JP2018017895A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device with which, of a nip width variable structure though, it is possible to prevent a poor image due to pressure relief, etc., and maintain appropriate image heatability (fixability) in accordance with the basis weight of paper.SOLUTION: The image heating device is characterized by having: a pair of rotors (105, 120) for forming nip parts (N1, N2) for heating a toner image (t) on a sheet, at least one of which is of an endless belt; a first pad member (173a) and a second pad member (173b) for pressing the endless belt from the inner face thereof toward the other rotor; and a movement mechanism (180) for moving the second pad member so that a state can be taken in which the first pad member and the second pad member come in contact with the endless belt and a state can be taken in which only the first pad member comes in contact with the endless belt.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image heating apparatus that heats a toner image on a sheet. This image heating apparatus can be used in, for example, an image forming apparatus such as a copying machine, a printer, a FAX, and a multifunction machine having a plurality of these functions.

  For example, in an image forming apparatus using an electrophotographic method, a sheet carrying a toner image at a nip portion (fixing nip) generally formed by a heating rotator and a pressure member is nipped and conveyed while being pressurized and heated. A fixing device (image heating device) that fixes an image on a sheet is often used. The sheet is a recording medium (recording material: hereinafter referred to as paper, paper, or medium) on which a toner image can be formed. In addition, in order to output high-speed and high-quality images, fixing devices that use a fixing belt that has a high sheet conveyance stability and can secure a wide nip portion on a heating rotator or a pressure member have been increasing.

  In such a type of fixing device, an appropriate fixing temperature condition for obtaining an optimum fixing property and separating ability varies depending on the basis weight of the paper. Generally, the set temperature (temperature control temperature) of the fixing device is changed according to the basis weight of the paper.

  In addition, with the recent diversification of media, the types of papers that are required to pass through are also diverse. In particular, the demand for passing ultra-thin paper is increasing from the viewpoint of saving resources and space. In order to pass ultra-thin paper stably, it is necessary to optimally set the temperature of the fixing device while improving the paper separating ability of the fixing device.

  When the set temperature (temperature adjustment temperature) of the fixing device is changed according to the basis weight of the paper, a temperature adjustment waiting time is generated when the set temperature differs according to each basis weight when the media is mixedly loaded. In particular, when the temperature control is changed from a high temperature to a low temperature, a great amount of time is required to cool the heating rotator of the fixing device. On the other hand, the structure which shortened temperature control time by the air cooling by a fan (FAN) is known (patent document 1).

  On the other hand, in order to secure the fixing property, it is sufficient to apply a necessary amount of heat to the sheet and the toner image on the sheet. Therefore, according to the basis weight of the sheet, the sheet conveyance speed is decreased and the fixing nip passage time is lengthened. There is a means. While this has the advantage of ensuring optimum fixing performance without complicating the configuration, a decrease in the sheet conveyance speed may affect productivity.

  On the other hand, as one of the means to ensure optimum fixing performance without affecting the productivity drop, the fixing nip width is made variable, and the fixing nip width is changed according to the basis weight of the paper. In particular, there is known a configuration (Patent Document 2) that lengthens the passage time of the sheet through the fixing nip.

  As means for changing the fixing nip width, Patent Document 2 describes a configuration in which the endless belt raceway is changed by attaching and detaching a belt raceway changing member disposed on the inner diameter side of the endless belt to expand the fixing nip width. . Moreover, the structure (patent document 3) which changes the winding angle with respect to the pressurization rotary body which an endless belt opposes is mentioned.

JP2013-45030A JP 2002-221866 A JP-A-2005-331637

  However, the fixing nip width changing means of Patent Document 2 has a gap between a fixing member such as a fixing roller and a fixing pad arranged on the inner surface side of the belt and the belt trajectory changing member. And image defects may occur. In addition, the fixing nip width changing unit of Patent Document 3 may give a large stress to the paper that is nipped and conveyed between the endless belt and the pressure rotator, which may increase paper curl and the like.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image heating apparatus capable of preventing image defects due to pressure loss and the like and having an optimum image heating property (fixing property) according to the basis weight of the paper while having a variable nip width. It is to be.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a pair of rotating bodies in which at least one forming an nip portion for heating a toner image on a sheet is an endless belt, A first pad member and a second pad member that press the endless belt from the inside toward the other rotating body, and a state in which the first pad member and the second pad member are in contact with the endless belt; And a moving mechanism that moves the second pad member so that only the first pad member can be brought into contact with the endless belt.

  According to the present invention, when changing the nip width according to the basis weight of a sheet (paper), it is possible to prevent image defects due to occurrence of pressure loss.

Cross-sectional left side view of the main part of the fixing device in the embodiment Schematic configuration diagram of an image forming apparatus in an embodiment External perspective view of fixing device Left side view of the main part of the device Cross-sectional left side view of the main part of the device (Part 1) Cross-sectional left side view of the main part of the device (Part 2) (A) And (b) is a perspective view of the pad variable mechanism of the left side and the right side of an upper side belt assembly. Exploded perspective view of fixing pad and variable pad Operational diagram of variable pad mechanism (Part 1) Operational diagram of variable pad mechanism (Part 2) Operational diagram of pad variable mechanism (Part 3) Operational diagram of variable pad mechanism (4) Perspective view of belt shift control mechanism Lower belt assembly attachment / detachment control flowchart Block diagram of control system Fixing process flowchart Temperature control flowchart Schematic diagram of the modification (part 1) Schematic diagram of modification (part 2)

  Hereinafter, preferred embodiments for carrying out the present invention will be described in detail with reference to the drawings.

<Embodiment>
(Image forming device)
FIG. 2 is a schematic configuration diagram of the image forming apparatus 1 according to the present exemplary embodiment, and is a schematic cross-sectional view along a conveyance direction (sheet conveyance direction) V of a sheet (recording material: hereinafter referred to as paper or paper) S. The image forming apparatus 1 is a full-color electrophotographic printer (hereinafter referred to as a printer) using an intermediate transfer member. In the printer 1, an image corresponding to image data (electrical image information) input from an external host device 23 connected to a printer control unit (hereinafter referred to as CPU) 10 via an interface 22 is printed on a sheet S. It is possible to form and output an image formed product.

  The CPU 10 is a control unit (execution unit) that comprehensively controls the operation of the printer 1, and exchanges various electrical information signals with the external host device 23 and the printer operation unit 24. It also controls electrical information signals input from various process devices and sensors, processing of command signals to various process devices, predetermined initial sequence control, and predetermined image forming sequence control. The external host device 23 is a personal computer, a network, an image reader, a facsimile, or the like.

