JP2012078679A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of reducing scratches on a fixing member by effectively shifting the running position of the fixing member and the sheet and printing a high-quality image on the sheet.
Image forming means for transferring a toner image formed on an image carrier to a sheet, fixing means for fixing the toner image transferred to the sheet, and fixing for heating and pressurizing toner on the sheet by the fixing means. A fixing member shifting unit that moves the fixing member in a direction orthogonal to the sheet conveying direction, a fixing member position detecting unit that detects a moving position of the fixing member, and a sheet disposed upstream of the image forming unit in the sheet conveying direction. In an image forming apparatus comprising: a sheet shift unit that moves a sheet in a direction orthogonal to the conveyance direction; and a sheet shift control unit that controls the sheet shift unit, the sheet shift control unit based on detection information of a fixing member position detection unit To control the sheet shift means.
[Selection] Figure 8

Description

  The present invention relates to an image forming unit that forms a toner image on an image carrier and transfers the image to a sheet, and a copying machine that includes a fixing member that heats and pressurizes the toner and fixes the toner image transferred to the sheet. The present invention relates to an image forming apparatus such as a printer, a fax machine, or a multifunction machine thereof.

  As a means for forming a toner image on an image carrier, an electrophotographic image forming process using a photoconductor as an image carrier, an electrostatic recording image forming process using a dielectric as an image carrier, and a magnetic material as an image carrier. Examples include a magnetic recording image forming process.

  A sheet is an image on which an image is formed by an image forming apparatus, and is a sheet (such as a sheet, an OHP sheet, an envelope, a postcard, or a label) (a sheet: hereinafter also referred to as a sheet, paper, or recording paper).

  As a fixing device (fixing means) in an electrophotographic image forming apparatus, a heat fixing device having a fixing member such as a fixing roller or a fixing belt is generally used. The fixing roller or the fixing belt is provided with an elastic layer made of silicone rubber or a fluorine tube as a surface layer, and its durability is a problem. For example, when sheets of the same size are continuously fed, the fixing member surface layer corresponding to the passing position of the edge portion of the paper is gradually roughened, and an area having a surface roughness higher than the surroundings is generated.

  As a result, the difference in surface roughness appears as uneven gloss on the fixed image. Further, when the sheet is continuously fed in this state, the surface layer of the surface layer member is torn, causing a fixing abnormality and a conveyance abnormality.

  In order to solve these problems, as disclosed in Patent Document 1, the fixing member is moved in a direction orthogonal to the paper conveyance direction so that the edge portion of the paper does not pass through the same position on the fixing member. A method for reducing the roughness of the surface of the fixing member has been proposed.

  In addition, when an endless belt or film is used as the fixing member, there is a method of moving the fixing member in a direction orthogonal to the paper transport direction by performing a shift control to prevent the fixing member from shifting due to running. It has been put into practical use.

  In addition, by shifting the paper passing position upstream of the fixing member in the paper conveying direction, the paper passing position is set as the paper conveying direction as a method for preventing the edge of the paper from passing the same position on the fixing member. Patent Documents 2 and 3 disclose a method of shifting in the orthogonal direction.

JP-A-7-134507 JP 2008-282003 A JP 2008-1473 A

  In the future, when image quality improvement of image forming devices and high durability and long life of fixing devices are required, there is an effect on the image due to wear of fixing members that occurs when paper edges pass over fixing members. It is expected to become more prominent. In order to reduce the wear on the fixing member and the difference in surface roughness from the surroundings, the edge of the paper is increased by increasing the amount of movement of the fixing member and the paper passing position in the direction perpendicular to the paper transport direction. It is effective to widen the area through which the toner passes on the fixing member. However, from the viewpoints of the width of the image forming apparatus and the fixing member and the consistency with the post-processing apparatus, there are many cases in which the movable amounts are limited.

  Another method for further expanding the paper passing area of the paper edge relative to the fixing member is to move both the fixing member and the paper passing position. By moving both the fixing member and the paper passing position, as shown in FIG. 20, the paper passing area can be widened by adding up the moving amounts of both.

  However, depending on the timing of movement of the fixing member and movement of the sheet passing position, as shown in FIG. 21 and FIG. 22, the sheet passing area on the obtained fixing member becomes narrower or the distribution of the sheet passing is biased. And a situation in which the effect of shifting both the paper passing positions cannot be obtained. Even when an endless belt or film is used as the fixing member, depending on the movement of the fixing member and the movement of the paper passing position, there may be a situation in which the effect of shifting the paper passing position cannot be obtained. It is expected that.

  The present invention has been proposed in view of the above prior art. In the present invention, the traveling positions of the fixing member and the sheet are controlled so as to optimally move with respect to the respective movement positions. Accordingly, an object of the present invention is to provide an image forming apparatus capable of reducing the gloss unevenness due to the difference in the surface roughness of the surface of the fixing member due to the wear of the sheet and the surface of the fixing member, and capable of printing a high-quality image on the sheet. And Another object of the present invention is to make it possible to extend the life of the fixing member in the fixing unit.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes an image forming unit that forms a toner image on an image carrier and transfers it to a sheet, and a fixing member that heats and pressurizes the toner. A fixing unit that fixes the toner image transferred to the sheet, a fixing member shift unit that moves the fixing member in a direction orthogonal to the sheet conveyance direction, and a sheet that is more than the toner image transfer unit of the image forming unit. A sheet shift means for moving a sheet, which is arranged on the upstream side in the conveyance direction and fed to the toner image transfer section, in a direction perpendicular to the sheet conveyance direction; and a sheet shift control section for controlling the sheet shift means. In the image forming apparatus, the sheet shift control unit controls the sheet shift unit based on the fixing member position information moved by the fixing member shift unit. And wherein the Rukoto.

  According to the present invention, it is possible to control the traveling positions of the fixing member and the sheet so as to optimally move with respect to the respective moving positions. Thereby, it is possible to reduce gloss unevenness due to wear and surface roughness difference of the paper on the fixing member surface layer, and to provide an image forming apparatus capable of printing a high-quality image on the sheet, The life of the fixing member can be extended.

