Patent ID: 12216422

DETAILED DESCRIPTION

In general, according to one embodiment, a fixing device includes a cylindrical fixing body, a heater unit, and a heat transfer member. The heater unit is in an interior region surrounded by the cylindrical fixing body and includes a heating element group. The heater unit extends lengthwise in a first direction parallel to an axial direction of the cylindrical fixing. The heat transfer member has a contact surface that contacts heater unit and an opposite surface on a side opposite the heater unit. The outer edges of the opposite surface in the first direction are at positions along the first direction that are beyond the outer edges of the contact surface in the first direction.

According to a first aspect, a fixing device includes a cylindrical body, a heater unit, and a heat transfer member. The cylindrical body has a film shape. The heater unit is disposed inside the cylindrical body. In the heater unit, an axial direction of the cylindrical body is defined as a longitudinal direction. The heater unit includes heating element group that includes a heating body which generates heat when supplied with electricity. The heat transfer member includes a contact portion and an opposite surface. The contact portion comes into contact with the heater unit. The opposite surface faces a side opposite to the contact portion. Both ends of the opposite surface in the longitudinal direction are outside of the contact portion in the longitudinal direction. Both ends of the contact portion in the longitudinal direction are in the longitudinal direction inside of both ends of the heating element group in the longitudinal direction.

According to a second aspect, a fixing device includes a cylindrical body, a heater unit, and a heat transfer member. The cylindrical body has a film shape. The heater unit is disposed inside the cylindrical body. In the heater unit, an axial direction of the cylindrical body is defined as a longitudinal direction. The heater unit includes a heating element group that includes a heating body which generates heat when electrified. The heat transfer member includes a heater facing surface and an opposite surface. The heater facing surface faces a side of the heater unit. The opposite surface faces a side opposite to the heater facing surface. The heater facing surface includes a contact portion and an end. The contact portion comes into contact with the heater unit. Both ends of the contact portion in the longitudinal direction are in the longitudinal direction inside of both ends of the heating element group in the longitudinal direction. The end is adjacent to the contact portion on both outsides in the longitudinal direction. A contact area of the end to the heater unit per unit length in the longitudinal direction is smaller than the contact portion.

According to a third aspect, in the fixing device according to the first aspect, an end of the heat transfer member in the longitudinal direction may not be in contact with the heater unit.

According to a fourth aspect, in the fixing device according to any one of the first to third aspects, the both ends of the heat transfer member in the longitudinal direction may be in the longitudinal direction outside of the both ends of the heating element group.

According to a fifth aspect, in the fixing device according to any one of the first to fourth aspects, the heat transfer member may have heat conductivity higher than that of a substrate of the heater unit.

According to a sixth aspect, in the fixing device according to any one of the first to fifth aspects, the heat transfer member may be a single member extending from the contact portion to the opposite surface.

According to a seventh aspect, in the fixing device according to any one of the first to sixth aspects, the heat transfer member may include a first plate which includes the contact portion and a second plate which includes the opposite surface and overlaps with the first plate and of which both ends in the longitudinal direction are in the longitudinal direction outside of both ends of the first plate in the longitudinal direction.

According to an eighth aspect, the fixing device according to any one of the first to seventh aspects may further include a heat insulation member disposed outside of the contact portion in the longitudinal direction and intervenes between the heat transfer member and the heater unit.

According to a ninth aspect, in the fixing device according to the eighth aspect, the heat insulation member may have heat conductivity lower than that of the heat transfer member.

Hereinafter, a fixing device according to certain example embodiments will be described with reference to the drawings. In the following description, the same reference numerals are given to aspects that have the same or substantially similar functions and repeated description of the same configurations or aspects may be omitted in some cases.

FIG.1is a diagram illustrating a schematic configuration of an image processing apparatus according to an embodiment.

FIG.1depicts image forming apparatus1, which is a multi-function peripheral (MPF) printer or a copy machine (copier). For example, the image forming apparatus1is installed at a work place. The image forming apparatus1performs a process of forming an image on a sheet S. The sheet S may be a sheet of paper. The image forming apparatus1includes a housing10, a scanner unit2, an image forming unit3, a sheet supply unit4, a conveyance unit5, a discharging tray7, a reversing unit9, a control panel8, and a control unit6.

The housing10forms the external shape of the image forming apparatus1.

The scanner unit2reads image information of an object to be copied based on brightness and darkness of light and generates an image signal accordingly. The scanner unit2outputs the generated image signal to the image forming unit3.

The image forming unit3forms a toner image based on the image signal received from the scanner unit2or an image signal received from the outside (e.g., from an external device). The image forming unit3transfers the toner image to a surface of the sheet S. The image forming unit3heats and presses the toner image on the sheet S to fix the toner image to the sheet S.

