermined width between the belt 201 and the pressure roller 202 in the recording material transport direction. The cross-section of the pad 203 is approximately rectangular, and it is a long member along the width direction perpendicular to the rotation direction of the belt 201. The material of the pad 203 needs to be heat-resistant, and LCP (liquid crystal polymer) is used.

[0032] A sliding sheet 207, whose surface is coated with PTFE, and silicone oil (hereinafter referred to as oil) are interposed between the pad 203 and the belt 201, allowing the belt 201 to slide smoothly against the pad 203. The sliding sheet 207 is formed by coating the surface of a 70 μm thick polyimide substrate with PTFE. The sliding sheet 207 is placed to improve the sliding properties between the pad 203 and the belt 201, and it is possible to substitute the sliding sheet 207 with a coating that improves sliding properties applied to the surface of the pad 203.

[0033] The pressure roller 202 is a roller (pressure rotating body) with an elastic layer formed on the outer circumference of its shaft and a release layer formed on the outer circumference of the elastic layer. The shaft is made of stainless steel. The elastic layer is 5 mm thick and made of conductive silicone rubber. The release layer is 50 μm thick and made of PFA as a fluororesin. The pressure roller 202 is supported by a pressure arm 380 that is movably mounted on the fixing device 200. A gear 202g (see Figure 3) is fixed to one end in the axial direction and is connected to a drive source (not shown) via the gear to rotate it. The belt 201 rotates in the direction of arrow R by being sandwiched between the rotating pressure roller 202 and the pad 203. The pressure roller 202 is also held at both ends in the axial direction by bearings. The pressure roller 202 is supported by the pressure arm 380 so as to be movable between a paper-feeding position (shown in Figure 1) where it presses against the pad 203 via the belt 201, and a separated position (shown in Figure 2) where it is separated from the belt 201, by means of attachment / detachment (not shown). In the paper-feeding position, a pressing force of approximately 1000 N acts on the pressure roller 202.

[0034] If the pressure roller 202 is left in the paper feeding position with the pressure roller stopped, permanent strain may occur in a part of the circumferential direction of the rubber part (elastic layer), which may result in rotational unevenness or surface unevenness. Therefore, when the image forming apparatus is not in use, for example when transporting the image forming apparatus from the manufacturer to the user, it is necessary to keep it in the aforementioned separated position (as shown in Figure 2). In this embodiment, the pressure roller 202 is moved to the aforementioned separated position when the cover (not shown) is opened to remove the fixing device 200 from the image forming apparatus 100, and when the power to the image forming apparatus 100 is turned off.

[0035] The oil supply roller 208 is a suspension member that rotatably suspends the belt 201 and is a supply member that abuts against the inner circumferential surface of the belt 201 to supply lubricant. The oil supply roller 208 is formed by impregnating a roll-shaped member, which is wrapped with a 100 μm thick nonwoven fabric, with silicone oil. The oil supply roller 208 is in contact with the inner surface of the belt 201 at a predetermined contact pressure (here, 3.0 N) by a compression spring 209 and is supported by the frame of the heating unit 210 so as to be driven and rotatable.

[0036] The oil applied as a lubricant between the pad 203 and the belt 201 deteriorates with the operation of the fixing device 200 and decreases due to leakage to the outside. If the oil between the pad 203 and the belt 201 can no longer be retained, the sliding resistance between the pad 203 and the belt 201 increases, which may cause problems such as poor driven rotation of the belt 201. The oil supply roller 208 makes it possible to supply oil to the inner surface of the belt 201 when it makes contact. This makes it possible to maintain the oil interposed between the belt 201 and the pad 203 (sliding seat 207) for a longer period of time and maintain stable operation of the fixing device 200.

[0037] In Figure 2, the stay 206 is a rigid reinforcing member with a long width in the belt 201 direction, positioned on the inside of the pad 203 (opposite the side of the sliding sheet 207) to back up the pad 203. It is made of 3mm thick extruded SUS304 stainless steel, and its strength is ensured by forming it into a hollow "square" shape in cross-section. The stay 206 provides strength to the pad 203 when it is pressed against the pressure roller 202, ensuring the applied pressure at the nip portion N. Although stainless steel is used for the material of the stay 206, it is not limited to stainless steel as long as strength can be ensured.

