JP6544108B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a facsimile, or a printer.

  In an image forming apparatus using an electrophotographic method, an electrostatic latent image is formed in an image forming unit, and then developed with toner as a developer to make a visible image as a toner image etc. The toner image is transferred onto a recording sheet, and then the fixing device fixes the image onto the recording sheet.

  The fixing device includes a heating member and a pressure roller, which are in pressure contact with each other to form a fixing nip portion, and the fixing nip portion passes and passes a recording sheet carrying an unfixed toner image. The toner image is configured to be fixed to the recording sheet by applying pressure and heating.

  In this type of heat fixing, since there is a temperature difference between the heating member and the pressure roller, when the recording paper passes through the fixing nip portion, the front and back of the recording paper (the surface of the heating member and the pressure roller There is a temperature difference on the back of the side). Specifically, the temperature of the surface of the recording paper in contact with the heating member is higher than the temperature of the back surface of the recording paper in contact with the pressure roller.

  As a result, after passing through the fixing nip portion, the water contained in the recording paper evaporates more from the front side, and water movement from the back side to the front side occurs, so the front side is more than the back side. As a result, the elongation of the paper fibers on the front side becomes larger than that on the back side, and a phenomenon that the recording paper curls to the back side (hereinafter referred to as "back curl") occurs.

  In particular, from the viewpoint of speeding up energy saving / warming up, a fixing device has been developed recently, in which the heat capacity of the heating member is reduced and the temperature rise is quick. In such a fixing device, since it becomes possible to pass the sheet before the pressure roller side warms up, the temperature difference between the heating member and the pressure roller becomes larger, and the temperature difference between the front and back of the recording sheet at the time of fixing becomes It is easy to grow. For this reason, back curling occurring on the recording sheet passing through the fixing nip portion is becoming large. In such a fixing device, there is a problem that the prescribed number of loaded sheets can not be discharged onto the sheet discharge tray or the load itself on the sheet discharge tray is disturbed by discharging the sheet in the state of large back curl. Do. Then, the invention which eliminates a back curl conventionally is proposed (refer to patent documents 1, 2, and 3).

  The image forming apparatus disclosed in Patent Document 1 passes the fixing nip portion along a conveyance path between a first conveyance roller and a second conveyance roller, which are sequentially disposed at different positions downstream of the fixing unit. A guide member is provided to guide the recording sheet while curving the recording sheet in the direction opposite to the direction of the back curl generated thereby. In this image forming apparatus, by setting the conveyance speed of the recording paper by the second conveyance roller to a large value as compared with the first conveyance roller, the guide in which the recording paper is curved in the opposite direction to the back curling direction The sheet is conveyed while being pressed against the member, and the curl of the recording sheet is corrected.

  The transfer sheet curl correction device of the image forming apparatus disclosed in Patent Document 2 uses a pair of roller members and a pair of roller members in the conveyance path on the downstream side of the fixing device as back curl correction means. A guide member is provided which guides the paper on the opposite side while curving in the direction opposite to the direction of the back curl. In this image forming apparatus, the curling of the recording sheet is corrected by bending in the direction opposite to the back curl that is generated on the recording sheet by passing through the fixing nip portion.

  In the discharge device disclosed in Patent Document 3, the guide member is movably disposed in contact with the back side of the paper between the fixing nip portion and the discharge nip provided on the downstream side of the fixing nip portion, and a back generated in fixing The curling of the recording paper is corrected by changing the contact force by the stiffness of the paper while bending in the direction opposite to the curling.

  However, the following problems occur with the conventional back curl correction method described above.

  First, in the techniques disclosed in Patent Documents 1 and 2, the recording paper is always forcedly pressed by the guide member and curled in the reverse direction to the back curl. For this reason, for example, in the case of a thick paper sheet, back curling that the recording paper curls to the back side does not occur in the fixing device, so when the guide plate is always at the first position, the guide plate causes face curl in the opposite direction. Become. In addition, since the contact force between the guide plate and the recording paper is strong, damage (scratch) / guide member wear occurs on the back surface of the paper by the guide member. Furthermore, since the paper rigidity is high, when the tip comes out from the roller pair and the tip contacts the guide member, the tip is bent or the like occurs, which makes it difficult to stabilize the conveyance.

  Next, the technology disclosed in Patent Document 3 is configured such that the guide member that deforms the recording sheet in a correct manner can move in the retraction direction due to the stiffness of the recording sheet, so even if the guide member is retracted, There is no change in being conveyed while in contact with the recording paper. Therefore, when double-sided sheet feeding is performed, there is an image of the first surface on the back surface of the recording paper in contact with the guide member, and the image surface and the guide member come in contact and the toner image is damaged. There is also a problem.

  The present invention has been made to solve the problems as described above, and it is possible to achieve both the reduction of back curling generated during fixing and the conveyance stabilization, and to reduce the damage to the recording paper / toner image. It is an object of the present invention to provide an image forming apparatus capable of suppressing unnecessary vibration, generation of noise accompanying vibration, and generation of banding image.

In order to solve the problems described above, the image forming apparatus according to the present invention is resilient on the surface to which the rotational driving force is transmitted from the drive source through the drive transmission means from the recording sheet on which the image is transferred by the image forming unit. A fixing device configured to fix an image on the recording sheet through a fixing nip portion formed by a pressure roller including a layer, a fixing member to which heat obtained from a fixing heating source is transmitted, and a delivery device from the fixing device An image forming apparatus comprising: a sheet conveyance path branching unit which sets the conveyance destination of the recording sheet to either an external discharge path or a reverse path for double-sided printing; A pair of transport assisting rollers, disposed between the apparatus and the sheet transport path branching unit, for transporting the recording sheet delivered from the fixing device toward the downstream side in the transport direction; the transport assist roller pair and the sheet A guide member disposed between the feed path branching means and on the opposite side of the latest image fixing surface of the recording sheet and guiding the recording sheet delivered from the conveyance auxiliary roller pair to the outside discharge path; A first position for guiding the guide member to a surface opposite to the latest image fixing surface of the recording sheet delivered from the transport auxiliary roller pair and guiding the guide member to the external discharge path; It is held by the guide member moving means set to any of the second positions not in contact, the pressure roller holding member holding the pressure roller, and the pressure roller holding member, and is transmitted to the pressure roller that the rotational driving force, and a rotational drive force transmission mechanism for transmitting the one conveying auxiliary rollers on the same side as the pressure roller of the transport assisting rollers, the sent from the fixing nip portion Record The pressure roller holding member is capable of holding a guide member which can be opened and closed to a position for guiding the transfer sheet to the transfer auxiliary roller pair and a position for removing the interrupted recording sheet; One is held by the guide member .

