JP7516108B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus using an electrophotographic method, an electrostatic recording method, or the like.

Conventionally, in image forming devices using electrophotography, an electrostatic latent image formed on a photosensitive drum serving as an image carrier is developed with toner in a developing device to form a toner image, which is then transferred to a recording material and then fixed to the recording material in a fixing device. One example of a fixing device that is widely used is a heat and pressure type that has a heating rotor and a pressure rotor that pressurizes the heating rotor, and conveys the recording material by nipping it in the fixing nip between the heating rotor and the pressure rotor, thereby fixing the toner carried on the recording material by heat and pressure.

As the recording material accumulates in the fixing device, friction scratches caused by the recording material may occur on the surfaces of the heating and pressure rotating bodies (hereinafter, both are referred to as the rotating bodies) due to the recording material being conveyed while being pressed in the fixing nip. If a toner image is softened by heating using a rotating body with friction scratches, and then fixed to the recording material, there is a risk that the surface condition of the rotating body will be transferred to the toner image. As a result, gloss unevenness may occur on the output recording material.

In order to prevent such uneven gloss and other defects, a fixing device has been proposed that includes a rubbing device having a rubbing rotor that can be brought into contact with and separated from a rotor. For example, a fixing device is known that has a rubbing rotor that can be brought into contact with and separated from a heating rotor and a rubbing rotor that can be brought into contact with and separated from a pressure rotor, and that simultaneously rubs each rubbing rotor for the same amount of time to restore the surface condition (see Patent Document 1).

Here, in order to improve the friction scratches on the multiple rotating bodies in the fixing device, the friction rotating bodies provided for the multiple rotating bodies must be controlled individually. However, the heating rotating body and the pressure rotating body have different cumulative numbers of sheets of recording material passed through that become apparent as image defects depending on their configuration and sheet type. For this reason, a counter that counts the cumulative number of sheets of recording material passed through the heating rotating body and a counter that counts the cumulative number of sheets of recording material passed through the pressure rotating body are separately provided. Then, when one of the counters reaches a target value, it is possible to control both rotating bodies to execute the friction mode simultaneously.

JP 2009-294453 A

However, in the fixing device described in Patent Document 1, if the friction mode is executed simultaneously on both rotors when the counter of one of the rotors reaches the target value, the following problem may occur. That is, in such a configuration, for example, when the counter of the heating rotor reaches the target value, the counter of the pressure rotor may not reach the target value, and there may be no friction scratches to be improved on the pressure rotor. However, even in such a case, the friction rotor is rubbed against both the heating rotor and the pressure rotor for the same amount of time, so that the friction rotor is unnecessarily driven even when there is no need to improve the friction scratches to be improved, which may shorten the life of each rotor.

On the other hand, it is possible to implement control in which the rubbing mode is executed only on the heating rotor when the counter for the heating rotor reaches a target value, and the rubbing mode is executed only on the pressure rotor when the counter for the pressure rotor reaches a target value. However, with this configuration, downtime increases due to executing the rubbing mode independently for each rotor, and this may reduce the productivity of the image forming device.

The present invention aims to provide an image forming apparatus that can achieve both longer life for the rotating body and the rubbing rotating body that form the fixing nip and improved productivity.

The image forming apparatus of the present invention is an image forming apparatus including a fixing device which fixes an unfixed toner image formed in an image forming section onto a recording material, and a control section which controls the fixing device, the fixing device including a first rotating body and a second rotating body which come into contact with each other and apply pressure to each other to form a fixing nip section, a heating means capable of heating at least one of the first rotating body and the second rotating body, a first rubbing device capable of moving a first rubbing means capable of rubbing the first rotating body by rubbing it against the first rotating body toward and away from the first rotating body, and a second rubbing device capable of moving a second rubbing means capable of rubbing the second rotating body by rubbing it against the second rotating body toward and away from the second rotating body, and the control section controls the fixing device to fix a second recording material having a basis weight larger than that of the first recording material through the fixing nip section without allowing the second recording material to pass through the fixing nip section. when the number of the first recording material that has passed through the fixing nip portion exceeds a first number, the first rubbing device is operated for a first rubbing time to rub the first rotating body, and the second rubbing device is further operated for a second rubbing time to rub the second rotating body; when the number of the second recording material that has passed through the fixing nip portion exceeds a second number which is less than the first number, without allowing the first recording material to pass through the fixing nip portion, the second rubbing device is operated for a third rubbing time to rub the second rotating body, and the first rubbing device is further operated for a fourth rubbing time to rub the first rotating body, and the first rubbing time and the second rubbing time are controlled so that they at least partially overlap, the third rubbing time and the fourth rubbing time overlap at least partially, and the third rubbing time is longer than the second rubbing time.

The present invention makes it possible to achieve both longer life for the rotating body and the rubbing rotating body that form the fixing nip and improved productivity.

1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a control block diagram of the image forming apparatus according to the embodiment. FIG. 2 is a cross-sectional view showing a fixing device according to the embodiment. 3A and 3B are diagrams illustrating a first rubbing roller of a fixing device according to an embodiment, in which FIG. 3A is a cross-sectional view and FIG. 3B is an enlarged cross-sectional view of a portion of FIG. FIG. 2 is a side view illustrating a fixing belt and a pressure roller of the fixing device according to the embodiment. 6 is a flowchart showing an operation procedure of fixing devices according to first and second comparative examples. 11 is a flowchart showing an operation procedure of fixing devices according to comparative examples 3 and 4. 4 is a flowchart showing an operation procedure of the fixing device according to the first and second embodiments.

Hereinafter, an embodiment of the present invention will be described in detail with reference to Figs. 1 to 5. In this embodiment, a tandem-type full-color printer is described as an example of an image forming device 1. However, the present invention is not limited to a tandem-type image forming device 1, but may be an image forming device of another type, and is not limited to being full-color, but may be monochrome or monocolor.

[Image forming apparatus]
As shown in FIG. 1, the image forming apparatus 1 is an electrophotographic full-color printer having image forming units PY, PM, PC, and PK of four colors (yellow, magenta, cyan, and black) in the main body of the apparatus. In this embodiment, the image forming units PY, PM, PC, and PK are arranged in an intermediate transfer tandem type along the rotation direction of an intermediate transfer belt 7 described later. The image forming apparatus 1 forms a toner image (image) on a recording material S in response to an image signal from a document reading device (not shown) connected to the main body of the apparatus or a host device such as a personal computer connected to the main body of the apparatus so as to be able to communicate with the main body of the apparatus. Examples of the recording material S include sheet materials such as paper, plastic film, and cloth. The image forming apparatus 1 also includes a control unit 20 for performing various controls such as an image forming process.

The image formation process will now be described. First, the image forming units PY, PM, PC, and PK will be described. In this embodiment, the image forming units PY, PM, PC, and PK are configured almost identically, except that the toner colors differ: yellow, magenta, cyan, and black. Therefore, the following description will be given using the yellow image forming unit PY as an example, and descriptions of the other image forming units PM, PC, and PK will be omitted.

