JP2018128630A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an image effect due to reciprocal movement of a belt while maintaining change of a direction for the reciprocal movement in a width direction of an endless belt.SOLUTION: An image formation device comprises: first and second rotating bodies in which at least one of them fixes at a toner image nip part on a recording material is an endless belt; position detection means that detects a position in a belt width direction; and control means that controls a belt to move reciprocally in a predetermined zone in the width direction according to a detection result. The position detection means can detect movement of the belt to one end and the other end in a reciprocal movement direction of the belt. The control means comprises first means for moving the belt by a first control amount to the other end side against a skew movement to one end side in the width direction of the belt detected by the position detection means; and second means for moving the belt to the other end side by changing a second control amount larger than the first control amount when it is detected that the belt does not move to the other end side in the first control amount.SELECTED DRAWING: Figure 1

Description

  In the present invention, the recording material is nipped and conveyed at the transfer nip portion to transfer the toner image onto the recording material, and the recording material from the transfer nip portion is nipped and conveyed at the fixing nip portion to fix the toner image. And an image forming apparatus including the fixing unit.

  In image forming apparatuses such as electrophotographic apparatuses and electrostatic recording apparatuses (copiers, printers, facsimiles, and multi-function machines having a plurality of these functions), it is undecided as a sheet-like recording material (hereinafter referred to as paper). Toner image is formed. The toner image is heated and pressed by a fixing device (image heating device) and fixed on the paper.

  In order to increase the glossiness of the image and increase the speed of image formation, it is preferable that the toner is sufficiently melted by widening the fixing nip portion (width in the paper conveyance direction). Therefore, in recent years, a fixing device of a belt fixing method that can widen the fixing nip portion while reducing the size of the device as compared with the conventional roll fixing method has been put into practical use.

  Specifically, in Patent Document 1, a fixing nip portion is formed by using a fixing belt and a pressure belt, both of which are endless belts, and in Patent Document 2, using a fixing roll and a pressure belt, which is an endless belt. It is wide.

  In a belt nip type fixing device using a so-called endless belt, such as the above-described fixing belt and pressure belt, one of the important technical problems is correction of belt misalignment. When the belt is shifted, that is, while the belt is rotating, it moves toward the end of the belt in the longitudinal direction (width direction) and is displaced, causing the belt to drop out of the belt running area and the belt end to come into contact with external parts. Problems occur.

  Regarding the belt offset correction, in Japanese Patent Laid-Open No. 2004-228688, the belt is predetermined by using the offset force generated in the belt by changing the end position of any one of the plurality of suspension rolls that span the belt. The belt shift control to keep the position is implemented.

  Further, in Patent Document 4, a means for detecting the belt shift position is provided, and when it is detected that one end side in the width direction of the belt has reached a predetermined position due to the shift movement, the belt shift direction is determined as the belt width direction. Belt misalignment control is performed so as to change to the other end side. Thus, a belt shift control system is used in which the movement movement in the belt width direction is an infinite reciprocating movement movement within a predetermined range.

JP 2004-341346 A Japanese Patent Application Laid-Open No. 11-194647 JP-A-4-104180 JP 2009-116141 A

  In the belt shift control method, a change in the reciprocating direction of the belt is obtained as a response by displacing one end of a roll member that suspends the belt using a belt shift control mechanism (hereinafter referred to as steering).

  Therefore, a sheet having a length equal to or greater than the distance between the transfer nip portion that transfers the toner image from the image carrier (photosensitive member or secondary transfer member) of the image forming portion to the sheet and the fixing nip portion of the fixing device is passed. Sometimes the balance of the paper is lost due to the reciprocating movement of the belt in the fixing device. As a result, the image transferred to the paper at the transfer nip is disturbed.

  Further, the reciprocating speed of the belt changes with the rotational speed of the belt at the same steering amount, and the reciprocating speed of the belt tends to increase as the rotating speed of the belt increases. For this reason, the above-mentioned phenomenon has become a more prominent issue due to recent high-speed copying machines.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to suppress a decrease in geometric characteristics due to the oblique running of the recording material due to belt deviation control.

A typical configuration of the image forming apparatus according to the present invention for achieving the above object is as follows:
An image forming unit for nipping and conveying the recording material at the transfer nip unit and transferring the toner image to the recording material;
A fixing unit for fixing the toner image by nipping and conveying the recording material from the transfer nip unit at the fixing nip unit,
The fixing unit includes first and second rotating bodies in which at least one of the fixing nip portion is an endless belt, a position detection unit that detects a position in the width direction of the endless belt, and a position detection unit Control means for controlling the endless belt to reciprocate within a predetermined zone in the width direction according to a detection result,
The position detection means is capable of detecting movement of the endless belt to one end in the reciprocating direction of the endless belt and the other end;
The control means is configured to move the endless belt to the other end side by a first control amount with respect to the movement of the endless belt to the one end side in the width direction detected by the position detecting means. And a second control amount smaller than the first control amount when the recording material having a length equal to or longer than the recording material conveyance distance from the transfer nip portion to the fixing nip portion is conveyed. And a second means for moving to the other end portion side.

  According to the present invention, it is possible to suppress a decrease in geometric characteristics due to the oblique running of the recording material due to belt deviation control.

