JP2018017947A - Fixing device and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device and an imaging device which have good paper feed characteristics to a fixing nip part, and can suppress wrinkle of paper having superposition part.SOLUTION: A fixing nip part heating and fixing a toner image formed on paper, an upthrust part main body 191a provided upstream of a paper conveyance direction of the fixing nip part, and a control part operating the upthrust part main body to bend a section of the paper before passing the fixing nip part to a convex direction of the fixing nip part when the paper has a superposition part after the tip of the paper reaches at the fixing nip part are provided.SELECTED DRAWING: Figure 3

Description

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

  Conventionally, an electrostatic latent image formed on a photoreceptor is developed with toner to form a toner image, the formed toner image is transferred to a sheet, and the transferred toner image is heated in a fixing device. 2. Description of the Related Art An electrophotographic image forming apparatus that heats and fixes a nip portion formed by a pressure member and a pressure member to form an image on a sheet is known.

  In such an image forming apparatus, transportability suitable for various types of recording materials is required. However, in the case where an overlapping portion such as an envelope exists as a recording material, a fixing member and a pressure member are particularly used during transport. When the sheet passes through the curved nip formed by the above, a difference in transport distance occurs between the upper sheet and the lower sheet, and wrinkles and misalignment occur.

  In order to cope with such a problem, a technique for changing the nip load using an urging means such as a spring is known (for example, see Patent Document 1). When passing through the envelope, the width of the nip portion curved in the paper conveyance direction, that is, the so-called nip width is reduced by reducing the nip load. As a result, the difference in the transport distance between the upper paper and the lower paper is suppressed, and the wrinkles and displacement of the envelope are suppressed. However, when the nip load is reduced and the nip width is reduced, the problem is that the fixability becomes insufficient.

  In addition, a technique for exchanging with a dedicated fixing device at the time of envelope printing is also known (see, for example, Patent Document 2). Because the fuser is optimized for fixing envelopes, high-quality images can be obtained without causing poor fixing, but the user must replace the fuser each time. It was to increase.

  Therefore, a technique for suppressing envelope wrinkles by giving the envelope passing through the nip portion a displacement opposite to the displacement generated at the nip portion is disclosed (for example, see Patent Document 3). That is, for example, in the case of an upward convex nip shape in which the nip portion is convex in the direction of the upper roller, the lower paper has a shorter transport distance than the upper paper, and thus wrinkles are generated. The wrinkles generated on the lower sheet are stretched by bending the sheet upward.

JP 2012-13914 A JP 2008-58365 A Japanese Patent Laid-Open No. 7-140819

  However, there is a problem that an angle suitable for smooth paper feeding to the fixing nip portion is contrary to a paper feeding angle for extending the envelope wrinkles. That is, it is desirable to smoothly feed the fixing nip along the convex direction. For example, when the fixing nip is convex toward the upper roller, it is suitable to feed from the lower direction. Therefore, coexistence with suppression of envelope wrinkles has been difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus that have good sheet-passing properties to a fixing nip portion and can suppress wrinkles of a sheet having an overlapping portion.

In order to achieve the above object, a fixing device according to claim 1 is provided.
A fixing nip for heating and fixing the toner image formed on the paper;
A sheet bending means installed upstream of the fixing nip in the sheet conveying direction;
When the paper is a paper having an overlapping portion, the portion of the paper before passing through the fixing nip is bent in the convex direction of the fixing nip after the leading edge of the paper reaches the fixing nip. Control means for operating the paper bending means;
It is characterized by providing.

According to a second aspect of the present invention, in the fixing device according to the first aspect,
The control means can change the amount of bending of the paper.

According to a third aspect of the present invention, in the fixing device according to the second aspect,
The control means is characterized in that the amount of paper bending can be changed according to the type of paper.

According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects,
The paper bending means has a contact portion with the paper,
The contact portion has a curved surface in which a contacted sheet bends in a direction opposite to a curved surface of the sheet in the fixing nip portion.

According to a fifth aspect of the present invention, in the fixing device according to any one of the first to fourth aspects,
The paper bending means has a function of adsorbing paper.

According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects,
The fixing nip portion is formed by press-contacting a fixing roller that heat-fixes a toner image on a sheet and a pressure roller that press-contacts the fixing roller,
The fixing nip portion has a convex shape on the fixing roller side,
The paper bending means bends the paper by acting from the non-fixing surface side of the paper.

