JP2006251432A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow even thin paper to be satisfactorily fixed and separated without using a separating claw in an image forming apparatus using a belt fixing device. <P>SOLUTION: A first pressing member 971 capable of being pressed to a supporting pressure roller 92 through a fixing belt 91 is provided downstream a nip part N of the rotating supporting pressure roller 92, and a second pressing member capable of being pressed to an external pressure roller 93 is provided downstream a nip part N of the rotating external pressure roller 93, and a paper thickness detection means for detecting the paper thickness of a transfer material or an operation display part allowing paper thickness information of the transfer material to be inputted is provided. When detecting that the transfer material is thin paper, a control part puts the first pressing member 971 into a pressing state when fixing an image on the thin paper having unfixed toner on a first surface and puts the second pressing member 981 into a pressing state when fixing an image on the thin paper having unfixed toner on a second surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly to an image forming apparatus using a belt fixing device.

  In an electrophotographic image forming apparatus, a toner image formed on an image carrier is transferred onto a transfer material (hereinafter also referred to as transfer paper or recording paper) by a transfer means, and the transfer material holding the toner image is fixed. While passing through the nip formed by the heating means and pressurizing means of the apparatus, fixing is performed by heating and pressurizing, and the transfer material is discharged outside the apparatus.

  The heating means (for example, the fixing roller) on which the toner image adheres to the transfer material passes through the nip portion, and the transfer material is easily wrapped around. A separation claw is provided to prevent this, and the tip of the separation claw contacts the heating means. It is done to contact. If the transfer material is thick paper with strong stiffness, it will be separated from the heating means such as the fixing roller with curvature even if there is no separation claw, but if it is thin paper with weak stiffness, it will be heated after passing through the nip. It progresses in a state of being wound around the means and is separated by the separation claw. In order for the thin transfer paper to be separated by the separation claw, the separation claw tip needs to be in pressure contact with the heating unit so that the thin paper does not enter between the separation claw tip and the heating unit. is there.

  The heating means and separation claw that are in pressure contact are worn together, and the fixed image has uneven glossiness of the stripes or defective separation, resulting in poor fixing performance, replacement of the heating means and separation claw, etc. Will be needed.

Patent Document 1 discloses a technique for separating transfer paper by bringing an external heating roller into contact with a fixing roller instead of a separation claw and elastically deforming a contact portion of the fixing roller.
Japanese Patent Laid-Open No. 2003-5551

  In an image forming apparatus, color images and high-speed processing are required, and in order to satisfy these requirements, it is required to widen the width of the nip portion and to increase the passage time of the nip portion of the transfer paper. Although studies have been made to use a fixing roller as an elastic body and to increase the roller diameter of the fixing roller, all have limitations and belt fixing devices are often used.

  The present invention relates to an image forming apparatus using a belt fixing device, which can perform good separation without using a separation claw even when fixing a single-sided and double-sided image on a thin paper transfer material having poor separation conditions. The purpose is to provide.

In order to solve the above problems and achieve the object, the present invention is configured as follows.
(Claim 1)
A support heating roller having a heating means, a support pressure roller disposed in parallel with and spaced from the support heat roller, and the support heating roller and the support pressure roller are wound endlessly and rotated. A fixing device comprising: a fixing belt; and an external pressure roller that presses against the supporting pressure roller through the fixing belt to form a nip portion;
In the image forming apparatus in which the transfer material holding the toner image is fixed in the process of passing through the nip portion,
On the downstream side of the nip portion of the supporting pressure roller that rotates, a first pressing member that can press the supporting pressure roller via the fixing belt;
On the downstream side of the nip portion of the rotating external pressure roller, a second pressing member that enables the external pressure roller to be pressed is provided.
A paper thickness detecting means for detecting the paper thickness of the transfer material, or an operation display unit capable of inputting paper thickness information of the transfer material;
When the control unit detects that the transfer material is thin paper, when fixing the thin paper holding the unfixed toner on the first side, the first pressing member is pressed to fix the thin paper holding the unfixed toner on the second side. In this case, the image forming apparatus is characterized in that the second pressing member is in a pressed state.
(Claim 2)
2. The image forming apparatus according to claim 1, wherein each of the first and second pressing members is a ceramic or metal round bar that is rotatable and has an outer diameter of 3 to 10 mm.
(Claim 3)
3. The image forming apparatus according to claim 1, wherein both the first and second pressing members are pressed with a pressing force of 30 N to 150 N during pressing.
(Claim 4)
4. The control unit according to claim 1, wherein the control unit holds the first and second pressing members at positions apart from each other except when the transfer material is detected as thin paper. 5. Image forming apparatus.
(Claim 5)
The image forming apparatus according to claim 1, wherein the thin paper is a transfer material having a wrinkle amount of 80 g / m ² or less.