The sheet supply unit4supplies the sheets S to the conveyance unit5one by one at a timing at which the image forming unit3forms the toner image. The sheet supply unit4includes a sheet accommodation unit20and a pickup roller21.

The sheet accommodation unit20accommodates a type of sheet S with a predetermined size (e.g., a standard paper size).

The pickup roller21picks up the sheets S from the sheet accommodation unit20one by one. The pickup roller21supplies the picked-up sheet S to the conveyance unit5.

The conveyance unit5conveys the sheet S to the image forming unit3. The conveyance unit5includes a conveyance roller23and a registration roller24.

The conveyance roller23conveys the sheet S from the pickup roller21to the registration roller24. The conveyance roller23causes the leading end of the sheet S in the conveyance direction to be butted against a nip N of the registration roller24.

The registration roller24appropriately positions of the leading end of the sheet S by bending the sheet S at the nip N. The registration roller24then conveys the sheet S at a time appropriate for the image forming unit3to transfer the toner image to the sheet S.

The image forming unit3includes a plurality of image forming units25, a laser scanning unit26, an intermediate transfer belt27, a transfer unit28, and a fixing device30.

Each image forming unit25includes a photosensitive drum29. The image forming unit25forms the toner image on the photosensitive drum29in accordance with the image signal from the scanner unit2or the outside. The plurality of image forming units25respectively form toner images with toner of a different color (e.g., yellow, magenta, cyan, or black).

A charging unit, a developing unit, and the like are disposed around the photosensitive drum29. The charging unit charges the surface of the photosensitive drum29. The developing unit accommodates developer containing the toner of the respective color (yellow, magenta, cyan, or black). The developing unit supplied toner (developer) to an electrostatic latent image formed on the photosensitive drum29. As a result, a toner image of single color is formed on the photosensitive drum29.

The laser scanning unit26scans laser light L to the charged photosensitive drums29to expose the photosensitive drums29according to the image signal. The laser scanning unit26exposes the photosensitive drums29of the image forming units25with the corresponding laser light L (laser light LY, laser light LM, laser light LC, and laser light LK). In this way, the laser scanning unit26forms electrostatic latent images on each of the photosensitive drums29.

The toner images on the surfaces of the photosensitive drums29are then transferred to the intermediate transfer belt27(primary transfer). The transfer unit28then transfers (secondary transfer) the toner images from the intermediate transfer belt27to the sheet S at a secondary transfer position.

The fixing device30heats and presses the toner images on the sheet S to fix the toner images to the sheet S.

The reversing unit9reverses the sheet S so an image can be formed on the back surface of the sheet S. The reversing unit9reverses the front and back surfaces of the sheet S after discharge from the fixing device30by a switchback. The reversing unit9then conveys the reversed sheet S to the registration roller24.

The discharged sheet S on which an image has been formed is placed on the discharging tray7.

The control panel8is an input unit by which an operator can input information (e.g., commands, parameter settings, etc.) for operating the image forming apparatus1. The control panel8includes a touch panel and/or various hard keys (buttons).

The control unit6controls each unit of the image forming apparatus1.

FIG.2is a diagram illustrating a hardware configuration of image forming apparatus1.

As illustrated inFIG.2, the image forming apparatus1includes a central processing unit (CPU)91, a memory92, an auxiliary storage device93connected via a bus. The CPU91executes a program (software) to permit the image forming apparatus1to perform various operations and functions. The image forming apparatus1includes a scanner unit2, an image forming unit3, a sheet supply unit4, a conveyance unit5, a reversing unit9, a control panel8, and a communication unit90.

The CPU91is a part of the control unit6along with the memory92and the auxiliary storage unit93. The memory92and the auxiliary storage device93may store a program (or programs) which may be executed by the CPU91. The control unit6controls the operations of each unit of the image forming apparatus1.

The auxiliary storage device93can be a magnetic hard disk device or a semiconductor storage device. The auxiliary storage device93stores information.

The communication unit90provides a communication interface for connecting the image forming apparatus1to an external apparatus. The communication unit90communicates with the external apparatus via the communication interface.

First Embodiment

FIG.3is a cross-sectional view illustrating the fixing device according to the first embodiment.

As illustrated inFIG.3, the fixing device30includes a pressurization roller31and a film unit35. A fixing nip FN is formed between the pressurization roller31and the film unit35. The pressurization roller31presses against the toner image on the sheets S passing through the fixing nip FN. The pressurization roller31rotates to convey the sheet S through the fixing nip FN. The film unit35heats the toner image on the sheets S passing through the fixing nip FN.

In the present specification, certain z, x, and y directions are defined as follows. The z direction is the direction in which the pressurization roller31and the film unit35are lined up. The +z direction is a direction going from the film unit35towards the pressurization roller31. The x direction is a conveyance direction of the sheet S through the fixing nip FN and the +x direction is a downstream side along the conveyance direction for the sheet S. The y direction is a direction perpendicular to the z and x directions and corresponds to an axial direction of the pressurization roller31.