  In the printer 1, four first to fourth image forming units U (UY, UM, UC, UK) are arranged in parallel from the left side to the right side in the drawing. Each image forming unit U has the same configuration except that the color of the toner, which is a developer contained in each developing device 5, is different from yellow (Y), magenta (M), cyan (C), and black (K). An electrophotographic image forming mechanism.

  That is, each image forming unit U includes an electrophotographic photosensitive member (hereinafter referred to as a drum) 2, and a charging roller 3, a laser scanner 4, a developing device 5, and a primary transfer as process devices acting on the drum 2. It has a roller 6 and the like.

  The drum 2 of each image forming unit U is rotated at a predetermined speed in the counterclockwise direction indicated by the arrow. Then, a Y color toner image corresponding to the Y color component image of the full color image to be formed is formed on the drum 2 of the first image forming unit UY. An M color toner image corresponding to the M color component image is formed on the drum 2 of the second image forming unit UM. Further, a C color toner image corresponding to the C color component image is formed on the drum 2 of the third image forming unit UC. A K-color toner image corresponding to the K-color component image is formed on the drum 2 of the fourth image forming unit UK. Since the process and principle of toner image formation on the drum 2 of each image forming unit U are known, the description thereof is omitted.

  An intermediate transfer belt unit 7 is disposed below each image forming unit U. This unit 7 has an endless intermediate transfer belt 8 having flexibility as an intermediate transfer member. The belt 8 is stretched around three rollers, that is, a driving roller 11, a tension roller 12, and a secondary transfer counter roller 13. The belt 8 is circulated and moved at a speed corresponding to the rotational speed of the drum 2 in the clockwise direction of the arrow by driving the driving roller 11. A secondary transfer roller 14 is in contact with the secondary transfer counter roller 13 with a predetermined pressing force via a belt 8. A contact portion between the belt 8 and the secondary transfer roller 14 is a secondary transfer nip portion.

  The primary transfer roller 6 of each image forming unit U is disposed inside the belt 8 and is in contact with the lower surface of the drum 2 via the belt 8. In each image forming unit U, a contact portion between the drum 2 and the belt 8 is a primary transfer nip portion. A predetermined primary transfer bias is applied to the primary transfer roller 6 at a predetermined control timing.

  The primary transfer is performed by sequentially superimposing the Y-color toner, M-color toner, C-color toner, and K-color toner formed on the drum 2 of each image forming unit U on the surface of the belt 8 that circulates at each primary transfer nip. Is done. As a result, a full-color toner image that is unfixed in four colors is synthesized and formed on the belt 8 and conveyed to the secondary transfer nip portion.

  On the other hand, the sheet S accommodated in the first or second paper feed cassette 15 or 16 is separated and fed by the operation of the paper feed mechanism, and sent to the registration roller pair 18 through the transport path 17. The registration roller pair 18 receives the paper S once and corrects it straight when the paper is skewed. Then, the registration roller pair 18 conveys the sheet S to the secondary transfer nip portion in synchronization with the toner image on the belt 8.

  While the sheet S is nipped and conveyed at the secondary transfer nip portion, a predetermined secondary transfer bias is applied to the secondary transfer roller 14. As a result, the full color toner image on the belt 8 side is secondarily transferred to the sheet S in sequence. Then, the sheet S exiting the secondary transfer nip portion is separated from the surface of the belt 8, passes through the conveyance path 19, and is introduced into the fixing device 100 as an image heating device. The sheet S is heated and pressurized by the fixing device 100, and the unfixed toner image on the sheet (on the sheet) is fixed as a fixed image. The sheet S exiting the fixing device 100 is conveyed to the discharge tray 21 by the discharge roller pair 20 and discharged as a full-color image formed product.

(Fixing device)
The fixing device 100 of this embodiment is an image heating device of a belt nip method, an electromagnetic induction heating (IH) method, or an oilless fixing method.

  Here, the front surface of the fixing device 100 is a surface on the paper entrance side, the back surface is a surface on the paper exit side, and the left and right are the left or right when the device is viewed from the front. In this embodiment, the left side is the front side and the right side is the back side. Up and down is up or down in the direction of gravity. The upstream side or the downstream side is the upstream side or the downstream side with respect to the conveyance direction (sheet conveyance direction) V of the paper S.

  Further, regarding the fixing device 100 or a member constituting the fixing device 100, a longitudinal direction (longitudinal) or a width direction (width) is a direction parallel to a direction perpendicular to the transport direction V of the sheet S in the sheet transport path surface of the fixing device. (Or dimensions in that direction). The short direction (short side) is a direction (or a dimension in that direction) parallel to the transport direction V of the paper S in the paper transport path surface of the fixing device 100.

  FIG. 3 is an external perspective view of the fixing device 100 according to the present embodiment. FIG. 4 is a left side view of the main part of the apparatus 100 and shows the lower belt assembly B in a pressurized state. FIG. 1 is a cross-sectional left side view of the main part of the apparatus 100, and shows a state in which the lower belt assembly B is pressed and the variable pad 173b is in contact. FIG. 5 is a cross-sectional left side view of the main part of the apparatus 100, and shows a state where the lower belt assembly B is pressed and the variable pad 173b is separated. FIG. 6 is a cross-sectional left side view of the main part of the apparatus 100, and shows a state in which the lower belt assembly B is separated.

  FIGS. 7A and 7B are perspective views of the left and right pad variable mechanisms (movement mechanism: switching mechanism) 180 of the upper belt assembly A, respectively. FIG. 7A is an exploded perspective view of the fixing pad 173a and the variable pad 173b. FIG. 7B is a left side view of the main part of the left pad variable mechanism 180, showing the variable pad 173b being separated. 7C, FIG. 7D, and FIG. 7E are left side views of the main part of the mechanism, respectively, showing the contact of the variable pad 173b. FIG. 8 is a perspective view of a belt deviation control mechanism portion.

  The fixing device 100 includes an upper belt assembly A as a heating unit in which each belt is driven by a motor 301 (FIG. 3), and a lower belt assembly B as a pressure unit. Further, it has a pressure-separation mechanism (contact / separation means) for the lower belt assembly B with respect to the upper belt assembly A, which is driven by the motor 302 (FIG. 3).

