JP6543977B2 - 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 much from the front side, and the amount of water movement from the back side to the front side becomes large, so the front side is the back side As a result, the elongation of the paper fiber 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, the back curl generated at 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 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, since the back sheet curls to the back side does not occur in the fixing device, when the guide plate is always at the first position, the guide plate is reversed. 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

  In order to solve the problems described above, the image forming apparatus according to the present invention passes the recording sheet on which the image is transferred by the image forming unit to the fixing nip portion and fixes the image on the recording sheet in the fixing nip portion. An image forming apparatus having a fixing device for moving the recording paper and a recording paper conveyance path branching unit for switching between an external discharge path for discharging the recording paper conveyed to the downstream side of the fixing device to the outside of the machine and a reverse path for double-sided printing In the above, the conveyance path between the fixing device and the recording sheet conveyance path branching means is provided with a back curl correction mechanism, and the back curl correction mechanism is provided on the side where back curling occurs in the recording sheet at the fixing nip portion. An auxiliary nip portion which is formed by a driving roller and a driven roller provided on the side to heat the recording sheet, and which holds the recording sheet and performs auxiliary conveyance, and on the same side as the driving roller Move the guide member for guiding the recording sheet, the guide member to a first position for pressing the recording sheet while passing through the auxiliary nip portion, and a second position for separating the recording sheet from the recording sheet And a guide member moving means.

  According to the present invention, it is possible to provide an image forming apparatus capable of achieving both reduction in back curling generated during fixing and conveyance stabilization, and capable of reducing damage to recording paper and toner images.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of the fixing device according to an embodiment of the present invention at the time of back curl correction. FIG. 2 is a schematic configuration view of a fixing device according to an embodiment of the present invention when backcurling is not corrected. It is the figure seen in the arrow IV direction about the pressurization side separation conveyance member, a drive roll, and a guide member in FIG. FIG. 7 is a perspective view of a part of the fixing device as viewed from the conveyance path side when the guide member is in the first position according to the embodiment of the present invention. FIG. 7 is an enlarged perspective view of a part of the fixing device as viewed from the conveyance path side when the guide member is in the second position according to the embodiment of the present invention. FIG. 7 is a view of a part of the fixing device as viewed from the conveyance path side when the guide member moving means is operated and the guide member is in the second position according to the embodiment of the present invention. FIG. 7 is a front view of a part of the fixing device when the guide member is in the first position according to the embodiment of the present invention as viewed from the conveyance path side. FIG. 7 is a front view of a part of the fixing device when the guide member is in the second position according to an embodiment of the present invention, as viewed from the conveyance path side. It is a perspective view which concerns on one embodiment of this invention, and shows arrangement | positioning of a branch member and a guide member. FIG. 7 is a view showing a plurality of sheet transport paths according to the embodiment of the present invention by combining the position of the branch member and the position of the guide member. FIG. 7 is a view for explaining an influence of a crossing angle between a recording sheet conveyance direction and a guide member in a correction nip portion on back curl correction according to an 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.

First, an overall configuration of an image forming apparatus according to an embodiment of the present invention will be described.
The image forming apparatus 1 illustrated in FIG. 1 is a color laser printer, and includes an image forming unit A, a sheet feeding unit B, a fixing device 20, a pair of sheet discharge rollers 13, a sheet discharge tray 14, and a pair of reverses. A roller 16 and a duplex unit 17 are provided.

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

  At the center of the image forming apparatus main body of the image forming apparatus 1, four image forming units 4Y, 4M, 4C, and 4K are provided. 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.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes 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 a surface of the photosensitive member 5. It includes a developing device 7 which supplies toner, and a cleaning device 8 which cleans the surface of the photosensitive member 5. In FIG. 1, only the photosensitive member 5, the charging device 6, the developing device 7, and the cleaning device 8 provided in the black image forming unit 4K are denoted by reference numerals, and the other image forming units 4Y, 4M, and 4C Since the configuration is the same as that of the black image forming unit 4K, the reference numerals are omitted.

  Below each image forming unit 4Y, 4M, 4C, 4K, an exposure device 9 for exposing the surface of the photosensitive member 5 is disposed. 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.

  A 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. A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  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, by driving the secondary transfer backup roller 32 to rotate, the intermediate transfer belt 30 travels (rotates) in the direction indicated by the arrow in the figure.

