JP2011197357A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device in which a nip formed by pressing a roughening member to a fixing belt is stabilized and the surface roughness of the fixing belt is stably kept, and to provide an image forming apparatus equipped with the fixing device.SOLUTION: The fixing device includes: the roughening member 400 for roughening the surface of an endless belt 105 by being in contact with the surface of the endless belt 105 other than a part suspended by suspension members 131, 132; and a belt pressurizing member 444 movable to a first position at which it is abutted on the inner surface side of the endless belt 105 and brings the endless belt 105 into contact with the roughening member 400 and a second position at which the endless belt 105 is separated from the roughening member 400.

Description

  The present invention relates to a fixing device that fixes an image formed on a recording material such as a multifunction peripheral, a copying machine, a printer, and a fax machine, and an image forming apparatus including the fixing device.

  As a fixing device in an electrophotographic image forming apparatus, a heat fixing device having a fixing member such as a fixing roller or a fixing belt is generally used. Since the fixing roller or the fixing belt is provided with an elastic layer made of silicone rubber or a fluorine tube as a surface layer, its durability is a problem. For example, when sheets of the same size are continuously fed, the fixing member surface layer corresponding to the passing position of the edge portion of the paper is gradually roughened in the fixing device, and an area having a surface roughness higher than the surroundings is generated. As a result, the difference in surface roughness appears as gloss unevenness on the recording sheet image after fixing.

  In order to solve this problem, Japanese Patent Application Laid-Open No. H10-228688 proposes a technique for bringing a roughening member into contact with the fixing roller in order to keep the surface roughness of the surface layer of the fixing roller constant. That is, as the roughening member, the roughening effect of the surface layer of the fixing roller is obtained by rotationally driving the roughening roller in contact with the surface layer of the fixing roller. In addition, by making the rough roller contactable to and away from the fixing roller, the life of the fixing roller is prevented from being shortened due to the surface of the fixing roller being constantly polished by the rough roller being in constant contact with the fixing roller. The system has also been put into practical use.

  As a configuration of a fixing device having a fixing belt, a method disclosed in Patent Document 2 has been proposed. In Patent Document 2, one of the two rollers for suspending the fixing belt constitutes a fixing nip. The other roller is a tension member that applies tension to the fixing belt, and the roller has a regular crown shape to prevent wrinkling of the recording sheet by applying tension to the axially central portion of the fixing belt.

JP 2007-199596 A JP-A-6-118823

  By the way, as arrangement | positioning when a roughening member is made to contact a fixing belt, between the opposing part of the suspension member which suspends a fixing belt, and the roller which suspends a fixing belt is considered.

  However, as described above, the roller that is a suspension member of the fixing belt may have a crown shape in order to form a good fixing nip. In other cases, among the suspension rollers, a roller for applying tension to the fixing belt has a crown shape in order to obtain good sheet conveyance. Furthermore, the suspension roller may warp due to the pressure for forming the nip and the tension force generated in the fixing belt itself, and the belt suspension member of the fixing belt does not use a straight roller in the first place. is there.

  In particular, with the recent increase in the speed of copying machines, the pressure required at the fixing nip is high, and further, a delicate design for the fixing nip shape is required. For this reason, it is expected that the suspension roller shape for optimizing the fixing nip is often increased against the pressure of the pressing member and the warping of the suspension member due to the fixing belt tension.

  Therefore, when the rough member is brought into contact with a position facing the member for suspending the fixing belt, it is expected that it becomes difficult to form an optimum nip between the suspension roller and the fixing belt. If a non-uniform nip is formed at the portion where the roughening member contacts, the surface property of the fixing belt becomes non-uniform in the direction perpendicular to the rotation of the fixing belt. For this reason, an image abnormality such as in-plane gloss unevenness occurs on the recording sheet after fixing.

  On the other hand, when the roughening member is disposed between the rollers for suspending the fixing belt, it can be considered that the fixing member is deformed in the direction opposite to the belt suspension of the fixing belt. In order to prevent the deformation caused by disposing the roughening member between the rollers for suspending the fixing belt, a backup for preventing the deformation at a position inside the fixing belt and facing the contact position of the roughening member. A method of arranging the members is conceivable. However, when the backup member is always in contact with the inner surface of the belt, the wear on the inner surface of the belt is promoted, and it is expected that the life of the belt is shortened and the belt conveying property of the fixing belt is abnormal due to wear powder.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to stabilize the nip formed by pressing a roughening member on the fixing belt, and to fix the surface of the fixing belt. Provided are a fixing device and an image forming apparatus capable of stably maintaining roughness.

