JP2017044907A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can correct back curl generated during fixation and can prevent the occurrence of a defect in image quality and failure in conveyance.SOLUTION: A back curl correction mechanism C comprises: a conveyance roller pair formed of a drive roller 204 and a driven roller 203 that hold and convey a recording sheet fed from a fixing device 20; and a guide member 205. The guide member 205 can move between a first position for guiding the recording sheet ejected from the conveyance roller pair at a predetermined ejection angle and a second position separated from the recording sheet. When the length of a conveyance path from the conveyance roller pair to a pair of ejection rollers 13 is changed due to the movement of the guide member 205 between the positions, a control part 300 adjusts a time interval for feeding a recording sheet to the conveyance path.SELECTED DRAWING: Figure 5

Description

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

  In an image forming apparatus using an electrophotographic system, an electrostatic latent image is formed in an image forming unit, and then developed with toner, which is a developer, to be visualized as a toner image, and then developed by a transfer device. The toner image is transferred onto a recording sheet, and then the image is fixed on the recording sheet with a fixing device.

  The fixing device includes a heating member and a pressure roller, and is configured such that they are pressed against each other to form a fixing nip portion. The recording paper onto which the toner image has been transferred in this fixing nip is conveyed to the fixing device, and the recording paper carrying the unfixed toner image is passed through the fixing nip, By heating, the toner image is thermally fixed on the recording paper.

  In this type of thermal 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 on the heating member side and the pressure roller) A temperature difference occurs on the back surface 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 part, the moisture contained in the recording paper evaporates more from the front side, and the amount of moisture movement from the back side to the front side increases, so the front side is the back side. More water content. As a result, the paper fiber on the front side has a larger elongation than the back side, and a phenomenon that the recording paper curls to the back side (hereinafter referred to as “back curl”) occurs.

  In particular, recently, from the viewpoint of energy saving / warming up, a fixing device has been developed which has a heating member with a low heat capacity and a high temperature rise. In such a fixing device, since the paper can be passed before the pressure roller side is warmed, 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 paper at the time of fixing is increased. Easy to grow. For this reason, the back curl generated at the fixing nip portion is increasing. In such a fixing device, there is a problem that when the paper is discharged in a state where the back curl is large, the specified number of sheets cannot be discharged onto the discharge tray, or the stack on the discharge tray itself is disturbed. To do. Therefore, conventionally, inventions that eliminate back curl have been proposed (see Patent Documents 1, 2, and 3).

  In the image forming apparatus disclosed in Patent Document 1, a first transport roller is disposed on the downstream side of the fixing unit, and a second transport roller is disposed on the downstream side thereof. In the conveyance path from the first conveyance roller to the second conveyance roller, a guide member that is curved in the direction opposite to the direction of the back curl generated on the recording paper by passing through the fixing nip portion is provided. The recording paper conveyance speed by the second conveyance roller is set to a value larger than the recording paper conveyance speed by the first conveyance roller. As a result, the recording paper is conveyed while being pressed against the guide member curved in the direction opposite to the direction of the back curl, and the curling of the recording paper is corrected.

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

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

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

  First, in the techniques disclosed in Patent Documents 1 and 2, the recording paper is always forcibly pressed by the guide member to curl in the opposite direction to the back curl. For this reason, for example, the following problem occurs in the case of passing the thick paper. First, since a back curl in which the recording paper curls on the back surface in the fixing device does not occur in the thick paper, the face curl is reversed by the guide member that always exerts pressing force. Further, since the contact force between the guide member and the recording paper is strong, the guide member causes damage (scratches) on the back surface of the paper or wear of the guide member. Further, since the paper rigidity is high, problems such as bending of the leading end of the thick paper coming out of the pair of rollers and contact with the guide member occur, making it difficult to stabilize the conveyance.

  Next, the technique disclosed in Patent Document 3 is configured such that the guide member that deforms the recording paper in a corrective manner can be moved in the retracting direction by the stiffness of the recording paper. When the contact pressure of the member increases, the guide member retracts and the contact pressure is adjusted. Therefore, it can be said that the above-described problem that occurs in the case of passing a cardboard can be avoided. However, even if the guide member moves to the final retracted position, the position of the guide member is basically determined by the stiffness of the recording paper, so that the recording paper is conveyed while contacting the guide member.

  Therefore, at the time of the second paper passing in double-sided printing, there is a toner image on the first surface on the back surface of the recording paper that contacts the guide member, and the toner image and the guide member come into contact. Since the second surface is immediately after fixing, the toner image on the back surface is not at a temperature at which the toner completely melts, but the toner image that has received heat comes into contact with the guide member. In such a situation, gloss unevenness (gloss difference between a portion in contact with the guide member and a portion not in contact) occurs even when lightly touched. Therefore, the occurrence of image quality defects such as uneven glossiness cannot be completely prevented by merely controlling the contact pressure between the guide member and the recording paper based only on the stiffness of the recording paper.

