JP2006189690A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt fixing device having a belt, which is designed such that a transfer material is steadily separated without being wrapped in the fixing belt at the exit of the fixing device. <P>SOLUTION: The fixing device includes a tension alteration means for altering the tension of the fixing belt. Before the leading end of a transfer material is passed through a nip, its tension is reduced. After the trailing end of the transfer material is passed through the nip, the tension is increased. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a printer or a copying machine.

  As a fixing device conventionally used in electrophotographic image forming apparatuses such as printers and copying machines, a heating roller containing a heating element and a pressure roller are rotated in a pressure contact state, and a toner image is held therebetween. There is a roller fixing system in which fixing is performed by passing a transfer material (recording paper). In the roller fixing method, the transfer material is pressed and heated while passing through the nip portion while the transfer material is in pressure contact with the heating roller. However, since the nip portion can only be set narrow, the transfer material (recording paper) In a color image forming apparatus that holds a large amount of toner and requires an elastic layer for image quality, it is difficult to increase the speed while achieving both fixing properties and durability. Further, in the monochrome image forming apparatus, since an elastic layer is not necessarily required in the nip portion, although restrictions on fixing property and durability are loose, it is an obstacle to aiming for higher speed.

  Therefore, a belt fixing method has been adopted in which heat is accumulated on a belt having a small heat capacity and fixing is performed, so that the warm-up time is fast and fixing is possible at a low temperature with a wide nip width. A belt fixing type fixing device (hereinafter referred to as a belt fixing device) uses an endless belt member (hereinafter referred to as a fixing belt) as a fixing member, and supports and stretches the fixing belt by a plurality of roller members. A fixing roller inside the belt, a pressure roller facing the fixing roller via the fixing belt, and a heating roller having a heating element for heating the fixing belt inside are provided.

  However, the belt fixing device has a disadvantage that the fixing roller with an elastic layer on the outer periphery is deformed near the exit of the transfer material due to the pressure contact of the pressure roller, and the transfer paper separation claw method often used in the roller fixing device cannot be adopted. There is.

  As means for separating the transfer material of the belt fixing device from the fixing belt, the hardness of the elastic body of the pressure roller is set to be 20 to 30 degrees larger than the hardness of the elastic body of the heating roller by a JIS-A hardness meter. Thus, Patent Document 1 discloses a method of increasing the separation angle of the transfer material from the heating roller and separating it.

  In addition, a fixing member is provided at a position corresponding to the exit separation portion of the nip formed by the fixing roller and the pressure roller via the fixing belt, and the exit separation portion surface has a shape with a large curvature inside the fixing belt. Patent Document 2 that improves the separation performance of a transfer material is known.

  In addition, a separation member for separating the transfer material from the fixing belt is disposed in non-contact with the belt, a driving roller is disposed on the downstream side of the nip portion in the transfer material conveyance direction, and the peripheral speed of the driving roller is set to the peripheral speed of the fixing belt. Patent Document 3 is known in which the belt is prevented from lifting by increasing the speed.

As another method of the separating means, Patent Document 4 has a vibrating member and a vibrating motor made of a wire provided on the outer peripheral surface of the fixing belt in the vicinity of the outlet of the nip portion. There has been proposed a method of cutting the threading of the fixing molten toner at the outlet.
JP 2000-338811 A Japanese Patent Laid-Open No. 2003-5565 JP 2004-93582 A JP 2002-268422 A

  However, problems remain in any of the prior arts. According to Patent Document 1, it is difficult to surely separate due to the effect of the nip shape under a condition where the toner adhesion amount is large. In particular, in a printer with a high printing speed, a wide nip is necessary to fix the toner. In order to secure the nip, a large-diameter fixing roller is required. However, when the fixing roller has a large diameter, it becomes difficult to separate the transfer material, and it is difficult to separate the transfer material from the fixing roller without a separation means such as a separation claw.

  Further, in Patent Document 2, a fixing member having a large curvature is provided in the vicinity of the outlet separation portion. However, when the fixing belt passes through the fixing member having a large curvature, extreme elastic deformation occurs, resulting in a problem in durability.