  The first feature of the embodiment of the present invention is that an image-formed sheet is nipped and conveyed by an endless belt that is rotated by being suspended by a plurality of suspension members and a pressure member that is rotated in pressure contact with the endless belt. In the fixing device for fixing the image by heating the sheet, the roughening member that contacts the surface of the endless belt other than the portion suspended by the suspension member and roughens the surface of the endless belt; A belt pressing member movable to a first position where the endless belt is brought into contact with the inner surface of the belt and brought into contact with the roughening member; and a second position where the endless belt is separated from the roughening member. Prepare.

  According to a second aspect of the present invention, there is provided an image forming apparatus that transfers an image formed by an image forming unit to a sheet, conveys the sheet to a fixing device, and fixes the image. A rough member that contacts the surface of the endless belt other than the portion suspended by the member and roughens the surface of the endless belt, and a first member that contacts the inner surface of the endless belt and contacts the rough member. A belt pressing member that is movable to a first position and a second position that separates the endless belt from the roughening member.

  According to the present invention, a nip formed by pressing a roughening member on the fixing belt can be stabilized, and the fixing device capable of stably maintaining the surface roughness of the fixing belt and the fixing device. An image forming apparatus including a fixing device can be provided.

1 is a cross-sectional view illustrating an entire image forming apparatus according to an embodiment of the present invention. 1 is a perspective view illustrating an entire fixing device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part of the fixing device cut along line AA in FIG. 2. FIG. 3 is an explanatory diagram illustrating a belt tension mechanism of a fixing device according to an embodiment of the present invention. It is explanatory drawing of the drive mechanism of the roughening member in embodiment of this invention. It is sectional drawing which shows the pressurization operation | movement to the roughening roller which concerns on 1st Embodiment of this invention. It is a perspective view for demonstrating the pressurization operation | movement to the roughening roller which concerns on 1st Embodiment of this invention. It is a perspective view for demonstrating the pressurization operation | movement to the roughening roller which concerns on 1st Embodiment of this invention. It is a flowchart which shows the flow of the pressurization operation | movement to the roughening roller which concerns on 1st Embodiment of this invention. It is a flowchart which shows the flow of the concrete pressurization operation | movement to the roughening roller which concerns on 1st Embodiment of this invention. It is a figure explaining the positional relationship of the tension axis | shaft for tension change and tension axis | shaft press stand in 1st Embodiment of this invention. It is a figure explaining the positional relationship of the tension axis | shaft for tension change and tension axis | shaft press stand in 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view showing a color electrophotographic printer as an example of an image forming apparatus 500 of the present embodiment, cut along the sheet conveyance direction. In the present embodiment, the color electrophotographic printer is hereinafter simply referred to as “printer”.

  The printer shown in FIG. 1 includes an image forming unit 510 for each color of Y (yellow), M (magenta), C (cyan), and Bk (black). The photosensitive drum 511 is charged in advance by the charging roller 512. Thereafter, a latent image is formed on the photosensitive drum 511 by the laser scanner 513. The latent image is converted into a toner image by the developing device 514. The toner image on the photosensitive drum 511 is sequentially transferred to an intermediate transfer belt 531 that is an image carrier.

  On the other hand, the sheets S are sent one by one from the feeding cassette 520 and fed to the registration roller pair 523. The registration roller pair 523 temporarily stops the sheet S, and straightens it when the sheet is skewed. The registration roller pair 523 conveys the sheet S between the intermediate transfer belt 531 and the secondary transfer roller 535 in synchronization with the toner image on the intermediate transfer belt 531. The color toner image on the intermediate transfer belt 531 is transferred to the sheet S by the secondary transfer roller 535 which is a transfer body. The toner image transferred onto the sheet S is fixed on the sheet S by being heated and pressed by the fixing device 100. The sheet S on which the toner image is fixed is conveyed and discharged by a discharge roller pair 540 to a discharge tray 565 at the top of the apparatus.

  Next, the fixing device 100 will be described in detail.

