JP2021113877A - Fixing device - Google Patents

Abstract

To provide a configuration that can suppress a speed difference between a recording material and a pressure roller 330 regardless of the kind of the recording material.SOLUTION: A pressure roller 330 has an elastic layer and rotates in contact with the outer peripheral surface of a fixing belt 310 to give a driving force to the fixing belt 310. An auxiliary driving roller 340 is disposed inside the fixing belt 310, stretches the fixing belt 310 together with a fixing pad 320 to rotate, and gives a driving force to the fixing belt 310. It is assumed that the peripheral speed of the pressure roller 330 is V0, and the peripheral speed of the auxiliary driving roller 340 is V1, and V1/V0 is a peripheral speed ratio. In this case, the peripheral speed of the auxiliary driving roller 340 is changed so that the peripheral speed ratio when the basis weight of the recording material is a first basis weight is a first peripheral speed ratio, and the peripheral speed ratio when the basis weight of the recording material is a second basis weight larger than the first basis weight is a second peripheral speed ratio larger than the first peripheral speed ratio.SELECTED DRAWING: Figure 2

Description

The present invention relates to a fixing device for fixing a toner image supported on a recording material to the recording material.

As a fixing device, a nip portion for sandwiching and transporting a recording material is formed between a fixing belt which is an endless belt and a pressure roll which abuts on the outer peripheral surface of the fixing belt, and toner is applied to the recording material passing through the nip portion. A configuration for fixing an image is known (Patent Document 1). The pressure roll has an elastic layer, and the elastic layer is elastically deformed to form the above-mentioned nip portion. Further, the pressure roll is a drive roller driven by a motor, and applies a driving force to the fixing belt by abutting with the fixing belt.

Japanese Unexamined Patent Publication No. 2014-228765

As described in Patent Document 1, when the pressure roll (driving roller) has an elastic layer, when the pressure roll (driving roller) passes through the nip portion of the recording material, the elastic layer starts to be distorted at the entrance of the nip portion, and the recording material has the nip portion. In the middle of passing through the elastic layer, the strain of the elastic layer is restored. Then, due to this behavior, a speed difference occurs between the recording material and the pressure roll, and there is a possibility that wear on the surface of the pressure roll is promoted. In particular, depending on the type of recording material, the amount of strain in the elastic layer may be large, or the range in which the elastic layer is distorted may be wide, so that the speed difference between the recording material and the pressure roll may be large.

An object of the present invention is to provide a configuration capable of suppressing a speed difference between a recording material and a driving roller regardless of the type of recording material.

The present invention is a fixing device for fixing a toner image carried on a recording material to the recording material, which has an endless and rotatable belt and an elastic layer, and rotates in contact with the outer peripheral surface of the belt. The drive roller that applies a driving force to the belt and the inside of the belt are arranged so as to face the drive roller with the belt sandwiched therein, and a recording material is placed between the belt and the drive roller. A nip portion forming member that forms a nip portion that is sandwiched and conveyed, and an auxiliary drive roller that is arranged inside the belt and stretches and rotates the belt together with the nip portion forming member to apply a driving force to the belt. When the peripheral speed of the drive roller is V0, the peripheral speed of the auxiliary drive roller is V1, and V1 / V0 is the peripheral speed ratio, the basis weight of the recording material conveyed by the nip portion is the first. In the case of the basis weight, the basis weight of the recording material conveyed by the nip portion is larger than the first basis weight so that the peripheral speed ratio becomes the first peripheral speed ratio. It is characterized in that the peripheral speed of the auxiliary drive roller is changed so that the peripheral speed ratio in a certain case becomes a second peripheral speed ratio larger than the first peripheral speed ratio.

Further, the present invention is a fixing device for fixing a toner image carried on a recording material to the recording material, which has an endless and rotatable belt and an elastic layer, and is in contact with the outer peripheral surface of the belt. A drive roller that rotates to apply a driving force to the belt and is arranged inside the belt so as to face the drive roller with the belt sandwiched therein, and is recorded between the belt and the drive roller. An auxiliary drive that is arranged inside the belt and stretches and rotates the belt together with the nip portion forming member that forms the nip portion that sandwiches and conveys the material, and applies a driving force to the belt. When the peripheral speed of the drive roller is V0, the peripheral speed of the auxiliary drive roller is V1, and V1 / V0 is the peripheral speed ratio, the recording material of the recording material conveyed by the nip portion is provided with a roller. In the width direction of the recording material transported by the nip portion, the peripheral speed ratio when the length in the width direction intersecting the transport direction is the first length becomes the third peripheral speed ratio. The auxiliary drive roller so that the peripheral speed ratio when the length is a second length longer than the first length is a fourth peripheral speed ratio larger than the third peripheral speed ratio. It is characterized by changing the peripheral speed of.

According to the present invention, the speed difference between the recording material and the drive roller can be suppressed regardless of the type of the recording material.

The schematic block sectional view of the image forming apparatus which concerns on 1st Embodiment. FIG. 6 is a schematic configuration sectional view of the fixing device according to the first embodiment. The schematic diagram which shows the relationship between a fixing pad and a fixing belt. The control block diagram which shows a part of the control structure of the image forming apparatus which concerns on 1st Embodiment. The graph which shows the strain amount of the elastic layer of a pressure roller with respect to the coordinate of a recording material transport direction in a nip part. FIG. 3 is a schematic configuration sectional view showing a drive transmission mechanism to the auxiliary drive roller according to the first embodiment. FIG. 3 is a schematic configuration sectional view showing a drive transmission mechanism to the pressure roller according to the first embodiment. (A) A schematic diagram showing an auxiliary driving force, and (b) a graph showing a relationship between a peripheral speed ratio and an auxiliary driving force. The schematic diagram for demonstrating the auxiliary driving force acting on a fixing belt. The graph which shows the relationship between the pressure roller and the slip amount of a recording material with respect to a peripheral speed ratio. The flowchart concerning the control of the fixing device which concerns on 1st Embodiment. The schematic diagram which shows the relationship between the width of a fixing belt and a recording material. The schematic diagram which shows the force acting on the fixing belt in the vicinity of a nip part. The graph which shows the relationship between the pressure roller and the slip amount of a recording material with respect to a peripheral speed ratio. The flowchart concerning the control of the fixing device which concerns on 2nd Embodiment.

<First Embodiment>
The first embodiment will be described with reference to FIGS. 1 to 11. First, the schematic configuration of the image forming apparatus of this embodiment will be described with reference to FIG.

[Image forming device]
The image forming apparatus 1 is an electrophotographic full-color printer having four image forming portions Pa, Pb, Pc, and Pd provided corresponding to four colors of yellow, magenta, cyan, and black. In the present embodiment, the image forming portions Pa, Pb, Pc, and Pd are arranged in a tandem type along the rotation direction of the intermediate transfer belt 204 described later. The image forming apparatus 1 responds to an image signal from a host device such as a personal computer that is communicably connected to the image reading unit (original reading apparatus) 2 connected to the image forming apparatus main body 3 or the image forming apparatus main body 3. A toner image (image) is formed on the recording material. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

The image forming apparatus 1 includes an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads a document placed on the platen glass 21, and the light emitted from the light source 22 is reflected by the document and imaged on the CCD sensor 24 via an optical system member 23 such as a lens. Will be done. By scanning in the direction of the arrow, such an optical system unit converts a document into an electric signal data string for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and the control unit 30 performs image processing according to each image forming unit described later. The control unit 30 also receives an external input from an external host device such as a print server as an image signal.

The image forming apparatus main body 3 includes a plurality of image forming units Pa, Pb, Pc, and Pd, and each image forming unit performs image forming based on the above-mentioned image signal. That is, the image signal is converted into a laser beam PWM (pulse width modulation control) by the control unit 30. The polygon scanner 31 as an exposure apparatus scans a laser beam according to an image signal. Then, the laser beams are applied to the photosensitive drums 200a to 200d as the image carriers of the image forming portions Pa to Pd.

Pa is a yellow (Y) image forming part, Pb is a magenta (M) image forming part, Pc is a cyan (C) image forming part, and Pd is a black (Bk) image forming part. , Each form an image of the corresponding color. Since the image forming units Pa to Pd are substantially the same, the details of the image forming unit Pa of Y will be described below, and the description of the other image forming units will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on the image signal as described below.

