Fixing device

Abstract

To provide a fixing device 8 that adopts a fixing belt 301 and yet can prevent radiation of heat from the fixing belt 301.SOLUTION: A heating roller 307 heats a fixing belt 301. A steering roller 308 tilts with respect to a rotation axis direction of the heating roller 307 to control the position of the fixing belt 301 with respect to the rotation axis direction. A covering member 500 is arranged at a distance from the fixing belt 301 to cover a part of the outside of the fixing belt 301. An area of the fixing belt 301 stretched by the heating roller 307 is defined as a first area α, and an area stretched by the steering roller 308 is defined as a second area β. In this case, the covering member 500 is arranged so that an average distance t1 between the covering member 500 and the first area α is larger than an average distance t2 between the covering member 500 and the second area β.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] The image forming apparatus has a fixing device that fixes a toner image carried on a recording material to the recording material. In the fixing device, the toner image on the recording material is heated and conveyed in a nip portion formed by a heating member and a nip portion forming member. Patent Document 1 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 insulating effect of the fixing device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-31562 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, as described in Patent Document 1, by providing a partition plate between the heating member and the housing, it is possible to suppress heat dissipation from the heating member to some extent. In order to save power in the fixing device, it is desirable to enhance the effect of suppressing heat dissipation from the heating member, and for this purpose, it is desirable to place the partition plate close to the heating member. In the configuration described in Patent Document 1, the heating member is a roller, but a configuration in which the heating member is a belt member is also known in the past.

[0005] The belt member is stretched by a plurality of tension rollers. When the heating member is a belt member, one of the plurality of tension rollers is often tilted relative to the other rollers in order to control the position of the belt member relative to the rotation axis direction of the tension roller. The roller that tilts to control the position of the belt member in this way is called a steering roller. As described above, it is preferable to bring the partition plate closer to the heating member in order to increase the heat dissipation suppression effect of the heating member, but when the heating member is a belt member, the steering roller tilts, so if the partition plate is brought too close, the belt member and the partition plate will interfere with each other when the steering roller tilts.

[0006] SUMMARY OF THE DISCLOSURE An object of the present invention is to provide a fixing device having a belt member that can suppress heat radiation from the belt member. [Means for solving the problem]

[0007] The fixing device of the present invention is a fixing device that heats a toner image carried on a recording material and fixes it to the recording material, and includes a rotatable endless belt member, a heating roller arranged inside the belt member, tensioning the belt member and heating the belt member, a steering roller arranged inside the belt member, tensioning the belt member together with the heating roller, and tilting relative to the rotational axis direction of the heating roller to control the position of the belt member relative to the rotational axis direction, a nip portion forming member that abuts against the outer peripheral surface of the belt member and forms a nip portion between the belt member and the nip portion that sandwiches and transports the recording material, and a covering member arranged with a gap between the covering member and the belt member so as to cover a portion of the outer side of the belt member, and the covering member is arranged such that, when the area of ​​the belt member tensioned by the heating roller is defined as a first area and the area of ​​the belt member tensioned by the steering roller is defined as a second area, the average distance between the covering member and the second area is greater than the average distance between the covering member and the first area. Effect of the Invention

[0008] According to the present invention, even if a fixing device employs a belt member, heat radiation from the belt member can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a fixing device according to the embodiment. [Diagram 3] 5A and 5B are schematic cross-sectional views of a fixing device according to an embodiment, showing a case where an end portion of one side of a steering roller is tilted upward, and a case where an end portion of the other side of the steering roller is tilted downward. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a configuration in which a cover member is arranged in the fixing device according to the embodiment. [Diagram 5] 11 is a graph showing the relationship between the distance between the fixing belt and the cover member and the amount of power reduction. [Figure 6] 11 is a table showing the relationship between the presence or absence of contact between the fixing belt and the cover member and the amount of power reduction in each of the comparative examples and the examples. [Figure 7] 11 is a graph showing the relationship between the coverage rate of the cover member with respect to the fixing belt and the amount of power consumption reduction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiment will be described with reference to Figures 1 to 7. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0011] [Image forming device] The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd provided corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are of a tandem type arranged along the rotation direction of an intermediate transfer belt 204 described later. The image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (original reading device) 2 connected to the image forming apparatus main body 3 or a host device such as a personal computer connected to the image forming apparatus main body 3 so as to be able to communicate with the image forming apparatus main body 3. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0012] The image forming apparatus 1 comprises an image reading section 2 and an image forming apparatus main body 3. The image reading section 2 reads an original placed on an original platen glass 21, and 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 member 23 such as a lens. Such an optical system unit converts the original into an electric signal data string for each line by scanning in the direction of the arrow. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and a control section 30 performs image processing in accordance with each image forming section described later. The control section 30 also receives external inputs as image signals from external host devices such as a print server.

