Fixing device

A fixing device that includes a heater, a first endless belt, a first roller, and a second roller is provided. The first endless belt confronts the heater at a confronting part and providing a nip region upon contacting the heater. The first endless belt is movable in a first direction at the confronting part, and has an inner peripheral surface. The first roller supports the inner peripheral surface, and nips the first endless belt in cooperation with the heater. The nip region has a part facing the first roller. The second roller is disposed downstream of the nip region in the first direction and supports the inner peripheral surface. The second roller is positioned such that a part of the endless belt mounted over the second roller is out of contact from the heater.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2013-071966 filed Mar. 29, 2013. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a fixing device that thermally fixes a transferred developing agent image to a sheet.

BACKGROUND

Japanese Patent Application Publication No. 2010-256696 discloses a fixing device including a heater, and a pressure belt providing a nip region in cooperation with the heater. The pressure belt is applied with a tension by a plurality of rollers. A pressure pad is disposed on an inner side of the pressure belt and at a portion where no roller is disposed in such a way that the nip region is provided between the heater and the pressure pad. Accordingly, an enlarged the nip region can be provided, and a portion of the heater that is in contact with a sheet can have an enlarged width, leading to an improvement in heating efficiency in the fixing device.

SUMMARY

In the nip region, if the contact pressure between the pressure belt and the heater is insufficient, sheet slippage relative to the pressure belt may occur at an entry position of the nip region. Therefore, an increase in contact pressure between the pressure belt and the heater is required.

However, according to the conventional fixing device, large pressing force is applied to the pressure belt due to the broad pressing area by the pressure pad. Therefore, if increase in contact pressure between the pressure belt and the heater at the entry position of the nip region is contemplated to prevent the sheet from being slipped at the entry position, the pressing force to be applied to the entire nip region must also be increased. As a result, the entire fixing device is subjected to larger load, which renders the structure of the fixing device more complex.

Therefore, the object of the present invention is to provide a fixing device with a simple structure yet capable of avoiding a failure of sheet conveyance at the entry position of the nip region.

In order to attain the above and other objects, the present invention provides a fixing device that includes a heater, a first endless belt, a first roller, and a second roller. The first endless belt confronts the heater at a confronting part and provides a nip region upon contacting the heater. The first endless belt is movable in a first direction at the confronting part, and has an inner peripheral surface. The first roller supports the inner peripheral surface, and nips the first endless belt in cooperation with the heater. The nip region has a part facing the first roller. The second roller is disposed downstream of the nip region in the first direction and supports the inner peripheral surface. The second roller is positioned such that a part of the endless belt mounted over the second roller is out of contact from the heater.

In another aspect of the invention, there is provided a fixing device including a first roller, a second roller, an endless belt, and a heater. The endless belt is arranged around the first roller and the second roller. The heater is configured to nip the endless belt in cooperation with the first roller, and to provide a nip region upon contacting the endless belt. The width of the nip region in a direction from the first roller toward the second roller is narrower than the distance between the first roller and the second roller.

DETAILED DESCRIPTION

A fixing device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. As shown inFIG. 1, the color laser printer1includes a main frame2, a sheet supplying unit5for supplying a sheet51as a recording medium, an image forming unit6for forming an image on the sheet51, and a sheet discharge unit7for discharging a sheet on which an image has been formed.

Incidentally, in the following description, unless otherwise stated, the vertical direction ofFIG. 1is referred to as a vertical direction; the left side ofFIG. 1is referred to as front, and the right side as rear; and the back side of the paper surface is referred to as left, and the front side of the paper surface as right. In this manner, each of the directions is indicated. In this case, the left and the right are defined based on the directions in which a person standing in front of a color laser printer1is viewing.

<General Structure of Laser Printer>

The sheet supplying unit5includes a sheet supply tray50and a sheet supplying mechanism M1. The sheet supply tray50is mounted in the main frame2and is detachable from the main frame2at a front side thereof by a sliding operation. The sheet supplying mechanism M1is configured for lifting the sheets51from a front side of the sheet supply tray50in a diagonally upward and frontward direction and then reversing the sheet51rearward.

