JP2018132738A - Fixation device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device capable of taking a larger contact area between a fixation belt and a heating member with a simpler configuration as much as possible in a belt heating method.SOLUTION: In a fixation device, a fixation nip 69 is formed by depressing a pressure roller 63 that is provided at an outside of a belt circulation path via a fixation belt 61 against a fixation roller 62 provided at an inside of the belt circulation path of an endless fixation belt 61 to make surfaces of the pressure roller 63 and the fixation belt 61 come into contact with each other. The fixation device includes a heating roller 64 disposed at the outside of the belt circulation path and a backup member 66 that is provided at the inside of the belt circulation path to bring the fixation belt 61 into pressure-contact with the heating roller 64. A surface in contact with a belt section 61a of the backup member 66 is a flexure shape along an outer peripheral surface 64a of the heating roller 64.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device and an image forming apparatus for fixing an unfixed image on a recording sheet.

Some image forming apparatuses such as printers include a so-called belt heating type fixing device using a fixing belt.
As a belt heating type fixing device, in Patent Document 1, as shown in FIG. 24, a fixing belt 901 and a fixing route disposed around the fixing belt 901 (hereinafter referred to as “belt rotating route”) are arranged. A roller 902, a heating roller 903, two tension rollers 904, 905, a tension roller 906 arranged outside the belt circulation path, and a fixing roller 902 arranged outside the belt circulation path via the fixing belt 901. The structure provided with the pressure roller 907 to press is disclosed.

The fixing belt 901 is stretched around a fixing roller 902, a heating roller 903, and tension rollers 904 to 906, and the recording sheet S passes through a fixing nip 910 that is a contact area between the pressure roller 907 and the surface of the fixing belt 901. Further, the unfixed image on the recording sheet S is fixed by the heat of the heated fixing belt 901 and the pressure of the pressure roller 907.
The tension roller 906 disposed outside the belt circulation path applies a pressing force in the direction of the arrow α to the portion of the fixing belt 901 between the heating roller 903 and the tension roller 905, whereby the fixing belt 901 is heated. The winding length 911 wound around 903 is increased, that is, the contact area between the fixing belt 901 and the heating roller 903 is increased, and more heat is applied from the heating roller 903 to the fixing belt 901 than in the configuration in which the contact area is small. Is to be supplied.

  In Patent Document 2, a pressure roller is disposed outside the belt circulation path of the cylindrical fixing belt, and the belt rotation is performed while forming a fixing nip by bringing the surface of the fixing belt into contact with the pressure roller. A planar heater is arranged inside the path, and the pressing roller arranged outside the belt circulation path is pressed against the planar heater arranged inside the belt circulation path via the fixing belt, thereby producing a planar shape. A fixing device configured to transmit heat of a heater to a fixing belt is disclosed.

  Such a belt heating method takes a larger contact area (length in the sheet conveyance direction of the fixing nip) between the surface of the fixing belt and the pressure roller than a method in which the pressure roller is directly pressed against the fixing roller. Therefore, the fixing property can be improved.

JP 2016-177206 A Japanese Patent Laying-Open No. 2015-84082

In the configuration of the above-mentioned Patent Document 1, in order to increase the contact area between the fixing belt 901 and the heating roller 903, a large number of tension rollers are required, the number of components increases, and the size of the fixing device increases.
In the configuration of Patent Document 2, the pressing roller presses the fixing belt against the planar heater, but only a part of the fixing belt that is in close contact with the planar heater is in contact with the surface of the pressing roller. The contact area is extremely small. For this reason, the amount of heat supplied per unit time from the planar heater to the fixing belt during the rotation of the fixing belt is reduced. In order to raise the temperature of the fixing belt in a short time with a small amount of heat supplied to the fixing belt, it is conceivable to reduce the thickness of the fixing belt to lower the heat capacity. The amount of heat that can be supplied to the recording sheet passing through the sheet also decreases, and uneven fixing tends to occur. Further, as the fixing belt is made thinner, there is a possibility that the belt is damaged when the belt is meandering.

  The present invention has been made in view of the above-described problems, and in a belt heating system, a fixing device and an image forming device capable of taking a larger contact area between a fixing belt and a heating member with a simple structure as much as possible. The object is to provide a device.

  In order to achieve the above object, a fixing device according to the present invention is disposed on a pressed member disposed on the inner side of a circulation path of an endless fixing belt, on the outer side of the circulation path of the fixing belt via the fixing belt. Fixing by pressing a pressure member to bring the pressure member into contact with the surface of the fixing belt to form a fixing nip, and passing a recording sheet through the fixing nip to fix an unfixed image on the recording sheet An external roller disposed outside a circulation path of the fixing belt; a backup member disposed inside the circulation path of the fixing belt and pressing the fixing belt against the external roller; and the external roller or the A heater that heats the backup member, and a belt portion sandwiched between the external roller and the backup member of the fixing belt is the external roller. So that the curved shape along the outer circumferential surface of, characterized in that the shape of the surface in contact with said belt portion in the backup member are determined.

Moreover, the surface which contacts the said belt part in the said backup member is good also as a curved shape along the outer peripheral surface of the said external roller.
Furthermore, the external roller may be disposed on the opposite side of the pressure member with the fixing belt interposed therebetween.
The pressure member may be a pressure roller, and the member to be pressed may be a pad-shaped fixing pad.

  Here, a support member that supports the member to be pressed is provided, the backup member is long along the rotation axis of the external roller, and the support member is long along the rotation axis of the external roller. A bottom plate portion to which the fixing pad is fixed to a surface facing the fixing pad, and first and second bent from the opposite ends of the bottom plate portion to the side where the backup member is located. The distance between the front end of the first side plate and the front end of the second side plate may be larger than the width of the backup member or the diameter of the external roller. .

Further, the peripheral length of the external roller may be longer than the peripheral length of the fixing belt.
Further, the backup member is elongated along the rotation axis of the external roller, and the width direction of the backup member is on an imaginary line connecting the rotation axis of the external roller and the center position in the sheet conveyance direction of the fixing nip. When the position where the central portion exists is defined as the reference position, the central portion in the width direction of the backup member is located at a position shifted from the reference position to the upstream side in the rotation direction of the external roller around the rotation axis of the external roller. In this case, a corner of the back surface of the backup member that is in contact with the belt portion may be formed in an R shape at the end on the upstream side in the rotation direction of the external roller.

  The backup member is elongated along the rotation axis of the external roller, and the width direction of the backup member is on a virtual line connecting the rotation axis of the external roller and the center position of the fixing nip in the sheet conveyance direction. When the position where the central portion exists is defined as the reference position, the central portion in the width direction of the backup member is located at a position shifted from the reference position to the downstream side in the rotation direction of the external roller around the rotation axis of the external roller. In this case, the corner of the back surface of the backup member that is in contact with the belt portion may be formed in an R shape at the end on the downstream side in the rotation direction of the external roller.

  Further, at least one of the member to be pressed and the pressing member is a roller, and a first driving unit that rotationally drives one of the rollers as a driving roller, and a second that rotationally drives the external roller. Of the driving means and the fixing belt, the peripheral speed of the first portion in contact with the pressure member in the fixing nip, and the peripheral speed of the second portion sandwiched between the external roller and the backup member. Detection means for detecting a difference, and control means for controlling the first drive means and the second drive means, wherein the control means has a predetermined speed at which the peripheral speed of the drive roller corresponds to the recording sheet conveyance speed. In accordance with the first control for adjusting the rotational speed of the driving roller so as to be stable, and the detection result of the detecting means, the rotational speed of the external roller is adjusted so as to eliminate the difference in the peripheral speed. A second control that integer may be to run.

Further, when a line in contact with the most upstream portion in the rotation direction of the outer peripheral surface of the external roller in the region in contact with the fixing belt is a virtual tangent, the fixing belt includes the outer peripheral surface of the external roller and the backup member. The approach angle γ with respect to the virtual tangent line when entering between may be 90 ° or less.
Furthermore, the set which consists of the said external roller, the said backup member, and the said heater further is provided, and the heating area of the axial direction of the external roller in a 1st set among 2 or more sets, and a 2nd set. The heating area in the axial direction of the external roller may be different.

The heater may heat the external roller, and the thermal conductivity of the backup member may be smaller than the thermal conductivity of the fixing belt.
Furthermore, the heater may heat the external roller, and a surface of the backup member that contacts the belt portion may have a mesh structure.
In addition, a first moving means capable of moving the external roller toward and away from the backup member via the fixing belt, and controlling the first moving means so that the fixing belt is rotated around Move the external roller closer to the backup member, press the fixing belt against the external roller by the backup member, and move the external roller away from the backup member while the fixing belt is stopped. It is good also as providing the 1st movement control means to which it moves to a direction and cancels | releases the said press-contact.

  And a first movement means capable of moving the outer roller and the backup member in a relatively approaching direction and a moving away direction, and a first movement control means for controlling the first movement means, and the fixing. A first fixing mode in which the belt orbits at a first speed and a second fixing mode in which the belt orbits at a second speed slower than the first speed can be switched, and the first movement control means includes: When the second fixing mode is executed, the backup roller and the external roller are moved in a direction farther away than when the first fixing mode is executed, so that the external roller and the fixing belt are moved. It is also possible to reduce the contact area.

  A second moving means capable of moving the pressed member and the pressing member in a relatively approaching direction and a moving away direction via the fixing belt; and controlling the second moving means, During the rotation of the fixing belt, the pressed member and the pressing member are moved in a relatively approaching direction, and the pressing member is pressed against the pressed member via the fixing belt. A second movement control means for releasing the pressure by moving the pressed material and the pressing member relatively away from each other while forming the fixing nip and stopping the fixing belt. , May be provided.

The backup member may include a base and a low friction sheet interposed between the base and the belt portion to reduce friction with the belt portion.
Furthermore, a lubricant may be applied to the inner surface of the fixing belt and the surface of the backup member that contacts the belt portion.
Further, a low friction layer for reducing friction with the backup member may be provided on the inner surface of the fixing belt.

Furthermore, it is good also as providing the cleaning member which contacts the surface of the said external roller, and removes the foreign material adhering to the surface of the said external roller.
Further, a release layer may be provided on the surface of the external roller.
An image forming apparatus according to the present invention is an image forming apparatus including a fixing unit that fixes an unfixed image formed on a conveyed recording sheet, and includes the above-described fixing device as the fixing unit. And

  As described above, the shape of the surface in contact with the belt portion of the backup member is determined so that the belt portion of the fixing belt sandwiched between the external roller and the backup member has a curved shape along the outer peripheral surface of the external roller. Therefore, the contact area between the external roller or backup member heated by the heater and the fixing belt can be increased with a simple configuration, and the heat of the external roller or backup member is supplied to the fixing belt more efficiently. It becomes possible.

