Fuser and image forming apparatus

A fuser includes a pressure application part that applies pressure to a medium for forming a print image; an annular body rotatably supported for carrying the medium for applying heat to the medium for forming the print image; a fuser part heat generation body arranged for generating heat to apply heat to the annular body; a first temperature detection end arranged in contact with one end part outside a medium carrying corresponding range of a surface of the annular body and detects temperature of the annular body outside the medium carrying corresponding range. The medium carrying corresponding range is a range in which the medium is carried. A heat generation interruption part that, in response to the temperature of the annular body that is detected via the first temperature detection end, interrupts heat generation of the fuser part heat generation body.

CROSS REFERENCE

The present application is related to, claims priorities from and incorporates by reference Japanese Patent Application No. 2013-154515 filed on Jul. 25, 2013.

TECHNICAL FIELD

The present invention relates to a fuser and an image forming apparatus, and can be suitably applied to, for example, an electrophotographic printer (hereinafter, this is also referred to as a printer) and a fuser unit provided in the printer.

BACKGROUND

In a conventional printer, there is a fuser part for fusing developer on a recording sheet, and a thermistor is provided on a fuser belt, which carries the recording sheet in the fuser part, for detecting temperature of the fuser belt (for example, see Japanese Patent Laid-Open Publication No. 2013-73207 (pages 5 and 12, and FIG. 1)).

SUMMARY

In the conventional printer, it is necessary to improve accuracy of the temperature detection of the thermistor so that the temperature of the fuser does not rise too high.

In order to resolve the subject, a fuser disclosed in the application includes, a pressure application part that applies pressure to a medium for forming a print image; an annular body that is rotatably supported for carrying the medium in a manner that the medium is sandwiched between the annular body and the pressure application part for applying heat to the medium for forming the print image; a fuser part heat generation body that is arranged on an inner side of the annular body for generating heat to apply heat to the annular body; a first temperature detection end that is arranged in contact with one end part outside a medium carrying corresponding range of a surface of the annular body and detects temperature of the annular body outside the medium carrying corresponding range, the medium carrying corresponding range being a range in which the medium is carried; and a heat generation interruption part that, in response to the temperature of the annular body that is detected via the first temperature detection end, interrupts heat generation of the fuser part heat generation body.

Therefore, in the present invention, temperature of a fuser is accurately detected and, in response to the detection, heat generation of a heat generation part can be interrupted.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, with reference to the drawings, best modes (hereinafter, these are also referred to as embodiments) for carrying out the invention are described. The description will be given in the following order:

(1) First Embodiment

(2) Second Embodiment

(3) Other Embodiments

(1) First Embodiment

(1-1) Internal Configuration of Color Printer

InFIG. 1, a reference numeral symbol1indicates as a whole a color printer according to a first embodiment. The color printer1has, for example, a substantially box-shaped case (hereinafter, this is also referred to as a printer case)2. In the following description, an upward direction of the color printer1as indicated by an arrow a1inFIG. 1when the color printer1is viewed from a direction opposing a front surface2A of the printer case2is also referred to as a printer upward direction; a direction opposite to the printer upward direction is also referred to as a printer downward direction; and, when it is not necessary to particularly distinguish between the printer upward direction and the printer downward direction, they both may also be collectively referred to as a printer up-down direction. Further, in the following description, a frontward direction of the color printer1as indicated by an arrow b1inFIG. 1when the color printer1is viewed from the direction opposing the front surface2A of the printer case2is also referred to as a printer frontward direction; a direction opposite to the printer frontward direction is also referred to as a printer rearward direction; and, when it is not necessary to particularly distinguish between the printer frontward direction and the printer rearward direction, they both may also be collectively referred to as a printer front-rear direction. Further, in the following description, a leftward direction of the color printer1as indicated by an arrow c1inFIG. 1when the color printer1is viewed from the direction opposing the front surface2A of the printer case2is also referred to as a printer leftward direction; a direction opposite to the printer leftward direction is also referred to as a printer rightward direction; and, when it is not necessary to particularly distinguish between the printer leftward direction and the printer rightward direction, they both may also be collectively referred to as a printer left-right direction.

As illustrated inFIG. 1, an arrow b1indicates a direction opposite to a carrying direction of a medium. The arrow b1indicates an upstream side of the medium carrying direction.

On a rear end part of an upper surface2B, for example, of the printer case2, a recess part (hereinafter, this is also referred to as a recording sheet delivery part)2BX is formed for placing thereon a quadrangular (for example, rectangular) recording sheet5as a medium, on a surface of which a print image is formed, to be delivered to a user. Further, at a predetermined position on a rear inner wall of the recording sheet delivery part2BX of the printer case2, a recording sheet ejection port (not illustrated in the drawings) is formed for ejecting the recording sheet5, on which the print image is formed, from inside of the printer case2to the recording sheet delivery part2BX.

On the other hand, at a central part inside the printer case2, an image forming part7is provided for forming a print image by printing a color image of a print target on a surface of the recording sheet5while carrying the rectangular recording sheet5in a manner that a short side of the recording sheet5on one side is oriented toward a carrying direction from a front side toward a rear side. Further, at a lower end part inside the printer case2, a recording sheet feeding part (hereinafter, this is also referred to as a sheet feeding part)8is provided for feeding (that is, sheet feeding) the recording sheet5from the short side on the one side to the image forming part7for forming a print image.

The image forming part7has four image forming units10-13corresponding to four colors of black (K), yellow (Y), magenta (M) and cyan (C) (that is, the four image forming units10-13use toners of the four colors of black (K), yellow (Y), magenta (M) and cyan (C) to each form a toner image using one color without duplicating). In the following description, the image forming unit10corresponding to black (K) is also referred to as a first image forming unit10, and the image forming unit11corresponding to yellow (Y) is also referred to as a second image forming unit11. Further, in the following description, the image forming unit12corresponding to magenta (M) is also referred to as a third image forming unit12, and the image forming unit13corresponding to cyan (C) is also referred to as a fourth image forming unit13. Further, the image forming part7also has a transfer part15for transferring the toner images of the four colors (that is, black, yellow, magenta and cyan) that are formed by the first-fourth image forming units10-13to the surface of the recording sheet5by sequentially superimposing the toner images while carrying the recording sheet5, for example, from the front side to the rear side. Further, the image forming part7has a fuser unit16for forming a print image on the surface of the recording sheet5by fusing the toner images of the four colors that are transferred by the transfer part15.

The first-fourth image forming units10-13are removably arranged at equal intervals from the front side to the rear side (that is, from an upstream side to a downstream side in the carrying direction when the recording sheet5is carried by the transfer part15) in the order of the first image forming unit10, the second image forming unit11, the third image forming unit12and the fourth image forming unit13. Further, the first-fourth image forming units10-13are similarly configured except that they each use a mutually different monochromatic color toner for the formation of the toner image. That is, in the first-fourth image forming units10-13, photosensitive drums20-23are provided each rotatable in an one rotation direction indicated by an arrow d1inFIG. 1about a rotation shaft parallel to the printer left-right direction. Further, in the first-fourth image forming units10-13, charging rollers24-27for charging surfaces of the respective photosensitive drums20-23into a state that allows an electrostatic latent image to be formed are provided each rotatable in the other rotation direction that is opposite to the one rotation direction about a roller rotation shaft parallel to the printer left-right direction. Further, in the first-fourth image forming units10-13, exposure heads28-31each having, for example, a plurality of LED elements and lens arrays are provided for exposing charged portions of the surfaces of the respective photosensitive drums20-23to form electrostatic latent image. Further, in the first-fourth image forming units10-13, development rollers32-35for transferring (attaching) toners to the electrostatic latent images on the surfaces of the respective photosensitive drums20-23to develop the electrostatic latent images (that is, to form toner images by visualizing the electrostatic latent images with the toners) are provided each rotatable in the other rotation direction about a roller rotation shaft parallel to the printer left-right direction. Further, in the first-fourth image forming units10-13, toner containers36-39containing toners of the respective corresponding colors are provided and supply rollers40-43supplying toners discharged from the toner containers36-39to the development rollers32-35are provided each rotatable in the other rotation direction about a rotation shaft parallel to the printer left-right direction.

In the first-fourth image forming units10-13, the rotation shafts of the photosensitive drums20-23, the charging rollers24-27, the development rollers32-35and the supply rollers40-43are respectively linked to an output shaft of a formation unit drive motor (not illustrated in the drawings) that is provided inside the printer case2. As a result, in the first-fourth image forming units10-13, during the formation of the print image, in response to operation of the formation unit drive motor, the photosensitive drums20-23, the charging rollers24-27, the development rollers32-35and the supply rollers40-43can be rotated in the one rotation direction or the other rotation direction. Further, in the first-fourth image forming units10-13, the charging rollers24-27, the development rollers32-35and the supply rollers40-43are respectively electrically connected to predetermined voltage sources (not illustrated in the drawings) that are provided inside the printer case2. As a result, in the first-fourth image forming units10-13, during the formation of the print image, in response to applications of a DC voltage from the voltage source, the surfaces of the photosensitive drums20-23can be charged, via the charging rollers24-27, into a state that allows an electrostatic latent image to be formed. Further, in the first-fourth image forming units10-13, during the formation of the print image, in response to applications of a DC voltage from the voltage source, toners can be supplied, via the supply rollers40-43, to the development rollers32-35, and, in response to application of a DC voltage from the voltage source, toners can be transferred (attached), via the development rollers32-35, to the electrostatic latent images on the surfaces of the photosensitive drums20-23and the electrostatic latent images can be developed.

The transfer part15is arranged at a central part in the printer case2extending from a position below the first image forming unit10to a position below the fourth image forming unit13. That is, in the transfer part15, below the fourth image forming unit13, a drive roller45is provided rotatable in the other rotation direction about a rotation shaft parallel to the printer left-right direction and, below the first image forming unit10, a tension roller46is provided rotatable in the other rotation direction about a rotation shaft parallel to the printer left-right direction. Further, in the transfer part15, an annular or endless carrying belt (hereinafter, this is also referred to as a transfer belt)47is stretched from the drive roller45to the tension roller46for carrying the recording sheet5for transferring the toner images. As a result, in the transfer part15, four places on a surface of a flat portion on an upper side (hereinafter, this is also referred to as an upper side flat portion), which is one of a pair of flat portions of the transfer belt47between the drive roller45and the tension roller46, are pressed against the surfaces of the first-fourth photosensitive drums20-23of the first-fourth image forming units10-13for transferring the toner images to the surface of the recording sheet5. In the following description, the four places on the surface of the upper side flat portion of the transfer belt47that are in contact with the surfaces of the first-fourth photosensitive drums20-23of the first-fourth image forming units10-13are also referred to as first-fourth transfer execution positions in the order from the front side to the rear side. In the transfer part15, the rotation shaft of the drive roller45is linked to an output shaft of a transfer part drive motor (not illustrated in the drawings) that is provided inside the printer case2. As a result, in the transfer part15, during the formation of the print image, in response to operation of the transfer part drive motor, the drive roller45can be rotated in the other rotation direction and, in conjunction with the rotation of the drive roller45, the tension roller46and the transfer belt47can also be rotated in the other rotation direction.

Further, in the transfer part15, on an inner side of the transfer belt47, four transfer rollers48-51for transferring the toner images to the surface of the recording sheet5are provided, at the first-fourth transfer execution positions, each rotatable in the other rotation direction about a rotation shaft parallel to the printer left-right direction. In the transfer part15, the transfer rollers48-51are respectively electrically connected to a predetermined voltage source that is provided inside the printer case2. As a result, in the transfer part15, during the formation of the print image, while the recording sheet5is carried by being sequentially sandwiched between the upper side flat portion of the transfer belt47and the first-fourth photosensitive drums20-23of the first-fourth image forming units10-13, due to the transfer rollers48-51, in response to application of a DC voltage from the voltage source, the toner images on the surfaces of the first-fourth photosensitive drums20-23can be transferred to the surface of the recording sheet5.

The fuser unit16has, for example, a relatively long and substantially box-shaped case (hereinafter, this is also referred to as a unit case)50, and is removably arranged on a rear side of the fourth image forming unit13and the transfer part15in a manner that a longitudinal direction of the unit case50(hereinafter, this is also referred to as a unit longitudinal direction) is parallel to the printer left-right direction. That is, the fuser unit16is removably arranged in a central part inside the printer case2on the rear side of the fourth image forming unit13and the transfer part15, the rear side being a more downstream side than the fourth image forming unit13and the transfer part15in the carrying direction of the recording sheet5. Further, in the fuser unit16, various parts are contained inside the unit case50for applying heat and pressure to the recording sheet5, to the surface of which the toner images of the four colors are transferred, and forming the print image on the surface of the recording sheet5. A description about a detailed configuration of the fuser unit16will be given later and is omitted here.

On the other hand, the sheet feeding part8has a sheet feeding tray52in which a plurality of the recording sheets5can be loaded in a stacked state, and a feeding-out roller53for feeding out the recording sheet5one by one from the sheet feeding tray52. The sheet feeding tray52is provided to be capable of being pulled out and put in with respect to the printer case2, and has a loading part that allows any of the recording sheets5of sizes of a plurality of kinds such as the A3 size and the A4 size to be loaded in a state in which a width direction of the recording sheet5(hereinafter, this is also referred to as a recording sheet width direction) is parallel to the printer left-right direction. The recording sheet width direction is a direction along a side of the recording sheet5parallel to a direction that is orthogonal to the carrying direction when the quadrangular recording sheet5is carried. In the case of this embodiment, the recording sheets5of sizes of a plurality of kinds are respectively formed in rectangular shapes such the A3 size and the A4 size. In the color printer1, for example, the recording sheets5of different sizes are respectively carried for formation of a print image in a carrying orientation in which a pair of short sides are parallel to a direction that is orthogonal to the carrying direction. Therefore, in the case of this embodiment, the recording sheet width direction is the direction along the short sides of the recording sheet5. In the following description, in the recording sheets5of sizes of a plurality of kinds, a direction orthogonal to the recording sheet width direction (that is, in this embodiment, a direction along long sides of the recording sheet5) is also referred to as a recording sheet longitudinal direction. Further, in the following description, in the recording sheets5of sizes of a plurality of kinds, a length of a side parallel to the recording sheet width direction (that is, in this embodiment, a short side of the recording sheet5) is also referred to as a sheet width, and a length of a side parallel to the recording sheet longitudinal direction (that is, in this embodiment, a long side of the recording sheet5) is also referred to as a sheet length.

In this case, in the sheet feeding tray52, a depth (that is, length in the printer front-rear direction) of the loading part is selected to be a predetermined length that is longer than a length of a long side of a recording sheet5that has a longest long side (that is, a side parallel to the recording sheet longitudinal direction) among the recording sheets5of the sizes of the plurality of kinds to be loaded. Further, in the sheet feeding tray52, a width (that is, length in the printer left-right direction) of the loading part is selected to be a predetermined length that is longer than a length of a short side of a recording sheet5that has a longest short side (that is, a side parallel to the recording sheet width direction) among the recording sheets5of the sizes of the plurality of kinds to be loaded. Further, in the sheet feeding tray52, at a rear end part, a rear guide (not illustrated in the drawings) is provided displaceable in the printer front-rear direction for defining a depth of a loading area of the recording sheets5in the loading part with respect to a front wall surface of the loading part to match a size (that is, sheet length) of the recording sheet5by narrowing frontward and extending rearward.

Further, in the sheet feeding tray52, at a right end part, a side guide (not illustrated in the drawings) is provided displaceable in the printer left-right direction for defining a width of the loading area of the recording sheets5in the loading part with respect to a left wall surface of the loading part to match a size (that is, sheet width) of the recording sheet5by narrowing leftward and extending rightward. As a result, in the sheet feeding tray52, in accordance with the size of the recording sheets5loaded in the loading part, by suitably displacing the rear guide and the side guide, a plurality of the recording sheets5of the same size can be loaded in the loading part in a stacked state in which short sides on one side (that is, sides on one side in the recording sheet width direction) of the recording sheets5are brought into contact with the front wall surface and are aligned and long sides on one side (that is, sides on one side in the recording sheet longitudinal direction) are brought into contact with the left wall surface and are aligned. Further, the feeding-out roller53is provided in a vicinity of an upper side of a front end part of the sheet feeding tray52in a manner rotatable in the other rotation direction about a rotation shaft parallel to the printer left-right direction, and the rotation shaft is linked to an output shaft of a feeding-out drive motor (not illustrated in the drawings) that is provided inside the printer case2. As a result, in the sheet feeding part8, during the formation of the print image, in response to operation of the feeding-out drive motor, the feeding-out roller53can be rotated in the other rotation direction.

In addition, in the printer case2, a carrying part (hereinafter, this is also referred to as a sheet feeding carrying part)54for carrying the recording sheet5to the image forming part7for sheet feeding is arranged extending from a vicinity of a front side of the sheet feeding tray52to a vicinity of a front side of the first image forming unit10and the transfer part15. The sheet feeding carrying part54has various kinds of carrying path formation parts such as a plurality of carrying rollers, a plurality of carrying guides and a carrying motor, and these various kinds of the carrying path formation parts form a carrying path (hereinafter, this is also referred to as a sheet feeding carrying path) for carrying the recording sheet5fed out from the sheet feeding tray52to the image forming part7as described above in a carrying orientation in which a pair of long sides of the recording sheet5are parallel to the carrying direction and a pair of short sides are parallel to the direction orthogonal to the carrying direction. Further, in the printer case2, a carrying part (hereinafter, this is also referred to as an ejection carrying part)55for carrying the recording sheet5(on a surface of which a print image is formed) for ejection from the recording sheet ejection port is arranged extending from a vicinity of a rear side of the fuser unit16to a vicinity of the recording sheet ejection port. Similar to the sheet feeding carrying part54, the ejection carrying part55also has various kinds of carrying path formation parts such as a plurality of carrying rollers, a plurality of carrying guides and a carrying motor, and these various kinds of the carrying path formation parts form a carrying path (hereinafter, this is also referred to as an ejection carrying path) for carrying the recording sheet5(that is, the recording sheet5on the surface of which a print image is formed) fed out from the fuser unit16toward the recording sheet ejection port as described above in a carrying orientation in which the pair of the long sides of the recording sheet5are parallel to the carrying direction and the pair of the short sides are parallel to the direction orthogonal to the carrying direction.

In the printer case2, a controller60such as a microcomputer or a CPU (Central Processing Unit) is provided that integrally controls the entire color printer1. Further, the color printer1is connected via a wired or wireless connection to a host device (not illustrated in the drawings), such as a personal computer, that instructs the color printer1to print a color image of a print target. Therefore, the controller60receives image data representing a color image of a print target from the host device and, when an instruction to print the color image is received, executes a print image formation process to form (that is, to print) a print image on the surface of the recording sheet5. When executing the print image formation process, the controller60drives the first-fourth image forming units10-13and the transfer part15via the above-described formation unit drive motor and the transfer part drive motor, and respectively applies DC voltages of corresponding voltage values via the above-described voltage sources to the first-fourth image forming units10-13and the transfer part15.