The pressurization roller31includes a core32, an elastic layer33, and a release layer.

The core32is formed of a metal material such as stainless steel in a cylindrical shape. Both ends of the core32in the axial direction are supported rotatably. The core32is driven to rotate by a motor. The core32comes into contact with a cam member. The cam member can be rotated to cause the core32to approach or separate from the film unit35.

The elastic layer33is formed of an elastic material such as silicone rubber. The elastic layer33is formed on the outer circumference surface of the core32.

The release layer is formed of a resin material such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). The release layer is formed as a thin film on the outer circumference surface of the elastic layer33.

Hardness of the outer circumference surface of the pressurization roller31is preferably in the range of 40° to 70° of a load of 9.8 N with an ASKER-C hardness meter. With such a hardness, an appropriate area (size) of the fixing nip FN and appropriate durability of the pressurization roller31can be provided.

The pressurization roller31can be moved towards and separated from the film unit35by rotation of the cam member. When the pressurization roller31is near the film unit35a pressurization spring presses the pressurization roller31against the film unit31, and the fixing nip FN is formed. On the other hand, when a sheet S jams in the fixing device30, the sheet S can be more easily removed by separating the pressurization roller31from the film unit35. In an operating state (mode) such as a sleep state (mode) in which rotation of a cylindrical body36is stopped, the pressurization roller31can be released from (moved away from) the film unit35to prevent deformation of the cylindrical body36.

The pressurization roller31is rotatably driven by a motor. If the pressurization roller31rotates while the fixing nip FN is formed, the cylindrical body36of the film unit35will follow the rotation of the pressurization roller31. That is, the cylindrical body36rotates in response to the rotation of the pressurization roller31when the fixing nip FN is formed. When a sheet S is disposed in the fixing nip FN, the rotation of the pressurization roller acts to convey the sheet S along a conveyance direction W.

The film unit35includes the cylindrical body36, a heater unit40, a heat transfer member80, a support member37, a stay38, a thermosensitive element60, and a film thermometer64.

The cylindrical body36is also called a fixing belt. The cylindrical body36is a cylindrical film that extends axially in the y direction. The cylindrical body36includes a base layer, an elastic layer, and a release layer formed in this order from the inner circumference side. The base layer is formed of a material such as polyimide in a cylindrical shape. The elastic layer is stacked on the outer circumference surface of the base layer. The elastic layer is formed of an elastic material such as silicone rubber. The release layer is stacked on the outer circumference surface of the elastic layer. The release layer is formed of a material such as a PFA resin.

The heater unit40is inside the cylindrical body36. The heater unit40is formed in a rectangular plate shape in which the y direction is as the longitudinal direction and the x direction is as the transverse (width) direction. In the x and y directions, a direction approaching the center of the heater unit40is referred to as an inner side and a direction going away from the center of the heater unit40is referred to as an outer side in some cases. The heater unit40includes a first surface41on the +z direction side and a second surface42on a side opposite the first surface41. The first surface41of the heater unit40heats the cylindrical body36. The first surface41comes into contact with the inner surface of the cylindrical body36via a grease47.

FIG.4is a cross-sectional view illustrating the heater unit taken along the line IV-IV ofFIG.5.FIG.5is a bottom view (a diagram viewed from the +z direction) illustrating the heater unit40according to the first embodiment.

As illustrated inFIGS.4and5, the heater unit40includes a substrate43, a heating element group45, and a wiring group55.

The substrate43can be formed of a metal material such as stainless steel, a ceramic material such as aluminum nitride, or other materials. The substrate43has a rectangular plate shape. An insulation layer44is formed of a glass material or the like on the +z direction surface of the substrate43. The −z direction surface of the substrate43is the second surface42of the heater unit40. The second surface42of the heater unit40is formed in a planar shape perpendicular to the z direction.

As illustrated inFIG.5, the heating element group45is disposed on the substrate43. The heating element group45includes in this example a plurality of heating bodies50. Each heating body50can be formed on the substrate43by disposing a material such as a silver-palladium alloy by screen printing on the substrate43. The entire external shape of the heating element group45is formed in a rectangular shape. Both y direction ends of the heating element group45are at a position along the y-direction that is inside the outer edges of the portion of the pressurization roller31that comes into contact with the cylindrical body36. The center (midpoint) of the heating element group45along the y direction is aligned with centerline width of the sheet S passing through the fixing device30. A center hc (midpoint) of the heating element group45along the x direction is offset in the −x direction from the center pc (midpoint) of the substrate43along the x direction.