The sheet supplying mechanism M1is disposed near the front end portion of the sheet supply tray50, and includes a pick-up roller52, a separation roller53, a separation pad54, a paper dust removing roller55, and a pinch roller56. A conveying path57is provided above the sheet supplying mechanism M1, and a conveyer belt73is provided above the sheet supply tray50and downstream of the conveying path57.

An uppermost sheet51of a sheet stack on the sheet supply tray50is separated in an upward direction through cooperative operation of the pick-up roller52, the separation roller53, and the separation pad54. As the sheet51fed in the upward direction passes between the paper dust removing roller55and the pinch roller56, paper dust is removed from the sheet51. Then, the sheet51is conveyed along the conveying path57while the conveying direction of the sheet51is changed to a rearward direction. Subsequently, the sheet51is conveyed onto the conveyor belt73.

The image forming unit6includes a scanning unit61, a process unit62, a transfer unit63, and a fixing device100.

The scanning unit61is disposed in an upper section of the main frame2, and includes four sub-scanning units each corresponding to one of four colors cyan, magenta, yellow, and black. Although not shown in the drawings, each of the sub-scanning units includes a laser emitting section, a polygon mirror, a plurality of lenses, and a reflecting mirror. The laser emitting section emits a laser beam, which is scanned at a high speed by the polygon mirror in the left-to-right direction and passes through and is reflected by the plurality of lenses and the reflecting mirror so as to irradiate a surface of a corresponding photosensitive drum31described later.

The process unit62is disposed below the scanning unit61and above the sheet supplying unit5, and includes a drum unit3. The drum unit3has four sub-drum units30and four developing cartridges40corresponding to the sub-drum units30.

Each sub-drum unit30includes the photosensitive drum31and a scorotron charger32. Each developing cartridge40includes a toner supply roller41, a developing roller42, and a doctor blade (toner layer thickness regulation blade)43, and accommodates therein toner of specific color.

During the image forming operation, the toner in the developing cartridges40is supplied to the developing roller42via the toner supply roller41. In this case, the toner is charged with a positive polarity by triboelectric charging. The toner conveyed on the developing roller42becomes a thin layer having a uniform thickness by the doctor blade43in accordance with the rotation of the developing roller42.

In the sub-drum units30, the surface of the photosensitive drum31is uniformly charged with a positive polarity by the scorotron charger32, Then, the surface is subjected to high speed scan of the laser beam from the scanning unit61based on the image data. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum31.

The developing roller42supplies the toner onto the electrostatic latent image on the rotating photosensitive drum31; the latent image has been formed by the discharge of the positively charged surface as a result of the exposure to the laser beam. Thus, the reversal development process is carried out in which the photosensitive drum31obtains a visible toner image formed of each color of the toner; in other words, the electrostatic latent image is converted into a toner color image.

The transfer unit63includes a drive roller71, a driven roller72, the conveyor belt73, a plurality of transfer rollers74, and a cleaning unit75. The drive roller71and the driven roller72are disposed in parallel with and separated from each other. The conveyor belt73is an endless belt disposed over the drive roller71and the driven roller72. An outer surface of the conveyor belt73serves as a conveying surface and contacts each of the photosensitive drums31. The transfer rollers74are disposed in opposition to the corresponding photosensitive drums31via the conveyor belt73, and are applied with transfer bias from a high-voltage circuit board (not shown). During the image forming operation, the conveyor belt73conveys the sheet. Subsequently, the sheet51conveyed by the conveyor belt73is nipped between the photosensitive drum31and the transfer roller74via the conveyor belt73, whereby a toner image is transferred from the photosensitive drum31onto the sheet51.