Further, the controller60causes the fuser unit16to operate to apply heat and pressure to the recording sheet5, as will be described later, via a fuser unit drive motor (not illustrated in the drawings) and a heater power source (not illustrated in the drawings) that are provided in the printer case2for driving the fuser unit16. Further, the controller60causes the carrying motor to operate to drive the sheet feeding carrying part54and the ejection carrying part55, and causes the feeding-out drive motor to operate to rotate the feeding-out roller53in the other rotation direction. As a result, the controller60feeds out via the feeding-out roller53the recording sheet5one by one from the sheet feeding tray52and carries the fed out recording sheet5via the sheet feeding carrying path toward the image forming part7while suitably correcting the carrying orientation of the recording sheet5. In this case, while carrying the recording sheet5via the sheet feeding carrying path toward the image forming part7, the controller60monitors via a sensor61whether or not the recording sheet5has arrived at a predetermined passing detection position on the sheet feeding carrying path. When the controller60detects via the sensor61that the recording sheet5has arrived at the passing detection position on the sheet feeding carrying path, in response to the detection, the controller60begins to sequentially control the exposure heads28-31of the first-fourth image forming units10-13in accordance with corresponding color components (black, yellow, magenta and cyan) of a color image of a print target based on the image data at predetermined time intervals before the recording sheet5sequentially arrives at the first-fourth transfer execution positions. Therefore, before the recording sheet5arrives at the first transfer execution position on the transfer belt47, the first image forming unit10, under the control of the controller60, forms an electrostatic latent image on the surface of the photosensitive drum20by using the exposure head28, and begins to form a toner image by developing the electrostatic latent image with the toner of the corresponding color (black) by using the development roller32. Further, similarly, before the recording sheet5arrives at the corresponding second-fourth transfer execution positions on the transfer belt47, the second-fourth image forming units11-13, under the control of the controller60, also sequentially form electrostatic latent images on the surfaces of the photosensitive drums21-23by using the exposure heads29-31, and begin to form toner images by developing the electrostatic latent images with the toners of the corresponding colors (yellow, magenta and cyan) by using the development rollers33-35.

In this way, while the controller60causes the first-fourth image forming units10-13to sequentially begin to form the toner images, when the recording sheet5is carried via the sheet feeding carrying path to the transfer part15, the controller60passes the recording sheet5on to the transfer belt47. When the recording sheet5arrives at the first transfer execution position in the transfer part15, while the recording sheet5is carried in a manner being sandwiched between the transfer belt47and the photosensitive drum20of the first image forming unit10, the controller60transfers the toner image (that is, the toner image of black) that is formed on the surface of the photosensitive drum20to the surface of the recording sheet5. Further, similarly, when the recording sheet5sequentially arrives at the second-fourth transfer execution positions in the transfer part15, while the recording sheet5is carried in a manner being sandwiched between the transfer belt47and the photosensitive drums21-23of the second-fourth image forming units11-13, the controller60transfers the toner images (that is, the toner images of yellow, magenta and cyan) that are formed on the surfaces of the photosensitive drums21-23to the surface of the recording sheet5. In this way, after the toner images of the four colors of black, yellow, magenta and cyan are transferred to the surface of the recording sheet5in the transfer part15by sequentially superimposing the toner images, controller60passes the recording sheet5, to which the toner images are transferred, on to the fuser unit16. In the fuser unit16, as will be described later, by applying heat and pressure to the recording sheet5, the toner images of the four colors are fused onto the surface of the recording sheet5by being temporarily melted once and a color print image is formed. Thereafter, the controller60passes the recording sheet5on to the ejection carrying path. In this way, the controller60can carry the recording sheet5on which the print image is formed by the fuser unit16toward the recording sheet ejection port via the ejection carrying path and can eject the recording sheet5to the recording sheet delivery part2BX to be passed on to a user.

(1-2) Configuration of Fuser Unit

Next, a specific configuration of the fuser unit16is described. As illustrated inFIGS. 2-4, the fuser unit16has the substantially box-shaped unit case50that is long in the printer left-right direction as described above. The unit case50has a lateral width (that is, a length from a left side plate50A to a right side plate (not illustrated in the drawings) along the unit longitudinal direction; this is also referred to as a case lateral width) that is selected to a predetermined length longer than a sheet width (hereinafter, this is also referred to as a maximum sheet width) that is the maximum among the various sheet widths of the recording sheets5of different sizes. Further, the unit case50has a slit (hereinafter, this is also referred to as a recording sheet inlet)50AX that is formed at a central part of a front plate50B extending from the left side plate50A to the right side plate for taking in a recording sheet. The unit case50has a substantially angle-shaped recording sheet inlet guide (hereinafter, this is also referred to as an upper side inlet guide)70that is provided at an upper edge portion of the recording sheet inlet50AX on an outer surface of the front plate50B in a manner that an edge portion of the upper side inlet guide70on one side enters into the recording sheet inlet50AX. Further, the unit case50has a substantially angle-shaped recording sheet inlet guide (hereinafter, this is also referred to as a lower side inlet guide)71that is provided at a lower side of the recording sheet inlet50AX on the outer surface of the front plate50B in a manner that an edge portion of the lower side inlet guide71on one side enters into the recording sheet inlet50AX. Further, the unit case50has an opening (hereinafter, this is also referred to as a recording sheet outlet)50CX that is formed in a range from a predetermined position near an upper edge of a rear plate50C to a bottom edge of the rear plate50C extending from the left side plate50A to the right side plate for feeding-out the recording sheet. Inside the unit case50, a fuser part75for fusing the toner images on the surface of the recording sheet5and a pressure application part76for applying pressure, together with the fuser part75, to the recording sheet5are provided adjacent to each other in an up-down direction.

The fuser part75has a roller80for driving a belt, a roller81that rotates along with rotation of a belt86to follow rotation of the roller80, a pair of a fuser part first heater82and a fuser part second heater83as fuser part heat generation bodies for applying heat to a belt, a pair of reflection plates84,85, the belt86for fusing the toner images onto the surface of the recording sheet5, a temperature sensor87for detecting temperature of an outer surface of the belt86, and a thermostat88for preventing a significant temperature rise of the fuser part75(that is, around the pair of heaters82,83). In the following description, in the fuser part75, the roller80for driving a belt is also referred to as a belt drive roller80, and the roller81that is rotated by the rotation of the belt drive roller80is also referred to as a fuser part driven roller81. Further, in the following description, in the fuser part75, one of the pair of the heaters82,83for applying heat to a belt is also referred to as a fuser part first heater82and the other is also referred to as a fuser part second heater83; and, one of the pair of the reflection plates84,85as reflection parts is also referred to as a fuser part first reflection plate84and the other is also referred to as a fuser part second reflection plate85. Further, in the following description, in the fuser part75, the belt86for fusing the toner images onto the surface of the recording sheet5is also referred to as a fuser belt86; the temperature sensor87for detecting the temperature of the outer surface of the fuser belt86is also referred to as a fuser part temperature sensor87; and the thermostat88as a fuser part heat generation interruption part for preventing a significant temperature rise of the fuser part75is also referred to as a fuser part thermostat88.

On the other hand, the pressure application part76has a roller90for applying pressure to the recording sheet5by being driven to rotate by the rotation of the belt drive roller80via the fuser belt86and a belt96, a roller91that rotates along with the rotation of the belt96and the rotation of the fuser part driven roller81to follow the rotation of the roller90, a pair of heaters92,93as pressure application part heat generation body for applying heat to a belt, a pair of reflection plates94,95, the belt96for applying pressure to the recording sheet5, a temperature sensor97for detecting temperature of an outer surface of the belt96, and a thermostat98for preventing a significant temperature rise of the pressure application part76(that is, around the pair of the heaters92,93). In the following description, in the pressure application part76, the roller90for applying pressure to the recording sheet5is also referred to as a pressure application roller90, and the roller91that rotates to follow the rotation of the pressure application roller90is also referred to as a pressure application part driven roller91. Further, in the following description, in the pressure application part76, one of the pair of the heaters92,93for applying heat to a belt is also referred to as a pressure application part first heater92and the other is also referred to as a pressure application part second heater93; and, one of the pair of the reflection plates94,95is also referred to as a pressure application part first reflection plate94and the other is also referred to as a pressure application part second reflection plate95. Further, in the following description, in the pressure application part76, the belt96for applying pressure to the recording sheet5is also referred to as a pressure application belt96; the temperature sensor97for detecting the temperature of the outer surface of the pressure application belt96is also referred to as a pressure application part temperature sensor97; and the thermostat98for preventing a significant temperature rise of the pressure application part76is also referred to as a pressure application part thermostat98.

As illustrated inFIGS. 5A and 5B, in the fuser part75, the belt drive roller80has a roller body80A that is formed, for example, by providing an elastic layer80AY having a substantially uniform predetermined thickness on an entire outer peripheral surface of a cylindrical core part80AX that has a predetermined diameter and of which two ends are closed. That is, the roller body80A of the belt drive roller80is formed to have a predetermined outer diameter that is substantially the same at any place between one end surface and the other end surface thereof. The core part80AX of the belt drive roller80is formed, for example, using STMK (carbon steel tubes for machine structural purposes), and the elastic layer80AY is formed, for example, using a silicon rubber that is selected to have heat resistance and a rubber hardness of, for example, about ASKER-C 75°-ASKER-C 80°. A length of the roller body80A of the belt drive roller80from the one end surface to the other end surface, for example, is selected to be a predetermined length that is longer than the maximum sheet width and slightly narrower than the case lateral width. Further, on the one end surface and the other end surface of the roller body80A of the belt drive roller80, for example, a pair of drive roller rotation shafts80B,80C are fixedly provided in a manner aligned with a central axis of the belt drive roller80.

Further, at predetermined opposing positions near centers of rear end parts of the left side plate50A and the right side plate of the unit case50(FIG. 2), shaft insertion holes are respectively drilled and rotation bearings100for the belt drive roller80are respectively provided in the shaft insertion holes. Therefore, in a manner that a longitudinal direction of the belt drive roller80is in parallel to the unit longitudinal direction (that is, the printer left-right direction), the drive roller rotation shaft80B on one side is installed in the rotation bearing100of the left side plate50A and the drive roller rotation shaft80C on the other side is installed in the rotation bearing of the right side plate. As a result, on the unit case50(FIGS. 2-4), via the pair of the rotation bearings100of the left side plate50A and the right side plate, the belt drive roller80is supported rotatable in the one rotation direction about the pair of the drive roller rotation shafts80B,80C parallel to the unit longitudinal direction (that is, the printer left-right direction).

As illustrated inFIGS. 6A and 6B, the fuser part driven roller81has a roller body81A that is formed, for example, by providing an elastic layer81AY having a substantially uniform predetermined thickness on an entire outer peripheral surface of a cylindrical core part81AX that has a predetermined diameter smaller than the diameter of the roller body80A of the belt drive roller80and of which two ends are closed. That is, although the roller body81A of the fuser part driven roller81has an outer diameter smaller than the outer diameter of the roller body80A of the belt drive roller80, the roller body81A of the fuser part driven roller81is formed to have a predetermined outer diameter that is substantially the same at any place between one end surface and the other end surface thereof. The core part81AX of the fuser part driven roller81is formed, for example, using STMK (carbon steel tubes for machine structural purposes), and the elastic layer81AY is formed, for example, using a foamed silicon rubber having heat resistance and heat insulation properties. A length of the roller body81A of the fuser part driven roller81from one end surface to the other end surface, for example, is selected to be substantially the same as the length of the roller body80A of the belt drive roller80. Further, on the one end surface and the other end surface of the roller body81A of the fuser part driven roller81, for example, a pair of driven roller rotation shafts81B,81C are fixedly provided in a manner aligned with a central axis of the fuser part driven roller81.

Further, at predetermined opposing positions near centers of front end parts of the left side plate50A and the right side plate of the unit case50(FIG. 2), shaft insertion holes are respectively drilled and rotation bearings101for the fuser part driven roller81are respectively provided in the shaft insertion holes. Therefore, in a manner that a longitudinal direction of the fuser part driven roller81is in parallel to the unit longitudinal direction (that is, the printer left-right direction), the driven roller rotation shaft81B on one side is installed in the rotation bearing101of the left side plate50A and the driven roller rotation shaft81C on the other side is installed in the rotation bearing of the right side plate. As a result, on the unit case50(FIGS. 2-4), via the pair of the rotation bearings101of the left side plate50A and the right side plate, the fuser part driven roller81is supported rotatable in the one rotation direction about the pair of the driven roller rotation shafts81B,81C parallel to the unit longitudinal direction (that is, the printer left-right direction). That is, in the unit case50, the fuser part driven roller81is at a predetermined distance away from the belt drive roller80, and is rotatably supported in a state in which a height position from a bottom plate50D to a lowermost portion of an outer peripheral surface of the roller body81A is aligned with a height position from the bottom plate50D to a lowermost portion of an outer peripheral surface of the roller body80A of the belt drive roller80.

The fuser part first heater82is, for example, a halogen lamp that generates heat as infrared rays, and a length of a cylindrical heater body is selected to be a predetermined length that is longer than the maximum sheet width and a width of the fuser belt86and is slightly narrower than the case lateral width. In this case, the fuser part first heater82is formed, for example, in such a manner that substantially an entire heater body becomes a heat generation part (that is, a light emitting part), and heater terminals are respectively provided on one end and the other end of the heater body. Further, at predetermined opposing positions near centers of upper end parts of the left side plate50A and the right side plate of the unit case50(FIG. 2), heater terminal insertion holes are respectively drilled. In the unit case50, in a state in which the heater terminal of the fuser part first heater82on one side is inserted into the heater terminal insertion hole of the left side plate50A and the heater terminal on the other side is inserted into the heater terminal insertion hole of the right side plate, these heater terminals on the one side and the other side are respectively supported by heater support parts102that are installed on the left side plate50A and the right side plate. That is, in the unit case50(FIGS. 3 and 4), for example, at a predetermined position on an obliquely rear and upper side of the fuser part driven roller81, the fuser part first heater82is supported in a state in which a longitudinal direction of the fuser part first heater82is parallel to the unit longitudinal direction (that is, the printer left-right direction).

The fuser part second heater83is, for example, a halogen lamp that generates heat as infrared rays, and a length of a cylindrical heater body is selected to be a length that is substantially equal to the length of the heater body of the fuser part first heater82. In this case, the fuser part second heater83is formed, for example, in such a manner that a portion of the heater body from a vicinity of one end to a central part becomes a heat generation part (that is, a light emitting part), and heater terminals are respectively provided on one end and the other end of the heater body. In the unit case50, in a state in which the heater terminal of the fuser part second heater83on one side is inserted into the heater terminal insertion hole of the left side plate50A and the heater terminal on the other side is inserted into the heater terminal insertion hole of the right side plate, these heater terminals on the one side and the other side are respectively supported by heater support parts103that are installed on the left side plate50A and the right side plate. That is, in the unit case50(FIGS. 3 and 4), for example, at a predetermined position between the belt drive roller80and the fuser part first heater82, the fuser part second heater83is supported in a state in which a longitudinal direction of the fuser part second heater83is parallel to the unit longitudinal direction (that is, the printer left-right direction).

As illustrated inFIGS. 7A and 7B, the fuser part first reflection plate84is formed, for example, by providing a reflection layer84B having a substantially uniform predetermined thickness on entire one surface of a plate part84A that is bent at multiple places along a portion of the outer peripheral surface of the roller body80A of the belt drive roller80. The plate part84A of the fuser part first reflection plate84is formed, for example, by bending aluminum plate, and the reflection layer84B is formed, for example, by vapor depositing highly reflective aluminum on the entire one surface of the plate part84A. An entire outer surface of the reflection layer84B of the fuser part first reflection plate84becomes a reflection surface that reflects radiant heat of the fuser part first heater82and the fuser part second heater83, and the other surface of the plate part84A becomes a back surface of the fuser part first reflection plate84itself. Further, a length of the fuser part first reflection plate84from one end to the other end, for example, is selected to be a predetermined length that longer than the maximum sheet width and the width of the fuser belt86and is substantially equal to the case lateral width. Further, one end and the other end of the fuser part first reflection plate84(FIGS. 3 and 4) are fixed on an inner surface of the left side plate50A and an inner surface of the right side plate in a state in which a longitudinal direction of the fuser part first reflection plate84is parallel to the unit longitudinal direction (that is, the printer left-right direction) and the back surface is brought close to a portion of the outer peripheral surface of the belt drive roller80extending from a front side portion to a portion on the fuser part second heater83side (that is, in a state in which the reflection surface is oriented toward the fuser part first heater82side and the fuser part second heater83side). However, in the unit case50, an arrangement position of the fuser part first reflection plate84is suitably selected in a manner that, even when the belt drive roller80thermally expands and rotationally vibrates, the back surface of the fuser part first reflection plate84does not come into contact with the outer peripheral surface of the belt drive roller80. In this way, in the unit case50, the fuser part first reflection plate84covers the elastic layer80AY of the belt drive roller80so that the elastic layer80AY does not directly receive the radiant heat of the fuser part first heater82and the fuser part second heater83.

The fuser part second reflection plate85is formed, for example, by providing a reflection layer having a substantially uniform predetermined thickness on entire one surface of a plate part that is bent at multiple places along a portion of the outer peripheral surface of the roller body81A of the fuser part driven roller81. Similar to the fuser part first reflection plate84, the plate part of the fuser part second reflection plate85is also formed, for example, by bending aluminum plate, and the reflection layer is also formed, for example, by vapor depositing highly reflective aluminum on the entire one surface of the plate part. An entire outer surface of the reflection layer of the fuser part second reflection plate85also becomes a reflection surface that reflects the radiant heat of the fuser part first heater82and the fuser part second heater83, and the other surface of the plate part also becomes a back surface of the fuser part second reflection plate85. Further, a length of the fuser part second reflection plate85from one end to the other end, for example, is selected to be a predetermined length that longer than the maximum sheet width and the width of the fuser belt86and is substantially equal to the case lateral width. Further, one end and the other end of the fuser part second reflection plate85(FIGS. 3 and 4) are fixed on the inner surface of the left side plate50A and the inner surface of the right side plate in a state in which a longitudinal direction of the fuser part second reflection plate85is parallel to the unit longitudinal direction (that is, the printer left-right direction) and the back surface is brought close to a portion of the outer peripheral surface of the fuser part driven roller81extending from a rear side portion to a portion on the fuser part first heater82side (that is, in a state in which the reflection surface is oriented toward the fuser part first heater82side and the fuser part second heater83side). However, in the unit case50, an arrangement position of the fuser part second reflection plate85is suitably selected in a manner that, even when the fuser part driven roller81thermally expands and rotationally vibrates, the back surface of the fuser part second reflection plate85does not come into contact with the outer peripheral surface of the fuser part driven roller81. In this way, in the unit case50, the fuser part second reflection plate85covers the elastic layer81AY of the fuser part driven roller81so that the elastic layer81AY does not directly receive the radiant heat of the fuser part first heater82and the fuser part second heater83.

