JP4750459B2 - Image heating device - Google Patents

Description

  The present invention relates to a first endless belt, a second endless belt that forms a nip portion for heating an image on a recording material between the first belt, and the first belt. The present invention relates to an image heating apparatus having first control means for controlling and second control means for controlling the deviation of the second belt.

  Patent Document 1 describes a twin belt type image heating apparatus (hereinafter referred to as a belt fixing apparatus) as described above.

  Such a belt fixing device has a fixing nip width (length of the fixing nip in the recording material traveling direction) in comparison with a heat roller type fixing device mainly composed of a rotating roller pair of a fixing roller and a pressure roller. Since the endless belt having a smaller heat capacity than the fixing roller is used as well as widening, the endless belt can be heated quickly, and the start-up time of the fixing device can be shortened.

  By the way, in the belt fixing device, the belt moves and moves in the width direction (a direction orthogonal to the direction of rotation and conveyance of the belt) during the rotation and conveyance of the belt, and therefore, it is necessary to take measures to restrict the movement of the belt.

  In a belt fixing device in which a nip is formed by an endless belt and a roller, as a belt shift movement regulating means, regulation by a rib or a flange member (Patent Document 2), or a shape of a belt suspension conveying roller as a belt suspension member For example, a crown shape.

In addition, there is a belt shift control mechanism that changes the shift movement in the belt width direction in the belt rotation conveyance process to an infinite reciprocation movement within a predetermined range (Patent Document 3). That is, a means for detecting the belt shift position is provided, and when it is detected that the belt shift toward one side in the width direction has reached a predetermined limit position, the belt shift in the return direction is detected as the belt width. For example, a means for displacing the belt suspension conveying roller is operated so as to change the direction to the other side. On the other hand, when it is detected that the movement of the belt toward the other side in the width direction has reached a predetermined limit position, the belt is suspended so that the movement of the belt is changed to the belt width direction, which is the return direction. A means for displacing the transport roller is operated.
JP-A-10-74004 JP-A-10-20691 Japanese Patent Laid-Open No. 5-238585

However, in the belt shift movement restricting means such as ribs, flange members, and crown- shaped belt suspension conveying rollers, it is difficult to control the shift when the belt is a thin film and the material is polyimide or the like with less elasticity. It is difficult to ensure stable rotation and conveyance of the belt.

  The belt shift movement control mechanism switches the belt shift direction between the forward and reverse directions under a certain condition. In the belt fixing device of the twin belt type, the fixing belt as the first belt and the pressure belt as the second belt have independent belt shift movement control mechanisms, and perform shift movement control independently. ing. However, when the shifting directions of the fixing belt and the pressure belt are aligned in the same direction, the shifting forces of both belts overlap, causing the belt to move at a rapid speed, and the belt shift control reciprocation condition is disrupted. The belt may not be able to reciprocate inside.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to further improve the reliability of belt shift control and improve the durability of the twin belt type image heating apparatus having a belt shift control mechanism.

  It is an object of the present invention to reduce the downtime of the apparatus due to a shift error by suppressing the shift and shift of the first and second belts.

  The object is to extend the life of the load related to the shift control by reducing the number of times of the belt shift control.

  A typical configuration of an image heating apparatus for achieving the above object is a first endless belt and a first nip portion for heating an image on a recording material between the first belt and the first belt. In the image heating apparatus, the first endless belt, first control means for controlling the deviation of the first belt, and second control means for controlling the deviation of the second belt, It is characterized in that control is performed so that the direction in which the belt is shifted and the direction in which the second belt is shifted are opposite to each other.

Another typical configuration of the image heating apparatus for achieving the above object is a first endless belt and a nip portion for heating an image on a recording material between the first belt and the first endless belt. In an image heating apparatus comprising: a second endless belt that forms a first belt; a first control unit that controls a shift of the first belt; and a second control unit that controls a shift of the second belt. ,
A first mode in which the second belt shift control is performed in accordance with the first belt shift control; and a second mode in which the second belt shift control is performed regardless of the first belt shift control. The mode is selectable.

  Still another typical configuration of the image heating apparatus for achieving the above object includes a first endless belt, a first roller that stretches the first belt, and the first belt. An image heating apparatus including: a second endless belt that forms a nip portion for heating an image on a recording material between the second belt and a second roller that stretches the second belt. The tilting direction of the first roller and the tilting direction of the second roller intersect each other.

  That is, in the state where the first and second belts are in contact with each other and rotating, the first and second deviation control means reverse the moving directions of the first and second belts to each other. It is possible to cancel the belt shift force and suppress the belt shift movement of both belts. As a result, it is possible to suppress the shift of the first and second belts and the occurrence of the shift, and to reduce the downtime of the apparatus due to the shift error. Even if a slippage occurs, it is possible to always cancel the shift force of both belts by performing the belt shift control so that the belt shift directions of both belts are opposite. By reducing the number of times the belt is controlled to be offset, the life of the load related to the offset control can be extended. As a result, it is possible to improve the reliability of belt deviation control and the durability of the apparatus.

<Overall Configuration of Image Forming Apparatus Example>
FIG. 1 is a schematic configuration model diagram of an image forming apparatus 100 in this embodiment. The image forming apparatus includes a laser beam scanning exposure type printer unit 300 using a transfer type electrophotographic process, an image reader unit 200, a document feeding device 1000, and a finisher 500. In this example, devices for forming an image on a recording material are collectively referred to as an image forming unit. Details of various devices constituting the image forming means will be described below.

  The document feeder 1000 feeds the document O set on the document tray 1001 one by one in order from the first page. The fed document O is fed downward on the platen glass 102 of the image reader unit 200 through a curved path. Further, the paper is conveyed from the left to the right on the platen glass 102 and discharged to the paper discharge tray 112.

  At this time, the reader scanner unit 104 of the image reader unit 200 sequentially flows an image of the downward surface of the document passing over the platen glass 102 that is held at a predetermined fixed position below the platen glass 102. Read photoelectrically by reading method.

  That is, the reader scanner unit 104 illuminates the downward surface of the document passing over the platen glass 102 with the light of the lamp 103 through the platen glass 102. Then, the reflected light of the illumination light from the document surface is guided to the image sensor 109 via the mirrors 105 to 107 and the lens 108 to form an image, and the document image is photoelectrically read.

  Photoelectric reading of a document image by the image sensor 109 can also be performed by an optical system moving method. That is, the document O is transported onto the platen glass 102 by the document feeder 1000 and temporarily stopped. Then, the reader scanner unit 104 and the mirrors 106 and 107 are moved from the left to the right along the lower surface of the platen glass 102, and the original image is photoelectrically read by the optical system moving method.

  The electrical signal of the original image read by the image sensor 109 is subjected to image processing and sent to an exposure control unit (laser scanner) 110. The exposure control unit 110 outputs a laser beam L that is modulated in accordance with the electrical signal of the document image that has undergone image processing.

  Reference numeral 111 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined speed. The photosensitive drum 111 is subjected to a uniform charging process with a predetermined polarity and potential by the charger 112 in the rotating state. Next, the charged surface is subjected to scanning exposure by the laser light L output from the exposure control unit 110. Thereby, an electrostatic latent image corresponding to the scanning exposure pattern is formed on the surface of the photosensitive drum 111. The electrostatic latent image is developed as a toner image by the developing device 113.

  The toner image formed on the photosensitive drum 111 is transferred in the transfer unit 117 to a sheet S as a fed recording material fed to the transfer unit 117 at a control timing. The sheet S is fed from one of the first or second sheet feeding cassettes 114 and 115, the manual sheet feeding unit 125, and the duplex conveyance path 124, and is transferred to the transfer unit 117 by the registration roller 116 at a predetermined control timing. Be fed.