  Further, when the guide member is moved due to the stiffness of the recording paper, the recording paper transport path length fluctuates before and after the movement, and the recording paper transport interval becomes narrower or wider than a predetermined target. As a result, a conveyance failure such as a jam may occur.

  The present invention has been made to solve the above-described problems, and an image forming apparatus capable of correcting back curl caused by fixing and preventing occurrence of poor image quality and conveyance failure. It is intended to provide.

  In order to solve the above-described problem, an image forming apparatus according to the present invention is provided on a downstream side of the fixing device, and a fixing device that fixes the image on a recording sheet onto which an image formed by the image forming unit is transferred. The back curl correction mechanism, and a pair of paper discharge rollers provided on the downstream side of the back curl correction mechanism for discharging the recording paper to the outside of the apparatus. A pair of transport rollers that sandwich and transport the recording paper delivered from the fixing device, and a recording paper that is provided on the downstream side of the pair of transport rollers and that is discharged from the pair of transport rollers. In the image forming apparatus including a first position guided at a discharge angle and a guide member movable between a second position away from the recording sheet, the pair of the pair is moved by the movement of the position of the guide members. Carrying If the length of the conveying path from the roller to the pair of discharge rollers is changed, it is further provided with configuration control means for adjusting the time interval for feeding the recording sheet to the conveying path.

  According to the present invention, it is possible to provide an image forming apparatus capable of correcting back curl caused by fixing and preventing occurrence of poor image quality and poor conveyance.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram of the fixing device according to the embodiment of the present invention during back curl correction. 2 is a schematic configuration diagram of the fixing device according to the embodiment of the present invention when back curl is not corrected. FIG. FIG. 6 is a diagram illustrating a plurality of sheet conveyance paths by combining the position of a branch member and the position of a guide member according to the embodiment of the present invention. FIG. 6 is a diagram illustrating a paper conveyance path when back curl is corrected and a paper conveyance path when back curl is not corrected according to the embodiment of the present invention. It is a schematic block diagram of the control part which concerns on embodiment of this invention. It is a functional block diagram of a control part concerning an embodiment of the invention.

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

First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described.
An image forming apparatus 1 illustrated in FIG. 1 is a color laser printer, and includes an image forming unit A, a paper feeding unit B, a fixing device 20, a pair of paper discharge rollers 13, a paper discharge tray 14, and a pair of reversals. 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, an exposure device 9, a transfer device 3, and the like, which will be described later. As a characteristic configuration, the image forming apparatus 1 includes a back curl correction mechanism C on the downstream side of the fixing device 20. This will be described in detail below.

  In 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. Each of the image forming units 4Y, 4M, 4C, and 4K stores developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals, and the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C are illustrated. Since the configuration is the same as that of the black image forming unit 4K, the reference numerals thereof are omitted.

  Below each image forming unit 4Y, 4M, 4C, 4K, an exposure device 9 for exposing the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a laser light source, a polygon mirror 51a, an f-θ lens 51b, a plurality of reflection mirrors 51c, and the like (not shown), and irradiates the surface of each photoconductor 5 with laser light based on image data. An electrostatic latent image is formed on the surface 5.

  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, four primary transfer rollers 31, a secondary transfer roller 36, a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35. Is 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 rotating the secondary transfer backup roller 32, the intermediate transfer belt 30 runs (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 photoconductor 5 to form a primary transfer nip. Further, a power source is connected to each primary transfer roller 31 so that a predetermined DC voltage (DC) or a predetermined AC 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. Similarly to the primary transfer roller 31, a power source 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 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. The waste toner collected by the belt cleaning device 35 is accommodated in a waste toner container via a waste toner transfer hose.

  A bottle container 2 is provided in the upper part of the image forming apparatus main body, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. ing. Toner is replenished from each toner bottle 2Y, 2M, 2C, 2K to each developing device 7 via a replenishment path (not shown) provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7. The

  On the other hand, a sheet feeding unit B is provided at the lower part of the image forming apparatus main body. The paper supply unit B includes a paper supply tray 10 that stores recording paper P as a recording medium, a paper supply roller 11 that carries the recording paper P out of the paper supply tray 10, and the like.

In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, a manual paper feed mechanism may be provided. In the present embodiment, cardboard 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 is provided for discharging the recording paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as timing rollers for transporting the recording paper P to the secondary transfer nip at the transport timing is arranged upstream of the position of the secondary transfer roller 36 in the recording paper transport direction. It is installed.

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

  A branch member 15 is provided between the paper 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 fixed to the main body so as to be rotatable.

  That is, the branching member 15 is configured to discharge the recording paper P conveyed downstream of the fixing device 20 to a discharge tray 14 outside the apparatus, and to perform duplex printing. The reversing path (path passing through the inside of the duplex unit 17 described later) is switched. Further, a back curl correction mechanism C described later is provided between the branching member 15 and the fixing device 20.