[0038] The heating roller 204 is a suspension member that rotatably suspends the belt 201 and is a heating rotating body that contacts the inner circumferential surface of the belt 201 to heat the belt 201. In Figure 2, the heating roller 204 is made of a stainless steel pipe with a thickness of 1 mm and an outer diameter of 80 mm. The heating roller 204 has a halogen heater (not shown) disposed inside as a heat source and is capable of generating heat up to a predetermined temperature. The belt 201 is heated by the heating roller 204 and controlled to a predetermined target temperature according to the type of paper based on temperature detection by a thermistor.

[0039] In Figure 2, the steer roller 205 suspends the belt 201 and is supported by the steer frame 213 via the steer bearing section 221. In this embodiment, the steer roller 205 is constructed by forming a 200 μm thick layer of silicone rubber on the surface of a hollow stainless steel roll section with an outer diameter of 20 mm. The steer roller 205 is rotatably supported on the steer roller shaft 223 via bearings.

[0040] The steer roller shaft 223 is supported at both ends by a pair of steer bearing sections 221. The steer bearing sections 221 are made of a resin material that can be used in high-temperature environments, such as PPS, and are mounted to move along the side walls of a box-shaped steer frame 213. The steer frame 213 is a support member that supports the steer roller 205 so that it can move between a pressing position where it presses against the belt 201 and a release position where it releases pressure on the belt 201. Furthermore, the steer bearing sections 221 are pressed by a spring 211 supported by the steer frame 213, thereby pressing (biasing) the steer roller 205 against the belt 201. As a result, the belt 201 is suspended with tension between the steer roller 205, the heating roller 204, and the pad 203. In this suspended state, the steer roller 205 is in contact with the belt 201 with a predetermined pressing force (here, 20N) by the spring 211.

[0041] Thus, the steer roller 205 is a suspension member that rotatably suspends the belt 201, and a tension-applying member that presses against the belt 201 to apply tension to it. The steer roller 205 is supported by the steer frame 213 so that it can move between a pressing position shown in Figures 4 and 7, where it presses against the belt 201, and a release position shown in Figures 5 and 8, where it releases pressure on the belt 201.

[0042] The steer roller 205 is mounted so as to be tiltable in the width direction of the belt 201 relative to the frame of the heating unit 210, with respect to a pivot axis 212 which serves as the pivot point. Specifically, the steer frame 213, which supports the steer roller 205 so as to be movable in the pressing direction, is mounted so as to be tiltable in the width direction of the belt 201 relative to the frame of the heating unit 210, with respect to the pivot axis 212. The pivot axis 212 is an axis whose axis is centered in a direction perpendicular to the rotational and width directions of the belt 201, and is located in the center in the width direction. Although the example given illustrates the pivot axis 212 being located in the center in the width direction, it is not limited to this configuration, and for example, it may be located at one end in the width direction. By tilting in the width direction of the belt 201 with respect to other suspension members that suspend the belt 201, the steer roller 205 changes its relative angle with respect to other suspension members that suspend the belt 201. This creates a tension difference between one side and the other side (front and back) in the width direction perpendicular to the rotation direction of the belt 201, thereby controlling the position of the belt 201 in the width direction (main scanning direction).

[0043] In other words, the steer roller 205 is a steering member that adjusts the position of the belt 201 in the width direction perpendicular to the rotation direction, and is also a tension roller (tension-applying member) that applies tension to the belt 201.

[0044] Next, the movement configuration of the steer roller 205, which is one of the belt suspension members in this embodiment, will be explained using Figures 4 to 9. When the fixing device 200 is removed from the image forming apparatus 100 and operations on the housing such as removing the cover are performed, the pressure roller 202 is moved to the separated position shown in Figure 2, separated from the belt 201.