  The sheet S that has received the transfer of the toner image in the transfer unit 117 is separated from the surface of the photosensitive drum 111 and is introduced into the fixing device F to be subjected to a toner image fixing process. Details of the configuration of the fixing device F will be described later.

  The surface of the photosensitive drum 111 after the sheet separation is cleaned by a cleaning device 118 after removal of residual deposits such as transfer residual toner and paper dust, and is repeatedly used for image formation.

  The sheet that has passed through the fixing device F is once guided to the path 122 by the flapper 121 in the single-sided image forming mode. Further, after the trailing edge of the sheet passes through the flapper 121, the sheet is switched back and guided to the discharge roller 123 by the flapper 121. Thus, the sheet is discharged from the printer unit 300 to the finisher 500 side by the discharge roller 123 with the image-formed surface facing downward (face down).

  In the mode in which a hard sheet such as an OHP sheet is supplied from the manual sheet feeding unit 125 to perform image formation, the sheet that has exited the fixing device F is moved straight without being guided to the path 122, and is discharged by the discharge roller 123. The part 300 is discharged to the finisher 500 side. That is, the sheet exiting the fixing device F is passed over the flapper 121 and discharged to the finisher 500 side by the discharge roller 123 with the image forming surface facing upward (face-up).

  In the double-sided printing mode in which images are formed on both sides of the sheet, the sheet that has been subjected to the fixing process on the first side by the fixing device F is guided to the discharge roller 123 through the upper side of the flapper 121. Then, immediately after the trailing edge of the sheet passes through the flapper 121, the sheet is switched back and guided by the flapper 121 from the path 122 to the duplex conveyance path 124. Then, the sheet is fed again from the double-sided conveyance path 124 to the transfer unit 117 in a reverse state. As a result, the toner image is transferred to the second surface of the sheet. The sheet is again introduced into the fixing device F, and the toner image is fixed to the second surface.

  Thereafter, the sheet on which the double-sided image is formed is discharged from the printer unit 300 to the finisher 500 side by the discharge roller 123 through the same discharge path as in the above-described single-sided image formation mode.

  The finisher 500 performs processing such as shift processing, binding processing, and punching. An inserter 1900 is provided on the finisher 500 and feeds a cover sheet, a slip sheet, and the like to the finisher 500. Further, the alignment plate 1702 moves to an angle perpendicular to the conveyance direction when the recording material is shifted and output, such as shift sorting, and discharges the sheet to the back or front of the tray 1701.

<Operation panel>
Next, an operation panel as an operation unit for setting various modes by the operator will be described. FIG. 2 is a diagram illustrating a configuration of the operation panel 60 provided in the image forming apparatus.

  Reference numeral 400 denotes a copy start key for instructing the start of copying. Reference numeral 401 denotes a reset key for returning to the standard mode. Reference numeral 402 denotes a guidance key that is pressed when the guidance function is used. Reference numeral 403 denotes a numeric keypad for inputting a numerical value such as a set number of sheets. Reference numeral 404 denotes a clear key for clearing a numerical value. Reference numeral 405 denotes a stop key for stopping copying during continuous copying. Reference numeral 406 denotes a liquid crystal display unit and a touch panel for displaying various mode settings such as a staple mode, a bookbinding mode, and a double-sided print setting, and a printer status. Reference numeral 407 denotes an interrupt key for interrupting and taking an emergency copy during continuous copying or during use as a fax or printer. Reference numeral 408 denotes a personal identification key for managing the number of copies by individual or department. Reference numeral 409 denotes a soft switch for turning on / off the power of the image forming apparatus main body. Reference numeral 410 denotes a function key used when changing the function of the image forming apparatus. Reference numeral 411 denotes a user mode key for entering a user mode in which the user sets items in advance, such as ON / OFF of auto cassette change or a change in setting time until entering an energy saving mode.

Reference numerals 450 to 452 denote recording material type setting keys (means for setting the type of recording material used for image formation). With this key, a transparency film for an overhead projector (hereinafter referred to as an OHP sheet) as a light-transmitting resin, a thick paper, a resin-coated paper which is a paper provided with a resin layer on the front surface or the back surface is set. In this embodiment, the cardboard is a recording material having a basis weight of 110 g / m ² or more. Reference numeral 453 denotes a key for performing duplex printing.

<Fixing device F>
FIG. 3 is an enlarged cross-sectional model view of a main part of the fixing device F and a block diagram of a control system. This fixing device is an electromagnetic induction heating type / belt fixing type heating device.

  U1 is a fixing belt unit, and U2 is a pressure belt unit. The two units U1 and U2 are arranged substantially in parallel vertically and pressed to form a fixing nip portion N therebetween.

(1) Fixing belt unit U1
In the fixing belt unit U1, reference numeral 3 denotes an endless fixing belt as a first belt. The fixing belt 3 is a flexible and electromagnetic induction heat generating belt. Specifically, the fixing belt 3 in this example has nickel as a magnetic material as a base layer (metal layer), and a heat-resistant silicone rubber layer as an elastic layer on the outer periphery. Further, a fluororesin layer (for example, PFA or PTFE) is provided on the outer periphery of the elastic layer as a surface release layer. A polyimide layer is provided on the inner peripheral surface.

  Reference numeral 1 is a fixing roller, 7 is a shift control roller, and 9 is a belt guide, which are arranged substantially in parallel. The fixing belt 3 is suspended around these three members 1, 7, and 9 as suspension members. The fixing roller 1 includes a cored bar made of an iron alloy and a silicon rubber sponge layer. The belt guide 9 is made of resin and functions as a tension member to apply a constant tension to the fixing belt 3. The belt guide 9 is provided with a belt guide cover 11 in order to reduce the frictional resistance with the inner surface of the fixing belt 3. FIG. 4 is an exploded perspective model view of the belt guide 9 and the belt guide cover 11. The belt guide cover 11 is formed by coating a glass fiber cloth coated with a fluororesin on the upstream side of the belt guide 9 in the fixing belt rotation direction with screws 11a.

  The fixing roller 1 receives a driving force of a motor M as a driving source through a driving transmission means (not shown) and is driven to rotate at a predetermined speed in a clockwise direction indicated by an arrow. The motor M is controlled by a control unit (CPU) 60. As the fixing roller 1 rotates, the fixing belt 3 is rotationally driven in the clockwise direction of the arrow by friction between the surface of the silicone rubber sponge of the fixing roller and the inner surface polyimide layer of the fixing belt 3. The deviation control roller 7 rotates following the rotation of the fixing belt 3.

  Reference numeral 18 denotes an excitation unit. The excitation unit 18 is a heating source (induction heating means) for inductively heating the fixing belt 3 and is disposed at a position upstream of the fixing nip portion N in the fixing belt moving direction. The excitation unit 18 includes an induction heating coil (excitation coil) 5 that uses, for example, a litz wire as an electric wire and is wound around a horizontally long and flat sheet-like spiral coil. Further, the magnetic core 6 that covers the induction heating coil 5 is provided so that the magnetic field generated by the induction heating coil 5 does not leak to any part other than the metal layer that is the magnetic material layer of the fixing belt 3. The excitation unit 18 is a horizontally long and thin plate member obtained by integrally molding the induction heating coil 5 and the magnetic core 6 with an electrically insulating resin.

  In the present embodiment, the above-described excitation unit 18 is straddled across the fixing roller 1 and the deviation control roller 7 on the upper surface side of the outer peripheral surface of the fixing belt 3 opposite to the fixing nip portion N. And facing each other with a predetermined gap (gap). More specifically, the fixing belt 3 and the induction heating coil 5 are electrically insulated by a 0.5 mm mold, and the distance between the fixing belt 3 and the induction heating coil 5 is constant at 1.5 mm.