1 is a schematic diagram illustrating an overall configuration of a printer according to a first embodiment. FIG. 2 is a block diagram illustrating a configuration of a control unit of a printer. FIG. 2 is a diagram illustrating a configuration of a fixing unit of a printer. It is a figure which shows the backup member, the fixing belt, and the heating roller in a state of being separated from each other. (A)-(c) is a schematic diagram which shows in stepwise the operation | movement which puts a heating roller close to a backup member from the state shown in FIG. 4, and pinches | interposes a fixing belt with a backup member and a heating roller. It is a figure which shows the structure of a comparative example. It is a figure which shows the example which provides a belt guide in a backup member. 6 is a diagram illustrating a configuration of a fixing unit according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a modification of the fixing unit according to the second embodiment. FIG. 10 is a diagram illustrating another modification of the fixing unit according to the second embodiment. 6 is a diagram illustrating a configuration of a fixing unit according to Embodiment 3. FIG. It is an enlarged view of the end of the backup member on the upstream side in the belt circumferential direction. 10 is a diagram illustrating a modification of the fixing unit according to Embodiment 3. FIG. FIG. 10 is a diagram illustrating a configuration of a fixing unit according to a fourth embodiment. It is a figure which shows the flowchart of 2nd control. FIG. 10 is a diagram schematically showing a force P that acts on a heating roller from a fixing belt during the circumferential running of the fixing belt in the fifth embodiment. FIG. 10 is a diagram illustrating a part of a circulation path of a fixing belt in a fixing unit according to a fifth embodiment. FIG. 10 is a diagram illustrating a modification of the fixing unit according to the fifth embodiment. (A) And (b) is a figure which shows the structure of the fixing | fixed part which concerns on Embodiment 6. FIG. It is a flowchart which shows the content of control of conveyance of a plain paper and a thick paper, and the position switching of a heating roller. 18 is a flowchart showing the contents of control for switching a heating roller between a separation position and a contact position in the seventh embodiment. It is a figure which shows the modification of a fixing | fixed part. FIG. 23 is a side view of a heating roller, a heater, and a fixing belt in the fixing unit illustrated in FIG. 22. It is a figure which shows the structural example of the conventional fixing device of a belt heating system.

Hereinafter, a case where the embodiments of the fixing device and the image forming apparatus according to the present invention are applied to a tandem color printer (hereinafter simply referred to as “printer”) will be described as an example.
[Embodiment 1]
(1) Configuration of Printer FIG. 1 is a schematic front view showing the configuration of the printer 1.

As shown in FIG. 1, the printer 1 includes an image forming unit 3, an intermediate transfer unit 4, a feeding unit 5, a fixing unit 6, a control unit 7, an operation panel 8, and the like.
When the printer 1 is connected to a network (for example, LAN) and receives a print job execution instruction from an external terminal device (not shown), the printer 1 forms a color toner image based on the instruction, and the formed toner image is displayed. A color image is formed by transfer to a recording sheet.

The image forming unit 3 includes image forming units 3Y, 3M, 3C, and 3K and an exposure unit 10.
The image forming unit 3K includes a photosensitive drum 31 that rotates in a direction indicated by an arrow A, a charging unit 32, a developing unit 33, and a cleaner 34 for cleaning the photosensitive drum 31 disposed around the photosensitive drum 31. Then, a black (K) toner image is formed on the photosensitive drum 31.
The image forming units 3Y, 3M, and 3C have basically the same configuration as the image forming unit 3K, and the reference numerals are omitted in FIG. The image forming unit 3Y forms a yellow (Y) toner image, the image forming unit 3M forms a magenta (M) toner image, and the image forming unit 3C uses a cyan (C) color image. Create a toner image. In the above description, the photosensitive drum 31 is used as the image carrier. However, the configuration is not limited thereto, and for example, a photosensitive belt can be used.

The intermediate transfer unit 4 includes a drive roller 42, a driven roller 43, a primary transfer roller 44, a secondary transfer roller 45, and the like in addition to the intermediate transfer belt 41 disposed above the image forming units 3Y to 3K. Yes.
The intermediate transfer belt 41 is stretched around a driving roller 42, a driven roller 43, and a primary transfer roller 44 disposed corresponding to each of the image forming units 3Y to 3K, and is driven in a direction indicated by an arrow B. Is done.

The primary transfer roller 44 is disposed to face the photosensitive drum 31 via the intermediate transfer belt 41 for each of the image forming units 3Y to 3K. The secondary transfer roller 45 is disposed to face the drive roller 42 with the intermediate transfer belt 41 interposed therebetween.
The exposure unit 10 is arranged below the image forming units 3Y to 3K, and generates light beams Ly, Lm, Lc, and Lk for image formation of Y to K colors by the drive signal from the control unit 7 in the image forming unit 3Y. Each of .about.3K is emitted toward the photosensitive drum 31 charged by the charging unit 32 of the image forming unit, and the photosensitive drum 31 is irradiated to perform exposure scanning. By this exposure scanning, electrostatic latent images are formed on the respective photosensitive drums 31 of the image forming units 3Y to 3K.

For each of the image forming units 3Y to 3K, the electrostatic latent image formed on the photosensitive drum 31 of the image forming unit is developed with the developer of the developing unit 33, thereby corresponding to the image forming unit. A toner image of the color to be formed is formed on the photosensitive drum 31.
The toner image formed on the photosensitive drum 31 is primarily transferred to the intermediate transfer belt 41 by the primary transfer roller 44 for each of the image forming units 3Y to 3K. At this time, the image forming operations for the respective colors are executed at different timings so that the toner images are superimposed and transferred at the same position on the intermediate transfer belt 41.

For each of the image forming units 3Y to 3K, of the toner image on the photosensitive drum 31 during the primary transfer, residual toner that remains on the photosensitive drum 31 without being transferred to the intermediate transfer belt 41 is removed by a cleaner. 34 is removed from the photosensitive drum 31.
The feeding unit 5 includes a paper feeding cassette 51 that stores recording sheets S, a feeding roller 52 that feeds the sheets S in the paper feeding cassette 51 one by one onto the conveyance path 53, and two fed sheets S. A timing roller 54 that conveys the sheet S at a timing at which the next transfer roller 45 is sent to the secondary transfer position 46 in contact with the intermediate transfer belt 41 is provided.

The timing roller 54 conveys the sheet S to the secondary transfer position 46 in synchronization with the timing at which the Y to K color toner images transferred onto the intermediate transfer belt 41 are conveyed to the secondary transfer position 46. Then, when the sheet S passes the secondary transfer position 46, the toner image on the intermediate transfer belt 41 is secondarily transferred onto the sheet S by the secondary transfer roller 45.
The sheet S on which the toner image is secondarily transferred at the secondary transfer position 46 is conveyed to the fixing unit 6.

The fixing unit 6 is disposed above the secondary transfer position 46 and heat-fixes the toner image (unfixed image) on the sheet S conveyed by the secondary transfer roller 45 by heating and pressing. The sheet S that has passed through the fixing unit 6 is discharged out of the apparatus by a discharge roller 55 and is stored in a discharge tray 56.
The operation panel 8 is disposed at a position where the user can easily operate when standing in front of the printer 1, here, at a position on the front side of the apparatus on the upper surface of the apparatus main body 2, and accepts execution instructions of various jobs from the user. A selection key for receiving a selection instruction of a job to be executed, a key for receiving a selection input of a type of sheet to be used, for example, plain paper, thick paper, and the like. Information received on the operation panel 8 is sent to the control unit 7.

(2) Configuration of Control Unit FIG. 2 is a block diagram showing the configuration of the control unit 7.
As shown in the figure, the control unit 7 includes a communication interface (I / F) unit 7a, a CPU 7b, a ROM 7c, a RAM 7d, and the like, which can communicate with each other.
The communication I / F unit 7a is an interface such as a LAN card or a LAN board for connecting to a network, for example, a LAN, and communicates with an external terminal device connected via the network.

  Based on information from the operation panel 8, the CPU 7b controls the image forming units 3Y to 3K, the exposure unit 10, the intermediate transfer unit 4, the feeding unit 5, and the fixing unit 6 to execute a print job smoothly. The ROM 7c stores a program necessary for controlling each unit such as the image forming units 3Y to 3K, and the program is read by the CPU 7b. The RAM 7d is used as a work area for the CPU 7b.

(3) Configuration of Fixing Unit 6 FIG. 3 is a diagram illustrating a configuration of the fixing unit 6.
As shown in the figure, the fixing unit 6 includes an endless fixing belt 61, a fixing roller 62 (fixing member), a pressure roller 63 (pressure member), a heating roller 64 (external roller), and a heater 65. And a backup member 66 and the like.

The fixing belt 61 has a cylindrical shape with an outer diameter of, for example, 40 mm, and runs around in the direction of arrow F following the pressure roller 63 that rotates in the direction of arrow E. The circumferential direction of the fixing belt 61 is referred to as a belt circumferential direction, and the width direction (corresponding to the Y-axis direction) of the fixing belt 61 orthogonal to the belt circumferential direction is referred to as a belt width direction.
The fixing belt 61 is formed by laminating an elastic layer and a surface layer in this order on a base layer. For example, PI (polyimide) resin is used as the material of the base layer, and the thickness of the base layer is, for example, 80 μm. For example, Si (silicone) rubber is used as the material of the elastic layer, and the thickness of the elastic layer is, for example, 200 μm. For example, a PFA (perfluoroalkoxyalkane) tube is used as the material of the surface layer, and the thickness of the surface layer is, for example, 30 μm. The base layer is the inner surface (back surface) side of the fixing belt 61, and the surface layer is the front surface side of the fixing belt 61. Needless to say, the material and thickness of each layer are not limited to these. Moreover, it is not restricted to 3 layers, The structure provided with 1 layer or 2 or more layers may be sufficient. The material, thickness, number of layers, and the like are not limited, and the same applies to each member such as the fixing roller 62 described later.

  The fixing roller 62 is disposed on the inner side of a circulation path of the fixing belt 61 (belt rotation path: corresponding to a travel path indicated by a thick line in the drawing). The fixing roller 62 has an outer diameter of, for example, 30 mm, and an elastic layer 62b such as silicone rubber and a sponge layer 62c are laminated in this order on the surface of a solid iron core 62a. The diameter of the cored bar 62a is, for example, 18 mm, the thickness of the elastic layer 62b is, for example, 4 mm, and the thickness of the sponge layer 62c is, for example, 2 mm. The length of the fixing roller 62 in the axial direction (perpendicular to the paper surface: corresponding to the direction orthogonal to the conveyance direction D of the sheet S) is slightly longer than the width of the sheet S (length in the direction orthogonal to the conveyance direction D). ing. The length in the axial direction is the same for the fixing belt 61, the pressure roller 63, the heating roller 64, the heater 65, and the backup member 66.