Flow chart of belt reciprocation control in fixing device of embodiment Configuration schematic diagram of an example of an image forming apparatus Schematic diagram of the left side of the fixing device Cross-sectional schematic diagram of the device Explanatory drawing of the sensor part (belt position detecting means) on the pressure belt unit side Explanatory drawing of the belt shift control mechanism on the pressure belt unit side Illustration of steering operation for belt reciprocation control Explanation of belt position detection Block diagram of belt reciprocation control system Schematic of belt position in belt reciprocation control Timing chart of belt reciprocation control (1) Timing chart of belt reciprocation control (2) Configuration diagram of another fixing device

"Example"
(Image forming device)
FIG. 2 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus 1 is a tandem four-color full-color printer using a transfer type electrophotographic process. The image forming apparatus 1 applies a toner image corresponding to image information input to a control unit (control means: CPU) 10 from a host device 23 such as a personal computer via an interface 22 on a recording material (hereinafter referred to as paper or paper) S. Form and output. Since the image forming mechanism itself of the image forming apparatus 1 belongs to a publicly known one, its description will be simplified.

  An image forming unit 9 forms an unfixed toner image on the paper S. Four image forming units U (UY, UM, and yellow) of yellow (Y), magenta (M), cyan (C), and black (K). UC, UK). In each image forming unit U, the photosensitive drum (first image carrier) 2 charged by the charging roll 3 emits laser light from the laser scanner 4 in accordance with image information input from the host device 23 to the control unit 10. It is exposed to form an electrostatic latent image. The drum 2 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed.

  The formed electrostatic latent image is developed as a toner image of each color by using the toner of each color by the developing device 5. The formed toner images of respective colors are transferred onto the transfer belt (second image carrier) 8 of the intermediate transfer unit 7 by the primary transfer roll 6 to form a full color toner image. The transfer belt 8 is suspended around a drive roll 11, a tension roll 12, and a secondary transfer counter roll 13, and is driven to rotate at a predetermined peripheral speed in the clockwise direction of an arrow.

  A secondary transfer roll 14 is in contact with the secondary transfer counter roll 13 via the transfer belt 8. As a result, a secondary transfer nip 102 is formed between the transfer belt 8 and the secondary transfer roll 14. The secondary transfer opposing roll 13 and the secondary transfer roll 14 are the secondary transfer device 101.

  On the other hand, the sheets S accommodated in the cassette 15 or 16 are separated and fed by the operation of the sheet feeding mechanism and are conveyed in the conveying path 17. Then, the sheet S is introduced into the secondary transfer nip portion 102 at a predetermined control timing by the registration roll pair 18 and is nipped and conveyed, and undergoes secondary transfer of the full color toner image on the transfer belt 8 side in this nipping and conveying process.

  The sheet S exiting the secondary transfer nip portion 102 is conveyed to the fixing device (fixing portion) 100 through the conveying path 19, introduced into the fixing nip portion N of the fixing device 100, and nipped and conveyed. The sheet S is heated and pressurized during the nipping and conveying process and undergoes a toner image fixing process. The sheet S exiting the fixing nip N is discharged to the discharge tray 21 by the discharge roll 20 as an image formed product (product). The control unit 10 manages all device control of the image forming apparatus 1. Reference numeral 24 denotes an operation unit (user interface) for inputting various types of information to the control unit 10, which has a display unit and displays various types of information by the control unit 10.

(Fixing device)
3 is a left side view of the fixing device 100, and FIG. 4 is a cross-sectional view of the device. Here, in this embodiment, the front surface of the fixing device 100 is a surface on the paper inlet side, and the rear surface is a surface on the paper outlet side. Left and right are left or right when the device is viewed from the front, the left side is the front side or one end side, and the right side is the back side or the other end side. Up and down is up or down in the direction of gravity. Upstream or downstream is upstream or downstream with respect to the paper transport direction (recording material transport direction) V.

  The fixing device 100 is a twin belt nip type and electromagnetic induction heating (IH) type image heating device. Broadly divided, it has a heating belt unit A, a pressure belt unit B, an IH heater (heater: induction heating coil) 135, and a housing 140 that accommodates these.

  The heating belt unit A has an endless heating belt (endless belt) 130 as a first rotating body. The heating belt 130 has a plurality of support rolls (support members: belt suspension means) that rotatably support (suspend) the heating belt 130 from the inner surface side. Here, as a support roll, a drive roll 131 and a tension roll 132 that applies belt tension are provided. Moreover, it has the pad stay 137 formed, for example with stainless steel (SUS material).

  The IH heater 135 is a dielectric heating means (induction heating means) as a heating means for heating the heating belt 130 and has an induction heating coil (excitation coil) for electromagnetically heating the heating belt 130.

  The heating belt 130 may be appropriately selected as long as it generates heat by the IH heater 135 and has heat resistance. 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, for example, 300 μm of silicon rubber, and a surface layer is coated with a PFA tube.

  The drive roll 131 is a roll in which a heat-resistant silicone rubber elastic layer is integrally formed on a core metal surface layer having an outer diameter of φ18 made of solid stainless steel, for example. The tension roll 132 is a hollow roll formed of, for example, stainless steel with an outer diameter of about 20 mm and an inner diameter of about 18 mm.

