JP6540997B2 - Image forming device - Google Patents

Description

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

  Conventionally, in an image forming apparatus such as a copying machine or a printer, the conveyance speed by the pair of paper discharge rollers is increased immediately after the rear end of the sheet has passed the position of the fixing device for the purpose of enhancing print productivity. There is known a technique for quickly discharging the sheet after the fixing process to the outside of the image forming apparatus main body (see, for example, Patent Document 1).

  On the other hand, Patent Document 2 discloses a guide member at a position downstream of the fixing device and upstream of the pair of discharge rollers (second discharge roller) in order to correct the curl produced on the sheet during the fixing process. There is disclosed a technique of providing a pair of transport rollers (first discharge roller) to cause the sheet to reverse curl and correct the curl by these members.

  In the conventional image forming apparatus, the first conveyance roller pair is provided downstream of the fixing device (fixing nip portion) and upstream of the discharge roller pair (second conveyance roller pair). When it is controlled to accelerate the linear velocity at the nip portion of the discharge roller pair immediately after the rear end of the sheet passes the position of the fixing device in order to enhance the sheet resistance, the sheet at the position of the first conveyance roller pair Could jam (paper jam).

  The present invention has been made to solve the problems as described above, and is a case where the first conveying roller pair is provided on the downstream side of the fixing nip portion and on the upstream side of the second conveying roller pair. Even when control is performed to increase the linear velocity by the second conveyance roller pair in order to improve print productivity, it is less likely to cause a problem in which the sheet is jammed at the position of the first conveyance roller pair, image formation It is in providing an apparatus.

  An image forming apparatus according to the present invention transports a sheet in a predetermined transport direction to a fixing nip portion in which a fixing member and a pressure member are in pressure contact, and fixes the toner image carried on the surface of the sheet. And the fixing nip portion is disposed on the downstream side in the conveying direction, and the first driving unit is driven to rotate along the conveying direction by the first driving unit, and the sheet fed from the fixing nip portion is conveyed in the conveying direction. A first conveying roller pair for conveying to the lower side, and a downstream side with respect to the first conveying roller pair in the conveying direction, and rotationally driven along a conveying direction by And a second transport roller pair configured to transport the sheet delivered from the roller pair in the transport direction, and the second drive unit can change a linear velocity at a nip portion of the second transport roller pair. When the thickness of the sheet is equal to or less than a predetermined value, the rear end of the sheet is after passing through the fixing nip and before reaching the nip of the first conveyance roller pair. The linear velocity is controlled to be accelerated, and when the thickness of the sheet exceeds the predetermined value, the linear velocity after the rear end of the sheet passes through the nip portion of the first conveyance roller pair Is controlled to be accelerated.

  According to the present invention, the first transport roller pair is provided downstream of the fixing nip portion and upstream of the second transport roller pair, and the second transport roller pair is used to enhance print productivity. It is possible to provide an image forming apparatus which is less likely to cause a problem that a sheet is jammed at the position of the first conveyance roller pair, even when control is performed to increase the linear velocity.

FIG. 1 is an overall configuration diagram showing an image forming apparatus in an embodiment of the present invention. FIG. 2 is an enlarged view showing a sheet discharge conveyance path from a fixing device to a sheet discharge roller pair. It is the schematic which shows the drive roller of a 1st conveyance roller pair, and a guide member in a rotating shaft direction. FIG. 6 is a diagram illustrating a paper discharge conveyance path when thick paper is conveyed as a sheet. (A) A graph showing the speed variation of the discharge roller pair when a sheet other than thick paper is conveyed as a sheet, and (B) a graph showing the speed fluctuation of the discharge roller pair when thick paper is conveyed as a sheet Is. During double-sided printing, (A) A diagram showing the trajectory of the sheet after the fixing process has been applied to the front surface, and (B) a diagram showing the trajectory of the sheet after the fixing process has been applied to the back surface. is there.

Embodiment.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the redundant description will be appropriately simplified or omitted.

First, the entire 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 toner bottles 102Y, 102M, 102C, 102K corresponding to the respective colors (yellow, magenta, cyan, black) are detachably (replaceably) 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 storage unit 101. Image forming units 4Y, 4M, 4C, 4K corresponding to respective colors (yellow, magenta, cyan, black) are juxtaposed 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 sheet feeding unit 12 (sheet feeding cassette) in which a plurality of sheets P (recording media) such as transfer sheets are stacked and stored is installed.
In the upper right 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 (switchback) and conveyed toward the both-side conveyance path K5. A transport device 30 is provided for this purpose.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. In addition, around the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing device 76, a cleaning device 77, a charge removing unit (not shown), and the like are disposed. Then, on each of the photosensitive drums 5Y, 5M, 5C, and 5K, an imaging process (charging step, exposing step, developing step, transferring step, cleaning step) is performed to form each photosensitive drum 5Y, 5M, 5C, An image of each color is formed on 5K.

The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven clockwise in FIG. 1 by a drive motor (image forming motor) (not shown). Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (charging step).
Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser light emitted from the exposure unit 3 (writing unit), and electrostatic latent corresponding to each color by exposure scanning at this position. An image is formed (exposure step).

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

Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, 5K reach the position facing the cleaning device 77, and the untransferred toner remaining on the photosensitive drums 5Y, 5M, 5C, 5K at this position is a cleaning device It is mechanically recovered by the cleaning blade 77 (cleaning step).
Finally, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the discharging unit (not shown), and the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed at this position. Ru.
Thus, a series of imaging processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K are completed.

Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are superimposed and transferred onto the intermediate transfer belt 78 as an image carrier. Thus, a color image is formed on the intermediate transfer belt 78.
Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78 as an image carrier, four primary transfer bias rollers 79Y, 79M, 79C, 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, It comprises an intermediate transfer cleaning device 80 and the like. The intermediate transfer belt 78 is stretched and supported by three rollers 82 to 84, and is endless in the direction of the arrow in FIG. 1 by rotational driving of one roller 82 connected to a motor (image forming motor) not shown. Be moved.

The four primary transfer bias rollers 79Y, 79M, 79C and 79K respectively sandwich the intermediate transfer belt 78 between the photosensitive drums 5Y, 5M, 5C and 5K to form a primary transfer nip. 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 arrow direction and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. Thus, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are superimposed on the intermediate transfer belt 78 and primarily transferred (this is a primary transfer step).

After that, the intermediate transfer belt 78 on which the toner images of the respective colors are transferred (carried) in an overlapping manner reaches a position opposite to the secondary transfer roller 89 as a transfer device. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 with the secondary transfer roller 89 (transfer device) to form a secondary transfer nip. Then, 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 (a secondary transfer process). At this time, untransferred toner which 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 are 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.
More specifically, the sheet feeding unit 12 stores a plurality of sheets P such as transfer sheets in an overlapping manner. Then, when the sheet feeding roller 31 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost sheet P sandwiched between the sheet feeding roller 31 and the friction pad 32 passes through the first conveyance path K1. The sheet is fed toward the space between the resist roller pair 33 (timing roller pair) while being guided by a guide plate (not shown) to be formed.

  The sheet P conveyed to the registration roller pair 33 (timing roller pair) is temporarily stopped at the position of the roller nip (nip portion) of the registration roller pair 33 whose rotational driving has been stopped. Then, the registration roller pair 33 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the sheet P is conveyed toward the secondary transfer nip (image forming portion). Thus, the 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 (fixing unit). Then, at this position (a fixing nip portion formed by pressing the fixing belt 21 as a fixing member (fixing rotary member) and the pressure roller 22 as a pressure member (pressure rotary member)). The heat and the pressure fix the toner image carried on the surface onto the sheet P (this is a fixing step).
Here, in the present embodiment, the fixing belt is used as the fixing member, but a fixing roller, a fixing film, or the like can also be used as the fixing member. Further, in the present embodiment, the pressure roller is used as the pressure member, but 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 (first conveying roller pair), and is discharged by the switching member 45 (branch claw). The sheet is guided to the outside of the apparatus by the sheet discharge roller pair 41 (second conveyance roller pair). The sheet P discharged to the outside of the apparatus by the discharge roller pair 41 is sequentially stacked on the stack unit 100 as an output image.
Thus, a series of image forming processes in the image forming apparatus are completed.

Here, the operation of the sheet P (or the image forming apparatus 1) from the sheet feeding unit 12 to the stack unit 100 described above is a single-sided print mode (a mode in which an image is formed only on the front side of the sheet P). It is the case when it is selected.
In the single-sided printing mode (or when the sheet P after printing on both sides is discharged in the double-sided printing mode is discharged to the stack unit 100), the paper discharge conveyance path K2 is opened to relay the relay conveyance path K3. The switching member 45 is stopped at a position (a position shown in FIG. 1) which is turned counterclockwise about the support shaft 45a (a rotation shaft) so as to close the lock (FIG. 2, FIG. 2). 4, see also FIG. 6 (B).

On the other hand, when the double-sided printing mode (a mode for forming an image on each of the front and back sides of the sheet P) is selected, the sheet P (or the image forming apparatus as described below) 1) will work.
The process until the sheet P fed from the paper feeding unit 12 reaches the fixing device 20 via the first conveyance path K1 and the second transfer nip is the same as that in the single-sided printing mode. Then, the sheet P (in which the image is formed on the front surface) after the fixing process 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 is stopped at a position rotated clockwise about the support shaft 45a (rotational shaft) so as to close the sheet discharge conveyance path K2 and open the relay conveyance path K3. (Also see FIG. 6 (A).)
Then, 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 When passing through the junction with the duplex conveying path K5), the rotational drive 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 held in the rear end portion by the switchback roller 42, and the front end portion is an exposed portion. 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 duplex conveyance path K5. At this time, the switching member 45 is stopped at a position rotated counterclockwise around the support shaft 45a so as to close the relay conveyance path K3 and open the discharged sheet conveyance path K2 (and the double-sided conveyance path K5). doing.

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

Next, the configuration and 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, the 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, and two heaters 25 (heat sources) as heating units. The pressure roller 22 as a pressure member, the reflection member 27, and the like are included.

Here, the fixing belt 21 (fixing member) is a thin and flexible endless belt, and rotates (travels) in the 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 is 1 mm or less. It 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, fluorine rubber, or the like. By providing the elastic layer, the minute unevenness on the surface of the fixing belt 21 in the nip portion is not formed, the heat is uniformly transmitted to the toner image T on the sheet P, and the generation of the dull skin image is suppressed.
The releasing layer of the fixing belt 21 has a layer thickness of 5 to 50 μm and is made of PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES ( It is formed of materials such as polyether sulfide) and the like. By providing the release layer, the releasability (peelability) to 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 to the inside (inner peripheral surface side) of the fixing belt 21.
Here, the fixing member 26 is fixed so as to be in sliding contact with the inner peripheral surface of the fixing belt 21. Then, the fixing member 26 is brought into pressure contact with the pressure roller 22 via the fixing belt 21 to form a nip portion for conveying the sheet P.
Then, the fixing belt 21 is directly heated by radiant heat (infrared light) of the heater 25 (heating unit) installed therein.