The cleaning unit75is disposed below the conveyor belt73for removing toner adhered to the conveyor belt73. A toner accumulation section76is disposed below the cleaning unit75for accumulating toner removed by the cleaning unit75.

The fixing device100is disposed rearward of the transfer unit63. The toner image transferred onto the sheet51is thermally fixed thereon as the sheet51passes through the fixing device100.

In the sheet discharge unit7, a paper-discharge-side conveying path91is so formed as to extend upward from an outlet of the fixing device100and to make a turn to the front side. A plurality of conveying rollers92for conveying the sheet51is disposed on the paper-discharge-side conveying path91. A discharge tray93is provided on the upper surface of the main frame2for accommodating the sheet51discharged from the paper-discharge-side conveying path91.

<Detailed Configuration of Fixing Device>

As shown inFIG. 2A, the fixing device100includes a heater101, a pressure belt200, and a fixing frame180that supports the above components (SeeFIG. 4). The pressure belt200will be described later.

The heater101includes a fusing belt110, a halogen lamp120, a nip plate130, a reflection plate140, a stay160, and a regulating member170(SeeFIG. 3A).

The fusing belt110is an endless belt that has heat resistance and flexibility. The fusing belt110is so formed as to come in contact with the pressure belt200(described later) and to follow the motion of the pressure belt200. The fusing belt110includes a metal element tube that is made of stainless steel or any other metal. The fusing belt110may include a rubber layer formed over a surface of the metal element tube, and may further include a nonmetallic release layer such as fluorine coating formed over a surface of the rubber layer. Incidentally, the fusing belt110of the present embodiment follows only the motion of the pressure belt200, and is not driven by other members.

The halogen lamp120is a heating element that heats the toner on the sheet51by heating the nip plate130and the fusing belt110. On the internal space of the fusing belt110, the halogen lamp120is disposed away from the inner surface of the fusing belt110and nip plate130by predetermined intervals.

The nip plate130is a plate-like member that receives radiation heat from the halogen lamp120. The fusing belt110is nipped between the pressure belt200and the nip plate130. The nip plate130conveys the radiation heat received from the halogen lamp120to the toner on the sheet51via the fusing belt110.

The nip plate130has a generally U-shaped cross-section and is made from a material such as aluminum having a thermal conductivity higher than that of the stay160(described later) made from steel. More specifically, for fabricating the nip plate130, an aluminum plate is bent into substantially U-shape to provide a base section131and bent sections132. When viewed in cross-section, the base section131extends in the frontward/rearward direction (or direction in which the pressure belt200moves), and the bent sections132are bent upward from both ends of the base section131. The bottom of the base section131provides a base surface131A in contact with the pressure belt200, and each bent section132has a bent surface132A in contact with the pressure belt200. Each bent surface132A has a radius of curvature smaller than that of the base surface131A.

The reflection plate140is adapted to reflect radiant heat from the halogen lamp120(most of the radiant heat is emitted in the frontward/rearward direction and in an upward direction) toward the nip plate130(an inner surface of the base section131). As shown inFIG. 2, the reflection plate140is positioned in the internal space of the fusing belt110and surrounds the halogen lamp120with a predetermined distance therefrom.

Thus, radiant heat from the halogen lamp120can be efficiently concentrated onto the nip plate130to promptly heat the nip plate130and the fusing belt110.

The reflection plate140has a substantially U-shaped cross-section and is made from a material such as aluminum having high reflection ratio regarding infrared rays or far infrared rays. The reflection plate140has a substantially U-shaped reflection portion141and a flange sections142extending outward from each end portion of the reflection portion141in the frontward/rearward direction. A mirror surface finishing is applicable on the surface of the reflection portion in order to enhance the heat reflection ratio of the reflection plate140.