  The four primary transfer rollers 31 respectively sandwich the intermediate transfer belt 30 with the respective photosensitive members 5 to form a primary transfer nip. Further, a power supply is connected to each primary transfer roller 31, and 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 also connected to the secondary transfer roller 36 so that a predetermined DC voltage (DC) or AC 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 disposed to abut 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.

  In the upper part of the image forming apparatus main body, a bottle housing portion 2 is provided, and in the bottle housing portion 2, four toner bottles 2Y, 2M, 2C, 2K for containing toner for replenishment are detachably mounted. ing. 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 Ru.

  On the other hand, the lower portion of the image forming apparatus main body is provided with a sheet feeding unit B. The sheet feeding unit B includes a sheet feeding tray 10 accommodating a recording sheet P 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. In addition, a manual sheet feeding mechanism may be provided. 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 main body, a conveyance 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 is disposed. On the transport path R, on the upstream side in the recording sheet conveyance direction with respect to the position of the secondary transfer roller 36, a pair of registration rollers 12 as a timing roller for conveying the recording sheet P to the secondary transfer nip is arranged by measuring the conveyance timing. It is set up.

  A fixing device 20 fixes the toner image on the recording sheet P by pressing and heating the recording sheet P carrying the unfixed toner image on the downstream side of the position of the secondary transfer roller 36 in the recording sheet conveyance direction. Is provided. Further, on the downstream side of the fixing device 20 in the recording paper conveyance direction of the conveyance path R, a pair of paper discharge rollers 13 for discharging the recording paper P to the outside of the apparatus is provided. Further, a sheet discharge tray 14 for stocking the recording paper P discharged to the outside of the apparatus is provided on the upper surface portion of the image forming apparatus main body.

  Further, a branching member 15 is provided between the sheet discharge roller 13 and the fixing device 20. The branching member 15 is in the first state shown in FIG. 1 in the single-sided sheet passing mode, and is in the second state closed in the arrow direction from the first state shown in FIG. 1 in the double-sided sheet passing mode. It is rotatably fixed to the main body.

  That is, the bifurcating member 15 has an external discharge path (path passing through the discharge roller 13) for discharging the recording sheet P conveyed to the downstream side of the fixing device 20 to the discharge tray 14 outside the machine; Since it is configured to switch between the reverse path (the path passing through the inside of the duplex unit 17 described later), the recording paper transport path branching means of the present invention is configured. Furthermore, a back curl correction mechanism C described later is provided between the branch member 15 and the fixing device 20.

  The duplex reversing path 40 is provided with a reversing roller 16 for switching back the recording paper P provided on the downstream side of the branching member 15, and a duplex unit 17 between the reversing roller 16 and the registration roller 12. The duplex unit 17 includes transport rollers 42 to 44 to form a reverse path for duplex printing, and the recording paper P after the first surface fixing is switched back by the reverse roller 16 to pass through the transport rollers 42 to 44. To the registration roller 12.

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

  First, when the image forming operation is started, each photosensitive member 5 in each of the image forming units 4Y, 4M, 4C, 4K is rotationally driven clockwise in the figure, and the surface of each photosensitive member 5 is predetermined by the charging device 6. It is uniformly charged to the 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.

  Further, 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.

  In addition, a primary transfer nip between each primary transfer roller 31 and each photosensitive member 5 is applied by applying to each primary transfer roller 31 a constant voltage or a constant current controlled polarity opposite to the charging polarity of the toner. A transfer electric field is formed at.

  Thereafter, when the image of each color on the photosensitive member 5 reaches the primary transfer nip as the photosensitive member 5 rotates, the image on each photosensitive member 5 is intermediated by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the transfer belt 30.

  In this manner, a full-color image is carried 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.

  At the lower part of the printer, the sheet feeding roller 11 starts to rotate and the recording sheet P is fed 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, rotational driving of the registration roller 12 is started at a predetermined timing, and the recording sheet P is conveyed to the secondary transfer nip in accordance with the timing at which the image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to that of the toner charging 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 sheet P is conveyed to the fixing device 20, and the image on the recording sheet P is fixed to the recording sheet P by the fixing device 20. The recording paper 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 a path for discharging the recording paper P out of the apparatus and a duplex reverse path. .

  In the single-sided sheet feeding mode, the branching member 15 is opened, and conveyed to the outside of the apparatus by the pair of discharge rollers 13 for discharging, and the recording paper discharged to the outside of the apparatus provided on the upper surface of the image forming apparatus main body It is discharged to the discharge tray 14 for stocking P.

