JP2019086587A - Image forming apparatus and fixing device - Google Patents

Abstract

To solve the problem in which: when a sheet curling after printing on a first surface does not smoothly enter a fixing nip, wrinkles may be generated on the sheet.SOLUTION: A fixing entry guide 66 is provided on the upstream side of a fixing nip N in a sheet conveyance direction, the fixing entry guide for guiding a sheet P to the fixing nip N by vibrating by an amount larger on the downstream side with respect to a base than that on the upstream side. An image forming apparatus determines the amount of curl of the sheet P and the shape of curl of the sheet P on the basis of the conveyance direction of the sheet P, performs control of changing the position and shape of the fixing entry guide 66 according to the amount of curl and the shape of curl of the sheet P, and performs control of causing the sheet P having an image formed on a second surface to enter a fixing unit.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus and a fixing device.

  In an electrophotographic image forming apparatus, toner is attached to an electrostatic latent image formed on the surface of a photosensitive member for development, and the developed toner image is transferred to a sheet (transferred material) such as a sheet, The toner image is fixed on the sheet by the fixing device.

  In a fixing device generally used, a sheet is passed through a fixing nip (nip portion) of a pair of pressure-contacted rollers, and heat and pressure are applied to fuse and fix a toner image on the sheet. In many fixing devices, a configuration is used in which only the roller in contact with the image forming surface of the sheet is heated.

Many image forming apparatuses can perform image formation on both sides of a sheet. When an image is formed on both sides of a sheet, the sheet may be warped (hereinafter referred to as “curled”) after the toner image is fixed on the first side (front side) of the sheet.
The curling occurs due to a phenomenon that when the fixing device fixes the toner image to the sheet, the heat of fixing applied to the sheet absorbs the moisture of the sheet and the sheet contracts. Usually, when an image with a low printing rate is fixed to the first side, the sheet curls to the second side, and when an image with a high printing rate is fixed to the first side, the sheet tends to curl to the first side. There is. In addition to the printing rate, the curling shape and the amount of curling of the paper also change depending on the type of paper, basis weight, paper eye direction, fixing conditions, environment, and the like.
Therefore, when the sheet on which the toner image is formed on the second surface is made to enter into the fixing nip, the sheet does not enter correctly into the fixing nip due to the curl of the sheet, and wrinkles occur in the sheet or the image There was a problem that bleeding occurred.

  In the following description, the smooth entrance of the sheet into the fixing nip is referred to as "the approachability is improved". Further, the fact that the sheet deviates from the press-contact line of the fixing nip and the sheet does not enter the fixing nip correctly is referred to as "the approachability is reduced".

  In Patent Document 1, a curl detection unit for measuring the curl amount of a transfer material is provided between the transfer nip and the fixing nip, and the guide is rotated about the rotation supporting point to fix the position on the downstream side of the guide to the fixing nip. Technology is disclosed to eliminate the impact of the sheet on the fixing member.

JP 2012-226140 A

  According to the technique disclosed in Patent Document 1, when a sheet having a different amount of curling in both ends in the main scanning direction enters the fixing nip, the movable amount of the guide is changed in accordance with the amount of curling of one of the ends. Ru. However, if the amount of curling at the other end is larger than the amount of curling at one end, even if the approachability of one end is improved by moving the guide, the approachability of the other end is not improved. There is a problem that it is difficult to enter into the fixing nip, and the approachability of the sheet is reduced.

  The present invention has been made in view of such a situation, and it is an object of the present invention to improve the accessibility of a sheet to a fixing nip.

  The image forming apparatus according to the present invention supports an image forming unit that forms an image on a sheet, a fixing unit that fixes an image formed by the image forming unit on the sheet, and entry of the sheet into the fixing unit. An approach supporting portion including a base including the entire upstream end in the transport direction and the vicinity of the center of the downstream end, and a rocking portion in which the amount of rocking on the downstream side is larger than the amount of rocking on the upstream side The curling shape of the sheet is determined based on the detection unit that detects the sheet on which the image is fixed on the first side, the curl amount of the sheet calculated from the detection result of the detection unit, and the sheet conveyance direction. A control unit is controlled to change the position and the shape of the entry support unit according to the amount and the curled shape, and to control the sheet having the image formed on the second surface to enter the fixing unit.

  In the image forming apparatus according to the present invention, for example, it is possible to improve the approachability of the sheet to the fixing unit by operating the entry support unit capable of coping with various curls of the sheet.

FIG. 1 is a schematic configuration view showing an image forming apparatus according to an embodiment of the present invention. It is an enlarged view showing an example of arrangement of a fixing approach guide concerning a 1 embodiment of the present invention. FIG. 1 is a hardware configuration diagram showing a configuration example of main parts of an image forming apparatus according to an embodiment of the present invention. It is an explanatory view showing an example of a curling shape of a sheet according to an embodiment of the present invention. FIG. 6 is a schematic view showing an example of the configuration of a fixing approach guide according to an embodiment of the present invention and an example of the configuration around the installation position of the fixing approach guide. It is explanatory drawing which shows the example at the time of the output by the detection part which concerns on one embodiment of this invention. FIG. 8 is an explanatory view showing an example of the shape of a sheet changed by the operation of the fixing approach guide according to the embodiment of the present invention. It is a block diagram which shows the structural example and operation example of the support part which concern on one embodiment of this invention. It is explanatory drawing which shows the operation example of the kind of CD curl which concerns on one embodiment of this invention, and a fixing approach guide. FIG. 6 is an explanatory view showing a type of FD curl and an operation example of a fixing approach guide according to the embodiment of the present invention. FIG. 8 is an explanatory view showing an operation example of the swinging portion according to the curled shape of the sheet according to the embodiment of the present invention. FIG. 7 is an explanatory view showing an example of the shape of a fixing approach guide having a plurality of broken lines according to an embodiment of the present invention. 7 is a flowchart showing an example of control of the image forming apparatus when the detection unit according to the embodiment of the present invention is installed at the upstream position of the fixing approach guide. It is a flowchart which shows the example of a curl determination processing which concerns on one embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the specification and the drawings, components having substantially the same function or configuration will be assigned the same reference numerals and overlapping descriptions will be omitted.

[1. One Embodiment]
<Hardware Configuration Example of Image Forming Apparatus>
FIG. 1 is a schematic block diagram showing the image forming apparatus 4. In this block diagram, only the elements considered necessary for the description of the present invention or their related elements are described, and the image forming apparatus is not limited to this example.

  The image forming apparatus 4 is, for example, an electrophotographic image forming apparatus such as a copying machine. The image forming apparatus 4 shown in FIG. 1 is also referred to as a so-called tandem type color image forming apparatus, and forms a full color image by arranging a plurality of photosensitive members in a longitudinal direction facing one intermediate transfer belt. Is possible.

The image forming apparatus 4 includes an image forming unit 40, a sheet conveyance unit 50, a fixing unit 60, and an automatic document feeder 20 (ADF: Auto Document Feeder).
The image forming unit 40 is an image forming unit that forms an image on a sheet P, and includes an image forming unit 40Y that forms an image of yellow (Y), an image forming unit 40M that forms an image of magenta (M), and cyan The image forming unit 40C that forms the image of (C) and the image forming unit 40K that forms the image of black (K) are provided.

  The image forming unit 40Y includes a photosensitive drum Y and a charging unit 42Y disposed around the photosensitive drum Y, an optical writing unit 43Y having a laser diode 41Y, a developing device 44Y, and a drum cleaner 45Y. Similarly, the image forming units 40M, 41C, and 41K are optical writing units having photosensitive drums M, C, and K, charging units 42M, 42C, and 42K disposed around them, and laser diodes 41M, 41C, and 41K. 43M, 43C, 43K, developing devices 44M, 44C, 44K and drum cleaners 45M, 45C, 45K.

