JP2016090888A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate a heating stopping device at an appropriate timing while suppressing a reduction in durability of members arranged on the inner diameter side of a fixing belt.SOLUTION: A fixing device 18 of the present invention includes a fixing belt 22 that is rotatably provided around a rotation axis A, a pressure member 23 that is in pressure contact with the fixing belt 22 to form a fixing nip 39, a heat source 24 that heats the fixing belt 22, a reflecting member 25 that reflects radiation heat emitted from the heat source 24, and a heating stopping device 29 that operates at a predetermined temperature to stop heating of the fixing belt 22 by the heat source 24. The reflecting member 25 includes a first reflecting part 44 that has a position in the rotation axis direction corresponding to that of the heating stopping device 29 and has a shape recessed toward a side separating from the heat source 24, and a second reflecting part 45 that has a position in the rotation axis direction different from that of the heating stopping device 29 and does not have a shape recessed toward a side separating from the heat source 24.SELECTED DRAWING: Figure 3

Description

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

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines and printers include a fixing device that fixes a toner image onto a recording medium such as paper.

  For example, a fixing belt, a pressure member that presses against the fixing belt to form a fixing nip, a heat source that heats the fixing belt, and a reflective member that reflects radiant heat radiated from the heat source toward the inner peripheral surface of the fixing belt In addition, there is known a fixing device including a heating stop device facing the outer peripheral surface of the fixing belt (see Patent Document 1). In such a fixing device, when the temperature of the fixing belt is excessively high, the heating stop device is activated to stop the heating of the fixing belt by the heat source.

JP 2013-178472 A

  In the fixing device as described above, a reflecting member having a shape that is recessed toward the side away from the heat source may be used (see FIG. 2 of Patent Document 1). By using the reflecting member having such a shape, it is possible to intensively reflect the radiant heat radiated from the heat source toward the inner peripheral surface of the fixing belt. On the other hand, when the reflection member having the shape as described above is used, the reflection member excessively absorbs the radiant heat radiated from the heat source, and the reflection member may be excessively heated. When the temperature of the reflecting member is excessively increased in this manner, the heat of the reflecting member is arranged on the inner diameter side of the fixing belt (for example, a pressing member that presses the fixing belt toward the pressing member or the pressing member is supported. The temperature of the member that is transmitted to the support member and disposed on the inner diameter side of the fixing belt also rises. As a result, the durability of the member disposed on the inner diameter side of the fixing belt may be reduced.

  Further, in the fixing device as described above, when the heat source runs away (when the heat source heats the fixing belt while the fixing belt is stopped), the facing distance between the fixing belt and the heating stop device is too wide. There is a risk that the timing at which the heating stop device operates will be delayed.

  In view of the above circumstances, an object of the present invention is to operate a heating stop device at an appropriate timing while suppressing a decrease in durability of a member disposed on the inner diameter side of the fixing belt.

  The fixing device of the present invention includes a fixing belt that is rotatably provided around a rotation shaft, a fixing nip that is pressed against the fixing belt, and a pressure member that is rotatably provided, and an inner diameter side of the fixing belt. A heat source that heats the fixing belt, a reflective member that reflects radiant heat radiated from the heat source toward the inner peripheral surface of the fixing belt, and presses the fixing belt toward the pressure member side. A pressing member that opposes the outer peripheral surface of the fixing belt, and a heating stop device that operates at a predetermined temperature to stop heating of the fixing belt by the heat source, and the reflecting member is in the direction of the rotation axis Unlike the heating stop device, the first reflecting portion having a shape corresponding to the heating stop device and having a shape recessed toward the side away from the heat source is different from the heating stop device. A second reflecting portion having no shape recessed toward the side that is characterized in that it comprises.

  Since the first reflecting portion has a shape that is recessed toward the side away from the heat source as described above, the radiant heat radiated from the heat source is reduced in the fixing belt in the region where the position in the rotation axis direction corresponds to the heating stop device. It becomes possible to reflect in a concentrated manner toward the peripheral surface. Accordingly, when the heat source heats the fixing belt while the rotation of the fixing belt is stopped, the thermal expansion of the fixing belt can be promoted, and the distance between the fixing belt and the heating stop device is widened. Can be suppressed. Therefore, it becomes possible to operate the heating stop device at an appropriate timing.