The charging roller 201a as the primary charging device charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for forming an electrostatic latent image. The laser beam from the polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a charged to a predetermined potential. The developer 202a develops an electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back surface of the intermediate transfer belt 204, applies a primary transfer bias having the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. The surface of the photosensitive drum 200a after transfer is cleaned with a cleaner 207a.

Further, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming section, and the toner images of each color formed in each image forming section are sequentially transferred in the order of Y, M, C, Bk, and 4 A color image is formed on its surface. Then, the toner image that has passed through the image forming unit Pd of Bk located at the most downstream in the rotation direction of the intermediate transfer belt 204 is conveyed to the secondary transfer unit composed of the secondary transfer rollers 205 and 206. Then, in the secondary transfer section, a secondary transfer electric field having a polarity opposite to that of the toner image on the intermediate transfer belt 204 is applied to perform secondary transfer to the recording material.

The recording material is housed in the cassette 9, and the recording material supplied from the cassette 9 is conveyed to, for example, a cash register unit 208 composed of a pair of registration rollers, and stands by at the cash register unit 208. After that, the cash register section 208 controls the timing in order to align the toner image on the intermediate transfer belt 204 with the paper, and the recording material is conveyed to the secondary transfer section.

The recording material on which the toner image is transferred in the secondary transfer unit is conveyed to the fixing device 8 and heated and pressurized in the fixing device 8 to fix the toner image supported on the recording material on the recording material. NS. The recording material that has passed through the fixing device 8 is discharged to the discharge tray 7. When image formation is performed on both sides of the recording material, when the transfer and fixing of the toner image to the first surface (front surface) of the recording material is completed, the front and back sides of the recording material are reversed via the reversing transport unit 10. The toner image is transferred and fixed on the second surface (back surface) of the recording material, and the toner image is loaded on the discharge tray 7.

[Fixing device]
Next, the configuration of the fixing device 8 in the present embodiment will be described with reference to FIG. In this embodiment, a belt heating type fixing device using an endless belt is adopted. In FIG. 2, the recording material is conveyed from right to left as indicated by the arrow α. The fixing device 8 has a heating unit 300 having a fixing belt 310 as an endless and rotatable belt, and a pressure roller as a pressure rotating body that comes into contact with the fixing belt 310 and forms a nip portion N together with the fixing belt 310. It has 330.

The heating unit 300 includes the above-mentioned fixing belt 310, a fixing pad 320 as a nip portion forming member and a pad member, an auxiliary drive roller 340 as a tension roller, and a steering roller 350. The pressure roller 330 is also a drive roller that abuts on the outer peripheral surface of the fixing belt 310 and rotates to apply a driving force to the fixing belt 310.

The fixing belt 310, which is an endless belt, has thermal conductivity, heat resistance, and the like, and has, for example, a thin cylindrical shape with an inner diameter of 120 mm. In the present embodiment, a three-layer structure is formed in which a base layer, an elastic layer is formed on the outer periphery of the base layer, and a release layer is formed on the outer periphery thereof. The base layer is 60 μm thick and the material is polyimide resin (PI), the elastic layer is 300 μm thick and silicone rubber, and the release layer is 30 μm thick and PFA (ethylene tetrafluoroalkoxy alkane) as a fluororesin. Ethylene copolymer resin) is used. Such a fixing belt 310 is stretched by a fixing pad 320, an auxiliary drive roller 340, and a steering roller 350.

The fixing pad 320 as a nip portion forming member is arranged inside the fixing belt 310 so as to face the pressure roller 330 with the fixing belt 310 sandwiched between them, and between the fixing belt 310 and the pressure roller 330. A nip portion N for sandwiching and transporting the recording material is formed. In the present embodiment, the fixing pad 320 is a substantially plate-shaped member that is long along the width direction of the fixing belt 310 (longitudinal direction intersecting the rotation direction of the fixing belt 310, rotation axis direction of the auxiliary drive roller 340). .. The nip portion N is formed by pressing the fixing pad 320 against the pressure roller 330 with the fixing belt 310 sandwiched between them. LCP (liquid crystal polymer) resin is used as the material of the fixing pad 320.

In the fixing pad 320, at least a part of the portion forming the nip portion N is formed in a flat shape. That is, the inner peripheral surface of the fixing belt 310 and the portion that comes into contact with each other via the lubricating sheet 370 described later are formed in a substantially flat shape, and the shape of the nip portion is substantially flat. With such a configuration, it is possible to suppress the occurrence of wrinkles and image shifts in the envelope, especially when the toner image is fixed on the envelope as a recording material.

The fixing pad 320 is supported by a stay 360 as a supporting member arranged inside the fixing belt 310. That is, the stay 360 is arranged on the side opposite to the pressure roller 330 of the fixing pad 320 and supports the fixing pad 320. Such a stay 360 is a reinforcing member having a long rigidity along the longitudinal direction of the fixing belt 310, and abuts on the fixing pad 320 to back up the fixing pad 320. That is, the stay 360 secures the pressing force at the nip portion N by giving the fixing pad 320 strength when the fixing pad 320 is pressed by the pressurizing roller 330.

The stay 360 is made of a metal such as stainless steel, and has a substantially rectangular cross section (cross section) orthogonal to the longitudinal direction of the stay 360 that intersects the rotation direction of the fixing belt 310. For example, the stay 360 uses a SUS304 (stainless steel) drawn material having a wall thickness of 3 mm, and the cross section is formed into a hollow shape having a substantially square shape to ensure strength. The stay 360 may be formed into a substantially rectangular cross section by combining a plurality of sheet metals and fixing them to each other by welding or the like. Further, the material of the stay 360 is not limited to stainless steel as long as the strength can be guaranteed.

Further, as shown in FIG. 3, both ends of the fixing pad 320 in the nip portion N in the recording material transport direction are curved surface shaped portions 320a and 320b, respectively. The curved surface shape portions 320a and 320b are curved surfaces that are curved in the direction away from the nip surface (upper in FIG. 3) toward the end portions, respectively. The nip surface is formed between the fixing belt 310 and the pressure roller 330, and is a surface along the surface (lower surface of FIG. 3) of the fixing pad 320 on the pressure roller 330 side.

As described above, in the present embodiment, the downstream end portion of the fixing pad 320 is a curved surface shape portion 320b, and the fixing belt 310 is curved by the curvature of the curved surface shape portion 320b. Then, the recording material that has passed through the nip portion N is separated from the fixing belt 310 by the curvature of the fixing belt 310.

A lubrication sheet 370 is interposed between the fixing pad 320 and the fixing belt 310. In the present embodiment, a PI (polyimide) sheet coated with PTFE (polytetrafluoroethylene) is used as the lubricating sheet 370, and the thickness is 100 μm. The PI sheet is formed with protrusions of 100 μm at 1 mm intervals, and the sliding resistance is reduced by reducing the contact area with the fixing belt 310.

Further, a lubricant is applied to the inner peripheral surface of the fixing belt 310 so that the fixing belt 310 slides smoothly with respect to the fixing pad 320 covered with the lubricating sheet 370. As the lubricating material, silicone oil having a viscosity of 100 cSt is used.

As shown in FIG. 2, the auxiliary drive roller 340 is arranged inside the fixing belt 310, and the fixing belt 310 is stretched together with the fixing pad 320 and the steering roller 350. As described above, since the inner peripheral surface of the fixing belt 310 is coated with a lubricant, the auxiliary drive roller 340 stretches the fixing belt 310 via the lubricant. Further, the auxiliary drive roller 340 is arranged downstream of the fixing pad 320 and upstream of the steering roller 350 in the rotation direction of the fixing belt 310. As a result, the fixing belt 310 that has passed through the nip portion N is directly pulled by the driving force of the auxiliary drive roller 340 without going through the tension roller in the middle.

The auxiliary drive roller 340 is formed in a cylindrical shape by a metal such as aluminum or stainless steel, and a halogen heater 340a as a heating source for heating the fixing belt 310 is arranged inside the auxiliary drive roller 340. Then, the auxiliary drive roller 340 is heated to a predetermined temperature by the halogen heater 340a. Such an auxiliary drive roller 340 is also a heating roller that heats the fixing belt 310.