  The surface of the photosensitive drum Y is uniformly charged by the charging unit 42Y, and a latent image is formed on the photosensitive drum Y by scanning exposure from the laser diode 41Y of the optical writing unit 43Y. Further, the developing device 44 Y develops the latent image on the photosensitive drum Y by developing with toner. Thereby, an image (toner image) of a predetermined color corresponding to yellow is formed on the photosensitive drum Y.

  Similarly, the surface of the photosensitive drum M is uniformly charged by the charging unit 42M, and a latent image is formed on the photosensitive drum M by scanning exposure from the laser diode 41M of the optical writing unit 43M. Ru. Further, the developing device 44M develops the latent image on the photosensitive drum M by developing with toner. As a result, a toner image of a predetermined color corresponding to magenta is formed on the photosensitive drum M.

  The surface of the photosensitive drum C is uniformly charged by the charging unit 42C, and a latent image is formed on the photosensitive drum C by scanning exposure from the laser diode 41C of the optical writing unit 43C. Further, the developing device 44C develops the latent image on the photosensitive drum C by developing with toner. As a result, a toner image of a predetermined color corresponding to cyan is formed on the photosensitive drum C.

  The surface of the photosensitive drum K is uniformly charged by the charging unit 42K, and a latent image is formed on the photosensitive drum K by scanning exposure from the laser diode 41K of the optical writing unit 43K. Further, the developing device 44K develops the latent image on the photosensitive drum K by developing with toner. As a result, a toner image of a predetermined color corresponding to black is formed on the photosensitive drum K.

  The toner images formed on the photosensitive drums Y, M, C, and K are moved by the primary transfer rollers 47Y, 47M, 47C, and 47K to a predetermined position on the intermediate transfer belt 46, which is a belt-like intermediate transfer member. Sequentially transferred. The toner image of each color transferred onto the intermediate transfer belt 46 is transferred by the secondary transfer unit 48 to the sheet P transported by the sheet transport unit 50 at a predetermined timing.

  The sheet conveyance unit 50 includes a plurality of sheet feeding trays 51 in which the sheets P are stored, and a sheet feeding unit 51 a that feeds out the sheets P stored in the sheet feeding tray 51. The sheet conveyance unit 50 also includes a main conveyance path 53 for conveying the sheet P fed from the paper feed tray 51, a reverse conveyance path 54 for reversing the front and back of the sheet P, and discharge for discharging the sheet P. A paper tray 55 is provided.

  The sheet conveyance unit 50 includes a switching gate 53 a at a branch point between the reverse conveyance path 54 branched from the main conveyance path 53 on the downstream side of the fixing unit 60 and the main conveyance path 53. In the image forming apparatus 4, an image is formed on the surface (first surface) of the sheet P which has been conveyed through the main conveyance path 53 and has passed through the secondary transfer portion 48 and the fixing portion 60. When forming an image on both sides of the sheet P, the sheet P on which the image is formed on the surface facing upward is conveyed from the main conveyance path 53 to the reverse conveyance path 54. Then, the sheet P is inverted by the sheet inverting conveyance path 56 provided in the inversion conveyance path 54, so that the image forming surface (first surface) of the sheet P faces downward. Thereafter, the sheet P is conveyed to the main conveyance path 53. As a result, the sheet P is turned upside down, and an image can be formed on the other side (second side) facing upward.

  The fixing unit 60 fixes the image formed by the image forming unit 40 on the sheet P. For this reason, the fixing unit 60 conveys the sheet P by the pair of upper pressure roller 61 and the lower pressure roller 62 in pressure contact, and fixes the image on the sheet P to which the image is transferred. Do. Inside the heating roller 64, a heater H is provided. The heater H heats the heat roller 64 so that the heat is transmitted to the sheet P passing through the fixing nip N between the fixing belt 68 and the lower pressure roller 62. The heated fixing belt 68 transfers heat to the upper pressure roller 61 by rotating, and transfers heat to the sheet P passing through the fixing nip N. By heating the sheet P, the toner image on the sheet P is melted. As a result, the toner image is fixed to the sheet P.

  The automatic document feeder 20 scans and exposes the image of the document by the optical system of the scanning exposure apparatus, and reads the reflected light by the line image sensor to obtain an image signal.

<Example of main configuration of fixing unit>
FIG. 2 is an enlarged view showing an arrangement example of the fixing entrance guide 66. As shown in FIG.

  As described above, the fixing unit 60 disposed downstream of the intermediate transfer belt 46 includes the upper pressure roller 61, the lower pressure roller 62, and the heating roller 64 provided with the heater H, via the fixing belt 68. Heat is transferred to the sheet P passing through the fixing nip N. The upper pressure roller 61 and the heating roller 64 are connected via the fixing belt 68 heated by the heating roller 64, and are driven clockwise (clockwise). On the other hand, the lower pressure roller 62 is driven counterclockwise (left rotation).

  A fixing approach guide 66 is provided upstream of the upper pressure roller 61 and the lower pressure roller 62. The fixing entry guide 66 is provided as an example of an entry support unit for assisting the entry of the downstream end of the sheet P into the fixing nip N. The sheet P is conveyed along the upper surface of the fixing entry guide 66, and the downstream end of the sheet P enters the fixing nip N. The fixing entry guide 66 can improve the approachability of the sheet P into the fixing nip N by moving or deforming in response to various curls of the sheet P as described later. A specific configuration example and operation example of the fixing entry guide 66 will be described later.

  A front guide 63 is provided on the upstream side of the fixing entry guide 66. The front guide 63 is provided to support conveyance of the sheet P when the distance from the fixing unit 60 to the secondary transfer unit 48 is long. The sheet P is conveyed along the upper surface of the front guide 63, and the downstream end of the sheet P enters the fixing entry guide 66.

  As shown in FIG. 2, when the front guide 63 is on the upstream side of the fixing entrance guide 66, the height relationship between the downstream end of the front guide 63 and the upstream end of the fixing entrance guide 66 is maintained at an appropriate value. . Therefore, the sheet P transported on the main transport path 53 enters the fixing approach guide 66 from the front guide 63. Even if the member on the upstream side of the fixing entry guide 66 is not the front guide 63 but a transfer member or the like, the sheet P can be similarly entered into the fixing entry guide 66. In this case, the fixing unit 60 may not be provided with the front guide 63.

  Although FIG. 1 and FIG. 2 show a configuration example in which the fixing entry guide 66 is included in the fixing unit 60, the fixing entry guide 66 may be configured separately from the fixing unit 60.

<Configuration of Main Part of Image Forming Apparatus>
FIG. 3 is a hardware configuration diagram showing a configuration example of main parts of the image forming apparatus 4.

  The image forming apparatus 4 includes a control unit 11, a storage unit 12, and a communication I / F (Interface) 13 in addition to the automatic document feeder 20 and the image forming unit 40 described above. Each unit in the image forming apparatus 4 is connected via a bus.

The control unit 11 includes a CPU 11a, a ROM 11b, and a RAM 11c. The control unit 11 is a computer that controls the operation of each unit in the image forming apparatus 4. The CPU 11a controls, for example, the image forming process (printing operation) of the image forming unit 40 based on the user's print instruction, and controls the position and shape of the fixing entry guide 66.
The ROM 11 b is a non-volatile memory, and the ROM 11 b stores programs and data required for the CPU 11 a to operate.
The RAM 11 c is a volatile memory, and information (data) necessary for each process performed by the CPU 11 a is temporarily stored in the RAM 11 c.

The storage unit 12 is, for example, an HDD, and the storage unit 12 stores a program for the CPU 11a to control each unit, an OS, a program such as a controller, and data. Some of the programs and data stored in the storage unit 12 are also stored in the ROM 11 b. The storage unit 12 is a computer readable non-transitory recording medium storing a program executed by the CPU 11a. The storage unit 12 is not limited to the HDD. For example, the recording medium may be a solid state drive (SSD), a CD-ROM, a DVD-ROM, or the like.
The communication I / F 13 is configured by a NIC (Network Interface Card), a modem, or the like, establishes a connection with a PC terminal (not shown) and a controller, and executes transmission and reception of various data.