  According to the first aspect of the present invention, the first and second pressing members that enable contact and separation are provided, and the first surface and the second surface that use a thin paper transfer material are respectively pressed when fixing. By setting the state, separation at the time of fixing thin paper with good one side or both sides is performed.

  According to the second aspect of the present invention, excellent separation performance can be obtained by using a small-diameter round bar as the first and second pressing members.

  According to the third aspect of the invention, by setting the pressing force of the first and second pressing members within a predetermined range, good fixing and separation can be performed without deteriorating the fixing performance. .

  According to the invention described in claim 4, good separation performance can be obtained over a long period of time by avoiding unnecessary operation when fixing a transfer material that can be separated satisfactorily without providing separation means. Will be maintained.

  According to the fifth aspect of the invention, by clarifying the amount range of the transfer material that easily causes separation failure, all separation failures at the time of fixing are eliminated.

  (1) An embodiment of the present invention will be described. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

  An image forming apparatus equipped with a belt fixing device according to the present invention will be described below with reference to FIG.

  In FIG. 1, the image forming apparatus GS includes an image forming apparatus main body GH and an image reading apparatus YS.

  The image forming apparatus main body GH is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 6, a sheet feeding and conveying unit, and a fixing unit to be described later. Device 17.

  An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus main body GH. The document d placed on the document table of the automatic document feeder 201 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202, and the line image sensor CCD is scanned. Is read. At this time, the document D conveyed from the document table is subjected to glossiness level detection sensor PKa used as a gloss level selection unit to determine the glossiness of the document image, monochrome and color of the document image, and double-sided image discrimination. Done.

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in the image processing unit, and once stored in the memory, the image writing unit (exposure means) ) Send signals to 3Y, 3M, 3C, 3K.

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 8Y disposed around a photosensitive drum 1Y as an image carrier. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 8M. The image forming unit 10C that forms a cyan (C) image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 8C. The image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 8K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  4Y, 4M, 4C, and 4K are developing devices that include a two-component developer composed of a toner having a small particle diameter and a carrier of yellow (Y), magenta (M), cyan (C), and black (K). .

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred (primary transfer) by the transfer means 7Y, 7M, 7C, and 7K onto the rotating intermediate transfer body 6 and synthesized. A color image is formed. The recording paper P as a transfer material accommodated in the paper feed cassette 20 is fed by the paper feed means 21 and is conveyed to the transfer means 7A via the paper feed rollers 22A, 22B, 22C, the registration rollers 23, etc. A color image is transferred onto the recording paper P (secondary transfer). The recording paper P onto which the color image has been transferred is sandwiched by a pressure nip portion N (see FIG. 2; not shown in FIG. 1) formed in the fixing device 9, and heat and pressure are applied. As a result, the color toner image (or toner image) on the recording paper P is fixed and fixed on the recording paper P, and is sandwiched between the discharge rollers 24 on the discharge path side and placed on the discharge tray 25 outside the apparatus. Is done.

  At the time of double-sided image formation, a color image (color toner image) is formed on one side (front surface), and the recording paper P discharged from the fixing device 9 is branched from the sheet discharge path by the branching unit 26 and is fed respectively. Through the lower circulating paper path 27A constituting the conveying means, the front and back are reversed by the reverse conveying path 27B which is a refeeding mechanism (ADU mechanism), and passes through the refeeding conveying section 27C to be fed by the feed roller. Merge at 22D. The recording paper P that has been reversely conveyed (circulated and reversed) is conveyed again to the secondary transfer roller 7A via the timing roller 23, and a color image (color toner image) is formed on the other side (back surface) of the recording paper P. Batch transfer. The recording paper P to which the color image has been transferred is fixed by the fixing device 9 and is sandwiched between the paper discharge rollers 24 on the paper discharge path side and placed on a paper discharge tray 25 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the transfer means 7A, the residual toner is removed by the cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  (2) A belt fixing device used in the image forming apparatus of the present invention will be described below with reference to FIG.

