JP4265458B2 - Fixing device - Google Patents

Description

  The present invention relates to a belt-type fixing device mounted on an image forming apparatus. In particular, even if a positional deviation occurs between a fuser roller and a belt unit with a simple configuration, a stable nip is always provided. The present invention relates to a fixing device that can be obtained.

  Conventionally, there is an electrophotographic image forming apparatus that forms an image using toner. Such an image forming apparatus is equipped with a fixing device for fixing the transferred toner image on the transfer paper. There are two types of fixing devices, a two-roll type and a belt type, but the belt-type fixing device has attracted attention because of its merit that the nip width can be set wider than the two-roll type and the power consumption is low. Yes.

As a conventional belt type fixing device, for example, in JP-A-5-165357, as shown in FIG. 8, an endless fixing belt 103 rotatably supported by a heat roll 101 and a support roll 102 is provided. When the transfer paper passes between the fixing belt 103 and the press roll 104, the position of the support roll 102 is moved according to the type of transfer paper used in the fixing device that heats and fixes the toner image on the transfer paper. Thus, there has been proposed a fixing device 100 configured to change the contact width between the fixing belt 103 and the press roll 104.
According to such a configuration, it is possible to select an optimum nip width corresponding to paper having various thicknesses, and it is possible to select fixing conditions according to the type of transfer paper.

  Further, in JP-A-2002-318502, as shown in FIG. 9, a press with a hollow cylindrical pressure roll 202 abutting on the heating roll 201 and the diameter of the central portion is expanded inside the pressure roll 202. There has been proposed a fixing device 200 having a configuration in which a pressing roller 203 is pressed against a heating roller 201 via a pressing roller 202 by inserting a roller 203 and energizing both ends 203a and 203b thereof.

  According to such a configuration, the diameter increase in the central portion of the pressing roll 203 and the bending rigidity of the heating roll 201, the pressing roll 202, and the pressing roll 203 are appropriately set, and the heating roll 201 and the pressing roll 203 When the pressure contact force is applied between the pressure roll 202 and the heating roll 201, the axial lines of the heating roll 201 and the pressing roll 203 are bent in opposite directions, and are appropriately distributed in the axial direction between the pressure roll 202 and the heating roll 201. Nip width and pressure contact force can be obtained. Thereby, wrinkles can be prevented from occurring when the recording paper P passes through the nip portion.

  Further, in Japanese Patent Laid-Open No. 2002-132080, as shown in FIG. 10, an elastic member 302a curved in a shape along the peripheral surface of the fixing roll 301, and a protrusion is formed on the downstream side of the process from the elastic member 302a. There has been proposed a fixing device 300 that includes a pressure member 302 having a pressure applying member 302b having a good thermal conductivity and presses the endless belt 303 against the fixing roll 301 by the pressure member 302.

According to such a configuration, when the recording paper P is fed between the fixing roll 301 and the endless belt 303, the heat supplied to the fixing roll 301 is transmitted to the pressure member 302 via the endless belt 303. Then, it is transmitted in the axial direction through the pressure applying member 302b having a large thermal conductivity, and is efficiently exchanged with the fixing roll 301. As a result, good fixing can be performed even when recording paper of a small size is continuously fed.
JP-A-5-165357 (Embodiments of the Invention [0019] to [0041], FIGS. 1 to 8) JP 2002-318502 A (Embodiments [0017] to [0026] of FIGS. 1 to 4) JP 2002-132080 A (Embodiments of the Invention [0029] to [0038], FIGS. 1 to 4)

  However, in the above-described fixing device 100 of JP-A-5-165357, in order to obtain an optimum nip, two rolls of a heat roll 101 and a support roll 102 are necessary inside the fixing belt 103, and further, these A mechanism for driving the support roll 102 to apply tension to the fixing belt 103 is required, and the configuration for obtaining a stable nip is complicated. For this reason, there existed a problem of increase in a number of parts, deterioration of assembling property, and cost increase.

