JP5072504B2 - Belt conveying device and image heating device - Google Patents

Description

  The present invention relates to a belt conveyance device and an image heating device configured to rotate endless belts in pressure contact with each other, such as a belt nip belt fixing device mounted on an image forming apparatus.

  Examples of the image heating device include a fixing device that fixes an unfixed image on a recording material, and a gloss increasing device that increases the gloss of the image by heating the image fixed on the recording material. .

  Conventionally, as a fixing device mounted on an electrophotographic image forming apparatus, an unfixed toner image is fixed while a recording material is nipped and conveyed by an endless fixing belt and a pressure belt which are rotated in pressure contact with each other. A configured fixing device has been proposed (Patent Document 1). This belt fixing type fixing device achieves a sufficient fixing nip width (length in the recording material conveyance direction) while achieving a reduction in size and speed of the apparatus as compared with a roller fixing type fixing device mainly composed of a roller pair. )).

  By the way, in a belt nip type fixing device using an endless fixing belt or a pressure belt, the belt moves so as to be shifted to one side or the other side in the width direction orthogonal to the recording material conveyance direction during the rotation of the belt. Phenomenon (hereinafter referred to as shift movement) occurs. If the belt shifts, the belt may fall off from the roller that stretches the belt, or the end of the belt may be damaged. Therefore, in order to prevent this, it is necessary to correct the shift of the belt.

  Therefore, conventionally, in order to correct the shift of the belt, a technique for correcting the shift of the belt by tilting one of the plurality of rollers that stretch the belt is used as a steering roller. Has been proposed (Patent Documents 2 and 3). Specifically, when it is detected that the belt has moved a predetermined amount or more in the width direction, the steering roller is tilted so that the belt moves in a direction opposite to the moving direction, thereby correcting the shift of the belt. is doing.

JP 2004-341346 A Japanese Patent Application Laid-Open No. 11-194647 JP-A-5-27622

  By the way, in the twin belt fixing type fixing device having the fixing belt and the pressure belt rotating in pressure contact with each other as in the above-mentioned Patent Document 1, it is necessary to independently correct the shift of each belt. is there.

  However, the fixing belt and the pressure belt are pressed to form a nip portion (nip portion), and fixing is performed while the recording material is held and conveyed. For this reason, when a force that corrects the above-described shift movement (a force that moves the belt in the width direction) is generated on the belt that sandwiches and conveys the recording material, the force affects the recording material. There is a fear.

  For example, it is assumed that the fixing belt moves toward one side in the width direction, and the pressure belt moves toward the other side in the width direction, which is the opposite direction. In this case, each correction control generates a correction force that moves to the other side in the width direction for the fixing belt, and generates a correction force that moves to one side in the width direction for the pressure belt. . However, if correction forces in opposite directions are applied to the recording material sandwiched and conveyed by both belts on the front and back surfaces, the recording material may be wrinkled, and good image formation may not be performed.

  That is, when the correction force acting on each belt is opposite in the belt width direction, the correction force may affect the recording material, and good image formation may not be performed.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to perform good movement correction control that prevents the influence on the recording material due to the generation of the movement correction force in the reverse direction on the belts that rotate in pressure contact with each other. That is.

In order to achieve the above object, the present invention corrects the endless first belt and the second belt that sandwich and convey the recording material, and the movement of each belt in the width direction perpendicular to the recording material conveyance direction. A belt conveyance device having a movement correcting means for allowing the belts to move in the width direction opposite to each other in an allowable mode and to move the belts in the width direction opposite to each other. and prohibition mode to prohibit become direction, one of a plurality of modes including, have a selecting means for selecting and executing in accordance with the thickness of the recording material, when the recording material is thinner than the predetermined thickness The prohibit mode is selected and executed, and when the recording material is thicker than a predetermined thickness, the allow mode is selected and executed .

  According to the present invention, it is possible to perform good movement correction control that prevents the influence on the recording material due to the generation of the movement correction force in the reverse direction on the belts that rotate in pressure contact with each other.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

  An image heating apparatus as a belt conveying apparatus and an image forming apparatus having the image heating apparatus will be described. Here, as the image heating apparatus, a belt fixing apparatus that fixes an unfixed image on a recording material is illustrated, but the present invention is not limited to this. For example, other image heating apparatuses such as a gloss increasing apparatus that increases the gloss of an image by heating an image fixed on a recording material may be used.

(Image forming device)
First, a basic configuration of an image forming apparatus having a belt fixing device will be described with reference to FIG. FIG. 2 is a longitudinal sectional view showing a schematic configuration of an electrophotographic full-color copying machine which is an example of an image forming apparatus equipped with a belt fixing device.

  In FIG. 2, reference numeral 1 denotes a digital color image reader unit, which photoelectrically reads an image of a color image document placed on the platen glass 2 as a color separation image signal by a full color sensor (CCD) 3. The color separation image signal is subjected to image processing by the image processing unit 4 and then sent to a control circuit unit (hereinafter referred to as CPU) 100 of the digital color image printer unit 5 (see FIG. 6).

  In the printer unit 5, UY, UM, UC, and UK are the first to fourth image forming units arranged in tandem. Each image forming unit is a laser exposure type electrophotographic process mechanism. Based on the color separation image signal sent from the image processing unit 4 to the CPU 100, each image forming unit forms a color toner image on the surface of the rotating electrophotographic photosensitive drum at a predetermined control timing. That is, the yellow toner image is formed on the drum surface in the first image forming unit UY, the magenta toner image is formed on the drum surface in the second image forming unit UM, and the cyan toner is formed on the drum surface in the third image forming unit UC. In the fourth image forming unit UK, a black toner image is formed on the drum surface.

  The color toner images formed on the drum surface of each image forming unit are sequentially superimposed and transferred by the primary transfer unit 6 on the surface of the intermediate transfer belt 7 rotating in the clockwise direction of the arrow. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the belt 7 by superimposing the four color toner images. The combined full-color toner image is secondarily transferred collectively onto the surface of the recording material P by the secondary transfer unit 8. The recording material P is fed from the cassette paper feeding mechanism 9, the deck paper feeding unit 10, or the manual paper feeding unit 11 to the secondary transfer unit 8 at a predetermined control timing.