  The double-side reversing path 40 includes a reversing roller 16 for switching back the recording paper P provided on the downstream side of the branching member 15, and a double-sided unit 17 between the reversing roller 16 and the registration roller 12. The duplex unit 17 includes conveyance rollers 42 to 44 to form a reversal path for duplex printing, and the recording paper P after fixing the first surface is switched back by the reversal roller 16 and passes through the conveyance rollers 42 to 44. Then, it is conveyed to the registration roller 12.

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

  First, when an image forming operation is started, each photoconductor 5 in each of the image forming units 4Y, 4M, 4C, and 4K is driven to rotate clockwise in the drawing, and the surface of each photoconductor 5 is predetermined by a charging device 6. Uniformly charged to polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5.

  At this time, the image information to be exposed on each photoconductor 5 is monochromatic image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. The toner is supplied to the electrostatic latent images formed on the respective photoreceptors 5 by the developing devices 7 in this way, whereby the electrostatic latent images are visualized (visualized) as images.

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure.

  Further, by applying a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current to each primary transfer roller 31, the primary transfer nip between each primary transfer roller 31 and each photoreceptor 5 is applied. A transfer electric field is formed.

  Thereafter, when each color image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the image on each photoconductor 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 way, a full color image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by the neutralization device, and the surface potential is initialized.

  In the lower part of the printer, the paper feed roller 11 starts to rotate, and the recording paper P is sent out from the paper feed tray 10 to the transport path R. The recording paper P delivered to the transport path R is temporarily stopped by the registration rollers 12.

  Thereafter, rotation of the registration roller 12 is started at a predetermined timing, and the recording paper P is conveyed to the secondary transfer nip in accordance with the timing when the image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. Then, the image on the intermediate transfer belt 30 is collectively transferred onto the recording paper P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto 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 to the recording paper P by the fixing device 20. The recording paper P conveyed from the fixing device 20 is guided in the discharging direction and the refeeding direction via the branching member 15 for switching the path for discharging the recording paper P to the outside of the apparatus and the double-side reversing path. .

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

  In the double-sided paper passing mode, the branching member 15 is closed in the direction of the arrow, so that the recording paper P after the first side fixing is guided to the double-sided reverse path 40. The recording sheet P guided to the duplex reversing path 40 is switched back by the pair of reversing rollers 16, conveyed to the duplex unit 17, conveyed again to the pair of registration rollers 12, and fed again. Similar to the first side, the second side image is printed on the back side of the recording paper P. Then, the recording paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full color image is formed on the recording paper P. A single color image is formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. It is also possible to form a two-color or three-color image using two or three image forming units.

Next, the fixing device 20 and 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 the fixing device and the back curl correction mechanism according to the present embodiment.

  As shown in FIG. 2, the fixing device 20 is used to fix the toner image T after being transferred, which is carried on the recording paper P, by melting and infiltrating it with heat and pressure. A fixing belt 21 having a possible flexibility is provided.

  The fixing device 20 passes the recording paper P onto which the toner image has been transferred by the image forming unit A through the fixing nip N and applies heat and pressure at the fixing nip N to fix the toner image on the recording paper P.

  In addition to the endless fixing belt 21, the fixing device 20 is a counter rotating body that forms a fixing nip portion N by applying pressure to the fixing belt 21 in contact with the fixing belt 21. A pressure roller 22 is provided. Inside the fixing belt 21, a heater 23 including a plurality of halogen lamps 23 a and 23 b for heating the inner surface side of the fixing belt 21 at a place other than the fixing nip portion N is provided.

  Inside the fixing belt 21, a nip forming member 24 that is a base member for forming a nip disposed inside the fixing belt 21, a stay 25 that supports the nip forming member 24, and light emitted from the heater 23. Is provided on the fixing belt 21.

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

  In the nip forming member 24 shown in FIG. 2, the shape of the fixing nip portion N is flat, but is not limited to this shape. For example, when the fixing nip portion N is formed in a concave shape along the circumferential surface of the pressure roller 22, the leading edge of the recording paper P passing through the fixing nip portion N is close to the pressure roller 22, and thus the fixing belt 21. There is an advantage that the separability from the 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 is used for feedback processing of the heater 23. In FIG. 2, an arrow F indicates the conveyance direction of the recording paper P.

  The fixing belt 21 is an endless belt formed in a thin and flexible sleeve shape, and is composed of a base material and a release layer located on the surface thereof. For the base material, a metal material such as nickel or A-SUS or a resin material such as polyimide is used. For the release layer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), or the like having releasability with respect to the toner is used.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluororubber provided on the peripheral surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Or it is comprised by the mold release layer which consists of PTFE etc.

  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 contact with the fixing belt 21.