Further, an image forming apparatus according to claim 7 is provided.
An image forming part having a transfer nip part for forming a toner image on paper;
A fixing device according to any one of claims 1 to 6, wherein the sheet on which the toner image is formed is heated and pressed to fix the toner image on the sheet.
The paper bending means is disposed downstream of the transfer nip portion in the paper conveyance direction,
The control means operates the paper bending means after the rear end of the paper has passed through the transfer nip portion.

An image forming apparatus according to claim 8 is provided.
An image forming part having a transfer nip part for forming a toner image on paper;
A fixing device according to any one of claims 1 to 6, wherein the sheet on which the toner image is formed is heated and pressed to fix the toner image on the sheet.
The paper bending means is disposed downstream of the transfer nip portion in the paper conveyance direction,
The paper conveyance speed in the transfer nip portion is faster than the paper conveyance speed in the fixing nip portion,
The control means operates the paper bending means after the leading edge of the paper reaches the fixing nip portion and before the trailing edge of the paper passes the transfer nip portion, and controls the transfer nip portion and the fixing nip portion. The amount of sheet bending by the sheet bending means is increased in accordance with the amount of sheet slack that increases with the paper.

  According to the present invention, it is possible to suppress the wrinkling of a sheet having an overlapping portion while having good sheet passing properties to the fixing nip portion.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment to which the present invention is applied. 2 is a block diagram illustrating a main functional configuration of the image forming apparatus. FIG. FIG. 3 is a schematic diagram illustrating a configuration of an image fixing unit according to the first embodiment. 3 is a flowchart illustrating an operation of the image forming apparatus according to the first embodiment. It is explanatory drawing which shows an example of the bending amount of a paper. FIG. 3 is a schematic diagram illustrating a configuration of an image fixing unit according to the first embodiment. FIG. 3 is a schematic diagram illustrating a configuration of an image fixing unit according to the first embodiment. It is a schematic diagram which shows the structure of the image fixing part which concerns on 2nd Embodiment. 10 is a flowchart illustrating an operation of the image forming apparatus according to the second embodiment.

[First Embodiment]
Hereinafter, an embodiment of the image forming apparatus of the present invention will be described with reference to the drawings. In the embodiment of the present invention, a color image forming apparatus will be described as an example. However, the present invention is not limited to this, and can be applied to, for example, a monochrome image forming apparatus.

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a main functional configuration of the image forming apparatus 1.

  The image forming apparatus 1 includes a control unit 10 having a CPU 101 (Central Processing Unit), a RAM 102 (Random Access Memory), and a ROM 103 (Read Only Memory), a storage unit 11, an operation unit 12, a display unit 13, an interface 14, a scanner 15, An image processing unit 16, an image forming unit 17, an image fixing unit 18, a sheet bending control unit 19, a conveyance unit 20, and the like are provided. The control unit 10 includes a storage unit 11, an operation unit 12, a display unit 13, an interface 14, a scanner 15, an image processing unit 16, an image forming unit 17, an image fixing unit 18, a sheet bending control unit 19, and a transport via a bus 21. Connected to the unit 20.

  The CPU 101 reads out and executes a control program stored in the ROM 103 or the storage unit 11 and performs various arithmetic processes.

  The RAM 102 provides a working memory space to the CPU 101 and stores temporary data.

  The ROM 103 stores various control programs executed by the CPU 101, setting data, and the like. Instead of the ROM 103, a rewritable nonvolatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

  The control unit 10 including the CPU 101, the RAM 102, and the ROM 103 performs overall control of each unit of the image forming apparatus 1 according to the various control programs described above. For example, the control unit 10 causes the image processing unit 16 to perform predetermined image processing on the image data and store the image data in the storage unit 11. In addition, the control unit 10 causes the conveyance unit 20 to convey the sheet, and causes the image forming unit 17 to form an image on the sheet based on the image data stored in the storage unit 11.

  The storage unit 11 includes storage means such as a DRAM (Dynamic Random Access Memory) or HDD (Hard Disk Drive), which is a semiconductor memory, and is input from the outside through image data acquired by the scanner 15 or the interface 14. Stored image data and the like. These image data and the like may be stored in the RAM 102.

  The operation unit 12 includes an input device such as an operation key or a touch panel arranged on the screen of the display unit 13. The operation unit 12 converts an input operation on these input devices into an operation signal and outputs the operation signal to the control unit 10.

  The display unit 13 includes a display device such as an LCD (Liquid crystal display), and displays an operation screen and the like indicating the state of the image forming apparatus 1 and the content of an input operation to the touch panel.

  The interface 14 is a unit that transmits and receives data to and from an external computer, another image forming apparatus, and the like, and includes, for example, any of various serial interfaces.

