Image forming device

Abstract

To provide a configuration that can reduce the difference in speed between a recording material and a pressure roller 330 regardless of the conveyance speed of the recording material.SOLUTION: A pressure roller 330 has an elastic layer, and rotates in contact with an outer peripheral surface of a fixing belt 310 to provide a driving force to the fixing belt 310. An auxiliary drive roller 340 is arranged inside the fixing belt 310, rotates while stretching the fixing belt 310 together with a fixing pad 320, and provides a driving force to the fixing belt 310. The peripheral speed of the pressure roller 330 is defined as V0, the peripheral speed of the auxiliary drive roller 340 as V1, and V1 / V0 as a peripheral speed ratio. In this case, the peripheral speed of the auxiliary drive roller 340 is changed so that the peripheral speed ratio when the conveyance speed of the recording material is a first conveyance speed becomes a first peripheral speed ratio, and the peripheral speed ratio when the conveyance speed of the recording material is a second conveyance speed faster than the first conveyance speed becomes a second peripheral speed ratio larger than the first peripheral speed ratio.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device for fixing a toner image carried on a recording material to the recording material. Image forming apparatus comprising: Regarding. [Background technology]

[0002] A known fixing device has a nip between an endless fixing belt and a pressure roll that contacts the outer peripheral surface of the fixing belt, and fixes a toner image onto the recording material passing through the nip (Patent Document 1). The pressure roll has an elastic layer, and the nip is formed by elastic deformation of the elastic layer. The pressure roll is a drive roller driven by a motor, and applies a driving force to the fixing belt by contacting the fixing belt. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-228765 Summary of the Invention [Problem to be solved by the invention]

[0004] As described in Patent Document 1, when the pressure roll (drive roller) has an elastic layer, the elastic layer begins to distort at the entrance of the nip when the recording material passes through the nip, and the distortion of the elastic layer is restored as the recording material passes through the nip. This behavior can cause a speed difference between the recording material and the pressure roll, which can accelerate wear on the surface of the pressure roll. In particular, depending on the conveyance speed of the recording material, the speed difference between the recording material and the pressure roll can become large.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can suppress the speed difference between the recording material and the drive roller regardless of the conveying speed of the recording material. [Means for solving the problem]

[0006] One aspect of the present invention is directed to a recording medium conveying apparatus including an image forming unit that forms a toner image on a recording material, a fixing device that fixes the toner image to the recording material on which the toner image has been formed by the image forming unit, and a control unit, wherein the fixing device includes an endless, rotatable belt, a drive roller that has an elastic layer and rotates in contact with the outer circumferential surface of the belt to apply a driving force to the belt, a nip portion forming member that is disposed inside the belt to face the drive roller across the belt and forms a nip portion between the belt and the drive roller to nip and convey the recording material, and an auxiliary drive roller that is disposed inside the belt and rotates together with the nip portion forming member while tensioning the belt and applying a driving force to the belt. the control unit is capable of executing a first mode in which a conveying speed of the recording material conveyed at the nip portion is a first conveying speed, and a second mode in which the conveying speed of the recording material conveyed at the nip portion is a second conveying speed faster than the first conveying speed, wherein a peripheral speed of the drive roller is V0, a ​​peripheral speed of the auxiliary drive roller is V1, and a peripheral speed ratio is V1 / V0, and when a toner image is fixed to the same type of recording material in the first mode and the second mode, the control unit changes the peripheral speed of the auxiliary drive roller so that the peripheral speed ratio becomes a first peripheral speed ratio in the first mode and so that the peripheral speed ratio becomes a second peripheral speed ratio that is greater than the first peripheral speed ratio in the second mode. [Effects of the Invention]

[0007] According to the present invention, the speed difference between the recording material and the drive roller can be suppressed regardless of the conveying speed of the recording material. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a fixing device according to the embodiment. [Figure 3] 5A and 5B are schematic diagrams showing the relationship between a fixing pad and a fixing belt. [Figure 4] FIG. 2 is a control block diagram showing a part of the control configuration of the image forming apparatus according to the embodiment. [Figure 5] 10 is a graph showing the amount of distortion of the elastic layer of the pressure roller with respect to the coordinate in the recording material conveyance direction at the nip portion. [Figure 6] FIG. 3 is a schematic cross-sectional view showing a drive transmission mechanism to an auxiliary drive roller according to the embodiment. [Figure 7] FIG. 2 is a cross-sectional view showing a schematic configuration of a drive transmission mechanism to a pressure roller according to the first embodiment. [Figure 8] FIG. 1A is a graph showing the relationship between the peripheral speed ratio and the auxiliary driving force, and FIG. 1B is a schematic diagram showing the auxiliary driving force. [Figure 9] 5A and 5B are schematic diagrams for explaining an auxiliary driving force acting on the fixing belt. [Figure 10] 10 is a graph showing the relationship between the amount of slippage between the pressure roller and the recording material and the peripheral speed ratio when the basis weight of the recording material is different. [Figure 11] 6 is a flowchart relating to control of the fixing device according to the embodiment, in which the peripheral speed ratio is changed based on the basis weight of the recording material. [Figure 12] 10 is a graph showing the relationship between the amount of slippage between the pressure roller and the recording material and the peripheral speed ratio when the conveying speed of the recording material is different. [Figure 13]10 is a flowchart relating to control of the fixing device according to the embodiment, in which the peripheral speed ratio is changed based on the conveying speed of the recording material. DETAILED DESCRIPTION OF THE INVENTION

[0009] The embodiment will be described with reference to Figures 1 to 13. First, the schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Figure 1.

[0010] [Image forming device] Image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in tandem along the rotation direction of an intermediate transfer belt 204 (described later). Image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) 2 connected to image forming apparatus main body 3 or from a host device such as a personal computer connected to image forming apparatus main body 3 so as to be able to communicate with the image forming apparatus main body 3. Examples of recording materials include sheet materials such as paper, plastic film, and cloth.

[0011] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via optical components 23 such as a lens. This optical unit scans in the direction of the arrow, converting the original into a line-by-line electrical signal data stream. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, where it is subjected to image processing in accordance with each image forming unit (described later) by a control unit 30. The control unit 30 also receives external inputs as image signals from external host devices such as a print server.

[0012] The image forming apparatus main body 3 includes multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. A polygon scanner 31 serving as an exposure device scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto photosensitive drums 200a to 200d serving as image carriers of each image forming unit Pa to Pd.

[0013] Note that Pa is a yellow (Y) image forming unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit, each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially identical, the Y image forming unit Pa will be described in detail below, and descriptions 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 an image signal, as will be described below.

[0014] A charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from a polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. A developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. A primary transfer roller 203a discharges electricity from the back surface of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0015] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming station, where the toner images of each color formed at each image forming station are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through Bk image forming station Pd, which is located at the most downstream side in the rotation direction of intermediate transfer belt 204, is conveyed to a secondary transfer station made up of a pair of secondary transfer rollers 205 and 206. In the secondary transfer station, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image onto the recording material.