  The two heaters 25 as heating means are both halogen heaters (infrared heaters), and both end portions thereof are fixed to the side plate of the fixing device 20. Then, due to the radiation 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 an opposing surface facing the heater 25 (a part of the fixing belt 21 in the circumferential direction). ) 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 (not shown) such as a thermopile facing the surface of the fixing belt 21. Further, the temperature (fixing temperature) of the fixing belt 21 can be set to a desired temperature by such output control of the heater 25.

Here, in the present embodiment, the reinforcing member 23 for reinforcing the strength of the fixing member 26 forming the nip portion is fixed on the inner peripheral surface side of the fixing belt 21. Then, the reinforcing member 23 abuts against the pressure roller 22 via the fixing member 26 and the fixing belt 21, thereby suppressing the problem that the fixing member 26 receives large pressure from the pressure roller 22 and largely deforms at the nip portion. ing.
Further, in the present embodiment, the reflecting member 27 (reflecting plate) is fixed on the side of the surface of the reinforcing member 23 facing the heater 25. That is, the heater 25 is disposed inside the reinforcing member 23 (inside the recess) via the reflecting member 27. As a result, the heat (heat for heating the reinforcing member 23) from the heater 25 toward 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 increased. It will be further improved. In addition, as a material of the reflection member 27, aluminum, stainless steel, etc. can be used.

  Referring to FIG. 2, the pressure roller 22 (a pressure member which is in contact with the outer peripheral surface of the fixing belt 21 at the position of the nip portion) has an elastic layer formed on a hollow cored bar. . The elastic layer of the pressure roller 22 (pressure rotating body) is formed of a material such as foamable silicone rubber, silicone rubber, or fluoro rubber. A thin release layer made of PFA, PTFE or the like may be provided on the surface of the elastic layer. The pressure roller 22 is in pressure contact with the fixing belt 21 to form a desired fixing nip between the two members. Further, the pressure roller 22 is provided with a gear engaged with the drive gear of the first drive motor 91 (first drive means), and the pressure roller 22 is rotationally driven in the arrow direction (clockwise direction) in FIG. Be done.

When the elastic layer of the pressure roller 22 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced, so the load on the fixing member 26 is reduced. can do. Furthermore, the heat insulation of the pressure roller 22 is enhanced, and the heat of the fixing belt 21 is less likely to move to the pressure roller 22 side, so the heating efficiency of the fixing belt 21 is improved.
Further, in the present embodiment, the diameter of the fixing belt 21 is formed to be substantially equal to the diameter of the pressure roller 22, but the diameter of the fixing belt 21 is formed to be smaller than the diameter of the pressure roller 22. You can also In that case, since the curvature of the fixing belt 21 at the nip portion is smaller than the curvature of the pressure roller 22, the sheet P delivered from the nip portion is easily separated from the fixing belt 21.

Further, in the present embodiment, the fixing member 26 in sliding contact with the inner circumferential surface of the fixing belt 21 is concave so that the surface (sliding surface) facing the pressure roller 22 follows the curvature of the pressure roller 22. Is formed. As a result, the sheet P is sent out from the fixing nip portion so as to conform to the curvature of the pressure roller 22, so that the problem that the sheet P after the fixing process is not adsorbed to the fixing belt 21 and separated does not occur. Can.
In the present embodiment, the fixing member 26 forming the fixing nip portion is formed in a concave shape, but the fixing member 26 forming the fixing nip portion may also be formed in a planar shape. That is, the sliding contact surface (a surface facing the pressure roller 22) of the fixing member 26 can be formed in a planar shape. As a result, the shape of the fixing nip portion becomes substantially parallel to the image surface of the sheet P, and the adhesion between the fixing belt 21 and the sheet P is enhanced, whereby the fixing property is improved. Furthermore, since the curvature of the fixing belt 21 at the exit side of the fixing nip portion is increased, the sheet P delivered from the fixing nip portion can be easily separated from the fixing belt 21.

Hereinafter, the normal operation of the fixing device 20 configured as described above will be briefly described.
When the power switch of the apparatus main body 1 is turned on, power is supplied to the heater 25 and rotation driving of the pressure roller 22 in the direction of the arrow in FIG. 2 is started. As a result, the fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 22 at the fixing nip portion.
Thereafter, the sheet P is fed from the sheet feeding unit 12, and the 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 conveyed to the nip portion of the fixing belt 21 and the pressure roller 22 in pressure contact. It is inserted.
Then, 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. Thereafter, the sheet P delivered from the fixing nip portion is further conveyed by the auxiliary roller pair 53 (first conveyance roller pair) in the dashed arrow direction after passing between the separation plate 52 and the conveyance guide plate 51. It will be.

  Although the heater 25 is used as a heating unit for heating the fixing belt 21 in the present embodiment, an electromagnetic induction coil or a resistance heating element can also be used as a heating unit for heating the fixing belt. Further, in the present embodiment, the fixing member (fixing belt 21) is heated from the inner peripheral surface side by the heating unit, but may be configured to heat the fixing member 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 in the present embodiment is directed to the fixing nip portion (the portion where the fixing belt 21 and the pressure roller 22 are in pressure contact). On the downstream side in the transport direction, an auxiliary roller pair 53 as a first transport roller pair is installed. The auxiliary roller pair 53 (first conveyance roller pair) is rotationally driven along the conveyance direction by the first drive motor 91 as a first drive unit, and conveys the sheet P delivered from the fixing nip portion in the conveyance direction. .

