JP6283461B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that heats and pressurizes an image on a paper to be passed to fix the image on the paper, and an image forming apparatus including the fixing device.

  2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive member, and toner is applied to the latent image. Thus, the visualized toner image is transferred to a sheet, and then the toner image on the sheet is fixed by a fixing device and discharged.

  As described above, the fixing device for fixing the toner image is formed by a fixing member such as a fixing roller and a fixing belt having a built-in halogen lamp and the like, and a pressure member such as a pressure roller and a pressure belt for pressing the fixing member. There is a heat-fixing type fixing device that heats and presses a sheet with a toner image transferred through the nip portion. Such a fixing device is widely used because of its simple configuration.

  By the way, in such a fixing device, there are many one-side driving devices in which one of the fixing member and the pressure member is rotationally driven, and the other member is driven by the rotation of a member that rotationally drives the paper. In the one-side drive, the sheet can be passed at a predetermined passing speed by controlling the rotation speed of one of the fixing member and the pressure member. However, in the one-side drive, if the pressure at the nip portion is increased to increase the driving load, slippage may occur during sheet conveyance, and conveyance may not be possible. If slippage occurs during paper conveyance, problems such as image shifting occur.

For this reason, a fixing device has been proposed in which the fixing member and the pressure member are independently rotated (see, for example, Patent Document 1). In the case where both the fixing member and the pressure member are rotationally driven, the instability of interference between the two drive systems is eliminated by controlling the torque of one of them.
In the fixing device of Patent Document 1, it is shown that the rotation speed of the fixing member and the pressure member is controlled to be controlled at a predetermined rotation speed in association with each other.

JP 2010-204510 A

By the way, in the fixing member and the pressure member, an elastic layer is provided in the surface layer portion that forms the nip portion, and the diameter changes particularly in the elastic layer when heated for fixing. Further, a diameter change is caused by a temperature change at the time of fixing or a temperature change caused by warm-up. This diameter change is not the same between the fixing member and the pressure member, and generally, the diameter change is large on one side and the diameter change is small on the other side. In the one-side drive, since the other member follows and follows regardless of such a diameter change, the influence of the diameter change is small.
However, in the case where both the fixing member and the pressure member are rotationally driven, if there is a change in the diameter of the member depending on the temperature, the constant torque control will affect the other member, resulting in unstable rotation or driving force. There is a problem that wear occurs in the gear that transmits the noise.

  The present invention has been made in the background of the above circumstances, and an object thereof is to provide a fixing device and an image forming apparatus capable of stably rotating a fixing member and a pressure member regardless of a diameter change due to heating. To do.

That is, among the fixing devices of the present invention, the first present invention is a fixing device that heats and presses an image on a sheet to be passed to fix the image on the sheet.
A rotatable first fixing portion; and a rotatable second fixing portion that forms a nip portion through which the paper is passed together with the first fixing portion;
A heating unit for heating at least one of the first fixing unit and the second fixing unit;
A temperature detection unit for detecting the temperature of the first fixing unit or the second fixing unit;
A first drive motor that rotationally drives the first fixing unit; a second drive motor that rotationally drives the second fixing unit;
A controller that controls driving of each of the first drive motor and the second drive motor,
The first fixing unit has a relatively large change in the rotation diameter due to the heating, and the second fixing unit has a relatively small change in the rotation diameter due to the heating,
The control unit controls the number of rotations of the second drive motor that rotationally drives the second fixing unit, and controls the first drive motor that rotationally drives the first fixing unit to the temperature detection unit. Based on the load at the nip portion that changes according to the detection result, torque is controlled so that the load applied to the first drive motor is constant, and the motor current of the second drive motor is set to a set value. If the motor current is smaller than the value, the PWM value of the first drive motor is lowered, and if the motor current is larger than the set value, the PWM value of the first drive motor is raised and the rotation is torque controlled.

The fixing device according to a second aspect of the present invention is characterized in that, in the first aspect of the present invention , the control unit controls the load at the nip portion to be constant during the rotation control.

According to a third aspect of the present invention, there is provided an image forming apparatus comprising: an image forming unit that forms an image and transfers the image onto a sheet ; and the fixing device according to the first or second aspect of the present invention .

