JP2018169524A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that sufficiently corrects a curl in a sheet generated during a fixing process.SOLUTION: An auxiliary roller pair 53 is installed at a downstream side of a fixing nip part (fixing device 20), and a guide member 55 configured by a movement mechanism 93 to be movable between a first position and a second position for correcting a curl is installed at a downstream side of the vicinity of the auxiliary roller pair 53. The guide member 55 is formed such that while being located at the second position, an angle formed by a guide surface W (rib surface) facing a sheet P to be corrected with respect to a virtual tangent Z in a conveyance direction (guide angle θ) becomes smaller at both ends in a width direction than that in a center part in the width direction.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a technique is known in which a back curl correction mechanism is provided on the downstream side of a fixing device in order to correct curl (back curl) generated in a sheet during a fixing process. (For example, refer to Patent Documents 1 and 2.)

Specifically, in the image forming apparatuses in Patent Documents 1 and 2, a conveying roller pair (auxiliary roller pair) including a driving roller and a driven roller is installed on the downstream side of the fixing device. Further, on the downstream side of the conveying roller pair, there are a retracted position that does not contact the sheet conveyed by the conveying roller pair, and a correction position that corrects the curl of the sheet by pressing the sheet conveyed by the conveying roller pair. A guide member configured to be switchable is provided.
Then, the drive roller and the driven roller are rotated along the conveying direction while the sheet is held in the nip portion formed by the pressure contact between the driving roller and the driven roller, so that the conveying roller pair performs the post-fixing process. The sheet is sandwiched and conveyed toward the position of the guide member. The sheet on which the back curl is generated is pushed and curled by the guide member moved to the correction position while being nipped and conveyed by the pair of conveying rollers.

  Although the conventional image forming apparatus described above can be expected to correct the curl of the sheet generated during the fixing process by the curl correcting mechanism installed on the downstream side of the fixing apparatus, the effect is still insufficient. It was.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an image forming apparatus in which curling of a sheet generated during a fixing process can be sufficiently corrected.

  The image forming apparatus according to the present invention transports a sheet in a predetermined transport direction to a fixing nip portion where the fixing member and the pressure member are in pressure contact, and fixes the toner image carried on the surface of the sheet. And a downstream of the fixing nip portion in the conveying direction, and includes a driving roller and a driven roller, and the sheet is sandwiched in the nip portion between the driving roller and the driven roller in the conveying direction. And an auxiliary roller pair that is rotationally driven along the conveying direction, and is installed in the vicinity of the auxiliary roller pair on the downstream side in the conveying direction with respect to the auxiliary roller pair, The first position of the auxiliary roller pair that does not block the virtual tangent passing through the nip portion, and the sheet that protrudes to block the virtual tangent and guides the conveyance of the sheet fed from the auxiliary roller pair. A guide member configured to be movable by a moving mechanism between a second position for forming a reverse curl in a direction opposite to a direction of the curl formed at the fixing nip portion with respect to the belt and correcting the curl. The guide member is positioned in the second position, and the angle formed by the guide surface facing the sheet to be corrected in the transport direction with respect to the virtual tangent is larger than that in the center in the width direction. It is formed so that both ends in the width direction become small.

  According to the present invention, it is possible to provide an image forming apparatus in which curling of a sheet generated during the fixing process is sufficiently corrected.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 4 is an enlarged view showing a paper discharge conveyance path from a fixing device to a paper discharge roller pair. It is the schematic which shows the drive roller of an auxiliary roller pair, and a guide member in the rotating shaft direction. FIG. 4A is a diagram showing a center portion in the width direction and FIG. 4B is a diagram showing both end portions in the width direction in the guide member in a state positioned at the second position. It is a figure which shows the paper discharge conveyance path when a thick paper is conveyed as a sheet | seat. In double-sided printing, (A) a diagram showing the trajectory of a sheet after the fixing step is applied to the front side, and (B) a diagram showing the trajectory of the sheet after the fixing step is applied to the back side. is there. (A) a view showing the first rib-like member, (B) a view showing the second rib-like member, and (C) a third rib-like shape of the guide member in the second position in the first modification. It is a figure which shows a member. It is the schematic which shows the drive roller of the auxiliary roller pair in a modification 2, and a guide member in a rotating shaft direction.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the overall configuration and operation of the image forming apparatus 1 will be described with reference to FIG.
As shown in FIG. 1, the image forming apparatus 1 in the present embodiment is a tandem color printer. Four bottles 102Y, 102M, 102C, and 102K corresponding to the respective colors (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.
An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming portions 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 (image carrier) of the intermediate transfer unit 85. .
Below the image forming apparatus main body 1, a paper feeding unit 12 (paper feeding cassette) in which a plurality of sheets P such as paper are stacked and stored is installed.
Further, on the upper right side of the image forming apparatus main body 1, the sheet P is conveyed (discharged) toward the stack unit 100, or the sheet P is reversed (switched back) and conveyed toward the double-sided conveyance path K5. A conveying device 30 is installed for this purpose.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing device 76, a cleaning device 77, a charge eliminating unit, and the like are disposed. Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process) is performed on each of the photoconductive drums 5Y, 5M, 5C, and 5K. An image of each color is formed on the surface of 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 1 by a main motor. Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (a charging process).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser beam emitted from the exposure unit 3 (writing unit), and electrostatic latent images corresponding to the respective colors are exposed by scanning at this position. An image is formed (exposure process).