  According to the present invention, it is possible to effectively reduce the back curling generated on the recording sheet by fixing heating and reduce the damage to the recording sheet and the toner image, and the conveyance stabilization of the recording sheet at the time of backcurling removal Thus, it is possible to provide an image forming apparatus capable of suppressing generation of noise due to unnecessary vibration and vibration, suppressing generation of a banding layer, and reducing the cost of a drive system of means for removing back curl.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a schematic configuration diagram of the image fixing device according to the embodiment of the present invention when the fixing device is in the back curl correction state. FIG. 6 is a schematic configuration diagram when the fixing device is in the non-back curled state in the image forming apparatus according to the embodiment of the present invention. It is the figure which looked at the pressure side separation conveyance member in FIG. 3, a drive roll, and a guide member in the arrow IV direction. FIG. 6 is a partial perspective view of the guide member in a state where it is set at the first position in the image forming apparatus according to the embodiment of the present invention, as viewed from the conveyance path side. FIG. 6 is a partial perspective view of the guide member in a state where it is set at the second position in the image forming member according to the embodiment of the present invention, as viewed from the conveyance path side. FIG. 6 is a partial view of the guide member in a state in which the guide member moving unit sets the second position in the image forming apparatus according to the embodiment of the present invention, as viewed from the conveyance path side. FIG. 6 is a partial front view of the guide member in a state where it is set at the first position in the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a partial front view of the guide member in a state where it is set at a second position in the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a view of a branch member and a guide member of the image forming apparatus according to the embodiment of the present invention as viewed from the conveyance path side. FIG. 6A is a schematic configuration diagram of the positional relationship between the branch member and the guide member in the image forming apparatus according to the embodiment of the present invention, and FIG. When a thick recording sheet is used in the single-sided sheet passing mode, (c) is the first side of the recording sheet in the double-sided sheet passing mode, and (d) is the second side of the recording sheet in the double-sided sheet passing mode. Indicates paper times. FIG. 7 is a view for explaining the influence of the crossing angle between the recording sheet conveyance direction and the guide member in the correction nip portion of the image forming apparatus according to the embodiment of the present invention on back curl correction. FIG. 3 is a schematic configuration view for explaining the positional relationship between a pressure roller, a drive roller, and a gear transmission mechanism in the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a partial perspective view for explaining the positional relationship between the pressure roller and the gear transmission mechanism in the image forming apparatus according to the embodiment of the present invention. FIG. 2 is a partial perspective view for explaining the positional relationship between a pressure roller, a drive roller, and a gear transmission mechanism in the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is a color laser printer, and includes an image forming unit A, a sheet feeding unit B, a fixing device 20, and a pair of paper discharge rollers 13. A sheet discharge tray 14, a pair of reversing rollers 16, a duplex unit 17 and the like are provided.

  The image forming unit A includes four image forming units 4Y, 4M, 4C, and 4K, an exposure device 9, and a transfer device 3 and the like. In the image forming apparatus 1, a back curl correction mechanism C described later is installed in the fixing device 20 as a characteristic configuration.

  The image forming apparatus 1 is provided with four image forming units 4Y, 4M, 4C, and 4K at the central portion of the apparatus main body. The image forming units 4Y, 4M, 4C and 4K contain developers of different colors of yellow (Y), magenta (M), cyan (C) and black (K) corresponding to color separation components of a color image. Other than the above, the configuration is the same.

  Each of the image forming units 4Y, 4M, 4C, 4K supplies a drum-shaped photosensitive member 5 as a latent image carrier, a charging device 6 for charging the surface of the photosensitive member 5, and supplies toner to the surface of the photosensitive member 5. The developing device 7 and the cleaning device 8 for cleaning the surface of the photosensitive member 5 are included.

  In FIG. 1, in the photosensitive member 5, the charging device 6, the developing device 7, and the cleaning device 8, only those provided in the black imaging unit 4K are denoted by reference numerals, and the other imaging units 4Y, 4M, 4C. Is the same as that of the image forming unit 4K for black, so the reference numerals are omitted.

  In the image forming apparatus 1, an exposure device 9 for exposing the surface of the photosensitive member 5 is disposed below the image forming units 4Y, 4M, 4C, and 4K. The exposure device 9 has a laser light source (not shown), a polygon mirror 51a, an f-θ lens 51b, a plurality of reflection mirrors 51c, etc., and irradiates the surface of each photosensitive element 5 with laser light based on image data An electrostatic latent image is formed on the surface of the fifth.

  In the image forming apparatus 1, the transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, and a secondary transfer backup roller 32. Is equipped. The transfer device 3 further includes a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33 and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 travels (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photosensitive member 5 to form a primary transfer nip. Further, a power supply is connected to each primary transfer roller 31 so that a predetermined direct current voltage (DC) or a predetermined alternating current voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, as in the case of the primary transfer roller 31, a power supply is connected to the secondary transfer roller 36 so that a predetermined DC voltage (DC) or alternating current voltage (AC) is applied to the secondary transfer roller 36. It has become.

  The belt cleaning device 35 has a cleaning brush and a cleaning blade arranged to abut on the intermediate transfer belt 30. The waste toner collected by the belt cleaning device 35 is stored in a waste toner storage container through a waste toner transfer hose.

  The image forming apparatus 1 is provided with a bottle storage unit 2 in the upper part of the apparatus main body, and the bottle storage unit 2 can have four toner bottles 2Y, 2M, 2C, and 2K for storing replenishment toner removable. It is attached to. Each toner bottle 2Y, 2M, 2C, 2K supplies toner to each developing device 7 through a replenishment path (not shown) provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7 It has become so.

  The image forming apparatus 1 includes a sheet feeding unit B at the lower part of the apparatus main body. The sheet feeding unit B includes a sheet feeding tray 10 accommodating a recording sheet P (recording sheet) as a recording medium, a sheet feeding roller 11 for discharging the recording sheet P from the sheet feeding tray 10 and the like.

The recording medium includes, in addition to plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, etc. The image forming apparatus 1 may also include a manual sheet feeding mechanism. In the present embodiment, thick paper refers to paper having a basis weight of 160 g / m ² or more.