The stay160is a member that ensures rigidity of the nip plate130by supporting both ends of the base section131of the nip plate130in the frontward/rearward direction through the flange sections142of the reflection plate140. The stay160is placed opposite to the pressure belt200with respect to the nip plate130. The stay160has a substantially U-shaped cross-section, including an upper wall161, a front wall162, and a rear wall163. The front wall162extends downward from the front end of the upper wall161, and the rear wall163extends downward from the rear end of the upper wall161. The stay160is so disposed as to cover the reflection plate140. The stay160is formed by bending a steel plate or any other plate having high rigidity into a U-shape.

The stay160holds the nip plate130and the reflection plate140at a lower surface162A of the front wall162and at a lower surface163A of the rear wall163. The stay160and the halogen lamp120are fixed to the left and the right regulating members170as shown inFIGS. 3A,3B, and3C. Alternatively, the halogen lamp120can be fixed to the fixing frame180.

Each of the regulating members170is disposed at each of the widthwise end portions of the fusing belt110for regulating the movement of the fusing belt110in the leftward/rightward direction. Incidentally, in the following description, only the right regulating member170will be described, because the left regulating member170has the structure the same as the right regulation member.

More specifically, the regulating member170includes an upper wall171, a pair of side walls172, and a holding wall173. The side walls172extend downward from both the front and the rear end portions of the upper wall171, and the holding wall173extends downward from an outer end portion of the upper wall171in the rightward/leftward direction. The regulating member170holds the stay160so that the upper wall171, the pair of side walls172, and the holding wall173surround the stay160.

Moreover, the regulating member170includes a belt regulating section174, and a guide portion175. The belt regulating section174is arcuate shaped that protrudes outward in the frontward/rearward direction from inner end portions of the pair of side walls172in the frontward/rearward direction. The belt regulating section174includes a belt regulating surface174A at an inner side in the leftward/rightward direction for restricting movement of the fusing belt110in the leftward/rightward direction.

The guide portion175is a rib protruding inward from the belt regulating surface174A in the leftward/rightward direction. The guide portion175has a C-shaped section with an opening at its lower side. The guide portion175is adapted to extend into the fusing belt110to suppress radially inward deformation of the fusing belt110. Incidentally, the shape of the regulating member170is not limited to the shape described above, but the regulating member170can be formed into any shape.

As shown inFIG. 4, the regulating member170is supported by the fixing frame180so as to be movable in a vertical direction. The fixing frame180includes an upper frame181and a lower frame182. On the upper frame181, a coil spring S is provided so as to urge the regulating member170downward. Since the coil spring S urges the upper wall171of the regulating member170downward, a suitable nip pressure can be applied between the nip plate130and the pressure belt200.

Substantially U-shaped support grooves182A is formed on each of the left and right walls of the lower frame182for supporting the regulating member170so that the regulating member170is movable in the vertical direction. A bearing190for supporting a first shaft211of a first roller210(described later), is provided on the front side of the bottom portion of the support groove182A. The lower frame182is formed with an elongated slot182B at a position rearward of the support grooves182A. The elongated slot182B is adapted to support a bearing191so that the bearing191can move in an obliquely-upward/downward direction. The bearing191rotatably supports a second shaft221of a second roller220, which will be described later.

<Configuration of Pressure Belt>

As shown inFIG. 2A, the pressure belt200is an endless belt that faces the fusing belt110and is in contact with the fusing belt110, thereby forming a nip region N. A portion of the pressure belt200that faces the fusing belt110is so configured as to move rearward.

The pressure belt200is made from a resin such as polyimide resin. An inner peripheral surface200A of the pressure belt200is supported by the first roller210and the second roller220. Incidentally, all that is required for the pressure belt200is to contain resin.

The first roller210faces the fusing belt110. The pressure belt200is held between the first roller210and the fusing belt110. The pressure belt200and the fusing belt110are held between the first roller210and the front side of the base surface131A in which the front side is an upstream side of the base surface131A in the running direction of the pressure belt200.

