JP2016118688A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can remove a curl without causing scratches and damage to an image on a sheet ejected from an exit of a nip part of a fixing device.SOLUTION: An image forming apparatus comprises: a fixing device 36 that fixes a toner image formed on a sheet P by passing the toner image through a heated fixing nip part N; a first roller pair 101 that is arranged in the vicinity of an exit of the fixing nip part, configured to hold the leading end of the sheet on which the toner image is fixed and to be displaceable between a first position DP1 and a second position DP2, and conveys the sheet in a sheet conveyance direction X; sheet conveyance means that is arranged on the downstream side in the sheet conveyance direction with respect to the first roller pair and conveys the sheet; and passage displacement means 108 that displaces the first roller pair from the first position to the second position after the leading end of the sheet on which the toner image is fixed is held by the first roller pair, to create a sheet conveyance passage having a curvature in a reverse direction to a direction in which the sheet curls.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, generally, a sheet on which an unfixed toner image is formed is passed through a nip formed by a heating member such as a heating roller and a pressure member such as a pressure roller. Thus, the toner image is thermally fixed on the paper. In this fixing process, the paper curls into a shape along the outer peripheral surface of the heating member or the pressure member due to the temperature difference between the heating member and the pressure member, the moisture content of the paper, the shape of the nip, and the like. It is known that the stackability at the paper discharge unit deteriorates (see, for example, Patent Document 1).

  In order to solve the above problem, Patent Document 1 discloses a transport mechanism having a transport path having a large curvature for transporting a sheet while curving the sheet in a direction opposite to the curling direction on the transport path after the exit of the nip portion of the fixing device. A technique for removing the curl of the paper by providing the paper is disclosed.

  However, in the above technique, when the leading edge of the sheet discharged from the exit of the nip portion of the fixing device enters the conveyance path having a large curvature, the contact force between the leading edge of the sheet and the conveyance path increases, and the image is rubbed. Or scratches.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of removing curl without causing image rubbing or scratching on a sheet discharged from a nip exit of a fixing device. .

  In order to achieve the above object, the present invention provides a fixing device that fixes a toner image formed on a sheet by passing it through a heated nip portion, and is disposed and fixed in the vicinity of the outlet of the nip portion. A first conveying member pair configured to be displaceable between a first position and a second position by sandwiching the leading end portion of the sheet, and conveying the sheet in the sheet conveying direction; and a first conveying member pair The sheet conveying unit disposed on the downstream side of the sheet conveying direction and the front end of the fixed sheet is sandwiched between the first conveying member pair, and then the first conveying member pair is moved to the first conveying member pair. A path displacing unit that is displaced from the position 1 to the second position and forms a sheet conveying path having a curvature opposite to a direction in which the fixed sheet curls between the exit of the nip portion and the sheet conveying unit. An image forming apparatus comprising: That.

  According to the present invention, it is possible to provide an image forming apparatus capable of removing curl without causing image rubbing or scratches on a fixed sheet.

1 is a schematic overall configuration diagram of an image forming apparatus to which the present invention is applicable. FIG. 6 is a schematic front view illustrating the periphery of a sheet conveyance path before displacement of a first roller pair in the first embodiment. FIG. 6 is a schematic front view illustrating the periphery of a sheet conveyance path after a first roller pair is moved up and down. It is a perspective view which shows the specific structure of the path | route displacement means which concerns on 1st Embodiment. (A), (b), (c) is a figure explaining the material and form of a paper conveyance guide member. It is a block diagram which shows the control structure of 1st and 2nd embodiment. FIG. 10 is a schematic front view illustrating a periphery of a sheet conveyance path before displacement of a first roller pair in a second embodiment. FIG. 6 is a schematic front view illustrating the periphery of a sheet conveyance path after a first roller pair is swung and displaced. It is a perspective view which shows the specific structure of the path | route displacement means which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings. In each embodiment and the like, components (members and components) having the same function and shape are described once unless they are confused, and the description thereof is omitted by giving the same reference numerals. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate.

FIG. 1 is a schematic overall configuration diagram of an image forming apparatus to which the present invention is applicable.
As shown in FIG. 1, the image forming apparatus 100 is an endless belt-like intermediate transfer belt 1 that is an intermediate transfer member, and an image carrier that is arranged along the stretched surface of the intermediate transfer belt 1. The photosensitive drums 2Y, 2M, 2C, and 2K are included. Y, M, C, and K added to the reference numerals indicate yellow, magenta, cyan, and black colors, respectively.
The yellow image forming station will be described as a representative. Around the photosensitive drum 2Y, a charging charger 3Y, an optical writing unit 4Y, a developing unit 5Y, a primary transfer roller 6Y, and a cleaning unit 7Y are arranged in the rotation direction. Has been. The charging charger 3Y is a charging unit, the optical writing unit 4Y is an exposure unit, the developing unit 5Y is a developing unit, the primary transfer roller 6Y is a primary transfer unit, and the cleaning unit 7Y is an image carrier cleaning unit. Function.

  Four image forming stations corresponding to yellow, magenta, cyan, and black colors constitute an image forming unit. That is, a yellow image forming station will be described as a representative. The photosensitive drum 2Y, the charger 3Y, the developing unit 5Y, and the cleaning unit 7Y are integrally provided in a unit case. As described above, the photosensitive drum 2Y, the charging charger 3Y, the developing unit 5Y, the cleaning unit 7Y, and the like are unitized as process cartridges so that replacement, maintenance, and maintenance can be facilitated and operability can be improved. It is configured. Other image forming stations corresponding to magenta, cyan, and black colors similarly form a process cartridge.

  The intermediate transfer belt 1 is rotatably supported by rollers 11, 12, and 13 as a plurality of support members. A belt cleaning unit 15 including a blade and a brush is provided at a portion of the intermediate transfer belt 1 facing the roller 12. These intermediate transfer belt 1, rollers 11, 12, 13 and belt cleaning unit 15 constitute an intermediate transfer unit 33.

  A secondary transfer roller 16 as a transfer unit is provided at a portion facing the roller 13. Above the optical writing unit 4 including the optical writing units 4Y, 4M, 4C, and 4K, a scanner unit 9 as an image reading unit, an ADF 10 as an automatic document supply unit, and the like are provided.

  A sheet feeding tray 17 as a plurality of sheet feeding units is provided at the lower part of the apparatus main body 99. A sheet P as a sheet-like recording medium accommodated in each sheet feed tray 17 is fed by a pickup roller 21 and a sheet feed roller 22 and is conveyed by a conveyance roller pair 23. Then, the intermediate transfer belt 1 and the secondary transfer roller 16 are sent to the secondary transfer nip portion facing each other by the registration roller pair 24 at a predetermined timing.

A fixing device 36 as a fixing unit is provided downstream of the secondary transfer nip portion in the sheet conveyance direction. The fixing device 36 includes a fixing roller 37 as a heating member and a pressure roller 38 as a pressure member. A heater 39 as a heat source is disposed inside the fixing roller 37.
In FIG. 1, reference numeral 25 denotes a paper discharge roller pair, reference numeral 26 denotes a paper discharge tray, reference numeral 27 denotes a switchback roller pair, and reference numeral 40 denotes a humidity sensor as humidity detection means for detecting humidity in the image forming apparatus 100. Respectively.