Specifically, referring to FIG. 2, FIG. 4 and the like, the auxiliary roller pair 53 (first conveying roller pair) is configured of a drive roller 53a and a driven roller 53b. In the driving roller 53a, a roller portion made of a solid rubber material having a high coefficient of friction such as silicon, EPDM, urethane, fluororubber or the like on a shaft portion 53a1 (core metal) made of a metal material has a width direction 3 is divided and formed at a plurality of places in FIG. 3), and the driven gear 96 is installed on one end side of the shaft portion 53a1. The driven gear 96 of the drive roller 53a is in mesh with a drive gear 95 installed on the motor shaft of the first drive motor 91 (first drive means).
The driven roller 53b has an elastic layer (tube) having a low friction coefficient and a thickness of about 30 to 300 μm and made of PFA, ETFA, FEP, etc. on a hollow shaft (core metal) made of a metal material. It is formed extending in a direction, and is urged by a spring (not shown) so as to be in pressure contact with the roller portion of the drive roller 53a to form a nip portion. By forming the shaft portion of the driven roller 53 b in a hollow structure, the heat capacity can be 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, the toner is less likely to adhere to the surface of the driven roller 53b.

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

Here, in the present embodiment, in the first driving means, the auxiliary roller pair 53 (first conveying roller pair) rotates only in the forward direction (in the direction of the arrow in FIG. 2) along the transport direction and reverses. There is provided a one-way clutch mechanism for transmitting the driving force to the auxiliary roller pair 53 so as not to rotate. Specifically, the driven gear 96 installed on the drive roller 53 a is a one-way gear in which the one-way clutch 97 is integrally formed on the inner peripheral portion, and the driven gear 96 is inserted into the shaft 53 a 1 via the one-way clutch 97 It is in a state of being With such a configuration, the drive roller 53a rotates in the direction only when the clockwise drive force in FIG. 2 acts, and does not rotate but idles when the counterclockwise drive force acts. As a result, good transportability of the sheet P is maintained, and when the sheet P jams at the position of the fixing device 20 (paper jam), the sheet P is pulled out in the reverse direction of the transport direction by the user. Can be prevented.
In the present embodiment, the auxiliary roller pair 53 also functions as a curl correcting unit that corrects the curl of the sheet P generated at the position of the fixing device 20 together with the guide member 55 described later. explain in detail.

  Further, in the image forming apparatus 1 according to the present embodiment, a discharge roller pair 41 as a second conveyance roller pair is disposed downstream of the auxiliary roller pair 53 (first conveyance roller pair) in the conveyance direction. ing. The paper discharge roller pair 41 (second conveyance roller pair) is composed of a drive roller and a driven roller, and is rotationally driven along the conveyance direction by a second drive motor 92 as a second drive unit. The conveyed sheet P is conveyed in the conveyance direction and discharged to the outside of the image forming apparatus main body 1. Each of the drive roller and the driven roller in the discharge roller pair 41 has a roller portion made of a rubber material, a resin material or the like formed on the shaft portion (core metal), and the second drive motor 92 By driving the drive rollers connected thereto to rotate, the respective rollers rotate in the direction of the arrow in FIG. 2 to hold and convey the sheet P.

Here, in the present embodiment, the second drive motor 92 (second drive means) is configured to be able to change the linear velocity V at the nip portion of the discharge roller pair 41 (second conveyance roller pair). . Specifically, the second drive motor 92 (second drive means) is a motor of variable rotation speed type, and the control unit can control the rotation speed of the discharge roller pair 41 (drive roller) appropriately. Is configured.
Then, when the thickness of the sheet P is equal to or less than the predetermined value X, the second drive motor 92 (second drive means) is after the rear end of the sheet P passes through the fixing nip portion and the auxiliary roller pair It is controlled so that the linear velocity V of the discharge roller pair 41 mentioned above is accelerated before reaching the nip portion 53 (first conveyance roller pair). On the other hand, when the thickness of the sheet P exceeds the predetermined value X, the linear velocity V of the discharge roller pair 41 is increased after the rear end of the sheet P passes through the nip portion of the auxiliary roller pair 53. As described above, the second drive motor 92 is controlled.

Specifically, when a sheet P such as plain paper or thin paper other than thick paper having a thickness (paper thickness) equal to or less than a predetermined value X (in this embodiment, the basis weight is 160 g / m ² ) is passed 5A, the linear velocity V (rotational speed) of the discharge roller pair 41 is increased from V1 to V2 after the trailing edge of the sheet P passes through the fixing nip portion. Control. On the other hand, when a thick sheet whose thickness (paper thickness) exceeds a predetermined value X (in the present embodiment, the basis weight is 160 g / m ² ) is passed as the sheet P, as shown in FIG. As shown in B), after the trailing edge of the sheet P passes through the nip portion of the auxiliary roller pair 53 (first conveying roller pair), the linear velocity V (rotational speed) of the sheet discharge roller pair 41 changes from V3 to V4. It is controlled to be accelerated. That is, when the sheet P to be fed is thick paper, the timing at which the speed of the discharge roller pair 41 is accelerated is controlled to be later than that in the case where it is not.

