JP4585204B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device that is mounted on an image forming apparatus such as an electrostatic copying machine, a printer, or a facsimile machine and melts and fixes unfixed toner on a sheet to the sheet.

A fixing device configured to heat the fixing roller not from the inside but from the outside is already known. One typical example of this type of fixing device includes a fixing roller, a pressure roller that is pressed against the fixing roller, and a plurality of heat rollers that are in pressure contact with the fixing roller and incorporate heating means (Patent Document 1). reference). The fixing roller is composed of a mandrel made of an iron hollow tube and silicon rubber covering the periphery of the mandrel. Each of the heat rollers is constituted by an aluminum hollow tube whose surface is coated with a fluororesin.

Since the fixing device directly heats the surface of the fixing roller, the temperature raising time of the fixing roller can be shortened, and therefore the warm-up time can be shortened. However, since the supply of heat to the fixing roller by the plurality of heat rollers is limited to a slight nip width between each of the heat rollers and the fixing roller, the amount of heat supply is limited. As a result, when it is desired to further shorten the heating time of the fixing roller, it is necessary to widen the nip width. However, when the nip width is widened, a local load on the fixing roller increases, so that fixing is performed. The driving torque of the roller increases, and it becomes necessary to strengthen the driving system. In addition, there is a possibility that the silicon rubber of the fixing roller is damaged early and the durability is impaired.

A fixing device that can solve the above problem has already been filed by Kyocera Mita Corporation, which is the present applicant (for example, Japanese Patent Application No. 2003-400247). A typical example of this fixing device is a fixing roller, a pressure roller pressed against the fixing roller, a plurality of belt support rollers arranged at intervals, and an endless belt wound around each of the belt support rollers. And a belt. A part of the outer peripheral surface of the endless belt is brought into pressure contact with a part of the outer peripheral surface of the fixing roller, and at least one belt support roller is constituted by a heat roller in which a heating unit is incorporated. The fixing device is configured such that a part of the outer peripheral surface of the endless belt is pressed against a part of the outer peripheral surface of the fixing roller. That is, a flexible endless belt is pressed against a part of the outer peripheral surface of the fixing roller to form a nip region, so that the nip width for heating the fixing roller is greatly increased as compared with the conventional case. Can do. As a result, it is possible to shorten the warm-up time by shortening the heating time of the fixing roller without increasing the local load on the fixing roller and without impairing the durability of the fixing roller.

However, it has been found that the fixing device further has the following technical problems to be solved. That is, in general, during the warm-up period from the start of warm-up to the end of warm-up immediately after the power is turned on, the entire fixing device is at the environmental temperature, so that the heat transfer efficiency from the endless belt to the fixing roller is as much as possible. It is desired to improve the heating temperature of the fixing roller and shorten the fixing device warm-up time. In particular, when the environmental temperature is low, it is anxious to satisfy such requirements. However, in the above fixing device, the circumferential width of the nip region formed by pressing a partial region of the outer peripheral surface of the endless belt against a partial region of the outer peripheral surface of the fixing roller, that is, the nip width is generally In consideration of requirements such as the operation speed and the amount of heat transfer during the fixing operation (that is, during the image forming operation such as printing and copying), the warm is started immediately after the power is turned on. At the time of up, the above nip width restricts the amount of heat transferred from the endless belt to the fixing roller, making it difficult to shorten the temperature rise time of the fixing roller. Become. For this reason, there has been a demand for further improvement of the fixing device.
JP 11-84934 A

An object of the present invention is to provide a novel fixing device capable of changing the amount of heat transferred from the endless belt to the fixing roller.

Another object of the present invention is to change the amount of heat transferred from the endless belt to the fixing roller, thereby making it possible to shorten the heating time of the fixing roller without increasing the heating means, and to reduce the warm-up time. It is an object of the present invention to provide a novel fixing device that can be shortened.