[0013] The image forming apparatus main 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 image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. A polygon scanner 31 as an exposure device scans with the laser beam according to the image signal. Then, the laser beam is irradiated onto photosensitive drums 200a to 200d as image carriers of the image forming units Pa to Pd.

[0014] Note that Pa is a yellow (Y) image forming section, Pb is a magenta (M) image forming section, Pc is a cyan (C) image forming section, and Pd is a black (Bk) image forming section, which form images of the corresponding colors. Since the image forming sections Pa to Pd are substantially the same, the Y image forming section Pa will be described in detail below, and the other image forming sections will not be described. In the image forming section Pa, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal, as described below.

[0015] The charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential, by a laser beam from the polygon 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 discharges electricity from the rear surface of the intermediate transfer belt 204, applies a primary transfer bias of opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0016] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming section, where the toner images of each color formed in each image forming section are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through Bk image forming section Pd, which is located at the most downstream side in the rotation direction of intermediate transfer belt 204, is conveyed to a secondary transfer section composed of a pair of secondary transfer rollers 205 and 206. In the secondary transfer section, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, so that the toner image is secondarily transferred to the recording material.

[0017] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208 consisting of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the registration unit 208 controls the timing to align the toner image on the intermediate transfer belt 204 with the position of the paper, and transports the recording material to a secondary transfer unit.

[0018] The recording material onto which the toner image has been transferred in the secondary transfer section is transported to a fixing device 8, where the toner image carried on the recording material is fixed to the recording material by heating and pressurizing it. The recording material that has passed through the fixing device 8 is discharged onto a discharge tray 7. When forming images on both sides of the recording material, once the transfer and fixing of the toner image onto the first side (front side) of the recording material is completed, the recording material is turned over via a reversing transport section 10, and the toner image is transferred and fixed onto the second side (rear side) of the recording material, and then stacked onto the discharge tray 7.

[0019] As described above, the control unit 30 controls the entire image forming apparatus 1. The control unit 30 can perform various settings based on input from the operation unit 4 of the image forming apparatus 1. Such a control unit 30 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit while reading a program corresponding to a control procedure stored in the ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the above-mentioned programs.

[0020] [Fixing device] Next, the configuration of the fixing device 8 in this embodiment will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing a schematic configuration of the fixing device 8. Note that in FIG. 2, a cover member 500, which will be described later, is omitted. In this embodiment, a fixing device of a belt heating type using an endless belt is adopted. In FIG. 2, the X direction indicates the conveying direction of the recording material P, the Y direction indicates the width direction intersecting with the conveying direction of the recording material P (perpendicular in this embodiment), and the Z direction indicates the pressure direction of the pressure roller 305, which will be described later. These are perpendicular to each other. Also, one side of 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 arranged and operated by the user. On the other hand, the other side of the width direction is the rear side of the image forming apparatus 1.

[0021] The fixing device 8 includes a heating unit 300 having a fixing belt 301 as an endless rotatable belt member, and a pressure roller 305 as a nip portion forming member and pressure rotating body that contacts the fixing belt 301 and forms a nip portion N together with the fixing belt 301.

[0022] The heating unit 300 includes the above-mentioned fixing belt 301, a fixing pad 303 as a pad member, a heating roller 307, and a steering roller 308. The pressure roller 305 rotates in contact with the outer circumferential surface of the fixing belt 301, and is also a driving rotor that applies a driving force to the fixing belt 301.

[0023] The fixing belt 301 as a heating member (fixing member) and a rotating body has thermal conductivity, heat resistance, etc., and is a thin cylindrical shape. In this embodiment, it has a three-layer structure with a base layer, an elastic layer on the outer periphery of the base layer, and a release layer on the outer periphery of the elastic layer. The base layer is 80 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. Such a fixing belt 301 is stretched by a fixing pad 303, a heating roller 307, and a steering roller 308.