  At the place where the pressure roller 22 and the fixing belt 21 contact each other, the elastic layer 22b of the pressure roller 22 is crushed so that pressure is applied to the fixing belt 21 and the nip forming member 24 has a predetermined width. The fixing nip portion N is secured.

  The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the image forming apparatus main body. When the pressure roller 22 is rotationally driven, 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, a heating source such as a halogen heater using radiant heat may be disposed inside the pressure roller 22. In addition, when the elastic layer 22b is not provided, the heat capacity is reduced and the fixability is improved. However, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image and the solid portion of the image is glossy. Unevenness may occur. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more.

  Aluminum, iron, stainless steel, or the like can be selected as the pipe-shaped metal used for the hollow roller. When providing a heat source in the pressure roller 22, in order to prevent the support from being heated by radiant heat from the heat source, a heat insulating layer is provided on the support surface or a heat ray reflecting surface is provided by mirror treatment. Is desirable. The heat source in this case is not limited to the halogen heater described above, and an IH heater, a resistance heating element, or a carbon heater can also be used.

  In the case of the fixing device 20 described above, since the heating member having a low heat capacity is directly heated, the fixing device 20 has a very fast temperature rise, so that there is an advantage that the first print can be accelerated. However, from the viewpoint of the occurrence of the back curl on the recording paper P, the fixing is performed before the pressure roller is sufficiently warmed. Therefore, the back curl (for example, the curve of the solid line P ′ shown in FIG. (Shape) becomes very large.

  On the recording paper exit side of the fixing device 20, a separation transport mechanism is provided that separates the recording paper P that has passed through the fixing nip portion N in the vicinity of the fixing nip portion and guides the recording paper P toward the paper discharge portion in the discharge direction.

  The separating and conveying mechanism includes a belt-side separating member 201 having a leading end 201a close to the fixing belt 21 on the downstream side in the moving direction of the recording paper P moving from the fixing nip N, and a swing close to the pressure roller 22 side. And a pressure side separating member 202 having an end 202a.

  The belt-side separation member 201 is provided to peel off the recording paper P that sticks and sticks to the fixing belt 21 from the fixing belt 21. For this reason, a metal sheet is used so as to obtain an accuracy capable of positioning the attached recording sheet P at a close position where the recording sheet P can be lifted from the surface of the fixing belt 21.

  A resin molded product is used for the pressure side separating member 202, and a support rod 202 </ b> A provided in a part thereof is rotatably supported on the housing side (not shown) so as to face the pressure roller 22. The swing end 202a can swing so as to be able to come into contact with and separate from the pressure roller 22.

  The pressure-side separating member 202 is swung with respect to the pressure roller 22 so that, for example, when the jammed recording paper P is removed from the fixing nip portion N, the pressure-side separation member 202 is largely swung in a direction away from the pressure roller 22. A space for inserting the hand into the fixing nip portion N can be created. Thereby, the recording paper P can be pulled out.

  The back curl correction mechanism C provided between the branching member 15 and the fixing device 20 includes a driving roller 204, a driven roller 203, and a guide member 205. The driving roller 204 and the driven roller 203 constitute a pair of conveying rollers of the present invention, and nipping and conveying the recording paper P sent from the fixing device 20.

  The driving roller 204 and the driven roller 203 are disposed on the downstream side of the belt side separating member 201 and the pressure side separating member 202. The driving roller 204 is supported by the pressure side separation member 202, and the driven roller 203 is supported by the holder 207.

  The driving roller 204 and the driven roller 203 are pressed against each other to form an auxiliary nip portion and roll and rotate to assist the conveyance of the recording paper P.

  The driving roller 204 may be formed of rubber at least on the roller peripheral surface, and the driven roller 203 may be formed such that at least the roller peripheral surface is harder than the roller peripheral surface of the driving roller 204 and has releasability.

  In the present embodiment, the driving roller 204 includes a cored bar 204a and a solid rubber material 204b having a high friction coefficient made of silicon, EPDM, urethane, fluororubber or the like provided on the surface of the cored bar 204a, and recording. The paper conveyance force can be obtained.

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

  The reason for using a hollow pipe-shaped metal is to reduce the heat capacity and prevent the water vapor generated from the paper evaporated during fixing from adhering to the driven roller side, so that the heat from the fixing heats up quickly. is there.

  The reason why the low μ tube is arranged on the surface is that a small amount of toner that has not melted after fixing is difficult to adhere and does not accumulate even if it adheres. That is, the driven roller 203 side is conveyed while always in contact with the image surface side, and thus has the above-described configuration. The driven roller 203 is held on the image forming apparatus main body by a spring member (not shown) via the holder 207. By pressing the holder 207 with the spring member, the driving roller 204 and the driven roller 203 come into contact with each other to form an auxiliary nip portion, and the recording paper P can be auxiliary conveyed.