  In addition, since the second reflecting portion does not have a shape that is recessed toward the side away from the heat source, the reflecting member can be prevented from excessively absorbing the radiant heat radiated from the heat source, and an excessive temperature rise of the reflecting member can be prevented. It becomes possible to do. Along with this, it becomes possible to suppress an increase in the temperature of the member disposed on the inner diameter side of the fixing belt due to the heat transfer from the reflecting member, and the durability of the member disposed on the inner diameter side of the fixing belt is improved. It can suppress that it falls.

  The first reflecting portion is bent toward the side closer to the heat source from a first main body portion extending along the recording medium conveyance direction and both end portions of the first main body portion in the recording medium conveyance direction. A second guide portion extending along the recording medium conveyance direction, and spaced apart from the heat source from both ends of the second main body portion in the recording medium conveyance direction. And a second guide portion bent toward the side.

  By adopting such a configuration, the configuration of the reflecting member can be simplified.

  Each said 1st guide part may be cut and raised from the said each 2nd guide part toward the side approaching the said heat source.

  By adopting such a configuration, each first guide portion can be easily formed.

  Each of the first guide portions may be bent at an obtuse angle from the both end portions of the first main body portion in the conveyance direction of the recording medium.

  By adopting such a configuration, the radiant heat radiated from the heat source can be reflected more intensively toward the inner peripheral surface of the fixing belt by the first guide portions.

  The fixing device may further include a support member that supports the pressing member, and at least a part of the support member may be inserted between the second guide portions.

  By adopting such a configuration, the support member and the reflection member can be easily positioned.

  The heat source is provided at a position offset with respect to the rotation shaft, and the heating stop device faces an outer peripheral surface of a portion of the fixing belt that is closest to the heat source, and the rotation of the fixing belt is stopped. In this state, when the heat source heats the fixing belt, a portion of the fixing belt that is closest to the heat source is deformed by thermal expansion and comes into contact with the heating stop device. good.

  By adopting such a configuration, when the heat source heats the fixing belt while the rotation of the fixing belt is stopped, the heating stop device can be reliably operated.

  The image forming apparatus of the present invention includes any one of the fixing devices described above.

  According to the present invention, it is possible to operate the heating stop device at an appropriate timing while suppressing the deterioration of the durability of the member disposed on the inner diameter side of the fixing belt.

1 is a schematic diagram illustrating an outline of a printer according to an embodiment of the present invention. 1 is a side view showing a fixing device according to an embodiment of the present invention. It is III-III sectional drawing of FIG. It is IV-IV sectional drawing of FIG. FIG. 5 is a perspective view showing a reflecting plate in the fixing device according to the embodiment of the present invention. 1 is a block diagram illustrating a control system for a fixing device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating a state in which the heater heats the fixing belt in a state where the rotation of the fixing belt is stopped in the fixing device according to the embodiment of the present invention.

  First, the overall configuration of an electrophotographic printer 1 (image forming apparatus) will be described with reference to FIG. Hereinafter, the front side of the sheet in FIG. Arrows Fr, Rr, L, R, U, and Lo appropriately attached to the drawings indicate the front side, rear side, left side, right side, upper side, and lower side of the printer 1, respectively.

  The printer 1 includes a box-shaped printer main body 2, and a paper feed cassette 3 that stores paper (recording medium) is accommodated in a lower portion of the printer main body 2. A paper discharge tray 4 is disposed on the upper surface of the printer main body 2. Is provided. An upper cover 5 is attached to the upper surface of the printer main body 2 so as to be openable and closable on the side of the paper discharge tray 4, and a toner container 6 is stored below the upper cover 5.

  An exposure unit 7 composed of a laser scanning unit (LSU) is disposed below the discharge tray 4 above the printer body 2, and an image forming unit 8 is provided below the exposure unit 7. Yes. The image forming unit 8 is rotatably provided with a photosensitive drum 10 as an image carrier. Around the photosensitive drum 10, a charger 11, a developing device 12, a transfer roller 13, and a cleaning device are provided. The apparatus 14 is disposed along the rotation direction of the photosensitive drum 10 (see arrow X in FIG. 1).

  A paper transport path 15 is provided inside the printer main body 2. A paper feed unit 16 is provided at the upstream end of the conveyance path 15, and a transfer unit 17 configured by the photosensitive drum 10 and the transfer roller 13 is provided at a middle portion of the conveyance path 15. Is provided with a fixing device 18, and a paper discharge unit 20 is provided at the downstream end of the conveyance path 15. A reverse path 21 for double-sided printing is formed below the transport path 15.