The heating element group45includes a plurality of heating bodies50. The plurality of heating bodies50includes a first end heating body51, a middle heating body52, and a second end heating body53lined up in the y direction. The middle heating body52is disposed in the middle of the heating element group45along the y direction. In some examples, the middle heating body52may comprise a combination of multiple smaller heating bodies lined up along the y direction. The first end heating body51is disposed on the +y direction side of the middle heating body52at the end of the heating element group45in the +y direction. The second end heating body53is disposed on the −y direction side of the middle heating body52at the end of the heating element group45in the −y direction. The length of the middle heating body52in the y direction is larger than the minimum width of the sheets S passing through the fixing device30. The length of the middle heating body52in the y direction is smaller than the maximum width of the sheets S passing through the fixing device30. The length of the heating element group45in the y direction is larger than the maximum width of the sheets S passing through the fixing device30. The length of the heating element group45in the y direction is a distance between an outer edge of the first end heating body51on the +y direction side and an outer edge of the second end heating body53on the −y direction side.

A wiring of the wiring group55is connected to each heating body50. The heating element group45generates heat when energized via the wiring group55. A sheet S that has a small width in the y direction passes through the middle portion of the fixing device30. In this case, the control unit6causes just the middle heating body52to generate heat. On the other hand, the control unit6can cause all the heating bodies50to generate heat if the width of the sheet S is large.

As illustrated inFIG.4, the heating element group45and the wiring group55are formed on the +z direction surface of the insulation layer44. A protective layer46is formed of a glass material or the like to cover the heating element group45and the wiring group55. The protective layer46forms the first surface41of the heater unit40. When the heater unit40generates heat, viscosity of the grease47between the protective layer46and the cylindrical body36decreases. Therefore, sliding of the heater unit40and the cylindrical body36is improved.

The insulation layer44formed on the +z direction side of the substrate43may be additionally formed on −z direction side of the substrate43. The protective layer46formed on the +z direction side of the substrate43may be additionally formed on the −z direction side of the substrate43. By such arrangements, bending/warping of the substrate43is inhibited.

As illustrated inFIG.3, a straight line CL connecting a center rc of the pressurization roller31to a center fc of the film unit35is defined. The center pc of the substrate43in the x direction is offset in the +x direction from the straight line CL. The center hc of the heating element group45in the x direction is located on the straight line CL. The entire heating element group45is contained within the area of the fixing nip FN and is disposed at the center of the fixing nip FN. Thus, a heat distribution of the fixing nip FN becomes more uniform, and thus a sheet S passing through the fixing nip FN will be uniformly heated.

The heat transfer member80overlaps with the heater unit40. The heat transfer member80comes into contact with at least a part of the second surface42of the heater unit40. The heat transfer member80serves to average variations in the temperature distribution of the heater unit40. The heat transfer member80has a rectangular plate shape corresponding to the external shape of the substrate43of the heater unit40.

The support member37is formed of a resin material such as a liquid crystal polymer. The support member37has a length in the y direction. The support member37covers both sides of the heater unit40in the x direction and is on the −z direction side of portions of the heater unit40. The support member37holds the heater unit40via the heat transfer member80. Both x direction ends of the support member37are chamfered. The support member37supports the inner circumference surface of the cylindrical body36on both x direction sides of the heater unit40.

The support member37includes a base portion70, an upstream wall portion71, and a downstream wall portion72. The base portion70supports the heater unit40on the side of the second surface42. The upstream wall portion71protrudes from the end of the base portion70in the −x direction toward the pressurization roller31. The downstream wall portion72protrudes from the end of the base portion70in the +x direction toward the pressurization roller31. The heater unit40is disposed between the upstream wall portion71and the downstream wall portion72.

The stay38is formed of a steel plate material or the like. The stay38has a length in the y direction. A cross section of the stay38perpendicular to the y direction has a U shape. The stay38is mounted on the −z direction side of the support member37with the opening of the U shape facing the base portion70of the support member37. Both y direction ends of the stay38in the are fixed to the housing10of the image forming apparatus1or the like. Thus, the film unit35is structurally supported in the image forming apparatus1. The stay38improves rigidity of the film unit35and thus limits bending and flexing of the film unit35.

The thermosensitive element60is disposed in the −z direction from the heater unit40. The thermosensitive element60comes into contact with the −z direction surface of the heat transfer member80. The thermosensitive element60is disposed inside a hole that penetrates through the base portion70of the support member37in the z direction. A wiring of the thermosensitive element60is extends from the hole of the support member37in the −z direction. The thermosensitive element60in this example is a heater thermometer61and a thermostat62. For example, the heater thermometer61is a thermistor.

FIG.6is a plan view (diagram viewed in the −z direction) illustrating positions of a heater thermometer61and a thermostat62according to the first embodiment. InFIG.6, the support member37is not illustrated so that other aspects may be explained.