  The guide member 205 is provided from the fixing unit so that the center of rotation is coaxial with the roller axis of the driving roller 204. The guide member 205 is moved to a first position (back curl correction position) shown in FIG. 2 by an arbitrary guide member moving means (not shown) driven based on a control signal from the control unit 300, as shown in FIG. It is moved to one of the second positions shown (back curl non-correcting position). The first position (back curl correction position) is the advance position where the guide member 205 contacts the recording paper P, and the second position (back curl non-correction position) is the guide member 205 away from the recording paper P ( It is the retreat position.

  In a state where the guide member 205 is located at the first position shown in FIG. 2, the guide member 205 slides so as to press the front side in the conveyance direction of the recording paper P passing through the auxiliary nip portion on the same side as the driving roller 204. The recording paper P functions to be bent in a concave shape on the opposite side to the back curl.

  That is, when the guide member 205 is held at the first position, the drive roller is opposite to the direction of the recording paper P passing through the auxiliary nip portion (perpendicular to the line connecting the centers of the roller pairs). It is arranged at a position that closes the route from the same side as 204.

  For this reason, the leading edge of the recording paper P comes into contact with the guide member 205 at the contact angle θ shown in FIG. 2, and the recording paper P is then pressed by the guide member 205 while the nip conveying force between the driving roller 204 and the driven roller 203 is reached. As a result, auxiliary conveyance is performed.

  As a result, the guide member 205 is transported (guided) with respect to the recording paper P, with the contact nip (discharge angle) θ1 being finally set from the auxiliary nip portion as a starting point. The back curl can be corrected. By using such a conveyance path, the recording paper P passing through the guide member 205 can improve the back curl generated by the fixing and can be discharged to the paper discharge tray 14.

  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 conveyance resistance between the back surface of the recording paper P and the guide member 205 is large, and stress is applied to the paper itself. It will be. In particular, for thick paper that is strong, contact marks with the guide member 205 may be generated on the back side of the paper, or the guide member 205 itself may be worn.

  When the second side of the recording paper P is passed in the double-sided mode, the guide member 205 is in contact with the side (first side) where the image is present, and image blurring and gloss streaks are likely to occur.

  In particular, when the second surface is passed, during fixing of the second image surface in the fixing unit, the first surface image as the back surface is also reheated through the fixing nip portion N. For this reason, when the warmed first-surface image is rubbed strongly by the guide member 205, image quality defects such as toner peeling and gloss change tend to occur.

  Therefore, the guide member 205 is positioned at the second position shown in FIG. The guide member 205 located at the second position is in non-contact with the recording paper P passing through the auxiliary nip portion, and functions so as not to bend the recording paper P.

  When the guide member 205 is positioned at the second position, the guide member 205 is largely retracted in the conveyance direction of the recording paper P discharged from the auxiliary nip portion (perpendicular to the line connecting the centers of the roller pair). Therefore, it will be in a position where it does not actively contact the paper. In this case, the back curl at the time of paper conveyance cannot be corrected, but stress on the paper is not applied, so that the above-described back surface scratches, abrasion, image blurring, and gloss streaks do not occur.

  When the recording paper P is passed through the second side in the double-sided paper passing mode, unlike the fixing of the first side image, the back curl does not occur. Therefore, it is advantageous that the guide member 205 is retracted to the second position. An effect is obtained.

  On the other hand, when the recording paper P is a strong thick paper or the like, the guide member 205 is positioned at the first position (back curl correction position), compared to the recording paper P which is a thin paper with weak stiffness. The contact resistance with the member 205 is large. For this reason, the stress applied to the paper itself is further increased, the trace of contact is likely to occur on the back side of the paper, and the wear of the guide member 205 itself is likely to occur.

  However, when the recording paper P is a strong thick paper or the like, no back curl occurs. Therefore, when the recording paper P is a strong thick paper or the like, a guide member moving means (not shown) is used when the first side of the single-sided printing mode and the second side of the double-sided paper passing mode. The guide member 205 is moved to the second position (back curl non-correcting position) shown in FIG.

As described above, by switching the guide member 205 between the first position and the second position, both back curl correction and avoidance of image blurring are realized. Specifically, according to the combination of the printing mode (single-sided printing, double-sided printing) and the thickness of the recording paper (thick paper having a basis weight of 160 g / m ² or more, ordinary thick recording paper having a basis weight of less than 160 g / m ² ), the guide The position of the member 205 and the position of the branch member 15 are switched as shown in FIG.

  4A to 4D show four recording paper conveyance paths formed by a combination of the first and second positions of the branching member 15 and the first and second positions of the guide member 205. Indicates. A one-dot chain line in the drawing indicates a conveyance path of the recording paper that passes through the auxiliary nip formed by the driving roller 204 and the driven roller 203.