The image forming unit PY is mainly composed of a photosensitive drum 2, a charging device 3, an exposure device 4, a developing device 5, etc. The surface of the photosensitive drum 2, which is an example of an image carrier that is rotated, is uniformly charged in advance by the charging device 3, and then an electrostatic latent image is formed by the exposure device 4, which is driven based on a signal of image information. That is, an electrostatic latent image is formed on the photosensitive drum 2. The electrostatic latent image formed on the photosensitive drum 2 is developed with toner by the developing device 5 and made visible as a toner image. In addition, the toner in the developer consumed in image formation is replenished together with carrier from a toner cartridge (not shown).

Then, a predetermined pressure and a primary transfer bias are applied by the primary transfer roller 6, which is disposed opposite the photosensitive drum 2 with the intermediate transfer belt 7 sandwiched between them, and the toner image formed on the photosensitive drum 2 is primarily transferred onto the intermediate transfer belt 7. The small amount of residual toner remaining on the photosensitive drum 2 after the primary transfer is removed by the cleaning device 8, and the image is prepared for the next image formation process.

The intermediate transfer belt 7 is tensioned by a tension roller 10, a secondary transfer inner roller 11, and a drive roller 12. The intermediate transfer belt 7 is driven by the drive roller 12 to move in the direction of the arrow R1 in the figure. The image formation process of each color processed by the image forming units PY, PM, PC, and PK described above is performed at a timing to sequentially superimpose the toner image of the color upstream in the moving direction that has been primarily transferred onto the intermediate transfer belt 7. As a result, a full-color toner image is finally formed on the intermediate transfer belt 7 and is transported to the secondary transfer unit 15. The secondary transfer unit 15 is a transfer nip portion formed by the part of the intermediate transfer belt 7 tensioned by the secondary transfer inner roller 11 and the secondary transfer outer roller 13. Note that the transfer residual toner after passing through the secondary transfer unit 15 is removed from the intermediate transfer belt 7 by the transfer cleaner device 14.

The process of transporting the recording material S to the secondary transfer unit 15 is executed at the same timing as the process of forming the toner image sent to the secondary transfer unit 15. In the transport process, the recording material S is fed from a sheet cassette (not shown) and sent to the secondary transfer unit 15 in accordance with the image formation timing. In the secondary transfer unit 15, a secondary transfer voltage is applied to the inner secondary transfer roller 11.

Through the image formation process and transport process described above, the toner image is secondarily transferred from the intermediate transfer belt 7 to the recording material S in the secondary transfer section 15. The recording material S is then transported to the fixing device 30, where it is heated and pressurized to melt and fix the toner image onto the recording material S. That is, the fixing device 30 fixes the unfixed toner image formed in the image forming section onto the recording material S. The recording material S with the fixed toner image is then discharged by the discharge rollers onto a discharge tray (not shown).

[Control unit]
The image forming apparatus 1 includes a control unit 20 for performing various controls such as the image forming operation described above. The operation of each part of the image forming apparatus 1 is controlled by the control unit 20 provided in the image forming apparatus 1. A series of image forming operations is controlled by the control unit 20 in accordance with each input signal input from an operation unit on the top surface of the apparatus body or via a network.

As shown in FIG. 2, the control unit 20 has a central processing unit (CPU) 21, a read only memory (ROM) 22, a random access memory (RAM) 23, etc., as a calculation control means. The CPU 21 controls each part of the image forming apparatus 1 while reading a program corresponding to a control procedure stored in the ROM 22. The RAM 23 stores work data and input data, and the CPU 21 performs control by referring to the data stored in the RAM 23 based on the above-mentioned program, etc. The control unit 20 is connected to a drive motor M1 for driving the fixing belt 41 and pressure roller 32 of the fixing device 30 described later, a heater 48, a thermistor 49, a first rubbing device 51, and a second rubbing device 52 described later, etc., and can control the fixing device 30. The CPU 21 or the RAM 23 has a first counter and a second counter described later.

[Fixing device]
Next, the fixing device 30 will be described in detail with reference to Fig. 3. As shown in Fig. 3, the fixing device 30 is a belt heating type heating device, and is formed in the shape of a cartridge that is detachable from the main body of the image forming apparatus 1 (see Fig. 1). The fixing device 30 has a housing 31, a heating unit 40, a pressure roller 32 as a second rotating body, and a separation unit 50.

The heating unit 40 has a fixing belt 41 as a first rotating body that is endless and rotatable, a pressure pad 42 as a fixing member, a heating roller 43, a steering roller 44, a stay 45, and a unit side plate 46 that integrates these in a cart lodge shape. The heating unit 40 is removably attached to the housing 31. The unit side plates 46 are provided on both sides of the heating unit 40 in the direction of the rotation axis.

The fixing belt 41 is a thin cylindrical belt member that can be heated by contacting the recording material S and has thermal conductivity, heat resistance, etc. In this embodiment, the fixing belt 41 has a three-layer structure with 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), and the elastic layer is 300 μm thick and made of silicone rubber. The release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 41 is stretched by a pressure pad 42, a heating roller 43, and a steering roller 44. The outer diameter of the fixing belt 41 is, for example, 120 mm.

The pressure pad 42 is supported by a stay 45 and is pressed against the pressure roller 32 with the fixing belt 41 sandwiched between them. The stay 45 is made of stainless steel, and both ends of the stay 45 in the direction of the rotation axis are supported by the fixing frame 33 of the housing 31 of the fixing device 30. The fixing nip N is formed by the contact area between the fixing belt 41 and the pressure roller 32. The direction of the rotation axis is perpendicular to the transport direction of the recording material S that has passed through the fixing nip N.

The pressure pad 42 is made of, for example, LCP (liquid crystal polymer) resin. A lubricating sheet 47 is interposed between the pressure pad 42 and the fixing belt 41. The lubricating sheet 47 is, for example, a PI (polyimide) sheet coated with PTFE (polytetrafluoroethylene) having a thickness of 100 μm. This PI sheet has 100 μm protrusions formed at 1 mm intervals, which reduces the contact area with the fixing belt 41 and thereby reduces sliding resistance. A lubricant is applied to the inner surface of the fixing belt 41, allowing the fixing belt 41 to slide smoothly against the pressure pad 42. Silicone oil, for example, is used as the lubricating material.

The heating roller 43 is a stainless steel pipe with a thickness of 1 mm, and a heater 48 (see FIG. 2) is disposed inside the pipe as a heating means, such as a halogen heater, and can heat the heating roller 43 to a predetermined temperature. The fixing belt 41 is heated by the heating roller 43, and is controlled to a predetermined target temperature according to the type of sheet based on the temperature detected by the thermistor 49. The thermistor 49 is disposed in contact with the heating roller 43. In addition, the heating roller 43 has a gear (not shown) fixed to one end in the rotation axis direction, and is connected to a drive motor M1 (see FIG. 2) via the gear and driven to rotate. The fixing belt 41 rotates following the rotation of the heating roller 43. In this embodiment, the heater 48 is described as being capable of heating the fixing belt 41, but this is not limited to the above, and at least one of the fixing belt 41 and the pressure roller 32 can be heated.