  Further, the above-described fixing device 200 of Japanese Patent Application Laid-Open No. 2002-318502 requires a special pressing roll 203 having an enlarged central portion, and also sets the diameter of the pressing roll 203, the heating roll 201, and the pressing roll. 202 and the pressing roll 203 must be appropriately set in bending rigidity. Further, it is necessary to always apply a large urging force to the pressing roll 203 so that the heating roll 201 and the pressure roll 202 are curved. Although not increasing, the configuration for obtaining a stable nip was complicated.

  Further, in the above-described fixing device 300 of Japanese Patent Laid-Open No. 2002-132080, the nip is formed by simply pressing the elastic member 302a of the pressure member 302 and the pressure applying member 302b to the fixing roll 301. When a dimensional tolerance is generated between the pressure member 301 and the pressure member 302, an optimal contact state between the elastic member 302a and the pressure applying member 302b with respect to the fixing roll 301 cannot be obtained, and a stable nip cannot be formed. There was a problem.

  The present invention has been made in view of the above problems, and has a simple configuration, and even when a positional deviation occurs between the fuser roller and the belt unit, it is possible to always obtain a stable nip. An object is to provide an apparatus.

  In order to achieve the above object, a fixing device according to the present invention includes a fuser roller and a belt unit that are pressed against each other to nip a sheet of paper, the belt unit including an endless fixing belt, and the fixing belt on an outer periphery. A cylindrical nip guide wound in a rotatable manner and provided with a concave nip portion that abuts on the paper introduction side and the discharge side of the outer peripheral surface of the fuser roller via the belt, and a cylindrical inner surface of the nip guide The nip guide is slidably supported on the paper introduction side and the discharge side, and is urged toward the fuser roller, and has a pressure contact shaft that presses the nip portion of the nip guide against the fuser roller. As a configuration.

  Preferably, the contact surfaces of the nip guide and the press contact shaft are flat, and the nip guide swings about the rotation shaft of the press contact shaft, or the nip guide and the press contact shaft The contact surfaces of each other are curved, and the nip guide swings around a contact portion with the pressure contact shaft.

  More preferably, the inner peripheral surface of the nip guide and the outer peripheral surface of the pressure contact shaft are circular in cross section having different diameters, and a rotation restricting portion that restricts excessive rotation of the nip guide alone. For example, the rotation restricting portion may be a protrusion provided on the inner peripheral surface of the nip guide or the outer peripheral surface of the press contact shaft.

  According to the fixing device of the present invention, the fuser roller and the belt have a simple configuration in which a nip guide formed with a nip portion that contacts the paper introduction side and the discharge side of the outer circumferential surface of the fuser roller is swingably supported. Even when a positional deviation occurs between the units, the nip guide can be made to follow the positional deviation to always obtain a stable nip.

  That is, when a positional deviation occurs between the fuser roller and the belt unit, an imbalance of the pressure contact force occurs between the paper introduction side and the discharge side of the concave nip portion formed in the nip guide. The nip guide swings so as to correct the imbalance, and the nip portion is brought into pressure contact with the paper introduction side and the discharge side on the outer peripheral surface of the fuser roller. Since the direction of each pressing force on the paper introduction side and discharge side of the nip portion is toward the center of the fuser roller, a stable nip is formed.

  Further, when the contact surfaces of the nip guide and the press contact shaft are flat, the nip guide and the press contact shaft always work together, for example, when releasing the nip with the fuser roller, The nip guide alone is not excessively rotated, and the nip portion can be prevented from being displaced with respect to the fuser roller.

  On the other hand, when the contact surfaces of the nip guide and the pressure contact shaft are curved, the nip guide swings around the contact portion with the pressure contact shaft. In this way, when the center point of the nip guide swings closer to the nip portion, the nip guide is moved slightly between the sheet introduction side and the discharge side of the outer peripheral surface of the fuser roller with a small swing of the nip guide. Each of them can be pressed against each other, and the follow-up operation of the nip guide becomes faster.

