JP6128368B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes an image on a recording medium, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Image forming apparatuses such as copiers, printers, facsimiles, and multifunction peripherals thereof are provided with a fixing device that fixes a toner image carried on a recording medium such as paper. Generally, a fixing device includes a fixing member that is heated by a heating source such as a heater, and an opposing member that forms a nip portion in contact with the fixing member. When the image forming operation is started in the image forming apparatus and the toner image is transferred to the sheet, the sheet passes through the nip portion between the fixing member heated to a predetermined temperature and the opposing member. The toner carried on the paper is heated and melted to fix the image.

  In the fixing device, since the heat of the fixing member is taken away by the sheet passing through the nip portion, the fixing member is managed to be maintained at an appropriate temperature by a temperature sensor or the like. On the other hand, in the non-sheet passing area where the sheet does not pass, the heat of the fixing member tends not to be taken away. For this reason, there is a problem that the fixing member overheats in the non-sheet passing region, particularly when the sheet is continuously passed.

  Therefore, conventionally, in order to solve this problem, there has been proposed a fixing device provided with a shielding member that shields heat from a heating source in a non-sheet passing region of the fixing member (fixing roller) (Patent Documents 1, 2, and 5). 3).

  In the fixing device provided with the shielding member as described above, the shielding member is rotated according to the paper size. However, when the rotation angle of the shielding member is determined based on only the paper size in this way, it may not be possible to reliably prevent overheating in the non-sheet passing region.

  In view of such circumstances, the present invention is intended to provide a fixing device capable of reliably preventing an excessive temperature rise in a non-sheet passing region of a fixing belt, and an image forming apparatus including the fixing device. is there.

  In order to solve the above problems, the present invention provides a rotatable fixing member, a heating source for heating the fixing member, an opposing member that forms an nip portion in contact with an outer peripheral surface of the fixing member, and the heating source. A shielding member that is rotatable around the heat source, shields heat from the heating source to the fixing member, temperature measuring means that measures the temperature of the fixing member or the opposing member, and a rotation angle of the shielding member. In the fixing device including the control unit for controlling, the control unit controls a rotation angle of the shielding member based on a temperature measured by the temperature measuring unit.

  According to the present invention, by measuring the temperature of the fixing member or the opposing member and controlling the rotation angle of the shielding member in real time based on the measured temperature, the shielding member is arranged at an appropriate position at an appropriate timing. Therefore, it is possible to reliably prevent overheating in the non-sheet passing region of the fixing sleeve.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a fixing device mounted on the image forming apparatus. It is a figure which shows the state which moved the shielding member to the retracted position. It is a perspective view of the fixing device. It is a figure which shows the support structure of a shielding member. It is a figure which shows the drive means of a shielding member. It is a figure which shows the relationship between the shape of a shielding member, the heat generating part of a halogen heater, and paper size. It is a figure which shows the state which moved the shielding member to the shielding position. It is an enlarged view of a shielding member. It is a flowchart which shows control of the rotation angle of a shielding member. It is a figure which shows other embodiment of a shielding member. It is a figure which shows the state which moved the shielding member to the shielding position.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

  First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Further, a power source (not shown) is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. . A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Although not shown, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as timing rollers for transporting the paper P to the secondary transfer nip at a transport timing is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction. ing.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

  Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG. When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Further, by applying a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current to each primary transfer roller 31, the primary transfer nip between each primary transfer roller 31 and each photoreceptor 5 is applied. A transfer electric field is formed.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by a neutralizing device (not shown), and the surface potential is initialized.

  In the lower part of the printer, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent to the transport path R is temporarily stopped by the registration rollers 12.

  Thereafter, rotation of the registration roller 12 is started at a predetermined timing, and the paper P is conveyed to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. . Then, the toner images on the intermediate transfer belt 30 are collectively transferred onto the paper P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

  FIG. 2 is a cross-sectional view of the fixing device of this embodiment. Hereinafter, the configuration of the fixing device 20 will be described with reference to FIG. As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a pressure roller 22 as an opposing member that contacts the outer peripheral surface of the fixing belt 21, and a heating source that heats the fixing belt 21. A halogen heater 23, a nip forming member 24 that contacts the pressure roller 22 from the inner peripheral side of the fixing belt 21 via the fixing belt 21, and a support member that supports the nip forming member 24. A stay 25, a reflection member 26 that reflects heat from the halogen heater 23 to the fixing belt 21, a shielding member 27 that shields heat from the halogen heater 23, and first temperature measurement means that measures the temperature of the fixing belt 21. The temperature sensor 28a as a temperature sensor, the temperature sensor 28b as a second temperature measuring means for measuring the temperature of the pressure roller 22, and the rotation angle of the shielding member 27 are controlled. Control unit comprises a (not shown) or the like.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven glossiness is formed on the solid portion of the image. It can happen. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided.

  In this embodiment, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is thin and has a small diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. Note that the fixing member and the facing member are not limited to being in pressure contact with each other, and may be configured to simply contact without pressing.