More specifically, the first roller210is disposed at a position where the lower surface162A supports the base section131, or is aligned with the front wall162in the frontward/rearward direction. The nip plate130, the pressure belt200, and the fusing belt110are held between the first roller210and the lower surface162A of the stay160. Incidentally, according to the present embodiment, only the first roller210nips the pressure belt200in cooperation with the fusing belt110.

As shown inFIG. 4, the first roller210is coupled to a first gear213, which is driven by a motor400disposed outside. The first roller210includes a first shaft211and a first elastic layer212formed over an outer peripheral surface of the first shaft211and made from a rubber. More specifically, when considering the section of the first roller210, the first elastic layer212has a thickness smaller than that of a second elastic layer222, which will be described later. Therefore, compared to a structure in which the thickness of the first elastic layer is equal to the thickness of the second elastic layer, the first elastic layer212is less compressed when the pressure belt200is nipped between the first roller210and the nip plate130. Accordingly, sufficient pressing force of the first roller210can be provided.

Incidentally, the thickness of the first elastic layer212of the first roller210can be, for example, not more than half the radius of the first shaft211. The thickness of the first elastic layer212may be in the range of 0.01 to 10.00 mm, or in the range of 0.1 to 5.00 mm, or in the range of 0.15 to 3.00 mm. The thickness of the second elastic layer222of the second roller220may be in the range of 0.10 to 40.00 mm, or in the range of 2.0 to 20.00 mm, or in the range of 5.00 to 15.00 mm.

As shown inFIG. 2A, the second roller220includes the second shaft221and the second elastic layer222formed over an outer peripheral surface of the second shaft221and made from a thermal insulation material such as foamable sponge material. The second roller220is driven by the first roller210.

The second roller220is positioned rearward of the first roller210and the nip region N (downstream of the first roller210and the nip region N in the running direction of the pressure belt200). Further, the second roller220supports the pressure belt200at a position higher than a position A at which the first roller210and the fusing belt110nip the pressure belt200therebetween (the position A is an upstream end position of the nip region in the running direction of the pressure belt200). Incidentally, the position of the second roller220suffices the requirement as long as at least a portion of the second roller220is located higher than the position A,

A coil spring230is connected to the second roller220for urging the second roller220in an obliquely-upward direction, i.e. in rearward and diagonally upward direction. The coil spring230has a lower end section231engaged with the bearing191(SeeFIG. 4) which rotatably supports the second shaft221of the second roller220, and has an upper end section232engaged with the main frame2or the fixing frame180. Incidentally, urging direction of the coil spring230is not limited to the obliquely-upward direction, but can be any direction as long as the direction contains a component of the upward direction defined as the direction from the first roller210to the heater101.

Since the second roller220is positioned higher than the position A, the pressure belt200can contact the fusing belt110in a region extending from the position where the lower surface162A supports the nip plate130, i.e. from the front end of the base surface131A, to the bent surface132A. That is, within the region, the nip region N is defined. Therefore, an elongated nip region N can be provided.

Within the nip region N, the reflection portion141is overlapped with a heated region of the nip plate130receiving radiation heat from the halogen lamp120. When viewed in the vertical direction, the heated region is at a position that does not overlap with the position A where the pressure belt200is nipped between the first roller210and the fusing belt110, i.e. the heated region is positioned rearward of the position A. Alternatively, the position A can be included in the region where the nip plate130receives radiation heat from the halogen lamp120, when viewed in the vertical direction. For example, the position A can be placed forward of the center of the region in the frontward/rearward direction.

With the construction described above, the nip region N is provided between the pressure belt200and the heater101. Here, comparative tests were carried out for demonstrating superiority of the fixing device according to the present embodiment in comparison with a comparative example according to the fixing device described in Japanese Patent Application Publication No. 2010-256696 shownFIG. 5A. The comparative example includes a heating roller310, a pressure belt320, and a pressure pad360. The pressure belt320forms a nip region N1between the pressure belt320and the heating roller310. The pressure pad360holds the pressure belt320between the pressure pad360and the heating roller310. The pressure belt320is stretched around a front roller330positioned frontward of the heating roller310, a rear roller340positioned rearward of the heating roller310, and a central roller350. The central roller350is positioned between the front roller330and the rear roller340, and is away from an area where the heating roller310is in contact with the pressure belt320.