<Example of shape of curled paper>
FIG. 4 is an explanatory view showing an example of the curled shape of the sheet P. As shown in FIG. In FIG. 4, the arrow attached to the sheet P indicates the transport direction of the sheet P.

  As the curled shape of the sheet P, a first curled shape in which the sheet P is curved in the main scanning direction shown in the left row of FIG. 4 (direction intersecting with the conveying direction of the sheet P) There is a second curled shape in which the sheet P is curved in a direction parallel to the conveyance direction of the sheet P). In the following description, the first curled shape is called "CD (Cross Direction) curl", and the second curled shape is called "FD (Feed Direction) curled".

Further, as shown in the upper part of FIG. 4, when the curling amount of the paper P in the main scanning direction is the same and when the curling amount of the paper P in the subscanning direction is the same, it is called "symmetrical".
Further, as shown in the lower part of FIG. 4, when the curling amount of the paper P in the main scanning direction is different, and when the curling amount of the paper P in the subscanning direction is different, it is called “left-right asymmetry”. Here, it is assumed that the CD curl and the FD curl do not occur at the same place on the sheet P at the same time.

<Example of configuration around fixing entry guide>
FIG. 5 is a schematic view showing an example of the configuration of the fixing approach guide 66 and an example of the installation position of the fixing approach guide 66. As shown in FIG. In the following description, the fixing belt 68 shown in FIG. 1 is omitted. In the following description, the surface on which the toner image formed on the sheet P is fixed is referred to as “upper side”, and the back surface is referred to as “lower side”.

FIG. 5A shows an example in which the fixing approach guide 66 and the lower pressure roller 62 are viewed from above in the direction A1 of FIG.
5B shows an example in which the fixing approach guide 66 and the lower pressure roller 62 are viewed from the front in the A2 direction of FIG.
The anchorage entry guide 66 has a base 140 that is elongated and plate-like and includes the entire upstream end and near the center of the downstream end. Further, the fixing entry guide 66 is swingable portion 142a pivotable about a broken line intersecting with the side end downstream of the upstream end of the fixing entry guide 66 and the downstream end of the fixing entry guide 66, 142b (an example of an end).

  Two swing support portions 141 a and 141 b are provided at both downstream ends of the base portion 140 so as to form a V shape in the fixing entry guide 66. The position at which the rocking support portions 141a and 141b are provided is the position of a broken line serving as a fulcrum of the rocking portions 142a and 142b that rock. The swing support portion 141a provided on the left side of the base 140 pivotally supports the swing portion 142a. Similarly, the swing support portion 141b provided on the right side of the base 140 pivotally supports the swing portion 142b. Therefore, the rocking portions 142 a and 142 b rock independently of the operation of the base 140 and can tilt with respect to the base 140. For this reason, the rocking portions 142a and 142b are either in the normal position where the surface direction of the rocking portions 142a and 142b is the same as the surface direction of the base 140 or in the rocking position different from the surface direction of the base 140. It is rocked. Then, the control unit 11 performs control to swing the swinging portions 142 a and 142 b in accordance with the curl amount of the end portion of the sheet P in the main scanning direction. In the following description, when the rocking support portions 141 a and 141 b are not distinguished from one another, they are referred to as “a rocking support portion 141”. Similarly, when the rocking portions 142a and 142b are not distinguished from each other, they are referred to as "rocking portion 142".

  FIG. 5C is a view showing an arrangement example of the detectors 67a and 67b (an example of a detection unit) that detects the curl amount of the sheet P, and a state before the sheet P enters the fixing entry guide 66. The detectors 67 a and 67 b can detect the sheet P on which the image is fixed on the first surface by the fixing unit 60. Then, the detectors 67a and 67b detect the distance from each of the installation locations to the upper surface of the sheet P. As described below, the distance to the upper surface of the sheet P detected by each of the detectors 67a and 67b is the detection result. Further, in the transport direction to the fixing entry guide 66, the location detected by the detector 67a is "left", and the location detected by the detector 67b is "right". When the detectors 67a and 67b are not distinguished from one another, they are collectively referred to as "detector 67".

  The detector 67 is disposed in a path until the sheet P having the image fixed on the first side by the fixing section 60 enters the fixing section 60 in order to fix the image on the second side. Detect the end in the scanning direction. The detector 67 may be installed between the secondary transfer unit 48 and the fixing unit 60 shown in FIG.

  The control unit 11 obtains the curl shape of the sheet P based on the curl amount of the sheet P calculated based on the detection result of the detector 67 and the conveyance direction of the sheet P. Then, the control unit 11 performs control to change the position and the shape of the fixing entry guide 66 according to the curl amount and the curled shape of the sheet P, and causes the sheet P on which the image is formed on the second surface to enter the fixing unit 60. Take control. Further, the control unit 11 calculates the curl amount of the sheet P being conveyed based on the detection result of the detector 67, and the time-series change of the curl amount and the curl shape of the sheet P passing the detection range of the detector 67. In accordance with the above, it is also possible to perform control to move the fixing entry guide 66 while the sheet P is being transported.

  The configuration of the detector 67 is not limited to an optical detector that can detect the distance to the sheet P in a non-contact manner, such as the detectors 67a and 67b, but may contact the sheet P to reach the sheet P. You may use the contact-type detector which can detect distance.

Here, an example of the positional relationship between the fixing entry guide 66 and the support portions 15a, 15b, 15c, 15d, and 15e provided on the lower surface of the fixing entry guide 66 and supporting the fixing entry guide 66 will be described. As shown in FIG. 5C, the support portion 15a is installed near the center of the swinging portion 142a. The support portion 15 b is installed near the center of the swinging portion 142 b. In the rocking portions 142a and 142b, the amount of rocking on the downstream side is rocked more than the amount of rocking on the upstream side. Here, the amount of rocking represents a size in which the upstream side and the downstream side of the side end of the rocking portions 142a and 142b are inclined with respect to the normal position of the base 140.
The support 15 c is located on the left side of the support 15 d when viewed from the transport direction, and is disposed upstream of the base 140 when viewed from the transport direction. The support portion 15 d is disposed near the center of the base 140 in the main scanning direction, and is disposed downstream as viewed in the transport direction. The support portion 15 e is located on the right side of the support portion 15 d when viewed from the transport direction, and is disposed upstream of the base 140 when viewed from the transport direction.
Then, the control of the control unit 11 causes the supporting units 15a to 15e to move independently, so that various operations of the fixing approach guide 66 are realized. Description of a detailed configuration example and operation example regarding the support portions 15a to 15e will be described later with reference to FIG.

<Example of detecting curled shape of paper>
FIG. 6 is an explanatory view showing an example in which the detector 67 detects the distance to the sheet P and an example of the time transition of the curl amount.
FIG. 6A is an example in which the detector 67a in FIG. 5C and the left side of the sheet P are viewed from the side.

  As shown in FIG. 5C, the detector 67a detects the distance from the installation position of the detector 67a to the left end of the sheet P. Then, based on the time-series change of the curling amount from the downstream end of the sheet P to a predetermined distance (for example, 10 cm from the downstream end) calculated by the detection result of the detector 67a, the control unit 11 Find the curled shape.

FIG. 6B and FIG. 6C are graphs showing the temporal transition of the curl amount of the sheet P expressed based on the detection result of the detector 67a from the downstream end of the sheet P to a certain distance.
The method of calculating the curl amount performed by the control unit 11 is performed in the following procedure. For example, the control unit 11 first obtains, as a reference value, the distance L to the conveyance road surface represented by a broken line in FIG. 5A. Next, the control unit 11 obtains the distance M from the detector 67a to the sheet P for each sheet P to be transported, based on the detection result of the detector 67a. Then, the control unit 11 obtains a value obtained by subtracting the distance M to the sheet P from the reference distance L as the amount of curl of the sheet P.