  In addition, an IH heater (magnetic flux generating means) 170 that is a heating means for heating the fixing belt 105 in the upper belt assembly A is provided. Further, it includes a left and right switching mechanism 180 (FIG. 7) for switching the position of the variable pad 173b, a shift control mechanism (FIG. 8) for the fixing belt 105, and the like. Hereinafter, these will be described sequentially.

1) Upper belt assembly A and IH heater 170
The upper belt assembly A is disposed between the left and right upper plates 140 of the apparatus housing. This assembly A has a release layer on the surface, and a flexible fixing belt (endless belt: endless) as a fixing rotating body (fixing member: first rotating body) facing the image carrying surface of the paper S Shaped belt member) 105. Further, a driving roller (support roller) 131, a steering roller 132 that also serves as a tension roller, and a fixing pad (first pad member) 173a are provided as a plurality of belt suspension members for suspending the fixing belt 105.

  The drive roller 131 is disposed on the paper exit side between the left and right upper plates 140, and the left and right shaft portions 131a (FIG. 7) are respectively interposed between the left and right upper plates 140 via bearings 154a (FIG. 8). It is rotatably supported. Steering roller support arms 154 (FIG. 4: the right side is not shown) extending from the driving roller 131 side to the paper inlet side are disposed outside the left and right upper plates 140, respectively. The right support arm 154 (not shown) is fixed to the right upper plate 140.

  Referring to FIG. 8, the left support arm 154 is supported on the left shaft 131a of the drive roller 131 via a bearing 154a, and can swing the shaft 131a in the center vertical direction. A pin 151 is planted at the free end of the left support arm 154. A shaft 160 is implanted on the outer surface of the left upper plate 140 on the paper inlet side.

  A worm wheel (helical gear) 152 provided integrally with a fork plate 161 having a U-shaped groove 161a with respect to the shaft 160 is rotatably supported. The pin 151 of the left support arm 154 is engaged with the groove 161 a of the fork plate 161. Here, a stepping motor 155 is disposed on the upper plate 140, and a worm 157 fixed to the rotating shaft of the stepping motor 155 meshes with the worm wheel 152.

  When the stepping motor 155 is driven forward or backward, the fork plate 161 rotates upward or downward via the worm 157 and the worm wheel 152. In conjunction with this, the left support arm 154 rotates upward or downward about the shaft 131a.

  The steering roller 132 is disposed on the sheet entrance side between the left and right upper plates 140, and the left and right shaft portions 132a (FIG. 7) are respectively connected to the left and right support arms 154 via bearings 153 (FIG. 8). It is rotatably supported. The bearing 153 is supported so as to be slidable in the belt tension direction with respect to the support arm 154 and is urged to move away from the driving roller 131 by a tension spring 156.

  Referring to FIGS. 1, 7, and 7A, the fixing pad 173a is a member formed of, for example, stainless steel (SUS material). The fixing pad 173 a is disposed on the inner side of the fixing belt 105, near the driving roller 131 between the driving roller 131 and the steering roller 132, with a pad receiving surface (sliding surface) facing downward. More specifically, the fixing pad 173a is supported by fixing the fixed portions 173a-1 at both left and right ends to the pad fixing portions 181a of the left and right pad support members 181, respectively. The left and right pad support members 181 are fixed to and supported by the left and right upper plates 140, respectively.

  The variable pad (second pad member) 173b is a member formed of, for example, stainless steel (SUS material). The variable pad 173b is movably disposed in the fixing belt 105 between the fixing pad 173a and the steering roller 132 with the pad receiving surface (sliding surface) facing downward and in the direction away from the fixing pad 173a. ing.

  More specifically, in the variable pad 173b, the slider portions 173b-1 at the left and right end portions are fitted and engaged with slide grooves 181b that are long in the front-rear direction on the left and right pad support members 181 side, respectively. It is supported by. Accordingly, the variable pad 173b is movably disposed in a direction approaching the direction opposite to the direction away from the fixing pad 173a while maintaining parallel to the fixing belt 105.

  In other words, the variable pad 173b is a member that is disposed on the inner side of the fixing belt 105 on the upstream side in the paper transport direction V with respect to the fixing pad 173a, and is movable in a direction away from the fixing pad 173a.

  A predetermined tension (tension) is applied to the fixing belt 105 that is stretched over the driving roller 131, the steering roller 132, the fixing pad 173a, and the variable pad 173b. Specifically, the tension is applied by the movement of the steering roller 132 in the belt tension direction by the urging force of the tension spring 156. In this embodiment, a tension of 200 N is applied. The inner surface of the lower belt portion of the fixing belt 105 is in contact with the downward pad receiving surface (pressure surface: sliding surface) of the fixing pad 173a.

  The fixing belt 105 may be appropriately selected as long as it generates heat by the IH heater 170 and has heat resistance. For example, a magnetic metal layer such as a nickel metal layer or stainless steel layer having a thickness of 75 μm, a width of 380 mm, and a circumference of 200 mm is coated with, for example, 300 μm of silicon rubber, and the surface layer (release layer) is coated with a PFA tube. Is used.

  The drive roller 131 is a roller in which a heat-resistant silicon rubber elastic layer is integrally formed on a core metal surface layer having an outer diameter of φ18 made of solid stainless steel, for example. The driving roller 131 is disposed on the sheet exit side of the nip region of the fixing nip portion N formed by the fixing belt 105 and a pressure belt 120 as a second rotating body described later. The elastic layer is elastically distorted by a predetermined amount by pressure welding.

  Here, in this embodiment, the nip shape formed by the drive roller 131 and the pressure roller 121 with the fixing belt 105 and the pressure belt 120 interposed therebetween is formed substantially straight. However, in order to control the buckling of the paper S due to the speed difference in the fixing nip portion N of the paper S, various shapes such as intentionally changing the crown shape of the driving roller 131 and the pressure roller 121 to an inverted crown shape, etc. It is also possible to take the crown shape of the roller.

  The steering roller 132 is a hollow roller formed of, for example, stainless steel with an outer diameter of about 20 mm and an inner diameter of about 18 mm. The steering roller 132 functions as a tension roller that stretches the fixing belt 105 and applies tension. At the same time, it functions as a roller (steering roller) that adjusts the meandering in the width direction orthogonal to the moving direction of the fixing belt 105 by controlling the inclination by a shift control mechanism described later.

