JP2011164320A - Fixing device, image forming apparatus and method for cooling fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which suppresses overshoot by making temperature of a fixing roller or a fixing belt fall, in a short time, and can attain improvement in productivity, and to provide an image forming apparatus and a method for cooling the fixing device. <P>SOLUTION: The fixing device 49 includes a fixing part F that heats paper P on which a toner image has been formed; a fan 495 and a duct 496 that send air between the paper P and the fixing part F; an exhaust mechanism 497, that exhausts the sent air to the outside of a housing in which the fixing part F is housed; and a control part 1 that controls the fan 495 to make the air amount sent increase when finishing fixing operation in comparison with a sent air amount, when the fixing operation is performed, and controls the exhaust mechanism 497 to exhaust the air sent, when finishing the operation to the outside of the housing is finished. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device, an image forming apparatus, and a cooling method for the fixing device.

  In recent years, fixing devices in which a fixing roller having a low heat capacity and a high-output heater are combined have become widespread. Energy saving is achieved by using a low heat capacity fixing roller, and productivity is improved by using a high output heater.

When a fixing roller having a low heat capacity is used, the temperature of the fixing roller during the fixing operation is maintained within a certain range because the heat held by the fixing roller is transmitted to the sheet through the fixing belt, but is transmitted to the sheet at the end of the fixing operation. The heat that has been kept is held by the fixing roller as it is. Therefore, the temperature of the fixing roller at the end of the fixing operation may overshoot.
When the temperature of the fixing roller overshoots remarkably, the durability of the fixing roller decreases, and problems such as generation of ultra fine particles occur.

Further, in the conventional image forming apparatus, in order to improve productivity, the second print job is generally performed after the first print job is performed and before the temperature of the fixing roller is sufficiently lowered. Is. In this case, during the fixing operation of the second print job, a quality defect such as curling of the paper due to excessive heat applied to the paper may occur.
For example, when the fixing operation is performed on the thin paper after the fixing operation is performed on the thick paper in the first print job, or the process speed is increased in the first print job to increase the process speed to a low-quality image. In the second print job, after the fixing operation is performed, when the fixing operation is performed on a high-quality image with a slow process speed and a high writing density, more heat than necessary is required during the fixing operation of the second print job. Adds to paper and causes poor quality.

From the above, if the temperature of the fixing roller can be lowered in a short time at the end of the fixing operation, it is possible to suppress the temperature of the fixing roller from overshooting significantly.
Further, if the temperature of the fixing roller can be lowered in a short time before the second print job in which the paper type or the image quality is changed, it is possible to prevent the occurrence of quality defects while improving productivity.

Patent Document 1 discloses a fixing device provided with a fan for forcibly cooling a heating roller to a specific temperature when printing is stopped.
Patent Document 2 discloses a fixing device that includes a cooling unit that cools the heating roller and includes a control unit that drives the cooling unit until the heating roller reaches a predetermined temperature for a certain period of time after the completion of fixing. Yes.

  Japanese Patent Application Laid-Open No. 2004-228688 includes a ventilation unit that discharges only the air around the fixing device to the outside when changing the sheet conveyance speed in order to perform printing with different pixel densities, and the fixing unit lowers the surface temperature of the fixing roller by the ventilation unit. An apparatus is disclosed.

JP 2006-227374 A JP 2001-343857 A JP 2001-242745 A

In the fixing devices of Patent Documents 1 and 2, the output of the heater is stopped immediately before the end of the print job, thereby suppressing overshoot at the end of the fixing operation. That is, the heater output is stopped during the fixing operation. For this reason, when a fixing roller having a low heat capacity is used, the heating temperature becomes low and fixing failure occurs.
If a fixing roller with a high heat capacity is used, fixing failure is unlikely to occur even if the heater output is stopped during the fixing operation immediately before the end of the print job, but the heat held by the fixing roller is transmitted to the roller surface. It is not possible to effectively suppress a significant overshoot of the temperature of.