For example, as shown in FIGS. 6B and 6C, if the curl amount is positive, it is indicated that the end of the sheet P is curled upward. On the other hand, if the amount of curling of the sheet not shown is negative, it is indicated that the end of the sheet P is curled downward.
And from FIG. 6B, the curling amount increases at the downstream end of the sheet P, and the curling amount tends to decrease immediately. From this, the control unit 11 determines that the curling shape of the sheet P is such that only the left downstream end curls upward. Similarly, the control unit 11 can also determine the curled shape of the sheet P at the upstream end of the sheet P.

  Further, FIG. 6C shows a tendency that the detection result that has become large at the downstream end of the sheet P continues in a constant state. From this, the control unit 11 can read that the curling continues upward to a certain distance from the downstream end on the left side of the sheet P. Similarly, the control unit 11 can determine that the curling continues at the upstream end of the sheet P as well.

The detector 67b also detects the distance from the installation position of the detector 67b to the right end of the sheet P, similarly to the detector 67a.
The control unit 11 determines that the curling shape of the sheet P is CD curl if the amount of curling on the left and right sides calculated based on the detection results of the detectors 67a and 67b continues a predetermined distance. On the other hand, the control unit 11 determines that the curled shape of the sheet P is FD curl if the curl amounts generated on the left and right sides calculated based on the detection results of the detectors 67a and 67b decrease immediately. The control unit 11 can also determine whether the CD curl and the FD curl are symmetrical or asymmetric based on the amounts of curl at the left and right ends of the sheet P.

  Furthermore, in FIG. 5C, the detectors 67a and 67b are provided at two places on the left and right sides of the sheet P, but another detector is provided near the center of the sheet P. Three locations may be detected. For example, based on the detection result of the detector 67 that detects the distances to three places at the downstream end of the sheet P, the control unit 11 does not curl the central portion of the sheet P, and the left and right ends of the sheet P If it is determined that the sheet P is curled, it can be understood that the curled shape of the downstream end of the sheet P is a CD curl. Further, when the control unit 11 determines that the left and right ends of the sheet P and the three locations near the central portion are curled to the same extent, the curled shape of the downstream end portion of the sheet P is FD curl.

  Here, the amount of movement of the entire fixing entry guide 66 and the amount of movement of the rocking portions 142a and 142b differ depending on the amount of curl of the sheet P and the shape of the curl. Specifically, the control unit 11 individually controls contact-type supporting units 15a to 15e shown in FIG. 8 described later based on the curling amount and the curling shape of the sheet P obtained based on the detection result of the detector 67. As a result, the fixing approach guide 66 and the swinging portions 142a and 142b are moved.

  Since the curl changes with time, in order to calculate the curl amount and the curl shape more accurately, the control unit 11 fixes the second side of the sheet P from immediately after fixing the image on the first side of the sheet P. It is desirable that the detectors 67a and 67b detect the amount of curling at a position close to the timing of entering N. For example, it is desirable to detect between the transfer nip and the fixing nip N. For this reason, as shown in FIG. 2, the detectors 67a and 67b are often provided between the transfer nip and the fixing nip N.

  However, the control unit 11 may temporarily stop the conveyance of the sheet P, and calculate the amount of curling based on the detection result of the sheet P detected by the detector 67 in this state. For example, the detector 67 is provided on the sheet reversing conveyance path 56 used in duplex printing, and the distance between the sheet P and the sheet P is detected by the detector 67 while the sheet P is temporarily stopped in the sheet reversing conveyance path 56. May be Alternatively, the detector 67 may be provided at the registration position 57 on the main conveyance path 53, and the distance to the sheet P may be detected by the detector 67 in a state where the sheet P is temporarily stopped at the registration position 57.

  Further, the detector 67 may be configured by one detector, and the detector may be provided in the sheet reversing conveyance path 56 through which the same surface of the sheet P passes twice. In this case, the position where one detector detects the sheet P which has passed the first time in the sheet reverse conveyance path 56 differs from the position where the detector P detects the sheet P which has passed the second time. I don't care. For this purpose, for example, one detector scans the sensing beam in the main scanning direction of the sheet P to obtain the distance from the installation position of the detector to the sheet P. Thus, the control unit 11 calculates the amount of curling of the left end of the sheet P when the sheet P passes the sheet reversing conveyance path 56 (first time) after fixing of the first surface, and then the sheet is reversed. When passing the conveyance path 56 (the second time), it is possible to calculate the curl amount of the right end of the sheet P.

<Example of change of paper by driving of fixing entrance guide>
FIG. 7 is an explanatory view showing an example of the shape of the sheet P changed by the operation of the fixing entry guide 66. As shown in FIG. In FIG. 7, the upper pressure roller 61 is not shown.
FIG. 7A shows an example of a normal position in which the surface direction of the swinging portions 142 a and 142 b provided in the fixing entry guide 66 is the same as the surface direction of the base 140. Both end portions Pe of the sheet P above the fixing entry guide 66 in the main scanning direction are curled upward, and are not in contact with the swinging portions 142a and 142b. The central portion Pc of the sheet P is not curled and is in contact with the base 140.

  FIG. 7B shows an example in which the rocking portions 142a and 142b are inclined below the normal position. When the rocking portions 142a and 142b are inclined downward, both end portions Pe fall following the rocking portions 142a and 142b, and the heights of the both end portions Pe become the same height as the central portion Pc. As a result, after the downstream end of the sheet P passes through the fixing entry guide 66, the both ends Pe and the center Pc of the sheet P enter the fixing nip N almost simultaneously, so the approachability of the sheet P is improved. It is possible to prevent the occurrence of wrinkles and bleeding on the sheet P.

<Moving example of rocking part>
FIG. 8 is an explanatory view showing a configuration example and an operation example of the support portions 15a to 15e. The support portions 15a to 15e shown in FIG. 8 are driven independently of each other by the control of the control portion 11, and the positional relationship of the support portions 15a to 15e is as shown in FIG. 5C. In the normal state, when looking at the fixing entry guide 66 from the upstream in the transport direction, the downstream end of the base 140 is on the front side, so the swinging portions 142a and 142b at the upstream end of the base 140 Although it can not be visually recognized, for convenience of explanation, the rocking portions 142a and 142b are shown in the figure.

  In FIG. 8A, the support portion 15a inclines the swinging portion 142a downward, the support portion 15b tilts the swinging portion 142b downward, and the support portions 15c, 15d, and 15e set the base portion 140 in the normal position. Is shown. For this reason, the rocking portions 142a and 142b can be visually recognized from the upstream in the transport direction.

  Since the support portions 15a to 15e have the same structure, the internal structure of the support portion 15a will be described below. The support portion 15 a includes a contact pin 151, a holder 152 which holds the contact pin 151 so as to be movable in the axial direction, and a motor M. A male screw member 154 is attached to the tip of the drive shaft 153 of the motor M, and the male screw member 154 is screwed to a female screw screwed on the inner peripheral surface of the hole 155 formed in the contact pin 151 . Then, by the drive of the motor M, the male screw member 154 is rotated together with the drive shaft 153 to move the contact pin 151 in the axial direction.

  The movement amount of the base 140 may be continuous or discontinuous (intermittent movement). In addition, on the upstream side of the base 140, a diagonally downward elastic force is applied by the tension springs 159c and 159e. However, the upward force of the contact pins 151 of the support portions 15 c and 159 e in contact with the lower surface of the base 140 balances the elastic force applied to the base 140, whereby the upstream position of the base 140 is fixed. Therefore, the upstream side of the base 140 is moved by the vertical movement of the contact pin 151 provided on the support portions 15c and 15e.

  Similarly, on the downstream side of the base 140, an obliquely downward elastic force is applied by the tension spring 159d. However, the pressing force of the contact pin 151 of the support portion 15d in contact with the lower surface of the base 140 balances the elastic force applied to the base 140, whereby the downstream position of the base 140 is fixed. Therefore, the downstream side of the base 140 is moved by the vertical movement of the contact pin 151 provided on the support portion 15d.