  As described above, according to the present invention, in the case where the nip portion is formed by the first fixing portion and the second fixing portion, the first fixing portion and the second fixing portion have different diameters due to heating. When the change occurs, both the fixing portions can be stably driven to rotate, the slip of the paper can be prevented, the nip pressure can be increased, and good fixing can be performed.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. Similarly, it is a figure which shows a fixing device. Similarly, it is a figure which shows the control block of an image forming apparatus. Similarly, it is a figure which shows an example of the control block of a fixing device. Similarly, it is a flowchart showing an example of a control procedure of the fixing device. Similarly, it is a figure which shows the other example of the control block of a fixing device. Similarly, it is a flowchart showing another example of the control procedure of the fixing device. It is a figure which shows the fixing device of other embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an image forming apparatus A according to the present invention.
The image forming apparatus A is called a tandem color image forming apparatus, and performs color image formation by four sets of image forming units. In this embodiment, an image forming apparatus that forms a color image will be described. However, the present invention may be an image forming apparatus that forms a monochrome image.

  The document placed on the document table is scanned and exposed by the optical system of the scanning exposure device of the image reading device SC, read by the line image sensor, and the photoelectrically converted image information signal is sent to the image processing unit (non-processing unit). In the figure, after analog processing, A / D conversion, shading correction, image compression processing, etc., it is input to the optical writing unit of the image forming unit.

  The four image forming units include an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, and an image forming unit that forms a cyan (C) image. 10C is an image forming unit 10K that forms a black (K) color image, and is denoted by symbols Y, M, C, and K representing colors formed after the common symbol 10, respectively.

The image forming unit 10Y includes a photosensitive drum 1Y and a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a drum cleaner 5Y arranged around the photosensitive drum 1Y.
Similarly, the image forming unit 10M includes the photosensitive drum 1M and the charging unit 2M, the optical writing unit 3M, the developing device 4M, and the drum cleaner 5M disposed around the photosensitive drum 1M. The image forming unit 10C includes the photosensitive drum 1C and the photosensitive drum 1C. The charging unit 2C, the optical writing unit 3C, the developing device 4C, and the drum cleaner 5C arranged around it, the image forming unit 10K, the photosensitive drum 1K, and the charging unit 2K arranged around it, the optical writing unit. 3K, developing device 4K, and drum cleaner 5K.

  Photosensitive drums 1Y, 1M, 1C, and 1K in the image forming units 10Y, 10M, 10C, and 10K, charging units 2Y, 2M, 2C, and 2K, optical writing units 3Y, 3M, 3C, and 3K, a developing device 4Y, 4M, 4C, and 4K and drum cleaners 5Y, 5M, 5C, and 5K have the same content. In the following description, symbols Y, M, C, and K are not used unless particularly distinguished.

The image forming unit 10 writes an image information signal on the photosensitive drum 1 in the optical writing unit 3, and forms a latent image based on the image information signal on the photosensitive drum 1. The latent image is developed by the developing device 4 to form a visible toner image on the photosensitive drum 1.
Yellow (Y), magenta (M), cyan (C), and black (K) are respectively applied to the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units 10Y, 10M, 10C, and 10K, respectively.
An image of color is formed.
The intermediate transfer belt 6 is wound around a plurality of rollers and supported so as to be able to run.

  The toner images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the traveling intermediate transfer belt 6 by the primary transfer units 7Y, 7M, 7C, and 7K, and Y (yellow), M ( A color image in which the color layers of magenta), C (cyan), and K (black) are superimposed is formed.

  The paper transport unit 20 transports the paper S. The paper S is stored in the paper feed trays 291, 292, 293, fed by the first paper feed unit 21, passed through the registration roller 22, and conveyed to the secondary transfer unit 7 A, and the intermediate transfer belt on the paper S. 6 color image is transferred. The sheet S on which the color image has been transferred is fixed with the toner image on the sheet S by applying heat and pressure by the fixing device 30, and is discharged out of the apparatus through the fixing conveyance roller and the discharge roller 25.

In addition, the image forming apparatus A includes a sheet reversing unit 24, and the fixed sheet is guided from the fixing conveyance roller to the sheet reversing unit 24 so as to be reversed and discharged, or image formation is performed on both sides of the sheet. It is possible.
The size, number of sheets, etc. of the paper S when performing image formation can be set from the operation display unit 50 installed at the top of the main body of the image forming apparatus A.
The control unit 40 controls the entire image forming apparatus A, and includes a CPU, a program for operating the CPU, and a storage unit such as a ROM, a RAM, and a flash memory.