As illustrated inFIGS. 8A and 8B, the fuser belt86is formed in a three-layer structure in which, on an entire outer surface of an annular belt body86A having a predetermined thickness, an elastic layer86B having a substantially uniform predetermined thickness and a release layer86C having a substantially uniform predetermined thickness are sequentially laminated. That is, an inner surface of the belt body86A of the fuser belt86is formed as an inner surface of the fuser belt86itself, and an outer surface of the release layer86C of the fuser belt86is formed as an outer surface of the fuser belt86itself. Further, the inner surface of the fuser belt86is coated, for example, with a predetermined coating material of black. As a result, efficiency in absorbing the radiant heat of the fuser part first heater82and the fuser part second heater83by the inner surface of the fuser belt86is increased and the fuser belt86can be easily heated. The belt body86A of the fuser belt86is formed, for example, using stainless steel (SUS: Steel Special Use Stainless) and the like to have a predetermined strength and a predetermined elasticity, and is preferably formed to have a thickness of about 40-70 [μm] and appropriate rigidity and flexibility. Further, the elastic layer86B of the fuser belt86is formed, for example, using a silicon rubber. The elastic layer86B deforms so as to match fine irregularities of the toner images that are transferred to the surface of the recording sheet5, thereby improving adhesion with respect to the surface of the recording sheet5. Further, the release layer86C of the fuser belt86is formed, for example, using a predetermined resin such as a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene) (for example, using fluorine-based resin tube covering or fluorine-based resin coating) to improve releasability from the surface of the recording sheet5and the toner images on the surface of the recording sheet5.

In this case, a width (hereinafter, this is also referred to as a fuser belt width) of the fuser belt86from one end (that is, an opening on one side) to the other end (that is, an opening on the other side) is selected, for example, to be a predetermined length that is wider than the maximum sheet width but is narrower than the case lateral width. Further, the fuser belt86has a perimeter that is selected to be a predetermined length that is relatively longer than a distance from a rearmost portion of the outer peripheral surface of the belt drive roller80to a foremost portion of the outer peripheral surface of the fuser part driven roller81. As a result, the fuser belt86is hung in a state in which one end is positioned on a left side and the other end is positioned on a right side, and a tensional force is not applied to the belt drive roller80and the fuser part driven roller81. In the following description, the one end of the fuser belt86that is positioned on the left side is also referred to as a left end and the other end that is positioned on the right side is also referred to as a left end.

The fuser part temperature sensor87(FIGS. 3 and 4) is, for example, a thermistor, and is installed on an inner surface of the front plate50B at a predetermined position of an upper edge portion of the recording sheet inlet50AX in a state in which a temperature detection end is brought close to the outer surface of the fuser belt86via a sensor holding part105(that is, in a non-contact state).

As illustrated inFIG. 9, the fuser part thermostat88has, for example, a substantially flat rectangular body part88A that is formed by embedding a conductor in a heat-resistant resin or a ceramic material, and a substantially column-shaped heat sensing part88B is provided in a projecting manner at a central part on one surface of the body part88A. Further, on one end and the other end of the body part88A of the fuser part thermostat88, terminals88C,88D are provided, and the pair of the terminals88C,88D are electrically and mechanically connected to two ends of the conductor in the body part88A. Further, the unit case50(FIGS. 2 and 3) has a slit that is formed, for example, at a predetermined position on a left end part of a top plate50E extending from the front plate50B to the rear plate50C. Further, the fuser part75has a substantially hat-shaped thermostat holding part106for holding the fuser part thermostat88. The thermostat holding part106is formed, for example, using a non-conductive resin to have a length that is substantially equal to a length of the slit of the unit case50, and a heat sensing part insertion hole is drilled at a central part of a bottom surface of a groove.

The fuser part thermostat88is arranged at the central part of the groove of the thermostat holding part106, and a front end portion of the heat sensing part88B of the fuser part thermostat88projects from a convex portion through the heat sensing part insertion hole. Further, the thermostat holding part106is installed on the top plate50E of the unit case50by inserting the convex portion of the thermostat holding part106into the slit. As a result, in the unit case50, a front end (that is, a heat sensing surface that is a circular end surface), which is a temperature detection end of the heat sensing part88B, of the fuser part thermostat88is pressed against an upper side portion of the outer surface of the fuser belt86. The terminal88C on one side of the fuser part thermostat88is electrically connected the heater terminal on one side of the fuser part first heater82and the heater terminal on one side of the fuser part second heater83.

On the other hand, in the pressure application part76, the pressure application roller90is formed, for example, in substantially the same manner as the belt drive roller80described above with respect toFIGS. 5A and 5B. That is, the pressure application roller90has a roller body90A that is formed by providing an elastic layer90AY on an entire outer peripheral surface of a core part90AX to have an outer diameter that is equal to the outer diameter of the roller body80A of the belt drive roller80. However, on one end surface and the other end surface of the roller body90A of the pressure application roller90, a pair of pressure application roller rotation shafts90B,90C having a predetermined length longer than the length of the pair of the drive roller rotation shafts80B,80C of the belt drive roller80are fixedly provided. Further, at predetermined opposing positions directly below the shaft insertion holes for the belt drive roller80on a rear end part of the left side plate50A and a rear end part of the right side plate of the unit case50(FIG. 2), shaft insertion long holes that are long in the up-down direction are respectively drilled. Further, at predetermined positions on front sides of the respective shaft insertion long holes on an outer surface of the left side plate50A and an outer surface of the right side plate of the unit case50, rotation shafts108are implanted. A front end part of each of the rotation shafts108is engaged by being inserted into an insertion hole that is drilled at one end part of a substantially L-shaped plate-like roller support part109. As a result, the roller support parts109are supported via the respective rotation shafts108on the left side plate50A and the right side plate of the unit case50in a manner rotatable in the one rotation direction and the other rotation direction. Further, shaft insertion holes are drilled at predetermined positions on central parts of the pair of the roller support parts109that oppose the respective left and right shaft insertion long holes of the unit case50, and rotation bearings110for the pressure application roller90are respectively provided in these shaft insertion holes.

Therefore, in a manner that a longitudinal direction of the pressure application roller90is in parallel to the unit longitudinal direction (that is, the printer left-right direction), the pressure application roller rotation shaft90B on one side is inserted through the shaft insertion long hole of the left side plate50A on one side and thereafter is installed on the rotation bearing110provided on the roller support part109on one side, and the pressure application roller rotation shaft90C on the other side is inserted through the shaft insertion long hole of the right side plate and thereafter is installed on the rotation bearing provided on the roller support part on the other side. As a result, the pressure application roller90is supported via the pair of the roller support parts109on the unit case50(FIGS. 2-4) in a manner displaceable in the up-down direction and rotatable in the other rotation direction about the pair of the pressure application roller rotation shafts90B,90C parallel to the unit longitudinal direction (that is, the printer left-right direction).

A left end part of the bottom plate50D of the unit case50protrudes to an outer surface side (that is, the left side) of the left side plate50A, and an right end part of the bottom plate50D protrudes to an outer surface side (that is, the right side) of the right side plate. Further, the pressure application part76has a pair of compression coil springs (hereinafter, these are also referred to as pressure application roller biasing springs)111for biasing the pressure application roller90. One end part of the pressure application roller biasing spring111on one side is engaged with a left rear end part of the bottom plate50D on the outer surface side of the left side plate50A of the unit case50, and the other end part of the pressure application roller biasing spring111is engaged with the other end part of the roller support part109on one side. Further, one end part of the pressure application roller biasing spring on the other side is engaged with a right rear end part of the bottom plate50D on the outer surface side of the right side plate of the unit case50, and the other end part of the pressure application roller biasing spring111is engaged with the other end part of the roller support part on the other side. As a result, in the unit case50, the pressure application roller90is biased by the pair of the pressure application roller biasing springs111to displace upward.

The pressure application part driven roller91is formed, for example, in the same manner as the fuser part driven roller81described above with respect toFIGS. 6A and 6B. That is, the pressure application part driven roller91has a pair of driven roller rotation shafts91B,91C that are fixedly provided on one end surface and the other end surface of a roller body91A that is formed by providing an elastic layer91AY on an entire outer peripheral surface of a core part91AX to have an outer diameter equal to the outer diameter of the roller body81A of the fuser part driven roller81Further, at predetermined opposing positions directly below the shaft insertion holes for the fuser part driven roller81on a rear end part of the left side plate50A and a front end part of the right side plate of the unit case50(FIG. 2), shaft insertion long holes that are long in the up-down direction are respectively drilled. Further, on the left side plate50A and the right side plate of the unit case50, rotation bearings112for the pressure application part driven roller91are respectively provided in these shaft insertion long holes in a manner displaceable in the up-down direction (that is, the printer up-down direction). Therefore, in a manner that a longitudinal direction of the pressure application part driven roller91is in parallel to the unit longitudinal direction (that is, the printer left-right direction), the driven roller rotation shaft91B on one side is installed in the rotation bearing112of the left side plate50A and the driven roller rotation shaft91C on the other side is installed in the rotation bearing of the right side plate. As a result, on the unit case50(FIGS. 2-4), via the pair of the rotation bearings112of the left side plate50A and the right side plate, the pressure application part driven roller91is supported in a manner displaceable in the up-down direction and rotatable in the other rotation direction about the pair of the driven roller rotation shafts91B,91C parallel to the unit longitudinal direction (that is, the printer left-right direction).

The pressure application part76has a pair of compression coil springs (hereinafter, these are also referred to as driven roller biasing springs)113for biasing the pressure application part driven roller91. One end part of the driven roller biasing spring113on one side is engaged with a lower edge of the shaft insertion long hole for the pressure application part driven roller91on the left side plate50A of the unit case50, and the other end part of the driven roller biasing spring113is engaged with the rotation bearing112on one side. Further, one end part of the driven roller biasing spring on the other side is engaged with a lower edge of the shaft insertion long hole for the pressure application part driven roller91on the right side plate of the unit case50, and the other end part of the driven roller biasing spring is engaged with the rotation bearing on the other side. As a result, in the unit case50, the pressure application part driven roller91is biased by the pair of the driven roller biasing springs113to displace upward.

The pressure application part first heater92is formed, for example, in the same manner as the above-described fuser part first heater82. That is, the pressure application part first heater92is formed in such a manner that substantially an entire heater body having a length that is longer than the maximum sheet width and the width of the fuser belt86and is equal to the length of the heater body of the fuser part first heater82becomes a heat generation part, and heater terminals are respectively provided on one end and the other end of the heater body. The pressure application part second heater93is formed, for example, in the same manner as the above-described fuser part second heater83. That is, the pressure application part second heater93is formed in such a manner that, in a heater body having a length that is longer than the maximum sheet width and the width of the fuser belt86and is equal to the length of the heater body of the fuser part second heater83, a portion of the heater body from a vicinity of one end to a central part becomes a heat generation part, and heater terminals are respectively provided on one end and the other end of the heater body. Further, at predetermined opposing positions near centers of lower end parts of the left side plate50A and the right side plate of the unit case50(FIG. 2), heater terminal insertion holes are respectively drilled. In the unit case50, in a state in which the heater terminals of the pressure application part first heater92and the pressure application part second heater93on one side are respectively inserted into the heater terminal insertion holes of the left side plate50A and the heater terminals on the other side are respectively inserted into the heater terminal insertion holes of the right side plate, these heater terminals on the one side and the other side are respectively supported by heater support parts114that are installed on the roller support parts109on one side and on the other side. That is, in the unit case50(FIGS. 3 and 4), for example, at a predetermined position on an obliquely rear and lower side of the pressure application part driven roller91, the pressure application part first heater92is supported in a state in which a longitudinal direction of the pressure application part first heater92is parallel to the unit longitudinal direction (that is, the printer left-right direction). Further, in the unit case50, for example, at a predetermined position between the pressure application roller90and the pressure application part first heater92, the pressure application part second heater93is supported in a state in which a longitudinal direction of the pressure application part second heater93is parallel to the unit longitudinal direction (that is, the printer left-right direction).

The pressure application part first reflection plate94is formed, for example, in the same manner as the fuser part first reflection plate84described above with respect toFIGS. 7A and 7B. That is, the pressure application part first reflection plate94has a length from one end to the other end that is selected to be a predetermined length that is longer than the maximum sheet width and the width of the fuser belt86and is also longer than the length of the roller body90A of the pressure application roller90, and is formed by providing a reflection layer94B on entire one surface of a plate part94A that is bent at multiple places along a portion of the outer peripheral surface of the roller body90A of the pressure application roller90. Further, one end and the other end of the pressure application part first reflection plate94(FIGS. 3 and 4) are fixed on the inner surface of the left side plate50A and the inner surface of the right side plate in a state in which a longitudinal direction of the pressure application part first reflection plate94is parallel to the unit longitudinal direction (that is, the printer left-right direction) and a back surface is brought close to a portion of the outer peripheral surface of the pressure application roller90extending from a front side portion to a portion on the pressure application part second heater93side (that is, in a state in which a reflection surface is oriented toward the pressure application part first heater92side and the pressure application part second heater93side). However, in the unit case50, an arrangement position of the pressure application part first reflection plate94is suitably selected in a manner that, even when the pressure application roller90thermally expands and rotationally vibrates, the back surface of the pressure application part first reflection plate94does not come into contact with the outer peripheral surface of the pressure application roller90. In this way, in the unit case50, the pressure application part first reflection plate94covers the elastic layer90AY of the pressure application roller90so that the elastic layer90AY does not directly receive radiant heat of the pressure application part first heater92and the pressure application part second heater93.

The pressure application part second reflection plate95is formed, for example, in the same manner as the above-described fuser part second reflection plate85. That is, the pressure application part second reflection plate95has a length from one end to the other end that is selected to be a predetermined length that is longer than the maximum sheet width and the width of the fuser belt86and is also longer than the length of the roller body91A of the pressure application part driven roller91, and is formed by providing a reflection layer on entire one surface of a plate part that is bent at multiple places along a portion of the outer peripheral surface of the roller body91A of the pressure application part driven roller91. Further, one end and the other end of the pressure application part second reflection plate95(FIGS. 3 and 4) are fixed on the inner surface of the left side plate50A and the inner surface of the right side plate in a state in which a longitudinal direction of the pressure application part second reflection plate95is parallel to the unit longitudinal direction (that is, the printer left-right direction) and a back surface is brought close to a portion of the outer peripheral surface of the pressure application part driven roller91extending from a rear side portion to a portion on the pressure application part first heater92side (that is, in a state in which a reflection surface is oriented toward the pressure application part first heater92side and the pressure application part second heater93side). However, in the unit case50, an arrangement position of the pressure application part second reflection plate95is suitably selected in a manner that, even when the pressure application part driven roller91thermally expands and rotationally vibrates, the back surface of the pressure application part second reflection plate95does not come into contact with the outer peripheral surface of the pressure application part driven roller91. In this way, in the unit case50, the pressure application part second reflection plate95covers the elastic layer91AY of the pressure application part driven roller91so that the elastic layer91AY does not directly receive the radiant heat of the pressure application part first heater92and the pressure application part second heater93.

The pressure application belt96is formed, for example, in the same manner as the fuser belt86described above with respect toFIGS. 8A and 8B. That is, the pressure application belt96is formed in a three-layer structure in which, on an entire outer surface of a annular belt body96A having a width (hereinafter, this is also referred to as a pressure application belt width) from one end (that is, an opening on one side) to the other end (that is, an opening on the other side) equal to the fuser belt width, an elastic layer96B and a release layer96C are sequentially laminated. Further, the inner surface of the pressure application belt96is coated with a predetermined coating material of black. As a result, efficiency in absorbing the radiant heat of the pressure application part first heater92and the pressure application part second heater93by the inner surface of the pressure application belt96is increased and the pressure application belt96can be easily heated. Further, since the pressure application belt96has a perimeter that is equal to the perimeter of the fuser belt86(that is, since the perimeter of the pressure application belt96is relatively longer than a distance from a rearmost portion of the outer peripheral surface of the pressure application roller90to a foremost portion of the outer peripheral surface of the pressure application part driven roller91), the pressure application belt96is hung in a state in which one end is positioned on a left side and the other end is positioned on a right side, and a tensional force is not applied to the pressure application roller90and the pressure application part driven roller91. In the following description, the one end of the pressure application belt96that is positioned on the left side is also referred to as a left end and the other end that is positioned on the right side is also referred to as a right end.

As described above, the pressure application roller90is biased by the pair of the pressure application roller biasing springs111to displace upward. Therefore, in accordance with the bias force due to the pair of the pressure application roller biasing springs111, an upper side portion of the outer peripheral surface of the pressure application roller90is pressed against a lower side portion of the outer peripheral surface of the belt drive roller80with a predetermined pressing force sequentially via the pressure application belt96and the fuser belt86. Further, as described above, the pressure application part driven roller91is biased by the pair of the driven roller biasing springs113to displace upward. Therefore, in accordance with the bias force due to the pair of the driven roller biasing springs113, an upper side portion of the outer peripheral surface of the pressure application part driven roller91is pressed against a lower side portion of the outer peripheral surface of the fuser part driven roller81with a predetermined pressing force sequentially via the pressure application belt96and the fuser belt86. The perimeter of the fuser belt86in the fuser unit16is suitably selected. Therefore, in the fuser unit16, with respect to the belt drive roller80and the fuser part driven roller81, the fuser belt86is hung by positioning an intersection point P1between an imaginary straight line VL1that bisects a distance between a foremost position and a rearmost position of the outer surface of the fuser belt86and an imaginary straight line VL2that bisects a distance between an uppermost position and lowermost position of the outer surface on an upper side of a center S1of the belt drive roller80and a center S2of the fuser part driven roller81. That is, in the fuser unit16, with respect to the belt drive roller80and the fuser part driven roller81, the fuser belt86is hung in a state being deformed with a curvature as small as possible without being given an extremely crushing load.

Further, in the fuser unit16, the perimeter of the pressure application belt96is selected in the same manner as the perimeter of the fuser belt86. Therefore, in the fuser unit16, with respect to the pressure application roller90and the pressure application part driven roller91, the pressure application belt96is hung by positioning an intersection point P2between the imaginary straight line VL1that bisects a distance between a foremost position and a rearmost position of the outer surface of the pressure application belt96and an imaginary straight line VL2that bisects a distance between an uppermost position and lowermost position of the outer surface on a lower side of a center S3of the pressure application roller90and a center S4of the pressure application part driven roller91. That is, in the fuser unit16, with respect to the pressure application roller90and the pressure application part driven roller91, the pressure application belt96is hung in a state being deformed with a curvature as small as possible without being given an extremely crushing load. As a result, in the pressure application part76, portions of the pressure application belt96and the fuser belt86from a pressing position of the outer peripheral surface of the pressure application roller90against the outer peripheral surface of the belt drive roller80to a pressing position of the outer peripheral surface of the pressure application part driven roller91against the outer peripheral surface of the fuser part driven roller81are mutually flat without being recessed, and these mutually flat portions form a sandwiching part115for carrying while sandwiching the recording sheet5for applying heat and pressure to the recording sheet5.

When the sandwiching part115is from a point Pt1sandwiched by the belt drive roller80and the pressure application roller to a point Pt2sandwiched by the fuser part driven roller81and the pressure application part driven roller91, other portions of the fuser belt86and the pressure application belt96are defined as flexible portions (1utp, 2utp). A length of the sandwiching part115is indicated using PTP inFIG. 3.