The moving amounts of the rocking portions 142a and 142b may also be continuous or discontinuous (intermittent movement). An elastic force directed obliquely downward by the tension springs 159a and 159b is applied to the swinging portions 142a and 142b. However, the pushing force of the contact pin 151 provided on each of the support portions 15a and 15b in contact with the lower surface of the rocking portions 142a and 142b balances with the elastic force applied to the rocking portions 142a and 142b. , 142b positions are fixed. For this reason, the swinging portions 142 a and 142 b swing by the vertical movement of the contact pin 151.
As means for tilting the swinging portions 142a and 142b, in addition to the above configuration, a conventionally known support such as a solenoid can be used.

  In FIG. 8B, the support portion 15a inclines the swinging portion 142a upward, the support portions 15c, 15d, and 15e have the base portion 140 in the normal position, and the support portion 15b has the swing portion 142b in the normal position. Is shown. For this reason, the swinging portion 142b can be visually recognized from the upstream in the transport direction.

  FIG. 8C shows a state in which the support portion 15a inclines the rocking portion 142a downward and the support portion 15b inclines the rocking portion 142b upward. For this reason, the rocking portions 142a and 142b can be visually recognized from the upstream in the transport direction. Further, FIG. 8C shows a state in which the support portions 15c and 15e have the base portion 140 in the normal position, and the support portion 15d (see FIG. 5C) has the downstream end of the base portion 140 inclined downward. Here, the hatched portion in FIG. 8C represents the back surface of the base 140 that is visible from the upstream in the transport direction by tilting the downstream end of the base 140 downward. As a result of the movement of the support portions 15a, 15b, 15d in this manner, the downstream end of the fixing entry guide 66 as a whole is inclined downward and to the left. That is, when the support portion 15 d is moved while the support portions 15 c and 15 e are fixed, the downstream end portion is pivoted about the upstream end portion of the fixing approach guide 66.

<Example of movable type of fixing approach guide>
Next, an example of how to move the fixing entry guide 66 when the second surface is made to enter the fixing nip N will be described according to the curl amount generated on the sheet P after fixing the toner image of the first surface.
FIG. 9 is an explanatory view showing a type of CD curl and an operation example of the fixing entry guide 66. As shown in FIG. An example in which the upper pressure roller 61, the lower pressure roller 62, and the fixing approach guide 66 are perspectively shown in the left row of FIG. 9, and the upper pressure roller 61, the lower pressure in the right row of FIG. An example is shown in which the roller 62 and the fixing approach guide 66 are viewed from the transport direction.

The control unit 11 is a broken line that crosses the side end portion on the downstream side of the upstream end portion of the fixing entry guide 66 and the downstream end portion of the fixing entry guide 66 before the sheet P with CD curled enters the fixing unit 60. Control is performed according to the amount of curling, at least one of the two end portions swinging around the pivot point.
The upper part of FIG. 9 shows an operation example of the fixing entry guide 66 when a normal sheet P without CD curl is conveyed. In this case, the surface direction of the downstream end of the fixing entry guide 66 is parallel to the surface direction of the surface on which the fixing nip N of the upper pressure roller 61 and the lower pressure roller 62 is formed. The base portion 140 of the fixing entry guide 66 and the swinging portions 142a and 142b are at the normal position.

  The middle part of FIG. 9 shows an operation example of the fixing entry guide 66 in the case where the sheet P in which the CD curl in the left / right symmetry has occurred is conveyed at the downstream end. In this case, the left and right curl amounts of the sheet P are the same, and both left and right ends of the sheet P are curled upward, so it is necessary to tilt the swinging portions 142a and 142b downward at the same angle with respect to the base 140 is there. Thus, the heights of the left and right downstream end portions of the sheet P can be matched with the height of the surface on which the fixing nip N is formed.

  The lower part of FIG. 9 shows an operation example of the fixing entry guide 66 in the case where the sheet P in which the CD curl in the left-right asymmetry is generated at the downstream end is conveyed. In this case, the amount of curling on the left side of the sheet P is larger than the amount of curling on the right side. Therefore, the inclination of the swinging portion 142a corresponding to the left side of the sheet P having a large curl amount is made larger than the inclination of the swinging portion 142b corresponding to the right side. Thereby, the height of the downstream end on the left side of the sheet P can be adjusted to the height of the surface on which the fixing nip N is formed.

If the amount of curling on the right side of the sheet P is larger than the amount of curling on the left side, the height of the downstream end of the sheet P is fixed by making the inclination of the rocking portion 142b larger than the inclination of the rocking portion 142a. It can be adjusted to the height of the forming surface of the nip N.
As described above, in the case of asymmetric CD curl in which the left and right curl amounts are different, one of the swinging portions 142a and 142b having the larger curl is inclined downward more.

  Further, if the left and right ends on the downstream side of the sheet P are curled downward, the rocking portions 142 a and 142 b are inclined upward with respect to the base 140. At this time, if the downstream side of the sheet P is a CD curl which is symmetrical in the left-right direction, the rocking portions 142a and 142b are inclined upward at the same angle. Further, if the downstream side of the sheet P is a CD curl that is asymmetrical to the lower side, one of the swinging portions 142a and 142b with the larger curl is inclined upward.

  FIG. 10 is an explanatory view showing a type of FD curl and an operation example of the fixing entrance guide 66. As shown in FIG. An example in which the upper pressure roller 61, the lower pressure roller 62, and the fixing approach guide 66 are perspectively shown in the left row of FIG. 10, and the upper pressure roller 61, the lower pressure in the right row of FIG. An example is shown in which the roller 62 and the fixing approach guide 66 are viewed from the transport direction.

  The control unit 11 rotates the base portion of the base portion 140 with the upstream end parallel to the main scanning direction of the fixing entry guide 66 as a fulcrum, before entering the FD-curled sheet P into the fixing portion 60, and / or One or a combination of operations of swinging the swinging portion 142 so as to tilt with respect to the base is performed.

The upper part of FIG. 10 shows an operation example of the fixing entry guide 66 when a normal sheet P without FD curl is conveyed. In this example, as shown in the upper part of FIG. 9, the base portion 140 of the fixing entry guide 66 and the swinging portions 142a and 142b are at the normal position.
The middle part of FIG. 10 shows an operation example of the fixing entry guide 66 in the case where the sheet P in which the symmetrical FD curl has occurred is conveyed. In this case, the amount of curling on the left and right sides of the sheet P is the same, and the upstream end and the downstream end of the sheet P are curled. Here, although not shown in FIG. 10, as shown in FIG. 2, a front guide 63 whose position is fixed is disposed upstream of the fixing approach guide 66. As shown in FIG. For this reason, it is necessary to fix the upstream end of the fixing entrance guide 66 and to tilt the entire fixing entrance guide 66 while maintaining the proper position with the downstream end of the front guide 63. As a result, the downstream end of the fixing entry guide 66 is pivoted downward about the upstream end, so the sheet P is conveyed following the inclination of the fixing entry guide 66, and the downstream end of the sheet P Can be adjusted to the height of the forming surface of the fixing nip N.

The lower part of FIG. 10 shows an operation example of the fixing entry guide 66 in the case where the sheet P in which the left and right asymmetrical FD curl has occurred is conveyed. In this case, the amount of curling on the left side of the sheet P is larger than the amount of curling on the right side. In this case, while fixing the upstream end of the fixing entrance guide 66 and maintaining the proper position with the downstream end of the front guide 63, the entire fixing entrance guide 66 is inclined and at the same time The moving part 142a is inclined downward and 142b is inclined upward.
As a result, the downstream end of the fixing entry guide 66 is inclined to the side where curling is large (for example, the left side) as shown in the lower part of FIG. 10, and the height of the downstream end of the sheet P It can be adjusted to the height.