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing device 76, and the electrostatic latent image is developed at this position to form toner images of each color (developing process). .)
Thereafter, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photoconductive drums 5Y, 5M. The toner images on 5C and 5K are transferred onto the intermediate transfer belt 78 (this is a primary transfer process). At this time, a small amount of untransferred toner remains on the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K.

Thereafter, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning device 77, and untransferred toner remaining on the photoconductor drums 5Y, 5M, 5C, and 5K is cleaned at this position. 77 is mechanically collected by a cleaning blade (cleaning process).
Finally, the surfaces of the photoconductive drums 5Y, 5M, 5C, and 5K reach a position facing the charge eliminating unit, and the residual potential on the photoconductive drums 5Y, 5M, 5C, and 5K is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

Thereafter, the toner images of the respective colors formed on the surfaces of the respective photosensitive drums through the development process are transferred onto the surface of the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the surface of the intermediate transfer belt 78.
The intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning device 80. , Etc. The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84, and is endlessly moved in the direction of the arrow in FIG. 1 by the rotational drive of one roller 82 connected to the main motor.

The four primary transfer bias rollers 79Y, 79M, 79C, and 79K sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K, respectively, thereby forming primary transfer nips. Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.
The intermediate transfer belt 78 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the surface of the intermediate transfer belt 78 (this is a primary transfer process).

Thereafter, the intermediate transfer belt 78 on which the toner images of the respective colors are primarily transferred and overlapped reaches a position facing a secondary transfer roller 89 as a transfer device. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 (transfer device) and forms a secondary transfer nip. The four-color toner images formed on the intermediate transfer belt 78 are transferred onto the sheet P conveyed to the position of the secondary transfer nip (secondary transfer process). At this time, untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 78.
Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning device 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed.

Here, the sheet P conveyed to the position of the secondary transfer nip is conveyed from the sheet feeding unit 12 disposed below the apparatus main body 1 via the first conveyance path K1.
Specifically, the sheet feeding unit 12 stores a plurality of sheets P such as transfer papers. When the paper feed roller 31 is driven to rotate counterclockwise in FIG. 1, the uppermost sheet P sandwiched between the paper feed roller 31 and the friction pad 32 passes through the first transport path K1. While being guided by the guide plate to be formed, the sheet is fed toward the rollers of the registration roller pair 33 (timing roller pair).

  The sheet P conveyed to the registration roller pair 33 (timing roller pair) temporarily stops at the position of the roller nip (nip portion) of the registration roller pair 33 that has stopped rotating. Then, the registration roller pair 33 is rotationally driven in time with the color image on the intermediate transfer belt 78, and the sheet P is conveyed toward the secondary transfer nip (image forming unit). Thus, a desired color image is transferred onto the sheet P.

Thereafter, the sheet P on which the color image is transferred at the position of the secondary transfer nip (image forming unit) is conveyed to the position of the fixing device 20. At this position (a fixing nip portion formed by pressing a fixing belt 21 as a fixing member and a pressure roller 22 as a pressure member), the toner is carried on the surface by heat and pressure. The toner image is fixed on the sheet P (fixing process).
In this embodiment, the fixing belt is used as the fixing member. However, a fixing roller, a fixing film, or the like can be used as the fixing member. In this embodiment, a pressure roller is used as the pressure member. However, a pressure belt, a pressure pad, or the like can be used as the pressure member.

Then, the sheet P after the fixing process passes through the position of the guide member 55 while being nipped and conveyed by the auxiliary roller pair 53, and is guided to the sheet discharge conveyance path K2 by the switching member 45 (branch claw). It is discharged out of the apparatus by a roller pair 41 (conveying roller pair). The sheets P discharged outside the apparatus by the discharge roller pair 41 are sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Here, the operation of the sheet P (or the image forming apparatus 1) from the paper feeding unit 12 to the stack unit 100 described above is a single-sided printing mode (a mode in which an image is formed only on the front side of the sheet P). If it is selected.
In the single-sided printing mode (or when discharging the sheet P after completion of printing on both sides in the double-sided printing mode), the paper discharge conveyance path K2 is opened and the relay conveyance path K3. The switching member 45 stops at a position (the position shown in FIG. 1) rotated counterclockwise about the support shaft 45a (rotating shaft) so as to close (FIG. 2, FIG. 2). 5. Reference can also be made to FIG.

On the other hand, when the double-sided printing mode (the mode in which images are formed on the front side and the back side of the sheet P, respectively) is selected, the sheet P (or the image forming apparatus) is as follows. 1) will work.
The process until the sheet P fed from the sheet feeding unit 12 reaches the fixing device 20 via the first conveyance path K1 and the secondary transfer nip is the same as that in the single-sided printing mode. The sheet P after the fixing process (in a state where an image is formed on the front side) is guided by the switching member 45 to the switchback conveyance path K4 via the relay conveyance path K3. At this time, the switching member 45 stops at a position rotated clockwise about the support shaft 45a (rotation shaft) so as to close the paper discharge conveyance path K2 and open the relay conveyance path K3. (See FIG. 6A.)
In the switchback conveyance path K4, when the rear end portion of the sheet P (the rear end portion in the conveyance direction) reaches the nip portion of the switchback roller 42 (the rear end portion of the sheet P is connected to the relay conveyance path K3). After passing through the branch point with the double-sided conveyance path K5), the rotational driving of the switchback roller 42 is temporarily stopped. At this time, the sheet P (the sheet P after the fixing process is applied to the front surface) is a device in which the rear end portion is held by the switchback roller 42 and the front end side is the exposed portion. Is exposed to the outside (the position above the stack portion 100).
Thereafter, the switchback roller 42 is rotationally driven in the reverse direction to reverse the conveyance direction of the sheet P and convey the sheet P toward the double-sided conveyance path K5. At this time, the switching member 45 stops at a position rotated counterclockwise about the support shaft 45a so as to close the relay conveyance path K3 and open the discharge conveyance path K2 (and the double-side conveyance path K5). doing.