(Normal thick recording paper single-sided printing mode)
FIG. 4A shows a conveyance path in a single-sided printing mode of a normal thickness recording paper having a basis weight of less than 160 g / m ² . The branch member 15 is in the first position (external discharge path), and the guide member 205 is in the first position (back curl correction position). The guide member 205 is brought into contact with the back surface (the surface on the back curl side) of the recording paper that is passing through the auxiliary nip portion and is bent so as to form a concave curved surface in the opposite direction to the back curl and is guided to the paper discharge roller 13.

(Cardboard single-sided printing mode)
FIG. 4B shows a conveyance path in a single-sided printing mode of cardboard having a basis weight of 160 g / m ² or more. The branching member 15 is in the first position (external discharge path), and the guide member 205 is in the second position (back curl non-correcting position). The guide member 205 does not come into contact with the back surface of the recording paper that has not passed back curl while passing through the auxiliary nip portion, and the branch member 15 softly curves the recording paper and guides it to the paper discharge roller 13.

(When the first side is fed in the double-sided printing mode for normal thickness recording paper)
FIG. 4C shows a conveyance path when the first surface of the normal thickness recording paper having a basis weight of less than 160 g / m ² is passed in the duplex printing mode. The branch member 15 is in the second position (reversal path), and the guide member 205 is in the second position (back curl non-correcting position). The guide member 205 makes slight contact with the back surface (second surface) of the recording paper passing through the auxiliary nip portion where the back curl has been slightly corrected at the auxiliary nip portion, and the branching member 15 causes the recording paper to contact the reverse roller 16. Lead.

(When the second side is passed in the double-sided printing mode for normal thickness recording paper)
FIG. 4D shows a conveyance path when the second surface of the normal thickness recording paper having a basis weight of less than 160 g / m ² is passed in the double-sided printing mode. The branching member 15 is in the first position (external discharge path), and the guide member 205 is in the second position (back curl non-correcting position). The guide member 205 does not contact the back surface (first surface) of the recording paper passing through the auxiliary nip portion, and the branching member 15 softly curves the recording paper and guides it to the paper discharge roller 13.

  As shown in FIGS. 4C and 4D, in the double-sided printing mode, the guide member 205 is in the second position (back curl non-correcting position) both when the first side passes and when the second side passes. Be placed. By switching the position of the branching member 15, the recording paper is guided to the reverse path after fixing the first surface and to the discharge path outside the apparatus after fixing the second surface.

  Next, the control part 300 which concerns on embodiment of this invention is demonstrated with reference to FIG. 6 and FIG.

  As illustrated in FIG. 6, the control unit 300 is a microcomputer that includes a CPU 310, a ROM 320, a RAM 330, an input / output interface 340, and the like, and controls each functional unit of the image forming apparatus 1.

  In addition, a storage unit (not shown) is connected to the control unit 300. The storage unit stores various data and control programs, and the control unit 300 reads and executes the control programs from the storage unit, and reads and writes various data to and from the storage unit during execution.

  As shown in FIG. 7, the control unit 300 includes functional modules such as an image formation control unit 350, a back curl correction switching unit 360, a print mode switching unit 370, and a recording paper transport unit 380.

  An image formation control unit 350 of the control unit 300 controls exposure, image formation, transfer, and fixing processes in the image forming unit A. It also adjusts the timing between processes.

  The back curl correction switching unit 360 of the control unit 300 switches back curl correction / non-correction in the back curl correction mechanism C.

  Specifically, when back curl correction is performed in the back curl correction mechanism C, the control unit 300 sends a control signal to the drive unit of the guide member 205 to move the guide member 205 to the first position (back curl correction). Position). When the back curl correction is not performed, the control unit 300 sends a control signal to the drive unit of the guide member 205 to move the guide member 205 to the second position (back curl non-correction position).

  A print mode switching unit 370 of the control unit 300 switches between single-sided / double-sided printing modes.

  Specifically, when the printing mode is set to the single-sided printing mode, the control unit 300 sends a control signal to the driving unit of the branching member 15 and moves the branching member 15 to the first position (external discharge path). Let In addition, when the first surface is passed in the duplex printing mode, the control unit 300 sends a control signal to the drive unit of the branching member 15 to move the branching member 15 to the second position (reverse path). At the time of passing the second side in the duplex printing mode, the control unit 300 sends a control signal to the driving unit of the branching member 15 to move the branching member 15 to the first position (external discharge path).

  A recording paper conveyance unit 380 of the control unit 300 controls recording paper conveyance in the apparatus.

  Specifically, the control unit 300 sends a control signal to each drive unit such as the feed roller 11, the registration roller 12, the reversing roller 16, and the conveyance rollers 42 to 44 in addition to the drive roller 204 and the paper discharge roller 13, The timing, conveyance speed, and conveyance interval of the recording paper P in the apparatus are controlled. In particular, when recording paper is continuously printed, the control unit 300 controls the driving roller 204 to adjust the timing at which the recording paper P is fed by the driving roller 204 and its driven roller 203 to perform recording before and after. The distance or time interval of the paper can be controlled.