  The optical writing units 4Y, 4M, 4C, and 4K drive the four semiconductor lasers based on the image information and are uniformly charged by the charging chargers 3Y, 3M, 3C, and 3K, and the photosensitive drums 2Y, 2M, and 2C. Four writing lights for irradiating each of 2K are emitted. The optical writing unit 4 scans each of the photosensitive drums 2Y, 2M, 2C, and 2K in the dark with this writing light, and Y, M, and N on the surface of the photosensitive drums 2Y, 2M, 2C, and 2K. Write electrostatic latent images for C and K.

  In the configuration shown in FIG. 1, an image forming operation will be described. When a print start command is input, the rollers in the periphery of the photosensitive drums 2Y, 2M, 2C, and 2K, the periphery of the intermediate transfer belt 1, the paper feed path, and the like start to rotate at a predetermined timing, and the paper feed tray 17 starts feeding paper.

Since the operation of the image forming station corresponding to each color is the same, the yellow image forming station will be described as a representative. The surface of each photosensitive drum 2Y is charged to a uniform potential by the charging charger 3Y (exposure process), and the surface is exposed according to the image data by the writing light emitted from the optical writing unit 4Y. In this way, electrostatic latent images are formed on the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2K (exposure process). The toner in the developer is supplied from the developing unit 5Y to the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2K that carry the electrostatic latent image, so that the electrostatic latent particles carried on the photosensitive drum 2Y are supplied. The image is developed to a yellow color (development process).
In the configuration of FIG. 1, there are four photosensitive drums 2Y, 2M, 2C, and 2K, so that toner images of yellow, magenta, cyan, and black (color order varies depending on the system) are respectively provided on the photosensitive drums 2Y, 2M. 2C and 2K are developed.

  The toner image developed on the photosensitive drum 2Y undergoes a primary transfer operation at a primary transfer portion (nip portion) that is a contact point between the photosensitive drum 2Y and the intermediate transfer belt 1. In other words, the image is transferred onto the intermediate transfer belt 1 by the primary transfer bias and the pressing force applied to the primary transfer roller 6Y installed facing the photosensitive drum 2Y (primary transfer process). By repeating this primary transfer operation for four colors while matching the timing, a full-color toner image is formed on the intermediate transfer belt 1.

  The full color toner image formed on the intermediate transfer belt 1 is collectively transferred onto the sheet P conveyed at the timing by the registration roller pair 24 at the secondary transfer nip portion. At this time, the secondary transfer is performed by the secondary transfer bias and the pressing force applied to the secondary transfer roller 16 (secondary transfer process). The paper P on which the full-color toner image has been transferred passes through the fixing device 36, whereby the toner image carried on the surface of the paper P is heated and fixed (fixing step).

  If it is single-sided printing, it is straightly conveyed and conveyed to the paper discharge tray 26. If it is double-sided printing, the conveying direction is changed downward and conveyed to the paper reversing unit 28. The paper P that has reached the paper reversing section 28 is reversed in the conveying direction by the switchback roller pair 27 and exits the paper reversing section 28 from the rear end of the paper. By this switchback operation, the front and back of the paper P are reversed. The sheet P that has been turned upside down does not return to the fixing device 36 but passes through the refeed conveyance path 29 and joins the original sheet feed path. Thereafter, the toner image is transferred in the same manner as in the front surface printing, and is discharged through the fixing device 36. This is a double-sided printing operation.

  The operation of each part will be described to the end. The photosensitive drums 2Y, 2M, 2C, and 2K that have passed through the primary transfer part carry primary transfer residual toner on the surface thereof, and these are used as cleaning units 7Y, 7M, It is removed by 7C and 7K. Thereafter, the surface of the surface is uniformly discharged by the discharging unit to prepare for charging for the next image. The intermediate transfer belt 1 that has passed through the nip portion N also carries secondary transfer residual toner on its surface, but this is also removed by the belt cleaning unit 15 to prepare for the transfer of the next toner image. . By repeating such an operation, single-sided printing or double-sided printing is performed.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. 2 to 6 (claims 1 to 4 and 7 to 10).
First, the characteristic part of the image forming apparatus according to the first embodiment will be described with reference to FIGS. FIG. 2 is a schematic front view illustrating the periphery of the sheet conveyance path before the first roller pair 101 is displaced in the first embodiment. FIG. 3 is a schematic front view showing the periphery of the sheet conveyance path after the first roller pair 101 is moved up and down. FIG. 4 is a perspective view showing a specific configuration of the path displacing means 108 according to the first embodiment.
In the first embodiment, compared to the image forming apparatus 100 of FIG. 1, a pair of sheet conveying members that convey sheets on the downstream side of the fixing device 36, a path displacing unit 108 that creates a sheet conveying path that can remove curl, And a sheet conveyance guide member that constitutes the sheet conveyance path is mainly different. The configuration and operation of the first embodiment other than this difference are the same as those of the image forming apparatus 100 described above.

  Before describing the details of the present embodiment, the configuration of the fixing device 36 will be supplementarily described. The fixing roller 37 includes a cored bar and an elastic layer that is provided on the outer peripheral part of the cored bar and forms a nip part. The fixing roller 37 has a general heating member configuration that transfers the heat of the heater 39 to the nip through the elastic layer. is there. The pressure roller 38 has a cored bar and an elastic layer that is provided on the outer peripheral part of the cored bar and forms a nip part, and pressurizes the outer peripheral part of the fixing roller 37 through a pressing means such as a spring. This is a configuration of a pressing member. By fixing the outer peripheral part of the elastic layer of the pressure roller 38 to the outer peripheral part of the elastic layer of the fixing roller 37, a fixing nip part N as a nip part is formed. In FIGS. 2 and 3, the casing case shown in FIG. 1 covering the fixing roller 37 and the pressure roller 38 constituting the fixing device 36 is simply omitted.

The shafts at both ends of the fixing roller 37 are rotatably supported by the housing case. The fixing roller 37 is rotationally driven in the direction of the arrow in the figure by a fixing motor 120 connected to one shaft end of the fixing roller 37 via a driving force transmission member such as a gear. The pressure roller 38 follows the rotation of the fixing roller 37 and rotates in the direction of the arrow in the figure.
As shown in FIGS. 2 and 3, a temperature sensor 110 as temperature detecting means for detecting the temperature of the fixing roller 37 is provided in the vicinity of the upper portion of the fixing roller 37, and the pressure roller 38 is provided in the vicinity of the lower portion of the pressing roller 38. A temperature sensor 111 for detecting the temperature is arranged.