In the case of asymmetrical FD curl with different curl amounts, the control unit 11 performs control to lower one of the rocking portions 142a and 142b and raise the other. Therefore, when the left and right curl amounts are different, it is not necessary to tilt the entire fixing entry guide 66 to the left or right with respect to the transport direction in the direction of the larger curl amount. Thereby, the upstream end of the fixing entry guide 66 can be fixed, and the proper position with the downstream end of the front guide 63 can be maintained. Therefore, the sheet P having passed through the front guide 63 is conveyed along the upper surface of the fixing entry guide 66 without colliding with the upstream end of the fixing entry guide 66.
If necessary, the downstream end of the fixing entry guide 66 may be moved up and down in parallel while the fixing entry guide 66 is inclined leftward or rightward.

  Further, when CD curl and FD curl are mixed in one sheet P, the control unit 11 causes the fixing entry guide 66 to perform both the operation at the time of the CD curl and the operation at the time of the FD curl. For example, CD curl may be present at the left end of the sheet P, and FD curl may be present at the right end of the sheet P. In this case, the control unit 11 causes the fixing entry guide 66 to perform an operation when there is a CD curl at the left end of the sheet P by controlling the support units 15 a to 15 e. Thereafter, the control unit 11 causes the fixing entry guide 66 to perform an operation when there is an FD curl at the right end of the sheet P.

  As described above, the control unit 11 controls the operation of the support units 15a to 15e such that the fixing entry guide 66 moves in the direction to cancel the curling of the sheet. For example, when the sheet P curls upward when the sheet P enters the fixing nip N, the control unit 11 causes the fixing entry guide 66 to move downward as opposed to the curl of the sheet P. Can cancel out. Therefore, if the sheet P is curled to the image side of the first surface, the control unit 11 can cancel the curl by moving the fixing entry guide 66 to the image side of the second surface.

  In FIGS. 9 and 10, only the operation of lowering the fixing entry guide 66 by the control unit 11 is described, but as shown in FIG. 4, the left and right end portions of the sheet P are CD curled downward, or If the upstream end and the downstream end of P are FD-curled downward, the fixing entry guide 66 may be raised according to the amount of curl.

<Movement Example of Swinging Unit According to Curl Shape>
FIG. 11 is an explanatory view showing an example of movement of the swinging portion 142 according to the curled shape of the sheet P. As shown in FIG. FIG. 11 is a perspective view of the fixing approach guide 66 as viewed from the upper side. In FIG. 11, the swinging portion 142 is illustrated by hatching.

If the rocking support portion 141 (see FIG. 5) provided in the fixing entry guide 66 is different, the shapes of the rocking portions 142a and 142b are also different, and the actions exerted on the sheet P are also different.
The control unit 11 performs control to swing the swinging portions 142 provided on both downstream sides of the fixing entry guide 66 without changing the position of the upstream end of the fixing entry guide 66. Here, as shown in FIG. 5, since the swinging portions 142a and 142b swing with the swing support portions 141a and 141b as fulcrums, respectively, in the following description, the swing entrance portion 66 has the swing support portions 141a and 141b. The position where the 141 b is installed is indicated by a “broken line”. In the present embodiment, since the fixing entrance guide 66 is provided with the plurality of swing support portions 141a and 141b, there are also a plurality of broken lines. However, a plurality of broken lines are usually formed in pairs downstream and on both sides of the fixing entry guide 66.
As described above, the swinging portions 142 a and 142 b swing with a broken line that intersects the side end downstream of the upstream end of the fixing approach guide 66 and the downstream end of the fixing approach guide 66 as a fulcrum.

  For example, in FIG. 11A, one point on the side of the downstream end of the fixing entry guide 66 formed in a rectangular shape and one point on the side of the side end on the downstream side of the upstream end of the fixing entry guide 66 are connected. An example of swinging parts 142a and 142b swinging around a broken line is shown. 11A shows three types of broken lines 1a and 1b, broken lines 2a and 2b, and broken lines 3a and 3b formed in the fixing entry guide 66. As shown in FIG.

  FIG. 11B shows a swinging portion 142a swinging around the broken line 1a and a swinging portion 142b swinging around the broken line 1b. The broken lines 1 a and 1 b connect a point near the center of the downstream end of the fixing entry guide 66 and a point near the upstream of the side end of the fixing entry guide 66. Since the area of the swinging parts 142a and 142b which are swung with the broken lines 1a and 1b as the fulcrum is very large, it is possible to improve the approachability of the FD-curled paper P into the fixing nip N, in particular.

  FIG. 11C shows a swinging portion 142a swinging around the broken line 2a and a swinging portion 142b swinging around the broken line 2b. The broken lines 2a and 2b connect a point closer to both sides of the fixing approach guide 66 than the broken lines 1a and 1b and a point closer to the upstream side of the side end of the fixing approach guide 66. The area of the rocking portions 142a and 142b rocked around the broken lines 2a and 2b is smaller than the area of the rocking portions 142a and 142b shown in FIG. 11B. However, since the rocking portions 142a and 142b are rocked at positions close to both sides of the fixing entry guide 66, it is possible to improve the approachability of the sheet P, which has been subjected to CD curling, into the fixing nip N.

  FIG. 11D shows a swinging portion 142a swinging around the broken line 3a and a swinging portion 142b swinging around the broken line 3b. The broken lines 3 a and 3 b connect a point at the center of the downstream end of the fixing entrance guide 66 and a point near the center of the side end of the fixing entrance guide 66. The swinging portions 142a and 142b are swung in a wide range on the downstream side of the fixing entry guide 66 with the broken lines 3a and 3b as fulcrums. For this reason, as compared with the case of the broken lines 1a and 1b shown in FIG. 11B, the approachability of the FD-curled sheet P into the fixing nip N can be improved.

  Since the curled shape of the sheet P is various and the position of the optimal broken line differs depending on the curled shape, it is desirable to provide a plurality of broken lines in one fixing entry guide 66.

<Example of Shape of Fixing Entry Guide Having Plural Swingers>
An example of the shape of the fixing entry guide 66 provided with the recommended combination of broken lines is shown below.
FIG. 12 is an explanatory view showing an example of the shape of the fixing approach guide 66 having a plurality of broken lines. FIG. 12 is a top view of the fixing entrance guide 66. As shown in FIG. Also in FIG. 12, the portion swinging as the swinging portion 142 is shaded and illustrated.
In the fixing entry guide 66 in which a plurality of broken lines are formed, the control unit 11 causes the broken line 142 to swing the swinging part 142 in accordance with the curl amount and the curled shape of the sheet P, and the broken line not to swing the swinging part 142. And the rocking portion 142 is rocked with the polygonal line rocking the rocking portion 142 as a fulcrum.

In the fixing entry guide 66 shown in FIG. 12A, a broken line in which one point at the side end of the fixing entry guide 66 is common is formed. The broken lines 1 a and 2 a and the broken lines 1 b and 2 b share one point at the side end of the fixing entry guide 66.
As shown on the left side of FIG. 12A, in the case where the swinging portions 142a and 142b are swung with the broken lines 1a and 1b as supporting points, the approachability of the FD-curled sheet P into the fixing nip N can be improved.
As shown on the right side of FIG. 12A, in the case where the swinging portions 142a and 142b are swung with the broken lines 2a and 2b as the fulcrum, the approachability of the CD-curled paper P to the fixing nip N can be improved.

In the fixing entrance guide 66 shown in FIG. 12B, parallel broken lines 1a and 4a and parallel broken lines 1b and 4b are formed side by side. The broken lines 4a and 4b are formed closer to both sides of the fixing entry guide 66 than the broken lines 1a and 1b.
As shown on the left side of FIG. 12B, when swinging the swinging portions 142a and 142b with the broken lines 1a and 1b as the fulcrum, the approachability of the FD-curled sheet P to the fixing nip N can be improved.
Further, as shown in the right side of FIG. 12B, when swinging the swinging portions 142a and 142b with the broken lines 4a and 4b as supporting points, the approachability of the CD-curled sheet P to the fixing nip N can be improved.