In the present embodiment, the auxiliary drive roller 340 is formed of, for example, an aluminum pipe having an outer diameter of 40 mm and a thickness of 1 mm from the viewpoint of thermal conductivity, and the surface layer is anodized. Further, the number of halogen heaters 340a may be one, but it is desirable that there are a plurality of halogen heaters 340a in consideration of temperature distribution control in the longitudinal direction (rotational axis direction) of the auxiliary drive roller 340. A plurality of halogen heaters 340a provided have different light distributions in the longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. In this embodiment, two halogen heaters 340a are arranged. The heating source is not limited to the halogen heater, and may be another heater capable of heating the auxiliary drive roller 340, such as a carbon heater.

The fixing belt 310 is heated by an auxiliary drive roller 340 heated by a halogen heater 340a, and is controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor (not shown). Further, as will be described in detail later, the auxiliary drive roller 340 has a gear fixed to one end in the direction of the rotation axis, and is connected to the motor M1 as an auxiliary drive roller drive source via the gear to be rotationally driven. NS. Then, a driving force is applied to the fixing belt 310 by the rotation of the auxiliary driving roller 340. Here, the force applied from the auxiliary drive roller 340 to the fixing belt 310 is used as the auxiliary drive force.

The steering roller 350 is arranged inside the fixing belt 310, stretches the fixing belt 310 together with the fixing pad 320 and the auxiliary drive roller 340, and rotates in a driven manner of the fixing belt 310. The steering roller 350 tilts with respect to the rotation axis direction (longitudinal direction) of the auxiliary drive roller 340 to control the position (close position) of the fixing belt 310 with respect to the rotation axis direction. That is, the steering roller 350 has a rotation center at the center of the steering roller 350 in the rotation axis direction (longitudinal direction), and swings around the rotation center with respect to the longitudinal direction of the auxiliary drive roller 340. Tilt. As a result, a tension difference is generated between one side and the other side of the fixing belt 310 in the longitudinal direction, and the fixing belt 310 is moved in the longitudinal direction.

The fixing belt 310 tends to approach any end during rotation due to the outer diameter accuracy of the rollers to be stretched, the alignment accuracy between the rollers, and the like. Therefore, the steering roller 350 controls such a shift. The steering roller 350 may be oscillated by a drive source such as a motor, or may be oscillated by self-alignment. Further, the center of rotation may be the center in the longitudinal direction as in the present embodiment, or may be the end portion in the longitudinal direction.

Further, in the case of the present embodiment, the steering roller 350 is urged by a spring supported by the frame of the heating unit 300, and is also a tension roller that applies a predetermined tension to the fixing belt 310. By applying tension to the fixing belt 310 by the steering roller 350 in this way, the fixing belt 310 is made to follow the curved surface shape portions 320a and 320b of the fixing pad 320. That is, the fixing belt 310 is curved along the curved surface shape portions 320a and 320b.

Further, the steering roller 350 is formed in a cylindrical shape by a metal such as aluminum or stainless steel. In the present embodiment, the steering roller 350 is a stainless steel or aluminum pipe having an outer diameter of 40 mm and a thickness of 1 mm, and its end is rotationally supported by a bearing (not shown). The tension roller arranged at the position of the steering roller 350 may be a roller that does not have such a steering function.

The pressure roller 330 as a drive roller abuts on the outer peripheral surface of the fixing belt 310 and rotates to apply a driving force to the fixing belt 310. In the present embodiment, the pressure roller 330 is a roller in which an elastic layer is formed on the outer periphery of the shaft and a releasable layer is formed on the outer periphery thereof. The shaft is made of stainless steel, the elastic layer is 5 mm thick and uses conductive silicone rubber, and the release layer is 50 μm thick and uses PFA (ethylene tetrafluoroalkoxyethylene copolymer resin) as a fluororesin. ing. The pressurizing roller 330 is rotatably supported by a fixing frame 380 of the fixing device 8. As will be described in detail later, a gear is fixed to one end of the pressurizing roller 330, and a motor as a pressurizing roller drive source is provided via the gear. It is connected to M0 and driven to rotate.

The fixing frame 380 is provided with a heating unit positioning portion 381, a pressure frame 383, and a pressure spring 384. The heating unit 300 is positioned on the fixing frame 380 by inserting the stay 360 into the heating unit positioning unit 381 and fixing the stay 360 to the heating unit positioning unit 381 by a fixing means (not shown). Here, the heating unit positioning unit 381 has a pressurizing direction regulating surface 381a facing the pressurizing roller 330 and a transport direction regulating surface 381b which is an abutting surface in the insertion direction of the heating unit 300. The stay 360 is fixed to the pressurizing direction regulating surface 381a and the transport direction regulating surface 318b in a state where movement is restricted. At this time, the pressure roller 330 is separated from the fixing belt 310.

After the heating unit 300 is positioned on the heating unit positioning unit 381, the pressure roller 330 comes into contact with the fixing belt 310 by moving the pressure frame 383 by a drive source and a cam (not shown). Then, the pressure roller 330 is pressed against the fixing pad 320 via the fixing belt 310. That is, in the present embodiment, the pressurizing roller 330 is also a pressurizing member that pressurizes toward the fixing belt 310. In this embodiment, the pressing force at the time of image formation is 1000 N.

Further, in the case of the present embodiment, a separation device 400 having a separation member (separation plate in the present embodiment) 401 for separating the recording material from the fixing belt 310 is provided on the downstream side of the nip portion N in the recording material transport direction. The separation member 401 is arranged with a gap from the outer peripheral surface of the fixing belt 310, and separates the recording material that has passed through the nip portion N from the fixing belt. Specifically, the separating member 401 is arranged close to the portion of the outer peripheral surface of the fixing belt 310 that is stretched between the fixing pad 320 and the auxiliary drive roller 340. Further, the separating member 401 is formed in a blade shape, and the tip thereof faces the outer peripheral surface of the fixing belt 310. Further, on the separating member 401, a fluorine-based tape is attached to a metal plate in order to prevent toner adhesion of the recording material and image scratches due to sliding. In the present embodiment, in order to arrange the separating member 401 with a gap from the outer peripheral surface of the fixing belt 310 in this way, the recording material is positioned in the transport direction (the lateral direction of the stay 360, the X direction) with respect to the stay 360. I try to do it.

The fixing device 8 configured as described above sandwiches the recording material P carrying the toner image in the nip portion N formed between the fixing belt 310 and the pressure roller 330, and conveys the toner image while conveying the toner image. Heat. As a result, the toner image is melted and fixed to the recording material. In the case of the present embodiment, the peripheral speed of the fixing belt 310 at the time of image formation is 300 mm / s, the pressing force at the nip portion N is 1000 N, and the temperature of the fixing belt 310 is 180 ° C.

[Control unit]
Next, the control configuration of the fixing device 8 of the control unit 30 of the image forming apparatus 1 will be described with reference to FIG. The control unit 30 has a memory 33 such as a CPU 32 (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory).

The CPU 32 acquires various data input by the operation unit 4 and the display unit 5 and stores them in the memory 33. The operation unit 4 and the display unit 5 are provided in the image forming apparatus 1, and are, for example, touch panels and buttons capable of touch operation.

Further, the CPU 32 can read a print (image formation) program (for example, FIG. 10 described later) from the memory 33 and execute it in response to a startup operation such as turning on the power of the image forming apparatus 1 by the user.

The memory 33 stores, for example, various programs such as a print program and an image forming job, and various data such as a peripheral speed ratio control table (Table 2) of the motors M0 and M1 described later. The memory 33 can also temporarily store the calculation processing results and the like accompanying the execution of various programs.

In the case of the present embodiment, the CPU 32 controls the operation of the image forming apparatus 1 regarding printing on the recording material by executing the printing program. The print program is not limited to the form of a software program, and can be implemented, for example, in the form of a microprogram processed by a DSP (digital signal processor). Therefore, the CPU 32 may be used in combination with one that executes a control program such as an image forming job to perform various controls such as an image forming operation, but is not limited to this, and is prepared exclusively for executing a printing program. May be used.

The peripheral speed ratio control unit 32a sets the auxiliary drive roller 340 so that the peripheral speed (peripheral speed) of the pressurizing roller 330 and the peripheral speed (peripheral speed) of the auxiliary drive roller become a desired peripheral speed ratio (peripheral speed ratio). The driving motor M1 can be controlled. Specifically, the peripheral speed ratio control unit 32a is based on the acquired information such as the basis weight of the recording material, and is based on the peripheral speed ratio control table (data) of the motor M0 and the motor M1 as shown in Table 2 described later. Controls M0 and M1.