  FIG. 2 is a perspective view showing the entire fixing device 100 according to the embodiment of the present invention. FIG. 3 is a cross-sectional view of the main part of the fixing device 100 shown cut along line AA in FIG. FIG. 4 is an explanatory view for explaining a belt tension mechanism in the fixing device 100, and FIG. 5 is an explanatory view of a roughing member driving mechanism.

  As shown in FIG. 2, a driving motor 301 that drives a driving roll is provided on one side of the fixing device 100, and a pressure motor 302 that drives a pressure roll is provided on the other side.

  The fixing belt 105 shown in FIG. 3 is a continuous endless belt having no breaks, and is suspended by a plurality of suspension members so as to be circulated and rotated. Suspension members for suspending the fixing belt 105 are a drive roll 131 and a steering roll 132. The steering roll 132 has a function of applying a belt tension to the fixing belt 105, and functions as a tension applying unit. The fixing belt 105 is stretched between the driving roll 131 and the steering roll 132 with a predetermined tension (for example, 200 N).

The fixing belt 105 may be appropriately selected as long as it has heat resistance since it is heated by an IH heater 170 described later. For example, a nickel metal layer having a thickness of 75 μm, a width of 380 mm, a circumferential length of 200 mm, or a magnetic metal layer such as a stainless steel layer is coated with, for example, 300 μm of silicon rubber, and a surface layer is coated with a PFA tube.

  On the other hand, the pressure belt 120 is a continuous endless belt that is continuous and is suspended by a plurality of suspension members so as to be circulated and rotated. Suspension members for suspending the pressure belt 120 are a pressure roll 121 and a tension roll 122. The tension roll 122 has a function of applying a belt tension to the pressure belt 120 and functions as a tension applying unit. The pressure belt 120 is stretched between the pressure roll 121 and the tension roll 122 with a predetermined tension (for example, 200 N).

  In this embodiment, the pressure belt 120 may be appropriately selected as long as it has heat resistance. For example, a nickel metal layer having a thickness of 50 μm, a width of 380 mm, and a circumference of 200 mm is coated with, for example, a 300 μm-thick silicon rubber and a surface layer is coated with a PFA tube.

  As shown in the cross-sectional view of FIG. 3, the IH heater 170 that is a magnetic flux generating means is composed of an excitation coil, a magnetic core, and a holder that holds them, not shown, and is provided near the upper surface layer of the fixing belt 105. . The exciting coil generates an alternating magnetic flux by an alternating current, and the alternating magnetic flux is guided to the core magnetic body to generate an eddy current in the fixing belt 105 which is an induction heating element. The eddy current generates Joule heat by the specific resistance of the induction heating element. The alternating current supplied to the coil is controlled so that the surface temperature of the fixing belt 105 is, for example, about 140 to 200 ° C. based on temperature information from the thermistor 220 for detecting the surface temperature of the fixing belt 105. Is done.

  Here, the operation of the fixing device 100 will be described with reference to FIG.

  The sheet S conveyed to the fixing device 100 by the photosensitive drum 511 and the secondary transfer roller 535 is guided to an entrance guide 184 provided on the lower frame 124. Thereafter, the toner enters the fixing nip N region of the fixing belt 105 and the pressure belt 120 that are rotationally driven via a driving input gear (not shown). The sheet S on which the toner image is fixed by being heated and pressed in the fixing nip N area formed by the fixing belt 105 and the pressure belt 120 is guided to the discharge guide 185 after passing through the fixing nip N area. . Thereafter, the sheet is conveyed and discharged to a discharge tray 565 at the top of the apparatus by a discharge roller pair 540.

  The separation claw 186 is provided to prevent the sheet S from being wrapped without being separated from the pressure belt 120. When the discharge detection sensor lever 180 is pushed by the leading end of the sheet S, the discharge detection sensor lever 180 rotates about the rotation shaft 180a. A sensor light-shielding portion 181 formed integrally with the discharge detection sensor lever 180 shields the light-receiving slit of the photosensor 182 to detect the passage of the sheet S. At this time, if the passage of the discharge detection sensor lever 180 is not detected within a predetermined time, it is determined that a jam has occurred, and the energization to the IH heater 170 and the rotation driving of the fixing belt are immediately stopped, and the jam processing by the user can be performed. To do. When the user instructs resumption of image formation by operating means (not shown) after the jam processing is finished, energization to the IH heater 170 and rotational driving of the fixing belt are resumed, and image formation can be performed again.