[0045] <Retaining member> The fixing device 200 includes a steer lock arm 222 and a regulating member 301. The steer lock arm 222 is a first holding member that holds the steer roller 205 in the release position shown in Figures 5 and 8, which is moved a first distance in the opposite direction to the pressing direction from the pressing position shown in Figures 4 and 7. The regulating member 301 is a second holding member that holds the steer roller 205 in the intermediate position shown in Figures 6 and 9, which is moved a second distance shorter than the first distance in the opposite direction to the pressing direction from the pressing position.

[0046] Therefore, the first pressing force F1 that presses the belt 201 when the steer roller 205 is held in the released position by the steer lock arm 222 is smaller than the second pressing force F2 that presses the belt 201 when the steer roller 205 is held in the intermediate position by the regulating member 301 (F1 <F2)。

[0047] Incidentally, the pressing force F that presses the belt when the steer roller 205 is not held by either the steer lock arm 222 or the regulating member 301 is greater than the first pressing force F1 and the second pressing force F2. Therefore, the second pressing force F2 that the steer roller 205 presses the belt 201 in the intermediate position is less than the pressing force F that the steer roller 205 presses the belt 201 in the pressed position, and greater than the first pressing force F1 that the steer roller 205 presses the belt 201 in the released position.

[0048] Figures 5 and 8 are perspective and cross-sectional views of the fixing device 200, illustrating the state in which the tension of the steer roller 205 is released by the steer lock arm 222. Here, the state in which the tension of the steer roller 205 is released by the steer lock arm 222 is the state in which the pressing force of the steer roller 205 against the belt 201 is the first pressing force F1, which is the smallest.

[0049] Steer lock arms 222, which serve as first retaining members, are held at both ends of the longitudinal direction of the steer frame 213. The steer lock arms 222 are formed from wire springs with a wire diameter of 1 mm and are rotatably mounted to the steer frame 213 in the direction of the arrow shown in Figure 5. A mounting surface 221a for attaching the steer lock arms 222 is formed in the steer bearing section 221. The mounting surface 221a is formed on the side of the steer bearing section 221 facing the belt 201. With the steer roller 205 pressed in the opposite direction to the pressing direction by the spring 211, the steer lock arms 222 are placed on the mounting surface 221a as shown in Figure 5. As a result, the steer lock arms 222 hold the steer roller 205 in a released position, retracted from the pressed position that suspends the belt 201 with a predetermined tension. This reduces the contact force (pressing force) of the steer roller 205 on the belt 201, making it possible to weaken the tension on the belt 201.

[0050] In this embodiment, the steer lock arm 222 is attached to the mounting surface 221a, thereby holding the steer roller 205 in a released position, which is moved in the direction opposite to the pressing direction by a first distance (in this case, 5 mm) from the pressing position. This separates the steer roller 205 from the belt 201, and the pressing force of the steer roller 205 against the belt 201 can be set to the smallest first pressing force F1. This makes it easier to remove and install the belt 201, thereby improving the workability of replacing the belt 201.

[0051] Figures 6 and 9 are perspective and cross-sectional views of the fixing device 200, illustrating the state in which the tension of the steer roller 205 is released by the regulating member 301. Here, the state in which the tension of the steer roller 205 is released by the regulating member 301 is a state in which the pressing force of the steer roller 205 against the belt 201 is less than the pressing force F and greater than the first pressing force F1, resulting in a second pressing force F2.

[0052] The regulating member 301, acting as a second retaining member, is provided on both sides of the steer roller 205 in the longitudinal direction, in the outer region in the width direction perpendicular to the rotation direction of the belt 201. Specifically, the regulating member 301 is detachably attached to the lower stay 303. The lower stay 303 is a component of the housing frame 300 of the fixing device 200. The regulating member 301 contacts the steer bearing portion 221 at the intermediate position, thereby restricting the movement of the steer roller 205 in the pressing direction.