  Further, in the fixing device disclosed in Patent Document 3, only the fixing roller is cooled by ventilation, and the cooling performance is low. Therefore, the temperature of the fixing roller cannot be lowered in a short time before the second print job in which the paper type or image quality is changed, and it is impossible to prevent the occurrence of quality defects while improving productivity.

  An object of the present invention is to provide a fixing device, an image forming apparatus, and a fixing device that can suppress overshoot by reducing the temperature of the fixing roller in a short time and can prevent the occurrence of poor quality while improving productivity. It is to provide a cooling method.

According to the present invention, a fixing unit that heats a sheet on which a toner image is formed;
An air blowing unit for blowing air between the paper and the fixing unit;
An exhaust mechanism that exhausts the blown air out of the housing that houses the fixing unit;
The blower unit is controlled so as to increase the air flow rate at the end of the fixing operation as compared with the air flow rate at the time of the fixing operation, and the exhaust mechanism is configured to exhaust the blown air to the outside of the housing at the end of the fixing operation. A control unit to control;
Is provided.

A fixing unit for heating the paper on which the toner image is formed;
An air blowing unit for blowing air between the paper and the fixing unit;
An exhaust mechanism that exhausts the blown air out of the housing that houses the fixing unit;
The blower unit is controlled so as to increase the air flow rate at the end of the fixing operation as compared with the air flow rate at the time of the fixing operation, and the exhaust mechanism is configured to exhaust the blown air to the outside of the housing at the end of the fixing operation. A control unit to control;
An image forming apparatus is provided.

A step of heating the paper on which the toner image is formed by the fixing unit;
A step of blowing air between the sheet and the fixing unit by a blowing unit;
Exhausting the blown air out of the housing that houses the fixing unit by an exhaust mechanism;
The control unit controls the air blowing unit to increase the air flow rate at the end of the fixing operation as compared to the air flow rate at the fixing operation, and exhausts the blown air outside the housing only at the end of the fixing operation. Controlling the exhaust mechanism,
A method for cooling a fixing device is provided.

  According to the present invention, since the temperature of the fixing unit can be lowered in a short time at the end of the fixing operation, it is possible to effectively suppress the temperature of the fixing roller from overshooting significantly. Further, it is possible to prevent the occurrence of quality defects while maintaining the productivity improvement.

1 is a schematic configuration diagram of an image forming apparatus. 1 is a schematic configuration diagram of a fixing device. It is a figure which shows the operation example of a duct. It is a flowchart which shows an overshoot suppression process. It is a figure which shows temperature transition. It is a flowchart which shows productivity improvement processing. It is a flowchart which shows an opening / closing process.

The configuration and operation of the image forming apparatus in this embodiment will be described in detail with reference to the drawings. In addition, this embodiment is an example and this invention is not limited to this. For example, in the present embodiment, a monochrome image forming apparatus has been described as an example. However, the present invention can also be implemented by a color image forming apparatus.

FIG. 1 shows a schematic configuration of the image forming apparatus 10.
The image forming apparatus 10 includes an automatic document feeder 20, a scanner unit 30, an image forming unit 40, a paper feeding unit 50, and the like.

The automatic document conveyance unit 20 conveys the document D placed on the document placement tray one by one to a predetermined conveyance path.
The scanner unit 30 irradiates the conveyed document D with a light source and receives reflected light reflected from the document D. The scanner unit 30 converts the received optical signal into an electrical signal (image data), and outputs the converted image data to the image forming unit 40.

  The image forming unit 40 forms a toner image on the photosensitive drum 41 based on the image data, and performs a series of image forming operations until the formed toner image is transferred to the paper P and fixed.