Both ends in the axial direction of the cored bar 62a of the fixing roller 62 are rotatably supported by a frame (not shown) of the fixing unit 6, and can be rotated in the direction of arrow C by being driven by the fixing belt 61.
The pressure roller 63 is outside the belt circulation path, and is disposed at a position opposite to the fixing roller 62 inside the belt circulation path with the fixing belt 61 interposed therebetween. The pressure roller 63 has an outer diameter of, for example, 30 mm, and an elastic layer 63b such as silicone rubber and a surface layer 63c such as a PFA tube are laminated in this order on the surface of a solid iron core 63a. The diameter of the cored bar 63a is, for example, 26 mm, the thickness of the elastic layer 63b is, for example, 2 mm, and the thickness of the surface layer 63c is, for example, 20 μm.

The pressure roller 63 is urged by a spring or the like while being supported so that both ends in the axial direction are rotatable with respect to the frame of the fixing unit 6 and movable in the direction approaching the fixing roller 62 (arrow Ha) and the direction moving away (arrow Hb). The member (not shown) is always urged in the direction approaching the fixing roller 62 (arrow Ha).
By this urging force, the pressure roller 63 presses the fixing roller 62 via the fixing belt 61. In the figure, an example is shown in which the sponge layer 62c of the fixing roller 62 is recessed inward due to this pressing. By this pressing, a region (fixing nip) 69 where the pressure roller 63 is in pressure contact with the surface of the fixing belt 61 is secured. This pressure contact force (nip load) can be set to 100 to 400 N, for example. The length (nip width) of the fixing nip 69 in the sheet conveyance direction can be set to 7 mm, for example. The pressure roller 63 is rotationally driven in the direction of arrow E by the rotational driving force from the drive motor 67.

The heating roller 64 is outside the belt circulation path, and is disposed on the opposite side of the pressure roller 63 with the fixing belt 61 interposed therebetween.
The heating roller 64 has, for example, an aluminum cylindrical shape having an outer diameter of 20 mm and a thickness of 0.5 mm, and a surface layer made of PTFE (polytetrafluoroethylene) having a thickness of 40 μm is laminated on the surface. Both ends of the heating roller 64 in the axial direction are rotatably supported by the frame of the fixing unit 6 and can rotate in the direction of arrow G.

The heater 65 is a rod-shaped, for example, 1000 W halogen heater, and is inserted into a cylindrical heating roller 64. Heat generated from the heater 65 is transmitted to the heating roller 64.
The backup member 66 is a plate-like member having an arc shape in cross section, is located inside the belt circulation path, and is positioned on the opposite side of the heating roller 64 disposed outside the belt circulation path with the fixing belt 61 interposed therebetween. It is arranged in.

  FIG. 4 is a view showing the backup member 66, the fixing belt 61, and the heating roller 64 in a state of being separated from each other in order to make the configuration of the backup member 66 easy to understand. A state in which the fixing belt 61 is not in contact with both the backup member 66 and the heating roller 64 is referred to as a natural state. In the natural state, an external force is not applied to the belt portion 61 a to be sandwiched between the heating roller 64 and the backup member 66 in the fixing belt 61, and the belt portion 61 a is viewed from the axial direction of the heating roller 64. The shape of the belt portion 61a is an arc shape that is curved in a direction opposite to the direction of curvature of the outer peripheral surface 64a of the opposed heating roller 64.

The backup member 66 includes a base 71, a pressing rubber 72, a sliding sheet 73, and the like.
The base 71 is a curved plate-like member along the outer peripheral surface 64a of the heating roller 64, and is made of, for example, PI (polyimide) resin and has a thickness of 2 mm.
The pressing rubber 72 is a plate-like silicone rubber that is attached to the curved surface 71a on the inner side of the base 71 and is curved along the curved surface 71a, and has a thickness of 2 mm, for example.

The sliding sheet 73 is a sheet having a mesh structure such as a glass cloth impregnated with a fluororesin, and the contact area with the fixing belt 61 is reduced due to unevenness on the surface, thereby reducing the frictional resistance with the fixing belt 61. Let
One end side 73 a of the sliding sheet 73 is fixed to the curved surface 71 b outside the base 71, the other end side 73 b is a free end, and the other end side 73 b is a curved surface inside the fixing belt 61 and the inside of the pressing rubber 72. It hangs down from the upper end of the base 71 in a state of being positioned between 72a.

FIG. 5 is a schematic diagram showing stepwise the operation of sandwiching the fixing belt 61 between the backup member 66 and the heating roller 64 by bringing the heating roller 64 and the heater 65 together with the backup member 66 from the state shown in FIG. The members other than the fixing belt 61, the heating roller 64, the heater 65, and the backup member 66 are not shown.
FIG. 5A shows the same state as the natural state shown in FIG. 5B, the belt portion 61a of the fixing belt 61 is pressed by the heating roller 64 to the side where the backup member 66 is located, and is slightly depressed from the natural state to the side where the backup member 66 is located. The state which deform | transformed into the shape along the surface 64a is shown. This deformed shape corresponds to an inversely curved shape that is curved in a direction opposite to the curve direction of the belt portion 61a in the natural state (FIG. 5A).

  FIG. 5C shows a state in which the heating roller 64 is further brought closer to the backup member 66 from FIG. 5B and the heating roller 64 is pressed against the backup member 66 through the fixing belt 61. This state corresponds to the state shown in FIG. 3, and the reversely curved belt portion 61 a is in pressure contact with the heating roller 64 while being in pressure contact with the pressing rubber 72 via the sliding sheet 73. A surface of the sliding sheet 73 that is in contact with the fixing belt 61 is a surface 66b (FIG. 3) of the backup member 66 that is in contact with the fixing belt 61.

  In the belt portion 61a deformed to bend in a direction opposite to the natural state, a direction to cancel the reverse curve shape and return to the original cylindrical state of the natural state (inflating direction: arrow J direction in FIG. 5B) ) Self-restoring force acts. The belt portion 61a is easily brought into close contact with the outer peripheral surface 64a of the heating roller 64 by the action of the self-restoring force of the belt portion 61a and the restoring force of the pressing rubber 72, and the curved backup member along the outer peripheral surface 64a of the heating roller 64 As a result, the contact area between the heating roller 64 as a heating source and the fixing belt 61 can be increased.

On the other hand, if a configuration (comparative example) in which the fixing belt 61 is simply wound around the heating roller 64 and the fixing roller 62 as shown in FIG.
That is, in the comparative example shown in FIG. 6, the belt portion 61b in contact with the heating roller 64 of the fixing belt 61 tends to swell in the direction of the arrow Ja (the direction away from the heating roller 64) by the self-restoring force. The contact area with the heating roller 64 cannot be increased.

  In order to increase the contact area in the configuration of the comparative example shown in FIG. 6, tension rollers as shown by the broken lines 68a and 68b are arranged, and the circulation path of the fixing belt 61 is changed to the path shown by the broken line 61d. A configuration in which the winding length of the fixing belt 61 around the heating roller 64 is longer can be considered. However, this configuration is substantially the same as the example shown in FIG. 24, and the number of components is increased. In addition, when the tension roller is arranged, it is necessary to secure the installation space, so in practice, the interval between the heating roller 64 and the fixing roller 62 must be further widened, and the size of the fixing device is increased.

  On the other hand, in the configuration of the embodiment shown in FIG. 3, the self-restoring force of the belt portion 61 a of the fixing belt 61 acts in a direction approaching the heating roller 64, so that the belt portion 61 a itself tries to adhere to the heating roller 64. The contact area with the heating roller 64 can be increased without increasing the pressing force for pressing the belt portion 61a against the heating roller 64 by the backup member 66. Further, since the contact area can be increased, the driving force in the circumferential direction of the fixing belt 61 is easily transmitted to the heating roller 64, and the heating roller 64 is smoothly driven to rotate. Thereby, it is suppressed that the heat transmitted from the heater 65 to the belt portion 61a via the heating roller 64 varies from one position in the belt rotation direction to another position as compared with the case where the rotation unevenness occurs in the heating roller 64, The amount of heat supplied to the fixing belt 61 can be equalized in the belt rotation direction, and temperature fluctuations in the fixing nip 69 can be further reduced.

FIG. 5 described above describes an example in which the heating roller 64 is positioned close to the backup member 66 during the actual assembly of the fixing unit 6. Instead, for example, the backup member 66 is brought close to the heating roller 64. It is possible to adopt a configuration for performing the positioning operation.
Specifically, the backup member 66 is supported by the frame of the fixing unit 6 so as to be movable in the perspective direction with respect to the heating roller 64, and the backup member 66 is attached to the belt portion of the fixing belt 61 when the fixing unit 6 is assembled. When the belt portion 61a is brought into pressure contact with both the heating roller 64 and the backup member 66 as shown in FIG. 5C, the positioning is completed. The operation of fixing 66 to the frame of the fixing unit 6 with a screw or the like can be performed.

  Returning to FIG. 3, when the drive motor 67 is rotationally driven, the rotational driving force is transmitted to the pressure roller 63, and when the pressure roller 63 is rotated in the direction of arrow E, the pressure roller 63 is rotationally driven. The force is transmitted to the fixing belt 61 and the fixing roller 62 that are pressed against each other at the fixing nip 69, and the fixing belt 61 is driven to rotate in the direction of arrow F while the fixing belt 61 is driven to rotate in the direction of arrow C. Then, the driving force in the circumferential direction of the fixing belt 61 that travels around is transmitted to the heating roller 64, whereby the heating roller 64 is driven to rotate in the direction of arrow G.

  In the above configuration, when the heater 65 is energized while the pressure roller 63 is driven to rotate, the heat generated from the heater 65 is fixed between the heating roller 64 and the heating roller 64 and the backup member 66. The belt 61 reaches the fixing nip 69 as the fixing belt 61 travels around the belt 61 a. As a result, heat from the heater 65 is supplied to the fixing nip 69.

