Fixing device

Abstract

A fixing device includes a belt member, a heating roller that tensions the belt member, a turning roller that tensions the belt member, and a cover member. The turning roller controls the position of the belt member with respect to the rotational axis direction by being inclined with respect to the rotational axis direction of the heating roller. The cover member is provided with a gap with the belt member so as to cover a portion of an outer side of the belt member. When the deflection roller is parallel to the heating roller, the distance between the cover member and the belt member in a first tension region tensioned by the deflection roller is greater than the distance between the cover member and the belt member in a second tension region tensioned by the heating roller.

Description

Technical Field

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

[0002] An image forming apparatus includes a fixing device that fixes a toner image carried on a recording material to the recording material. In the fixing device, the toner image carried on the recording material is conveyed while being heated in a nip formed by a heating member and a nip forming member. JP 2005-31562 A discloses a configuration in which a partition plate is provided between a housing of the fixing device and the heating member to enhance the heat insulation effect of the fixing device.

[0003] Here, as described in JP 2005-31562 A, by providing a partition plate between the heating component and the housing, the heat radiation of the heating component can be suppressed to a certain extent. In order to achieve power saving of the fixing device, it is preferable to enhance the heat radiation suppression effect of the heating component. For this reason, it is preferable to make the partition plate close to the heating component. In the configuration described in JP 2005-31562 A, the heating component is a roller. However, a configuration in which the heating component is a belt component is also conventionally known.

[0004] The belt component is tensioned by a plurality of tension rollers. In addition, in the case where the heating component is a belt component, in order to control the position of the belt component in the direction of the rotation axis of the tension roller, in most cases, one of the plurality of tension rollers is tilted relative to the other tension rollers. The roller tilted in this way to control the position of the belt component is called a steering roller. As described above, in order to enhance the heat radiation suppression effect of the heating component, it is preferred to make the partition plate close to the heating component. However, in the case where the heating component is a belt component, the steering roller is tilted. Therefore, if the partition plate is too close to the belt component, the belt component and the partition plate will interfere with each other when the steering roller is tilted. Summary of the invention

[0005] The present invention provides a configuration capable of suppressing heat radiation from a belt member even in a configuration employing a belt member in a fixing device.

[0006] According to one aspect of the present invention, there is provided a fixing device for fixing a toner image to a recording material by heating a toner image carried on the recording material, the fixing device comprising: a rotatable endless belt member; a heating roller, the heating roller being arranged inside the belt member and configured to tension the belt member and heat the belt member; a steering roller, the steering roller being arranged inside the belt member and configured to tension the belt member together with the heating roller and control the position of the belt member relative to the rotation axis direction by tilting relative to the rotation axis direction of the heating roller; a gripping portion forming member, the gripping portion forming member being in contact with the outer peripheral surface of the belt member and configured to form a gripping portion for gripping and conveying the recording material between the gripping portion forming member and the belt member; and a covering member, the covering member being arranged to have a gap with the belt member so as to cover a part of the outer side of the belt member. The belt member has a region whose distance from the covering member changes when the steering roller is tilted relative to the heating roller, and the region includes a first tensioning region tensioned by the steering roller and a second tensioning region tensioned by the heating roller. In the case where the deflection roller is parallel to the heating roller, the distance between the covering member and the belt member in the first tensioning area is greater than the distance between the covering member and the belt member in the second tensioning area.

[0007] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus according to the embodiment.

[0009] Figure 2 is a schematic cross-sectional view showing a configuration of a fixing device according to the embodiment.

[0010] Figure 3A is a schematic diagram illustrating a case where one end of a steering roller is tilted upward in a cross-sectional view of a fixing device according to an embodiment.

[0011] Figure 3B : is a schematic diagram showing a case where the other end of the steering roller is tilted downward in a cross-sectional view of the fixing device according to the embodiment.

[0012] Figure 4 is a schematic cross-sectional view showing a configuration in which a covering member is provided near the fixing device according to the embodiment.

[0013] Figure 5 3 is a graph showing the relationship between the distance between the fixing belt and the covering member and the amount of power reduction.

[0014] Figure 6 TABLE 2 is a table showing the relationship between whether or not the fixing belt and the covering member are in contact with each other and the amount of power reduction in each of the comparative example and the example.

[0015] Figure 7 Graph showing the relationship between the coverage ratio of the fixing belt by the covering member and the amount of power reduction. DETAILED DESCRIPTION

[0016] Will refer to Figures 1 to 7 First, reference will be made to the embodiment. Figure 1 A schematic configuration of an image forming apparatus according to the present embodiment is described.

[0017] Image forming equipment

[0018] The image forming apparatus 1 is an electrophotographic full-color printer, which includes four image forming units Pa, Pb, Pc, and Pd arranged to correspond to four colors of yellow, magenta, cyan, and black. In the present embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in a tandem type along the rotation direction of the intermediate transfer belt 204 to be described below. The image forming apparatus 1 forms a toner image (image) on a recording material according to an image signal from an image reading unit (original reading device) 2 connected to the image forming apparatus body 3 or a host device such as a personal computer communicably connected to the image forming apparatus body 3. Examples of the recording material include sheets such as paper, plastic film, and cloth.

[0019] The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus body 3. The image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original, and an image is formed on a CCD sensor 24 via an optical system component 23 such as a lens. Such an optical system unit converts the original into an electric signal data string for each line by scanning the original in the direction of an arrow. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus body 3, and the control unit 30 performs image processing according to each image forming unit to be described below. The control unit 30 also receives an external input as an image signal from an external host device such as a print server.