As illustrated inFIG.6, the heater thermometer61includes a middle heater thermometer611and an end heater thermometer612. The thermostat62includes a middle thermostat621and an end thermostat622. The middle heater thermometer611and the middle thermostat621are disposed in the −z direction of the middle heating body52. The end heater thermometer612and the end thermostat622are disposed in the −z direction of the first end heating body51and the second end heating body53.

The heater thermometer61detects a temperature of the heater unit40via the heat transfer member80. The control unit6(seeFIG.1) measures a temperature of the heating element group using the heater thermometer61when the fixing device30starts. If the temperature of the heating element group45is lower than a predetermined temperature, the control unit6causes the heating element group45to generate heat for a short time before starting rotation of the pressurization roller31. The heat generated by the heating element group45at this startup time serves to decrease the viscosity of the grease47coated on the inner circumference surface of the cylindrical body36. Thus, friction between the heater unit40and the cylindrical body36is improved for when the rotation of the pressurization roller31starts.

The heater thermometer61detects a temperature of the heat transfer member80.

The control unit6measures the temperature of the heat transfer member80using the heater thermometer61while the fixing device30is running. The control unit6controls energization of the heating element group45based on a temperature measurement result of the heat transfer member80. Thus, a temperature of the heat transfer member80in contact with the support member37is kept at a temperature less than a heat resistance temperature (e.g., maximum permissible temperature) of the support member37.

The thermostat62cuts off the energization of the heating element group45if the temperature of the heater unit40detected via the heat transfer member80exceeds a predetermined temperature. As a result, excessive heating of the cylindrical body36by the heater unit40is avoided.

As illustrated inFIG.3, the film thermometer64comes into contact with an inner circumference surface of a part of the cylindrical body36. A plurality of film thermometers64may be lined up at intervals along the y direction. Each such film thermometer64detects a temperature of a different portion in the cylindrical body36in the y direction.

The control unit6measures a temperature for each portion of the cylindrical body36arranged along the y direction using a film thermometer64when the fixing device30is running. The control unit6controls the energization of the heating element group45based on a temperature measurement result for each portion of the cylindrical body36.

FIG.7is a diagram illustrating an yz cross section of the heater unit40and the heat transfer member80according to the first embodiment.FIG.8is a perspective view illustrating the heat transfer member80according to the first embodiment.

As illustrated inFIGS.7and8, the heat transfer member80has an overall thin plate shape. The heat transfer member80is formed of a material that has heat conductivity higher than that of the substrate43. The heat transfer member80is formed of a metal material such as copper or aluminum that has a relatively high heat conductivity. A thickness direction of the heat transfer member80is in the z direction. The heat transfer member80has a rectangular shape in which the y direction is the longitudinal direction and the x direction the transverse (width) direction. The heat transfer member80comes into contact with the second surface42of the heater unit40. The heat transfer member80overlaps with all the heating bodies50when seen in a plan view from the z direction. The heat transfer member80overlaps with the entire heating element group45in the plan view. The center of the heat transfer member80in the y direction is aligned with the center of the heating element group45in the y direction. Both y direction ends of the heat transfer member80extend beyond the y direction ends of the heating element group45in the y direction. The length of the heat transfer member80in the y direction is equal to or greater than the maximum width of a sheet S passing through the fixing device30. Both y direction ends of the heat transfer member80extend beyond the y direction ends of the portions of the pressurization roller31that come into contact with the cylindrical body36.

The heat transfer member80is a single component. The heat transfer member80includes a heater facing surface81facing the heater unit40and an opposite surface84facing away from the heater facing surface81. The heat transfer member80, in some examples, may be configured as a plurality of components that are thermally continuous with one another.

The center of the heater facing surface81in the y direction is aligned with the center of the heating element group45in the y direction. The heater facing surface81includes a contact portion82that is formed in a middle portion and comes into contact with the second surface42of the heater unit40and a pair of ends83that are adjacent to the contact portion82in the y direction.

The contact portion82is a planar surface oriented in the x and y directions. The contact portion82comes into contact with the heater unit40across the entire dimensions in the x and y directions. The contact portion82is formed in a rectangular shape in a plan view. The center of the contact portion82in the y direction is aligned with the center of the heater facing surface81in the y direction. Both y direction ends of the contact portion82in the are positioned inside of y direction ends of the heating element group45. The length of the contact portion82in the y direction is equal to or greater than the maximum width of a sheet S passing through the fixing device30.

Each end83is a planar surface oriented in the x and y directions. Each end83is connected to an edge of the contact portion82at a stepped surface facing outwards in the y direction. No portion of the ends83is in contact with the second surface42of the heater unit40. In some examples, the contact area between each end83and the heater unit40per unit length in the y direction is less than a contact area between the contact portion82and the heater unit40per unit length in the y direction. In the present embodiment, since each end83is entirely separated from the heater unit40, the contact area between each end83and the heater unit40per unit length in the y direction is equal to zero.