In this embodiment, although not shown, a sensor that detects the surface temperature of the fixing belt 61 and sends the detection result to the control unit 7 is disposed in the fixing unit 6. Based on the temperature detected by the sensor, the controller 7 performs temperature control that switches on and off the heater 65 so that the temperature of the fixing nip 69 is maintained at a fixing temperature necessary for fixing (for example, 170 ° C.).
By this temperature control, the temperature of the fixing nip 69 is stabilized at the fixing temperature, and when the sheet S after secondary transfer conveyed along the conveyance path 53 along the arrow D direction passes through the fixing nip 69. The unfixed toner image on the sheet S is heated and melted and pressed to be fixed on the sheet S.

  In the configuration shown in FIG. 3, the belt rotation direction of the belt portion 61 a of the fixing belt 61 sandwiched between the heating roller 64 and the backup member 66 and the rotation direction (roller rotation direction) of the heating roller 64 are the same direction. . Of the fixing belt 61, a portion 61 f that is wound around an upstream end 66 f of the backup member 66 in the belt circumferential direction (roller rotation direction) has a bent shape with a certain degree of curvature, and the roller rotation of the backup member 66. A portion 61g wound around the end 66g on the downstream side in the direction also has a bent shape having a certain degree of curvature.

  However, the belt portion 61 a is only pressed against the heating roller 64 by the restoring force of the pressing rubber 72 of the backup member 66, and the restoring force of the pressing rubber 72 is not so strong. The friction between the belt portions 61a is considerably reduced. As a result, the bending (deformation) of the upstream end 61f and the downstream end 61g of the fixing belt 61 does not cause a large load on the fixing belt 61, and the life of the fixing belt 61 may be shortened. Absent.

As described above, in the present embodiment, the belt portion 61 a of the fixing belt 61 sandwiched between the heating roller 64 and the curved backup member 66 along the outer peripheral surface 64 a of the heating roller 64 is the heating roller 64. The curved shape along the outer peripheral surface 64a, that is, the curved shape is deformed into a reverse curved shape (concave shape) opposite to the natural state.
Since the self-restoring force of the belt portion 61a deformed into the reversely curved shape acts in a direction approaching the heating roller 64, the belt portion 61a itself is easily brought into close contact with the heating roller 64, and the contact area with the heating roller 64 can be increased. The heat of the heating roller 64 can be efficiently supplied to the fixing belt 61 without arranging components such as a tension roller. In addition, since the contact area with the heating roller 64 can be widened, the fixing belt 61 can be sufficiently heated even if the fixing belt 61 is thick.

  In the above description, the backup member 66 is configured by the base 71, the pressing rubber 72, and the sliding sheet 73, but is not limited thereto. For example, as shown in the schematic diagram of FIG. 7, a curved belt guide 77 extending from the upstream end 71d in the belt circumferential direction of the arc-shaped base 71 toward the upstream side is provided, and from the downstream end 71e to the downstream side. It is also possible to employ a configuration in which a curved belt guide 78 extending toward the surface is provided.

The fixing belt 61 traveling around is guided on belt guides 77 and 78 serving as guide portions, so that the fixing belt 61 can be prevented from swinging during the traveling around and the fixing belt 61 can travel more stably. It becomes possible.
[Embodiment 2]
In the first embodiment, the configuration example in which the fixing roller 62 is provided as a fixing member disposed to face the pressure roller 63 via the fixing belt 61 has been described. However, in the second embodiment, a pad is used instead of the roller. This point is different from the first embodiment. Hereinafter, in order to avoid duplication of description, the description of the same contents as those of Embodiment 1 is omitted, and the same components are denoted by the same reference numerals.

FIG. 8 is a diagram illustrating a configuration of the fixing unit 6 according to the second embodiment.
As shown in the figure, a fixing pad 162 and a supporting member 170 for supporting the fixing pad 162 are provided as a fixing member disposed to face the pressure roller 63 via the fixing belt 61. By using the fixing pad 162, it is possible to reduce the size and heat capacity compared to the fixing roller.

As a material for the fixing pad 162, for example, rubber, more specifically, silicone rubber can be used. For example, resin, more specifically, LCP (liquid crystal polymer), PPS (polyphenylene sulfide), or the like is used. Can do.
As in the first embodiment, the pressure roller 63 presses the fixing pad 162 through the fixing belt 61 to secure the nip load (nip pressure) of the fixing nip 69. The fixing nip 69 is as described above. It becomes quite heavy. In order to secure this high load, it is almost not sufficient to dispose the fixing pad 162. Therefore, in the present embodiment, the supporting member 170 that supports the fixing pad 162 is disposed and the supporting member 170 is also disposed. The one with high rigidity is used.

The support member 170 is a member formed by bending a flat plate member into a U-shape in cross section as shown in the figure, and is long along the axial direction of the pressure roller 63, and both ends in the longitudinal direction. Is fixed to the frame of the fixing unit 6.
The support member 170 includes a bottom plate portion 171 to which the fixing pad 162 is fixed, and first and second side plate portions 172 and 173 that are bent from both lateral ends of the bottom plate portion 171 to the side where the backup member 66 is located. . By forming the U-shaped cross section, the bending rigidity in the pressing direction (in the direction of the arrow Ha) by the pressure roller 63 can be increased compared to a configuration using a flat plate, and the fixing nip 69 has a high load. A nip pressure can be applied.

  The distance in the short direction (Z-axis direction) between the tip 172a of the first side plate 172 and the tip 173a of the second side plate 173 of the support member 170 is Wa, and the width in the short direction of the backup member 66 is When Wb is set, the configuration has a relationship of Wa> Wb. With this configuration, in the space 179 between the first and second side plate portions 172 and 173 of the support member 170, the central portion of the backup member 66 in the roller rotation direction (most of the backup member 66 to the bottom plate portion 171 of the support member 170 is provided. 66a can be accommodated, the distance between the heating roller 64 and the pressure roller 63 in the X-axis direction can be narrowed, and the dimension of the fixing unit 6 in the X-axis direction can be further reduced. In addition, the fixing unit 6 can be downsized.

  In the case of the configuration shown in the figure, the fixing unit 6 can be reduced in size in the X-axis direction, but the fixing belt 61 is located downstream of the fixing nip 69 in the belt circumferential direction and upstream of the backup member 66 in the belt circumferential direction. The curvatures of the respective circumferential paths of the belt portion 61p downstream of the belt portion 61p and the backup member 66 in the belt circumferential direction and upstream of the fixing nip 69 in the belt circumferential direction are larger than those of the configuration of the first embodiment.

  This means that the deformation of the fixing belt 61 becomes larger, and the burden on the fixing belt 61 increases. If the load on the fixing belt 61 increases and the service life is affected, as shown in FIG. 9, the distance between the heating roller 64 and the pressure roller 63 is slightly wider than the configuration of FIG. Thus, by reducing the curvature of the circulation path of the belt portions 61p and 61q of the fixing belt 61, the curvature of the belt portions 61p and 61q can be reduced to reduce the burden on the fixing belt 61.

In the configuration shown in FIGS. 8 and 9, the tips of the first side plate portion 172 and the second side plate portion 173 of the support member 170 are in contact with the back surface 61 z of the fixing belt 61 while the fixing belt 61 is traveling around. If there is a possibility of contact, the belt guides 77 and 78 shown in FIG. 7 may be provided.
Further, depending on the configuration of the apparatus, there may be a configuration in which the nip load of the fixing nip 69 can be made lower than the above-described high load. In such a configuration, the support member 170 may have a low bending rigidity. . In such a case, as shown in FIG. 10, by extending the lengths 17a and 17b from the bottom plate portion 171 of the first side plate portion 172 and the second side plate portion 173 of the support member 170, the side plate portion The dimensions of 172 and 173 can be reduced. In this configuration, as shown in the figure, the interval Wa and the width Wb may have a relationship of Wa <Wb. Since the support member 170 itself becomes small, the heat capacity can be reduced accordingly.

Further, as in the configuration of FIG. 10, for example, if the relationship that the circumference of the heating roller 64 (external roller) is longer than the circumference of the fixing belt 61 is satisfied, the area on the heating side is larger than the circumference of the belt. Therefore, heating unevenness in the circumferential direction of the fixing belt 61 can be suppressed.
Further, when the outer diameter of the heating roller 64 is Wh, a configuration satisfying the relationship of Wa>Wb> Wh or a configuration satisfying the relationship of Wa>Wh> Wb can be adopted.

[Embodiment 3]
In the first embodiment, the configuration example in which the heating roller 64, the backup member 66, the fixing roller 62, and the pressure roller 63 are arranged so as to be aligned on one straight line has been described, but in the third embodiment, the configuration is described. The position of the backup member 66 is arranged at a position slightly deviated from the straight line in the circumferential direction of the heating roller 64, and this is different from the first embodiment.

FIG. 11 is a diagram illustrating a configuration of the fixing unit 6 according to the third embodiment.
As shown in the figure, the rotation axis of the heating roller 64 is 64e, the position of the fixing nip 69 in the center of the sheet conveyance direction is 69e, the central portion of the backup member 66 in the bending direction (corresponding to the central portion in the width direction) is 66a, and the heating roller 64 The imaginary line (first imaginary line) connecting the rotation shaft 64e of the fixing nip 69 and the position 69e in the center of the sheet conveyance direction of the fixing nip 69 is 301, and the width direction central portion 66a of the backup member 66 exists on the imaginary line 301 (implementation) In the third embodiment, the central portion 66a in the width direction of the backup member 66 is heated from the reference position around the rotation shaft 64e of the heating roller 64. The configuration is such that the roller 64 is shifted by an angle θa on the upstream side in the rotational direction.

  When the pressure roller 63 is on the driving side, in the configuration in which the backup member 66 is positioned at the reference position, the belt portion 61q of the fixing belt 61 tends to be pulled and the belt portion 61p tends to become loose. When the slack of the belt portion 61p increases (see 61u in FIG. 13), the angle θb formed between the recording sheet S that has passed through the fixing nip 69 and the surface of the fixing belt 61 decreases, and the recording sheet S comes from the fixing belt 61. Separability is likely to decrease.

  In order to eliminate the slack of the belt portion 61p of the fixing belt 61, it is only necessary to apply a tension to the belt portion 61p. To apply a tension to the belt portion 61p, the other belt portion 61q is intentionally slackened. It ’s fine. As a configuration that makes the belt portion 61q slack, the configuration in which the backup member 66 is disposed at a position that is shifted from the reference position by an angle θa on the upstream side in the rotation direction of the heating roller 64 is employed.

  With this configuration, the angle θb can be increased, so that the separation of the recording sheet S can be improved. If tension is applied to the belt portion 61p, an end portion 61f on the upstream side in the belt circumferential direction of the belt portion 61a of the fixing belt 61 sandwiched between the heating roller 64 and the backup member 66 and the end of the backup member 66 corresponding thereto. The contact pressure with the portion 66f increases, and the load on the bent belt portion 61f also increases.