  In a state where the fixing belt 3 is rotated, a high frequency current of 20 to 50 kHz is passed through the induction heating coil 5 from the excitation circuit 61, so that the metal layer of the fixing belt 3 generates induction heat. As a result, the fixing belt 3 is heated and the temperature rises. Further, the control unit 60 outputs from the excitation circuit 61 to the induction heating coil 5 based on the detection value of the temperature sensor 13 that detects the temperature of the fixing belt 3 so that the fixing belt 3 becomes constant at a predetermined temperature (fixing temperature). The temperature is adjusted by changing the frequency of the high-frequency current to be controlled and controlling the power input to the induction heating coil 5.

  The temperature sensor 13 is attached to the belt guide 9 via a spring plate member 13a so as to elastically contact a position where the amount of heat generated by the induction heating coil 5 on the inner surface of the fixing belt 3 is the highest. That is, since the metal layer of the fixing belt 3 generates heat, the temperature of the fixing belt 3 can be detected very accurately and at a high response speed by arranging the temperature sensor 13 as in this embodiment. FIG. 5 shows the heat generation distribution of the fixing belt 3 at the portion facing the excitation unit 18 (development view). There are two portions H and H having a large amount of heat generation in the fixing belt moving direction. The temperature sensor 13 is disposed in contact with the inner surface portion of the fixing belt at a position corresponding to the portion where the heat generation amount is large.

(2) Pressure belt unit U2
In the pressure belt unit U2, 4 is a pressure belt as a second belt. The pressure belt 4 is an endless belt having heat resistance and flexibility. In this embodiment, the same layer structure as that of the fixing belt 3 is used. 2 is a pressure roller, 8 is a shift control roller, 10 is a belt guide, and these are arranged substantially in parallel. The pressure belt 4 is suspended around these three members 2, 8, 10 as suspension members. The pressure roller 2 includes a cored bar made of an iron alloy and a silicon rubber layer. The belt guide 10 is made of resin and functions as a tension member to apply a constant tension to the pressure belt 4. The belt guide 9 is provided with a belt guide cover 12 in order to reduce frictional resistance with the inner surface of the fixing belt 3. The belt guide cover 12 is a glass fiber cloth coated with a fluororesin, which is fixed to the upstream portion of the belt guide 10 in the rotation direction of the pressure belt with screws 12a.

The pressure roller 2 receives the driving force of the motor M, which is a driving source, via a driving transmission means (not shown) and is driven to rotate at a predetermined speed in the counterclockwise direction of the arrow. The motor M is controlled by the control unit 60. Due to the rotation of the pressure roller 2, the pressure belt 4 is rotationally driven in the counterclockwise direction indicated by the arrow by friction between the silicon rubber surface of the pressure roller 2 and the inner surface polyimide layer of the pressure belt 4. The shift control roller 8 rotates following the rotation of the pressure belt 4.

The pressure belt unit U2 is controlled to be switched between a wearing state in which the pressure belt unit U2 is pressed against the fixing belt unit U1 and a detached state in which the pressure belt unit U2 is separated from the fixing belt unit U1. Although a specific configuration of the detaching mechanism 62 is omitted in the drawing, for example, it can be configured by a swing mechanism ( shift mechanism) using a cam coupled to an electromagnetic solenoid or a motor.

  When the pressure belt unit U2 is pressed against the fixing belt unit U1 by the detaching mechanism 62, the belt guide 10 on the pressure belt unit U2 side faces the belt guide 9 on the fixing belt unit U1 side. 4 and the fixing belt 3 are pressed. The pressure roller 2 on the pressure belt unit U2 side is pressed toward the fixing roller 1 on the fixing belt unit U1 side with the pressure belt 4 and the fixing belt 3 interposed therebetween. As a result, the fixing belt 3 of the fixing belt unit U1 and the pressure belt 4 of the pressure belt unit U2 come into contact with each other to form a fixing nip portion N therebetween.

  Further, by making the pressure roller 2 harder than the fixing roller 1, the deformation of the fixing roller 1 becomes larger at the fixing nip exit, which is a pressure contact portion between the fixing belt 3 and the pressure belt 4. As a result, the fixing belt 3 is also greatly deformed, and the toner image fixed by heat and pressure on the surface of the sheet S in the fixing nip N is self-separated from the fixing belt 3 at the fixing nip exit, and the sheet S is removed from the fixing belt 3. It can be well separated and transported.

  In this embodiment, the control unit 60 sets the detaching mechanism 62 so that the pressure belt unit U2 is held in the detached state separated from the fixing belt unit U1 during the standby for the image forming job to start. I have control. During this standby, the fixing belt 3 and the pressure belt 4 are driven to rotate.

(3) Fixing Operation The control unit 60 activates the image forming unit based on the image forming JOB start signal to start the image forming operation. The fixing device F is switched and held in a wearing state in which the pressure belt unit U2 is pressed against the fixing belt unit U1 by controlling the detaching mechanism 62. The fixing belt 3 and the pressure belt 4 are in a rotationally driven state, and move at substantially the same predetermined speed in the same direction in a fixing nip portion N that is a pressure contact portion between them. In addition, the control unit 60 controls the temperature so that a high-frequency current flows from the excitation circuit 61 to the induction heating coil 5 to cause the fixing belt 3 to generate heat by heating to a predetermined fixing temperature and to maintain the temperature.

  In this state, the sheet S on which the unfixed toner image t is formed is introduced into the fixing nip portion N. The sheet S is sandwiched between the fixing belt 3 and the pressure belt 4 and conveyed through the fixing nip portion N, and the toner image t is subjected to heat and pressure fixing by the heat of the fixing belt 3 and the pressure of the fixing nip portion N. The fixing belt 3 and the pressure belt 4 are rotationally driven so that their peripheral speeds coincide with each other, so that the sheet S sent between the belts 3 and 4 can be stably conveyed. Since the sheet S adheres to the fixing belt 3 and the pressure belt 4 at the fixing nip portion N and is heated at that portion, the heat transfer efficiency to the sheet S is increased. At the exit of the fixing nip N, the sheet S is separated from the surface of the fixing belt 3 and discharged.

  Such a belt fixing type apparatus can set the length of the fixing nip portion N, which is a heating portion, in the belt moving direction to be long, so that fixing can be performed at high speed.

(4) Belt Deviation Control FIG. 6 is a schematic diagram for explaining deviation control means for controlling the movement movement of the fixing belt 3 in the width direction. FIG. 7 is a schematic diagram for explaining a shift control means for controlling the shift movement of the pressure belt 4 in the width direction.

  Here, a direction perpendicular to the belt rotation direction G in the belt surface of the fixing belt 3 and the pressure belt 4 is defined as a width direction W of the belt.

  a: Consider the case where the fixing belt 3 and the pressure belt 4 are driven to rotate apart.

  In this case, in the fixing belt unit U1, the parallelism (X axis, Y axis, Z axis) among the fixing roller 1, the belt guide 9, and the shift control roller 7 which are fixing belt suspension members is not set to ± 0. As far as the fixing belt 3 is concerned, the lateral movement of the fixing belt 3 occurs. That is, the fixing belt 3 moves toward the left (back side) Q or the right (front side) P along the longitudinal direction (axial direction) of the fixing roller 1.

  Further, in the pressure belt unit U2, the pressure belt 4 is arranged in the width direction unless the parallelism between the pressure roller 2, the belt guide 10, and the shift control roller 8, which are pressure belt suspension members, is ± 0. This causes a movement movement toward the side. That is, the pressure belt 4 moves toward the left Q or the right P along the longitudinal direction (axial direction) of the pressure roller 2.

  b: Consider the case where the fixing belt 3 and the pressure belt 4 are in contact with each other and are driven to rotate.

  In this case, unless both the fixing belt unit U1 and the pressure belt unit U2 have a parallelism between the fixing roller 1 and the pressure roller 2, the belt guides 9 and 10 and the shift control rollers 7 and 8 within ± 0. The belt moves in the lateral direction. That is, the fixing belt 3 or the pressure belt 4 moves toward the left Q or the right P along the longitudinal direction of the fixing roller 1 or the pressure roller 2.