Thereafter, referring to FIG. 1, the sheet P guided to the double-sided conveyance path K5 is conveyed by a plurality of conveyance rollers 46 and 47 installed in the double-sided conveyance path K5, and is guided to the position of the secondary transfer nip. . Then, the sheet P is subjected to the secondary transfer process to the back surface at this position in the same manner as in the secondary transfer process to the front surface, and is then conveyed toward the fixing device 20 to be back. The fixing process to the surface is performed.
The sheet P after the fixing process (the sheet P after the printing on both sides is completed) is guided to the nip portion of the discharge roller pair 41 through the discharge conveyance path K2, as described above. Accordingly, the paper is discharged out of the apparatus by the pair of paper discharge rollers 41 and sequentially stacked on the stack unit 100.

Next, the configuration / operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG.
Referring to FIG. 2, a fixing device 20 includes a fixing belt 21 (belt member) as a fixing member, a fixing member 26 (nip portion forming member), a reinforcing member 23, two heaters 25 (heat sources) as heating means, It comprises a pressure roller 22 as a pressure member, a reflection member 27, and the like.

Here, the fixing belt 21 (fixing member) is a thin and flexible endless belt, and rotates (runs) in an arrow direction (counterclockwise direction) in FIG. The fixing belt 21 has a base material layer, an elastic layer, and a release layer sequentially laminated from the inner peripheral surface (the sliding contact surface with the fixing member 26) side, and the total thickness thereof is 1 mm or less. Is set.
The base material layer of the fixing belt 21 has a layer thickness of 30 to 50 μm, and is formed of a metal material such as stainless steel or nickel, or a resin material such as polyimide.
The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion are not formed, and heat is uniformly transmitted to the toner image T on the sheet P, so that generation of a scum skin image is suppressed.
The release layer of the fixing belt 21 has a layer thickness of 5 to 50 μm, and includes PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES ( Polyether sulfide) and the like. By providing the release layer, the releasability (peelability) for the toner T (toner image) is secured.

A fixing member 26, two heaters 25, a reinforcing member 23, a reflecting member 27, and the like are fixed inside the fixing belt 21 (inner peripheral surface side).
Here, the fixing member 26 is fixed so as to be in sliding contact with the inner peripheral surface of the fixing belt 21. The fixing member 26 is in pressure contact with the pressure roller 22 via the fixing belt 21 to form a nip portion where the sheet P is conveyed.
The fixing belt 21 is directly heated by the radiant heat (infrared light) of the heater 25 installed therein.

  The two heaters 25 serving as heating means are both halogen heaters, and both end portions thereof are fixed to the side plate of the fixing device 20. Then, due to the radiant heat of the heater 25 whose output is controlled by the power supply unit of the apparatus main body 1, the fixing belt 21 is a portion mainly excluding the nip portion and is opposed to the heater 25 (part of the circumferential direction of the fixing belt 21). Is heated). Further, heat is applied to the toner image on the sheet P from the surface of the heated fixing belt 21. The output control of the heater 25 is performed based on the detection result of the belt surface temperature by a temperature sensor such as a thermopile facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 25.

Here, in the present embodiment, the reinforcing member 23 that reinforces the strength of the fixing member 26 that forms the nip portion is fixed to the inner peripheral surface side of the fixing belt 21. The reinforcing member 23 abuts against the pressure roller 22 via the fixing member 26 and the fixing belt 21, thereby preventing the fixing member 26 from being greatly deformed by the pressure applied by the pressure roller 22 in the fixing nip portion. doing.
In the present embodiment, a reflecting member 27 (reflecting plate) is fixed on the side of the reinforcing member 23 facing the heater 25. In other words, the reinforcing member 23 is provided with the heater 25 through the reflecting member 27 inside (inside the recess). As a result, heat from the heater 25 toward the reinforcing member 23 (heat for heating the reinforcing member 23) is reflected by the reflecting member 27 and used for heating the fixing belt 21, so that the heating efficiency of the fixing belt 21 is improved. It will be further improved. In addition, as a material of the reflecting member 27, aluminum, stainless steel, or the like can be used.

  Referring to FIG. 2, the pressure roller 22 (a pressure member that abuts the outer peripheral surface of the fixing belt 21 at the position of the nip portion) is formed by forming an elastic layer on a hollow cored bar. . The elastic layer of the pressure roller 22 is formed of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. A thin release layer made of PFA, PTFE, or the like can be provided on the surface layer of the elastic layer. The pressure roller 22 is in pressure contact with the fixing belt 21 to form a desired fixing nip portion between both members. The pressure roller 22 is provided with a gear that meshes with the drive gear of the drive motor 91 (drive means), and the pressure roller 22 is rotationally driven in the direction of the arrow (clockwise) in FIG.