  As shown in FIGS. 2 and 3, in the vicinity of the fixing nip exit Na, a first roller pair 101 that functions as a first conveying member pair that sandwiches and conveys the sheet P is disposed. A second roller pair 102 is arranged adjacent to the downstream side of the sheet conveying direction X from the first roller pair 101, and a third roller pair 103 is arranged adjacent to the downstream side of the sheet conveying direction X from the second roller pair 102. Has been. In the first roller pair 101, the second roller pair 102, and the third roller pair 103, for example, three roller portions are fixed in a skewered manner on the shaft, and the lower roller is a spring or the like on the upper roller on the driving side The nip portion is formed by being pressurized by the pressure means.

  The first roller pair 101 is displaced between the first position DP1 indicated by the solid line in FIG. 2 and the one-dot chain line in FIG. 3 and the second position DP2 indicated by the solid line in FIG. It is configured to be possible. One of the first roller pair 101 (upper side in the figure) is rotationally driven in the direction of the arrow in FIGS. 2 and 3 by a drive motor 117 directly connected to one shaft end of the first roller pair 101. The other of the first roller pair 101 (downward in the drawing) is rotated in the direction of the arrow in FIGS. 2 and 3 following the rotation of the first roller pair 101.

  The second roller pair 102 functions as a second conveying member pair that sandwiches and rotates the paper P. The third roller pair 103 has a function corresponding to the paper discharge roller pair 25 of FIG. 1 and also functions as a third transport member pair that sandwiches and rotates the paper P. The shafts at both ends of the second roller pair 102 and the third roller pair 103 are rotatably supported by the main body frame of the image forming apparatus. One of the second roller pair 102 (upper side in the figure) is a drive for driving the second roller pair 102 connected to one shaft end of the second roller pair 102 via a driving force transmission member such as a gear. The motor 118 is rotationally driven in the direction of the arrow in the figure. The other of the second roller pair 102 (downward in the figure) is rotated in the direction of the arrow in the figure following the rotation of one of the second roller pair 102.

  One end (upper side of the figure) of the third roller pair 103 is connected to a driving motor 118 for driving the second roller pair 102 via a driving force transmission member such as a gear. It is rotationally driven in the direction of the arrow in the figure. The other of the third roller pair 103 (downward in the figure) is rotated in the direction of the arrow in the figure following the rotation of one of the third roller pair 103. The second roller pair 102 and the third roller pair 103 are arranged next to the first roller pair 101 on the downstream side of the fixing nip exit Na, and function as sheet conveying means for conveying the fixed paper P.

In this embodiment, the elastic layer of the pressure roller 38 has a higher hardness than the elastic layer of the fixing roller 37, and a convex curl is generated on the non-image surface side (lower surface side in the drawing) of the paper P. A path displacement means 108 is provided as a mechanism for suppressing and removing the curl. The path displacing means 108 displaces the first roller pair 101 from the first position DP1 to the second position DP2 after the leading end portion of the fixed sheet P is sandwiched between the first roller pair 101, and the first roller When the pair 101 occupies the second position DP2, the curvature (the downward convex shape) is opposite to the direction in which the paper curls between the fixing nip exit Na and the sheet conveying means including the first roller pair 101. ) Has a function of changing to the sheet transport paths R2 and R4.
Hereinafter, when it is clear that the toner image on the paper P is fixed, the fixed paper P is also simply referred to as the paper P. The first position DP1 is an initial position, and the second position DP2 is also a curl removal position for removing the curl of the paper P.

The sheet transport path R1 as the sheet transport path shown in FIG. 2 is the second transport path from the fixing nip exit Na to the second roller pair 101 when the first roller pair 101 occupies the first position DP1. This is a first sheet conveyance path to the roller pair 102. 2 is the first sheet conveyance path from the first roller pair 101 to the second roller pair 102 when the first roller pair 101 occupies the first position DP1. It is a conveyance route included in.
The sheet transport path R2 shown in FIG. 3 reaches the second roller pair 102 from the fixing nip exit Na through the first roller pair 101 when the first roller pair 101 occupies the second position DP2. A second sheet conveyance path. 3 is a second sheet conveyance path from the first roller pair 101 to the second roller pair 102 when the first roller pair 101 occupies the second position DP2. It is a conveyance route included in.

  The sheet conveyance paths R1 and R3 formed when the first roller pair 101 occupies the first position DP1 conveys the sheet conveyed to the downstream side of the fixing device 36 without being thermally fixed by the fixing device 36, for example. A sheet conveyance path for this purpose is assumed. As a matter of course, the first sheet transport path (paper transport paths R1, R3) is changed to the second sheet transport path (paper transport paths R2, R4) by the path displacing means 108 for removing the curl of the paper. It is also a premise.

In the case where the paper is transported to the paper transport paths R1 and R3 as described above, as a post-processing device that is appropriately mounted on the paper discharge tray 26 side of the image forming apparatus 100 shown in FIG. 1, for example, a sorter device or the like. It may be a slip sheet that does not form a toner image used for alignment. Further, as an example in which the post-processing device is not mounted, the sorting device configuration that sorts the sheets so that the sheets stacked on the paper discharge tray 26 are stacked while being shifted in the width direction orthogonal to the sheet conveying direction. It may be provided on the downstream side of the fixing device 36 in the forming apparatus 100.
In order to convey such a special sheet, the fixing device 36 passes through a state where the nip portion N is not formed (a state where the pressure roller 38 is separated from and not in contact with the fixing roller 37). So-called skip feeding may be used.

As shown in FIGS. 3 and 4, the displacement / movement of the first roller pair 101 is a reciprocating straight line that moves up and down in the vertical direction Z while keeping a straight line connecting the axial centers of the two rollers of the first roller pair 101 in parallel. It is exercise.
The path displacing means 108 includes a lift unit 109 that rotatably supports the first roller pair 101 and can be moved up and down in the vertical direction Z, a pair of cams 113 having the same shape, a filler 114, a filler detection sensor 115, and a cam motor. 116. The elevating unit 109 includes a first roller pair 101, a pair of brackets 112, a drive motor 117, a connecting member 112 a that firmly connects and fixes each bracket 112, and a paper transport guide member 105. The pair of brackets 112 rotatably supports the shafts at both ends of the first roller pair 101, and attaches and fixes both ends of the paper transport guide member 105. Details of the paper transport guide member 105 will be described later. The drive motor 117 is a drive source that is fixed to one bracket 112 and rotationally drives the first roller pair 101. 4 shows a state in which the first roller pair 101 occupies the first position DP1 in FIGS.

  The two cams 113 are, for example, eccentric cams, and are fixed to the camshaft 113a so as to always contact the immediate lower surface of each bracket 112 with the same phase. Both ends of the cam shaft 113a are rotatably supported by the main body frame, and a cam motor 116 is connected to one end of the cam shaft 113a. On the cam shaft 113a, a filler attachment disk 114a is fixed, which has a filler 114 as a light shielding piece fixed to the outer peripheral surface. Below the filler 114, a filler detection sensor 115 for detecting an initial rotation position (home position) of the cam 113 corresponding to the first position DP1 of the first roller pair 101 is attached and fixed to the main body frame. The filler detection sensor 115 is composed of, for example, a transmissive photosensor. The amount of displacement of the first roller pair 101 can be freely changed by controlling the time after the filler detection sensor 115 detects the position of the filler 114 by a control unit described later.