For this reason, as shown in the enlarged view of FIG. 12, the belt 66 is bent by applying an R shape to the corners 66p, 66q of the upstream end 66f of the backup member 66 in the roller rotation direction G (belt rotation direction F). It is desirable to reduce the load on the portion 61f.
If the separation of the recording sheet S from the fixing belt 61 hardly deteriorates, the configuration shown in FIG. 13 can be adopted.

Specifically, the central portion 66a in the curving direction of the backup member 66 is located at a position shifted from the reference position by the angle θc on the downstream side in the rotation direction of the heating roller 64 around the rotation axis 64e of the heating roller 64. .
In the case of this configuration, it is desirable that the corner portions 661 and 662 (see FIG. 12) of the end portion 66g on the downstream side in the roller rotation direction (belt rotation direction) of the backup member 66 be formed in the same manner as described above.

  In the above description, when the backup member 66 is not positioned at the reference position, an R shape is provided at the corner of the upstream end 66f or the downstream end 66g of the backup member 66 in the roller rotation direction. However, it is not limited to this. For example, even in the configuration of the first embodiment in which the backup member 66 is located at the reference position, each of the corners of the upstream end portion 66f and the downstream end portion 66g of the backup member 66 in the roller rotation direction has an R shape. May be provided.

[Embodiment 4]
In the first to third embodiments, the configuration example in which the pressure roller 63 is on the driving side and the fixing belt 61, the fixing roller 62, and the heating roller 64 are on the driven side has been described, but in the fourth embodiment, The pressure roller 63 and the heating roller 64 are configured to be separate drive sides, and this is different from the first to third embodiments.

FIG. 14 is a diagram illustrating a configuration of the fixing unit 6 according to the fourth embodiment.
As shown in the figure, a drive motor 67a for rotating the heating roller 64 is arranged separately from the drive motor 67 for rotating the pressure roller 63, and the drive motors 67 and 67a can be driven separately. It has become. In the fourth embodiment, a fixing pad 162 similar to that in the second embodiment is disposed as a member to be pressed that is disposed to face the pressure roller 63 with the fixing belt 61 interposed therebetween.

The rotation driving force from the pressure roller 63 is transmitted to the belt portion 61m (the portion constituting the fixing nip 69) in contact with the pressure roller 63 in the fixing belt 61, and the heating roller 64 and the backup member 66 are transmitted. The rotational driving force from the heating roller 64 is transmitted to the belt portion 61a sandwiched between the two.
In the configuration in which the rotational driving force from the pressure roller 63 is transmitted only to the belt portion 61m as in the first to third embodiments, the backup is performed when the belt portion 61a passes between the heating roller 64 and the backup member 66. Due to the sliding resistance with the member 66, the peripheral speed of the belt portion 61a is likely to vary. When fluctuation occurs with respect to the case where the peripheral speed of the belt portion 61m is constant, one of the belt portions 61p and 61q is likely to be loosened and the other is easily pulled, and the fixing belt 61 is deformed during the circular running. It becomes easy.

Therefore, in the fourth embodiment, in order to suppress the deformation of the fixing belt 61 due to the change in the peripheral speed, the rotational driving force is transmitted to each of the belt portions 61m and 61a independently. The configuration is such that the peripheral speeds of the belt portions 61m and 61a are individually controlled so that the peripheral speed difference of 61a does not occur.
Specifically, first detection means such as an encoder that detects the rotation speed of the rotation shaft of the pressure roller 63 is arranged, and the peripheral speed of the pressure roller 63 can be detected.

  Further, a lever 11 a that is in contact with the inner surface 611 of the belt portion 61 q of the fixing belt 61 is disposed inside the circulation path of the fixing belt 61. The lever 11a is always in contact with the inner surface 611 of the belt portion 61q by its own weight, and is displaced up and down following up and down fluctuations (positions indicated by a solid line, a broken line, and a one-dot chain line) of the belt portion 61q. Here, on the basis of the position of the solid line, the position of the broken line indicates the state where the tension is generated, and the position of the alternate long and short dash line indicates the state where the slack is generated.

When the peripheral speed of the belt portion 61m is constant (reference value), when the peripheral speed of the belt portion 61a becomes slower than the reference value, the belt portion 61q is pulled and becomes a bit (dashed line), and the position of the lever 11a is raised. . At this time, the belt portion 61p becomes loose.
On the other hand, when the peripheral speed of the belt portion 61a becomes faster than the reference value, the belt portion 61q becomes loose (dashed line), and the position of the lever 11a is lowered. At this time, the belt portion 61p is pulled and feels like it.

  A belt slack detection sensor 11 (FIG. 2) is arranged as a sensor for detecting the vertical position of the lever 11a. Based on the detection result of the belt slack detection sensor 11, the belt portion 61q is vertically changed, that is, the belt portion 61q is detected. It is possible to detect whether it is loose or pulled. The belt slack detection sensor 11 can be said to be second detection means for detecting a difference in peripheral speed between the belt portion 61m (first portion) and the belt portion 61a (second portion) of the fixing belt 61 that is traveling around.

  Then, the control unit 7 controls the driving motor 67 (first driving unit) that rotationally drives the pressure roller 63 so that the peripheral speed of the pressure roller 63 is stabilized at a predetermined speed corresponding to the recording sheet conveyance speed. The first control for adjusting the rotation speed of the pressure roller 63 and the driving motor 67a (second driving means) for rotating the heating roller 64 are controlled, and the belt is detected according to the detection result of the belt slack detection sensor 11. Second control for adjusting the rotation speed of the heating roller 64 so as to eliminate the difference between the peripheral speeds of the portions 61m and 61a is executed.

FIG. 15 is a flowchart of the second control executed by the control unit 7, and is repeatedly executed every time it is called by a main routine (not shown). The second control is performed on the assumption that the peripheral speed of the pressure roller 63 is kept constant at a predetermined speed by the first control.
As shown in the figure, the control unit 7 acquires the detection result of the belt slack detection sensor 11 (step S1). Based on the detection result of the belt slack detection sensor 11, it is determined whether or not the vertical position of the belt portion 61q is at the reference position (step S2).

If it is determined that the vertical position of the belt portion 61q is at the reference position (“Yes” in step S2), the process returns. In this case, there is no difference in peripheral speed between the belt portions 61m and 61a.
If it is determined that it is not at the reference position (“No” in step S2), it is determined whether or not slack has occurred (step S3). If it is determined that slack has occurred, that is, the peripheral speed of the belt portion 61a is higher than the peripheral speed of the belt portion 61m (“Yes” in step S3), the peripheral speed of the heating roller 64 is increased by a predetermined amount, for example, Control is performed to slow down the peripheral speed (constant) of the pressure roller 63 by 2% (step S4), and the process returns.

On the other hand, when it is determined that tension is generated, not slack, that is, the peripheral speed of the belt portion 61a is slower than the peripheral speed of the belt portion 61m ("No" in step S3), the peripheral speed of the heating roller 64 is changed. Control is performed to increase by a predetermined amount, for example, 2% with respect to the peripheral speed of the pressure roller 63 (step 5), and the process returns.
Accordingly, if the peripheral speed of the belt portion 61m is maintained at a predetermined speed, it is possible to prevent the belt portions 61p and 61q from being slackened or pulled, and to make the fixing belt 61 travel more stably.

[Embodiment 5]
In the above embodiment, the configuration example in which the curvature of the belt portion 61f (FIGS. 3 and 12) wound around the end portion 66f of the backup member 66 in the fixing belt 61 is large to some extent has been described. In form 5, the curvature is small (the degree of bending is small), and this is different from the above-described embodiment.

  FIG. 16 is a diagram schematically showing what force P acts on the heating roller 64 from the belt portion 61f during the circumferential running of the fixing belt 61 in a configuration in which the curvature of the belt portion 61f of the fixing belt 61 is considerably large. is there. In order to make the explanation easy to understand, the belt portion 61f and the heating roller 64 that are originally in contact with each other are shown in a separated state in the drawing, and members such as the backup member 66 that are not necessary for explanation are shown in the drawing. Is omitted.

The force P acting on the heating roller 64 from the belt portion 61f is adjacent to the upstream side in the belt circumferential direction more than the portion 619 on the upstream side in the belt circumferential direction in the region in contact with the heating roller 64 in the fixing belt 61. The force in the direction along the tangent line 614 that contacts the surface of the belt portion 618 (the direction along the traveling direction of the belt portion 618).
A portion 649 in contact with the end portion 619 of the fixing belt 61 on the outer peripheral surface 64 a of the heating roller 64 corresponds to the most upstream portion in the rotation direction of the region in contact with the fixing belt 61 on the outer peripheral surface 64 a of the heating roller 64. The line tangent to the part 649 is a virtual tangent 615 (separated in the figure but is actually in contact), the virtual line connecting the part 649 and the rotation axis 64e of the heating roller 64 is 616, and the force P Is divided into a component force Pa along the direction of the virtual tangent 615 and a component force Pb along the virtual line 616 perpendicular to the virtual tangent 615, the direction of the component force Pa is opposite to the rotation direction of the heating roller 64. Become the direction.

  In the configuration in which the heating roller 64 is driven to rotate around the fixing belt 61 that circulates around, the frictional force between the heating roller 64 and the belt portion 61 a sandwiched between the heating roller 64 and the backup member 66 in the fixing belt 61 is mainly used. The driving force of the driven rotation of the heating roller 64 becomes a driving force. If the component P is included in the force P in the direction opposite to the rotation direction of the heating roller 64, the driving force of the driven rotation is reduced accordingly. It becomes difficult to do. As a result, for example, if the heating roller 64 can alternately follow the rotation of the fixing belt 61 and rotation unevenness occurs in the heating roller 64, the heating roller 64 per unit time from the heating roller 64 to the fixing belt 61 may be increased. There is a risk that the heating amount fluctuates and heating unevenness occurs.

  This uneven heating is a configuration in which the curvature of the belt portion 61 f of the fixing belt 61 is considerably large, specifically, the angle γ of entry of the fixing belt 61 into the heating roller 64, more specifically, the outer periphery of the heating roller 64. The large entry angle with respect to the virtual tangent 615 when entering between the surface 64a and the backup member 66 is a major factor. Note that the angle γ is equal to the angle obtained by subtracting the angle formed by the direction in which the fixing belt 61 enters the heating roller 64 (the direction of the force P) and the virtual tangent 615 from 180 °.