  In the double-sided sheet passing mode, the recording sheet P after the first surface fixing is guided to the both-side reversing path 40 by the branching member 15 closing in the direction of the arrow. 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. Similar to the one side, the second side image is printed on the back side of the recording paper P. Then, the recording paper P is discharged to the outside of the apparatus by the paper discharge roller 13 and is stocked on the paper discharge tray 14.

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

Next, the fixing device 20 having the back curl correction mechanism C of the image forming apparatus 1 according to the embodiment of the present invention will be described in detail.
FIG. 2 is a cross-sectional view of a fixing device having a back curl correction mechanism according to the present embodiment.

  As shown in FIG. 2, the fixing device 20 is used to melt and penetrate the transferred toner image T carried on the recording paper P by heat and pressure and fix it, and it is endlessly heated while being heated. A fixing belt 21 with possible flexibility is provided.

  The fixing device 20 causes the recording sheet P to which the toner image is transferred in the image forming unit A to pass through the fixing nip portion N and applies heat and pressure in the fixing nip portion N to fix the toner image onto the recording sheet P.

  In the fixing device 20, in addition to the endless fixing belt (fixing member) 21, a pressure is applied between the fixing belt 21 and the fixing belt 21 in a contact state in contact with the fixing belt 21 to form a fixing nip portion N A pressure roller (pressure member) 22 which is a rotating body is provided. Inside the fixing belt 21 is provided a heater (heat source) 23 provided with a plurality of halogen lamps 23 a and 23 b for heating the inner surface side of the fixing belt 21 at locations other than the fixing nip portion N.

  Inside the fixing belt 21, a nip forming member 24 as a nip forming base member disposed inside the fixing belt 21, a stay 25 for supporting the nip forming member 24, and light emitted from the heater 23. A reflection member 26 is provided to reflect the light to the fixing belt 21.

  Although not shown in detail, the nip forming member 24 which is a base member for forming the nip has a sliding sheet (low friction sheet) which is wound around the base pad.

  In the nip forming member 24 shown in FIG. 2, 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, and is used for feedback processing of the heater 23. The arrow F in FIG. 2 indicates the conveyance direction of the recording sheet P.

  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. As the base material, a metal material such as nickel or A-SUS or a resin material such as polyimide is used. Further, for the releasing layer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE) or the like having releasing property to the toner is used.

  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.

  At a portion where the pressure roller 22 and the fixing belt 21 abut, the elastic layer 22b of the pressure roller 22 is crushed, 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 be rotationally driven by a drive source such as a motor (not shown) provided on the printer main body. 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 fixing device 20 according to the present embodiment, the pressure roller 22 is a solid roller, but 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. 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 belt surface is transferred to the image and the gloss of the solid portion of the image Unevenness may occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more.

  As a pipe-like metal used for the hollow roller, aluminum, iron, stainless steel or the like can be selected. 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.

  In the case of the fixing device 20 described above, since the heating device with a low heat capacity is directly heated, the fixing device is very fast in temperature rise, so there is an advantage that the first print can be made fast. However, from the viewpoint of back curling of the recording paper P, fixing is performed before the pressure roller is sufficiently heated, so backcurling due to the temperature difference between the front and back as described above (for example, curvature of solid line P ′ shown in FIG. 2) Shape is very large.

  On the recording paper outlet side of the fixing device 20, a separation conveyance mechanism is provided which separates the recording paper P having passed through the fixing nip N near the fixing nip and guides the recording paper P in the discharge direction toward the paper discharge unit.

  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 moved from the fixing nip portion, and a swinging end approaching the pressure roller 22 side. And a pressure-side separation member 202 having 202a.

  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.

  A resin molded product is used for the pressure-side separating member 202, and the pressure-sensitive separating member 202 is opposed to the pressure roller 22 by supporting a support rod 202A provided in a part rotatably on the housing side (not shown). The rocking end 202 a can be rocked so as to be able to contact and separate with the pressure roller 22.

  When the pressure side separation member 202 swings with respect to the pressure roller 22, for example, when removing the recording sheet P having a jam from the fixing nip portion N, the pressure side separation member 202 is largely swung away from the pressure roller 22. The insertion space of the hand to the fixing nip N can be made. Thereby, the recording paper P can be pulled out.