[0020] The image forming apparatus body 3 includes a plurality of image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the above-mentioned image signal. That is, the image signal is converted into a laser beam subjected to pulse width modulation (PWM) by the control unit 30. A polygonal mirror scanner 31 serving as an exposure unit scans a laser beam corresponding to the image signal. Then, the photosensitive drums 200a to 200d serving as image bearing members of the image forming units Pa to Pd are irradiated with the laser beam.

[0021] It should be noted that Pa, Pb, Pc, and Pd represent an image forming unit for yellow (Y), an image forming unit for magenta (M), an image forming unit for cyan (C), and an image forming unit for black (Bk), respectively, and form images of corresponding colors. Since the image forming units Pa to Pd are substantially the same, the image forming unit Pa for yellow (Y) will be described in detail below, and the description of the other image forming units will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal as described below.

[0022] The charging roller 201a used as a primary charger charges the surface of the photosensitive drum 200a to a predetermined potential in preparation for forming an electrostatic latent image. An electrostatic latent image is formed on the surface of the photosensitive drum 200a charged to a predetermined potential by a laser beam from the polygonal mirror scanner 31. The developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a performs discharge from the back side of the intermediate transfer belt 204, applies a primary transfer bias having a polarity opposite to that of the toner, and transfers the toner image on the photosensitive drum 200a to the intermediate transfer belt 204. The surface of the photosensitive drum 200a is cleaned by the cleaner 207a after the transfer.

[0023] In addition, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming unit, and the toner images of the corresponding colors formed by the corresponding image forming units are sequentially transferred in the order of Y, M, C, and Bk, and four-color images are formed on the surface thereof. Then, the toner image that has passed through the image forming unit Pd for Bk located on the most downstream side in the rotation direction of the intermediate transfer belt 204 is conveyed to the secondary transfer portion including a pair of secondary transfer rollers 205 and 206. Then, in the secondary transfer portion, a secondary transfer electric field having a polarity opposite to that of the toner image on the intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image to the recording material.

[0024] The recording material is accommodated in the cartridge 9, and the recording material fed from the cartridge 9 is conveyed to, for example, a registration portion 208 including a pair of registration rollers, and stands by at the registration portion 208. Subsequently, the registration portion 208 conveys the recording material to the secondary transfer portion at a timing controlled to align the toner image on the intermediate transfer belt 204 with the paper.

[0025] The recording material to which the toner image has been transferred by the secondary transfer portion is conveyed to the fixing device 8, and the toner image carried on the recording material is fixed to the recording material by heating and pressurizing in the fixing device 8. The recording material that has passed through the fixing device 8 is discharged to the sheet discharge tray 7. It is to be noted that, in the case where images are to be formed on both surfaces of the recording material, when the toner image is transferred and fixed to the first surface (front surface) of the recording material, the front surface and the rear surface of the recording material are reversed via the reverse conveying portion 10, the toner image is transferred and fixed to the second surface (rear surface) of the recording material, and the recording material is placed on the sheet discharge tray 7.

[0026] It is to be noted that, as described above, the control unit 30 controls the entire image forming apparatus 1. In addition, the control unit 30 can perform various settings and the like based on input from the operation unit 4 included in the image forming apparatus 1. The control unit 30 includes a central processing unit (CPU), a read-only memory (ROM), and a random access memory (RAM). The CPU controls each unit while reading a program corresponding to a control process stored in the ROM. In addition, work data and input data are stored in the RAM, and the CPU performs control based on the above-mentioned program and the like with reference to the data stored in the RAM.

[0027] Fixing device

[0028] Next, we will refer to Figure 2 The configuration of the fixing device 8 according to the present embodiment is described. Figure 2 is a cross-sectional view schematically showing a schematic configuration of the fixing device 8. Figure 2 In the embodiment, a cover member 500 to be described below is omitted. In the present embodiment, a belt heating type fixing device using an endless belt is used. Figure 2 , the X direction indicates the conveying direction of the recording material P, the Y direction indicates the width direction intersecting (orthogonal in the present embodiment) the conveying direction of the recording material P, and the Z direction indicates the pressing direction of the pressing roller 305 to be described below. These directions are orthogonal to each other. In addition, one side in the width direction (Y direction) is the front side of the image forming apparatus 1 (for example, the side where the operation unit 4 is provided and operated by the user). On the other hand, the other side in the width direction is the rear side of the image forming apparatus 1.

[0029] The fixing device 8 includes a heating unit 300 having a fixing belt 301 serving as an endless rotatable belt member and a pressing roller 305 serving as a nip forming member and a pressing rotating member that contacts the fixing belt 301 and forms a nip N with the fixing belt 301 .

[0030] The heating unit 300 includes the fixing belt 301 described above, a fixing pad 303 serving as a pad member, a heating roller 307, and a steering roller 308. The pressure roller 305 is also a driving rotating member that rotates in contact with the outer peripheral surface of the fixing belt 301 to apply a driving force to the fixing belt 301.