[0016] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208, which is made up of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the position of the paper, and the recording material is transported to the secondary transfer unit.

[0017] The recording material onto which the toner image has been transferred in the secondary transfer section is transported to a fixing device 8, where the toner image carried on the recording material is fixed to the recording material by heating and pressing. The recording material that has passed through the fixing device 8 is discharged onto a discharge tray 7. When forming images on both sides of the recording material, after the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via a reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (rear side) of the recording material, and the recording material is then stacked on the discharge tray 7.

[0018] [Fusing device] Next, the configuration of the fixing device 8 in this embodiment will be described with reference to FIG. 2. This embodiment employs a fixing device of a belt heating type using an endless belt. 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 rotatable belt, and a pressure roller 330 as a pressure rotating body that contacts the fixing belt 310 and forms a nip N together with the fixing belt 310.

[0019] The heating unit 300 includes the above-mentioned fixing belt 310, a fixing pad 320 serving as a nip portion forming member and a pad member, an auxiliary driving roller 340 serving as a tension roller, and a steering roller 350. The pressure roller 330 rotates in contact with the outer peripheral surface of the fixing belt 310 and also serves as a driving roller that applies a driving force to the fixing belt 310.

[0020] The endless fixing belt 310 has thermal conductivity, heat resistance, and the like, and is, for example, a thin-walled cylindrical shape with an inner diameter of 120 mm. In this embodiment, it has a three-layer structure consisting of a base layer, an elastic layer on the outer periphery of the base layer, and a release layer on the outer periphery of the elastic layer. The base layer is 60 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 310 is stretched by a fixing pad 320, an auxiliary drive roller 340, and a steering roller 350.

[0021] The fixing pad 320, which serves as a nip portion forming member, is disposed inside the fixing belt 310 so as to face the pressure roller 330 with the fixing belt 310 sandwiched therebetween, and forms a nip portion N between the fixing belt 310 and the pressure roller 330, which sandwiches and conveys the recording material. In this embodiment, the fixing pad 320 is a substantially plate-shaped member that is long in the width direction of the fixing belt 310 (the longitudinal direction intersecting the rotation direction of the fixing belt 310, the direction of the rotation axis of the auxiliary drive roller 340). The fixing pad 320 is pressed against the pressure roller 330 with the fixing belt 310 sandwiched therebetween, thereby forming the nip portion N. The fixing pad 320 is made of an LCP (liquid crystal polymer) resin.

[0022] At least a portion of the portion of fixing pad 320 that forms nip portion N is formed in a flat shape. That is, the portion that comes into contact with the inner circumferential surface of fixing belt 310 via lubricating sheet 370 (described later) is formed in a substantially flat shape, making the shape of the nip portion substantially flat. This configuration can prevent wrinkles and image misalignment from occurring on the envelope, particularly when a toner image is fixed to an envelope as a recording material.

[0023] The fixing pad 320 is supported by a stay 360 serving as a support member disposed inside the fixing belt 310. That is, the stay 360 is disposed on the opposite side of the fixing pad 320 from the pressure roller 330, and supports the fixing pad 320. Such a stay 360 is a reinforcing member having long rigidity along the longitudinal direction of the fixing belt 310, and contacts the fixing pad 320 to back it up. That is, the stay 360 provides strength to the fixing pad 320 and ensures the pressure force at the nip N when the fixing pad 320 is pressed by the pressure roller 330.

[0024] The stay 360 is made of a metal such as stainless steel, and has a substantially rectangular cross section (transverse cross section) perpendicular to the longitudinal direction of the stay 360, which intersects with the rotation direction of the fixing belt 310. For example, the stay 360 is made of a 3 mm thick drawn material of SUS304 (stainless steel), and the transverse cross section is formed into a hollow, substantially square shape to ensure strength. Note that the stay 360 may also be formed into a substantially rectangular cross section by combining multiple metal plates and fixing them together by welding or the like. The material of the stay 360 is not limited to stainless steel as long as strength can be ensured.

[0025] 3, both ends of the nip portion N of the fixing pad 320 in the recording material conveyance direction are formed as curved portions 320a and 320b. The curved portions 320a and 320b are curved in a direction (upward in FIG. 3) that moves away from the nip surface toward the ends. The nip surface is formed between the fixing belt 310 and the pressure roller 330, and is a surface that follows the surface of the fixing pad 320 facing the pressure roller 330 (the lower surface in FIG. 3).

[0026] In this manner, in this embodiment, the downstream end of the fixing pad 320 is formed as the curved surface portion 320b, and the curvature of the curved surface portion 320b curves the fixing belt 310. 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.

[0027] A lubricating sheet 370 is interposed between the fixing pad 320 and the fixing belt 310. In this embodiment, a PTFE (polytetrafluoroethylene) coated PI (polyimide) sheet with a thickness of 100 μm is used as the lubricating sheet 370. The PI sheet has 100 μm protrusions formed at 1 mm intervals, which reduces the contact area with the fixing belt 310 and thereby reduces sliding resistance.

[0028] A lubricant is applied to the inner peripheral surface of fixing belt 310, so that fixing belt 310 slides smoothly against fixing pad 320 covered with lubricating sheet 370. Silicone oil with a viscosity of 100 cSt is used as the lubricant.

[0029] 2, the auxiliary drive roller 340 is disposed inside the fixing belt 310 and tensions the fixing belt 310 together with the fixing pad 320 and the steering roller 350. As described above, the inner peripheral surface of the fixing belt 310 is coated with a lubricant, and the auxiliary drive roller 340 tensions the fixing belt 310 via this lubricant. The auxiliary drive roller 340 is disposed downstream of the fixing pad 320 and upstream of the steering roller 350 in terms of the rotation direction of the fixing belt 310. This allows the driving force of the auxiliary drive roller 340 to directly tension the fixing belt 310 that has passed through the nip portion N without using a tension roller in between.

[0030] Auxiliary drive roller 340 is formed into a cylindrical shape from metal such as aluminum or stainless steel, and has a halogen heater 340a disposed inside as a heat source for heating fixing belt 310. Auxiliary drive roller 340 is heated to a predetermined temperature by halogen heater 340a. Such auxiliary drive roller 340 also functions as a heating roller for heating fixing belt 310.

[0031] In this embodiment, the auxiliary drive roller 340 is formed from an aluminum pipe, for example, with an outer diameter of 40 mm and a thickness of 1 mm, from the viewpoint of thermal conductivity, and the surface is anodized. Although a single halogen heater 340a is sufficient, it is preferable to have multiple heaters in consideration of temperature distribution control in the longitudinal direction (direction of the rotation axis) of the auxiliary drive roller 340. The multiple halogen heaters 340a 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 provided. The heat source is not limited to a halogen heater, and may be another heater capable of heating the auxiliary drive roller 340, such as a carbon heater.