  The back curl correction mechanism C provided between the branch member 15 and the fixing device 20 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 constitutes the driving roller of the present invention, and the driven roller 203 constitutes the driven roller of the present invention.

  The driving roller 204 is provided on the side (pressure roller 22 side) where the back curling occurs on the recording paper P in the fixing nip portion, 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 portion 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 press each other to form an auxiliary nip portion, roll and rotate, and assist the conveyance of the recording sheet P. The distance between the fixing nip portion and the auxiliary nip portion is set to be shorter than the length of the recording paper P.

  It is configured as follows to prevent the occurrence of jams. First, the diameter of the drive roller 204 is set larger than the diameter of the driven roller 203 as required. The recording paper conveyance speed in the auxiliary nip portion is set to be slightly smaller than the recording paper conveyance speed in the fixing nip portion. The nip pressure of the auxiliary nip portion is set smaller than the nip pressure of the fixing nip portion. With this configuration, the occurrence of jamming on the recording paper P does not occur between the fixing nip portion and the auxiliary nip portion.

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

  In the present embodiment, the drive roller 204 has a core metal 204a (hereinafter referred to as a roller shaft 204a), and a high friction coefficient made of silicon, EPDM, urethane, fluororubber, etc. provided on the surface of the core metal 204a. And the solid rubber material 204b of FIG.

  The driven roller 203 has a hollow pipe-like metal surface covered with a low-μ tube (thickness: 30 to 300 μm) such as PFA, ETFA, or FEP.

  The reason for using a hollow pipe-like metal is to prevent condensation that water vapor generated by evaporation from paper adheres to the driven roller during fixing, thereby reducing heat capacity and immediately warming up with heat from fixing. is there.

  The reason for arranging a low μ tube on the surface is to make it difficult for a small amount of toner that can not be melted after fixing to adhere and not to be deposited even if it adheres. That is, since the driven roller 203 side is conveyed while always in contact with the image surface side, the configuration is as described above. The driven roller 203 is held in the main body of the image forming apparatus by a spring member (not shown) via a holder, and by pressing the holder with the spring, the drive roller 204 and the driven roller 203 contact and an auxiliary nip portion The recording sheet P which has been formed can be auxiliary-conveyed.

  The guide member 205 is provided by the fixing unit so that the center of rotation is coaxial with the roller axis 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, as shown in FIG. 3 and at a first position shown in FIG. It is moved to one of the second positions shown (retracted position away from the recording sheet P (non-contact)).

  In the state where the guide member 205 is positioned at the first position shown in FIG. 2, the guide member 205 slides so as to press the conveyance direction front side portion of the recording sheet P passing through the auxiliary nip portion on the same side as the drive roller 204. It contacts and functions so as to bend the recording paper P in a concave shape opposite to the back curl.

  That is, when the guide member 205 is held at the first position, the drive roller is driven relative to the direction of the recording paper P passing through the auxiliary nip (the direction perpendicular to the line connecting the centers of the roller pair). From the same side as 204, it is arranged in the position which blocks a path.

  Therefore, the leading edge of the recording sheet P contacts the guide member 205 at the contact angle θ shown in FIG. 2 and the recording sheet P is thereafter pressed by the guide member 205 while the nip conveying force of the drive roller 204 and the driven roller 203 As a result, auxiliary transportation will be performed.

  Then, since the guide member 205 transports the recording paper P while finally making the contact angle θ1 from the auxiliary nip portion as a starting point, the guide member 205 is curved to have a concave surface on the opposite side to the back curl. We can do back curl correction. By using such a conveyance path, the recording sheet P passing through the guide member 205 can be discharged to the sheet discharge tray 14 by improving the back curl generated in the fixing.

  However, since the first position is a position where the guide member 205 is positively brought into contact with the back surface of the recording paper P, the transport resistance between the back surface of the recording paper P and the guide member 205 is large, and the paper itself is stressed. It will be.

  When the recording sheet P, which is not a thick sheet, passes through the second side in the double-sided sheet passing mode, the surface (first side) on which the image is present comes in contact with the guide member 205, and image distortion and gloss streaks easily occur.

  In particular, when passing the second surface, during fixing of the second image surface in the fixing unit portion, the first surface image to be the back surface also passes through the fixing nip portion again and is reheated. Therefore, when the heated first surface image is strongly rubbed by the guide member 205, the toner is likely to be peeled off, the gloss is likely to be changed, and the like.