[0031] The fixing belt 301 used as a heating component (fixing component) and a rotating component has thermal conductivity, heat resistance, etc., and has a thin cylindrical shape. In the present embodiment, the fixing belt 301 has a three-layer structure in which a base layer, an elastic layer on the periphery of the base layer, and a release layer on the periphery of the elastic layer are formed. In addition, polyimide resin (PI) is used as a material for a base layer with a thickness of 80 μm, silicone rubber is used for an elastic layer with a thickness of 300 μm, and PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer resin) is used as a fluororesin for a release layer with a thickness of 30 μm. The fixing belt 301 is tensioned by a fixing pad 303, a heating roller 307, and a steering roller 308.

[0032] The fixing pad 303 serving as a contact member is disposed inside the fixing belt 301 so as to face the pressure roller 305 across the fixing belt 301 and to contact the inner peripheral surface of the fixing belt 301. The fixing pad 303 forms a clamping portion N for clamping and conveying a recording material between the fixing belt 301 and the pressure roller 305. In the present embodiment, the fixing pad 303 is a generally plate-shaped member that is long in the width direction of the fixing belt 301 (a longitudinal direction intersecting the rotation direction of the fixing belt 301 and the rotation axis direction of the heating roller 307). The clamping portion N is formed by pressing the fixing pad 303 against the pressure roller 305 across the fixing belt 301. As a material for the fixing pad 303, a liquid crystal polymer (LCP) resin is used.

[0033] The fixing pad 303 is supported by a stay 302 serving as a supporting member provided inside the fixing belt 301. That is, the stay 302 is provided on the side of the fixing pad 303 opposite to the pressure roller 305 to support the fixing pad 303. The stay 302, which is a reinforcing member having rigidity and having a long length in the longitudinal direction of the fixing belt 301, contacts the fixing pad 303 to support the fixing pad 303 from the back. That is, when the fixing pad 303 is pressed against the pressure roller 305, the stay 302 applies strength to the fixing pad 303 to ensure the pressure in the nip N.

[0034] A lubricating sheet (not shown) is interposed between the fixing pad 303 and the fixing belt 301. Lubricant is applied to the inner peripheral surface of the fixing belt 301 to smoothly slide the fixing belt 301 relative to the fixing pad 303 covered with the lubricating sheet. As the lubricant, silicone oil is used.

[0035] The heating roller 307 is provided inside the fixing belt 301 to tension the fixing belt 301 together with the fixing pad 303 and the steering roller 308. The heating roller 307 is formed into a cylindrical shape by metal such as aluminum or stainless steel, and a halogen heater 306 serving as a heating portion for heating the fixing belt 301 is provided inside the heating roller 307. Then, the heating roller 307 is heated to a predetermined temperature by the halogen heater 306.

[0036] In the present embodiment, the heating roller 307 is formed of, for example, a stainless steel pipe having a thickness of 1 mm. One or more halogen heaters 306 may be installed. It is to be noted that the heating portion is not limited to the halogen heater, and may be other heaters capable of heating the roller 307, such as a carbon heater. The fixing belt 301 is heated by the heating roller 307 heated by the halogen heater 306, and is controlled to a predetermined target temperature corresponding to the type of recording material based on the temperature detected by the thermistor (not shown).

[0037] The steering roller 308 is provided inside the fixing belt 301, tensions the fixing belt 301 together with the fixing pad 303 and the heating roller 307, and rotates as the fixing belt 301 rotates. The steering roller 308 is tilted relative to the rotation axis direction (width direction or longitudinal direction) of the heating roller 307 to control the position (displacement position) of the fixing belt 301 relative to the rotation axis direction. That is, the steering roller 308 has a pivot center at the center or one end of the steering roller 308 along the rotation axis direction (longitudinal direction), and swings around the pivot center to be tilted relative to the longitudinal direction of the heating roller 307. As a result, a tension difference is generated between one side and the other side of the fixing belt 301 along the longitudinal direction, thereby causing the fixing belt 301 to move in the longitudinal direction.

[0038] The fixing belt 301 may be displaced toward one end during rotation depending on the accuracy of the outer diameter of the roller that tensions the fixing belt 301, the alignment accuracy between the rollers, etc. Therefore, such displacement is controlled by the steering roller 308. The steering roller 308 may be swung by a driving source such as a motor, or may be configured to be swung by automatic centering.

[0039] In the present embodiment, the steering roller 308 is also a tension roller that is biased by a spring supported by the frame of the heating unit 300 to apply a predetermined tension to the fixing belt 301. In addition, the steering roller 308 is formed into a cylindrical shape by a metal such as aluminum or stainless steel. In the present embodiment, the steering roller 308 is formed by a hollow stainless steel pipe with an outer diameter of 20 mm. A rubber material or the like may be provided on the surface of the steering roller 308 in order to increase the clamping force relative to the fixing belt 301.

[0040] The pressure roller 305 used as a clamping portion forming member rotates in a manner of contacting the outer peripheral surface of the fixing belt 301 to apply a driving force to the fixing belt 301. In addition, the pressure roller 305 is pressed against the fixing belt 301 to form a clamping portion N between the fixing belt 301 and the pressure roller 305. In the present embodiment, the pressure roller 305 is a roller that forms an elastic layer on the outer periphery of the shaft and a releasable layer on the outer periphery of the elastic layer. In addition, stainless steel with a diameter of 72 mm is used for the shaft, conductive silicone rubber with a thickness of 8 mm is used for the elastic layer, and PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer resin) is used as a fluororesin with a thickness of 100 μm for the releasable layer. The pressure roller 305 is rotatably supported by a fixing frame (not shown) of the fixing device 8 in a manner that a gear is fixed to one end thereof, and is connected to a motor M used as a pressure roller driving source via the gear to be rotationally driven.