  Further, in Patent Document 3, if the nip shape is convex toward the fixing roller, the deformation of the fixing roller at the nip is large, so that a gap is formed between the fixing belt and the fixing roller before and after the nip, and belt floating occurs. A problem occurs. In order to solve this problem, Patent Document 3 discloses that a driving roller is newly provided on the outer side of the belt and the peripheral speed of the driving roller is higher than the peripheral speed of the fixing belt. In this case, molten toner or paper dust of the transfer material adheres, and some of the toner passes through the drive roller and is transferred onto the next transfer material, resulting in a new problem of poor image quality.

  Patent Document 4 describes a method in which threading of the fixing molten toner is cut by a vibrating member made of a wire provided on the outer peripheral surface of the fixing belt near the exit of the nip portion and a vibration motor. In some cases, it is difficult to achieve both separability and securing of fixing quality.

  An object of the present invention is to provide a fixing device capable of reliably separating a transfer material from a fixing belt over a long period of time without causing image quality defects.

  The above object can be achieved by the following configuration.

(Claim 1)
A fixing roller; a heating roller having a heat source; a fixing roller; a fixing belt stretched around the heating roller; and a pressure roller that presses the fixing roller through an outer peripheral surface of the fixing belt; In a fixing device that performs fixing through a transfer material carrying an unfixed toner image in a nip formed by a roller and the pressure roller,
A fixing device comprising tension force changing means for changing the tension force of the fixing belt.

(Claim 2)
Detecting means for detecting the leading edge or the trailing edge of the transfer material;
Control means for controlling the tension force changing means so that the tension force of the fixing belt is reduced before the leading edge of the transfer material passes through the nip portion based on the result detected by the detection means; The fixing device according to claim 1, further comprising: a fixing device;

(Claim 3)
Detecting means for detecting the leading edge or the trailing edge of the transfer material;
Control means for controlling the tension force changing means so that the tension force of the fixing belt is increased after the rear end of the transfer material has passed through the nip portion based on the result detected by the detection means. The fixing device according to claim 1, wherein

  According to the first aspect of the present invention, the tension force changing means for changing the tension force of the fixing belt is provided, whereby the tension force can be arbitrarily adjusted, and the image quality is not deteriorated over a long period of time. Thus, the transfer material can be reliably separated from the fixing belt.

  According to the second aspect of the present invention, it is possible to prevent the transfer material from being wound around the belt of the belt fixing device by loosening the tension before the transfer material front end passes through the nip portion.

  According to the third aspect of the present invention, even if the belt of the belt fixing device is rotating by increasing the tension after the rear end of the transfer material passes through the nip portion, it is possible to prevent the belt from shifting or meandering.

  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 including the 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 301 and a document image scanning exposure device 302 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 301 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 302, 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 contain a two-component developer composed of a toner and a carrier having a small particle diameter for 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 to which the color image has been transferred is sandwiched by the fixing device 17, and the color toner image (or toner image) on the recording paper P is fixed by applying heat and pressure to the recording paper P. The sheet is fixed on the upper side, is sandwiched between the sheet discharge rollers 24 on the sheet discharge path side, and is placed on the sheet discharge tray 25 outside the apparatus.

  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 17 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 onto which the color image has been transferred is fixed by the fixing device 17 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.

  Next, the fixing device according to the present invention will be described below.

  The main object of the present invention is to ensure that the transfer material is separated from the fixing belt. Here, the reason why the transfer material is wound around the belt in the belt fixing device will be described.

In general, separation occurs when the bending moment due to the rigidity of the paper (transfer paper) is greater than the moment due to the adhesive force between the toner and the roller surface at the nip exit separation portion (no wrapping occurs).
The bending moment of the paper is expressed by the curvature of the nip exit (1 / r) × the strength of the paper.
r: radius of curvature of the nip exit portion, that is, the greater the curvature (1 / r) of the nip exit portion, the stronger the paper, and the weaker the adhesive force between the toner and the roller surface, the better the separation performance. The adhesion between the toner and the roller surface varies greatly between the toner image and the solid image when the toner image is a line image. Regardless of which means is used, it is difficult to find a stable design condition with respect to separability. Therefore, increasing the curvature is often adopted as a means for improving the separation performance.