The steering roller 44 has a rotation center in the substantially vertical direction at one end of the rotation axis or near the center, and rotates relative to the fixing belt 41 to generate a tension difference in the main scanning direction, thereby adjusting the position of the fixing belt 41 in the main scanning direction. The steering roller 44 is biased by a biasing spring (not shown) supported by the frame of the heating unit 40, and is also a tension roller that applies a predetermined tension to the fixing belt 41.

The pressure roller 32 faces the fixing belt 41 and abuts against it, forming a pressurized fixing nip N between the fixing belt 41 and the pressure roller 32. The pressure roller 32 is a roller with an elastic layer formed on the outer circumference of the shaft and a release layer formed on the outer circumference of the elastic layer. In this pressure roller 32, the shaft is made of stainless steel, and the elastic layer is 5 mm thick and made of conductive silicone rubber. The release layer is 50 μm thick and uses PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The pressure roller 32 is axially supported by the fixing frame 33 of the housing 31 of the fixing device 30, and a gear is fixed to one end of the rotation axis direction, and is connected to the drive motor M1 (see Figure 2) via the gear to be rotated.

In the fixing nip N formed between the fixing belt 41 and the pressure roller 32, the recording material S (see FIG. 1) carrying a toner image is sandwiched and the toner image is heated while being transported. In this way, the fixing device 30 fixes the toner image to the recording material S while sandwiching and transporting the recording material S. Therefore, it is necessary to achieve both the function of applying heat and pressure and the function of transporting the recording material S.

The fixing frame 33 is fixed to both sides of the housing 31 in the direction of the rotation axis, and is provided with a guide portion 34, a pressure frame 35, and a pressure spring 36. The stay 45 of the heating unit 40 is inserted into the guide portion 34 and is fixed by being pressed against the guide portion 34 by a pressing portion (not shown). After the stay 45 is fixed to the guide portion 34, the pressure frame 35 is moved toward the heating unit 40 by a driving source and a cam (not shown), so that the pressure roller 32 is pressed against the pressure pad 42 via the fixing belt 41. The pressure applied to the pressure pad 42 by the pressure roller 32 during image formation is, for example, 1000 N. The fixing frame 33 supports a separation unit 50 that separates the recording material S that has passed through the fixing nip portion N from the fixing belt 41.

The guide portion 34 has a support surface 34a, a positioning surface 34b, and a sliding surface 34c. The support surface 34a is formed on the opposite side of the pressure roller 32 along the mounting direction D1 in which the heating unit 40 is inserted, and supports the reaction force that the fixing belt 41 receives from the pressure roller 32 on the inner peripheral side of the fixing belt 41 when the heating unit 40 is located at the mounting position shown in FIG. 3. The positioning surface 34b is formed approximately vertically at the innermost part of the guide portion 34 in the mounting direction D1, and when the heating unit 40 is located at the mounting position, it abuts against the heating unit 40 in the mounting direction D1 to position it. The sliding surface 34c is formed along the mounting direction D1 opposite the support surface 34a, and guides the stay 45 by sliding it when inserting or removing the heating unit 40. The heating unit 40 can be moved to the mounting position by inserting the stay 45 into the guide portion 34, and the heating unit 40 can be removed from the housing 31 by removing the stay 45 from the outside of the guide portion 34.

In this embodiment, the mounting direction D1 for inserting the heating unit 40 is a direction along the conveying direction of the recording material S held in the fixing nip N, and is set parallel here. However, the mounting direction D1 does not have to be completely parallel to the sheet conveying direction in the fixing nip N, but may be roughly parallel, and the mounting direction D1 and the sheet conveying direction may be set in the opposite direction.

[Rubbing device]
The fixing device 30 has a first rubbing device 51 and a second rubbing device 52. The first rubbing device 51 and the second rubbing device 52 will be described in detail below with reference to FIGS. 3 and 4. As shown in FIG. 3, the first rubbing device 51 has a first rubbing roller 53 as an example of a first rubbing means capable of rubbing the fixing belt 41 by rubbing against the fixing belt 41, and a main body 54. The main body 54 allows the first rubbing roller 53 to be moved toward and away from the fixing belt 41 while rotating as a refresh roller. The second rubbing device 52 has a second rubbing roller 55 as an example of a second rubbing means capable of rubbing the pressure roller 32 by rubbing against the pressure roller 32, and a main body 56. The main body 56 allows the second rubbing roller 55 to be moved toward and away from the pressure roller 32 while rotating as a refresh roller. In this embodiment, the first rubbing roller 53 and the second rubbing roller 55 are polishing rollers capable of polishing the rubbing target by rotation. The first rubbing device 51 and the second rubbing device 52 are configured with the same mechanism. Therefore, the following description will be given using the first rubbing device 51 as a representative example, and the description of the second rubbing device 52 will be omitted.

4(a) and (b), the first rubbing roller 53 is configured by providing a rubbing layer (surface layer) 53c formed by densely bonding abrasive grains to a core metal 53a of SUS304 (stainless steel) having an outer diameter of 12 mm via an adhesive layer (intermediate layer) 53b. The first rubbing roller 53 is supported by biasing both ends of the core metal 53a in the direction of the rotation axis toward the heating roller 43 by a pressure spring (not shown). The thickness of the rubbing layer 53c is 5 μm or more and 20 μm or less. As the abrasive grains, aluminum oxide, aluminum hydroxide oxide, silicon oxide, cerium oxide, titanium oxide, zirconia, lithium silicate, silicon nitride, silicon carbide, iron oxide, chromium oxide, antimony oxide, diamond, and mixtures thereof can be used. Here, aluminum oxide-based (also called alumina, alundum, or molandum) abrasive grains having a grain size of 5 μm or more and 10 μm or less are used as the abrasive grains. Aluminum oxide is the most widely used abrasive grain, and is sufficiently hard compared to the release layer of the fixing belt 41 suspended on the heating roller 43, is inexpensive, and has excellent cutting properties due to its acute angle shape. It has been confirmed that the use of the first rubbing roller 53 with such a configuration achieves both a refreshing effect on the surface of the fixing belt 41 and the surface properties of the fixed image after refreshing.

As shown in FIG. 2, the main body 54 brings the first rubbing roller 53 into contact with and away from the fixing belt 41. The first rubbing roller 53 is driven by the main body 54 and contacts the fixing belt 41 with a predetermined pressure due to the biasing force of a spring, forming a rubbing nip (not shown) having a predetermined width in the rotational direction. The first rubbing roller 53 is driven to rotate, and a difference in peripheral speed is provided between the rotational speed of the fixing belt 41 and the first rubbing roller 53, so that the first rubbing roller 53 rubs the fixing belt 41 in the rubbing nip.