In a fixing device including a fixing roller and a pressure roller pressed against the fixing roller, a plurality of belt support rollers arranged at intervals from each other, and an endless belt wound around each of the belt support rollers An endless belt in which a partial area of the outer peripheral surface is in pressure contact with a partial area of the outer peripheral surface of the fixing roller, a heating unit that heats at least one belt support roller, and an outer peripheral surface of the endless belt. and the nip width varying means capable of changing the nip width of the nip region formed by the part region is pressed in a partial region of the outer peripheral surface of the fixing roller, is provided with a controller for controlling the device, The controller rotates and drives the fixing roller, pressure roller, belt support roller and endless belt within the preset nip width during the fixing operation after the power is turned on. At the same time, warm-up is started by starting heating with the heating means, and after a predetermined time has elapsed since the start of warm-up, the nip width variable means is operated so that the nip width is larger than the nip width during the fixing operation. When the surface temperature of the fixing roller reaches a predetermined temperature at which fixing can be performed , the fixing device is characterized in that the nip width varying means is operated again to return the nip width to the nip width at the time of fixing operation. It is provided.
Of belts supporting rollers, one of the belt support rollers are spaced outwardly of the outer circumferential surface of the fixing roller in the rotation direction upstream side or downstream side of the fixing roller,
It is preferable that the nip width varying means is composed of a single belt support roller displacement mechanism that can displace the single belt support roller in a direction approaching or separating from the outer peripheral surface of the fixing roller.
Among the belt support rollers, the two belt support rollers are arranged on the outer side of the outer peripheral surface of the fixing roller at an interval on the upstream side and the downstream side in the rotation direction of the fixing roller,
The partial region of the outer peripheral surface of the endless belt that is in pressure contact with the partial region of the outer peripheral surface of the fixing roller is disposed between the two belt support rollers, and the nip width varying means includes the two belt support rollers. One belt support roller displacement mechanism capable of displacing one of the two belt support rollers in a direction approaching or separating from the outer peripheral surface of the fixing roller, or one and the other of the two belt support rollers, It is preferable that each of the belt support roller displacement mechanisms can be displaced in a direction approaching or separating from the outer peripheral surface of the fixing roller.
The belt support roller displacement mechanism includes a support member rotatably attached to each of a pair of side walls arranged to face each other with a space therebetween and rotatably supported at both ends of the belt support roller. Preferably, each of the support members is provided with a drive unit that can displace the belt support roller in a direction in which the belt support roller approaches and separates from the outer peripheral surface of the fixing roller.
The belt support roller displacement mechanism is provided corresponding to each of the support members, and includes a biasing unit that constantly biases each of the support members in a direction in which the belt support roller is separated from the outer peripheral surface of the fixing roller. The driving means are arranged in contact with each of the support members so as to prevent the biasing means from rotating in the separating direction; It is preferable to include an actuator that rotates each of them.
The driving means is configured to correspond to each of the support members, and includes an actuator that rotates each of the support members in a direction in which the belt support roller approaches and separates from the outer peripheral surface of the fixing roller. Is preferred.

Preferred embodiments of a fixing device constructed according to the present invention will be described below in detail with reference to the accompanying drawings.

Referring to FIGS. 1 and 3, one embodiment of a fixing device configured in accordance with the present invention includes a fixing roller 2 and a pressure roller 4 that is pressed against the fixing roller 2 from below, with a space therebetween. A plurality of arranged belt support rollers 6 and 8 and an endless belt 10 wound around each of the belt support rollers 6 and 8 are provided. A part of the outer peripheral surface of the endless belt 10 is in pressure contact with a part of the outer peripheral surface of the fixing roller 2. The at least one belt support roller is configured to be heated by heating means disposed inside or outside.

In the embodiment, one belt support roller 6 is composed of a heat roller in which a heating means 6H is built. That is, the belt support roller 6 is configured to be heated by the heating means 6H disposed inside. In the space surrounded by the endless belt 10 and the belt support rollers 6 and 8, a temperature sensor, specifically, the thermistor S1, which is a control device for controlling the temperature of the belt support roller 6 that is a heat roller, is provided in the belt. The support roller 6 is disposed so as to contact the outer peripheral surface. The thermistor S <b> 2 for detecting the surface temperature of the fixing roller 2 is also disposed in the fixing device so as to contact the outer peripheral surface of the fixing roller 2. The paper P is conveyed substantially horizontally from right to left in FIG.