  A drive input gear G (FIG. 4) is coaxially fixed to the drive roller 131 on the left end side of the roller shaft 131a. A drive input is made to the gear G from a drive motor 301 (FIG. 3) through a drive transmission means (not shown), and the drive roller 131 is rotationally driven in a clockwise direction indicated by an arrow in FIG. By the rotation of the driving roller 131, the fixing belt 105 is circulated and conveyed in a clockwise direction indicated by an arrow at a speed corresponding to the speed of the driving roller 131. The steering roller 132 rotates following the circulating conveyance of the belt 105.

  The inner surface of the descending belt portion of the fixing belt 105 slides and moves with respect to the downward pad receiving surface (sliding surface) of the fixing pad 173a. In order to stably convey the sheet S at the fixing nip portion N described later, the driving is reliably transmitted between the fixing belt 105 and the driving roller 131.

  The IH heater 170 as a heating means for heating the fixing belt 105 is an induction heating coil unit including an exciting coil, a magnetic core, a holder for holding them, and the like. The upper belt assembly A is disposed on the upper side of the upper belt 140 so that the upper surface portion of the fixing belt 105 and the steering roller 132 are opposed to the fixing belt 105 in a non-contact manner with a predetermined gap therebetween. It is fixedly arranged.

  An alternating current is supplied to the excitation coil of the IH heater 170 via a heater controller 170C and a heater driver 170D (FIG. 9A) controlled by the CPU 10. As a result, the exciting coil generates an alternating magnetic flux, and the alternating magnetic flux is guided to the magnetic core to generate an eddy current in the magnetic metal layer of the fixing belt 105 that is an induction heating element. The eddy current generates Joule heat by the specific resistance of the induction heating element.

  As a result, the fixing belt 105 is suddenly heated by electromagnetic induction. The surface temperature of the fixing belt 105 is detected by a thermistor (temperature sensor) 220. Then, temperature information detected by the thermistor 220 is fed back to the CPU 10. The CPU 10 controls (temperature control) the power supplied to the exciting coil of the IH heater 170 so that the detected temperature input from the thermistor 220 is maintained at a predetermined target temperature.

2) Pad variable mechanism 180
With reference to FIGS. 7 and 7A to 7D, a pad variable mechanism 180 that is a switching mechanism for switching the position of the variable pad 173b will be described.

  In the upper belt assembly A, the fixing pad 173a is in contact with the inner surface of the fixing belt 105, and the first nip portion N1 (with a predetermined width in the sheet conveying direction V) between the fixing belt 105 and the pressure belt 120 opposed thereto. It is a pad member for forming FIG. The variable pad 173 b is a movable pad member disposed on the inner side of the fixing belt 105 and upstream of the fixing pad 173 a in the paper transport direction V.

  The pad variable mechanism 180 is a mechanism for switching the position of the variable pad 173b with respect to the fixing pad 173a. Specifically, the pad variable mechanism 180 can execute a first operation in which the variable pad 173b is disposed at a first position that is separated from the fixing pad 173a by a predetermined distance. Further, the pad variable mechanism 180 forms the nip portion N2 (FIG. 1) having a second width wider than the first width together with the fixing pad 173a by making the variable pad 173b adjacent to the fixing pad 173a. It is possible to execute the second operation to be arranged at the second position.

  That is, the first operation is performed by the pad variable mechanism 180 that moves the variable pad 173b (second pad member) so that only the fixing pad 173a (first pad member) can be brought into contact with the fixing belt 105. Is the action. The second operation is an operation of the pad variable mechanism 180 that moves the variable pad 173b so that the fixing pad 173a and the variable pad 173b can be in contact with the fixing belt 105.

  In the present embodiment, the pad variable mechanism 180 for switching the position of the variable pad 173b as described above is disposed on the left side and the right side of the fixing device 100 as shown in FIGS. 7 (a) and 7 (b). The left and right pad variable mechanisms 180 are symmetrical and operate in synchronism. Therefore, in the following description, the left pad variable mechanism 180 will be mainly described.

  The pad variable mechanism 180 includes a variable pad 173b, a pad support member 181, a pad separation cam 182, a pad biasing spring 183, a drive train 184, and the like. The position of the variable pad 173b is controlled by the pad variable mechanism 180 in accordance with the basis weight of the sheet S on which the fixing process is performed. That is, the CPU 10 executes the first operation or the second operation by controlling the pad variable mechanism 180 in accordance with the basis weight of the paper introduced and used in the apparatus.

  More specifically, the CPU 10 controls the pad variable mechanism 180 so that the second operation is executed when the basis weight of the sheet S on which the fixing process is performed is equal to or greater than a predetermined value. Further, when it is less than the predetermined value, the pad variable mechanism 180 is controlled so that the first operation is executed.

  In the present embodiment, when the fixing process is performed on a sheet having a basis weight of less than 151 gsm, the variable pad 173b is disposed at the separation position (first position) X as shown in FIGS. . When the fixing process is performed on a sheet of 151 gsm or more, the variable pad 173b is disposed at the contact position (second position) Y as shown in FIGS. 1, 7C, 7D, and 7E.

  Initially (always), the variable pad 173b is moved and held at the separation position X with the separation position X as the home position, as shown in FIG. 7B. Therefore, when the fixing process is performed on a sheet of less than 151 gsm, the fixing process is executed while the variable pad 173b is held at the separation position X which is the home position.

  When the fixing process is performed on the paper S having a basis weight of 151 gsm or more, the variable pad 173b is moved from the separation position X, which is the home position, to the contact position Y in FIGS. 1, 7C, 7D, and 7E. The fixing process is executed.

  Specifically, when the fixing process is performed on the paper S having a basis weight of 151 gsm or more, the CPU 10 rotates the drive motor 401 CW at a predetermined rotation number. As a result, the variable pad cam 182 rotates via the drive train 184. Then, the variable pad 173b approaches the fixing pad 173a by the urging force of the pad urging spring 183 disposed on the left and right spring seat surfaces 173b-2 of the variable pad 173b and the left and right spring seat surfaces 181c of the pad support member 181. Move to. That is, the variable pad 173b moves along the slide groove 181b provided in the pad support member 181 in a direction approaching the fixing pad 173a.

  The variable pad 173b is positioned with the left and right contact portions 173c coming into contact with and received by the left and right receiving portions 173a-2 of the fixing pad 173a (FIGS. 7C, 7D, and 7E). By this positioning, the gap W between the rear end of the fixing pad 173a with respect to the sheet conveyance direction V and the front end of the variable pad 173b is about 0.2 mm, and is held with a gap that does not cause image defects.