[Refresh Mode Overview]
Next, a first mode in which the first rubbing device 51 is operated to rub the first rubbing roller 53 and a second mode in which the second rubbing device 52 is operated to rub the second rubbing roller 55 will be described in detail. The first rubbing roller 53 and the second rubbing roller 55 can oscillate independently of each other. Therefore, the first rubbing roller 53 and the second rubbing roller 55 can be brought into contact with and separated from the fixing belt 41 and the pressure roller 32, respectively. The control unit 20 operates the main body unit 54 and the main body unit 56 at an appropriate timing, and controls the start timing and execution time of the first mode, which is the fixing belt refresh mode, and the second mode, which is the pressure roller refresh mode. In this embodiment, the control unit 20 can execute the first mode and the second mode as the refresh mode simultaneously or separately.

The control unit 20 controls the start of the first mode based on the count value of the first counter, and controls the start of the second mode based on the count value of the second counter. The count value of each counter is calculated according to the size of the recording material passed through the fixing device 30 and the number of sheets passed. When the count value of each counter reaches a predetermined count threshold, each mode is operated. The counting method and count threshold of the count value of each counter will be described later.

When the control unit 20 starts to execute the first mode, the first rubbing device 51 brings the first rubbing roller 53 into contact with the fixing belt 41, thereby restoring the surface condition of the fixing belt 41. When the control unit 20 starts to execute the second mode, the second rubbing device 52 brings the second rubbing roller 55 into contact with the pressure roller 32, thereby restoring the surface condition of the pressure roller 32. When the first or second mode is executed, the passage of paper through the fixing device 30 is temporarily stopped.

In this embodiment, the first rubbing roller 53 is set to contact the fixing belt 41 at a speed 300 mm/s faster than the rotation of the fixing belt 41, and the second rubbing roller 55 is also set to contact the pressure roller 32 at a speed 300 mm/s faster than the rotation of the pressure roller 32. When the first rubbing roller 53 contacts the fixing belt 41, the surface temperature of the fixing belt 41 is adjusted to 170°C, and when the second rubbing roller 55 contacts the pressure roller 32, the surface temperature of the pressure roller 32 is adjusted to 90°C. The start timing and execution time of the first rubbing roller 53 and the second rubbing roller 55 will be described later.

[Changes in surface condition of fixing belt and pressure roller]
When fixing the unfixed toner image onto the recording material S, the fixing device 30 applies heat and pressure to the recording material S. At this time, there is a possibility that minute surface conditions of the fixing belt 41 and the pressure roller 32 are transferred to the surface of the fixed image. A difference in the surface condition of the fixed image occurs corresponding to the difference on the fixing belt 41 and the pressure roller 32, and there is a possibility that gloss unevenness occurs in the fixed image.

The change in the surface condition of the fixing belt 41 and the pressure roller 32 will be described with reference to FIG. 5. FIG. 5 is a view of the vicinity of the fixing nip portion N of the fixing device 30 shown in FIG. 2, viewed from the downstream side in the sheet conveying direction. As shown in FIG. 5, the fixing belt 41 and the pressure roller 32 have a paper passing portion Ar1 through which the recording material S passes and a non-paper passing portion Ar2 through which the recording material S does not pass, which are arranged adjacent to each other in the width direction of the paper passing portion Ar1. The surface condition of the paper passing portion Ar1 and the non-paper passing portion Ar2 of the fixing belt 41 and the pressure roller 32 differs depending on the cumulative number of sheets of the recording material S that have passed through, and this difference in the surface condition may cause gloss unevenness in the output image. The arithmetic mean height Sa (ISO 25178) used in the following description was measured using a confocal microscope (Keyence Corporation's confocal microscope VK-X1100).

The arithmetic mean height Sa of the surfaces of the fixing belt 41 and pressure roller 32 in the initial state is about 0.05 μm. Thereafter, as the recording material S passes through the fixing device 30, different degrees of surface roughness occur in the paper passing portion Ar1 and non-paper passing portion Ar2 of the fixing belt 41 and pressure roller 32. In the paper passing portion Ar1, the surfaces of the fixing belt 41 and pressure roller 32 are gradually roughened, and the arithmetic mean height Sa becomes about 0.08 μm to 0.1 μm. On the other hand, in the non-paper passing portion Ar2, the surfaces of the fixing belt 41 and pressure roller 32 are roughened, and the arithmetic mean height Sa reaches about 0.15 μm to 0.2 μm.

Therefore, in this embodiment, the rough surface condition of the fixing belt 41 and the pressure roller 32 caused by the above is rubbed by the first rubbing roller 53 and the second rubbing roller 55. The difference in the surface condition of the fixing belt 41 and the pressure roller 32 is made uniform by the surface shape of the first rubbing roller 53 and the second rubbing roller 55, thereby improving the gloss unevenness.

[Conditions for uneven gloss occurrence]
Here, a paper passing test was carried out in which the recording material S was passed through the fixing device 30, and the conditions under which gloss unevenness occurs were confirmed. First, 500 sheets of the recording material S were continuously passed through the fixing device 30, and then, when a verification sample was passed through, the occurrence state of gloss unevenness in the verification sample was confirmed. This process was repeated until gloss unevenness occurred (until the cumulative number of sheets passed reached 3500 sheets at the maximum). As the recording material S, A4 size CS-068 (manufactured by Canon Inc.) was used when passing plain paper, and A4 size GF-C300 (manufactured by Canon Inc.) was used when passing thick paper. When passing the recording material S, the surface temperature of the fixing belt 41 was adjusted to 170° C., and the surface temperature of the pressure roller 32 was adjusted to 85° C. The recording material S was continuously passed through the fixing device 30 so that the paper passing direction was the longitudinal direction of the recording material S. The speed of the fixing belt was set to 400 mm/s.

The verification sample used was an A3 size OK topcoat (manufactured by Oji Paper Co., Ltd.) of 127.9 g/ ^m2 , with black characters printed all over. The verification sample was passed through under two conditions, one in which the printed surface of the verification sample abutted against the fixing belt 41, and one in which the printed surface of the verification sample abutted against the pressure roller 32, to check the occurrence of gloss unevenness caused by the surfaces of the fixing belt 41 and the pressure roller 32. When the verification sample was passed through, the surface temperature of the fixing belt 41 was adjusted to 230°C, and the surface temperature of the pressure roller was adjusted to 110°C.

The results of checking the occurrence of gloss unevenness are shown in Table 1. In Table 1, "x" indicates no occurrence, "o" indicates occurrence, and "Δ" indicates slight occurrence.

As shown in Table 1, when plain paper was passed, gloss unevenness on the fixing belt 41 side was confirmed when the number of sheets of recording material S passed reached 2500, and gloss unevenness on the pressure roller 32 side was confirmed when the number of sheets of recording material S passed reached 3500. When thick paper was passed, gloss unevenness on the fixing belt 41 side was confirmed when the number of sheets of recording material S passed reached 2500, and gloss unevenness on the pressure roller 32 side was confirmed when the number of sheets of recording material S passed reached 2000. Therefore, in both cases when plain paper and thick paper were passed, it was confirmed that the occurrence of gloss unevenness gradually progressed as the number of sheets passed increased.

