JP2010208744A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of restraining a curl of paper ejected to a paper ejecting part. <P>SOLUTION: A fixing device 80 of the image forming device 10 includes a heating roller 81 for heating a developer image transferred to the paper and a pressurizing roller 82 brought into pressure contact with the heating roller 81 by sandwiching the paper between the heating roller 81 and itself, and fixes the developer image to the paper. A curl correcting part is arranged on the downstream side of the fixing device 80 in the paper carrying direction, and can be freely displaced to a first position for curving the paper in the direction of projecting to the heating roller 81 side in the direction for connecting the heating roller 81 and the pressurizing roller 82 and a second position of not curving the paper. A detecting part 60 is arranged on the upstream side more than the curl correcting part in the paper carrying direction, and detects an obverse-reverse arranging state of the paper. A control unit 70 displaces the curl correcting part based on a detection result of the detecting part 60. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that transfers a developer image onto a sheet.

  In an electrophotographic image forming apparatus, an image is formed by transferring a developer image formed on a peripheral surface of an electrostatic latent image carrier onto a sheet and fixing it on a fixing unit. The sheet on which the developer image is fixed is discharged to a paper discharge unit. The fixing unit includes, for example, a heating roller and a pressure roller that is in pressure contact with the heating roller. When the paper passes through the fixing unit, the paper is conveyed so that the surface on which the developer image is transferred is pressed against the heating roller, and the development transferred to the paper between the heating roller and the pressure roller. The developer image is fixed on the sheet by heating and pressurizing the agent image. As described above, a device that heats a sheet only from one side of the sheet is often used as the fixing unit.

  Further, due to the manufacturing method by the papermaking machine, the paper has a surface with excellent smoothness called a felt surface and a back surface also called a wire surface and less smooth than the surface. For this reason, the paper has the property that the degree of shrinkage when heated and dried differs between the front surface and the back surface. Specifically, the degree of shrinking on the front surface is small, and the degree of shrinking on the back surface is large.

  Therefore, when the sheet passes through the fixing unit, the sheet curls to the back side depending on the inherent property of the sheet regardless of which side of the sheet the developer image is fixed. However, when the fixing unit heats the paper from only one side of the paper, the amount of heat supplied is different between the front and back surfaces. Therefore, when the developer image is fixed on the front surface, the curl of the paper is small, and development is performed on the back surface. When the agent image is fixed, the curl of the paper increases.

  When the paper is curled, the paper is stacked in a curled state on the paper discharge unit, so that fewer sheets are discharged to the paper discharge unit than when uncurled paper is discharged to the paper discharge unit. Sometimes paper jams are likely to occur.

  Therefore, as a technique for suppressing paper jamming due to the curling of the paper, a technique for detecting the curled state of the paper, determining an appropriate number of sheets stored in the paper discharge unit based on the detection result, and continuing or stopping the image forming process. Is known (for example, see Patent Document 1).

JP 2007-91399 A

  However, although the above-described conventional technology can be expected to suppress paper jamming, it cannot suppress the curling of the paper itself. For this reason, when the curled sheets are stacked on the sheet discharge unit, the appropriate number of sheets that can be stored in the sheet discharge unit is reduced. Therefore, when mass printing is performed, it is necessary to frequently remove the paper on the paper discharge unit.

  An object of the present invention is to provide an image forming apparatus capable of suppressing curling of paper discharged to a paper discharge unit.

  An image forming apparatus according to the present invention is an image forming apparatus that performs electrophotographic image forming processing on a sheet, and includes a storage unit, an image forming unit, a fixing unit, a curl correcting unit, a detecting unit, and a control unit. The storage unit stores paper. The image forming unit transfers the developer image onto the sheet conveyed from the storage unit. The fixing unit includes a heating unit that heats the developer image transferred to the sheet, and a pressure unit that presses the sheet between the heating unit and presses the sheet, and fixes the developer image on the sheet. The curl correction unit is disposed on the downstream side of the fixing unit in the sheet conveyance direction, and has a first position that curves the sheet in a direction that protrudes toward the heating unit in a direction connecting the heating unit and the pressing unit. It can be freely displaced to a second position where the sheet is not curved. The detection unit is arranged on the upstream side of the curl correction unit in the paper conveyance direction, and detects the arrangement state of the front and back of the paper. The control unit displaces the curl correction unit based on the detection result of the detection unit.