  The tension roll 132 and the drive roll 131 are disposed substantially parallel to the upstream side and the downstream side in the paper transport direction V with a predetermined interval. The pad stay 137 is disposed between the tension roll 132 and the drive roll 131 so as to be close to the drive roll 131 and parallel to the drive roll 131. The heating belt 130 is stretched between the drive roll 131, the tension roll 132, and the pad stay 137 with a predetermined tension (for example, 200 N).

  The pressure belt unit B has an endless pressure belt (endless belt) 120 as a second rotating body. The pressure belt 120 has a plurality of support rolls (support members: belt suspension means) that rotatably support (suspend) the pressure belt 120 from the inner surface side. Here, as the support roll, a pressure roll 121 and a tension roll 122 for applying belt tension are provided. For example, the pressure pad 125 made of rubber is provided. The pressure pad 125 is covered with a sliding sheet 128. Further, an oil application roll (lubricant application member) 126 is provided.

  The pressure belt 120 may be appropriately selected as long as it has heat resistance. For example, a nickel metal layer having a thickness of 50 μm, a width of 380 mm, and a circumferential length of 200 mm is coated with, for example, a 300 μm-thick silicon rubber and a surface layer is coated with a PFA tube. The pressure roll 121 is a roll having an outer diameter of φ20 made of, for example, solid stainless steel. The tension roll 122 is a hollow roll formed of, for example, stainless steel with an outer diameter of about 20 mm and an inner diameter of about 18 mm.

  The tension roll 122 and the pressure roll 121 are disposed substantially parallel to the upstream side and the downstream side in the paper transport direction V with a predetermined interval. The pressure pad 125 is disposed between the tension roll 122 and the pressure roll 121 so as to be close to the pressure roll 121 and parallel to the pressure roll 121. The oil application roll 126 is disposed in parallel with the tension roll 122 between the pressure pad 125 and the tension roll 122. The pressure belt 120 is stretched between the pressure roll 121, the tension roll 122, the pressure pad 125, and the oil application roll 126 with a predetermined tension (for example, 200 N).

  As shown in FIG. 5, the oil application roll 126 is rotatably supported by an arm 127 that is rotatably supported around a shaft portion 122 a of the tension roll 122. The arm 127 is urged to rotate by a biasing member (not shown) such as a spring in a direction in which the oil application roll 126 contacts the inner surface of the pressure belt 120.

  The oil application roll 126 includes a heat-resistant aramid felt impregnated with a heat-resistant silicone oil having a viscosity of about 1000 CS as a lubricant so that a certain amount of oil is supplied (applied) to the inner surface of the pressure belt 120. It is configured. As a result, the frictional force between the inner surface of the pressure belt 120 and the sliding sheet 128 covering the pressure pad 125 is reduced, and the durability is improved. The heat resistant silicone oil supplied to the inner surface of the pressure belt 120 is also applied to the surfaces of the pressure roll 121 and the tension roll 122 via the inner surface of the pressure belt 120.

  The pressure belt unit B is disposed below the heating belt unit A. The pressurizing unit B is pressed against the heating unit A with a predetermined pressing force by a pressurizing operation of a pressurizing mechanism which is not described here.

  In this pressurized state, the drive roll 131 and the pressure roll 121 are pressed against each other with a predetermined pressing force with the heating belt 130 and the pressure belt 120 interposed therebetween. The driving roll 131 is one in which the elastic layer is elastically distorted by a predetermined amount by the pressure contact of the pressure roll 121. Further, the pad stay 137 and the pressure pad 125 are pressed against each other with a predetermined pressing force (for example, 400 N) with the heating belt 130 and the pressure belt 120 interposed therebetween. As a result, a wide nip portion (fixing nip portion) N is formed between the heating belt 130 and the pressure belt 120 in the paper conveyance direction V.

  Then, the driving force of the driving motor 163 controlled by the control unit 10 is transmitted to the driving gear G attached to the shaft part 131a of the driving roll 131, so that the driving roll 131 is rotationally driven, and the heating belt 130 is shown by an arrow in FIG. Rotate in a clockwise direction. In order to stably convey the paper S, the drive is reliably transmitted between the heating belt 130 and the drive roll 131. The pressure belt 120 on the pressure unit B side also rotates in a counterclockwise direction indicated by an arrow following the rotation of the heating belt 130 by the frictional force with the heating belt 130 in the nip portion N. The heating belt 130 is heated by the IH heater 135 and raised to a predetermined fixing temperature, and the temperature is adjusted.

  In this state, the sheet S carrying the unfixed toner image t is introduced into the fixing device 100 from the entrance side, guided by a guide member (not shown), enters the nip portion N, and is nipped and conveyed. As a result, the toner image t is fixed to the paper S as a fixed image by heat and pressure. The sheet S exits the nip portion N and is discharged from the fixing device 100 from the exit side.

  As described above, in this embodiment, the fixing belt nip N for fixing (heating) the toner image t on the paper (on the recording material) by sandwiching and conveying the paper S by the heating belt 130 and the pressure belt 120. Is a pair of rotating bodies, at least one of which is an endless belt.