[Refresh mode start condition]
Based on the above results, in this embodiment, the counter calculation method and the initial value of the count threshold are determined for the control unit 20 as follows.
(1) The control unit 20 counts the number of sheets of paper that have passed through the fixing device 30 as a refresh counter, independently for the fixing belt 41 and the pressure roller 32 .
(Hereinafter, the count value counted for the fixing belt 41 will be referred to as a first counter, and the count value counted for the pressure roller 32 will be referred to as a second counter.)
(2) When the type of sheet passed through is plain paper, the control unit 20 causes both the first counter and the second counter to count the number of A4 size sheets passed through the fixing device 30. When the type of sheet passed through is thick paper, the first counter counts the number of A4 size sheets passed through the fixing device 30, and the second counter counts 1.75 times the number of A4 size sheets passed through the fixing device 30.
(3) A first threshold, which is a count threshold of a first counter preset for the fixing belt 41, is set to 2500, and when the first counter reaches the first threshold, the first rubbing device 51 is driven to operate the first rubbing roller 53, thereby executing the first mode.
(4) A second threshold value, which is a count threshold value of the second counter preset for the pressure roller 32, is set to 3500, and when the second counter reaches the second threshold value, the second rubbing device 52 is driven to operate the second rubbing roller 55, thereby executing the second mode. Note that in this embodiment, the first threshold value is smaller than the second threshold value.

The control unit 20 can therefore execute a first mode in which the first rubbing device 51 is operated to rub the fixing belt 41, and a second mode in which the second rubbing device 52 is operated to rub the pressure roller 32, depending on the number of sheets of recording material S that have passed through the fixing nip N. By having the control unit 20 process as described above, the difference in the surface conditions of the fixing belt 41 and the pressure roller 32 can be made uniform by operating the first rubbing roller 53 and the second rubbing roller 55 at an appropriate time when gloss unevenness occurs, thereby improving gloss unevenness.

[Refresh mode execution time]
Next, a rubbing test was carried out in which the first rubbing roller 53 or the second rubbing roller 55 was rubbed when gloss unevenness occurred, and the contact time of the first rubbing roller 53 or the second rubbing roller 55 required to improve the gloss unevenness was verified. Here, after gloss unevenness occurred in the paper passing test shown in Table 1, the first rubbing roller 53 was brought into contact with the fixing belt 41 for 10 seconds, or the second rubbing roller 55 was brought into contact with the pressure roller 32 for 10 seconds, and the above-mentioned verification sample was passed through to confirm the occurrence of gloss unevenness. This process was repeated until the gloss unevenness was eliminated (until the maximum contact time reached 60 seconds). The paper passing of the verification sample was performed under two conditions, a case in which the printed surface of the verification sample was in contact with the fixing belt 41 and a case in which the printed surface of the verification sample was in contact with the pressure roller 32, as in the paper passing test in Table 1, and the occurrence of gloss unevenness was confirmed under each condition. When the verification sample was passed through, the surface temperature of the fixing belt 41 was adjusted to 230° C., and the surface temperature of the pressure roller was adjusted to 110° C. The pressure of the first rubbing roller 53 and the second rubbing roller 55 was set to 30 N, and the rubbing speed in the forward direction was set to 300 mm/s.

Table 2 shows the results of checking the occurrence of gloss unevenness versus the contact time of the refreshing roller. In Table 2, ◯ indicates occurrence, × indicates no occurrence, and △ indicates improvement (slight occurrence). In Table 2, "plain paper" indicates the results of an investigation into gloss unevenness that occurred when plain paper was passed through, and "thick paper" indicates the results of an investigation into gloss unevenness that occurred when thick paper was passed through.

As shown in Table 2, it was confirmed that the gloss unevenness occurring in both plain paper and thick paper was improved by contacting the first rubbing roller 53 for 50 seconds with the fixing belt 41. Similarly, it was confirmed that the gloss unevenness occurring in both plain paper and thick paper was improved by contacting the second rubbing roller 55 for 60 seconds with the pressure roller 32. Based on the above results, in this embodiment, the control unit 20 is initially set to a contact time of 60 seconds for the first rubbing roller 53 and the second rubbing roller 55. In this embodiment, the contact time of the first rubbing roller 53 and the second rubbing roller 55 is set to 60 seconds, but this is not limited to this and may be other lengths. In addition, the contact time of the first rubbing roller 53 and the second rubbing roller 55 is not limited to being the same and may be different.

The results of the paper feed test shown in Table 1 confirmed that the occurrence of gloss unevenness progresses as the number of sheets fed increases. In addition, the results of the rubbing test shown in Table 2 confirmed that the improvement of gloss unevenness progresses as the contact time of the first rubbing roller 53 and the second rubbing roller 55 increases. Therefore, these results confirmed that the surface roughness of the fixing belt 41 and the pressure roller 32 changes depending on the contact time of the first rubbing roller 53 and the second rubbing roller 55.

[Comparative Examples 1 and 2]
Next, regarding the control of the fixing device 30, the execution procedure of the refresh mode in Comparative Examples 1 and 2 will be described with reference to the flowchart shown in Fig. 6. In Comparative Examples 1 and 2, independent processes are executed for the first rubbing roller 53 and the second rubbing roller 55, and here, the operation process on the first rubbing device 51 side and the operation process on the second rubbing device 52 side are executed one by one in sequence. In Comparative Example 1, plain paper is passed, and in Comparative Example 2, thick paper is passed.

When the control unit 20 receives a signal indicating that sheet transport is to be performed in the fixing device 30 (step S1), it first starts the operation process on the first rubbing device 51 side. The control unit 20 also executes the process from step S1 each time a sheet is passed through. The control unit 20 determines whether the first counter, which is a sheet passing counter for the fixing belt 41, has exceeded 2500 (step S2). The first counter is set to the same number as the number of sheets that have actually been passed through, regardless of whether the sheets being passed through are plain paper or thick paper.

If the control unit 20 determines that the first counter has exceeded 2500 (YES in step S2), it drives the first rubbing device 51 to perform a rubbing operation on the fixing belt 41 with the first rubbing roller 53 for 60 seconds (step S3), and then separates it. After this, the control unit 20 resets the first counter to 1 (step S4). On the other hand, if the control unit 20 determines that the first counter has not exceeded 2500 (NO in step S2), it increments the first counter by 1 (step S5).

When the operation process on the first rubbing device 51 side is completed (steps S4 and S5), the control unit 20 starts the operation process on the second rubbing device 52 side. The control unit 20 judges whether the second counter, which is a paper passing counter of the pressure roller 32, has exceeded 3500 (step S6). Note that the second counter is set to the same number of sheets actually passed if the sheets being passed are plain paper, and is set to the number of sheets actually passed multiplied by 1.75 if the sheets are thick paper.