[0024] The fixing pad 303 as a contact member is disposed inside the fixing belt 301 so as to face the pressure roller 305 with the fixing belt 301 sandwiched therebetween, and contacts the inner circumferential surface of the fixing belt 301. The fixing pad 303 forms a nip portion N between the fixing belt 301 and the pressure roller 305 for sandwiching and conveying the recording material. In this embodiment, the fixing pad 303 is a substantially plate-shaped member that is long along the width direction of the fixing belt 301 (the longitudinal direction intersecting the rotation direction of the fixing belt 301, the direction of the rotation axis of the heating roller 307). The fixing pad 303 is pressed against the pressure roller 305 with the fixing belt 301 sandwiched therebetween, thereby forming the nip portion N. The fixing pad 303 is made of LCP (liquid crystal polymer) resin.

[0025] The fixing pad 303 is supported by a stay 302 serving as a support member disposed inside the fixing belt 301. That is, the stay 302 is disposed on the opposite side of the fixing pad 303 from the pressure roller 305, and supports the fixing pad 303. Such a stay 302 is a reinforcing member having long rigidity along the longitudinal direction of the fixing belt 301, and contacts the fixing pad 303 to back up the fixing pad 303. That is, the stay 302 provides strength to the fixing pad 303 to ensure the pressure force at the nip portion N when the fixing pad 303 is pressed by the pressure roller 305.

[0026] A lubricating sheet (not shown) is interposed between fixing pad 303 and fixing belt 301. A lubricant is applied to the inner peripheral surface of fixing belt 301 so that fixing belt 301 slides smoothly against fixing pad 303 covered with the lubricating sheet. Silicone oil is used as the lubricant.

[0027] Heating roller 307 is disposed inside fixing belt 301, and stretches fixing belt 301 together with fixing pad 303 and steering roller 308. Heating roller 307 is formed into a cylindrical shape from metal such as aluminum or stainless steel, and has a halogen heater 306 disposed therein as a heating unit for heating fixing belt 301. Heating roller 307 is heated by halogen heater 306 to a predetermined temperature.

[0028] In this embodiment, the heating roller 307 is formed of, for example, a stainless steel pipe having a thickness of 1 mm. The halogen heater 306 may be one or more. The heating unit is not limited to a halogen heater, and may be another heater capable of heating the heating 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 according to the type of recording material based on temperature detection by a thermistor (not shown).

[0029] The steering roller 308 is disposed inside the fixing belt 301, stretches the fixing belt 301 together with the fixing pad 303 and the heating roller 307, and rotates in a driven manner with the fixing belt 301. The steering roller 308 tilts with respect to the rotation axis direction (width direction, length direction) of the heating roller 307 to control the position (shift position) of the fixing belt 301 with respect to the rotation axis direction. That is, the steering roller 308 has a rotation center at the center or one end of the rotation axis direction (length direction) of the steering roller 308, and tilts with respect to the length direction of the heating roller 307 by swinging about this rotation center. This generates a tension difference between one side and the other side of the length direction of the fixing belt 301, and moves the fixing belt 301 in the length direction.

[0030] Fixing belt 301 tends to shift to one end during rotation depending on the outer diameter accuracy of the rollers that tension it and the alignment accuracy between the rollers. For this reason, such shifting is controlled by steering roller 308. Note that steering roller 308 may be swung by a driving source such as a motor, or may be configured to swung by automatic centering.

[0031] In this embodiment, the steering roller 308 is biased by a spring supported by the frame of the heating unit 300, and also serves as a tension roller that applies a predetermined tension to the fixing belt 301. The steering roller 308 is formed in a cylindrical shape from a metal such as aluminum or stainless steel. In this embodiment, the steering roller 308 is formed from a hollow stainless steel pipe having an outer diameter of 20 mm. The steering roller 308 may be provided with a rubber material or the like on its surface in order to increase its gripping force on the fixing belt 301.

[0032] The pressure roller 305 as a nip forming member rotates in contact with the outer circumferential surface of the fixing belt 301 and applies a driving force to the fixing belt 301. The pressure roller 305 is pressed against the fixing belt 301 to form a nip N between the pressure roller 305 and the fixing belt 301. In this embodiment, the pressure roller 305 is a roller having an elastic layer formed on the outer periphery of the shaft and a release layer formed on the outer periphery of the elastic layer. The shaft is made of stainless steel with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. The pressure roller 305 is rotatably supported by a fixing frame (not shown) of the fixing device 8, and a gear is fixed to one end of the pressure roller 305. The pressure roller 305 is connected to a motor M as a pressure roller drive source via the gear, and is driven to rotate.