  In the present embodiment, the fixing member 26 that is in sliding contact with the inner peripheral surface of the fixing belt 21 is concave so that the surface facing the pressure roller 22 (sliding contact surface) follows the curvature of the pressure roller 22. Is formed. Thereby, since the sheet P is sent out from the fixing nip portion so as to follow the curvature of the pressure roller 22, a problem that the sheet P after the fixing process is not attracted to and separated from the fixing belt 21 is suppressed. Can do.

The normal operation of the fixing device 20 configured as described above will be briefly described below.
When the power switch of the apparatus main body 1 is turned on, power is supplied to the heater 25, and the rotational driving of the pressure roller 22 in the direction of the arrow in FIG. Accordingly, the fixing belt 21 is also rotated in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 22 in the fixing nip portion.
Thereafter, the sheet P is fed from the sheet feeding unit 12, and an unfixed color image is carried (transferred) on the sheet P at the position of the secondary transfer roller 89. The sheet P carrying the unfixed image (toner image) is conveyed in the direction of the broken line arrow in FIG. 2 while being guided by the conveyance guide plate, and then is fixed to the fixing nip portion of the fixing belt 21 and the pressure roller 22 in the pressure contact state. Sent in.
The toner image is fixed on the surface of the sheet P by the heating by the fixing belt 21 heated by the heater 25 and the pressing force of the fixing member 26 reinforced by the reinforcing member 23 and the pressure roller 22. After that, the sheet P sent out from the fixing nip portion passes between the separation plate 52 and the conveyance guide plate 51 and is further conveyed by the auxiliary roller pair 53 in the direction of the broken arrow.

  In the present embodiment, the heater 25 is used as a heating unit for heating the fixing belt 21, but an electromagnetic induction coil, a resistance heating element, or the like can be used as a heating unit for heating the fixing belt. In this embodiment, the fixing member (fixing belt 21) is heated from the inner peripheral surface side by the heating unit. However, the fixing member may be heated from the outer peripheral surface side by the heating unit. it can.

Hereinafter, the characteristic configuration and operation of the image forming apparatus 1 according to the present embodiment will be described in detail with reference to FIGS.
As described above with reference to FIGS. 1 and 2, the image forming apparatus 1 according to the present embodiment has a fixing nip portion (a portion where the fixing belt 21 and the pressure roller 22 are in pressure contact). Thus, an auxiliary roller pair 53 is installed on the downstream side in the transport direction. The auxiliary roller pair 53 is rotationally driven along the conveyance direction by a drive motor 91 as a driving unit, and conveys the sheet P sent from the fixing nip portion in the conveyance direction.

Specifically, with reference to FIGS. 2 and 3, etc., the auxiliary roller pair 53 includes a driving roller 53a and a driven roller 53b. The driving roller 53a has a shaft portion 53a1 (core metal) made of a metal material and a roller portion 53a2 made of a solid rubber material having a high friction coefficient such as silicon, EPDM, urethane, fluororubber, etc. The vertical direction is the left-right direction in FIG. 3). That is, the driving roller 53a (the roller disposed on the side of the driving roller 53a and the driven roller 53b facing the guide member 55) has a plurality of roller portions 53a2 disposed at intervals in the width direction. (In this embodiment, there are four roller portions 53a2). A driven gear 96 is provided on one end side of the shaft portion 53a1 of the drive roller 53a. Further, the driven gear 96 of the driving roller 53a meshes with a driving gear 95 installed on the motor shaft of the driving motor 91 (driving means).
The driven roller 53b has a low friction coefficient elastic layer (tube) made of PFA, ETFA, FEP or the like having a thickness of about 30 to 300 μm on a hollow shaft portion (core metal) made of a metal material. It is formed over the direction, and is urged so as to form a nip portion by being pressed against the roller portion 53a2 of the driving roller 53a by a spring. By making the shaft portion of the driven roller 53b have a hollow structure, the heat capacity is reduced, and condensation due to water vapor generated from the sheet P can be prevented. Further, by providing an elastic layer having a low friction coefficient on the shaft portion of the driven roller 53b, it becomes difficult for toner to adhere to the surface of the driven roller 53b.
In the present embodiment, the driving roller 53a is disposed on the side in contact with the non-fixing surface of the sheet P after the fixing step, and the driven roller 53b is a fixing surface of the sheet P after the fixing step (fixing immediately after fixing). The surface on which the image is carried).

  With such a configuration, the driving roller 53a is rotated in the clockwise direction in FIG. 2 by the operation of the driving motor 91, and the driven roller 53b is also rotated in the counterclockwise direction in FIG. 2 by the frictional resistance with the driving roller 53a. It will be. In this way, the auxiliary roller pair 53 holds and conveys the sheet P in the direction of the broken line arrow (conveying direction) in FIG. That is, the drive motor 91, the drive gear 95, the driven gear 96, and the like function as drive means that rotationally drives the auxiliary roller pair 53.

  Here, in the present embodiment, the driving means assists the auxiliary roller 53 so that the auxiliary roller pair 53 rotates only in the forward direction (in the direction of the arrow in FIG. 2) along the transport direction and does not rotate in the reverse direction. A one-way clutch mechanism that transmits driving force to the pair 53 is provided. Specifically, the driven gear 96 installed on the drive roller 53a is a one-way gear in which a one-way clutch 97 is integrally formed on the inner periphery, and the driven gear 96 is inserted into the shaft portion 53a1 via the one-way clutch 97. It is in the state that was done. With such a configuration, the drive roller 53a rotates in that direction only when the clockwise driving force in FIG. 2 is applied, and idles without rotating when the counterclockwise driving force is applied. Therefore, good transportability of the sheet P is maintained, and when the sheet P is jammed (paper jam) at the position of the fixing device 20, the sheet P is pulled out in the direction opposite to the transport direction by the user. It is possible to prevent problems that occur.