Schematic configuration diagram of an example of an image forming apparatus Schematic diagram for explaining the skew feeding mechanism, shift roller, and transfer roller Explanatory drawing of the seat shift mechanism (1) Explanatory drawing of the seat shift mechanism (2) Explanatory drawing of the seat shift mechanism (part 3) Explanation of fixing device (A) is a table for explaining the relationship between the fixing belt position and sensor logic, and (b) is a flowchart for explaining the fixing belt shift control. (A) is a block diagram showing a control system of the image forming apparatus, and (b) and (c) are tables showing a correspondence relationship between a roller shift amount and an image fine adjustment amount corresponding to a shift position stored in the SRAM. Explanatory drawing of the image writing position changed by the image position control part and laser driver in (a) of FIG. Explanatory drawing of shift operation in the sheet width direction by the sheet shift mechanism Explanatory drawing of an example of image forming operation to the photosensitive drum Explanatory drawing of operation example of seat shift mechanism The figure explaining the outline of the relationship of the shift amount from the heating belt center of the heating belt position, the sheet passing position of the sheet, and the sheet passing position on the heating belt. Explanatory drawing of the fixing member shift mechanism of the fixing device in Embodiment 2. FIG. 3 is a block diagram showing a control system of an image forming apparatus in Embodiment 2. (A) is a table diagram for determining the sheet shift amount and the image shift amount, and (b) is the relationship between the position of the heating belt, the sheet passing position, and the shift amount from the center of the heating belt of the sheet passing position on the heating belt. Chart explaining the outline of Schematic diagram for explaining the shift position of the sheet shift mechanism and the fixing member in Embodiment 3. FIG. 6 is a block diagram illustrating a control system of an image forming apparatus according to a third embodiment. (A) is a table for determining a fixing member shift amount from a signal detected by a sheet edge position detection sensor, (b) is a heating belt position, a sheet passing position, and a heating belt at a sheet passing position on the heating belt. Graph showing the outline of the relationship between the shift amount from the center FIG. 3 is a graph for explaining a sheet passing area on a fixing member according to a fixing member and a sheet passing position (No. 1). FIG. 2 is a graph for explaining a sheet passing area on a fixing member according to a fixing member and a sheet passing position (part 2). FIG. 3 is a graph for explaining a sheet passing area on the fixing member according to the fixing member and the sheet passing position (No. 3).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Example 1]
(1) Overall Schematic Configuration of Example Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus 1 according to the present invention. This apparatus 1 is an electrophotographic laser printer. A toner image corresponding to electrical image information input from a host device 300 connected to the CPU (control means) 13 of the apparatus 1 so as to be communicable with the sheet (recording material: recording material) P (Pa, Pb) ) And output.

  The CPU 13 performs image formation sequence control by exchanging electrical signals with the apparatus 300, the operation unit (console unit) 200, and various image forming devices. The device 300 is, for example, a personal computer, an image reader, a facsimile, or the like. The sheet P can form a toner image by the apparatus 1 and includes, for example, paper, an OHT sheet, a postcard, an envelope, and the like.

  Inside the apparatus 1, in order from the upstream side to the downstream side of the sheet conveyance path, a sheet feeding mechanism 7, a sheet oblique feeding mechanism 2, a sheet shift mechanism (sheet shift unit) 3, an image forming unit (image forming unit) 5, A fixing device (fixing means) 6 and the like are provided.

  The image forming unit 5 is an image forming unit that forms an unfixed toner image on the image carrier 5 a and transfers it to the sheet P. In this example, it is a transfer type electrophotographic image forming mechanism. The image forming unit 5 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a drum) 5a as an image carrier. The drum 5a is rotationally driven at a predetermined speed (process speed) in the clockwise direction indicated by an arrow by a drive unit (not shown). Around the drum 5a, a charger 5b, an image exposure device 5c, a developing device 5d, a transfer device 4, and a cleaning device 5e are disposed as process means acting on the drum 5a along the drum rotation direction. .

  The charger 5a is a charging unit that uniformly charges the surface of the rotating drum 5a to a predetermined polarity and potential. In this example, a contact charging roller (a predetermined charging bias is applied from a power supply unit (not shown)). Conductive roller).

  The exposure device 5c is an image exposure unit that performs image exposure corresponding to image information on the charging surface of the drum 5a. In this example, the laser scanner receives an image signal from the CPU 13. The scanner 5c scans the laser beam modulated and emitted from the laser light source according to the image signal by rotating the polygon mirror, polarizes the light beam of the scanning beam by the reflection mirror, and on the bus of the drum 5a by the fθ lens. The light is condensed and exposed. As a result, an electrostatic latent image having an image pattern corresponding to the image signal is formed on the surface of the drum 5a.

  The developing device 5d is developing means for developing (developing) the electrostatic latent image formed on the surface of the drum 5a as an unfixed toner image with toner (developer). The transfer unit 4 is a toner image transfer unit that transfers the toner image formed on the drum 5 a to the sheet P fed to the transfer position T of the image forming unit 5. In this example, a transfer roller (conductive roller) to which a predetermined transfer bias is applied from a power supply unit (not shown). The transfer roller 4 is pressed against the drum 5a with a predetermined pressing force. The pressure contact portion is a transfer position (toner image transfer portion: hereinafter referred to as a transfer nip portion) T.

  The cleaning device 5e is a drum cleaning unit that cleans the drum surface by removing residual deposits such as transfer residual toner from the surface of the drum 5a after the toner image is transferred to the sheet P. The sheet feeding mechanism 7 is a sheet feeding unit that feeds the sheet P to the transfer nip T of the image forming unit 5. The mechanism 7 of this example has upper and lower two-stage first and second cassettes 7a and 7b. In the cassettes 7a and 7b, a plurality of sheets Pa and Pb having different sizes are regulated and accommodated by size regulation plates (side guide plates) 71a and 71b so as to be stacked in parallel to the sheet conveyance direction. ing.

  When a printer job is input from the operation unit 200 or the apparatus 300 to the CPU 13, the separation roller (feed roller) 8a or 8b of the cassette 7a or 7b that stores a sheet of a specified size is driven. As a result, the sheets P are separated one by one from the cassette 7a or 7b and introduced into the oblique feeding mechanism 2 through the sheet conveying path 10 having the conveying rollers 9a or 9b and 9a. The skew feeding mechanism 2 is a mechanism for correcting (correcting) the skew of the sheet P. The skew feeding mechanism 2 will be described in detail in section (2).

  When the sheet P that has exited the skew feeding mechanism 2 is a small-sized sheet that is smaller than the maximum sheet passing width WPmax, the sheet P is moved in the sheet conveyance direction B within the sheet conveyance path surface by the sheet shift mechanism (sheet shift means) 3. On the other hand, the shift amount described later is moved in the orthogonal direction. The shift mechanism 3 will be described in detail in section (3). Then, the sheet P shifted by the shift mechanism 3 is introduced into the transfer nip T of the image forming unit 5 and sequentially receives the unfixed toner image on the drum 5a side.

  The sheet P exiting the transfer nip T is sequentially separated (separated) from the surface of the drum 5 a and introduced into the fixing device 6. The toner image is fixed on the sheet P as a fixed image by heat and pressure in the fixing device 6. The sheet P on which the image is fixed is discharged out of the apparatus. The fixing device 6 will be described in detail in section (4).

(2) Slope feeding mechanism 2
FIG. 2 is a schematic plan view of portions of the oblique feeding mechanism 2, the shift mechanism 3, and the transfer roller 4. The skew feeding mechanism 2 corrects the skew of the sheet P fed from the sheet feeding mechanism 7 through the conveyance path 10 before the sheet P enters the shift mechanism 3 and also performs the sheet feeding direction B with respect to the sheet conveying direction B. Registration (lateral registration) in the orthogonal sheet width direction is performed.