  The cam motor 116 is, for example, a stepping motor that rotates by pulse input, and is controlled by the number of pulses applied to the cam motor 116 when the filler detection sensor 115 detects the position of the filler 114 (home position of the cam 113). You may do it. Further, each bracket 112 always contacts the outer peripheral surface of the cam 113 in accordance with the rotation of each cam 113 and is displaced in the vertical direction Z as shown in FIG. 3, but in order to realize a stable displacement, each bracket 112 A guide member for assisting the displacement in the vertical direction Z may be provided as appropriate.

  In the vicinity of the exit of the sheet conveyance path R1 in the first roller pair 101 occupying the first position DP1, the leading edge Pa of the sheet P has reached the first roller pair 101 (the leading end of the sheet P is the first roller). A paper detection sensor 104 for detecting that the paper is pinched by the pair 101 is disposed. The sheet detection sensor 104 functions as a sheet detection unit that detects the leading edge of the sheet.

When the first roller pair 101 is displaced, the sheet conveyance guide member 105 indicated by the broken lines that form the sheet conveyance paths R1 and R2 between the fixing nip exit Na and the first roller pair 101 is the same as that of the first roller pair 101. It is composed of a shape and material that at least follow the displacement. Similarly, a sheet conveyance guide member 106 indicated by a broken line that forms the sheet conveyance paths R3 and R4 between the first roller pair 101 and the second roller pair 102 has a shape that follows at least the displacement of the first roller pair 101 and Consists of materials.
In the present embodiment, the sheet conveyance guide members 105 and 106 are arranged between the fixing nip exit Na and the first roller pair 101 and between the first roller pair 101 and the sheet conveying unit, respectively, to guide the sheet. Functions as a first sheet guide member.

  Specifically, for example, the sheet conveyance guide members 105 and 106 are caused to follow an angle according to the entrance and exit of the first roller pair 101. For this purpose, the material of the paper transport guide members 105 and 106 is made of an elastic material, and the first roller pair 101 creates a post-displacement paper transport path by expanding and contracting with the expansion of the paper transport path due to the displacement of the first roller pair 101. Further, for example, in order to prevent the paper transport guide members 105 and 106 from being caught and caught by the paper transport guide members 105 and 106 when the elastic material is used, the paper transport guide members 105 and 106 are elastic bodies having a low friction coefficient with respect to the paper P. Or a low friction agent may be coated on the contact surface with the front end Pa of the paper P.

  The arrangement positions of the sheet conveyance guide members 105 and 106 shown in FIGS. 2 and 3 are merely examples, and are not necessarily provided over the entire area of the sheet conveyance paths R1, R2, R3, and R4. In other words, the sheet conveyance guide member 105 only needs to be able to guide the leading edge of the sheet P from the fixing nip portion outlet Na to the nip portion of the first roller pair 101 without any trouble. It may be provided in a part or the entire area of the transport paths R1 and R2. The sheet conveyance guide member 106 only needs to be able to guide the leading edge of the sheet P and reliably transfer it to the second roller pair 102 on the downstream side. “From the first roller pair 101 to the second roller pair 102” May be provided in a part or the entire area of the sheet transport paths R3, R4.

  The material (elastic body) of the paper transport guide member 106 described above is merely an example, and it is only necessary to be able to guide the front end Pa of the paper P without hindrance, and FIGS. 5A, 5B, and 5C. As shown in FIG. 4, the “material or form having a variable length” may be used. For example, as shown in FIG. 5 (a), in response to the displacement from the paper transport path R3 to the paper transport path R4, only the stretched portion is made the elastic body E indicated by the broken line, and the others are formed by the rigid body G. . For example, as shown in FIG. 5 (b), a bellows shape J is used instead of the rigid body G in FIG. 5 (a) (JA indicates an extended portion of the bellows shape J). Further, for example, as shown in FIG. 5C, an elastic body E and a rigid body G may be combined.

In FIG. 2, FIG. 3, etc., the first roller pair 101, the second roller pair 102, and the third roller pair 103 are arranged such that straight lines connecting the centers of the axes of the upper and lower roller pairs are arranged in parallel in the vertical direction. It is not limited to this. That is, the angle between the vertical line of the upper and lower roller pairs may be changed depending on the degree of curling of the paper P, and the angle may be set as appropriate.
2 and 3 and the like, the sheet conveyance guide members 106 and 107 and the sheet conveyance path from the first roller pair 101 to the third roller pair 103 are inclined with respect to the extension line of the nip portion of each roller pair. However, it is not limited to this. That is, the inclination between the first roller pair 101 and the second roller pair 102 is necessary because the curvature of the paper transport path can be increased, but the paper transport guide from the first roller pair 101 to the third roller pair 103 is required. The member and the paper transport path may be arranged in an inclined or horizontal (flat) shape.

  The control configuration of this embodiment will be described with reference to FIG. The control unit 130 functions as a broadly defined control unit, and includes a CPU 131 having functions of a calculation unit and a control unit, an information storage unit, and a microcomputer having a timer as a time measuring unit. The information storage unit includes a RAM including a nonvolatile RAM as a storage unit for storing data, a ROM including a PROM, a HDD (Hard Disk Drive), and the like. In the present embodiment, for example, various control programs necessary for the printer process, initial setting values of the system, ROM 132 storing relational data described in Tables 1 to 3 and the like described later for exhibiting the functions of the CPU 131, It is composed of a work memory RAM 133 and the like.

  The CPU 131 receives the cam motor 116, the drive motors 117 and 118, the fixing motor 120, the operation display via the information storage unit based on the signals from the various sensors in FIG. The liquid crystal display unit of the unit 121 is controlled. Examples of the various sensors include a humidity sensor 40, a paper detection sensor 104, temperature sensors 110 and 111, a filler detection sensor 115, a home position sensor, and the like. The signals set with the various keys or the touch panel of the operation display unit 121 include a signal for automatically or selectively setting the paper type, but a known sensor for detecting the paper type may be provided. Good.

  First, the CPU 131 of the control unit 130 of the present embodiment (hereinafter also simply referred to as the control unit 130) first calls the data in Table 2 to be described later from the ROM 132, and presents the current conditions (environment such as paper type, temperature and humidity). The amount of paper curl to be predicted is determined by comparing with the conditions and image forming conditions). The control unit 130 has a basic function of controlling the cam motor 116 by determining a displacement amount of the first roller pair 101 suitable for removing the predicted curl amount.

Secondly, the control unit 130 controls the rotational linear velocity (hereinafter simply referred to as linear velocity) of the first roller pair 101 according to the displacement amount of the first roller pair 101, that is, the control for controlling the drive motor 117. Functions as a means.
Thirdly, when the control unit 130 is configured by the second roller pair 102 and the third roller pair 103 as the sheet conveying unit as in the present embodiment, the control unit 130 responds to changes in the displacement amount and the linear velocity of the first roller pair 101. Thus, the linear speeds of the second roller pair 102 and the third roller pair 103 are controlled. That is, the control unit 130 has a function of controlling the drive motor 118 so as to change the linear speed of the second roller pair 102 and the third roller pair 103.