  In this configuration, it is possible to determine from which side the sheet is heated in the fixing unit by detecting the arrangement state of the front and back sides of the sheet. Since the degree of shrinkage when the paper is heated and dried is larger on the back side than on the front side, the paper on which the developer image has been fixed after passing through the fixing unit is curled toward the back side. However, since the amount of heat supplied differs between the front and back surfaces depending on from which side the paper is heated in the fixing unit, if the curl correction unit of the present invention is not provided, the paper is heated from the front surface, that is, developed on the front surface. When the agent image is fixed, the curl of the sheet is small, and when the sheet is heated from the back side, that is, when the developer image is fixed on the back side, the curl of the sheet is large. Therefore, when the developer image is fixed on the back side, the curl correction unit is displaced to the first position to curve the sheet in the direction opposite to the curl direction. Can be suppressed. In addition, this makes it possible to increase the appropriate number of sheets that can be stored in the paper discharge unit.

  In the above configuration, the control unit can be configured to displace the curl correction unit to the first position when fixing the developer image on the back surface of the sheet. Accordingly, when the curl of the paper that has passed through the fixing unit is large, the paper is curved in a direction to correct the curl, and thus curling of the paper discharged to the paper discharge unit can be suppressed.

  The curl correction unit is a sheet guide member that forms a wall surface on the heating unit side of the sheet conveyance path on the downstream side of the fixing unit in the sheet conveyance direction, and has a sheet conveyance path at an intermediate portion of the sheet guide member in the sheet conveyance direction. A sheet guide member that is curved so as to expand in a direction connecting the heating unit and the pressure unit, and a displacement unit that is displaceable between a first position and a second position, and is discharged from the fixing unit at the first position. And a displacement unit that guides the sheet so that the sheet is conveyed along the sheet guide member. When the developer image is fixed on the back surface, the paper can be transported along the paper guide member by displacing the displacement portion to the first position. The sheet guide member is curved so that the sheet conveyance path expands in the direction connecting the heating unit and the pressure unit at the intermediate part of the sheet guide member in the sheet conveyance direction, that is, protrudes in a direction opposite to the curl direction of the sheet. And when the paper is conveyed along the paper guide member, the paper is pressed against the paper guide member by the conveying force, so that the curl of the paper is corrected. Therefore, curling of the paper discharged to the paper discharge unit can be suppressed.

  Further, the displacement part can be configured to have a swinging part that can swing freely in a direction in which the open end part is in contact with and away from the paper guide member. By having the oscillating portion, the paper is bent in a direction that protrudes toward the heating portion in the direction connecting the heating portion and the pressure portion according to the curl size of the paper discharged from the fixing portion. It can be easily displaced to the second position that is not curved.

  Further, the control unit displaces the displacement unit to the first position at the timing when the open end of the sheet discharged from the fixing unit pushes the sheet toward the sheet guide member, and the sheet is displaced after the sheet passes through the displacement unit. The part can be configured to return to the second position. The paper can be conveyed along the paper guide member by pushing the leading end of the paper discharged from the fixing unit toward the paper guide member by the open end of the swinging part. By displacing the displacement portion to the first position at a predetermined timing and returning the displacement portion to the second position after the sheet passes through the displacement portion, it is possible to save power.

  Further, it is further provided with a pair of conveying rollers that are disposed downstream of the curl correction unit in the sheet conveying direction and convey the sheet on which the developer image has been fixed to the downstream side in the sheet conveying direction while being pressed between the rollers. The unit can be configured to guide the sheet discharged from the fixing unit linearly toward the conveyance roller pair at the second position. When the oscillating portion is disposed at the second position, the oscillating portion serves as a guide member that guides the sheet linearly toward the pair of conveyance rollers, thereby reducing the number of parts and manufacturing cost. be able to.