  WPmax is the maximum sheet passing width of the sheet P that can be passed through the apparatus 1. The skew feeding mechanism 2 has a skew feeding roller 22 including a butting plate 21 and a pair of upper and lower sheet conveying rollers. The plate 21 is disposed on one side of the maximum sheet passing width WPmax of the sheet conveyance path 10, and the inner surface side is a regulation surface 21 a for abutting the sheet side. The regulation surface 21 a is a surface parallel to the sheet conveyance direction B. The plate 21 is disposed (movable in position) in a D direction perpendicular to the sheet conveying direction B by a shift mechanism 21A including a stepping motor (not shown) controlled by the CUP 13.

  The skew feeding roller 22 is disposed upstream of the plate 21 in the sheet conveyance direction B. The skew feeding mechanism 2 is switched to a contact state in which a driving mechanism (not shown) for rotating the skew feeding roller 22 and a pair of upper and lower rollers are brought into contact with each other with a predetermined nip pressure and a separated state in which the pair is separated. It has a mechanism (not shown). The drive mechanism and the switching mechanism are controlled by the CPU 13.

  The skew feeding roller 22 sandwiches and conveys the sheet P fed from the feeding mechanism 7 and tilts the rotation axis direction with respect to the sheet conveying direction B so as to move toward the regulating surface 21 a side of the abutting plate 21. It is arranged. Accordingly, the sheet P is conveyed obliquely in the direction of arrow C toward the abutting plate 21 by the skew feeding roller 22. The nip pressure of the oblique feeding roller 22 is set to be weak to a predetermined level. For this reason, even if the sheet P is fed obliquely from the feeding mechanism 7 side, the sheet P moves while rotating along the regulating surface 21a of the abutting plate 21, thereby correcting the skew. Further, the lateral registration of the sheet P is performed.

  The skew feeding is corrected by the skew feeding mechanism 2 and the laterally registered sheet P reaches the nip portion of the pair of upper and lower shift rollers 31 and 32 of the shift mechanism 3 and is nipped. The CPU 13 separates the pair of the oblique feeding rollers 22 by the operation of the switching mechanism at the timing when the leading end of the sheet P reaches the roller pair 31 and 32 and is nipped. The above timing can be calculated from the conveyance speed and size (size in the conveyance direction) of the sheet P.

  Alternatively, a sensor that detects that the leading end of the sheet P has reached and pinched the roller pair 31 and 32 is disposed, and the switching mechanism is operated based on the sheet detection signal input from the sensor. It is also possible to adopt a configuration in which the pair of feed rollers 22 is separated.

  When the pair of the skew feeding rollers 22 is separated, the nipping of the sheet P by the skew feeding rollers 22 is released. As a result, a predetermined amount of movement of the sheet P in the direction orthogonal to the sheet conveyance direction B by the shift mechanism 3 to be described below is made without being obstructed by the skew feeding roller 22.

(3) Shift mechanism 3
The shift mechanism 3 is disposed upstream of the transfer nip portion T of the image forming unit 5 in the sheet conveyance direction, and receives the sheet P that has been subjected to skew correction and lateral registration by the skew feeding mechanism 2. When the sheet P is a small-sized sheet smaller than the maximum sheet passing width WPmax, in order to align the sheet P with the main scanning position of the image on the drum P and the drum 5a (in the generatrix direction of the drum 5a), The sheet P is conveyed toward the transfer nip T while moving in the scanning direction. That is, the sheet fed to the transfer nip T is moved by a shift amount described later in a direction orthogonal to the sheet conveyance direction B.

  FIG. 3 is an explanatory diagram of the shift mechanism 3. The shift mechanism 3 includes a pair of upper and lower shift rollers 31 and 32 disposed with the rotation axis direction orthogonal to the sheet conveyance direction B. The left and right ends of the shaft 32a of the lower roller 31 are supported so as to be rotatable with respect to the fixed device frame plates 11L and 11R on the respective sides via a bearing member 41 and slidable in the thrust direction. . The left and right end portions of the shaft 31a of the upper roller 31 are inserted into the vertical slot 42 provided in the apparatus frame plates 11L and 11R on the respective sides and can be rotated, and vertically along the slot 42. It is slidably supported.

  The rollers 31 and 32 are connected by a connecting frame 43 between the apparatus frame plates 11L and 11R. The frame body 43 includes an upper plate portion 43A that is long in the left-right direction, and left and right leg plate portions 43L and 43R that are formed by bending the left and right sides of the upper plate portion 43A downward by 90 °. The left shaft 32a of the lower roller 32 is rotatably inserted into a round hole 44 provided in the left leg plate portion 43L, and the retaining ring 45 prevents movement in the thrust direction with respect to the leg plate portion 43L. Yes. The right shaft 32a is rotatably inserted in a round hole 44 provided in the right leg plate portion 43R, and the retaining ring 45 prevents movement in the thrust direction with respect to the leg plate portion 43R.

  The left shaft 31a of the upper roller 31 is inserted into a vertically elongated hole 46 provided in the left leg plate portion 43L so as to be rotatable and slidable in the vertically direction along the elongated hole 46. 45 prevents the leg plate portion 43L from moving in the thrust direction. The right shaft 31a is inserted in a vertically elongated slot 46 provided in the right leg plate portion 43R so as to be rotatable and slidable vertically along the elongated hole 46. Movement in the thrust direction with respect to the portion 43R is prevented.

  Roller contacting / separating mechanisms 47L and 47R for bringing the upper roller 32 into and out of contact with the lower roller 32 are disposed on the left and right portions of the frame body 43, respectively. In this embodiment, the contact / separation mechanisms 47L and 47R are electromagnetic solenoid plungers. That is, solenoids 47a are fixedly disposed on the left and right portions of the frame body 43, respectively. Plungers 47b of the left and right solenoids 47a are respectively disposed downward, and a bearing portion 47c is provided at the lower end.

  The left shaft portion 31a of the upper roller 31 is rotatably inserted in the left bearing portion 47c, and the left shaft portion 31a is rotatably inserted in the left bearing portion 47c. Further, coil springs 47d as urging members are fitted on the left and right plungers 47b, respectively, and are contracted between the solenoid 47a and the bearing portion 47c. The left and right solenoids 47a are on / off controlled by the CPU 13.

  When the energization to the left and right solenoids 47a is off, the left and right plungers 47b are pushed down by the tension force of the spring 47d until the rollers 31 are received by the rollers 32. Thus, the upper roller 31 is held in contact with the lower roller 32 with a predetermined pressing force by the tension force of the spring 47d, and the sheet P is sandwiched between the rollers 31 and 32 and conveyed. A nip portion N3 is formed.

  On the other hand, when energization to the left and right solenoids 47a is on, the left and right plungers 47b are pulled up against the tension of the springs 47d by the magnetic force of the solenoids 47a. As a result, the upper roller 31 is lifted and moved by a predetermined amount from the lower roller 32, and is held in the separated state separated by α as shown in FIG. That is, the nip portion N3 between the rollers 31 and 32 is held in a released state.