Further, in the image forming apparatus 1 according to the present exemplary embodiment, a discharge roller pair 41 is installed on the downstream side in the transport direction with respect to the auxiliary roller pair 53. The paper discharge roller pair 41 includes a driving roller and a driven roller, and is rotationally driven by the driving motor 91 along the conveyance direction to convey the sheet P sent from the auxiliary roller pair 53 in the conveyance direction to form an image forming apparatus. It is discharged outside the main body 1. Each of the driving roller and the driven roller in the paper discharge roller pair 41 is such that a roller portion made of a rubber material, a resin material, or the like is formed on a shaft portion (core metal). When the driving rollers connected via the rows are rotationally driven, the respective rollers rotate in the direction of the arrow in FIG. 2 to sandwich and convey the sheet P.
Further, the auxiliary roller pair 53 as a pair of conveyance rollers is a sheet discharge conveyance path K2 curved from the nip portion toward the driven roller 53b (a conveyance path curved from the lower side in the vertical direction to the left in the horizontal direction in FIG. 2). Is installed).

2 to 6 and the like, the image forming apparatus 1 according to the present embodiment includes a driving roller on the downstream side of the auxiliary roller pair 53 in the transport direction and in the vicinity of the auxiliary roller pair 53. A guide member 55 is installed on the side facing 53a.
The guide member 55 has a first position (at a position shown in FIG. 5) that does not block a virtual tangent line Z (a tangent indicated by a one-dot chain line in FIGS. 2, 4, and 5) passing through the nip portion of the auxiliary roller pair 53. And the direction of curl formed in the fixing nip portion with respect to the sheet P while guiding the conveyance of the sheet P fed out from the auxiliary roller pair 53 by projecting so as to block the virtual tangent line Z. A second position (the position in FIGS. 2 and 4) that forms a reverse curl in the direction and corrects the curl is configured to be movable by a moving mechanism 93.

Specifically, referring to FIG. 3, the guide member 55 has a plurality of rib-like members arranged at intervals in the width direction (the vertical direction in FIG. 2 and the left-right direction in FIG. 3). 55A to 55C (in the present embodiment, five rib-like members) are provided.
The plurality of rib-like members 55A to 55C have a rib surface W (see FIG. 4 and the like) that functions as a guide surface that faces the sheet P to be corrected.

  More specifically, the guide member 55 has a substantially triangular rib-like member at a plurality of positions on the support shaft 55b corresponding to the space between the roller portion 53a2 and the roller portion 53a2 of the drive roller 53a (auxiliary roller pair 53). 55A to 55C are formed, and are installed so as to be rotatable with respect to the shaft portion 53a1 with a bearing 55a installed on the shaft portion 53a1 of the drive roller 53a as a rotation center.

Referring to FIG. 3, the guide member 55 has a spring 94 that urges the guide member 55 to rotate counterclockwise in FIGS. 2 and 5 with the shaft portion 53a1 (bearing 55a) as the center of rotation. It is connected. Although not shown, the guide member 55 is a protrusion formed on the apparatus main body 1 without the guide member 55 biased by the spring 94 rotating without limitation in the counterclockwise direction of FIGS. A stopper portion is formed which engages with the portion and is locked so that the rotation is restricted at the position shown in FIG.
Referring to FIG. 3, the guide member 55 is rotated in the clockwise direction in FIGS. 2 and 5 with the shaft portion 53a1 (bearing 55a) as the rotation center so as to resist the urging force of the spring 94. A solenoid 93 for energizing is connected.
That is, the solenoid 93, the spring 94, and the like function as a moving mechanism that rotates the guide member 55 between the first position shown in FIG. 5 and the second position shown in FIG.

When the thickness of the sheet P is equal to or less than the predetermined value X, the moving mechanism configured as described above moves the guide member 55 at least from before the sheet P reaches the position of the guide member 55 until after it passes. Control is made to move to the second position. Specifically, when a sheet P having a thickness of not more than a predetermined value X (a sheet P having a basis weight of 160 g / m ² or less) is passed, the energization to the solenoid 93 is turned off by the control unit. Thus, the guide member 55 is rotated to the rotation position shown in FIGS.
On the other hand, when the thickness of the sheet P exceeds the predetermined value X, the moving mechanism moves the guide member 55 to the first position at least from before the sheet P reaches the position of the guide member 55 until after passing. Controlled to move. Specifically, when the sheet P having a thickness exceeding the predetermined value X (the sheet P having a basis weight exceeding 160 g / m ² ) is passed, the energization to the solenoid 93 is turned on by the control unit. Thus, the guide member 55 is rotated to the rotation position shown in FIG.