The pressure application part temperature sensor97(FIGS. 3 and 4) is formed in the same manner as the above-described fuser part temperature sensor87, and is installed at a predetermined position directly below the fuser part temperature sensor87, in an upper end part on an inner surface of the lower side inlet guide71, in a state in which a temperature detection end is brought close to the outer surface of the pressure application belt96via a sensor holding part116(that is, in a non-contact state).

The pressure application part thermostat98is formed, for example, in the same manner as the fuser part thermostat88described above with respect toFIG. 9. That is, a heat sensing part98B is provided in a projecting manner at a central part on one surface of a body part98A of the pressure application part thermostat98, and terminals98C,98D are provided on one end and the other end of the body part98A. The pair of the terminals98C,98D are electrically and mechanically connected to two ends of a conductor in the body part98A. Further, the pressure application part76(FIG. 3) has a substantially hat-shaped thermostat holding part117for holding the pressure application part thermostat98. The thermostat holding part117is formed, for example, using a non-conductive resin to have a predetermined length, and a heat sensing part insertion hole is drilled at a central part of a bottom surface of a groove. The pressure application part thermostat98is arranged at the central part of the groove of the thermostat holding part117, and a front end portion of the heat sensing part98B of the pressure application part thermostat98projects from a convex portion through the heat sensing part insertion hole. Further, at a position on the bottom plate SOD of the unit case50and directly below the fuser part thermostat88, thermostat holding part117is installed with the convex portion facing upward. As a result, in the unit case50, a front end (that is, a heat sensing surface that is a circular end surface), which is a temperature detection end of the heat sensing part98B, of the pressure application part thermostat98is pressed against a lower side portion of the outer surface of the pressure application belt96. The terminal98C on one side of the pressure application part thermostat98is electrically connected the heater terminal on one side of the pressure application part first heater92and the heater terminal on one side of the pressure application part second heater93.

In the printer case2, for example, at a predetermined position opposing the left side plate50A of the unit case50, a predetermined rotation transmission mechanism (not illustrated in the drawings) is provided for transmitting rotation of an output shaft of the fuser unit drive motor to the belt drive roller80as rotation in the one rotation direction. Further, the drive roller rotation shaft80B on one side of the belt drive roller80protrudes from the left side plate50A of the unit case50, and a predetermined drive roller link mechanism (not illustrated in the drawings) for linking the drive roller rotation shaft80B on one side to the rotation transmission mechanism is provided on the left side plate50A. When the fuser unit16is installed in the color printer1, the drive roller rotation shaft80B on one side of the belt drive roller80is linked via the drive roller link mechanism to the rotation transmission mechanism. As a result, in the fuser unit16, during the formation of the print image, in response to operation of the fuser unit drive motor, the belt drive roller80can be rotated in the one rotation direction and, in conjunction with the rotation of the belt drive roller80, the fuser part driven roller81and the fuser belt86can also be rotated in the one rotation direction. Further, in the fuser unit16, by pressing the pressure application roller90and the pressure application part driven roller91against the belt drive roller80and the fuser part driven roller81, in this case, in conjunction with the rotation of the fuser belt86in the one rotation direction, the pressure application belt96, together with the pressure application roller90and the pressure application part driven roller91, can be rotated in the other rotation direction opposite to the rotation direction of the fuser belt86. Therefore, in the fuser unit16, during the formation of the print image, due to the fuser belt86and the pressure application belt96that are rotating in mutually opposite directions, the above-described sandwiching part115is formed, and the recording sheet5that is taken in via the recording sheet inlet50AX from the transfer part15can be pressed while being carried in a manner being sandwiched by the sandwiching part115.

In addition, when the fuser unit16is installed in the color printer1, together with the terminal88D on the other side of the fuser part thermostat88, the heater terminal on the other side of the fuser part first heater82and the heater terminal on the other side of the fuser part second heater83are respectively electrically connected to a first heater power source on one side of a pair of the first heater power source and a second heater power source. Further, when the fuser unit16is installed in the color printer1, together with the terminal98D on the other side of the pressure application part thermostat98, the heater terminal on the other side of the pressure application part first heater92and the heater terminal on the other side of the pressure application part second heater93are respectively electrically connected to the second heater power source on the other side of the pair of the first heater power source and the second heater power source. Further, when the fuser unit16is installed in the color printer1, the fuser part temperature sensor87and the pressure application part temperature sensor97are electrically connected to the above-described controller60. Therefore, in the fuser unit16, during the formation of the print image, in response to a current (that is, an AC current, which is hereinafter also referred to as a heat generation control current) of a predetermined current value for heater heat generation that is supplied from the first heater power source to the fuser part first heater82and the fuser part second heater83, the fuser part first heater82and the fuser part second heater83are caused to generate heat and thereby, the fuser belt86can be heated from an inner surface side while being rotated in the one rotation direction. Further, the fuser unit16causes the controller60to detect, via the fuser part temperature sensor87, the temperature of the outer surface of the fuser belt86and, in response to the detection result, to ON/OFF-control the first heater power source (that is, to ON/OFF-control the supply of the heat generation control current from the first heater power source to the fuser part first heater82and the fuser part second heater83), and thereby, the temperature of the outer surface of the fuser belt86can be adjusted to a predetermined temperature that is required for fusing the toner images on the recording sheet5(that is, required for melting the toners).

Therefore, in the fuser unit16, during the formation of the print image, in response to a heat generation control current that is supplied from the second heater power source to the pressure application part first heater92and the pressure application part second heater93, the pressure application part first heater92and the pressure application part second heater93are caused to generate heat and thereby, the pressure application belt96can be heated from an inner surface side while being rotated in the other rotation direction. Further, the fuser unit16causes the controller60to detect, via the pressure application part temperature sensor97, the temperature of the outer surface of the pressure application belt96and, in response to the detection result, to ON/OFF-control second heater power source (that is, to ON/OFF-control the supply of the heat generation control current from the second heater power source to the pressure application part first heater92and the pressure application part second heater93), and thereby, the temperature of the outer surface of the pressure application belt96can be adjusted in the same manner as the temperature of the outer surface of the fuser belt86. As a result, in the fuser unit16, during the formation of the print image, the recording sheet5that is taken in via the recording sheet inlet50AX from the transfer part15can be heated, in addition to being pressed, while being carried in a manner being sandwiched by the sandwiching part115of the fuser belt86and the pressure application belt96that are rotating in mutually opposite directions.

Here, in the fuser unit16, the belt drive roller80, fuser part driven roller81, fuser part first heater82, fuser part second heater83, fuser part first reflection plate84, fuser part second reflection plate85and fuser belt86of the fuser part75and the respective corresponding pressure application roller90, pressure application part driven roller91, pressure application part first heater92, pressure application part second heater93, pressure application part first reflection plate94, pressure application part second reflection plate95and pressure application belt96of the pressure application part76are formed in the same manner, and are symmetrically arranged with respect to the flat outer surfaces of the fuser belt86and the pressure application belt96at the sandwiching part115. As a result, in the fuser unit16, during the formation of the print image, although the fuser belt86and the pressure application belt96are individually heated, the temperatures of the fuser belt86and the pressure application belt96can be made substantially equal each other. Therefore, in the fuser unit16, in the elastic layer80AY of the belt drive roller80and the elastic layer90AY of the pressure application roller90, in which temperatures of the fuser belt86and the pressure application belt96propagate, temperatures can be made substantially equal to each other and thermal expansion amounts can also be made substantially equal to each other. Therefore, in the fuser unit16, occurrence of a difference between the adhesion of the surface of the belt drive roller80with respect to the inner surface of the fuser belt86and the adhesion of the surface of the pressure application roller90with respect to the inner surface of the pressure application belt96can be prevented.

Further, in the fuser unit16, in the elastic layer81AY of the fuser part driven roller81and the elastic layer91AY of the pressure application part driven roller91, in which the temperatures of the fuser belt86and the pressure application belt96propagate, temperatures can be made substantially equal to each other and thermal expansion amounts can also be made substantially equal to each other. Therefore, in the fuser unit16, occurrence of a difference between the adhesion of the surface of the fuser part driven roller81with respect to the inner surface of the fuser belt86and the adhesion of the surface of the pressure application part driven roller91with respect to the inner surface of the pressure application belt96can also be prevented. Therefore, in the fuser unit16, when the fuser belt86and the pressure application belt96rotate in a state of having been heated, without causing any sliding of the upper side flat portion of the outer surface of the pressure application belt96with respect to the lower side flat portion of the outer surface of the fuser belt86, the sandwiching part115can be formed by the mutually flat portions. That is, in the fuser unit16, when the fuser belt86and the pressure application belt96rotate in the state of having been heated, by the mutually flat portions, the sandwiching part115can be formed that allows the recording sheet5to be unerringly sandwiched without any sliding with respect to the flat portions.

In the color printer1, as described above, even when the recording sheets5of any size are loaded in the sheet feeding tray52, sides of the recording sheets5on one side in the recording sheet width direction (that is, long sides of the recording sheets5positioned on the left side when the recording sheets5are loaded) are brought into contact with the left wall surface of the sheet feeding tray52and are aligned and, in this state, the recording sheets5are fed out from the sheet feeding tray52for the formation of the print image. Therefore, as illustrated inFIG. 10, in the fuser unit16, even when the recording sheet5taken in from the transfer part15for fusing the toner images has a sheet width of any size, in the sandwiching part115, the recording sheet5is sandwiched in a manner that a side of the recording sheet5on one side in the recording sheet width direction ((that is, a long side on the left side) substantially matches a predetermined position AP1near the left ends of the outer surface of the fuser belt86and the outer surface of the pressure application belt96(that is, a predetermined position PA1on inner sides of the outer surface of the fuser belt86and the outer surface of the inner side of the pressure application belt96). Therefore, in the fuser unit16, a medium carrying corresponding range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96that rotate in mutually opposite directions when the recording sheet5is carried in a manner being sandwiched for applying heat and pressure thereto (that is, a range in which the recording sheet5is sandwiched between the outer surfaces; hereinafter, this is also referred to as a sandwiching range) becomes a range corresponding to the sheet width of the recording sheet5with the position AP1near the left ends as a reference. In the following description, the predetermined position AP1near the left ends of the outer surface of the fuser belt86and the outer surface of the pressure application belt96that is used as a reference for the sandwiching range AR1, AR2when the recording sheet5is sandwiched for applying heat and pressure thereto is also referred to as a sandwiching range reference position PA1.

In practice, in the user unit16, for example, when the recording sheet5having the widest sheet width is taken in, a range in the outer surface of the fuser belt86and the outer surface of the pressure application belt96from the sandwiching range reference position PA1to a predetermined position near the right end corresponding to the sheet width of the recording sheet5becomes the sandwiching range AR1where the recording sheet5is sandwiched for applying heat and pressure thereto. Further, in the fuser unit16, for example, when the recording sheet5having a sheet width less than ½ the fuser belt width (or the pressure application belt width) is taken in, a range in the outer surface of the fuser belt86and the outer surface of the pressure application belt96from the sandwiching range reference position PA1to a predetermined position of a central part corresponding to the sheet width of the recording sheet5becomes the sandwiching range AR2where the recording sheet5is sandwiched for applying heat and pressure thereto. Therefore, in the fuser unit16, a range in the outer surface of the fuser belt86and the outer surface of the pressure application belt96from the sandwiching range reference position PA1to the left ends becomes a non-sandwiching range AR3where the recording sheet5is not sandwiched for applying heat and pressure thereto. In the fuser unit16, as described above, the fuser part first heater82is formed in the manner that substantially the entire heater body becomes the heat generation part, and is arranged in the manner that the heat generation part from one end to the other end opposes the inner surface of the fuser belt86from the left end to the right end. Further, in the fuser unit16, as described above, the fuser part second heater83is formed in the manner that the portion of the heater body from the vicinity of one end to the central part becomes the heat generation part, and is arranged in the manner that the heat generation part from one end to the other end opposes the inner surface of the fuser belt86from the left end to the central part. Therefore, in the fuser unit16, due to the fuser part first heater82, the inner surface of the fuser belt86from the left end to the right end can be heated and, due to the fuser part second heater83, the inner surface of the fuser belt86from the left end to the central part can be heated.

In the fuser unit16, as described above, the pressure application part first heater92is formed in the manner that substantially the entire heater body becomes the heat generation part, and is arranged in the manner that the heat generation part from one end to the other end opposes the inner surface of the pressure application belt96from the left end to the right end. Further, in the fuser unit16, as described above, the pressure application part second heater93is formed in the manner that the portion of the heater body from the vicinity of one end to the central part becomes the heat generation part, and is arranged in the manner that the heat generation part from one end to the other end opposes the inner surface of the pressure application belt96from the left end to the central part. Therefore, in the fuser unit16, due to the pressure application part first heater92, the inner surface of the pressure application belt96from the left end to the right end can be heated and, due to the pressure application part second heater93, the inner surface of the pressure application belt96from the left end to the central part can be heated. Therefore, in the fuser unit16, when the recording sheet5is sandwiched for fusing the toner images by the fuser belt86and the pressure application belt96that are rotating in opposite directions, according the sheet width of the recording sheet5(that is, the sandwiching range AR1, AR2with respect to the recording sheet5in this case), the fuser part first heater82and the fuser part second heater83can be selectively used. Further, in the fuser unit16, when the recording sheet5is sandwiched for fusing the toner images by the fuser belt86and the pressure application belt96that are rotating in opposite directions, according the sheet width of the recording sheet5(that is, the sandwiching range AR1, AR2with respect to the recording sheet5in this case), the pressure application part first heater92and the pressure application part second heater93can also be selectively used. That is, in the fuser unit16, for example, when the recording sheet5having a sheet width larger than substantially ½ of the fuser belt width (and the pressure application belt width) is sandwiched for fusing the toner images by the fuser belt86and the pressure application belt96, the heat generation control current is supplied from the first heater power source120to the fuser part first heater82to generate heat and, thereby, the entire inner surface of the fuser belt86is heated as a heat application range and temperature is increased in the entire outer surface as a temperature raising range. Further, in the fuser unit16, in this case, the heat generation control current is supplied from the second heater power source121to the pressure application part first heater92to generate heat and, thereby, the entire inner surface of the pressure application belt96is heated as a heat application range and temperature is increased in the entire outer surface as a temperature raising range.

In contrast, in the fuser unit16, for example, when the recording sheet5having a sheet width less than ½ of the fuser belt width (and the pressure application belt width) is sandwiched for fusing the toner images by the fuser belt86and the pressure application belt96, the heat generation control current is supplied from the first heater power source120to the fuser part second heater83to generate heat and, thereby, the inner surface of the fuser belt86from the left end to the central part is heated as a heat application range and temperature is increased in the outer surface from the left end to the central part as a temperature raising range. Further, in the fuser unit16, in this case, the heat generation control current is supplied from the second heater power source121to the pressure application part second heater93to generate heat and, thereby, the inner surface of the pressure application belt96from the left end to the central part is heated as a heat application range and temperature is increased in the outer surface from the left end to the central part as a temperature raising range. In the fuser unit16, although not particularly illustrated in the drawings, one end part and the other end part of each of the fuser part first reflection plate84and the fuser part second reflection plate85are arranged in a manner projecting outwardly from the left end and the right end of the fuser belt86, and the radiant heat of the fuser part first heater82and the fuser part second heater83is reflected by the respective reflection surfaces of the fuser part first reflection plate84and the fuser part second reflection plate85. Therefore, in the fuser unit16, due to the fuser part first reflection plate84and the fuser part second reflection plate85, not only the belt drive roller80and the fuser part driven roller81are protected from the radiant heat of the fuser part first heater82and the fuser part second heater83, but also heat application efficiency of the entire fuser belt86or the portion of the fuser belt86from the left end to the central part is increased. Further, in the fuser unit16, one end part and the other end part of each of the pressure application part first reflection plate94and the pressure application part second reflection plate95are arranged in a manner projecting outwardly from the left end and the right end of the pressure application belt96, and the radiant heat of the pressure application part first heater92and the pressure application part second heater93is reflected by the respective reflection surfaces of the pressure application part first reflection plate94and the pressure application part second reflection plate95. Therefore, in the fuser unit16, due to the pressure application part first reflection plate94and the pressure application part second reflection plate95, not only the pressure application roller90and the pressure application part driven roller91are protected from the radiant heat of the pressure application part first heater92and the pressure application part second heater93, but also heat application efficiency of the entire pressure application belt96or the portion of the pressure application belt96from the left end to the central part is increased. In this way, in the fuser unit16, during the formation of the print image, it can be avoided that the fuser belt86and the pressure application belt96are wastefully heated and power consumption is increased.

In the fuser unit16, in this way, when the recording sheet5is sandwiched for applying heat and pressure thereto in the state in which the fuser belt86and the pressure application belt96are heated while being rotated, an amount of heat required for fusing the toner images (that is, required for melting the toners) is supplied to the recording sheet5from the sandwiching range AR1, AR2where the recording sheet5is in contact with the outer surfaces of the fuser belt86and the pressure application belt96. Therefore, in the fuser unit16, there is a tendency on the outer surface of the fuser belt86and the outer surface of the pressure application belt96, for example, that the temperature of the sandwiching range AR1, AR2where the recording sheet5is in contact with is lowered/reduced more than the temperature of a portion in the temperature raising range where the recording sheet5is not in contact with like the non-sandwiching range AR3. Therefore, in the fuser unit16, the controller60is caused to detect via the fuser part temperature sensor87the temperature of the outer surface of the fuser belt86and, in response to the detection result, control via the first heater power source120the heat generation of the fuser part first heater82and the fuser part second heater83. Thereby, the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86can be adjusted so as to not drop below a minimum temperature required for fusing the toner images (hereinafter, this is also referred to as a minimum fusing temperature). Further, in the fuser unit16, the controller60is caused to detect via the pressure application part temperature sensor97the temperature of the outer surface of the pressure application belt96and, in response to the detection result, control via the second heater power source121the heat generation of the pressure application part first heater92and the pressure application part second heater93. Thereby, the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96can be adjusted so as to not drop below the minimum fusing temperature.

However, in the fuser unit16, even when either the fuser part first heater82and the pressure application part first heater92, or the fuser part second heater83and the pressure application part second heater93, are used for the heat application of the fuser belt86and the pressure application belt96according to the sheet width of the recording sheet5to which heat and pressure are applied, on the outer surface of the fuser belt86and the outer surface of the pressure application belt96, it is necessary ti increase the temperature in at least a portion larger than the sandwiching range of the recording sheet5having the narrowest sheet width. Therefore, in the fuser unit16(FIG. 4), at positions opposing the sandwiching range of the recording sheet5having the narrowest sheet width on the outer surface of the fuser belt86and the outer surface of the pressure application belt96, the fuser part temperature sensor87and the pressure application part temperature sensor97are arranged in a non-contact manner. As a result, even when heat and pressure are applied to the recording sheet5of any sheet width, the fuser unit16can cause the controller60, through the fuser part temperature sensor87and the pressure application part temperature sensor97, to respectively detect temperatures of the portions of the outer surface of the fuser belt86and the outer surface of the pressure application belt96that are in contact with the recording sheet5.