  On one end side of the lower roller 32, a drive unit 33 having a function of rotating the roller 32 and a shift function of moving the rollers 31 and 32 in the sheet width direction perpendicular to the sheet conveying direction B. Is arranged.

  In the present embodiment, the drive unit 33 is disposed on the device frame plate 11L side on the left side. That is, the left end portion of the shaft 32a of the roller 32 protrudes from the bearing member 41 to the outside of the apparatus frame plate 11L. A wide gear G2 is fixedly disposed on the protruding shaft portion. The gear G1 on the first motor (shift roller motor: stepping motor) M1 side meshes with the gear G2. The motor M1 is fixedly disposed on an apparatus frame (not shown).

  The drive of the motor M1 is on / off controlled by the CPU 13. When the motor M1 is driven in a predetermined rotation direction, the rotational force is transmitted to the shaft 32a by the gears G1 and G2. As a result, the lower roller 32 is rotationally driven in the sheet conveying direction. If the upper roller 31 is in contact with the lower roller 32, the upper roller 31 is rotated by the rotation of the roller 32. That is, when the motor M1 is driven, the rollers 31 and 32 perform a rotation operation of conveying the sheet P in the conveyance direction B. The upper roller 31 does not rotate when it is separated from the lower roller 32 (FIG. 5).

  Further, a bearing member 34 is disposed at the left end portion of the shaft 32a outside the gear G2 so as to be thrust-moved with respect to the shaft 32a by a retaining ring 45. Further, a second motor (shift motor: stepping motor) M2 and a belt pulley 35b are disposed on an apparatus frame (not shown). A belt (timing belt) 35c is stretched between a pulley 35b and a drive pulley 35a disposed on the shaft of the motor M2. And the bearing member 34 is couple | bonded via the connection part 34a with respect to the descending belt part of the belt 35c.

  The motor M2 is controlled to be driven forward by a predetermined number of control pulses by the CPU 13, and conversely, is controlled to be driven reversely by the same number of pulses. At the time when the forward rotation driving of the motor M2 is started, the connecting portion 34a is located at the home position SL in FIG. As a result, the frame body 43 including the rollers 31 and 32 is located at the left-justified position E that moves toward the left device frame plate 11L as shown in FIG. 3 between the left and right device frame plates 11L and 11R.

  In this state, when the motor M2 is driven to rotate forward by a predetermined number of control pulses, the belt 35c rotates counterclockwise, and the connecting portion 34a moves to the right from the home position SL in FIG. 3 by a predetermined control amount. Move to the right end point SR and stop. As a result, the shaft 32a is slid in the left direction, and the frame 43 including the rollers 31 and 32 moves from the left justified position E in FIG. 3 to the right justified position F as shown in FIG. 4 between the left and right device frame plates 11L and 11R. Move a predetermined control amount in the right direction R.

  Then, when the frame body 43 including the rollers 31 and 32 is moved R toward the right apparatus frame plate 11R side by a predetermined control amount as shown in FIG. 4, the motor M2 is reversely driven by the same predetermined number of pulses as in the normal rotation driving. Is done. Accordingly, the connecting portion 34a is moved back from the predetermined right end point SR to the predetermined left home position SL. Accordingly, the frame body 43 including the rollers 31 and 32 is moved back to the first left-justified position E in FIG.

  As described above, the motor M2 is driven forward by a predetermined number of control pulses and conversely by reverse rotation by the same number of pulses, so that the rollers 31 and 32 are orthogonal to the conveyance direction B of the sheet P in the sheet conveyance path surface. It is possible to reciprocate (shift) in the sheet width direction R · L.

  The CPU 13 controls the shift mechanism 3 as follows. Normally, the connecting portion 34a is located at the home position SL. Thereby, the frame 43 including the rollers 31 and 32 is located at the left-justified position E in FIG. In this state, the power supply to the solenoid 37a is controlled to be off. Thereby, the upper roller 31 is in contact with the lower roller 32.

  The CPU 13 (sheet shift control unit) turns on the motor M1 based on the paper feed start signal. Thereby, the rollers 31 and 32 are rotationally driven in the sheet conveying direction. In this state, the leading end portion of the sheet P conveyed along the regulating surface 21a of the plate 21 from the skew feeding mechanism 2 side reaches the nip portion N3 of the rollers 31 and 32 and is nipped. The CPU 13 detects that the leading end portion of the sheet P has reached the nip portion N3 of the rollers 31 and 32 and is nipped as follows, for example.

  That is, the detection is performed by calculation based on the sheet feeding start time from the sheet feeding mechanism 7, the conveyance speed of the sheet P, and the conveyance path length of the sheet P from the sheet feeding mechanism 7 to the nip portion N3. Alternatively, it is detected by a sheet sensor (not shown) disposed on the sheet exit side of the nip portion N3 of the rollers 31 and 32. Based on the detection signal, the CPU 13 separates the pair of skew feeding rollers 22 on the skew feeding mechanism 2 side. Thereby, the holding of the sheet P by the skew feeding roller 22 is released.

  In addition, when the sheet P is a small-sized sheet smaller than the maximum sheet passing width WPmax, the CPU 13 drives the second motor M2 of the shift mechanism 3 to rotate forward by a predetermined number of control pulses based on the detection signal. . Then, the frame 43 including the rollers 31 and 32 moves in the right direction R from the left justified position E (FIG. 3) to the right justified position F (FIG. 4). That is, the sheet P sandwiched between the rollers 31 and 32 is moved (shifted) in the right direction R in the sheet width direction orthogonal to the sheet conveyance direction B while being conveyed in the B direction.

  Then, the CPU 13 turns on the energization of the left and right solenoids 47a at the timing when the leading end of the sheet P that is nipped by the rollers 31 and 32 and conveyed in the B direction reaches the transfer nip T and is nipped. As a result, the roller 31 is pulled up from the roller 32 and separated (FIG. 5). That is, the holding of the sheet P by the rollers 31 and 32 is released. The sheet P is nipped by the transfer nip portion T and continuously conveyed.

  The CPU 13 detects that the leading end portion of the sheet P reaches the transfer nip portion T and is nipped, for example, as follows. That is, when it is detected that the leading edge of the sheet P has reached the nip portion N3 and is nipped, the sheet conveyance speed by the rollers 31 and 32, and the sheet conveyance path between the nip portion N3 and the transfer nip portion T. Detected by calculating from the length. Alternatively, it is detected by a sheet sensor (not shown) disposed on the sheet exit side of the transfer nip T.

  Based on the detection signal, the CPU 13 drives the second motor M2 of the shift mechanism 3 in reverse by the same predetermined number of pulses as in normal rotation. Then, the frame body 43 including the rollers 31 and 32 held in the separated state is moved in the left direction F from the right alignment position E (FIG. 3) side and returned to the initial left alignment position F (FIG. 4).