  Further, the step Z between the pressure pad contact surface of the fixing pad 173a and the pressure pad contact surface of the variable pad 173b is about 0.2 mm, and is held in a gap that does not cause image defects (FIG. 7E). That is, the variable pad 173b is held in a state where it is disposed from the separation position X to the contact position Y.

  When the job for performing the fixing process on the paper S having a basis weight of 151 gsm or more is completed, the CPU 10 rotates the drive motor 401 CCW at a predetermined rotational speed. As a result, the variable pad cam 182 rotates in reverse via the drive train 184. Then, the variable pad 173b moves in a direction away from the fixing pad 173a along the slide groove 181b provided in the pad support member 181 while compressing the pad biasing spring 183. That is, the variable pad 173b is moved back from the contact position Y to the separation position X, which is the home position, and is held.

3) Lower belt assembly B and pressure-separation mechanism Referring to FIG. 1, lower belt assembly B is disposed below upper belt assembly A. This assembly B has a lower frame (additional) supported so as to be pivotable in the vertical direction around a hinge shaft 304 (FIG. 4) fixedly provided on the left and right lower plates 303 on the sheet exit side of the fixing device 100. Pressure frame) 306 is assembled.

  This assembly B is a fixing rotating body (pressure member: forming a first nip portion N1 (FIG. 5) or a second nip portion N2 (FIG. 1) with the fixing belt 105 on the upper belt assembly A side. Second rotating body) 120. In this embodiment, the fixing rotator 120 is a flexible pressure belt (endless belt: an endless belt member). Further, a pressure roller (pressure roller) 121, a tension roller 122, and a pressure pad 125 are provided as a plurality of belt suspension members that suspend the pressure belt 120 with tension.

  As shown in FIG. 4, the pressure roller 121 has left and right shaft portions 121 a rotatably supported between the left and right side plates of the lower frame 306 via bearings 159. In the tension roller 122, left and right shaft portions 122a are rotatably supported by left and right side plates of the lower frame 306 via bearings 158, respectively. The bearing 158 is supported so as to be slidable in the belt tension direction with respect to the lower frame 306, and is urged to move away from the pressure roller 121 by a tension spring 127.

  Although the shaft 121a, bearings 159 and 122a, bearing 158, and tension spring 127 on the right side of the fixing device 100 are not shown, they have a symmetrical configuration with the left side of the fixing device 100.

  Returning to FIG. 1, the pressure pad 125 is a member formed of, for example, silicon rubber, and the left and right end portions are fixed and supported between the left and right side plates of the lower frame 306. The pressure roller 121 is located on the paper exit side between the left and right side plates of the lower frame 306. On the other hand, the tension roller 122 is positioned on the sheet entrance side between the left and right side plates of the lower frame 306. The pressure pad 125 is fixedly disposed on the inner side of the pressure belt 120 and supported near the pressure roller 121 between the pressure roller 121 and the tension roller 122 in a non-rotating manner with the pad surface facing upward.

  A predetermined tension (tension) is applied to the pressure belt 120 that is stretched around the pressure roller 121, the tension roller 122, and the pressure pad 125. Specifically, a predetermined tension is applied by the movement of the tension roller 122 in the belt tension direction by the urging force of the tension spring 127 on the left and right sides of the fixing device. In this embodiment, a tension of 200 N is applied. Here, the inner surface of the upward belt portion of the pressure belt 120 is in contact with the upward pad surface of the pressure pad 125.

  The pressure belt 120 may be appropriately selected as long as it has heat resistance. For example, a nickel metal layer having a thickness of 50 μm, a width of 380 mm, and a circumferential length of 200 mm is coated with, for example, 300 μm of silicon rubber, and a surface layer (release layer) is covered with a PFA tube. The pressure roller 121 is a roller having an outer diameter of φ20 made of solid stainless steel, for example, and the tension roller 122 is a hollow roller having an outer diameter of φ20 and an inner diameter of φ18, for example, made of stainless steel.

  Here, the lower belt assembly B is controlled to rotate in the vertical direction about the hinge shaft 304 (FIG. 4) by a pressurization / separation mechanism as a contact / separation means. That is, the lower belt assembly B is lifted and turned by the pressure-separation mechanism and moved to the pressure position U as shown in FIG. 1 or FIG. In such a manner, it is moved to the separation position (pressure release position) D. Then, the lower belt assembly B is moved to the pressing position U (FIGS. 1 and 2) to form a fixing nip portion with the upper belt assembly A.

  In this case, the case where the variable pad 173b of the upper belt assembly A is moved to the separation position X as shown in FIG. 7B is as follows. The pressure roller 121 and the pressure pad 125 are in pressure contact with the driving roller 131 and the fixing pad 173a of the upper belt assembly A, respectively, with the pressure belt 120 and the fixing belt 105 interposed therebetween with a predetermined pressure.

  As a result, a fixing nip portion N1 having a predetermined first width in the sheet conveying direction V is formed between the fixing belt 105 of the upper belt assembly A and the pressure belt 120 of the lower belt assembly B (FIG. 5). . Here, the width of the fixing nip portion N1 in this embodiment is about 20 mm.

  On the other hand, the case where the variable pad 173b of the upper belt assembly A is moved to the contact position Y as shown in FIGS. 7C, 7D, and 7E is as follows. The pressure roller 121 and the pressure pad 125 are pressed against the driving roller 131, the fixing pad 173a, and the variable pad 173b of the upper belt assembly A with a predetermined pressure with the pressure belt 120 and the fixing belt 105 interposed therebetween, respectively. .

  As a result, the fixing belt 105 of the upper belt assembly A and the pressure belt 120 of the lower belt assembly B are set to be smaller than the first width of the fixing nip portion N1 (FIG. 5) in the sheet conveyance direction V. A second wide fixing nip portion N2 is formed (FIG. 1). Here, the fixing nip portion N2 in this embodiment is about 45 mm.

  Further, the lower belt assembly B is moved from the pressurization position U to the separation position D, so that the pressurization is released (nip release) from the upper belt assembly A and separated in a non-contact manner (FIG. 6).

  In the present embodiment, as described above, the variable pad 173b is provided on the upper belt assembly A side. The sheet S is conveyed along the pressure belt 120 when entering the fixing nip portion. For this reason, when the variable pad is provided on the lower belt assembly B side, there is a concern about the influence on the posture change of the sheet S when the fixing nip portion enters. In the case where there is no influence on the conveying posture of the sheet S, there is no problem even if a variable pad is provided on the lower belt assembly B side.