[0032] The fixing belt 310 is heated by an auxiliary driving 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). The auxiliary driving roller 340 has a gear fixed to one end of its rotational axis, as will be described in detail later, and is connected to a motor M1, which serves as a driving source for the auxiliary driving roller, via the gear, to be rotated. The fixing belt 310 is provided with a driving force by the rotation of the auxiliary driving roller 340. The force applied to the fixing belt 310 by the auxiliary driving roller 340 is referred to as the auxiliary driving force.

[0033] The steering roller 350 is disposed inside the fixing belt 310, stretches the fixing belt 310 together with the fixing pad 320 and the auxiliary drive roller 340, and is rotated by the fixing belt 310. The steering roller 350 tilts relative to the rotation axis direction (longitudinal direction) of the auxiliary drive roller 340 to control the position (offset position) of the fixing belt 310 relative to the rotation axis direction. That is, the steering roller 350 has a rotation center at the center of the rotation axis direction (longitudinal direction) of the steering roller 350, and tilts relative to the longitudinal direction of the auxiliary drive roller 340 by swinging around this rotation center. This generates a tension difference between one side and the other side of the fixing belt 310 in the longitudinal direction, causing the fixing belt 310 to move in the longitudinal direction.

[0034] The fixing belt 310 tends to shift to one of its ends during rotation, depending on the outer diameter accuracy of the rollers that tension it and the alignment accuracy between the rollers. Therefore, the steering roller 350 controls this shift. The steering roller 350 may be swung by a drive source such as a motor, or may be configured to swung by automatic centering. The center of rotation may be the center in the longitudinal direction, as in this embodiment, or it may be one of the ends in the longitudinal direction.

[0035] In this embodiment, the steering roller 350 is biased by a spring supported by the frame of the heating unit 300, and also serves as a tension roller that applies a predetermined tension to the fixing belt 310. By applying tension to the fixing belt 310 using the steering roller 350 in this manner, the fixing belt 310 is caused to follow the curved portions 320a and 320b of the fixing pad 320. In other words, the fixing belt 310 is curved along the curved portions 320a and 320b.

[0036] The steering roller 350 is formed into a cylindrical shape from a metal such as aluminum or stainless steel. In this embodiment, the steering roller 350 is a stainless steel or aluminum pipe with an outer diameter of 40 mm and a thickness of 1 mm, and its ends are rotatably supported by bearings (not shown). Note that the tension roller placed at the position of the steering roller 350 may be a roller that does not have such a steering function.

[0037] The pressure roller 330, which serves as a drive roller, rotates in contact with the outer circumferential surface of the fixing belt 310, applying a driving force to the fixing belt 310. In this embodiment, the pressure roller 330 is a roller having an elastic layer formed on the outer periphery of its shaft and a release layer formed on the outer periphery of the elastic layer. The shaft is made of stainless steel, the elastic layer is 5 mm thick and made of conductive silicone rubber, and the release layer is 50 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The pressure roller 330 is rotatably supported by the fixing frame 380 of the fixing device 8, and as will be described in detail later, a gear is fixed to one end of the pressure roller. The pressure roller 330 is connected to a motor M0, which serves as a pressure roller drive source, via the gear, and is driven to rotate.

[0038] 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 a stay 360 into the heating unit positioning portion 381 and fixing the stay 360 to the heating unit positioning portion 381 by a fixing means (not shown). The heating unit positioning portion 381 has a pressure direction regulating surface 381a facing the pressure roller 330 and a conveying direction regulating surface 381b that is an abutting surface in the insertion direction of the heating unit 300. The stay 360 is fixed in a state where its movement is restricted by the pressure direction regulating surface 381a and the conveying direction regulating surface 318b. At this time, the pressure roller 330 is separated from the fixing belt 310.

[0039] After the heating unit 300 is positioned in the heating unit positioning portion 381, the pressure roller 330 comes into contact with the fixing belt 310 as a result of the pressure frame 383 being moved by a drive source and a cam (not shown). The pressure roller 330 is then pressed against the fixing pad 320 via the fixing belt 310. That is, in this embodiment, the pressure roller 330 also serves as a pressure member that applies pressure toward the fixing belt 310. In this embodiment, the pressure applied during image formation is 1000 N.

[0040] In this embodiment, a separating device 400 having a separating member (a separating plate in this embodiment) 401 that separates the recording material from the fixing belt 310 is provided downstream of the nip N in the recording material conveyance direction. The separating member 401 is disposed with a gap between it and the outer peripheral surface of the fixing belt 310, and separates the recording material that has passed through the nip N from the fixing belt. Specifically, the separating member 401 is disposed close to a 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. The separating member 401 is formed in a blade shape, with its tip facing the outer peripheral surface of the fixing belt 310. A fluorine-based tape is attached to the metal plate of the separating member 401 to prevent toner adhesion to the recording material and image scratches due to sliding. In this embodiment, the separating member 401 is positioned with respect to the stay 360 in the recording material conveyance direction (the widthwise direction of the stay 360, the X direction) so as to be disposed with a gap between it and the outer peripheral surface of the fixing belt 310.

[0041] The fixing device 8 configured as described above sandwiches the recording material P bearing a toner image at the nip portion N formed between the fixing belt 310 and the pressure roller 330, and heats the toner image while conveying the recording material P. This melts the toner image and fixes it to the recording material. In this embodiment, during image formation, the peripheral speed of the fixing belt 310 is 300 mm / s, the pressure at the nip portion N is 1000 N, and the temperature of the fixing belt 310 is 180°C.

[0042] [Control Unit] Next, the control configuration of the control unit 30 of the image forming apparatus 1 regarding the fixing device 8 will be described with reference to Fig. 4. The control unit 30 has a CPU 32 (Central Processing Unit) and a memory 33 such as a ROM (Read Only Memory) or a RAM (Random Access Memory).

[0043] The CPU 32 acquires various data input via the operation unit 4 and the display unit 5 and stores the data 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, a touch panel or buttons that can be operated by touch.

[0044] Furthermore, the CPU 32 can read out and execute a printing (image forming) program from the memory 33 in response to a start-up operation, such as turning on the power of the image forming apparatus 1, by the user.

[0045] The memory 33 stores various programs such as a printing program and an image forming job, and various data such as a peripheral speed ratio control table (Table 2) for the motors M0 and M1, which will be described later. The memory 33 can also temporarily store the results of calculations performed in conjunction with the execution of the various programs.

[0046] In this embodiment, CPU 32 executes a printing program to control the operation of image forming apparatus 1 related to printing on recording materials. Note that the printing program is not limited to the form of a software program, and can also be implemented in the form of a microprogram processed by a DSP (digital signal processor), for example. Therefore, CPU 32 may be used in combination with a program that executes a control program such as an image formation job to perform various controls such as image formation operations, but is not limited to this, and a program specifically prepared for executing the printing program may also be used.