[0053] Figure 9 is a cross-sectional view of the fixing device 200 illustrating the state in which the tension of the steer roller 205 is released by the restricting member 301. The restricting member 301 is a sheet metal part with a bend of about 2 mm in thickness, and is detachably fixed to the lower stay 303 with fixing means such as screws. When attaching the restricting member 301, the restricting member 301 is pressed against the outer shape of the steer bearing portion 221, and the position is fixed by tightening screws to the lower stay 303 while the steer bearing portion 221 is swung in the opposite direction to the pressing direction. The fixed restricting member 301 pushes the steer bearing portion 221 in the opposite direction to the pressing direction against the force of the spring 211, thereby reducing the tension on the belt 201.

[0054] In this embodiment, with the regulating member 301 fixed to the lower stay 303, the steer roller 205 is held in an intermediate position, moved in the direction away from the pressing position by a second distance (1 mm in this case) which is smaller than the first distance. As a result, the second pressing force F2 at which the steer roller 205 presses the belt 201 in the intermediate position is smaller than the pressing force F at which the steer roller 205 presses the belt in the pressing position, and is larger than the first pressing force F1 at which the steer roller 205 presses the belt in the release position, thereby reducing the tension on the belt 201 by about 4N.

[0055] Furthermore, oil is applied to the inner circumferential surface of the belt 201. The oil is set to have a kinematic viscosity of 50-500 CST at high temperatures to satisfy the desired sliding performance at high temperatures during fixing operations. When the image forming apparatus is transported from the manufacturer to the user, the aforementioned heating unit 210 does not operate, so the viscosity of the oil increases. As a result, the heating roller 204 and the steer roller 205 that suspend the belt 201 come into close contact with the belt 201 via the oil. The area in which the belt 201 contacts the heating roller 204 is larger than the area in which the belt 201 contacts the steer roller 205. Therefore, the restraining force is greater at the heating roller 204 than at the steer roller 205.

[0056] In the separated state where the belt 201 and the pressure roller 202 are separated, the contact force between the pad 203 and the belt 201 weakens. Therefore, in the separated state described above, the widthwise position of the belt 201 is held by the heating roller 204 and the steer roller 205. When the image forming apparatus is subjected to vibration during transport, the heating roller 204 and the steer roller 205 also vibrate and move in the widthwise direction. At this time, the belt 201 vibrates while being held by the heating roller 204, which has a large restraining force, but is affected by the restraining force of the steer roller 205, causing a relative positional displacement with respect to the heating roller 204.

[0057] By holding the steer roller 205 in an intermediate position with the restricting member 301, the pressing force of the steer roller 205 against the belt 201 can be reduced compared to the pressing position and increased compared to the release position. Therefore, it becomes possible to suppress the displacement of the belt 201 caused by the difference in restraining force mentioned above. However, if the steer roller 205 is completely separated from the belt 201, the holding force of the heating roller 204 alone would have to withstand vibrations during transport, which may actually reduce the effect of suppressing displacement. Therefore, in order to improve the ease of replacing the belt 201 as described above, the amount of movement of the steer bearing section 221 when the pressure is released by the steer lock arm 222 is set to be smaller than the amount of movement of the steer bearing section 221 when the pressure is released by the steer lock arm 222.

[0058] The product is transported with the tension on the belt 201 reduced by the restricting member 301, and when the product is installed, the screws are loosened and the restricting member 301 is removed from the lower stay 303, thereby restoring the tension on the belt 201 to its original state when the product is in operation.

[0059] With the above configuration, when replacing the belt 201, the steer roller 205 is moved in the opposite direction using the steer lock arm 222, and when transporting the product, the stabilizing member 301 is used to move the steer roller 205 in the opposite direction. This makes it possible to provide a fixing device 200 that can suppress displacement of the belt 201 due to vibration during transport and allows for easy replacement of the belt 201.

[0060] [Example 2] An image forming apparatus equipped with a fixing device according to Example 2 will now be described. Since the general configuration of the fixing device and the image forming apparatus is the same as in the previously described example, components with equivalent functions are denoted by the same reference numerals, and their descriptions are omitted here.