  Therefore, for example, as shown in FIG. 17, in the fixing belt 61, the belt portion 618 upstream of the belt portion 619 in the belt circumferential direction is positioned upstream of the virtual line 616 in the rotation direction of the heating roller 64. 61 circuit routes can be set. FIG. 17 shows an example in which the curvature of the circulation path in the belt portion 618 is the same as the curvature of the outer peripheral surface 64 a of the heating roller 64.

  In this way, the approach angle γ is reduced, and the component force Pa of the force P is also in the same direction as the rotation direction of the heating roller 64. Therefore, the heating roller 64 is easily driven and the above-described heating unevenness is less likely to occur. . The component force Pa is in the same direction as the rotation direction of the heating roller 64 when the approach angle γ is smaller than 90 °. Therefore, it is desirable to configure the approach angle γ to be 90 ° or less.

Further, for example, the configuration shown in FIG.
FIG. 18 is a diagram illustrating a configuration example in which the heating roller 64 is disposed on the upper side with respect to the fixing belt 61. If the configuration in which the heating roller 64 is disposed laterally with respect to the fixing belt 61 as in the first embodiment is a lateral configuration, the configuration illustrated in FIG.
In the vertical arrangement, as shown in FIG. 18, the backup member 66 is considerably close to the support member 170 that supports the fixing pad 162 in the circulation path of the fixing belt 61. It is easy to be restricted by the length (corresponding to the circumferential length of the heating roller 64). On the other hand, in the lateral arrangement, since the space for arranging the backup member 66 can be widened in the circulation path of the fixing belt 61, the length of the backup member 66 in the width direction is increased so that the contact area between the heating roller 64 and the fixing belt 61 is increased. That is, it is easy to take a wide heating region.

  On the other hand, in the vertical arrangement shown in FIG. 18, the belt portion 61p of the fixing belt 61 immediately after exiting the fixing nip 69 has a feed speed by the pressure roller 63 on the driving side, and the heating roller 64 on the driven side. The belt portion 61a sandwiched between the backup member 66 and the belt member 61a has a bulge that has a considerably small curvature. Due to this bulge, the approach angle γ becomes considerably smaller than 90 °. As described above, the heating roller 64 can be easily driven by the vertical arrangement.

Considering the increase in the heating area of the fixing belt 61 and the smooth driven rotation of the heating roller 64, for example, the configuration shown in FIGS. 11 and 13, the middle between the vertical arrangement and the horizontal arrangement, specifically fixing. Arrangements suitable for the apparatus configuration, such as a configuration in which the belt 61 is disposed obliquely at the upper left, etc., can be employed.
[Embodiment 6]
In the above description, the sheet type of the recording sheet S to be used (for example, plain paper and thick paper) is not particularly mentioned, but in the sixth embodiment, the printing condition, here, the sheet conveyance speed is changed according to the sheet type. This is different from the first to fifth embodiments in this respect.

  In the case of thick paper, the heat capacity of the sheet itself is increased by the amount thicker than that of plain paper. Therefore, in order to maintain the same fixing temperature as that of plain paper, it is necessary to supply more heat than plain paper. In the present embodiment, the conveyance speed while the thick paper passes through the fixing nip 69, that is, the rotational speed of the driving-side pressure roller 63 is made slower than that of plain paper (for example, half speed). Accordingly, the peripheral speed of the fixing belt 61 and the heating roller 64 on the driven side is slower than that of plain paper, for example, half speed, and the time required for the thick paper to pass through the fixing nip 69 (nip time) is shorter than that of plain paper. The amount of heat supplied to the thick paper per unit time of the fixing nip 69 increases as compared with plain paper.

  If this transport speed control is applied to thick paper, it is not necessary to vary the power supplied to the heater 65 in accordance with the sheet type. However, if the supply power of the heater 65 is kept as large as that for plain paper, the contact speed between the heating roller 64 and the fixing belt 61 is longer than that for plain paper because the peripheral speed of the fixing belt 61 is slow. Therefore, the amount of heat supplied from the heating roller 64 to the fixing belt 61 may increase, and the amount of heat supplied to the thick paper passing through the fixing nip 69 at half speed may be excessive.

Therefore, in the sixth embodiment, the contact length in the circumferential direction between the heating roller 64 and the fixing belt 61 (hereinafter referred to as “heating nip length Q”) according to the sheet type of the recording sheet S to be used. By changing the above, the amount of heat per unit time supplied from the heating roller 64 to the fixing belt 61 is adjusted.
Specifically, as shown in FIG. 19, the heating roller 64 is configured to be movable in a direction approaching the backup member 66 (arrow Hb direction) and in a direction away from the backup member 66 (arrow Ha direction). The distance to 64 backup members 66 is changed. The moving direction of the heating roller 64 is referred to as a perspective direction.

  FIG. 19A shows a first state where the heating nip length Q is Qa, and FIG. 19B shows a second state where Qb (<Qa). The heating nip length Qa is, for example, 15 mm, and the heating nip length Qb is, for example, 7.5 mm. Even in the second state, the belt portion 61 a comes into contact with the outer peripheral surface 64 a of the heating roller 64 by the restoring force of the fixing belt 61, and the heating nip length Qb is formed.

The second state shown in FIG. 19B is a state in which the heating roller 64 and the heater 65 are integrally moved away from the backup member 66 by a distance δ with respect to the first state shown in FIG. It has become. Hereinafter, the position in the perspective direction (corresponding to the X-axis direction) of the heating roller 64 in the first state is referred to as a first position, and the position in the perspective direction of the heating roller 64 in the second state is referred to as a second position.
In the present embodiment, both end portions of the heating roller 64 and the heater 65 are supported by a subframe (not shown) different from the frame of the fixing unit 6, and the subframe is attached to the frame of the fixing unit 6. It is supported so that it can move in the perspective direction. A cam (not shown) for determining the far and near positions (first position and second position) of the heating roller 64 is engaged with the subframe. When the cam is rotated by the driving force of the actuator 12 such as a motor (FIG. 2), the sub-frame moves in the perspective direction, and the heating roller 64 and the heater 65 move together in the perspective direction with respect to the backup member 66. It is configured.

The rotation angle of the cam when the heating roller 64 is in the first position and the rotation angle of the cam when the heating roller 64 is in the second position are determined in advance, and the heating roller is rotated by rotating the cam by the determined rotation angle. The 64 positions can be switched between the first position and the second position. The actuator 12 and the cam serve as moving means for moving the heating roller 64.
The longer the heating nip length Q, the wider the contact area between the heating roller 64 and the fixing belt 61, and the more heat is supplied from the heating roller 64 to the fixing belt 61. Conversely, the shorter heating nip length Q is. However, the contact area between the heating roller 64 and the fixing belt 61 is reduced, and the amount of heat supplied from the heating roller 64 to the fixing belt 61 is reduced.

Accordingly, if the position of the heating roller 64 is switched and controlled so that the first state shown in FIG. 19A is applied to plain paper and the second state shown in FIG. On the other hand, it is possible to supply an appropriate amount of heat for heat-fixing at the fixing nip 69 even for thick paper having a slower conveying speed.
FIG. 20 is a flowchart showing the contents of control of conveyance of plain paper and thick paper and position switching of the heating roller 64, and is executed each time one recording sheet S is conveyed by the control unit 7. Here, an example in which the first fixing mode in which plain paper is used as the recording sheet S and the second fixing mode in which thick paper is used is selectively used will be described.

As shown in the figure, the sheet type of the recording sheet S conveyed is acquired (step S11). This acquisition is performed, for example, by acquiring sheet type information set and input by the user from the operation panel 8. If the print job data includes sheet type information, it can be obtained by reading the information.
If it is determined that the recording sheet S to be conveyed is not thick paper, that is, plain paper (“No” in step S12), it is determined that the first fixing mode has been selected, and the actuator 12 is controlled so that the heating roller 64 is turned on. The position is moved to the position 1 (FIG. 19A) (step S13). Then, the driving motor 67 is controlled to rotate the pressure roller 63 at a reference speed (speed determined in advance for plain paper: for example, 166 mm / second) (step S14), and the process is finished. As a result, the fixing belt 61 travels at a reference speed (first speed).

On the other hand, if it is determined that the recording sheet S to be transported is thick paper (“Yes” in step S12), the actuator 12 is controlled and the heating roller 64 is moved to the second position (“Yes” in step S12). It moves to FIG.19 (b)) (step S15). As a result, the contact area between the heating roller 64 and the fixing belt 61 is reduced as compared with the case of plain paper.
Then, the drive motor 67 is controlled to rotate the pressure roller 63 at a lower speed (a predetermined speed for cardboard: for example, 83 mm / second) slower than the reference speed (step S16), and the process ends. To do. As a result, the fixing belt 61 travels at a second speed slower than the reference speed (first speed).

  As shown in FIG. 19A, substantially the entire length of the belt portion 61 a sandwiched between the heating roller 64 and the backup member 66 in the fixing belt 61 in the circumferential direction is curved along the outer circumferential surface 64 a of the heating roller 64. Of course, when contacting the heating roller 64, as shown in FIG. 19B, a part of the length of the belt portion 61a in the circumferential direction becomes a curved shape along the outer circumferential surface 64a of the heating roller 64. In this case, the belt portion 61 a is included in a configuration that is curved along the outer peripheral surface 64 a of the heating roller 64.

  In the above description, two types of sheets, plain paper and thick paper, have been described. However, other types such as thin paper, coated paper, and postcards may be included. In a configuration in which the conveying speed of the sheet passing through the fixing nip 69 (corresponding to the peripheral speed of the fixing belt 61) is varied depending on the sheet type, the heating nip length Q is shortened as the conveying speed is decreased. In addition, it is possible to control to increase the distance in the perspective direction of the heating roller 64 with respect to the backup member 66.

  Further, although the example of the sheet type has been described as the condition for changing the sheet conveyance speed (the peripheral speed of the fixing belt 61), the present invention is not limited to this. For example, in the monochrome image formation mode of only the K color, this is set as the first fixing mode, the sheet conveyance speed is set to the reference speed (first speed), and in the Y to K color full color image formation mode, this is set. The second fixing mode can be applied to a configuration in which the sheet conveyance speed is switched to a low speed (second speed) slower than the reference.

  Furthermore, although the backup member 66 is fixed and the heating roller 64 can be moved in the perspective direction with respect to the backup member 66, the invention is not limited thereto. The backup member 66 can be moved in the perspective direction with respect to the fixed heating roller 64, or both can be moved in the perspective direction. That is, it is possible to adopt a configuration in which the heating roller 64 and the backup member 66 can be moved relatively in the perspective direction.