  The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  The halogen heater 23 is disposed on the inner peripheral side of the fixing belt 21 and on the upstream side of the nip portion N in the sheet conveyance direction. Specifically, in FIG. 2, assuming that a virtual straight line passing through the center Q of the nip portion N in the paper transport direction and the rotation center O of the pressure roller 22 is L, the halogen heater 23 is closer to the paper transport direction than the virtual straight line L It is arranged on the upstream side (lower side in FIG. 2). The halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 28a. Is called. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  In this embodiment, two halogen heaters 23 are provided, but the number of halogen heaters 23 may be one or three or more according to the size of the paper used in the printer. However, in consideration of the cost of the halogen heater 23 itself, the inner circumferential space of the fixing belt 21, and the like, it is desirable that the number of halogen heaters 23 be two or less. The heating source for heating the fixing belt 21 is one that heats by radiant heat, and a resistance heating element, a carbon heater, or the like can be used in addition to the halogen heater.

  The nip forming member 24 includes a base pad 241 and a low friction sliding sheet 240 provided on a surface of the base pad 241 facing the fixing belt 21. The base pad 241 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22. The shape of the nip portion N is determined by the base pad 241 receiving the pressure applied by the pressure roller 22. In the present embodiment, the shape of the nip portion N is flat, but may be a concave shape or other shapes. The sliding sheet 240 is provided to reduce sliding friction when the fixing belt 21 rotates. Note that when the base pad 241 itself is formed of a low-friction member, the sliding sheet 240 may not be provided.

  The base pad 241 is made of a heat-resistant member having a heat-resistant temperature of 200 ° C. or more, prevents deformation of the nip forming member 24 due to heat in the toner fixing temperature region, and ensures a stable state of the nip portion N for output. Stabilizes image quality. Examples of the material of the base pad 241 include polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), and polyether ether ketone (PEEK). A general heat resistant resin can be used.

  The base pad 241 is fixedly supported by the stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending. The base pad 241 is also preferably made of a material that is hard to some extent to ensure strength. As a material for the base pad 241, a resin such as a liquid crystal polymer (LCP), a metal, a ceramic, or the like can be used.

  The reflection member 26 is fixedly supported by the stay 25 so as to face the halogen heater 23. By reflecting the heat (or light) radiated from the halogen heater 23 to the fixing belt 21 by the reflecting member 26, the heat is suppressed from being transmitted to the stay 25 and the like, and the fixing belt 21 is efficiently heated. At the same time, we are trying to save energy. As the material of the reflecting member 26, aluminum, stainless steel or the like is used. In particular, in the case of using a material obtained by vapor-depositing silver having a low emissivity (high reflectivity) on an aluminum base material, the heating efficiency of the fixing belt 21 can be improved. A surface of the reflecting member 26 facing the halogen heater 23 is formed so as to expand toward the inner peripheral surface of the fixing belt 21. In the reflecting member 26 shown in FIG. 2, a portion facing the lower side of the halogen heater 23 (portion extending along the circumferential direction of the fixing belt 21) is provided to shield heat at both ends of the halogen heater 23. However, it is not provided over the entire longitudinal direction of the reflecting member 26.

  The shielding member 27 is configured by forming a metal plate having a thickness of 0.1 mm to 1.0 mm in a cross-sectional shape along the inner peripheral surface of the fixing belt 21. In the illustrated example, the shielding member 27 has an endless cross-sectional shape that is not annular in the circumferential direction, and specifically has a partial arc-shaped cross-sectional shape. Further, the shielding member 27 is rotatable around the halogen heater 23, and is rotatable along the circumferential direction of the fixing belt 21 in the present embodiment. Specifically, in the circumferential region of the fixing belt 21, a direct heating region in which the halogen heater 23 directly heats the fixing belt 21 is heated, and other than the shielding member 27 between the halogen heater 23 and the fixing belt 21. There are non-direct heating regions where members (reflecting member 26, stay 25, nip forming member 24, etc.) intervene, but when it is necessary to shield heat, shield member 27 is directly heated region as shown in FIG. It is arranged at the shielding position on the side. On the other hand, when there is no need for heat shielding, as shown in FIG. 3, the shielding member 27 is moved to the retracted position on the non-direct heating region side, and the shielding member 27 is retracted to the back side of the reflecting member 26 and the stay 25. Is possible. Moreover, since the shielding member 27 requires heat resistance, it is preferable to use a metal material such as aluminum, iron, stainless steel, or ceramic as the material.

  FIG. 4 is a perspective view of the fixing device of this embodiment. As shown in FIG. 4, flange members 40 as belt holding members are inserted into both ends of the fixing belt 21, and the fixing belt 21 is rotatably held by the flange members 40. Each flange member 40, halogen heater 23 and stay 25 are fixedly supported by a pair of side plates (not shown) of the fixing device 20.

  FIG. 5 is a diagram illustrating a support structure of the shielding member. As shown in FIG. 5, the shielding member 27 is supported via an arcuate slide member 41 attached to the flange member 40. Specifically, the projection 27 a provided at the end of the shielding member 27 is inserted into the hole 41 a provided in the slide member 41, so that the shielding member 27 is attached to the slide member 41. Also, the slide member 41 is provided with a convex portion 41b, and when the convex portion 41b is inserted into an arcuate groove portion 40a provided in the flange member 40, the slide member 41 slides along the groove portion 40a. It is possible. Thereby, the shielding member 27 can rotate and move integrally with the slide member 41 in the circumferential direction of the flange member 40. In the present embodiment, the flange member 40 and the slide member 41 are made of resin.