The fixing device includes a housing (not shown) including a pair of side walls 12 that are spaced apart from each other. The fixing roller 2, the pressure roller 4, and the belt support roller 6 that is a heat roller are provided on the side wall 12. They are supported between them in a rotatable manner and in parallel with each other. The thermistors S <b> 1 and S <b> 2 are attached to a support frame (not shown) arranged to extend between the side walls 12. The support of the belt support roller 8 will be described later. The belt support rollers 6 and 8 are spaced apart from the outer peripheral surface of the fixing roller 2 on the upstream side (left side in FIG. 1) and downstream side (right side in FIG. 1) of the fixing roller 2 in the rotation direction (clockwise in FIG. 1). Arranged. The partial region of the outer peripheral surface of the endless belt 10 that is pressed against the partial region of the outer peripheral surface of the fixing roller 2 is disposed between the two belt support rollers 6 and 8. In FIG. 1, reference numeral 8 </ b> A is a large-diameter portion disposed at both ends of the belt support roller 8, and prevents the endless belt 10 from falling off and meandering. Such a large-diameter portion is also disposed at both ends of the belt support roller 6 although not shown. The endless belt 10 is wound around a region between the large diameter portions of the belt support rollers 6 and 8.

When the fixing roller 2 is viewed in the axial direction (in FIG. 1, the paper surface is viewed from the front to the back), the virtual horizontal line passing through the axis of the fixing roller 2 is orthogonal to the x axis through the axis of the fixing roller 2 When the imaginary vertical line is the y axis, the belt support roller 6 is disposed outside the fixing roller 2 at a substantially intermediate position in the circumferential direction in the second quadrant with respect to the outer peripheral surface of the fixing roller 2. On the other hand, the belt support roller 8 is disposed on the outer side of the outer peripheral surface of the fixing roller 2 with respect to the belt support roller 6 on the downstream side in the rotation direction of the fixing roller 2 and on the upstream side in the conveyance direction of the paper P. (It is arranged at a substantially intermediate position in the circumferential direction in the first quadrant with respect to the outer circumferential surface of the fixing roller 2). The heating means 6H is supported in a stationary state between the side walls 12 in the central region of the belt support roller 6 which is a heat roller.

The fixing roller 2 is drivingly coupled to the electric motor M1 that is a driving source via gears 14 and 16. Therefore, the electric motor M1 can be said to be a fixing roller driving motor. The gear 14 is fixed to the drive shaft of the electric motor M1, and the gear 16 is fixed to the shaft of the fixing roller 2. The belt support roller 6, which is a heat roller, is drivingly coupled to the gear 16 of the fixing roller 2 through a gear (not shown), and is configured to be rotationally driven by the fixing roller 2. In place of this embodiment, there is another embodiment in which the belt support roller 6 is configured to be driven and rotated by the fixing roller 2 via the endless belt 10.

The fixing roller 2 and the pressure roller 4 are made of metal, for example, SUS or iron mandrel, solid silicon rubber or foamed silicon rubber which is an elastic member covering the mandrel, and PFA tube covering the silicon rubber or foamed silicon rubber. It can consist of Instead of the configuration in which the outer peripheral surface of the silicon rubber or the foamed silicon rubber is covered with the PFA tube, the outer peripheral surface of the silicon rubber or the foamed silicon rubber may be coated with a fluororesin that is a toner release layer. The belt supporting rollers 6 and 8 are made of a hollow tube made of metal such as SUS or aluminum. The endless belt 10 can be formed from polyimide resin, Ni, or SUS. The heating means 6H is constituted by a halogen heater, but may be constituted by other heating means, for example, an exciting coil (IH coil) for electromagnetic induction heating. In the case where the heating means is composed of an IH coil, there is an embodiment in which the IH coil is arranged so as to cover a part of the outer peripheral surface of the belt support roller 6 with a gap from the outside.