(Belt shift control mechanism)
The heating belt 130 in the heating belt unit A has a phenomenon (belt shift) that moves so as to be shifted toward the front side or the back side in the width direction orthogonal to the paper transport direction V in the rotation process. In addition, a phenomenon occurs in which the pressure belt 120 in the pressure belt unit B also moves toward the front side or the back side in the width direction orthogonal to the paper conveyance direction V during the rotation process. FIG. 7 shows a state in which the pressure belt 120 in the pressure belt unit B moves so as to be deviated toward the front side or the back side in the width direction W perpendicular to the paper transport direction V in the rotation process.

  In this embodiment, the belt shift is stabilized within a predetermined shift range (predetermined zone) by swing-type shift control. Swing-type shift control is a method of tilting in the direction opposite to the belt shift direction using the tension roll as a steering member when it is detected that the belt position has moved by a predetermined amount or more from the center in the width direction.

  By repeating swing-type shift control (belt shift control: meandering control), the belt periodically moves from one side in the width direction (one direction in the width direction) to the other side (the other direction in the width direction). Therefore, it is possible to stably control the shift of the belt. That is, the belt is configured to be able to reciprocate in a direction W perpendicular to the conveyance direction V of the paper S.

  A similar belt shift control mechanism (belt steering mechanism) is provided on each of the heating belt unit A side and the pressure belt unit B side, and the shift control of the heating belt 130 and the pressure belt 120 is independently performed in the same manner. Therefore, in the following, the belt deviation control mechanism on the pressure belt unit B side and the deviation control on the pressure belt 120 will be described as a representative, and the belt deviation control mechanism on the heating belt unit A side and the deviation of the heating belt 130 will be described. The explanation of the control is omitted.

  Referring to FIGS. 3 and 6, a support arm 154 is disposed on the side plate on the front side of the housing 140. The support arm 154 is supported by a shaft portion 121a on the front side of the pressure roll 121 via a bearing 154a, is rotatable about the shaft portion 121a as a center (fulcrum), and extends to the paper inlet side. A pin 159 is planted at the free end of the support arm 154.

  A movable bearing 153 is provided between the bearing 154a and the pin 159 of the support arm 154. The movable bearing 153 is fitted in a long slot along the length of the support arm 154 and has a degree of freedom to move along the slot. ing. A shaft 122a on the front side of the tension roll 122 is supported by the bearing 153. The bearing 153 is biased by a tension spring (biasing member) 156 in a direction in which the pressure belt 120 is tensioned. A tension spring 156 applies a tension of 200 N to the pressure belt 120.

  A shaft 160 is implanted on the side plate on the front side of the housing 140 on the paper entrance side. A worm wheel (helical gear) 157 a is rotatably supported on the shaft 160. A folk wheel (control arm) 152 having a U-shaped groove 152a is integrally provided on the worm wheel 157a. The pin 159 of the support arm 154 is engaged with and supported by the groove portion 152a of the fork plate 152. A stepping motor 155 is disposed on the side plate on the front side of the housing 140. A worm 157 fixed to the rotating shaft of the motor 155 meshes with the worm wheel 157a.

  When the stepping motor 155 is driven forward or reversely, the fork plate 152 is rotated upward or downward via the worm 157 and the worm wheel 157a. In conjunction with this, the support arm 154 rotates upward or downward about the shaft portion 121a. Accordingly, the shaft 122a on the near side of the tension roll 122 is moved upward or downward with the shaft 122a on the back side as a fulcrum. As a result, belt inclination correction is performed by changing the inclination of the tension roll 122.

  That is, the tension roll 122 functions as a steering roll that adjusts the meandering in the width direction (longitudinal direction) orthogonal to the moving direction of the pressure belt 120. Therefore, hereinafter, the tension roll 122 is referred to as a steering roll.

  Belt reciprocation control means for moving the pressure belt 120 in the width direction orthogonal to the paper transport direction V by the steering roll 122, fork plate (control arm) 152, worm wheel 157a, worm 157, stepping motor 155, etc. It is. That is, it is a belt steering mechanism (a displacement mechanism that displaces one end side in the longitudinal direction of the steering roll 122 as a support member from the reference position to the first position).

  Referring to FIGS. 4 and 5, the housing 140 is provided near the end of the front side of the fixing device in the width direction perpendicular to the paper conveyance direction V of the pressure belt 120 below the pressure belt unit B. A sensor unit 150 is provided for detecting the belt end position. That is, the position detection means (detecting that the belt has deviated from a predetermined zone in the width direction) can be detected by the sensor unit 150 in the width direction of the pressure belt 120 toward the one end side and the other end side. Detection unit).

  The control unit 10 detects the position of the end of the pressure belt 120 by the sensor unit 150, and changes the inclination of the steering roll 122 that constitutes the belt steering mechanism in accordance with the detection result to perform belt deviation correction. Thus, control is performed so that the pressure belt 120 is reciprocated between the near side (one end side) and the far side (the other end side) in the width direction. That is, the belt steering mechanism is controlled so that the pressure belt reciprocates within a predetermined zone in the width direction.

  In addition, the operation | movement of the belt deviation control in the near side using the sensor part 150 and the operation | movement of the same belt deviation control in the back | inner side are performed independently. That is, the sensor unit 150 is provided at both ends of the pressure belt 120 in the width direction, and executes a first control mode and a second control mode, which will be described later, on one end side, and a first on the other end side. The execution of the control mode and the second control mode is performed independently.