  Then, if the belt moves excessively, the belt end will rub against the left side plate 26 or the right side plate 27 of the fixing belt unit U1 or the left side plate 36 or the right side plate 37 of the pressure belt unit U2.

  However, in consideration of the accuracy and assembly accuracy of each component itself, it is obvious that the above parallelism is not practical, and some belt deviation control is necessary.

  Therefore, the belt deviation control means in this embodiment will be described.

In the fixing belt unit U1, with respect to the shift control roller 7 (first shift control roller : first roller ), an arrow is moved by a swing mechanism including a stepping motor 23 with the center portion 22 in the longitudinal direction (axial direction) as a center. 24 or the direction of the arrow 25 can be freely swung. The stepping motor 23 is controlled by the control unit 60. Note that such a swing mechanism of the shift control roller itself is well known, and its specific configuration is omitted in the drawing. In this embodiment, when the stepping motor 23 rotates in the clockwise direction, the shift control roller 7 is displaced in the direction of the arrow 24 by rotating in the direction of the arrow 25 and in the counterclockwise direction. At this time, the fixing belt 3 in the rotationally driven state is moved in the direction of the arrow Q and in the direction of the arrow 24 when the shift control roller 7 is displaced in the direction of the arrow 25 according to the displacement direction of the shift control roller 7. When it is displaced, the direction of shift toward the front side of the arrow P changes.

Similarly, in the pressure belt unit U2, with respect to the shift control roller 8 (second shift control roller : second roller ), the swing including the stepping motor 33 is centered on the center portion in the longitudinal direction (axial direction). The moving mechanism can swing freely in the direction of arrow 34 or arrow 35. The stepping motor 33 is controlled by the control unit 60. Note that such a swing mechanism of the shift control roller itself is well known, and its specific configuration is omitted in the drawing. When the stepping motor 33 is rotated in the clockwise direction, the shift control roller 8 is displaced in the direction of the arrow 35 and is displaced in the direction of the arrow 34 by being rotated in the counterclockwise direction. At this time, the pressure belt 4 in the rotating state is displaced in the direction of the arrow Q when displaced in the direction of the arrow 35 and in the direction of the arrow 24 according to the displacement direction of the shift control roller 8. Is shifted toward the front side of the arrow P.

  The belt position detection flags 14 and 15 that are movable pieces that move along both ends of the fixing belt 3 are used as the light source of the photosensor 20 when the fixing belt 3 approaches the near side P. The optical path between the light receiving elements is shielded. When the fixing belt 3 moves closer to the back side Q, the belt position detection flag 14 blocks the optical path between the light source of the photosensor 20 and the light receiving element.

  Further, the belt position detection flags 16 and 17 which are movable pieces that move along both end portions of the pressure belt 4 are arranged so that the belt position detection flag 16 of the photosensor 30 when the pressure belt 4 approaches the near side P. The optical path between the light source and the light receiving element is shielded. When the pressure belt 4 moves toward the back Q, the belt position detection flag 17 blocks the light path between the light source of the photosensor 31 and the light receiving element.

  Here, the output states of the photosensors 20, 21, 30, and 31 by the belt position detection flags 14, 15, 16, and 17 will be described with reference to the schematic diagrams of FIGS.

  The belt position detection flags 14, 15, 16, and 17 have the shapes shown in FIGS. The control unit 60 can detect the belt shift state based on the outputs of the photosensors 20, 21, 30, and 31 that are shielded by the belt position detection flag. In states A and E in the figure, the optical paths 20a (30a) and 21a (31a) of the photosensors 20 (30) and 21 (31) on both the front side and the back side are shielded (blocked), and the belt is cut off. Means that has occurred. In the state C, the optical paths 20a (30a) and 21a (31a) of the photosensors 20 (30) and 21 (31) on both the front side and the rear side are light-transmitted (open), and the belt is offset. Means no. When the sensor output is a combination of light shielding and light transmission (states B and D), it indicates that a shift has occurred. The control unit 60 can determine whether the fixing belt 3 or the pressure belt 4 is closer to the front side / back side than the output of the photosensors 20, 21, 30, 31 (see ( b)).

Next, the shift force when the shift control rollers 7 and 8 are displaced will be described with reference to FIG. Here, in FIGS. 6 and 7, the center lines in the state where the shift control rollers 7 and 8 are not displaced are set to 28 and 38. The center lines of the shift control rollers 7 and 8 in the state displaced in the directions of the arrows 24 and 25 or the arrows 34 and 35 are defined as 28-a and 38-a. FIG. 12 shows the relationship of the shifting force that the fixing belt 3 or the pressure belt 4 moves in the directions of arrows P and Q when the angle formed by the center lines 28 and 28-a and 38 and 38-a is θ. FIG. The vertical axis represents the shifting force, and the shifting force in the direction of arrow P is positive (Kg / s ² ), and the shifting force in the direction of arrow Q is negative (Kg / s ² ). As for the horizontal axis, the angle θ formed when displaced in the direction of the arrow 24 or 34 is positive, and the angle formed every time displaced in the direction of the arrow 25 or 35 is negative. The solid line 50 is the case where the parallelism described above is ± 0. A case where the parallelism is not ± 0 is a dotted line 51 or 52. When the parallelism is ± 0, when θ is 0, there is no belt shift and no shift control is required. However, when the parallelism is not ± 0, for example, in the case of the dotted line 51, the position of the point A is a portion having no shift force, and the shift control roller 7 or 8 needs to be displaced in the direction of the arrow 28 or 38. . Similarly, in the case of the dotted line 52, the position of the point B is a portion having no shift force, and the shift control roller 7 or 8 needs to be displaced in the direction of the arrow 29 or 39.

Here, when the offset force of the fixing belt 3 is F1 (Kg / s ² ) and the offset force of the pressure belt 4 is F2 (Kg / s ² ), the fixing belt 3 and the pressure belt 4 are in contact with each other. In the state where F1 and F2 are in a state of being present, each acts. At this time, it can be seen that if F1 + F2 = 0 (Kg / s ² ), the shifting force between the fixing belt 3 and the pressure belt 4 is canceled out, so that the shifting between the belts itself disappears.

  In this embodiment, originally, the inclination direction of the deviation control roller 7 (first deviation control roller) of the fixing belt unit U1 and the inclination of the deviation control roller 8 (second deviation control roller) of the pressure belt unit U2. It is configured so that the directions intersect. As a result, the shifting force between the fixing belt 3 and the pressure belt 4 is canceled out, so that the shifting itself between the belts 3 and 4 is eliminated.

(4-1) Belt Deviation Control When Fixing Belt 3 and Pressure Belt 4 are Rotated and Driven In the present embodiment, as described above, the image forming apparatus waits for the start of image forming JOB. During the standby, the pressure belt unit U2 is separated from the fixing belt unit U1. That is, the fixing belt 3 and the pressure belt 4 are in a separated state. The fixing belt 3 and the pressure belt 4 are rotationally driven. In this state, the fixing belt 3 and the pressure belt 4 are independently controlled to shift the shifting movement in the belt width direction to an infinite reciprocating movement within a predetermined range to prevent the belt from shifting. Yes.

  FIG. 12 is a deviation control flowchart for the fixing belt 3.

  During the standby of S100, it waits for the photosensor 20 or 21 to be shielded from light in S101. If the light is not shielded, both photosensors are repeatedly monitored until the light is shielded. If the light is blocked, the sensor light blocking time T1 is updated in S102.

  In S103, the position of the fixing belt 3 is determined from the table of FIG. 10B, and it is determined which of the photosensors 20 and 21 is shielded from light. If it is closer to the front side (photosensor 20: light shielding, photosensor 21: translucent), the process proceeds to S104. If it is close to the back side (photo sensor 20: light transmission, photo sensor 21: light shielding), the process proceeds to S108.