  Next, an image forming operation of the printer 1 having such a configuration will be described.

  When the printer 1 is turned on, various parameters are initialized, and initial setting such as temperature setting of the fixing device 18 is executed. Then, when image data is input from a computer or the like connected to the printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 10 is charged by the charger 11, exposure corresponding to the image data is performed on the photosensitive drum 10 by laser light from the exposure device 7 (see the two-dot chain line P in FIG. 1). The electrostatic latent image is formed on the surface of the photosensitive drum 10. Next, the electrostatic latent image is developed by the developing device 12 into a toner image with toner.

  On the other hand, the sheet taken out from the sheet cassette 3 by the sheet feeding unit 16 is conveyed to the transfer unit 17 in synchronization with the above-described image forming operation, and the toner image on the photosensitive drum 10 is transferred to the sheet by the transfer unit 17. Is transcribed. The sheet on which the toner image has been transferred is conveyed downstream in the conveyance path 15 and enters the fixing device 18 where the toner image is fixed on the sheet. The paper on which the toner image is fixed is discharged from the paper discharge unit 20 to the paper discharge tray 4. The toner remaining on the photosensitive drum 10 is collected by the cleaning device 14.

  Next, the fixing device 18 will be described in detail with reference to FIGS. The arrows Y in FIGS. 3 to 5 indicate the sheet conveyance direction. 2 and 5 indicate the inner side in the front-rear direction, and the arrow O in FIGS. 2 and 5 indicates the outer side in the front-rear direction.

  As shown in FIGS. 2 to 4, the fixing device 18 includes a fixing belt 22, a pressure roller 23 (pressure member) disposed on the lower side (outside) of the fixing belt 22, and the fixing belt 22. A heater 24 (heat source) disposed on the inner diameter side, a reflection plate 25 (reflection member) disposed on the lower side of the heater 24 on the inner diameter side of the fixing belt 22, and a lower side of the reflection plate 25 on the inner diameter side of the fixing belt 22. A support member 26 arranged on the side, a pressing member 27 arranged below the support member 26 on the inner diameter side of the fixing belt 22, and fixed to both front and rear ends of the support member 26 on the inner diameter side of the fixing belt 22. A cover member 28, a thermocut 29 (heating stop device) disposed on the upper side (outside) of the fixing belt 22, and a shape regulating member 30 mounted on both front and rear ends of the fixing belt 22 are provided. In FIG. 2, the inside of the fixing belt 22 is seen through.

  The fixing belt 22 has a substantially cylindrical shape that is long in the front-rear direction. The fixing belt 22 is provided to be rotatable around a rotation axis A extending in the front-rear direction. That is, in the present embodiment, the front-rear direction is the rotation axis direction of the fixing belt 22. The fixing belt 22 includes a sheet passing area R1 and a non-sheet passing area R2 provided on both front and rear sides of the sheet passing area R1 (outside in the front and rear direction of the sheet passing area R1). The sheet passing area R1 is an area through which the maximum size sheet passes. The non-sheet passing area R2 is an area through which a maximum size sheet does not pass.

  The fixing belt 22 has flexibility and is endless in the circumferential direction. The fixing belt 22 includes, for example, a base material layer 35, an elastic layer 36 provided around the base material layer 35, and a release layer 37 that covers the elastic layer 36. The base material layer 35 of the fixing belt 22 is formed of a metal such as SUS or nickel, for example. The base material layer 35 of the fixing belt 22 may be formed of a resin such as PI (polyimide). The elastic layer 36 of the fixing belt 22 is made of, for example, silicon rubber, and has a thermal expansion coefficient larger than that of the base material layer 35 of the fixing belt 22. The thickness of the elastic layer 36 of the fixing belt 22 is, for example, 270 μm. The release layer 37 of the fixing belt 22 is formed of, for example, a PFA tube. The thickness of the release layer 37 of the fixing belt 22 is, for example, 20 μm.

  The pressure roller 23 has a substantially cylindrical shape that is long in the front-rear direction. The pressure roller 23 is in pressure contact with the fixing belt 22, and a fixing nip 39 is formed between the fixing belt 22 and the pressure roller 23. The pressure roller 23 is rotatably provided.