  According to the present invention, it is possible to suppress curling of the paper discharged to the paper discharge unit.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. It is a partial expanded sectional view of the detection part vicinity. FIG. 3 is a configuration diagram of a curl correction unit, and shows a state in which a developer image is fixed on the surface of a sheet. FIG. 3 is a configuration diagram of a curl correction unit, and shows a state in which a developer image is fixed on the back surface of a sheet. FIG. 6A is a diagram illustrating a curled state of a sheet when a developer image is fixed on the surface of the sheet, and FIG. 4A illustrates a case where the sheet is conveyed in a direction in which the longitudinal direction of the sheet is orthogonal to the rotation axis of the heating roller. (B) shows the case where the paper is conveyed in the direction in which the longitudinal direction of the paper is parallel to the rotation axis of the heating roller. FIG. 7A is a diagram illustrating a curled state of a sheet when a developer image is fixed on the back surface of the sheet, and FIG. (B) shows the case where the paper is conveyed in the direction in which the longitudinal direction of the paper is parallel to the rotation axis of the heating roller.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated based on drawing. FIG. 1 shows a schematic cross section of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus 10 includes an image forming unit 20 and a paper feeding unit 30.

  The image forming unit 20 includes an image forming unit 40, a paper discharge tray (paper discharge unit) 50, a detection unit 60, and a control unit 70.

  The image forming unit 40 includes a photosensitive drum 41, a charging device 42, an exposure unit 43, a developing device 44, a transfer device 45, a cleaning unit 46, and a fixing device (fixing unit) 80, and performs an electrophotographic image forming process. Do.

  The photosensitive drum 41 is an electrostatic latent image carrier, and has a conductive substrate and a photosensitive layer. As the conductive substrate, for example, a cylindrical or columnar aluminum element tube is used. The diameter of the aluminum tube is, for example, 30 mm. The photosensitive layer is formed on the peripheral surface of the conductive substrate, and is, for example, an organic photosensitive layer including a charge generation layer containing a charge generation material and a charge transport layer laminated on the charge generation layer containing a charge transport material. . The layer thickness of the organic photosensitive layer is, for example, 30 μm.

  The charging device 42 uniformly charges the peripheral surface of the photosensitive drum 41 to a predetermined potential. As the charging device 42, for example, a charging roller is used. As the charging device, a brush type charging device, a charger type charging device, or a corona charging device such as a scorotron may be used.

  The exposure unit 43 forms an electrostatic latent image corresponding to the image data on the peripheral surface of the photosensitive drum 41 by exposing the peripheral surface of the charged photosensitive drum 41 according to the image data. Image data is input from the control unit 70. As the exposure unit 43, for example, a laser scanning unit (LSU) provided with a laser emitting portion, a reflection mirror, and the like is used.

  The developing device 44 visualizes the electrostatic latent image formed on the peripheral surface of the photosensitive drum 41 with a developer such as toner, and forms a developer image.

  The transfer device 45 is in pressure contact with the peripheral surface of the photosensitive drum 41. The transfer device 45 transfers the developer image formed on the peripheral surface of the photoconductive drum 41 onto a sheet conveyed to a transfer position 47 between the transfer device 45 and the peripheral surface of the photoconductive drum 41.

  The cleaning unit 46 removes and collects the developer remaining on the peripheral surface of the photosensitive drum 41 after the developer image is transferred to the sheet.

  The fixing device 80 includes a heating roller (heating unit) 81 and a pressure roller (pressing unit) 82. The pressure roller 82 is in pressure contact with the heating roller 81 with a predetermined pressure. The fixing device 80 conveys the sheet on which the unfixed developer image has been transferred while being sandwiched between the heating roller 81 and the pressure roller 82, thereby fixing the image to the sheet by heating and pressing the developer image. Let

  A pair of conveyance rollers 90 is disposed on the downstream side of the fixing device 80 in the sheet conveyance direction. The conveyance roller pair 90 conveys the sheet, on which the developer image has been fixed by passing through the fixing device 80, toward the sheet discharge tray 50 while being pressed between the rollers. The paper discharge tray 50 is disposed on the upper surface of the image forming unit 20. The paper on which the developer image is fixed is discharged to the paper discharge tray 50.