  When the CPU 13 detects by a calculation or a sheet sensor (not shown) that the trailing edge of the sheet P conveyed by the transfer nip T has passed the position of the roller pair in the state of separation of the roller 22 of the skew feeding mechanism 2. The roller pair is returned from the separated state to the contact state. Further, when it is detected by calculation or a sheet sensor (not shown) that the rear end portion of the sheet P has passed between the rollers 31 and 32 in a separated state, the energization to the left and right solenoids 47a is turned off. Thereby, the rollers 31 and 32 are returned from the separated state to the contact state. In this state, the sheet shift mechanism 3 waits for the next sheet P to arrive from the skew feeding mechanism 2 side.

(4) Fixing device 6
FIG. 6 is an explanatory diagram of the configuration of the fixing device 6 in this embodiment. In this embodiment, the fixing device 6 is an induction heating belt type fixing device. The sheet P carrying the unfixed toner image is transferred to a fixing nip portion N6 which is a pressure contact portion between the heating belt 130 (fixing member) heated to a temperature of about 200 ° C. in the fixing device 6 and the pressure belt 120. It is introduced and nipped and conveyed. The unfixed toner image is fixed as a fixed image on the sheet P by heat and nip pressure at the fixing nip portion N6. The sheet P on which the image is fixed is discharged out of the apparatus.

  6A is a transverse sectional view of the fixing device 6, FIG. 6B is a left side view, and FIG. 6C is a right side view. The pressure belt 120 is looped around two support rolls, that is, a pressure roll 121 and a tension roll 122 having a function of applying belt tension, and is circulated and rotated with a predetermined tension (for example, 200 N). In this embodiment, the pressure belt 120 may be appropriately selected as long as it has heat resistance. For example, a belt is used in which 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 covered with a PFA tube.

  The heating belt 130 is looped around two support rolls, that is, a driving roll 131 and a steering roll 132 having a function of applying belt tension, and is circulated and rotated with a predetermined tension (for example, 200 N). The heating belt 130 may be appropriately selected as long as it generates heat by the induction heating coil 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 circumference of 200 mm is coated with, for example, a 300 μm-thick silicon rubber, and a surface layer is coated with a PFA tube.

  A pad 125 is disposed on the inner side of the pressure belt 120 corresponding to the inlet side (upstream side of the pressure roll 121) of the nip region, which is a pressure contact portion between the pressure belt 120 and the heating belt 130. The pad 125 is made of, for example, silicon rubber. The pad 125 is pressed against the pressure belt 120 with a predetermined pressure (for example, 400 N), and forms a nip portion N6 together with the pressure roll 121.

  The pressure roll 121 is a roll for suspending a pressure belt 120 having an outer diameter of φ20 made of, for example, solid stainless steel, and is disposed on the outlet side of the nip region between the pressure belt 120 and the heating belt 130. Further, 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 and functions as a belt tension roll. Both ends of the tension roll 122 are supported by bearings 126 as shown in FIGS. 6B and 6C, and a tension of 20 kgf is applied to the belt 120 by a tension spring 127.

  A pad stay 137 is disposed inside the heating belt 130 corresponding to the inlet side (upstream side of the drive roll 31) of the nip region between the heating belt 130 and the pressure belt 120. The stay 137 is made of, for example, stainless steel (SUS material). The stay 137 is pressed against the pressure pad 125 with a predetermined pressure (for example, 400 N), and forms a nip together with the drive roll 131.

  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 roll 131 is disposed on the exit side of the nip region between the heating belt 130 and the pressure belt 120, and the elastic layer is elastically distorted by a predetermined amount by the pressure contact of the pressure roll 121. Further, the steering roll 132 is a hollow roll made of stainless steel, for example, having an outer diameter of about φ20 and an inner diameter of φ18. The steering roll 132 functions as a steering roll that adjusts the meandering in the width direction perpendicular to the moving direction of the heating belt 130 and Also works as a rack roll.

  Drive is input from the outside by a motor (not shown) as a drive source to the drive roll 131, and the heating belt 130 is conveyed by the rotation of the drive roll 131. In order to stably convey the sheet P, driving is reliably transmitted between the heating belt 130 and the driving roll 131. Near the end of the heating belt 130 on the front side of the fixing device (on the left side of the device), a sensor unit 150 for detecting the position of the belt end is provided. By detecting the position of the end of the heating belt 130 by the sensor unit 150 and changing the inclination of the steering roll 132 accordingly, the deviation control of the belt is performed.

  A steering roll support arm 154 is supported on a shaft 151 fixed to the outside of the side plate 140 so as to be rotatable about the shaft 151. The arm 154 is provided with a steering roll bearing 153 that supports the steering roll 132 so as to be rotatable and slidable in the belt tension direction. The arm 154 is provided with a tension spring 156 for urging and applying tension to the bearing 153 in the belt tension direction, and a tension of 20 kgf is applied to the heating belt 130.

  A sector gear 152 is fixed to the outer periphery of the arm 154 and meshes with a worm 157 that can be driven to rotate by driving a stepping motor 159. By detecting the end position of the heating belt 130 by the sensor unit 150 and rotating the stepping motor 159 at a predetermined number of rotations in accordance therewith to change the inclination of the steering roll 132, the deviation control of the belt is performed. .

  The sensor unit 150 includes two sensors 150a and 150b, a sensor flag 150c, and a sensor arm 150d. Further, the sensor arm 150d has a sensor spring 150e for operating the sensor arm 150d following the movement of the heating belt 130, and the sensor arm 150d is pressed against the end surface of the heating belt 130 with a force of 3 gf. Then, position detection (belt deviation detection) in the belt width direction along the axial direction of the rollers 131 and 132 of the belt 130 is performed based on a combination of ON / OFF signals of the sensors 150a and 150b.

  In the above, the steering roll 132, the arm 154, the sector gear 152, the worm 157, the stepping motor 159, and the like are fixing member shift means for moving the belt 130 (fixing member) in a direction orthogonal to the sheet conveying direction B. The CPU (sheet shift control unit) 13 controls the shift mechanism (sheet shift means) 3 based on the fixing member position information of the belt 130 moved by the fixing member shift means. The sensor unit 150 is a fixing member position detecting unit that detects a moving position of the belt 130 (fixing member) in a direction orthogonal to the sheet conveying direction B as fixing member position information.

  FIG. 7A shows the relationship between the ON / OFF signal combinations of the sensors 150a and 150b and the end face position of the heating belt 130 at that time, FIG. 6E shows the position at that time, and FIG. As shown in (b) of FIG. It should be noted that the signal is turned off when the flag of each sensor 150a, 150b is shielded, and turned on when the light is projected.

  As shown in FIGS. 7A and 7B, the heating belt 130 is in a position where the sensor 150a is ON and the sensor 150b is OFF (step S106) and a position where the sensor 150a is OFF and the sensor 150b is ON (step S109). Go back and forth between them. Then, the deviation control is performed so that the heating belt 130 exists in the section. The distance of the section is set to ± 1.5 mm from the center position of the heating belt 130 in the rotation axis direction.