  In FIG. 5, only the support structure of one end portion is shown, but the other end portion is similarly held rotatably via the slide member 41.

  FIG. 6 is a diagram illustrating a driving unit of the shielding member. As shown in FIG. 6, in the present embodiment, as a driving unit for the shielding member 27, a motor 42 that is a driving source and a gear train including a plurality of transmission gears 43, 44, and 45 are provided. In the gear train, the gear 43 on one end side is connected to the motor 42, and the gear 45 on the other end side is connected to a gear portion 41 c provided in the circumferential direction of the slide member 41. Thus, when the motor 42 is driven, the driving force is transmitted to the slide member 41 via the gear train, and the shielding member 27 is rotated.

  FIG. 7 is a diagram showing the relationship between the shape of the shielding member, the heat generating portion of the halogen heater, and the paper size. First, the shape of the shielding member 27 will be described in detail with reference to FIG. In the following description, the rotation axis direction of the shielding member 27 is referred to as “axial direction”, and the rotation direction of the shielding member 27, that is, the circumferential direction of the fixing belt 21 is referred to as “circumferential direction”.

  As shown in FIG. 7, the shielding member 27 of the present embodiment is provided adjacent to one of the shielding part 48 in the axial direction of the shielding part 48 and the shielding part 48 provided in a region covering a part of the halogen heater 23 in the axial direction. And an opening 50. Specifically, it includes a pair of shielding portions 48 provided at both ends in the axial direction of the shielding member 27 and a connecting portion 49 that connects the shielding portions 48 in the axial direction. In the present embodiment, the shielding member 27, that is, the pair of shielding portions 48 and the connecting portion 49 are integrally formed using a single metal plate. A region adjacent to the shielding portion 48 in the axial direction is an opening 50 that emits radiant heat from the halogen heater 23 without shielding it. In the present embodiment, the region between the shielding portions 48 in the axial direction, specifically, the region surrounded by the inner edge in the axial direction of the shielding portions 48 and one circumferential edge 54 of the connecting portion 49 is the opening 50. It becomes.

  One circumferential edge 53 of the shielding portion 48 has a straight line portion extending along the axial direction. In the illustrated example, the entire circumferential one edge 53 (a region excluding an inclined portion 52 described later) is a straight line portion. Become. One edge 53 in the circumferential direction of the shielding part 48 is arranged on one side in the circumferential direction from one edge 54 in the circumferential direction of the connecting part 49. That is, when the side on which the shielding member 27 rotates to the shielding position is defined as the shielding side Y, the shielding part 48 extends to the shielding side Y from the connecting part 49. One circumferential edge 54 of the connecting portion 49 and one circumferential edge 53 of the shielding portion 48 are connected by an inner edge in the axial direction of the shielding portion 48 (an inner edge of each shielding portion 48 facing each other). . A straight portion 51 that is parallel to the rotation direction of the shielding member 27 and an inclined portion 52 that is inclined with respect to the rotation direction are formed at the inner edge of the shielding portion 48 in the axial direction. In FIG. 7, each inclined portion 52 is continuously provided on the shielding side Y of the straight portion 51, and is inclined so as to be separated from each other toward the shielding side Y. Thereby, the opening part 50 is formed in the same width | variety between the straight parts 51 toward the shielding side Y, and is formed so that a width | variety may spread between the inclination parts 52. FIG. The other circumferential edge 55 of the shielding member 27, that is, the other circumferential edge of the shielding portion 48 and the connecting portion 49 is a single straight line extending along the axial direction.

  Next, the relationship between the heat generating part of the halogen heater and the paper size will be described. As shown in FIG. 7, in the present embodiment, the length and the arrangement position of the heat generating portions of the halogen heaters 23 are varied in order to change the heating area according to the paper size. Of the two halogen heaters 23, the heat generating portion 23a of one (lower side in the figure) of the halogen heater 23 is disposed on the center in the longitudinal direction, and the heat generating portion 23b of the other halogen heater 23 (upper side in the figure) is It is arrange | positioned at the longitudinal direction both ends, respectively. In this example, the heat generating part 23a on the center side is disposed in a range corresponding to the medium-size sheet passing width W2, and the heat generating part 23b on both ends is larger than the medium-sized sheet passing width W2 and has a large size. And an extra large size sheet passing width W3, W4.

  Further, in the relationship between the shape of the shielding member 27 and the paper size, each straight portion 51 is disposed near the inner side in the axial direction with respect to the end of the paper passing area of the large size paper P3 (paper passing width W3). Each inclined portion 52 is disposed at a position straddling the end of a standard size sheet in the axial direction. In the present embodiment, each inclined portion 52 is disposed at a position straddling the end portion of the paper passing area of the large size paper P3 in the axial direction.