The opposite surface84is a planar surface in the x and y directions. Both y direction ends of the opposite surface84are outside the outer edges of the contact portion82of the heater facing surface81. The opposite surface84faces the base portion70of the support member37. The opposite surface84may come into direct contact with the base portion70or another member may be interposed between the opposite surface84and the base portion70.

Operations of the fixing device30and the image forming apparatus1according to an embodiment will be described.

When the heating element group45is caused to generate heat for heating of the cylindrical body36, a temperature distribution will be generated in the heater unit40. In particular, since the temperature of the heater unit40is generally higher than that of the heat transfer member80in an early heating stage, heat is released from the heater unit40into the heat transfer member80, and thus irregularity in the temperature distribution easily occurs in heater unit40.

In the present embodiment, the heater facing surface81of the heat transfer member80includes the contact portion82and the ends83. Both y direction ends of the contact portion82are positioned to be inside of the y direction ends of the heating element group45in the y direction. The contact area between the end83and the heater unit40per unit length in the y direction is less than the contact area between the contact portion82and the heater unit40per unit length in the y direction.

With this configuration, the contact portion82can be provided so that positions corresponding to both y direction ends of the heating element group45are avoided. Transfer of the heat to the heat transfer member80from the y direction ends (at which heat is particularly easily released) of the heating element group can be inhibited. Accordingly, it is possible to prevent the temperature of portions corresponding to the ends of the heating element group45from being lower than the temperature of the middle portion of the heating element group45.

Further, since the ends83are adjacent to the contact portion82on the heater facing surface81, the opposite surface84can be expanded in size in the y direction, compared to a configuration in which the entire length of the heat transfer member80in the y direction simply matches the length of the contact portion82in the y direction. Thus, the heat moving from the contact portion82to the opposite surface84in the heat transfer member80can diffuse in the y direction. Accordingly, it is possible to limit an increase in the temperature of the opposite surface84of the heat transfer member80and it is possible to prevent damage to the heat transfer member80that might otherwise be caused by an increase in the temperature of the support member37.

The ends83of the heater facing surface81are not in contact with the heater unit40. In this configuration, compared to a configuration in which the ends of the heater facing surface come into contact with the heater unit, it is possible to more effectively inhibit the transfer of the heat from the y direction ends of the heating element group45to the heat transfer member in the early heating stage of the heater unit40.

Incidentally, if a sheet S passes through the fixing device30after the start of the heating of the heater unit40, heat transfers from the heater unit40to the sheet S. When heat transfers from the heater unit40to the sheet S, the temperature can decrease in the middle portion of the heater unit40corresponding to the passage range (e.g., the corresponding width dimension of sheet S as it passes through the fixing nip FN. If the heating element group45is caused to generate heat in order to limit or prevent the decrease in the temperature of the middle portion, the temperature at the ends of the heating element group45outside of the passage range of the sheet S may increase.

In the present embodiment, since the length of the contact portion82in the y direction is equal to or greater than the maximum width of the sheet S, the heat from the ends of the heating element group45can be efficiently transferred away. Accordingly, it is possible to average the temperature distribution of the heater unit40in the fixing device30after a sheet S passes.

Furthermore, in the present embodiment, both y direction ends of the opposite surface84extend in the y direction beyond the y direction ends of the contact portion82, thus the heat at the ends of the contact portion82can diffuse to outward in the y direction toward the opposite surface84. Accordingly, it is possible to limit a local increase in the temperature of the opposite surface84of the heat transfer member80and it is possible to prevent damage to the heat transfer member80that might otherwise be caused by an increase in the temperature of the support member37.

Both ends of the heat transfer member80in the y direction extend to the outside of the y direction ends of the heating element group45. With this configuration, the opposite surface84is formed to be longer in the y direction than the heating element group45. Therefore, if sheets S continuously pass through the fixing device30, an increase in the temperature of a portion of the heat transfer member80out of the passage range of the sheet S in the y direction can be inhibited. Accordingly, it is possible to inhibit damage caused due to an increase in the temperature of the support member37.

The heat transfer member80has heat conductivity higher than that of the substrate43of the heater unit40. With this configuration, the heat transfer member80can transfer heat more quickly than the substrate43. Accordingly, it is possible to efficiently average (uniformize) the temperature distribution of the heater unit40.

If the heat transfer member80is configured as a plurality of components and then one or more junction portion will be formed between the contact portion82of the heater facing surface81and the opposite surface84. Movement of heat in a junction portion is likely to be worse than the through the components. In the present embodiment, the heat transfer member80is a single member extending from the contact portion82of the heater facing surface81to the opposite surface84. With this configuration, as compared to a case with a junction portion, heat can more efficiently transfer from the contact portion82of the heater facing surface81to the opposite surface84in the heat transfer member80. Accordingly, it is possible to efficiently diffuse the heat using the entire thickness direction of the heat transfer member80.