  The fixing device according to the present invention will be described in detail with reference to FIGS. In addition, the same code | symbol is attached | subjected to the structure same as FIG. 1, and the description is abbreviate | omitted.

  FIG. 2 shows a fixing belt 27 made of an endless belt member, a fixing roller 17 a that supports and stretches the fixing belt 27 on one of the inner peripheral surfaces of the fixing belt 27, and a fixing belt on the other inner peripheral surface of the fixing belt 27. 27, a fixing nip portion Nb is formed between a heating roller 17c having a heater 27 and a heating heater 173c therein, and a pressure roller 17b that contacts and presses the fixing roller 17a via the fixing belt 27, and The toner image on the recording paper P is fixed and fixed by heating and pressing upstream of the fixing nip portion Nb.

  Further, the pressure applied by the pressure roller that presses the fixing roller is desirably 800 N to 1200 N in consideration of gloss after transfer and curling of the transfer material. At this time, the rotation shaft on the fixing roller side is fixed (does not move up and down), and a pressure release mechanism (not shown) is provided on the pressure roller side.

  Here, the fixing belt 27 uses a nickel electroformed belt having an inner diameter of about 80 to 150 mm and a thickness of about 20 to 80 μm as a base, or a heat resistant resin belt such as polyimide having a thickness of about 50 to 200 μm as a base. The outer surface (outer peripheral surface) of the substrate is coated with silicon rubber having a thickness of about 100 to 500 μm, and PFA (perfluoroalkoxy) or fluorine resin having a thickness of about 30 to 50 μm is applied to the surface as a release layer. Alternatively, the PFA tube is covered. The silicon rubber layer is preferable as a condition for obtaining good fixability and thermal responsiveness in a rubber hardness range of 20 to 40 degrees (JIS-A hardness meter).

  The fixing roller 17a includes a cylindrical metal pipe 171a having a thickness of about 2 to 5 mm using a steel material such as STKM (carbon steel pipe for mechanical structure), and a thickness of 5 to 15 mm on the outer peripheral surface of the metal pipe 171a. A silicon sponge layer 172a having a hardness of 25 to 35 degrees (Asker-C hardness meter) is provided, and is configured as a soft roller having an outer diameter of about 20 to 50 mm.

  The pressure roller 17b is made of, for example, a cylindrical metal pipe 171b having a thickness of about 2 to 5 mm using a steel material such as STKM (carbon steel pipe for mechanical structure) or an aluminum material, and a thick outer peripheral surface of the metal pipe 171b. A silicon rubber layer 172b having a thickness of 1 to 3 mm is provided, and a release layer 173b using a PFA (perfluoroalkoxy) tube having a thickness of about 20 to 50 μm outside the silicon rubber layer 172b. It is configured as a soft roller of about 80 mm, and has a pressure roller heater 174b made of a halogen heater inside. The silicon rubber layer has a rubber hardness of 5 to 15 degrees (JIS-A hardness meter), and is provided with a pressure roller temperature sensor 175b that is in contact with or not in contact with the pressure roller 17b, so that the temperature of the pressure roller 17b can be controlled. It is possible.

  The heating roller 17c includes a cylindrical metal pipe 171c having a thickness of about 1 to 2 mm using, for example, an aluminum material as a base, and a PFA (perfluoroalkoxy) having a thickness of about 10 to 30 μm on the outer peripheral surface of the metal pipe 171c. It is configured as a roller member having an outer diameter of about 40 to 80 mm formed with a coating 172c, and has a heating roller heater 173c made of a halogen heater inside. Further, a heating roller temperature sensor 174c is provided so as to be in contact with or not in contact with the heating roller 17c, and the temperature of the heating roller 17c can be controlled.