  In S104, the sensor light shielding information D1 is set as the photosensor 20, and the process proceeds to S105. In step S105, the stepping motor 23 is rotated in the clockwise direction, and the shift control roller 7 is displaced in the direction of the arrow 25. Subsequently, in S106, the output of the photosensor 20 is confirmed again. If the light is transmitted, that is, if the shift of the fixing belt 3 returns, the process returns to S101. If the light is continuously shielded, the process proceeds to S107.

  In S107, it is confirmed whether or not the photosensor 21 is shielded from light. If the light is shielded, it is determined that the fixing belt 3 has approached the front side, and the process proceeds to S112. If the photosensor 21 is transparent, the process returns to S106.

  If it is determined in S112 that there is a deadline error, the operation of the image forming apparatus is urgently stopped, a message to that effect, and a service man call.

  Similarly, in S108, the sensor light shielding information D1 is used as the photosensor 21, and the process proceeds to S109. In S109, the stepping motor 23 is rotated counterclockwise, and the shift control roller 7 is displaced in the direction of the arrow 24. Subsequently, in S110, it is confirmed again whether the photosensor 21 is shielded from light. If the light is transmitted, the process returns to S101. When the light is shielded, the process proceeds to S111. If the photosensor 20 is shielded from light in S111, that is, it is determined that the fixing belt 3 is close to the back side, and the process proceeds to S112. If the photosensor 20 is transparent, the process returns to S110.

  FIG. 13 is a flowchart for controlling the shift of the pressure belt 4.

  During the standby of S200, it waits for the photosensor 30 or 31 to be shielded from light in S201. If the light is not shielded, both photosensors are repeatedly monitored until the light is shielded. If the light is shielded, the sensor light shielding time T2 is updated in S202. In S203, the position of the pressure belt 4 is determined from Table 1, and it is determined which of the photosensors 30 and 31 is shielded from light. If it is closer to the front side (photosensor 30: light shielding, photosensor 31: translucent), the process proceeds to S204. If it is close to the back side (photo sensor 30: light transmission, photo sensor 31: light shielding), the process proceeds to S207.

  In S204, the sensor light shielding information D2 is set as the photosensor 30, and the process proceeds to S205. In step S205, the stepping motor 33 is rotated in the clockwise direction, and the shift control roller 8 is displaced in the direction of the arrow 35. Subsequently, in S206, the output of the photosensor 30 is confirmed again. If light is transmitted, that is, if the shift of the pressure belt 4 returns, the process returns to S201. If the light is continuously shielded, the process proceeds to S207.

  In S207, it is confirmed whether or not the photosensor 31 is shielded from light. If the light is shielded, it is determined that the pressure belt 4 has moved to the near side, and the process proceeds to S212. If the photo sensor 31 is transparent, the process returns to S206.

  Similarly, in S208, the sensor light shielding information D2 is used as the photosensor 31, and the process proceeds to S209. In step S209, the stepping motor 33 is rotated counterclockwise, and the shift control roller 8 is displaced in the direction of the arrow 34. Subsequently, in S210, it is confirmed again whether the photosensor 31 is shielded from light. If the light is transmitted, the process returns to S201. When the light is shielded, the process proceeds to S211. If the photosensor 30 is shielded from light in S211, that is, it is determined that the pressure belt 4 is close to the back side, and the process proceeds to S212. If the photosensor 30 is transparent, the process returns to S210.

  As described above, when the fixing belt 3 and the pressure belt 4 are separated from each other during standby, the belts 3 and 4 are independently controlled to prevent the belt from slipping.

(4-2) Belt Deviation Control when Fixing Belt 3 and Pressure Belt 4 Abut and Drive Rotation FIG. 14 is a flowchart of this deviation control.

  When the job starts in S300, the control unit 60 checks in S301 whether the shift control direction of the fixing belt 3 and the shift control direction of the pressure belt 4 are the same. If they are not the same, the fixing belt 3 and the pressure belt 4 are brought into contact with the attaching / detaching mechanism 62 in S309. If they are the same, the process proceeds to S302.

  In S302, it is confirmed which of the fixing belt 3 and the pressure belt 4 has shielded the photosensors 20, 21 or 30, 31 immediately before the start of JOB. This is determined based on the sensor light shielding time T1 (sensor light shielding time on the fixing belt side) and T2 (sensor light shielding time on the pressure belt side) updated in S102 (FIG. 12) and S202 (FIG. 13). In this embodiment, a sensor that is shielded from light immediately before the start of JOB is used as a reference. The purpose of this is to reverse the amount of return closer to the belt as the time elapsed since the sensor was shielded is shorter, and to reverse the one with the larger return amount.

  In S303, if T1 <T2, that is, if the sensor light shielding on the pressure belt side occurs after the sensor light shielding on the fixing belt side, the deviation control roller 7 of the fixing belt 3 that seems to have a large amount of deviation. The process proceeds to S306 to invert. Further, in the case of T1> T2, that is, the case where the sensor light shielding on the fixing belt side occurs after the sensor light shielding on the pressure belt side, the deviation control roller 8 of the pressure belt 4 that seems to have a large deviation amount is reversed. Therefore, the process proceeds to S303.

  In S303, the sensor light shielding information D2 on the pressure belt side is confirmed, and it is confirmed which direction of the shift movement by the shift control roller 8 is. When the sensor shading information D2 is the photosensor 30, it can be seen that the shift control roller 8 is displaced in the direction of the arrow 35 and the shift movement direction of the pressure belt 4 is the arrow Q. That is, by setting the shift control direction to the direction of arrow P, the shift control direction of the fixing belt 3 can be reversed. Further, when the sensor light shielding information D2 is the photo sensor 31, it can be seen that the shift control roller 8 is displaced in the direction of the arrow 34 and the shift movement direction of the pressure belt 4 is the arrow P. That is, by setting the shift control direction to the direction of arrow Q, the shift control direction of the fixing belt 3 can be reversed.

  If the sensor light shielding information D2 is the photosensor 30 in S303, the process proceeds to S304, and the stepping motor 33 is rotated counterclockwise by a predetermined pulse. If the sensor shading information D2 is the photosensor 31 in S303, the process proceeds to S305, and the stepping motor 33 is rotated clockwise by a predetermined pulse.

  Similarly, in the case of S306, if the sensor shading information D1 is the photosensor 20, the stepping motor 23 is rotated counterclockwise by a predetermined pulse in S308, and the sensor shading information D1 is the photosensor 21. If this is the case, in step S307, the stepping motor 23 is rotated by a predetermined number of pulses in the clockwise direction.

  Finally, in S309, the fixing belt 3 and the pressure belt 4 are brought into contact with each other using a detaching mechanism (not shown).

  That is, in Embodiment 1 described above, the belt shift control when the fixing belt 3 and the pressure belt 4 are in contact with each other and rotationally driven is performed in the direction in which the fixing belt 3 moves by the fixing belt shift control means (first Direction) and the direction (second direction) in which the pressure belt 4 is moved by the pressure belt deviation control means are opposite, that is, the direction in which the fixing belt 3 and the pressure belt 4 are opposite to each other. It is controlled to become. Further, when the belt deviation is detected by the fixing belt deviation detecting means or the pressure belt deviation detecting means, the direction in which the fixing belt 3 moves by the fixing belt deviation control means, and the pressure belt 4 by the pressure belt deviation control means. The fixing belt shift control means and the pressure belt shift control means are controlled so that the moving direction of the belt is opposite. That is, when a predetermined shift of one of the fixing belt 3 and the pressure belt 4 is detected, control is performed to change the shift direction of the other belt as the shift direction of the one belt is changed. is doing.

  As a result, the shifting force between the first belt 3 and the second belt 4 is canceled out, so that the shifting itself between the belts 3 and 4 is eliminated.