Second Embodiment

The film unit35according to a second embodiment will be described with reference toFIGS.9and10.FIG.9is a view illustrating the yz cross section of a heater unit40, a heat transfer member80, and a heat insulation member86according to the second embodiment.FIG.10is a perspective view illustrating the heat transfer member80and the heat insulation member(s)86according to the second embodiment.

The second embodiment differs from the first embodiment in that heat insulation members86at between the ends83and the second surface42of the heater unit40. The heat insulation members86are disposed outside of the contact portion82. The heat insulation members86come into contact with the ends83and the second surface42of the heater unit40to help regulate mutual approach (that is spacing between these different elements). The heat insulation members86are formed of a material that has heat conductivity lower than that of the heat transfer member80overall. For example, the heat insulation member86can be formed of a resin, a felt, or the like. A resin forming the heat insulation member86may be the same as the resin forming the support member37in some examples. The shape of the heat insulation member86matches the shape of the corresponding end83of the heater facing surface81in a plan view. However, in some examples, the shape of the heat insulation member86need not match the shape of the end83in a plan view. For example, the heat insulation member86may be smaller in size (area) than the end83in a plan view.

In the second embodiment, advantages similar to those of the first embodiment can also be obtained. In addition, with the second embodiment the heat insulation members86can prevent the heater unit40from being pressed by the pressurization roller31and bent towards the end83of the heater facing surface81. Accordingly, it is possible to more reliably form the fixing nip FN within a desired range in the y direction.

Third Embodiment

A heat transfer member180according to a third embodiment will be described with reference toFIG.11.FIG.11is a diagram illustrating the yz cross section of a heater unit40and a heat transfer member180according to the third embodiment.

In the first embodiment, the heat transfer member80is a single (unitary) component. However, the third embodiment differs from the first embodiment in that the heat transfer member180is formed by a plurality of components. The heat transfer member180is formed by overlapping a first plate187and a second plate188with each other. The first plate187and the second plate188are each formed of a metal material that has relatively high heat conductivity such as copper or aluminum. In some examples, the first plate187and the second plate188may be graphite sheets, or the like.

The first plate187is located between the second plate188and the heater unit40. The first plate187is formed in a rectangular shape. The first plate187provides the contact portion82of the heater facing surface81. The second plate188overlaps with the first plate187on the side opposite to the heater unit40. The second plate188is formed in a rectangular shape. The second plate188has the same width as that of the first plate187in the x direction. Both y direction ends of the second plate188extend in the y direction beyond the y direction ends of the first plate187. The external shape of the second plate188matches the overall external shape of the heat transfer member180in a plan view. The second plate188provides the opposite surface84of the heat transfer member180. The second plate188includes the ends83of the heater facing surface81outside of the first plate187. The second plate188may be bonded to the first plate187. In some examples, a grease or the like that has excellent heat conductivity may be disposed between the first plate187and the second plate188.

In the third embodiment, advantages similar to those of the first embodiment can be obtained. In addition to these advantages, in the third embodiment, the contact portion82and the ends83can be formed on the heater facing surface81by simply overlapping the first plate187and the second plate188with each other. Therefore, it is possible to easily manufacture the heat transfer member180.

The heat insulation member86according to the second embodiment may be combined with the heat transfer member180according to the third embodiment. In this configuration, the heat insulation member86can help regulate bending of the ends of the heat transfer member180toward the heater unit40. Accordingly, it is possible to maintain the heat transfer member180in a desired shape. This configuration may be particularly effective if the first plate187and the second plate188are formed of a flexible graphite sheet or the like.

Fourth Embodiment

A heat transfer member280according to a fourth embodiment will be described with reference toFIG.12.FIG.12is a perspective view illustrating a heat transfer member280according to the fourth embodiment.

In the first embodiment, the no portion of the ends83of the heater facing surface81of the heat transfer member80are in contact with the heater unit40. However, the fourth embodiment differs from the first embodiment in that ends283of the heater facing surface281include recessed portions289to limit contact with the heater unit40.

In the ends283of the heater facing surface281of the heat transfer member280, the recessed portions289are formed. The recessed portion289may have a bottom surface or may be a through hole in the heat transfer member280. The ends283include the recessed portions289, and thus a contact area between the heater unit40to the second surface42is reduced from what would otherwise be the case without the presence of the recessed portions289. As a result, the contact area between ends283and the heater unit40per unit length in the y direction is less than the contact area between the contact portion282and the heater unit40per unit length in the y direction.