  Here, the pressure-separation mechanism in the present embodiment will be described. In FIG. 4, the lower frame 306 has a pressure spring unit having a pressure spring 305 for elastically pressing the lower belt assembly B against the upper belt assembly A on the side opposite to the hinge shaft 304 side. Is arranged.

  A pressure cam shaft 307 is rotatably supported in the lower part between the left and right lower plates 303. A pair of eccentric pressure cams 308 having the same shape and the same phase for supporting the lower surface of the lower frame 306 are fixedly disposed on the left and right sides of the pressure cam shaft 307. A pressure gear 309 (FIG. 3) is coaxially fixed and disposed on the right end side of the pressure cam shaft 307. A driving input is made from the pressurizing motor 302 to the gear 309 via a drive transmission means (not shown), and the pressurizing camshaft 307 is rotationally driven.

  The pressure cam shaft 307 has a first rotation angle position with the large bulge portion facing upward as shown in FIGS. 4, 1 and 5 with respect to the eccentric pressure cam 308, and the large bulge portion downward as shown in FIG. The second rotation angle position is formed.

  When the pressure cam shaft 307 is rotated to the first rotation angle position and stopped, the lower frame 306 on which the lower belt assembly B is mounted is lifted by the large raised portion of the eccentric pressure cam 308. Then, the lower belt assembly B contacts the upper belt assembly A while pressing and compressing the pressure spring 305 of the pressure spring unit. As a result, the lower belt assembly B is elastically pressed and urged against the upper belt assembly A by a compression reaction force of the pressure spring 305 at a predetermined pressure (for example, 400 N). Held in position U.

  Here, the pressure contact of the pressure roller 121 to the drive roller 131 causes the drive roller 131 to be warped by a few hundred microns on the opposite side to the direction in contact with the pressure roller 121. The warping deformation of the fixing roller 131 causes a pressure drop at the center in the longitudinal direction of the fixing nips N1 (FIG. 5) and N2 (FIG. 1). In order to eliminate this pressure loss, the driving roller 131 or the driving roller 131 and the pressure roller 121 have a crown shape so that the nip shape by the driving roller 131 and the pressure roller 121 is formed substantially straight. In this embodiment, the driving roller 131 is provided with a 300 μm regular crown shape.

  Further, when the pressure cam shaft 307 is rotated to the second rotational angle position and stopped, the large bulge portion of the eccentric pressure cam 308 is directed downward, and the small bulge portion is lowered corresponding to the lower surface of the lower frame 306. The side belt assembly B is lowered. That is, the lower belt assembly B is released from the pressure applied to the upper belt assembly A and is held at the separation position D in FIG.

  Here, the vertical movement control of the lower belt assembly B will be described with reference to the control flowchart of FIG. 9 and the block diagram of the control system of FIG. 9A. The lower belt assembly B is always held at the separation position D in FIG. In response to a pressure command from the CPU 10, <S9-001>, the pressure motor 302 is rotated N times at a predetermined rotational speed in the CW direction via the motor driver 302D <S9-002>, and the pressure camshaft 307 is driven half-turn Is done.

  As a result, the eccentric pressure cam 308 is converted from the second rotation angle position of FIG. 6 to the first rotation angle position of FIGS. 1 and 5, and the lower belt assembly B is lifted and rotated to pressurize the pressure roller 121. Then, the pressure pad 125 moves to the pressure position U <S9-003>.

  That is, as shown in FIG. 1, the pressure roller 121 and the pressure pad 125 are connected to the driving roller 131, the fixing pad 173a, and the variable pad 173b of the upper belt assembly A with the pressure belt 120 and the fixing belt 105 interposed therebetween. Press contact with contact pressure. Alternatively, as shown in FIG. 5, the pressure roller 121 and the pressure pad 125 are brought into pressure contact with the driving roller 131 and the fixing pad 173a of the upper belt assembly A with the pressure belt 120 and the fixing belt 105 sandwiched therebetween with a predetermined contact pressure. To do.

  As a result, a fixing nip portion N2 (FIG. 1) or a fixing nip portion N1 (FIG. 5) having a predetermined width is formed between the fixing belt 105 and the pressure belt 120 in the sheet conveying direction V <S9-004>.

  Further, in a state where the lower belt assembly B is held at the pressurization position of FIG. 1 or FIG. 5, the separation command from the CPU 10 <S9-005>, and the pressurization motor 302 is moved in the CCW direction via the motor driver 302D. N rotations that are a predetermined number of rotations are performed <S9-006>. As a result, the pressure cam shaft 307 is driven by half rotation, and the eccentric pressure cam 308 is converted from the first rotation angle position of FIGS. 1 and 5 to the second rotation angle position of FIG.

  That is, the lower belt assembly B is pivoted down and the pressure roller 121 and the pressure pad 125 move to the separation position D <S9-007>. As a result, the formation of the fixing nip N1 or N2 is canceled <S9-008>.

4) Fixing Operation and Temperature Control Control Next, the fixing operation of the fixing device 100 will be described with reference to the control system block diagram of FIG. 9A and the control flowchart of FIG. When the fixing device 100 is in a standby state, the variable pad 173b of the upper belt assembly A is held at the separation position X in FIG. Further, the lower belt assembly B is held at the separation position D in FIG. Driving of the drive motor 301 is stopped, and power supply to the IH heater 170 is also stopped.

  The CPU 10 starts predetermined image forming sequence control based on the input of the print job start signal. For the fixing device 100, the operation is determined according to the basis weight setting of the paper S used in the print job <S10-001>.

  If the basis weight of the paper to be used (sheet basis weight) is 151 gsm or more, the CPU 10 determines whether or not the variable pad 173b is at the separation position X in FIG. 7A by a signal from the variable pad position detecting means (not shown). to decide. If it is determined that it is in the separation position X, the pad drive motor 410 is driven via the motor driver 410D to drive the variable pad cam 182 half a turn. That is, the variable pad 173b is moved from the separation position X in FIG. 7B to the contact position Y in FIGS. 7C and 7D <S10-002>. If it is determined that it is not in the separation position X, the pad drive motor 410 is not driven and the variable pad 173b is kept in the standby position Y.

  If the basis weight of the paper to be used is less than 151 gsm, the CPU 10 determines whether or not the variable pad 173b is at the separation position X in FIG. 7B based on a signal from the variable pad position detecting means. If it is determined that it is in the separation position X, the pad drive motor 410 is not driven, and the variable pad 173b is kept waiting in the separation position X. If it is determined that the position is not in the separation position X, the pad drive motor 410 is driven via the motor driver 410D to drive the variable pad cam 182 half a turn. That is, the variable pad 173b is moved from the contact position Y in FIGS. 7C and 7D to the separation position X in FIG. 7B.