  In the image forming apparatus 1, a transport path R for disposing the recording sheet P from the sheet feeding tray 10 through the secondary transfer nip and discharging the recording sheet P to the outside of the apparatus main body is disposed in the apparatus main body. The conveyance path R has a pair of registration rollers 12 as timing rollers for conveying the recording sheet P to the secondary transfer nip by measuring the conveyance timing upstream of the position of the secondary transfer roller 36 in the recording sheet conveyance direction. It is done.

  The image forming apparatus 1 presses and heats the recording sheet P carrying the unfixed toner image on the downstream side of the recording sheet conveyance direction with respect to the position of the secondary transfer roller 36 in the apparatus main body to record the toner image A fixing device 20 for fixing on P is provided.

  The image forming apparatus 1 is provided with a pair of paper discharge rollers 13 for discharging the recording paper P to the outside of the apparatus main body on the downstream side of the recording paper conveyance direction of the conveyance path R with respect to the fixing device 20 in the apparatus main body. . Further, the image forming apparatus 1 is provided with a paper discharge tray 14 for stocking the recording paper P discharged to the outside of the apparatus main body on the upper surface portion of the apparatus main body.

  In the image forming apparatus 1, a branch member 15 is provided between the sheet discharge roller 13 and the fixing device 20. The branch member 15 is rotatably provided in the main body of the image forming apparatus 1 and opens in the first state shown in FIG. 1 in the single-sided sheet passing mode in which the image is fixed only on the first surface of the recording sheet P. Is configured as. In the double-sided sheet passing mode in which the image is fixed on the second surface of the recording paper P on which the image is fixed on the first surface, the branching member 15 is closed in the arrow direction from the first state shown in FIG. It is configured to be in the state of 2. The branch member 15 constitutes a sheet conveyance path branch unit in the present invention.

  That is, the branching member 15 selects the recording sheet P conveyed to the downstream side of the fixing device 20 as either an out-of-machine discharge path for discharging the recording sheet P to the discharge tray 14 outside the apparatus main body or a reverse path for double-sided printing. The recording sheet conveyance path branching means of the present invention is configured to be guided uniformly. Here, the external discharge path is a path through which the recording sheet P passes through the sheet discharge roller 13, and the reverse path is a path through which the recording sheet P passes in the duplex unit 17 described later (double-sided reverse path 40). is there.

  Further, the image forming apparatus 1 has a back curl correction mechanism C described later installed between the branch member 15 and the fixing device 20.

  The duplex reversing path 40 includes a reversing roller 16 for switching back the recording paper P provided on the downstream side of the diverging member 15 and a duplex unit 17 provided between the reversing roller 16 and the registration roller 12. . The duplex unit 17 includes transport rollers 42 to 44 and constitutes a reverse path of duplex printing, and switches back the recording paper P after the image is fixed on the first surface by the reverse roller 16 to transport the transport roller 42. The sheet is conveyed to the registration roller 12 through 〜44.

  Next, the basic operation of the image forming apparatus 1 according to the embodiment of the present invention will be described.

  In the image forming apparatus 1, when the image forming operation is started, each photosensitive member 5 in each image forming unit 4Y, 4M, 4C, 4K is rotationally driven clockwise in the figure, and the surface of each photosensitive member 5 is charged 6 uniformly charge to a predetermined polarity. Laser light is irradiated from the exposure device 9 on the surface of each charged photosensitive member 5 to form an electrostatic latent image on the surface of each photosensitive member 5.

  At this time, the image information to be exposed on each photosensitive member 5 is monochrome image information in which a desired full color image is separated into color information of yellow, magenta, cyan and black. Thus, the electrostatic latent images formed on the respective photosensitive members 5 are supplied with toner by the respective developing devices 7, whereby the electrostatic latent images are visualized (visualized) as images.

  In the image forming apparatus 1, when the image forming operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the figure to cause the intermediate transfer belt 30 to run in the direction shown by the arrow in the figure.

  Further, in the image forming apparatus 1, each primary transfer roller 31 and each photosensitive member 5 are applied with the application of a constant voltage or a constant current controlled polarity opposite to the charging polarity of the toner to each primary transfer roller 31. A transfer electric field is formed in the primary transfer nip between them.

  After that, when the image of each color on the photosensitive member 5 reaches the primary transfer nip as the photosensitive members 5 rotate, the image forming apparatus 1 causes the photosensitive members to transfer electric fields formed in the primary transfer nip. The images on 5 are sequentially superimposed and transferred onto the intermediate transfer belt 30.

  Thus, the image forming apparatus 1 carries a full-color image on the surface of the intermediate transfer belt 30. Further, the toner on each photosensitive member 5 that can not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photosensitive member 5 is discharged by the discharging device, and the surface potential is initialized.

  In the image forming apparatus 1, the sheet feeding roller 11 starts rotational driving, and the recording sheet P is sent out from the sheet feeding tray 10 to the conveyance path R. The recording paper P delivered to the conveyance path R is temporarily stopped by the registration roller 12.

  Thereafter, the image forming apparatus 1 starts rotational driving of the registration roller 12 at a predetermined timing, and adjusts the recording sheet P to the secondary transfer nip in accordance with the timing when the image on the intermediate transfer belt 30 reaches the secondary transfer nip. Transport

  At this time, a transfer voltage having a polarity opposite to that of the toner charge polarity of the image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip. Then, the images on the intermediate transfer belt 30 are collectively transferred onto the recording paper P by the transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 which can not be transferred to the recording paper P is removed by the belt cleaning device 35 and conveyed to a waste toner container.

  Thereafter, the recording paper P is conveyed to the fixing device 20, and the image on the recording paper P is fixed by the fixing device 20. The recording sheet P conveyed from the fixing device 20 is guided in the discharge direction and the re-feed direction via a branch member 15 for switching the path for discharging the recording sheet P out of the apparatus main body and the both-side reverse path 40. Be done.

  In the single-sided sheet passing mode, the image forming apparatus 1 opens the branch member 15 in the first state described above. As a result, the recording paper P is discharged onto the paper discharge tray 14 outside the apparatus main body of the image forming apparatus 1 by the paper discharge roller 13.

  In the double-sided sheet passing mode, the image forming apparatus 1 closes the branch member 15 in the above-described second state. As a result, the recording sheet P after the image is fixed on the first side is guided to the both-side reversing path 40. The recording paper P guided to the duplex reversing path 40 is switched back by the pair of reversing rollers 16, transported to the duplex unit 17, transported again to the pair of registration rollers 12, and re-fed.

  Thus, the recording sheet P is conveyed to the fixing device 20, and the image is fixed on the second surface of the recording sheet P by the fixing device 20 in the same manner as the first surface. Then, the recording paper P is discharged onto the paper discharge tray 14 outside the apparatus main body of the image forming apparatus 1 by the paper discharge roller 13.