If the control unit 20 determines that the second counter has exceeded 3,500 (YES in step S6), it drives the second rubbing device 52 to perform a rubbing operation on the pressure roller 32 by the second rubbing roller 55 for 60 seconds (step S7), and then separates it. After this, the control unit 20 resets the second counter to 1 (step S8), and ends the process. On the other hand, if the control unit 20 determines that the second counter has not exceeded 3,500 (NO in step S6), it increments the second counter by 1 (step S9), and ends the process.

[Comparative Examples 3 and 4]
Next, regarding the control of the fixing device 30, the execution procedure of the refresh mode in Comparative Example 2 will be described with reference to the flowchart shown in FIG. 7. In Comparative Examples 3 and 4, a common counter is used for the first rubbing roller 53 and the second rubbing roller 55, and both refresh modes are executed when the smallest count threshold is reached, regardless of whether the sheet passed is plain paper or thick paper. Here, the counter counts the number of A4 size sheets passed through the fixing device 30, and the count threshold is set to 2000 so as to avoid gloss unevenness on the pressure roller 32 side when thick paper is passed, which has the smallest count threshold. In Comparative Example 3, plain paper is passed, and in Comparative Example 4, thick paper is passed.

When the control unit 20 receives a signal indicating that sheet transport is being performed in the fixing device 30 (step S11), it determines whether the counter has exceeded 2000 (step S12). If the control unit 20 determines that the counter has exceeded 2000 (YES in step S12), it drives the first rubbing device 51 to perform a rubbing operation on the fixing belt 41 with the first rubbing roller 53 for 60 seconds and then separates. At the same time, the control unit 20 drives the second rubbing device 52 to perform a rubbing operation on the pressure roller 32 with the second rubbing roller 55 for 60 seconds (step S3) and then separates. After this, the control unit 20 resets the first counter to 1 (step S14) and ends the process. On the other hand, if the control unit 20 determines that the counter has not exceeded 2000 (NO in step S12), it increments the counter by 1 (step S15) and ends the process. The control unit 20 executes the process from step S1 every time one sheet is passed through.

[Examples 1 and 2]
Next, regarding the control of the fixing device 30, the execution procedure of the refresh mode in the first and second embodiments will be described with reference to the flowchart shown in FIG. 8. In the first and second embodiments, the first rubbing device 51 and the second rubbing device 52 are operated simultaneously for different periods of time. In addition, in the first embodiment, plain paper is passed through, and in the second embodiment, thick paper is passed through. In this embodiment, the basis weight of the plain paper is a first basis weight, and the basis weight of the thick paper is a second basis weight that is greater than the first basis weight.

When the control unit 20 receives a signal indicating that sheet transport is to be performed in the fixing device 30 (step S21), it first starts the operation process based on the first counter. The control unit 20 also executes the process from step S21 each time a sheet is passed through. The control unit 20 determines whether the first counter, which is a sheet passing counter for the fixing belt 41, has exceeded 2500 (step S22). The first counter is set to the same number of sheets that have actually passed through the fixing nip N, regardless of whether the sheets passing through the fixing nip N are plain paper or thick paper.

When the control unit 20 determines that the first counter has exceeded 2500 (YES in step S22), it drives the first rubbing device 51 to perform the rubbing operation (i.e., first mode) on the fixing belt 41 by the first rubbing roller 53 for 60 seconds, and then separates. Here, the first rubbing time T1, which is the time for rubbing the fixing belt 41 in the first mode, is set to 60 seconds. At the same time, the control unit 20 drives the second rubbing device 52 to perform the rubbing operation (i.e., second mode) on the pressure roller 32 by the second rubbing roller 55 for (second counter number x 60/3500) seconds (step S23), and then separates. Here, the second rubbing time T2, which is the time for rubbing the pressure roller 32 in the second mode, is set to (second counter number x 60/3500) seconds, which is shorter than the first rubbing time T1.

That is, after the first and second modes are completed, when the number of sheets of recording material S that have passed through the fixing nip N (number of sheets equivalent to passing) reaches the first threshold value of 2,500 sheets, the control unit 20 rubs the fixing belt 41 for 60 seconds, which is the first rubbing time T1, in the first mode. At the same time, the control unit 20 rubs the pressure roller 32 for (second counter number x 60/3,500) seconds, which is the second rubbing time T2, in the second mode. Note that the second rubbing time T2 is set to satisfy the relationship of P/S1 x first rubbing time T1, where S1 is the first threshold value and P is the number of sheets of recording material S that have passed through the fixing nip N (number of sheets equivalent to passing).

As a result, the control unit 20 executes the first mode and the second mode so that the second rubbing time T2 is shorter than the first rubbing time T1 and the first rubbing time T1 and the second rubbing time T2 overlap at least partially. Therefore, it is possible to realize the rubbing operation required for the pressure roller 32, and unnecessary rubbing can be suppressed. In this embodiment, the control unit 20 executes the first mode and the second mode so that the entire second rubbing time T2 overlaps with the first rubbing time T1. Furthermore, in this embodiment, the control unit 20 executes the first mode and the second mode so that the second rubbing time T2 and the first rubbing time T1 start at the same time. After execution, the control unit 20 resets both the first counter and the second counter to 1 (step S24). On the other hand, if the control unit 20 determines that the first counter does not exceed 2500 (NO in step S22), it increments the first counter by 1 (step S25).

When the control unit 20 finishes the operation process based on the first counter (steps S24 and S25), it starts the operation process based on the second counter. The control unit 20 judges whether the second counter, which is a paper passing counter of the pressure roller 32, has exceeded 3500 (step S26). If the sheet passing through the fixing nip N is a regular paper, the second counter is set to the same number of sheets that have actually passed through, and if it is a thick paper, the second counter is set to the number of sheets that have actually passed through multiplied by 1.75.

When the control unit 20 determines that the second counter has exceeded 3500 (YES in step S26), it drives the second rubbing device 52 to perform the rubbing operation (i.e., second mode) on the pressure roller 32 by the second rubbing roller 55 for 60 seconds, and then separates them. Here, the third rubbing time T3, which is the time for rubbing the pressure roller 32 in the second mode, is set to 60 seconds. At the same time, the control unit 20 drives the first rubbing device 51 to perform the rubbing operation (i.e., first mode) on the fixing belt 41 by the first rubbing roller 53 for (first counter number x 60/2500) seconds (step S27), and then separates them. Here, the fourth rubbing time T4, which is the time for rubbing the fixing belt 41 in the first mode, is set to (first counter number x 60/2500) seconds, which is shorter than the third rubbing time T3.

That is, after the first and second modes are completed, when the number of sheets of recording material S that have passed through the fixing nip N (number of sheets equivalent to passing) reaches the second threshold value of 3,500 sheets, the control unit 20 rubs the pressure roller 32 for 60 seconds, which is the third rubbing time T3, in the second mode. At the same time, the control unit 20 rubs the fixing belt 41 for (first counter number x 60/2,500) seconds, which is the fourth rubbing time T4, in the first mode. Note that the fourth rubbing time T4 is set to satisfy the relationship of P/S2 x third rubbing time T3, where S2 is the second threshold value and P is the number of sheets of recording material S that have passed through the fixing nip N (number of sheets equivalent to passing).