  The pressure roller 23 includes, for example, a cylindrical core member 40, an elastic layer 41 provided around the core member 40, and a release layer 42 that covers the elastic layer 41. The core material 40 of the pressure roller 23 is made of metal such as iron, for example. The elastic layer 41 of the pressure roller 23 is made of, for example, silicon rubber. The release layer 42 of the pressure roller 23 is formed by, for example, a PFA tube.

  The heater 24 is constituted by, for example, a halogen heater. The heater 24 is disposed in the upper part of the internal space of the fixing belt 22 (the portion on the side away from the pressure roller 23), and is located above the rotation axis A of the fixing belt 22 (on the side away from the pressure roller 23). ). Therefore, in the present embodiment, the upper end portion 22 a of the fixing belt 22 is the portion of the fixing belt 22 that is closest to the heater 24.

  The reflector 25 has a shape that is long in the front-rear direction. The reflector 25 is made of a metal such as bright aluminum, for example. The reflection plate 25 is disposed between the heater 24 and the support member 26.

  As shown in FIG. 5, the reflecting plate 25 includes a first reflecting portion 44 and second reflecting portions 45 provided on both front and rear sides (front and rear direction outside) of the first reflecting portion 44.

  As shown in FIG. 2, the first reflecting portion 44 is provided at a position corresponding to the front-rear direction center portion Z (corresponding to the front-rear direction center portion of the entire fixing belt 22) of the sheet passing region R <b> 1 of the fixing belt 22. It has been. The position of the first reflecting portion 44 in the front-rear direction corresponds to the thermocut 29.

  As shown in FIGS. 3 and 5, the first reflecting portion 44 has a shape that is recessed toward the lower side (side away from the heater 24). A concave portion 48 that is open upward is formed in the first reflecting portion 44, and the lower portion of the heater 24 is inserted into the concave portion 48.

  The first reflecting portion 44 includes a first main body portion 46 extending horizontally along the left-right direction (paper transport direction), and an upper side (heater) from the left and right end portions (both end portions in the paper transport direction) of the first main body portion 46. 1st guide part 47 bent at an obtuse angle toward the side (approaching 24). The upper surface of the first main body 46 is opposed to the heater 24 and is a reflective surface (mirror surface) that reflects the radiant heat radiated from the heater 24 toward the inner peripheral surface of the fixing belt 22. The spacing between the first guide portions 47 is wider toward the upper side (side approaching the heater 24).

  As shown in FIG. 2, each of the second reflecting portions 45 is provided at a position corresponding to the front and rear side portions (portions excluding the center portion Z in the front-rear direction) of the fixing belt 22 and the non-sheet passing region R2. It has been. Each second reflecting portion 45 is different from the thermo-cut 29 in the position in the front-rear direction.

  As shown in FIGS. 4 and 5, each second reflecting portion 45 has a shape that is recessed toward the upper side (side approaching the heater 24). That is, each second reflecting portion 45 does not have a shape recessed toward the lower side (side away from the heater 24).

  Each of the second reflecting portions 45 includes a second main body portion 49 that extends horizontally along the left-right direction (paper transport direction), and the left and right ends of the second main body portion 49 (both ends in the paper transport direction). And a second guide portion 50 bent at a right angle toward the side away from the heater 24.

  The upper surface of the second main body portion 49 of each second reflecting portion 45 faces the heater 24, and a reflecting surface (mirror surface) that reflects the radiant heat radiated from the heater 24 toward the inner peripheral surface of the fixing belt 22. It has become. The second main body portion 49 is continuous with the first main body portion 46 of the first reflecting portion 44, and constitutes a flat plate portion together with the first main body portion 46. A two-dot chain line L in FIG. 5 indicates a boundary between the first main body portion 46 and the second main body portion 49.

  A portion between each second guide portion 50 of the front second reflecting portion 45 and each second guide portion 50 of the second rear reflecting portion 45 is cut and raised toward the upper side (side approaching the heater 24). The cut and raised portions serve as the first guide portions 47 of the first reflecting portion 44. In other words, each first guide portion 47 of the first reflecting portion 44 is raised upward from each second guide portion 50 of each second reflecting portion 45.