  Further, the control unit 300 may be configured to receive various status information such as the image forming unit A, the guide member 205, the branching member 15, and the driving roller 204.

  When the length of the transport path (hereinafter referred to as “discharge transport path”) from the driving roller 204 and the driven roller 203 to the pair of paper discharge rollers 13 is changed by the movement of the position of the guide member 205, the control unit 300 The time interval for feeding the recording paper P to the discharge conveyance path is adjusted.

  Here, the “time interval for feeding the recording paper to the discharge conveyance path” is the time when the trailing edge of the preceding recording paper P passes through the auxiliary nip formed by the driving roller 204 and the driven roller 203, and the subsequent time This is the length of time with the time when the trailing edge of the recording paper P passes through the auxiliary nip as the end point. However, it is arbitrary which part of the recording paper is considered as the passage time of the auxiliary nip portion, and may be the leading edge of the recording paper or the trailing edge.

  The time interval for feeding the recording paper P to the discharge conveyance path can be adjusted by changing the conveyance speed by controlling the rotation driving of the drive roller 204 and, if necessary, the discharge roller 13 by the recording paper conveyance unit 380 of the control unit 300. This time interval can also be adjusted by comprehensively adjusting the interval of each process under the control of the recording paper conveyance unit 380 and the image formation control unit 350 of the control unit 300.

  The controller 300 adjusts the time interval for feeding the recording paper P into the discharge conveyance path so that the time interval of the recording paper P at the end of the discharge conveyance path is kept constant before and after the change of the length of the discharge conveyance path. May be.

  Here, “the time interval of the recording paper at the end of the discharge conveyance path” starts from the time when the trailing edge of the preceding recording paper P passes through the paper discharge nip formed by the pair of paper discharge rollers 13, and the subsequent This is the length of time when the trailing edge of the recording paper P passes through the paper discharge nip portion. However, it is arbitrary which part of the recording paper is used as a reference to consider the passage time of the paper discharge nip, and may be the leading edge or the trailing edge of the recording paper.

  Further, the control unit 300 sets the time interval for feeding the recording paper P to the discharge conveyance path so that the distance interval of the recording paper P at the end of the discharge conveyance path is kept constant before and after the change of the length of the discharge conveyance path. You may adjust.

  Here, “the distance between the recording sheets at the end of the discharge conveyance path” means the preceding recording at the time when the trailing end of the preceding recording sheet P passes through the discharge nip formed by the pair of discharge rollers 13. This is the distance between the trailing edge of the paper and the leading edge of the subsequent recording paper. However, which part of the recording paper is considered as a reference is arbitrary, and may be the leading edge or the trailing edge of the recording paper.

  Next, how the length of the discharge conveyance path from the driving roller 204 and the driven roller 203 to the pair of discharge rollers 13 is changed by the movement of the position of the guide member 205 will be described.

As an example, a case where the type of recording paper is switched from normal thick recording paper (basis weight less than 160 g / m ² ) to thick paper (basis weight 160 g / m ² or more) in the single-sided printing mode will be described with reference to FIG. FIG. 5A shows a discharge path outside the apparatus in the case where the back curl correction is performed by the guide member 205 on the normal thickness recording paper by a one-dot chain line. FIG. 5B shows a discharge path outside the apparatus when the back curl correction is not performed on the thick recording paper by the guide member 205 by a one-dot chain line.

  In this example, the position of the guide member 205 is switched from the first position where back curl correction is performed (FIG. 5A) to the second position where back curl correction is not performed (FIG. 5B). . At this time, when the transport distance of the recording paper transport path (discharge transport path) from the auxiliary nip portion between the driving roller 204 and the driven roller 203 to the paper discharge roller 13 is seen, it is the distance La in FIG. On the other hand, the distance Lb is shown in FIG. That is, the conveyance distance of the recording paper discharge conveyance path changes depending on the position of the guide member 205.

  For this reason, if the position of the guide member 205 is changed while the recording paper is continuously fed into the discharge conveyance path, the conveyance distance of the recording paper also changes. Clogs or spreads. Such a variation in the distance between recording sheets may cause a conveyance failure such as a jam.

  Therefore, a control unit 300 is provided for adjusting the time interval for feeding the recording paper into the discharge conveyance path. The control unit 300 changes the timing at which the recording sheet is fed into the discharge conveyance path in accordance with the switching of the position of the guide member 205. By such control, the interval between the recording sheets when the recording sheets are continuously fed can be kept constant. As a result, unintended clogging and spreading between the recording papers can be eliminated, and the recording paper P can be transported satisfactorily.