  The fixing nip N is formed by the pressure belt 120 and the fixing belt 105. A pressure pad 125 is pressed against the pressure belt 120 at a predetermined pressure (for example, 400 N) inside the pressure belt 120 corresponding to the inlet side (upstream side of the pressure roll 121) of the fixing nip N region. Yes. The pressure pad 125 is made of, for example, silicon rubber, and forms a fixing nip N area together with the pressure roll 121.

  The pressure roll 121 is a member that suspends the pressure belt 120 that is one of the pressure members, and has a roll shape. The pressure roll 121 is made of, for example, solid stainless steel. The pressure roll 121 is disposed on the exit side of the fixing nip N region between the pressure belt 120 and the fixing belt 105.

  The tension roll 122 is a hollow roll formed of, for example, stainless steel and functions as a belt tension roll for the pressure belt 120. As shown in FIG. 4, both ends of the tension roll 122 are supported by bearings 126, and a tension spring 127 applies, for example, a tension of 20 kgf to the belt.

  On the inner side of the fixing belt 105 corresponding to the inlet side (upstream side of the driving roll 131) of the fixing nip N area between the fixing belt 105 and the pressure belt 120, a pad stay 137 is a pressure pad with a predetermined pressure (for example, 400 N). It is pressed against 125. The pad stay 137 is made of, for example, stainless steel (SUS material), and forms a fixing nip N area together with the drive roll 131.

  The driving roll 131 rotates when driving is externally input by the driving motor 301 and conveys the fixing belt 105. The drive roll 131 is formed by integrally molding a heat-resistant silicon rubber elastic layer on a core metal surface layer made of, for example, solid stainless steel. The driving roll 131 is disposed on the exit side of the fixing nip N region between the fixing belt 105 and the pressure belt 120, and the elastic layer is elastically distorted by a predetermined amount by the pressure contact of the pressure roll 121.

  Further, when the pressure roll 121 is pressed against and contacts the drive roll 131, the drive roll 131 and the pressure roll 121 are warped and deformed by several hundred microns, which causes pressure loss at the center of the pressure contact portion. Therefore, the driving roll 131 alone or the driving roll 131 and the pressure roll 121 adopts a crown shape, so that the nip shape of the driving roll 131 and the pressure roll 121 is formed in a substantially straight shape. In the present embodiment, for example, the driving roll 131 is provided with a 300 μm regular crown shape.

  As described above, in this embodiment, the nip shape of the drive roll 131 and the pressure roll 121 is formed in a substantially straight shape, but various roller crown shapes may be employed. For example, in order to control the buckling of the sheet S due to the speed difference in the fixing nip N of the sheet S, the crown shape of the drive roll 131 and the pressure roll 121 is intentionally made into an inverted crown shape.

  The steering roll 132 is a hollow roll formed of, for example, stainless steel. The steering roll 132 functions as a steering roll that adjusts meandering in the width direction orthogonal to the moving direction of the fixing belt 105 and also functions as a belt stretching roll for the fixing belt 105.

  The fixing device 100 can be roughly divided into an upper frame and a lower frame, and both are rotatably supported by a hinge shaft provided on the lower plate 303, although not shown in FIG. The upper frame includes an upper plate 140 that rotatably supports the drive roll 131 and holds the end of the pad stay 137. The lower frame includes a lower plate 303 that rotatably supports the pressure roll 121 and holds the end of the pressure pad 125. The two frames are biased by a pressure spring (not shown) around the hinge axis so that the upstream side is pressed by the pad stay 137 and the pressure pad 125 and the downstream side is pressed by the drive roll 131 and the pressure roll 121. The The former is pressed through the fixing belt 105 and the latter is pressed through the pressure belt 120 to form a fixing nip N area.

  As shown in FIG. 4, a sensor 150 for detecting the belt end position of the fixing belt 105 is provided on the upper portion of the drive roll 131. The sensor 150 detects the position of the end portion of the fixing belt 105 and changes the inclination of the steering roll 132 accordingly, thereby controlling the deviation of the fixing belt 105.