  The support member 26 has a shape that is long in the front-rear direction. The upper portion of the support member 26 is inserted between the second guide portions 50 of the second reflection portions 45 of the reflection plate 25. The support member 26 supports the reflection plate 25 via the spacer 51, and is not in direct contact with the reflection plate 25. The support member 26 is formed by combining a pair of L-shaped metal plates 52 and has a substantially rectangular cross-sectional shape. An engagement protrusion 53 that protrudes downward is provided at the lower right corner of the support member 26. The engagement protrusion 53 is formed by extending one sheet metal 52 downward.

  The pressing member 27 has a flat plate shape that is long in the front-rear direction. The pressing member 27 is made of a heat resistant resin such as LCP (liquid crystal polymer). An engaging recess 55 is provided at the right end of the upper surface of the pressing member 27. The engagement protrusions 53 of the support member 26 are engaged with the engagement recesses 55. A plurality of bosses 56 protrude from the upper surface of the pressing member 27. The upper end portion of each boss 56 is in contact with the lower surface of the support member 26. With the configuration as described above, the pressing member 27 is supported by the support member 26, and the warping of the pressing member 27 is restricted.

  The right side portion (the portion on the downstream side in the paper transport direction) of the lower surface of the pressing member 27 is the lower side (the pressure roller 23 side) from the left side (upstream side in the paper transport direction) to the right side (downstream side in the paper transport direction). ). The lower surface of the pressing member 27 presses the fixing belt 22 toward the lower side (pressure roller 23 side).

  Each cover member 28 is substantially U-shaped when viewed from the front. Each cover member 28 has a position in the front-rear direction corresponding to each non-sheet passing region R2 of the fixing belt 22, and has a function of blocking radiant heat from the heater 24 toward each non-sheet passing region R2 of the fixing belt 22. ing.

  Each cover member 28 is bent downward from a curved portion 57 that is curved in an arc shape upward, and from both left and right end portions (upstream and downstream ends in the paper transport direction) of the curved portion 57. And an attachment portion 58. The curved portion 57 is disposed along the inner peripheral surface of the fixing belt 22. The lower end of each attachment portion 58 is attached to the left and right side surfaces of the support member 26.

  The thermocut 29 is, for example, a thermostat of a bimetal system (a system in which a contact is formed by two kinds of metals having different coefficients of thermal expansion). The thermo cut 29 is disposed immediately above the upper end portion 22 a of the fixing belt 22 (the portion of the fixing belt 22 that is closest to the heater 24) and faces the outer peripheral surface of the upper end portion 22 a of the fixing belt 22. . The thermocut 29 is provided at a position corresponding to the front-rear direction center portion Z (corresponding to the front-rear direction center portion of the entire fixing belt 22) of the sheet passing region R1 of the fixing belt 22.

  Each shape regulating member 30 is arranged on the outer side in the front-rear direction than each cover member 28. Each shape regulating member 30 includes a regulating piece 60 and a ring piece 61 attached to the regulating piece 60.

  The restricting piece 60 of each shape restricting member 30 includes a base portion 62 and a restricting portion 63 that projects from the inner surface of the base portion 62 in the front-rear direction. The restriction piece 60 is provided with a through hole 64 penetrating the base portion 62 and the restriction portion 63 along the front-rear direction, and the heater 24 passes through the through hole 64. The restricting portion 63 is curved in an arc shape along the outer periphery of the through hole 64 and has a substantially downward C-shape. The restricting portion 63 is inserted at both front and rear end portions of the fixing belt 22. Thereby, the shape of the fixing belt 22 is regulated (deformation of the fixing belt 22 is suppressed).

  The ring piece 61 of each shape regulating member 30 has an annular shape. The ring piece 61 is attached to the outer periphery of the restriction portion 63 of the restriction piece 60. The ring piece 61 is disposed outside the front and rear ends of the fixing belt 22 in the front-rear direction, and regulates the meandering (moving outward in the front-rear direction) of the fixing belt 22. The ring piece 61 is disposed on the inner side in the front-rear direction of the base portion 62 of the restriction piece 60, thereby restricting the movement of the ring piece 61 outward in the front-rear direction.

  Next, the control system of the fixing device 18 will be described with reference to FIG.

  The fixing device 18 is provided with a control unit 71 (CPU). The control unit 71 is connected to a storage unit 72 configured by a storage device such as a ROM or a RAM. Based on the control program and control data stored in the storage unit 72, the control unit 71 is connected to the fixing device 18. It is configured to control each part. The storage unit 72 stores the operating temperature T of the thermocut 29.