The fixing device changes the circumferential width, that is, the nip width of the nip region 10N formed by pressing a partial region of the outer peripheral surface of the endless belt 10 against a partial region of the outer peripheral surface of the fixing roller 2. Nip width varying means is provided. In the embodiment, the nip width varying means is arranged on the outer side of the outer peripheral surface of the fixing roller 2 on the downstream side in the rotation direction of the fixing roller 2 and downstream of the nip region 10N. The belt support roller displacement mechanism 20 can be displaced in a direction approaching or separating from the outer peripheral surface of the fixing roller 2.

The belt support roller displacing mechanism 20 is rotatably attached to each of the side walls 12, and both ends of the belt support roller 8 are rotatably supported, and each of the support members 22 is belt-supported. The roller 8 includes a driving unit that can be displaced in a direction in which the roller 8 approaches and separates from the outer peripheral surface of the fixing roller 2. Each of the support members 22 having substantially the same configuration is composed of a substantially trapezoidal support plate and is rotatably supported on the inside of the corresponding side wall 12 via a shaft 22a. Between each of the support members 22 and the corresponding side wall 12, each of the support members 22 is always in a direction in which the belt support roller 8 is separated from the outer peripheral surface of the fixing roller 2 (counterclockwise in FIG. 1). A biasing means for biasing, in the embodiment, a tension coil spring 24 is provided.

The driving means corresponds to each of the cam 26 and the cam 26 arranged in contact with one side surface 22s of each of the support members 22 so as to prevent the tension coil spring 24 from rotating in the separating direction. And an actuator for rotating each of the cams 26, in the embodiment, an electric motor M2. Since each of the support members 22 is constantly urged counterclockwise in FIG. 1 by the corresponding tension coil spring 24, one side surface 22s of each of the support members 22 is always pressed against the cam surface of the corresponding cam 26. It has been. Each of the cams 26 is fixed to a shaft 26 a that is rotatably supported between the side walls 12. One end of the shaft 26a is drivably coupled to the drive shaft of the electric motor M2. By rotation of the electric motor M2, each of the cams 26 is rotated counterclockwise in FIG. Therefore, it can be said that the electric motor M2 is a cam drive motor. Each shaft 26a of the cam 26, each shaft 22a of the support member 22 and the belt support roller 8 are disposed substantially in parallel with the fixing roller 2, the pressure roller 4 and the belt support roller 6.

The state of the belt support roller displacement mechanism 20 shown in FIG. 1 indicates a state during a fixing operation (that is, during an image forming operation such as printing or copying). Each of the cams 26 is positioned such that the cam surface having the smallest distance from the shaft 26 a comes into contact with the one side surface 22 s of the corresponding support member 22 (fixing operation position). The nip width of the nip region 10N formed by pressing a part of the outer peripheral surface of the endless belt 10 against a part of the outer peripheral surface of the fixing roller 2 is a nip width suitable for the fixing operation. The nip width at the time is preset.

The fixing device includes a controller 30 that controls the operation of the fixing device. The controller 30 is configured by a microcomputer, and includes a central processing unit (CPU) that performs arithmetic processing according to a control program, a ROM that stores a control program, a readable / writable RAM that stores arithmetic results, a timer, a counter, an input interface, It has an output interface. The input interface of the controller 30 configured in this way includes thermistors S1 and S2, other detectors, and a power switch MSW of the image forming machine in which the fixing device is disposed (and thus also the power switch MSW of the fixing device), Detection signals from other switches and the like are input, and control signals are output from the output interface to the electric motors M1 and M2. The fixing device is disposed in the main body of the image forming machine (not shown), but the control of the fixing device may be controlled by a controller that controls the operation of the entire image forming machine disposed in the main body of the image forming machine. .