  The above description is an image forming operation for forming a full color image on the recording paper P, but one of four image forming units 4Y, 4M, 4C, and 4K is used to form a monochromatic image. It is also possible. It is also possible to use two or three imaging units to form a two or three color image.

  As shown in FIG. 2 and FIG. 3, the fixing device 20 is used for melting and permeating the toner image T carried on the recording paper P after transfer by heat and pressure, and fixing the toner image T while being heated. A fixing belt 21 having flexibility capable of endless traveling is provided. The fixing belt 21 constitutes a fixing member in the present invention.

  The fixing device 20 passes the recording sheet P, to which the toner image has been transferred in the image forming section A, in the conveyance direction F to the fixing nip N, and applies heat and pressure to the recording sheet P. It is supposed to be fixed.

  The fixing device 20 is an opposing rotating member that forms a fixing nip N by applying pressure to the fixing belt 21 in addition to the endless fixing belt 21 and in an abutting state in contact with the fixing belt 21. A pressure roller 22 is provided.

  Inside the fixing belt 21 is provided a heater (heat source) 23 provided with a plurality of halogen lamps 23a and 23b for heating the inner surface side of the fixing belt 21 at a portion other than the fixing nip portion N.

  Further, inside the fixing belt 21, a nip forming member 24 forming the fixing nip portion N, a stay 25 supporting the nip forming member 24, and light emitted from the heater 23 are reflected toward the fixing belt 21. A reflective member 26 is provided. Although not shown in detail, the nip forming member 24 has a sliding sheet (low friction sheet) wound with a base pad.

  In the nip forming member 24 shown in FIGS. 2 and 3, the shape of the fixing nip portion N is flat, but the shape is not limited to this. For example, when the fixing nip N is formed in a concave shape along the circumferential surface of the pressure roller 22, the leading end of the recording sheet P passing through the fixing nip N is closer to the pressure roller 22. There is an advantage that the separability from is improved.

  The temperature of the fixing belt 21 is detected by a temperature sensor 27 provided on the side where the recording paper P enters the fixing nip portion N, and feedback temperature control of the heater 23 is performed.

  The fixing belt 21 is an endless belt formed in a thin and flexible sleeve shape, and is configured of a base material and a releasing layer located on the surface thereof.

  The fixing belt 21 uses, as a base material, a metal material such as nickel or stainless steel or a resin material such as polyimide. The fixing belt 21 uses a tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like having a releasing property with respect to the toner in the releasing layer.

  The pressure roller 22 includes a core metal 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, fluorocarbon rubber or the like provided on the peripheral surface of the core metal 22a, and a PFA provided on the surface of the elastic layer 22b. Or a release layer made of PTFE or the like.

  The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown), and is in contact with the nip forming member 24 as a base member in a state of being in contact with the fixing belt 21.

  The elastic layer 22b of the pressure roller 22 is crushed at the portion where the pressure roller 22 and the fixing belt 21 abut, so that the nip forming member 24 receives a predetermined pressure with the fixing belt 21 and has a predetermined width. The fixing nip N is secured.

  The pressure roller 22 is configured to transmit a rotational drive force from a drive source such as a motor provided in the apparatus main body of the image forming apparatus 1 via a drive transmission unit such as a gear train to rotationally drive the pressure roller 22. When the pressure roller 22 is driven to rotate, the driving force is transmitted to the fixing belt 21 at the fixing nip portion N, and the fixing belt 21 is driven to rotate.

  In the image forming apparatus 1 according to the present embodiment, the pressure roller 22 of the fixing device 20 is a solid roller, but the pressure roller 22 may be a hollow roller. In that case, it is also possible to arrange a heating source such as a halogen heater using radiant heat inside the pressure roller 22. Further, when the elastic layer 22b is not provided, the heat capacity is reduced and the fixing property is improved. However, when the unfixed toner is crushed and fixed, the minute unevenness of the surface of the fixing belt 21 is transferred to the image to make the image solid. Uneven gloss may occur on the part. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more.

  Aluminum, steel, stainless steel or the like can be selected as the pipe-like metal used for the hollow roller. In the case where a heat source is provided in the pressure roller 22, a heat insulating layer may be provided on the surface of the support or a heat ray reflecting surface by mirror processing may be provided in order to suppress heating of the support by radiant heat from the heat source. Is desirable. The heat source in this case is not limited to the halogen heater described above, and it is also possible to use an IH heater, a resistance heating element, or a carbon heater.

  Since the fixing device 20 described above is configured to directly heat the fixing belt 21 which is a heating member with low heat capacity by the heater 23 as a heat source, the temperature of the fixing belt 21 is rapidly raised, and the first print can be made faster. is there. However, focusing on the back curling that occurs on the recording paper P, the fixing is performed before the pressure roller 22 is sufficiently warmed, so backcurling due to the temperature difference between the front and back of the recording paper P as described above (for example, FIG. The curved shape of the recording paper P ′ drawn by the broken line becomes very large.

  The image forming apparatus 1 according to the present embodiment has a separation conveyance mechanism that separates the recording sheet P immediately after passing through the fixing nip portion N from the fixing belt 21 on the recording sheet outlet side of the fixing device 20 and guides it in the discharge direction. Is provided.

  The separation conveyance mechanism includes a belt side separation member 201 having a leading end 201a approaching the fixing belt 21 side on the downstream side in the moving direction of the recording paper P moving from the fixing nip portion N, and a swing approaching the pressure roller 22 side. And a pressure side separation member 202 having an end 202a. The pressurizing side separation member 202 constitutes a guide member in the present invention.

  The belt side separation member 201 is provided to peel off the recording sheet P, which is sticky and stuck to the fixing belt 21, from the fixing belt 21. For this reason, metal is used so that the accuracy in which the recording sheet P being stuck can be positioned at a close position where the recording sheet P can be lifted from the surface of the fixing belt 21 can be obtained.

  The pressure side separating member 202 is a resin molded body, a support rod 202A provided at one end is supported by the main body of the image forming apparatus 1, and a swinging end 202a facing the pressure roller 22 is a pressure roller 22. It is configured to be pivotable so as to be in contact with and away from.

  The pressure side separating member 202 is configured to be largely inclined in a direction away from the pressure roller 22 when, for example, the recording sheet P having a jam is removed from the fixing nip portion N, and the pressure side separating member 202 to the fixing nip portion N. It is possible to make the insertion space of the hand. As a result, it is possible to pull out the recording sheet P or the like which has caused the jam.