[0047] The peripheral speed ratio control unit 32a can control the motor M1 that drives the auxiliary drive roller 340 so that the peripheral speed (peripheral speed) of the pressure roller 330 and the peripheral speed (peripheral speed) of the auxiliary drive roller become a desired peripheral speed ratio. Specifically, the peripheral speed ratio control unit 32a controls the motors M0 and M1 in accordance with peripheral speed ratio control tables (data) for the motors M0 and M1, such as Tables 2 and 4 described below, based on the acquired information such as the conveyance speed and basis weight of the recording material.

[0048] [Distortion of the elastic layer of the pressure roller] Next, the distortion of the elastic layer of the pressure roller when a recording material passes through the nip portion N will be described with reference to FIG. 5. In FIG. 5, the comparative example is a configuration in which the auxiliary drive roller 340 does not receive an auxiliary drive force in the configuration shown in FIG. 2. In other words, the fixing belt is driven only by the pressure roller. On the other hand, the example is a configuration in which the auxiliary drive roller 340 receives an auxiliary drive force, as shown in FIG. 2.

[0049] Figure 5 shows the amount of strain in the elastic layer of the pressure roller from the entrance to the exit of the nip in the conveying direction of the recording material when the recording material passes through the nip in both the comparative example and the working example. Figure 5 shows that the amount of strain (solid line) in the elastic layer of the pressure roller in the comparative example gradually increases from the entrance to the center of the nip, and then is eliminated and restored from the center to the downstream portion. From the entrance to the center of the nip, the pressure roller moves while following the recording material, accumulating strain in the elastic layer. Meanwhile, from the center to the downstream portion of the nip, the pressure roller moves while releasing the accumulated strain in the elastic layer toward the downstream portion of the conveying direction. Therefore, from the center to the downstream portion of the nip, the peripheral speed of the pressure roller exceeds the conveying speed of the recording material. As a result, the recording material cannot keep up with the conveying speed of the pressure roller and slips, accelerating wear on the surface of the pressure roller.

[0050] In particular, when the recording material has a large basis weight, such as cardboard, the elastic layer of the pressure roller is distorted significantly when the recording material passes through the nip. Therefore, the increase in the peripheral speed of the pressure roller due to the release of this distortion tends to be greater the greater the basis weight of the recording material. Therefore, the greater the basis weight of the recording material, the greater the amount of slippage that occurs when the recording material is unable to keep up with the speed of the pressure roller, i.e., the greater the amount of slippage between the pressure roller and the recording material.

[0051] Generally, the surface layer of the pressure roller wears over time as the recording material passes through it. Particularly, the portion corresponding to the edge of the recording material is prone to accelerated wear due to the abrasive effect of burrs on 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 cannot keep up with the speed of the pressure roller and slips, the wear on the surface layer of the pressure roller is further accelerated. If the surface layer of the pressure roller continues to wear, it may affect the fixed image.

[0052] In contrast to this, in the embodiment, the peripheral speed of the auxiliary drive roller 340, which is arranged so as to contact the inner peripheral surface of the fixing belt 310, is set to be high, so that the auxiliary drive roller 340 applies an auxiliary drive force to the fixing belt 310. By applying an auxiliary drive force to the fixing belt 310 in this way, the conveyance speed of the recording material can be made to follow the speed of the pressure roller 330, and the acceleration of wear on the surface of the pressure roller due to the recording material can be suppressed.

[0053] The dashed line graph in Figure 5 shows the amount of distortion of the elastic layer of the pressure roller in this embodiment. As can be seen from Figure 5, applying an auxiliary driving force to the fixing belt reduced the amount of distortion of the elastic layer of the pressure roller in the nip portion, and at the same time, reduced the amount of distortion released. In other words, the recording material follows the speed of the pressure roller, reducing the amount of distortion in the elastic layer of the pressure roller, and reducing the amount of distortion also reduces the amount of distortion released. As a result, it was found that the difference between the conveying speed of the recording material and the conveying speed of the pressure roller was reduced, and wear on the surface of the pressure roller was suppressed.

[0054] [Outline of this embodiment] An outline of this embodiment is described below. A peripheral speed V1 of an auxiliary driving roller disposed on the inner peripheral surface of the fixing belt 310 is set faster than a peripheral speed V0 of the pressure roller 330 that rotates the fixing belt 310, so that an auxiliary driving force is applied to the fixing belt 310 from the auxiliary driving roller 340.

[0055] In this way, in this embodiment, by applying an auxiliary driving force to the fixing belt 310, it is possible to reduce the amount of distortion of the elastic layer of the pressure roller 330 that occurs at the nip portion N of the fixing belt 310, and to suppress the difference in conveying speed at the nip portion. As a result, the object of this embodiment is to reduce wear due to slippage that occurs between the recording material and the pressure roller 330.

[0056] First, a drive configuration for rotating and driving auxiliary drive roller 340 for applying auxiliary drive force to fixing belt 310 and pressure roller 330 will be described.

[0057] [Drive configuration of auxiliary drive roller] 6 shows an example of an auxiliary drive roller drive unit 410 that drives and rotates the auxiliary drive roller 340. The auxiliary drive roller 340 has a gear 385a fixed to one end of its shaft, and is 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, and is driven to rotate. The motor M1 is a drive motor independent of the motor M0, which is a drive source for driving the pressure roller, and is fixed to a mounting plate 386.

[0058] A gear 385c is fixed to the output shaft of the motor M1, and this gear 385c meshes with a gear 385b. The gear 385b is rotatably supported on a fixed shaft fixed to the frame 382 that supports the heating unit 300 and to the mounting plate 386, and transmits a rotational driving force to the auxiliary drive roller 340 by meshing with the gears 385c and 385a. As described above, the drive transmission mechanism of the auxiliary drive roller 340 is made up of the motor M1 and the auxiliary drive roller drive gear train 385.

[0059] In addition, in this embodiment, the peripheral speed of the auxiliary driving roller 340 is changed by controlling the rotation speed of the motor M1 without using a speed-changing mechanism using a speed-changing gear. 2 The table 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 of (gsm) or less is passed through the nip portion. [Table 1]

[0060] 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 becomes 191.1 rpm due to the drive force being transmitted by the auxiliary drive roller drive gear train 385, and the peripheral speed at this time becomes 400 mm / s.

[0061] The motor rotation speed of the motor M1 is controlled by the control unit 30 so that the peripheral speed of the pressure roller 330 satisfies a predetermined peripheral speed ratio with respect to the peripheral speed of the auxiliary drive roller 340. The gears constituting the auxiliary drive roller drive gear train 385 may be spur gears, helical gears, or any other gear type.

[0062] [Pressure roller drive configuration] 7 shows an example of a pressure roller drive unit 420 that rotates and drives the pressure roller 330. The pressure roller 330 has a gear 387a fixed to one end of its shaft, and is connected to a motor M0, which is a drive source for driving the pressure roller, via a pressure roller drive gear train 387, and is thereby rotated. The motor M0 is fixed to a mounting plate 388.