[0041] In the fixing device 8 configured as described above, the toner image is heated and the recording material P carrying the toner image is conveyed in a nipped state in the nip portion N formed between the fixing belt 301 and the pressure roller 305. Then, the toner image is fixed to the recording material P. Therefore, the fixing device 8 needs to have both a heating and pressing function and a function of conveying the recording material P. The pressure roller 305 is pressed against the fixing pad 303 via the fixing belt 301 by a driving source (not shown). In the present embodiment, the pressing force (NF) in the nip portion N for forming an image is set to 1600N, the length of the nip portion N in the X direction (conveying direction) is set to 24.5mm, and the length of the nip portion N in the Y direction (width direction) is set to 326mm.

[0042] In addition, a discharge unit 350 for discharging the recording material P that has passed through the clamping portion N to the outside of the fixing device 8 is arranged downstream of the clamping portion N along the conveying direction of the recording material P. In the discharge unit 350, an air nozzle 401, a sheet discharge roller pair 400a, and a lower separation guide 400b are provided. The air nozzle 401 blows out air (compressed air) for separating the recording material P from the fixing belt 301. Specifically, the air nozzle 401 is arranged downstream of the clamping portion N along the conveying direction of the recording material (hereinafter may be simply referred to as "conveying direction") and is arranged above the clamping portion N along the vertical direction to blow air upstream of the conveying direction and downward along the vertical direction. Then, the recording material P is separated from the fixing belt 301 by blowing air to the vicinity of the front end of the recording material P after the recording material P passes through the clamping portion N.

[0043] The lower separation guide 400b is disposed downstream of the nip N in the conveying direction of the recording material and below the nip N in the vertical direction, and its distal end faces the pressure roller 305 near the nip N. Then, when the recording material P is attached to the pressure roller 305, the lower separation guide 400b separates the recording material P from the pressure roller 305. In addition, the lower separation guide 400b supports the lower surface of the recording material P discharged from the nip N and guides the recording material P to the sheet discharge roller pair 400a. The sheet discharge roller pair 400a discharges the recording material P discharged from the nip N to the outside of the fixing device 8. In the present embodiment, the sheet discharge roller pair 400a is disposed about 40 mm downstream of the nip N in the conveying direction.

[0044] Furthermore, a guide unit 94 for guiding the recording material P to the nip N and a detection sensor 95 for detecting the recording material P just before the nip N are provided upstream of the nip N of the fixing device 8 in the conveying direction. The control unit 30 detects the timing at which the recording material P enters the nip N using the detection sensor 95.

[0045] Tilt of steering roller

[0046] Will refer to Figure 3A and Figure 3B The tilt of the steering roller 308 when the shift position of the fixing belt 301 is controlled by the steering roller 308 (shift control) is described. In this embodiment, the steering roller 308 is tilted about the pivot center. Figure 2 , Figure 3A and Figure 3B The steering roller 308 is tilted in the vertical direction as shown to perform the shift control. Figure 3A When the steering roller 308 is tilted upward at one end in the Y direction as shown in FIG. Figure 3B The other end of the Y direction is shown to be inclined downward. Then, the steering roller 308 is alternately repeated Figure 3A and Figure 3B The fixing belt 301 is tilted in a state of being in a state, thereby controlling the shift position of the fixing belt 301.

[0047] Covering parts

[0048] As described above, in order to save power in the fixing device 8, it is preferable to suppress heat radiation from the fixing belt 301. Figure 4As shown, the fixing device 8 according to the present embodiment includes a covering member 500 as a member for suppressing such heat radiation. The covering member 500 is arranged to cover a portion of the outer side of the fixing belt 301 in a manner having a gap with the fixing belt 301. The covering member 500 in the present embodiment uses a liquid crystal polymer (LCP) with a thickness of 2 mm. The covering member 500 is a plate-like member formed by a resin member or a metal member having heat resistance. Such a covering member 500 may be a resin or foam member other than LCP, or may be a metal member such as iron, stainless steel or copper. In addition, a reflective sheet or the like may be attached to the side of the covering member 500 facing the fixing belt 301.

[0049] like Figure 4 As shown, the covering member 500 is arranged to extend from the heating roller facing portion (second portion) L1 facing the first area (second tensioning area) α of the fixing belt 301 stretched by the heating roller 307 to the turning roller facing portion (first portion) L2 facing the second area (first tensioning area) β of the fixing belt 301 stretched by the turning roller 308. The fixing belt 301 has a third area (third tensioning area) γ between the first area α and the second area β in the rotation direction of the fixing belt 301. The portion (third portion) L3 facing the third area γ is a portion connecting the heating roller facing portion L1 and the turning roller facing portion L2 to each other. The covering member 500 is arranged on the heating roller facing portion L1, the portion L3 facing the third area γ, and the turning roller facing portion L2. The covering member 500 in this embodiment is arranged so that when the fixing device 8 is observed from above in the vertical direction, the fixing device 8 is not visible due to the covering member 500. In the first region α, the covering member 500 may be formed in an arc shape parallel to the arc shape of the heating roller 307. In the second region β, the covering member 500 does not have an arc shape parallel to the arc shape of the steering roller 308, but has a shape that prevents the fixing belt 301 from hitting the covering member 500 even if the steering roller 308 tilts. Specifically, the covering member 500 in the second region β may be formed in an arc shape, or may be formed in a shape corresponding to a trajectory followed by the steering roller 308 tilting.