  Specifically, in the belt shift control, the position of the end of the pressure belt 120 is detected by the sensor unit 150, and the stepping motor 155 is driven at a predetermined rotational speed and the inclination of the steering roll 122 is changed accordingly. This is done by rotating the pressure belt 120. Thereby, deviation correction in the axial direction (width direction) of the belt is realized. Here, the amount of movement of the pressure belt 120 in the width direction can be controlled by changing the alignment of the steering roll 122.

  The sensor unit 150 is a belt position detection unit that detects the movement position of the pressure belt 120 in the axial direction (width direction) of the belt. The sensor unit 150 includes first and second sensors 150a and 150b that are optical detection means, a sensor flag 150c that is a flag member, a sensor arm 150d, and a sensor spring 150e. The sensor spring 150e is a member for operating the sensor arm 150d following the movement of the pressure belt 120. The sensor flag 150c rotates around the fulcrum 150f in conjunction with the sensor arm 150d.

  Then, the sensor arm 150d, which is an arm member, is brought into pressure contact (contact) with the front end surface 120a, which is one end side of the heating belt 120, with a force of 0.03N. As a result, the pressure belt 120 is combined with a combination of ON / OFF signals of the sensors 150a and 150b as flag detection means for optically detecting the sensor flag 150c, which is a flag member that rotates according to the position in the belt width direction. Detect the position in the width direction.

  The description of the belt shift control mechanism on the heating belt unit A side and the shift control of the heating belt 130 is omitted, but it is the same as the belt shift control mechanism and belt shift control of the pressure belt unit B described above. 3 and 4, 150A corresponds to the sensor unit 150 on the pressure belt unit B side. Reference numerals 154A, 153A, 156A, and 160A correspond to the support arm 154, the bearing 153, the tension spring 156, and the shaft 160 on the pressure belt unit B side. 152A, 157A, and 155A correspond to the fork plate 152, the worm 157, and the stepping motor 155 on the pressure belt unit B side.

  FIG. 8 shows the relationship between the ON / OFF signal combination of the first sensor 150a and the second sensor 150b and the position of the end face of the pressure belt 120 at that time. When the sensor flag 150c shields the sensors 150a and 150b, the signal is turned OFF, and when the light is transmitted, the signal is turned ON.

  FIG. 1 is a flowchart of the belt reciprocation control, and FIG. 9 is a block diagram of a control system for driving the steering roller 122. FIG. 10 shows the operation of the steering roller for reciprocating the pressure belt 120. FIG. 10 shows the positional relationship between the reciprocating position of the pressure belt 120 and the sensors 150a and 150b.

  The pressure belt 120 reciprocates between a position where the first sensor 150a is ON and the second sensor 150b is OFF and a position where the first sensor 150a is OFF and the second 150b is ON. The reciprocating control is performed so that the pressure belt 120 exists within the section (predetermined zone). The distance of the section is set to ± 1.5 mm from the center position of the pressure belt 120 in the rotation axis direction.

  As shown in FIG. 10, when the pressure belt 120 moves from the center position to the near side, the sensor flag 150c operates via the sensor arm 150d that contacts the pressure belt 120. When the pressure belt 120 reaches the position of -1.5 mm on the near side, the first sensor 150a detects the sensor flag 150c, and the signal of the sensor 150a is turned OFF to move the pressure belt 120 in the rear direction. Then, the steering roll 122 operates.

  When the moving direction of the pressure belt 120 is reversed and enters the range of ± 1.5 mm, the sensor flag 150C moves from the position detected by the first sensor 150a, and the signal of the sensor 150a is turned on ( The signal of the second sensor 150b is also ON).

  Conversely, when the pressure belt 120 reaches the position of the rear side +1.5 mm, the sensor flag 150c is detected by the second sensor 150b, the signal of the sensor 150a is turned OFF, and the pressure belt 120 is moved toward the front side. In order to make this happen, the steering roll 122 operates. When the moving direction of the pressure belt 120 is reversed and enters the range of ± 1.5 mm, the sensor flag 150C moves from the position detected by the second sensor 150b, and the signal of the sensor 150b is ON. (The signal of the first sensor 150a is also ON).

  The arm wall surface 127a of the arm 127 exists at a position of ± 3.5 mm in the reciprocating direction of the pressure belt 120 (exists on both the near side and the back side). In order to prevent the pressure belt 120 from coming into contact with the arm wall surface 127a and being damaged due to the movement in the reciprocating direction, the position where the pressure belt 120 is ± 3.0 mm is set as the movement restriction position.

  That is, as shown in FIG. 10, when the pressure belt 120 reaches the position of −3.0 mm which is the movement restriction position, the sensor flag 150c is detected by both the first sensor 150a and the second sensor 150b. Move to position. Thereby, the signals of both the sensors 150a and 150b are turned off. Conversely, the same applies when the pressure belt 120 reaches the position of +3.0 mm, which is the movement restriction position.

(Belt reciprocating control)
Next, belt reciprocation control in this embodiment will be described with reference to the operation flow chart of FIG. 1 and the timing charts of FIGS. 11 and 12. FIGS. 11 and 12 are timing charts based on the signals of the first sensor 150 a and the second sensor 150 b and the operating angle of the steering roll 122.