  The paper supply unit 30 includes a plurality of paper cassettes 31, 32, 33, and 34 that are paper storage units. The paper stored in each of the paper cassettes 31 to 34 is transported to the transfer position 47 of the image forming unit 40 through the first paper transport path (paper transport path) 35 or the second paper transport path 36. The first paper transport path 35 is arranged in the vertical direction from the paper feed unit 30 to the paper discharge tray 50 via the image forming unit 40. The second paper transport path 36 extends in the horizontal direction in the paper feed unit 30 and then joins the first paper transport path 35.

  A registration roller 48 is disposed on the upstream side of the transfer position 47 in the paper transport direction. The inclination of the sheet conveyed through the first sheet conveyance path 35 is corrected by being abutted against the resist roller 48 in a stopped state. The registration roller 48 conveys the sheet to the transfer position 47 at a predetermined timing when the electrostatic latent image carried on the peripheral surface of the photosensitive drum 41 and the sheet coincide with each other at the transfer position 47.

  A third paper conveyance path 37 is disposed from the downstream side of the fixing device 80 to the upstream side of the registration roller 48 in the paper conveyance direction. The third paper transport path 37 is used when images are formed on both sides of the paper.

  The control unit 70 comprehensively controls the entire image forming apparatus 10.

  FIG. 2 shows a partially enlarged cross section near the detection unit 60.

  The detection unit 60 is disposed upstream of the fixing device 80 in the paper transport direction and between the paper feed cassettes 31 to 34 and the registration roller 48. The detection unit 60 detects the arrangement state of the front and back sides of the paper based on the glossiness of the paper, and outputs the detection result to the control unit 70. An optical sensor is used as the detection unit 60. For example, “ZHPA3000” manufactured by Nichicon Corporation is used as the detection unit 60.

  In this embodiment, the detection unit 60 includes two optical sensors 61 and 62. Each of the optical sensors 61 and 62 irradiates light on the sheet before the developer image is transferred, detects the amount of reflected light, and outputs the detection result to the control unit 70. The optical sensor 61 and the optical sensor 62 are disposed so as to face each other with the first paper transport path 35 interposed therebetween so that the amount of reflected light on the front and back surfaces of the paper can be detected.

  The control unit 70 compares the received light amount of the optical sensor 61 with the received light amount of the optical sensor 62 based on the detection result input from the detection unit 60, and the surface facing the optical sensor with the larger received light amount is the sheet surface. It is determined that the surface facing the optical sensor having the smaller received light amount is the back surface of the sheet. By comparing the amounts of light received by the two optical sensors 61 and 62, it is possible to detect the arrangement state of the front and back of the paper easily and accurately.

  Since the detection unit 60 is arranged between the paper cassettes 31 to 34 and the registration roller 48, it is possible to detect the arrangement state of the front and back sides of the sheet on which the developer image is not transferred. For this reason, more accurate detection can be performed. Further, since the registration roller 48 is disposed in the vicinity of the upstream side of the transfer position 47 in the sheet conveyance direction, the sheet cassettes 31 to 34 are compared with the case where the detection unit 60 is disposed between the registration roller 48 and the transfer position 47. And the registration roller 48 can further prevent the detection unit 60 from being contaminated by the developer, and can detect a sheet that is not contaminated by the developer. Therefore, more accurate detection can be performed.

  3 and 4 show the configuration of the curl correction unit 110. FIG. 3 shows a state in which the developer image is fixed on the front surface of the paper 99, and FIG. 4 shows a state in which the developer image is fixed on the back surface of the paper 99.

  The fixing device 80 includes a heating roller 81, a pressure roller 82, a first paper peeling claw 83, a second paper peeling claw 84, and a temperature sensor 85.

  The heating roller 81 can be rotated clockwise in FIG. 3 by a driving source (not shown). The heating roller 81 has heater lamps 811 and 812 inside.

  The heating roller 81 is configured using, for example, a cylindrical aluminum element tube 813 and a coating layer 814 containing a fluororesin formed on the surface of the aluminum element tube 813. The heater lamps 811 and 812 are disposed inside the aluminum base tube 813. For example, the rotation speed of the heating roller 81 can be changed by using a motor capable of changing the drive speed as the drive source.