[Distortion of elastic layer of pressure roller]
Next, the strain of the elastic layer of the pressure roller when the recording material is passed through the nip portion N will be described with reference to FIG. In FIG. 5, in the comparative example, in the configuration shown in FIG. 2, the auxiliary driving roller 340 does not have an auxiliary driving force. That is, the fixing belt is driven only by the pressure roller. On the other hand, in the embodiment, as shown in FIG. 2, the auxiliary drive roller 340 has an auxiliary drive force.

FIG. 5 shows the amount of strain of the elastic layer of the pressure roller from the inlet to the outlet of the nip portion with respect to the transport direction of the recording material when the recording material is passed through the nip portion in each of the comparative example and the embodiment. .. From FIG. 5, the strain amount of the elastic layer of the pressure roller in the comparative example gradually increases from the inlet of the nip portion to the center of the nip portion, and the strain amount is eliminated and restored from the center of the nip portion to the downstream portion. You can see that. At this time, from the inlet of the nip portion to the center of the nip portion, the pressure roller moves while accumulating the strain of the elastic layer and following the recording material. On the other hand, from the center of the nip portion to the downstream portion, the pressure roller moves while releasing the accumulated strain amount of the elastic layer toward the downstream portion in the transport direction. Therefore, from the center of the nip portion to the downstream portion, the peripheral speed of the pressurizing roller exceeds the transport speed of the recording material. As a result, the recording material cannot follow the transport speed of the pressure roller and slips, and the wear of the surface layer of the pressure roller is promoted.

In particular, when the basis weight of the recording material is large as in thick paper, the strain of the elastic layer of the pressure roller when the recording material passes through the nip portion is also large. Therefore, the increase in the peripheral speed of the pressure roller due to the release of strain tends to increase as the basis weight of the recording material increases. Therefore, the larger the basis weight of the recording material, the larger the amount of slip that occurs when the recording material cannot follow the speed of the pressure roller, that is, the amount of slip between the pressure roller and the recording material.

Here, in general, the surface layer of the pressure roller wears over time due to the passage of the recording material. In particular, the portion corresponding to the edge of the recording material is likely to be worn due to the polishing effect due to the burr of the recording material and the concentration of deformation stress on the surface layer due to the thickness of the recording material. Therefore, as described above, if the recording material passing through the nip portion slips without being able to follow the speed of the pressure roller, the wear of the surface layer of the pressure roller is further promoted. If the surface layer of the pressure roller continues to wear, it may affect the fixed image.

On the other hand, in the embodiment, by setting the peripheral speed of the auxiliary drive roller 340 arranged so as to come into contact with the inner peripheral surface of the fixing belt 310 to be high, the auxiliary driving force from the auxiliary driving roller 340 to the fixing belt 310 is applied. I try to give. By applying the auxiliary driving force to the fixing belt 310 in this way, the transport speed of the recording material can be made to follow the speed of the pressure roller 330, and the acceleration of wear of the surface layer of the pressure roller by the recording material can be suppressed.

The graph of the broken line in FIG. 5 shows the amount of strain in the elastic layer of the pressure roller in the present embodiment. As can be seen from FIG. 5, by applying an auxiliary driving force to the fixing belt, the amount of strain in the elastic layer of the pressure roller at the nip portion was reduced, and at the same time, the amount of strain released was also reduced. That is, since the recording material follows the speed of the pressure roller, the amount of strain in the elastic layer of the pressure roller is reduced, and the amount of strain is reduced, so that the amount of strain released is also reduced. As a result, it was found that the occurrence of a difference between the transport speed of the recording material and the transport speed of the pressurizing roller was reduced, and the wear of the surface layer of the pressurizing roller was suppressed.

[Outline of the present embodiment]
The outline of this embodiment will be described below. By setting the peripheral speed V1 of the auxiliary drive roller arranged on the inner peripheral surface side of the fixing belt 310 faster than the peripheral speed V0 of the pressure roller 330 that drives and rotates the fixing belt 310, the auxiliary drive roller 340 can be used. An auxiliary driving force is applied to the fixing belt 310.

As described above, in the present embodiment, by applying an auxiliary driving force to the fixing belt 310, the amount of distortion of the elastic layer of the pressure roller 330 generated at the nip portion N of the fixing belt 310 is reduced, and the transport speed at the nip portion is reduced. The difference can be suppressed. Thereby, it is an object of the present embodiment to reduce wear due to slippage that occurs between the recording material and the pressure roller 330.

First, a drive configuration for rotationally driving the auxiliary drive roller 340 and the pressure roller 330 for applying the auxiliary drive force to the fixing belt 310 will be described.

[Auxiliary drive roller drive configuration]
FIG. 6 shows an example of the auxiliary drive roller drive unit 410 that rotationally drives the auxiliary drive roller 340. A gear 385a is fixed to one end of the shaft of the auxiliary drive roller 340, and the auxiliary drive roller 340 is rotationally driven by being connected to a motor M1 which is a drive source for driving the auxiliary drive roller via an auxiliary drive roller drive gear train 385. The motor M1 is a drive motor independent of the motor M0, which is a drive source for driving the pressurizing roller, and is fixed to the mounting plate 386.

A gear 385c is fixed to the output shaft of the motor M1, and the gear 385c and the gear 385b are engaged with each other. The gear 385b is rotatably supported by a fixed shaft fixed to a frame 382 supporting the heating unit 300 and a mounting plate 386, and meshes with the gear 385c and the gear 385a to transmit a rotational driving force to the auxiliary drive roller 340. .. From the above, the drive transmission mechanism of the auxiliary drive roller 340 is composed of the motor M1 and the auxiliary drive roller drive gear train 385.

Further, the peripheral speed of the auxiliary drive roller 340 in the present embodiment is changed by controlling the rotation speed of the motor M1 without using a speed change mechanism using a speed change gear. As an example, Table 1 shows the motor rotation speed of the motor M1 and the rotation speed and peripheral speed of the auxiliary drive roller 340 when a recording material having a basis weight of 81 g / m ^{2 (gsm) or less is passed through the nip portion.}

At this time, the motor rotation speed of the motor M1 is set to 1970 rpm, and the rotation speed of the auxiliary drive roller 340 is 191.1 rpm by being driven and transmitted by the auxiliary drive roller drive gear train 385, and the peripheral speed at that time is 400 mm / s. Become.

The motor rotation speed of the motor M1 is controlled by the control unit 30 so that the peripheral speed of the pressurizing roller 330 satisfies a predetermined peripheral speed ratio with respect to the peripheral speed of the auxiliary drive roller 340. Further, the gears constituting the auxiliary drive roller drive gear train 385 may be of any gear type such as a spur tooth gear and a helical tooth gear.

[Pressure roller drive configuration]
FIG. 7 shows an example of a pressure roller drive unit 420 that rotationally drives the pressure roller 330. A gear 387a is fixed to one end of the shaft of the pressure roller 330, and the pressure roller 330 is rotationally driven by being connected to a motor M0, which is a drive source for driving the pressure roller, via a pressure roller drive gear train 387. The motor M0 is fixed to the mounting plate 388.

A gear 387e is fixed to the output shaft of the motor M0, and the gear 387e and the gear 387d are engaged with each other. The gears 387b, 387c, and 387d are rotatably supported by a fixed shaft fixed to the fixing frame 380 and the mounting plate 388, and engage with the gear 387d, the gear 387c, and the gear 387b to apply a rotational driving force to the pressurizing roller 330. introduce. From the above, the drive configuration of the pressurizing roller 330 is composed of the motor M0 and the pressurizing roller drive gear train 387.

The number of gears in the pressurizing roller drive gear row 387 is larger than that in the auxiliary drive roller drive gear row 385 in order to increase the reduction ratio and increase the drive torque of the pressurizing roller 330. If the drive torque of the motor M0 is large, the number of gears may be reduced, and the gear train of the pressurizing roller may be configured in the same manner as the gear train of the auxiliary drive roller.