As a result, the control unit 20 executes the first mode and the second mode so that the fourth rubbing time T4 is shorter than the third rubbing time T3 and the third rubbing time T3 and the fourth rubbing time T4 overlap at least partially. Therefore, it is possible to realize the rubbing operation required for the fixing belt 41, and unnecessary rubbing can be suppressed. In this embodiment, the control unit 20 executes the first mode and the second mode so that the entire fourth rubbing time T4 overlaps with the third rubbing time T3. Furthermore, in this embodiment, the control unit 20 executes the first mode and the second mode so that the fourth rubbing time T4 and the third rubbing time T3 start at the same time. After execution, the control unit 20 resets both the first counter and the second counter to 1 (step S28) and ends the process. On the other hand, if the control unit 20 determines that the second counter does not exceed 3500 (NO in step S26), it increments the second counter by 1 (step S29) and ends the process.

In the first embodiment, plain paper of a first basis weight is used. In this case, when the number of sheets of recording material S that have passed through the fixing nip N (the number of sheets equivalent to passing) reaches a first threshold value, the control unit 20 rubs the fixing belt 41 for a first rubbing time T1 in the first mode and rubs the pressure roller 32 for a second rubbing time T2 in the second mode. On the other hand, in the second embodiment, thick paper of a second basis weight is used. In this case, when the number of sheets of recording material S that have passed through the fixing nip N (the number of sheets equivalent to passing) reaches a second threshold value, the control unit 20 rubs the pressure roller 32 for a third rubbing time T3 in the second mode and rubs the fixing belt 41 for a fourth rubbing time T4 in the first mode.

[Comparison of results of Examples 1 and 2 with Comparative Examples 1 to 4]
In each of the control flows shown in Figures 6 to 8, 100,000 sheets of plain paper were passed through. The control according to the control flow shown in Figure 6 was Comparative Example 1, the control according to the control flow shown in Figure 7 was Comparative Example 3, and the control according to the control flow shown in Figure 8 was Example 1. In addition, in each of the control flows shown in Figures 6 to 8, 100,000 sheets of thick paper were passed through. The control according to the control flow shown in Figure 6 was Comparative Example 2, the control according to the control flow shown in Figure 7 was Comparative Example 4, and the control according to the control flow shown in Figure 8 was Example 2.

In both controls, the rubbing time of the fixing belt 41 and the rubbing time of the pressure roller 32 were calculated from the recorded counter value in the control unit 20 when 100,000 sheets were passed through. The total time during which at least one of the first rubbing device 51 and the second rubbing device 52 was operating was calculated as the necessary downtime. The extra rubbing time was calculated as the belt unnecessary rubbing time, compared to the rubbing time of the fixing belt 41 when the fixing belt 41 and the pressure roller 32 were rubbed separately, calculated in Comparative Examples 1 and 2. The extra rubbing time was calculated as the roller unnecessary rubbing time, compared to the rubbing time of the fixing belt 41 when the fixing belt 41 and the pressure roller 32 were rubbed separately, calculated in Comparative Examples 1 and 2. The results are shown in Table 3.

As shown in Table 3, in Comparative Examples 1 and 2, the first rubbing device 51 and the second rubbing device 52 are operated separately, so the required downtime is the sum of the rubbing times of the first rubbing device 51 and the second rubbing device 52. Among the thresholds in Comparative Examples 1 and 2, the second threshold for rubbing the pressure roller 32 when the thick paper is passed in Comparative Example 2 is the smallest, so among the rubbing times in Comparative Examples 1 and 2, the rubbing time of the pressure roller 32 when the thick paper is passed in Comparative Example 2 (3000 seconds) is the longest.

In Comparative Examples 3 and 4, the second threshold value for rubbing the pressure roller 32 when thick paper is passed is adopted, so all the rubbing times are the same as the rubbing time (3000 seconds) of the pressure roller 32 when thick paper is passed in Comparative Example 2. In addition, since the first rubbing device 51 and the second rubbing device 52 are operated simultaneously, the necessary downtime is the same as the rubbing time of each of the first rubbing device 51 and the second rubbing device 52. Therefore, Comparative Examples 3 and 4 were able to reduce the necessary downtime compared to Comparative Examples 1 and 2. Here, comparing Comparative Example 3 with Comparative Example 1, the rubbing time of the fixing belt 41 was 600 seconds longer, and the rubbing time of the pressure roller 32 was 1320 seconds longer. Also, comparing Comparative Example 4 with Comparative Example 2, the rubbing time of the fixing belt 41 was 600 seconds longer. Therefore, in Comparative Examples 3 and 4, the unnecessary rubbing time is longer than in Comparative Examples 1 and 2, and there is a possibility that the life of the fixing belt 41 and the pressure roller 32 may be shortened by rubbing them more than necessary. As such, it was difficult to simultaneously reduce the required downtime and extend the life of the fixing belt 41 and pressure roller 32.

Therefore, in the first and second embodiments, when the first counter reaches the first threshold value, the fixing belt 41 is rubbed for the normal time, and at the same time, the pressure roller 32 is rubbed for the required time. When the second counter reaches the second threshold value, the pressure roller 32 is rubbed for the normal time, and at the same time, the fixing belt 41 is rubbed for the required time. In this way, the fixing belt 41 and the pressure roller 32 are rubbed simultaneously, thereby shortening the required downtime, and by avoiding unnecessary rubbing, the life of the fixing belt 41 and the pressure roller 32 can be extended.

That is, as shown in Table 3, in Examples 1 and 2, the first rubbing device 51 and the second rubbing device 52 are operated simultaneously, so the necessary downtime is the same as the longer rubbing time of the first rubbing device 51 or the second rubbing device 52. Therefore, in Examples 1 and 2, the necessary downtime was the same or shorter than in Comparative Examples 1 to 4. Also, in Examples 1 and 2, when the counter has not reached the count threshold, rubbing is performed only as much as necessary, so both the belt unnecessary rubbing time and the roller unnecessary rubbing time were 0. Therefore, it was confirmed that in Examples 1 and 2, it is possible to achieve both a reduction in the necessary downtime and an extension of the life of the fixing belt 41 and the pressure roller 32.

As described above, in the fixing device 30 of this embodiment, the first mode and the second mode are executed so that the second rubbing time T2 is shorter than the first rubbing time T1 and the first rubbing time T1 and the second rubbing time T2 overlap at least partially. Also, the first mode and the second mode are executed so that the fourth rubbing time T4 is shorter than the third rubbing time T3 and the third rubbing time T3 and the fourth rubbing time T4 overlap at least partially. That is, since the second rubbing time T2 is shorter than the first rubbing time T1 and the fourth rubbing time T4 is shorter than the third rubbing time T3, it is possible to avoid performing rubbing more than necessary compared to when the lengths are the same. Also, since the first rubbing time T1 and the second rubbing time T2 overlap at least partially and the third rubbing time T3 and the fourth rubbing time T4 overlap at least partially, the required downtime can be shortened compared to when they do not overlap. Therefore, it is possible to achieve both a longer life for the fixing belt 41, the pressure roller 32, the first rubbing roller 53, and the second rubbing roller 55, and improved productivity.