Such control is performed because the sheet P such as plain paper or thin paper whose thickness is equal to or less than the predetermined value X is weak, and is subjected to curl (in the present embodiment) due to pressure in the fixing nip portion during the fixing process. As described above, the curl is in the direction along the curvature of the pressure roller 22.) The thick paper sheet P having a thickness exceeding the predetermined value X is strong and has a strong stiffness during the fixing process. This is because curling is unlikely to occur even when pressure is applied to the fixing nip portion. Therefore, when a sheet P such as plain paper or thin paper having a thickness equal to or less than the predetermined value X is passed, the sheet P sent from the fixing nip portion (the sheet P on which the curl is formed). Thus, the curling is corrected by causing the guide member 55 to bend in the reverse curl direction while being sandwiched and conveyed by the auxiliary roller pair 53.
Further, in addition to the fact that the thick sheet P exceeding the predetermined value X is not easily curled as described above, if the guide member 55 is rotated to the position shown in FIG. The strength of sliding contact with the guide member 55 becomes too strong due to the strength, and a rubbing trace is formed on the back surface of the sheet P or the guide member 55 is worn. For this reason as well, when a thick sheet P having a thickness exceeding the predetermined value X is passed, the guide member 55 is rotated to a position where it does not interfere with the sheet P.

  In the present embodiment, the thickness of the sheet P described above is provided by the user on the operation unit (a personal computer connected to the image forming apparatus 1 so as to be communicable or an exterior part of the image forming apparatus 1). Based on information relating to the sheet P input to the operation panel, etc.), or directly by a known paper thickness sensor installed in the paper feed unit 12 or the conveyance path. It can also be detected. Based on the thickness of the sheet P thus detected, the above-described guide member 55 is controlled.

Here, in the present embodiment, as described above, when the solenoid 93 is in the OFF state, the rotation position of the guide member 55 is configured to be the position of FIG. 2 (second position). Yes. This is because the second position (the position shown in FIG. 2) for performing the curl correction needs to have higher positional accuracy than the first position (the position shown in FIG. 5) that simply avoids interference with the sheet P. Because there is. That is, the position accuracy of the second position is relatively easily increased by increasing the accuracy of the configuration in which the guide member 55 is engaged with the protrusion of the apparatus main body 1 to restrict the rotation.
In the present embodiment, as shown in FIG. 2, when the guide member 55 is rotated to the second position, a part of the guide member 55 (rib-shaped members 55A to 55C) is driven by the drive roller 53a ( The guide member 55 is configured to be close to the driving roller 53a (auxiliary roller pair 53) so as to overlap the roller portion of the auxiliary roller pair 53). In such a configuration, the auxiliary roller pair 53 is used as compared with the case where the guide member 55 (rib-shaped members 55A to 55C) is installed at a position away from the drive roller 53a (auxiliary roller pair 53). Curling correction can be performed efficiently and reliably on the sheet P to be sandwiched and conveyed.

Here, referring to FIG. 4, in the present embodiment, guide member 55 faces sheet P to be corrected in a state where it is located at the second position (the position shown in FIGS. 2 and 4). An angle θ (hereinafter referred to as a “guide angle” where appropriate) in the transport direction with respect to the virtual tangent line Z (the virtual tangent line passing through the nip portion of the auxiliary roller pair 53). However, both end portions in the width direction are formed to be smaller than the center portion in the width direction.
Specifically, among the five rib-like members 55A to 55C (see FIG. 3) arranged at intervals in the width direction, the guide angle θ2 of the two rib-like members 55C arranged at both ends in the width direction. However, it is configured to be smaller than the guide angle θ1 of the three rib-like members 55A and 55B disposed in the other part (widthwise center) (θ1> θ2).

  That is, in the state where the guide member 55 is moved to the second position, the rib-like members at both ends are provided at both ends in the width direction with respect to the sheet P fed from the nip portion of the auxiliary roller pair 53. A force that greatly curves in the reverse curl direction acts at a relatively steep guide angle θ2 by 55C, and the other portions are reversed at a relatively gentle guide angle θ1 by the other rib-like members 55A and 55B. A force that slightly curves in the curl direction acts.

When configured in this manner, the guide angles of all the rib-like members 55A to 55C are all set to the same angle (for example, a relatively gentle guide angle θ1 or a relatively steep guide angle θ2). Compared to the case, the curl correction can be efficiently performed in a balanced manner on the sheet P sandwiched and conveyed by the auxiliary roller pair 53.
Specifically, the curl (inverted curl) generated in the sheet P after the fixing process is larger at both ends in the width direction than at the center in the width direction. In the present embodiment, at both ends in the width direction where a large curl is generated, the rib-like member 55C set at a relatively steep guide angle θ2 is greatly curved in the reverse curl direction, and at the center in the width direction where a small curl is generated. Since the rib-shaped members 55A and 55B set at a relatively gentle guide angle θ1 are slightly curved in the reverse curl direction, the sheet P is curled and efficiently curled with good balance in the width direction by the guide member 55. become. That is, since the curl correction force is varied depending on the position in the width direction in accordance with the size of the curl that varies depending on the position in the width direction, the sheet P is uniformly curled in the width direction.

  Here, in the present embodiment, the switching member 45 (branch claw) described above with reference to FIG. 1 or the like is installed in the vicinity of the guide member 55 on the downstream side of the guide member 55 in the transport direction. ing. The switching member 45 includes a sheet conveyance path K2 for guiding the sheet P sent out from the fixing nip portion to the position of the sheet discharge roller pair 41, and a sheet conveyance path K5 (switch). This is for switching to one of the relay conveyance path K3 for guiding to the back conveyance path K4), and is configured to be rotatable about a support shaft 45a by a motor (not shown).