  The recording material P onto which the toner image has been transferred is separated from the surface of the belt 7 and is introduced into the belt fixing device 12, and is nipped and conveyed at the fixing nip portion. In the nipping and conveying process, an unfixed full-color toner image is melted and mixed by heat and pressure and fixed on the surface of the recording material P as a full-color fixed image. The recording material P that has exited the belt fixing device 12 is switched by a flapper 13 and discharged to a FU (face-up) discharge tray 14 or an FD (face-down) discharge tray 15.

  When the double-sided printing mode is selected, the recording material P printed on the first side from the belt fixing device 12 is sent by the flapper 13 to a sheet path that once leads to the FD paper discharge layout 15. The recording material P is switched back and conveyed, introduced into the re-conveying sheet path 16, turned upside down, and introduced into the secondary transfer unit 8 again. As a result, a toner image is secondarily transferred and formed on the second surface side of the recording material P. Thereafter, the recording material P is introduced into the belt fixing device 12 as in the case of the first side printing. As a result, the double-side printed recording material is discharged to the FU discharge tray 14 or the FD discharge tray 15.

(Belt fixing device)
Next, the configuration of the belt fixing device 12 will be described with reference to FIG. FIG. 1 is a cross-sectional view showing a schematic configuration of the belt fixing device 12. The fixing device 12 is a twin-belt type belt conveyance device having an endless first belt and a second belt which are rotated in pressure contact with each other.

  Here, in the following description, with respect to the fixing device 12, the front surface is a device surface viewed from the front side of the device as shown in FIGS. 1 and 2. Left and right are, as shown in FIG. 4 and the like, when the fixing device 12 is viewed from the front, the front side is right and the back side is left. The upstream side and the downstream side are the upstream side and the downstream side in the recording material conveyance direction. The width direction and the width are a direction orthogonal to the recording material conveyance direction on the recording material conveyance path surface and a length in that direction.

  The fixing device 12 includes a fixing belt unit 21 and a pressure belt unit 31 that are arranged vertically.

  The fixing belt unit 21 is an assembly in which a fixing belt 27 as an endless (endless) second belt, a driving roller 24, a steering roller 26, a pressure pad 28, an induction heating coil 29, and the like are incorporated inside a casing 22. It is.

  The drive roller 24 is a belt support member (belt suspension member) that rotationally drives the fixing belt 27. The roller 24 is disposed such that the left and right end shaft portions thereof are rotatably supported between the left and right side plates of the casing 22 via bearings.

  The steering roller 26 is a belt support member that constitutes a second movement correction unit that corrects the movement of the fixing belt 27 in the width direction. The roller 26 is disposed substantially in parallel with the driving roller 24 on the upstream side of the driving roller 24, with the left and right end shafts thereof rotatably supported via bearings between the left and right side plates of the casing 22. It is. The roller 26 corrects the movement of the fixing belt 27 by switching the inclination (position) of the roller 26 based on detection information from a detection sensor unit 65 described later.

  The fixing belt 27 is wound around the two rollers 24 and 26. The fixing belt 27 is heated by an induction heating coil 29 as a heating means disposed in the upper part. As the fixing belt 27, for example, a magnetic metal layer such as a nickel metal layer or a stainless steel layer having a thickness of 75 μm, a width of 380 mm, and a circumferential length of 200 mm is coated with silicon rubber having a thickness of 300 μm.

  The pressure pad 28 is disposed inside the fixing belt 27, and both left and right ends thereof are supported between the left and right side plates of the casing 22, respectively. The pressure pad 28 contacts the lower inner surface of the fixing belt 27 at a position close to the driving roller 24.

  The steering roller 26 also functions as a tension roller that applies tension to the fixing belt 27 by urging and moving the left and right bearings away from the driving roller 24 by spring members.

  The pressure belt unit 31 is an assembly in which a pressure belt 32 as an endless first belt, a driving roller 33, a steering roller 34, a pressure pad 38, and the like are incorporated inside a casing 35.

  The drive roller 33 is a belt support member (belt suspension member) that rotationally drives the pressure belt 33. The roller 33 is disposed such that the left and right end shaft portions thereof are rotatably supported between the left and right side plates of the casing 35 via bearings.

  The steering roller 34 is a belt support member that constitutes a first movement correction unit that corrects the movement of the pressure belt 27 in the width direction. The roller 34 is disposed substantially parallel to the drive roller 33 on the upstream side of the drive roller 33, with the left and right end shafts rotatably supported via bearings between the left and right side plates of the casing 35. It is. The roller 34 corrects the movement of the pressure belt 32 by switching the inclination (position) of the roller 34 based on detection information from a detection sensor unit 66 described later.

  The pressure belt 32 is suspended between the two rollers 33 and 34.

  The pressure pad 38 is disposed inside the pressure belt 32, and both left and right ends thereof are supported between the left and right side plates of the casing 35. The pressure pad 38 contacts the upper inner surface of the pressure belt 32 at a position close to the drive roller 33.

  The steering roller 34 also functions as a tension roller that applies tension to the pressure belt 32 by biasing the left and right bearings in a direction away from the drive roller 33 by spring members.

  The pressure belt unit 31 is separated from a belt pressure contact position (see FIG. 1) where the belts 27 and 32 are in pressure contact with each other with the belt attachment / detachment mechanism 102 shown in FIG. The position is switched (see FIG. 3). That is, the fixing belt unit 21 and the pressure belt unit 31 are brought into the pressed state shown in FIG. 1 when the recording material P is nipped and conveyed by the belt attaching / detaching mechanism 102, and in the separated state shown in FIG. 3 in other cases. Can be switched. As a result, unnecessary pressure is prevented from being applied between the fixing belt unit and the pressure belt unit, and wear of the members is prevented.

  An oil application roller 45 is provided on the inner surface of the pressure belt 32 to reduce the frictional force. The oil application roller 45 follows the rotation of the pressure belt 32 and uniformly applies oil to the inner surface of the belt. As a result, friction on the inner surface of the pressure belt is prevented.