Next, details of the fixing device 30 will be described with reference to FIG.
The fixing device 30 includes a fixing roller 31 and a pressure roller 32, and a nip portion N is formed between the fixing roller 31 and the pressure roller 32. The toner image on the paper is fixed by heating and pressing at the nip N. The fixing roller 31 corresponds to a first fixing unit of the present invention. The fixing roller 31 rotates in the clockwise direction in the figure by driving of the drive motor 31D. The drive motor 31D corresponds to the first drive motor of the present invention, and is rotationally controlled by the control unit 40. The type of drive motor 31D is not particularly limited, and a known one can be used.

  The fixing roller 31 includes a cored bar 31A, an elastic layer 31B that covers the cored bar 31A, and a surface layer 31C that covers the elastic layer 31B. The core metal 31A is made of a metal such as aluminum or iron and is formed in a cylindrical shape. The elastic layer 31B is made of silicone rubber or fluorine rubber. The surface layer 31C is made of PFA (perfluoro resin) or PTFE (tetrafluoroethylene resin), and is coated or covered with a tube. At the time of fixing, the toner image contacts the toner image.

The pressure roller 32 corresponds to a second fixing unit of the present invention, and includes a halogen heater H built in the center, a core metal 32A containing the halogen heater H, an elastic layer 32B covering the core metal 32A, And a surface layer 32C covering the elastic layer 32B. The halogen heater H corresponds to the heating unit of the present invention.
The core metal 32A is made of a metal such as aluminum or iron, and is formed in a cylindrical shape. The elastic layer 32B is made of silicone rubber or fluorine rubber. The surface layer 32C is made of PFA or PTFE, and is coated or covered with a tube. The pressure roller 32 is biased by a biasing member (not shown) and presses the fixing roller 31 from below.

  Further, the pressure roller 32 rotates counterclockwise in the figure by driving of the drive motor 32D. The drive motor 32D corresponds to the second drive motor of the present invention, and is rotationally controlled by the control unit 40. The type of the drive motor 32D is not particularly limited, and a known one can be used.

The configuration of the heating unit that heats the pressure roller 32 is not particularly limited, and may be anything as long as it heats the pressure roller 32. The heating unit may heat the fixing roller 31 instead of the pressure roller 32.
Note that the elastic layer 31 </ b> B included in the fixing roller 31 is usually thicker than the elastic layer 32 </ b> B included in the pressure roller 32. For this reason, when the fixing roller 31 and the pressure roller 32 are heated by the heating of the halogen heater H, the diameter change of the fixing roller 31 becomes relatively larger than the diameter change of the pressure roller 32. The magnitude of the diameter change here can be compared by the rate of change in diameter.

  The separation claw 34 is made of a heat-resistant resin such as PI (polyimide), has a sharp tip, and is in pressure contact with the outer peripheral surface of the fixing roller 31.

  Further, the temperature of the fixing roller 31 can be detected by the temperature sensor 35. The temperature sensor 35 corresponds to a temperature detection unit of the present invention. The detection result of the temperature sensor 35 is transmitted to the control unit 40. The temperature sensor 35 may detect the temperature of the fixing roller 31 in contact with the fixing roller 31, or may detect the temperature of the fixing roller 31 in a non-contact manner with the fixing roller 31. The configuration is not particularly limited. The point is that it can detect the temperature of the fixing roller 31.

FIG. 3 is a diagram showing a control block of the image forming apparatus of the present invention.
The control unit 40 is connected to the image forming unit 10 in a controllable manner, and controls image formation and transfer onto a sheet.

  The control unit 40 is connected to the paper conveyance unit 20 in a controllable manner. The paper transport unit 20 transports the paper stored in the paper feed trays 291, 292, and 293 to the image forming unit 10, and further transports the paper onto which the image has been transferred by the image forming unit 10 to the fixing device 30. After fixing, the sheet is discharged out of the image forming apparatus A.

  An operation display unit 50 is connected to the control unit 40 in a controllable manner. The operation display unit 50 can be operated by a user or the like under the control of the control unit 40, and can display information under the control of the control unit 40.

  Further, the fixing device 30 is connected to the control unit 40 in a controllable manner.