  Therefore, the guide member 205 is positioned at the second position shown in FIG. The guide member 205 positioned at the second position does not contact 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 positioned at the second position, the guide member 205 is largely retracted with respect to the conveyance direction of the recording sheet P discharged from the auxiliary nip (perpendicular to the line connecting the centers of the roller pair). And will be in a position not to touch the paper positively. In this case, although the back curl during paper conveyance can not be corrected, since the paper is not stressed, the above-mentioned back surface scratch, abrasion, image smearing and gloss streaks do not occur.

  Unlike the fixing of the first side image, when the second side of the recording sheet P, which is not a thick sheet, is in the double-side passing mode, back curling does not occur, so the guide member 205 is retracted to the second position. An advantageous effect is obtained.

  The guide member 205, which is not retracted to the second position when passing the second side in the double-sided sheet feeding mode of the recording paper P which is not thick paper, is positioned between the single-sided printing and the double-sided printing. When printing on at least one side, it is configured to come to the first position.

  On the other hand, when the recording sheet P is a thick sheet or the like with high stiffness, when the guide member 205 is positioned at the first position, the contact resistance with the guide member 205 is lower than that of the recording sheet P which is a thin sheet with low stiffness. Is large. For this reason, the stress given to the paper itself is further increased, the mark of the contact is easily generated on the back surface of the paper, and the guide member 205 itself is easily abraded or the like.

  However, when the recording paper P is a thick paper or the like with high stiffness, back curling does not occur. Therefore, when the recording paper P is a thick paper or the like having a strong stiffness, the guide member moving means D performs the first side sheet passing mode in the single side sheet passing mode and the second side sheet passing in the double side sheet passing mode. The paper sheet is moved to the second position shown in FIG.

  As described above, by switching the guide member 205 between the first position and the second position, both the back curl correction and the avoidance of the image distortion and the like are made compatible.

  Subsequently, the configurations of the guide member 205 and the guide member moving means D will be described with reference to FIGS. 4 to 9.

  As shown in FIG. 4, the drive roller 204 is fixedly engaged with the roller shaft 204a rotatably supported at both ends on the pressure side separation member 202 via the slide bearing 208 and the roller shaft 204a. It consists of a plurality of short cylindrical portions 204b made of an elastic material such as rubber.

  The driving roller 204 is rotatable by transmitting the rotational driving force from the guide member moving means D shown in FIG. 6 to the driving gear 210 fixed to the end of the roller shaft 204a via the idler gear 211.

  As shown in FIGS. 4 to 7, the guide member 205 is fixed to a support shaft 205 a rotatably supported at the upper end portions of the pair of bracket arms 206. The pair of bracket arms 206 is rotatably fitted on the outer diameter portion of the slide bearing 208. A plurality of guide members 205 are respectively provided on a plurality of bosses 205b fixedly fitted to the support shaft 205a.

  The guide member 205 is fixed such that its proximal end is fixed to the boss 205 b and the overhanging end is covered by the driving roller 204. The guide member 205 is configured to be stopped at a position where the stopper portion 206 b of the bracket arm 206 is in contact with a part of the pressurizing side separation member 202. The posture position of the guide member 205 corresponding to this position is the first position for changing the angle of the recording sheet 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 operation of the solenoid 220, and a tension spring 209. The solenoid 220 has a housing fixed to the image forming apparatus main body.

  One end of the tension spring 209 is locked to the side surface portion of the pressing side separation member 202, and the other end is locked to the middle of the arm portion 206 a of the bracket arm 206. The tension spring 209 applies a tensile force of the spring so as to turn the bracket arm 206 in the direction in which the guide member 205 is at the first position shown in FIG.

  As shown in FIG. 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 as the other end surrounds the tip of the arm portion 206a of the bracket arm 206 from below. A long hole 207 d provided at the upper end of the upper extension 207 c that contacts the middle of the horizontal direction and is connected with the extension rod 220 a of the solenoid 220 by a pin.

  As shown in FIG. 7, the extension rod 220 a of the solenoid 220 is extended (the position shown by the dotted line), and as shown in FIG. 6, the actuating end 207 b of the link mechanism 207 is the tip of the arm 206 a of the bracket arm 206. It is in the state of being separated downward to.

