JP6237184B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device.

  In general, in an image forming apparatus (printer, copying machine, facsimile, etc.) using an electrophotographic process technology, a laser beam based on image data is irradiated (exposed) to a uniformly charged photoconductor (for example, a photoconductive drum). ), An electrostatic latent image is formed on the surface of the photoreceptor. Then, toner is supplied to the photoconductor on which the electrostatic latent image is formed, so that the electrostatic latent image is visualized and a toner image is formed. The toner image is transferred directly or indirectly to the sheet via an intermediate transfer member, and then heated and pressed by a fixing device, whereby an image is formed on the sheet.

The fixing device is arranged on an upper fixing portion having a fixing surface side member arranged on the image forming surface (surface on which the toner image is formed) side of the paper, and on the back surface (surface opposite to the fixing surface) side of the paper. A lower fixing unit having a back side support member, a heating source, and the like are provided.
FIG. 1 is a perspective view of an essential part of a belt nip type fixing device. In the belt nip type fixing device shown in FIG. 1, an endless fixing belt 613 stretched between a fixing roller 611 and a support roller 612 serves as a fixing surface side member, and is pressed against the fixing roller 611 via the fixing belt 613. The pressure roller 621 is a back side support member. When the pressure roller 621 is pressed against the fixing roller 611 via the fixing belt 613, a fixing nip for nipping and transporting the sheet is formed.

  Further, in order to maintain the surface temperature of the fixing belt 613 (hereinafter referred to as “fixing temperature”) within a predetermined fixing allowable temperature range, a fixing temperature detection sensor 64 for detecting the fixing temperature is disposed in the vicinity of the fixing belt 613. . For example, the fixing temperature detection sensor 64 is pressed against the support roller 612 and contacts the fixing belt 613.

  In such a belt nip type fixing device, it is known that the fixing belt 613 is shifted to one end side in the roller axial direction (main scanning direction) due to factors such as mechanical displacement of components and a difference in expansion rate. ing. When the fixing belt 613 is offset, the fixing belt 613 eventually falls off the fixing roller 611 or the support roller 612. As a technique for avoiding such a problem, for example, there is steering control in which the support roller 612 is configured by a steering roller that can be displaced in the axial direction, and the displacement of the fixing belt 613 is corrected by displacing the axial direction.

When the steering control is performed, the end portion of the support roller 612 is usually outside the end portion of the fixing belt 613 (for example, Patent Documents 1 and 2). That is, as shown in FIG. 2, the length to the end of the fixing belt 613 is B and the end of the support roller 612 is based on the sheet passing center (the center in the width direction of the sheet passing through the fixing nip). When the length of C is C, the roller width of the support roller 612 and the belt width of the fixing belt 613 are set so that C <B.
If the distance from the sheet passing center to the fixing temperature detecting sensor (the distance to the detecting element) is A, the fixing temperature detecting sensor 64 corresponds to the non-sheet passing area of the fixing belt 613 so that A <C. Is placed.

JP 2000-81804 A JP 2009-31613 A

  As described above, when the fixing belt 613 and the fixing temperature detection sensor 64 are in contact with each other, the surface of the fixing belt 613 is scraped as the fixing belt 613 travels, and the shaving powder is covered with the surface of the support roller 612 (covered by the fixing belt 613). Adhere to no exposed part). This shaving powder enters between the fixing belt 613 and the support roller 612 when the fixing belt 613 moves in the axial direction by steering control, and causes a problem. In particular, when a heat source is built in the support roller 612 (hereinafter referred to as “heating roller 612”), since the shaving powder is interposed in the gap between the heating roller 612 and the fixing belt 613, uniform heat is applied to the fixing belt 613. Transmission is hindered, resulting in spotted uneven luster in the image.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus that can prevent the occurrence of problems caused by shavings generated by contact between a fixing temperature detection sensor and a fixing belt.