In the fuser unit16, for example, when, due to malfunction of the fuser part temperature sensor87and the pressure application part temperature sensor97, the controller60erroneously detects via the fuser part temperature sensor87and the pressure application part temperature sensor97that the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96are lower than actual temperatures, there is a possibility that, in order to apply heat to the fuser belt86and the pressure application belt96, the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, are caused to continue to generate heat. In the fuser unit16, as just described, when the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, are caused to continue to generate heat, there is a possibility that ambient temperatures (that is, temperature of the inner side of the fuser belt86and temperature of the inner side of the pressure application belt96) significantly rise and cause damage to the fuser unit16. Therefore, in the fuser unit16, the fuser part thermostat88and the pressure application part thermostat98are provided capable of accurately detecting ambient temperatures of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, as the temperatures of the outer surface of the fuser belt86and the temperatures of the outer surface of the pressure application belt96.

In practice, in the fuser unit16, as can be seen fromFIG. 10, even when either the fuser part first heater82and the pressure application part first heater92, or the fuser part second heater83and the pressure application part second heater93, are used for the heat application of the fuser belt86and the pressure application belt96according to the sheet width of the recording sheet5to which heat and pressure are applied, heat is applied to portions of the respective inner surfaces of the fuser belt86and the pressure application belt96from the left ends to the central parts as a common heat application range, and temperature is increased in portions of the respective outer surfaces from the left ends to the central parts as a common temperature raising range. Therefore, in the fuser unit16, when the recording sheet5is sandwiched for applying heat and pressure by the outer surface of the fuser belt86and the outer surface of the pressure application belt96while heat is suitably applied to the inner surface of the fuser belt86and the inner surface of the pressure application belt96by the fuser part first heater82and the pressure application part first heater92or by the fuser part second heater83and the pressure application part second heater93, even when the temperature drops in the sandwiching range AR1, AR2of the recording sheet5, in the non-sandwiching range AR3on the left side of the sandwiching range reference position PA1, without any drop in the temperature, the temperature remains at a temperature corresponding the heat applied. In other words, in the fuser unit16, one end part of the heat generation part of the fuser part first heater82and one end part of the heat generation part of the fuser part second heater83oppose a left end part of the inner surface of the fuser belt86(that is, a portion on an under side of the non-sandwiching range AR3of the outer surface), and heat is directly applied to the left end part of the inner surface of the fuser belt86by the fuser part first heater82or the fuser part second heater83. In the fuser unit16, in response to the heat application, although the temperature rises in the non-sandwiching range AR3, which is the left end part of the outer surface of the fuser belt86, since temperature drop due to contact with the recording sheet5does not occur, it can be said that the temperature in the non-sandwiching range AR3is a temperature that unerringly reflects the ambient temperature of the heat generation part of the fuser part first heater82or the fuser part second heater83(that is, the temperature of the inner side of the fuser belt86).

Further, in the fuser unit16, one end part of the heat generation part of the pressure application part first heater92and one end part of the heat generation part of the pressure application part second heater93oppose a left end part of the inner surface of the pressure application belt96(that is, a portion on an under side of the non-sandwiching range AR3of the outer surface), and heat is directly applied to the left end part of the inner surface of the pressure application belt96by the pressure application part first heater92or the pressure application part second heater93. In the fuser unit16, in response to the heat application, although the temperature rises in the non-sandwiching range AR3, which is the left end part of the outer surface of the pressure application belt96, since temperature drop due to contact with the recording sheet5does not occur, it can be said that the temperature in the non-sandwiching range AR3is a temperature that unerringly reflects the ambient temperature of the heat generation part of the pressure application part first heater92or the pressure application part second heater93(that is, the temperature of the inner side of the pressure application belt96).

Therefore, as illustrated inFIG. 11, in the fuser unit16, the fuser part thermostat88is arranged in a manner that the front end of the heat sensing part88B is in contact with the left end part (that is, the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the fuser belt86, even when heat and pressure are applied to the recording sheet5of any sheet width. As a result, in the fuser unit16, due to the fuser part thermostat88, the ambient temperature of the fuser part first heater82or the fuser part second heater83is accurately detected as the temperature in the non-sandwiching range AR3on the outer surface of the fuser belt86, which is not affected by the temperature drop due to contact with the recording sheet5. Further, in the fuser unit16, the pressure application part thermostat98is arranged in a manner that the front end of the heat sensing part98B is in contact with the left end part (that is, the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the pressure application belt96, even when heat and pressure are applied to the recording sheet5of any sheet width. As a result, in the fuser unit16, due to the pressure application part thermostat98, the ambient temperature of the pressure application part first heater92or the pressure application part second heater93is accurately detected as the temperature in the non-sandwiching range AR3on the outer surface of the pressure application belt96, which is not affected by the temperature drop due to contact with the recording sheet5. Further, in the fuser unit16, for example, even when the outer surface of the fuser belt86and the outer surface of the pressure application belt96are worn and damaged due to sliding with respect to the front end of the heat sensing part88B of the fuser part thermostat88and the front end of the heat sensing part98B of the pressure application part thermostat98, the contact positions of the front ends of the heat sensing parts88B,98B are in the non-sandwiching range AR3. Therefore, fusing failure of the toner images on the surface of the recording sheet5due to the wear and damage of the belts can be prevented from occurring.

As illustrated inFIG. 12, the fuser belt86has a certain degree of elasticity and thus, in a state of being hung over the belt drive roller80and the fuser part driven roller81, has a shape in which an upper side portion that opposes the sandwiching part115projects upwardly forming a bow-like shape (that is, a shape indicated by a dotted line inFIG. 12). When the fuser belt86rotates in the one rotation direction in response to driving of the belt drive roller80, due to pulling by the belt drive roller80to rotate the fuser belt86in the one rotation direction, a front side portion and a side portion of the fuser belt86vibrate back and forth, and along with the vibration, it is possible that the upper side portion vibrates up and down. However, even when such vibration occurs in the fuser belt86, since the vibration is due to the pulling by the belt drive roller80, an amplitude of the up-down vibration of the upper side portion is significantly small as compared to an amplitude of the vibration of the front side portion and the rear side portion. Therefore, the fuser part thermostat88is fixed on the unit case50via the thermostat holding part106by pressing the front end of the heat sensing part88B against the outer surface of the upper side portion of the fuser belt86in a state in which the upper side portion is pressed down by a predetermined amount L1that is larger than the amplitude of the up-down vibration that is possible to occur in the upper side portion. As a result, in the fuser unit16, the upper side portion of the fuser belt86does not vibrate and is constantly acted in a manner being pushed back upwardly due to the elasticity of the fuser belt86and thus, even when the fuser belt86rotates in the one rotation direction, the front end (that is, the heat sensing surface that is a circular end surface) of the heat sensing part88B of the fuser part thermostat88can be stably in contact with the outer surface of the fuser belt86.

On the surface of the heat sensing part88B of the fuser part thermostat88, a predetermined resin layer such as that of fluorine-based resin such as PFA or PTFE is formed (for example, using fluorine-based resin tube covering or fluorine-based resin coating) to improve adhesion of the front end of the heat sensing part88B with respect to the outer surface of the fuser belt86. As a result, even when the outer surface of the fuser belt86slides with respect to the front end of the heat sensing part88B of the fuser part thermostat88, that the outer surface of the fuser belt86is worn and damaged due to the front end is significantly reduced and the releasability of toner on the surface of the heat sensing part88B is improved. Therefore, during the formation of the print image, it is avoided as much as possible that the accuracy of the temperature detection is reduced due to that wear powder and toner enter between the front end of the heat sensing part88B of the fuser part thermostat88and the outer surface of the fuser belt86and the outer surface is damaged.

On the other hand, similar to the fuser belt86, the pressure application belt96also has a certain degree of elasticity and thus, in a state of being hung over the pressure application roller90and the pressure application part driven roller91, has a shape in which a lower side portion that opposes the sandwiching part115projects downwardly forming a bow-like shape (that is, a shape indicated by a dotted line inFIG. 12). When the pressure application belt96rotates in the other rotation direction in conjunction with the rotation of the fuser belt86in the one rotation direction, due to pulling by the fuser belt86to rotate the pressure application belt96in the other rotation direction, a front side portion and a side portion of the pressure application belt96vibrate back and forth, and along with the vibration, it is possible that the lower side portion vibrates up and down. However, even when such vibration occurs in the pressure application belt96, since the vibration is due to the pulling by the fuser belt86, an amplitude of the up-down vibration of the lower side portion is significantly small as compared to an amplitude of the vibration of the front side portion and the rear side portion. Therefore, the pressure application part thermostat98is fixed on the unit case50via the thermostat holding part117by pressing the front end of the heat sensing part98B against the outer surface of the lower side portion of the pressure application belt96in a state in which the lower side portion is pressed down by the predetermined amount L1that is larger than the amplitude of the up-down vibration that is possible to occur in the lower side portion. As a result, in the fuser unit16, the lower side portion of the pressure application belt96does not vibrate and is constantly acted in a manner being pushed back downwardly due to the elasticity of the pressure application belt96and thus, even when the pressure application belt96rotates in the other rotation direction, the front end (that is, the heat sensing surface that is a circular end surface) of the heat sensing part98B of the pressure application part thermostat98can be stably in contact with the outer surface of the pressure application belt96. Similar to the fuser part thermostat88, also on the surface of the heat sensing part98B of the pressure application part thermostat98, a predetermined resin layer such as that of fluorine-based resin such as PFA or PTFE is formed (for example, using fluorine-based resin tube covering or fluorine-based resin coating) to improve adhesion of the front end of the heat sensing part98B with respect to the outer surface of the pressure application belt96. As a result, also for the pressure application part thermostat98, even when the outer surface of the pressure application part thermostat98slides with respect to the front end of the heat sensing part98B, that the outer surface of the pressure application belt96is worn and damaged due to the front end is significantly reduced and the releasability of toner on the surface of the heat sensing part98B is improved. Therefore, also for the pressure application part thermostat98, during the formation of the print image, it is avoided as much as possible that the accuracy of the temperature detection is reduced due to that wear powder and toner enter between the front end of the heat sensing part98B and the outer surface of the pressure application belt96and the outer surface is damaged.

The fuser part thermostat88is formed to detect, using the heat sensing part88B, a predetermined temperature (hereinafter, this is also referred to as a damage prevention temperature) that is pre-selected for preventing damage by heat to the fuser unit16, such as an upper limit temperature of a temperature range that is higher than the predetermined temperature required for fusing the toner images on the surface of the recording sheet5(that is, required for melting the toners) and, for example, allows the fuser unit16to safely operate. Further, the fuser part thermostat88is formed to block the heat generation control currents supplied by the first heater power source120to the fuser part first heater82and the fuser part second heater83by, for example, melting down the conductor in the body part88A when it is detected by the heat sensing part88B that the temperature of the outer surface of the fuser belt86has reached the damage prevention temperature. Further, similar to the fuser part thermostat88, the pressure application part thermostat98also is formed to block the heat generation control currents supplied by the second heater power source121to the pressure application part first heater92and the pressure application part second heater93by melting down the conductor in the body part98A when it is detected by the heat sensing part98B that the temperature of the outer surface of the pressure application belt96has reached the damage prevention temperature. Therefore, in the fuser unit16, for example, due to malfunction of the fuser part temperature sensor87and the pressure application part temperature sensor97, the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96are erroneously detected as temperatures lower than actual temperatures and, as a result, the fuser part first heater82or the fuser part second heater83and the pressure application part first heater92or the pressure application part second heater93are caused to continue to generate heat for applying heat to the fuser belt86and the pressure application belt96; even in this case, when the temperatures of the outer surfaces of the fuser belt86and the pressure application belt96reach the damage prevention temperature, at this time, the heat generation of the fuser part first heater82or the fuser part second heater83and the pressure application part first heater92or the pressure application part second heater93can be interrupted. As a result, in the fuser unit16, significant temperature rise due to heat generation of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, can be prevented, and damage by heat to the fuser unit16can be prevented.

Here, a heat and pressure application process that in practice the controller60executes during the formation of the print image for causing the fuser unit16to operate to apply heat and pressure to the recording sheet5is described in detail. In the following, for example, the heat and pressure application process in a case where a print image is continuously formed (that is, continuous printed) on surfaces of a plurality of the recording sheets5is described. As illustrated inFIG. 13, during the formation of the print image, the controller60causes the fuser unit drive motor to operate to rotate in the fuser unit16the belt drive roller80in the one rotation direction and thereby, in conjunction with the rotation, the fuser part driven roller81and the fuser belt86are caused to rotate at a predetermined rotational speed in the one rotation direction. In this case, in conjunction with the rotation of the fuser belt86in the one rotation direction, the controller60causes the pressure application belt96, together with the pressure application roller90and the pressure application part driven roller91, to rotate in the other rotation direction at a rotational speed same as that of the fuser belt86in the state in which the outer surface of the pressure application belt96is pressed against the outer surface of the fuser belt86.

Further, the controller60supplies the heat generation control current from the first heater power source120to one of the fuser part first heater82and the fuser part second heater83according to the sheet width of the recording sheet5of a print image formation target in this case to generate heat and begins applying heat to the fuser belt86. Further, the controller60supplies the heat generation control current from the second heater power source121to one of the pressure application part first heater92and the pressure application part second heater93according to the sheet width of the recording sheet5of the print image formation target in this case to generate heat and begins applying heat to the pressure application belt96. Further, the controller60detects, via the fuser part temperature sensor87, the temperature of the outer surface of the fuser belt86and, in response to the detection result, suitably ON/OFF-controls the first heater power source120. As a result, as illustrated by a sandwiching range temperature characteristic curve TE1and a non-sandwiching range temperature characteristic curve TE2inFIG. 12, the controller60adjusts the temperature of the sandwiching range AR1, AR2and the temperature of the non-sandwiching range AR3on the outer surface of the fuser belt86to a predetermined target temperature TS1. Further, the controller60detects, via the pressure application part temperature sensor97, the temperature of the outer surface of the pressure application belt96and, in response to the detection result, suitably ON/OFF-controls the second heater power source121. As a result, similar to that for the fuser belt86, the controller60adjusts the temperature of the sandwiching range AR1, AR2and the temperature of the non-sandwiching range AR3on the outer surface of the pressure application belt96to the target temperature TS1. The target temperature TS1is selected to be a predetermined temperature that is higher than the minimum fusing temperature in such a manner that, when the recording sheet5is sandwiched by the outer surface of the fuser belt86and the outer surface of the pressure application belt96for applying heat and pressure, the temperature of the sandwiching range AR1, AR2does not drop below the minimum fusing temperature. In this way, when the controller60raises the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96to the target temperature TS1in the fuser unit16, as described above, the recording sheet5is fed out from the sheet feeding tray52, and the first-fourth image forming units10-13and the transfer part15transfer the toner images of the four colors to the surface of the recording sheet5by sequentially superimposing the toner images.

Next, in the fuser unit16, the controller60takes in the recording sheet5, to the surface of which the toner images of the four colors are transferred, from the recording sheet inlet50AX. As a result, the controller60applies heat and pressure to the recording sheet5while carrying the recording sheet5by sandwiching the recording sheet5in the sandwiching part115between the outer surface of the fuser belt86and the outer surface of the pressure application belt96that are rotating in opposite direction in the fuser unit16, and the toner images of the four colors are fused onto the surface of the recording sheet5by being temporarily melted once. Thereafter, the controller60feeds out the recording sheet5from the recording sheet outlet50CX to the ejection carrying path. In this way, the controller60can form the color print image on the surface of the recording sheet5in the fuser unit16, the color print image being the toner images of the four colors that are fused onto the surface of the recording sheet5. Thereafter, each time the recording sheet5, to the surface of which the toner images of the four colors are transferred, is taken in from the recording sheet inlet50AX, similarly, heat and pressure are applied to the recording sheet5and the recording sheet is fed out from the recording sheet outlet50CX to the ejection carrying path.

In the fuser unit16, in the case of such continuous print, each time the recording sheet5is sandwiched between the outer surface of the fuser belt86and the outer surface of the pressure application belt96, an amount of heat required for fusing the toner images is supplied from the sandwiching range AR1, AR2to the recording sheet5. Thereby, there is a tendency that the temperature of the sandwiching range AR1, AR2that has been adjusted to the target temperature TS1gradually drops. When the controller60detects via the fuser part temperature sensor87that, in practice, the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86has dropped due to that the recording sheet5is sandwiched between the outer surface of the fuser belt86and the outer surface of the pressure application belt96, in response to the detection result, the controller60repeatedly ON/OFF-controls the first heater power source120. As a result, the controller60intermittently causes, via the first heater power source120, the fuser part first heater82or the fuser part second heater83to generate heat to apply heat to the fuser belt86. In this way, during continuous print, even when the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86gradually drops, during this period, the controller60intermittently causes the fuser part first heater82or the fuser part second heater83to generate heat to apply heat to the fuser belt86and thereby the temperature of the sandwiching range AR1, AR2can be maintained at a temperature that is higher to some extent than the minimum fusing temperature. Further, when the controller60detects via the pressure application part temperature sensor97that, in practice, the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96has dropped due to that the recording sheet5is sandwiched between the outer surface of the fuser belt86and the outer surface of the pressure application belt96, in response to the detection result, the controller60repeatedly ON/OFF-controls the second heater power source121. As a result, the controller60intermittently causes, via the second heater power source121, the pressure application part first heater92or the pressure application part second heater93to generate heat to apply heat to the pressure application belt96. In this way, during continuous print, even when the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96gradually drops, during this period, the controller60intermittently causes the pressure application part first heater92or the pressure application part second heater93to generate heat to apply heat to the pressure application belt96and thereby, similar to the case of the fuser belt86, the temperature of the sandwiching range AR1, AR2can also be maintained at a temperature that is higher to some extent than the minimum fusing temperature.

However, in this case, when the controller60intermittently causes, via the first heater power source120, the fuser part first heater82or the fuser part second heater83to generate heat to apply heat to the fuser belt86, since there is no factor that particularly causes the temperature of the non-sandwiching range AR3on the outer surface of the fuser belt86to drop, the temperature of the non-sandwiching range AR3on the outer surface of the fuser belt86gradually rises to above the target temperature TS1. Further, when the controller60intermittently causes, via the second heater power source121, the pressure application part first heater92or the pressure application part second heater93to generate heat to apply heat to the pressure application belt96, since there is no factor that particularly causes the temperature of the non-sandwiching range AR3on the outer surface of the pressure application belt96to drop, the temperature of the non-sandwiching range AR3on the outer surface of the pressure application belt96also gradually rises to above the target temperature TS1. Since the controller60intermittently causes the fuser part first heater82or the fuser part second heater83to generate heat and also intermittently causes the pressure application part first heater92or the pressure application part second heater93to generate heat, the temperature of the non-sandwiching range AR3on the outer surface of the fuser belt86and the outer surface of the pressure application belt96can be made substantially constant while has not been raised too high. When the continuous print ends, the controller60terminates supply of the heat generation control current from the first heater power source120to the fuser part first heater82or the fuser part second heater83and causes the fuser part first heater82or the fuser part second heater83to terminate heat generation. Further, in this case, the controller60also terminates supply of the heat generation control current from the second heater power source121to the pressure application part first heater92or the pressure application part second heater93and causes the pressure application part first heater92or the pressure application part second heater93to terminate heat generation.