In the fourth embodiment, advantages similar to those of the first embodiment can be obtained. In addition to these advantages, in the fourth embodiment, since the ends283of the heater facing surface281actually come into contact with the heater unit40, it is possible to prevent the heater unit40from being pressed by the pressurization roller31and bent towards the heat transfer member280. Accordingly, it is possible to more reliably form the fixing nip FN within a desired range in the y direction.

Fifth Embodiment

A heater unit340according to a fifth embodiment will be described with reference toFIG.13.FIG.13is a bottom view illustrating a heater unit340according to the fifth embodiment.

The fifth embodiment differs from the first embodiment in the disposition of heating bodies350(heating elements) of the heater unit340. The heater unit340includes a substrate43, a heating element group345, and a wiring group355.

The heating element group345is disposed on the substrate43. The entire external shape of the heating element group345is a rectangular shape in which the y direction is defined as its longitudinal direction and the x direction is defined as its transverse direction.

The heating element group345includes a plurality of heating bodies350. The plurality of heating bodies350include a pair of first heating bodies351, a second heating body352, and a third heating body353. The heating bodies350are disposed in the order of one first heating body351, the second heating body352, the third heating body353, and the other first heating body351along the x direction. Each heating body350has a length corresponding to a sheet width. The second heating body352is shorter than the first heating bodies351in the y direction. The third heating body353is shorter than the second heating body352in the y direction. A wiring of the wiring group355is connected to each heating body350. The heating element group345generates heat when energized (electrified) via the wiring group355. The control unit6causes the appropriate heating bodies350to generate heat in accordance with the width of the passing sheet S.

In the fifth embodiment, as in the other embodiments, the heat transfer members80,180, and280may overlap with the heater unit340. In this case, both y direction ends of the contact portion82of the heater facing surface81are disposed to be inside of the ends of the heating element group345in the y direction, and thus advantages similar to those of the foregoing embodiments can be obtained.

Sixth Embodiment

A heater unit440according to a sixth embodiment will be described with reference toFIG.14.FIG.14is a bottom view illustrating a heater unit440according to the sixth embodiment.

The sixth embodiment differs from the first embodiment in disposition of heating bodies450of the heater unit440. The heater unit440includes a substrate43, a heating element group445, and a wiring group455.

The wiring group455is disposed on the substrate43. The overall external shape of the heating element group445is a rectangular shape.

The heating element group445includes a plurality of heating bodies450. The plurality of heating bodies450include a pair of first heating bodies451and a second heating body452. The plurality of heating bodies450are disposed in the order of one first heating body451, the second heating body452, and the other first heating body451along the x direction. The first heating body451has a shape that becomes thinner in the middle than at the ends. The y direction ends of the pair of first heating bodies451in are located at substantially the same positions. The second heating body452has a shape that becomes thicker in the middle than the ends. The ends of the second heating body452are located at substantially the same positions as the ends of each first heating body451.

A wiring of the wiring group455is connected to each heating body450. The heating element group445generates heat by energization (electrification) via the wiring group455. The control unit6causes the corresponding heating bodies450to generate heat in accordance with the width of the passing sheet S. If only the first heating body451is caused to generate heat, the amount of generated heat in the heating element group445decreases from the middle towards the ends in the y direction. On the other hand, if the pair of first heating bodies451and second heating body452are all caused to generate heat simultaneously, the amount of generated heat in the heating element group445can be more uniform across the entire length in the y direction as compared to a case where only the first heating body451generates heat. Accordingly, the control unit6electrifies only the first heating bodies451when a sheet S that has a small width passes. The control unit6electrifies a first heating body451and the second heating body452if a sheet S that has a large width passes.

In the sixth embodiment, as in the foregoing embodiments, the heat transfer members80,180, and280may overlap with the heater unit440. In this case, both y direction ends of the contact portion82of the heater facing surface81are positioned inside of the y direction ends of the heating element group, and thus advantages similar to those of the other embodiments can be obtained.

In the foregoing embodiments, the first surface41of the heater unit40comes into contact with the inner surface of the cylindrical body36. However, in other examples, another member (a heat sink member) may be interposed between the first surface of the heater unit40and the inner circumference surface of the cylindrical body36.

According to an embodiment, both ends of the contact portion of the heat transfer member in the longitudinal direction are positioned inside of the ends of the heating element group along the longitudinal direction. Both ends of the opposite surface of the heat transfer member are positioned outside of the contact portion. Thus, it is possible to prevent the temperature of the portions corresponding to the ends of the heating element group in the heater unit from being lower than that of the portion corresponding to the middle portion of the heating element group, and it is possible to limit an increase in the temperature of the opposite surface of the heat transfer member. Thus, it is possible to avoid damage to the heat transfer member that might otherwise be caused by an increase in a temperature of the support member disposed on the side opposite to the heater unit.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.