  Next, a belt shift control mechanism of the belt fixing device 12 will be described with reference to FIG. The belt shift control mechanism is a mechanism that controls movement of the fixing belt unit 21 and the pressure belt unit 31 so as to return the shift in the lateral direction that occurs when the fixing belt 27 and the pressure belt 32 are rotated. Since the belt shift control mechanisms of the fixing belt unit 21 and the pressure belt unit 31 have substantially the same configuration, the belt shift control mechanism of the fixing belt unit 21 will be described as an example here.

  The belt shift control mechanism includes a steering control stepping motor 60, a worm gear 61, a fan gear 62, a steering roller bearing 63, and a side plate 64 that supports them. The steering roller bearing 63 supports the shaft of the fixing steering roller 26.

  Reference numeral 65 denotes a fixing belt shift detection sensor unit, which is a second belt position detection unit that detects the position of the fixing belt 27 in the width direction stepwise. The fixing belt deviation detection sensor unit 65 is disposed at the left and right ends of the fixing belt 27 in the width direction, and includes upper photosensor SL1 and upper SL2 that detect left belt deviation, and upper photosensor SR1 that detects right belt deviation. , And upper SR2. Details thereof will be described later. Note that a similar pressure belt shift detection sensor unit 66 (see FIG. 1) is also disposed on the left and right ends of the pressure belt 32 in the width direction on the pressure belt unit 31 side. The pressure belt shift detection sensor unit 66 is a first belt position detection unit that detects the position of the pressure belt 32 in the width direction stepwise. In order to distinguish from the fixing belt deviation detection sensor unit 65, the photo sensors on the pressure belt deviation detection sensor unit 66 side are described as lower SL1, lower SL2, upper SR1, and upper SR2.

  When the stepping motor 60 is driven in the CW direction (clockwise), the worm gear 61 rotates, and the sector gear 62 swings downward about the shaft. Accordingly, since the steering roller bearing 63 moves downward, the fixing steering roller 26 is slightly inclined to the back side (left side), and the entire fixing belt unit 21 is inclined to the back side. Accordingly, the fixing belt 27 is in a state where the tension on the back side is lower than that on the near side, so that the fixing belt 27 gradually moves to the back side (left side) where the tension is low as the fixing belt 27 rotates.

  Conversely, when the stepping motor 60 is driven in the CCW direction (counterclockwise), the worm gear 61 rotates and the sector gear 62 swings upward about the axis. Accordingly, the steering roller bearing 63 moves upward, so that the fixing steering roller 26 is slightly inclined toward the front side (right side), and the entire fixing belt unit 21 is also inclined toward the front side. As a result, the fixing belt 27 is in a state where the tension on the near side is lower than that on the far side, so that the fixing belt 27 gradually moves to the near side (right side) where the tension is low as the fixing belt 27 rotates.

  FIG. 5A is a diagram when the fixing steering roller 26 is tilted to return the fixing belt 27 of the fixing belt unit 21 to the left side when viewed from the front. Since the control mechanism for inclining the fixing steering roller 26 is on the back side as described above, the end portion of the steering roller 26 is raised by the stepping motor 60. The amount of displacement of the height of the end portion is hereinafter referred to as the amount of displacement D of the end portion. The + direction of the displacement amount D is the upper side and is a direction that returns toward the front side (right side) of the apparatus, and the − direction is the lower side and is a direction that returns toward the back side (left side) of the apparatus.

  Similarly, FIG. 5B is a view when the pressure steering roller 34 is inclined to return the pressure belt 32 of the pressure belt unit 31 to the right side when viewed from the front. Since the control mechanism for inclining the pressure steering roller 26 is on the back side as described above, the end portion of the pressure steering roller 34 is lowered by the stepping motor 67. The + direction of the displacement amount D is the upper side and returns toward the back side (left side) of the device, and the − direction is the lower side and returns toward the front side (right side) of the device.

  Since the position in the width direction of the belt tends to move according to the change in the displacement amount D at the end, ideally, the displacement amount becomes a substantially horizontal inclination angle so that the belt position does not move from side to side as much as possible from the current position. Is expressed as a reference amount ± 0 state. Ideally, if the displacement amount D is set to the reference amount ± 0, the belt does not move left and right from that position, but in reality, the belt is shifted due to various factors, and the belt moves left and right with respect to the stretching roller. To do.

  As described with reference to FIG. 5, the fixing belt and the pressure belt are rotated toward the abutment surface that is on the inner side, so that a deviation in the width direction occurs with respect to the inclination of the steering roller. The direction is reversed.

  Therefore, when the fixing belt 27 and the pressure belt 32 are moved in the same direction in the width direction, the inclination angles of the fixing steering roller 26 and the pressure steering roller 34 are displaced in the opposite directions.

  FIG. 6 is a block diagram showing a control system of an image forming apparatus including a belt fixing device. The entire control is performed by the CPU 100 which is a control circuit unit, and an operation unit 101 composed of a liquid crystal touch panel, buttons, and the like is connected thereto. In response to a user input from the operation unit 101, the image forming apparatus starts operation.

  The CPU 100 is connected to the belt attaching / detaching mechanism 102, the belt deviation control mechanism 106, the fixing belt deviation detection sensor unit 65, and the pressure belt deviation detection sensor unit 66, and performs control and state detection from the CPU 100. Further, a fixing belt driving roller driving mechanism 103, a pressure belt driving roller driving mechanism 104, a heater power supply circuit unit 105, and the like are connected to the CPU 100, and control and state detection are performed from the CPU 100.

  The belt attaching / detaching mechanism 102 is a mechanism for performing a pressure contact and separation operation between the fixing belt unit 21 and the pressure belt unit 31 described above. The fixing belt driving roller driving mechanism 103 drives the fixing driving roller 24 of the fixing belt unit 31 and rotates the stretched fixing belt 27. Similarly, the pressure belt drive roller drive mechanism 104 drives the pressure drive roller 33 of the pressure belt unit 31 to rotate the stretched pressure belt 32. The heater power supply circuit unit 105 is a circuit that controls power supply to the induction heating coil 29, and turns the power supply on and off in response to a signal from the CPU 100.

  The belt shift control mechanism 106 drives the steering control stepping motor 60 shown in FIG. 4 in accordance with a signal from the CPU 100, and performs control to correct the shift movement of the fixing belt 27 and the pressure belt 32 in the width direction. The shift detection sensors SL1, SL2, SR1, and SR2 included in each of the detection sensor units 65 and 66 stepwise (in this case, two levels) the belt shift amount of the fixing belt 27 and the pressure belt 32 in one or the other in the width direction. ) To detect.