  From the state shown in FIG. 6, when current flows in the internal coil of the solenoid 220 based on the control signal of the control device, the extension rod 220a of the solenoid 220 retracts. Thereby, the link mechanism 207 is rotated against the tensile force of the tension spring 209, and the actuating end 207b lifts the tip of the arm portion 206a of the bracket arm 206 (state shown in FIG. 7). Thereby, the guide member 205 is retracted from the first position shown in FIGS. 2 and 8 to the second position shown in FIGS. 3 and 9.

  On the other hand, when the current to the internal coil of the solenoid 220 is cut off from the state shown in FIG. 7 based on the control signal of the control device, the bracket arm 206 is rotated by the tensile force of the tension spring 209, and the guide member 205 is illustrated. It returns to the first position shown in FIG. Along with this, the extension rod 220a of the solenoid 220 is retracted by the tensile force of the tension spring 209, and the state shown in FIGS. 5 and 6 is obtained.

  With the above-described configuration, the gap between the drive roller 204 and the guide member 205 can be configured to minimize buildup of dimensional tolerances of components (only radial distance tolerance from the axial center of each component). . For this reason, the guide member 205 can move while the gap between the drive roller 204 and the guide member 205 is kept constant with high accuracy.

  As shown in FIG. 10, the branch members 15 are arranged in a plurality of claws corresponding to the width direction orthogonal to the recording sheet conveyance direction, and the guide members 205 are also orthogonal to the recording sheet conveyance direction. It is arranged in a plurality of claws corresponding to the width direction. Moreover, the branch members 15 and the guide members 205 are alternately arranged.

  As a result, even if the swing area of the branch member 15 and the swing area of the guide member 205 overlap on the recording paper conveyance line, they are independently rocked to guide the recording paper. ing.

  11 (a) to 11 (d) show four conveyance paths for the recording sheet formed by the combination of the first and second positions of the branch member 15 and the first and second positions of the guide member 205. Indicates The alternate long and short dash line in the drawing indicates the conveyance path of the recording sheet passing through the auxiliary nip portion formed by the driving roller 204 and the driven roller 203.

  FIG. 11A shows the conveyance path of the recording paper in the single-sided printing mode of thin paper, and the branching member 15 is in the second position and the guide member 205 is in the first position. The guide member 205 is brought into contact with the back surface (surface on the back curl side) of the recording sheet passing through the auxiliary nip portion and is curved so as to be in a concave phase in the reverse direction to the back curl and guided to the sheet discharge roller 13. It has become.

  FIG. 11B shows the conveyance path of the recording sheet in the single-sided printing mode of the thick sheet, and both the branch member 15 and the guide member 205 are in the second position. The guide member 205 is not in contact with the back surface of the recording sheet which does not cause back curling while passing through the auxiliary nip portion, and the branch member 15 causes the recording sheet to be softly curved and guided to the sheet discharge roller 13. There is.

  FIG. 11C shows the conveyance path of the recording sheet of the first side passing sheet in the double-sided printing mode of thin paper, and the branching member 15 is in the first position and the guide member 205 is in the second position. The guide member 205 makes slight contact with the back surface (second surface) of the recording sheet passing through the auxiliary nip portion in which the back curl is slightly corrected at the auxiliary nip portion, and the branch member 15 applies the recording sheet to the reversing roller 16. It is supposed to lead.

  FIG. 11D shows the conveyance path of the recording sheet of the second sheet passing in the double-sided printing mode of thin paper, and both the branch member 15 and the guide member 205 are in the second position. The guide member 205 is not in contact with the back surface (first surface) of the recording sheet which does not cause back curling while passing through the auxiliary nip portion, and the branch member 15 causes the recording sheet to be softly curved and the discharge roller 13 It is supposed to lead.

  Note that, as shown in FIG. 4, the guide member 205 has a plurality of rib shapes over its length, and a rib-like branch member 15 is inserted between the guide members 205.

  In FIG. 12, when the rotation center of the guide member 205 is aligned with the rotation center of the drive roller 204 (the position shown by the solid line in the drawing), the rotation center of the guide member 205 is the rotation center of the drive roller 204. Are arranged at a certain gap from the rotation center of the drive roller 204 (the position of the dotted line indicated by reference numeral 205 'in the figure).

  As seen in FIG. 12, the curl correction effect when the guide member 205 is at the solid line position and the curl correction effect when the guide member 205 is at the dotted line position are the same.