[0033] In the fixing device 8 configured as above, the toner image is heated while the recording material P carrying the toner image is sandwiched and conveyed 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 function of applying heat and pressure 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 this embodiment, the pressure force (NF) in the nip portion N during image formation is set to 1600 N, and the length of the nip portion N in the X direction (conveyance direction) is set to 24.5 mm, and the length in the Y direction (width direction) is set to 326 mm.

[0034] Further, downstream of the nip portion N in the conveying direction of the recording material P, a discharge unit 350 is disposed for discharging the recording material P that has passed through the nip portion N to the outside of the fixing device 8. The discharge unit 350 is provided with an air nozzle 401, a pair of discharge rollers 400a, and a lower separation guide 400b. The air nozzle 401 blows out air (compressed air) for peeling the recording material P from the fixing belt 301. Specifically, the air nozzle 401 is disposed downstream of the nip portion N in the conveying direction of the recording material (hereinafter, sometimes simply referred to as the "conveying direction") and vertically above the nip portion N, and blows out air upstream of the conveying direction and vertically downward. Then, the recording material P is peeled off from the fixing belt 301 by blowing air near the leading end of the recording material P after passing through the nip portion N.

[0035] The lower separation guide 400b is disposed downstream of the nip portion N in the recording material conveying direction and vertically below the nip portion N, with its tip facing closely to the vicinity of the nip portion N of the pressure roller 305. When the recording material P sticks to the pressure roller 305, the lower separation guide 400b separates the recording material P from the pressure roller 305. The lower separation guide 400b also supports the lower surface of the recording material P discharged from the nip portion N and guides the recording material P to the discharge roller 40a. The discharge roller pair 400a discharges the recording material P discharged from the nip portion N to the outside of the fixing device 8. In this embodiment, the discharge roller pair 400a is disposed about 40 mm downstream of the nip portion N in the conveying direction.

[0036] Further, upstream of the nip portion N of the fixing device 8 in the conveying direction, there are disposed a guide portion 94 for guiding the recording material P to the nip portion N, and a detection sensor 95 for detecting the recording material P immediately before the nip portion N. The control portion 30 detects the timing at which the recording material P enters the nip portion N by the detection sensor 95.

[0037] [Steering roller tilt] The tilting of the steering roller 308 when controlling the deviation position of the fixing belt 301 by the steering roller 308 will be described with reference to FIGS. 3(a) and 3(b). In this embodiment, deviation control is performed by the steering roller 308 tilting in the vertical direction in FIGS. 2, 3(a) and 3(b) about the center of rotation. When the steering roller 308 tilts upward at an end on one side in the Y direction as shown in FIG. 3(a), the steering roller 308 tilts downward at an end on the other side in the Y direction as shown in FIG. 3(b). The deviation position of the fixing belt 301 is controlled by the steering roller 308 tilting while alternately repeating the states of FIG. 3(a) and FIG. 3(b).

[0038] [Covering material] As described above, in order to reduce the power consumption of the fixing device 8, it is desirable to suppress the heat radiation from the fixing belt 301. For this reason, as shown in FIG. 4, the fixing device 8 of this embodiment has a cover member 500 as a member for suppressing such heat radiation. The cover member 500 is arranged with a gap between it and the fixing belt 301 so as to cover a part of the outer side of the fixing belt 301. The cover member 500 in this embodiment is made of LCP (liquid crystal polymer) having a thickness of 2 mm. The cover member 500 is a plate-shaped member formed of a resin member or a metal member having heat resistance. Such a cover member 500 may be a resin other than LCP, a foam member, or 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 cover member 500 facing the fixing belt 301.