An example of a control block in the fixing device 30 will be described with reference to FIG.
As described above, the drive motor 31D and the drive motor 32D are connected to the control unit 40 in a controllable manner. The drive motor 31D performs torque control, and the drive motor 32D performs rotation speed control.
The motor current of the drive motor 32D is detected by the current monitor unit 36, and the detection result is transmitted to the control unit 40.

  The controller 40 controls the drive motor 32D so that the drive motor 32D has a predetermined rotational speed. Specifically, a motor voltage or PWM value corresponding to the rotation speed is set in advance and driven by the motor voltage, and the rotation speed of the drive motor 32D is detected by a rotation speed sensor (not shown). The control unit 40 performs feedback control based on the detection result relating to the rotational speed so that the drive motor 32D can obtain a predetermined rotational speed.

  The controller 40 controls the torque of the drive motor 31D using the set PWM value. The set PWM value is set from the relationship between the motor current in the drive motor 32D and the PWM command value as an initial value. If the PWM value is already stored in the storage unit of the control unit 40 by feedback control, the stored PWM value becomes the set PWM value. In the controller 40, the PWM generator 41 generates a PWM signal based on the PWM value, and controls the rotation of the drive motor 31D.

Next, the control procedure of the drive motor 31D by the control unit 40 will be described based on the flowchart of FIG.
Waiting for the start of printing (step s1), and when printing is started (step s1, YES), the rotational drive of the drive motor 32D for controlling the rotational speed is turned on and controlled to a predetermined rotational speed (step). s2). As for the value of the drive motor 31D, a PWM signal is generated by the PWM generator 41 based on the set PWM value, and the drive motor 31D is torque controlled by the PWM signal (step s4).
Next, the current monitor unit 36 detects the motor current value generated in the drive motor 32 </ b> D and transmits it to the control unit 40. The control unit 40 determines whether or not the detected motor current value is larger than a set value (step s4). The set value is set assuming a torque obtained from a PWM value determined as an initial setting by the drive motor 31D. The detected motor current value has a correlation with the load at the nip portion N, and the motor current value increases as the load increases, and the motor current value decreases as the load decreases.

  As a result of the determination, if the detected current does not exceed the set value (step s4, NO), the PWM value in the drive motor 31D is lowered (step s5). That is, if the detected current does not exceed the set value, the load generated in the nip portion N is less than expected, so the torque of the drive motor 31D is excessive, and the PWM value is reduced to reduce the nip by the drive motor 31D. The torque applied to the part N is reduced. As a result, the drive motor 32D can stably rotate without receiving interference from the drive of the drive motor 31D. If the control for decreasing the PWM value is not performed in this state, the drive motor 31D has an excessive torque, and the drive of the drive motor 31D affects the drive motor 32D. If the detected current is the same as the set value, the PWM value need not be changed.

  If the detected current exceeds the set value as a result of the determination (step s4, YES), the PWM value in the drive motor 31D is increased (step s6). That is, if the detected current exceeds the set value, the load generated in the nip portion N exceeds the assumed value, so the torque of the drive motor 31D is in an excessively small state, and the PWM value is increased to increase the drive motor. The torque applied to the nip portion N is increased by 31D. As a result, the drive motor 32D can stably rotate without receiving interference from the drive of the drive motor 31D. If control for increasing the PWM value is not performed in this state, the torque of the drive motor 31D is excessively small, and the drive of the drive motor 31D affects the drive motor 32D.

After step s5 or step s6, it is determined whether or not printing has been completed (step s7). If printing has been completed (step s7, Yes), the PWM value is stored in the storage unit of the control unit 40. (Step s8) Waiting for the start of printing (to Step 1). If printing has not ended (No at step s7), the process proceeds to a process of comparing the detected current value with the set value (to step s4).
In this configuration, the influence of the torque control motor can be fed back by monitoring the current value of the motor with the smaller diameter change due to temperature (rotational speed control), and stable driving can be achieved.

  In the above embodiment, the rotation control of the drive motor 31D is performed by the PWM value, and the drive motor 31D is controlled by the PWM signal generated by the PWM generation unit 41. However, the motor voltage depends on the type of the drive motor 31D. It may be controlled by. In this case, the control unit 40 can be provided with a voltage variable unit to adjust the motor voltage.