The operation of the present embodiment will be described with reference to FIGS. After the leading edge Pa of the fixed paper P is detected by the paper detection sensor 104, the path displacing means 108 is operated to displace the first roller pair 101 to the second position DP2. That is, when the cam motor 116 starts to rotate from the state of FIG. 4, the drive motor 117 and the first roller pair 101 supported by the bracket 112 are displaced downward. At this time, by changing from the paper transport paths R1, R3 to the paper transport paths R2, R4, the downwardly convex paper transport paths R2, R4 are created, so the curl of the paper P generated on the non-image surface side is eliminated. It will be suppressed / removed. When the leading edge of the sheet P reaches the first roller pair 101 and is nipped, the path is changed in a state of being nipped by the nip portion of the first roller pair 101, so that the sheet P can be fed even in the sheet conveyance path R2 having a large curvature. The contact with the tip portion is suppressed, and the image can be conveyed while being prevented from being rubbed or scratched.
Thereafter, when the paper detection sensor 104 detects that the trailing edge of the paper P has passed through the first roller pair 101, the first roller pair 101 is returned from the second position DP2 to the original first position DP1. Prepare for the next paper transport.

  Next, changes in the linear speed of the first roller pair 101 and the second roller pair 102 in the present embodiment will be described with reference to FIGS. Table 1 below shows the relationship between the linear velocity change timing and the linear velocity of the first roller pair 101 and the second roller pair 102.

  As shown in FIG. 3 and Table 1, before the leading edge Pa of the paper P reaches the first roller pair 101 (initial), the first roller pair 101 is at the first linear velocity, and the second roller pair 102 is Each is rotating at the third linear velocity. Then, after the leading edge Pa of the paper P reaches the first roller pair 101 and the leading edge of the paper P is nipped by the nip portion of the first roller pair 101, the first roller pair 101 starts to be displaced downward. The linear velocity of the first roller pair 101 is changed to the second linear velocity. This suppresses the pulling of the sheet between the fixing nip exit Na and the first roller pair 101, which is caused by the length of the conveyance path during the displacement of the first roller pair 101. For example, when the sheet conveyance distance between the fixing nip exit Na and the first roller pair 101 is increased by 10 mm per second due to the displacement of the first roller pair 101, the linear velocity of the first roller pair 101 is set to the first line speed. Set slower than the speed by 10 mm / sec.

Further, when the leading edge Pa of the paper P reaches the second roller pair 102 while the first roller pair 101 is displaced to the second position DP2, a method of setting the linear velocity of the first roller pair 101. In the same way as described above, the linear velocity of the second roller pair 102 is changed to the fourth linear velocity, and the pulling of the paper between the first roller pair 101 and the second roller pair 102 is suppressed. At the timing when the first roller pair 101 stops displacing at the second position DP2, the linear velocity of each roller pair is returned to the original, and the slack of the paper P is suppressed.
At the timing when the trailing edge of the sheet P reaches the first roller pair 101, the linear speed of the second roller pair 102 is changed to a fifth linear speed higher than the third linear speed, and the path change and the first roller pair are changed. 101, the conveyance delay of the paper P caused by reducing the linear velocity of the second roller pair 102 is recovered.

  When the trailing edge of the paper P reaches the second roller pair 102, the linear speed of the second roller pair 102 is returned to the third linear speed to prepare for the next paper conveyance. The detection that the trailing edge of the paper P has reached the second roller pair 102 is the time after the paper detection sensor 104 detects that the trailing edge of the paper P has reached the first roller pair 101. This is implemented by measuring time by the timer of the control unit 130. When a roller pair is provided downstream of the second roller pair 102 in the paper conveyance direction like the third roller pair 103 in the present embodiment, the third roller pair 102 is changed according to the change in the linear speed of the second roller pair 102. The linear speed of the roller pair 103 is changed, and the pulling and loosening of the sheet with the second roller pair 102 is suppressed.

Next, a method for determining the displacement amount of the first roller pair 101 will be described.
The displacement amount of the first roller pair 101 is determined based on the predicted curl amount after the paper curl amount is predicted immediately before paper feeding. The amount of curling of the paper is determined by the amount of heat applied to the paper P at the fixing nip Na, the transport path after the exit of the fixing nip Na, the amount of moisture in the paper feed tray, the type of paper as the sheet type, and the like. . Of these, the amount of water in the paper feed tray and the paper type other than the paper type depend on the machine (image forming device). Measure in advance and create a database in advance as shown in Table 2 below. In this way, the amount of paper curl can be predicted by detecting the amount of water and the type of paper before feeding.

  It is also desirable to create a database of the predicted curl amount in the database of Table 2 and the displacement amount of the first roller pair 101 commensurate with removing the curl amount. Such a database is stored in advance in the ROM 132 of the control unit 130 described with reference to FIG. In this way, based on the database, the displacement amount of the first roller pair 101 can be increased if the predicted curl amount is large, and the displacement amount can be automatically decreased if the predicted curl amount is small. Become. For example, the amount of displacement may change continuously according to the value of the predicted curl amount, and if the predicted curl amount is greater than or equal to a threshold value, the displacement amount is α, and if it is less than the threshold value, the displacement amount is β. It may be changed step by step.

From the above prediction, the displacement amount of the first roller pair 101 in the first sheet passing is determined. However, when the paper is continuously passed through the machine, the paper curl may gradually deteriorate (the amount of curl increases). In particular, in a machine that does not have a heat source for the pressure roller 38 or does not operate the heat source of the pressure roller 38 during paper passing, the temperature of the pressure roller 38 that has been deprived of heat by the paper during continuous paper passing decreases. As a result, the temperature difference from the fixing roller 37 gradually increases, and the curl amount increases. In order to suppress the increase in the curl amount during the continuous sheet passing, the temperatures of the fixing roller 37 and the pressure roller 38 are detected by the temperature detection sensors 110 and 111 shown in FIGS. 2 and 3, respectively, and the temperatures of the two rollers are detected. The predicted curl amount is corrected by the difference. The correction increases the predicted curl amount if the temperature difference is large, and decreases the predicted curl amount if the temperature difference is small.
That is, the amount of displacement of the first roller pair 101 from the first position to the second position is calculated by at least one of the sheet type and the temperature detecting means and the humidity detecting means attached in the image forming apparatus. It is determined from the curl amount of the paper predicted based on the moisture amount and the image forming conditions.

  An upper limit value is set for the displacement amount of the first roller pair 101. This upper limit value is a value that does not allow the first roller pair 101 and the sheet transport guide members 105 and 106 to contact the surrounding members such as the pressure roller 38 in the arrangement / position after the first roller pair 101 is displaced. This is the upper limit. The upper limit is also set according to the paper thickness to be passed. If the thick paper is passed through a conveyance path having a large curvature, the paper repels due to the stiffness of the paper and the image is rubbed or scratched by contact with the paper conveyance guide member. Therefore, it is desirable to set the upper limit value small for thick paper. That is, the upper limit value of the displacement amount of the first roller pair 101 is set for each sheet thickness, and the upper limit value is set to be lower for thick sheets having a large sheet thickness.