  FIG. 8A is a block diagram of a control system of the apparatus 1. A predetermined drive pulse is output to the stepping motor 159 via the motor driver 160 from the position of the heating belt 130 detected by the sensor unit 150 via the belt offset control (steps S107 and S110). The steering roll 132 is driven by the motor 159 and controlled by tilting ± 2 ° with respect to the drive roll 131 (steps S108 and S111).

  In a state in which the deviation control is disabled, when the end face of the heating belt 130 comes to a position ± 3 mm from the center position, both the sensors 150a and 150b are turned off (step S03). At this time, the CPU 13 determines that an abnormality has occurred (step S104), and stops the heating of the fixing device 6 and the rotation operation of the heating belt 130 (step S105).

(5) Cooperating operation of fixing member shifting means and sheet shifting means A fixing member shift control unit (CPU) 13 for controlling the fixing member shifting means based on the recorded fixing member shift amount is provided, and fixing member position information is fixed. This is the fixing member shift amount recorded in the member shift control unit 13.

  As shown in FIG. 8A, the CPU 13 interprets a program stored in the ROM and reads / writes data to / from the RAM, SRAM (storage means) 15 and other peripheral circuits. Take control. When the CPU 13 receives a job from the operation unit 200 or a host device 300 such as a network-connected host computer, the CPU 13 accumulates job data in the job management unit 14 and performs an image forming operation for each page.

  Further, the CPU 13 performs the following control based on the position of the heating belt 130 detected by the sensor unit 150 and the size of the sheet P in the sheet width direction via the belt deviation control unit 161. That is, the shift positions of the shift rollers 31 and 32 (hereinafter referred to as roller shift amounts) are set in the shift amount control unit (shift control unit) 12 based on the table shown in FIG.

  The shift amount control unit 12 drives the stepping motor M2 that shifts the shift rollers 31 and 32 according to the set roller shift amount. Further, the CPU 13 changes the setting of the image writing position with respect to the drum 5a in the image position control unit 41 based on the table shown in FIG. 8C, and the laser scanner so that an image is formed at the set image writing position. The laser driver 42 of 5c is operated.

  FIGS. 9A to 9C are diagrams for explaining the image position writing position changed by the image position control unit 41 and the laser driver 42 in FIG. Normally, as shown in (A), the CPU 13 controls the image position control unit 41 and the laser driver 42 so that the center of the image in the sheet width direction comes to the drum surface center line (the center part in the drum axis direction) of the drum 5a. To do. The reference position of the laser scanning is detected by a BD (Beam Detector), and the section mask is canceled when the image clock is counted for the distance L1.

  This release position is a position obtained by subtracting half of the image length in the sheet width direction from the drum surface center line. The position obtained by adding half of the image length in the sheet width direction from the center line of the drum surface is the position at which the release of the section mask ends. Image data is formed into a latent image on the drum 5a by a laser in synchronization with the image clock within the area where the section mask is released.

  When the image is shifted in the R direction in FIG. 2, as shown in FIG. 9B, the image writing position is changed to a position obtained by counting the image clock by the distance L2. When the image is shifted in the F direction in FIG. 2 (the direction opposite to the R direction), as shown in FIG. 9C, the image writing position is changed to a position obtained by counting the image clock by the distance L3.

  FIG. 10 is a diagram for explaining the shift operation of the sheet P in the sheet width direction by the shift mechanism 3. As described above, the sheet P is abutted against the regulation surface 21a of the abutting plate 21 of the skew feeding mechanism 2, and the skew is corrected. After the correction, the sheet is conveyed while being moved in the sheet width direction by the shift rollers 31 and 32 until reaching the transfer nip T. The shift positions of the shift rollers 31 and 32 are set in three stages (a plurality of set values) R1 to R3. The shift rollers 31 and 32 move the distance from the shift positions R1 to R3 to the origin position (HP) of the butting plate 21 according to the roller shift amount set in the shift amount control unit 12 by the CPU 13.

  Next, an example of an image forming operation on the drum 5a of the apparatus 1 will be described with reference to FIG. 11 is executed by the CPU 13 via the image position control unit 41 and the laser driver 42 after the program stored in the ROM or the like in FIG.

  First, the CPU 13 charges the drum 5a with the charger 5b (step S100). Then, the size of the image formed on the drum 5a in the sheet width direction is determined (step S101). Note that the size may be determined from parameters associated with the image data. Then, the CPU 13 determines the shift amount of the image formation position with reference to the table shown in FIG. 8B (step S102).

  Next, the CPU 13 determines the image writing position in the sheet width direction by (drum center position−image width / 2 + shift amount), and sets it in the image position control unit 41 (step S103). Further, the image writing end position is determined by (drum center position + image width / 2 + shift amount) and set in the image position control unit 41 (step S104).

  Next, the CPU 13 determines the size of the image formed on the drum 5a in the sheet conveyance direction (step S105). Then, the CPU 13 sets the image length section in the sheet conveyance direction in the image position control unit 41 (step S106). The CPU 13 controls the image position control unit 41 and the laser driver 42 to form a latent image on the drum 5a so that image formation is performed according to the set image writing position, image writing end position, and image length section. (Step S107). Then, the CPU 13 develops the latent image formed on the drum 5a with a developer such as toner (step S108) and transfers it to the sheet P (step S109).

  Next, an operation example of the shift mechanism 3 will be described with reference to FIG. 12 is executed by the CPU 13 via the shift amount control unit 12 and the stepping motor M2 after the program stored in the ROM or the like in FIG. 8A is loaded into the RAM.

  First, the CPU 13 sets a roller shift amount (step S200). Next, the CPU 13 reads the data of the shift positions R1 to R3 from the SRAM 15 (step S201) and converts it into the number of drive pulses of the stepping motor 31 (step S202). Then, the CPU 13 sets the converted drive pulse number in the shift amount control unit 12, and drives the stepping motor 31 according to the drive pulse number set in the shift amount control unit 12 (step S203).

  The above processing is performed by selecting any one of the shift positions R1 to R3 for each conveyed sheet. If the CPU 13 sets the roller shift amount in the shift amount control unit 12, the shift amount control unit 12 may determine the number of drive pulses.

  Next, an outline of the relationship between the position of the heating belt 130 of the fixing device 6 and the sheet passing position of the sheet P and the shift amount of the sheet passing position on the heating belt 130 from the center of the heating belt will be described with reference to FIG.

  Based on the detection position of the heating belt 130 by the detection unit 150, the movement amount 170 from the center in the shift movement region of the heating belt 130 moves from the center in the shift movement region of the sheet P based on the table in FIG. The quantity 171 is controlled as shown in FIG.

  That is, the CPU (sheet shift control unit) 13 controls the shift mechanism (sheet shift means) 3 as follows. The CPU 13 shifts the movement position of the sheet P so that the movement position of the sheet P becomes the front side (one side) from the center in the sheet movement area when the heating belt 130 moves from the center in the movement area to the back side (the other side). The mechanism 3 is controlled. Further, the CPU 13 shifts the movement position of the sheet P from the center in the sheet movement area to the back side (the other side) when the heating belt 130 moves from the center in the movement area to the front side (one side). The mechanism 3 is controlled.