A fixing device according to the present invention includes a plurality of support rollers including a fixing roller,
An endless fixing belt stretched around the plurality of support rollers;
A heating source for heating the fixing belt;
A back-side support member that is pressed against the fixing roller via the fixing belt and forms a fixing nip together with the fixing belt;
A contact-type fixing temperature detection sensor that is arranged in a state of being pressed against a specific roller among the plurality of support rollers and detects a surface temperature of the fixing belt, and a fixing device comprising:
The fixing belt has a flat shape over the entire surface including both ends in the width direction,
When the distance from the sheet passing center to one end of the specific roller is B, and the distance from the one end of the fixing belt is C, the relationship of B <C is satisfied regardless of the swinging operation of the fixing belt. Features.

  An image forming apparatus according to the present invention includes the above-described fixing device.

  According to the present invention, even if the surface of the fixing belt is shaved, the generated shaving powder does not adhere to the surface of the support roller. Therefore, the shaving powder does not enter between the fixing belt and the support roller, and it is possible to prevent the occurrence of problems such as image defects due to the shaving powder.

It is a principal part perspective view of the conventional belt nip type fixing device. FIG. 10 is a diagram illustrating a positional relationship among a fixing belt, a support roller, and a fixing temperature detection sensor in a conventional fixing device. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the embodiment. FIG. 3 is a cross-sectional view schematically illustrating a main part of a fixing unit according to an embodiment. FIG. 3 is a perspective view of a main part of a fixing unit according to an embodiment. It is a figure which shows the specific structure of a fixing temperature detection sensor. FIG. 4 is a diagram illustrating a positional relationship among a fixing belt, a heating roller, and a fixing temperature detection sensor in the fixing unit according to the embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 is a diagram showing an overall configuration of the image forming apparatus 1 according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a main part of a control system of the image forming apparatus 1 according to the embodiment.
An image forming apparatus 1 shown in FIGS. 3 and 4 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. In the image forming apparatus 1, photosensitive drums 413 corresponding to four colors of CMYK are arranged in series in the running direction (vertical direction) of the intermediate transfer belt 421, and each color toner image is sequentially transferred to the intermediate transfer belt 421 in one procedure. The vertical tandem system is adopted.
That is, the image forming apparatus 1 primarily transfers Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421, After the four color toner images are superimposed on the transfer belt 421, the image is formed by secondary transfer onto the paper.

  As shown in FIGS. 3 and 4, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100. .

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads out a program corresponding to the processing content from the ROM 102 or the storage unit 72, develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program.

  The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive. The storage unit 72 stores a lookup table LUT that is referred to when, for example, controlling the operation of each block.

  The control unit 100 also exchanges various data with an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Send and receive. For example, the control unit 100 receives image data (input image data) in a page description language (PDL) transmitted from an external device, and forms an image on a sheet based on the received image data. The communication unit 71 has various interfaces such as a network interface card (NIC), a modem-demodulator (MODEM), and a universal serial bus (USB).

The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.
The automatic document feeder 11 conveys the document placed on the document tray by the conveyance mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents placed on the document tray.
The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.
The user can operate the operation display unit 20 to perform settings relating to image formation such as document setting, image quality setting, magnification setting, application setting, output setting, single-sided / double-sided setting, paper setting, and swing amount adjustment. .

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs tone correction based on tone correction data (tone correction table) under the control of the control unit 100 (image density control). Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, compression process, and the like on the input image data. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 includes an image forming unit 41 and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component based on input image data.

  The image forming unit 41 includes four image forming units 41Y, 41M, 41C, and 41K for Y component, M component, C component, and K component. Since the image forming units 41Y, 41M, 41C, and 41K have the same configuration, for convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and when distinguished from each other, the reference numerals Y, M, and C are used. Or K. In FIG. 3, reference numerals are given only to the components of the image forming unit 41 </ b> Y for the Y component, and reference numerals of the constituent elements of the other image forming units 41 </ b> M, 41 </ b> C, 41 </ b> K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

The photosensitive drum 413 includes, for example, an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). : A negatively charged organic photoconductor (OPC) in which Charge Transport Layers are sequentially stacked.
The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges upon exposure by the exposure device 411. The charge transport layer consists of a hole transport material (electron donating nitrogen-containing compound) dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The charging device 414 is constituted by a corona discharge generator such as a scorotron charging device or a corotron charging device. The charging device 414 uniformly charges the surface of the photosensitive drum 413 to a negative polarity by corona discharge.