  As an example of the paper size in the present embodiment, for example, the medium size is letter size (paper passing width 215.9 mm) or A4 size (paper passing width 210 mm), and the large size is double letter size (paper passing width 279.4 mm) or A3 size (sheet passing width 297 mm), extra large size A3 Nobi (sheet passing width 329 mm), and the like. However, the paper size example is not limited to this. The medium size, large size, and extra large size referred to here indicate the relative relationship between the sizes, and may be a small size, a medium size, a large size, or the like.

  Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG. When the power switch of the printer main body is turned on, power is supplied to the halogen heater 23 and the pressure roller 22 starts to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the paper P carrying the unfixed toner image T in the above-described image forming process is conveyed in the direction of the arrow A1 in FIG. 2 while being guided by a guide plate (not shown), and the fixing belt 21 in the pressure contact state and It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the fixing belt 21 heated by the halogen heater 23 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper P on which the toner image T is fixed is carried out from the nip portion N in the direction of the arrow A2 in FIG. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of a separation member (not shown). Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

  Next, control of the halogen heater and control of the shielding member for each paper size will be described. First, when passing the medium-size paper P2 shown in FIG. 7, only the range corresponding to the medium-size paper passing width W2 is heated by heating only the heat generating portion 23a on the center side. When passing oversized paper P4, in addition to the heat generating portion 23a on the center side, the heat generating portions 23b on both ends are also heated, and the range corresponding to the oversized paper passing width W4 is heated.

  However, in the present embodiment, the heating range of the halogen heater 23 corresponds only to the medium-size sheet passing width W2 and the extra-large-size sheet passing width W4. For this reason, when passing large size paper P3, if only the heat generating part 23a on the center side is heated, the necessary range is not heated, and the heat generating parts 23a, 23b on the center side and both ends are heated. As a result, the heated range exceeds the large sheet passing width W3. If the large-size sheet P3 is passed as it is in a state in which the heat generating portions 23a and 23b on the both ends on the center side are heated, the fixing belt in the non-sheet-passing area outside the large-size sheet passing width W3. There is a problem that the temperature of 21 rises excessively.

  Therefore, in the present embodiment, when passing the large size paper P3, as shown in FIG. 8, the shielding member 27 is moved to the shielding position. As a result, the shield 48 on both ends can cover the outer area from the vicinity of the end of the large sheet passing width W3, so that the temperature rise of the fixing belt 21 can be suppressed in the non-sheet passing area.

  In the present embodiment, since the shielding portion 48 has an end shape in the circumferential direction, the shielding member 27 is rotated to shield the radiation heat from the halogen heater 23 to the fixing belt 21 by rotating the shielding member 27 ( The shielding range can be adjusted. That is, when the shielding member 27 is rotated to the shielding side Y, the shielding range by the shielding portion 48 can be increased, and when the shielding member 27 is rotated to the open side (the side opposite to the shielding side Y), the shielding portion 48 causes The shielding range can be reduced.

  Further, in the present embodiment, since the inclined portion 52 is provided in the shielding portion 48, the shortest distance between the heat generating portion 23 b and the fixing belt 21 by the shielding range, in particular, the shielding portion 48, by changing the rotation angle of the shielding member 27. It is possible to adjust the range that blocks the route steplessly. In the present embodiment, as shown in FIG. 9, a plurality of rotation angles corresponding to the paper size are set. Specifically, the inclined portion 52 provided at the axial position across the edge of the large-size sheet straddles the heat generating portion 23b (only the center is shown in FIG. 9) on both ends of the halogen heater 23 in the circumferential direction. In the angle region, the rotation angle of the shielding member 27 is set in a plurality of stages. In the illustrated example, the rotation angle of the shielding member 27 is set in three stages of a first stage P1, a second stage P2, and a third stage P3. Note that the rotation angle set according to the paper size is not limited to three steps, and may be two steps or four or more steps.

  By the way, for example, as shown by a one-dot chain line in FIG. 8, if the entire one edge 53 ′ in the circumferential direction of the shielding portion 48 is inclined with respect to the axial direction, the region in which the shielding range can be adjusted can be expanded. However, in this case, since the radiant heat from the heating source leaks from the inclined edge 53 ′, the shielding of the radiant heat by the shielding part 48 becomes insufficient, and the fixing belt 21 may be overheated. Therefore, it is preferable to provide a straight line portion extending along the axial direction as shown by a solid line in FIG.

  Further, for example, as shown by a two-dot chain line in FIG. 8, when the inclined portion 52 ′ of the shielding portion 48 is extended inward in the axial direction, the area of the opening 50 is reduced, so that the sheet passing area of the fixing belt 21 is heated. There is a risk of becoming insufficient. Therefore, it is preferable to provide the straight part 51 at one edge (edge on the opening part 50 side) in the axial direction of the shielding part 48 to ensure the area of the opening part 50.