[0063] A gear 387e is fixed to the output shaft of motor M0, and gear 387e meshes with gear 387d. Gears 387b, 387c, and 387d are rotatably supported on fixed shafts fixed to fixing frame 380 and mounting plate 388, and transmit rotational driving force to pressure roller 330 by meshing with gears 387d, 387c, and 387b. As described above, the drive configuration for pressure roller 330 is made up of motor M0 and pressure roller drive gear train 387.

[0064] The reason why the number of gears in the pressure roller drive gear train 387 is greater than that of the auxiliary drive roller drive gear train 385 is to increase the reduction ratio and thereby the drive torque of the pressure 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 pressure roller may be configured in the same way as the gear train of the auxiliary drive roller.

[0065] In addition, in this embodiment, the peripheral speed of the pressure roller 330 is changed by controlling the rotation speed of the motor M0 without using a speed change mechanism using a speed change gear. 2 The table shows the motor rotation speed of the motor M0 and the rotation speed and peripheral speed of the pressure roller 330 when a recording material of (gsm) or less is passed through the nip portion.

[0066] 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 as a result of the drive force being transmitted by the pressure roller drive gear train 387, and the peripheral speed at this time becomes 400 mm / s.

[0067] The motor rotation speed of the motor M0 is controlled by the control unit 30 so that the peripheral speed of the pressure roller 330 satisfies a predetermined peripheral speed ratio with respect to the peripheral speed of the auxiliary drive roller 340. The gears constituting the pressure roller drive gear train 387 may be spur gears, helical gears, or any other type of gear.

[0068] [Peripheral speed ratio of pressure roller and auxiliary drive roller] Next, the peripheral speed ratio between the pressure roller 330 and the auxiliary drive roller 340 will be described. First, in this embodiment, when the peripheral speed of the pressure roller 330 is V0 and the peripheral speed of the auxiliary drive roller 340 is V1, the relationship V1≧V0 is satisfied, and the ratio of the peripheral speeds V0 and V1 is defined as the peripheral speed ratio V1 / V0. In this embodiment, the peripheral speed ratio V1 / V0 is changed depending on the basis weight of the recording material and the conveying speed of the recording material. First, a case where the peripheral speed ratio V1 / V0 is changed depending on the basis weight of the recording material will be described. First, the peripheral speed ratio V1 / V0 when the basis weight of the recording material conveyed at the nip portion N is a first basis weight is defined as the peripheral speed ratio A. Furthermore, the peripheral speed ratio V1 / V0 when the basis weight of the recording material conveyed at the nip portion N is a second basis weight that is greater than the first basis weight is defined as the peripheral speed ratio B, which is greater than the peripheral speed ratio A.

[0069] In this embodiment, the peripheral speed V0 of the pressure roller 330 is set to a peripheral speed that matches the process speed, and the peripheral speed V1 of the auxiliary drive roller 340 is changed to change the peripheral speed ratio V1 / V0. For example, if the process speed is the same for a recording material of a first basis weight and a recording material of a second basis weight, the peripheral speed V1 of the auxiliary drive roller 340 is increased for the recording material of the second basis weight, which has a larger basis weight, thereby increasing the peripheral speed ratio V1 / V0. Furthermore, the relationship between the peripheral speeds V0 and V1 is set to satisfy V1≧V0.

[0070] In this embodiment, the basis weight of the recording material is 81 g / m 2 If the peripheral speed ratio is less than 100%, 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 also 400 mm / s.

[0071] Next, the basis weight of the recording material is 81 g / m 2 More than 400g / m 2 When the pressure roller 330 is rotated at a speed of 400 mm / s, the peripheral speed ratio is set to 110%. In this case, 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 driving roller 340 is 440 mm / s.

[0072] The basis weight of the recording material is 400 g / m 2 In the above case, the peripheral speed ratio is set to 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.

[0073] The basis weight of the recording material is 400 g / m 2 The reason why the peripheral speed of the pressure roller 330 is set to a lower speed than for other basis weights in the above cases is to ensure satisfactory toner fixation even for recording materials that do not easily transfer heat, such as cardboard. That is, for recording materials that do not easily transfer heat, such as cardboard, the process speed of the image forming apparatus is reduced so that the recording material passes through the nip at a low speed. This ensures that sufficient heat is applied to the recording material to ensure fixation.

[0074] Table 2 shows the relationship between the basis weight of the recording material, the peripheral speed ratio, and the peripheral speeds of the motors M0 and M1 in this embodiment. [Table 2]

[0075] [Relationship between tip 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 drive force applied to the fixing belt 310 will be described with reference to Figures 8(a), (b) and 9. In this embodiment, as shown in Figure 8(b), the auxiliary drive roller 340 applies an auxiliary drive force to the fixing belt 310, reducing the sliding resistance at the nip portion on the inner circumferential surface of the belt, thereby reducing the increase in the conveying speed at the nip portion of the pressure roller 330.

[0076] When the peripheral speed ratio control is performed, the fixing belt 310 is driven by the pressure roller 330, and a difference in peripheral speed occurs between the fixing belt 310 and the auxiliary drive roller 340. As a result, 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. Meanwhile, the auxiliary drive roller 340 can apply a desired auxiliary drive force to the fixing belt 310 by interposing a lubricant between the roller and the inner peripheral surface of the fixing belt 310 and by creating friction with the lubricant and setting a wrap angle with respect to the fixing belt 310, which will be described later.

[0077] The effect of the auxiliary driving force due to the rotational drive of the auxiliary driving roller 340 is shown below. Figure 8(a) shows the relationship between the auxiliary driving force and the peripheral speed ratio. The auxiliary driving force was calculated from the axial torque applied when the auxiliary driving roller 340 is driven and the diameter of the auxiliary driving roller 340. Figure 8(a) confirms that the auxiliary driving force increases as the peripheral speed ratio increases.

[0078] The auxiliary driving force will be explained using Euler's belt theory formula shown in formula (1) and FIG.

number

[0079] Here, Tt is the tension applied to the fixing belt 310 by the driving of the auxiliary drive roller 340, and Te is the effective tension (friction force). θ is the wrap angle, which is the angle between the center of the fixing belt 310 and the auxiliary drive roller 340 when the fixing belt 310 is wrapped around the roller, and μ is the coefficient of friction. Tc is the tension of the fixing belt 310 acting as a horizontal component of the centrifugal force acting radially on the belt. Furthermore, m is the mass per unit length of the belt, and v is the belt speed (circumferential velocity).

[0080] According to formula (1), the tension side tension Tt increases as the friction coefficient μ and the winding angle θ increase. Also, since Tt increases as the peripheral speed of the fixing belt 310 increases, it becomes possible to increase the auxiliary driving force as the peripheral speed ratio increases, as shown in FIG. 8(a).