Further, the peripheral speed of the pressure roller 330 in the present embodiment is changed by controlling the rotation speed of the motor M0 without using a speed change mechanism using a speed change gear. As an example, Table 1 above shows the motor rotation speed of the motor M0, the rotation speed of the pressurizing roller 330, and the peripheral speed when a recording material having a ^{basis weight of 81 g / m 2 (gsm) or less is passed through the nip portion.}

At this time, the motor rotation speed of the motor M0 is set to 2620 rpm, and the rotation speed of the pressure roller 330 becomes 127.4 rpm by being driven and transmitted by the pressure roller drive gear train 387, and the peripheral speed at that time is 400 mm / s. Become.

The motor rotation speed of the motor M0 is controlled by the control unit 30 so that the peripheral speed of the pressurizing roller 330 satisfies a predetermined peripheral speed ratio with respect to the peripheral speed of the auxiliary drive roller 340. Further, the gears constituting the pressure roller drive gear train 387 may be of any gear type such as a spur tooth gear and a tooth tooth gear.

[Peripheral speed ratio between pressure roller and auxiliary drive roller]
Next, the peripheral speed ratio of the pressure roller 330 and the auxiliary drive roller 340 will be described. First, in the present embodiment, when the peripheral speed of the pressurizing roller 330 is V0 and the peripheral speed of the auxiliary drive roller 340 is V1, the relationship of V1 ≧ V0 is satisfied, and the ratio of the peripheral speed by V0 and V1 is the peripheral speed. The ratio is V1 / V0. Then, the peripheral speed ratio V1 / V0 when the basis weight of the recording material conveyed by the nip portion N is the first basis weight is set as the first peripheral speed ratio. Further, when the basis weight of the recording material conveyed by the nip portion N is the second basis weight larger than the first basis weight, the peripheral speed ratio V1 / V0 is larger than the first peripheral speed ratio. The peripheral speed ratio of.

In the present embodiment, the peripheral speed V0 of the pressurizing roller 330 is set to the peripheral speed according to the process speed, and the peripheral speed V1 of the auxiliary drive roller 340 is changed to change the peripheral speed ratio V1 / V0. ing. For example, if the process speed is the same for the recording material of the first basis weight and the recording material of the second basis weight, the auxiliary drive roller 340 is used for the recording material of the second basis weight having a large basis weight. By increasing the peripheral speed V1, the peripheral speed ratio V1 / V0 is increased. Further, the relationship between the peripheral speeds V0 and V1 satisfies V1 ≧ V0.

This will be described in detail. In the present embodiment, when the basis weight of the recording material is ^{less than 81 g / m 2} , the peripheral speed ratio is set to 100%. At this time, the rotation speeds of the motors M0 and M1 are controlled so that the peripheral speed of the pressurizing roller 330 is 400 mm / s and the peripheral speed of the auxiliary drive roller 340 is also 400 mm / s.

Next, when the basis weight of the recording material is 81 g / m ² or more and less than 400 g / m ² , the peripheral speed ratio is set to 110%. At this time, the rotation speeds of the motors M0 and M1 are controlled so that the peripheral speed of the pressure roller 330 is 400 mm / s and the peripheral speed of the auxiliary drive roller 340 is 440 mm / s.

When the basis weight of the recording material is 400 g / m ² or more, the peripheral speed ratio is 115%. At this time, the rotation speeds of the motors M0 and M1 are controlled so that the peripheral speed of the pressure roller 330 is 300 mm / s and the peripheral speed of the auxiliary drive roller 340 is 345 mm / s.

The reason why the peripheral speed of the pressurizing roller 330 is slower than other basis weights when the basis weight of the recording material is 400 g / m ² or more is that toner is used even for recording materials such as thick paper where heat is difficult to transfer. This is to satisfy the fixing property of. That is, in the case of a recording material such as thick paper, which is difficult to transfer heat, the process speed of the image forming apparatus is lowered so that the nip portion is passed at a low speed. Then, a sufficient amount of heat is given to the recording material to ensure fixability.

Table 2 shows the relationship between the basis weight of the recording material, the peripheral speed ratio, the peripheral speed of the motor M0, and the peripheral speed of the motor M1 in the present embodiment.

[Relationship between peripheral speed ratio and auxiliary driving force]
Next, the relationship between the peripheral speed ratio of the pressure roller 330 and the auxiliary drive roller 340 and the auxiliary driving force applied to the fixing belt 310 will be described with reference to FIGS. 8 (a), 8 (b) and 9. In the present embodiment, as shown in FIG. 8A, the auxiliary drive roller 340 applies an auxiliary drive force to the fixing belt 310 to reduce the sliding resistance of the nip portion on the inner peripheral surface of the belt, thereby reducing the sliding resistance of the pressure roller. The increase in the transport speed at the nip portion of the 330 is reduced.

When the peripheral speed ratio control is executed, the fixing belt 310 follows the pressure roller 330, so that a peripheral speed difference occurs between the fixing belt 310 and the auxiliary drive roller 340. Therefore, the auxiliary drive roller 340 is driven at a set peripheral speed ratio while slipping on the inner peripheral surface of the fixing belt 310. On the other hand, the auxiliary drive roller 340 is formed on the fixing belt 310 by interposing a lubricant between the inner peripheral surface of the fixing belt 310 and providing friction with the lubricant and a winding angle with respect to the fixing belt 310 described later. It is possible to provide the desired auxiliary driving force.

The effect of the auxiliary driving force due to the rotational drive of the auxiliary drive roller 340 is shown below. FIG. 8B shows the relationship of the auxiliary driving force with respect to the peripheral speed ratio. The auxiliary driving force was calculated from the on-axis torque applied when the auxiliary drive roller 340 was driven and the diameter of the auxiliary drive roller 340. From FIG. 8B, it can be confirmed that the auxiliary driving force increases as the peripheral speed ratio increases.

The auxiliary driving force will be described with reference to Euler's belt theory equation shown in equation (1) and FIG.

Here, Tt is the tension on the tension side applied to the fixing belt 310 by driving the auxiliary drive roller 340, and Te is the effective tension (friction force). θ is a winding angle which is an angle formed with the center of the roller by winding the fixing belt 310 around the auxiliary drive roller 340, and μ indicates a friction coefficient. Tc is the tension of the fixing belt 310 that acts as a horizontal component of the centrifugal force that acts radially on the belt. Further, m is the mass per unit length of the belt, and v is the speed (peripheral speed) of the belt.

From the equation (1), the tension Tt on the tension side increases as the friction coefficient μ and the winding angle θ increase. Further, since the Tt increases as the peripheral speed of the fixing belt 310 increases, as shown in FIG. 8B, the auxiliary driving force can be increased as the peripheral speed ratio is increased.

[Effect of improving slip amount by auxiliary drive roller]
Next, the effect of improving slippage between the recording material and the pressure roller 330 by applying an auxiliary driving force to the fixing belt 310 will be described with reference to FIG. FIG. 10 shows the amount of slip between the recording material passing through the nip and the pressure roller 330 when the peripheral speed ratio is changed with respect to the basis weight of the recording material, and the basis weight of the recording material is 81 g / m ^2. , The ratio is shown based on the case where the peripheral speed ratio is 100%. In other words, the ratio of the slip amount is 100% when the basis weight of the recording material is 81 g / m ² , that is, the peripheral speed of the pressure roller 330 and the peripheral speed of the auxiliary drive roller 340 are the same. , The ratio to the slip amount when the recording material is passed through the nip portion N.

From FIG. 10, when the peripheral speed ratio V1 / V0 of the auxiliary drive roller 340 with respect to the pressure roller 330 is increased, the slip amount decreases regardless of the basis weight of the recording material. This is because by applying an auxiliary driving force to the fixing belt 310, the sliding resistance generated on the inner peripheral surface of the fixing belt 310 is reduced, and as a result, the transfer speed difference between the pressure roller 330 and the nip portion of the recording material is increased. This is because it has been reduced.

As shown in FIG. 10, when the case where the peripheral speed ratio is 100% is set as the first peripheral speed ratio, ^{a recording material having a basis weight of 400 g / m 2} at this first peripheral speed ratio is passed through the nip portion. The amount of slippage when the material is allowed to slide is about 10% larger than the basis weight of the recording material having a basis weight of 81 g / m ^2. On the other hand, the peripheral speed ratio is increased to about 110%, which is the second peripheral speed ratio larger than the first peripheral speed ratio. Then, the slip amount when the recording material having a basis weight of 400 g / m ² is passed through the nip portion is the case where ^{the recording material having a basis weight of 81 g / m 2} is passed through the nip portion at the first peripheral speed ratio. Can be equal to the amount of slippage. The first peripheral speed ratio and the second peripheral speed ratio are not limited to the above values and can be set as appropriate.