[0039] As shown in FIG. 4, the cover member 500 is disposed from the heating roller facing portion L1, which faces the first region α stretched by the heating roller 307, to the steering roller facing portion L2, which faces the second region β stretched by the steering roller 308, of the fixing belt 301. The fixing belt 301 has a third region γ between the first region α and the second region β in the rotation direction of the fixing belt 301. The portion L3 facing the third region γ is a portion that connects the heating roller facing portion L1 and the steering roller facing portion L2. The cover member 500 is disposed across the heating roller facing portion L1, the portion L3 facing the third region γ, and the steering roller facing portion L2. The cover member 500 in this embodiment is configured so that the fixing device 8 is not visible when the fixing device 8 is viewed from above in the vertical direction.

[0040] Here, the first region α is a region where the inner circumferential surface of the fixing belt 301 contacts with the outer circumferential surface of the heating roller 307, and the second region β is a region where the inner circumferential surface of the fixing belt 301 contacts with the outer circumferential surface of the steering roller 308. The third region γ is a region downstream of the heating roller 307 and upstream of the steering roller 308 in the rotation direction of the fixing belt 301, and is a region outside the fixing pad 303.

[0041] The region where the covering member 500 covers the fixing belt 301 may include at least the region facing the first region α and the second region β, and for example, the covering member 500 may be omitted in the region facing the third region γ. However, from the viewpoint of suppressing heat dissipation 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 this embodiment, the outer side of the fixing belt 301 on the opposite side to the pressure roller 305 is covered with the covering member 500. In particular, in this embodiment, since the fixing belt 301 is located above the pressure roller 305, the covering member 500 is arranged to cover the region above the fixing belt 301. Note that the covering member 500 may cover the fixing belt 301 in a wider range than the above-mentioned region as long as it does not interfere with the conveyance of the recording material P to the nip portion N or the discharge unit 350.

[0042] In addition, with respect to the width direction (Y direction) of the fixing belt 301, it is preferable that the covering member 500 covers the fixing belt 301 over as wide an area as possible, and it is more preferable that the covering member 500 covers the entire width direction of the fixing belt 301. Furthermore, the length of the covering member 500 in the width direction may be made longer than the length of the fixing belt 301 in the width direction so that the covering member 500 protrudes from both ends of the fixing belt 301 in the width direction. That is, it is preferable that the covering member 500 is larger than the fixing belt 301 in the width direction. However, even if the covering member 500 does not cover the entire width direction of the fixing belt 301, as long as at least a part is covered, the effect of suppressing heat dissipation can be obtained. It is preferable that the covering member 500 is arranged so as to cover ¼ or more of the circumference of the fixing belt 301. In addition, the covering member 500 may be composed of one member, or may be composed of multiple members.

[0043] When the covering member 500 is made longer in the width direction than the fixing belt 301, it is preferable to set the length of the covering member 500 in consideration of the range of movement of the fixing belt 301 in the width direction. The fixing belt 301 moves a predetermined distance in the width direction due to the swinging of the steering roller. If the length of the covering member 500 is longer than the sum of this predetermined distance and the length of the fixing belt 301, the configuration becomes more difficult to let heat escape.

[0044] As described above, the covering member 500 is disposed with a gap between it and the fixing belt 301. It is preferable to dispose the covering member 500 as close as possible to the fixing belt 301 in order to suppress heat radiation from the fixing belt 301. However, as described in FIGS. 3A and 3B, the steering roller 308 around which the fixing belt 301 is stretched tilts with respect to the rotation axis direction of the heating roller 307 in order to control the deviation of the fixing belt 301. Therefore, the trajectory of the fixing belt 301 changes with the tilt of the steering roller 308. Therefore, it is difficult to dispose the covering member 500 close to the fixing belt 301 at least in the steering roller facing portion L2 facing the second region β of the fixing belt 301 stretched by the steering roller 308.

[0045] Therefore, in the present embodiment, the average distance t2 between the covering member 500 and the second region β of the fixing belt 301 is made larger than the average distance t1 between the covering member 500 and the first region α of the fixing belt 301 (t1 < t2), and the covering member 500 is arranged accordingly. That is, the distance between the steering roller facing portion L2 of the covering member 500 and the fixing belt 301 is increased, and the distance between the heating roller facing portion L1 of the covering member 500 and the fixing belt 301 is decreased. Thereby, it is possible to achieve both prevention of interference between the covering member 500 and the fixing belt 301 even when the steering roller 308 tilts and suppression of heat radiation from the fixing belt 301.