  The scanner 15 reads an image formed on a sheet, generates image data including single-color image data for each of R (red), G (green), and B (blue) color components, and stores the image data in the storage unit 11.

  The image processing unit 16 includes, for example, a rasterization processing unit, a color conversion unit, a gradation correction unit, and a halftone processing unit. The image processing unit 16 performs various types of image processing on the image data stored in the storage unit 11 and stores the image data in the storage unit 11. .

  The image forming unit 17 forms an image on a sheet based on the image data stored in the storage unit 11. The image forming unit 17 includes four exposure units 171, a photosensitive drum 172, and a developing unit 173 that respectively correspond to C (cyan), M (magenta), Y (yellow), and K (black) color components. Yes. Further, the image forming unit 17 includes a transfer body 174 and a secondary transfer roller 175.

The exposure unit 171 includes an LD (Laser Diode) as a light emitting element. The exposure unit 171 drives the LD based on the image data, irradiates and exposes a laser beam on the photosensitive drum 172 to be charged, and forms an electrostatic latent image on the photosensitive drum 172. The developing unit 173 supplies toner (color material) of a predetermined color (any one of C, M, Y, and K) by a developing roller that is charged on the exposed photosensitive drum 172, The electrostatic latent image formed on the surface is developed.
Images (single color images) formed with C, M, Y, and K toners on the four photosensitive drums 172 corresponding to C, M, Y, and K respectively are transferred from the photosensitive drums 172 to the transfer member 174. Sequentially superimposed and transferred. As a result, a color image having C, M, Y, and K as color components is formed on the transfer body 174. The transfer body 174 is an endless belt wound around a plurality of transfer body transport rollers, and rotates according to the rotation of each transfer body transport roller.
The secondary transfer roller 175 transfers the color image on the transfer body 174 onto a sheet fed from the sheet feeding tray 22 or a sheet feeding device provided outside. Specifically, the sheet and the transfer body 174 are sandwiched at a transfer nip portion formed by press-contacting a pair of secondary transfer rollers 175, and a predetermined transfer voltage is applied to the secondary transfer roller 175, thereby transferring the transfer body 174. The toner forming the color image is attracted to the sheet side and transferred to the sheet.

  The image fixing unit 18 performs a fixing process for fixing the toner onto the paper by heating and pressurizing the paper on which the toner has been transferred.

  FIG. 3 is a schematic diagram showing the configuration of the image fixing unit 18. The image fixing unit 18 includes a fixing roller 181, a heating roller 182, a fixing belt 183, a pressure roller 184, and a paper feed guide 185. The image fixing unit 18 and the control unit 10 constitute a fixing device.

The fixing belt 183 is stretched between a fixing roller 181 and a heating roller 182, and the fixing roller 181 and the pressure roller 184 are fixing nip portions as pressure contact portions that sandwich and convey the sheet via the fixing belt 183. Configure.
The fixing belt 183 has a configuration in which, for example, an elastic layer made of silicone rubber and a surface release layer made of fluorine-based resin are sequentially laminated on the outer peripheral surface of a film base made of heat-resistant polyimide. The fluororesin contains or preferably consists mainly of either PFA (perfluoroalkoxyalkane), PTFE (polytetrafluoroethylene), or FEP (tetrafluoroethylene / hexafluoropropylene copolymer). Is done. As a result, the surface releasability of the fixing belt 183 with respect to the wax contained in the toner resin or toner particles is also improved, and toner adhesion to the fixing belt 183 during fixing can be prevented.

The heating roller 182 has a configuration in which a resin layer made of PFTE or the like is formed on the outer peripheral surface of a core metal synthesized from aluminum or the like. A halogen lamp heater 182a extending in the direction of the rotation axis is provided inside the cored bar. The halogen lamp heater 182a generates heat when energized under the control of the control unit 10, and heats the fixing belt 183 via the cored bar and the resin layer.
Note that the fixing belt 183 may be heated by electromagnetic induction heating (IH: Induction Heating) without using the heating roller 182. In this case, the base of the fixing belt 183 is made of a material that can generate electromagnetic induction heat, such as Ni.

The fixing roller 181 is driven to rotate by a rotation driving unit such as a motor (not shown) under the control of the control unit 10. Note that not the fixing roller 181 but the heating roller 182 interlocked by the tension of the fixing belt 183 may be driven and rotated by a rotation driving means such as a motor (not shown) under the control of the control unit 10.
The fixing roller 181 has a configuration in which an elastic layer made of silicone rubber or the like is formed on the outer peripheral surface of a columnar core made of iron or the like. Furthermore, it is also possible to form a surface release layer made of a fluorine-based resin as described above on the outer peripheral surface of the elastic layer.