  The adjustment of the conveyance timing by the control unit 300 shortens the time interval for feeding the recording paper to the discharge conveyance path when the guide member 205 is switched from the position shown in FIG. 5A to the position shown in FIG. Further, when switching from the position shown in FIG. 5B to the position shown in FIG. 5A, the time interval for feeding the recording sheet into the discharge conveyance path is lengthened. By controlling in this way, it is possible to prevent the recording paper interval after the paper discharge roller 13 from being too clogged or widened.

  According to the image forming apparatus of the present embodiment, when the length of the discharge conveyance path is changed by the movement of the position of the guide member 205, the control unit 300 adjusts the time interval for feeding the recording paper P to the discharge conveyance path. To do. Accordingly, it is possible to control the time interval between the recording sheets P at the end of the discharge conveyance path so as to be kept constant before and after the change of the discharge conveyance path, and it is possible to prevent a conveyance failure such as a jam.

  The guide member 205 of the back curl correction mechanism C includes a first position for guiding the recording paper P discharged from the driving roller 204 and the driven roller 203 (conveying roller pair) at a predetermined discharge angle, and the recording paper P. The second position away from the second position is movable. For this reason, the toner on the first surface is transported to the discharge roller 13 while the guide member 205 is moved to the second position (back curl non-correction position) when the second surface is passed in the duplex printing mode. The guide member 205 does not rub the image and image quality defects such as uneven gloss do not occur.

  Further, when printing on thick paper, since the back curl hardly occurs in the fixing device 20, the guide member 205 may be set to the second position (back curl non-correcting position). By doing so, face curl that may occur when passing thick paper through the back curl correction mechanism C, damage to the back surface of the paper by the guide member 205, wear of the guide member 205 by thick paper, bending of the thick paper tip, etc. Problems can be prevented.

  In the present embodiment, the control unit 300 adjusts the time interval for sending the recording paper to the discharge conveyance path, but instead, the control unit 300 may adjust the conveyance speed in the discharge conveyance path. The conveyance speed in the discharge conveyance path can be adjusted by controlling the rotational driving of the drive roller 204 and the discharge roller 13 under the control of the recording paper conveyance unit 380 of the control unit 300.

  According to the image forming apparatus of the present embodiment, the control unit 300 records the recording paper P so that the time interval of the recording paper P at the end of the discharge conveyance path is kept constant before and after the change of the length of the discharge conveyance path. Adjust the time interval for feeding the to the discharge conveyance path. Thereby, conveyance failure, such as jam, can be prevented.

  Further, according to the image forming apparatus of the present embodiment, when the length of the discharge conveyance path is changed by the movement of the position of the guide member 205, the control unit 300 discharges the recording paper P. Set the time interval for sending to to shorter than before the change. By controlling in this way, it is possible to prevent the recording paper interval from being excessively widened.

  Further, when the length of the discharge conveyance path is changed by the movement of the position of the guide member 205, the control unit 300 makes the time interval for feeding the recording paper P into the discharge conveyance path longer than before the change. By controlling in this way, it is possible to prevent the recording paper interval from being clogged too much.

  The control unit 300 can be realized by hardware, software, or a combination thereof. Here, “realized by software” means realized by a computer reading and executing a program.

  As described above, the image forming apparatus according to the present invention can correct the back curl caused by fixing and can prevent the occurrence of poor image quality and conveyance failure. It is useful for all image forming apparatuses such as facsimiles and printers.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 13 Paper discharge roller 15 Branch member 20 Fixing device 203 Followed roller (conveyance roller)
204 Drive roller (conveyance roller)
205 Guide member 300 Control unit (control means)
A Image forming part C Back curl correction mechanism N Fixing nip part P Recording paper

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

Claims (3)

A fixing device for fixing the image on a recording sheet onto which the image formed by the image forming unit is transferred;
A back curl correction mechanism provided on the downstream side of the fixing device;
A pair of paper discharge rollers provided on the downstream side of the back curl correction mechanism for discharging the recording paper out of the apparatus,
The back curl correction mechanism is:
A pair of conveying rollers for nipping and conveying the recording paper delivered from the fixing device;
A first position provided downstream of the pair of transport rollers and guiding the recording paper discharged from the pair of transport rollers at a predetermined discharge angle; and a second position separated from the recording paper. A guide member movable between positions;
In an image forming apparatus including:
Control means for adjusting a time interval for feeding the recording paper into the transport path when the length of the transport path from the pair of transport rollers to the pair of paper discharge rollers is changed by the movement of the position of the guide member. An image forming apparatus, further comprising:   The control means adjusts a time interval for feeding the recording paper into the transport path so as to keep the time interval of the recording paper at the end of the transport path constant before and after the change. The image forming apparatus according to 1.   When the length of the transport path becomes longer than before the change due to the movement of the position of the guide member, the control means shortens the time interval for feeding the recording paper into the transport path from the time before the change. 3. The time interval for feeding the recording paper into the transport path is made longer than before the change when the length of the transport path becomes shorter than before the change due to the movement of the position of the member. The image forming apparatus described in 1.

Images