More specifically, when a sheet P other than thick paper is passed in the present embodiment, the normal linear velocity V1 of the discharge roller pair 41 (before acceleration is performed, as shown in FIG. 5A). Linear velocity and the linear velocity after the sheet P is discharged at an accelerated linear velocity V 2) is set to 256 mm / s, and the linear velocity takes 17.2 ms. The speed is increased to V2 (450 mm / s).
Further, when a thick sheet P is passed in the present embodiment, the normal linear velocity V3 of the discharge roller pair 41 (the linear velocity before acceleration is shown in FIG. 5B). , And the linear velocity after the sheet P is discharged at an accelerated linear velocity V4 is set to 73 mm / s, taking 17.2 ms, linear velocity V2 (108 mm / 108 mm / s). It is set to be accelerated to s).

Here, the reason why the linear velocities V1 and V2 in FIG. 5A and the linear velocities V3 and V4 in FIG. 5B do not match is that the thickness of the sheet P has a predetermined value X in the present embodiment. (When the sheet P having a basis weight of 160 g / m ² or more is passed), the process linear velocity in the image forming apparatus main body 1 (photosensitive drum in the image forming process described above) This is because the linear velocity of 5Y, 5M, 5C, 5K and the intermediate transfer belt 78) and the conveyance speed of the sheet P are controlled to be overall low. Such control is referred to as “cardboard mode”, and in the present embodiment, the process linear velocity (and the conveyance speed of the sheet P) is from 256 mm / s to 73 mm when paper is normally passed. It will be decelerated to / s.
By performing the “thick paper mode” in this manner, when the fixing process is performed on the thick paper in the fixing device 20, sufficient heat and pressure can be applied to the thick paper in the fixing nip portion. The problem that the fixing failure occurs in the fixed image above is reduced.
In the image forming apparatus in which the above-described "cardboard mode" is not executed, the linear velocities V1 and V2 in FIG. 5A and the linear velocities V3 and V4 in FIG. 5B match. It will be set.

As described above, after the rear end of the sheet P passes the position of the fixing device 20 (fixing nip portion) (after the fixing process is performed), the linear velocity in the nip portion of the sheet discharge roller pair 41 is increased. By controlling to, it is possible to improve the print productivity as a whole, such as the first print speed being accelerated.
Further, in the present embodiment, even if the auxiliary roller pair 53 is provided on the downstream side of the fixing device 20 (fixing nip portion) and on the upstream side of the sheet discharge roller pair 41 (second conveying roller pair) Since the timing to accelerate the discharge roller pair 41 is variable according to the thickness of the sheet P, the sheet P is jammed (mainly a slip jam) at the position of the auxiliary roller pair 53. Can be reduced.

Specifically, in order to accelerate the sheet discharge roller pair 41 and enhance the print productivity (sheet discharge speed) while maintaining a good fixing process, the rear end of the sheet P is the fixing device 20 (fixing nip portion). It is preferable to accelerate the paper discharge roller pair 41 uniformly at the timing immediately after passing the position. At this time, when the thickness of the sheet P is not so thick (in the case where it is the predetermined value X or less), the one-way clutch 97 pinches the auxiliary roller pair 53 configured to rotate only in one direction. Even if the sheet P is pulled in the transport direction by the accelerated discharge roller pair 41, it behaves as it slips through the nip portion of the auxiliary roller pair 53 where a load corresponding to idling torque is generated. As a result, jamming (slip jamming) does not occur at the position of the auxiliary roller pair 53. However, when the thickness of the sheet P is increased to a certain extent (when it exceeds the predetermined value X), the one-way clutch 97 clamps the auxiliary roller pair 53 configured to rotate only in one direction. When the sheet P is pulled in the transport direction by the accelerated discharge roller pair 41, it slips through the nip portion of the auxiliary roller pair 53 which causes a load corresponding to idling torque. Without this, jamming (slip jamming) occurs at the position of the auxiliary roller pair 53.
On the other hand, in the present embodiment, when the thickness of the sheet P is increased to a certain extent (when it exceeds the predetermined value X), after the sheet P passes the position of the auxiliary roller pair 53 Since the discharge roller pair 41 is accelerated, the occurrence of a jam (slip jam) at the position of such an auxiliary roller pair 53 can be reliably reduced.
Further, in the present embodiment, as shown in FIG. 5, when the linear velocity V of the discharge roller pair 41 is increased, the linear velocity changes from V1 (or V3) to V2 (or V4) at a stretch. Since the acceleration is performed while gradually increasing from V1 (or V3) to V2 (or V4) over a short period of time instead of acceleration, good transportability of the sheet P is maintained. become.

In the present embodiment, according to the thickness of the sheet P described above for the image forming apparatus 1 in which the one-way clutch mechanism (one-way clutch 97) is provided in the first drive means for rotationally driving the auxiliary roller pair 53. The control for changing the speed-up timing of the discharge roller pair 41 is used.
On the other hand, even for an image forming apparatus in which the one-way clutch mechanism (one-way clutch) is not provided in the first drive means for rotationally driving the auxiliary roller pair, the discharge roller pair is also provided according to the sheet thickness described above. It is possible to use control to vary the acceleration timing of
Also in such a case, when the sheet nipped by the auxiliary roller pair is pulled in the transport direction by the accelerated discharge roller pair in accordance with the thickness of the sheet, Since the frictional resistance of the pair of auxiliary rollers acting on the sheet is different and the occurrence frequency of the slip jam is different, substantially the same effect as that of the present embodiment can be obtained.