  When the fixing device 100 is driven and the rotation of the pressure belt 120 is started by the drive motor 163 (FIG. 3), the belt reciprocation control is started (S1-01, S1-02, S1-03). When the pressure belt 120 approaches the end in the width direction, the sensor unit 150 detects that the reciprocating direction change position has been reached (S1-9 or S1-24). Then, the first means (control unit 10) constituting the control means is operated, and the movement direction in the width direction of the pressure belt 120 is changed to the reverse direction via the steering roll 122 with the first control amount at the time of operation. .

  That is, a predetermined drive pulse is output to the stepping motor 155 via the motor driver 155D (FIG. 9) (S1-11 or S1-26). Then, as shown in FIG. 7, the front end of the steering roll 122 is moved up and down to tilt the steering roll 122 to + α ° or −β ° with respect to the drive roll 131 (S1-12 or S1-27). .

  When the pressure belt 120 changes its reciprocating direction and starts moving, the belt position detector 150 detects that the pressure belt 120 changes its reciprocating direction and passes through the sensor 150a and the sensor 150b (S1- 13 or S1-28). The angles α and β of the steering roll 122 are set so that the reciprocating direction of the pressure belt 120 is maintained so that the reciprocating direction is not changed by disturbance.

  When the belt shift is detected, the first means decelerates the shift toward the end of the pressure belt 120 with the + α ° or −β ° inclination of the steering roll 122 and the rotation of the pressure belt 120. The pressure belt 120 accelerates in the opposite direction. That is, the reversal of the belt in the reciprocating direction is performed in this way (operation of FIG. 11). In the present embodiment, adjustment is made for each unit so that α is in the range of 0.4 ± 0.2 [deg] and the sum of α and β is 0.8 [deg].

  By the way, due to the horizontal state of the image forming apparatus 1 and the tolerances of the components of the fixing device 100, alignment deviation of the members that suspend the pressure belt 120 occurs, and the reciprocating movement of the pressure belt 120 becomes uneven. There is a case. For example, when the movement of the pressure belt 120 in the front direction (− direction) is fast and the movement in the back direction (+ direction) is slow, the movement direction of the pressure belt 120 is changed from the front side to the back direction. The responsiveness when doing so decreases.

  In such a case, it is effective to reduce the absolute speed of the angle β and reduce the moving speed of the pressure belt 120 from the back to the front. This makes it possible to reduce the deceleration / acceleration time of the pressure belt 120 when the reciprocating direction is changed in the front direction, and a response when the moving direction of the pressure belt 130 is changed from the front to the back side. Can be improved.

  In this embodiment, the pressure belt 120 has been described, but the above-described control may be performed by the fixing belt 130.

  Here, when a sheet S having a length s longer than the sheet conveying path distance L (more than the recording material conveying distance) from the transfer nip 102 (FIG. 2) to the fixing nip N of the secondary transfer apparatus 101 is passed through. The paper behavior will be described. In this embodiment, L is 250 [mm]. The control unit 10 confirms the length of the sheet from the passage time of the sheet by a sheet passage detection sensor (detection means) arranged on the sheet passage path before the sheet S enters the fixing device 200. In FIGS. 2 and 4, reference numeral 25 denotes a paper passage detection sensor disposed at a paper inlet portion (recording material inlet portion) of the fixing device 200.

  In the fixing nip portion N, the sheet receives a force from the belt in the direction toward the belt forming the nip. Due to the force, the skew amount of the sheet changes while passing through the nip. Therefore, when a sheet having a length equal to or longer than L is passed, an image transferred to the sheet by the secondary transfer device 101 (secondary transfer nip portion 102) is disturbed. That is, the image is transferred with distortion by the amount of change in the skew of the paper that occurs between the time when the leading edge of the paper enters the fixing nip portion N and the time when the trailing edge of the paper passes through the transfer nip portion 102. become.

  Therefore, in this embodiment, when it is detected that the paper length s (JOB paper size) is equal to or longer than the conveyance path distance L from the secondary transfer apparatus 101 to the fixing nip N (S1-10 or S1-25). The second means (control unit 10) constituting the control means operates. The controller 10 uniformly reduces the tilt angles α and β of the steering roll 122 by the second control amount, and controls α ′ and β ′ (α ′ = α−ψ, β ′ = β−ψ) and control (S1− 15 or S1-32). Thus, the distortion of the transferred image is reduced by suppressing the belt shift speed.

  ψ is a value that is determined in view of the angle at which the reciprocating direction of the pressure belt 120 can be changed with respect to component variations and disturbances. In this embodiment, ψ is calculated by the control unit 10 so as to use a value obtained by multiplying the smaller one of the absolute values of α or β by 0.3.

  However, when it is detected (S1-16 or S1-33) that the pressure belt 120 does not change the reciprocating direction in a predetermined time X seconds due to an unexpected disturbance, the control unit 10 operates, and the first operation is performed. The steering roll 122 is tilted again by the control amount. That is, when the detection time t of the sensors 150a and 150b reaches a predetermined time X seconds, a predetermined drive pulse is output to the stepping motor 155 via the motor driver 150D (S1-22 or S1-37). Then, the steering roll 122 is inclined α or β with respect to the drive roll 131 (S1-23 or S1-38).