  The back curl correction mechanism C has a drive roller 204, a driven roller 203, a guide member 205, and a guide member moving means D.

  The driving roller 204 and the driven roller 203 are disposed downstream of the separating members 201 and 202. The driving roller 204 and the driven roller 203 constitute a conveyance auxiliary roller pair in the present invention.

  The driving roller 204 is provided on the side (pressure roller 22 side) where back curling occurs on the recording sheet P in the fixing nip portion N, with respect to the conveyance path between the fixing device 20 and the branch member 15.

  The driven roller 203 is provided on the side of the fixing nip N where the recording paper P is heated (the fixing belt 21 side), with respect to the conveyance path between the fixing device 20 and the branch member 15.

  The driving roller 204 and the driven roller 203 contact each other to form an auxiliary nip portion, and assist the conveyance of the recording sheet P. The distance between the fixing nip N and the auxiliary nip is set shorter than the length of the recording paper P.

  In the back curl correction mechanism C, the diameter of the drive roller 204 is set larger than the diameter of the driven roller 203 as required. In the back curl correction mechanism C, the recording sheet conveyance speed in the auxiliary nip portion is set slightly lower than the recording sheet conveyance speed in the fixing nip portion N, and the nip pressure of the auxiliary nip portion is the nip pressure of the fixing nip portion N It is set smaller than required. With this configuration, the back curl correction mechanism C does not cause jamming of the recording paper P between the fixing nip N and the auxiliary nip.

  At least the roller circumferential surface portion of the driving roller 204 may be formed of rubber. The driven roller 203 may be formed so that at least the roller circumferential surface is harder than the roller circumferential surface of the driving roller 204 and has releasability.

  In the image forming apparatus 1 according to the present embodiment, the drive roller 204 includes a roller shaft 204 a and a short cylindrical portion 204 b fitted and fixed to the roller shaft 204 a. The short cylindrical portion 204b is made of a high friction coefficient elastic material made of silicon, EPDM, urethane, fluorine rubber or the like so that the recording paper conveying force can be obtained.

  The driven roller 203 has a configuration in which a low μ tube (thickness 30 to 300 μm) such as PFA, ETFA, FEP, etc. is covered on the surface of a hollow pipe-like metal member.

  The reason why a pipe-like metal member is used for the driven roller 203 is that the heat capacity of the driven roller 203 is reduced so that the driven roller 203 is immediately warmed by the heat at the time of image fixing, and the water vapor evaporated from the recording paper P is This is to prevent condensation on the driven roller 203 and the like.

  The reason for disposing a low μ tube on the surface of the above-mentioned pipe-shaped metal member is to prevent a small amount of toner which can not be melted after image fixation from adhering to the surface of the driven roller 203 and preventing accumulation. is there. That is, since the driven roller 203 conveys the recording sheet P while always contacting the image surface side of the recording sheet P, the above-described configuration is employed.

  The driven roller 203 is held by the main body of the image forming apparatus 1 via the holder 210 and a tension spring not shown. The driven roller 203 contacts the driving roller 204 to form an auxiliary nip portion by the holder 210 being pressed by a tension spring, and the recording sheet P is conveyed as an auxiliary.

  The guide member 205 is incorporated in the fixing device 20 such that the center of rotation is coaxial with the roller shaft 204 a of the drive roller 204. The guide member 205 is driven by a guide member moving unit D described later, which is driven based on a control signal from the main body control unit of the image forming apparatus 1, the first position shown in FIG. 2 and the second position shown in FIG. It is set to be either of Here, the first position is an advanced position at which the guide member 205 contacts the recording sheet P, and the second position is a retracted position at which the guide member 205 is separated from the recording sheet P and not in contact. .

  When the guide member 205 is set at the first position shown in FIG. 2, the guide member 205 is pressed on the same side as the drive roller 204 on the front side in the conveyance direction of the recording sheet P passing through the auxiliary nip portion, sliding contact Function to concavely bend the recording sheet P opposite to the back curl.

  That is, when the guide member 205 is set to the first position, the guide member 205 is disposed at a position that blocks the path from the same side as the drive roller 204 with respect to the direction of the recording sheet P passing through the auxiliary nip portion. It is supposed to be. Here, the direction of the recording sheet P passing through the auxiliary nip portion is a direction perpendicular to a line connecting the centers of the driving roller 204 and the driven roller 203.

  Therefore, as shown in FIG. 2, the leading end of the recording paper P contacts the guide member 205 at the contact angle θ. Thereafter, the recording sheet P is auxiliary-conveyed by the drive roller 204 and the driven roller 203 while being pressed by the guide member 205.

  Accordingly, as shown in FIG. 2, the guide member 205 finally conveys the recording paper P while making the contact angle θ1 starting from the auxiliary nip portion, so that the recording paper P has a back curl. The back side of the recording paper P is corrected such that it is curved to have a concave surface on the opposite side. By using such a conveyance path, the back curl generated at the time of image fixing is corrected by the guide member 205 and the recording sheet P passing through the auxiliary nip portion is discharged to the sheet discharge tray 14.

  However, when the guide member 205 is in the state set at the first position described above, the back surface of the recording sheet P positively contacts the guide member 205, and the conveyance of the back surface of the recording sheet P and the guide member 205 is performed. The resistance is large, and the recording paper P itself is stressed.

  Therefore, in the double-sided sheet passing mode, when the second surface is to be fixed to the second surface of the recording paper P, the first surface on which the image is already fixed and the guide member 205 come into contact. Rubbing, scratches and the like are likely to occur on the image of the surface.

  In particular, when passing the second surface, the fixed image on the first surface, which is the back surface, is also reheated through the fixing nip portion N during image fixing of the second surface of the fixing device 20. For this reason, when the image on the first surface which has been warmed is strongly rubbed by the guide member 205, it is likely that the toner may be peeled off, the gloss may be changed, and the like.

  Therefore, at the time of second surface sheet passing, the guide member 205 is set to the second position shown in FIG. In the state where the guide member 205 is set to the second position, the guide member 205 is not in contact with the recording sheet P passing through the auxiliary nip portion, and functions so as not to bend the recording sheet P.

  When the guide member 205 is set to the second position, the guide member 205 largely retreats in the conveyance direction of the recording sheet P discharged from the auxiliary nip portion, and does not positively contact the recording sheet P. No rubbing, abrasion, scratches, or gloss streaks occur on the surface image.