According to the comparative example, the nip region N1is formed in the range where the pressure belt320is nipped between the heating roller310and the pressure pad360. In the range of the nip region N1, the pressure belt320is pressed by the pressure pad360against the heating roller310.FIG. 5B is a graphical representation showing a relationship between a contact pressure P between the heating roller310and the pressure belt320and a contact position C between the pressure belt320and the heating roller310. As shown inFIG. 5B, the contact pressure P is substantially uniform in the frontward/rearward direction along the contact area.

In the comparative example, if the contact pressure between the heating roller310and the pressure belt320is to be further increased at an entry position of the sheet51, pressing force applied to the entire nip region N1needs to be increased. As a result, the entire fixing device is subjected to larger load, which renders the structure of the fixing device more complex.

On the other hand, according to the present embodiment, as shown inFIG. 2A, the first roller210faces the fusing belt110supported by the nip plate130, so that the pressure belt200is nipped between the first roller210and the fusing belt110. In addition, the second roller220supports the pressure belt200at a position rearward of the nip region N. Therefore, the pressure belt200can be urged by the first roller210against the fusing belt110supported by the nip plate130.

Accordingly, as shown inFIG. 2B, the contact pressure between the pressure belt200and the fusing belt110at the position of the first roller210, i.e. at the entry position of the sheet51, can be increased, thereby preventing the sheet51from being slipped relative to the pressure belt200at the entry position of the sheet51. As a result, a failure of sheet entry can be prevented. Moreover, only the first roller210is pressed against the pressure belt200. Therefore, the pressing force of the entire nip region N does not have to be increased. Consequently, in comparison with the comparative example, the simplified structure of the entire fixing device100can be provided.

Further, the second roller220supports the pressure belt200at the position higher than the position A where the pressure belt200is nipped between the first roller210and the fusing belt110. Therefore, the pressure belt200can be pressed upward when the pressure belt200comes in contact with the fusing belt110supported by the nip plate130. Therefore, as shown inFIG. 2B, the contact pressure P between the pressure belt200and the heater101behind the first roller210can be increased.

Further, the second roller220supports the pressure belt200at a position rearward of the nip region N. Therefore, the second roller220is unlikely to absorb heat from the nip region N.

Further, the coil spring230pulls the second roller220in the rearward and obliquely-upward direction. Therefore, the pressure belt200can be pulled rearward and obliquely-upward direction, so that sufficient tension of the pressure belt200can be maintained.

Further, a rear end portion of the nip region N is defined by the bent surface132A, which is part of the rear bent section132of the nip plate130. Therefore, the pressure belt200can be pressed against the rear bent surface132A whose radius of curvature is smaller than that of the base surface131A of the base section131. Thus, as shown inFIG. 2B, the contact pressure between the pressure belt200and the fusing belt110can be increased at the rear end portion of the nip region N. Consequently, the sheet51can be properly discharged from the nip region N.

Further, the nip plate130, the pressure belt200, and the fusing belt110are nipped between the first roller210and the lower surface162A. Therefore, the contact pressure between the pressure belt200and the fusing belt110can be increased at the position of the first roller210.

Further, if the first roller210is located at a position corresponding to the front bent section132having a smaller curvature radius than the base section131of the nip plate130, and if the heater101becomes inclined, a contacting state between the pressure belt200and the fusing belt110may be unstable at the position of the first roller210.

On the other hand, according to the present embodiment, the pressure belt200and the fusing belt110are nipped between the first roller210and the base surface131A having the radius of curvature greater than that of the bent sections132. Therefore, the pressure belt200can be appropriately in contact with the heater101at the position of the first roller210regardless of accidental inclination of the heater191.