  The exposure apparatus 411 is composed of, for example, a semiconductor laser. The exposure device 411 irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. The positive charge generated in the charge generation layer of the photosensitive drum 413 is transported to the surface of the charge transport layer, so that the surface charge (negative charge) of the photosensitive drum 413 is neutralized. Thereby, an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 accommodates developer of each color component (two-component developer composed of toner and magnetic carrier), and visualizes the electrostatic latent image by attaching the toner of each color component to the surface of the photosensitive drum 413. Thus, a toner image is formed. Specifically, a developing bias voltage is applied to the developer carrying member (developing roller), and the charged toner on the developer carrying member is applied to the surface of the photosensitive drum 413 by the potential difference between the surface of the photosensitive drum 413 and the developer carrying member. Move to and adhere to exposed areas.

  The drum cleaning device 415 includes a drum cleaning blade that is in sliding contact with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, the support roller 423A disposed on the downstream side in the belt traveling direction from the primary transfer roller 422 for the K component is preferably a drive roller (hereinafter referred to as “drive roller 423A”). This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, whereby a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421 is formed.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face a support roller 423B (hereinafter referred to as “backup roller 423B”) disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the sheet.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photosensitive drum 413 are primarily transferred to the intermediate transfer belt 421 in order. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet. Specifically, by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper (the side in contact with the secondary transfer roller 424), the toner image becomes It is electrostatically transferred to the paper. The sheet on which the toner image has been transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

  In the intermediate transfer unit 42, instead of the secondary transfer roller 424, a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller (so-called belt-type secondary transfer). Unit) may be adopted.

  The fixing unit 60 is disposed on the upper fixing unit 61 having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) side of the paper, and on the back surface (surface opposite to the fixing surface) side of the paper. A lower fixing unit 62 having a back surface side support member, a heating source 63 for heating the fixing surface side member, and the like.

  In the present embodiment, the upper fixing unit 61 employs a belt heating method. That is, the fixing belt 613 (see FIG. 5) serves as a fixing surface side member. Further, when the lower fixing unit 62 is a roller pressurization method, the pressure roller is a back surface side support member, and when the lower fixing unit 62 is a belt pressure method, the pressure belt is a back surface side support member. When the back surface side support member is pressed against the fixing belt 613 as the fixing surface side member, a fixing nip for nipping and conveying the sheet is formed. The sheet onto which the toner image has been secondarily transferred and conveyed is heated and pressurized when passing through the fixing nip. As a result, the toner image is fixed on the paper.

  The fixing unit 60 may include a separation air blowing unit that blows air to the fixing surface side member or the back surface side support member and separates the sheet from the fixing surface side member or the back surface side support member. In addition, the fixing unit 60 may include a heating source for heating the pressure roller 621 in order to suppress a temperature drop of the fixing belt 613 accompanying the fixing process (suppress heat dissipation from the fixing belt 613). . Details of the fixing unit 60 will be described later.

The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a first transport unit 53, a second transport unit 54, and the like.
In the three paper feed tray units 511 to 513 constituting the paper feed unit 51, paper (standard paper, special paper) identified based on basis weight, size, etc. is stored for each preset paper type. .

  The first transport unit 53 includes a plurality of transport roller units including an intermediate transport roller unit 531, a loop roller unit 532, and a registration roller unit 533. The first transport unit 53 transports paper fed from the paper feed unit 51 or an external paper feed device (not shown) to the image forming unit 40 (secondary transfer unit).