[Embodiment 7]
In the above embodiment, the configuration example in which the fixing belt 61 and the heating roller 64 are always in contact has been described. However, in the seventh embodiment, the heating roller 64 is connected to the fixing belt 61 when the fixing belt 61 is stopped. This is different from this point.
The reason why the heating roller 64 is separated from the fixing belt 61 is to prevent deformation of the fixing belt 61. That is, if printing is not performed at all for a long period of time, for example, a period of consecutive holidays (when left for a long period of time), the fixing belt 61 does not move at all for a long period of time. This is because the reversely curved shape remains in the belt portion 61a that is curved in the opposite direction along the peripheral surface, which may lead to deformation of the fixing belt 61. If the heating roller 64 is separated from the fixing belt 61 when the fixing belt 61 is stopped, the fixing belt 61 returns to the original natural posture (FIG. 4) by its own restoring force. It is possible to prevent deformation to the curved shape of the direction.

The configuration in which the heating roller 64 is separated from or brought into contact with the fixing belt 61 is the same as that in the sixth embodiment in which the heating roller 64 can be moved in the contact / separation direction with respect to the backup member 66, that is, heating is performed according to the cam rotation angle. This can be realized by adopting a configuration in which the roller 64 can move to a position (contact position) where the roller 64 moves away from the fixing belt 61 and a position (contact position) where the roller 64 comes into contact.
FIG. 21 is a flowchart showing the contents of control for switching the heating roller 64 between the separation position and the contact position, and is executed each time a print job is executed by the control unit 7.

It is assumed that at the start of the print job, the pressure roller 63 is in a stopped state, and the heating roller 64 is located at the separation position (steps S25 and S26 described later).
When it is determined that the print job is started ("Yes" in step S21), the actuator 12 is controlled to change the heating roller 64 from the separated position to the contact position (FIG. 3) (step S22). As a result, the fixing belt 61 is brought into a normal state where it is pressed against the heating roller 64 by the backup member 66. Thereafter, the drive motor 67 is controlled to start the rotation of the pressure roller 63 (step S23), and the process proceeds to step S24. Thereby, the circumferential running of the fixing belt 61 is started.

In step 24, it is determined whether or not the print job is finished. When the end of the print job is determined (“Yes” in step S24), the drive motor 67 is controlled to stop the rotation of the pressure roller 63 (step S25). As a result, the fixing belt 61 stops.
Thereafter, the actuator 12 is controlled to cause the heating roller 64 to transition from the contact position to the separated position (step S26), and the process is terminated. As a result, the fixing belt 61 is naturally separated from the heating roller 64. Note that the fixing belt 61 is not deformed as long as the heating roller 64 does not completely separate from the fixing belt 61 and is in a line contact state. It is called releasing the pressure contact including separation and line contact.

In this way, it is possible to perform the switching control in which the fixing belt 61 is brought into pressure contact during the lap driving and the pressure contact is released while the fixing belt 61 is stopped.
In the present embodiment as well, as in the sixth embodiment, a configuration is possible in which the heating roller 64 and the backup member 66 can be moved relatively in the perspective direction.
In FIG. 21, the rotation of the pressure roller 63 is started after the heating roller 64 is moved to the contact position (step 22, S23), but this order can be reversed. Similarly, after the rotation of the pressure roller 63 is stopped, the heating roller 64 is moved to the separated position (step 25, S26), but this order can be reversed. This also applies to, for example, steps S13 and S14 and steps S15 and S16 shown in FIG. 20, and the order of each can be reversed.

In the above description, the control for bringing the heating roller 64 into contact with and separating from the fixing belt 61 has been described. Similarly, the direction in which the fixing roller 62 and the pressure roller 63 are relatively approached and moved away from each other via the fixing belt 61. It can also be made movable.
In this case, during the rotation of the fixing belt 61, the fixing roller 62 and the pressure roller 63 are moved in a relatively approaching direction, and the pressure roller 63 is pressed against the fixing roller 62 via the fixing belt 61. Then, the fixing nip 69 is formed (FIG. 3), and when the fixing belt 61 is stopped, the fixing roller 62 and the pressure roller 63 are moved away from each other to control the release. You can also.

As shown in FIG. 3, the fixing belt 61 receives a strong pressing force from the pressure roller 63 in the fixing nip 69, and bends in a direction opposite to the natural posture along the peripheral surface of the pressure roller 63. Therefore, there is a possibility that the curved shape in the opposite direction may remain when left for a long time.
(Modification)
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications may be considered.

  (1) In the above embodiment, the heating roller 64, the heater 65, and the backup member 66 are arranged one by one, but the present invention is not limited to this. For example, as shown in FIG. 22, a first set of a heating roller 64, a heater 65, and a backup member 66, and another heating roller 264, a heater 265, and a second set of a backup member 266 are fixed together. The structure provided with respect to the belt 61 can also be taken.

When this configuration is adopted, the heating region of the heating roller 64 in the first set and the heating region of the heating roller 64 in the second set are made different in the axial direction, whereby the heating region in the belt width direction of the fixing belt 61 is changed. Further different configurations can be taken.
FIG. 23 is a view when the heating rollers 64 and 264, the heaters 65 and 265, and the fixing belt 61 shown in FIG. 22 are viewed from the direction of the arrow X. The heating rollers 64 and 264 have different heating regions in the belt width direction. This is shown schematically.

Of the rod-like heater 65 inserted into the cylindrical heating roller 64, only the portion existing in the central region in the belt width direction becomes a heat generating portion, and the heat generated from the heat generating portion is transmitted to the heating region 271 of the heating roller 64. The heat is transmitted from the heating area 271 to the heating area 261 of the fixing belt 61.
Similarly, only a portion of the rod-shaped heater 265 inserted in the cylindrical heating roller 264 that exists in both outer regions across the central region in the belt width direction becomes a heat generating portion, and is emitted from each heat generating portion. Heat is transmitted to the heating areas 272 and 273 of the heating roller 64, and is transmitted from the respective heating areas 272 and 273 to the heating areas 262 and 263 of the fixing belt 61.

  A central area 261 in the belt width direction is an area in the belt width direction in which a so-called small size paper such as B5 size or A4 size of the fixing belt 61 contacts the small size paper when passing through the fixing nip 69. On the other hand, areas 262 and 263 on the outer side in the belt width direction are those in the belt width direction that come into contact with the large size paper when the so-called large size paper such as B4 size or A3 size of the fixing belt 61 passes through the fixing nip 69. It is an area.

  Therefore, when small-size paper is used, only the small-size width corresponding to the small-size paper can be heated when only the heater 65 is energized. When large size paper is used, when both heaters 65 and 265 are energized, the large size width corresponding to the large size paper can be heated, corresponding to the size (width) of the recording sheet, A region suitable for each width can be heated.

In addition, it can replace with said 2 sets and can also take the structure provided with 3 or more sets.
Further, instead of the configuration including a plurality of sets, in the configuration including only one set as in the first embodiment, a plurality of heaters 65 having different heating regions in the belt width direction are inserted into the cylindrical heating roller 64. Thus, the heater 65 to be energized can be switched according to the size of the recording sheet.

(2) In the above embodiment, the shape of the surface 66b (FIG. 3: hereinafter referred to as “pressure contact surface”) that contacts the belt portion 61a of the backup member 66 is a curved shape along the outer peripheral surface 64a of the heating roller 64. However, it is not limited to this.
The fixing belt 61 has a curved shape along the outer peripheral surface 64a of the heating roller 64 by self-restoring force (FIGS. 19A, 19B, etc.), and is opposite to the heating roller 64 with the fixing belt 61 interposed therebetween. Any shape that allows the fixing belt 61 to be in pressure contact with the outer peripheral surface 64a of the heating roller 64 existing outside the belt rotation path from the inside of the belt rotation path may be used.

The shape of the pressure contact surface 66b of the backup member 66 can be a curved shape such as an arc shape having the same curvature as a concentric circle around the rotation axis of the heating roller 64, or an arc shape having a slightly smaller curvature. In addition, for example, when viewed from the axial direction of the heating roller 64, it may be considered that the belt portion 61a side is expanded in a V shape or a “<” shape.
(3) In the above embodiment, the backup member 66 includes the base 71, the pressing rubber 72, and the sliding sheet 73. However, the present invention is not limited to this. For example, a configuration including the base 71 and the pressing rubber 72, a configuration including the base 71 and the sliding sheet 73, a configuration including only the base 71, and the like can be employed. In the above description, the glass sheet is used as the sliding sheet 73, but the present invention is not limited to this, and a heat-resistant and low-friction sheet can be used. Further, when only the base 71 is configured, a configuration in which a low friction layer is provided on a curved surface of the base 71 that is in contact with the belt portion 61a can be employed.

  Further, in order to reduce the frictional force between the inner surface 61z of the fixing belt 61 and the pressure contact surface 66b of the backup member 66, it is possible to adopt a configuration in which a lubricant is applied to each of them. As the lubricant, for example, silicon oil, fluorine grease or the like can be used. Further, it is possible to adopt a configuration in which a low friction layer, for example, fluorine coating, is applied to the inner surface 61z of the fixing belt 61. Any one or a combination of the above may be employed.

  (4) In the above embodiment, the material of the base layer of the fixing belt 61 and the base 71 of the backup member 66 is PI resin, but it goes without saying that the present invention is not limited to this. When the heating roller 64 is a heat source and the backup member 66 is not a heat source, the heat of the fixing belt 61 escapes to the backup member 66 and heat loss as the heat of the fixing belt 61 is more easily transmitted (absorbed) to the backup member 66. Therefore, it is desirable that the thermal conductivity of the backup member 66 be smaller than the thermal conductivity of the fixing belt 61. In the case where the degree of heat loss is within a small range that is sufficiently acceptable in design, the reverse relationship can be obtained.

In the above description, the rod-shaped heater 65 is inserted into the cylindrical heating roller 64. However, the present invention is not limited to this. The heating roller 64 may be configured to be heated by the heater 65. For example, a configuration in which the outer surface of the solid heating roller is heated by a plate-shaped heater may be employed.
Furthermore, although the heating roller 64 is heated by the heater 65, it is not limited to this. For example, the backup member 66 may be heated by a heater and the heating roller 64 may not be heated by the heater. When this configuration is adopted, both the backup member 66 and a heater for heating the backup member 66 can be arranged inside the belt circulation path of the fixing belt 61.

  (5) In the above embodiment, no particular mention was made of cleaning the outer peripheral surface 64 a of the heating roller 64. For example, when the recording sheet S passes through the fixing nip 69, toner particles on the recording sheet S are recorded. In a configuration in which a part of the toner is transferred to the surface of the fixing belt 61 as so-called offset toner and is likely to be further transferred and adhered from the fixing belt 61 to the outer peripheral surface 64 a of the heating roller 64, the offset toner is transferred to the outer peripheral surface of the heating roller 64. The structure which provides the cleaner removed from 64a can be taken.