  The pressure roller 82 is in pressure contact with the heating roller 81 and is rotatably arranged. The pressure roller 82 rotates following the rotation of the heating roller 81. The pressure roller 82 is configured using, for example, an aluminum element tube 821 and an elastic body layer 822 formed on the surface of the aluminum element tube 821.

  Although there is no restriction | limiting in particular as an elastic body which comprises the elastic body layer 822, Silicone rubber is preferable. By using silicone rubber as the elastic body constituting the elastic body layer 822, the following advantages can be obtained. That is, while the hardness of the surface layer of the heating roller 81 is high, the silicone rubber constituting the elastic body layer 822 that is the surface layer of the pressure roller 82 is rich in elasticity, so that the heating roller 81 and the pressure roller 82 are in pressure contact with each other. At the nip portion 86, the surface layer of the pressure roller 82 is deformed, and the sheet 99 is slightly wound around the peripheral surface of the heating roller 81, so that the fixing of the developer image onto the sheet 99 becomes more reliable. Further, the area of the nip portion 86 is increased, and the heating capacity for the paper 99 is increased. Furthermore, by pressing with a flexible pressure roller 82, the developer can be fixed without being deformed. The paper 99 wound around the heating roller 81 can be easily peeled off from the peripheral surface of the heating roller 81 by the first paper peeling claw 83.

  On the upstream side of the nip portion 86 between the heating roller 81 and the pressure roller 82 in the paper conveyance direction, a paper entry guide plate for guiding the paper 99 to the nip portion 86 is disposed. The paper 99 carrying the developer image is conveyed to the nip portion 86 via the paper entry guide plate. Since the heating roller 81 and the photosensitive drum 41 are arranged on the same side with respect to the first paper transport path 35, when the paper 99 is transported to the nip portion 86, the developer image carrying surface of the paper 99 is It contacts the peripheral surface of the heating roller 81. On the downstream side of the nip portion 86 in the paper transport direction, a paper output guide plate 87 for guiding the paper 99 toward the transport roller pair 90 is disposed.

  The heating roller 81 and the pressure roller 82 rotate while being pressed against each other, and the sheet 99 carrying the developer image passes through the nip portion 86, whereby the developer image is heated and pressurized to the sheet 99. The developer image is fixed on the sheet 99.

  The first sheet peeling claw 83 is disposed so that the tip end is in light contact with the peripheral surface of the heating roller 81 on the downstream side of the nip portion 86 in the rotation direction of the heating roller 81. In this embodiment, a plurality of first paper peeling claws 83 are provided along the rotation axis of the heating roller 81, but only one may be provided. The first paper peeling claw 83 peels the paper 99 wound around the circumferential surface of the heating roller 81 from the circumferential surface of the heating roller 81. Examples of the material of the first sheet peeling claw 83 include synthetic resins such as polyimide and polyamideimide. Further, at least the tip of the first sheet peeling claw 83 can be coated with a fluororesin such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA).

  The second paper peeling claw 84 is disposed so as to lightly contact the peripheral surface of the pressure roller 82 on the downstream side of the nip portion 86 in the rotation direction of the pressure roller 82 that follows the rotation of the heating roller 81. The second paper peeling claw 84 peels the paper 99 wound around the circumferential surface of the pressure roller 82 from the circumferential surface of the pressure roller 82. The second paper peeling claw 84 is made of the same material as the first paper peeling claw 83.

  The temperature sensor 85 is disposed in the vicinity of the opposite side of the nip portion 86 with the heating roller 81 interposed therebetween, detects the peripheral surface temperature of the heating roller 81, and outputs temperature data to the control unit 70. The control unit 70 controls a power source (not shown) that applies a voltage to the heater lamps 811 and 812 based on the temperature data input from the temperature sensor 85, thereby setting the peripheral surface temperature of the heating roller 81 to a predetermined temperature. The heating temperature of the heater lamps 811 and 812 is controlled so as to be close to. For example, a thermistor is used as the temperature sensor 85.