  When it is no longer necessary to shield the heat, such as when the fixing process is completed, or when the temperature of the non-sheet passing area of the fixing belt 21 falls below a predetermined threshold, the shielding member 27 is returned to the retracted position. In this way, by moving the shielding member 27 to the shielding position as necessary, good fixing can be performed without reducing the sheet passing speed. Note that the connecting portion 49 of the shielding member 27 is disposed in the non-direct heating region regardless of whether the shielding member 27 is in the shielding position (see FIG. 2) or the retracted position (see FIG. 3). Therefore, the connecting portion 49 does not receive the radiant heat of the halogen heater 23 directly.

  In the illustrated example, the rotation center of the shielding member 27 is disposed closer to the center of the circumferential cross section of the fixing belt 21, and each center of the halogen heater 23 (the center of the filament included in the halogen heater 23) is the rotation center of the shielding member 27. Rather than the inner peripheral surface of the fixing belt 21. Accordingly, the shielding member 27 approaches the halogen heater 23 at the shielding position (see FIG. 2), and conversely, the shielding member 27 moves away from the halogen heater 23 at the retracted position (see FIG. 3). Therefore, since the shielding member 27 is not easily affected by the heat from the halogen heater 23 at the retracted position, it is possible to suppress the temperature rise of the shielding member 27 itself.

  Further, as described above, in the configuration in which the nip forming member 24 is provided in the fixing belt 21, it is difficult to retract the shielding member 27 to the nip portion N side. Therefore, in the above embodiment, the halogen heater 23 is disposed on the upstream side of the nip portion N in the sheet conveyance direction, and the shielding member 27 can be moved between the upstream shielding position and the downstream retracted position. It is composed. Thereby, the shielding member 27 can be retracted without interfering with the nip forming member 24, and a large moving stroke of the shielding member 27 can be ensured. In addition, such a configuration capable of ensuring a large movement stroke of the shielding member 27 is because, in the configuration in which the diameter of the fixing belt 21 is reduced in order to reduce the heat capacity as described above, the inner space of the fixing belt 21 is particularly small. Is preferred.

  Note that the temperature sensor 28 a that detects the temperature of the fixing belt 21 is desirably disposed in a region where the temperature increase in the axial direction of the fixing belt 21 is remarkable. In the case of the present embodiment, the temperature is likely to rise particularly in the region outside the large-size sheet passing width W3. Therefore, it is desirable to dispose the temperature sensor 28a outside the large-size sheet passing width W3 (FIG. 7). reference). Further, in the present embodiment, of the two halogen heaters 23, it is the halogen heater 23 having the heat generating portions 23 b on both end sides that is largely caused by the temperature rise, and therefore the heat generating portion 23 b of the halogen heater 23. It is desirable to arrange the temperature sensor 28a at a position opposite to.

  Next, an example of control of the rotation angle of the shielding member 27 will be described with reference to the flowchart of FIG. In this embodiment, the case where the initial position of the shielding member 27 is the retracted position shown in FIG. 3 is shown.

  First, a print request is received, and information such as the paper size (A3 size in the present embodiment) and the number of printed sheets is input to the control unit (step S1). Immediately after receiving the print request, the heat storage state of the fixing device is determined based on the temperature of the surface of the pressure roller 22 measured by the temperature sensor 28b (step S2). Specifically, the heat storage state is determined based on whether the temperature of the pressure roller 22 is equal to or lower than a predetermined temperature (for example, 80 ° C.). When the temperature of the pressure roller 22 is 80 ° C. or less, it is determined that the heat storage of the fixing device is insufficient, and the shielding member 27 is not moved and is maintained in the initial position (retracted position). (Step S3). On the other hand, when the temperature of the pressure roller 22 exceeds 80 ° C., it is determined that the fixing device is storing heat, and the shielding member 27 is rotated to the shielding position (step S4). At this time, the shielding member 27 is arranged at the rotation angle of the first stage P1 in the set angle group (see FIG. 9) corresponding to the A3 size paper width. The temperature measurement of the pressure roller 22 and the determination of the heat storage state are performed immediately after receiving the print request. However, the rotation of the shielding member 27 based on the determination result of the heat storage state causes the surface temperature of the fixing belt 21 to be a predetermined fixing. This is performed after the temperature is reached and before the nip portion N starts to be fed.

  As described above, before passing the nip, the shielding member 27 is rotated by using the heat storage state of the fixing device (specifically, the temperature of the pressure roller 22) as a trigger, and the rotation angle depends on the paper size and the heat storage state (pressure application). The temperature of the roller 22).

  Thereafter, the sheet feeding to the nip portion N is started (step S5). The temperature of the fixing belt 21 is constantly monitored while printing is being performed after the nip sheet starts. Specifically, it is monitored whether or not the temperature of the fixing belt 21 is equal to or higher than a first set temperature (for example, 200 ° C.) (step S6). If the temperature of the fixing belt 21 is 200 ° C. or higher, the shielding member 27 is disposed at the rotation angle of the first stage P1 among the plurality of rotation angles corresponding to the A3 size (step S8). On the other hand, if the temperature of the fixing belt 21 is less than 200 ° C., the shielding member 27 is not rotated (step S9). If the shielding member 27 is already arranged at the rotation angle of the first stage P1 based on the heat storage state or the printing time described later, even if the temperature of the fixing belt 21 is 200 ° C. or higher, The shielding member 27 is not rotated and is maintained at the rotation angle of the first stage P1.