The configuration and operation around the photosensitive drum 41 will be briefly described.
The charging device 42 uniformly charges the surface of the photosensitive drum 41.
The exposure device 43 exposes a non-image area of the photosensitive drum 41 and forms an electrostatic latent image in the image area by removing the charge in the exposed portion.
The developing device 44 develops the toner image by attaching toner to the electrostatic latent image.
The transfer device 45 applies a charge having a polarity opposite to that of the toner from the back surface of the paper P, and transfers the toner image attached to the photosensitive drum 41 to the paper P by electrostatic force.
The separation device 46 adds a charge having a polarity opposite to that at the time of transfer from the back surface of the paper P, and separates the paper P and the photosensitive drum 41.
The separation claw 47 contacts the surface of the photosensitive drum 41 and separates the paper P and the photosensitive drum 41 when the paper P and the photosensitive drum 41 are not separated even after the separation processing by the separation device 46.
The cleaning device 48 removes residual toner adhering to the photosensitive drum 41 without being transferred to the paper P with a brush or a blade.
The fixing device 49 heats and presses the conveyed paper P to fix the toner image formed on the paper P.

FIG. 2 shows a schematic configuration of the fixing device 49.
The fixing device 49 includes a heating roller 491, a first pressure roller 492, a second pressure roller 493, a fixing belt 494, a fan 495, a duct 496, an exhaust mechanism 497, and the like.

  The heating roller 491 is a roller made of an aluminum material having a diameter = 52 mm and a thickness = 3.0 mm, and includes a high output heater inside. The heating roller 491 rotates in the forward direction with respect to the conveyance direction of the paper P, and heats the first pressure roller 492 and the fixing belt 494 via the fixing belt 494.

  The first pressure roller 492 is a roller made of a rubber material having a diameter = 40 mm and a thickness of 7.5 mm, and includes a SUS solid shaft having a diameter = 25 mm inside. The first pressure roller 492 rotates in the forward direction with respect to the transport direction of the paper P, and heats or pressurizes the surface of the transported paper P.

  The second pressure roller 493 is a roller in which a roller made of an aluminum material having a diameter = 50 mm and a thickness = 3.0 mm is covered with a rubber material having a thickness = 2.0 mm, and includes a high output heater therein. The second pressure roller 493 rotates in the forward direction with respect to the transport direction of the paper P, and heats or pressurizes the back surface of the transported paper P.

  The fixing belt 494 is a belt having a diameter of 80 mm, and rotates the heating roller 491 and the first pressure roller 492 in conjunction with the conveyance direction of the paper P in the forward direction.

  Hereinafter, the heating roller 491, the first pressure roller 492, the second pressure roller 493, and the fixing belt 494 are collectively referred to as “fixing portion F”.

The fan 495 blows outside air in a range of 5 to 10 m / s by rotating.
The duct 496 conveys air from the fan 495 to the nip portion or the fixing belt 494.

  The “nip portion” refers to a constant region centered between the first pressure roller 492 and the second pressure roller 493 that sandwich the paper P.

FIG. 3 shows an operation example of the duct 496.
For example, as shown by a broken line in FIG. 3, the duct 496 rotates the tip portion B counterclockwise by a certain range with the tip A of the air blowing outlet as a rotation axis. The duct 496 can switch the blowing direction from the fan 495 by rotating the tip portion B.

  For example, the duct 496 switches the blowing direction so that the blowing from the fan 495 hits the nip during the fixing operation. When the air blown from the fan 495 strikes the nip portion, the paper P stuck to the first pressure roller 492 can be separated. Although described later, this is called “air separation”.

  Further, the duct 496 rotates the front end portion B at the end of the fixing operation, and switches the blowing direction so that the blowing from the fan 495 directly hits the first pressure roller 492 or the fixing belt 494. When the air blown from the fan 495 directly hits the first pressure roller 492 or the fixing belt 494, the fixing unit F can be effectively cooled, and the temperature of the fixing unit F can be lowered in a short time.