  When the displacement amount of the first roller pair 101 determined from the paper curl amount prediction and the correction due to the temperature difference between the fixing roller 37 and the pressure roller 38 exceeds the upper limit value, the actual displacement amount becomes the upper limit value. At this time, the curl amount suppression effect of the paper P by the transport path is not sufficient, so by widening the paper passing interval (the distance between the rear end of the previous paper and the front edge of the next paper transported), The temperature difference between the fixing roller 37 and the pressure roller 38 is reduced to suppress the curl amount. That is, an upper limit value is set for the displacement amount of the first roller pair 101, and when the displacement amount calculated from the predicted curl amount of the sheet exceeds the upper limit value, the displacement passes through the nip portion N of the fixing device 36. The interval between sheets is increased (claim 10).

As described above, according to the present embodiment, the following effects are achieved by the following first technical configuration. The first technical configuration according to the present embodiment is a fixing device such as a fixing device 36 that fixes a toner image formed on a sheet such as paper P by passing it through a nip portion such as a heated fixing nip portion N. A first position such as a first position DP1 and a second position such as a second position DP2 that are disposed in the vicinity of the apparatus and the fixing nip exit Na and sandwich the leading edge of the fixed sheet; Between the first conveyance member pair such as the first roller pair 101 that conveys the sheet in the sheet conveyance direction such as the sheet conveyance direction X, and in the sheet conveyance direction more than the first conveyance member pair. After the sheet conveying means such as the second roller pair 102 and the third roller pair 103 arranged on the downstream side and conveying the sheet and the leading end of the fixed sheet are sandwiched between the first conveying member pair, the first The conveying member pair at the first position And a path displacing unit such as a path displacing unit 108 that forms a sheet transport path such as the sheet transport paths R2 and R4 having a curvature opposite to the direction in which the sheet curls. It was an image forming apparatus such as the apparatus 100.
With the first technical configuration, there is a basic effect that it is possible to provide an image forming apparatus capable of removing curl without causing image rubbing or scratching on a fixed sheet. In other words, there is an effect that curling can be suppressed while maintaining good image quality.

The second technical configuration according to the present embodiment is the same as that in the first technical configuration, when the rear end of the fixed sheet passes through the first conveying member pair and Before the leading end reaches the nip exit, the first conveying member pair is returned from the second position to the first position by the path displacing means.
With the second technical configuration, the basic effect of the first technical configuration is achieved even when the fixed sheets are continuously discharged and stacked.

The third technical configuration according to the present embodiment is the second technical configuration, in which the displacement of the first conveying member pair is parallel to a straight line connecting the axial centers of the two rollers constituting the first conveying member pair. It is a reciprocating linear motion that is maintained.
With this third technical configuration, the basic effects of the first technical configuration are achieved.

The fourth technical configuration according to the present embodiment is the same as any one of the first to third technical configurations, between the nip portion outlet and the first conveying member pair and between the first conveying member pair and the sheet conveying means. And a first sheet guide member such as a sheet conveyance guide member 106 and a sheet conveyance guide member 106 that guide the fixed sheet, and the first sheet guide member is a first conveyance member. The shape and material at least follow the displacement of the member pair.
According to the fourth technical configuration, the fixed sheet can be conveyed on the sheet conveyance path formed by the path displacement unit without causing image rubbing or scratches.

The fifth technical configuration according to the present embodiment controls the linear velocity of the first conveying member pair in accordance with the displacement of the first conveying member pair in any one of the first to fourth technical configurations. Control means such as the control unit 130 is included.
With the fifth technical configuration, the sheet pulling between the nip portion outlet and the first conveying member pair, which is caused by the length of the sheet conveying path generated according to the displacement of the first conveying member pair, is suppressed. be able to. Further, the slack of the sheet can be suppressed by returning the linear velocity of the first conveying member pair to the original timing when the first conveying member pair occupies the second position and stops displacing.

According to the sixth technical configuration of the present embodiment, in the fifth technical configuration, when the sheet conveying unit is configured by two or more conveying member pairs, the displacement of the first conveying member pair and the change of the linear velocity are determined. Thus, two or more pairs of conveying members constituting the sheet conveying unit are controlled by the control unit.
With this sixth technical configuration, when the trailing edge of the sheet passes through the second conveying member pair, the linear velocity of the second conveying member pair is returned to the original linear velocity, thereby preparing for the next sheet conveyance. be able to.

The seventh technical configuration according to the present embodiment is the same as any one of the first to sixth technical configurations, in which the amount of displacement of the first transport member pair from the first position to the second position is the paper type. And the curl amount of the sheet predicted based on the moisture amount calculated by at least one of the temperature detection unit and the humidity detection unit provided in the image forming apparatus and the image forming conditions.
With the seventh technical configuration, it is possible to accurately predict the curl amount of the sheet without excess or deficiency, and based on the curl amount of the sheet accurately predicted without excess or deficiency, the first of the first conveying member pair The displacement from the first position to the second position can be performed automatically and accurately.

In an eighth technical configuration according to the present embodiment, in the seventh technical configuration, an upper limit value is set for the displacement amount of the first conveying member pair, and the displacement amount calculated from the predicted sheet curl amount When the value exceeds the upper limit, the interval between sheets passing through the nip portion of the fixing device is increased.
According to the eighth technical configuration, when the displacement amount of the first conveying member pair determined from the prediction of the curl amount of the sheet and, for example, the correction due to the temperature difference on both sides of the heated nip portion of the fixing device exceeds the upper limit value. The actual displacement amount is an upper limit value. At this time, since the curl amount suppressing effect of the sheet by the sheet conveyance path is not sufficient, the curl amount is reduced by reducing the temperature difference of the fixing device by widening the interval between the sheets passing through the nip portion of the fixing device. It becomes possible to suppress.

In the ninth technical configuration according to this embodiment, in any one of the first to eighth technical configurations, the upper limit value of the displacement amount of the first conveying member pair is set for each thickness of the sheet. The upper limit is set to be low for thick sheets such as.
With the ninth technical configuration, when a thick sheet such as thick paper is passed through a sheet conveyance path having a large curvature, the sheet repels due to the stiffness of the sheet, and the image is rubbed or scratched by contact with the sheet guide member. However, such a problem can be prevented in advance.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. 6 to 9 (claims 1 to 2, 5 to 10).
First, the characteristic part of the image forming apparatus according to the second embodiment will be described with reference to FIGS. FIG. 7 is a schematic front view showing the periphery of the sheet conveyance path before the displacement of the first roller pair 101 in the second embodiment. FIG. 8 is a schematic front view showing the periphery of the sheet conveyance path after the first roller pair 101 is swung and displaced. FIG. 9 is a perspective view showing a specific configuration of the path displacing means 108A according to the second embodiment.
Compared with the first embodiment shown in FIGS. 2 to 6, the second embodiment uses a path displacing means 108 </ b> A instead of the path displacing means 108, and correspondingly, a paper transport guide member And the point which changed a part of control structure is mainly different. The configuration and operation of the second embodiment other than this difference are the same as those of the image forming apparatus 100 of the first embodiment described above. Hereinafter, the second embodiment will be described in detail with a focus on the content different from the first embodiment.