  As described above, the transport roller pair 90 is disposed on the downstream side of the fixing device 80 in the paper transport direction. The conveyance roller pair 90 includes a first roller 91 and a second roller 92. The outer diameter of the first roller 91 and the outer diameter of the second roller 92 are the same. For example, the first roller 91 is a driving roller, and the second roller 92 is a driven roller. The second roller 92 is in pressure contact with the first roller 91. The conveyance roller pair 90 conveys the sheet 99 on which the developer image has been fixed by passing through the fixing device 80 toward the sheet discharge tray 50 while being pressed between the first roller 91 and the second roller 92.

  The curl correction unit 110 is disposed on the downstream side of the fixing device 80 and the upstream side of the conveyance roller pair 90 in the paper conveyance direction. The curl correction unit 110 has a first position where the paper 99 is bent in a direction protruding toward the heating roller 81 and a second position where the paper 99 is not bent in the direction connecting the heating roller 81 and the pressure roller 82. Displaceable. The curl correction unit 110 includes a paper guide member 120 and a displacement unit 130.

  The paper guide member 120 is disposed on the same side as the heating roller 81 with respect to the first paper transport path 35. The sheet guide member 120 forms a wall surface on the heating roller 81 side of the first sheet conveyance path 35 on the downstream side of the fixing device 80 in the sheet conveyance direction and on the upstream side of the conveyance roller pair 90. The paper guide member 120 is curved so that the first paper transport path 35 expands in a direction connecting the heating roller 81 and the pressure roller 82 at an intermediate portion of the paper guide member 120 in the paper transport direction. That is, the paper guide member 120 is curved so as to protrude in the direction opposite to the curl direction of the paper 99 discharged from the fixing device 80. The size of the paper guide member 120 in the rotation axis direction of the heating roller 81 is preferably substantially the same as the width of the maximum size paper used in the image forming apparatus 10.

  The displacement unit 130 is disposed between the fixing device 80 and the paper ejection guide plate 87 in the paper conveyance direction and is opposed to the paper guide member 120 with the first paper conveyance path 35 interposed therebetween. The displacement unit 130 is freely displaceable between a first position and a second position, and the sheet 99 discharged from the fixing device 80 at the first position is conveyed along the sheet guide member 120. To guide you.

  The displacement part 130 includes a swing part 131, a support shaft 132, a solenoid 133, a spring 134, and a substrate 135.

  The substrate 135 is fixed at a predetermined position of the image forming apparatus 10. The support shaft 132, the solenoid 133, and the spring 134 are fixed to the substrate 135.

  The oscillating portion 131 is, for example, a rod shape, and an intermediate portion is pivotally supported by a support shaft 132. As a result, the swinging part 131 is swingable about the shaft fulcrum 132A by the support shaft 132 as an axis. In this embodiment, the swinging portion 131 is disposed such that the open end portion 131A is upstream of the shaft fulcrum 132A in the paper transport direction. The open end 131A is disposed in the vicinity of the upstream end of the paper guide member 120 in the paper transport direction.

  A base end portion 131B, which is an end portion on the opposite end side of the open end portion 131A across the shaft fulcrum 132A, is fixed to the solenoid 133. The solenoid 133 is on / off controlled by the control unit 70. Further, one end of the spring 134 is fixed to the open end 131A side from the pivot point 132A of the swinging portion 131, and the other end of the spring 134 is fixed to the substrate 135. The spring 134 biases the swinging portion 131 in a direction away from the first paper transport path 35.

  As shown in FIG. 3, in the state where the solenoid 133 is off, the swinging portion 131 is disposed at the second position. In the second position, the oscillating portion 131 has a downstream end portion (base end portion 131B in this embodiment) in the paper transport direction disposed in the vicinity of the paper output guide plate 87, and slightly moves downstream in the paper transport direction. It is arranged so as to incline and climb. As a result, the sheet 99 discharged from the fixing device 80 is smoothly conveyed to the upper surface of the oscillating unit 131, and is linearly guided toward the conveying roller pair 90 by the oscillating unit 131 and the sheet ejection guide plate 87. The The oscillating portion 131 can also be arranged in the second position so as to be parallel to the direction connecting the nip portion 86 between the heating roller 81 and the pressure roller 82 and the nip portion of the conveying roller pair 90.