The exhaust mechanism 497 is an open / close type window, and exhausts the wind blown to the fixing unit F to the outside of the casing of the fixing device 49. For example, the exhaust mechanism 497 can perform the exhaust operation by fully opening the window at the end of the fixing operation, thereby reducing the temperature in the casing of the fixing device 49. Further, the exhaust mechanism 497 can maintain the temperature inside the casing of the fixing device 49 by closing the window during the fixing operation.
The exhaust mechanism 497 is not limited to an openable / closable window, and may be an exhaust fan.

  Returning to FIG. 1, the paper feed unit 50 stores a plurality of types of paper P in the tray, and feeds the paper P to the image forming unit 40 via a predetermined transport path.

  The control unit 1 includes a CPU, a RAM, a ROM, and the like. The CPU 1 expands various programs stored in the ROM into the RAM, and executes the expanded various programs, thereby executing the fixing device 49 and the image forming apparatus. The overall operation of the 10 is controlled.

The overshoot suppression process will be described with reference to FIG.
The overshoot suppression process is a process for suppressing the temperature of the fixing unit F from overshooting significantly by reducing the temperature of the fixing unit F in a short time at the end of the print job (at the end of the fixing operation).

  When a print job start signal is input, for example, when a print start button is pressed from an operation panel (not shown), the control unit 1 starts a print job (step S1).

The control unit 1 determines whether air separation is necessary (step S2).
“Air separation” means that when the paper P passing through the nip portion sticks to the first pressure roller 492 and does not leave when passing, the first paper P is blown to the nip portion by blowing air from the fan 495. Separation from the pressure roller 492.
For example, the sheet P tends to stick to the first pressure roller 492 during the fixing operation of thin paper or the fixing operation of a solid image in which a lot of toner is used, and air separation is required. The control unit 1 inputs a print job start signal and refers to the print job data to determine whether the print job is a thin paper or a solid image. When the print job is a thin paper or a solid image, air separation is necessary. Judge that there is.

When air separation is necessary (step S2; Y), the control unit 1 rotates the fan 495 to perform air separation (step S3).
The control unit 1 determines whether or not the current paper P being subjected to the print job is the final paper (step S4).

If it is not the final sheet (step S4; N), the controller 1 proceeds to step S3.
If it is the final sheet (step S4; Y), the control unit 1 proceeds to step S7.

  Returning to step S2, if air separation is not required (step S2; N), the control unit 1 maintains the fan 495 stopped (step S5).

The control unit 1 determines whether or not the current sheet P being subjected to the print job is the final sheet (step S6).
If it is not the final sheet (step S6; N), the control unit 1 proceeds to step S5.
If it is the final sheet (step S6; Y), the control unit 1 proceeds to step S7.

The controller 1 determines whether the trailing edge of the final sheet has passed between the first pressure roller 492 and the second pressure roller 493 (step S7).
When determining whether or not it has passed, the control unit 1 inputs a signal from a sensor or the like (not shown) and makes a determination based on the input signal.

When it has not passed (step S7; N), the control part 1 waits until it passes.
If it has passed (step S7; Y), the control unit 1 determines that the print job has ended, that is, determines that the fixing operation has ended, and performs processing for any or all of the following (1) to (3) (step) S8).
(1) The fan 495 is rotated at the maximum air volume.
(2) The exhaust mechanism 497 is opened.
(3) The tip portion B is rotated to switch the blowing direction.
The control unit 1 performs the above (1) to (3) while rotating the fixing unit F.

The control unit 1 determines whether or not a certain time has elapsed since the end of the print job (step S9).
When the predetermined time has not elapsed (step S9; N), the control unit 1 proceeds to step S8.
When the predetermined time has elapsed (step S9; Y), the control unit 1 restores the process performed in step S8. Specifically, processing is performed for any or all of the following (1) to (3) (step S10).
(1) The fan 495 is stopped.
(2) The exhaust mechanism 497 is closed.
(3) Rotate the tip to return the blowing direction.
Thus, the overshoot suppression process is terminated.