In the present embodiment, in the double-sided printing mode, regardless of the thickness of the sheet P, as shown in FIG. 6A, when the sheet P that has been subjected to the fixing process on the front side passes, switching is performed. The discharge conveyance path K2 is closed by the member 45 and the relay conveyance path K3 is opened, and the guide member 55 is moved to the first position by the moving mechanism 93, as shown in FIG. When the sheet P on which the fixing process has been performed passes, the sheet discharge conveyance path K2 is opened by the switching member 45 and the relay conveyance path K3 is closed, and the guide member 55 is moved to the first position by the moving mechanism 93. Moved.
That is, in the double-sided printing mode, the switching member 45 is rotated so as to appropriately switch the conveyance path, whereas the guide member 55 is always in the first position (a position that does not interfere with the sheet P regardless of the thickness of the sheet P). The solenoid 93 is controlled to be in an ON state so as to be rotated.

Such a control is performed in the double-sided printing mode, although a fixing process on the front side is performed and a curl is formed on the sheet P after passing through the fixing nip portion, but a fixing process on the back side is performed. This is because a curl that cancels the curl is formed on the sheet P after passing through the fixing nip portion. That is, at the time of duplex printing, the sheet P that is finally discharged by the discharge roller pair 41 is corrected even if the sheet P is not corrected by the guide member 55 or the driven roller 53b. Become.
Further, when the sheet P after passing through the fixing nip portion after the fixing process on the back surface is brought into sliding contact with the guide member 55, the toner image already fixed on the front surface of the sheet P is applied to the guide member 55. This is because the image is scraped and abnormal images such as image blur and gloss streaks occur.

<Modification 1>
FIG. 7 is a view showing a state in which the guide member 55 in the first modification is located at the second position, and FIG. 7A is a view showing the first rib-like member 55A located at the center in the width direction. FIG. 7B shows the second rib-like member 55B located on both sides of the first rib-like member 55A, and FIG. 7C shows the third rib-like shape located at both ends in the width direction. It is a figure showing member 55C. The positional relationship in the width direction of these rib-like members 55A to 55C can be referred to FIG.
As shown in FIG. 7, in the first modification, the plurality of rib-like members 55 </ b> A to 55 </ b> C has an angle (in the transport direction with respect to the virtual tangent Z) that the guide surface W (rib surface) is in the second position. The guide angle θ) is formed so as to gradually decrease from the one disposed at the center in the width direction to the one disposed at both ends in the width direction. That is, the guide angle θ1 of the first rib-like member 55A, the guide angle θ2 of the second rib-like member 55B, and the guide angle θ2 of the third rib-like member 55C are in a relationship of θ1>θ2> θ3. Yes.
Since the curl generated in the sheet P after the fixing process gradually increases from the width direction center to both ends in the width direction, the guide angle θ gradually decreases from the width direction center to the width direction both ends. Further, a guide member 55 is configured. As a result, the sheet P is efficiently curled with good balance in the width direction by the guide member 55.

Further, as shown in FIG. 7, in the first modification, the plurality of rib-like members 55 </ b> A to 55 </ b> C is such that the length M in the conveyance direction of the guide surface W (rib surface) is arranged at the center in the width direction. It is formed so as to increase gradually as it is arranged at both ends in the width direction. That is, the length M1 of the guide surface W of the first rib-like member 55A, the length M2 of the guide surface W of the second rib-like member 55B, the length M3 of the guide surface W of the third rib-like member 55C, Has a relationship of M1 <M2 <M3.
As the length M of the guide surface W (rib surface) of the rib-shaped member is increased, the time for performing the curl correction on the sheet P is increased, and the curl correction force is increased. In the first modification, the length M of the guide surface W is increased from the center in the width direction toward both ends in the width direction in accordance with the curl that increases from the center in the width direction toward both ends in the width direction. Therefore, the sheet P is uniformly curled in the width direction.

<Modification 2>
FIG. 8 is a schematic diagram illustrating the driving roller 53a of the auxiliary roller pair 53 and the guide member 55 in the rotation axis direction (width direction) in Modification Example 2, and corresponds to FIG. 3 in the present embodiment. FIG.
Referring to FIG. 8, in the driving roller 53a according to the second modification, the plurality of roller portions 53a2 are smaller in hardness than those arranged in the widthwise center portion than those arranged in the widthwise center portion. It is formed to become. Specifically, among the four roller portions 53a2 of the drive roller 53a, the rubber hardness of the two roller portions 53a2 at both ends in the width direction is formed to be smaller than the rubber hardness of the other two roller portions 53a2. ing.
With this configuration, the nip portion of the auxiliary roller pair 53 has a roller portion having hardness higher than that of the driven roller 53b (the roller portion 53a2 of the driving roller 53a) at both ends in the width direction compared to the center portion in the width direction. It is formed in a concavely curved shape so as to follow the curvature. Therefore, the auxiliary roller pair 53 performs curl correction on the sheet P on which curling has occurred after the fixing step by applying a force that causes the curl to bend in the opposite curl direction at both ends in the width direction. Can do.
In the case where a difference in linear velocity occurs between the driving roller 53a and the driven roller 53b by differentiating the hardness of the plurality of roller portions 53a2 of the driving roller 53a in this way, outside the sheet passing area, The driving roller 53a may be provided with a roller portion that contacts the roller portion of the driven roller 53b, and the hardness of the roller portion may be set high.