  The present embodiment is another example of the shift control mode executed by the control unit 60 based on the start of image formation JOB. It is. FIGS. 15A and 15B are flowcharts of the shift control.

  When JOB starts in S400, it is checked in S401 whether the shift control direction of the fixing belt 3 and the shift control direction of the pressure belt 4 are the same. If they are not the same, the fixing belt 3 and the pressure belt 4 are brought into contact with each other by the detaching mechanism 62 in S409. If they are the same, the process proceeds to S402.

  In S402, it is confirmed which of the fixing belt 3 and the pressure belt 4 has shielded the photosensors 20, 21 or 30, 31 immediately before the start of JOB. This is determined based on the sensor light shielding time T1 (sensor light shielding time on the fixing belt side) and T2 (sensor light shielding time on the pressure belt side) updated in S102 (FIG. 12) and S202 (FIG. 13). In this embodiment, a sensor that is shielded from light immediately before starting JOB is used as a reference. The purpose of this is to reverse the amount of return closer to the belt as the time elapsed since the sensor was shielded is shorter, and to reverse the one with the larger return amount.

  In S403, if T <T2, that is, if the sensor belt on the pressure belt side has been shielded after the sensor belt on the fixing belt side, the deviation control roller 7 of the fixing belt 3 that seems to have a larger return amount. The process proceeds to S406 to invert. In the case of T1> T2, that is, when the sensor light shielding on the fixing belt side occurs after the sensor light shielding on the pressure belt side, in order to reverse the deviation control roller 8 of the pressure belt 4 that seems to have a large deviation amount. To S403.

  In S403, the sensor light shielding information D2 on the pressure belt side is confirmed, and it is confirmed which direction the shift movement direction by the shift control roller 8 is. When the sensor shading information D2 is the photosensor 30, it can be seen that the shift control roller 8 is displaced in the direction of the arrow 35 and the shift movement direction is the arrow Q. That is, by setting the shift control direction of the pressure belt 4 to the direction of the arrow P, the shift control direction of the fixing belt 3 can be reversed. Further, when the sensor light shielding information D2 is the photo sensor 31, it can be seen that the shift control roller 8 is displaced in the direction of the arrow 34 and the shift movement direction of the pressure belt 4 is the arrow P. That is, by setting the shift control direction to the direction of arrow Q, the shift control direction of the fixing belt 3 can be reversed.

  If the sensor shading information D2 is the photosensor 30 in S403, the process proceeds to S404 and the stepping motor 33 is rotated counterclockwise by a predetermined pulse. If the sensor shading information D2 is the photosensor 31 in S403, the process proceeds to S405, and the stepping motor 33 is rotated clockwise by a predetermined pulse.

  Similarly, in the case of S406, if the sensor shading information D1 is the photosensor 20, the stepping motor 23 is rotated counterclockwise by a predetermined pulse in S408, and the sensor shading information D1 is the photosensor 21. If this is the case, in step S407, the stepping motor 23 is rotated by a predetermined number of pulses in the clockwise direction.

  Finally, the process proceeds to S409, where the fixing belt 3 and the pressure belt 4 are brought into contact with each other using a detaching mechanism (not shown).

  Next, in S410, the input of the photosensors 20, 21, 30, 31 is awaited. If there is an input, the process proceeds to S411 in the case of the photosensors 20 and 21, and the process proceeds to S416 in the case of the photosensors 30 and 31.

  If the photosensor 20 is shielded from light in S411, the process proceeds to S412 and the stepping motor 23 is operated clockwise by a predetermined pulse, and the stepping motor 33 is operated counterclockwise by a predetermined pulse in S413. As a result, the moving direction of the fixing belt 3 and the pressure belt 4 can be reversed.

  Similarly, if it is determined in S411 that the photosensor 21 is shielded from light, the process proceeds to S414, the stepping motor 23 is rotated counterclockwise by a predetermined pulse, and the stepping motor 33 is rotated clockwise by a predetermined pulse in S415. Rotate only minutes.

  When the rotation of each stepping motor is completed, the process returns to S410 and waits for the input of the photo sensor.

  Similarly, if the photosensor 31 is shielded from light in S416, the stepping motor 33 is rotated counterclockwise by a predetermined pulse in S417, and the stepping motor 23 is rotated clockwise by a predetermined pulse in S418. If the photosensor 30 is shielded from light, the stepping motor 33 is rotated clockwise by a predetermined pulse in S419, and the stepping motor 23 is rotated counterclockwise by a predetermined pulse in S420. When the rotation of each stepping motor is completed, the process returns to S410.

  Here, the above-described F1 + F2 is obtained by correcting the predetermined pulse in the present embodiment from the history of light shielding by the photosensors 20, 21 and the photosensors 30, 31 in a state where the fixing belt 3 and the pressure belt 4 are separated from each other. Needless to say, it can be made closer to 0, and the effects of the present invention can be further obtained.

  That is, in the second embodiment, the belt shift control when the fixing belt 3 and the pressure belt 4 are in contact with each other and rotationally driven is performed in the direction in which the fixing belt 3 moves by the fixing belt shift control means (the first belt 1). ) And the pressure belt shift control means control the fixing belt shift control means and the pressure belt shift control means so that the direction in which the pressure belt 4 moves (second direction) is opposite. .

  Further, when the belt deviation is detected by the fixing belt deviation detecting means or the pressure belt deviation detecting means, the direction in which the fixing belt 3 moves by the fixing belt deviation control means, and the pressure belt 4 by the pressure belt deviation control means. The fixing belt shift control means and the pressure belt shift control means are controlled so that the moving direction of the belt is opposite.

  As a result, the shifting force between the fixing belt 3 and the pressure belt 4 is canceled out, so that the shifting between the belts 3 and 4 is eliminated.

  Further, a shift force F1 (first shift force) applied to the fixing belt 3 by the fixing belt shift control means and a shift force F2 (second shift force) applied to the pressure belt 4 by the pressure belt shift control means. ) Is changed according to the output results of the fixing belt deviation detecting means and the pressure belt deviation detecting means, so that the offset difference between the deviation forces of the fixing belt 3 and the pressure belt 4 can be made closer to zero. .

  In the above-described first and second embodiments, it has been described that the fixing belt 3 and the pressure belt 4 can be prevented from being shifted when the fixing belt 3 and the pressure belt 4 are rotationally driven in contact with each other. However, in a special operating environment in which the recording material is coated paper and the same amount of toner as the solid image is placed on the recording material and the fixing process is continuously performed in units of 1000 sheets, the fixing belt 3 and the pressure are applied. There is still a possibility that the shift of the belt 4 occurs. This depends on the relationship between the frictional resistance between the surface of the recording material (the state where the toner is placed) and the surface of the fixing belt, and the frictional resistance between the back surface of the recording material (including when a double-sided image is formed) and the pressure belt surface Yes. For this reason, when each frictional resistance is reduced (especially when double-side coated paper is used), the substantial frictional resistance between the fixing belt 3 and the pressure belt 4 is also reduced, so that each belt is shifted. . It can also be assumed that the relationship between the shifting forces is disrupted due to unexpected changes in the parallelism due to the life span of the components on which the belts are stretched, the belts themselves, vibrations, or the like. In this case, a phenomenon occurs in which the other belt is pulled by the movement of one belt.

  In the third embodiment, the shift control between the fixing belt 3 and the pressure belt 4 assuming that the parallelism is largely changed due to a factor such as vibration is described with reference to the flowcharts of FIGS. 16 (A) and 16 (B). explain.