FIG. 5 shows a temperature transition diagram.
The temperature transition shown in FIG. 5 is the temperature transition of the fixing unit F when the air is blown only for air separation, and the temperature of the fixing unit F when the cooling process is performed by blowing other than the air separation (see FIG. 4). It is temperature transition.

  When the air is blown only for air separation, it is not possible to prevent the temperature of the fixing unit F from overshooting at the end of the print job. At this time, since the temperature of the fixing unit F rises to approximately 200 ° C., the durability of the fixing unit F decreases, and problems such as generation of ultrafine particles occur.

  In addition to air separation, when the process of cooling the fixing unit F and the fixing belt 494 is performed, that is, when the process of step S8 in FIG. 4 is performed, the temperature of the fixing unit F overshoots at the end of the print job. I can suppress it. At this time, the temperature of the fixing portion F is suppressed to a level that does not rise above about 190 ° C. Note that the temperature of the fixing unit F maintained during idling by the control unit 1 for improving productivity is around 190 ° C.

The productivity improvement process will be described with reference to FIG.
In the productivity improvement process, when the second print job is executed after changing the paper type or image quality after the first print job is executed, the temperature of the fixing unit F is lowered in a short time before the second print job is executed. This is a process for preventing the occurrence of poor quality while improving productivity.

When the print start signal is input, for example, when the print start button is pressed from an operation panel (not shown), the control unit 1 determines the print mode based on the input signal (step S11).
The “print mode” includes, for example, a thin paper mode using thin paper, a thick paper mode using thick paper, a low image quality mode for printing with low image quality, and a high image quality mode for printing with high image quality.

The control unit 1 determines whether or not the temperature of the fixing unit F needs to be lowered based on the determined print mode information (step S12).
For example, when the determined print mode is the thin paper mode, the control unit 1 determines that the temperature of the fixing unit F needs to be lowered if the current temperature of the fixing unit F is higher than a temperature suitable for thin paper. Further, when the determined print mode is the high image quality mode, if the current temperature of the fixing unit F is higher than the temperature suitable for high image quality in relation to the process speed, it is determined that the temperature of the fixing unit F needs to be lowered. To do.

  When it is not necessary to lower the temperature of the fixing unit F (step S12; N), the control unit 1 maintains the fan 495 stopped (step S13).

When it is necessary to lower the temperature of the fixing unit F (step S12; Y), the control unit 1 performs processing for any or all of the following (1) to (3) (step S14).
(1) The fan 495 is rotated at the maximum air volume.
(2) The exhaust mechanism 497 is opened.
(3) The tip portion B is rotated to switch the blowing direction.
The control unit 1 performs the above (1) to (3) while rotating the fixing unit F.

  The control unit 1 determines whether or not a predetermined target temperature has been reached for each mode (step S15).

When the target temperature has not been reached (step S15; N), the control unit 1 proceeds to step S14.
When the target temperature is reached (step S15; Y), the control unit 1 restores the process performed in step S14. Specifically, processing is performed for any or all of the following (1) to (3) (step S16).
(1) The fan 495 is stopped.
(2) The exhaust mechanism 497 is closed.
(3) The tip portion B is rotated to return the air blowing direction.
Thereafter, the control unit 5 starts a print job (step S17) and ends this processing.

  When the temperature of the fixing portion F reached 180 ° C. for 5 minutes in an environment of room temperature of 20 ° C., the time required to decrease to 160 ° C. after measuring for 5 minutes was measured. When not performing (refer FIG. 6), the time required was 3 minutes. On the other hand, when the above process (see FIG. 6) was performed, the time required was 30 seconds. Thus, by performing the above processing (see FIG. 6), the temperature can be lowered to an appropriate temperature in a short time, and a print job can be started immediately. Therefore, it is possible to prevent the occurrence of quality defects while improving productivity.