  As shown in FIG. 4, the steering support arm 154 is supported so as to be rotatable around a shaft 151 fixed to the outside of the upper plate 140. A gear 152 is fixed to the outer periphery of the shaft 151 outside the steering support arm 154. The gear 152 meshes with a worm 157 that can be rotationally driven by the driving of the stepping motor 155.

  The support arm 158 is supported so as to be rotatable about the drive roll 131. The support arm 158 is moved in the rotation direction about the shaft 151 by the fixed shaft 159 and the steering support arm 154 on the support arm 158.

  The support arm 158 holds a steering roll bearing 153 and a tension spring 156 via a tension shaft 160. The tension shaft 160 is pressed at the end opposite to the side held by the steering roll bearing 153 by a tension shaft pressing base 432 (see FIG. 7, which will be described later). A tension spring 156 urges the steering roll 132 in a rotatable state via the tension shaft 160. Further, the steering roll bearing 153 supported so as to be slidable in the belt tension direction is urged in the tension direction. On the opposite side of the steering roll 132, the steering roll bearing 153 is urged in the tension direction by the support member 480 instead of the support arm 158 (see FIG. 7).

  Returning to FIG. 3, the roughening roller 400 is provided at a position in contact with the surface of the fixing belt 105 other than the portion suspended by the drive roll 131 and the steering roll 132 which are suspension members. Specifically, it is rotatably supported via a bearing by an RF support arm 141 rotatably supported by a fixed shaft 142 on the upper plate 140. In the roughening roller 400, for example, abrasive grains are closely bonded to the surface of a stainless steel core through an adhesive layer. The abrasive grains are changed to # 1000 to # 4000 in accordance with the application (target glossiness of the image). The abrasive grains are alumina-based (also called “alundum” or “morundum”). Alumina is the most widely used abrasive grain in the industry, has higher hardness in each step than the surface of the fixing belt 105, and has excellent abrasiveness because the particles have an acute-angled shape.

  In this embodiment, as an example of the roughening member, an example using a roller (rotary body) bonded with alumina-based abrasive grains as described above will be described. However, any configuration that recovers the belt surface property may be used. The roughening member may have a shape with irregularities formed by blasting or the like, or may have a structure in which a wrapping film or sandpaper is wound. Further, the shape of the roughening member may not be a roller shape as long as it is configured to uniformly contact the belt.

  As shown in FIG. 5, the roughing roller 400 is driven by an RF drive gear 401 fixed to the end of the drive roll, an RF idler gear 402, and an RF gear 403 fixed to the end of the roughing roller. Rotate in the same direction at 105 with a substantially constant peripheral speed.

  Further, when the fixing belt 105 is pressed against the roughening roller 400 via the RF pressure member 444, the roughing roller 400 is urged by the RF pressure spring 404 and pressed against the fixing belt 105. As a result, the roughening roller 400 having a polishing layer on its surface rotates in the counter direction (the direction in which the surface moves in the reverse direction) with respect to the fixing belt 105 to uniformly roughen the surface of the fixing belt 105 ( Level the surface).

  Next, a roughing operation using the roughing roller 400 on the fixing belt 105 will be described. FIG. 6 is a cross-sectional view showing the pressing operation to the roughing roller according to the first embodiment of the present invention. 7 and 8 are perspective views for explaining the pressing operation to the roughing roller according to the first embodiment of the present invention. FIG. 9 is a flowchart showing the flow of the pressing operation to the roughing roller according to the first embodiment of the present invention.

  As shown in FIG. 7, driving force is transmitted to the pressure mechanism 31 via the worm gear 421 by the pressure motor 302 attached to the outer fixing frame 101. Here, the pressure mechanism 31 refers to a mechanism for pressing the roughing roller 400 against the fixing belt 105. As shown in FIG. 7 or FIG. 8, the pressure mechanism 31 is rotatably supported by pressure idler gears 422b and 422c fixed to a pressure idler shaft 422a that is rotatably supported, and a fixed shaft 424. The pressure idler gear 425 is configured. The driving of the pressurizing motor 302 is transmitted to the sector gear 426 (see FIG. 8) via each part of the pressurizing mechanism 31 described above. The sector gear 426 is fixed to a pressure shaft 305, and a fixing pressure cam 427 and an RF pressure cam 428 (see FIG. 7) are fixed to the pressure shaft 305.