  When JOB starts in S500, it is determined in S501 whether any one of the photosensors 20, 21, 30, and 31 is in a light shielding state. Before JOB is started in S500, as described in (4-1) of the first embodiment, the fixing belt 3 and the pressure belt 4 are rotationally driven apart from each other, and the fixing belt 3 and the pressure are pressed. The belts 4 are independently shifted and controlled. Therefore, if there is a light-shielded sensor, the process waits in step S501 until the deviation returns. If the belt deviation between the fixing belt 3 and the pressure belt 4 returns to normal, the process proceeds to S502.

  In S502, it is confirmed whether the shift control direction of the fixing belt 3 and the shift control direction of the pressure belt 4 are the same. If they are not the same, the fixing belt 3 and the pressure belt 4 are brought into contact with each other by the detaching mechanism 62 in S510. If they are the same, the process proceeds to S503.

  In S503, it is confirmed which of the fixing belt 3 and the pressure belt 4 shields the photosensors 20, 21 or 30, 31 immediately before the start of JOB. If T1 <T2 in S503, the process proceeds to S507. If T1> T2, the process proceeds to S504.

  In S504, the sensor light shielding information D2 on the pressure belt side is confirmed, and it is confirmed which direction the shift movement by the shift control roller 7 is. If the sensor light shielding information D2 is the photosensor 30, the process proceeds to S505, and the stepping motor 33 is rotated counterclockwise by a predetermined pulse P4. If the sensor shading information D2 is the photosensor 31 in S504, the process proceeds to S506, and the stepping motor 33 is rotated clockwise by a predetermined pulse P3.

  Similarly, in the case of S507, if the sensor shading information D1 is the photosensor 20, the stepping motor 23 is rotated counterclockwise by a predetermined pulse P2 in S509, and the sensor shading information D1 is obtained by the photosensor 21. If there is, the stepping motor 23 is rotated in the clockwise direction by a predetermined pulse P1 in S508.

  In step S510, the fixing belt 3 and the pressure belt 4 are brought into contact with each other using the detaching mechanism 62, and in step S511, the input of the photo sensor is awaited. If there is no input, the sensor shading information D3 is cleared in S512, and the process returns to S511. If there is an input, it is determined whether or not the light-shielded sensor and the sensor light-shielding information D3 are the same in S513, and if they are not the same, the process proceeds to S514. In the same case, either the displacement control roller is displaced until the belt is displaced and light is transmitted through the light-shielded sensor, or the sensor is kept shielded from light because the occurrence of displacement is prevented. Since there is no need for control, the process returns to S511.

  If there is a change in the light-shielded sensor in S514, it is determined whether the photosensors 20, 30 or the photosensors 21, 31 are simultaneously shielded from light. The state in which the light is shielded at the same time means that the shift movements of the fixing belt 3 and the heating belt 4 are reversed by the shift control rollers 7 and 8 and each shift force is offset, but the shift of one belt shifts. In this state, the other belt is moving toward the other side.

  In this state, when the same control as that in FIGS. 15A and 15B described in the second embodiment is performed, the belt having the photosensor stored in the sensor light shielding information D3 is more likely to return. In addition, the control depending on the newly shielded sensor is performed first. As a result, it can be seen that the moving direction of the belt having the photosensor stored in the sensor light shielding information D3 is changed in the approaching direction. Therefore, if it is determined in S514 that light is shielded simultaneously, the process proceeds to S515, and if the input sensor is the photosensor 20, 21, the process proceeds to S700, and otherwise the process proceeds to S800. If the light is not shielded simultaneously, the process proceeds from S514 to S600.

  In the present embodiment, as the event for selecting the shift control means, a state in which the sensors in the same direction are simultaneously shielded from light is used. This is intended to switch a plurality of shift control methods, and does not limit the scope of the present invention. That is, in addition to this, for example, the shift control means may be selected in a state where the fixing belt 3 or the pressure belt 4 is close, or in a state where the input interval of each sensor is smaller than a predetermined interval.

  The control from S600 will be described with reference to FIG. In S601, D3 on the sensor light shielding is updated. In step S602, the photosensor that is shielded from light is determined. In the case of the photo sensors 20 and 21, the process proceeds to S603, and in the case of the photo sensors 30 and 31, the process proceeds to S608.

  In step S603, the sensor light shielding information D1 is first updated to determine the position of the fixing belt 3. If the photosensor 20 is shielded from light, the process proceeds to S604, the stepping motor 23 is operated clockwise by the predetermined pulse P1, and the stepping motor 33 is operated counterclockwise by the predetermined pulse P4 at S605. As a result, the moving direction of the fixing belt 3 and the pressure belt 4 can be reversed.

  Similarly, if it is determined in S603 that the photosensor 21 is shielded from light, the process proceeds to S606, the stepping motor 23 is rotated counterclockwise by a predetermined pulse P2, and the stepping motor 33 is rotated clockwise in S607. Rotate by pulse P3.

  When the rotation of each stepping motor is completed, the process returns to S511 to wait for the input of the photo sensor.

  Similarly in S608, the sensor light shielding information D2 is first updated, and the position of the pressure belt 4 is determined. If the photosensor 31 is shielded from light, the stepping motor 33 is rotated counterclockwise by a predetermined pulse P2 in S609, and the stepping motor 23 is rotated clockwise by a predetermined pulse P3 in S610. If the photosensor 30 is shielded from light, the stepping motor 33 is rotated clockwise by a predetermined pulse P1 in S611, and the stepping motor 23 is rotated counterclockwise by a predetermined pulse P4 in S612. When the rotation of each stepping motor is completed, the process returns to S511.

  Next, the control from S700 will be described with reference to FIG. In S701, the sensor light shielding time T1, the sensor light shielding information D1, and the sensor light shielding information D3 are updated. Next, in S702, it is determined whether or not the sensor light shielding information D3 is the photosensor 20, and in the case of the photosensor 20, the process proceeds to S703, and in other cases, the process proceeds to S706.

  In step S703, the stepping motor 23 is rotated clockwise by a predetermined pulse P1A, and the shift control roller 7 is displaced in the direction of the arrow 25. Subsequently, in S704, the output of the photosensor 20 is confirmed again, and if the light is transmitted (when the shift of the fixing belt 3 returns), the process returns to S502. If the light is continuously shielded, the process proceeds to S705.

  In S705, it is confirmed whether or not the photosensor 21 is shielded from light. If the light is shielded, it is determined that the fixing belt 3 has moved to the near side, and the process proceeds to S709. If the photosensor 21 is transparent, the process returns to S704.

  Similarly, in step S706, the stepping motor 23 is rotated counterclockwise by a predetermined pulse P2A, and the shift control roller 7 is displaced in the direction of the arrow 24. Subsequently, in S707, it is confirmed again whether the photosensor 21 is shielded from light. If the light is transmitted, the process returns to S502. When the light is shielded, the process proceeds to S708. If the photosensor 20 is shielded from light in S708, that is, it is determined that the fixing belt 3 is close to the back side, and the process proceeds to S709. If the photosensor 20 is transparent, the process returns to S707.

  FIG. 19 is a flowchart in the control from S800. In S801, the sensor shading time T2, the sensor shading information D2, and the sensor shading information D3 are updated. Next, in S802, it is determined whether the sensor light shielding information D3 is the photosensor 30, and in the case of the photosensor 30, the process proceeds to S803, and in other cases, the process proceeds to S806.

  In step S803, the stepping motor 33 is rotated clockwise by a predetermined pulse P3A, and the shift control roller 8 is displaced in the direction of the arrow 35. Subsequently, in S804, the output of the photosensor 30 is confirmed again. If light is transmitted (when the pressure belt 4 is returned), the process returns to S502. If the light is continuously shielded, the process proceeds to S805. In S805, it is confirmed whether or not the photo sensor 31 is shielded from light. If it is shielded, it is determined that the pressure belt 4 has approached the front side, and the process proceeds to S809. If the photosensor 31 is transparent, the process returns to S804.