  In addition, the fixing roller 17a in the present embodiment does not include a heating element, but a halogen heater or the like that is a heating element may be provided in order to further reduce the warm-up time and suppress the temperature decrease during standby. Is possible. However, since the silicon rubber layer 172a is provided on the outer peripheral surface of the metal pipe 171a, when the heating roller is provided inside the fixing roller 17a, the temperature inside the fixing roller 17a is higher than the temperature on the surface of the fixing roller 17a. Therefore, it is necessary to take measures such as increasing the heat resistance of the silicon rubber layer and reducing the thickness of the silicon rubber layer. In this embodiment, the thickness of the silicon rubber layer 172a is set to be as thin as 1 to 3 mm. However, when the thickness is increased to increase the nip width or the like, the silicon rubber layer It is necessary to improve heat resistance.

  The pre-fixing passage detection sensor 177a uses a reflection type optical sensor having a switching function that turns on / off a signal when light is blocked, and is attached to the entrance guide plate 177b. It functions as a transfer material detection unit that detects that it is before passing through Nb and detects that the rear end of the transfer material P has passed.

  FIG. 3 is a perspective view of the drive unit of the fixing device 17 according to the present invention. The fixing roller 17a is rotationally driven by the drive motor 176a, and the fixing belt 27 is driven to rotate by the rotation of the fixing roller 17a. Alternatively, as another embodiment (not shown), the pressure roller 17b may have a drive source, and the fixing belt 27, the fixing roller 17a, and the heating roller 17c may be driven to rotate by the rotation of the pressure roller 17b.

  Next, the tension force changing means will be described with reference to FIG. FIG. 4A is an exploded perspective view showing the first embodiment of the tension force changing means. Note that a mechanism having substantially the same shape is provided on both side plates of the fixing device in order to simultaneously move the heating roller up and down. Here, the left side as viewed from the paper discharge side will be described.

  An end portion of the heating roller 17c is inserted into a vertically long hole of both side plates of the fixing device via a bearing 176c, and a cam receiving disc 176d is attached to the outside thereof. The cam receiving disk 176d is stretched by a spring 176f so as to always come into contact with the cam plate 176e.

  The cam plate 176e is an eccentric cam having a rotation shaft at a position separated by Lmm from the center of the disc. The cam plate 176e is fitted into the cam shaft 176g that penetrates both side plates of the fixing device, and a gear 1GA is attached to obtain driving. It has been.

  The gear 1GA is meshed with a gear 2GB attached to the main shaft of the cam motor 176b, and the cam plate 176e rotates through the gear by the rotation of the cam motor 176b, and the heating roller 17c moves up and down by the eccentric distance of the cam receiving disk 176d. It can be done.

  The cam plate 176e has an L position adjusting mechanism (not shown) so that the value of L can be arbitrarily determined. Note that if the L value is obtained in advance from experiments or the like, the eccentric distance can be fixed, so that an adjustment mechanism need not be provided.

  Further, as the second embodiment, a system in which the heating roller 17c is moved by L mm by using a solenoid 176h as shown in FIG. 4B instead of the cam motor 176b in the first embodiment may be used. In FIG. 4B, when a voltage is input to the solenoid 176h, the plunger 176i is attracted by the electromagnet in the solenoid, and the heating roller 17c moves up and down via the link 176j.

  Furthermore, as a third embodiment, a method using a rotary solenoid 176k shown in FIG. The rotary solenoid 176k is a system that attracts while rotating the plunger with an electromagnet, and moves the heating roller 17c up and down by attaching a cam plate 176e to the plunger shaft. This embodiment has an advantage that the mechanism can be simplified.

  In the fixing device 17 provided with the tension force changing means, when the signal of the pre-fixing passage detection sensor 177a is turned ON, the cam motor 176b of the tension force changing means is rotated and heated by the eccentric distance Lmm of the cam plate 176e. The roller 17c moves downward and stops in a state where the tension force is loosened.

  Further, the pre-fixing passage detection sensor 177a turns on a signal for rotating the cam motor 176b by determining in advance the time until the transfer paper is discharged after detecting that the trailing edge of the transfer paper P has passed. . Then, the heating roller 17c moves upward by an eccentric distance Lmm and stops.