  The control unit 71 is connected to a drive source 73 configured by a motor or the like, and the drive source 73 is connected to the pressure roller 23. The drive source 73 rotates the pressure roller 23 based on a signal from the control unit 71.

  The controller 71 is connected to a power source 74, and the power source 74 is connected to the heater 24. The heater 24 is operated by supplying power from the power source 74 to the heater 24 based on a signal from the control unit 71. A thermocut 29 is provided in the power supply path from the power supply 74 to the heater 24. The thermo cut 29 is configured to operate at the operating temperature T, cut off the supply of power from the power source 74 to the heater 24, and stop the heating of the fixing belt 22 by the heater 24.

  In the fixing device 18 configured as described above, when the toner image is fixed on the paper, the pressure roller 23 is rotated by the drive source 73 (see arrow B in FIGS. 3 and 4). When the pressure roller 23 rotates in this manner, the fixing belt 22 that is in pressure contact with the pressure roller 23 is driven to rotate in the opposite direction to the pressure roller 23 (see arrow C in FIGS. 3 and 4). When the fixing belt 22 rotates in this way, the fixing belt 22 slides with respect to the pressing member 27.

  Further, when fixing the toner image on the sheet, power is supplied from the power source 74 to the heater 24 to operate the heater 24. When the heater 24 is operated in this way, radiant heat is radiated from the heater 24.

  A part of the radiant heat radiated from the heater 24 is directly irradiated onto the inner peripheral surface of the fixing belt 22 and absorbed, as indicated by an arrow D in FIGS. Further, a part of the radiant heat radiated from the heater 24 is caused by the upper surface of the first main body 46 of the first reflecting portion 44 of the reflecting plate 25 as shown by an arrow E in FIG. And is absorbed by the inner peripheral surface of the fixing belt 22. Further, a part of the radiant heat radiated from the heater 24 is caused by the inner surface of the fixing belt 22 by the inner surface of each first guide portion 47 of the first reflecting portion 44 of the reflecting plate 25 as indicated by an arrow F in FIG. Reflected toward the surface and absorbed by the inner peripheral surface of the fixing belt 22. Further, as shown by an arrow G in FIG. 4, a part of the radiant heat radiated from the heater 24 is formed on the inner peripheral surface of the fixing belt 22 by the upper surface of the second main body portion 49 of the second reflecting portion 45 of the reflecting plate 25. And is absorbed by the inner peripheral surface of the fixing belt 22.

  Due to the above operation, the fixing belt 22 is heated by the heater 24. When the sheet passes through the fixing nip 39 in this state, the toner image is heated and melted, and the toner image is fixed on the sheet.

  When the fixing belt 22 is heated by the heater 24 as described above, if the radiant heat from the heater 24 is reflected by the reflecting plate 25 having an overall shape that is recessed downward, the radiant heat from the heater 24 is reflected by the reflecting plate. 25 may absorb excessively and the reflector 25 may overheat.

  Considering this point, the reflecting plate 25 of the present embodiment has a shape in which only the first reflecting portion 44 disposed immediately below the thermo-cut 29 is recessed downward, and each second reflecting portion 45. Does not have a shape that is recessed downward. By adopting such a configuration, it is possible to prevent the reflection plate 25 from excessively absorbing the radiant heat from the heater 24 and to prevent the reflection plate 25 from being excessively heated. Along with this, it becomes possible to suppress the temperature of the support member 26 and the pressing member 27 from rising due to heat transfer from the reflecting plate 25, and to suppress the durability of the support member 26 and the pressing member 27 from being lowered. can do.

  As described above, the first reflecting portion 44 of the reflecting plate 25 reflects the radiant heat from the heater 24 toward the inner peripheral surface of the fixing belt 22 by both the first main body portion 46 and each first guide portion 47. Let On the other hand, each second reflecting portion 45 of the reflecting plate 25 reflects the radiant heat from the heater 24 toward the inner peripheral surface of the fixing belt 22 only by the second main body portion 49. Therefore, when the fixing belt 22 is heated by the heater 24, the first reflecting portion 44 of the reflecting plate 25 becomes hotter than each second reflecting portion 45, and accordingly, the center portion in the front-rear direction of the support member 26 and the pressing member 27. (The portion corresponding to the first reflecting portion 44 of the reflecting plate 25) is hotter than the other portions. However, even in such a case, the heat of the center part in the front-rear direction of the support member 26 and the pressing member 27 is diffused to other portions, so that the temperature rises so that the durability of the support member 26 and the pressing member 27 is reduced. do not do.