  Next, the belt position detecting means for detecting the position in the width direction of the belt will be described in detail with reference to FIGS. Since the configuration for detecting the positions in the width direction of the fixing belt 27 and the pressure belt 32 (deviation in the width direction) is basically the same, the fixing belt unit 21 will be described as an example.

  FIG. 7 is a view of the fixing belt portion between the belt driving roller 24 and the steering roller 26. The photosensors SL1 and SL2 and the photosensors SR1 and SR2 are belt position detection means arranged at predetermined intervals on both the left and right sides of the fixing belt 27 in the width direction. The belt position detecting means includes photosensors SL1 and SR1 on the inner side in the width direction and photosensors SL2 and SR2 on the outer side in the width direction on the left side and the right side in the belt width direction, respectively. Each sensor is a light detection type sensor (photo sensor) in which a light transmitting element a and a light receiving element b are combined as shown in FIG. In each sensor, when the fixing belt 27 moves more than a predetermined amount to the left or right in the width direction in the process of rotating the fixing belt, the belt edge on the side of the movement is between the light transmitting element a and the light receiving element b. It is configured to enter and block the optical path between them. Each sensor is turned on when the light path is open, and turned off when the light path is cut off.

  7 and 8A show a state in which the fixing belt 27 is rotationally driven within an allowable shift range between the left first sensor SL1 and the right first sensor SR1, and the left first sensor. Both SL1 and right first sensor SR1 are on. The control circuit unit 100 determines that the fixing belt 27 is rotationally driven within an allowable shift range by turning on the sensors SL1 and SR1. The allowable shift range of the fixing belt 27 at this time is represented as a shift normal range 51 (see FIG. 8A) as a predetermined range.

  When the fixing belt 27 moves to the left side and the left first sensor SL1 is turned off at the left belt edge as shown in FIG. 8B, the control circuit unit 100 indicates that the fixing belt 27 has moved too far to the left side. to decide. Then, a belt shift control mechanism 106 (steering roller displacement mechanism), which will be described later, is operated to displace the end portion of the fixing steering roller 26 so that the fixing belt 27 is moved back to the opposite right side, thereby tilting the roller. Nevertheless, when the fixing belt 27 moves further to the left side and the left second sensor SL2 is also turned off at the left belt edge as shown in FIG. 8C, the displacement of the fixing steering roller 26 is changed. Is further increased to increase the inclination of the roller. Even in this state, if the left-side second sensor SL2 remains off for a predetermined time (here, 10 seconds), it is determined that the fixing belt 27 has moved to the left, and the fixing belt 27 is prevented from being damaged. The operation of the fixing driving roller 24 that drives the motor 27 is stopped. Further, after the image forming operation of the entire apparatus is stopped, an error is displayed on the operation unit 101 to display that the customer is informed of the service person. The moving range of the left end of the fixing belt is referred to as a left-side abnormal range 52 (see FIG. 8A) outside the normal range 51 in the width direction.

  When the fixing belt 27 moves to the right side and the right first sensor SR1 is turned off at the right belt edge as shown in FIG. 8D, the control circuit unit 100 causes the fixing belt 27 to move to the right side. Judge that it has passed. Then, a belt shift control mechanism 106 described later is operated to displace the end portion of the fixing steering roller 26 in a direction in which the fixing belt 27 is moved back to the opposite left side, and the roller is inclined. Nevertheless, when the fixing belt 27 further moves to the right side and the right second sensor SR2 is also turned off at the right belt edge as shown in FIG. 8E, the displacement of the fixing steering roller 26 is changed. To further increase the inclination of the roller. Even in this state, if the right-side second sensor SR2 remains off for a predetermined time (here, 10 seconds), it is determined that the fixing belt 27 has moved to the right and the fixing belt 27 is prevented from being damaged. The operation of the fixing driving roller 24 that drives the motor 27 is stopped. Further, after the image forming operation of the entire apparatus is stopped, an error is displayed on the operation unit 101 to display that the customer is informed of the service person. The movement range of the right end of the fixing belt is referred to as a right-side abnormal range 53 (see FIG. 8A) outside the normal range 51 in the width direction.

  When the states of the light detection type sensor with respect to the fixing belt position shown in FIGS. 8A to 8E are arranged, the table of FIG. 9 is obtained.

  Next, regarding the belt deviation detection and deviation correction control described with reference to FIGS. 7 to 9, the control determination flow of the CPU 100 will be described in detail with reference to FIG.

  Step S201 in FIG. 10A is a processing procedure executed by the CPU 100 every 100 ms by the interval timer. In the initial state, the detection values of the belt deviation detection sensors 65 and 66 are ON at both the left and right ends, and the deviation of the belt is not detected. The displacement D of the end of the fixing steering roller 26 is the reference amount ± 0. That is, the fixing steering roller 26 is in the first position for holding the fixing belt 27 in the central zone (predetermined range 51).

  When step S201 is started, first, in step S202, it is detected whether or not the belt is closer to the left first stage belt. Here, if the deviation detection sensor SL1 is not ON, the process proceeds to step S203 to return the belt to the central range (the normal range 51 in FIG. 8A). In step S203, the steering control stepping motor 60 is driven by 400 pulses in the CCW direction so that the displacement amount D of the fixing steering roller 26 becomes a predetermined value DL1. As a result, the fixing steering roller 26 is displaced from the first position for holding the fixing belt 27 in the central zone to the second position for correcting the shift movement of the fixing belt 27.

  Subsequently, a loop is performed until the belt reaches the center range by the belt deviation correction control in step S203 (step S204). During this loop, if the belt is close to the belt in the second stage on the left, the amount of displacement is changed again for further correction, but this is omitted here. When the belt returns to the center range, the position of the belt has just passed the slip detection sensor SL1, and has not yet returned to the center position sufficiently. Therefore, a timer Tret for reversely driving the steering control stepping motor 60 is set so that the displacement amount D of the fixing steering roller 26 returns to the reference amount ± 0 after a predetermined time has elapsed in step S205, and the sequence is ended in step S206. To do. That is, the fixing steering roller 26 is displaced to the second position, and after a predetermined time has elapsed, the fixing steering roller 26 is returned from the second position to the first position.