[0081] [Slippage improvement effect of auxiliary drive rollers] 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. 10. Fig. 10 shows the amount of slippage between the recording material passing through the nip portion and the pressure roller 330 when the peripheral speed ratio is changed relative to the basis weight of the recording material, with the basis weight of the recording material being 81 g / m². 2 The slippage rate is shown as a percentage with the peripheral speed ratio at 100% as the reference. In other words, the slippage rate is 2 The peripheral speed ratio at this time is 100%, that is, the peripheral speed of the pressure roller 330 and the peripheral speed of the auxiliary drive roller 340 are the same, and the ratio is relative to the amount of slippage when the recording material is passed through the nip portion N.

[0082] 10, when the peripheral speed ratio V1 / V0 of the auxiliary drive roller 340 to the pressure roller 330 is increased, the amount of slippage decreases regardless of the basis weight of the recording material. This is because applying an auxiliary drive force to the fixing belt 310 reduces the sliding resistance generated on the inner peripheral surface of the fixing belt 310, and as a result, the difference in conveying speed at the nip between the pressure roller 330 and the recording material is reduced.

[0083] As shown in Figure 10, when the peripheral speed ratio is 100%, the peripheral speed ratio A is used. 2 When a recording material with a basis weight of 81 g / m is passed through the nip, the slippage is 2 In response to this, the peripheral speed ratio is increased to a peripheral speed ratio B, which is larger than the peripheral speed ratio A, of about 110%. Then, the basis weight of the recording material is 400 g / m 2 The slippage when the recording material is passed through the nip at a peripheral speed ratio of A and a basis weight of 81 g / m 2 The slippage amount can be made equal to the slippage amount when the recording material is passed through the nip portion. Note that the peripheral speed ratios A and B are not limited to the above values ​​and can be set appropriately.

[0084] As described above, the amount of slippage is reduced by increasing the peripheral speed ratio between the pressure roller 330 and the auxiliary drive roller 340 using the auxiliary drive force, regardless of the basis weight of the recording material. However, if a uniformly high peripheral speed ratio is set, the running distance of the fixing belt 310 increases, raising concerns about a shortened lifespan of the lubricating sheet 370. Therefore, in this embodiment, in consideration of shortening the lifespan of the lubricating sheet 370, the peripheral speed ratio between the pressure roller 330 and the auxiliary drive roller 340 is set to at least two speeds. The peripheral speed ratio is then changed depending on the basis weight of the recording material. Specifically, as shown in Table 2, the peripheral speed ratio is set to three levels depending on the basis weight of the recording material.

[0085] [Controlling peripheral speed ratio according to recording material basis weight] Next, the flow of control of the peripheral speed ratio according to the basis weight of the recording material in this embodiment will be described using Fig. 11 with reference to Fig. 2 and Fig. 4. Fig. 11 shows an example of control of the fixing device 8 from when the basis weight of the recording material is input and an image forming job starts until the job ends.

[0086] The control unit 30 starts an image formation job when, for example, the start key of the operation unit 4 is operated, and ends the image formation job when the image formation operation on the last recording material of the image formation job is completed. Note that an image formation job is the period from the start of image formation based on a print signal (image formation signal) for forming an image on a recording material to the completion of image formation. In other words, an image formation job is a period during which a series of operations are performed, based on the input of an image formation signal, including a pre-operation (pre-rotation) performed before the image formation operation, an image formation operation, and a post-operation (post-rotation) performed after the image formation operation.

[0087] In the image forming apparatus 1 (FIG. 1), the control unit 30 displays an input screen 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. The control unit 30 then stores the information in the memory 33 (S1). Next, the control unit 30 acquires the information regarding the paper type and basis weight of the recording material from the memory 33 (S2). The control unit 30 also reads out a peripheral speed ratio control table (e.g., Table 2) from the memory 33 (S3).

[0088] The control unit 30 determines that the basis weight of the recording material is 81 g / m 2 It is determined whether the basis weight is 81 g / m or less (S4). 2 In the following cases (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). 2 If the basis weight of the recording material is greater than 400 g / m (NO in S4), the control unit 30 2 It is determined whether the basis weight is 400 g / m or less (S6). 2 In the following cases (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). 2 If it is greater than (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 motors M0 and M1 to achieve the set peripheral speed ratio (S9).

[0089] Then, the control unit 30 determines whether the start of an image formation job has been instructed by a user operation (S10). If the start of an image formation job has not been instructed (NO in S10), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S11), and sets the rotation speeds of the motors M0 and M1 to achieve the set peripheral speed ratio (S12). Thereafter, the control unit 30 repeats the processes of S1 to S9 described above. If the start of an image formation job has been instructed (YES in S10), the motors M0 and M1 are driven at the set rotation speeds (S13).

[0090] Next, the control unit 30 determines whether the image formation job has ended (S14). If the image formation job has not ended (NO in S14), the control unit 30 waits for the image formation job to end. If the image formation job has ended (YES in S14), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S15), sets the rotation speeds of the motors M0 and M1 to achieve the set peripheral speed ratio (S16), and stops driving the motors M0 and M1 (S17). Then, the control unit 30 ends this control.

[0091] In this embodiment, the speed difference between the recording material and the pressure roller 330 can be reduced regardless of the type of recording material. This reduces the amount of slippage of the recording material relative to the pressure roller 330, thereby preventing wear on the surface of the pressure roller 330. In other words, when the basis weight of the recording material is high, the amount of slippage of the recording material relative to the pressure roller 330 tends to increase. However, in this embodiment, the peripheral speed ratio is increased, i.e., the peripheral speed of the auxiliary drive roller 340 relative to the pressure roller 330 is increased. This increases the auxiliary drive force acting on the fixing belt 310, making it easier for the recording material to follow the pressure roller 330 even if the basis weight of the recording material is high. As a result, wear on the surface of the pressure roller caused by the recording material can be prevented.

[0092] The above-mentioned peripheral speed ratio relative to the basis weight of the recording material is an example, and is not uniquely determined by the configuration of the fixing device, etc. Furthermore, the effect of this embodiment is not limited to the above-mentioned peripheral speed ratio, and it is sufficient that the relationship between the peripheral speed V0 of the pressure roller 330 and the peripheral speed V1 of the auxiliary drive roller 340 satisfies V0≦V1.

[0093] [Peripheral speed ratio control according to the recording material conveying speed] Next, a case where the peripheral speed ratio V1 / V0 is changed depending on the conveying speed of the recording material will be described. First, the image forming apparatus 1 of this embodiment is capable of executing a first productivity priority mode, a second productivity priority mode, and an image quality priority mode. The first productivity priority mode is a mode that allows image formation to be performed most quickly depending on the type of recording material. That is, the first productivity priority mode is a mode in which the process speed and the conveying speed of the recording material are the fastest in the image forming apparatus 1. The second productivity priority mode is a mode that achieves both a certain level of productivity and image quality, and is a mode in which the process speed and the conveying speed of the recording material are slower than those in the first productivity mode.

[0094] The image quality priority mode is a mode in which the highest quality image can be formed in the image forming apparatus 1. The image quality priority mode is a mode in which the process speed and recording material conveyance speed are slower than those in the second productivity priority mode, for example, for thick coated paper. The user can select one of the image formation modes from the first productivity priority mode, the second productivity priority mode, and the image quality priority mode, for example, by using the operation unit 4.