  X seconds, which is a time for detecting a trouble in changing the belt reciprocating direction, is a value determined by the moving speed in the belt reciprocating direction caused by the rotational speed of the pressure belt 120 and the like. It is preferable to select a time during which the belt does not fall out of the belt travel region and the end of the belt does not come into contact with external parts. In this embodiment, when the sheet passing speed is V, X = 1730 / V is set. For example, if V = 320 [mm / s], X is 5.4 [s].

  Further, when the inclination is changed to + α ° or −β °, an image transferred to the sheet by the secondary transfer device 101 in a state where a part of the sheet exists in the fixing nip portion N has a large distortion. Therefore, the control unit 10 performs control so as not to change the steering inclination from α ′ to α ° or −β ′ to −β ° for Y seconds after the leading edge of the sheet enters the fixing nip portion N (S1-42 or S1- 46). Until the change in the reciprocating direction is confirmed (S1-21 or S1-36), it is determined that paper cannot be passed, and control is performed so as to open a gap (S1-43 or S1-47).

  Here, in order that the tilt angle of the steering roll 122 is not changed to + α ° or −β ° until the trailing edge of the paper being fixed by the fixing device 200 passes through the secondary transfer device 101, Y seconds is the length of the paper. When s, the paper feeding speed is V, it is necessary to be (s−L) / V or more.

  Thus, by reducing the amount of steering for belt reciprocation control, it is possible to perform stable belt reciprocation control and suppress distortion of a transfer image onto a sheet.

  The above control is summarized as follows. The control unit 10 is a first means for moving the belt 120 to the other end side by the first control amount with respect to the movement toward the one end side in the width direction of the belt 120 detected by the position detection means 150. Have Further, when a sheet having a length s longer than the sheet conveying distance from the transfer nip N to the fixing nip N is conveyed, the belt 120 is changed to a second control amount smaller than the first control amount. There is a second means for moving to the other end side.

  The amount of movement of the belt 120 in the width direction is controlled by changing the alignment of the steering roll 122. The control target for controlling the amount of movement of the belt 120 in the width direction is the inclination angle of the steering roll 122. The inclination angle of the steering roll 122 is set to the first inclination angle when the first means is operated, and is set to the second inclination angle equal to or less than the first inclination angle with the same inclination when the second means is operated.

  The second means operates when a sheet having a length s longer than the sheet conveying distance is conveyed. Then, the second means shifts to the first means when the position detecting means 150 detects that the belt 120 moving to the other end side does not pass within a predetermined time.

  A sheet passing detection sensor 25 is provided at the sheet inlet portion of the fixing device 200, and the second means is activated when a sheet having a length s longer than the sheet conveying distance is conveyed. The second means detects that the belt 120 moving to the other end side does not pass within a predetermined time by the position detecting means 150 and detects the paper by the paper passing detection sensor 25 and then the predetermined means. When time passes, the process proceeds to the first means.

  The second means operates when a sheet having a length s longer than the sheet conveying distance is conveyed. Then, the second means shifts to the first means when the position detecting means 150 detects that the belt 120 moving to the other end side does not pass within a predetermined time. Thereafter, when it is detected by the position detection means 150 that the position detection means 150 has moved to the other end, the process proceeds to the second means again.

  The passage detection time of the belt 120 that moves to the other end side is changed according to the sheet conveyance speed.

  The object to be controlled is not limited to the above-mentioned angle, and is applied to angle changing means such as an input pulse to the stepping motor 155 for operating the steering roller 132 and changing the angles α ° and β °. The contents are not limited to those described in the examples.

  Further, by determining the change in the reciprocating direction of the pressure belt 120 using the detection time by the detection means 150, it is possible to detect the change in the reciprocating behavior of the pressure belt 120 with the minimum detection means. . That is, the end detection area of the pressure belt 120 (the area on the near side in FIG. 10 -1.5 mm and -3.0 mm) is monitored using a plurality of detection means. As a result, the number of detecting means can be reduced as compared with a method of detecting a change in the reciprocating behavior of the pressure belt 120 according to the amount of movement, and it is possible to reduce costs and prevent the apparatus from becoming large.

  In a state where reciprocal control is disabled, when the end face of the pressure belt 120 comes to a position ± 3 mm from the center position, both the sensors 150a and 150b are turned off (S1-04). At this time, the control unit 10 of the image forming apparatus 1 determines that an abnormality has occurred, stops the rotation operation of the pressure belt 120 of the fixing device 200 (S1-05), and stops the apparatus (S1-06).

  In this embodiment, the reciprocation time of the belt is about 18 [s] at the steering roller angles α ° and β °, and is about 25.7 [s] when the steering roller angles α ′ and β ′ are used.

  As described above, according to the present embodiment, by reducing the steering amount for the belt reciprocation control, it is possible to achieve stable belt reciprocation control and stabilization of paper transfer behavior.

(Effect of this embodiment)
According to the present embodiment, by reducing the steering amount for the belt reciprocation control, it is possible to achieve stable belt reciprocation control and stabilization of paper transfer behavior.