As shown in FIG. 3, the pressure roller 184 is urged in a direction approaching the fixing roller 181 by an elastic member (not shown), and is pressed against the fixing roller 181 via the fixing belt 183. The fixing roller 181 rotates with the rotation of the fixing roller 181 while forming a fixing nip portion therebetween. The pressure roller 184 may be driven and rotated by a rotation driving unit such as a motor (not shown) under the control of the control unit 10.
The configuration of the pressure roller 184 is the same as the configuration of the fixing roller 181, but a heating source such as a halogen heater may be incorporated therein.

In the present embodiment, for example, the thicknesses of the elastic layers of the fixing roller 181 and the pressure roller 184 are 10 mm and 2 mm, respectively. In this case, since the fixing roller 181 having a thick elastic layer is more easily deformed, the fixing nip portion is convex toward the fixing roller 181 side. Hereinafter, such a nip shape is referred to as an upward convex nip shape.
Since the convex direction of the fixing nip portion differs depending on the thickness and hardness of the elastic layer, it may be convex toward the pressure roller 184 side. Hereinafter, such a nip shape is referred to as a downward convex nip shape.

The fixing roller 181 and the pressure roller 184 sandwich the sheet at the fixing nip portion, heat and press the sheet while conveying it in a predetermined conveying direction, and melt and fix the toner on the sheet. The halogen lamp heater 182a heats the heating roller 182 via the heating roller 182 so that the temperature of the fixing belt 183 is, for example, in the range of 180 ° C. or higher and 200 ° C. or lower.
A paper feed guide 185 is provided upstream of the fixing nip portion in the paper conveyance direction. As shown in FIG. 3, the paper feed guide 185 feeds paper from the tangential direction of the fixing nip portion of the pressure roller 184. That is, by feeding paper along the curved surface of the fixing nip portion, smooth paper feeding is possible.

The sheet bending control unit 19 controls the push-up unit 191 so that the trailing end of the sheet whose leading end reaches the fixing nip portion is bent.
The push-up unit 191 includes a push-up unit main body 191a that comes into contact with the paper, and a push-up drive unit 191b that moves the push-up unit main body 191a up and down using a driving force such as a motor. . As shown in FIG. 3, the push-up portion main body 191a is disposed on the upstream side of the fixing nip portion and on the downstream side of the transfer nip portion and in the vicinity of the fixing nip portion. Push the paper up from the fixing side. The push-up unit main body 191a is a member formed along the axial direction of the fixing roller 181 and the pressure roller 184, and has a contact surface with a sheet in the axial direction of the roller.

  As shown in FIG. 1, the transport unit 20 includes a plurality of paper transport rollers that transport paper by rotating while sandwiching the paper, and transports the paper through a predetermined transport path. The transport unit 20 includes a reversing mechanism 201 that reverses the front and back of the paper on which the fixing process has been performed by the image fixing unit 18 and transports the paper to the secondary transfer roller 175. In the image forming apparatus 1, when images are formed on both sides of the paper, the reversing mechanism 201 reverses the front and back of the paper to form images on both sides, and then the paper is discharged to the paper discharge tray 23. When an image is formed only on one side of the paper, the paper on which the image is formed on one side is discharged to the paper discharge tray 23 without reversing the front and back of the paper by the reversing mechanism 201.

Next, the operation of the image forming apparatus 1 according to the first embodiment will be described based on the flowchart of FIG.
As shown in FIG. 4, the control unit 10 determines whether or not there is a print instruction (step S401). If it is determined that there is no print instruction (step S401: No), the process of step S401 is repeated, but the print instruction is not received. When it is determined that there has been (step S401: Yes), the process proceeds to step S402.
Here, the image forming apparatus 1 according to the present embodiment has a first mode corresponding to printing of a single sheet such as copy paper and a second mode corresponding to printing of two sheets having an overlapping portion such as an envelope. Mode.
In step S402, the control unit 10 determines whether or not it is a two-sheet printing instruction. When it is determined that the instruction is for printing two sheets, that is, when it is determined that the second mode is selected (step S402: Yes), the process proceeds to step S403, but it is determined that the instruction is not for printing two sheets. If it is determined that the current mode is the first mode (step S402: No), the process proceeds to step S415.

  In step S403, the paper bending control unit 19 functions as a control unit and sets the amount of paper bending. The ease of occurrence of wrinkles varies depending on the type of paper, particularly the width, length, and thickness of the paper, so that the amount of paper bending can be adjusted by providing a plurality of stages.