  As shown in FIG. 4, when the solenoid 133 is on, the solenoid 133 continues to pull the base end portion 131 </ b> B of the swinging portion 131 in the direction away from the first paper transport path 35. Accordingly, the swinging portion 131 swings in the direction in which the open end portion 131A approaches the paper guide member 120, and is disposed at the first position. When the solenoid 133 is turned off, the swinging portion 131 swings in a direction in which the open end portion 131A is separated from the paper guide member 120 by the biasing force of the spring 134, and is moved to the second position as shown in FIG. Return.

  The paper 99 has a surface having excellent smoothness, also called a felt surface, and a back surface, also called a wire surface, which is inferior in smoothness to the surface due to the manufacturing method by the papermaking machine. When the paper 99 is heated and dried, the degree to which the front surface shrinks is small, and the degree to which the back surface shrinks is large. For this reason, when the sheet 99 passes through the fixing device 80, the sheet 99 generally curls to the back side.

  Further, when the developer image is fixed on the surface of the paper 99, that is, when the surface is the developer image carrying surface, the surface comes into contact with the heating roller 81, so that more heat is supplied to the surface than the back surface. On the other hand, when the developer image is fixed on the back surface of the paper 99, that is, when the back surface is the developer image carrying surface, the back surface contacts the heating roller 81, so that more heat is supplied to the back surface than the front surface. Therefore, if the curl correction unit 110 of the present invention is not provided, the degree of curling of the paper 99 after passing through the fixing device 80 is such that the surface is a developer image as shown in FIGS. 5 (A) and 5 (B). The size is small when it is a carrying surface, and it is large when the back surface is a developer image carrying surface as shown in FIGS. 6 (A) and 6 (B). 5A and 6A show a case where the sheet 99 is conveyed in a direction in which the longitudinal direction of the sheet 99 is orthogonal to the rotation axis of the heating roller 81, and FIGS. B) shows a case where the sheet 99 is conveyed in a direction in which the longitudinal direction of the sheet 99 is parallel to the rotation axis of the heating roller 81.

  The detection unit 60 is disposed on the upstream side of the curl correction unit 110 in the paper conveyance direction. When the control unit 70 determines that the surface of the paper 99 is disposed on the heating roller 81 side based on the detection result by the detection unit 60, that is, when it determines that the surface is the developer image carrying surface, the control unit 70 133 is turned off. Thus, when the developer image is fixed on the surface, the sheet 99 can be conveyed linearly toward the conveyance roller pair 90.

  When the control unit determines that the back surface is disposed on the heating roller 81 side based on the detection result by the detection unit 60, that is, when it determines that the back surface is the developer image carrying surface, the fixing device 80. The solenoid 133 is turned on at a predetermined timing when the open end 131 </ b> A of the swinging portion 131 pushes the leading end of the paper 99 discharged from the paper 99 toward the paper guide member 120. The control unit 70 turns off the solenoid 133 after the paper 99 has passed through the displacement unit 130.

  As a result, when the developer image is fixed on the back surface, the paper 99 can be conveyed along the paper guide member 120. The paper guide member 120 is curved so that the first paper transport path 35 expands in the direction connecting the heating roller 81 and the pressure roller 82 at the intermediate portion of the paper guide member 120 in the paper transport direction. It is curved so as to be convex in the direction opposite to the curl direction, and when the sheet 99 is conveyed along the sheet guide member 120, the sheet 99 is pressed against the sheet guide member 120 by the conveying force. The paper 99 is bent in the direction opposite to the curl direction, and the curl of the paper 99 is corrected. For this reason, curling of the paper discharged to the paper discharge tray 50 can be suppressed. Accordingly, it is possible to increase the appropriate number of sheets 99 that can be stored in the sheet discharge tray 50.

  Further, it is possible to save power by displacing the displacement portion 130 to the first position at a predetermined timing and returning the displacement portion 130 to the second position after the paper 99 has passed the displacement portion 130.

  Further, when the swinging portion 131 is disposed at the second position, the swinging portion 131 serves as a guide member that guides the sheet 99 linearly from the fixing device 80 toward the conveyance roller pair 90. In addition, the number of parts can be reduced and the manufacturing cost can be reduced.