As described above, when the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, are formed as halogen lamps, because of characteristics of the halogen lamps, even when the supply of the heat generation control currents from the first heater power source120and the second heater power source121is terminated to terminate heat generation, the temperatures of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, cannot immediately drop. Therefore, even when the continuous print terminates and the heat generation of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, are terminated, due to the heat generated by the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, it is possible that the temperatures of the sandwiching range AR1, AR2and the non-sandwiching range AR3on the outer surfaces of the fuser belt86and the pressure application belt96rise slightly above the temperatures at the time when the heat generation is terminated. Therefore, the above-described damage prevention temperature TS2is suitably selected by also taking into account the characteristics of such fuser part first heater82, fuser part second heater83, pressure application part first heater92and pressure application part second heater93as halogen lamps.

However, although not particularly illustrated in the drawings, for example, when, due to malfunction of the fuser part temperature sensor87, the controller60erroneously detects the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86as a temperature lower than an actual temperature, depending on the erroneously detected temperature (that is, the erroneously detected temperature is relatively low), the controller60continuously supplies the heat generation control current from the first heater power source120to the fuser part first heater82or the fuser part second heater83to generate heat and thereby it is possible that the ambient temperature of the fuser part first heater82or the fuser part second heater83(that is, the temperature on the inner side of the fuser belt86) significantly rises. In this way, when the ambient temperature of the fuser part first heater82or the fuser part second heater83(that is, the temperature on the inner side of the fuser belt86) rises, this temperature can be reflected in the temperature of the non-sandwiching range AR3on the outer surface of the fuser belt86. Therefore, even when the ambient temperature of the fuser part first heater82or the fuser part second heater83(that is, the temperature on the inner side of the fuser belt86) rises, when the temperature of the non-sandwiching range AR3on the outer surface of the fuser belt86that reflects the temperature on the inner side of the fuser belt86reaches the damage prevention temperature TS2, by detecting this, the fuser part thermostat88can forcibly block the supply of the heat generation control current from the first heater power source120to the fuser part first heater82or the fuser part second heater83. As a result, the fuser part thermostat88interrupts the heat generation of the fuser part first heater82or the fuser part second heater83, and a significant temperature rise around the fuser part first heater82or the fuser part second heater83(that is, on the inner side of the fuser belt86) can be prevented.

Further, for example, when, due to malfunction of the pressure application part temperature sensor97, the controller60erroneously detects the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96as a temperature lower than an actual temperature, depending on the erroneously detected temperature, the controller60continuously supplies the heat generation control current from the second heater power source121to the pressure application part first heater92or the pressure application part second heater93to generate heat and thereby it is possible that the ambient temperature of the pressure application part first heater92or the pressure application part second heater93(that is, the temperature on the inner side of the pressure application belt96) significantly rises. In this way, when the ambient temperature of the pressure application part first heater92or the pressure application part second heater93(that is, the temperature on the inner side of the pressure application belt96) rises, this temperature can be reflected in the temperature of the non-sandwiching range AR3on the outer surface of the pressure application belt96. Therefore, even when the ambient temperature of the pressure application part first heater92or the pressure application part second heater93(that is, the temperature on the inner side of the pressure application belt96) rises, when the temperature of the non-sandwiching range AR3on the outer surface of the pressure application belt96that reflects the temperature on the inner side of the pressure application belt96reaches the damage prevention temperature TS2, by detecting this, the pressure application part thermostat98can forcibly block the supply of the heat generation control current from the second heater power source121to the pressure application part first heater92or the pressure application part second heater93. As a result, the pressure application part thermostat98interrupts the heat generation of the pressure application part first heater92or the pressure application part second heater93, and a significant temperature rise around the pressure application part first heater92or the pressure application part second heater93(that is, on the inner side of the pressure application belt96) can be prevented. In this way, even when the ambient temperatures of the fuser part first heater82or the fuser part second heater83and the ambient temperature of the pressure application part first heater92or the pressure application part second heater93rise, the fuser part thermostat88and the pressure application part thermostat98can accurately detect the ambient temperatures and interrupt the heat generation, and thus damage to the fuser unit16can be prevented from occurring.

(1-3) Operation and Effect of First Embodiment

In the above-describe configuration, in the color printer1, in the fuser unit16, the fuser belt86is provided rotatable in the one rotation direction, and the pressure application belt96is provided rotatable in the other rotation direction in the state in which a portion of the outer surface of the pressure application belt96is pressed against a portion of the outer surface of the fuser belt86. Further, in the color printer1, in the fuser unit16, the fuser part first heater82and the fuser part second heater83are provided inside the fuser belt86, and the pressure application part first heater92and the pressure application part second heater93are provided inside the pressure application belt96. Further, in the color printer1, in the fuser unit16, the fuser part temperature sensor87is provided capable of detecting the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86, and the pressure application part temperature sensor97is provided capable of detecting the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96.

During the formation of the print image, while causing the fuser belt86and the pressure application belt96to rotate in mutually opposite directions in the fuser unit16, the color printer1detects, via the fuser part temperature sensor87, the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86and, in response to the detection result, causes the fuser part first heater82or the fuser part second heater83to generate heat to apply heat to the fuser belt86. Further, in this case, in the fuser unit16, the color printer1detects, via the pressure application part temperature sensor97, the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96and, in response to the detection result, causes the pressure application part first heater92or the pressure application part second heater93to generate heat to apply heat to the pressure application belt96.

In this state, in the fuser unit16, the color printer1applies heat and pressure to the recording sheet5, to the surface of which the toner images are transferred, while carrying the recording sheet5in the manner sandwiching the recording sheet5between the sandwiching range AR1, AR2of the outer surface of the fuser belt86and the sandwiching range AR1, AR2of the outer surface of the pressure application belt96. As a result, in the fuser unit16, the color printer1can form the print image by fusing the toner images onto the surface of the recording sheet5by temporarily melting once the toner images. In the color printer1, in the fuser unit16, the fuser part thermostat88is provided in the manner that the front end of the heat sensing part88B is in contact with the left end part (the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the fuser belt86for detecting, when the temperature of the outer surface of the fuser belt86has reached the damage prevention temperature TS2, the temperature of the outer surface that has reached the damage prevention temperature TS2and, in response to the detection result, interrupting the heat generation of the fuser part first heater82or the fuser part second heater83. Further, in the color printer1, in the fuser unit16, the pressure application part thermostat98is provided in the manner that the front end of the heat sensing part98B is in contact with the left end part (the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the pressure application belt96for detecting, when the temperature of the outer surface of the pressure application belt96has reached the damage prevention temperature TS2, the temperature of the outer surface that has reached the damage prevention temperature TS2and, in response to the detection result, interrupting the heat generation of the pressure application part first heater92or the pressure application part second heater93.

Therefore, during the formation of the print image, regardless whether or not the recording sheet5is carried for applying heat and pressure thereto by the fuser belt86and the pressure application belt96, when the ambient temperature of the fuser part first heater82or the fuser part second heater83rises, the color printer1can accurately detect the ambient temperature as the temperature of the outer surface of the fuser belt86without being influenced by the temperature drop due to contact with the recording sheet5and interrupt the heat generation of the fuser part first heater82or the fuser part second heater83, and thus a significant temperature rise of the fuser unit16can be prevented from occurring. Further, regardless whether or not the recording sheet5is carried for applying heat and pressure thereto by the fuser belt86and the pressure application belt96, due to the pressure application part thermostat98, when the ambient temperature of the pressure application part first heater92or the pressure application part second heater93rises, the color printer1can accurately detect the ambient temperature as the temperature of the outer surface of the pressure application belt96without being influenced by the temperature drop due to contact with the recording sheet5and interrupt the heat generation of the pressure application part first heater92or the pressure application part second heater93, and thus a significant temperature rise of the fuser unit16can be prevented from occurring.

According to the above-described configuration, in the color printer1, in the fuser unit16, the fuser belt86and the pressure application belt96are provided rotatable in mutually opposite the one rotation direction and the other rotation direction for carrying the recording sheet5, for carrying the recording sheet5, to the surface of which the toner images are transferred, by sandwiching the recording sheet5between the sandwiching range AR1, AR2of the outer surface of the fuser belt86and the sandwiching range AR1, AR2of the outer surface of the pressure application belt96; the fuser part first heater82and the fuser part second heater83are provided inside the fuser belt86for applying heat to the fuser belt86and the pressure application part first heater92and the pressure application part second heater93are provided inside the pressure application belt96for applying heat to the pressure application belt96; and further, the fuser part thermostat88is provided in the manner that the front end of the heat sensing part88B is in contact with the left end part outside the sandwiching range AR1, AR2of the outer surface of the fuser belt86, for detecting that the temperature of the outer surface of the fuser belt86has reached the damage prevention temperature TS2and interrupting the heat generation of the fuser part first heater82and the fuser part second heater83, and the pressure application part thermostat98is provided in the manner that the front end of the heat sensing part98B is in contact with the left end part outside the sandwiching range AR1, AR2of the outer surface of the pressure application belt96, for detecting that the temperature of the outer surface of the pressure application belt96has reached the damage prevention temperature TS2and interrupting the heat generation of the pressure application part first heater92and the pressure application part second heater93.

As a result, during the formation of the print image, regardless whether or not the recording sheet5is carried for applying heat and pressure thereto by the fuser belt86and the pressure application belt96, when the ambient temperature of the fuser part first heater82and the fuser part second heater83and the ambient temperature of the pressure application part first heater92and pressure application part second heater93rise, the color printer1can accurately detect the ambient temperatures as the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96without being influenced by the temperature drop due to contact with the recording sheet5and interrupt the heat generation of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93. Therefore, the color printer1can prevent damage to the fuser unit16due to a significant temperature rise from occurring.

In the color printer1, as described above, the fuser part first heater82and the fuser part second heater83are provided inside the fuser belt86for applying heat to the fuser belt86, and the pressure application part first heater92and the pressure application part second heater93are provided inside the pressure application belt96for applying heat to the pressure application belt96. Therefore, when applying heat and pressure to the recording sheet5while carrying the recording sheet5by sandwiching the recording sheet5between the fuser belt86and the pressure application belt96that rotate in mutually opposite directions, the color printer1can efficiently apply heat to the recording sheet5from its front surface and back surface.

Further, in the color printer1, as described above, the front end of the heat sensing part88B of the fuser part thermostat88is in contact with the non-sandwiching range AR3for detecting the temperature of the outer surface of the fuser belt86, and the front end of the heat sensing part98B of the pressure application part thermostat98is in contact with the non-sandwiching range AR3for detecting the temperature of the outer surface of the pressure application belt96. Therefore, in the color printer1, even when the outer surface of the fuser belt86and the outer surface of the pressure application belt96are worn and damaged due to sliding with respect to the front end of the heat sensing part88B of the fuser part thermostat88and the front end of the heat sensing part98B of the pressure application part thermostat98, fusing failure of the toner images on the surface of the recording sheet5due to the wear and damage of the belts can be prevented from occurring.

In addition, according to the configuration of the color printer1, the fuser part thermostat88and the pressure application part thermostat98are arranged on the outer surface sides of the fuser belt86and the pressure application belt96. Therefore, that the fuser part thermostat88and the pressure application part thermostat98deteriorates and malfunctions due to heat being directly applied thereto by the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, can be prevented. Further, in the color printer1, the temperatures of the outer surfaces of the fuser belt86and the pressure application belt96are lower than the temperatures of the inner surfaces of the fuser belt86and the pressure application belt96, to which heat is directly applied by the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93. Therefore, the temperature to be detected by the fuser part thermostat88and the pressure application part thermostat98for preventing damage to the fuser unit16(that is, the damage prevention temperature TS2) can be lowered as compared to a case where the detection is performed on the inner surfaces. In other words, even without a configuration that allows the fuser part thermostat88and the pressure application part thermostat98to operate in a high temperature environment (that is, with a simple configuration), the color printer1can accurately detect the ambient temperature of the fuser part first heater82and the fuser part second heater83and the ambient temperature of the pressure application part first heater92and the pressure application part second heater93.

Further, in the color printer1, the one end parts of the respective heat generation parts of the fuser part first heater82and the fuser part second heater83are arranged to oppose the left end part of the inner surface, which is the under side of the non-sandwiching range AR3of the outer surface, of the fuser belt86, and the one end parts of the respective heat generation parts of the pressure application part first heater92and the pressure application part second heater93are arranged to oppose the left end part of the inner surface, which is the under side of the non-sandwiching range AR3of the outer surface, of the pressure application belt96. Therefore, in the color printer1, in the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86and the temperature of the non-sandwiching range AR3of the outer surface of the pressure application belt96, which are to be detected by the fuser part thermostat88and the pressure application part thermostat98as the ambient temperatures of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, these ambient temperatures that change due to the heat generation of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, can be unerringly reflected. Therefore, in the color printer1, regardless whether or not the recording sheet5is carried for applying heat and pressure thereto by the fuser belt86and the pressure application belt96, the detection accuracy of the ambient temperature of the fuser part first heater82and the fuser part second heater83and the ambient temperature of the pressure application part first heater92and the pressure application part second heater93by the fuser part thermostat88and the pressure application part thermostat98can be further improved.

Further, in the color printer1, the fuser belt86is hung in the state in which a tensional force is not applied to the belt drive roller80and the fuser part driven roller81, and the pressure application belt96is hung in the state in which a tensional force is not applied to the pressure application roller90and the pressure application part driven roller91. By pressing the pressure application roller90and the pressure application part driven roller91sequentially via the pressure application belt96and the fuser belt86against the belt drive roller80and the fuser part driven roller81, the sandwiching part115in which the recording sheet5is sandwiched by the pressure application belt96and the fuser belt86is formed. In color printer1, the fuser part thermostat88is fixed by pressing the front end of the heat sensing part88B against the outer surface of the portion (that is, the upper side portion) of the fuser belt86that opposes the sandwiching part115in the state in which the opposing portion is displaced (that is, pressed down), and the pressure application part thermostat98is fixed by pressing the front end of the heat sensing part98B against the outer surface of the portion (that is, the lower side portion) of the pressure application belt96that opposes the sandwiching part115in the state in which the opposing portion is displaced (that is, pressed up).

Therefore, in the color printer1, regardless whether or not the recording sheet5is carried for applying heat and pressure thereto by the fuser belt86and the pressure application belt96, the front end of the heat sensing part88B of the fuser part thermostat88can be stably in contact with the outer surface of the fuser belt86, and the front end of the heat sensing part98B of the pressure application part thermostat98can be stably in contact with the outer surface of the pressure application belt96. Therefore, in the color printer1, regardless whether or not the recording sheet5is carried for applying heat and pressure thereto by the fuser belt86and the pressure application belt96, the ambient temperature of the fuser part first heater82and fuser part second heater83can be further accurately detected as the temperature of the outer surface of the fuser belt86by the fuser part thermostat88, and the ambient temperature of the pressure application part first heater92and the pressure application part second heater93can be further accurately detected as the temperature of the outer surface of the pressure application belt96by the pressure application part thermostat98.

In the color printer1, the resin layers are formed on the surface of the heat sensing part88B of the fuser part thermostat88and the surface of the heat sensing part98B of the pressure application part thermostat98. Therefore, in the color printer1, the adhesion of the front end of the heat sensing part88B of the fuser part thermostat88and the front end of the heat sensing part98B of the pressure application part thermostat98with respect to the outer surface of the fuser belt86and the outer surface of the pressure application belt96is improved and, even when the outer surfaces of the fuser belt86and the pressure application belt96slide with respect to the front ends of the heat sensing parts88B,98B, that the outer surfaces of the fuser belt86and the pressure application belt96are worn and damaged due to the front ends can be significantly reduced and the releasability of toner on the surfaces of the heat sensing parts88B,98B can be improved. As a result, in the color printer1, during the formation of the print image, it can be avoided as much as possible that the accuracy of the temperature detection is reduced due to that wear powder and toner enter or the outer surfaces are damaged, the wear powder entering between the front end of the heat sensing part88B of the fuser part thermostat88and the outer surface of the fuser belt86or between the front end of the heat sensing part98B of the pressure application part thermostat98and the outer surface of the pressure application belt96.

Further, in the color printer1, the fuser part first reflection plate84and the fuser part second reflection plate85are arranged on the inner side of the fuser belt86, and the pressure application part first reflection plate94and the pressure application part second reflection plate95are arranged on the inner side of the pressure application belt96. Therefore, in the color printer1, a part of the radiant heat of the fuser part first heater82and the fuser part second heater83can be reflected by the reflection surface of the fuser part first reflection plate84and the reflection surface of the fuser part second reflection plate85toward the inner surface of the fuser belt86and a part of the radiant heat of the pressure application part first heater92and the pressure application part second heater93can be reflected by the reflection surface of the pressure application part first reflection plate94and the reflection surface of the pressure application part second reflection plate95toward the inner surface of the pressure application belt96, and thus heat can be efficiently applied to the fuser belt86and the pressure application belt96. In the color printer1, the fuser part first reflection plate84and the fuser part second reflection plate85are formed to be longer than the fuser belt width, and one end part and the other end part of each of the fuser part first reflection plate84and the fuser part second reflection plate85are arranged in the manner projecting outwardly from the left end and the right end of the fuser belt86; and the pressure application part first reflection plate94and the pressure application part second reflection plate95are formed to be longer than the pressure application belt width, and one end and the other end of each of the pressure application part first reflection plate94and the pressure application part second reflection plate95are arranged in the manner projecting outwardly from the left end and the right end of the of the pressure application belt96. Therefore, in the color printer1, in the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86and the temperature of the non-sandwiching range AR3of the outer surface of the pressure application belt96, which are to be detected by the fuser part thermostat88and the pressure application part thermostat98as the ambient temperatures of the fuser part first heater82and the fuser part second heater83, and the pressure application part first heater92and the pressure application part second heater93, the ambient temperature of the heat generation of the fuser part first heater82and the fuser part second heater83and the ambient temperature of the pressure application part first heater92and the pressure application part second heater93can be further unerringly reflected.

In addition, in the color printer1, the fuser part first reflection plate84is arranged between the fuser part first heater82and the fuser part second heater83and the belt drive roller80in the manner that the back surface of the fuser part first reflection plate84is brought close to the outer peripheral surface of the belt drive roller80; and the fuser part second reflection plate85is arranged between the fuser part first heater82and the fuser part second heater83and the fuser part driven roller81in the manner that the back surface of the fuser part second reflection plate85is brought close to the outer peripheral surface of the fuser part driven roller81. Further, in the color printer1, the pressure application part first reflection plate94is arranged between the pressure application part first heater92and the pressure application part second heater93and the pressure application roller90in the manner that the back surface of the pressure application part first reflection plate94is brought close to the outer peripheral surface of the pressure application roller90; and the pressure application part second reflection plate95is arranged between the pressure application part first heater92and the pressure application part second heater93and the pressure application part driven roller91in the manner that the back surface of the pressure application part second reflection plate95is brought close to the outer peripheral surface of the pressure application part driven roller91. Therefore, in the color printer1, the belt drive roller80and the fuser part driven roller81can be protected from the radiant heat of the fuser part first heater82and the fuser part second heater83, and the pressure application roller90and the pressure application part driven roller91can be protected from the radiant heat of the pressure application part first heater92and the pressure application part second heater93.