In the fixing entry guide 66 shown in FIG. 12C, an example in which the broken lines 2a and 3a intersect and the broken lines 2b and 3b intersect is shown.
As shown on the left side of FIG. 12C, in the case where the swinging portions 142a and 142b are swung with the broken lines 3a and 3b as supporting points, the approachability of the FD-curled sheet P to the fixing nip N can be improved.
As shown on the right side of FIG. 12C, in the case where the swinging portions 142a and 142b are swung with the broken lines 2a and 2b as the fulcrum, the approachability of the CD-curled sheet P to the fixing nip N can be improved.

  As shown in FIG. 5C and FIG. 8, the fixing entry guide 66 is provided with a pair of bent lines, the upstream end of the fixing entry guide 66 is fixed by the support parts 15 c and 15 e, and the substantially central part of the downstream end is the support part 15 d After the fixing, the supporting portions 15a and 15b swing the swinging portions 142a and 142b independently. As a result, the upstream end of the fixing entry guide 66 does not move, and the swinging portion 142 moves with the polygonal line as a fulcrum.

  On the other hand, if there are a plurality of pairs of broken lines in the fixing entry guide 66, the rocking portions 142a and 142b can be rocked about any pair of broken lines. For example, FIG. 12A shows an example in which two types of broken lines of broken lines 1a and 1b and broken lines 2a and 2b are provided. Then, the broken lines 1a and 1b and the broken lines 2a and 2b are switched according to the curled shape of the sheet P, and the rocking portions 142a and 142b can be rocked.

  Here, the upstream end of the fixing entry guide 66 is fixed by the support portions 15 c and 15 e. Further, on the back side of the downstream end of the fixing entry guide 66, a support portion 15d-1 which swings the swinging portion 142a with the broken line 2a, a support portion 15d-2 which swings the swinging portion 142a with the broken line 1a, a swing A support 15d-3 for swinging the moving part 142b with the broken line 1b and a support 15d-4 for swinging the swinging part 142b with the broken line 2b are provided.

  For example, as shown on the left side of FIG. 12A, when the downstream end of the fixing entry guide 66 is swung with the broken lines 1a and 1b as the fulcrum, the broken lines 2a and 2b are fixed and the broken lines 1a and 1b can be swung. Do. At this time, the rocking portions 142a and 142b are rocked by moving the support portions 15d-1 to 15d-4 up and down, respectively.

  Further, as shown on the right side of FIG. 12A, when the downstream end of the fixing entry guide 66 is swung with the broken lines 2a and 2b as the fulcrum, the broken lines 1a and 1b are fixed and the broken lines 2a and 2b can be swung. Do. At this time, the rocking portions 142 a and 142 b are rocked by moving the support portions 15 d-1 to 15 d-4 up and down. Thereby, the swinging portions 142a and 142b suitable for the curled shape can be swung.

  Further, in FIGS. 12A to 12C, simultaneously, an operation of rotating the downstream end of the fixing entrance guide 66 may be simultaneously performed with the upstream end of the fixing entrance guide 66 as a fulcrum.

  The fixing entry guide 66 may be made of a thin metal plate or a flexible material such as a heat resistant resin material. Thus, the positions of the fixing entry guide 66 and the swing support portion 141 can be determined according to the curl amount and the curled shape of the sheet P. For example, when swinging the broken line with a hinge, it is desirable that the material of the fixing entry guide 66 be made of a material having a strength and thickness that does not bend.

  However, when a plurality of broken lines are formed in the fixing entry guide 66, the number of movable fulcrums may be limited due to the complexity of the configuration. For this reason, when the material of the fixing entrance guide 66 is a flexible material, the fixing entrance guide 66 is made of a thin sheet that can be bent using the elastic force of the flexible material itself, or a heat resistant resin. It is desirable to be created. Thus, when the fixing ingress guide 66 is made of a flexible material, it is possible to bend at any position without having to make a mechanical structure such as a hinge. As a result, it is not necessary to provide a switching mechanism that can freely swing when the broken line is fixed, and the degree of freedom in the position of the broken line is expanded. As a result, it is possible to improve the approachability to the fixing nip N with respect to the sheet P of more various curled shapes.

<Example of control of image forming apparatus>
FIG. 13 is a flowchart showing a control example of the image forming apparatus 4 when the detector 67 is installed on the upstream side of the fixing entry guide 66. In this process, since the detector 67 is installed at the upstream position of the fixing entry guide 66, the control unit 11 causes the sheet P to be curled and curled while entering the fixing nip N. At the same time, the fixing entry guide 66 can be deformed at any time. In the figure, the fixing entry guide 66 is abbreviated as a "guide".

  First, the control unit 11 determines whether the image formation on the sheet P is double-sided printing (S1), and if not double-sided printing (NO in S1), controls the fixing entry guide 66 to the normal position. (S7). After that, the control unit 11 determines whether the job has ended (S6). For example, the number of printed sheets is set in the job. Therefore, if the job has not ended (NO in S6), the process returns to step S1 and the process is repeated. When the job ends (YES in S6), this process ends.

  If the image formation is double-sided printing (YES in S1), the control unit 11 determines whether the second-side printing is performed to fix the toner image on the second side to the second side of the sheet P (S2) . If the control unit 11 determines that the second side printing is not performed (NO in S2), that is, the first side printing in which the toner image on the first side is fixed to the first side of the sheet P, the fixing entry guide 66 is selected. Control to the normal position (S7). Then, the toner image on the first side is fixed to the first side of the sheet P. Thereafter, the process of step S6 described above is performed. If it is a job for which duplex printing is set, the control unit 11 does not end the job (NO in S6), and returns to step S1 to repeat the process.

  When the image formation is double-sided printing (YES in S1) and the toner image on the first side is already fixed to the first side of the sheet P, the control unit 11 determines that the second side printing is performed (S2 YES), the detector 67 is activated (S3). Then, the control unit 11 detects the amount of curling of the sheet P by the detector 67 so that the amount of curling of the sheet P from the downstream end (front end) to the upstream end (rear end) of the sheet P is detected. It is started.

  The control unit 11 performs a curl determination process for determining the curled shape from the curl amount of the sheet P (S4). The curl determination process of step S4 will be described later with reference to FIG.

Next, based on the instruction data for moving the fixing approach guide 66 instructed by the control unit 11 in step 4, the supporting units 15a to 15e are moved, and the fixing approach guide 66 is moved (S5). Then, the toner image on the second side is fixed to the second side of the sheet P.
Thereafter, the process of step S6 described above is performed.

<Curl judgment processing example>
FIG. 14 is a flowchart showing an example of the curl determination process of step S4 of FIG.

  First, the control unit 11 determines whether the sheet P has an FD curl (S11). If there is an FD curl (YES in S11), the control unit 11 determines whether the curl shape of the FD curl is symmetrical (S12).

  If the FD curl is symmetrical (YES in S12), the control unit 11 instructs the parallel movement or rotation of the downstream end of the fixing approach guide 66 according to the curl amount (S14). If the FD curl is not symmetrical (NO at S12), the control unit 11 selects the swinging portions 142a and 142b to be swung (S13). If the broken line formed in the fixing entry guide 66 is a pair (see FIG. 5C), the control unit 11 obtains the moving amount of the swinging parts 142a and 142b with the broken line as a fulcrum. On the other hand, if there are a plurality of pairs of broken lines formed in the fixing entry guide 66 (see FIGS. 11 and 12), the control unit 11 selects a broken line as a fulcrum and then swings the selected broken line as a fulcrum The movement amounts of the units 142a and 142b are obtained. Then, the control unit 11 instructs to tilt the swinging portions 142a and 142b of the fixing entry guide 66 in accordance with the curl amount of the sheet P (S15).