  Furthermore, when both the inner peripheral surface of the nip guide and the outer peripheral surface of the press contact shaft are circular in cross section, and a rotation restricting portion that restricts excessive rotation of the nip guide alone is provided, The center point of the swing of the nip guide is closer to the fuser roller, the follow-up operation of the nip guide becomes quicker, and the rotation restricting portion prevents the nip portion from being displaced relative to the fuser roller. be able to.

  In addition, when the rotation restricting portion is a protrusion provided on the inner peripheral surface of the nip guide or the outer peripheral surface of the press contact shaft, an excessive rotation of the nip guide alone can be achieved with a very simple configuration. Movement can be regulated.

Hereinafter, a fixing device according to an embodiment of the present invention will be described. First, an image forming apparatus (printer) equipped with a fixing device according to the present embodiment will be described with reference to FIG.
FIG. 1 is a cross-sectional view illustrating an internal configuration of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. In FIG. 1, an image forming apparatus 1 is an electrophotographic tandem color image forming apparatus, and includes an image forming unit 2, an intermediate transfer belt unit 3, a paper feeding unit 4, and a duplex printing transport unit 5. It is.

  The image forming unit 2 has a configuration in which four image forming units 2M, 2C, 2Y, and 2K are arranged side by side in a multistage manner from right to left in FIG. Of these image forming units 2M, 2C, 2Y, and 2K, the three upstream image forming units 2M, 2C, and 2Y are magenta (M) and cyan (C), which are subtractive three primary colors, respectively. The monochromatic image is formed with yellow (Y) color toner, and the image forming unit 2K forms a monochrome image with black (K) toner mainly used for dark portions of characters and images.

  Each of the image forming units 2M, 2C, 2Y, and 2K has the same configuration except for the color of the toner stored in the toner container. Accordingly, the configuration of the black (K) image forming unit 2K will be described below as an example.

  The image forming unit 2K includes a photosensitive drum 21 at the bottom. The peripheral surface of the photosensitive drum 21 is made of, for example, an organic photoconductive material. A cleaner 22, a charger 23, an optical writing head 24, and a developing roller 26 of a developing unit 25 are arranged around the periphery of the photosensitive drum 21. The optical writing head 24 is separate from the image forming unit 2K. Further, the image forming unit 2K is configured to be able to be inserted and removed in the depth direction of the drawing by opening a front door (not shown) in front of the printer 1 (front side of the drawing).

  The developing unit 25 applies magenta (M), cyan (C), yellow (Y), or black (K) toner to the upper toner container as indicated by M, C, Y, and K in FIG. An intermediate portion is provided with a toner replenishing mechanism at a lower portion, a lower portion is provided with the above-described developing roller 26 at a side opening, a toner stirring member, a toner supply roller for supplying toner to the developing roller 26, a developing A doctor blade or the like for regulating the toner layer on the roller 13 to a constant layer thickness is provided.

  The intermediate transfer belt unit 3 includes a transfer belt 31 that extends in a substantially loop shape from substantially the left and right sides of the drawing at the center of the main body device, and circulates the transfer belt 31 in the counterclockwise direction of the drawing. A driving roller 32 to be moved and a driven roller 33 are provided.

  The transfer belt 31 directly transfers the toner image onto the belt surface (primary transfer) and conveys the toner image to the transfer position to the paper for further transfer (secondary transfer). The whole is called an intermediate transfer belt unit.

  The intermediate transfer belt unit 3 includes a belt position control mechanism 34 in the loop of the flat loop-shaped transfer belt 31. The belt position control mechanism 34 includes a primary transfer roller 35 made of a conductive foam sponge that presses against the lower peripheral surface of the photosensitive drum 21 via the transfer belt 31.

  The belt position control mechanism 34 includes three primary transfer rollers 35 corresponding to the three image forming units 2M, 2C, and 2Y of magenta (M), cyan (C), and yellow (Y) with a bowl-shaped support shaft. The image is transferred to the center at the same cycle, and one primary transfer roller 35 corresponding to the black (K) image forming unit 2K is rotated and moved at a rotation cycle different from the cycle of the three primary transfer rollers 35. The belt 31 is moved away from the photosensitive drum 21, and the full color mode (all four primary transfer rollers 35 are in contact with the transfer belt 31) and the monochrome mode (only the primary transfer roller 35 corresponding to the image forming unit 2K is the transfer belt). 31) and all non-transfer modes (all four primary transfer rollers 35 are separated from the transfer belt 31).