  As shown in the schematic diagram of FIG. 5A, in the fixing device 17 having such a configuration, when the fixing belt 27 is stretched by the heating roller 17c, the fixing belt 27 has a curvature at the transfer paper outlet portion of the fixing roller 17a. A radius r1 is formed. Usually, the fixing belt 27 is driven and rotated in a state of being stretched by 100N to 150N, which is an appropriate value with respect to the deviation, meandering, and rotational deviation of the fixing belt.

  Next, when the tension of the fixing belt 27 is weakened to 20N to 40N, as shown in the schematic diagram 5 (b), the fixing belt is greatly bent at the transfer paper exit portion, and the radius of curvature r2 is reduced (the curvature is large). Therefore, loosening the tension of the fixing belt easily separates the transfer material from the fixing belt.

  5A and 5B indicate the rotation direction of the fixing belt 27.

  The control system of the image forming apparatus according to the present invention will be described below with reference to the block diagram of FIG.

  The image forming apparatus is controlled based on a control program stored in a ROM (not shown) by a CPU (not shown) which is a control means of the present invention. This is realized by cooperating with each configuration shown in FIG. The control system of the image forming apparatus according to the present invention includes a system control unit 101, a reading control unit 102, an image processing unit 103, a conveyance drive control unit 104, an image formation control unit 105, a display operation control unit 106, a memory 107, and a fixing control. Part 108.

  The system control unit 101 manages the entire control units of the image forming apparatus and performs requested image formation scheduling and the like.

  The reading control unit 102 controls the operation of the image reading device YS, the image processing unit 103 performs image processing, the transport driving control unit 104 controls the operation of the paper feeding / conveying means, and the image formation control unit 105 is an image forming unit. 10Y, 10M, 10C, and 10K and the operation of the intermediate transfer body 6 are controlled. The display operation control unit 106 controls display on the operation panel and reception of operation input, and the memory 107 stores image data and the like.

  The fixing control unit 108 receives signals transmitted from various temperature sensors such as the pressure roller temperature sensor 175b and the heating roller temperature sensor 174c, and controls energization to various heaters such as the pressure roller heater 174b and the heating roller heater 173c. The drive motor 109 is controlled.

  The control system according to the present invention includes a pre-fixing passage detection sensor 177a, a fixing motor motor 176a, a cam motor 176b, a paper discharge sensor 177b, a lower limit detection sensor SW2, an upper limit detection sensor SW1, and the like.

  Here, the sequence when the pre-fixing passage detection sensor detects the fixing control unit 108 will be described with reference to the timing chart of FIG. 7 taking the fixing device shown in FIG. 4A as an example. When the leading edge of the recording material P passes the pre-fixing passage detection sensor 177a (T1), the recording material conveyance is temporarily stopped by the sensor signal, and at the same time, the cam motor 176b rotates. The cam motor 176b is stopped by a signal detected by the lower limit detection sensor SW2 that the heating roller 17c has reached the lowest limit (T2). At the same time, the recording material p once stopped is started again. The pre-fixing passage detection sensor 177a detects the trailing edge of the recording material P (T3), and after a time t2 when the recording material passes through the fixing nip Nb, the cam motor 176b rotates again (T4) and moves the heating roller 17c upward. It is stopped by the signal of the upper limit detection sensor SW1 that detects that the upper limit position has been reached (T5). When the recording material discharge sensor 177b detects that the recording material is discharged (T6), the rotation of the recording material conveyance motor (not shown) and the fixing motor stops (T7). In addition, energization of various heaters of the pressure roller heater 174b and the heating roller heater 173c is controlled by the fixing control unit 108.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

  The fixing device shown in FIGS. 2 and 4A is mounted on the image forming apparatus shown in FIG. 1 and the control shown in FIG. 7 is performed to determine whether or not the recording material is wound around the fixing belt. Separation performance was evaluated.