As described above, the slip amount is reduced by increasing the peripheral speed ratio between the pressure roller 330 and the auxiliary drive roller 340 by the auxiliary driving force regardless of the basis weight of the recording material. However, when the peripheral speed ratio is uniformly set to be high, there is a concern that the life of the lubricating sheet 370 may be shortened due to the increase in the mileage of the fixing belt 310. Therefore, in the present embodiment, in consideration of shortening the life of the lubricating sheet 370, the peripheral speed ratio of the pressurizing roller 330 and the auxiliary drive roller 340 is set to at least two speeds or more. Then, the peripheral speed ratio is changed according to the basis weight of the recording material. Specifically, as shown in Table 2, the peripheral speed ratio is set in three stages according to the basis weight of the recording material.

[Peripheral speed ratio control]
Next, the control of the peripheral speed ratio of the present embodiment will be described with reference to FIGS. 2 and 4 with reference to FIG. FIG. 11 shows an example of control of the fixing device 8 from the start of the image forming job to the end of the job after the basis weight of the recording material is input.

The control unit 30 starts the image forming job when, for example, the start key of the operation unit 4 is operated, and ends the image forming job when the image forming operation on the recording material at the end of the image forming job is completed. The image formation job is a period from the start of image formation to the completion of image formation based on the print signal (image formation signal) that forms an image on the recording material. That is, the image forming job performs a series of operations of a pre-operation (forward rotation) performed before the image forming operation, an image forming operation, and a post-operation (rear rotation) performed after the image forming operation by inputting the image forming signal. The period.

In the image forming apparatus 1 (FIG. 1), the control unit 30 displays an input screen or the like on the display unit 5, and receives information such as the paper type and basis weight of the recording material through the displayed input screen. Then, the control unit 30 stores the information in the memory 33 (S1). Next, the control unit 30 acquires information on the paper type and basis weight of the recording material from the memory 33 (S2). Further, the control unit 30 reads the peripheral speed ratio control table (for example, Table 2) from the memory 33 (S3).

The control unit 30 determines whether the basis weight of the acquired recording material is 81 g / m ² or less (S4). When the basis weight is 81 g / m ² or less (YES in S4), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 100% (S5). When the basis weight is ^{larger than 81 g / m 2} (NO in S4), the control unit 30 determines whether the basis weight of the acquired recording material is 400 g / m ² or less (S6). When the basis weight is 400 g / m ² or less (YES in S6), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 110% (S7). When the basis weight is ^{larger than 400 g / m 2} (NO in S6), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 115% (S8). The peripheral speed ratio control unit 32a sets the rotation speeds of the motor M0 and the motor M1 so as to obtain the set peripheral speed ratio (S9).

Then, the control unit 30 determines whether or not the start of the image forming job by the user operation is instructed (S10). When the start of the image formation job is not instructed (NO in S10), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S11), and the motor M0 and the motor M0 and the peripheral speed ratio are set to the set peripheral speed ratio. The rotation speed of the motor M1 is set (S12). After that, the control unit 30 repeats the processes of S1 to S9 described above. When the start of the image forming job is instructed (YES in S10), the motor M0 and the motor M1 are driven at the set rotation speed (S13).

Next, the control unit 30 determines whether the image forming job has been completed (S14). If the image formation job has not been completed (NO in S14), the end of the image formation job is awaited. When the image formation job is completed (YES in S14), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S15), and rotates the motor M0 and the motor M1 so as to obtain the set peripheral speed ratio. The number is set (S16), and the driving of the motors M0 and M1 is stopped (S17). Then, the control unit 30 ends this control.

In the case of the present embodiment as described above, the speed difference between the recording material and the pressure roller 330 can be suppressed regardless of the type of the recording material. Then, the amount of slippage of the recording material with respect to the pressure roller 330 can be reduced, and the promotion of wear on the surface of the pressure roller 330 can be suppressed. That is, when the basis weight of the recording material is large, the amount of sliding of the recording material with respect to the pressure roller 330 tends to be large, but in the case of the present embodiment, the peripheral speed ratio is increased, that is, the auxiliary drive roller. The peripheral speed with respect to the pressure roller 330 of 340 is increased. As a result, the auxiliary driving force acting on the fixing belt 310 is increased so that the recording material can easily follow the pressure roller 330 even if the basis weight of the recording material is large. As a result, it is possible to suppress the acceleration of wear of the surface layer of the pressure roller due to the recording material.

The peripheral speed ratio to the basis weight of the recording material described above is an example, and is not uniquely determined by the configuration of the fixing device or the like. Further, the effect of the present embodiment is not limited to the above-mentioned peripheral speed ratio, and the relationship between the peripheral speed V0 of the pressurizing roller 330 and the peripheral speed V1 of the auxiliary drive roller 340 may satisfy V0 ≦ V1. ..

<Second embodiment>
The second embodiment will be described with reference to FIGS. 1, 2, and 4 with reference to FIGS. 12 to 15. In the above-described embodiment, the peripheral speed ratio is changed according to the basis weight of the recording material, but in the present embodiment, the peripheral speed ratio is changed according to the length in the width direction of the recording material intersecting the transport direction of the recording material. I am trying to change it. Since other configurations and operations are the same as those of the first embodiment described above, the same configurations are designated by the same reference numerals to omit or simplify the description and illustration, and the same configurations are different from those of the first embodiment. The explanation will focus on the points.

In this embodiment, in addition to the control of the first embodiment, the peripheral speed ratio is adjusted to an appropriate value according to the length in the width direction orthogonal to the transport direction of the recording material (hereinafter, also referred to as the width of the recording material). It is an addition of a sequence that is controlled to be controlled. First, with reference to FIG. 12, the point that the width of the recording material affects the speed difference between the recording material and the pressure roller 330 at the nip portion will be described.

FIG. 12 is a schematic view of the fixing device 8 as viewed from the fixing belt 310 side (upper side of FIG. 2). When the recording material P is conveyed and sandwiched between the nip portions N, the pressure roller 330 and the fixing belt 310 come into direct contact with each other in the regions A at both ends of the nip portion N in the width direction. On the other hand, since the recording material P is inserted in the central region B, the pressure roller 330 and the fixing belt 310 do not come into direct contact with each other. When the width of the recording material P is large, the contact area A becomes small, and when the width of the recording material P becomes small, the contact area A becomes large.

Here, in the central region B, the recording material P is inserted between the pressure roller 330 and the fixing belt 310, and the driving force is not directly transmitted from the pressure roller 330 to the fixing belt 310. On the other hand, in the contact region A, since the pressure roller 330 and the fixing belt 310 are in contact with each other, the driving force is directly transmitted from the pressure roller 330 to the fixing belt 310.

Therefore, when the width of the recording material P is large, the contact region A between the pressure roller 330 and the fixing belt 310 is relatively small, and the central region B is large, so that the drive transmitted from the pressure roller 330 to the fixing belt 310 is large. The force is relatively small. On the contrary, when the width of the recording material P is small, the contact region A is relatively large and the central region B is small, so that the region where the pressure roller 330 and the fixing belt 310 are in contact with each other is relatively large. .. Therefore, the driving force transmitted from the pressure roller 330 to the fixing belt 310 becomes relatively large.

FIG. 13 shows a diagram showing the relationship between the forces applied to the fixing belt 310. In the vicinity of the nip portion N, the fixing belt driving force F1, the auxiliary driving force F2, and the sliding resistance F3 are applied to the fixing belt 310, and the following relationship is satisfied. F1 is the driving force applied to the fixing belt 310 from the pressurizing roller 330, F2 is the driving force applied to the fixing belt 310 from the auxiliary drive roller 340, and F3 is the fixing pad 320 covered with the fixing belt 310 and the lubricating sheet 370. It is a sliding resistance between and. Further, V2 is the peripheral speed of the fixing belt 310.
F1 + F2-F3∝V2

When the peripheral speed of the pressure roller 330 is constant, if the width of the recording material P is small, the contact region A is large, so that the fixing belt driving force F1 is increased as compared with the case where the width of the recording material P is large. Therefore, even if the auxiliary driving force F2 by the auxiliary drive roller 340 is reduced by that amount, the peripheral speed V2 of the fixing belt 310 can be brought close to the peripheral speed of the pressure roller 330. If the peripheral speed of the fixing belt 310 can be brought close to the peripheral speed of the pressure roller 330, the increase in the peripheral speed due to the strain in the elastic layer of the pressure roller 330 can be suppressed, and the amount of slippage of the recording material with respect to the pressure roller 330 also increases. It can be suppressed. In other words, by changing the auxiliary driving force F2 according to the width of the recording material, that is, by changing the peripheral speed ratio of the auxiliary driving roller 340 to the pressure roller 330, the slip amount of the recording material with respect to the pressure roller 330 can be recorded. Can be made equal regardless of the width of.