  Incidentally, in the fixing device 18 configured as described above, even when the heating of the fixing belt 22 by the heater 24 is stopped as the fixing belt 22 stops, the upper end portion 22a of the fixing belt 22 is stopped. May be locally heated by the residual heat of the heater 24 and may overshoot (temperature rise). If the facing distance between the upper end portion 22a of the fixing belt 22 and the thermo-cut 29 (hereinafter referred to as the facing distance) is too narrow, the fixing belt 22 will be excessive if the upper end portion 22a of the fixing belt 22 overshoots as described above. There is a possibility that the thermo-cut 29 may be activated even though the temperature is not raised. Once the thermocut 29 is activated, it is difficult to restore the thermocut 29 to the state before the operation, and therefore it is usually necessary to replace the entire fixing device 18.

  In order to avoid such a situation, it is necessary to increase the facing interval. However, if the facing interval is widened, the timing at which the thermo-cut 29 operates is delayed when the heater 24 runs away (when the heater 24 heats the fixing belt 22 while the fixing belt 22 stops rotating). There is a risk of becoming. Therefore, in the present embodiment, the thermocut 29 is operated at an appropriate timing even when the heater 24 runs away as follows.

  As shown in FIG. 3, when the heater 24 is in normal use (when the heater 24 heats the fixing belt 22 while the fixing belt 22 is rotating), the upper end portion 22 a of the fixing belt 22 is thermo-cut 29. And facing each other through a certain distance.

  On the other hand, when the heater 24 runs away (when the heater 24 heats the fixing belt 22 with the rotation of the fixing belt 22 stopped), as shown in FIG. Radiant heat (see arrow D in FIG. 7), radiant heat (see arrow E in FIG. 7) reflected by the first main body 46 of the first reflecting portion 44 of the reflecting plate 25, and the first reflecting portion 44 of the reflecting plate 25. Due to the radiant heat reflected by the first guide portions 47 (see arrow F in FIG. 7), the upper end portion 22a of the central portion Z in the front-rear direction of the fixing belt 22 is intensively heated. Along with this, the upper end portion 22 a of the center portion Z in the front-rear direction of the fixing belt 22 is deformed to the upper side (side approaching the thermocut 29) due to thermal expansion and contacts the thermocut 29. Along with this, the temperature of the thermo cut 29 reaches the operating temperature T, the thermo cut 29 is activated, and the power supply from the power source 74 to the heater 24 is stopped.

  In the present embodiment, as described above, the upper end portion 22a of the center portion Z in the front-rear direction of the fixing belt 22 can be intensively heated when the heater 24 runs away. Accordingly, it is possible to promote thermal expansion of the upper end portion 22a of the center portion Z in the front-rear direction of the fixing belt 22, and it is possible to suppress an increase in the facing interval. Therefore, it becomes possible to operate the thermocut 29 at an appropriate timing.

  Particularly in this embodiment, when the heater 24 runs away, the upper end portion 22a of the center portion Z in the front-rear direction of the fixing belt 22 is deformed by thermal expansion and comes into contact with the thermocut 29, so that the thermocut 29 is activated. . Therefore, when the heater 24 runs away, the thermo cut 29 can be reliably operated.

  Further, the first reflecting portion 44 includes a first main body portion 46 and each first guide portion 47, and each second reflecting portion 45 includes a second main body portion 49 and each second guide portion 50. By adopting such a configuration, the configuration of the reflector 25 can be simplified.

  In addition, each first guide portion 47 of the first reflection portion 44 is cut and raised from each second guide portion 50 of each second reflection portion 45 toward the upper side (side approaching the heater 24). By adopting such a configuration, each first guide portion 47 can be easily formed.

  Each first guide portion 47 is bent at an obtuse angle from the left and right end portions of the first main body portion 46 toward the upper side. By adopting such a configuration, the radiant heat radiated from the heater 24 can be reflected more intensively toward the inner peripheral surface of the fixing belt 22 by the first guide portions 47.

  Further, the upper portion of the support member 26 is inserted between the second guide portions 50 of the second reflecting portions 45. By adopting such a configuration, the support member 26 and the reflecting plate 25 can be easily positioned.