  Similarly, in step S806, the stepping motor 33 is rotated counterclockwise by a predetermined pulse P4A, and the shift control roller 8 is displaced in the direction of the arrow 34. Subsequently, in S807, it is confirmed again whether or not the photosensor 31 is shielded from light. If the light is transmitted, the process returns to S502. When the light is shielded, the process proceeds to S808. If the photosensor 30 is shielded from light in S808, that is, it is determined that the pressure belt 4 is close to the back side, and the process proceeds to S809. If the photosensor 30 is transparent, the process returns to S807.

  In this embodiment, the predetermined pulses for rotating each stepping motor clockwise / counterclockwise are P1, P2, P3, P4 in the control from S500 / S600, and P1A, P2A, P3A in the control from S700 / S800. , P4A. At this time, each predetermined pulse has the following relationship.

P1> P1A
P2> P2A
P3> P3A
P4> P4A
This is intended to prevent the deviation of both belts 3 and 4 due to abrupt speed even if the deviation movement directions by the deviation control rollers 7 and 8 are evenly aligned.

Also, P1 <P1A as follows
P2 <P2A
P3 <P3A
P4 <P4A
Thus, it is possible to increase the moving speed of each belt, reduce the time required for the control performed from S700 and S800 as much as possible, and increase the time during which the shifting forces of the belts 3 and 4 cancel each other. Needless to say.

  Finally, the case where the process returns to S502 via S700 or S800 will be described. First, in S502, it is confirmed whether or not the moving directions of the belts 3 and 4 are the same. Of course, in S700 and S800, the process proceeds to S503 because they are the same. Since the sensor light shielding time T1 or T2 is updated in S701 or S801, the shift movement direction on the pressure belt 4 side is reversed after S700, and the shift movement direction on the fixing belt 3 side is reversed in S800. Will do. In other words, even if the process returns to S502 via S700 or S800, it can be seen that the purpose of inverting the one with the larger return amount is achieved.

  In the third embodiment, it has been described that it corresponds to an unexpected change in parallelism when the fixing belt 3 and the pressure belt 4 are kept in contact with each other. This is also for avoiding the temporary interruption of the image forming apparatus during the image forming process and ensuring the maximum productivity of the image forming apparatus. However, in order to obtain the maximum effect of the present invention, the image forming process is temporarily interrupted at the timing of selecting the above-described shift control means, and the fixing belt 3 and the pressure belt 4 are separated from each other. It is desirable to execute the process consisting of S300 independently and restart the image forming process when it is determined that the deviation of both belts has returned, and it goes without saying that such a configuration may be adopted.

  As described above, by making the deviation control directions of the fixing belt 3 and the pressure belt 4 reverse, the deviation forces of both belts can be offset, and machine downtime such as belt breakage due to deviation cuts can be reduced. be able to.

  Further, even if a cross-cut occurs as in the second embodiment, it is possible to cancel the shift force again by changing the shift control direction of both belts in accordance with the belt to which the cross-cut is performed, so that stable fixing processing can be performed. It becomes possible to carry out.

  Here, in the above description, if the control in consideration of the shifting force between the fixing belt 3 and the pressure belt 4 is the first control mode, the control not considering the shifting force between the fixing belt 3 and the pressure belt 4 is the second control mode. is there. This second control mode is to perform FIG. 12 and FIG. 13 independently.

Then, the control means unit is provided with mode selection means (mode switching means), and the first control mode and the second control mode can be selected and executed by the external means. That is, both modes can be selected.

  Examples of this control include the following forms.

  The control unit selects and executes the first control mode and the second control mode according to the detection results of the first and second belt deviation detection units.

  The control unit selects and executes the first control mode and the second control mode according to the detection results of the first and second belt deviation detection units and the first and second directions.

  In the above description, the first shift force is the force that moves the fixing belt 3 and the pressure belt 4 toward each other by the first and second shift control units in the first control mode, and the first and second shift modes in the second control mode. When the force for moving the fixing belt 3 and the pressure belt 4 by the second shift control means is the second shift force, the first and second shift forces are made different.

  In the first mode, as the shifting direction of one of the fixing belt 3 and the pressure belt 4 is changed, the shifting direction of the other belt is changed.

  In the first mode, the shift direction of the fixing belt 3 and the shift direction of the pressure belt 4 are controlled to be opposite to each other, and switching from the first mode to the second mode is performed. This is performed according to the position of the pressure belt 4 and the position of the pressure belt 4 in the width direction.

  When the fixing belt 3 and the pressure belt 4 are separated from each other, the second mode is selected.

  Here, in the belt fixing devices of Embodiments 1 to 3, the heating means of the fixing belt 3 is not limited to electromagnetic induction heating, but may be configured to be heated by another heating source such as a halogen heater or a ceramic heater. it can. The pressure belt 4 can also be heated.

Schematic configuration model diagram of image forming apparatus in embodiment The figure which shows the structure of the operation panel provided in the image forming apparatus. Expanded cross-sectional model diagram of main part of fixing device and block diagram of control system Exploded perspective model of belt guide and belt guide cover Diagram showing the heat distribution of the fixing belt at the part facing the excitation unit (development) Explanatory drawing of fixing belt deviation control means Explanatory diagram of pressure belt offset control means Explanatory diagram of belt misalignment judgment by combination of shape of belt position detection flag and output of photo sensor (part 1) Explanatory drawing of belt deviation judgment by combination of shape of belt position detection flag and output of photo sensor (part 2) Explanatory diagram of belt misalignment judgment by combination of shape of belt position detection flag and output of photo sensor (Part 3) Illustration of relationship between shifting force and shifting control roller Flow control flowchart of fixing belt in shift control mode 1 Flow chart of pressure belt shift control in shift control mode 1 Shift control flowchart in shift control mode 2 Shift control flowchart in the second embodiment (part 1) Flow control flowchart in the second embodiment (part 2) Flow control flowchart in the third embodiment (part 1) Flow control flowchart in the third embodiment (part 2) Flow control flowchart in embodiment 3 (part 3) Flow control flowchart in the third embodiment (part 4) Flow control flowchart in the third embodiment (No. 5)

Explanation of symbols

  1. . . Fixing roller, 2. . . 2. pressure roller; . . 3. fixing belt (first belt); . . Pressure belt (second belt), 7-8. . . Shift control roller, 9/10. . . Belt guide, 14, 15, 16, 17. . . Belt position detection flag, 20, 21, 30, 31. . Photo sensor

Claims (6)

A first endless belt, a second endless belt that forms a nip portion for heating an image on the recording material between the first belt, and a first that controls the deviation of the first belt. In the image heating apparatus having the control means, and the second control means for controlling the deviation of the second belt,
An image heating apparatus, wherein a control is performed such that a direction in which the first belt is shifted and a direction in which the second belt is shifted are opposite to each other.   When a predetermined shift of one of the first belt and the second belt is detected, the shift direction of the other belt is changed as the shift direction of the one belt is changed. 2. The image heating apparatus according to claim 1, wherein A first endless belt, a second endless belt that forms a nip portion for heating an image on the recording material between the first belt, and a first that controls the deviation of the first belt. In the image heating apparatus having the control means, and the second control means for controlling the deviation of the second belt,
A first mode in which the second belt shift control is performed in accordance with the first belt shift control; and a second mode in which the second belt shift control is performed regardless of the first belt shift control. The image heating apparatus can be selected from the following modes.   4. The image according to claim 3, wherein in the first mode, the shifting direction of one of the first belt and the second belt is changed in accordance with the shifting direction of the other belt. Heating device.   In the first mode, the shifting direction of the first belt and the shifting direction of the second belt are controlled to be opposite to each other, and the first mode is changed to the second mode. The image heating apparatus according to claim 3 or 4, wherein the switching is performed according to a position in a direction in which the second belt is shifted and a position in the width direction of the second belt.   6. The image heating apparatus according to claim 3, wherein the second mode is selected when the first belt and the second belt are separated from each other.