[0046] In particular, the heating roller 307 is a roller that has a halogen heater 306 as a heat source inside and heats the fixing belt 301. For this reason, the heat radiation amount of the first region α stretched by the heating roller 307 of the fixing belt 301 is larger than that of the second region β stretched by the steering roller 308 of the fixing belt 301. Therefore, by arranging the covering member 500 close to the first region α, the heat radiation from the first region α can be efficiently suppressed, and it is easy to achieve power saving of the fixing device 8.

[0047] In the present embodiment, the distance between the fixing belt 301 and the covering member 500 in the heating roller facing portion L1 is made substantially uniform over the entire area where the covering member 500 and the first region α of the fixing belt 301 face each other, for example, 3 mm. Note that the distance between the fixing belt 301 and the covering member 500 in the heating roller facing portion L1 does not have to be uniform over the entire area where the covering member 500 and the first region α face each other, as long as the average distance t1 in this entire area is smaller than the average distance t2 in the entire area where the covering member 500 and the second region β face each other.

[0048] On the other hand, the distance between the fixing belt 301 and the cover member 500 at the steering roller facing portion L2 is set to a maximum of 8 mm. This distance is set so that even if the steering roller 308 tilts, the fixing belt 301 and the cover member 500 do not come into contact with each other, and the cover member 500 can be brought as close as possible to the fixing belt 301. That is, the portion where the distance is maximum is a portion located in the tilting direction of the steering roller 308. In this embodiment, the tilting distance of the steering roller 308 (the distance that the end portion on one side in the Y direction moves in the tilting direction) is set to a maximum of 5 mm. Therefore, the distance between the fixing belt 301 and the cover member 500 at the steering roller facing portion L2 at the maximum tilt is set to be equal to the distance of 3 mm between the fixing belt 301 and the cover member 500 at the heating roller facing portion L1.

[0049] In this manner, in this embodiment, the distance between the cover member 500 and the second region β is maximized in the tilting direction of the steering roller 308 (the vertical direction in FIG. 4), and the cover member 500 is made closer to the second region β in other portions. That is, the distance between the outer portion of the fixing belt 301 (the right portion of the steering roller 308 in FIG. 4) and the cover member 500 in the directions perpendicular to the tilting direction of the steering roller 308 and the rotation axis direction of the steering roller 308 (the horizontal direction in FIG. 4) is made smaller than the distance between the cover member 500 and both side portions of the fixing belt 301 in the tilting direction of the steering roller 308 (the upper and lower portions of the steering roller 308 in FIG. 4) and the cover member 500.

[0050] The distance between the fixing belt 301 and the cover member 500 at the steering roller facing portion L2 may be substantially uniform (e.g., 8 mm) over the entire area where the cover member 500 faces the first region α of the fixing belt 301. However, as in this embodiment, in the area of ​​the second region β of the fixing belt 301 that is out of the tilting direction of the steering roller 308, it is preferable to arrange the cover member 500 close enough to the fixing belt 301 so as not to interfere with the fixing belt 301 when the steering roller 308 tilts. This makes it possible to efficiently suppress heat dissipation from the second region β.

[0051] Also, in consideration of the variation in the tilting distance of the steering roller 308, the distance between the fixing belt 301 and the cover member 500 at the steering roller opposing portion L2 may be set to be greater than the above-mentioned 8 mm. In any case, the distance between the fixing belt 301 and the cover member 500 at the steering roller opposing portion L2 may be appropriately set according to the tilting distance of the steering roller 308 so that the fixing belt 301 and the cover member 500 do not come into contact with each other. However, it is preferable that the cover member 500 is disposed so that the distance from the fixing belt 301 is 10 mm or less. That is, from the viewpoint of suppressing heat radiation from the fixing belt 301, it is preferable that the distance (maximum distance) between the cover member 500 and the fixing belt 301 at the furthest portion is 10 mm or less.

[0052] Here, the above-mentioned average distances t1 and t2 respectively indicate the average distance of the entire heating roller facing portion L1 and the average distance of the entire steering roller facing portion L2, but when holes are made in the covering member 500, these portions are excluded from the calculation of the average distance. Also, the average distance t2 in the steering roller facing portion L2 is the distance when the steering roller 308 is at the rotation center (tilt center) position.