[0095] Table 3 shows the relationship between the recording material conveying speed according to each mode and type in this embodiment. Table 3 shows thin uncoated paper and thick coated paper as the types of recording material. [Table 3]

[0096] As described above, in this embodiment, there are three types of modes, and the conveying speed of the recording material is different in each mode. The peripheral speed ratio V1 / V0 is changed according to the conveying speed of the recording material. That is, the peripheral speed ratio V1 / V0 when the conveying speed of the recording material conveyed at the nip portion N is the first conveying speed is set as the first peripheral speed ratio. Conveying speed is a second conveying speed faster than the first conveying speed, the peripheral speed ratio V1 / V0 is set to be a second peripheral speed ratio greater than the first peripheral speed ratio.

[0097] As described above, in this embodiment, the peripheral speed ratio V1 / V0 is changed by setting the peripheral speed V0 of the pressure roller 330 to a peripheral speed that matches the process speed (the conveying speed of the recording material) and changing the peripheral speed V1 of the auxiliary drive roller 340. In addition, the relationship between the peripheral speeds V0 and V1 is set to satisfy V1≧V0.

[0098] As an example, Table 4 shows the relationship between the conveying speed of the recording material for each image forming mode of thick coated paper, and the peripheral speeds and peripheral speed ratios of the motor M0 that drives the pressure roller 330 and the motor M1 that drives the auxiliary drive roller 340. [Table 4]

[0099] First, when the image forming mode is the first productivity priority mode, the recording material conveying speed is 600 mm / s and the peripheral speed ratio is 120%. Therefore, the rotation speeds of the motors M0 and M1 are controlled so that the peripheral speed of the pressure roller 330 is 600 mm / s and the peripheral speed of the auxiliary drive roller 340 is 720 mm / s.

[0100] Next, when the image formation mode is the second productivity priority mode, the recording material conveyance speed is 500 mm / s and the peripheral speed ratio is 110%. Therefore, the rotation speeds of the motors M0 and M1 are controlled so that the peripheral speed of the pressure roller 330 is 500 mm / s and the peripheral speed of the auxiliary drive roller 340 is 550 mm / s.

[0101] When the image formation mode is the image quality priority mode, the conveying speed of the recording material is 300 mm / s and the peripheral speed ratio is 100%. Therefore, 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 also 300 mm / s.

[0102] [Slippage improvement effect of auxiliary drive rollers] The effect of the peripheral speed ratio between the auxiliary drive roller 340 and the pressure roller 330 on the amount of slippage will now be described. Figure 12 shows the amount of slippage, expressed as a percentage, between the recording material passing through the nip portion and the pressure roller 330 when the peripheral speed ratio is changed relative to the conveying speed of the recording material. Note that this percentage is a value based on the amount of slippage when the conveying speed is 300 mm / s and the peripheral speed ratio is 100%.

[0103] 12, when the peripheral speed ratio V1 / V0 of the auxiliary drive roller 340 to the pressure roller 330 is increased, the amount of slippage decreases regardless of the conveyance speed of the recording material. This is because applying an auxiliary drive force to the fixing belt 310 reduces the sliding resistance generated on the inner peripheral surface of the fixing belt 310, and as a result, the difference in conveyance speed at the nip between the pressure roller 330 and the recording material is reduced.

[0104] As shown in Figure 12, when the circumferential speed ratio is 100%, which is the first circumferential speed ratio, the amount of slippage at a conveying speed of 500 mm / s is approximately 10% larger than at a conveying speed of 300 mm / s. In contrast, when the conveying speed is 500 mm / s, the circumferential speed ratio is increased to approximately 110%, which is the second circumferential speed ratio. This makes it possible to make the amount of slippage at a conveying speed of 500 mm / s equivalent to the amount of slippage at a conveying speed of 300 mm / s. Note that the first and second circumferential speed ratios are not limited to the values ​​described above and can be set as appropriate.

[0105] Next, the flow of control of the peripheral speed ratio according to the conveying speed of the recording material in this embodiment will be described using Fig. 13 while also referring to Fig. 2 and Fig. 4. Here, as an example, image formation processing on thick coated paper will be described.

[0106] The control unit 30 starts an image formation job when, for example, the start key on the operation unit 4 is operated, and ends the image formation job when the image formation operation on the last recording material of the image formation job is completed. In the image forming apparatus 1 (FIG. 1), the control unit 30 displays an input screen, etc. on the display unit 5, and receives information such as the paper type and basis weight of the recording material, and the print mode (image formation mode) through the displayed input screen. The control unit 30 then stores the information in the memory 33 (S101). Next, the control unit 30 acquires information regarding the paper type of the recording material from the memory 33 (S102). The control unit 30 also acquires information regarding the print mode from the memory 33 (S103). Furthermore, the control unit 30 reads out a peripheral speed ratio control table (e.g., Table 4) from the memory 33 (S104).

[0107] The control unit 30 determines whether the acquired print mode is the first productivity priority mode (SS105). If the print mode is the first productivity priority mode (YES in S105), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 120% (S106). If the print mode is not the first productivity priority mode (NO in S105), the control unit 30 determines whether the acquired print mode is the second productivity priority mode (S107). If the print mode is the second productivity priority mode (YES in S107), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 110% (S108). If the print mode is not the second productivity priority mode (NO in S107), the peripheral speed ratio control unit 32a refers to the peripheral speed ratio control table and sets the peripheral speed ratio to 100% (S109). The peripheral speed ratio control unit 32a sets the rotation speeds of the motors M0 and M1 to achieve the set peripheral speed ratio (S110).

[0108] Then, the control unit 30 determines whether the start of an image formation job has been instructed by a user operation (S111). If the start of an image formation job has not been instructed (NO in S111), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S112), and sets the rotation speeds of the motors M0 and M1 to achieve the set peripheral speed ratio (S113). Thereafter, the control unit 30 repeats the above-described processes of S101 to S110. If the start of an image formation job has been instructed (YES in S111), the motors M0 and M1 are driven at the set rotation speeds (S114).

[0109] Next, the control unit 30 determines whether the image formation job has ended (S115). If the image formation job has not ended (NO in S115), the control unit 30 waits for the image formation job to end. If the image formation job has ended (YES in S115), the peripheral speed ratio control unit 32a sets the peripheral speed ratio to 100% (S116), sets the rotation speeds of the motors M0 and M1 to achieve the set peripheral speed ratio (S117), and stops driving the motors M0 and M1 (S118). Then, the control unit 30 ends this control.