Further, in the present embodiment, the thickness of the sheet P described above is provided on the operation unit (a personal computer communicably connected to the image forming apparatus 1 by the user, or the exterior of the image forming apparatus 1). And the like, etc.) based on the information on the sheet P. That is, the speed-up timing of the discharge roller pair 41 is varied based on the information on the sheet P input to the operation unit by the user.
5A and 5B, the timing at which the discharge roller pair 41 is accelerated is such that the trailing edge of the sheet P is the nip between the fixing nip and the auxiliary roller pair 53 (first conveying roller pair). The timing is set to be slightly later than the timing at which the sheet P passes through the sheet P. The sheet P is discharged before the trailing edge of the sheet P passes the fixing nip and the auxiliary roller pair 53 while securing a control margin. This is to prevent the roller pair 41 from being accelerated.

Here, in the present embodiment, the first drive unit (first drive motor 91) that rotationally drives the auxiliary roller pair 53 is configured to also drive (rotationally drive) the fixing device 20 (pressure roller 22). It is done. That is, the driving force of the first drive motor 91 is configured to be transmitted to the shaft portion of the pressure roller 22 via a gear train (not shown). The first drive means is configured such that the linear velocity at the fixing nip portion and the linear velocity at the nip portion of the auxiliary roller pair 53 are substantially the same.
The second drive unit (second drive unit) that rotationally drives the discharge roller pair 41 (second conveyance roller pair) has a linear velocity V1 (or V2) when the discharge roller pair 41 is not accelerating. Is controlled to be substantially the same as the linear velocity at the fixing nip portion and the linear velocity at the nip portion of the auxiliary roller pair 53. As a result, the conveyance speed of the sheet P in the conveyance path until the discharge roller pair 41 is accelerated can be maintained constant.

Here, referring to FIGS. 2 to 4 and the like, image forming apparatus 1 in the present embodiment is located downstream of auxiliary roller pair 53 (first conveying roller pair) in the conveyance direction, In the vicinity of the roller pair 53, a guide member 55 is installed.
The guide member 55 has a first position (the position shown in FIG. 4) which does not block an imaginary tangent (which is a tangent shown by a dot and dash line in FIGS. 2 and 4) passing through the nip portion of the auxiliary roller pair 53. While guiding the conveyance of the sheet P delivered from the auxiliary roller pair 53 by protruding so as to intercept the virtual tangent, the reverse curl in the direction opposite to the direction of the curl formed at the fixing nip portion with respect to the sheet P The second position (the position shown in FIG. 2) for forming and correcting the curl is configured to be movable by the moving mechanism 93.

More specifically, the guide member 55 has substantially triangular rib-like members formed at a plurality of positions corresponding to the roller portion and the roller portion of the drive roller 53a (auxiliary roller pair 53) on the support shaft 55b. It is rotatably installed relative to the shaft portion 53a1 with the bearing 55a installed on the shaft portion 53a1 of the drive roller 53a as the center of rotation.
Further, referring to FIG. 3, the guide member 55 is provided with a spring 94 for urging the guide member 55 in the counterclockwise direction of FIG. 2 and FIG. 4 about the shaft 53a1 (bearing 55a) as a rotation center. It is connected. Moreover, although illustration is abbreviate | omitted, in the guide member 55, the protrusion formed in the apparatus main body 1, without the guide member 55 urged | biased by the spring 94 rotating in the counterclockwise direction of FIG. 2, FIG. 4 without restriction. A stop is formed which engages the part and is locked in such a way that its rotation is restricted in the position shown in FIG.
Further, referring to FIG. 3, in the guide member 55, the guide member 55 is rotated in the clockwise direction in FIGS. 2 and 4 with the shaft portion 53a1 (bearing 55a) as the rotation center so as to resist the biasing force of the spring 94. A solenoid 93 is connected to bias the motor.
That is, the solenoid 93, the spring 94, etc. function as a moving mechanism for rotating the guide member 55 between the first position shown in FIG. 4 and the second position shown in FIG.

Then, when the thickness of the sheet P is equal to or less than the predetermined value X, the moving mechanism configured in this manner causes the guide member 55 to be at least from before the sheet P reaches the position of the guide member 55 until after passing through. It is controlled to move to the second position. Specifically, when a sheet P (having a basis weight of 160 g / m ² or less) having a thickness equal to or less than a predetermined value X is passed, the control unit turns off the energization of the solenoid 93 Then, the guide member 55 is pivoted to the pivoting position of FIG.
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 the sheet P passes through. It is controlled to move. Specifically, when the sheet P whose thickness exceeds the predetermined value X (the basis weight is the sheet P exceeding 160 g / m ² ) is fed, the control unit turns on the solenoid 93 in the on state As a result, the guide member 55 is pivoted to the pivoting position of FIG.

Such control is performed because a sheet P such as plain paper or thin paper having a thickness equal to or less than a predetermined value X is weak in stiffness and receives pressure in the fixing nip portion during the fixing process and curls (in the present embodiment) As described above, curling in a direction along the curvature of the pressure roller 22 is likely to occur, and the thick sheet P having a thickness exceeding a predetermined value X is strong in stiffness and This is because curling is less likely to occur even under pressure at the fixing nip portion. Therefore, when a sheet P such as plain paper or thin paper having a thickness equal to or less than a predetermined value X is passed, the sheet P (curled sheet P) delivered from the fixing nip portion is sent. While the sheet is nipped and conveyed by the auxiliary roller pair 53, the guide member 55 exerts a force that causes it to curve in the reverse curl direction to correct the curl.
Further, in addition to the fact that the sheet P of thick paper whose thickness exceeds the predetermined value X is hardly curled as described above, when the guide member 55 is rotated to the position of FIG. The strength causes the force of sliding contact with the guide member 55 to be too strong, and a rubbing mark is formed on the back surface of the sheet P, and the guide member 55 is abraded. Also in this case, when a thick sheet P whose thickness exceeds the predetermined value X is passed, the guide member 55 is rotated to a position not interfering with the sheet P.