  Accordingly, since the heating belt 130 and the sheet P do not move in the same direction, the amount of movement 172 from the center in the passing region of the edge portion of the sheet P on the heating belt 130 is obtained. A wide shift range of the sheet P of the heating belt 130 can be taken.

  Further, when the paper size (sheet size) is large with respect to the paper path width (sheet conveyance path width) and the shift amount cannot be secured, the shift position is set so that the sheet P is passed to the position R2 depending on the size in the width direction of the sheet P. Select. In this embodiment, the CPU 13 selects the position of R2 when the sheet width direction is 330 mm or more.

  In the above description, the movement of the belt 130 by the belt shift control is expressed by a sine wave. However, the fixing member moves in the sheet width direction, and the sheet shift is performed based on the detection information. The present invention is not limited to this embodiment as long as the position is controlled.

  In the above description, there is a time lag between the time when the sheet shift is performed and the time when the sheet P reaches the fixing member. However, since the arrival time of the fixing member from the execution of the sheet shift of the normal sheet P is sufficiently short relative to the reciprocation time in the deviation control of the fixing member, the influence on the effect on the shift of the heating belt 130 and the sheet P is small.

  Further, the sheet shift amount is determined by the position of the heating belt 130 during the sheet shift control. However, a table for predicting the relationship between the sheet shift amount at the time of sheet shift control and the position of the fixing belt when the shifted sheet P reaches the fixing device 6 is stored in advance, and the sheet shift amount is referenced from the table. It is good also as a structure. In that case, it becomes possible to suppress the influence of the above-mentioned time lag.

  In the above description, the shift position of the sheet passing position with respect to the position of the heating belt 130 is set in three stages from R1 to R3, but the shift position may be increased. In this case, by finely detecting the position of the heating belt 130, it is possible to control the sheet passing area on the heating belt 130 more efficiently.

  In the above description, the shift position is changed to one of R1, R2, and R3 each time one sheet P is conveyed according to the size of the sheet P in the sheet conveying direction and the position of the heating belt 130. It is supposed to be. However, the shift position may be changed every time a predetermined number of sheets, for example, two sheets are conveyed, or every print job.

  In the above description, the image writing position and the image writing end position are obtained by calculation. However, a table indicating the relationship between the image size, the shift positions of the shift rollers 31 and 32, the image writing position, and the image writing end position is stored in advance, and the image writing position and the image writing end position are referred to from the table. It is also good.

  The sheet width direction described above corresponds to a main scanning direction generally used in the description of an electrophotographic image forming apparatus, and the sheet conveyance direction corresponds to a sub-scanning direction.

  Note that the embodiment is not limited to the structure described in this embodiment. Control for suitably widening the sheet passing area on the fixing member by determining the movement of the fixing member in the direction orthogonal to the sheet passing position from the movement amount of the fixing member moved in the direction orthogonal to the sheet passing position. This is applied to the configuration in which

[Example 2]
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 14 is a schematic diagram for explaining a fixing member shift mechanism (fixing member shift means) of the fixing device 6 in this embodiment, and FIG. 15 is a block diagram showing a control system in the image forming apparatus 1 (FIG. 1). . The image formation and sheet shift processes are the same as those in the first embodiment.

  In FIG. 14, the end of a heating belt 130 as a fixing member is supported by a belt shift flange 170. A belt shift arm 171 is attached to the flange 170 so that the heating belt 130 can be moved by operating the flange 170. The arm 171 is pressed against the reciprocating cam 174 attached to the stepping motor 173 by the biasing spring 172.

  The stepping motor 173 inputs a predetermined drive pulse to the motor driver 150 according to the belt shift amount recorded in the CPU 13, whereby the stepping motor 173 rotates and the reciprocating cam 174 presses the belt shift arm 171. Accordingly, the heating belt 130 is moved in a direction orthogonal to the sheet passing direction of the heating belt 130.

  In this embodiment, the flange 170, the arm 171, the cam 174, the spring 172, and the motor 173 are fixing member shift means for moving the heating belt 130 as a fixing member in a substantially horizontal direction perpendicular to the sheet conveying direction B. is there.

  FIG. 16A is a table diagram for determining the sheet shift amount and the image shift amount. FIG. 6B is a graph illustrating an outline of the relationship between the position of the heating belt 130, the sheet passing position of the sheet P, and the shift amount of the sheet passing position on the heating belt 130 from the center of the heating belt 130;

  The CPU 13 inputs a predetermined driving pulse to the motor driver 150 based on the number of sheets that have been detected by the sheet passing number counting means (counter) 13 a and information recorded in the SRAM 15. Accordingly, the reciprocating cam 174 is rotated and moved so that the positions of U1, U2, and U3 are in contact with the belt shift arm 171.

  The sheet shift control unit 12 and the image position control unit 41 move the sheet passing position and the image forming position of the sheet P by controlling the stepping motor M2 and the laser driver 42 according to the table of FIG. The movement amount 176 from the center in the shift movement region of the sheet P is controlled as shown in FIG. 16B, with respect to the movement amount 175 from the center in the shift movement region of the heating belt 130. Thereby, the movement amount 177 from the center in the passing region of the edge portion of the sheet P on the heating belt 130 can widen the shift movement range of the sheet P of the heating belt 130.

  In this embodiment, the shift amount of the sheet passing position is determined on a one-to-one basis with the shift amount of the fixing member by using a table recorded in the CPU 13. It is good also as a table which matches a position.

  In the above description, the position of the heating belt 130 is moved one by one. However, the shift position may be changed every time a predetermined number of sheets, for example, two sheets are conveyed, or for each print job.

  In the above description, the shift position is changed to one of R1, R2, and R3 each time one sheet P is conveyed according to the size of the sheet in the sheet conveyance direction and the position of the heating belt 130. It is said. However, the shift position may be changed every time a predetermined number of sheets, for example, two sheets are conveyed, or every print job.

[Example 3]
Hereinafter, Embodiment 3 of the present invention will be described in detail with reference to the drawings.

  FIG. 17 is a schematic diagram for explaining the shift positions of the sheet shift mechanism 3 and the fixing member 130 in this embodiment. FIG. 18 is a block diagram showing a control system in the image forming apparatus 1 (FIG. 1). FIG. 19A is a table for determining the fixing member shift amount from the signal detected by the sheet end position detection sensor 180. FIG. 19B is a graph illustrating an outline of the relationship between the position of the heating belt 130, the sheet passing position of the sheet P, and the shift amount from the center of the heating belt 130 at the sheet passing position on the heating belt 130. . In this embodiment, the image forming and sheet P transfer process is the same as that of the first embodiment, and the fixing device configuration is the same as that of the second embodiment.