  The 2nd conveyance part 54 is provided with the switchback path | route 541 and the conveyance path 542 for back surfaces by which the some conveyance roller part is arrange | positioned. The second transport unit 54 once transports the paper to the switchback path 541, switches back and transports the paper to the back-side transport path 542, thereby reversing the paper, and the first transport unit 53 (loop roller unit 532). Upstream).

  A sheet fed from the sheet feeding unit 51 or an external sheet feeding device (not shown) is conveyed to the image forming unit 40 by the first conveying unit 53. Then, when the sheet passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to one side (fixing surface) of the sheet at once and subjected to a fixing process in the fixing unit 60. . The paper on which the image is formed is discharged out of the apparatus by a paper discharge unit 52 having a paper discharge roller 52a. When images are formed on both sides of the paper, the paper on which the image is formed on the front surface is sent to the second transport unit 54, and after being inverted, an image is formed on the back surface.

Hereinafter, the configuration of the fixing unit 60 will be described in detail. FIG. 5 is a cross-sectional view schematically showing a main part of the fixing unit 60. FIG. 6 is a perspective view of a main part of the fixing unit 60.
5 and 6 includes a belt heating type upper fixing unit 61, a roller pressing type lower fixing unit 62, a heating source 63, a fixing temperature detection sensor 64, and the like.

  The upper fixing unit 61 includes a fixing roller 611, a heating roller 612, and an endless fixing belt 613 stretched around these.

The fixing roller 611 has a configuration in which an elastic layer made of silicone rubber or the like is formed on the outer peripheral surface of a columnar core made of iron or the like. A surface release layer made of a fluororesin such as PTFE may be formed on the outer peripheral surface of the elastic layer.
The fixing roller 611 is connected to a fixing roller driving unit 614 (see FIG. 4), and rotates at a constant peripheral speed by power transmitted from the fixing roller driving unit 614. The operation of the fixing roller driving unit 614 is controlled by the control unit 100.

The heating roller 612 has a configuration in which a resin layer made of PTFE or the like is formed on the outer peripheral surface of a cylindrical metal core made of aluminum or the like. A heating source 63 such as a halogen lamp is built in the heating roller 612. The heat of the heating source 63 is transmitted through the heating roller 612, whereby the fixing belt 613 is heated.
The heating source 63 may heat the fixing belt 613 by an electromagnetic induction heating method. In this case, the heating source 63 is disposed outside the heating roller 612, and the fixing belt 613 is directly heated.

  The heating roller 612 rotates following the traveling of the fixing belt 613. The heating roller 612 is connected to a steering drive unit 615 (see FIG. 4), and functions as a steering roller whose axial direction can be displaced by the steering drive unit 615. The operation of the steering drive unit 615 is controlled by the control unit 100. For example, when the control unit 100 operates the steering drive unit 615 based on the detection result of the belt deviation detection unit (not shown), the heating roller 612 tilts with the one end side in the axial direction as a fixed end. As a result, the fixing belt 613 swings in the axial direction, and the deviation is corrected.

  The fixing belt 613 has a configuration in which, for example, an elastic layer made of silicone rubber and a surface release layer made of a fluorine-based resin are sequentially laminated on a film base made of heat-resistant polyimide. As the fluorine-based resin, a material containing any of PFA (perfluoroalkoxyalkane), PTFE (polytetrafluoroethylene), and FEP (hexafluoropropylene copolymer) can be applied. Accordingly, the surface releasability of the fixing belt 613 with respect to the wax contained in the toner resin or toner particles is improved, and the toner is easily separated from the surface of the fixing belt 613 at the time of fixing.

  The lower fixing unit 62 includes a pressure roller 621 serving as a back side support member. The pressure roller 621 has the same configuration as the fixing roller 611. A pressure contact / separation portion (not shown) is connected to the pressure roller 621. The pressure contact / separation unit includes a biasing unit that biases the pressure roller 621 against the fixing roller 611, and switches the state of the pressure roller 621 with respect to the fixing belt 613 between a pressure contact state and a separation state.