  Thereafter, the CPU 10 drives the pressurizing motor 302 via the motor driver 302D at a predetermined control timing to drive the pressurizing cam shaft 307 by half rotation, whereby the lower belt assembly B is moved from the separated position D in FIG. It moves to the pressurization position U of FIG. 1, FIG.

  Accordingly, when the basis weight of the sheet S is 151 gsm or more, that is, when the variable pad 173b is in the contact position Y, the fixing nip portion N2 is provided between the fixing belt 105 and the pressure belt 120 shown in FIG. Formed <S10-003>.

  When the basis weight of the paper S is less than 151 gsm, that is, when the variable pad 173b is at the separation position X, a fixing nip portion N1 is formed between the fixing belt 105 and the pressure belt 120 shown in FIG. <S10-003>.

  Next, the CPU 10 drives the drive motor 301 via the motor driver 301D to input drive to the drive input gear G (FIG. 4). As a result, the driving roller 131 of the upper belt assembly A is driven as described above, and the rotation of the fixing belt 105 is started.

  Further, the rotational force of the drive input gear G is transmitted to the pressure roller 121 of the lower belt assembly B through a drive gear train (not shown), and the pressure roller 120 is rotated in the counterclockwise direction of the arrow in FIG. Driven by rotation. With the rotation of the pressure roller 121 and by the frictional force with the rotating fixing belt 105, the pressure belt 120 starts rotating in the counterclockwise direction indicated by the arrow in FIG. 1 <S10-004>. The moving directions of the fixing belt 105 and the pressure belt 120 are the same in the fixing nip portions N2 (FIG. 1) and N1 (FIG. 5), and the moving speeds are almost the same.

  Next, the CPU 100 supplies power to the IH heater 170 via the heater controller 170C and the heater driver 170D. Thereby, the rotating fixing belt 105 is heated by electromagnetic induction to rise to a predetermined target temperature and temperature control is performed. That is, temperature control for starting and maintaining the fixing belt 105 at a target temperature of 140 ° C. to 200 ° C. according to the basis weight and paper type of the paper S to be passed is started <S10-005>.

  In this way, the formation of the first fixing nip N1 (FIG. 5) or the second fixing nip N2 (FIG. 1), the rotation of the fixing belt 105 and the pressure belt 120, and the temperature rise of the fixing belt 105 are performed. Temperature is adjusted. In this state, the sheet S on which the unfixed toner image t is formed on the surface is introduced into the fixing device 100 from the image forming unit.

  The sheet S is guided by an inlet guide 184 disposed at the sheet inlet portion of the fixing device 100, and the first fixing nip portion N1 or the second fixing portion which is a pressure contact portion between the fixing belt 105 and the pressure belt 120. The nip portion N2 is entered. A flag sensor 185 including a photo interrupter is disposed in the entrance guide 184 and detects the passage timing of the paper S.

  The sheet S is nipped and conveyed by the first fixing nip portion N1 or the second fixing nip portion N2 with the image carrying surface facing the fixing belt 105 and the opposite surface facing the pressure belt 120. The unfixed toner image t is fixed as a fixed image on the sheet surface by the heat of the fixing belt 105 and the nip pressure. The sheet S that has passed through the fixing nip N2 or N1 is separated from the surface by the fixing belt 105, exits from the sheet exit side of the fixing device 100, and is conveyed and discharged to the discharge tray 21 by the discharge roller pair 20 (FIG. 2). Is done.

  When the conveyance of the sheet S in a predetermined one or a plurality of continuous print jobs is completed, the CPU 10 ends the heating and temperature control of the fixing belt 105 and turns off the power supply to the IH heater 170 <S10. -006>. Further, the drive motor 301 is turned off to stop the rotation of the fixing belt 105 and the pressure belt 120 <S10-007>.

  Further, by driving the pressurizing motor 302 via the motor driver 302D and driving the pressurizing cam shaft 307 by half rotation, the lower belt assembly B is separated from the pressurizing position U of FIG. 1 or FIG. Move to D. As a result, the fixing belt 105, the pressure belt 120, and the fixing nip N2 or N1 are released <S10-008>. Further, when the variable pad 173b is in the contact position Y shown in FIGS. 7C and 7D, the pad drive motor 410 is driven by half rotation via the motor driver 410D so that the variable pad 173b is separated from the separation position X shown in FIG. 7B. <S10-009>.

  In this state, the CPU 10 waits for input of the next print job start signal.

  Here, the temperature control of the fixing belt 105 will be described with reference to the block diagram of the control system of FIG. 9A and the control flowchart of FIG. The upper belt assembly A is provided with a thermistor 220 as a temperature detection member that detects the surface temperature of the fixing belt 105. The CPU 10 applies power to the IH heater 170 via the heater controller 170C and heater driver 170D at a predetermined control timing based on the input of the print job start signal <S11-001>. The fixing belt 105 is heated by electromagnetic induction heating by the IH heater 170.

  The temperature of the fixing belt 105 is detected by the thermistor 220, and detected temperature information (electrical information related to temperature) is input to the CPU 10. When the temperature detected by the thermistor 220 becomes equal to or higher than a predetermined specified value (target temperature), the CPU 10 stops power to the IH heater 170. Thereafter, when the temperature detected by the thermistor 220 becomes lower than a predetermined specified value, the CPU 10 resumes application of power to the IH heater 170 <S11-001> when <S11-004 No>.

  By repeating the above steps S11-001 to S11-004, the temperature of the fixing belt 105 is maintained at a predetermined target temperature. Then, the above fixing belt temperature control is executed until the end of a predetermined print job or a plurality of continuous print jobs <S11-005>.

5) Belt Deviation Control Mechanism A phenomenon (belt deviation movement) that the fixing belt 105 moves so as to be deviated toward one side or the other side in the width direction orthogonal to the paper conveyance direction V during the rotation process. The pressure belt 120 that presses against the fixing belt 105 to form the first fixing nip portion N1 (FIG. 5) or the second fixing nip portion N2 (FIG. 1) also moves along with the fixing belt 105.