[0053] In this embodiment, the portion L3 facing the third region γ is inclined with respect to the outer circumferential surface of the fixing belt 301 in the third region α so that the distance from the fixing belt 301 increases from the position facing the first region α to the position facing the second region β in a cross section perpendicular to the rotation axis of the heating roller 307. 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 this embodiment, the steering roller facing portion L2 and the heating roller facing portion L1, which have different distances from the fixing belt 301, are smoothly connected to each other by inclining the portion L3 facing the third region γ with respect to the outer circumferential surface of the fixing belt 301. For example, the cross section of the portion L3 facing the third region γ is linear.

[0054] Here, the portion L3 facing the third region γ may be formed, for example, in a stepped shape to gradually change the distance from the fixing belt 301. However, in consideration of the workability of the covering member 500, it is preferable to form the portion L3 facing the third region γ in a shape having a linear cross section (flat plate shape) as in this embodiment.

[0055] [Power saving effect of distance between fixing belt and cover member] Next, a description will be given of the relationship between the distance between the fixing belt 301 and the covering member 500 and the power consumption reduction effect in the fixing device 8. Fig. 5 is a graph showing the results of an experiment conducted to examine the effect of the distance between the fixing belt 301 and the covering member 500 on the power consumption reduction. In the experiment, the steering roller 308 was fixed at the center of rotation to make it easier to compare the effect of the distance on the power consumption reduction.

[0056] In the experiment, three cover members were fabricated and examined, each having a uniform distance between the fixing belt 301 and the cover member 500 from the heating roller facing portion L1 to the steering roller facing portion L2. That is, a cover member with a distance of 3 mm was prepared as Comparative Example 1, a cover member with a distance of 5 mm was prepared as Comparative Example 2, and a cover member with a distance of 8 mm was prepared as Comparative Example 3. In addition, the required power was measured when the temperature of the fixing belt 301 was controlled to be 180° C. while rotating at 300 mm / s, and the amount of power reduction was compared with the case without the cover member. At this time, the required power in Comparative Example 1 was 420 W.

[0057] 5, it was found that the power consumption reduction effect is greater when the distance between the fixing belt 301 and the covering member 500 is shorter. When the reason for this was investigated, it was found that the shorter the distance is, the higher the temperature of the space between the fixing belt 301 and the covering member 500 is measured, and the greater the heat insulation effect is.

[0058] Next, in the present embodiment, the above-mentioned experiment was performed using the cover member 500 (Example) shown in FIG. 4 in a configuration in which the steering roller 308 tilts, and the effect of power reduction was confirmed. As in the above, the reduction in the required power when the temperature was controlled so that the surface temperature was 180° C. was measured and found to be 162 W. The experimental results of the above-mentioned Comparative Examples 1 to 3 and the Example are shown in FIG. 6. In FIG. 6, in addition to the power reduction effect, the steering roller 308 was also configured to tilt in Comparative Examples 1 to 3, and it was confirmed whether the fixing belt 301 and the cover member 500 contacted each other. In Comparative Examples 1 and 2, the distance between the cover member and the fixing belt was 3 mm and 5 mm, respectively, so that in a configuration in which the tilt distance of the steering roller 308 was a maximum of 5 mm, the fixing belt contacted the cover member. In Example 3 and Example, there was no contact. From FIG. 6, it can be seen that the configuration of the Example can greatly reduce the power without the fixing belt 301 and the cover member 500 contacting each other.

[0059] In addition, the smaller the distance between the fixing belt 301 and the covering member 500, the higher the spatial temperature becomes, and heat radiation from the fixing belt 301 can be more effectively suppressed, resulting in a greater power reduction effect. Even if the distance between the fixing belt 301 and the covering member 500 is relatively large, for example, 30 mm, there is an effect of suppressing heat radiation. However, as is clear from FIG. 5, the greater the distance between the fixing belt 301 and the covering member 500, the lower the power reduction effect becomes. For this reason, 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.

[0060] On the other hand, the smaller the distance between the fixing belt 301 and the covering member 500, the greater the power saving effect, but if the distance is too small, there is a risk that the fixing belt 301 and the covering member 500 may come into contact with each other even in an area outside the area where the steering roller 308 tilts. For this reason, it is preferable that the distance between the fixing belt 301 and the covering member 500 is at least 1 mm. In this embodiment, the distance between the fixing belt 301 and the covering member 500 is set to 1 mm or more, and preferably 3 mm or more.