  In the present embodiment, in addition to the temperature of the fixing belt 21, the printing time (for example, the time from the start of paper feeding) is also monitored. Specifically, it is monitored whether the printing time has passed the first set time (step S7). When the first set time (for example, 10 seconds) elapses, the shielding member 27 is arranged at the rotation angle of the first stage P1 among the plurality of rotation angles corresponding to the A3 size (step S8). . On the other hand, if the printing time has not passed 10 seconds, the shielding member 27 is not rotated (step S9). If the shielding member 27 is already arranged at the rotation angle of the first stage P1 based on the heat storage state or the temperature of the fixing belt 21, the shielding is performed even if the paper passing time has passed 10 seconds. The member 27 is not rotated but is maintained at the rotation angle of the first stage P1.

  Thereafter, printing is continued, and it is monitored whether or not the temperature of the fixing belt 21 is equal to or higher than a second set temperature (eg, 210 ° C.) (step S10), and the print time is set to a second set time (eg, 20 seconds) Whether or not has passed has been monitored (step S11). When the temperature of the fixing belt 21 is equal to or higher than the second set temperature or the printing time has passed the second set time, the shielding member 27 is disposed at the rotation angle of the second stage P2 (step S12). On the other hand, if the temperature of the fixing belt 21 is lower than the second set temperature and the printing time has not passed 20 seconds, the shielding member 27 is not rotated (step S13).

  Thereafter, printing is continued, and it is monitored whether or not the temperature of the fixing belt 21 is equal to or higher than the third set temperature (for example, 220 ° C.) (step S14), and the print time is set to the second set time (for example, 20 seconds). It is monitored whether or not elapses (step S15). When the temperature of the fixing belt 21 is equal to or higher than the second set temperature or the printing time has passed the second set time, the shielding member 27 is disposed at the rotation angle of the second stage P2 (step S16). On the other hand, if the temperature of the fixing belt 21 is lower than the second set temperature and the printing time has not passed 20 seconds, the shielding member 27 is not rotated (step S17).

  As described above, during the period from the start of nip feeding to the end of printing (that is, during printing), the shielding member 27 is rotated using the temperature of the fixing belt 21 as a trigger, and the rotation angle is determined by the paper size and the temperature of the fixing belt 21. To be determined.

  Through the above steps, printing is completed (step S18). When all the input jobs are completed, printing is finished even in the middle of the above steps.

  For example, when the rotation angle of the shielding member 27 is controlled based only on the paper size, if the paper size is input to the control unit, the input paper size is irrespective of the actual temperature of the fixing belt 21 or the pressure roller 22. The shielding member 27 is arranged at a rotation angle corresponding to the angle. In this case, for example, when the fixing device is almost at room temperature, such as when printing is started after a long stop, the shielding member 27 rotates and shields the radiant heat of the halogen heater 23 while the fixing belt 21 is not sufficiently warmed. Therefore, there is a possibility that the warm-up time becomes long. Further, once the shielding member 27 is arranged at a rotation angle corresponding to the paper size, the rotation angle of the shielding member 27 is not changed until the end of printing. Therefore, even if the temperature of the fixing belt 21 rises for some reason, The shielding member 27 cannot be rotated.

  Therefore, in the above-described fixing device, the shielding member 27 is rotated by using the heat storage state of the fixing device, that is, the temperature of the pressure roller 22 as a trigger before passing the nip, and the shielding member 27 is triggered by the temperature of the fixing belt 21 during printing. Is rotating. Accordingly, the heat of the halogen heater 23 can be shielded by rotating the shielding member 27 at an appropriate timing based on the actual heating state of the fixing belt 21 or the pressure roller 22.

  Further, in the above fixing device, the temperature sensor 28a is provided in a part of the fixing belt 21 in the axial direction, and therefore the temperature in the axial region where the temperature sensor 28a is not provided cannot be monitored. Further, the temperature of the fixing belt 21 may suddenly rise during printing. In such a case, it may be too late to rotate the shielding member 27 after the temperature of the fixing belt 21 is detected by the temperature sensor 28a. is there. In these cases, if the shielding member 27 is rotated using only the temperature of the fixing belt 21 as a trigger, the shielding member 27 cannot be rotated at an appropriate timing, which may cause an excessive temperature rise at the end of the fixing belt 21. is there. Therefore, in the fixing device described above, the shielding member 27 is rotated using the printing time as a trigger in addition to the temperature of the fixing belt 21. That is, the relationship between the printing time of the paper size and the temperature of the fixing belt 21 is acquired in advance from past printing data and experimental results, and the printing time for rotating the shielding member 27 is set based on this relationship. . In this way, by rotating the shielding member 27 using the temperature of the fixing belt 21 and the printing time as a trigger, even when monitoring based on the temperature of the fixing belt 21 is not sufficient, the shielding member 27 can be appropriately timed. It is possible to shield the heat of the halogen heater 23 by rotating at.