  In this embodiment, the shifting of the fixing belt 105 is stabilized within a predetermined shifting range by swing-type shifting control. The swing-type shift control is a method in which the steering roller 132 is tilted in the direction opposite to the shift movement direction of the fixing belt 105 when it is detected that the belt position has moved by a predetermined amount or more from the central portion in the width direction.

  By repeating this swing-type deviation control, the fixing belt 105 periodically moves from one side to the other side in the width direction, so that the deviation movement of the fixing belt 105 can be controlled stably. That is, the fixing belt 105 is configured to reciprocate in a direction orthogonal to the conveyance direction V of the sheet S.

  In the upper belt assembly A, a sensor section (not shown) for detecting the position of the end of the fixing belt is provided at a position near the steering roller 132 on the left side (front side) of the fixing belt 105. The CPU 10 detects the end position (belt shift position) of the fixing belt 105 by this sensor unit, and rotates the stepping motor 155 by a predetermined number of rotations in the forward rotation direction (CW) or the reverse rotation direction (CCW) accordingly. .

  As a result, the left steering roller support arm 154 is rotated upward or downward about the shaft 131a by a predetermined control amount via the above-described mechanisms 157, 152, 161, 151 of FIG. In conjunction with this, the inclination of the steering roller 132 changes and the deviation control of the fixing belt 105 is performed.

<Modification>
Although the embodiments according to the present invention have been described above, the above-described various configurations can be replaced with known configurations within the scope of the idea of the present invention.

(Modification 1)
In the present embodiment described above, when the second fixing nip portion N2 (FIG. 1) is formed, the variable pad 173b contacts the receiving portion 173a-2 of the fixing pad 173a 173c (FIGS. 7D and 7E). It is configured to abut.

  Not limited to this configuration, as shown in the schematic diagram of FIG. 12A, the variable pad 173b may simply be brought into contact with the fixing pad 173a to narrow the gap W between the pads.

  At that time, as shown in FIG. 12C, a configuration in which the gap W between the fixing pad 173a and the variable pad 173b is reduced to 0.2 mm or less by providing an elastic member 181d at the contact portion may be adopted.

  In FIG. 12B, the variable pad 173b in FIG. 12A is moved to the separation position X, and the first fixing nip portion N1 is formed between the fixing belt 105 and the pressure belt 120. It is a schematic diagram at the time of a state.

  Further, as shown in FIG. 12A (d), by providing an elastic member 181e at the contact portion between the variable pad 173b and the pressure pad 125, the gap W between the fixing pad 173a and the variable pad 173b is set to 0.2 mm or less. The structure which stuffs may be sufficient.

  Further, as shown in FIG. 5E, an elastic member 181d is provided on the contact surface between the fixing pad 173a and the variable pad 173b. At the same time, an elastic member 181e is provided at the contact portion between the variable pad 173b and the pressure pad 125. Accordingly, the gap W between the fixing pad 173a and the variable pad 173b may be reduced to 0.2 mm or less.

(Modification 2)
In the fixing device 100 of the embodiment, the variable pad 173b (second pad member) is arranged on the inner side of the belt 105 upstream of the fixing pad 173a (first pad member) in the paper conveyance direction V. Not limited to. On the contrary, in other words, the variable pad 173b can be arranged downstream of the fixing pad 173a in the sheet conveyance direction V.

(Modification 3)
In the above-described embodiment, the electromagnetic induction heating method has been described as the heating mechanism. Specifically, for example, a heating mechanism such as a halogen heater is disposed inside the driving roller 131 and the pressure roller 121.

(Modification 4)
In the fixing device 100 of the embodiment, each of the pair of rotating bodies 105 and 120 forming the first fixing nip portion N1 or the second fixing nip portion N2 for heating the toner image t on the sheet is endless. However, the present invention is not limited to this. One of the rotating bodies 105 and 120 may be an endless belt member, and the other may be a roller body. That is, an apparatus configuration in which at least one of the rotating bodies 105 and 120 is an endless belt member can be obtained.

(Modification 5)
In the above-described embodiment, the fixing device that fixes the unfixed toner image t to the paper S has been described as an example. However, the present invention is not limited to this, and the toner image that is assumed on the paper S in order to improve the gloss of the image. The present invention can be similarly applied to a device that heats and presses (also called a fixing device in this case).

  100 ·· Image heating device (fixing device), 105 · 120 · · A pair of rotating bodies (fixing belt and pressure belt), N1 · · First nip, N2 · · · Second nip, S · · · Sheet (paper), t ... toner image, V ... sheet transport direction, 173a ... first pad member (fixing pad), 173b ... second pad member (variable pad), 180 ... switching mechanism ( (Movement mechanism: Pad variable mechanism)

Claims (8)

A pair of rotating bodies, at least one of which is an endless belt forming a nip for heating a toner image on a sheet;
A first pad member and a second pad member that press the endless belt from the inside toward the other rotating body;
The second pad member is arranged such that the first pad member and the second pad member can be in contact with the endless belt and the first pad member can be in contact with the endless belt. An image heating apparatus comprising: a moving mechanism that moves the image heating apparatus.   Only the first pad member and the state where the first pad member and the second pad member are in contact with the endless belt by controlling the moving mechanism according to the basis weight of the sheet introduced and used in the apparatus The image heating apparatus according to claim 1, further comprising a control unit that switches between a state in which the belt is in contact with the endless belt.   The control unit controls the moving mechanism so that the first pad member and the second pad member are in contact with the endless belt when the basis weight of the sheet is equal to or greater than a predetermined value. 3. The image heating apparatus according to claim 2, wherein the moving mechanism is controlled to switch to a state in which only the first pad member is in contact with the endless belt when the number is less than 3.   The said 2nd pad member has a contact part positioned in contact with the said 1st pad member in the state contact | abutted with the said endless belt with the said 1st pad member, The 1st thru | or 3 characterized by the above-mentioned. The image heating apparatus according to any one of the above.   The said 2nd pad member has an elastic member in the surface contact | abutted with a said 1st pad member in the state contact | abutted with the said endless belt with the said 1st pad member. The image heating apparatus according to one item.   The said 2nd pad member has an elastic member in the surface which forms the nip part of the said 2nd pad member in the state contact | abutted with the said endless belt with the said 1st pad member. The image heating apparatus according to any one of the above.   7. The image heating according to claim 1, wherein the second pad member is disposed upstream of the first pad member in the sheet conveyance direction in the nip portion. apparatus.   The image heating according to any one of claims 1 to 6, wherein the second pad member is disposed downstream of the first pad member in the sheet conveyance direction in the nip portion. apparatus.