  If it is determined in step S202 that the belt is not near the left first stage belt, it is detected in step S207 whether the belt is near the right first stage belt. Here, as in the case of the left side, if the belt is closer to the right first stage belt, the process proceeds to step S208. Then, in order to return the belt from the right first stage to the center range, the steering control stepping motor 60 is driven by 400 pulses in the CW direction so that the displacement amount D of the fixing steering roller 26 becomes a predetermined value DR1. As a result, the fixing steering roller 26 is displaced from the first position for holding the fixing belt 27 in the central zone to the second position for correcting the shift movement of the fixing belt 27.

  Subsequently, a loop is performed until the belt reaches the center range by the belt deviation correction control in step S208 (step S209). When the belt returns to the center range, the position of the belt has just passed the slip detection sensor SR1, and has not yet returned to the center position sufficiently. Therefore, a timer Tret that reversely drives the steering control stepping motor 60 is set so that the displacement amount D of the fixing steering roller 26 returns to the reference amount ± 0 after a predetermined time has passed in step S210, and the sequence is ended in step S206. To do. That is, the fixing steering roller 26 is displaced to the second position, and after a predetermined time has elapsed, the fixing steering roller 26 is returned from the second position to the first position.

  If the belt is not close to the left first stage belt in step S202 and is not close to the right first stage belt in step S207, the fixing belt 27 is stable at the center (normal range 51) as shown in FIG. to decide. As described above, when it is determined in steps S202 and S207 that the fixing belt is stable at the center, no control is performed and the sequence is terminated in step S206.

  The timer Tret set in step S205 or step S210 activates the timer handler in step S251 in FIG. 10B when a predetermined time has elapsed. Subsequently, in step S252, the stepping motor 60 is reversely rotated so that the displacement amount D = ± 0. When the timer is set from step S205, the stepping motor 60 is rotated backward by 400 pulses in the CW direction, and the timer handler is terminated in step S253. When the timer is set from step S210, the stepping motor 60 is reversely rotated by 400 pulses in the CCW direction, and the timer handler is terminated in step S253.

  Next, the belt deviation detection and deviation correction control described with reference to FIGS. 7 to 9 will be described in detail with reference to FIG.

  FIG. 11A is a diagram showing the timing of the correction control when the fixing belt 27 moves to the left and the sensor SL1 is turned off so as to be closer to the left first stage belt. In this description, the state shown in FIG. 8A is changed to the state shown in FIG. 8B, and the state shown in FIG. 8A is restored.

  A graph 301 in FIG. 11A is a detection amount of the left side detection sensor SL1, and is a signal input to the CPU 100. Similarly, the graph 303 represents the rotation speed of the fixing driving roller 24 controlled by the output signal of the CPU 100, and is set to 200 mm / sec here. A graph 304 is a displacement amount D of the fixing steering roller 26 controlled by an output signal from the CPU 100.

  First, when the left side detection sensor SL1 is turned off at the point 305, the CPU 100 performs the following control in order to return the belt from the left first stage to the center. The CPU 100 rotates the steering control stepping motor 60 in the CCW direction by a predetermined pulse, and sets the displacement amount D of the fixing steering roller 26 to a predetermined value DL1 in the minus direction from the reference amount ± 0. As a result, the fixing steering roller 26 is tilted, so that the deviation of the belt is gradually corrected. At the point 306, the left-side deviation detection sensor SL1 is turned ON and the belt returns to the center range. However, at this time, the left end of the fixing belt 27 is still located near the left side detection sensor SL1. Therefore, this displacement DL1 is maintained until time 308 when the fixing belt 27 will move so as to be positioned at the approximate center between the deviation detection sensor SL1 and the deviation detection sensor SR1. When the point 307 at which the time 308 has elapsed is reached, the steering control stepping motor 60 is rotated by a predetermined pulse in the CW direction so as to return the displacement amount D of the fixing steering roller 26 to the reference amount ± 0. The time 308 until the displacement amount D of the fixing steering roller 26 is returned to the reference amount ± 0 is calculated by the rotation speed of the fixing belt and the displacement amount D until the reference amount ± 0 is returned. DL1 = 2.0 mm, belt When the rotation speed is 200 mm / sec, it is 10 sec.

  FIG. 11B is a diagram showing the timing of correction control when the fixing belt 27 is moved to the left and the sensor SL1 is turned off so that the belt is close to the first left stage. 11A and 11B is that the rotation speed of the fixing drive roller 24 shown in the graph 303 is set to 100 mm / sec.

  In the case of FIG. 11B as well as in the case of FIG. 11A, when the left side detection sensor SL1 is turned OFF at the point 311, the CPU 100 performs the following control to return the belt from the first left stage to the center. Do. The CPU 100 rotates the steering control stepping motor 60 by a predetermined pulse in the CCW direction so that the displacement amount D of the fixing steering roller 26 becomes DL1. As a result, the deviation of the belt is gradually corrected, and at the point 312, the left deviation detection sensor SL1 is turned ON, so that the belt is in the central range. However, at this time, the left end of the fixing belt 27 is still located near the left side detection sensor SL1. Therefore, the displacement amount D1 of the fixing steering roller 26 is set to the reference amount ± after maintaining the displacement amount DL1 until the time 314 when the fixing belt 27 will move so as to be positioned at the approximate center between the displacement detection sensor SL1 and the displacement detection sensor SR1. Return to zero. The time 314 until the displacement amount D is returned to the reference amount ± 0 is long when the fixing driving roller 24 rotates at 200 mm / sec because the time required for the belt position to return is long when the rotational speed of the fixing belt 27 is low. The time 308 is longer than the time 308 in accordance with the rotation speed ratio. The time 314 is about twice as short as the time 308, and is 18 sec when DL1 = 2.0 mm and the belt rotation speed is 100 mm / sec.

  Here, with reference to FIG. 12, an example will be described in which the displacement amount D of the fixing steering roller 26 is set to DL1 and the inclination of the fixing belt 27 is not sufficiently returned despite the predetermined inclination angle. .