  The recording sheet passing through the auxiliary nip portion is discharged in a direction perpendicular to a line connecting the centers of the driving roller 204 and the driven roller 203. Therefore, when the guide member 205 is at the dotted line position, the contact angle θ ′ between the leading end of the sheet near the auxiliary nip portion and the guide member 205 is the sheet near the auxiliary nip portion when the guide member 205 is at the solid line position. The contact angle θ between the tip and the guide member 205 is smaller.

  If this contact angle becomes smaller, the leading end of the sheet is buckled and bent for conveyance, and in the worst case, the risk of jamming increases. Conversely, when the extension line of the surface of the guide member 205 in contact with the recording sheet 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 This leads to a reduction in the curl correction effect of bending the sheet.

  Therefore, in the present embodiment, the center of rotation of the guide member 205 is aligned with the center of rotation of the drive roller 204 so that the contact angle is large, and the extension line of the surface of the guide member 205 in contact with the recording paper is It is made to pass through the rotation center of the drive roller 204.

  In order to obtain the curl correction effect, it is necessary to bring the tip end of the guide member 205 close to the auxiliary nip portion, and therefore, a plurality of rubber portions of the drive roller 204 are provided to be spaced apart. The guide member 205 is configured to be inserted between the and the rubber portion.

  According to the image forming apparatus of the present embodiment, the drive roller 204 and the driven roller 203 are provided immediately downstream of the fixing device 20, and the guide member 205 is disposed at the first position and second immediately downstream of the auxiliary nip. It is configured to be switchable to the position of. As a result, by bending the back curl of the recording paper P to the opposite side by the fixing device 20, it is possible to make correction possible only under the condition where the back curl needs to be corrected.

  For example, in the case of a thick paper sheet, since the fixing device 20 does not cause back curling that the recording paper P curls to the back side, when the guide member 205 is always at the first position, conversely, the guide plate become. Further, since the contact force between the guide member 205 and the recording sheet is strong, damage (scratch) is generated on the back surface of the sheet by the guide member 205 and wear of the guide member 205 is generated. Furthermore, the back curl is corrected also from the point that side effects such as bending of the tip occur when the tip comes out from the auxiliary nip portion of the drive roller 204 and the driven roller 203 and the tip contacts the guide member 205 because paper rigidity is high. There is no need to position.

  According to the image forming apparatus of the present embodiment, from the above point of view, the image forming apparatus has drive means for switching the position of the guide member 205, and the position of the guide member 205 can be switched depending on the conditions. As a result, it is possible to provide an image forming apparatus in which damage to the recording paper P and the toner image is reduced by simultaneously achieving both reduction in back curling and conveyance stabilization that occur during fixing.

  According to the image forming apparatus of the present embodiment, the rotation center of the guide member 205 is configured coaxially with the axis of the drive roller 204. Therefore, the angular accuracy of the guide member 205 is reduced by the minimum component configuration so as to correct the curl. It can be configured with high accuracy.

  According to the image forming apparatus of the present embodiment, at the time of single-sided printing, by disposing the guide member 205 at the first position, the fixing device discharges the recording sheet P in a state in which back curling is corrected. can do. As a result, it is possible to prevent that the specified number of sheets can not be stacked on the sheet discharge tray 14 and that the stack itself on the sheet discharge tray 14 is disturbed. Further, at the time of double-sided printing, by disposing the guide member 205 at the second position, it is possible to prevent the occurrence of image distortion and gloss flaws on the first surface.

  Since the back curling when the first surface is fixed is corrected at the time of the second surface fixing, when being discharged, the back curl is reduced, and the guide member 205 is disposed at the first position. There is no need to correct curls. On the other hand, in the case of the first position, when the guide member 205 and the first surface strongly contact with each other, image distortion and gloss streaks occur, and therefore it is necessary to arrange the second position.

  According to the image forming apparatus of the present embodiment, the guide member 205 can be retracted to the second position in the case of the second side sheet passing in the double-sided printing mode of thin paper and in the case of thick sheet passing, the guide member 205 Can be avoided when it remains fixed in the first position.