[0061] Using Figures 10 to 11, the movement configuration of the steer roller 205, which is one of the belt suspension members in this embodiment, will be explained. When the fixing device 200 is removed from the image forming apparatus 100 and operations are performed on the housing, such as removing the cover, the pressure roller 202 is moved to the separated position shown in Figure 2, separated from the belt 201.

[0062] <Retaining member> The fixing device 200 includes a steer lock arm 222 and a release screw 304. The steer lock arm 222 is a first retaining member and is the same as in the embodiment described above, so its description is omitted here. The release screw 304 is a second retaining member that holds the steer roller 205 at an intermediate position, which is moved from the pressing position by a second distance shorter than the first distance in the opposite direction to the pressing direction.

[0063] In the embodiment described above, a regulating member 301 was exemplified as the second retaining member, which is detachably attached to the housing frame 300 of the fixing device 200, abuts against the steer bearing portion 221 at an intermediate position, and restricts the movement of the steer roller 205 in the pressing direction. However, the second retaining member is not limited to this.

[0064] In this embodiment, a release screw 304 is provided as a second retaining member. The release screw 304 is removably attached to the steer frame 213 and, by tightening it into the steer frame 213 which supports the steer roller 205 so that it can move, moves the position of the steer roller 205 in the opposite direction to the pressing direction.

[0065] The state in which the tension of the steer roller 205 is released by the steer lock arm 222 is the same as in the previously described embodiment (see Figures 5 and 8), so the explanation is omitted here.

[0066] Figures 10 and 11 are perspective and cross-sectional views of the fixing device 200, illustrating the state in which the tension of the steer roller 205 is released by the release screw 304. Here, the state in which the tension of the steer roller 205 is released by the release screw 304 is a state in which the pressing force of the steer roller 205 against the belt 201 is less than the pressing force F and greater than the first pressing force F1, resulting in a second pressing force F2.

[0067] The second retaining member, the release screw 304, is provided on both sides of the longitudinal direction of the steer roller 205 in the outer region in the width direction perpendicular to the rotation direction of the belt 201. Specifically, the release screw 304 is attached to the steer bearing section 221 that supports both ends of the steer roller 205 (steer roller shaft 223). By tightening the release screw 304 onto the steer frame 213, the steer bearing section 221 is moved in the opposite direction to the pressing direction, and in the released position, the movement of the steer roller 205 in the pressing direction is restricted.

[0068] The fixing device 200 covers the belt 201 and the steer roller 205 that suspends the belt 201 with a fixing cover 250. As mentioned above, when the tension is released by the steer lock arm 222 and the belt 201 is replaced, the fixing cover 250 is opened to access the inside.

[0069] The fixing cover 250 is formed from a cover portion 251 made of resin and a metal plate portion 252 that holds the cover portion 251. Openings 302 are formed in the cover portion 251 and the plate portion 252 at positions corresponding to each release screw 304, and the release screws 304 can be attached from outside the fixing device 200 by connecting to the openings 302. In other words, when releasing the tension of the steer roller 205 with the release screws 304, it is not necessary to open the fixing cover 250.

[0070] Figure 11 is a cross-sectional view of the fixing device 200 to illustrate the state in which the tension of the steer roller 205 is released by the release screw 304, and shows a cross-section cut along the central axis of the release screw 304 as viewed from the direction of arrow A in Figure 10. The release screw 304 has a body length of about 30 mm and is a stepped screw with a small diameter section at the tip and a large diameter section at the screw head, separated by a stepped portion. When installing the release screw 304, the release screw 304 is passed through the through hole 221b provided in the steer bearing portion 221, and the small diameter section of the release screw 304 is fastened to the tapped hole 213a provided in the steer frame 213. By fastening the release screw 304 to the tapped hole 213a, the screw head of the release screw 304 pushes the steer bearing portion 221 in the opposite direction to the pressing direction against the force of the spring 211, thereby weakening the tension on the belt 201.