(2) Second Embodiment

(2-1) Internal Configuration of Color Printer

Next, an internal configuration of a color printer150(FIG. 1) according a second embodiment is described. The color printer150according to the second embodiment is configured in the same way as the above-described color printer1according to the first embodiment except a part of a configuration of a fuser unit151(FIG. 1) and a part of a process that a controller152executes. The color printer150according to the second embodiment, basically, operates in the same way as the above-described color printer1according to the first embodiment to form a print image on the surface of the recording sheet5. Therefore, for details of the configuration of the color printer150according to the second embodiment, see the description of the configuration of the color printer1according to the first embodiment described above usingFIG. 1. A description about the details of the configuration of the color printer150is omitted here.

(2-2) Configuration of Fuser Unit

Next, the configuration of the fuser unit151is described. As illustrated inFIGS. 14-16, in which the same reference numeral symbols are used to indicate corresponding parts inFIGS. 2-4, the fuser unit151has an upper side inlet guide160and a lower side inlet guide161that ate provided on the unit case50and have configurations partially different from those of the above-described upper side inlet guide70and lower side inlet guide71according to the first embodiment. The upper side inlet guide160has a substantially U-shaped slit formed at a predetermined position of a left end part of the upper side inlet guide160, and a base of a plate part (hereinafter, this is also referred to as an upper side sensor holding part) for holding a sensor in the slit is bent at a predetermined angle. As a result, the upper side inlet guide160enters into the unit case50in a manner that the upper side sensor holding part is parallel to an obliquely rearward and downward direction. Further, the lower side inlet guide161has a substantially U-shaped slit formed at a predetermined position directly below the upper side sensor holding part, and a base of a plate part (hereinafter, this is also referred to as a lower side sensor holding part) for holding a sensor in the slit is bent at a predetermined angle. As a result, the lower side inlet guide161enters into the unit case50in a manner that the lower side sensor holding part is parallel to an obliquely rearward and upward direction.

In addition to the above-described fuser part temperature sensor (hereinafter, this is also particularly referred to as a fuser part first temperature sensor)87for detecting the temperature of the outer surface of the fuser belt86in a non-contact manner, a fuser part165also has a temperature sensor (hereinafter, this is also referred to as a fuser part second temperature sensor)166for detecting the temperature of the outer surface of the fuser belt86for controlling a heat and pressure application process. The fuser part second temperature sensor166is formed by providing a substantially plate-like elastic sensor lever of a predetermined length on one end of a sensor body. The fuser part second temperature sensor166is installed in the upper side sensor holding part of the upper side inlet guide160in a manner that a front end part of the sensor lever is oriented toward an obliquely rearward and downward side and is in contact with a portion on an obliquely forward and downward side of the outer surface of the fuser belt86.

On the other hand, in addition to the above-described pressure application part temperature sensor (hereinafter, this is also particularly referred to as a pressure application part first temperature sensor)97for detecting the temperature of the outer surface of the pressure application belt96in a non-contact manner, a pressure application part167also has a temperature sensor (hereinafter, this is also referred to as a pressure application part second temperature sensor)168for detecting the temperature of the outer surface of the pressure application belt96for controlling the heat and pressure application process. The pressure application part second temperature sensor168is formed in the same manner as the fuser part second temperature sensor166. That is, the pressure application part second temperature sensor168is formed by providing a substantially plate-like elastic sensor lever of a predetermined length on one end of a sensor body. The pressure application part second temperature sensor168is installed in the lower side sensor holding part of the lower side inlet guide161in a manner that a front end part of the sensor lever is oriented toward an obliquely rearward and upward side and is in contact with a portion on an obliquely forward and upward side of the outer surface of the pressure application belt96.

As illustrated inFIG. 17, in which the same reference numeral symbols are used to indicate corresponding parts inFIG. 11, the front end part of the sensor lever of the fuser part second temperature sensor166is in contact with the left end part (that is, the non-sandwiching range AR3) outside of the sandwiching range AR1, AR2of the outer surface of the fuser belt86, even when heat and pressure are applied to the recording sheet5of any sheet width. Further, the front end part of the sensor lever of the pressure application part second temperature sensor168is in contact with the left end part (that is, the non-sandwiching range AR3) outside of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96, even when heat and pressure are applied to the recording sheet5of any sheet width. More specifically, as illustrated inFIG. 18, in which the same reference numeral symbols are used to indicate corresponding parts inFIG. 12, the fuser part second temperature sensor166is fixed on the upper side sensor holding part in a manner that the front end part of the sensor lever is pressed against the outer surface of the portion on the obliquely forward and downward side of the fuser belt86with a predetermined pressing force. Therefore, in fuser unit151, when the fuser belt86rotates in the one rotation direction, the outer surface of the fuser belt86can slide from the base side toward the front end side of the sensor lever with respect to the front end part of the sensor lever of the fuser part second temperature sensor166. In the fuser unit151, since the sensor lever of the fuser part second temperature sensor166is elastic, even when the front side portion of the fuser belt86that is rotating in the one rotation direction vibrates back and forth, the front end part of the sensor lever can be suitably displaced so as to match the vibration. Therefore, in the fuser unit151, the front end part of the sensor lever of the fuser part second temperature sensor166can be stably in contact with the non-sandwiching range AR3of the outer surface of the fuser belt86. As a result, in the fuser unit151, the temperature of the outer surface of the fuser belt86can be accurately detected by the fuser part second temperature sensor166without being influenced by the temperature drop due to contact with the recording sheet5.

On the front end part of the sensor lever of the fuser part second temperature sensor166, a predetermined resin layer such as that of fluorine-based resin such as PFA or PTFE is formed (for example, using fluorine-based resin tube covering or fluorine-based resin coating) to improve adhesion of the front end part of the sensor lever with respect to the outer surface of the fuser belt86. As a result, even when the outer surface of the fuser belt86slides with respect to the front end part of the sensor lever of the fuser part second temperature sensor166, that the outer surface of the fuser belt86is worn and damaged due to the front end part is significantly reduced and the releasability of toner on the front end part of the sensor lever is improved. Therefore, during the formation of the print image, it is avoided as much as possible that the accuracy of the temperature detection is reduced due to that wear powder and toner enter between the front end part of the sensor lever of the fuser part second temperature sensor166and the outer surface of the fuser belt86and the outer surface is damaged. Further, even when the outer surface of the fuser belt86is damaged due to sliding with respect to the front end part of the sensor lever of the fuser part second temperature sensor166, a contact position of the front end part of the sensor lever is in the non-sandwiching range AR3. Therefore, fusing failure of the toner images on the surface of the recording sheet5due to the damage can also be prevented from occurring.

On the other hand, the pressure application part second temperature sensor168is fixed on the lower side sensor holding part in a manner that the front end part of the sensor lever is pressed against the outer surface of the portion on the obliquely forward and upward side of the pressure application belt96with a predetermined pressing force. Therefore, in fuser unit151, when the pressure application belt96rotates in the other rotation direction, the outer surface of the pressure application belt96can slide from the base side toward the front end side of the sensor lever with respect to the front end part of the sensor lever of the pressure application part second temperature sensor168. In the fuser unit151, since the sensor lever of the pressure application part second temperature sensor168is elastic, even when the front side portion of the pressure application belt96that is rotating in the other rotation direction vibrates back and forth, the front end part of the sensor lever can be suitably displaced so as to match the vibration. Therefore, in the fuser unit151, the front end part of the sensor lever of the pressure application part second temperature sensor168can be stably in contact with the non-sandwiching range AR3of the outer surface of the pressure application belt96. As a result, in the fuser unit151, similar to the case of the fuser part second temperature sensor166, the temperature of the outer surface of the pressure application belt96can be accurately detected by the pressure application part second temperature sensor168without being influenced by the temperature drop due to contact with the recording sheet5.

Similar to the fuser part second temperature sensor166, on the front end part of the sensor lever of the pressure application part second temperature sensor168, a predetermined resin layer such as that of fluorine-based resin such as PFA or PTFE is formed (for example, using fluorine-based resin tube covering or fluorine-based resin coating) to improve adhesion of the front end part of the sensor lever with respect to the outer surface of the pressure application belt96. As a result, even when the outer surface of the pressure application belt96slides with respect to the front end part of the sensor lever of the pressure application part second temperature sensor168, that the outer surface of the pressure application belt96is worn and damaged due to the front end part is significantly reduced and the releasability of toner on the front end part of the sensor lever is improved. Therefore, during the formation of the print image, it is avoided as much as possible that the accuracy of the temperature detection is reduced due to that wear powder and toner enter between the front end part of the sensor lever of the pressure application part second temperature sensor168and the outer surface of the pressure application belt96and the outer surface is damaged. Further, similar to the fuser part second temperature sensor166, even when the outer surface of the pressure application belt96is damaged due to sliding with respect to the front end part of the sensor lever of the pressure application part second temperature sensor168, a contact position of the front end part of the sensor lever is in the non-sandwiching range AR3. Therefore, pressure application failure of the toner images on the surface of the recording sheet5due to the damage can also be prevented from occurring.

When the fuser unit151is installed in the color printer150, together with the fuser part first temperature sensor87and the pressure application part first temperature sensor97, the fuser part second temperature sensor166and the pressure application part second temperature sensor168are also electrically connected to the controller152. Therefore, in the fuser unit151, similar to the case of the above-described first embodiment, the controller152detects, via the fuser part first temperature sensor87, the temperature of the outer surface of the fuser belt86and, in response to the detection result, ON/OFF-controls the first heater power source120to adjust the temperature of the outer surface of the fuser belt86to a temperature required for fusing the toner images onto the recording sheet5. Further, in the fuser unit151, similar to the case of the above-described first embodiment, the controller152detects, via the pressure application part first temperature sensor97, the temperature of the outer surface of the pressure application belt96and, in response to the detection result, ON/OFF-controls the second heater power source121to adjust the temperature of the outer surface of the pressure application belt96to a temperature required for fusing to the toner images on the recording sheet5.

In addition, in the fuser unit151, the controller152detects, via the fuser part second temperature sensor166, the temperature of the outer surface of the fuser belt86and detects, via the pressure application part second temperature sensor168, the temperature of the outer surface of the pressure application belt96and, in response to the detection results, switches a processing mode of the heat and pressure application process. Here, as the processing modes of the heat and pressure application process, for example, when the heat and pressure are applied to the recording sheet5while the recording sheet5is carried in a manner being sandwiched in the sandwiching part115of the fuser belt86and the pressure application belt96that are rotating in opposite directions, there are two kinds of processing modes (a first processing mode and a second processing mode) for which carrying speeds are different. The first processing mode is, for example, a mode in which heat and pressure are applied to the recording sheet5while the recording sheet5is carried by the sandwiching part115at a predetermined carrying speed (hereinafter, this is also referred to as a first carrying speed) by causing the fuser belt86and the pressure application belt96to rotate in mutually opposite directions at a rotational speed (hereinafter, this is also referred to as a first rotational speed) that is the same as in the case of the above-described first embodiment. Further, the second processing mode is, for example, a mode in which heat and pressure are applied to the recording sheet5while the recording sheet5is carried by the sandwiching part115at a predetermined carrying speed (hereinafter, this is also referred to as a second carrying speed) that is slower than the first carrying speed by causing the fuser belt86and the pressure application belt96to rotate in mutually opposite directions at a rotational speed (hereinafter, this is also referred to as a second rotational speed) that is slower than the first rotational speed.

In practice, as illustrated inFIG. 19, during the formation of the print image, in the fuser unit151, the controller152starts the heat and pressure application process in the first processing mode. As a result, similar to the case of the above-described first embodiment, the controller152causes the fuser belt86to rotate in the one rotation direction at the first rotational speed and, in conjunction with this, causes the pressure application belt96to rotate in the other rotation direction at the first rotational speed. Further, the controller152supplies the heat generation control current from the first heater power source120to one of the fuser part first heater82and the fuser part second heater83according to the sheet width of the recording sheet5of a print image formation target in this case to generate heat and begins applying heat to the fuser belt86. Further, the controller152supplies the heat generation control current from the second heater power source121to one of the pressure application part first heater92and the pressure application part second heater93according to the sheet width of the recording sheet5of the print image formation target in this case to generate heat and begins applying heat to the pressure application belt96.

Further, the controller152detects, via the fuser part first temperature sensor87, the temperature of the outer surface of the fuser belt86and, in response to the detection result, suitably ON/OFF-controls the first heater power source120, and thereby, as illustrated inFIG. 12by a sandwiching range temperature characteristic curve TE3and a non-sandwiching range temperature characteristic curve TE4, adjusts the temperature of the sandwiching range AR1, AR2and the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86to the predetermined target temperature TS1. Further, the controller152detects, via the pressure application part first temperature sensor97, the temperature of the outer surface of the pressure application belt96and, in response to the detection result, suitably ON/OFF-controls the second heater power source121, and thereby, similar to the fuser belt86, also adjusts the temperature of the sandwiching range AR1, AR2and the temperature of the non-sandwiching range AR3of the outer surface of the pressure application belt96to the predetermined target temperature TS1. In this way, when the controller152raises the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96to the target temperature TS1in the fuser unit151, similar to the case of the above-described first embodiment, in the fuser unit151, the controller152sequentially applies, via the fuser belt86and the pressure application belt96, heat and pressure to the recording sheet5to form a color print image on the surface of the recording sheet5.

In this case, when the controller152detects, via the fuser part first temperature sensor87, that the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86has dropped, in response to the detection, the controller152repeatedly ON/OFF-controls the first heater power source120, and thereby causes the fuser part first heater82or the fuser part second heater83to intermittently generate heat to apply heat to the fuser belt86. Further, when the controller152detects, via the pressure application part first temperature sensor97, that the temperature of the sandwiching range AR1, AR2of the outer surface of the pressure application belt96has dropped, in response to the detection, the controller152repeatedly ON/OFF-controls the second heater power source121, and thereby causes the pressure application part first heater92or the pressure application part second heater93to intermittently generate heat to apply heat to the pressure application belt96. In this way, similar to the case of the above-described first embodiment, during continuous print, even when the temperatures of the sandwiching ranges AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96gradually drop, by applying heat to the fuser belt86and the pressure application belt96, the controller152can maintain the temperatures of the sandwiching ranges AR1, AR2at temperatures that are higher to some extent than the minimum fusing temperature.

However, in the fuser unit151, for example, the relatively more the number of the recording sheets5that are continuously printed, the larger the drop amount of the temperature of the sandwiching range AR1, AR2of the outer surface of the fuser belt86and the pressure application belt96(that is, the drop amount of the temperature from the target temperature TS1). Further, for example, the more the temperature of the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96is close to the minimum fusing temperature, the more the controller152shortens the time interval of the ON/OFF-control with respect to the first heater power source120and the second heater power source121. As a result, the controller152shortens the time interval between heat generation and pause of the fuser part first heater82or the fuser part second heater83and the pressure application part first heater92or the pressure application part second heater93to increase the heat generation amount, and maintains the temperature of the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96at a temperature that is higher to some extent than the minimum fusing temperature.

Further, similar to the case of the above-described first embodiment, when, due to malfunction of the fuser part first temperature sensor87and the pressure application part first temperature sensor97, the controller152erroneously detects the temperature of the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96as a temperature lower than an actual temperature, depending on the erroneously detected temperature, the controller152continuously ON-controls the first heater power source120and the second heater power source121, and thereby causes the fuser part first heater82or the fuser part second heater83and the pressure application part first heater92or the pressure application part second heater93to continuously generate heat to increase the heat generation amount. In this way, the controller152increases the heat generation amount of the fuser part first heater82or the fuser part second heater83and the pressure application part first heater92or the pressure application part second heater93by adjusting the time interval of the ON/OFF-control, or the continuous ON-control, of the first heater power source120and the second heater power source121.

Therefore, during the formation of the print image, the controller152detects, via the fuser part second temperature sensor166, the ambient temperature of the fuser part first heater82or the fuser part second heater83(that is, the temperature on the inner side of the fuser belt86) as the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86that reflects the temperature on the inner side of the fuser belt86. For example, when the temperature that is detected by the controller152via the fuser part second temperature sensor166reaches a predetermined temperature (hereinafter, this is also referred to as a mode switching judging temperature) TS3for processing mode switching judging that is pre-selected as a temperature that higher than the target temperature TS1and lower than the damage prevention temperature TS2, the controller152switches the heat and pressure application process from the first processing mode to the second processing mode and continues to execute the heat and pressure application process.

Further, the controller152detects, via the pressure application part second temperature sensor168, the ambient temperature of the pressure application part first heater92or the pressure application part second heater93(that is, the temperature on the inner side of the pressure application belt96) as the temperature of the non-sandwiching range AR3of the outer surface of the pressure application belt96that reflects the temperature on the inner side of the pressure application belt96. Also when the temperature that is detected by the controller152via the pressure application part second temperature sensor168reaches the mode switching judging temperature TS3, similarly, the controller152switches the heat and pressure application process from the first processing mode to the second processing mode and continues to execute the heat and pressure application process.

In this way, when the controller152switches the processing mode of the heat and pressure application process from the first processing mode to the second processing mode, the controller152controls the fuser unit drive motor to slow the rotational speed of the belt drive roller80in the one rotation direction. As a result, the controller152switches from the first rotational speed to the second rotational speed to rotate the fuser belt86in the one rotation direction and, in conjunction with this, also switches from the first rotational speed to the second rotational speed to rotate the pressure application belt96in the other rotation direction, to apply heat and pressure to the recording sheet5while carrying the recording sheet5in the sandwiching part115at the second carrying speed, which is slower than the first carrying speed.

Here, the larger the amount of heat is supplied from the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96, the shorter the time period is required for the toner (that is, toner images) on the surface of the recording sheet5to melt. In other words, in the fuser unit151, when the temperature of the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96is higher than the minimum fusing temperature, the toner images can be fused onto the surface of the recording sheet5by temporarily melting once the toner images even when the carrying speed at which the recording sheet5is carried in the sandwiching part115for applying heat and pressure thereto is increased to some extent. Further, in the fuser unit151, when the temperature of the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96is close to the minimum fusing temperature, even when the carrying speed at which the recording sheet5is carried in the sandwiching part115for applying heat and pressure thereto is reduced to some extent, the toner images can be fused onto the surface of the recording sheet5by temporarily melting once the toner images.

Therefore, when the recording sheet5is carried in the sandwiching part115at the second carrying speed, the controller152increases the time interval of an ON/OFF-control of the first heater power source120and the second heater power source121or switches from a continuous ON-control to an ON/OFF-control. As a result, while reducing the heat generation amount of the fuser part first heater82or the fuser part second heater83and the heat generation amount of the pressure application part first heater92or the pressure application part second heater93to cause the ambient temperatures thereof to drop, the controller152performs control in a manner that the temperature of the sandwiching range AR1, AR2, which is detected via the fuser part first temperature sensor87and the pressure application part first temperature sensor97, does not drop below the minimum fusing temperature.