Here, a method for setting the bending amount of the sheet will be described with reference to FIG.
FIG. 5 shows an example of the amount of bending according to the type of paper. Here, the rising height of the push-up portion main body 191a is divided into three stages, and the bending amount by the push-up portion main body 191a is provided from 1 to 3 in order from the smallest increase amount. For example, in the case of the bending amount 3 with the largest raising amount of the push-up portion main body 191a, as shown in FIG. 3, the same distance as the width α of the fixing nip portion is set from the fixing nip portion entrance to the upstream side in the transport direction. It is pushed up under the condition that the average curvature in the advanced range is equal to or greater than the average curvature in the fixing nip.
It is desirable to push up the paper with the minimum bend amount that can suppress envelope wrinkles. Envelope wrinkles are more likely to occur as the paper width increases and the paper length increases. Basically, to increase For example, in the case of a Western-style No. 6 envelope with a paper size of 98 mm × 190 mm, the bending amount is 1, the long size No. 3 with a paper size of 120 mm × 235 mm is bent 2, and the square No. 2 with a paper size of 240 mm × 332 mm is bent. When each is pushed up by the amount 3, envelope wrinkles are suppressed.
The bending amount may be set by the user on the operation panel, or the sheet bending control unit 19 may automatically set the bending amount based on the control table according to the type of the sheet. .

  When the sheet bending amount is set, the controller 10 starts heating and rotating the fixing belt 183 (step S404) and starts conveying the sheet (step S405).

Next, the sheet bending control unit 19 functions as a control unit and determines whether or not the leading end of the sheet has reached the fixing nip (step S406). When it is determined that it has not reached the fixing nip (step S406: No), the process of step S406 is repeated, but when it is determined that it has reached (step S406: Yes), the process proceeds to step S407.
In step S407, the sheet bending control unit 19 functions as a control unit, and determines whether the trailing edge of the sheet has passed through the transfer nip portion. When it is determined that it has not passed through the transfer nip (step S407: No), the process of step S407 is repeated, but when it is determined that it has passed (step S407: Yes), the push-up drive unit 191b is operated, The push-up unit main body 191a is pushed up (step S408).

  Next, the sheet bending control unit 19 functions as a control unit, and determines whether the bending amount has reached the set bending amount (step S409). When it is determined that the set bending amount has not been reached (step S409: No), the process of step S409 is repeated, but when it is determined that the set bending amount has been reached (step S409: Yes), the push-up drive unit 191b. Is stopped (step S410), and the process proceeds to step S411.

  In step S411, the sheet bending control unit 19 functions as a control unit, determines whether the trailing edge of the sheet has reached the fixing nip (step S411), and determines that it has not reached (step S411: No). ), The process of step S411 is repeated, but if it is determined that it has been reached (step S411: Yes), the push-up drive unit 191b is driven to return the push-up unit body 191a to the initial position (step S412).

Next, the control unit 10 determines whether or not the sheet passing through the fixing nip portion is the last page (step S413). If it is determined that the sheet is the last page (step S413: Yes), the fixing belt 183 is heated and rotated. Is stopped (step S414), and printing is terminated.
If it is determined that the page is not the last page (step S413: No), the process returns to step S406.

  In step S402, when it is determined that there is no instruction to print two sheets (step S402: No), the control unit 10 starts heating and rotating the fixing belt 183 (step S415) and starts conveying the sheet (step S415). S416).

  Next, the control unit 10 determines whether or not the sheet passing through the fixing nip is the last page (step S417). If it is determined that the sheet is not the last page (step S417: No), the process of step S417 is repeated. If it is determined that the current page is the last page (step S417: Yes), the process proceeds to step S414.

As described above, the image forming apparatus 1 according to the first embodiment feeds paper from the tangential direction of the fixing roller 181, the heating roller 182, the fixing belt 183, the pressure roller 184, and the nip portion. The sheet feeding guide 185 disposed on the sheet, a push-up section 191 that pushes up the sheet upstream of the fixing nip, and a sheet bending that activates the push-up section when printing two sheets having an overlapping section such as an envelope. And a control unit 19.
Therefore, according to the image forming apparatus 1 according to the first embodiment, when the two sheets are passed, the sheet passing through the fixing nip portion is preliminarily given a displacement opposite to the displacement of the upper and lower sheets generated in the fixing nip portion. Envelope wrinkles can be suppressed.
Further, paper is fed from the tangential direction of the pressure roller 184 excellent in paper feeding until the leading edge of the sheet passes through the fixing nip portion, and the sheet is bent by the push-up portion 191 after the leading edge of the sheet passes through the fixing nip portion. For this reason, it is possible to suppress envelope wrinkles while ensuring the paper passing property of the fixing nip portion.