Further, as shown in FIG. 8, in the driving roller 53a according to the second modification, the plurality of roller portions 53a2 are arranged at both ends in the width direction and the outer diameter D2 is arranged at the center portion in the width direction. It is formed to be larger than D1 (D1 <D2).
As the outer diameter D of the roller portion 53a2 increases, the time for holding the sheet P at the nip portion of the auxiliary roller pair 53 becomes longer, the time for performing the curl correction by the auxiliary roller pair 53 becomes longer, and the curl correcting force increases. . In Modification 2, the curl correction force is increased by increasing the outer diameter D2 of the roller portion 53a2 at both ends in the width direction in accordance with the large curl generated at both ends in the width direction of the sheet P. The curl is corrected uniformly over the direction.

As described above, in the image forming apparatus 1 according to the present embodiment, the auxiliary roller pair 53 is installed on the downstream side of the fixing nip portion (fixing device 20), and the first position and the second position for curl correction are set. A guide member 55 configured to be movable by the moving mechanism 93 is installed on the downstream side in the vicinity of the auxiliary roller pair 53. And the angle (guide angle (theta)) which the guide surface W (rib surface) which opposes the sheet | seat P to be corrected makes in the conveyance direction with respect to the virtual tangent Z in the state where the guide member 55 is located at the second position, The both ends in the width direction are formed to be smaller than the central portion in the width direction.
Thereby, the curl of the sheet P generated during the fixing process can be sufficiently corrected.

In the present embodiment, the toner image carried on the intermediate transfer belt 78 (intermediate transfer member) is transferred to the color image forming apparatus 1 on the sheet P by a secondary transfer roller 89 as a transfer device. Although the invention is applied, a monochrome image forming apparatus in which a toner image carried on a photosensitive drum (or a photosensitive belt) is transferred onto a sheet P by a transfer roller (or a transfer belt or a transfer charger) as a transfer device. Of course, the present invention can be applied to the above.
Even in such a case, the same effect as that of the present embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 image forming apparatus (image forming apparatus main body),
20 fixing device,
21 fixing belt (fixing member),
22 pressure roller (pressure member),
41 Paper discharge roller pair,
45 switching member,
53 Auxiliary roller pair,
53a driving roller,
53a1 shaft portion, 53a2 roller portion,
53b driven roller,
53a1 shaft (rotation center),
55 guide members,
55A-55C rib-shaped member,
55a bearing (rotation center), 55b spindle,
91 Drive motor (drive means),
93 Movement mechanism (solenoid),
94 Spring (biasing member),
Z virtual tangent, W guide surface (rib surface), θ guide angle,
K2 paper discharge conveyance path, K3 relay conveyance path, K4 switchback conveyance path,
K5 Double-sided conveyance path, P sheet (recording medium).

JP 2016-173500 A JP, 2006-177063, A

Claims (6)

A fixing device that conveys a sheet in a predetermined conveying direction to a fixing nip portion where the fixing member and the pressure member are in pressure contact, and fixes a toner image carried on the surface of the sheet;
Installed downstream of the fixing nip portion in the conveyance direction, and includes a driving roller and a driven roller, and the sheet is sandwiched between the nip portion of the driving roller and the driven roller along the conveyance direction. A pair of auxiliary rollers that are rotationally driven to convey the sheet in the conveyance direction,
A first position that is located downstream of the auxiliary roller pair in the transport direction and in the vicinity of the auxiliary roller pair and does not block a virtual tangent passing through the nip portion of the auxiliary roller pair; and the virtual tangent A reverse curl is formed on the sheet in a direction opposite to the curl direction formed at the fixing nip portion while guiding the conveyance of the sheet fed from the auxiliary roller pair. A second position for correcting curl; and a guide member configured to be movable by a moving mechanism;
With
In the state where the guide member is located at the second position, the angle formed in the conveyance direction by the guide surface facing the sheet to be corrected with respect to the virtual tangent is both ends in the width direction compared to the center portion in the width direction. An image forming apparatus formed so as to be small. The guide member comprises a plurality of rib-like members arranged at intervals in the width direction,
The plurality of rib-shaped members are
Each has a rib surface that functions as the guide surface,
The angle formed by the rib surface in the transport direction with respect to the virtual tangent in the state where the rib is located at the second position is changed from the one disposed at the center in the width direction to the one disposed at both ends in the width direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed so as to gradually decrease.   The plurality of rib-shaped members are formed such that the length of the rib surface in the transport direction gradually increases from the one disposed at the widthwise center portion to the one disposed at both widthwise end portions. The image forming apparatus according to claim 2. Of the driving roller and the driven roller, the roller disposed on the side facing the guide member includes a plurality of roller portions disposed at intervals in the width direction,
The plurality of roller portions are formed so that the hardness of those arranged at both ends in the width direction is smaller than the hardness of those arranged at the center portion in the width direction. Item 4. The image forming apparatus according to Item 3.   5. The plurality of roller portions are formed such that an outer diameter of those arranged at both ends in the width direction is larger than an outer diameter of those arranged at a center portion in the width direction. The image forming apparatus described in 1. The moving mechanism is
When the thickness of the sheet is equal to or less than a predetermined value, the guide member is moved to the second position at least until the sheet passes through the position before reaching the position of the guide member,
When the thickness of the sheet exceeds the predetermined value, the guide member is moved to the first position at least from before the sheet reaches the position of the guide member to after passing. The image forming apparatus according to claim 1.

Images