Separation performance was evaluated under the following conditions.
Print test chart Konica Minolta standard color chart (printing rate 4%)
Passing test paper Konica Minolta copy paper NR-A80 A4 size Number of paper passes 2000 paper feed direction The long side of the paper is parallel to the transfer material transport direction Temperature change range of the fixing belt Every 10 ° C from 150 ° C to 200 ° C The temperature of was measured by connecting both terminals of the heating roller temperature sensor 174C to a thermometer.
Belt tension tension (at high tension) 120N
(At low tension) 2 levels of 40N and 20N The belt tension has the following relationship with the eccentric amount Lmm of the eccentric cam 176e.

20N when L = 2mm
40N when L = 4mm
The configuration of the fixing device is as follows.
Fixing belt: Base material Polyimide.

Base thickness 0.07mm
Elastic layer thickness 0.2mm
Material of elastic layer Silicon rubber (hardness JIS-A 30 degrees)
0.03mm PFA tube covered fixing roller: Outer diameter 45mm
Base material Carbon steel pipe for machine structure
Base thickness 2mm
Outer diameter of substrate 25mm
Elastic layer thickness 10mm
Material of elastic layer Silicone sponge (hardness Asker-C30 degree)
Heating roller: 50mm outer diameter
Base material Aluminum pipe PFA coating thickness 10μm
Base thickness 2mm
Pressure roller: 50mm outer diameter
Base material Carbon steel pipe for machine structure
Base thickness 2mm
44mm outer diameter of substrate
Elastic layer thickness 3mm
Elastic layer material Silicon rubber (hardness JIS-A 10 degrees)
0.05mm PFA tube coating system speed: 300mm / sec Nip pressure contact force: 1000N
In the above-described embodiment, the transfer material was not wound when the fixing belt temperature ranged from 150 ° C. to 200 ° C., and the separation performance was good. On the other hand, when the belt tension was always 120 N, the transfer material was wound. That is, it was found that the fixing belt is greatly bent at the transfer paper exit portion by loosening the tension and the curvature r2 is increased, so that the separation performance is improved.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus including a fixing device according to the present invention. 1 is a schematic sectional view of a fixing device according to the present invention. 1 is a perspective view of a fixing device according to the present invention. It is a perspective view which shows schematic structure of the tension force change means based on this invention. 5A is a cross-sectional view of a main part of the fixing device in which the fixing belt is stretched with a high tension force, and FIG. 5B is a main part of the fixing device in which the fixing belt is tensioned with a low tension force. It is sectional drawing. 2 is a block diagram showing a control system of the image forming apparatus according to the present invention. FIG. 6 is a timing chart illustrating an example of fixing control of the image forming apparatus according to the present invention.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 2Y, 2M, 2C, 2K Charging unit 3Y, 3M, 3C, 3K Exposure unit 4Y, 4M, 4C, 4K Developing device 101 System control unit 102 Reading control unit 103 Image processing unit 104 Conveyance drive control unit 105 Image formation control unit 106 Display operation control unit 107 Memory 108 Fixing control unit 17 Fixing device 17a Fixing roller 17b Pressure roller 17c Heating roller 173c Heating heater 174b Pressure roller heater 174c Heating roller temperature sensor 175b Pressure roller temperature Sensor 176a Drive motor 176b Cam motor layer 177a Passing detection sensor before fixing 177b Paper discharge sensor 27 Fixing belt Nb Main nip P Recording paper

Claims (3)

A fixing roller; a heating roller having a heat source; a fixing roller; a fixing belt stretched around the heating roller; and a pressure roller that presses the fixing roller through an outer peripheral surface of the fixing belt; In a fixing device that performs fixing through a transfer material carrying an unfixed toner image in a nip formed by a roller and the pressure roller,
A fixing device comprising tension force changing means for changing the tension force of the fixing belt. Detecting means for detecting the leading edge or the trailing edge of the transfer material;
Control means for controlling the tension force changing means so that the tension force of the fixing belt is reduced before the leading edge of the transfer material passes through the nip portion based on the result detected by the detection means; The fixing device according to claim 1, further comprising: a fixing device; Detecting means for detecting the leading edge or the trailing edge of the transfer material;
Control means for controlling the tension force changing means so that the tension force of the fixing belt is increased after the rear end of the transfer material has passed through the nip portion based on the result detected by the detection means. The fixing device according to claim 1, wherein

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