  In the intermediate transfer belt unit 3, a belt cleaner unit 36 is disposed further upstream of the uppermost image forming unit 2M in the belt moving direction on the upper surface portion, and is flat so as to be almost along the entire lower surface portion. A thin waste toner collecting container 37 is detachably disposed.

  The paper feed unit 4 includes two paper feed cassettes 41 arranged in two upper and lower stages. A paper take-out roller 42 and a paper feed are provided near the paper feed opening (right side in the drawing) of these paper feed cassettes 41, respectively. A roller 43, a separating roller 44, and a conveying roller pair 45 are arranged. In the sheet conveyance direction (vertical direction in the figure) of the conveyance roller pair 45, a secondary transfer roller 46 that is in pressure contact with the driven roller 33 via the transfer belt 31 is disposed, and a secondary transfer portion to the sheet is provided. Forming.

  A fixing device 60 according to the present embodiment is disposed downstream (upward in the drawing) of the secondary transfer portion, which will be described in detail later. Further downstream of the fixing device 60, a pair of discharge rollers 47 for discharging the fixed paper from the fixing device 60, and a pair of discharge rollers for discharging the discharged paper to a paper discharge tray 48 formed on the upper surface of the device. 49 is arranged.

  The duplex printing conveyance unit 5 includes a start return path 51a branched from the intermediate conveyance path between the carry-out roller pair 47 and the discharge roller pair 49 in the right lateral direction in the figure, an intermediate return path 51b bent downward from this, A terminal return path 51c that bends in the left lateral direction opposite to the above and eventually reverses the return sheet, and three return roller pairs 52a, 52b, and 52c arranged in the middle of these return paths are provided. . At the outlet of the end return path 51c, a pair of carry-in rollers 53 is disposed inside the main body.

  Next, the fixing device according to the first embodiment of the present invention mounted on the image forming apparatus will be described with reference to FIGS. FIG. 2 is a cross-sectional view showing the fixing device according to the first embodiment of the present invention, and FIG. 3 is an explanatory diagram showing the direction of each pressing force of the nip guide in the fixing device of FIG. 4 is a cross-sectional view showing the nip released state of the fixing device of FIG.

  In FIG. 2, the fixing device 60 of the present embodiment includes a fuser roller 61 and a belt unit 62 that are in pressure contact with each other and nip a sheet (not shown). That is, the belt unit 62 is pressed against the fuser roller 61, and the fuser roller 61 is rotationally driven by a driving unit (not shown), so that the fixing belt 63 of the belt unit 62 is driven to carry and fix the paper.

  The fuser roller 61 has a structure in which the surface of a thin AL tube is coated with Teflon (registered trademark) and a halogen heater 61a is disposed therein. The halogen heater 61a is a tube-shaped halogen lamp, and is a clean, safe, small and light heat source that radiates most of the input electric power by converting it into infrared rays (heat). Further, since the halogen heater 61a uses a filament having a small heat capacity as a heat source, it can start radiating heat almost simultaneously with the power ON. When the halogen heater 61a emits light, the AL tube is rapidly heated, and a continuous heat supply is performed to the fixing belt 63 that is pressed against the AL tube.

The belt unit 62 is mainly composed of the fixing belt 63, the nip guide 64, the press contact shaft 65, and the rotation shaft 66.
The fixing belt 63 is a cylindrical endless belt, and is made of Si rubber having excellent elasticity, heat resistance, and separation property from toner as a base material. The fixing belt 63 stably transfers the heat supplied from the fuser roller 61 to the paper due to the excellent elasticity of Si rubber.