  The pressure roller 621 is pressed against the fixing roller 611 via the fixing belt 613 by the press-separation unit. Thereby, a fixing nip for nipping and conveying the sheet is formed. The sheet on which the toner image has been secondarily transferred and conveyed is pressurized when passing through the fixing nip and is heated at a fixing temperature (for example, 160 to 200 ° C.) while being in contact with the fixing belt 613. As a result, the toner image is fixed on the paper.

  The fixing temperature detection sensor 64 is a contact-type temperature sensor that is disposed in a state of being pressed against the heating roller 612 and detects a fixing temperature (a surface temperature of the fixing belt 613). Based on the detection result of the fixing temperature detection sensor 64, the control unit 100 controls the output of the heating source 63 and the like so that the fixing temperature is maintained within a predetermined allowable fixing temperature range.

  For example, as shown in FIG. 7, the fixing temperature detection sensor 64 includes a detection element 641 for detecting the fixing temperature, and a holding portion (for example, an elastic material such as a sponge) in which the detection element 641 is embedded and forms a contact portion with the fixing belt 613. Body) 642 and a pressing portion (for example, a compression coil spring) 643 that presses the holding portion 642 toward the fixing belt 613. A protective tape may be attached to a contact portion of the holding unit 642 with the fixing belt 613.

  The fixing temperature detection sensor 64 is disposed at a position corresponding to the non-sheet passing region of the fixing belt 613, that is, near the end of the heating roller 612. The non-sheet passing area is an area that does not come into contact with the sheet that is passed through the fixing nip. If the fixing temperature detection sensor 64 is disposed at a position corresponding to the sheet passing area of the fixing belt 613, a flaw due to rubbing may occur at a contact portion of the fixing belt 613 with the fixing temperature detection sensor 64, thereby causing an image defect. Because there is.

  In addition, the fixing temperature detection sensor 64 operates integrally with the heating roller 612 following the axial displacement of the heating roller 612 so that the relative positional relationship with the heating roller 612 is maintained. . As a result, even if the axial direction of the heating roller 612 is displaced, the pressure contact state between the fixing temperature detection sensor 64 and the fixing belt 613 is maintained, so that the fixing temperature detection sensor 64 can accurately detect the fixing temperature.

  As described above, the fixing unit 60 (fixing device) according to the embodiment stretches between the plurality of support rollers including the fixing roller 611 and the heating roller 612 (steering roller) that can be displaced in the axial direction, and the plurality of support rollers. An endless fixing belt 613, a heating source 63 for heating the fixing belt 613, and a pressure roller 621 (on the back side) that is pressed against the fixing roller 611 via the fixing belt 613 and forms a fixing nip together with the fixing belt 613. A supporting member) and a contact-type fixing temperature detection sensor 64 that is arranged in a state of being pressed against the heating roller 621 (a specific roller of the plurality of supporting rollers) and detects the surface temperature of the fixing belt 613. A fixing belt in the roller axis direction by steering control of a heating roller 621 (steering roller) 13 swings.

FIG. 8 is a diagram showing the positional relationship between the fixing belt 613, the heating roller 612, and the fixing temperature detection sensor 64 in the fixing unit 60. FIG. 8 shows a case where the fixing belt 613 swings most to the right.
As shown in FIG. 8, in this embodiment, the distance from the paper passing center (the paper passing position is constant) to one end (the left end in FIG. 8) of the heating roller 621 is B, When the distance to one end of the fixing belt 613 is C, the relationship of B <C is satisfied regardless of the swinging operation of the fixing belt 613. “Regardless of the swinging movement of the fixing belt 613” means that the fixing belt 613 swings most to the one end side (left side in FIG. 8), and most to the other end side (right side in FIG. 8). This is also the case when it moves.

  When the contact-type fixing temperature detection sensor 64 is applied, the fixing belt 613 is rubbed to generate a considerable amount of shavings. However, the surface of the heating roller 612 is always covered with the fixing belt 613. The shaving powder does not adhere to the surface of the heating roller 612. Therefore, the shaving powder does not enter between the fixing belt 613 and the heating roller 612, and good heat transfer from the heating roller 612 to the fixing belt 613 is realized, and the fixing belt 613 is heated uniformly. Therefore, it is possible to prevent the occurrence of defects such as image defects (for example, uneven spot-like gloss) due to shaving powder.