Next, a mode in which the drive motor 31D is controlled based on the temperature of the fixing roller 31 will be described.
FIG. 6 is a diagram showing a control block of this form.
The drive motor 31D and the drive motor 32D are connected to the control unit 40 in a controllable manner. The drive motor 31D performs torque control, and the drive motor 32D performs rotation speed control. Further, the temperature of the fixing roller 31 is detected by the temperature sensor 35, and the detection result is transmitted to the control unit 40.

The controller 40 controls the drive motor 32D so that the drive motor 32D has a predetermined rotational speed. Specifically, a motor voltage corresponding to the rotational speed is set in advance and driven by the motor voltage, and the rotational speed of the drive motor 32D is detected by a sensor (not shown). The control unit 40 performs feedback control based on the detection result relating to the rotational speed so that the drive motor 32D can obtain a predetermined rotational speed.
The control unit 40 controls the torque of the drive motor 31D with a PWM value corresponding to the temperature of the fixing roller 31. The relationship between the PWM value and the temperature of the fixing roller 31 is stored in the storage unit of the control unit 40 as a temperature table.

A control procedure of the drive motor 31D by the control unit 40 will be described based on the flowchart of FIG.
Waiting for the start of printing (step s10) and when printing is started (step s10, YES), the rotational drive of the drive motor 32D for controlling the rotational speed is turned on to control it to a predetermined rotational speed (step). s11).

  Next, the detection result of the temperature sensor 35 is received (step s12), the PWM value corresponding to the detected temperature is read from the temperature table indicating the relationship between the temperature and the PWM value, and the PWM generator 41 generates a PWM signal. The rotation of the drive motor 31D is controlled (step s13).

Steps s12 and s13 are loop-controlled at regular intervals, and during that time, it is determined whether printing has been completed (step s15). If printing has ended (step s15, Yes), the process proceeds to step s10 and waits for the start of printing. If printing has not ended, the loop control in steps s12 and s13 is continued.
In this embodiment, it is possible to perform appropriate torque control by monitoring the temperature of the fixing unit instead of monitoring the motor current and estimating the load change at the nip portion due to the change in the diameter of the fixing unit.

  In the above-described embodiment, the first fixing unit and the second fixing unit are each composed of a roller. However, the present invention is not limited thereto, and may be a belt-shaped one. Good. Even in the belt shape, a diameter change can occur in the nip portion.

Hereinafter, a fixing device 300 having a fixing unit using a belt will be described with reference to FIG. In addition, about the structure similar to the said embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted or simplified.
The fixing device 300 includes a fixing belt 310 as a fixing member for heating a toner image on a sheet, a heating roller 311 incorporating a halogen heater H1 for heating the fixing belt 310, and the fixing belt 310 as a heating roller 311. In addition, a conveying roller 312 that stretches and conveys, and a pressure roller 32 that presses the conveying roller 312 through a sheet together with the fixing belt 310 are provided.
The fixing belt 310, the heating roller 311 and the conveying roller 312 constitute a first fixing unit, and the pressure roller 32 constitutes a second fixing unit. The halogen heater H1 and the halogen heater H serve as the heating unit of the present invention. Configure. The pressure roller 32 has the same configuration as that of the above embodiment.
A nip portion N is formed by the conveying roller 312 and the pressure roller 32.

The transport roller 312 includes a cylindrical cored bar 312A using, for example, an aluminum alloy, carbon steel, and the like, and a silicone rubber layer 312B is provided on the outer peripheral surface of the cored bar 312A, and a silicone sponge layer 312C is further provided outside the silicone rubber layer 312B. Provided and configured.
The transport roller 312 rotates in the clockwise direction in the figure by driving of the drive motor 31D. The drive motor 31D corresponds to the first drive motor of the present invention, and is rotationally controlled by the control unit 40.

The fixing belt 310 stretched by the conveying roller 312 and the heating roller 311 is, for example, a material excellent in heat release and toner releasability on the outer peripheral surface of a polyimide film alone or a nickel belt as a base material. Can be used. Examples of the coating material include silicone rubber, fluororubber, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), PTFE (tetrafluoroethylene), FEP (copolymer of tetrafluoroethylene / hexafluoroethylene). Polymers) and fluororesins such as PFEP (tetrafluoroethylene / hexafluoropropylene copolymer) are preferred. Or what mixed these may be sufficient.
Further, a temperature sensor 35 is disposed on the outer peripheral side of the conveying roller 312 so that the temperature can be detected. The temperature sensor 35 corresponds to a temperature detection unit of the present invention. The detection result of the temperature sensor 35 is transmitted to the control unit 40.