As shown in FIGS. 8 and 9, the displacement / movement of the first roller pair 101 is integrated with the paper conveyance guide member 105A, and is supported by a support shaft 53 disposed near the fixing nip exit Na. Reciprocating rocking motion.
As shown in FIG. 9, the path displacing means 108A is disposed between a pair of face plates 59a, 59b and a pair of face plates 59a, 59b indicated by a two-dot chain line, and can swing around the support shaft 53 as a fulcrum. The unit 50 and drive means 52 for swinging the swing unit 50 are provided. The face plates 59a and 59b are fixed to the apparatus main body 99 of FIG.
The swing unit 50 includes a unit frame 51, a first roller pair 101, a drive motor 117, and a paper transport guide member 105A. The unit frame 51 is configured to be swingable with the support shaft 53 as a fulcrum, and has a casing shape in which the upstream side and the downstream side (left front side and right back side in FIG. 9) in the paper transport direction X are opened. Each shaft end portion of the first roller pair 101 is rotatably supported by the unit frame 51. The drive motor 117 is fixed to one outer wall of the unit frame 51, and its output shaft is directly connected to one end of the first roller pair 101. The sheet conveyance guide member 105 </ b> A is attached and fixed to the inner walls on both sides of the unit frame 51 so as to guide the sheet to the nip portion of the first roller pair 101. In addition, the 1st roller pair 101 shown in FIG. 9 has shown the state which occupies 1st position DP1 of FIG.

The drive means 52 includes racks 58a and 58b provided on the pair of face plates 59a and 59b, pinions 57a and 57b meshing with the racks 58a and 58b, and a connecting shaft 56 that connects the pinions 57a and 57b on both sides. The worm wheel 55 is provided on the connecting shaft 56, the worm 54 meshes with the worm wheel 55, and the unit motor 60 connected to the worm 54. The racks 58a and 58b are formed in an arc shape or a partial fan shape with the support shaft 53 as the center.
The worm 54, the worm wheel 55, the connecting shaft 56, the pinions 57 a and 57 b, and the unit motor 60 are provided on the unit frame 51 side of the swing unit 50 and are displaced together with the swing unit 50. The connecting shaft 56 is supported on both side walls of the lower part of the unit frame 51 so as to be rotatable (meaning circular movement in forward and reverse directions). The unit motor 60 is fixed to the bottom wall portion of the unit frame 51.

  In the swing displacement of the first roller pair 101 in this embodiment, the sheet conveyance path is extended only between the first roller pair 101 and the second roller pair 102, and the fixing nip exit Na and the first roller The paper conveyance guide member 105A between the pair 101 need not be an elastic body. Further, the sheet conveyance guide member 106 between the first roller pair 101 and the second roller pair 102 has a length up to the upper limit at which the first roller pair 101 is displaced, as shown in FIGS. By installing the paper conveyance guide member 106, it is not necessary to expand and contract, and there is no restriction on the material.

  A supplementary explanation of the control configuration of this embodiment will be given with reference to FIG. The control configuration of this embodiment is different from that of the first embodiment only in that a unit motor 60 that is a drive source of the swing unit 50 is used instead of the cam motor 116, and the rest is the first embodiment. It is the same. Therefore, regarding the control contents already described in the first embodiment, if the cam motor 116 is replaced with the unit motor 60, those skilled in the art can easily understand and implement it. Is omitted.

The operation of this embodiment will be described with reference to FIGS. After the leading edge Pa of the fixed paper P is detected by the paper detection sensor 104, the path displacing means 108A operates to displace the first roller pair 101 to the second position DP2. That is, when the unit motor 60 starts to rotate from the state of FIG. 9, the drive motor 117 and the first roller pair 101 supported by the unit frame 51 swing and displace toward the second position DP2 together with the unit frame 51. To do. At this time, the sheet conveyance paths R2 and R4 are created by changing from the sheet conveyance paths R1 and R3 to the sheet conveyance paths R2 and R4. Thereby, curling of the paper P generated on the non-image surface side is suppressed / removed. When the leading edge of the sheet P reaches the first roller pair 101 and is nipped, the path is changed in a state of being nipped by the nip portion of the first roller pair 101, so that the sheet P can be fed even in the sheet conveyance path R2 having a large curvature. The contact with the tip portion is suppressed, and the image can be conveyed while being prevented from being rubbed or scratched.
Thereafter, when the paper detection sensor 104 detects that the trailing edge of the paper P has passed through the first roller pair 101, the first roller pair 101 is returned from the second position DP2 to the original first position DP1. Prepare for the next paper transport.

  Next, the change in the linear velocity of the second roller pair 102 in the present embodiment will be described with reference to FIGS. Table 3 below shows the relationship between the linear velocity change timing and the linear velocity of the first roller pair 101 and the second roller pair 102.

  In this embodiment, since the sheet conveyance distance between the fixing nip exit Na and the first roller pair 101 does not change, it is not necessary to change the linear velocity of the first roller pair 101. When the leading edge Pa of the paper P reaches the second roller pair 102 while the first roller pair 101 is displaced to the second position DP2, the linear velocity of the second roller pair 102 is set to the third line. The speed is changed to a sixth linear speed that is slower than the speed, and the pulling of the paper P between the first roller pair 101 and the second roller pair 102 is suppressed.

At the timing when the displacement of the first roller pair 101 stops, the linear velocity of the second roller pair 102 is returned to the third linear velocity, and the slack of the paper P is suppressed. At the timing when the trailing edge of the sheet P passes through the first roller pair 101 (reaches the first roller pair 101), the linear velocity of the second roller pair 102 is changed to a seventh linear velocity that is faster than the third linear velocity. Then, the conveyance delay of the paper P caused by the change of the path and the reduction of the linear velocity of the second roller pair 102 is recovered.
At the timing when the trailing edge of the paper P passes through the second roller pair 102 (reaches the second roller pair 102), the linear speed of the second roller pair 102 is returned to the third linear speed to prepare for the next paper conveyance. The detection that the trailing edge of the paper P has reached the second roller pair 102 is performed in a time period after the paper detection sensor 104 detects that the trailing edge of the paper P has reached the first roller pair 101. To do. When the roller pair is provided downstream of the second roller pair 102 like the third roller pair 103 in this embodiment, the linear speed is changed according to the change of the linear speed of the second roller pair 102. Then, pulling and loosening of the paper between the second roller pair 102 is suppressed.

  As described above, according to the second embodiment, the technical configuration excluding the third and fourth technical configurations in the first embodiment described above provides the same effects as those of the first embodiment corresponding thereto. Play. That is, in addition to the effects of the first and second technical configurations and the fifth to ninth technical configurations, the following advantages are achieved by the unique technical configuration of the present embodiment.

The third technical configuration according to the present embodiment is a paper transport guide member 105A that is arranged between the exit of the nip portion and the first transport member pair and guides a fixed sheet in the second technical configuration. The displacement of the first conveying member pair having the second sheet guide member is a reciprocating rocking motion that is integrated with the second sheet guide member and that is performed near the exit of the nip portion as a fulcrum.
With this third technical configuration, the basic effects of the first technical configuration are achieved.