  Further, the position of the fixing temperature detection sensor 64 is a position satisfying A <B, where A is the distance from the sheet passing center to the detection element 641. Even if the position of the end portion (left end portion in FIG. 8) of the fixing temperature sensor 64 is within the range of the heating roller 612 (A1 ≦ B, A1: distance from the sheet passing center to the end portion of the fixing temperature sensor 64). , And out of range (A1> B). That is, it is only necessary that the heating roller 612 is located at a position facing the detection element 641 and that the heating roller 612 reliably functions as a backup roller when the fixing temperature detection sensor 64 is pressed. As a result, the pressure contact state between the fixing temperature detection sensor 64 and the fixing belt 613 is stabilized, so that the fixing temperature detection sensor 64 can accurately detect the fixing temperature.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.

For example, in addition to the fixing roller 611 and the heating roller 612, the fixing unit 60 (upper fixing unit 61) may include a support roller on which the fixing belt 613 is stretched. In this case, support rollers other than the heating roller 612 may function as a steering roller.
Further, for example, the support roller disposed to face the fixing temperature detection sensor 64 may be the fixing roller 611 or another support roller.

  Further, even in a fixing device in which steering control is not performed by the steering roller, the fixing belt may move in the axial direction due to a pressure release operation or the like. And the heating roller (specific roller). The present invention can also be applied to a fixing device that does not include such a steering roller.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 30 Image processing part 40 Image forming part 50 Paper conveyance part 60 Fixing part 61 Upper fixing part 611 Fixing roller 612 Heating roller (steering roller, specific roller)
613 Fixing belt (fixing surface side member)
614 Fixing roller driving unit 615 Steering driving unit 62 Lower fixing unit 621 Pressure roller (back side support member)
622 Pressure roller drive unit 63 Heating source 64 Fixing temperature detection sensor 641 Detection element 642 Holding unit 643 Pressing unit 100 Control unit

Claims (8)

A plurality of support rollers including a fixing roller;
An endless fixing belt stretched around the plurality of support rollers;
A heating source for heating the fixing belt;
A back-side support member that is pressed against the fixing roller via the fixing belt and forms a fixing nip together with the fixing belt;
A contact-type fixing temperature detection sensor that is arranged in a state of being pressed against a specific roller among the plurality of support rollers and detects a surface temperature of the fixing belt, and a fixing device comprising:
The fixing belt has a flat shape over the entire surface including both ends in the width direction,
When the distance from the sheet passing center to one end of the specific roller is B, and the distance from the one end of the fixing belt is C, the relationship of B <C is satisfied regardless of the swinging operation of the fixing belt. A fixing device characterized. The plurality of support rollers include a steering roller capable of axial displacement.
The fixing device according to claim 1, wherein the fixing belt swings in a roller axial direction by steering control of the steering roller. The specific roller is composed of the steering roller,
The fixing device according to claim 2, wherein the fixing temperature detection sensor follows a displacement in the axial direction of the specific roller and maintains a relative positional relationship with the specific roller. When the distance from the paper passing center to the detection element of the fixing temperature detection sensor is A,
The fixing device according to claim 1, wherein the fixing temperature detection sensor is arranged so as to satisfy A <B.   5. The fixing device according to claim 1, wherein the fixing temperature detection sensor is disposed at a position corresponding to a non-sheet passing region of the fixing belt.   The fixing temperature detection sensor includes a detection element that detects a fixing temperature, a holding part that includes the detection element and contacts the fixing belt, and a pressing part that presses the holding part toward the fixing belt. The fixing device according to any one of claims 1 to 5.   The fixing device according to claim 1, wherein the specific roller is a heating roller including the heating source.   An image forming apparatus comprising the fixing device according to claim 1.

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