The opening / closing process will be described with reference to FIG.
The opening / closing process is a process for controlling the opening / closing of the window of the exhaust mechanism 497 to maintain the temperature in the casing of the fixing device 49 at an appropriate temperature.

  When the print start signal is input, for example, when the print start button is pressed from an operation panel (not shown), the control unit 1 starts a print job (step S21).

The control unit 1 acquires paper type information, paper passing information, printing information, and the like based on the input print start signal (step S22).
The paper type information is information related to paper types such as normal paper, thin paper, and thick paper.
The paper passing information is information relating to the time until the paper P finishes passing between the first pressure roller 492 and the second pressure roller 493.
The print information is information relating to image quality such as low image quality, high image quality, and solid images.

The controller 1 determines whether air separation is necessary (step S23).
For example, based on the acquired paper type information, the control unit 1 determines that air separation is necessary when executing a thin paper print job. Further, the control unit 1 determines that air separation is necessary when a solid image print job is performed based on the acquired print information.

When air separation is not necessary (step S23; N), the control unit 1 ends the opening / closing process.
When air separation is necessary (step S23; Y), the control unit 1 determines an air volume for air separation (step S24).

  The air volume for air separation is determined according to the paper type and image quality. For example, when the paper type is thin paper or the image quality is a solid image, the control unit 1 increases the air volume for air separation because the paper P easily sticks to the first pressure roller 492 and is difficult to separate. Specifically, when the wind speed from the fan 495 is variable from 5 to 10 m / s, the control unit 1 determines the air volume for air separation to about 8 m / s when printing thin paper or a solid image. In addition, when the paper type is plain paper, the control unit 1 makes it difficult for the paper P to stick to the first pressure roller 492 and can be easily separated even if it sticks, so the air volume for air separation is reduced. Specifically, the control unit 1 determines the air volume to a minimum of 5 m / s.

  The controller 1 determines whether or not to start the rotation of the fan 495 for air separation (step S25).

When the rotation has not started yet (step S25; N), the control unit 1 stands by until the rotation is started.
When the rotation is started (step S25; Y), the control unit 1 starts the rotation of the fan 495 and opens the window of the exhaust mechanism 497 halfway (step S26).

The controller 1 determines whether or not to stop the rotation of the fan 495 for air separation (step S27).
When the rotation is not yet stopped (step S27; N), the control unit 1 stands by until the rotation is stopped.
When the rotation is stopped (step S27; Y), the control unit 1 determines whether or not the print job is finished (step S28).

If it is not at the end of the print job (step S28; N), the control unit 1 stands by with the window of the exhaust mechanism 497 half open until the end of the print job.
When it is time to finish the print job (step S28; Y), the control unit 1 fully opens the window of the exhaust mechanism 497 (step S29).
At this time, the control unit 1 fully opens the window of the exhaust mechanism 497 and maximizes the air volume from the fan 495 (for example, 10 m / s), so that the air is directly applied to the first pressure roller 492 or the fixing belt 494. Switch the air blowing direction so that it hits.

The control unit 1 determines whether or not the temperature of the fixing unit F has reached a predetermined target temperature (step S30).
When the target temperature has not been reached (step S30; N), the control unit 1 fully opens the window of the exhaust mechanism 497 until the target temperature is reached.
When the target temperature is reached (step S30; Y), the control unit 1 closes the window of the exhaust mechanism 497 (step S31) and ends the opening / closing process.

  As described above, according to the present embodiment, the air from the fan 495 is used for air separation, the air is blown at the maximum air volume at the end of the fixing operation, and the exhaust mechanism 497 is opened to exhaust the air. By creating a flow, overshoot can be effectively suppressed. Moreover, it is possible to prevent the occurrence of quality defects while improving productivity.

  Further, by providing a mechanism for appropriately switching between the air blowing direction during air separation and the air blowing direction when cooling the fixing unit F, it is possible to effectively overshoot using a general apparatus configuration capable of performing air separation. Therefore, it is possible to prevent the occurrence of quality defects while improving productivity.