  The controller 70 is configured to stop the image forming process when the number of sheets 99 discharged to the discharge tray 50 exceeds a predetermined number. When the number of sheets 99 discharged to the discharge tray 50 exceeds a predetermined number, the image forming process stops, so that even if curl remains on the sheet 99 stored in the discharge tray 50, the image forming process is stopped in the vicinity of the discharge tray 50. Paper jams can be prevented. Alternatively, the image forming process can be continued by removing the paper from the paper discharge tray 50.

  Note that the size of the swinging portion 131 in the rotation axis direction of the heating roller 81 can be configured to be substantially the same as the width of the maximum size sheet used in the image forming apparatus 10.

  The sheet guide member 120 can be configured to constitute a wall surface on the heating roller 81 side of at least a part of the first sheet conveyance path 35 between the fixing device 80 and the conveyance roller pair 90 in the sheet conveyance direction.

  The displacement part 130 can also be arranged so that the open end 131A of the swinging part 131 is on the downstream side of the shaft fulcrum 132A in the paper transport direction. According to this, since the sheet 99 can be conveyed along the inclination of the upper surface of the swinging part 131 in a state where the swinging part 131 is displaced to the first position, the swinging part 131 is moved from the second position. The tolerance of the deviation of the timing to be displaced to the first position is increased.

  The present invention can also be applied to a color image forming apparatus including a plurality of image forming units that form images using developers of different hues.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 20 Image forming unit 30 Paper feed unit 31-34 Paper feed cassette (accommodating part)
35 First paper transport path (paper transport path)
40 Image forming unit 48 Registration roller 50 Paper discharge tray 60 Detection unit 70 Control unit 80 Fixing device (fixing unit)
81 Heating roller (heating unit)
82 Pressure roller (Pressure part)
90 Conveying roller pair 99 Paper 110 Curl correction part 120 Paper guide member 130 Displacement part 131 Swing part

Claims (6)

An image forming apparatus that performs electrophotographic image forming processing on paper,
A storage section for storing paper;
An image forming unit that transfers a developer image onto a sheet conveyed from the storage unit;
A heating unit that heats the developer image transferred onto the paper, and a fixing unit that presses the paper between the heating unit and presses against the heating unit, and fixes the developer image on the paper;
A first position that is arranged on the downstream side of the fixing unit in the sheet conveyance direction and that curves the sheet in a direction that protrudes toward the heating unit in a direction connecting the heating unit and the pressure unit, and does not curve the sheet. A curl correction unit that is displaceable to a second position;
A detection unit that is arranged upstream of the curl correction unit in the paper conveyance direction and detects the arrangement state of the front and back sides of the paper;
An image forming apparatus comprising: a control unit that displaces the curl correction unit based on a detection result of the detection unit.   The image forming apparatus according to claim 1, wherein the control unit displaces the curl correction unit to the first position when fixing the developer image on the back surface of the sheet. The curl correction part is
A sheet guide member constituting a wall surface on the heating unit side of a sheet conveyance path on the downstream side of the fixing unit in the sheet conveyance direction, wherein the sheet conveyance path is at an intermediate portion of the sheet guide member in the sheet conveyance direction; A paper guide member curved so as to expand in a direction connecting the heating unit and the pressure unit;
A displacement unit that is displaceable between the first position and the second position, and the sheet is discharged so that the sheet discharged from the fixing unit at the first position is conveyed along the sheet guide member. The image forming apparatus according to claim 1, further comprising a displacement unit that guides the image forming apparatus.   The image forming apparatus according to claim 3, wherein the displacement portion includes a swinging portion that is swingable in a direction in which an open end portion is separated from and contacting the sheet guide member.   The control unit displaces the displacement unit to the first position at a timing when the open end pushes the leading end of the sheet discharged from the fixing unit toward the sheet guide member, and the sheet moves to the displacement unit. The image forming apparatus according to claim 4, wherein the displacement portion is returned to the second position after passing through. A conveyance roller pair that is disposed downstream of the curl correction unit in the sheet conveyance direction and conveys the sheet on which the developer image is fixed to the downstream side in the sheet conveyance direction while being pressed between the rollers;
The image forming apparatus according to claim 4, wherein the swinging unit guides the sheet discharged from the fixing unit linearly toward the pair of conveying rollers at the second position.

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