  Next, when it is determined that there is no FD curl in the processing in any of steps S13 and S14 or in step S11 (NO in S11), the control unit 11 determines whether or not the sheet P has a CD curl. . If there is no CD curl (NO in S16), the process ends. If there is a CD curl (YES in S16), the control unit 11 selects the swinging portions 142a and 142b to be swung (S17). The polygonal lines selected by the control unit 11 in step S17 and the moving amounts of the swinging units 142a and 142b determined by the control unit 11 are determined in the same manner as the process shown in step S13. Then, the control unit 11 instructs the rocking portions 142a and 142b of the fixing entry guide 66 to perform an operation in accordance with the curl amount of the sheet P (S18), and ends the process.

  In the image forming apparatus 4 according to the embodiment described above, the downstream end portion of the sheet P is fixed by moving the fixing entry guide 66 even when the sheet P is curled with CD or FD. The approachability when entering into the nip N can be improved. For this reason, it is possible to prevent the occurrence of wrinkles, bleeding and the like on the sheet P which has passed through the fixing nip N.

  In addition to the rotation of the downstream end of the fixing entry guide 66, the swinging parts 142a and 142b are the side end of the fixing entry guide 66 on the downstream side of the upstream end and the downstream end of the fixing entry guide 66. Swing around multiple broken lines that intersect with. Further, in the rocking portions 142a and 142b, the rocking fulcrum switches between the plurality of intersecting polygonal lines. For this reason, even if CD paper or FD curl that is asymmetrical to the left and right is generated on the paper P, the approachability of the paper P to the fixing nip N can be improved by deforming the fixing approach guide 66 in accordance with the curled shape. it can.

[Modification]
In the embodiment described above, the approachability of the second surface to the fixing nip N can be improved by operating the fixing approach guide 66 before the second surface of the sheet P enters the fixing nip N. it can. In addition to this, after the second surface of the sheet P enters the fixing nip N, the fixing entry guide 66 may be further operated during sheet passing. In this case, by detecting the amount of curling at a plurality of locations in the conveyance direction of the sheet P by the detector 67, a time-series change in the amount of curling in the conveyance direction of the sheet P is detected.

  For example, the detector 67 detects three points, that is, the leading edge, the center, and the trailing edge of the sheet P. When the length of the sheet P such as long sheet is long, the number of detection points may be increased. Then, the control unit 11 controls the fixing entry guide 66 to move during sheet passing in accordance with the time-series change of the curl amount in the conveyance direction detected. By moving the fixing entry guide 66 while passing the sheet, not only the approachability of the leading end of the sheet to the fixing nip N is improved, but the approachability of the fixing nip N of the entire sheet is improved, thereby suppressing paper wrinkles and image defects. be able to.

  In the above-described embodiment, the fixing unit 60 is incorporated in the image forming apparatus 4. However, only the fixing unit 60 may be detachable from the image forming apparatus 4. In this case, the fixing unit 60 is used as a single fixing device. Then, if the control unit 11, the storage unit 12, the communication I / F 13 and the fixing entry guide 66 as shown in FIG. 3 are provided in this fixing device, the embodiment in which the fixing device is independently described. The processing in can be performed.

  In addition, although the fixing entry guide 66 is formed in a rectangular shape as a whole of the base portion 140 and the swinging parts 142a and 142b, the entire fixing entry guide 66 is formed in an elliptical or polygonal shape, or the swinging part 142a , 142b may be formed in an obliquely cut shape. In addition, the fixing entry guide 66 may be divided into a plurality of pieces along the conveyance direction of the sheet P. By moving the divided fixing entry guides 66 independently, it is possible to improve the entry of the sheet P.

  Further, FIG. 2 shows a configuration example in which the front guide 63 is provided on the upstream side of the fixing entry guide 66, but the front guide 63 may not be provided. In this case, the upstream end of the fixing entry guide 66 may move with the downstream end. For example, the entire fixing approach guide 66 may move up and down. In addition, after the entire fixing entry guide 66 is moved, the downstream end of the fixing entry guide 66 may be rotated while the upstream end of the fixing entry guide 66 is fixed.

Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various other applications and modifications can be taken without departing from the scope of the present invention described in the claims.
The above-described embodiment is a detailed and specific description of the configuration of the apparatus and system in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to one having all the configurations described. Moreover, it is possible to replace a part of the configuration of the embodiment described here with the configuration of another embodiment, and furthermore, to add the configuration of another embodiment to the configuration of one embodiment. It is possible. Moreover, it is also possible to add, delete, and replace other configurations for part of the configurations of the respective embodiments.
Further, control lines and information lines indicate what is considered to be necessary for the description, and not all control lines and information lines in the product are necessarily shown. In practice, almost all configurations may be considered to be mutually connected.

  4 image forming apparatus 11 control unit 60 fixing unit 61 upper pressure roller 62 lower pressure roller 64 heating roller 66 fixing entrance guide 68 fixing belt H heater H N: Fixing nip, P: Paper

Claims (9)

An image forming unit that forms an image on a sheet;
A fixing unit that fixes the image formed by the image forming unit on the sheet;
A base that supports the entry of the sheet into the fixing unit, and a base including the entire upstream end in the transport direction of the sheet and the vicinity of the center of the downstream end, and a swing amount on the downstream side relative to the base An approach supporting portion including a swinging portion that swings more than a swing amount;
A detection unit that detects the sheet on which the image is fixed on the first surface;
The curling shape of the sheet is obtained based on the curling amount of the sheet calculated from the detection result of the detection unit and the conveyance direction of the sheet, and the entrance support portion is obtained according to the curling amount of the sheet and the curling shape. An image forming apparatus comprising: a control unit that performs control to change a position and a shape and causes the sheet on which an image is formed on a second surface to enter the fixing unit; The swinging portion is swingable relative to the base with a broken line provided in the entry support portion as a fulcrum,
The image forming apparatus according to claim 1, wherein the polygonal line is formed from a side end to a downstream end of the entry support unit. A plurality of the polygonal lines are provided in the entry support unit,
The image forming apparatus according to claim 2, wherein the plurality of polygonal lines are formed side by side in the entry support unit, and are formed in pairs on both sides of the entry support unit. A plurality of the polygonal lines are provided in the entry support unit,
The image forming apparatus according to claim 2, wherein the plurality of broken lines are formed to intersect with the entry support unit and are formed in pairs on both sides of the entry support unit. The control unit performs control of rotating the base or control of moving the entire entry support unit in a state in which the position of the upstream end of the entry support unit is fixed. The image forming apparatus according to claim 1. The detection unit is disposed in a path until the sheet on which the image is fixed on the first surface by the fixing unit enters the fixing unit in order to fix the image on the second surface. The image forming apparatus according to any one of claims 1 to 5, wherein an end portion in the main scanning direction of the image forming apparatus is detected. The control unit calculates the curl amount of the sheet being conveyed based on the detection result, and the curl shape of the sheet passing through the detection range of the detection unit and the time-series change of the curl amount The image forming apparatus according to claim 6, wherein control is performed to move the entry support unit during conveyance of the sheet. The image forming apparatus according to any one of claims 1 to 7, wherein the entry support unit is formed of a flexible material. A fixing unit that fixes an image formed on a sheet of paper to the sheet;
A base that supports the entry of the sheet into the fixing unit, and a base including the entire upstream end in the transport direction of the sheet and the vicinity of the center of the downstream end, and a swing amount on the downstream side relative to the base An approach supporting portion including a swinging portion that swings more than a swing amount;
A detection unit that detects the sheet on which the image is fixed on the first surface;
The curling shape of the sheet is obtained based on the curling amount of the sheet calculated from the detection result of the detection unit and the conveyance direction of the sheet, and the entrance support portion is obtained according to the curling amount of the sheet and the curling shape. A control unit that performs control to change the position and the shape and causes the sheet on which an image is formed on the second surface to enter the fixing unit.

Images