[0071] In this embodiment, the release screw 304 is tightened until the stepped portion of the release screw abuts against the steer frame 213, thereby holding the steer roller 205 in an intermediate position, which is moved in the direction of a second distance (1 mm in this case) that is smaller than the first distance from the pressing position. As a result, the second pressing force F2 that the steer roller 205 presses against the belt 201 at the intermediate position is smaller than the pressing force F that the steer roller 205 presses against the belt at the pressing position, but larger than the first pressing force F1 that the steer roller 205 presses against the belt at the release position, thereby reducing the tension on the belt 201 by about 4 N.

[0072] By holding the steer roller 205 in an intermediate position with the release screw 304, the pressing force of the steer roller 205 on the belt 201 can be reduced compared to the pressing position and increased compared to the release position. Therefore, it is possible to suppress the displacement of the belt 201 caused by the difference in restraining force between the heating roller 204 and the belt 201. However, if the steer roller 205 is completely separated from the belt 201, the belt must withstand vibrations during transport with only the holding force of the heating roller 204, which may actually reduce the effect of suppressing displacement. Therefore, to improve the ease of replacing the belt 201 as described above, the amount of movement of the steer bearing section 221 when the pressure is released by the steer lock arm 222 is set to be smaller than the amount of movement of the steer bearing section 221 when the pressure is released by the steer lock arm 222.

[0073] The tension on the belt 201 is reduced by the release screw 304 during product transport, and the tension on the belt 201 can be restored to its original state when the product is in operation by loosening the release screw 304 and removing it from the tapped hole 213a during product installation. The release screw 304 may be completely removed during product installation, or it may be left inside the product if it is removed from the tapped hole 213a. If it is left inside, it is desirable to provide measures, for example on the fixing cover 250, to prevent the release screw 304 from falling from its designated position.

[0074] With the above configuration, when replacing the belt 201, the steer roller 205 is moved in the opposite direction using the steer lock arm 222, and when transporting the product, the steer roller 205 is moved in the opposite direction using the release screw 304. This makes it possible to provide a fixing device 200 that can suppress displacement of the belt 201 due to vibration during transport and allows for easy replacement of the belt 201.

[0075] [Other examples] In the embodiments described above, a fixing device was exemplified as a fixing device that fixes an unfixed toner image formed on a recording material to the recording material. However, the present invention is not limited to such a fixing device, and can also be applied to image heating devices such as gloss-enhancing devices that improve the glossiness of an image formed on a recording material. Furthermore, although a fixing device mounted on an image forming apparatus such as a printer or copier was exemplified as a fixing device, the present invention is not limited to this, and can also be applied to image heating devices not mounted on an image forming apparatus, such as an image heating device mounted on a device that can be optionally attached to an image forming apparatus.

[0076] Furthermore, in the embodiments described above, a fixing device was exemplified that uses an endless belt to which tension is applied by a tension-applying member to fix an unfixed toner image formed on a recording material to the recording material. However, the present invention is not limited to such fixing devices. For example, it may be a belt conveying device that uses an endless belt to which tension is applied by a tension-applying member to carry and convey a recording material. Alternatively, it may be a belt conveying device that uses an endless belt to which tension is applied by a tension-applying member to carry and convey an image. By applying the present invention to these belt conveying devices, that is, by configuring the belt conveying device to have the endless belt described above, a tension-applying member, a first holding member, and a second holding member, similar effects can be expected.

[0077] Furthermore, in the embodiments described above, the tension-applying member is an example in which it is a steering roller that adjusts the position of the belt 201 in the width direction perpendicular to the rotation direction of the belt 201, and is also a tension roller that applies tension to the belt 201, but the invention is not limited to this. The tension-applying member may simply be a tension roller that applies tension to the belt 201.

[0078] Furthermore, in the embodiment described above, the image forming unit uses four stations as image forming units, but the number of stations used is not limited and can be set as appropriate as needed.

[0079] Furthermore, although a laser scanner was used as the exposure means in the above-described embodiment, the invention is not limited to this, and an LED array or the like may be used instead.