(Modification)
(1) Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications are possible within the scope of identity. For example, the present invention is applied to a configuration in which the belt-like member 120 in the fixing device 200A as shown in FIG. 13 is reciprocated with a substantially predetermined width, and in particular, a configuration capable of reducing the reciprocating speed after changing the reciprocating direction. Applies to

  The fixing device 200A of FIG. 13 uses a fixing roller 130A incorporating a halogen heater H as a first rotating body. The pressure belt unit B is brought into contact with this, and a wide fixing nip portion N in the sheet conveying direction V is formed between the fixing roller 130A and the pressure belt 120.

  (2) Although the pressure belt 120 has been described, it can also be applied to the heating belt 130. That is, the present invention can be applied to a case where at least one of the first rotating body and the second rotating body constituting the nip portion N includes an endless belt.

  (3) In the embodiment, a fixing device that fixes an unfixed toner image onto a sheet has been described as an example. However, the present invention is not limited to this, and is assumed to be attached to a sheet in order to improve the glossiness of the image. The present invention can be similarly applied to a device that heats and presses a toner image (also referred to as a fixing device in this case).

  (4) The image forming apparatus is not limited to an image forming apparatus that forms a full-color image as in the embodiment, and may be an image forming apparatus that forms a monochrome image. In addition, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multifunction machine having a plurality of these functions in addition to necessary equipment, equipment, and housing structure.

  1 .... Image forming device, 9 .... Image forming portion, 200 .... Fixing portion (fixing device), 102 .... Transfer nip portion, N..Fixing nip portion, S..Recording material, t..Toner image 130.120..First and second rotating bodies 150..Position detecting means 10..Control means

Claims (12)

An image forming unit for nipping and conveying the recording material at the transfer nip unit and transferring the toner image to the recording material;
A fixing unit for fixing the toner image by nipping and conveying the recording material from the transfer nip unit at the fixing nip unit,
The fixing unit includes first and second rotating bodies in which at least one of the fixing nip portion is an endless belt, a position detection unit that detects a position in the width direction of the endless belt, and a position detection unit Control means for controlling the endless belt to reciprocate within a predetermined zone in the width direction according to a detection result,
The position detection means is capable of detecting movement of the endless belt to one end in the reciprocating direction of the endless belt and the other end;
The control means is configured to move the endless belt to the other end side by a first control amount with respect to the movement of the endless belt to the one end side in the width direction detected by the position detecting means. And a second control amount smaller than the first control amount when the recording material having a length equal to or longer than the recording material conveyance distance from the transfer nip portion to the fixing nip portion is conveyed. And a second means for moving to the other end side.   In the fixing unit, the endless belt is suspended by a plurality of belt suspension means, and belt steering means for controlling the amount of movement of the endless belt in the width direction by changing the alignment of at least one belt suspension means. The image forming apparatus according to claim 1, further comprising:   3. The image forming apparatus according to claim 2, wherein a control target for controlling a movement amount of the endless belt in the width direction is an inclination angle of at least one belt suspension unit in the belt steering unit. .   The inclination angle of at least one of the belt suspension means in the belt steering means is a first inclination angle when the first means is operated, and the first inclination angle is inclined in the same direction when the second means is operated. The image forming apparatus according to claim 3, wherein the second inclination angle is equal to or smaller than the second angle.   The control object for controlling the movement amount of the endless belt in the width direction is an input pulse of a drive motor of at least one belt suspension means in the belt steering means. Image forming apparatus.   The second means operates when a recording material having a length equal to or longer than the recording material conveyance distance is conveyed, and the second means is configured such that the endless belt moving to the other end side has a predetermined value. 6. The image forming apparatus according to claim 1, wherein when the position detection unit detects that it does not pass within the time, the image forming apparatus shifts to the first unit. A detecting means for detecting a recording material at a recording material inlet of the fixing unit;
The second means operates when a recording material having a length equal to or longer than the recording material conveyance distance is conveyed, and the second means is configured such that the endless belt moving to the other end side has a predetermined value. When the position detecting means detects that the recording medium does not pass within the time, and the recording material is detected by the detecting means, the process proceeds to the first means when a predetermined time has elapsed. The image forming apparatus according to claim 1.   The second means operates when a recording material having a length equal to or longer than the recording material conveyance distance is conveyed, and the second means is configured such that the endless belt moving to the other end side has a predetermined value. When it is detected by the position detection means that it does not pass within the time, when the position detection means detects that the position detection means has moved to the other end side, 8. The image forming apparatus according to claim 1, wherein the image forming apparatus shifts to the second unit.   The position detection means includes an arm member that contacts one end side in the width direction of the endless belt, a flag member that rotates around a fulcrum in conjunction with the arm member, and flag detection that detects the flag member. The image forming apparatus according to claim 1, further comprising: an image forming unit.   The image forming apparatus according to claim 9, wherein the flag detection unit is two optical detection units.   The position detecting means is provided at both ends in the width direction, the operation of the first means and the second means on the one end side, and the first means and the first on the other end side. The image forming apparatus according to claim 1, wherein the operation of the second unit is performed independently.   12. The image forming apparatus according to claim 1, wherein a passage detection time of the endless belt moving to the other end portion side is changed according to a conveyance speed of the recording material.