Here, in the present embodiment, as described above, when a sheet P such as plain paper or thin paper having a thickness equal to or less than a predetermined value X is passed, the rear end of the sheet P is a fixing nip portion. Since the linear velocity V of the discharge roller pair 41 is increased at the timing of removal, the sheet P nipped by the auxiliary roller pair 53 is pulled in the transport direction by the increased discharge roller pair 41. While the sheet P is pressed by the guide member 55 and curled, the sheet P behaves as if it slips through the nip portion of the auxiliary roller pair 53, so a jam (slip jam) at the position of the auxiliary roller pair 53 Does not occur.
Further, as described above, when a thick sheet P whose thickness exceeds the predetermined value X is passed, the sheet P is discharged at a timing when the rear end of the sheet P passes through the nip portion of the auxiliary roller pair 53. The linear velocity V of the roller pair 41 is increased, and the guide member 55 is moved to a position not in sliding contact with the sheet P. Therefore, a large load is generated on the sheet P, and the position of the auxiliary roller pair 53 The sheet P is discharged by the accelerated discharge roller pair 41 without causing a jam (slip jam) at this time.

In the present embodiment, as described above, when the solenoid 93 is in the off state, the rotational position of the guide member 55 is configured to be the position (second position) of FIG. . This is because the second position (the position shown in FIG. 2) for performing the curl correction needs to be improved in position accuracy as compared to the first position (the position shown in FIG. 4) merely avoiding the interference with the sheet P. It is because there is. That is, the position accuracy of the second position can be relatively easily enhanced by engaging the guide member 55 with the projection of the apparatus main body 1 and enhancing the accuracy of the configuration that limits the rotation thereof.
Further, in the present embodiment, as shown in FIG. 2, when the guide member 55 is rotated to the second position, a portion of the guide member 55 is a roller portion of the drive roller 53a (auxiliary roller pair 53) The guide member 55 is configured to be close to the drive roller 53a (auxiliary roller pair 53). When configured in this manner, the sheet P nipped and conveyed by the auxiliary roller pair 53 is compared with the case where the guide member 55 is installed at a position away from the drive roller 53a (auxiliary roller pair 53). On the other hand, the curl correction can be performed efficiently and reliably.

  Further, in the present embodiment, the switching member 45 (branch claw) described above with reference to FIG. 1 and the like is disposed downstream of the guide member 55 in the transport direction and in the vicinity of the guide member 55. There is. The switching member 45 includes a sheet discharge conveyance path K2 for guiding the sheet P to the position of the sheet discharge roller pair 41, and a double-sided conveyance path K5 (switch It is for switching to either of the relay conveyance path K3 for leading to the back conveyance path K4), and is configured to be rotatable around 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 subjected to the fixing process on the front surface passes, switching is performed. The sheet 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 movement mechanism 93, as shown in FIG. 6B. 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, the relay conveyance path K3 is closed, and the guide member 55 is moved to the first position by the moving mechanism 93. Be moved.
That is, in the double-sided printing mode, the switching member 45 is pivoted so as to appropriately switch the conveyance path, but the guide member 55 is always at the first position (a position not interfering with the sheet P regardless of the thickness of the sheet P The solenoid 93 is controlled to be in the on state so that it is turned to the

Such control is performed in the double-sided printing mode, the fixing process is performed on the front side, and the sheet P after passing through the fixing nip is curled, but the fixing process on the back side is performed. As a result, a curl that offsets the curl is formed on the sheet P after passing through the fixing nip portion. That is, at the time of double-sided printing, even if the sheet P is not subjected to the curl correction by the guide member 55, the sheet P finally discharged by the sheet discharge roller pair 41 is subjected to the curl correction.
Further, when the sheet P after passing through the fixing nip portion is subjected to a sliding contact with the guide member 55 after the fixing process to the back surface is performed, the toner image already fixed on the front surface of the sheet P This is because an abnormal image such as an image blur or a glossy streak is generated if it is scraped off.
Even when the double-sided printing mode is performed as described above, as shown in FIG. 6B, when the sheet P for which the fixing process to the rear surface is completed passes the sheet discharge conveyance path K2, Control for varying the speed-up timing of the discharge roller pair 41 according to the thickness of the sheet P described with reference to FIG. 5 and the like is performed. Thus, jamming at the position of the auxiliary roller pair 53 can be reduced.

As described above, in the present embodiment, when the thickness of the sheet P is equal to or less than the predetermined value X, the second drive motor 92 (second drive means) fixes the rear end of the sheet P to the fixing nip portion. Control so that the linear velocity V of the discharge roller pair 41 (second conveyance roller pair) is accelerated before reaching the nip portion of the auxiliary roller pair 53 (first conveyance roller pair) after passing through When the thickness of the sheet P exceeds the predetermined value X, the linear velocity V of the discharge roller pair 41 is increased after the rear end of the sheet P passes the nip portion of the auxiliary roller pair 53. To be controlled.
Thus, the auxiliary roller pair 53 is provided on the downstream side of the fixing nip portion and on the upstream side of the paper discharge roller pair 41, and the linear velocity by the paper discharge roller pair 41 is increased to improve print productivity. Even in the case where control is performed to accelerate, it is possible to prevent a problem in which the sheet P is jammed at the position of the auxiliary roller pair 53 is less likely to occur.