  In the present embodiment, the case where each first guide portion 47 of the first reflecting portion 44 is bent at an obtuse angle from the left and right end portions of the first main body portion 46 toward the upper side (side approaching the heater 24) has been described. On the other hand, in other different embodiments, each first guide portion 47 of the first reflecting portion 44 is bent at a right angle or an acute angle from the left and right end portions of the first main body portion 46 toward the upper side (side approaching the heater 24). May be.

  In the present embodiment, the case where each second guide portion 50 of each second reflecting portion 45 is bent at a right angle from the left and right end portions of the second main body portion 49 toward the lower side (side away from the heater 24) will be described. did. On the other hand, in another different embodiment, each 2nd guide part 50 of each 2nd reflection part 45 is an obtuse angle or an acute angle toward the lower side (side spaced apart from the heater 24) from the right-and-left both ends of the 2nd main-body part 49. It may be bent.

  In this embodiment, the case where the 1st reflection part 44 and each 2nd reflection part 45 were comprised by the some flat plate-shaped part was demonstrated. On the other hand, in other different embodiment, a part or all of the 1st reflection part 44 and each 2nd reflection part 45 may be curving in circular arc shape.

  In the present embodiment, the case where a halogen heater is used as the heater 24 has been described. However, in another different embodiment, a ceramic heater or the like may be used as the heater.

  In this embodiment, the case where the configuration of the present invention is applied to the printer 1 has been described. However, in another different embodiment, the configuration of the present invention is applied to other image forming apparatuses such as a copying machine, a facsimile machine, and a multifunction machine. It is also possible.

1 Printer (image forming device)
18 Fixing device 22 Fixing belt 22a Upper end of fixing belt (the part closest to the heater)
23 Pressure roller (pressure member)
24 Heater (heat source)
25 Reflector (reflective member)
26 Support Member 27 Press Member 29 Thermo Cut (Heating Stop Device)
39 fixing nip 44 first reflecting portion 45 second reflecting portion 46 first body portion 47 first guide portion 49 second body portion 50 second guide portion A (fixing belt) rotating shaft

Claims (7)

A fixing belt provided to be rotatable around a rotation axis;
A pressure member provided in a rotatable manner to form a fixing nip by pressing against the fixing belt;
A heat source disposed on the inner diameter side of the fixing belt and heating the fixing belt;
A reflecting member that reflects radiant heat radiated from the heat source toward an inner peripheral surface of the fixing belt;
A pressing member that presses the fixing belt toward the pressing member;
A heating stop device facing the outer peripheral surface of the fixing belt and operating at a predetermined temperature to stop heating of the fixing belt by the heat source,
The reflective member is
A first reflecting portion having a shape in which the position in the rotation axis direction corresponds to the heating stop device and is recessed toward the side away from the heat source;
A fixing device comprising: a second reflecting portion that is different from the heating stop device in a position in the rotation axis direction and does not have a shape recessed toward a side away from the heat source. The first reflecting portion is
A first main body extending along the conveyance direction of the recording medium;
A first guide portion bent toward the side approaching the heat source from both end portions of the first main body portion in the conveyance direction of the recording medium,
The second reflecting portion is
A second main body extending along the conveyance direction of the recording medium;
The fixing device according to claim 1, further comprising: a second guide portion that is bent from both end portions of the second main body portion in the recording medium conveyance direction toward a side away from the heat source. .   The fixing device according to claim 2, wherein each first guide portion is cut and raised from each second guide portion toward a side approaching the heat source.   4. The fixing device according to claim 2, wherein each of the first guide portions is bent at an obtuse angle from the both end portions of the first main body portion in the conveyance direction of the recording medium. A support member for supporting the pressing member;
The fixing device according to claim 2, wherein at least a part of the support member is inserted between the second guide portions. The heat source is provided at a position biased with respect to the rotation axis,
The heating stop device faces an outer peripheral surface of a portion of the fixing belt that is closest to the heat source,
When the heat source heats the fixing belt in a state where the rotation of the fixing belt is stopped, a portion of the fixing belt that is closest to the heat source is deformed by thermal expansion and contacts the heating stop device. The fixing device according to claim 1, wherein a stopping device is operated.   An image forming apparatus comprising the fixing device according to claim 1.

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