  In addition, by rotating the fixing unit F when air is blown at the maximum air volume, the temperature of the fixing unit F can be reduced in a short time, effectively suppressing overshoot and improving productivity. However, it is possible to prevent the occurrence of quality defects.

  Further, after a certain period of time has elapsed since the start of blowing with the maximum air volume, or after the fixing unit F reaches a predetermined target temperature or less, the blowing from the fan 495 can be stopped, and the fixing device 49 is unnecessary. It is possible to prevent the temperature inside the casing from being lowered.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 20 Automatic document conveyance part 30 Scanner part 40 Image forming part 49 Fixing apparatus 491 Heating roller 492 First pressure roller 493 Second pressure roller 494 Belt 495 Fan 496 Exhaust mechanism 50 Paper feeding part 1 Control part F Fixing part

Claims (12)

A fixing unit for heating the paper on which the toner image is formed;
An air blowing unit for blowing air between the paper and the fixing unit;
An exhaust mechanism that exhausts the blown air out of the housing that houses the fixing unit;
The blower unit is controlled so as to increase the air flow rate at the end of the fixing operation as compared with the air flow rate at the time of the fixing operation, and the exhaust mechanism is configured to exhaust the blown air to the outside of the housing at the end of the fixing operation. A control unit to control;
A fixing device provided with The air blowing unit includes a switching mechanism that switches the air blowing direction to either the nip part or the fixing part where the paper is sandwiched by the fixing part,
The fixing device according to claim 1, wherein the control unit controls the switching mechanism so as to switch a blowing direction at the end of the fixing operation to the fixing unit side and switch a blowing direction at the time of the fixing operation to the nip portion side.   The fixing device according to claim 1, wherein the control unit rotates the fixing unit at the end of the fixing operation.   4. The control unit according to claim 1, wherein the control unit stops air blowing at the end of the fixing operation when a predetermined time has elapsed or when the temperature of the fixing unit becomes lower than a predetermined temperature. Fixing device.   The control unit controls the air blowing unit to increase the air flow rate before starting the fixing operation as compared with the air flow rate during the fixing operation, and exhausts the blown air to the outside of the housing before the fixing operation starts. The fixing device according to any one of claims 1 to 4, wherein the exhaust mechanism is controlled to do so.   The fixing device according to claim 2, wherein the control unit controls the switching mechanism to switch a blowing direction before starting a fixing operation to the fixing unit side.   The fixing device according to claim 1, wherein the control unit rotates the fixing unit before starting a fixing operation.   8. The control unit according to claim 1, wherein the control unit stops air blowing before the start of the fixing operation when a certain time has elapsed or when the temperature of the fixing unit becomes lower than a predetermined temperature. Fixing device.   The fixing device according to claim 1, wherein the fixing unit is a fixing roller, or a fixing roller and a fixing belt.   The fixing device according to claim 1, wherein the exhaust mechanism is a window or an exhaust fan. A fixing unit for heating the paper on which the toner image is formed;
An air blowing unit for blowing air between the paper and the fixing unit;
An exhaust mechanism that exhausts the blown air out of the housing that houses the fixing unit;
The blower unit is controlled so as to increase the air flow rate at the end of the fixing operation as compared with the air flow rate at the time of the fixing operation, and the exhaust mechanism is configured to exhaust the blown air to the outside of the housing at the end of the fixing operation. A control unit to control;
An image forming apparatus. Heating the paper on which the toner image is formed by the fixing unit;
A step of blowing air between the paper and the fixing belt by a blower;
Exhausting the blown air out of the housing housing the fixing belt by an exhaust mechanism;
The control unit controls the air blowing unit to increase the air flow rate at the end of the fixing operation as compared to the air flow rate at the fixing operation, and exhausts the blown air outside the housing only at the end of the fixing operation. Controlling the exhaust mechanism,
A cooling method for a fixing device comprising:

Images