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

Further, in the present embodiment, the present invention is applied to the image forming apparatus 1 in which the auxiliary roller pair 53 is used as the first conveyance roller pair, and the discharge roller pair 41 is used as the second conveyance roller pair. did. On the other hand, in the case where the speed increase control is performed by the second conveyance roller pair even in the case of an image forming apparatus in which different roller pairs are used as the first conveyance roller pair and the second conveyance roller pair, respectively. Can apply the present invention.
And even in such a case, substantially the same effect as that of the present embodiment can be obtained.

  It is to be noted that the present invention is not limited to the present embodiment, and it is apparent that the present embodiment can be appropriately modified within the scope of the technical idea of the present invention other than suggested in the present embodiment. is there. Further, the number, the position, the shape, and the like of the constituent members are not limited to the present embodiment, and the number, the position, the shape, and the like suitable for practicing the present invention can be set.

1 Image forming device (image forming device main body),
20 fixing devices,
21 Fixing belt (fixing member),
22 pressure roller (pressure member),
41 Ejection roller pair (second conveying roller pair),
45 switching members,
51 transport guide plate,
52 separate plates,
53 Auxiliary roller pair (first conveying roller pair),
53a drive roller, 53b driven roller,
53a1 shaft (rotation center),
55 guide members,
55a bearing (rotation center), 55b support shaft,
91 first drive motor (first drive means),
92 second drive motor (second drive means),
93 Movement mechanism (solenoid),
94 Spring (biasing member),
97 one-way clutch,
K2 delivery conveyance path, K3 relay conveyance path, K4 switchback conveyance path,
K5 Double-sided transport path, P sheet (recording medium).

Patent No. 3402895 Patent No. 3282257

Claims (6)

A fixing device configured to convey a sheet in a predetermined conveyance direction to a fixing nip portion in which a fixing member and a pressure member are in pressure contact, and to fix a toner image carried on the surface of the sheet;
The sheet is disposed downstream of the fixing nip portion in the conveying direction, and is conveyed to the conveying direction by being driven to rotate along the conveying direction by the first driving unit and fed from the fixing nip portion. A first pair of transport rollers,
The sheet is disposed downstream of the first conveyance roller pair in the conveyance direction, and is driven to rotate along the conveyance direction by a second driving unit, and the sheet delivered from the first conveyance roller pair is A second transport roller pair that transports in the transport direction;
Equipped with
The second driving means is
The linear velocity at the nip portion of the second conveyance roller pair can be varied.
When the thickness of the sheet is equal to or less than a predetermined value, the linear velocity is increased after the rear end of the sheet passes through the fixing nip and before reaching the nip of the first conveyance roller pair. The linear velocity is controlled to be accelerated after the rear end of the sheet passes through the nip portion of the first conveyance roller pair when the thickness of the sheet exceeds the predetermined value. An image forming apparatus characterized by being controlled to   The first drive means transmits a driving force to the first transport roller pair so that the first transport roller pair rotates only in the forward direction along the transport direction and does not rotate in the reverse direction. The image forming apparatus according to claim 1, further comprising a clutch mechanism. A first position installed downstream of the first transport roller pair in the transport direction and in the vicinity of the first transport roller pair and not blocking an imaginary tangent passing through the nip portion of the first transport roller pair And guiding the conveyance of the sheet delivered from the pair of first conveyance rollers while protruding so as to intercept the imaginary tangent, while the direction opposite to the direction of the curl formed in the fixing nip portion with respect to the sheet A second position for correcting the curl by forming a reverse curl, and a guide member configured to be movable by the movement mechanism,
The movement mechanism is
When the thickness of the sheet is equal to or less than the predetermined value, the guide member is moved to the second position at least from before the sheet reaches the position of the guide member until after the sheet passes.
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 until after the sheet passes. An image forming apparatus according to claim 1 or 2. The second conveyance roller pair is a discharge roller pair that discharges the sheet to the outside of the image forming apparatus main body.
The sheet is disposed at the downstream side of the conveying direction with respect to the guide member and in the vicinity of the guide member, and the conveyance path of the sheet delivered from the fixing nip portion is the sheet at the position of the discharge roller pair. And a switching member for switching between the sheet discharge conveyance path for guiding the sheet to the relay conveyance path for guiding the sheet to the double-sided conveyance path.
In the double-sided printing mode, regardless of the thickness of the sheet, when the sheet subjected to the fixing process on the front surface passes, the sheet discharge conveyance path is closed by the switching member and the relay conveyance path is opened. At the same time, the guide member is moved to the first position by the moving mechanism, and the sheet discharge conveyance path is opened by the switching member when the sheet subjected to the fixing process on the rear surface passes. The image forming apparatus according to claim 3, wherein the relay conveyance path is closed, and the guide member is moved to the first position by the movement mechanism.   4. The method according to claim 1, wherein when the thickness of the sheet exceeds the predetermined value, the process linear velocity in the main body of the image forming apparatus and the conveyance speed of the sheet are controlled to be low as a whole. An image forming apparatus according to any one of Items 4 to 5. The first drive means is also configured to drive the fixing device,
The second driving means is configured to calculate the linear velocity at the fixing nip portion when the second conveying roller pair is not accelerated, the linear velocity at the fixing nip portion, and the linear velocity at the nip portion of the first conveying roller pair. The image forming apparatus according to any one of claims 1 to 5, which is controlled to be the same.

Images