The offset toner adhering to the outer peripheral surface 64 a of the heating roller 64 returns to the surface of the fixing belt 61 from the heating roller 64 again by the rotation of the heating roller 64 and reaches the fixing nip 69 and passes through the fixing nip 69 at that time. This is because the recording sheet S is moved to the inside, and the recording sheet S may be soiled.
As the cleaner, for example, a scraper 64b shown in FIG. 9 can be used. A configuration in which the tip of the scraper 64b abuts on the outer peripheral surface 64a of the heating roller 64 can be employed. The scraper 64b is long along the axial direction of the heating roller 64, and is made of, for example, silicone rubber, and is disposed so as to contact the outer peripheral surface 64a of the heating roller 64 in the axial direction. The scraper 64b scrapes off deposits such as offset toner and dust adhered to the outer peripheral surface 64a of the heating roller 64, thereby cleaning the outer peripheral surface 64a of the heating roller 64.

Further, by applying a release layer, for example, a PTFE fluorine coat, to the outer peripheral surface 64a of the heating roller 64, it is possible to prevent adhesion of the deposit on the outer peripheral surface 64a of the heating roller 64.
(6) In the above embodiment, the fixing roller 62 or the fixing pad 162 as the member to be pressed is disposed inside the belt circulation path with the fixing belt 61 interposed therebetween, and the pressure member as the pressure member is disposed outside the belt circulation path. The configuration example in which the pressure roller 63 is disposed has been described, but the configuration is not limited thereto as long as the fixing nip 69 can be formed. For example, when the member to be pressed is the fixing roller 62, a configuration in which the pressing member is replaced with the pressing roller 63 to form a pressing pad can be taken. In this case, the fixing roller 62 is on the driving side. In the first embodiment, the driving side may be replaced with the pressure roller 63 and the fixing roller 62 may be used. Either one becomes the drive roller.

  (7) In the above embodiment, an example in which the image forming apparatus according to the present invention is applied to a tandem type color printer has been described. However, the present invention is not limited to this. The present invention can be applied to a fixing device having a fixing belt and an image forming apparatus including the fixing device. The image forming apparatus can be applied to an apparatus capable of performing color image formation or an apparatus capable of performing only monochrome image formation, and is not limited to a printer. For example, an image of a copying machine, a facsimile apparatus, an MFP (Multiple Function Peripheral), or the like. Applicable to forming apparatus.

Further, although the control unit 7 and the fixing unit 6 are configured separately, in the configuration in which the control such as the movement of the heating roller 64 is performed, it can be understood that the control unit 7 and the fixing unit 6 configure a fixing device.
Furthermore, the numerical values such as the material of each member, the above temperature, the size of the member, and the electric power are examples, and suitable materials, temperature, dimensions, and the like are determined in advance according to the apparatus configuration.
Further, the contents of the above embodiment and the above modification may be combined as much as possible. As long as the effect of the present invention can be obtained, the mechanisms and members of the respective parts such as the fixing unit may be applied in place of other mechanisms or members having different shapes.

  The present invention can be widely applied to a fixing device having a fixing belt.

DESCRIPTION OF SYMBOLS 1 Printer 6 Fixing part 7 Control part 11 Belt slack detection sensor 61 Fixing belt 61a Belt part 62 Fixing roller 63 Pressure roller 64, 264 Heating roller (external roller)
64b Cleaner 65, 265 Heater 66, 266 Backup member 66p, 66q, 661, 662 Corner portion 67, 67a Drive motor 69 Fixing nip 71 Base 73 Sliding sheet 162 Fixing pad 170 Support member 171 Bottom plate portion 172, 173 Side plate portion 615 Virtual Tangent line 616 Virtual line 649 The most upstream part in the rotation direction of the area in contact with the fixing belt on the outer peripheral surface of the heating roller Qa, Qb Heating nip length (contact area length between the heating roller and the fixing belt)
S Recording sheet

Claims (22)

The pressure member and the fixing unit are pressed by pressing the pressure member disposed on the outer side of the fixing belt via the fixing belt to the pressed member disposed on the inner side of the circulation path of the endless fixing belt. A fixing device that contacts a belt surface to form a fixing nip, passes a recording sheet through the fixing nip, and fixes an unfixed image on the recording sheet;
An external roller disposed outside the circulation path of the fixing belt;
A backup member that is arranged on the inside of the circulation path of the fixing belt and presses the fixing belt against the external roller;
A heater for heating the external roller or the backup member;
With
The shape of the surface of the backup member that contacts the belt portion is determined so that the belt portion sandwiched between the external roller and the backup member has a curved shape along the outer peripheral surface of the external roller. A fixing device.   The fixing device according to claim 1, wherein a surface of the backup member that contacts the belt portion has a curved shape along an outer peripheral surface of the external roller.   The fixing device according to claim 1, wherein the external roller is disposed on a side opposite to the pressure member with the fixing belt interposed therebetween.   The fixing device according to claim 1, wherein the pressure member is a pressure roller, and the member to be pressed is a pad-shaped fixing pad. A support member for supporting the pressed member;
The backup member is elongated along the rotation axis of the external roller,
The support member is
A bottom plate portion that is long along the rotation axis of the external roller and is fixed to a surface on the side facing the fixing pad, and the backup member is positioned from both ends in the short direction of the bottom plate portion. Having first and second side plates bent to the side,
The distance between the front end of the first side plate portion and the front end of the second side plate portion in the short direction is larger than the width of the backup member or the diameter of the external roller. Fixing device.   The fixing device according to claim 1, wherein a peripheral length of the external roller is longer than a peripheral length of the fixing belt. The backup member is elongated along the rotation axis of the external roller,
When the position where the central portion in the width direction of the backup member exists on the imaginary line connecting the rotation axis of the external roller and the central position in the sheet conveyance direction of the fixing nip is a reference position, the central portion in the width direction of the backup member is In the case of a configuration that exists at a position shifted from the reference position to the upstream side in the rotation direction of the external roller around the rotation axis of the external roller,
The corner portion of the end of the backup member in contact with the belt portion on the upstream side in the rotation direction of the external roller is formed in an R shape. The fixing device described. The backup member is elongated along the rotation axis of the external roller,
When the position where the central portion in the width direction of the backup member exists on the imaginary line connecting the rotation axis of the external roller and the central position in the sheet conveyance direction of the fixing nip is a reference position, the central portion in the width direction of the backup member is In the case of a configuration that exists at a position shifted from the reference position to the downstream side in the rotation direction of the external roller around the rotation axis of the external roller,
The corner of the end of the surface of the backup member in contact with the belt portion on the downstream side in the rotation direction of the external roller is formed in an R shape. The fixing device described. At least one of the pressed member and the pressing member is a roller,
First driving means for rotationally driving any one of the rollers as a driving roller;
Second driving means for rotationally driving the external roller;
A difference between the peripheral speed of the first portion of the fixing belt that is in contact with the pressure member in the fixing nip and the peripheral speed of the second portion sandwiched between the external roller and the backup member is detected. Detection means;
Control means for controlling the first drive means and the second drive means;
With
The control means includes
A first control for adjusting the rotational speed of the drive roller so that the peripheral speed of the drive roller is stabilized at a predetermined speed corresponding to a recording sheet conveyance speed;
A second control for adjusting the rotational speed of the external roller so as to eliminate the difference in the peripheral speed according to the detection result of the detection means;
The fixing device according to claim 1, wherein the fixing device is executed. When a line in contact with the most upstream portion in the rotational direction of the region in contact with the fixing belt on the outer peripheral surface of the external roller is a virtual tangent,
The entry angle γ with respect to the virtual tangent when the fixing belt enters between the outer peripheral surface of the external roller and the backup member is 90 ° or less. The fixing device according to 1. One or more sets comprising the external roller, the backup member and the heater,
11. The heating area in the axial direction of the external roller in the first group and the heating area in the axial direction of the external roller in the second group among the two or more groups are different from each other. The fixing device according to Item 1. The heater heats the external roller;
The fixing device according to claim 1, wherein the thermal conductivity of the backup member is smaller than the thermal conductivity of the fixing belt. The heater heats the external roller;
The fixing device according to claim 1, wherein a surface of the backup member that contacts the belt portion has a mesh structure. First moving means capable of moving the external roller in a direction approaching the backup member via the fixing belt and a direction moving away from the backup member;
Controlling the first moving means to move the external roller in a direction approaching the backup member during the rotation of the fixing belt, and press the fixing belt against the external roller by the backup member; A first movement control means for releasing the pressure contact by moving the external roller away from the backup member while the fixing belt is stopped;
The fixing device according to claim 1, further comprising: A first moving means capable of moving in a direction toward and away from the external roller and the backup member;
First movement control means for controlling the first movement means;
With
It is possible to switch between a first fixing mode in which the fixing belt runs around at a first speed and a second fixing mode in which the fixing belt runs around at a second speed slower than the first speed,
The first movement control means includes
When the second fixing mode is executed, the backup roller and the external roller are moved in a direction farther away than when the first fixing mode is executed, so that the external roller and the fixing belt are moved. The fixing device according to claim 1, wherein a contact area with the fixing device is reduced. Second moving means capable of moving the pressed member and the pressing member in a direction relatively approaching and moving away from the fixing belt;
The second moving means is controlled to move the pressed member and the pressing member in a relatively approaching direction while the fixing belt is traveling around, so that the pressing member is moved through the fixing belt. The pressure member is pressed against the member to be pressed to form the fixing nip, and while the fixing belt is stopped, the member to be pressed and the pressure member are moved away from each other, Second movement control means for releasing the pressing;
The fixing device according to claim 1, further comprising:   17. The backup member according to claim 1, further comprising: a base; and a low friction sheet interposed between the base and the belt portion to reduce friction with the belt portion. The fixing device according to claim 1.   The fixing device according to claim 1, wherein a lubricant is applied to an inner surface of the fixing belt and a surface of the backup member that contacts the belt portion.   The fixing device according to claim 1, wherein a low friction layer for reducing friction with the backup member is provided on an inner surface of the fixing belt.   20. The fixing device according to claim 1, further comprising a cleaning member that contacts a surface of the external roller and removes a foreign substance attached to the surface of the external roller.   21. The fixing device according to claim 1, wherein a release layer is provided on a surface of the external roller. An image forming apparatus including a fixing unit that fixes an unfixed image formed on a conveyed recording sheet,
An image forming apparatus comprising the fixing device according to claim 1 as the fixing unit.

Images