The friction coefficient between the fuser roller 61 and the fixing belt 63 described above is set to be larger than the friction coefficient between the fixing belt 63 and the nip guide 64 so that the fuser roller 61 can follow the fixing belt 63 smoothly. ing.
The nip guide 64 is a long, substantially cylindrical member formed of a heat-resistant synthetic resin that absorbs very little heat. The nip guide 64 is wound around the outer circumference having a dimension slightly smaller than the diameter of the fixing belt 63. It is wound freely. The outer peripheral surface of the nip guide 64 includes a concave nip portion 64A that is a contact surface with the fuser roller 61, and a belt guide portion 64B that is the remaining arc surface.

  The nip portion 64 </ b> A is a concave circular arc surface having substantially the same radius of curvature as the outer peripheral surface of the fuser roller 61, and a wide nip width is secured along the outer peripheral surface of the fuser roller 61. The nip portion 64A is divided into a contact surface 64a that contacts the paper introduction side of the fuser roller 61 and a contact surface 64b that contacts the paper discharge side.

  In this embodiment, the diameter of the belt guide portion 64B of the nip guide 64 is set to be slightly smaller than the diameter of the fixing belt 63 so that the fixing belt 63 is not loosened or bent.

Further, a first flat surface portion 64 </ b> C that is a contact surface with the pressure contact shaft 65 is formed on the back surface of the nip portion 64 </ b> A on the inner surface of the cylinder of the nip guide 64.
The pressure contact shaft 65 is a long member having a substantially D-shaped cross-section in which a cylindrical rotation shaft 66 is inserted, and is disposed in the cylinder of the nip guide 64. The pressure contact shaft 65 is formed with a second flat surface portion 65A that comes into contact with the first flat surface portion 64C of the nip guide 64. By bringing the first and second flat surface portions 64C and 65A into contact with each other, the nip guide 64 is supported so as to be swingable around a center point 66 a of the rotary shaft 66.

  Although not shown, the pressure contact shaft 65 presses the both end bearing portions of the rotation shaft 66 toward the fuser roller 61 with a spring or the like, thereby pressing the nip portion 64 </ b> A of the nip guide 64 against the fuser roller 61.

  In this embodiment, as shown in FIG. 4, the urging of the rotating shaft 66 by the spring or the like can be released. For example, when the image forming apparatus 1 is in a non-job state, the fuser roller 61 and the nip guide 64 are Non-contact nip released. As a result, it is possible to prevent deterioration of the durability, shortening of the life, and wrinkling of the fixing belt 63 under high temperature heating.

  Next, the operation of the fixing device 60 configured as described above will be described. For example, when a positional deviation occurs between the fuser roller 61 and the belt unit 62 due to a dimensional tolerance or the like, the sheet in the nip portion 64A of the nip guide 64 is detected. An imbalance of the pressure contact force occurs between the introduction side contact surface 64a and the paper discharge side contact surface 64b.

  Then, as shown in FIG. 3, the nip guide 64 swings about the center point 66 of the rotating shaft 66 as if to correct the imbalance, and the sheet introduction side contact surface 64a of the nip portion 64A and the sheet discharge. The side contact surfaces 64b are brought into pressure contact with the fuser roller 61, respectively. At this time, the direction of each pressing force between the paper introduction side contact surface 64a and the paper discharge side contact surface 64b is directed to the center point 61b of the fuser roller 61, so that a stable nip is formed.

  Further, since the nip guide 64 and the pressure contact shaft 65 are in contact with each other by the first and second flat portions 64C and 65A, the nip guide 64 and the pressure contact shaft 65 always co-operate, for example, as shown in FIG. Thus, when the nip between the fuser roller 61 and the nip guide 64 is released, the nip guide 64 does not rotate excessively alone, and the positional deviation of the nip portion 64A with respect to the fuser roller 61 can be prevented. it can.

  According to the fixing device 60 of this embodiment, the nip guide 64 formed with the nip portion 64A formed of the paper introduction side contact surface 64a and the paper discharge side contact surface 64b is swingably supported. With the configuration, even when a positional deviation occurs between the fuser roller 61 and the belt unit 62, the nip guide 64 can be made to follow the positional deviation to always obtain a stable nip.