The fourth technical configuration according to the present embodiment is a paper transport guide member 106 that is arranged between the first transport member pair and the sheet transport unit and guides the fixed sheet in the third technical configuration. The third sheet guide member includes a third sheet guide member, and the third sheet guide member has a shape and material that at least follow the displacement of the first conveying member pair.
According to the sixth technical configuration, the fixed sheet can be conveyed on the sheet conveyance path formed by the path displacement unit without causing image rubbing or scratches.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  The fixing device 36 is not limited to the heat roller type as described above, and any configuration may be used as long as the toner image formed on the sheet is fixed by passing through a heated nip portion. For example, an endless belt is used. Any known fixing device such as a fixing belt method may be used.

For example, an image forming apparatus to which the present invention is applied is a copier, a printer, a facsimile multi-function machine, a color digital multi-function machine capable of performing full-color image formation, and other copiers, printers, facsimiles, plotters. It may be a single unit or a combination machine of another combination such as a combination machine of a copying machine and a printer. In recent years, in response to demands from the market, there are an increasing number of image forming apparatuses capable of forming color images, such as color copiers and color printers. However, image forming apparatuses to which the present invention is applied are limited to monocolor images. It may be formed.
Further, FIG. 1 shows a configuration example of a full color machine of a quadruple tandem type intermediate transfer system as an electrophotographic image forming apparatus to which the present invention can be applied. The present invention is not limited to the full-color machine illustrated in FIG. 1, but can be applied to other image forming apparatuses such as a four-drum tandem direct transfer type full-color machine and a one-drum intermediate transfer type full-color machine. The present invention is also applicable to a monochrome machine such as a one-drum direct transfer system.

  Such an image forming apparatus forms an image on a sheet-like recording medium (sheet) using not only plain paper generally used for copying and the like, but also OHP sheets, cardboard, postcards and other thick paper, envelopes and the like. It is desirable that it is possible. Such an image forming apparatus may be an image forming apparatus capable of forming an image on one side of a transfer sheet as a sheet. The developer used in such an image forming apparatus is not limited to a two-component developer, and may be a one-component developer.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

2Y, 2M, 2C, 2K photosensitive drum (image carrier)
3Y, 3M, 3C, 3K Charger (charging means)
4Y, 4M, 4C, 4K Optical writing unit (exposure means)
5Y, 5M, 5C, 5K Development unit (development means)
36 Fixing device (fixing means)
37 Fixing roller (heating member)
38 Pressure roller (Pressure member)
40 Humidity sensor (humidity detection means)
DESCRIPTION OF SYMBOLS 50 Oscillation unit 60 Unit motor 99 Apparatus main body 100 Image forming apparatus 101 1st roller pair (an example of 1st conveyance member pair)
102 Second roller pair (second conveying member pair, an example of sheet conveying means)
101 Third roller pair (third conveying member pair, an example of sheet conveying means)
104 Paper detection sensor (sheet detection means)
105 Paper transport guide member (an example of a first sheet guide member)
105A Paper transport guide member (an example of a second sheet guide member)
106 Paper transport guide member (an example of a first sheet guide member and a third sheet guide member)
108, 108A Path displacement means 109 Elevating unit 110, 111 Temperature detection sensor 116 Cam motor 117 Drive motor 118 Drive motor 120 Fixing motor 121 Operation display section 130 Control section (an example of control means)
DP1 First position DP2 Second position N Nip part Na Fixing nip part outlet (nip part outlet)
R1, R2, R3, R4 Paper transport path (an example of a sheet transport path)
P paper (example of sheet)
X Paper transport direction (sheet transport direction)

JP 2008-056430 A

Claims (10)

A fixing device that fixes a toner image formed on a sheet by passing the heated nip portion; and
A first sheet that is disposed in the vicinity of the exit of the nip portion and is configured to be displaceable between a first position and a second position by sandwiching the leading end portion of the fixed sheet, and conveys the sheet in the sheet conveying direction. A pair of conveying members,
A sheet conveying means arranged on the downstream side in the sheet conveying direction from the first conveying member pair, and conveys the sheet;
After the leading edge of the fixed sheet is sandwiched between the first conveying member pair, the first conveying member pair is displaced from the first position to the second position, and the nip portion outlet, the sheet conveying means, A path displacing means for creating a sheet transport path having a curvature opposite to the direction in which the fixed sheet curls,
An image forming apparatus comprising: The image forming apparatus according to claim 1.
When the trailing edge of the fixed sheet passes through the first conveying member pair and before the leading end of the fixed sheet to be conveyed next reaches the nip exit, the first conveying member pair Is returned from the second position to the first position by the path displacement means. The image forming apparatus according to claim 2.
2. The image forming apparatus according to claim 1, wherein the displacement of the first conveying member pair is a reciprocating linear motion performed while keeping a straight line connecting the axial centers of two rollers constituting the first conveying member pair in parallel. The image forming apparatus according to any one of claims 1 to 3,
A first sheet guiding member disposed between the nip exit and the first conveying member pair and between the first conveying member pair and the sheet conveying unit, and for guiding the fixed sheet; ,
The image forming apparatus according to claim 1, wherein the first sheet guide member has a shape and a material that at least follow the displacement of the first conveying member pair. The image forming apparatus according to claim 2.
A second sheet guiding member disposed between the nip exit and the first conveying member pair for guiding the fixed sheet;
2. The image forming apparatus according to claim 1, wherein the displacement of the first conveying member pair is a reciprocating rocking motion integrally with the second sheet guide member and performed near the nip exit. The image forming apparatus according to claim 5.
A third sheet guiding member disposed between the first conveying member pair and the sheet conveying unit and guiding the fixed sheet;
3. The image forming apparatus according to claim 1, wherein the third sheet guiding member is formed of a shape and a material that at least follow the displacement of the first conveying member pair. The image forming apparatus according to any one of claims 1 to 6,
An image forming apparatus comprising control means for controlling a linear velocity of the first conveying member pair in accordance with the displacement of the first conveying member pair. The image forming apparatus according to claim 7.
In the case where the sheet conveying means is constituted by two or more conveying member pairs, two or more conveying member pairs constituting the sheet conveying means according to the displacement of the first conveying member pair and the change of the linear velocity. Is controlled by the control means. The image forming apparatus according to any one of claims 1 to 8,
The amount of displacement of the first conveying member pair from the first position to the second position is calculated by at least one of the sheet type and temperature detecting means and humidity detecting means provided in the image forming apparatus. An image forming apparatus characterized by being determined from a curl amount of a sheet predicted based on a moisture amount and image forming conditions. The image forming apparatus according to claim 9.
An upper limit value is set for the displacement amount of the first conveying member pair, and when the displacement amount calculated from the predicted curl amount of the sheet exceeds the upper limit value, the displacement of the sheet passing through the nip portion is determined. An image forming apparatus characterized in that the interval is widened.

Images