Further, the first shaft211made from metal can increase the contact pressure between the heater101and the first roller210. In addition, the first elastic layer212is formed over the surface of the first shaft211, thereby keeping gripping force against the pressure belt200while maintaining high contact pressure between the heater101and the first roller210.

If the pressure belt is made from metal, the pressure belt may absorb heat from the heater, because the metal has high thermal conductivity. In contrast, according to the present embodiment, the pressure belt200is made from resin, thereby keeping low thermal conductivity of the pressure belt200. Consequently, the pressure belt200made from resin can restrain heat removal from the heater101while maintaining durability.

Further, the second roller220has the second elastic layer222as an outer layer, and the elastic layer has heat insulation characteristics. Therefore, the second roller220is unlikely to absorb heat from the pressure belt200. As a result, the pressure belt200is unlikely to absorb heat from the heater101.

Further, the nip region N can have an enlarged area, resulting in an improvement in heating efficiency in the nip region N.

A fixing device100′ according to a modified embodiment of the present invention will be described with reference toFIGS. 6 and 7. According to the above-described embodiment, the second roller220is pulled by the coil spring230. However, the present invention is not limited to this configuration, but a second roller220may not have to be pulled by a coil spring.

As shown inFIG. 6, a pressure belt200faces a fusing belt110in a manner the same as the above-described embodiment in which a nip region N is provided between the pressure belt200and the fusing belt110. Further, as shown inFIG. 7, a second roller220is positioned behind a support groove182A of a lower frame182′ of a fixing frame180′. A bearing191is supported to the lower frame182′, and a second shaft221is rotatably supported by the bearing191. With this structure, the pressure belt200can be nipped between a first roller210and a nip plate130. Therefore, the contact pressure between the pressure belt200and the fusing belt110can be increased.

Further, the second roller220is coupled with a second gear223which is driven by a motor400disposed outside of the fixing device100′. Here, the circumferential velocity of the second roller220is set to be higher than that of the first roller210. In this manner, the rotation of the second roller220pulls an upper portion of the pressure belt200rearward. As a result, sufficient tension can be applied to an upper portion of the pressure belt200, or to a portion of the pressure belt200in contact with the fusing belt110. Incidentally, the second roller220can receive a drive force directly or indirectly from the motor400.

According to the above-described embodiment, the first roller210is disposed at a position where the nip plate130is nipped between the first roller210and the lower surface162A. However, the first roller210may not need to be placed at that position.

Further, according to the above-described embodiment, the two rollers, the first and second rollers210and220, support the inner peripheral surface of the pressure belt200. However, the present invention is not limited to this configuration. For example, three or more rollers can be used for supporting the pressure belt.

Further, according to the above-described embodiment, the heater101includes the fusing belt110and the nip plate130. Instead, a heating roller is available as the heater.

Further, according to the above-described embodiment, the first roller210is driven by the motor400disposed outside of the fixing device100. However, the motor for driving the first roller210is not required, if the heater is a heating roller and if the rotation force is imparted on heating roller. In addition, the first roller may not have to be driven by a motor, if driving force is directly imparted on the second roller and provided that slippage of the pressure belt relative to the first roller does not occur.

Further, according to the above-described embodiment, the first elastic layer212is formed over the metallic first shaft211in the first roller210. However, the elastic layer can be dispensed with. Alternatively, a metallic layer and an elastic layer can be formed over a non-metallic shaft member to provide the first roller.

Further, according to the above-described embodiment, the second roller220includes as an outer layer the second elastic layer222made from thermally insulating material. However, an elastic layer with no heat insulating characteristic is available as the outer layer.

Further, according to the above-described embodiment, the pressure belt200is made from resin. Instead, the pressure belt200can be made from metal.

Further, the above-described embodiment is applied to the color laser printer1. However, the present invention is also available to an image formation device other than color laser printer, such as a monochromatic printer, a copying machine and a multifunction device.

While the invention has been described in detail and with reference to specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.