In addition, according to the fixing device 30 of this embodiment, the control unit 20 executes the first mode and the second mode so that the entire second rubbing time T2 overlaps with the first rubbing time T1, and the entire fourth rubbing time T4 overlaps with the third rubbing time T3. This makes it possible to more effectively reduce the required downtime compared to when there is only a partial overlap.

In addition, according to the fixing device 30 of this embodiment, the control unit 20 executes the first mode and the second mode so that the second rubbing time T2 and the first rubbing time T1 start at the same time, and so that the fourth rubbing time T4 and the third rubbing time T3 start at the same time. Therefore, compared to the case where the first mode and the second mode start with a time difference, the entire rubbing time can be overlapped with simple control.

In the fixing device 30 of the present embodiment described above, when the count value of one of the rotating bodies reaches the count threshold, the corresponding rotating body is refreshed, and at the same time, the other rotating body is refreshed for a rubbing time according to the count value. That is, the control unit 20 has described a case in which the second rubbing time T2 and the first rubbing time T1 start simultaneously, and the fourth rubbing time T4 and the third rubbing time T3 start simultaneously, but this is not limited to this. The refresh mode of the rotating body that has not reached the count threshold may be included, at least in part, during the refresh mode of the rotating body that reached the count threshold first. For this reason, for example, the start timing of the refresh mode of the rotating body that has not reached the count threshold may be shifted from the start timing of the refresh mode of the rotating body that reached the count threshold first.

In addition, in the fixing device 30 of the present embodiment described above, in the case of plain paper, the counter on the fixing belt 41 side reaches the first threshold value first, and the rubbing action on the pressure roller 32 side is linked, but this is not limited to the above. For example, even in the case of plain paper, the pressure roller 32 side may reach the second threshold value first, and the second rubbing roller 55 may be driven first, and the first rubbing roller 53 may be linked.

In addition, in the above-described embodiment of the fixing device 30, a single fixing device 30 having two rubbing devices has been described, but this is not limited to the above. For example, the present invention can be applied even if a single fixing device 30 has three or more rubbing devices. Alternatively, the fixing device having rubbing devices may be configured to be divided into multiple parts.

In addition, in the above-described fixing device 30 of the present embodiment, the first rubbing roller 53 and the second rubbing roller 55 are both surface polishing members, but this is not limited to the above. The first rubbing roller 53 and the second rubbing roller 55 may be any rubbing means that can polish or clean the fixing belt 41 and the pressure roller 32 by moving them in contact with and away from them, and may be, for example, a cleaning member such as a cleaning roller or a cleaning brush.

In addition, in the fixing device 30 of the present embodiment described above, a belt is used as the first rotating body, but this is not limited thereto, and the first rotating body may be, for example, in the shape of a roller. Also, a configuration may be adopted in which the heating roller 43 is not provided, and the heating source for heating the heating unit 40 heats the first rotating body from outside the heating unit 40.

In addition, in the fixing device 30 of the present embodiment described above, each count threshold is set to a fixed value, but this is not limited thereto, and each count threshold may be variable.

1...image forming apparatus, 20...control section, 30...fixing device, 32...pressure roller (second rotating body), 41...fixing belt (first rotating body), 48...heater (heating means), 51...first rubbing device, 52...second rubbing device, 53...first rubbing roller (first rubbing means), 55...second rubbing roller (second rubbing means), N...fixing nip section, P...number of sheets passed, PC, PK, PM, PY...image forming section, S...recording material, S1...first threshold, S2...second threshold, T1...first rubbing time, T2...second rubbing time, T3...third rubbing time, T4...fourth rubbing time

Claims (10)

An image forming apparatus including a fixing device that fixes an unfixed toner image formed in an image forming section onto a recording material, and a control section that controls the fixing device,
The fixing device includes a first rotating body and a second rotating body which come into contact with each other and apply pressure to each other to form a fixing nip portion, a heating means capable of heating at least one of the first rotating body and the second rotating body, a first rubbing device capable of moving a first rubbing means capable of rubbing the first rotating body by rubbing it against the first rotating body toward and away from the first rotating body, and a second rubbing device capable of moving a second rubbing means capable of rubbing the second rotating body by rubbing it against the second rotating body toward and away from the second rotating body,
The control unit is
when the number of the first recording materials passing through the fixing nip portion exceeds a first number without passing a second recording material having a basis weight larger than that of the first recording material , the first rubbing device is operated for a first rubbing time to rub the first rotating body, and the second rubbing device is further operated for a second rubbing time to rub the second rotating body,
when the number of the second recording materials that have passed through the fixing nip portion exceeds a second number that is smaller than the first number without passing the first recording material through the fixing nip portion, the second rubbing device is operated for a third rubbing time to rub the second rotating body, and the first rubbing device is further operated for a fourth rubbing time to rub the first rotating body,
Control is performed such that the first rubbing time and the second rubbing time at least partially overlap, the third rubbing time and the fourth rubbing time at least partially overlap, and the third rubbing time is longer than the second rubbing time.
1. An image forming apparatus comprising: The control unit controls the second rubbing time so that the entire second rubbing time overlaps with the first rubbing time.
2. The image forming apparatus according to claim 1, The control unit controls the second rubbing time and the first rubbing time to start simultaneously.
3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. The control unit controls the third rubbing time and the fourth rubbing time to start simultaneously .
4. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. The control unit controls the first rubbing time and the second rubbing time so that the first rubbing time and the second rubbing time are at least partially overlapped with each other, and the first rubbing time is longer than the fourth rubbing time.
5. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. the control unit satisfies a relationship of T4=P1/S1×T1, where S1 is the first number of sheets, T1 is the first rubbing time, P1 is the number of sheets of the first recording material that have passed through the fixing nip portion, and T4 is the fourth rubbing time.
6. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. the control unit satisfies a relationship of T2=P2/S1×T3, where S2 is the second number of sheets, T2 is the second rubbing time, P2 is the number of sheets of the second recording material that have passed through the fixing nip portion, and T3 is the third rubbing time.
7. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. The heating means heats the first rotating body,
the first rotating body is an endless fixing belt,
The second rotating body is a roller.
8. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. the control unit has a count unit that counts the number of recording materials that have passed through the fixing nip portion,
The control unit operates the first rubbing device for the first rubbing time to rub the first rotating body for the first rubbing time, and further operates the second rubbing device for the second rubbing time to rub the second rotating body,
resetting the number of sheets in the counting unit;
9. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. the control unit has a count unit that counts the number of recording materials that have passed through the fixing nip portion,
The control unit operates the second rubbing device for the third rubbing time to rub the second rotating body for the third rubbing time, and further operates the first rubbing device for the fourth rubbing time to rub the first rotating body,
resetting the number of sheets in the counting unit;
9. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

Images