[0050] Here, the first region α is a region where the inner peripheral surface of the fixing belt 301 and the outer peripheral surface of the heating roller 307 are in contact with each other, and the second region β is a region where the inner peripheral surface of the fixing belt 301 and the outer peripheral surface of the steering roller 308 are in contact with each other. In addition, the third region γ is a region located upstream of the steering roller 308 and downstream of the heating roller 307 in the rotation direction of the fixing belt 301, and is a region away from the fixing pad 303.

[0051] The area where the covering member 500 covers the fixing belt 301 may include at least an area facing the first area α and the second area β, and, for example, the covering member 500 may be omitted in the area facing the third area γ. However, from the viewpoint of suppressing the heat radiation of the fixing belt 301, it is preferable to cover the periphery of the fixing belt 301 with the covering member 500 as much as possible. In the present embodiment, the outer side of the fixing belt 301 is covered with the covering member 500 on the side opposite to the pressure roller 305. In particular, in the present embodiment, since the fixing belt 301 is located above the pressure roller 305, the covering member 500 is arranged to cover the area above the fixing belt 301. It is to be noted that the covering member 500 can cover the fixing belt 301 in a wider range than the above-mentioned area in a manner that does not interfere with the conveyance of the recording material P to the nip portion N or the discharge unit 350.

[0052] In addition, it is preferred that the covering member 500 covers the fixing belt 301 as wide as possible in the width direction (Y direction) of the fixing belt 301, and it is more preferred that the covering member 500 covers the entire area in the width direction of the fixing belt 301. In addition, the length of the covering member 500 in the width direction can be greater than the length of the fixing belt 301 in the width direction, so that the covering member 500 can protrude from both ends of the width direction of the fixing belt 301. That is, the covering member 500 is preferably larger than the fixing belt 301 in the width direction. However, even if the covering member 500 does not cover the entire area in the width direction of the fixing belt 301, the heat radiation suppression effect can be obtained as long as at least a portion of the fixing belt 301 is covered. The covering member 500 is preferably arranged to cover more than 1 / 4 of the circumference of the fixing belt 301. In addition, the covering member 500 can be composed of one component, or can be composed of multiple components.

[0053] In the case where the covering member 500 is formed to be longer than the fixing belt 301 in the width direction, it is preferable to set the length of the covering member 500 in consideration of the moving range of the fixing belt 301 in the width direction. As the steering roller swings, the fixing belt 301 moves a predetermined distance in the width direction. When the length of the covering member 500 is greater than the sum of the predetermined distance and the length of the fixing belt 301, heat is hardly released.

[0054] As described above, the covering member 500 is disposed with a gap from the fixing belt 301. From the viewpoint of suppressing the heat radiation of the fixing belt 301, the covering member 500 is preferably disposed as close to the fixing belt 301 as possible. Figure 3A and 3BAs described above, the turning roller 308 for tensioning the fixing belt 301 is inclined with respect to the rotation axis direction of the heating roller 307 so as to perform the shift control of the fixing belt 301. Therefore, the locus of the fixing belt 301 changes as the turning roller 308 is inclined. That is, when the turning roller 308 is inclined with respect to the heating roller 307, the fixing belt 301 has a region where the distance from the covering member 500 changes. Therefore, it is difficult to dispose the covering member 500 close to the fixing belt 301 at least in the turning roller facing portion L2 facing the second region β of the fixing belt 301 tensioned by the turning roller 308.

[0055] Therefore, in the present embodiment, when the turning roller 308 is parallel to the heating roller 307, the distance between the covering member 500 and the fixing belt 301 in the region (second region β) tensioned by the turning roller 308 is set to be greater than the distance between the covering member 500 and the fixing belt 301 in the region (first region α) tensioned by the heating roller 307. In particular, the covering member 500 is disposed such that the average distance t2 between the covering member 500 and the second region β of the fixing belt 301 is greater than the average distance t1 between the covering member 500 and the first region α of the fixing belt 301 (t1 < t2). That is, the distance between the turning roller facing portion L2 of the covering member 500 and the fixing belt 301 is set to be large, and the distance between the heating roller facing portion L1 of the covering member 500 and the fixing belt 301 is set to be small. As a result, even when the turning roller 308 is inclined, both prevention of interference between the covering member 500 and the fixing belt 301 and suppression of heat radiation from the fixing belt 301 can be achieved.

[0056] In particular, the heating roller 307 is a roller having a halogen heater 306 as a heat source therein to heat the fixing belt 301. Therefore, the amount of heat radiation in the first region α of the fixing belt 301 tensioned by the heating roller 307 is greater than the amount of heat radiation in the second region β of the fixing belt 301 tensioned by the turning roller 308. For this reason, by disposing the covering member 500 close to the first region α, heat radiation from the first region α can be effectively suppressed, and power saving of the fixing device 8 can be easily achieved.

[0057] In the present embodiment, the distance between the fixing belt 301 and the covering member 500 in the heating roller facing portion L1 is substantially uniform over the entire region where the first region α of the covering member 500 and the fixing belt 301 face each other, and is, for example, 3 mm. It should be noted that it is not required that the distance between the fixing belt 301 and the covering member 500 in the heating roller facing portion L1 be uniform over the entire region where the covering member 500 and the first region α face each other, and it is only required that the average distance t1 in the entire region where the covering member 500 and the first region α face each other be smaller than the average distance t2 in the entire region where the covering member 500 and the second region β face each other.