  In the image forming apparatus 1 according to the first embodiment, the rear end of the sheet passes through the transfer nip portion, and the push-up portion 191 is operated after the transfer is completed. As a result, there is no possibility of causing side effects such as transfer displacement caused by applying force to the paper being transferred.

  In the image forming apparatus 1 according to the first embodiment, the push-up unit 191 is installed very close to the fixing nip unit. Accordingly, the sheet can be bent until the last end of the sheet reaches the fixing nip portion, and envelope wrinkles can be more effectively suppressed.

  In the image forming apparatus 1 according to the first embodiment, the push-up unit 191 acts on the lower paper that is the non-fixing surface side. When the push-up unit 191 touches the toner before fixing, the toner is disturbed and noise may be generated in the image. In this embodiment, since the sheet can be bent without touching unfixed toner, the above problems can be prevented.

Further, in the image forming apparatus 1 according to the first embodiment, a plurality of levels of paper bending are provided and can be changed according to the type of paper. If the paper before fixing is pushed up more than necessary, fine wrinkles will occur at the edge of the envelope, or the upper and lower sheets of paper upstream of the nip will be too large, causing wrinkles. May disturb the toner before fixing. In this embodiment, by making the amount of bending variable according to the type of paper, it is possible to perform with the minimum amount of bending that can suppress envelope wrinkles, and the above-described problems can be prevented.
Further, the bending amount can be determined by the user or automatically. Therefore, it is possible to use the function according to the situation, for example, the user himself / herself sets it strictly when he / she wants to make an adjustment according to the user's preference, or automatically sets the user's trouble.

  In the image forming apparatus 1 according to the first embodiment, the push-up unit 191 operates only when printing an envelope, and does not operate when printing a normal sheet such as copy paper, that is, in the first mode. . As a result, good sheet-passability is maintained when printing one sheet, and there is no possibility that side effects such as disturbance of unfixed toner due to the operation of the push-up unit 191 occur.

The sheet bending means is not particularly limited as long as it is a member that can bend the sheet passing through the fixing nip portion without affecting the image upstream of the fixing nip portion.
In the above embodiment, the push-up portion 191 that protrudes from the upper surface of the paper feed guide 185 is used as the paper bending means. However, as shown in FIGS. A push-up unit 191 that rotates about a part as a fulcrum may be used. In this case, it is possible to function as the push-up unit 191 by adding an operation to the existing paper feed guide 185 without newly installing a paper bending unit, so that the configuration is simpler and more economical.

  The push-up unit main body 191a is not limited to a single member, and is composed of a plurality of members arranged in the axial direction of the fixing member, and protrudes from other members of the image forming unit and gaps between the units. It is good also as what to do. Accordingly, the push-up unit 191 can be operated without affecting the configuration of the image forming unit in which many members, units, and the like are densely packed.

In the above embodiment, the contact surface of the push-up unit main body 191a with the sheet is a flat surface as shown in FIG. 3, but the present invention is not limited to this, and a curved surface as shown in FIG. .
In this case, the contact surface is curved in a direction opposite to the curved surface of the fixing nip portion. That is, when the fixing nip portion has an upward convex nip shape as in the present embodiment, the curved surface is recessed toward the pressure roller 184 side. As a result, it is possible to increase the displacement opposite to the displacement of the upper and lower sheets generated at the nip portion, more effectively suppress wrinkles, and cope with severe envelope wrinkles.

Further, the sheet bending means may be a member that adsorbs the lower sheet by air suction or the like. Accordingly, it is possible to prevent the sheet from being violated at the moment when the sheet is pushed up, and to prevent the unfixed toner from being disturbed.
Further, by combining this with the push-up unit 191 having the curved surface, the paper can easily follow the curved surface of the push-up unit 191, and the paper can be curved more effectively.

In the above embodiment, the case where the fixing nip portion has an upward convex nip shape has been described. However, in the case of a downward convex nip shape that protrudes toward the pressure roller 184 side, as shown in FIG. The guide 185 is arranged so that paper is fed from the fixing roller 181 side, so that an angle suitable for paper feeding is obtained.
At this time, it is necessary to bend the rear end of the paper toward the pressure roller 184 in order to suppress wrinkling of the paper having the overlapping portion. Accordingly, when the fixing nip portion has a downward convex nip shape, as shown in FIG. 7, the suction unit 192 is used to control the sheet to be pulled down toward the pressure roller 184 side. The suction unit 192 includes a suction unit main body 192a that comes into contact with the paper, and a drive unit 192b that moves the suction unit main body 192a up and down using a driving force such as a motor.
As shown in FIG. 7, the suction portion main body 192a is disposed on the upstream side of the fixing nip portion and on the downstream side of the transfer nip portion and in the vicinity of the fixing nip portion. Pull down while adsorbing paper from the front side. The suction unit main body 192a is a member formed along the axial direction of the fixing roller 181 and the pressure roller 184, and has a contact surface with a sheet in the axial direction of the roller.