Therefore, in the present embodiment, when the peripheral speed of the pressurizing roller 330 is V0 and the peripheral speed of the auxiliary drive roller 340 is V1, the relationship of V1 ≧ V0 is satisfied, and the ratio of the peripheral speed due to V0 and V1 is calculated. The speed ratio is V1 / V0. Then, the peripheral speed ratio V1 / V0 when the length in the width direction of the recording material conveyed by the nip portion N is the first length is set as the third peripheral speed ratio. Further, when the length in the width direction of the recording material conveyed by the nip portion is the second length longer than the first length, the peripheral speed ratio V1 / V0 is larger than the third peripheral speed ratio. The peripheral speed ratio is 4.

Further, also in the present embodiment, the peripheral speed ratio V1 / V0 is changed by setting the peripheral speed V0 of the pressurizing roller 330 to the peripheral speed according to the process speed and changing the peripheral speed V1 of the auxiliary drive roller 340. I try to do it. For example, if the length (width) in the width direction is the same for the recording material having the first length and the recording material having the second length, the recording material having a larger width can be used as the recording material having a second length. On the other hand, by increasing the peripheral speed V1 of the auxiliary drive roller 340, the peripheral speed ratio V1 / V0 is increased. Further, the relationship between the peripheral speeds V0 and V1 satisfies V1 ≧ V0.

Further, in the present embodiment, the peripheral speed ratio V1 / V0 is set for each basis weight of the recording material, and further, for the recording material having the same basis weight, the peripheral speed ratio V1 / V0 is set for each width of the recording material. I am trying to change. For example, when the recording materials have the same basis weight, the larger the length of the recording material in the width direction, the larger the peripheral speed ratio.

Similar to FIG. 10, FIG. 14 shows the amount of slip between the recording material passing through the nip portion and the pressure roller 330 when the peripheral speed ratio is changed with respect to the basis weight of the recording material. The ratio is based on the case where the amount is 81 g / m ² and the peripheral speed ratio is 100%. Further, the small size paper indicates that it is a recording material (paper in this case) having a narrower width than the example shown in FIG. In FIG. 14, in addition to the example shown in FIG. 10, an example of a small size paper ^{having a basis weight of 400 g / m 2 is added.}

Compared with the slip amount of the basis weight of 400 g / m ² shown in FIG. 10, the slip amount of the small size paper having the basis weight of 400 g / m ^{2 is smaller.} This is because, as described above, when the width of the small size paper, that is, the recording material is narrow, the fixing belt driving force F1 is increased as compared with the case where the recording material having a large width is passed through the nip portion.

As described with reference to FIG. 10, in order to make the slip amount equivalent to the slip amount when the peripheral speed ratio is 100% ^{at a basis weight of 81 g / m 2 , when the basis weight is 400 g / m 2} which is not a small size paper, the circumference is changed. It was necessary to increase the speed ratio to about 110% (for example, the second peripheral speed ratio). On the other hand, in the case of small size paper with a basis weight of 400 g / m ² , the peripheral speed ratio can be increased to about 106% (for example, the third peripheral speed ratio), which is lower than the second peripheral speed ratio. The slip amount is equivalent to that of a recording material having a basis weight of 81 g / m ^2.

Therefore, in the case of the recording material having a basis weight of 400 g / m ² in FIG. 14, the peripheral speed ratio is set to the third peripheral speed ratio when the recording material is small size paper, and the peripheral speed ratio is set to the peripheral speed ratio when it is not small size paper. Is set to the second peripheral speed ratio (corresponding to the fourth peripheral speed ratio), which is larger than the third peripheral speed ratio. Further, in the third peripheral speed ratio, the peripheral speed ratio at a basis weight of 81 g / m ² is larger than 100% (for example, the first peripheral speed ratio). By setting the peripheral speed ratio in this way, even if the basis weight and the length of the recording material in the width direction are different, the slip amount of the recording material can be made the same.

On the other hand, the amount of slippage decreases by increasing the peripheral speed ratio regardless of the basis weight of the recording material. However, when the peripheral speed ratio is uniformly set to be high, there is a concern that the life of the lubricating sheet 370 may be shortened due to the increase in the mileage of the fixing belt 310. Therefore, it is desirable not to increase the peripheral speed ratio more than necessary. Therefore, even if the basis weight of the recording material is large, such as a recording material having a basis weight of 400 g / m ² , it is preferable to set the peripheral speed ratio low if the width of the recording material is small.

Based on the above, in the fixing device 8 of the present embodiment, the basis weight of the recording material, the length in the width direction (paper width), the peripheral speed ratio, and the motor M0 for suppressing the surface layer wear of the pressure roller 330. Table 3 shows the relationship between the peripheral speeds of the motor M1. The condition that the paper width is 210 mm or more is the same as the numerical value shown in Table 2 in the first embodiment.

As is clear from Table 3, the peripheral speed ratio is slightly smaller so that the slip amount between the pressure roller 330 and the recording material for each basis weight is appropriate under the condition that the paper width is 210 mm or less. ..

When the basis weight of the recording material ^{is less than 81 g / m 2, the} slip amount is sufficiently small even if the paper width is less than 210 mm, so the peripheral speed ratio is set to 100% in order to satisfy the condition of V1 ≧ V0.

And if the basis weight of the recording material is less than 81 g / ^{m 2} or more 400 g / ^{m 2,} in the case of 400 g / ^{m 2} or more, and if the paper width is more than 210mm, respectively, the peripheral speed ratio between the case of less than 210mm I'm making a difference.

In the present embodiment, the desired pressure roller 330 surface layer wear can be sufficiently realized only by dividing the paper width into two levels of less than 210 mm and 210 mm or more, so the level is limited to two levels. However, depending on the device configuration, it may be subdivided into a plurality of levels as appropriate.

[Peripheral speed ratio control]
Next, the control of the peripheral speed ratio of the present embodiment will be described with reference to FIGS. 2 and 4 with reference to FIG. FIG. 15 shows an example of control of the fixing device 8 from the start of the image forming job to the end of the job after the basis weight of the recording material is input.

The control unit 30 starts the image forming job when, for example, the start key of the operation unit 4 is operated, and ends the image forming job when the image forming operation on the recording material at the end of the image forming job is completed.

In the image forming apparatus 1 (FIG. 1), the control unit 30 displays an input screen or the like on the display unit 5, and receives information such as the paper type, basis weight, and paper width of the recording material through the displayed input screen. Then, the control unit 30 stores the information in the memory 33 (S21). Next, the control unit 30 acquires information on the paper type, basis weight, and paper width of the recording material from the memory 33 (S22). Further, the control unit 30 reads the peripheral speed ratio control table (for example, Table 3) from the memory 33 (S23).

The control unit 30 determines whether the basis weight of the acquired recording material is 81 g / m ² or less (S24). When the basis weight is 81 g / m ² or less (YES in S24), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 100% (S25). When the basis weight is ^{larger than 81 g / m 2} (NO in S24), the control unit 30 determines whether the basis weight of the acquired recording material is 400 g / m ² or less (S26).

When the basis weight is ^{larger than 400 g / m 2} (NO in S26), the control unit 30 determines whether the acquired paper width is 210 mm or less (S27). When the paper width is 210 mm or less (YES in S27), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 111% (S29). When the paper width is larger than 210 mm (NO in S27), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 115% (S30).

When the basis weight is 400 g / m ² or less (YES in S26), the control unit 30 determines whether or not the acquired paper width is 210 mm or less (S28). When the paper width is 210 mm or less (YES in S28), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 106% (S31). When the paper width is larger than 210 mm (NO in S28), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 110% (S32). The peripheral speed ratio control unit 32a sets the rotation speeds of the motor M0 and the motor M1 so as to obtain the set peripheral speed ratio (S33).