  Next, a fixing device according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a cross-sectional view showing a fixing device according to a second embodiment of the present invention, and FIG. 6 is an explanatory view showing directions of each pressing force of a nip guide in the fixing device of FIG. FIG. 7 is a cross-sectional view showing the nip released state of the fixing device of FIG.

  In FIG. 5, the fixing device 70 of the present embodiment includes a fuser roller 71 and a belt unit 72 as main parts. As in the first embodiment, the fuser roller 71 is rotationally driven by a driving unit (not shown), thereby forming a belt. The fixing belt 73 of the unit 72 is driven to carry and fix the paper.

As in the first embodiment, the fuser roller 71 has a configuration in which the surface of a thin AL tube is coated with Teflon (registered trademark), and a halogen heater 71a is disposed therein.
The belt unit 72 mainly includes a fixing belt 73, a nip guide 74, a pressure contact shaft 75, and a rotation shaft 76.

The fixing belt 73 is a cylindrical endless belt as in the first embodiment, and is made of Si rubber having excellent elasticity, heat resistance, and separation property from toner as a base material.
As in the first embodiment, the nip guide 74 is a long, substantially cylindrical member formed of a heat-resistant synthetic resin that absorbs very little heat, and has a slightly smaller outer diameter than the diameter of the fixing belt 73. The fixing belt 73 is rotatably wound. The outer peripheral surface of the nip guide 74 includes a concave nip portion 74A that is a contact surface with the fuser roller 71, and a belt guide portion 74B that is the remaining arc surface.

  Similar to the first embodiment, the nip portion 74A is a concave circular arc surface having the same radius of curvature as the outer peripheral surface of the fuser roller 71, and a contact surface 74a that contacts the paper introduction side of the fuser roller 71, and a paper discharge side. And a contact surface 74b that contacts the surface.

  In this embodiment, unlike the first embodiment, the inner peripheral surface 74C of the nip guide 74 has a circular cross section, and the outer peripheral surface 75A of the press contact shaft 75 inserted through the nip guide 74 The cross-sectional circular shape is slightly smaller in diameter than the peripheral surface 74C. As a result, the nip guide 74 swings independently of the pressure contact shaft 75 around the contact portion 77a with the pressure contact shaft 75, not the center point 76a of the rotation shaft 76.

  Further, a rotation restricting portion (protrusion portion) 75B that restricts excessive rotation of the nip guide 74 alone is provided at the lowermost end of the outer peripheral surface of the press contact shaft 75. That is, the rotation restricting portion 75B allows the nip guide 74 to swing within a predetermined range, and when the nip guide 74 attempts to rotate excessively beyond the range, Abutting on the peripheral surface 74C, the rotation is limited.

  According to the fixing device 70 of the present embodiment as described above, as shown in FIG. 6, the swing center (contact portion 77 b) of the nip guide 74 is approximately 1 / compared to the center point 76 a of the rotation shaft 76. Close to fuser roller 71 up to a distance of two. As a result, the torque (μF × R) for swinging the nip guide 74 generated by the frictional force (μF) with the fixing belt 73 is smaller than the case around the center point 76a of the rotating shaft 76 (μF × R). Torque (μF × r) is sufficient, and the follow-up operation of the nip guide 74 can be made quicker.

  Further, the nip guide 74 is provided with a very simple configuration in which a protruding rotation restricting member 75B is provided on the pressure contact shaft 75, for example, when the nip between the fuser roller 71 and the nip guide 74 is released as shown in FIG. However, the position of the nip portion 74A relative to the fuser roller 71 can be prevented from being excessively rotated.

  The fixing device of the present invention is not limited to the above-described embodiments. For example, in the second embodiment, the inner peripheral surface 74C of the nip guide 74 and the outer peripheral surface of the press contact shaft 75 are circular in cross section, but the entire nip guide 74 and the press contact shaft 75 must be curved surfaces such as arcuate surfaces. However, even if only the contact surfaces are curved within the range necessary for the swing of the nip guide 74, the same effect can be obtained.

  Further, the contact surface between the nip guide and the pressure contact shaft is not limited to the circular arc surface as in the second embodiment, and may be, for example, an elliptical surface or a curved surface based on a free curve.