  As shown in FIGS. 4 to 7, the drive roller 204 is engaged with the roller shaft 204a rotatably supported at both ends by the pressure side separation member 202 via the slide bearing 208 and the roller shaft 204a at a required interval. It is comprised by the short cylindrical part 204b fixed.

  The driving roller 204 is configured such that the rotational force of a motor, which will be described later, is transmitted via a gear 248 supported by the pressing side separation member 202 and a gear 249 fitted to the end of the roller shaft 204a.

  As shown in FIGS. 4 to 7, the guide member 205 is fixed to a support shaft 205 a supported at both ends by the upper ends of the pair of bracket arms 206. A plurality of guide members 205 are provided for each of a plurality of bosses 205b fixed to the support shaft 205a.

  The bracket arm 206 is rotatably fitted around the roller shaft 204 a of the drive roller 204 via the slide bearing 208. Thereby, each guide member 205 is configured to rotate around the roller shaft 204 a of the drive roller 204.

  The guide member 205 has a proximal end fixed to the boss 205 b and an overhanging end extending so as to cover the drive roller 204. The guide member 205 is configured to stop at a position where a stopper portion 206 b provided at an end of the bracket arm 206 abuts on a predetermined position of the pressurizing side separation member 202. The posture position of the guide member 205 corresponding to this state is a first position for changing the angle of the recording paper P discharged from the auxiliary nip portion.

  As shown in FIGS. 5 to 7, the guide member moving means D includes a solenoid 220 as a drive source, a link mechanism 207 that swings by the operation of the solenoid 220, and a tension spring 209. The housing of the solenoid 220 is fixed to the main body of the image forming apparatus 1.

  One end portion of the tension spring 209 is locked to the side surface portion of the pressing side separation member 202, and the other end portion is locked to an arm portion 206a provided at the end portion of the bracket arm 206. The tension spring 209 rotates the bracket arm 206 in the direction in which the guide member 205 is in the first position shown in FIG.

  As shown in FIGS. 6 and 7, in the link mechanism 207, one end 207a in the horizontal direction is supported by the fixing pin shaft 207A, and the actuating end 207b which is the other end is the tip of the arm 206a of the bracket arm 206. It is located on the lower side. Further, in the link mechanism 207, a long hole 207d provided in the upper extension portion 207c extending upward from the middle portion in the horizontal direction is pin-connected to the telescopic rod 220a of the solenoid 220.

  When the solenoid 220 is de-energized, the extension rod 220a protrudes downward to a position shown by a broken line in FIG. When the solenoid 220 is excited based on a control signal from the main control unit of the image forming apparatus 1, the telescopic rod 220a is pulled upward to a position shown by a solid line in FIG.

  When the solenoid 220 is not excited, the guide member moving means D is in a state in which the actuating end 207 b of the link mechanism 207 is separated downward from the tip of the arm portion 206 a of the bracket arm 206. In the guide member moving mechanism D, when the solenoid 220 is excited, the actuating end 207 b of the link mechanism 207 pushes up the tip of the arm portion 206 a of the bracket arm 206. Thus, the guide member 205 is moved from the first position shown in FIGS. 2 and 8 to the second position shown in FIGS. 3 and 9.

  In the guide member moving means D, when the solenoid 220 is interrupted, the link mechanism 207 is pivoted by the tensile force of the tension spring 209, and the actuating end 207b separates downward with respect to the tip of the arm portion 206a of the bracket arm 206. It will be As a result, the guide member 205 is moved from the second position shown in FIGS. 3 and 9 to the first position shown in FIGS. As the guide member moving means D, a stepping motor or the like can be used instead of the solenoid 220.

  By adopting the configuration as described above, the back curl correction mechanism C can set the gap between the drive roller 204 and the guide member 205 in a state where the dimensional tolerances of the parts have the least build-up (from the axial center of each part Only radial distance tolerances can be made. Therefore, the guide member 205 can be moved in a state in which the gap between the drive roller 204 and the guide member 205 is maintained with high accuracy.

  As shown in FIG. 10, the branch members 15 are formed in a claw shape, and arranged alternately with the guide members 205 in the width direction orthogonal to the conveyance direction of the recording paper P. Thus, even if the swing range of the branch member 15 and the swing range of the guide member 205 overlap on the conveyance path of the recording paper P, the branch member 15 and the guide member 205 do not interfere with each other and interfere with each other. It is possible to guide the recording paper P.

The image forming apparatus 1 according to the present embodiment opens and closes the branch member 15 according to the sheet thickness (g / m ² ) of the recording paper P, and sets the guide member 205 in the first position or the second position. It is made to set it.

In the single-sided sheet feeding mode, for example, when using a recording sheet P having a sheet thickness of less than 160 g / m ² , as shown in FIG. 11A, the branch member 15 is opened to the first state and the guide member 205 is Set to the first position. As a result, the second surface of the recording sheet P contacts the guide member 205 and is bent in a concave shape opposite to the back curl, and the recording sheet P is discharged by the discharge roller 13 outside the main body of the image forming apparatus 1. It is discharged onto the paper tray 14.

In the single-sided sheet passing mode, for example, when using a recording sheet P having a sheet thickness of 160 g / m ² or more, as shown in FIG. 11B, the branch member 15 is opened to the first state and the guide member 205 is Set to the second position. As a result, the thick recording sheet P having a strong stiffness is discharged onto the discharge tray 14 outside the main body of the image forming apparatus 1 by the discharge roller 13 without the second surface contacting the guide member 205. And the second surface of the recording paper P is not scratched. In addition, the recording sheet P having a thick sheet and being strong in stiffness does not cause back curling as a matter of course.

  In the double-sided sheet passing mode, when the recording sheet P is to be passed on the first side, the branch member 15 is closed to the second state as shown in FIG. 11C, and the guide member 205 is set to the second position. As a result, the recording sheet P with the image fixed on the first side is not sent to the side of the sheet discharge roller 13, and is guided to the both-side reversing path 40.

  In the double-sided sheet passing mode, when the recording sheet P is to be fed on the second surface, the branch member 15 is opened to the first state and the guide member 205 is set to the second position as shown in FIG. Thus, the recording paper P is discharged onto the paper discharge tray 14 outside the apparatus main body of the image forming apparatus 1 by the paper discharge roller 13 without the first surface (the latest image fixing surface) contacting the guide member 205. The image on the first side of the recording paper P is free from rubbing, abrasion, scratches, gloss streaks and the like.

  In the double-sided sheet passing mode, when the recording sheet P which is not a thick sheet is passed on the second side, unlike the image fixing of the first side, no back curling occurs in the recording sheet P, so the guide member 205 is the second sheet. Setting the position is preferable in that the image on the first surface of the recording sheet P is protected.