  The fixing device 9 includes a fixing belt 91 in which a metal substrate or a heat-resistant resin substrate and silicon rubber are molded into a belt shape, and supports and conveys the fixing belt 91 with the transfer material and the fixing belt 91 sandwiched therebetween. It comprises a roller 92, an external pressure roller 93 opposed thereto, and a support heating roller 94 incorporating a heater 94a that supports and conveys the fixing belt 91. Further, in order to maintain the surface temperature of the external pressure roller 93 at a temperature suitable for fixing, an external heating roller 95 that contacts the outer periphery of the external pressure roller 93 may be provided. In the belt fixing device 9 configured as described above, the pressure nip portion N is formed by the support pressure roller 92 and the external pressure roller 93.

  The supporting pressure roller 92 includes a rotating shaft 921 using a cylindrical metal pipe or a metal shaft having a thickness of 2 to 5 mm, and an outer surface of the rotating shaft 921 fixed with an elastic layer 922 of 10 mm thick Si sponge. A soft roller having a diameter of 45 mm. The hardness of the soft roller having the Si sponge elastic layer 922 fixed to the rotating shaft 921 according to the Asker C display is Asker C30 ° in this embodiment. The Asker C display conforms to JIS K7312 and JIS 6050, and is a display used for measuring the hardness of soft rubber or sponge.

  The external pressure roller 93 has a rotating shaft 931 using a cylindrical metal pipe having a thickness of 2 to 5 mm, and a 3 mm thick Si rubber elastic layer 932 fixed to the outer peripheral surface of the rotating shaft 931, and further to the outside. And a soft roller having an outer diameter of 50 mm covered with a PFA (perfluoroalkoxy) tube 933 as a release layer. In this embodiment, the hardness of the soft roller having the Si rubber elastic layer 932 fixed to the rotating shaft 931 is 65 ° in Asker C.

  The elastic layer 922 of the support pressure roller 92 uses a softer material than the elastic layer 932 of the external pressure roller 93, and the elastic layer is thicker. 92 is mainly deformed to maintain the pressure contact state. In the embodiment, a nip portion of 16 mm is formed by applying a load of 900 N.

  The fixing belt 91 wound around the supporting pressure roller 92 is an endless belt having a diameter of 80 mm having a 200 μm Si rubber layer and a 30 μm PFA (perfluoroalkoxy) tube layer outside a 70 μm thick polyimide substrate. The fixing belt 91 is heat-transferred and heated through a heating roller by a heater 94a built in a support heating roller 94 that is also wound around.

  The support heating roller 94 is a roller having an outer diameter of 50 mm in which a fluororesin layer is provided on the outer periphery of an aluminum core having a thickness of 2 mm, and a fixing belt is provided at the end of the roller so that the fixing belt extends in the axial direction. The position is regulated so as not to slip.

  (3) In the image forming apparatus of the present embodiment, the first pressing member that can press the support pressure roller 92 via the fixing belt 91 on the downstream side of the nip portion N of the support pressure roller 92 to be transferred. 971 is provided. A second pressing member 981 that can press the external pressure roller 93 is provided on the downstream side of the nip portion N of the rotating external pressure roller 93.

  Each of the first and second pressing members 971 and 981 is a small-diameter round bar that can rotate, and is preferably a ceramic round bar or a metal round bar such as SUS. For example, a round bar with PFA coating is used. Both the first and second pressing members 971 and 981 have a small diameter, which is advantageous for improving the separation performance, and is used in a round bar having a diameter of 3 to 10 mm. When the outer diameter is less than 3 mm, the round bar is deformed in the axial direction at the time of pressing, and the contact state with the fixing belt 91 or the external pressure roller 93 becomes unbalanced and the separation performance is lowered. When the outer diameter is 10 mm or more, when the leading edge of the transfer material P to be conveyed comes into contact with the pressing members 971, 981, the pressing members 971, 981 get over the separation without being separated, and a jam occurs. Since it becomes easy to generate | occur | produce, it is not preferable.

  Further, it is desirable that the pressing force of the pressing members 971 and 981 to the fixing belt 91 or the external pressure roller 93 is between 30N and 150N. When the pressing force is less than 30 N, the amount of deformation due to the pressing of the fixing belt 91 or the external pressure roller 93 is insufficient, and the separation performance deteriorates. Further, when the pressing force exceeds 150 N, it acts as a resistance to the rotation operation of the fixing belt 91 or the external pressure roller 93, thereby hindering the fixing performance.