  As shown in the flowchart of FIG. 9, when the pressurization control to the roughing roller 400 is started and the pressurization operation is started by the pressurization mechanism 31 (S9-1), the rotation by the pressurization motor 302 is performed. (S9-2), the fixing pressure cam 427 operates. Thus, the lower plate 303 is pressed. As described above, the biasing spring (not shown) is biased about the hinge shaft. Accordingly, the pad stay 137 and the pressure pad 125, and the drive roll 131 and the pressure roll 121 are pressed through the fixing belt 105 and the pressure belt 120, respectively, and a fixing nip N is formed (S9-3).

  When the roughing roller 400 is moved to the pressure position relative to the fixing belt 105 (Y in S9-4), the pressure shaft 305 is further rotated by the pressure motor 302. When the pressure shaft 305 rotates, the RF pressure arm 429 is pushed up by the RF pressure cam 428. The RF pressure arm 429 supports the RF link arm 430 via the rotation shaft 440. The RF link arm 430 further supports a tension shaft pressing base 432 so as to be movable in the direction of arrow B through a guide hole 443 opened in the pressure side plate 442 via the rotation shaft 441. An RF pressure member 444 that is a belt pressing member for the fixing belt 105 is supported on the tension shaft pressing table 432. The RF pressure member 444 is a contact member that directly contacts the inner surface side of the fixing belt 105 (the side that contacts the driving roll 131 and the steering roll 132), and is a roller member that rotates as the fixing belt 105 rotates.

  The rotation of the pressure motor 302 moves the tension shaft pressing base 432 to the position (pressing position) in FIG. 6, so that the RF pressing member 444 is pressed against the roughing roller 400 via the fixing belt 105 (S9). -5). The position where the pressing member 444 is pressed against the roughing roller 400 via the fixing belt 105 is hereinafter referred to as “first position” as appropriate.

  In this embodiment, the belt rotation trajectory when the fixing belt 105 contacts the roughing roller 400 is moved about, for example, about 3 mm outside the rotation belt by the RF pressure member 444 from the normal rotation trajectory. ing. At this time, the angle formed by the fixing belt 105 by the RF pressure member 444 is about 140 degrees. The angle formed by the fixing belt 105 is desirably about 90 to 180 degrees (180 degrees when not pressed) in order to prevent reverse warping and excessive deformation of the fixing belt 105.

  The drive motor 300 is rotated for a predetermined time while the RF pressure member 444 is pressed by the roughening roller 400 via the fixing belt 105 (S9-6). Then, the fixing belt 105 and the roughing roller 400 rotate with a predetermined speed difference, and the surface of the fixing belt 105 is roughened by the roughing roller 400 (S9-7). Although the setting can be arbitrarily performed, in this embodiment, for example, the pressure, speed, and rotation time are set so that the surface of the fixing belt 105 has a 10-point average roughness of about 1.5.

  When the drive motor 300 stops at a predetermined time (S9-8), an operation for separating the roughing roller 400 from the fixing belt 105 is started (S9-9). The separation operation is performed in the reverse order of pressurization by reversing the pressure motor 302 (S9-10). The position at which the pressure member 444 is roughened from the roughening roller 400 via the fixing belt 105 is hereinafter referred to as “second position” as appropriate. When the roughing roller 400 is separated from the fixing belt 105 and the pressure member 444 is separated to the second position, the pressure motor 302 is stopped (S9-11).

  Next, the control for bringing the fixing belt 105 and the roughening roller 400 into contact with each other will be described more specifically with reference to the flowchart of FIG.

  It is assumed that the CPU (not shown) of the printer counts the number N of sheets to be passed after roughing control. When the printing operation of the printer 500 is finished <S10-1>, if the CPU determines that the number N of sheets to be passed exceeds a predetermined number <S10-2>, the fixing belt 105 and the roughing roller 400 are pressed. To rotate. That is, roughening control for recovering the surface roughness of the fixing belt 105 is started <S10-3>. In the present embodiment, the predetermined number of sheets is set to 5000 sheets, which is the number of sheets that the gloss unevenness of the printed image starts to be noticeable due to the difference in surface roughness on the fixing belt 105. It is desirable to set the optimum number according to the number.