  Since the belt has become closer to the left first stage belt, if the displacement amount D of the fixing steering roller 26 is set to DL1, normally, if the fixing belt 27 is rotating in this state, the deviation of the belt is eliminated. However, in the case of a belt that is highly endured and severely worn, there is a case where the offset is not sufficiently corrected. FIG. 12 is a diagram showing a control flow when the belt deviation correction is started, but the belt deviation does not return and the left second deviation detection sensor SL2 is turned off and the process proceeds to the left second stage belt deviation.

  Steps S211 to S213 in FIG. 12 are a flow when the belt is close to the right first stage or right second stage, and are the same as the first left stage or the second left stage, and thus description thereof is omitted. .

  In step S215, the displacement amount of the fixing steering roller 26 is changed to DL1 in order to return the belt from the left first stage belt to the center (step S214), and then the left side first deviation detection sensor SL1 is turned on. It is a part waiting for. In this state, there is a possibility that the deviation of the belt does not return and the second deviation detection sensor SL2 on the left side is turned OFF and the deviation advances. Therefore, in step S217, it is confirmed whether or not the belt is in the second left stage. If it is not close to the belt in the second left stage in step S217, the left end of the belt is between the sensors SL1 and SL2, so that the belt waits for the central range as it is. If the belt is shifted to the left second stage in step S217, the steering control stepping motor is set so that the displacement D of the fixing steering roller 26 is DL2 = 4.0 mm in order to return the belt from the left second stage to the center. 60 is driven by a difference amount from DL1. Here, since the number of pulses of the steering control stepping motor 60 necessary for the displacement from the displacement amount ± 0 state to DL2 is 110 pulses, the CCW direction is further increased by 50 pulses which is a difference when the DL1 is moved. (Step S218).

  Thus, when the belt returns to the central range in step S219, the position of the belt is beyond the sensor SL1, and it cannot be said that the belt has sufficiently returned to the central position. For this reason, a timer Tret for reversely driving the steering control stepping motor 60 is set so that the displacement amount D of the fixing steering roller 26 is returned to ± 0 after a predetermined time has elapsed in step S216, and the sequence is ended in S213. However, if the belt does not return to the central range in step S219 and continues for a predetermined time (here, 10 seconds), the operation of the fixing driving roller 24 is stopped to prevent damage to the fixing belt as described with reference to FIG. The image forming apparatus is stopped.

  FIG. 13 is a diagram showing control timing when further belt deviation correction control is performed according to the flowchart of FIG. 12 described above. That is, the fixing belt 27 moves to the left, performs correction control according to the left first stage belt, and then performs further belt deviation correction control when the left belt is shifted to the second stage. The control timing in this case is shown.

  A graph 302 in FIG. 13 is a detection amount of the left side detection sensor SL2, and is a signal input to the CPU 100. 13 are the detection force of the left side detection sensor SL1, the rotational speed of the fixing drive roller 24, and the displacement amount D of the fixing steering roller 26, respectively, as described in FIG.

  In the initial state of FIG. 13, both the left first belt shift detection sensor SL1 and the second belt shift detection sensor SL2 are in the ON state. From this state, as the fixing belt 27 rotates, the left first stage belt deviation as shown in FIG. 8B occurs. Then, the steering control stepping motor 60 is rotated by a predetermined pulse in the CCW direction so that the displacement amount D of the fixing steering roller 26 becomes a predetermined value DL1 in the minus direction from the reference amount ± 0 as indicated by a point 321. However, the shift toward the left side of the belt further proceeds as it is, and the second belt shift detection sensor on the left side may be turned OFF as shown in FIG. 8C (point 322). In such a case, the belt is closer to the left second stage belt. Therefore, in order to more strongly correct the deviation of the belt, the steering control stepping motor 60 is rotated by a predetermined pulse difference so that the displacement amount D of the fixing steering roller 26 is set to a predetermined value DL2 larger than the predetermined value DL1.

  When the belt shift finally starts to return in this state, the left second belt shift detection sensor is first turned ON (point 323), and the belt is shifted to the left first stage. However, if the displacement amount D of the fixing steering roller 26 is returned to DL1, there is a possibility that it will start moving again. Therefore, at point 323, the displacement D of the fixing steering roller 26 is maintained at DL2. When the belt shift sufficiently returns, the first belt shift detection sensor is also turned on (point 324), and the belt returns to the center range, but the displacement amount D of the fixing steering roller 26 is still maintained at DL2. The displacement amount D of the fixing steering roller 26 is returned to the reference amount ± 0 when the time (point 325) when the fixing belt 27 moves so as to be positioned approximately at the center between the deviation detection sensors SL1 and SR1 is reached. That is, the steering control stepping motor 60 is rotated in the reverse direction by a predetermined pulse to return the displacement amount D of the fixing steering roller 26 to the reference amount ± 0.

  Since the displacement amount DL2 of the fixing steering roller 26 is larger than DL1, when the displacement amount D of the fixing steering roller 26 is displaced to DL2, the amount of movement per unit time by belt deviation correction than when the displacement amount D is DL1. Is big. For this reason, the time from when the first belt shift detection sensor SL1 returns to ON until the fixing belt 27 returns to the approximate center between the shift detection sensor SL1 and the shift detection sensor SR1 is also shorter than when the displacement amount D is DL1. Therefore, the time 326 needs to be set shorter than the time 308 in the case of the displacement DL1, and when DL2 = 4.0 mm and the belt rotation speed is 200 mm / sec, the time 326 is 7 sec.

  As described above, the control for returning the steering roller displacement amount to the reference value after the elapse of the time from the end of the belt passing through the innermost detection sensor until the return to the center position is performed more reliably. Returning to the center position can be realized. And the phenomenon which repeats reciprocation in the width direction with respect to the roller on which the belt is stretched can be suppressed.

  Also, when calculating the elapsed time for the fixing belt to return to the center position, the rotation speed of the fixing belt and the displacement amount of the steering roller are used as coefficients, so that the position of the fixing belt can be stably controlled without being affected by various operating conditions. Can be kept central. As a result, it is possible to reduce downtime due to the fixing belt approaching.