1, 2, and 4, the controller 30 operates after a power switch MSW (not shown) of the image forming machine, and thus a power switch MSW of the fixing device is turned on (that is, after power is turned on). The fixing roller 2, the pressure roller 4, the belt support roller 6, the endless belt 10 and the belt support roller 8 are rotationally driven and heated at a preset nip width during the fixing operation (nip width shown in FIG. 1). Warm-up is started by starting heating by means 6H (time t1 in FIG. 4). The controller 30 can change the belt support roller, which is a nip width variable means, so that the nip width is larger than the nip width during the fixing operation after a predetermined time (time t2-t1 in FIG. 4) has elapsed since the start of warm-up. Actuate mechanism 20. Specifically, the electric motor M2 is rotated by a predetermined angle, and each of the cams 26 is rotated counterclockwise in FIG. 1 from the fixing operation position shown in FIG. 1 to the nip width increasing position shown in FIG. . Each of the cams 26 is positioned such that the cam surface having the longest distance from the shaft 26 a comes into contact with the one side surface 22 s of the corresponding support member 22 (nip width increasing position). Each of the support members 22 is rotated around the shaft 22a by a predetermined angle in the clockwise direction in FIG. 1 (see FIG. 2). As a result, the nip width of the nip region 10N is increased, as can be easily understood by comparing FIG. 1 and FIG.

In the present invention, after the power switch MSW is turned on (that is, after the power is turned on), the fixing roller 2, the pressure roller 4, the belt support roller 6, the endless belt 10, After the belt support roller 8 is rotationally driven (time t1 in FIG. 4), the nip width is controlled to increase (time t2 in FIG. 4), so that an excessive increase in the initial torque that rotationally drives each roller is suppressed. In addition, the burden on the drive system can be reduced.

When the surface temperature of the fixing roller 2 reaches a predetermined fixing temperature (time t3 in FIG. 4), the controller 30 turns off the heating unit 6H to stop heating and stop driving the electric motor M1. Then, the rotation of the fixing roller 2, the belt support roller 6, the endless belt 10 and the belt support roller 8 is stopped. At the same time, the belt support roller variable mechanism 20 as the nip width variable means is operated to restore the increased nip width to the nip width during the fixing operation. Specifically, the electric motor M2 is rotated in the same direction by a predetermined angle so that each of the cams 26 is counterclockwise in FIG. 2 from the nip width increasing position shown in FIG. 2 to the fixing operation position shown in FIG. Rotate. Each of the cams 26 is positioned such that the cam surface having the smallest distance from the shaft 26a comes into contact with the one side surface 22s of the corresponding support member 22 (fixing operation position). Each of the support members 22 is rotated around the shaft 22a by a predetermined angle in the counterclockwise direction in FIG. 1 by the spring force of the tension coil spring 24 (see FIG. 1). As a result, as easily understood by comparing FIGS. 1 and 2, the nip width of the nip region 10N is returned to the nip width during the fixing operation. Needless to say, the surface temperature of the fixing roller 2 is detected by the thermistor S2.

The fixing device operates the belt support roller variable mechanism 20 so that the nip width is larger than the nip width during the fixing operation after a predetermined time (time t2-t1 in FIG. 4) has elapsed from the start of warm-up. When the surface temperature of the fixing roller 2 reaches a predetermined fixable temperature (time t3 in FIG. 4), the belt support roller variable mechanism 20 is operated to return the nip width to the nip width during the fixing operation. Has been. As a result, after the power switch MSW is turned on (that is, after the power is turned on), the nip width is increased from the endless belt 10 to the fixing roller 2 at a so-called rising time, compared with that at the time of fixing operation. The amount of heat transfer of the fixing roller 2 can be increased as compared with that during the fixing operation, so that the heating time of the fixing roller 2 from the normal temperature to the predetermined fixing temperature can be shortened without increasing the heating means. The warm-up time of the fixing device can be shortened.

As is apparent from the above description, in the fixing device, the amount of heat transferred from the endless belt 10 to the fixing roller 2 can be freely changed within a certain range at an arbitrary timing, not limited to when the fixing device starts up. Therefore, the amount of heat transferred from the endless belt 10 to the fixing roller 2 can be controlled as needed, and fine temperature control of the fixing roller 2 can be easily performed.