[0058] On the other hand, the distance between the fixing belt 301 and the covering member 500 in the steering roller facing portion L2 is set to a maximum of 8 mm. This is a distance at which the covering member 500 can be as close to the fixing belt 301 as possible when the fixing belt 301 and the covering member 500 do not contact each other even when the steering roller 308 is tilted. That is, the portion of the covering member 500 where the distance is the largest is the portion located in the tilt direction of the steering roller 308. In other words, in the case where the steering roller 308 is parallel to the heating roller 307, the position of the fixing belt 301 where the distance between the covering member 500 and the fixing belt 301 in the area stretched by the steering roller 308 is greater than the distance between the covering member 500 and the fixing belt 301 in the area stretched by the heating roller 307 is the position where the fixing belt 301 is stretched by the steering roller 308 at the position where the steering roller 308 is most tilted when the steering roller 308 is most tilted. In the present embodiment, the tilt distance of the steering roller 308 (the distance that one end in the Y direction moves in the tilt direction) is set to a maximum of 5 mm. Therefore, when the steering roller 308 is most inclined, the distance between the fixing belt 301 and the covering member 500 in the steering roller facing portion L2 becomes equal to the distance of 3 mm between the fixing belt 301 and the covering member 500 in the heating roller facing portion L1.

[0059] As described above, in this embodiment, the distance between the covering member 500 and the second region β is in the inclination direction ( Figure 4 The maximum value is in the vertical direction of the steering roller 308, and the covering member 500 is close to the second region β in other parts. That is, in the direction orthogonal to each of the inclination direction of the steering roller 308 and the rotation axis direction of the steering roller 308 ( Figure 4 The outer side ( Figure 4 The distance between the right side of the steering roller 308 in the fixing belt 301 and the covering member 500 is set to be smaller than the distance between the right side of the steering roller 308 and the covering member 500. Figure 4 Each of the distances between the upper and lower sides of the steering roller 308 in the cover 500.

[0060] The distance between the fixing belt 301 and the covering member 500 in the turning roller facing portion L2 may be a substantially uniform distance (e.g., 8 mm) in the entire region where the covering member 500 and the second region β of the fixing belt 301 face each other. However, as in the present embodiment, it is preferred that the covering member 500 and the fixing belt 301 be arranged close to each other in the region deviating from the tilting direction of the turning roller 308 within the second region β of the fixing belt 301 so that the covering member 500 and the fixing belt 301 do not interfere with each other when the turning roller 308 is tilted. As a result, heat radiation from the second region β can be effectively suppressed.

[0061] In addition, considering the change in the tilt distance of the steering roller 308, the distance between the fixing belt 301 and the covering member 500 in the steering roller facing portion L2 can be greater than 8 mm as described above. In any case, it is only necessary to appropriately set the distance between the fixing belt 301 and the covering member 500 in the steering roller facing portion L2 according to the tilt distance of the steering roller 308 so that the fixing belt 301 and the covering member 500 do not contact each other. However, it is preferred that the covering member 500 is set to be less than 10 mm away from the fixing belt 301. That is, from the perspective of suppressing heat radiation from the fixing belt 301, the distance (maximum distance) between the covering member 500 and the fixing belt 301 at the portion where they are farthest from each other is preferably less than 10 mm.

[0062] Here, the average distances t1 and t2 represent the average distance of the entire heating roller facing portion L1 and the average distance of the entire steering roller facing portion L2, respectively. However, in the case where a hole is formed in the covering member 500, the average distance is calculated excluding the hole. In addition, the average distance t2 in the steering roller facing portion L2 is the distance when the steering roller 308 is located at the pivot center (tilt center) position.

[0063] In the present embodiment, in a cross section orthogonal to the rotation axis of the heating roller 307, the portion L3 facing the third region γ is inclined relative to the outer peripheral surface of the fixing belt 301 in the third region γ so that the distance from the fixing belt 301 to the portion L3 increases as the portion L3 extends in a direction from a position facing the first region α toward a position facing the second region β. As described above, the average distance t2 in the steering roller facing portion L2 of the covering member 500 is greater than the average distance t1 in the heating roller facing portion L1 of the covering member 500. In the present embodiment, the steering roller facing portion L2 and the heating roller facing portion L1, which differ in distance from the fixing belt 301 as described above, are smoothly connected by inclining the portion L3 facing the third region γ relative to the outer peripheral surface of the fixing belt 301. For example, the portion L3 facing the third region γ has a linear cross section.

[0064] Here, the portion L3 facing the third region γ may be formed, for example, in a stepped shape so as to change the distance from the fixing belt 301 in stages. However, considering the workability of the covering member 500, it is preferred that the portion L3 facing the third region γ has a linear cross section (flat plate shape) as in this embodiment.

[0065] Power reduction effect of the distance between the fuser belt and the cover part

[0066] Next, the relationship between the distance between the fixing belt 301 and the covering member 500 and the power reduction effect in the fixing device 8 will be described. Figure 53 is a graph showing the results of an experiment performed to examine the influence of the distance between the fixing belt 301 and the covering member 500 on power reduction. In the experiment, in order to facilitate comparison of the influence of the distance on power reduction, the inspection was performed in a state where the steering roller 308 was fixed at the pivot center.