  According to the image forming apparatus of the present embodiment, in the case of the second side sheet passing in the double-sided printing mode of thin paper and in the case of the thick sheet passing, back curling does not occur in the fixing device 20, so On the other hand, the guide member 205 can avoid the problem of face curling. Further, it is possible to avoid the problem that damage (scratch) occurs on the back side of the paper and the guide member 205 is worn out. Furthermore, since the paper rigidity is high, it is possible to avoid the problem that the front end is bent without being buckled when the front end is out of the auxiliary nip portion and the front end is in the guide member 205.

  According to the image forming apparatus of the present embodiment, by using the solenoid 220 as the driving means of the guide member moving means D, connection with the link mechanism 207 is easy, and inexpensive and space saving can be achieved. On the other hand, when using a motor such as a stepping motor, the cost of the motor itself is high, and including a gear train or the like for transmitting a drive requires a large space as a driving means, resulting in upsizing of the machine.

  According to the image forming apparatus of the present embodiment, the drive roller 204 has a roller circumferential surface formed of rubber, and the driven roller 203 has a roller circumferential surface harder than the roller circumferential surface of the drive roller 204 and having releasability. It is a configuration formed to have. Therefore, when the guide member 205 is at the first position (at the time of curl correction), the recording sheet discharged from the auxiliary nip portion of the drive roller 204 and the driven roller 203 collides with the guide member 205 and the angle is largely changed. For this reason, although a large conveyance resistance can be obtained, a high conveyance force can be obtained which is not inferior to the conveyance resistance, and a small amount of toner which can not be completely melted after fixing is hard to adhere to the follower roller 203 on the image surface side. Even deposition can be prevented. As a result, it is possible to prevent the toner image after fixing from being peeled off during passage through the auxiliary nip portion or generation of flaws.

  In the present embodiment, the positional relationship between the guide member 205 and the driven roller 203 is such that the first position of the guide member 205 which is severe is completed within the unit, and the second position is on the main body side. Although it was configured to be determined by the driving means, it may be reversed. In addition, by using a stepping motor or the like as the drive unit of the guide member 205, the posture position of the guide member 205 may be determined in multiple steps.

  As described above, the image forming apparatus according to the present invention has the effect of achieving both reduction in back curling that occurs during fixing and conveyance stabilization, and being able to reduce damage to recording paper and toner images. Is useful for image forming apparatuses.

DESCRIPTION OF SYMBOLS 1 image forming apparatus A image forming unit C back curl correction mechanism D guide member moving means N fixing nip portion P recording paper 15 branching member (recording paper conveyance path branching means)
Reference Signs List 20 fixing device 203 driven roller 204 drive roller 204a roller shaft 205 guide member 207 link mechanism 220 solenoid

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

Claims (6)

A fixing device for causing a recording sheet to which an image has been transferred in an image forming unit to pass through a fixing nip portion and fixing the image on the recording sheet in the fixing nip portion; the recording sheet conveyed downstream of the fixing device In an image forming apparatus having a recording paper conveyance path branching means for switching between an out-of-machine discharge path for discharging the sheet out of the machine and a reverse path of double-sided printing,
The conveyance path between the fixing device and the recording sheet conveyance path branching means is provided with a back curl correction mechanism.
The back curl correction mechanism is
An auxiliary nip portion formed by a drive roller provided on the side where back curling occurs on the recording paper in the fixing nip portion and a driven roller provided on the side where the recording paper is heated, and pressing the recording paper to perform auxiliary conveyance;
A guide member provided on the same side as the drive roller for guiding the recording paper;
A guide member moving means is provided for moving the guide member to a first position for pressing the recording sheet required while passing through the auxiliary nip portion and a second position for separating the recording sheet from the recording sheet. Image forming device.   The guide member is provided so that the rotation center is coaxial with the roller axis of the drive roller, and is moved to the first position and the second position by the guide member moving means. An image forming apparatus according to claim 1.   2. The image forming apparatus according to claim 1, wherein the guide member is positioned at the first position during at least one-sided printing between single-sided printing and double-sided printing.   The guide member moving means is configured to move the guide member to the second position when the recording sheet is a thick sheet. Image forming apparatus as described.   The guide member moving means has a solenoid as a drive source, and a link mechanism for moving the guide member to either the first position or the second position by operating the solenoid. The image forming apparatus according to any one of claims 1 to 4, wherein   The roller peripheral surface portion is formed of an elastic material, and the driven roller is formed so that the roller peripheral surface portion is harder than the roller peripheral surface portion of the driving roller and has releasability. An image forming apparatus according to any one of Items 1 to 5.

Images