  In the fixing device, the rotation angle of the shielding member 27 is determined based on the paper size and the temperature of the pressure roller 22 or the fixing belt 21. Thereby, since the shielding range of the radiant heat by the shielding member 27 can be set so that the temperature of the fixing belt 21 falls within an appropriate range, it is possible to reliably prevent the temperature increase of the fixing belt 21. In particular, in this embodiment, since the shielding range can be finely adjusted by providing the shielding member 27 with the inclined portion 52, the shielding member 27 is optimally rotated based on the temperature of the pressure roller 22 or the fixing belt 21. Can be placed on the corner. Further, by selecting one rotation angle based on the temperature of the pressure roller 22 or the fixing belt 21 from a plurality of rotation angles set for each paper size, the rotation angle can be determined with simple control. Can do.

  In addition, in the above fixing device, the shielding member 27 is determined based on the paper size and the printing time. Accordingly, even when the rotation angle of the shielding member 27 cannot be determined by the temperature of the fixing belt 21 during printing, the rotation angle of the shielding member 27 is appropriately determined by estimating the heating state of the fixing belt 21 from the printing time. can do.

  In the above fixing device, the rotation angle of the shielding member 27 is controlled based on the temperature of the fixing belt 21 during printing. However, the present invention is not limited to this, and the shielding member 27 is based on the temperature of the pressure roller 22. May be controlled (see parentheses in FIG. 10). This is because the pressure roller 22 rotates while being in contact with the fixing belt 21, so that the temperature of the fixing belt 21 can be estimated from the temperature of the pressure roller 22. As a result, even if it is difficult to arrange the temperature sensor 28a for measuring the temperature of the fixing belt 21 due to restrictions on the layout inside the image forming apparatus, etc., the pressure roller 22 of the temperature sensor 28b is used. Based on the measured temperature, the timing and angle of rotation of the shielding member 27 can be controlled. In this case, it is desirable that the temperature sensor 28b for measuring the temperature of the pressure roller 22 is disposed in the same axial position as the temperature sensor 28a, that is, outside the large sheet passing width W3 (FIG. 7). reference).

  In the above embodiment, the rotation angle of the shielding member 27 during printing is determined based on the paper size and the printing time (steps S7, S11, S15). In addition to this, or instead of this, The rotation angle of the shielding member 27 during printing may be determined based on the paper size and the number of printed sheets. That is, the relationship between the number of printed sheets of the paper size and the temperature of the fixing belt 21 is acquired in advance from past print data and experimental results, and the number of printed sheets on which the shielding member 27 is to be rotated is set based on this relationship. . When the actual number of printed sheets exceeds a preset number of printed sheets, the shielding member 27 is disposed at a rotation angle corresponding to the number of printed sheets.

  Further, the case where the shielding member 27 is rotated to the shielding side Y has been described above. However, the shielding member 27 is moved to the open side (the opposite side to the shielding side Y) based on the temperature of the fixing belt 21 or the pressure roller 22. It may be rotated. Specifically, when the fixing belt 21 or the pressure roller 22 is at a predetermined temperature or lower during printing, the shielding member 27 is rotated to the open side, thereby radiating heat from the halogen heater 23 to the fixing belt 21. By increasing the temperature, the fixing belt 21 can be raised to a desired temperature (for example, a fixing temperature) at an early stage.

  FIG. 11 shows another embodiment of the shielding member. In the shielding member 27 shown in FIG. 11, the shielding portions 48 on both ends are each formed in a shape having two step portions. Specifically, each shielding part 48 is comprised by the 1st shielding part 48b with a large longitudinal direction width | variety, and the 2nd shielding part 48a with a small longitudinal direction width | variety. The first shielding portions 48b are connected to each other through a connecting portion 49, and the second shielding portion 48a is continuously provided on the outer side in the axial direction of the first shielding portion 48b. One edge 53a in the circumferential direction of the second shielding part 48a is provided on one side in the circumferential direction (shielding side Y) with respect to one edge 53b in the circumferential direction of the first shielding part 48b, and one edge in the circumferential direction of the first shielding part 48b. The edge 53 b is provided on one side in the circumferential direction (shielding side Y) with respect to one edge 54 in the circumferential direction of the connecting portion 49. In addition, inclined portions 52a and 52b are formed on the inner edges of the second shielding portion 48a that face each other and the inner edges of the first shielding portion 48b that face each other. In the illustrated example, both inner edges are composed of only the inclined portions 52a and 52b. Has been. The inner edge (inclined part 52b) of the pair of shielding parts 48b and one edge 53b in the circumferential direction, the inner edge (inclined part 52a) of the pair of second shielding parts 48a, and the one edge 54 in the circumferential direction of the connecting part 49 are surrounded. This area becomes the opening 50.

  In the embodiment shown in FIG. 11, at least four types of paper are used: small size paper P1, medium size paper P2, large size paper P3, and extra large size paper P4. As an example of the paper size in this embodiment, for example, a small size is a postcard size (paper passing width 100 mm), a medium size is A4 size (paper passing width 210 mm), a large size is A3 size (paper passing width 297 mm), and an extra large size is A3. Nobi (sheet passing width 329 mm). However, the paper size example is not limited to this.