In the fixing device, one belt support roller 8 out of the plurality of belt support rollers 6 and 8 is disposed on the outer side of the outer peripheral surface of the fixing roller 2 at a downstream side in the rotation direction of the fixing roller 2, and The belt width varying means includes a single belt support roller variable mechanism 20 that can displace the single belt support roller 8 in a direction approaching or separating from the outer peripheral surface of the fixing roller 2. The belt width varying means is arranged on the upstream side in the rotation direction of the fixing roller 2 with an interval outside the outer peripheral surface of the fixing roller 2, and moves one belt support roller 6 toward or away from the outer peripheral surface of the fixing roller 2. There are other embodiments that consist of a single belt support roller variable mechanism 20 that can be displaced in the direction. In the above two embodiments, there is also an embodiment in which the other belt support roller 6 or 8 that is not displaced by one belt support roller variable mechanism 20 is brought into pressure contact with the surface of the fixing roller 2 via the endless belt 10.

Furthermore, of the plurality of belt support rollers, the two belt support rollers 6 and 8 are arranged at intervals outside the outer peripheral surface of the fixing roller 2 on the upstream side and the downstream side in the rotation direction of the fixing roller 2. The partial region of the outer peripheral surface of the endless belt 10 that is pressed against the partial region of the outer peripheral surface of the fixing roller 2 is disposed between the two belt support rollers 6 and 8, and the nip width varying means includes the The belt support roller displacement mechanism 20 includes two belt support roller displacement mechanisms 20 that can displace one or the other of the two belt support rollers 6 and 8 toward or away from the outer peripheral surface of the fixing roller 2. There are other embodiments.

As shown in FIG. 5, driving means that can displace each support member 22 in a direction in which the belt support roller 6 approaches and separates from the outer peripheral surface of the fixing roller 2 is an actuator, in the embodiment, from a solenoid SOL. There are other embodiments to configure. The solenoid SOL is disposed corresponding to each of the support members 22 and rotates each of the support members 22 in a direction in which the belt support roller 6 approaches and separates from the outer peripheral surface of the fixing roller 2. Such a solenoid SOL is disposed on each of the side walls 12, and each movable iron core of the solenoid SOL is drivingly connected to the corresponding support member 22. As an actuator, in place of the solenoid SOL, there is another embodiment constituted by a fluid pressure cylinder mechanism, for example, an air cylinder mechanism.

Referring to FIG. 1, when the fixing roller 2 is driven to rotate clockwise in FIG. 1 by the electric motor M1 during the fixing operation, the pressure roller 4 is driven counterclockwise. At the same time, the belt support roller 6 as a heat roller is driven to rotate counterclockwise in FIG. As a result, the endless belt 10 is rotationally driven in the same counterclockwise direction, and the belt support roller 8 is also rotationally driven through the endless belt 10 in the same counterclockwise direction. When the halogen heater constituting the heating unit 6H is energized and heat generation is started, heat from the heating unit 6H is transmitted from the belt support roller 6 which is a heat roller to the endless belt 10 and from the endless belt 10 to the fixing roller 2. The fixing roller 2 is heated. The heat transmitted to the fixing roller 2 is also transmitted to the pressure roller 4. The sheet P on which the toner is transferred on one side (upper surface) is conveyed substantially horizontally from right to left in FIG. 1 and passes through the nip portion between the fixing roller 2 and the pressure roller 4 and is transferred to one side of the sheet P. Unfixed toner is melted and fixed on one side of the paper P by the fixing roller 2.

According to the fixing device according to the present invention, a partial region of the outer peripheral surface of the endless belt 10 is configured to be in pressure contact with a partial region of the outer peripheral surface of the fixing roller 2. That is, the flexible endless belt 10 is pressed and formed along a partial region of the outer peripheral surface of the fixing roller 2 to form the nip region 10N, so that the nip width for heating the fixing roller 2 is significantly larger than the conventional one. Can be increased. As a result, the heating time of the fixing roller 2 can be shortened and the warm-up time of the fixing device can be shortened without increasing the local load on the fixing roller 2 and without impairing the durability of the fixing roller 2. Can do.