As described above, the heating roller 311 incorporates the halogen heater H1 as a heating source inside, and the outer peripheral surface of the cylindrical hollow rotating body 311A formed of a metal such as aluminum alloy, carbon steel, and stainless steel has a heat resistance. Covered with a PFA tube 311B. A heater control temperature sensor 313 for measuring the temperature of the fixing belt 310 is disposed on the outer peripheral portion of the heating roller 311. The output of the heater control temperature sensor 313 is transmitted to the control unit 40 to control the heating temperature by the halogen heater H1.

The pressure roller 32 rotates counterclockwise in the figure by driving the drive motor 32D, as in the above embodiment. The drive motor 32D corresponds to the second drive motor of the present invention, and is rotationally controlled by the control unit 40.
Note that when the transport roller 312 and the pressure roller 32 are heated by the heating of the halogen heaters H <b> 1 and H, the diameter change of the transport roller 312 becomes relatively larger than the diameter change of the pressure roller 32. The magnitude of the diameter change here can be compared by the rate of change in diameter.

  In the fixing device 300 as well, as in the above embodiment, the control unit 40 controls the drive motor 32D so that the drive motor 32D has a predetermined rotational speed. The control unit 40 can perform torque control on the drive motor 31 </ b> D with the set PWM value. That is, the drive motor 31D performs torque control, and the drive motor 32D performs rotation speed control.

Further, in each of the above embodiments, the motor current value of the drive motor that controls the rotation speed or the temperature of the fixing unit is detected as the load of the nip portion, but the present invention is not limited to this. Instead, the motor current value or PWM value of the drive motor that is rotationally controlled according to the load at the nip portion can be used for control as being correlated with the load at the nip portion.
Further, although the motor is controlled by the PWM value, it may be controlled by changing the voltage.

  As mentioned above, although this invention was demonstrated based on the said embodiment, this invention is not limited to the content of the said embodiment, A suitable change is possible unless it deviates from the scope of the present invention.

A Image forming apparatus SC Image reading apparatus 10Y, 10M, 10C, 10K Image forming section 6 Intermediate transfer belt 7Y, 7M, 7C, 7K Primary transfer section 7A Secondary transfer section 20 Paper transport section 21 Paper feed section 24 Paper reversing section 25 Paper discharge rollers 291, 292, 293 Paper feed tray 30 Fixing device 300 Fixing device 31 Fixing roller 31D drive motor 310 Fixing belt 311 Heating roller 312 Conveying roller 32 Pressure roller 32D drive motor 35 Temperature sensor 40 Control unit 50 Operation display unit

Claims (3)

In a fixing device that heats and presses an image on a sheet to be passed to fix the image on the sheet,
A rotatable first fixing portion; and a rotatable second fixing portion that forms a nip portion through which the paper is passed together with the first fixing portion;
A heating unit for heating at least one of the first fixing unit and the second fixing unit;
A temperature detection unit for detecting the temperature of the first fixing unit or the second fixing unit;
A first drive motor that rotationally drives the first fixing unit; a second drive motor that rotationally drives the second fixing unit;
A controller that controls driving of each of the first drive motor and the second drive motor,
The first fixing unit has a relatively large change in the rotation diameter due to the heating, and the second fixing unit has a relatively small change in the rotation diameter due to the heating,
The control unit controls the number of rotations of the second drive motor that rotationally drives the second fixing unit, and controls the first drive motor that rotationally drives the first fixing unit to the temperature detection unit. Based on the load at the nip portion that changes according to the detection result, torque is controlled so that the load applied to the first drive motor is constant, and the motor current of the second drive motor is set to a set value. If the motor current is smaller, the PWM value of the first drive motor is lowered, and if the motor current is larger than the set value, the PWM value of the first drive motor is raised and the rotation is torque controlled. apparatus.   The fixing device according to claim 1, wherein the control unit controls the load at the nip portion to be constant in the rotation control. An image forming unit that forms an image and transfers the image to paper;
An image forming apparatus comprising: the fixing device according to claim 1.

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