  An ON / OFF detection signal detected by the sheet passing position sensor 180 that detects the sheet passing position of the sheet P is transmitted to the CPU 13 via the sheet position detection control unit 181. Here, the detection signal of the sheet passing position sensor 180 indicates that when the sheet P is on the front side (one side) from the center at the sheet passing position, the sheet passing position sensor 180 is shielded from light and off, and on the far side (the other side). In some cases, the light is transmitted and turned ON.

  The sheet passing position sensor 180 is a sheet position detecting unit that detects the moving position of the sheet P in the direction R orthogonal to the sheet conveying direction B as sheet position information. Then, based on the sheet position information of the sheet P moved by the shift mechanism 3, the fixing member shift means 170, 171, 174, 172, and 173 (FIG. 14) is controlled by the CPU (fixing member shift control unit) 13.

  The CPU 13 inputs a predetermined drive pulse to the motor driver 150 from the information stored in the SRAM 15 according to the table in FIG. 19A, whereby the stepping motor 173 rotates and the reciprocating cam 174 presses the belt shift arm. Accordingly, the heating belt 130 is moved in a direction orthogonal to the sheet passing direction of the heating belt 130.

  In FIG. 19B, the movement amount 183 from the center in the shift movement region of the heating belt 130 is controlled as shown in FIG. 16B, with respect to the movement amount 182 from the center in the shift movement region of the sheet P. Is done. In other words, the amount of movement 184 from the center in the passing region of the edge portion of the sheet P on the heating belt 130 can widen the shift movement range of the sheet P of the heating belt 130.

  In the above-described embodiment, the shift amount of the fixing member is controlled based on the detection information of the sheet passing position sensor. However, the fixing shift amount may be controlled from the sheet shift amount stored in the SRAM 15. That is, the sheet shift control unit (CPU) 13 that controls the shift mechanism 3 based on the recorded sheet shift amount has a sheet shift amount recorded in the sheet shift control unit 13.

  In the above description, the shift position of the fixing member 130 is changed to either the position V1 or the position V3 each time one sheet P is transported according to the size and position of the sheet in the sheet transport direction. . However, the shift position of the fixing member may be changed every time a predetermined number of sheets, for example, two sheets are conveyed, or for each print job.

  In the above-described embodiment, only the fixing member is shifted. However, a structure that shifts the fixing member for each configuration, for example, a frame that supports the fixing member, or a structure that shifts the fixing device also obtains the same effect. be able to.

  The embodiment is not limited to the configuration described in this embodiment, and the movement of the fixing member in the direction orthogonal to the sheet passing is determined from the amount of movement of the fixing member moved in the direction orthogonal to the sheet passing position. Thus, the present invention is applied to a configuration that performs control to suitably widen the sheet passing area on the fixing member.

  That is, the CPU (fixing member shift control unit) 13 controls the fixing member shift means as follows. The CPU 13 fixes the heating belt 130 so that the heating belt 130 is positioned on the front side (one side) from the center in the movement region when the movement position of the sheet P moves from the center in the sheet movement region to the back side (the other side). Control the member shifting means. Further, the CPU 13 shifts the fixing member so that the heating belt 130 is located at the back side from the center in the movement region when the movement position of the sheet P is moved from the center in the sheet movement region to the front side (one side). Control means.

  According to the present invention, in the image forming layer and the fixing device, by controlling the traveling position of the fixing member and the sheet so as to be optimally moved with respect to the respective moving positions, the wear due to the edge of the sheet on the surface of the fixing member. And uneven gloss due to the difference in surface roughness can be reduced. In addition, it is possible to provide an image forming apparatus capable of printing a high-quality image on a sheet and to extend the life of the fixing member.

  5 .. Image forming means, 5 a ..Image carrier, 6 ..Fixing means, 130 ..Fixing member, 132 .154 .152 .157 .159 ..Fixing member shifting means, 132. .. arm, 152 .. fan gear, 157 .. worm, 159 .. stepping motor, T .. toner image transfer portion, B... Sheet conveying direction, R. ..Sheet shift means, 13 ..CPU (sheet shift controller, fixing member shift controller)

Claims (8)

Image forming means for forming a toner image on an image carrier and transferring it to a sheet;
A fixing unit having a fixing member for heating and pressurizing the toner and fixing the toner image transferred to the sheet;
Fixing member shift means for moving the fixing member in a direction perpendicular to the sheet conveying direction;
A sheet shift unit disposed upstream of the toner image transfer unit of the image forming unit and moving the sheet fed to the toner image transfer unit in a direction perpendicular to the sheet conveyance direction;
A sheet shift control unit for controlling the sheet shift means;
In an image forming apparatus comprising:
An image forming apparatus, wherein the sheet shift control unit controls the sheet shift unit based on fixing member position information of a fixing member moved by the fixing member shift unit.   The image forming apparatus according to claim 1, further comprising a fixing member position detecting unit configured to detect a moving position of the fixing member in a direction orthogonal to the sheet conveying direction as the fixing member position information.   A fixing member shift control unit that controls the fixing member shift unit based on the recorded fixing member shift amount, and the fixing member position information is the fixing member shift amount recorded in the fixing member shift control unit; The image forming apparatus according to claim 1.   When the fixing member moves from the center in the moving region to the position on the back side, the moving position of the sheet is set to the front side position from the center in the sheet moving region, and the fixing member is moved to the center in the moving region. 2. The sheet shift control unit controls the sheet shift means so that the position of the sheet moves from the center to the back side in the sheet movement area when the sheet is moved from the front side to the near side position. The image forming apparatus according to claim 3. Image forming means for forming a toner image on an image carrier and transferring it to a sheet;
A fixing unit having a fixing member for heating and pressurizing the toner and fixing the toner image transferred to the sheet;
Fixing member shift means for moving the fixing member in a direction orthogonal to the sheet conveying direction;
A fixing member shift control unit for controlling movement of the fixing member by controlling the fixing member shift means;
A sheet shift unit disposed upstream of the toner image transfer unit of the image forming unit and moving the sheet fed to the toner image transfer unit in a direction perpendicular to the sheet conveyance direction;
In an image forming apparatus comprising:
An image forming apparatus, wherein the fixing member shift control unit controls the fixing member shift unit based on sheet position information moved by the sheet shift unit.   The image forming apparatus according to claim 5, further comprising a sheet position detecting unit configured to detect a moving position of the sheet in a direction orthogonal to the sheet conveying direction as the sheet position information.   The sheet shift control unit that controls the sheet shift unit based on the recorded sheet shift amount, wherein the sheet position information is the sheet shift amount recorded in the sheet shift control unit. The image forming apparatus according to 5.   When the sheet movement position moves from the center in the sheet movement area to the position on the back side, the fixing member is positioned on the near side from the center in the movement area, and the sheet movement position is the center in the sheet movement area. 6. The fixing member shift unit is controlled by the fixing member shift control unit so that the fixing member is positioned at the back side from the center in the moving region when the fixing member moves from the front side to the front side. The image forming apparatus according to claim 7.