1 is a cross-sectional view illustrating an internal configuration of an image forming apparatus equipped with a fixing device according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to a first embodiment of the present invention. FIG. 3 is an explanatory diagram showing directions of each pressing force of a nip guide in the fixing device of FIG. 2. FIG. 3 is a cross-sectional view showing a nip release state of the fixing device of FIG. 2. FIG. 6 is a cross-sectional view illustrating a fixing device according to a second embodiment of the present invention. FIG. 6 is an explanatory diagram showing directions of each pressing force of a nip guide in the fixing device of FIG. 5. FIG. 6 is a cross-sectional view illustrating a nip release state of the fixing device of FIG. 5. It is sectional drawing which shows the fixing device which concerns on a 1st prior art example. 2 shows a fixing device according to a second conventional example, in which FIG. 1A is a longitudinal sectional view and FIG. 1B is a lateral sectional view. It is sectional drawing which shows the fixing device which concerns on a 3rd prior art example.

Explanation of symbols

1 Image forming device (printer)
2 Image forming unit 2M, 2C, 2Y, 2K Image forming unit 21 Photosensitive drum 22 Cleaner 23 Charger 24 Optical writing head 25 Developer 26 Developing roller 3 Intermediate transfer belt unit 31 Transfer belt 32 Drive roller 33 Driven roller 34 Belt Position control mechanism 35 Primary transfer roller 36 Belt cleaner unit 37 Waste toner collection container 4 Paper feed unit 41 Paper feed cassette 42 Paper take-out roller 43 Feed roller 44 Rolling roller 45 Conveying roller pair 46 Secondary transfer roller 47 Unloading roller pair 48 Ejection Paper tray 49 Discharge roller pair 5 Duplex printing transport unit 51a Start return path 51b Intermediate return path 51c End return path 52a, 52b, 52c Return roller pair 53 Carry-in roller pair 60 Fixing device 61 Fuse roller 61a Heater 61b Center point 62 Belt Unit 63 Fixing belt 64 Nip guide 64A Nip portion 64a Paper introduction side contact surface 64b Paper discharge side contact surface 64B Belt guide portion 64C First flat surface portion 65 Pressure contact shaft 65A Second flat surface portion 66 Rotating shaft 66a Center point 70 Fixing device 71 Fuser roller 71a Heater 71b Center point 72 Belt unit 73 Fixing belt 74 Nip guide 74A Nip part 74a Paper introduction side contact surface 74b Paper discharge side contact surface 74B Belt guide part 74C Inner peripheral surface 75 Pressure contact shaft 75A Outer peripheral surface 75B times Movement regulating member (protrusion)
76 Rotating shaft 76a Center point 77a Contact part

Claims (5)

  A fuser roller and a belt unit that press-contact each other and nip the paper are provided, the belt unit being wound around an endless fixing belt and the fixing belt so as to be rotatable around the fuser roller. A cylindrical nip guide provided with a concave nip that contacts the paper introduction side and the discharge side of the outer peripheral surface, and a cylindrical inner surface of the nip guide, and the nip guide is swung to the paper introduction side and the discharge side. A fixing device having a pressure contact shaft that is movably supported and biased toward the fuser roller and presses the nip portion of the nip guide against the fuser roller.   2. The fixing device according to claim 1, wherein the contact surfaces of the nip guide and the pressure contact shaft are flat, and the nip guide swings about a rotation axis of the pressure contact shaft. .   2. The contact surface of the nip guide and the pressure contact shaft is curved, and the nip guide swings about a contact portion with the pressure contact shaft. Fixing device.   The inner peripheral surface of the nip guide and the outer peripheral surface of the press contact shaft are circular in cross section having different diameters, respectively, and a rotation restricting portion that restricts excessive rotation of the nip guide alone is provided. The fixing device according to claim 3, wherein:   The fixing device according to claim 4, wherein the rotation restricting portion is a protrusion provided on an inner peripheral surface of the nip guide or an outer peripheral surface of the press contact shaft.

Images