  As shown in FIG. 12, the recording sheet P passing through the auxiliary nip portion formed by the drive roller 204 and the driven roller 203 is discharged in the direction perpendicular to the line connecting the centers of the drive roller 204 and the driven roller 203. Be done. For this reason, when the guide member 205 is set to the position drawn by the broken line, the contact angle θ 'formed by the recording paper P and the guide member 205 is set to the position drawn by the solid line. Is smaller than the contact angle θ between the recording paper P and the guide member 205. Here, the position where the guide member 205 is drawn with a broken line is the position where the tip of the guide member 205 overlaps the drive roller 204, and the position where the guide member 205 is drawn with a solid line is the tip of the guide member 205. The part is located away from the outer peripheral surface of the drive roller 204.

  If the contact angle is reduced, the leading end of the recording paper P is buckled and bent and conveyed, and in the worst case, the risk of jamming is increased. Conversely, when the extension line of the surface of the guide member 205 in contact with the recording paper P is shifted from the rotation center of the drive roller 204 and the contact angle is larger than the contact angle θ, the guide member 205 is arranged. Leading to a reduction in the curl correction effect of bending the recording paper P.

  Therefore, in order to obtain the curl correction effect, the back curl correction mechanism C is provided with a plurality of short cylindrical portions 204b of the drive roller 204 at intervals, and a guide member is provided between the adjacent short cylindrical portions 204b. It has a configuration in which 205 enters.

  As shown in FIGS. 13 to 15, the drive roller 204, which is one of the conveyance auxiliary roller pair, has a roller shaft 204a rotatably supported by the pressure side separation member 202, and rotation drive from the pressure roller 22 is described later. It is configured to be transmitted via a force transmission mechanism. The driven roller 203, which is the other of the conveyance auxiliary roller pair, is held by the main body of the image forming apparatus 1 via the holder 210 and a tension spring (not shown).

  When the holder 210 is pressed by a tension spring, the driven roller 203 contacts the driving roller 204 to form an auxiliary nip portion, and rotates along with the driving roller 204 to auxiliary-convey the recording sheet P. There is.

  The pressure roller 22 is supported by a pressure roller holding member 230. The pressure roller holding member 230 is rotatably supported by a bracket 231 disposed in the main body of the image forming apparatus 1 via a support rod 232.

  The pressure roller holding member 230 is released from the position where the pressure roller 22 is pressed toward the fixing belt 21 and the nip forming member 24 by a known pressure releasing mechanism 233 having an eccentric cam 233a. It is set to the position where Here, the position where the pressure is released is a position where the pressure roller holding member 230 is inclined rearward in a direction away from the pressure roller 22 with the support rod 232 as the center.

  When the eccentric cam 233 a protrudes toward the fixing belt 21, the pressure releasing mechanism 233 presses the pressure roller 22 toward the fixing belt 21 and the nip forming member 24. When the eccentric cam 233 a protrudes to the side opposite to the fixing belt 21, the pressure releasing mechanism 233 does not press the pressure roller 22 toward the fixing belt 21 and the nip forming member 24.

  In the pressure roller 22, gears 244 and 245 are fitted at the end of the metal core 22a, and gears 241 and 242 are engaged in order from the upstream side to the downstream side of the driving force transmission direction with the rotation of a motor (not shown). , 243, 244 are to be transmitted.

  The pressure roller holding member 230 supports the gears 246 and 247. The pressure side separating member 202 supports the gear 248. The drive roller 204 has a gear 249 fitted to the end of the roller shaft 204a, and gears 245, 246, 247 in which the rotation of the pressure roller 22 is sequentially engaged from the upstream side to the downstream side in the driving force transmission direction. , 248, 249 are transmitted.

  The gears 245, 246, 247, 248, and 249 constitute a rotational driving force transmission mechanism according to the present invention, and the rotational driving force transmitted to the pressure roller 22 is the same as that of the pressure roller 22 of the pair of conveyance auxiliary rollers. It is transmitted to the drive roller 204 which is one of the side conveyance auxiliary rollers. As a result, the rotational driving of the driving roller 204 can be advantageously performed at a lower cost by transmitting it from the fixing device or the driving source of the sheet discharging device than providing a new driving source. The gears 246, 247, and 248 may be, for example, ordinary spur gears or stepped gears in which spur gears having different diameters are integrally arranged.

  The rotation of the motor is transmitted to the pressure roller 22 via the gears 241, 242, 243 and 244 and is further transmitted to the drive roller 204 via the gears 245, 246, 247, 248 and 249. The gears 245, 246, 247, 248, 249 for transmitting the rotation to the drive roller 204 are supported by the pressure roller holding member 230 and the pressure side separating member 202.

  In the pressure side separating member 202, a support rod 202A provided at one end is supported by the pressure roller holding member 230, and a swinging end 202a opposed to the pressure roller 22 contacts or separates from the pressure roller 22. It is configured to be rotatable.

  The pressurizing side separation member 202 is set to be openable and closable at a closed position and an open position. Here, the closed position is a position for guiding the recording sheet P delivered from the fixing nip N to the auxiliary nip between the driving roller 204 and the driven roller 203 as shown in FIGS. 2 and 3. Further, the open position is, for example, a position which is largely inclined in a direction away from the pressure roller 22 when removing the recording sheet P which has been interrupted due to jamming from the fixing nip portion N.

  The positioning member 251 is attached to the upper part of the pressure roller holding member 230. The positioning member 251 is attached to the upper part of the pressurizing side separation member 202. The positioning member 251 of the pressure roller holding member 230 follows the positioning member 252 of the pressure side separation member 202 when the pressure roller holding member 230 is pressed toward the pressure roller 22 by the pressure release mechanism 233. The roller 203 is pressed toward the roller 203 side. As a result, the pressing side separation member 202 and the drive roller 204 are set to the normal position when the recording sheet P is passed.

  In addition, when the pressing roller holding member 230 is released by the pressing and pressure releasing mechanism 233, the pressing side separating member 202 is set to the open position largely inclined in the direction away from the pressing roller 22. become able to.

  The image forming apparatus 1 according to the present embodiment transmits the rotation of the pressure roller 22 to the driving roller 204 to the pressure roller holding member 230 which holds the pressure roller 22, and the gears 245, 246, 247, 248, 249. I am holding For this reason, in the image forming apparatus 1 according to the present embodiment, the pitch of the gears 245, 246, 247, 248, 249 does not shift even if the variation of the elastic layer 22b of the pressure roller 22 or the aged deterioration occurs. Therefore, the image forming apparatus 1 according to the present embodiment can suppress the generation of unnecessary vibration and noise due to the vibration and the generation of the banding layer.