Therefore, in this case, when the fuser part first temperature sensor87and the pressure application part first temperature sensor97do not malfunction in any way, while the controller152controls in a manner that the ambient temperature of the fuser part first heater82or the fuser part second heater83and the ambient temperature of the pressure application part first heater92or the pressure application part second heater93do not significantly rise, print images can be continuously formed on the surfaces of a plurality of the recording sheets5. Further, in this case, even when the fuser part first temperature sensor87and pressure application part first temperature sensor97malfunction, when the actual temperature of the sandwiching range AR1, AR2of the outer surfaces of the fuser belt86and the pressure application belt96is not below the minimum fusing temperature, similarly, while the controller152controls in the manner that the ambient temperature of the fuser part first heater82or the fuser part second heater83and the ambient temperature of the pressure application part first heater92or the pressure application part second heater93do not significantly rise, print images can be continuously formed on the surfaces of a plurality of the recording sheets5.

In this way, even when the ambient temperature of the fuser part first heater82or the fuser part second heater83and the ambient temperature of the pressure application part first heater92or the pressure application part second heater93gradually rise, when the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86and the temperature of the non-sandwiching range AR3of the pressure application belt96, which reflect the ambient temperatures, reach the mode switching judging temperature TS3, the controller152controls the heat generation of the fuser part first heater82or the fuser part second heater83and the heat generation of the pressure application part first heater92or the pressure application part second heater93to suppress the rising the ambient temperatures. As a result, the controller152can avoid, or delay, as much as possible that the fuser part thermostat88and the pressure application part thermostat98function to interrupt the heat generation of the fuser part first heater82or the fuser part second heater83and the pressure application part first heater92or the pressure application part second heater93, and can continue as much as possible to perform the continuous print, and thus print images can be sequentially formed on the surfaces of a plurality of the recording sheets5.

However, for example, when the fuser part second temperature sensor166malfunctions and the controller152erroneously detects, via the fuser part second temperature sensor166, the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86as a temperature lower than an actual temperature, similar to the case of the above-described first embodiment, at the time when it is detected that the temperature of the non-sandwiching range AR3has reached the damage prevention temperature TS2, the fuser part thermostat88can forcibly block the supply of the heat generation control current from the first heater power source120to the fuser part first heater82or the fuser part second heater83. Further, for example, when the pressure application part second temperature sensor168malfunctions and the controller152erroneously detects, via the pressure application part second temperature sensor168, the temperature of the non-sandwiching range AR3of the outer surface of the pressure application belt96as a temperature lower than an actual temperature, similar to the case of the above-described first embodiment, at the time when it is detected that the temperature of the non-sandwiching range AR3has reached the damage prevention temperature TS2, the pressure application part thermostat98can forcibly block the supply of the heat generation control current from the second heater power source121to the pressure application part first heater92or the pressure application part second heater93. In this way, the fuser part thermostat88and the pressure application part thermostat98can prevent damage to the fuser unit151due a significant temperature rise from occurring.

(2-3) Operation and Effect of Second Embodiment

In the above-described configuration, in the fuser unit151of the color printer150, in addition to the configuration of the fuser unit16according to the above-described first embodiment, the fuser part second temperature sensor166is provided in the manner that the front end part of the sensor lever is in contact with the left end part (the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the fuser belt86. Further, in the fuser unit151of the color printer150, the pressure application part second temperature sensor168is provided in the manner that the front end part of the sensor lever is in contact with the left end part (the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the pressure application belt96.

When the color printer150detects, via the fuser part second temperature sensor166, the ambient temperature of the fuser part first heater82or the fuser part second heater83as the temperature of the non-sandwiching range AR3of the outer surface of the fuser belt86and the detected temperature reaches the mode switching judging temperature TS3, the color printer150reduces the rotational speeds of the fuser belt86and the pressure application belt96that are caused to rotate in mutually opposite directions and also reduces the carrying speed of the recording sheet5. Further, also when the color printer150detects, via the pressure application part second temperature sensor168, the ambient temperature of the pressure application part first heater92or the pressure application part second heater93as the temperature of the non-sandwiching range AR3of the outer surface of the pressure application belt96and the detected temperature reaches the mode switching judging temperature TS3, the color printer150reduces the rotational speeds of the fuser belt86and the pressure application belt96that are caused to rotate in mutually opposite directions and also reduces the carrying speed of the recording sheet5. When, as described above, the carrying speed of the recording sheet5is reduced, the color printer150controls the heat generation of the fuser part first heater82and the fuser part second heater83and the heat generation of the pressure application part first heater92and the pressure application part second heater93to reduce the heat generation amount. Therefore, even when the ambient temperature of the fuser part first heater82and the fuser part second heater83and the ambient temperature of the pressure application part first heater92and the pressure application part second heater93gradually rise, the color printer150can accurately detect the ambient temperatures as the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96without being influenced by the temperature drop due to contact with the recording sheet5, and suppress the rising of the ambient temperatures.

According to the above-described configuration, in the fuser unit151of the color printer150, in addition to the configuration of the fuser unit16according to the above-described first embodiment, the fuser part second temperature sensor166is provided in the manner that the front end part of the sensor lever is in contact with the left end part (the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the fuser belt86, and the pressure application part second temperature sensor168is provided in the manner that the front end part of the sensor lever is in contact with the left end part (the non-sandwiching range AR3) outside the sandwiching range AR1, AR2of the outer surface of the pressure application belt96. As a result, in the color printer150, effects that are the same as those obtained by the above-described first embodiment can be obtained and, in addition, even when the ambient temperature of the fuser part first heater82and the fuser part second heater83and the ambient temperature of the pressure application part first heater92and the pressure application part second heater93gradually rise, the color printer150can accurately detect the ambient temperatures as the temperature of the outer surface of the fuser belt86and the temperature of the outer surface of the pressure application belt96without being influenced by the temperature drop due to contact with the recording sheet5, and suppress the rising of the ambient temperatures. Therefore, the color printer150can avoid, or delay, as much as possible that the fuser part thermostat88and the pressure application part thermostat98function to interrupt the heat generation of the fuser part first heater82and the fuser part second heater83and the heat generation of the pressure application part first heater92and the pressure application part second heater93, and can continue as much as possible to perform the continuous print, and thus can improve convenience.

(3) Other Embodiments

(3-1) First Other Embodiment

In the above-described first and second embodiments, the case is described where, in the fuser unit16,151, the fuser part75,165that has the belt drive roller80, the fuser part driven roller81, the fuser part first heater82, the fuser part second heater83, the fuser belt86and the fuser part thermostat88, and the pressure application part76,167that has the pressure application roller90, the pressure application part driven roller91, the pressure application part first heater92, the pressure application part second heater93, the pressure application belt96and the pressure application part thermostat98are provided. However, the present invention is not limited to this. For example, as illustrated inFIG. 20, in a fuser unit180, a cylindrical roller (hereinafter, this is also referred to as a heat application roller)181having a length longer than the sheet width for applying heat to the recording sheet5is provided rotatable in the one rotation direction; and, inside the heat application roller181, two heaters, a first heater182and a second heater183, each of which having a light emitting part of a different length, are arranged; and further, a temperature sensor (not illustrated in the drawings) for detecting temperature of an outer peripheral surface of the heat application roller181is provided. Further, in the present invention, a cylindrical or column-shaped roller (hereinafter, this is also referred to as a pressure application roller)184having a length longer than the sheet width for applying pressure to the recording sheet5is provided rotatable in the other rotation direction that is opposite to the rotation direction of the heat application roller181in a state in which a portion of an outer peripheral surface of the pressure application roller184is pressed against a portion of the outer peripheral surface of the heat application roller181with a predetermined pressing force. By causing the heat application roller181and the pressure application roller184to rotate in mutually opposite directions, the recording sheet5can be carried in a manner being sandwiched by the heat application roller181and the pressure application roller184. In the present invention, it is also possible that a thermostat185is provided via a thermostat holding part186in a manner that a front end (that is, a heat sensing surface) of a heat sensing part of the thermostat185is brought into contact with one end part outside a sandwiching range of the recording sheet5on the outer peripheral surface of the heat application roller181. In the present invention, such a configuration also allows a function substantially the same as that of the above described fuser unit16,151of the first and second embodiments to be realized, and the same effects to be achieved. In the present invention, in the case of such a configuration, by making structures of the first heater182and the second heater183and positional relations of the first heater182and the second heater183with respect to the heat application roller181to be the same as the structures of the above-described fuser part first heater82and fuser part second heater83and the positional relations of the above-described fuser part first heater82and fuser part second heater83with respect to the fuser belt86, similar to the above-described fuser unit16,151of the first and second embodiments, detection accuracy of the ambient temperature of the first heater182and the ambient temperature of the second heater183can be significantly improved.

In addition, in the present invention, in the fuser unit16,151, it is also possible that, on at least one of the inner side of the fuser belt86and the inner side of the pressure application belt96, one or a plurality of pressing parts are provided in a manner being pressed against the inner surface of the fuser belt86and the inner surface of the pressure application belt96with a predetermined pressing force, to apply a tensional force to the fuser belt86and the pressure application belt96. Further, in the present invention, it is also possible that, in the fuser unit16,151, such pressing parts are provided in place of the fuser part driven roller81and the pressure application part driven roller91. Further, in the present invention, it is also possible that, in the fuser unit16,151, a pressure application roller having an outer diameter larger than that of the belt drive roller80is provided in place of the pressure application belt96, or a heat application roller having an outer diameter larger than that of the pressure application roller90is provided in place of the fuser belt86. Further, in the present invention, for example, it is also possible that the pressure application part first heater92and the pressure application part second heater93are not provided on the inner side of the pressure application belt96, and the fuser part first heater82and the fuser part second heater83for applying heat to the recording sheet5are provided only on the inner side of the fuser belt86. That is, in the present invention, in the fuser unit, as far as the function of applying heat and pressure to the recording sheet5and the function of detecting the ambient temperature of a heat generation part such as a heater for applying heat to the recording sheet5can be realized, similarly to the above-described first and second embodiments, as the fuser unit, various other kinds of configurations can be suitably applied. In the present invention, such various configurations also allow effects the same as those achieved by the above-described first and second embodiments to be achieved.

(3-2) Second Other Embodiment

In the above-described first and second embodiments, the case is described where the fuser according to the present invention is applied to the fuser unit16,151,180that is removably installed in the color printer1,150that is described in the above with reference toFIGS. 1-20. However, the present invention is not limited to this, but can be broadly applied to fusers of various other kinds of configurations such as a fuser unit that is fixedly provided in the color printer1,150and fuser units that are removably installed or fixedly provided in image forming apparatuses that form print images, such as a black-and-white electrophotographic printer, a multifunction printer, a facsimile, a multifunction machine, and a copying machine.

(3-3) Third Other Embodiment

Further, in the above-described first and second embodiments, the case is described where the image forming apparatus according to the present invention is applied to the color printer1,150that is described in the above with reference toFIGS. 1-20. However, the present invention is not limited to this, but can be broadly applied to image forming apparatuses of various other kinds of configurations such as a black-and-white electrophotographic printer, a multifunction printer, a facsimile, a multifunction machine, and a copying machine.

(3-4) Fourth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a medium for forming a print image, the recording sheet5that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply various other kinds of media such as an OHP sheet, a letter sheet and a disk-like medium.

(3-5) Fifth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a pressure application part for applying pressure for forming a print image on a medium, the pressure application belt96that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply pressure application parts of various other kinds of configurations such as a pressure application belt that is formed by directly laminating a release layer on an entire outer surface of an annular belt body of a predetermined thickness without laminating an elastic layer, and a pressure application roller that is pressed against the fuser belt86or a heat application roller.

(3-6) Sixth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as an annular body that is rotatably supported for carrying a medium by sandwiching the medium between the annular body and a pressure application part for applying heat to the medium for forming a print image, the fuser belt86that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply annular bodies of various other kinds of configurations such as a fuser belt that is formed by directly laminating a release layer on an entire outer surface of an annular belt body of a predetermined thickness without laminating an elastic layer, and a heat application roller against which the pressure application belt96or a pressure application roller is pressed.

(3-7) Seventh Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a heat generation part that is arranged on an inner side of an annular body and generates heat to apply heat to the annular body, the fuser part first heater82and the fuser part second heater83that are described in the above with reference toFIGS. 1-20are applied. However, the present invention is not limited to this, but can broadly apply heat generation parts of various other configurations and various other numbers of heat generation parts, such as a heater formed by one or three or more halogen lamps, and, for example, one or a plurality of planer heat generation bodies that are formed by embedding resistance wires for heat generation in a substantially rectangular body part of a multilayer structure.

(3-8) Eighth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a heat generation interruption part that is arranged in a manner that a temperature detection end thereof is in contact with one end part outside a medium carrying corresponding range of an annular body and that interrupts heat generation of a heat generation part in response to temperature of the annular body that is detected via the temperature detection end, the fuser part thermostat88that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply heat generation interruption parts of various other kinds of configurations such as a heat generation interruption part that is arranged in a manner that a temperature detection end thereof is in contact with an inner surface of an annular body.

(3-9) Ninth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a drive roller driving an annular body to rotate, the belt drive roller80that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply drive rollers of various other kinds of configurations such as belt drive rollers having, for example, a core part formed by an aluminum pipe, a core part formed by pure sulfur and sulfur free-cutting steel composite steel (SUM: Steel Use Machinability), and a core part formed by pure stainless steel.

(3-10) Tenth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a reflection part that is arranged on an inner side of an annular body and, together with at least a medium carrying corresponding range of the annular body, reflects radiant heat of a heat generation part toward one end part, the fuser part first reflection plate84and the fuser part second reflection plate85that are described in the above with reference toFIGS. 1-20are applied. However, the present invention is not limited to this, but can broadly apply reflection parts of various other configurations and various other numbers of reflection parts, such as a reflection plate that is formed by vapor depositing silver on one surface of a plate part to form a reflection layer, a reflection plate that is formed by stainless steel (SUS304BA) in a manner that one surface thereof becomes a reflection surface, a reflection plate that is formed in a manner that a reflection surface is formed by subjecting one surface of a plate part that is formed by stainless steel (SUS304BA) to mirror polishing of about class #700 or class #800, a reflection plate capable of collectively covering the belt drive roller80and the fuser part driven roller81, and a block-shaped reflection part of a predetermined shape that is formed as a pressing part that is pressed against the inner surface of the fuser belt86to apply a tensional force thereto.

(3-11) Eleventh Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a temperature sensor that is arranged in a manner that a temperature detection end thereof is in contact with one end part outside a medium carrying corresponding range of an annular body for detecting, via the temperature detection end, temperature of the annular body, the fuser part second temperature sensor166that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply temperature sensors of various other kinds of configurations such as a temperature sensor that is arranged, for example, in a manner that a temperature detection end thereof is in contact with an inner surface of an annular body, and a thermocouple.

(3-12) Twelfth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as another heat generation part that is arranged on an inner side of a pressure application annular body and generates heat to apply heat to the pressure application annular body, the pressure application part first heater92and the pressure application part second heater93that are described in the above with reference toFIGS. 1-20are applied. However, the present invention is not limited to this, but can broadly apply other heat generation parts of various other configurations and various other numbers of other heat generation parts, such as a heater formed by one or three or more halogen lamps, and, for example, one or a plurality of planer heat generation bodies that are formed by embedding resistance wires for heat generation in a substantially rectangular body part of a multilayer structure.

(3-13) Thirteenth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as another heat generation interruption part that is arranged in a manner that a temperature detection end thereof is in contact with one end part outside a medium carrying corresponding range of a pressure application annular body and that interrupts heat generation of another heat generation part in response to temperature of the pressure application annular body that is detected via the temperature detection end, the pressure application part thermostat98that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply other heat generation interruption parts of various other kinds of configurations such as a heat generation interruption part that is arranged in a manner that a temperature detection end thereof is in contact with an inner surface of a pressure application annular body.

(3-14) Fourteenth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as a pressure application roller that is supported rotatable in an opposite rotation direction for applying pressure to a medium, the pressure application roller90that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply pressure application rollers of various other kinds of configurations such as pressure application rollers having, for example, a core part formed by an aluminum pipe, a core part formed by pure sulfur and sulfur free-cutting steel composite steel, and a core part formed by pure stainless steel.

(3-15) Fifteenth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as another reflection part that is arranged on an inner side of a pressure application annular body and, together with at least a medium carrying corresponding range of the pressure application annular body, reflects radiant heat of another heat generation part toward one end part, the pressure application part first reflection plate94and the pressure application part second reflection plate95that are described in the above with reference toFIGS. 1-20are applied. However, the present invention is not limited to this, but can broadly apply other reflection parts of various other configurations and various other numbers of other reflection parts, such as a reflection plate that is formed by vapor depositing silver on one surface of a plate part to form a reflection layer, a reflection plate that is formed by stainless steel (SUS304BA) in a manner that one surface thereof becomes a reflection surface, a reflection plate that is formed in a manner that a reflection surface is formed by subjecting one surface of a plate part that is formed by stainless steel (SUS304BA) to mirror polishing of about class #700 or class #800, a reflection plate capable of collectively covering the pressure application roller90and the pressure application part driven roller91, and a block-shaped reflection part of a predetermined shape that is formed as a pressing part that is pressed against the inner surface of the pressure application belt96to apply a tensional force thereto.

(3-16) Sixteenth Other Embodiment

Further, in the above-described first and second embodiments, the case is described where, as another temperature sensor that is arranged in a manner that a temperature detection end thereof is in contact with one end part outside a medium carrying corresponding range of a pressure application annular body for detecting, via the temperature detection end, temperature of the pressure application annular body, the pressure application part second temperature sensor168that is described in the above with reference toFIGS. 1-20is applied. However, the present invention is not limited to this, but can broadly apply other temperature sensors of various other kinds of configurations such as a temperature sensor that is arranged, for example, in a manner that a temperature detection end thereof is in contact with an inner surface of a pressure application annular body, and a thermocouple.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a fuser unit provided in an image forming apparatus such as a color electrophotographic printer, a black-and-white electrophotographic printer, a multifunction printer, a facsimile, a multifunction machine and a copying machine, and to an image forming apparatus such as the color electrophotographic printer, the black-and-white electrophotographic printer, the multifunction printer, the facsimile, the multifunction machine and the copying machine.

In the present invention, the fuser part driven roller is a form of a fuser contact member. A place where the fuser part driven roller and the pressure application part driven roller sandwich the fuser belt and the pressure application belt is a second sandwiching point (pt2). A place where the belt drive roller and the pressure application roller sandwich the fuser belt and the pressure application belt is a first sandwiching point (pt1).

The form of the fuser contact member is not limited to a roller, but can be any structure capable of pairing with an opposing pressure application part to apply a predetermined pressure to an annular body passing through therebetween.

As illustrated inFIG. 3, the flexible portion of the fuser belt is a first flexible portion (1utp), and the flexible portion of the pressure application belt is a second flexible portion (2utp).