  When the roughing control is started <S10-3>, the pressure motor 302 is rotationally driven by an operation according to the flowchart of FIG. 9 <S10-4>, the fixing belt 105 is roughened, and the RF pressure member 444 is applied to the roller 400. <S10-5>. In this state, the drive motor 300 is rotated for a predetermined time <S10-6>, and the surface of the fixing belt 105 is roughened and rubbed by the roller 400. In the present embodiment, the predetermined time Ts is set to 5 seconds. If Ts is too long, the surface layer of the fixing belt 105 is excessively scraped by the roughening roller 400, which may shorten the life. If it is too short, the effect of restoring the belt surface property is not sufficient. Setting is required.

  When the predetermined time Ts has elapsed <Y in S10-7>, the drive motor 300 is stopped <S10-8>. Thereafter, the pressure motor 302 is driven to rotate <S10-9>, and the fixing belt 105 is roughened and retracted from the roller 400 to the second position <S10-10>. Then, the sheet passing number N after the roughing control on the CPU is reset to 0 <S10-11>.

  In this embodiment, whether or not roughing control is performed is determined from the number N of sheets to be passed at the end of the printing operation. However, when the predetermined number of sheets is reached, the printer operation is interrupted and roughing control is performed. Thereafter, the printing operation may be resumed. In addition, a user / serviceman or the like may perform roughing control from an input device of a printer such as a service panel.

  Next, a configuration for maintaining the tension of the fixing belt 105 accompanying the movement of the tension shaft pressing base 432 will be described with reference to FIGS. FIG. 11 is a diagram illustrating the positional relationship between the tension shaft 160 and the tension shaft pressing base 432 for changing the tension. FIG. 11a shows a case where the second position (position where the fixing belt 105 and the roughing roller 400 are separated) is shown, and FIG. 11b shows the first position (fixing belt 105 and the roughing roller 400). This is a case where the position is in a contact position.

  The tension shaft 160 is supported by the steering roll bearing 153 so as to be movable in the tension urging direction C of the steering roll 132 (see FIG. 8). As shown in FIG. 11, the tension shaft 160 has one end in contact with the flange surface 160 a of the tension spring 156 and the other end in contact with the pressing surface 432 a of the tension shaft pressing base 432. Therefore, the urging force in the tension urging direction C by the tension spring 156 changes depending on the positional relationship between the tension shaft 160 and the steering roll bearing 153.

  When the RF pressure member 444 and the roughing roller 400 are separated (second position, FIG. 11 a), the tension shaft 160 is pressed by the pressing surface 432 a of the tension shaft pressing base 432. At that time, the tension shaft 160 takes a position where the distance between the drive roll 131 and the steering roll 132 becomes the length D shown in FIG. As a result, the tension spring 156 applies tension to the fixing belt 105 via the steering roll bearing 153 and the steering roll 132 as described above.

  On the other hand, when the RF pressure member 444 and the roughing roller 400 are in contact (first position, FIG. 11b), the tension shaft 160 is pressed by the pressing surface 432b by the movement of the tension shaft pressing base 432. At this time, since the fixing belt 105 is suspended by the RF pressure member 444, the tension of the fixing belt 105 increases. However, the tension shaft 160 takes a position where the distance between the drive roll 131 and the steering roll 132 becomes the length E by the movement of the tension shaft pressing base 432. The distance E shown in FIG. 11b is shorter than the distance D shown in FIG. 11a.

  Therefore, when the RF pressure member 444 contacts the fixing belt 105, the distance between the drive roll 131 and the steering roll 132 is smaller than when the RF pressure member 444 is separated from the fixing belt 105. In other words, the tension of the fixing belt 105 can be adjusted regardless of the position of the first position or the second position by moving the steering roll 132 as the tension applying means in conjunction with the movement of the RF pressure member 444. It will be maintained substantially the same. In the present embodiment, the tension spring 156 is provided so as to maintain the tension of the fixing belt 105 in the same manner as in the second position even when the belt is suspended by the RF pressure member 444 (when the belt is in the first position). It is set.

  In this embodiment, the phases of the fixing pressure cam and the RF pressure cam are set so that the fixing belt and the pressure belt are separated from each other when the roughing roller and the fixing belt are in contact with each other. However, in particular, when setting a roughing operation during paper passing, the cam phase may be set so as to pressurize the roughening member at the phase at which the fixing nip N is formed. In this case, since the belt tension does not change due to pressurization with the roughening member, the influence of the nip can be suppressed, which is more effective.