[0061] [Effect of Covering Material on the Covering Rate of the Fixing Belt] Next, a description will be given of the relationship between the coverage rate of the covering member 500 to the fixing belt 301, that is, the proportion of the periphery of the fixing belt 301 that is covered by the covering member 500 with respect to the entire circumference of the fixing belt 301, and the power reduction effect. Fig. 7 is a graph showing the results of an experiment conducted to examine the effect of the coverage rate of the covering member 500 to the fixing belt 301 on power reduction. Here, the coverage rate is the ratio of the area that the covering member 500 faces to the area of ​​the entire circumference of the fixing belt 301 excluding the nip portion N.

[0062] In the experiment, in order to easily compare the effect of the coverage on power reduction, the steering roller 308 was fixed at the center of rotation and examined. In addition, three cover members with different coverage rates were produced as prototypes and examined. That is, a cover member with a coverage rate of 80% was prepared as Comparative Example 4, a cover member with a coverage rate of 60% was prepared as Comparative Example 5, and a cover member with a coverage rate of 20% was prepared as Comparative Example 6. In Comparative Examples 4 to 6, the distance between the fixing belt 301 and the cover member 500 was set to a uniform distance of 5 mm from the heating roller facing portion L1 to the steering roller facing portion L2.

[0063] In addition, the power required was measured when controlling the temperature of the fixing belt 301 so that the surface temperature was 180° C. while rotating at 300 mm / s, and the amount of power reduction was compared with the case where there was no covering member.

[0064] 7, it was found that the power consumption reduction effect is greater when the coverage rate of the covering member 500 on the fixing belt 301 is greater. This means that even if there is a shaft or an auxiliary member arranged by design in a portion facing the outer circumferential surface of the fixing belt 301, there is almost no power consumption reduction effect if the coverage rate of the covering member 500 on the fixing belt 301 is small. Therefore, in order to obtain a power consumption reduction effect, it is preferable that the coverage rate of the covering member on the fixing belt 301 is 25% or more.

[0065] Thus, it is desirable that the coverage rate of the covering member 500 covering the fixing belt 301 is as high as possible. This is because the temperature of the space between the fixing belt 301 and the covering member 500 increases as the coverage rate increases, and heat dissipation can be suppressed. Even if the coverage rate is small, for example 10%, it is slightly effective. However, as is clear from FIG. 7, the smaller the coverage rate, the lower the power reduction effect. For this reason, in this embodiment, the coverage rate of the covering member 500 covering the fixing belt 301 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 high, the covering member 500 may come into contact with the recording material P passing through the nip portion N, so the coverage rate is preferably 80% or less.

[0066] In the case of this embodiment, even if the fixing device 8 is configured to employ a belt member such as the fixing belt 301, the heat dissipation of the belt member can be suppressed. That is, the deviation position of the fixing belt 301 is controlled by tilting the steering roller 308. For this reason, if the cover member 500 for suppressing heat dissipation of the fixing belt 301 is brought too close to the fixing belt 301, there is a risk that the cover member 500 will come into contact with the fixing belt 301. On the other hand, if the cover member 500 is disposed away from the fixing belt 301, the effect of suppressing heat dissipation is reduced.

[0067] For this reason, in this embodiment, the covering member 500 is disposed around the fixing belt 301 so that the average distance t2 between the covering member 500 and the second region β stretched by the steering roller 308 is greater than the average distance t1 between the covering member 500 and the first region α stretched by the heating roller 307 that heats the fixing belt 301. This makes it possible to prevent the covering member 500 from coming into contact with the fixing belt 301 even when the steering roller 308 tilts, while suppressing heat dissipation from the fixing belt 301. As a result, power consumption of the fixing device 8 can be reduced.

[0068] <Other embodiments> In the above embodiment, a configuration has been described in which fixing pad 303 is provided as a contact member on the inner side of fixing belt 301 in order to form a nip portion between fixing belt 301 and pressure roller 305. However, the contact member is not limited to fixing pad 303, and may be a roller member or the like. Also, the method of heating fixing belt 301 is not limited to halogen heater 306 in heating roller 307, and other means such as an electromagnetic induction method or a ceramic heater may be used. [Explanation of symbols]

[0069] 8. Fixing device 301 Fixing belt (belt member) 303 Fixing pad (contact member) 305 Pressure roller (nip forming member) 307 Heating roller 308···Steering roller 500 Covering member

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