[0110] In this embodiment, the speed difference between the recording material and the pressure roller 330 can be reduced regardless of the recording material conveyance speed. This reduces the amount of slippage of the recording material relative to the pressure roller 330, thereby preventing wear on the surface of the pressure roller 330. While the amount of slippage of the recording material relative to the pressure roller 330 tends to increase when the recording material conveyance speed is high, this embodiment increases the peripheral speed ratio, i.e., increases the peripheral speed of the auxiliary drive roller 340 relative to the pressure roller 330. This increases the auxiliary drive force acting on the fixing belt 310, making it easier for the recording material to follow the pressure roller 330 even when the recording material conveyance speed is high. As a result, wear on the surface of the pressure roller caused by the recording material can be prevented.

[0111] It should be noted that the peripheral speed ratios for the above-described print modes (image forming modes) are merely examples and are not uniquely determined by the configuration of the fixing device, etc. The effects of this embodiment are not limited to the above-described peripheral speed ratios, and it is sufficient that the relationship between the peripheral speed V0 of the pressure roller 330 and the peripheral speed V1 of the auxiliary drive roller 340 satisfies V0≦V1.

[0112] In the above embodiment, the control according to the basis weight of the recording material and the control according to the conveying speed of the recording material (i.e., the image forming mode) are described separately, but these may also be combined. That is, information on the basis weight of the recording material and information according to the conveying speed of the recording material (the image forming mode) are used to control the peripheral speed ratio.

[0113] For example, when the conveying speed of the recording material conveyed at the nip portion is the second conveying speed (for example, the first productivity priority mode), the peripheral speed ratio V1 / V0 when the recording material has a first basis weight is set to the third peripheral speed ratio, and the peripheral speed ratio V1 / V0 when the recording material has a second basis weight that is larger than the first basis weight is set to the fourth peripheral speed ratio that is larger than the third peripheral speed ratio. In other words, when the same image forming mode is used, the peripheral speed ratio is made larger when the recording material has a larger basis weight. Note that, when different image forming modes are used for recording material of the same basis weight, the peripheral speed ratio is made larger when the image forming mode in which the recording material is conveyed at a faster speed is used, as described above.

[0114] For example, the peripheral speed ratio is set by multiplying the peripheral speed ratio according to the basis weight of the recording material corresponding to the image forming job by the peripheral speed ratio according to the image forming mode. The peripheral speed ratio according to the basis weight of the recording material shown in Table 2 and the peripheral speed ratio according to the image forming mode shown in Table 4 are referenced, and the peripheral speed ratio is set for thick paper (81 to 400 g / m 2 ), the first productivity priority mode is executed as an example. From Table 2, the peripheral speed ratio for thick paper is 110%, and from Table 4, the peripheral speed ratio for the first productivity priority mode is 120%, so the peripheral speed ratio setting for this condition is 110% for thick paper × 120% for the first productivity priority mode = 132%.

[0115] In this way, by setting the peripheral speed ratio taking into consideration the basis weight of the recording material and the conveying speed of the recording material, it is possible to reduce the speed difference between the recording material and the pressure roller 330, regardless of the basis weight and conveying speed of the recording material. This reduces the amount of slippage of the recording material against the pressure roller 330, and prevents the surface of the pressure roller 330 from wearing out.

[0116] <Other embodiments> In each of the above-described embodiments, the motor M0 for the pressure roller and the motor M1 for the auxiliary drive roller are provided independently. However, a common motor may be used for the pressure roller and the auxiliary drive roller. That is, the pressure roller and the auxiliary drive roller may be driven by a common drive source. In this case, a speed change mechanism is provided between one motor and one of the rollers, allowing the peripheral speed ratio to be controlled as described above.

[0117] In addition, in the above-described embodiments, the auxiliary driving roller 340 is disposed downstream of the fixing pad 320 and upstream of the steering roller 350 with respect to the rotation direction of the fixing belt 310. However, the positions of the auxiliary driving roller 340 and the steering roller 350 may be interchanged. That is, with respect to the rotation direction of the fixing belt 310, the auxiliary driving roller 340 may be disposed downstream of the steering roller 350 and upstream of the fixing pad 320.

[0118] In the above-described embodiments, a halogen heater is provided on the auxiliary drive roller as a heat source for heating the fixing belt. However, the heat source may be provided on another tension member, such as a steering roller, instead of on the auxiliary drive roller. It may also 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. The fixing belt may also be heated by electromagnetic induction.

[0119] In addition, in each of the above-described embodiments, a fixing device in which the fixing belt is stretched by a fixing pad, an auxiliary drive roller, and a steering roller has been described. However, fixing devices to which the present invention can be applied are not limited to this, and may have a configuration in which the fixing belt is stretched by only one tension roller and a fixing pad. The key is to have at least one tension roller that stretches the fixing belt together with the fixing pad. [Explanation of symbols]

[0120] 8··· Fixing device / 310··· Fixing belt (belt) / 320··· Fixing pad (nip forming member, pad member) / 330··· Pressure roller (drive roller) / 340··· Auxiliary drive roller / 350··· Steering roller (tension roller)

Claims

1. An image forming unit that forms a toner image on a recording material; a fixing device that fixes the toner image on the recording material on which the toner image has been formed by the image forming unit; a control unit, the fixing device, an endless rotatable belt; a drive roller having an elastic layer, which rotates in contact with the outer peripheral surface of the belt to apply a driving force to the belt; a nip portion forming member disposed inside the belt so as to face the drive roller across the belt, and which forms a nip portion between the belt and the drive roller for nipping and conveying a recording material; an auxiliary drive roller that is disposed inside the belt, rotates together with the nip portion forming member while tensioning the belt, and applies a driving force to the belt; The control unit a first mode in which the conveying speed of the recording material conveyed at the nip portion is set to a first conveying speed, and a second mode in which the conveying speed of the recording material conveyed at the nip portion is set to a second conveying speed that is faster than the first conveying speed, When a peripheral speed of the drive roller is V0, a ​​peripheral speed of the auxiliary drive roller is V1, and V1 / V0 is a peripheral speed ratio, and a toner image is fixed to the same type of recording material in the first mode and the second mode, the peripheral speed of the auxiliary drive roller is changed so that the peripheral speed ratio becomes a first peripheral speed ratio in the first mode and so that the peripheral speed ratio becomes a second peripheral speed ratio that is greater than the first peripheral speed ratio in the second mode. An image forming apparatus characterized by:

2. In the second mode, the peripheral speed of the auxiliary driving roller is changed so that the peripheral speed ratio when the basis weight of the recording material is a first basis weight is a third peripheral speed ratio, and so that the peripheral speed ratio when the basis weight of the recording material is a second basis weight that is larger than the first basis weight is a fourth peripheral speed ratio that is larger than the third peripheral speed ratio.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. V1≧V0 3. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first ink jet head;

4. The fixing device includes a tension roller that is disposed inside the belt, tensions the belt together with the nip portion forming member and the auxiliary drive roller, and rotates in response to the belt; The auxiliary driving roller is disposed downstream of the nip forming member and upstream of the tension roller in the rotation direction of the belt.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

5. The nip portion forming member is a pad member in which at least a part of the portion that forms the nip portion is formed in a flat shape.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

6. The auxiliary driving roller stretches the belt via a lubricant.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

Images