[0067] In addition, in the experiment, the inspection was performed with three covering members, each of which was trial-made so that the distance between the fixing belt 301 and the covering member 500 was uniform from the heating roller facing portion L1 to the steering roller facing portion L2. That is, a covering member with a distance of 3 mm was prepared as Comparative Example 1, a covering member with a distance of 5 mm was prepared as Comparative Example 2, and a covering member with a distance of 8 mm was prepared as Comparative Example 3. In addition, the power required when the fixing belt 301 was rotated at 300 mm / s while performing temperature control so that the surface temperature became 180°C was measured, and it was confirmed how much power could be reduced compared with the power required when the covering member was not provided. At this time, the power required in Comparative Example 1 was 420W.

[0068] from Figure 5 As can be clearly seen, it has been found that the power reduction effect is greater when the distance between the fixing belt 301 and the covering member 500 is shorter. As a result of studying the cause, it has been found that as the distance between the fixing belt 301 and the covering member 500 is shorter, the temperature of the space between the fixing belt 301 and the covering member 500 is higher, resulting in a better heat insulation effect.

[0069] Next, regarding the configuration in which the steering roller 308 is tilted as in the present embodiment, Figure 4 The above experiment was conducted to confirm the power reduction effect of the cover member 500 (example) shown in the figure. By measuring the power required when the temperature control is performed so that the surface temperature becomes 180°C, the power reduction amount is 162W. The experimental results of Comparative Examples 1 to 3 and the above example are Figure 6 In Figure 6 In addition to the power reduction effect, it was confirmed whether the fixing belt 301 and the covering member 500 contact each other when the steering roller 308 is configured to be inclined in each of Comparative Examples 1 to 3. Since the distance between the covering member and the fixing belt is 3 mm in Comparative Example 1, and the distance between the covering member and the fixing belt is 5 mm in Comparative Example 2, the fixing belt contacts the covering member in the configuration in which the tilt distance of the steering roller 308 is a maximum of 5 mm. In each of Comparative Example 3 and the example, the fixing belt does not contact the covering member. Figure 6 It can be seen that the configuration of the embodiment results in a greater power reduction effect when the fixing belt 301 and the covering member 500 are not in contact with each other.

[0070] It should be noted that as the distance between the fixing belt 301 and the covering member 500 becomes shorter, the temperature of the space between the fixing belt 301 and the covering member 500 becomes higher, and the heat radiation from the fixing belt 301 can be further suppressed, resulting in a greater power reduction effect. Even if the distance between the fixing belt 301 and the covering member 500 is set to a certain extent (for example, set to 30 mm), there is a heat radiation suppression effect. However, Figure 5 It can be clearly seen that the longer the distance between the fixing belt 301 and the covering member 500 is, the smaller the power reduction effect is. Therefore, in this embodiment, the distance between the fixing belt 301 and the covering member 500 is set to 10 mm or less, preferably 8 mm or less.

[0071] On the other hand, although a greater power reduction effect can be obtained when the distance between the fixing belt 301 and the covering member 500 is small, if the distance is too small, the fixing belt 301 and the covering member 500 may contact each other even in an area deviated from the area where the steering roller 308 is inclined. Therefore, the distance between the fixing belt 301 and the covering member 500 is preferably 1 mm at minimum. In the present embodiment, the distance between the fixing belt 301 and the covering member 500 is set to 1 mm or more, preferably 3 mm or more.

[0072] Influence of the coverage ratio of the covering member on the fixing belt

[0073] Next, the relationship between the coverage ratio of the covering member 500 with respect to the fixing belt 301 (ie, the ratio of the covering member 500 covering the periphery of the fixing belt 301 with respect to the entire periphery of the fixing belt 301 ) and the power reduction effect will be described. Figure 7 3 is a graph showing the results of an experiment performed to examine the influence of the coverage ratio of the covering member 500 with respect to the fixing belt 301 on power reduction. Here, the coverage ratio is the ratio of the area faced by the covering member 500 to the area of ​​the entire circumference of the fixing belt 301 excluding the nip N.

[0074] In the experiment, in order to facilitate comparison of the influence of the coverage on the power reduction, the inspection was carried out in a state where the steering roller 308 was fixed at the pivot center. In addition, the inspection was carried out using three covering members that were trial-made to have different coverage. That is, a covering member with a coverage of 80% was prepared as Comparative Example 4, a covering member with a coverage of 60% was prepared as Comparative Example 5, and a covering member with a coverage of 20% was prepared as Comparative Example 6. In addition, in each of Comparative Examples 4 to 6, the distance between the fixing belt 301 and the covering member 500 was set to a uniform distance from the heating roller facing portion L1 to the steering roller facing portion L2, and the uniform distance was 5 mm.

[0075] In addition, the power required when temperature control was performed so that the surface temperature became 180° C. while the fixing belt 301 was rotated at 300 mm / s was measured, and it was confirmed how much power could be reduced compared with the power required in the case where the covering member was not provided.

[0076] from Figure 7 As is clear, it has been found that the power reduction effect is greater when the coverage ratio of the covering member 500 with respect to the fixing belt 301 is greater. This means that even if it is designed to provide a shaft or an auxiliary member at a portion facing the outer peripheral surface of the fixing belt 301, if the coverage ratio of the covering member 500 with respect to the fixing belt 301 is small, the power reduction effect is hardly obtained. Therefore, in order to obtain the power reduction effect, it is preferable to set the coverage ratio of the covering member with respect to the fixing belt 301 to 25% or more.