  FIG. 3 is an explanatory view showing a state in which the first pressing member 971 presses the supporting pressure roller 92 via the fixing belt 91, and is transferred in a cross-sectional state that rises conversely before and after the pressing portion. It shows that the front end of the material P is separated from the fixing belt 91 having a large curvature (small curvature radius) before reaching the first pressing member 971.

  The operation mechanism of the first and second pressing members 971 and 981 that make contact with the fixing belt 91 or the external pressure roller 93 will be described. Since both have the same configuration, the second pressing member 981 will be described with reference to FIG. Both end portions of the shaft core 981 a of the second pressing member 981 are rotatably supported by end portions of the lever 982, and the lever 982 can swing around the central shaft 983. One end of a tension spring 984 having the other end fixed is attached to the lever 982 and acts to pull the second pressing member 981 in the direction of the external pressure roller 93 (right direction in the drawing).

  Reference numeral 985 denotes an operating means using a cam. In the cam posture shown by a solid line, the lever 982 is operated to push up against the spring tension in the left direction with the central axis 983 as the center, and the second pressing member 981 is in a state of being separated from the external pressure roller 93. In the cam posture in which the cam 985 indicated by the dotted line is retracted, the second pressing member 981 is in contact with the external pressure roller 93. The pressing force of the second pressing member 981 against the external pressure roller 93 is determined by the tension of the tension spring 984, and a spring having an appropriate tension so as to obtain an optimal pressing force between 30N and 150N in advance. Select and use.

  The cam posture of the cam 975 for the first pressing member 971 and the cam posture of the cam 985 for the second pressing member 981 are controlled by a control unit described below.

(4) FIG. 5 shows an outline of the electric control system. Reference numeral 110 denotes a CPU that performs arithmetic control processing, and is connected to a RAM 111, a ROM 112, and a nonvolatile memory 113. The ROM 112 stores basic calculation data, one-sided and double-sided image forming programs, and an operation program in the fixing device 9 at the time of thin paper fixing, and the nonvolatile memory 113 has a standard corresponding to 80 g / m ² as a thin paper discrimination standard. Paper thickness data and the like are stored, and the CPU 110 is connected to an external device via the interface 120.

  On the input side of the interface 120, a paper thickness detection unit 112 and the like are connected to the input port. The paper thickness detection unit 122 is provided in the transfer material conveyance path, and directly measures the paper thickness of the transfer material passing between the hard rollers, or passes the transfer material passing between the light emitting element and the light receiving element. The light quantity is measured, and the paper thickness is estimated using a conversion formula between the transmitted light quantity and the paper thickness.

  On the output side of the interface 120, an image forming means driving unit 121 including a charging control driving unit, a laser emission driving unit, a developing bias driving unit, a transfer bias driving unit, a fixing device driving unit, and the like is connected to an output port. Yes.

  The output side of the interface 120 is connected to the fixing device 9 by a first pressing member actuating means 975 that acts to press the first pressing member 971 against the fixing belt 91, and the second pressing member. A second pressing member actuating means 985 that acts to press 981 against the external pressure roller 93 is connected.

  The image forming apparatus shown in FIG. 1 is provided with an operation / display unit 14, and in addition to a start button 141 for instructing the start of a printing operation, a single-sided double-sided selection button for selecting either single-sided printing or double-sided printing. 142, in addition to a numeric keypad for instructing the number of prints of recording paper, an image density selection button for image density is provided.

  In the present invention, a special paper selection button 143 is provided in the operation / display unit 14 in place of the paper thickness detecting means 122 provided in the recording paper conveyance path, and a thin paper or a thick paper is selected as the print paper instead of the plain paper. It is also made to. For example, when thin paper is loaded in the uppermost sheet cassette 20 and the thin sheet is selected with the special paper selection button 143, image recording is performed on the thin sheet by feeding from the uppermost sheet cassette 20. It will be.

  (5) Image formation will be described.

  When an image is formed using plain paper, when the user selects single-sided printing or double-sided printing with the single-sided / double-sided selection button 142 of the operation / display unit 14, sets the number of prints, etc., and presses the start button 141, the CPU 110 reads the ROM 112. The image forming program recorded in the above is called and the image forming means driving unit 121 is controlled to form an image using plain paper.