  Here, the paper passing width W1 of the small size paper P1 is in a range smaller than the length of the heat generating portion 23a on the center side. Further, in relation to the shape of the shielding member 27, each inclined portion 52b of the first shielding portion 48b is disposed at a position straddling the end portion of the small size paper passing width W1, and each inclined portion of the second shielding portion 48a. 52a is disposed at a position across the end of the large sheet passing width W3. Note that the positional relationship between the paper sizes other than the small size (medium, large, extra large) and each of the heat generating portions 23a, 23b is the same as in the above embodiment, and thus the description thereof is omitted.

  When the small size paper P1 is passed, only the heat generating portion 23a on the center side is heated. However, in this case, the range heated by the heat generating part 23a on the center side exceeds the small sheet passing width W1, so that the shielding member 27 is moved to the shielding position as shown in FIG. As a result, since both the first shielding portions 48b can cover the outer area from the vicinity of the end of the small sheet passing width W1, the temperature increase of the fixing belt 21 can be suppressed in the non-sheet passing area.

  The control of the halogen heater 23 and the shielding member 27 when passing other size sheets (medium, large, extra large) is the same as in the above embodiment. In this case, the function as the shielding part 48 in the embodiment is performed by the second shielding part 48a.

  In the case of the embodiment shown in FIG. 11, similarly to the shielding portion 48 of the above embodiment, the inclined portions 52a and 52b are provided in the second shielding portion 48a and the first shielding portion 48b, respectively. It is possible to adjust the range which covers each heat-emitting part 23a, 23b by each shielding part 48a, 48b by changing the rotation position of.

  The present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention. In the above embodiment, the case where the present invention is applied to a fixing device using a fixing belt has been described as an example. However, a configuration in which a hollow (cylindrical) or solid fixing roller is used instead of the fixing belt. It is possible to apply the present invention. Further, the shape of the shielding member is not limited to the above-described embodiment. Depending on the paper size used, the shielding member may be formed in a shape having three or more step portions.

  In the above embodiment, when the shielding member 27 is disposed at the retracted position (see FIG. 3), a part of the shielding member 27 is directly disposed in the heating region. By devising the shape and rotation stroke of the shielding member 27, or the shape of the stay 25 and the reflecting member 26, when the shielding member 27 is disposed at the retracted position, the entire shielding member 27 is disposed in the indirect heating region. May be. In this case, since the shielding member 27 is not heated at the retracted position, deformation and deterioration due to heating can be prevented more reliably.

  Further, the image forming apparatus equipped with the fixing device according to the present invention is not limited to the printer as shown in FIG. 1, but can be a copying machine, a facsimile, or a complex machine thereof.

20 Fixing device 21 Fixing belt (fixing member)
22 Pressure roller (opposing member)
23 Halogen heater (heating source)
24 Nip forming member 25 Stay (support member)
26 Reflecting member 27 Shielding member 28a, 28b Temperature sensor (temperature measuring means)
48 shielding part 49 connecting part 50 opening part 51 straight part 52 inclined part N nip part P paper (recording medium)

Japanese Patent No. 4130898 JP 2008-58833 A JP 2008-139779 A

Claims (9)

A rotatable fixing member; a heating source that heats the fixing member by radiant heat ; an opposing member that contacts the outer peripheral surface of the fixing member to form a nip portion; and a rotatable around the heating source. A fixing device comprising: a shielding member that shields radiant heat from the heating source to the fixing member; a temperature measuring unit that measures the temperature of the fixing member or the opposing member; and a control unit that controls a rotation angle of the shielding member. In the device
The heating source includes a central heat generating portion disposed in a longitudinal central portion, and end heat generating portions disposed at both longitudinal end portions,
When printing a sheet having a width equal to or less than the longitudinal dimension of the central heating portion, the central heating portion is heated and the end heating portion is not heated.
The fixing device, wherein the control unit controls a rotation angle of the shielding member based on a temperature measured by the temperature measuring unit.   The fixing device according to claim 1, wherein when the temperature measured by the temperature measuring unit reaches a predetermined temperature, the control unit rotates the shielding member to the shielding side.   The fixing device according to claim 2, wherein when the printing time reaches a predetermined time, the control unit rotates the shielding member to the shielding side.   The temperature of the counter member is measured by the temperature measuring means after the printing request is received and before the start of nip feeding, and the control unit rotates the shielding member based on the measured temperature. The fixing device according to any one of the above.   The fixing device according to claim 4, wherein the control unit rotates the shielding member after the temperature of the facing member reaches a temperature at which fixing can be performed.   6. The control unit according to claim 1, wherein when the temperature measured by the temperature measuring unit reaches a predetermined temperature between the start of nip feeding and the end of printing, the control unit rotates the shielding member to the shielding side. The fixing device according to 1. The fixing member is an endless fixing belt;
7. The fixing device according to claim 1, further comprising a nip forming member that forms the nip portion in contact with the opposing member via the fixing belt. The fixing device according to claim 1, wherein the temperature measuring unit is disposed at a position facing the end heat generating portion. An image forming apparatus having a fixing device according to any one of claims 1 to 8.

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