[Second Embodiment]
Next, the image forming apparatus 1 according to the second embodiment will be described.
Compared with the image forming apparatus 1 according to the first embodiment, the image forming apparatus 1 according to the second embodiment, as shown in FIG. 8, looses paper due to a difference in the sheet conveyance speed between the transfer nip portion and the fixing nip portion. Is different in that the sheet bending means acts before the trailing edge of the sheet passes through the transfer nip portion.
For simplification of description, the same reference numerals are given to the same configurations as those in the first embodiment, and detailed description thereof is omitted.

Next, the operation of the image forming apparatus 1 according to the second embodiment will be described based on the flowchart of FIG.
The processes in steps S901 to S903 and steps S905 to S907 are the same as the processes in steps S401 to S403 and steps S404 to S406 in the first embodiment, respectively, and thus description thereof is omitted.
In step S904, the paper bending control unit 19 sets the paper conveyance speed of the transfer nip portion to be higher than the paper conveyance speed of the fixing nip portion.

  When it is determined in step S907 that the leading edge of the sheet has reached the fixing nip (step S907: Yes), the sheet bending control unit 19 functions as a control unit and activates the push-up unit 191 (step S908). Henceforth, since the process of step S909-step S914 is the same as the process of step S409-step S414 in 1st Embodiment, description is abbreviate | omitted. Also, the processing of step S915 to step S917 is the same as that of step S415 to step S417 in the first embodiment, and thus description thereof is omitted.

As described above, in the image forming apparatus 1 according to the second embodiment, the paper conveyance speed of the transfer nip portion is made faster than the paper conveyance speed of the fixing nip portion, and between the transfer nip portion and the fixing nip portion. The slack amount of the paper being conveyed is gradually increased. As shown in FIG. 8B, when the leading edge of the paper reaches the fixing nip portion, the pushing-up by the pushing-up portion main body 191a is started, and the bending amount is gradually increased according to the increasing amount of slackness of the paper, The push-up portion main body 191a is raised until the bending amount suitable for the paper is reached, and as shown in FIG. 8D, the rear end passes through the fixing nip portion even after the rear end of the paper passes through the transfer nip portion. It acts on the paper until it does.
Note that the stop position of the push-up unit main body 191a at this time is a position set according to the type of paper, as in the first embodiment.
Therefore, according to the image forming apparatus 1 according to the second embodiment, the pushing-up unit 191 starts pushing up the paper at an early stage, so that the pushing-up speed can be slowed down. As a result, there is no possibility that the unfixed toner is disturbed by the force that is suddenly pushed up and the image is damaged.

In addition, according to the image forming apparatus 1 according to the second embodiment, since the sheet starts to be pushed up regardless of whether or not the trailing edge of the sheet has passed the transfer nip portion, the nip portion is attached to the envelope at an earlier stage. And give the opposite displacement.
That is, it is possible to suppress envelope wrinkles not only from the rear end side of the paper but also from the front end side, for example, more severe envelope wrinkles that generate long wrinkles from the middle of the envelope to the rear end, It can also handle envelope wrinkles of envelopes that are short in the paper transport direction.

If the transfer nip and the fixing nip are far apart from the length of the paper in the conveyance direction, the trailing edge of the paper has passed through the transfer nip when the leading edge of the paper reaches the fixing nip. Therefore, the first embodiment can provide the same effects as those of the second embodiment.
On the other hand, the second embodiment is effective when the transfer nip portion and the fixing nip portion are arranged close to each other and the distance between the two nip portions is smaller than the length in the sheet conveyance direction.

In addition, if the difference in sheet conveyance speed between the transfer nip portion and the fixing nip portion is small, the amount of slackness of the sheet being conveyed is too small, so that a sufficient effect cannot be obtained. The sheet conveyance speed difference between the transfer nip portion and the fixing nip portion is preferably 1.2 times or more.
Further, the difference in paper conveyance speed may be variable according to the type of paper. For example, when the difference in the conveyance speed is increased as the length of the paper is shorter in the paper conveyance direction or the bending amount at the completion of the push-up is increased, the amount of slackness of the paper becomes more noticeable, and the paper is more effectively removed. Bend.