[0080] Furthermore, although a printer was used as an example of an image forming apparatus in the embodiments described above, the present invention is not limited thereto. For example, other image forming apparatuses such as photocopiers and facsimile machines, or other image forming apparatuses such as multifunction devices that combine these functions, may also be used. Alternatively, an image forming apparatus that uses a recording material carrier and sequentially overlays and transfers toner images of each color onto the recording material carried on the recording material carrier may also be used. Similar effects can be obtained by applying the present invention to these image forming apparatuses or fixing devices used in image forming apparatuses. [Explanation of Symbols]

[0081] N...nippet part P... Recording material 100 ...Image forming apparatus 110 ...Image forming unit 200 ... Fixing device 201... belt 202... Pressure roller 203 ... pad 204 ...Heating roller 205... Steerola 207 ... Sliding sheet 208... Oil supply roller 210 ... Heating unit 211 ... Spring 213... Steer frame 221 ... Steering bearing section 222... Steering lock arm 223... Steerola axis 250 ... Fixing cover 251 ...Cover part 252...Plate part 300 ... enclosure frame 301 ... Regulating member 302 ... opening 303 ... Lower stay 304 ...Release screw

Claims

1. An endless belt rotatably suspended by multiple suspension members, A pressing member that contacts the outer circumferential surface of the endless belt, A nip-forming member that contacts the inner circumferential surface of the endless belt at a position opposite to the pressurizing member and forms a nip portion between the endless belt and the pressurizing member, A tension-applying member that rotatably suspends the endless belt and applies tension to the endless belt by pressing it, The tension-applying member is supported so as to be able to move between a pressing position that presses the endless belt and a release position that releases the pressure on the endless belt. A first holding member holds the tension-applying member at the release position, which is obtained by moving the tension-applying member a first distance in the direction opposite to the pressing direction from the pressing position, A fixing device characterized by having a second holding member that holds the tension-applying member at an intermediate position obtained by moving the tension-applying member from the pressing position by a second distance shorter than the first distance in the opposite direction to the pressing direction.

2. The fixing device according to claim 1, characterized in that the tension-applying member has a pivot point at one end or the center in the width direction perpendicular to the rotation direction of the endless belt, and rotates with respect to the endless belt around the pivot point to generate a tension difference between one side and the other side in the width direction of the endless belt, thereby controlling the position of the endless belt in the width direction.

3. The fixing device according to claim 1, characterized in that the tension-applying member is a tension roller that is biased by a spring and applies a predetermined tension to the endless belt.

4. The fixing device according to claim 1, wherein the second holding member is provided on both sides of the tension-applying member in an outer region in the width direction perpendicular to the rotation direction of the endless belt, and contacts the tension-applying member to restrict the movement of the tension-applying member in the pressing direction.

5. The fixing device according to claim 4, characterized in that the second retaining member is a screw that is detachably attached to a support member that supports the tension-applying member so that it can move, and which contacts the tension-applying member and moves the tension-applying member to the intermediate position by tightening it to the support member, thereby restricting the movement of the tension-applying member.

6. The fixing device according to claim 4, characterized in that the second holding member is a restricting member that is detachably attached to the housing frame of the fixing device and contacts the tension-applying member at the intermediate position to restrict the movement of the tension-applying member.

7. The fixing device according to claim 1, characterized in that the first pressing force that presses the endless belt when the tension-applying member is held in the release position by the first holding member is smaller than the second pressing force that presses the endless belt when it is held in the intermediate position by the second holding member.

8. The endless belt is rotatably suspended and has a heating rotating body that contacts the inner circumferential surface of the endless belt to heat the endless belt, The fixing device according to claim 1, characterized in that the area in contact between the heating rotating body and the endless belt is larger than the area in contact between the tension-applying member and the endless belt.

9. The fixing device according to claim 8, characterized in that it has a supply member that rotatably suspends the endless belt and contacts the inner circumferential surface of the endless belt to supply a lubricant.

10. An image forming unit that forms an image on a sheet, An image forming apparatus comprising a fixing device according to any one of claims 1 to 9 for fixing an image formed on a sheet.

Images