1 is a schematic configuration diagram illustrating an embodiment of a fixing device according to the present invention. FIG. 6 is a schematic configuration diagram illustrating another operation mode of the fixing device illustrated in FIG. 1. It is principal part sectional drawing of FIG. 2 is a time chart schematically showing an operation procedure during warm-up of the fixing device shown in FIG. 1. FIG. 6 is a schematic configuration diagram illustrating another embodiment of a fixing device according to the present invention.

Explanation of symbols

2: fixing roller 4: pressure roller 6, 8: belt support roller 10: endless belt 12: side wall 14, 16: gear 20: belt support roller displacement mechanism 22: support member 22a: shaft 24: tension coil spring 26: cam 26a : Shaft 30: Controller 6H: Heating means (halogen heater)
M1, M2: Electric motor MSW: Power switch SOL: Solenoid P: Paper S1, S2: Thermistor

Claims (6)

In a fixing device including a fixing roller and a pressure roller pressed against the fixing roller,
A plurality of belt support rollers arranged at a distance from each other and an endless belt wound around each of the belt support rollers, wherein a partial area of the outer peripheral surface is a partial area of the outer peripheral surface of the fixing roller It is formed by press-contacting an endless belt, a heating means for heating at least one belt support roller, and a partial region of the outer peripheral surface of the endless belt being pressed into a partial region of the outer peripheral surface of the fixing roller. and the nip width varying means capable of changing the nip width of the nip region, is provided with a controller for controlling the device,
The controller warms up by rotating the fixing roller, pressure roller, belt support roller and endless belt at the preset nip width during the fixing operation and starting heating by the heating means after the power is turned on. After a predetermined time has elapsed since the start of warm-up, the nip width variable means is operated so that the nip width is larger than the nip width during the fixing operation, and the surface temperature of the fixing roller can be fixed at a predetermined temperature. When the value reaches the nip width, the nip width variable means is operated again to return the nip width to the nip width at the time of fixing operation.
A fixing device. Of the belt support rollers, one belt support roller is disposed on the outer side of the outer peripheral surface of the fixing roller at an upstream side or a downstream side in the rotation direction of the fixing roller.
Nip width varying means is composed of one belt support roller displacement mechanism which can be displaced in a direction approaching or away from the one of the belt support rollers relative to the outer peripheral surface of the fixing roller, according to claim 1 Symbol The fixing device. Among the belt support rollers, the two belt support rollers are arranged on the outer side of the outer peripheral surface of the fixing roller at an interval on the upstream side and the downstream side in the rotation direction of the fixing roller,
The partial region of the outer peripheral surface of the endless belt pressed against the partial region of the outer peripheral surface of the fixing roller is disposed between the two belt support rollers,
The nip width varying means is composed of one belt support roller displacement mechanism capable of displacing one of the two belt support rollers toward or away from the outer peripheral surface of the fixing roller, or 2. The belt support roller displacement mechanism according to claim 1 , wherein one of the two belt support rollers and the other of the two belt support rollers are each displaced in a direction approaching or separating from the outer peripheral surface of the fixing roller. serial mounting of the fixing device. The belt support roller displacement mechanism includes a support member rotatably attached to each of a pair of side walls arranged to face each other with a space therebetween and rotatably supported at both ends of the belt support roller. 4. The fixing device according to claim 2 , further comprising: a driving unit configured to displace each of the support members in a direction in which the belt support roller approaches and separates from the outer peripheral surface of the fixing roller. The belt support roller displacement mechanism is provided corresponding to each of the support members, and includes a biasing unit that constantly biases each of the support members in a direction in which the belt support roller is separated from the outer peripheral surface of the fixing roller. ,
The drive means includes a cam disposed in contact with each of the support members so as to prevent the biasing means from rotating in the direction of separation, and a drive means disposed corresponding to each of the cams. The fixing device according to claim 4 , further comprising an actuator that rotates the actuator. Driving means is arranged each disposed in correspondence to each of the support members and the support member, an actuator for rotating the direction in which the belt support rollers toward and spaced relative to the outer peripheral surface of the fixing roller, wherein Item 5. The fixing device according to Item 4 .

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