  In the present exemplary embodiment, the case where the push-up unit 191 having a flat contact surface with the sheet is used as the sheet bending unit. However, the present invention is not limited to this. For example, as in the first embodiment, a push-up unit 191 having a curved contact surface, a push-up unit 191 configured to rotate one end of the paper feed guide 185, or the like may be used.

[Other Embodiments]
As mentioned above, although concretely demonstrated based on embodiment which concerns on this invention, said embodiment is a suitable example of this invention, and is not limited to this.

For example, in the above embodiment, the image forming apparatus 1 in which the fixing roller 181 and the pressure roller 184 are arranged vertically and the paper is conveyed in the horizontal direction has been described. However, the fixing roller 181 and the pressure roller 184 are arranged on the left and right. Similarly, the sheet bending means can be applied to the image forming apparatus 1 in which the sheet is conveyed in the vertical direction.
In this case, the paper bending means acts in the horizontal direction, but the configuration of the paper bending means is suitable for the fixing roller 181 side or the pressure roller 184 side according to the convex direction of the fixing nip portion as in the above embodiment. It shall act from the direction.

  In the above embodiment, the fixing device using the biaxially stretched fixing belt 183 has been described. However, the present invention is not limited to this. For example, the present invention can be applied to a heat roller type fixing device that does not use the fixing belt 183 and a fixing device that uses a fixed pad instead of the pressure roller 184.

  In addition, the detailed configuration of each apparatus constituting the image forming apparatus and the detailed operation of each apparatus can be appropriately changed without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 11 Storage part 12 Operation part 13 Display part 14 Interface 15 Scanner 16 Image processing part 17 Image forming part 175 Secondary transfer roller 18 Image fixing part 181 Fixing roller 182 Heating roller 182a Halogen lamp heater 183 Fixing belt 184 Pressure roller 185 Paper feed guide 19 Paper bending control section (control means)
191a Push-up body (paper bending means)
192a Suction unit body (paper bending means)
20 Transport unit 22 Paper feed tray 23 Paper discharge tray S Recording material

Claims (8)

A fixing nip for heating and fixing the toner image formed on the paper;
A sheet bending means installed upstream of the fixing nip in the sheet conveying direction;
When the paper is a paper having an overlapping portion, the portion of the paper before passing through the fixing nip is bent in the convex direction of the fixing nip after the leading edge of the paper reaches the fixing nip. Control means for operating the paper bending means;
A fixing device comprising:   The fixing device according to claim 1, wherein the control unit is capable of changing a bending amount of the sheet.   The fixing device according to claim 2, wherein the control unit is capable of changing a bending amount of the sheet according to a type of the sheet. The paper bending means has a contact portion with the paper,
4. The fixing device according to claim 1, wherein the contact portion has a curved surface in which a contacted sheet bends in a direction opposite to a curved surface of the sheet in the fixing nip portion.   The fixing device according to claim 1, wherein the paper bending unit has a function of adsorbing paper. The fixing nip portion is formed by press-contacting a fixing roller that heat-fixes a toner image on a sheet and a pressure roller that press-contacts the fixing roller,
The fixing nip portion has a convex shape on the fixing roller side,
The fixing device according to claim 1, wherein the sheet bending unit bends the sheet by acting from a non-fixing surface side of the sheet. An image forming part having a transfer nip part for forming a toner image on paper;
A fixing device according to any one of claims 1 to 6, wherein the sheet on which the toner image is formed is heated and pressed to fix the toner image on the sheet.
The paper bending means is disposed downstream of the transfer nip portion in the paper conveyance direction,
The image forming apparatus according to claim 1, wherein the control unit operates the sheet bending unit after a rear end of the sheet passes through the transfer nip portion. An image forming part having a transfer nip part for forming a toner image on paper;
A fixing device according to any one of claims 1 to 6, wherein the sheet on which the toner image is formed is heated and pressed to fix the toner image on the sheet.
The paper bending means is disposed downstream of the transfer nip portion in the paper conveyance direction,
The paper conveyance speed in the transfer nip portion is faster than the paper conveyance speed in the fixing nip portion,
The control means operates the paper bending means after the leading edge of the paper reaches the fixing nip portion and before the trailing edge of the paper passes the transfer nip portion, and controls the transfer nip portion and the fixing nip portion. An image forming apparatus characterized in that the amount of bending of the sheet by the sheet bending means is increased in accordance with the amount of looseness of the sheet that increases with the unit.

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