[0077] As described above, it is preferable that the coverage ratio of the fixing belt 301 covered by the covering member 500 is large. This is because, as the coverage ratio is large, the temperature of the space between the fixing belt 301 and the covering member 500 is high, so that heat radiation can be suppressed. Even when the coverage ratio is small (e.g., 10%), there is a slight effect. However, from Figure 7 As can be clearly seen in FIG. 1 , as the coverage rate decreases, the power reduction effect decreases. Therefore, in the present embodiment, the coverage rate of the fixing belt 301 covered by the covering member 500 is set to 25% or more, preferably 50% or more, and more preferably 60% or more. On the other hand, if the coverage rate is too large, there is a possibility that the covering member 500 contacts the recording material P passing through the clamping portion N. Therefore, the coverage rate is preferably 80% or less.

[0078] In the present embodiment, even in a configuration in which the fixing device 8 adopts a belt member such as the fixing belt 301, heat radiation of the belt member can be suppressed. That is, the shift position of the fixing belt 301 is controlled by tilting the steering roller 308. Therefore, if the covering member 500 for suppressing heat radiation of the fixing belt 301 is too close to the fixing belt 301, the covering member 500 may come into contact with the fixing belt 301. On the other hand, when the covering member 500 is disposed away from the fixing belt 301, the heat radiation suppression effect is reduced.

[0079] Therefore, in the present embodiment, the covering member 500 is disposed near the fixing belt 301 so that the average distance t2 between the second region β stretched by the steering roller 308 and the covering member 500 is greater than the average distance t1 between the first region α stretched by the heating roller 307 that heats the fixing belt 301 and the covering member 500. As a result, even if the steering roller 308 is tilted, the heat radiation of the fixing belt 301 can be suppressed while preventing the covering member 500 from contacting the fixing belt 301. Therefore, power saving of the fixing device 8 can be achieved.

[0080] Other embodiments

[0081] In the above-described embodiment, the configuration has been described in which the fixing pad 303 is provided as a contact member inside the fixing belt 301 so as to form a nip portion between the fixing belt 301 and the pressure roller 305. However, the contact member is not limited to the fixing pad 303, and may be a roller member, etc. The method of heating the fixing belt 301 is not limited to the halogen heater 306 inside the heating roller 307, and another device such as a device using an electromagnetic induction method or a device using a ceramic heater may be adopted.

[0082] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A fixing device for fixing a toner image to a recording material by heating the toner image carried on the recording material, the fixing device comprising: a rotatable endless belt member; a heating roller disposed inside the belt member and configured to tension the belt member and heat the belt member; a steering roller disposed inside the belt member and configured to tension the belt member together with the heating roller and to control the position of the belt member relative to the rotation axis direction by tilting relative to the rotation axis direction of the heating roller; a grip portion forming member which is in contact with an outer peripheral surface of the belt member and is configured to form a grip portion for gripping and conveying a recording material between the grip portion forming member and the belt member; as well as a covering member provided with a gap between the covering member and the belt member so as to cover a part of the outer side of the belt member, wherein The belt member has a region where the distance from the covering member changes when the steering roller is tilted relative to the heating roller, and the region includes a first tensioning region tensioned by the steering roller and a second tensioning region tensioned by the heating roller, and In the case where the deflection roller is parallel to the heating roller, the distance between the covering member and the belt member in the first tensioning area is greater than the distance between the covering member and the belt member in the second tensioning area.

2. The fixing device according to claim 1, wherein The covering member is provided at a distance of 10 mm or less from the belt member.

3. The fixing device according to claim 1 or 2, wherein The covering member is composed of one or more members provided to cover 1 / 4 or more of the circumference of the belt member.

4. The fixing device according to claim 1 or 2, wherein The region includes a third tensioning region disposed between the first tensioning region and the second tensioning region in the rotational direction of the belt member, The covering member has a first portion facing the first tensioning area, a second portion facing the second tensioning area, and a third portion facing the third tensioning area, and the third portion is inclined relative to the outer peripheral surface of the belt member so that in a cross section orthogonal to the rotation axis direction of the heating roller, the distance from the belt member to the third portion increases as the third portion extends in a direction from the second portion toward the first portion.

5. The fixing device according to claim 1 or 2, wherein The nip forming member is a pressure roller pressed against the belt member.

6. The fixing device according to claim 1 or 2, further comprising: A contact member is provided at a position facing the gripping portion forming member across the belt member on the inner side of the belt member, and the contact member is in contact with an inner peripheral surface of the belt member.

7. The fixing device according to claim 1 or 2, wherein The covering member is larger than the belt member in the rotation axis direction.

8. The fixing device according to claim 1 or 2, wherein The covering member is arranged such that an average distance between the covering member and the first tensioning area is greater than an average distance between the covering member and the second tensioning area.

9. The fixing device according to claim 1 or 2, The position of the belt member in which the distance between the covering member and the belt member in the first tensioning area is greater than the distance between the covering member and the belt member in the second tensioning area when the steering roller is parallel to the heating roller is the position of the belt member tensioned by the steering roller at the position where the steering roller is most inclined when the steering roller is most inclined.

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