  When single-sided printing is selected, the toner image is transferred to the first side of the plain paper by the transfer means 7A, and the plain paper holding the toner image is fixed to the first side by the fixing device 9, and then outside the machine. Discharged. When double-sided printing is selected, the transfer unit 7A transfers the first side toner image onto the first side of the plain paper, and the fixing device 9 fixes the plain paper holding the toner image on the first side. After that, the plain paper passes through the circulation paper passage path 27A, the reverse conveyance path 27B, and the refeed conveyance path 27C, and is conveyed with the front and back reversed, and the second surface of the plain paper is transferred to the second surface by the transfer means 7A. The toner image is transferred, and the fixing device 9 fixes the plain paper holding the toner image on the second side, and then is discharged outside the apparatus.

  The present invention prevents the occurrence of a separation failure or the like in the fixing device 9 when forming an image using thin paper. When the user selects the thin paper with the special paper selection button 143 on the operation / display unit 14 or the CPU 110. However, when the paper thickness of the recording paper being transported detected by the paper thickness detection means 122 is compared with the reference paper thickness data recorded in the nonvolatile memory 113, the CPU 110 determines that the image is recorded in the ROM 112. A thin paper fixing operation program is called together with the forming program, and the image forming means driving unit 121 is controlled to form an image using thin paper.

  The difference from the image formation using plain paper is that when the CPU 110 fixes the thin paper holding the toner image on the first surface, the first operation is performed when the thin paper passes through the nip portion N by operating the operation means 975. When the pressing member 971 is pressed against the fixing belt 91 and the thin paper holding the toner image on the second surface is fixed, the operating means 985 is operated and the second paper is passed when the thin paper passes the nip portion N. The pressing member 981 is pressed against the external pressure roller 93.

  By performing such control, a good fixed image can be obtained without performing poor separation even during single-sided printing using thin paper or double-sided printing, and the fixing device can be used for a long time without replacement or repair. A good fixing mechanism is maintained over the entire period.

  In the present invention, when fixing the thin paper with the toner image maintained on the second surface, the image formed on the first surface adheres to the external pressure roller 93 and causes separation failure. Although control is performed to press 981 against the external pressure roller 93, the pressing of the first pressing member 971 against the fixing belt 91 is simultaneously performed with the pressing of the second pressing member 981 against the external pressure roller 93. Control may be performed.

1 is a schematic sectional view of an image forming apparatus. FIG. 3 is a cross-sectional view illustrating a configuration of a fixing device. Explanatory drawing which shows the press state of a press member. Explanatory drawing which shows the action | operation of a pressing member. The block diagram which shows the outline | summary of an electric control system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Fixing device 10 Image forming part 14 Operation / display part 91 Fixing belt 92 Supporting pressure roller 93 External pressure roller 100 Control part 110 CPU
DESCRIPTION OF SYMBOLS 120 Interface 122 Paper thickness detection means 971 1st press member 975 Actuating means, cam (1st press member)
981 Second pressing member 985 Actuating means, cam (second pressing member)
N Nip part

Claims (5)

A support heating roller having a heating means, a support pressure roller disposed in parallel with and spaced from the support heat roller, and the support heating roller and the support pressure roller are wound endlessly and rotated. A fixing device comprising: a fixing belt; and an external pressure roller that presses against the supporting pressure roller via the fixing belt to form a nip portion;
In the image forming apparatus in which the transfer material holding the toner image is fixed in the process of passing through the nip portion,
A first pressing member that is capable of pressing the supporting pressure roller via the fixing belt on the downstream side of the nip portion of the rotating supporting pressure roller;
On the downstream side of the nip portion of the rotating external pressure roller, a second pressing member that enables the external pressure roller to be pressed is provided,
A paper thickness detecting means for detecting the paper thickness of the transfer material, or an operation display unit capable of inputting paper thickness information of the transfer material;
When the control unit detects that the transfer material is thin paper, when fixing the thin paper holding the unfixed toner on the first side, the first pressing member is pressed to fix the thin paper holding the unfixed toner on the second side. In this case, the image forming apparatus is characterized in that the second pressing member is in a pressed state. 2. The image forming apparatus according to claim 1, wherein the first and second pressing members are both ceramic or metal round bars that are rotatable and have an outer diameter of 3 to 10 mm. 3. The image forming apparatus according to claim 1, wherein both of the first and second pressing members are pressed with a pressing force of 30 N to 150 N when pressed. 4. The control unit according to claim 1, wherein the control unit holds the first and second pressing members at positions apart from each other except when the transfer material is detected as thin paper. 5. Image forming apparatus. The image forming apparatus according to claim 1, wherein the thin paper is a transfer material having a wrinkle amount of 80 g / m ² or less.

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