  Here, in the twin belt fixing method, before the recording material P passes through the fixing nip portion N, control for switching the fixing belt 27 and the pressure belt 32 from the non-contact state (separated state) to the contact state (pressure contact state). explain. Further, a method for realizing the shift control while prohibiting the fixing belt 27 and the pressure belt 32 from moving in the opposite directions in the contact state will be described.

  As shown in FIG. 1, in a state where the pressure belt unit 31 is switched to the contact position, the fixing belt 27 and the pressure belt 32 are pressed against each other, and a wide fixing is performed between the fixing belt 27 and the pressure belt 32. A nip portion N is formed. During the operation of thermally fixing the unfixed toner image on the recording material P, switching control is performed so that the fixing nip portion is formed as described above.

  The attachment / detachment control for pressing or separating the belt of the belt fixing device 12 will be described with reference to the block diagram of FIG. When the image forming apparatus is on standby, the CPU 100 as the control unit controls the belt attaching / detaching mechanism 102 of the belt fixing device 12 to rotate the pressure belt unit 31 from the fixing belt unit 21 around the attaching / detaching shaft 43 in the pulling-down direction. . As shown in FIG. 3, the pressure belt 32 is held at a non-contact position in a non-contact state from the lower surface of the fixing belt 27. Thereby, the heat loss of the pressure belt 32 is reduced. Even during the print job operation, when the recording material P is not spaced and the recording material P does not pass through the fixing nip portion N, the control of switching the belt fixing device 12 to the non-contact position further reduces the heat loss of the pressure belt 32. Reduced.

  Based on the image formation start signal, the CPU 100 controls the belt attaching / detaching mechanism 102 to switch the belt fixing device 12 to the contact position and keep the pressure belt 32 in contact with the fixing belt 27. Further, the fixing belt driving roller driving mechanism 103 and the pressure belt driving roller driving mechanism 104 are controlled so that the fixing belt 27 and the pressure belt 32 are rotationally driven at a speed of 200 mm / s in accordance with the conveyance speed of the recording material P. To. Further, the heater power supply circuit 105 is controlled to supply electric power to the induction heating coil 29 of the fixing belt 27 to raise the temperature of the fixing belt 27. The surface temperature of the fixing belt 27 is detected by the temperature detecting means 21e, and the temperature detection signal is input to the CPU 100. The CPU 100 controls the heater power supply circuit unit 105 to vary the power supply to the power supply unit 21d so that the temperature detection signal input from the temperature detection unit 21e is maintained at a detection amount corresponding to a predetermined fixing temperature, and the fixing belt. The surface of 21 is kept at a constant temperature.

  Subsequently, the recording material P carrying an unfixed toner image is introduced into the fixing nip portion from the secondary transfer portion 8 side to the belt fixing device 12 and is nipped and conveyed to the fixing nip portion. In this process, the unfixed toner image surface of the recording material P is brought into close contact with the surface of the fixing belt 27, and the toner image is heated by the heat of the fixing belt 27 and fixed to the surface of the recording material P by heating and pressure. It is discharged and conveyed.

In the case where the recording material P passes through the fixing nip N in the print job operation, the shift control of the fixing belt 27 in the fixing belt unit 21 and the pressure belt unit 31 contact, it will be described. This control is executed before FIG. 10 and FIG. When this control is started, the paper thickness setting determines whether thin paper. Here, the thin paper is a recording material having a basis weight of 64 g / m ² or less. Prior to the start of the print job operation, the user performs a paper thickness setting on the operation unit 101 according to the basis weight of the recording material to be output. When the user sets thin paper, the process shifts to belt deviation detection of the fixing belt (which may be replaced with a pressure belt) .

Note that when the paper thickness setting is other than thin paper, moves to allowance mode to allow the movement direction of the width direction of the belts is in opposite directions, the shift control of the fixing belt and the pressure belt of the contact Allow implementation. Here, for example, the control of the flowcharts described in FIGS. 10 and 12 is performed. FIG. 10 illustrates a flow for sequentially performing the shift control of the fixing belt and the pressure belt, but it is also possible to simultaneously perform the shift control of both belts in the allowable mode. In addition, FIG. 12 illustrates a flow for performing the shift control of one belt, but it is also possible to simultaneously perform the shift control of both belts in the allowable mode. Thus, when the thickness (basis weight) t of the recording material P is larger than the thickness of the predetermined recording material (here, t> 64 g / m ² ), the CPU (selecting means) 100 determines the width direction of both belts. A permissible mode that allows the moving directions to be opposite to each other is selected and executed.

When the paper thickness setting is thin paper and the first stage belt deviation is detected, the direction of correcting the deviation of the fixing belt (which may be replaced with a pressure belt) is the current pressure belt (fixing belt). It is determined whether the direction is opposite to the direction of correcting the deviation. In the same direction or when the correction of displacement of the pressure belt (which may be replaced with a fixing belt) is not performed, the mode shifts to an allowable mode that allows the movement directions of both belts in the width direction to be opposite to each other. The deviation control between the fixing belt and the pressure belt in the contact state is performed . However, if it is in the reverse direction, it shifts to a prohibit mode in which the shift control of the fixing belt (which may be replaced with a pressure belt) is prohibited, and the fixing belt and the pressure belt are not corrected in the reverse direction. To. That is, when the thickness (basis weight) t of the recording material P is thinner than a predetermined recording material (here, t ≦ 64 g / m ² ), the CPU (selection means) 100 determines the width of both belts in the width direction. Select and execute a prohibit mode that prohibits the movement directions from being opposite to each other.

On the other hand, when a belt deviation in the second stage is detected, the direction of correcting the deviation of the fixing belt (which may be replaced with a pressure belt) is the same as the current pressure belt (which may be replaced with a fixing belt). It is determined whether the direction is the reverse of the direction to be corrected. In the same direction or when the correction of displacement of the pressure belt (which may be replaced with a fixing belt) is not performed, the mode shifts to an allowable mode that allows the movement directions of both belts in the width direction to be opposite to each other. The deviation control between the fixing belt and the pressure belt in the contact state is performed . However, in the reverse direction, in order to prevent the belt from moving further , the print job operation is interrupted, and the feeding of the succeeding paper is stopped so that the recording material P does not pass through the fixing nip portion N. Then, the fixing belt and the pressure belt are brought into a non-contact state by the belt attaching / detaching mechanism 102. After that, the mode shifts to an allowable mode in which the moving directions of both belts in the width direction are opposite to each other, and the deviation control between the fixing belt and the pressure belt in the non-contact state is permitted. Thereby, the deviation control is performed in a state where the fixing belt and the pressure belt are not in contact with each other.