Then, the control unit 30 determines whether or not the start of the image forming job by the user operation is instructed (S34). When the start of the image formation job is not instructed (NO in S34), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S35), and the motor M0 and the motor M0 and the peripheral speed ratio are set to the set peripheral speed ratio. The rotation speed of the motor M1 is set (S36). After that, the control unit 30 repeats the process of S21 to 33 described above. When the start of the image forming job is instructed (YES in S34), the motor M0 and the motor M1 are driven at the set rotation speed (S37).

Next, the control unit 30 determines whether the image forming job has been completed (S38). If the image formation job has not been completed (NO in S38), the end of the image formation job is awaited. When the image formation job is completed (YES in S38), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S39), and rotates the motor M0 and the motor M1 so as to obtain the set peripheral speed ratio. The number is set (S40), and the driving of the motors M0 and M1 is stopped (S41). Then, the control unit 30 ends this control.

Also in the case of the present embodiment as described above, the speed difference between the recording material and the pressure roller 330 can be suppressed regardless of the type of the recording material. Then, the amount of slippage of the recording material with respect to the pressure roller 330 can be reduced, and the promotion of wear on the surface of the pressure roller 330 can be suppressed. That is, when the length of the recording material in the width direction is long, the amount of sliding of the recording material with respect to the pressure roller 330 tends to increase, but in the case of the present embodiment, the peripheral speed ratio is increased, that is, The peripheral speed of the auxiliary drive roller 340 with respect to the pressure roller 330 is increased. As a result, the auxiliary driving force acting on the fixing belt 310 is increased so that the recording material can easily follow the pressure roller 330 even if the width of the recording material is large. As a result, it is possible to suppress the acceleration of wear of the surface layer of the pressure roller due to the recording material.

Further, in the present embodiment, in addition to controlling the peripheral speed ratio according to the basis weight of the recording material of the first embodiment, the peripheral speed ratio also depends on the length in the width direction of the recording material as described above. It is in control. Therefore, even if the basis weight of the recording material is large, if the length of the recording material in the width direction is short, the increase in the peripheral speed ratio with respect to the reference value (for example, 100%) can be suppressed. Therefore, an increase in the mileage of the fixing belt 310 can be suppressed, and the life of the lubricating sheet 370 can be extended.

The peripheral speed ratio to the length in the width direction of the recording material described above is an example, and is not uniquely determined by the configuration of the fixing device or the like. Further, the effect of the present embodiment is not limited to the above-mentioned peripheral speed ratio, and the relationship between the peripheral speed V0 of the pressurizing roller 330 and the peripheral speed V1 of the auxiliary drive roller 340 may satisfy V0 ≦ V1. ..

<Other Embodiments>
In each of the above-described embodiments, the motor M0 for the pressurizing roller and the motor M1 for the auxiliary drive roller are provided independently. However, the motor for the pressurizing roller and the motor for the auxiliary drive roller may be shared. That is, the pressure roller and the auxiliary drive roller may be driven by a common drive source. In this case, a transmission mechanism is provided between one motor and one of the rollers so that the peripheral speed ratio can be controlled as described above.

Further, in each of the above-described embodiments, the auxiliary drive roller 340 is arranged downstream of the fixing pad 320 and upstream of the steering roller 350 in the rotation direction of the fixing belt 310. However, the position of the auxiliary drive roller 340 and the position of the steering roller 350 may be exchanged. That is, with respect to the rotation direction of the fixing belt 310, the auxiliary drive roller 340 may be arranged downstream of the steering roller 350 and upstream of the fixing pad 320.

In the second embodiment described above, the peripheral speed ratio is set in consideration of the basis weight of the recording material and the length in the width direction of the recording material. However, the peripheral speed ratio may be set only according to the length of the recording material in the width direction. That is, the peripheral speed ratio may be changed based on the information on the width of the recording material regardless of the basis weight of the recording material. The method of changing the peripheral speed ratio is the same as that of the second embodiment.

In each of the above-described embodiments, a configuration in which a halogen heater as a heating source for heating the fixing belt is provided on the auxiliary drive roller has been described. However, the heat source may not be provided on the auxiliary drive roller, but may be provided on another tension member such as a steering roller. Further, it may be provided on the pad member. For example, a plate-shaped heat generating member such as a ceramic heater may be provided on the fixing belt side of the pad member. Further, the fixing belt may be heated by electromagnetic induction.

Further, in each of the above-described embodiments, the fixing device for tensioning the fixing belt by the fixing pad, the auxiliary drive roller, and the steering roller has been described. However, the fixing device to which the present invention can be applied is not limited to this, and for example, the fixing belt may be stretched only by one tension roller and a fixing pad. In short, it suffices to provide at least one tension roller for tensioning the fixing belt together with the fixing pad.

8 ... Fixing device / 310 ... Fixing belt (belt) / 320 ... Fixing pad (nip part forming member, pad member) / 330 ... Pressurizing roller (drive roller) / 340 ... Auxiliary Drive roller / 350 ・ ・ ・ Steering roller (tension roller)

Claims (6)

A fixing device that fixes a toner image supported on a recording material to the recording material.
An endless, rotatable belt and
A drive roller having an elastic layer and rotating in contact with the outer peripheral surface of the belt to apply a driving force to the belt.
A nip portion forming member that is arranged inside the belt so as to face the drive roller with the belt sandwiched therein, and forms a nip portion that sandwiches and conveys a recording material between the belt and the drive roller. ,
An auxiliary drive roller, which is arranged inside the belt and stretches and rotates the belt together with the nip portion forming member to apply a driving force to the belt, is provided.
When the peripheral speed of the drive roller is V0, the peripheral speed of the auxiliary drive roller is V1, and V1 / V0 is the peripheral speed ratio, the basis weight of the recording material conveyed by the nip portion is the first basis weight. The case where the basis weight of the recording material conveyed by the nip portion is a second basis weight larger than the first basis weight so that the peripheral speed ratio in the case becomes the first peripheral speed ratio. The peripheral speed of the auxiliary drive roller is changed so that the peripheral speed ratio becomes the second peripheral speed ratio larger than the first peripheral speed ratio.
A fixing device characterized in that. A fixing device that fixes a toner image supported on a recording material to the recording material.
An endless, rotatable belt and
A drive roller having an elastic layer and rotating in contact with the outer peripheral surface of the belt to apply a driving force to the belt.
A nip portion forming member that is arranged inside the belt so as to face the drive roller with the belt sandwiched therein, and forms a nip portion that sandwiches and conveys a recording material between the belt and the drive roller. ,
An auxiliary drive roller, which is arranged inside the belt and stretches and rotates the belt together with the nip portion forming member to apply a driving force to the belt, is provided.
When the peripheral speed of the drive roller is V0, the peripheral speed of the auxiliary drive roller is V1, and V1 / V0 is the peripheral speed ratio, the width of the recording material transported by the nip portion intersects the transport direction of the recording material. The length in the width direction of the recording material conveyed by the nip portion is the first, so that the peripheral speed ratio when the length in the direction is the first length is the third peripheral speed ratio. The peripheral speed of the auxiliary drive roller is changed so that the peripheral speed ratio in the case of a second length longer than the third peripheral speed ratio becomes a fourth peripheral speed ratio larger than the third peripheral speed ratio. ,
A fixing device characterized in that. Satisfy V1 ≥ V0,
The fixing device according to claim 1 or 2, wherein the fixing device is characterized by the above. A tension roller, which is arranged inside the belt, stretches the belt together with the nip portion forming member and the auxiliary drive roller, and rotates in accordance with the belt.
The auxiliary drive roller is arranged downstream of the nip portion forming member and upstream of the tension roller in the rotation direction of the belt.
The fixing device according to any one of claims 1 to 3, wherein the fixing device is characterized by the above. The nip portion forming member is a pad member in which at least a part of a portion forming the nip portion is formed in a plane shape.
The fixing device according to any one of claims 1 to 4, wherein the fixing device is characterized by the above. The auxiliary drive roller stretches the belt via a lubricant.
The fixing device according to any one of claims 1 to 5, wherein the fixing device is characterized by the above.

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