  The image forming apparatus 1 according to the present embodiment causes the pressure roller holding member 230 to hold the pressure side separation member 202 so as to be set to the closed position and the open position. Therefore, the image forming apparatus 1 according to the present embodiment can easily confirm whether or not a jam has occurred on the recording paper P between the fixing nip N and the driving roller 204 and the driven roller 203. .

  In the present embodiment, the image forming apparatus 1 sets the pressure side separating member 202 and the driving roller 204 at the regular positions in the state where the recording sheet P is fed to the pressure roller holding member 230 and the pressure side separating member 202. Positioning members 251 and 252 are provided. For this reason, in the image forming apparatus 1 according to the present embodiment, when a force is applied to the guide member 205 by the passage of the recording paper P, the position of the pressing side separation member 202 does not change.

  The image forming apparatus 1 according to the present embodiment has a pressure releasing mechanism 233 capable of pressing the pressure roller 22 toward the fixing belt 21, and the pressure side separation member at the time of pressure release of the pressure roller 22. The positioning of 202 is configured to be released. Therefore, the image forming apparatus 1 according to the present embodiment can immediately and easily check whether or not a jam has occurred on the recording paper P between the fixing nip N and the driving roller 204 and the driven roller 203. And the recording paper P can be removed quickly.

  The image forming apparatus 1 according to the present embodiment rotatably supports the guide member 205 coaxially with the roller shaft 204a of the drive roller 204, and is configured to be switchable between the first position and the second position. . Therefore, the image forming apparatus 1 according to the present embodiment can move the guide member 205 in a state in which the gap between the drive roller 204 and the guide member 205 is maintained with high accuracy.

  The image forming apparatus 1 according to the present embodiment is configured such that the guide member 205 is set to the first position when printing on at least one side of the recording paper P. Therefore, the image forming apparatus 1 according to the present embodiment can correct the recording paper P delivered in a curled state from the fixing nip N by the guide member 205 at the time of single-sided printing. Therefore, in the image forming apparatus 1 according to the present embodiment, the fact that the specified number of recording sheets P can not be stacked on the discharge tray 14 is resolved, and the recording sheets P stacked on the discharge tray 14 are disordered. There is no

  The image forming apparatus 1 according to the present embodiment is configured such that the guide member 205 is set to the second position at the time of double-sided printing of the recording paper P. Therefore, in the image forming apparatus 1 according to the present embodiment, the first surface of the recording paper P does not contact the guide member 205 at the time of double-sided printing. Therefore, in the image forming apparatus 1 according to the present embodiment, rubbing, abrasion, scratches, gloss streaks and the like do not occur on the image of the first surface of the recording paper P.

  As described above, the image forming apparatus according to the present invention can effectively reduce the back curling generated on the recording sheet by the fixing heating and reduce the damage to the recording sheet and the toner image, and the back curling Stabilization of the recording sheet at the time of removal, suppression of generation of noise due to unnecessary vibration and vibration, suppression of generation of banding layer, and cost reduction of drive system of means for removing back curl And is useful for an image forming apparatus.

1 Image Forming Device 15 Branching Member (Sheet Transport Path Branching Means)
20 fixing device 21 fixing belt (fixing member)
22 pressure roller 40 double-sided reversing path 202 pressure side separation member (guide member)
203 Followed Roller (Conveying Auxiliary Roller Pair)
204 Drive roller (pair of conveyance auxiliary rollers)
205 Guide Member 230 Pressure Roller Holding Member 233 Pressure Depressurizing Mechanism 245, 246, 247, 248, 249 Gear 251, 252 Positioning Member A Image Forming Section D Guide Member Moving Means N Fixing Nip Section P Recording Paper

JP 2001-48399 A JP-A-9-188456 JP, 2012-91891, A

Claims (5)

The recording sheet on which the image has been transferred in the image forming unit is transferred from the heat source obtained from the fixing heating source with a pressure roller provided with an elastic layer on the surface to which rotational driving force is transmitted A fixing member for fixing an image on the recording sheet through a fixing nip portion formed by the fixing member;
An image forming apparatus comprising: a sheet conveyance path branching unit configured to alternatively set the conveyance destination of the recording sheet sent from the fixing device to either an external discharge path or a reverse path for double-sided printing; There,
A conveyance auxiliary roller pair disposed between the fixing device and the sheet conveyance path branching unit, for conveying the recording sheet delivered from the fixing device toward the downstream side in the conveyance direction;
The recording sheet, which is disposed between the conveyance auxiliary roller pair and the sheet conveyance path branching means and opposite to the latest image fixing surface of the recording sheet, is sent out of the machine from the recording sheet delivered from the conveyance auxiliary roller pair. A guide member for guiding to the discharge path;
A first position for contacting the guide member to the surface opposite to the latest image fixing surface of the recording sheet delivered from the transport auxiliary roller pair and guiding the guide member to the external discharge path, and contacting the surface Guide member moving means which is set to any of the second positions where
A pressure roller holding member for holding the pressure roller;
A rotational drive that is held by the pressure roller holding member and transmits the rotational driving force transmitted to the pressure roller to one conveyance auxiliary roller on the same side as the pressure roller of the conveyance auxiliary roller pair And a force transfer mechanism ,
The pressure roller holding member is a guide member that can be opened and closed to a position for guiding the recording sheet delivered from the fixing nip portion to the conveyance auxiliary roller pair and a position for removing the recording sheet that has become interrupted. The image forming apparatus according to claim 1, wherein one of the pair of conveyance auxiliary rollers is held by the guide member . Wherein the pressure roller holding member and the guide member, according to claim 1, characterized in that a positioning member for setting one of said guide member and the auxiliary conveyance roller pair to the normal position while passing the recording sheet Image forming device. A pressure releasing mechanism capable of pressing the pressure roller toward the fixing member is provided, and the positioning of the guide member is released when the pressure roller is released. An image forming apparatus according to claim 2 . The guide member, the auxiliary conveyance roller rotatably supported on one coaxial pairs claims 1 to 3, characterized in that it is configured to be switched to the first position and the second position The image forming apparatus according to any one of the above. The guide member is set to a first position when printing on at least one side of the recording sheet, and the guide member is set to a second position when printing on both sides of the recording sheet. The image forming apparatus according to any one of claims 1 to 4 .

Images