  In the present embodiment, the configuration in which the RF pressing member 444 is pressed against the roughening roller 400 via the fixing belt 105 by the pressurizing mechanism 31 has been described. Any structure may be used as long as the pressure member is pressed. For example, the back surface of the fixing pad in the fixing belt may also serve as the RF pressure member.

  As described above, according to the pressing method for the roughening means described in the present embodiment, a good nip independent of the shape of the belt suspension member can be obtained in the contact between the roughening means and the belt member, and the uniform belt surface can be obtained. It becomes possible to maintain sex. Further, by suppressing the deformation of the belt member in the direction opposite to the suspension direction, it is possible to suppress the occurrence of cracks and wrinkles of the belt due to the deformation in the reverse direction.

  Further, if the belt tension maintaining means described in the present embodiment is used, it is not necessary to apply excessive tension when the roughing means and the belt member are in contact with each other, and belt cracks and wrinkles caused by applying excessive tension to the fixing belt. Can be prevented.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and the description of the same components is omitted because it is duplicated.

  FIG. 12 is a diagram for explaining the positional relationship between a tension shaft for tension change and a tension shaft pressing base in the second embodiment of the present invention.

  An RF pressure shaft 460 is rotatably supported on the tension shaft pressing base 432. An oil-impregnated member 461 made of a nonwoven fabric is formed on the surface layer of the RF pressure shaft 460. In the second embodiment, the oil impregnated in the oil-impregnated member is, for example, dimethyl silicone oil.

  The rotation of the pressure motor 302 causes the tension shaft pressing base 432 to move to the position shown in FIG. 12 b, so that the RF pressure member 444 including the RF pressure shaft 460 and the oil impregnated member 461 passes through the fixing belt 105. It is pressed by the roughening roller 400 (first position). Accordingly, the oil impregnation member 461 comes into contact with the inner surface of the fixing belt 105, so that oil can be supplied into the fixing belt 105.

  By using the configuration of the second embodiment, it is possible to apply oil to the inner surface of the belt only when the fixing belt and the roughing roller are in contact with each other while achieving the effects described in the first embodiment. Life expectancy is possible.

DESCRIPTION OF SYMBOLS 105 ... Fixing belt 120 ... Pressure belt 121 ... Drive roller 131 ... Pressure roller 132 ... Tension roller 156 ... Tension spring 160 ... Tension shaft 400 ... Roughening roller 500 ... Image forming apparatus 1,100 ... Fixing device

Claims (8)

An endless belt that is suspended and rotated by a plurality of suspension members, and a pressure member that rotates in pressure contact with the endless belt, when the image-formed sheet is conveyed in a nip, the sheet is heated to fix the image. In the fixing device,
A rough member that contacts the surface of the endless belt other than the portion suspended by the suspension member, and roughens the surface of the endless belt;
A belt pressing member that is movable to a first position where the endless belt comes into contact with the roughening member by contacting the inner surface side of the endless belt and a second position where the endless belt is separated from the roughening member. When,
A fixing device. Having tension applying means for applying tension to the endless belt;
The tension applying means interlocks with the movement of the belt pressing member, and maintains the tension of the endless belt substantially equal when the belt pressing member is in the first position and when in the second position. The fixing device according to claim 1, wherein:   The fixing device according to claim 2, wherein the tension applying unit changes the tension of the endless belt by moving at least one suspension member that suspends the endless belt. The belt pressing member has a contact member that contacts the endless belt,
The fixing device according to claim 1, wherein the contact member is a roller member.   The fixing device according to claim 1, wherein the belt pressing member can supply oil to an inner surface side of the endless belt.   The belt rotation locus when the belt pressing member moves to the first position and the endless belt contacts the roughening member is outside the rotation locus when the belt pressing member is at the second position. The fixing device according to any one of claims 1 to 5, wherein the fixing device moves to the position.   The fixing device according to claim 1, wherein the roughening member is a rotating body that rotates at a substantially constant peripheral speed with respect to the endless belt. In an image forming apparatus that transfers an image formed by an image forming unit to a sheet, conveys the sheet to a fixing device, and fixes the image.
An image forming apparatus comprising the fixing device according to claim 1 as the fixing device.

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