Here, the interruption of the print job operation, the recording material P to the fixing nip N to stop feeding of the subsequent sheet so as not to pass through, is to already continue feeding papers only printing operation. Then, after confirming that the fixing belt and the pressure belt are not in contact with each other and the belt has returned to the center range, the feeding of the succeeding paper is resumed and the remaining print job is executed.

  As described above, when the fixing belt unit 21 and the pressure belt unit 31 are in contact with each other in a thin paper print job operation, the belt shift control operates in each belt unit, and the belts move in opposite directions. Is prohibited. As a result, the movement correction force in the reverse direction is not generated in the belts rotating in pressure contact with each other, and the movement correction force in the reverse direction does not act on the recording material. Therefore, it is possible to implement good movement correction control that prevents the influence on the recording material due to the generation of the movement correction force in the reverse direction on the belts that rotate in pressure contact with each other. Since the influence of the movement correction force in the reverse direction on the recording material can be prevented, the image defect of the recording material due to the movement correction force in the reverse direction can also be prevented.

  Furthermore, not only the mode is selected and executed according to the thickness of the recording material, but also a better movement correction control can be performed by selecting and executing the mode according to the position of the belt.

  INDUSTRIAL APPLICABILITY The present invention is applied to an apparatus that needs to perform control to correct a shift of a belt generated in a width direction orthogonal to the rotation direction in all belt conveying apparatuses configured to rotate by pressing endless belts against each other. Is possible.

It is sectional drawing of a belt fixing apparatus. 1 is a cross-sectional view showing an example of an image forming apparatus equipped with a belt fixing device. FIG. 3 is a cross-sectional view of a belt fixing device in which a fixing belt unit and a pressure belt unit are separated from each other. It is a perspective view of the principal part of a belt fixing device. It is operation | movement explanatory drawing of a steering roller. 2 is a block diagram illustrating a control system of an image forming apparatus including a belt-type fixing device. FIG. It is explanatory drawing of the position of a belt of a belt fixing device, and a belt shift | offset | difference detection sensor. It is explanatory drawing of the position of a belt of a belt fixing device, and a belt shift | offset | difference detection sensor. FIG. 10 is a table showing a relationship between a belt shift of the belt fixing device and a detection state of a belt shift detection sensor. It is a flowchart figure which shows the flow of correction | amendment control operation | movement at the time of detecting the belt | deviation of a belt. It is a figure which shows the correction | amendment control timing when the shift | offset | difference of a belt is detected. It is a flowchart figure which shows the flow of correction | amendment control operation | movement when the deviation further advances although what started the belt deviation correction. It is a figure which shows the correction | amendment control timing when the shift | offset | difference further advances although what started the belt | deviation correction | amendment of a belt. FIG. 10 is a flowchart showing a flow of control operation when a deviation between the fixing belt and the pressure belt is detected.

Explanation of symbols

P: Recording material SL1, SL2, SR1, SR2 ... Photo sensor 12 ... Belt fixing device 21 ... Fixing belt unit 22 ... Casing 24 ... Drive roller 26 ... Steering roller 27 ... Fixing belt 28 ... Pressure pad 29 ... Induction heating coil 31 ... pressure belt unit 32 ... pressure belt 33 ... drive roller 34 ... steering roller 35 ... casing 38 ... pressure pad 43 ... detachable shaft 45 ... oil application roller 50 ... belt-side normal range 51 ... belt-side left side abnormal range 52 ... belt side deviation abnormal range 60 ... steering control stepping motor 61 ... worm gear 62 ... sector gear 63 ... steering roller bearing 64 ... side plate 65 ... fixing belt side detection sensor unit 66 ... pressure belt side detection sensor unit 100 ... CPU
DESCRIPTION OF SYMBOLS 101 ... Operation part 102 ... Belt attaching / detaching mechanism 103 ... Fixing belt drive roller drive mechanism 104 ... Pressure belt drive roller drive mechanism 105 ... Heater feeding circuit part 106 ... Belt shift control mechanism

Claims (4)

Belt conveying apparatus having endless first and second belts that sandwich and convey a recording material, and movement correction means for correcting movement of each belt in the width direction orthogonal to the recording material conveying direction Because
A plurality of allowable modes that allow the movement directions in the width direction of both belts to be opposite to each other, and a prohibit mode that prohibits the movement directions in the width direction of both belts from being opposite to each other. A selection means for selecting and executing one of the modes according to the thickness of the recording material;
The belt conveying apparatus, wherein the prohibit mode is selected and executed when the recording material is thinner than a predetermined thickness, and the permissible mode is selected and executed when the recording material is thicker than the predetermined thickness.   Belt position detecting means for detecting the position of each belt in the width direction in stages, even if the recording material is thinner than a predetermined thickness, the position of the belt is located on the outer side in the width direction from the first stage. The belt conveyance device according to claim 1, wherein in the second stage, the permissible mode is selected and executed after the first belt and the second belt are brought into a non-contact state. Endless first belt and second belt that sandwich and convey the recording material, belt position detecting means for detecting a shift position of each belt in the width direction orthogonal to the recording material conveying direction, A belt conveyance device having movement correction means for correcting movement in the width direction,
A plurality of allowable modes that allow the movement directions in the width direction of both belts to be opposite to each other, and a prohibit mode that prohibits the movement directions in the width direction of both belts from being opposite to each other. A selection means for selecting and executing one of the modes according to the position of the belt;
The belt position detecting means detects the position of the belt in the width direction stepwise. When the belt position is in the first stage, the prohibit mode is selected and executed, and the belt position is the first position. In the second stage outside the width direction, the permissible mode is selected and executed after the first belt and the second belt are brought into a non-contact state. A belt conveying device according to any one of claims 1 to 3, heating the image on the recording material by said first belt and the nip forming a second belt pressed against An image heating apparatus.

Images