JP5966378B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an electrostatic recording image forming apparatus such as a copying machine, a facsimile machine, and a printer. More specifically, the present invention relates to a nip formed between an endless fixing member and a pressure member. The present invention relates to a fixing device that performs a fixing process on a recording medium that passes through and an image forming apparatus equipped with the fixing device.

In recent years, market demands for energy saving and high speed are increasing for image forming apparatuses such as printers, copiers, and facsimiles.
In an image forming apparatus, an unfixed toner image is recorded on a recording material sheet, printing paper, photosensitive paper, electrostatic recording using an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, or magnetic recording. It is formed on a recording medium such as paper. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

  As an example of such a fixing device, a belt-type fixing device (for example, Patent Document 1) and a surf fixing (film fixing) fixing device (for example, Patent Document 2) using a ceramic heater are known.

  In recent years, belt-type fixing devices have undergone warm-up time, which is the time required to reach a predetermined printable temperature (reload temperature) when the power is turned on, etc. There is a demand for further shortening of the first print time, which is the time from the printing operation to the completion of paper discharge (Problem 1). Further, as the speed of the image forming apparatus increases, the number of sheets passed per unit time increases and the required heat amount increases, so that a so-called temperature drop, in which the heat amount is insufficient particularly at the beginning of continuous printing, is also a problem ( Problem 2).

  As a solution to the problem 1, surf fixing using a ceramic heater has been proposed, and this method makes it possible to reduce the heat capacity and reduce the size of the device as compared with a belt-type fixing device. However, since only the nip portion is locally heated, the other portions are not heated, and the belt is in the coldest state at the entrance of the sheet or the like in the nip portion, so that fixing failure is likely to occur. In particular, in a high-speed machine, there is a problem that fixing failure is more likely to occur because the belt rotates fast and the heat radiation of the belt outside the nip increases (problem 3).

  In order to solve the above problems 1 to 3, in the configuration using an endless belt, the entire belt can be heated, the first print time from the heating standby time can be shortened, and at the time of high-speed rotation There has been proposed a fixing device that can solve the shortage of heat and can obtain good fixing performance even when mounted in a high-production image forming apparatus (Patent Document 3).

FIG. 7 is a schematic diagram of a fixing device described in Patent Document 3.
A pipe-shaped metal heat conductor 82 is fixed inside the endless belt 81 so that the movement of the endless belt 81 can be guided, and the heat source 83 in the metal heat conductor 82 passes through the metal heat conductor 82. The endless belt 81 is heated. Further, a pressure roller 84 that forms a nip portion N in contact with the metal heat conductor 82 via the endless belt 81 is provided, and the endless belt 81 is moved in the circumferential direction so as to rotate as the pressure roller 84 rotates. Move. With this configuration, it is possible to warm the entire endless belt constituting the fixing device, to shorten the first print time from the heating standby time, and to solve the shortage of heat during high-speed rotation. Yes.

  However, in order to further save energy and improve the first print time, it is necessary to further improve the thermal efficiency. From the configuration in which the endless belt is indirectly heated through the metal heat conductor, the endless belt is made of the metal heat conductor. A configuration in which heating is performed directly without intervening has been devised. With this configuration, it is possible to significantly improve the heat transfer efficiency and reduce power consumption, and to further shorten the first print time from the heating standby time. In addition, since a metal heat conductor is not required, the cost can be reduced.

  By directly heating the endless belt, energy saving is high and it is possible to further shorten the first print time from the standby time of heating, but the temperature rise performance is extremely high, so if the temperature control runs out of control, In particular, when the temperature control runs away while the endless belt is in a non-rotating state, a new problem has arisen in which the risk of increased ignition increases.

  Therefore, in the present invention, a fixing device capable of controlling the temperature of the fixing belt safely by using a short warm-up time, high energy saving, and capable of further shortening the first print time from the heating standby time. An object of the present invention is to provide an image forming apparatus.

In order to solve this problem, a fixing device of the present invention includes a rotatable fixing member having a heat source, a pressing member that can be rotated by a driving source and pressurizes the fixing member to form a nip, An abnormal temperature detecting means disposed at a position facing the fixing member to detect an abnormal temperature rise of the fixing member; and a position changing means for changing the position of the abnormal temperature detecting means with respect to the fixing member. The fixing member is directly heated without using a heat conductor to fix the recording medium passing through the nip, and the abnormal temperature detecting means and the fixing member when the fixing member is not rotated. Is set to be smaller than that during rotation of the fixing member by the position changing means, and a pressing means for pressing the pressing member against the fixing member is provided on the pressing member. Whether the pressure member is the fixing member When separated, the fixing member is in a non-rotating state, and the position changing means for the abnormal temperature detecting means synchronizes with the separation of the pressurizing member by the pressurizing means, and the abnormal temperature detecting means and the fixing The gap between the members is smaller than that during rotation .

  In a fixing device that directly heats the fixing member without using a metal heat conductor, the temperature rise performance is high. Therefore, the fixing member in a non-rotating / stationary state may be locally heated to ignite. However, according to the present invention, the gap between the abnormal temperature detecting means and the fixing member when the fixing member is not rotating is set smaller than that during the rotation by the position changing means that brings the abnormal temperature detecting means into contact with and away from the fixing member. Therefore, the smaller the gap with the fixing member, the easier it is for the abnormal temperature detection means to operate at the rated temperature, so even if the temperature control runs out of control, the current of the heat source is safely cut off to avoid dangers such as ignition be able to. Further, even if the gap between the fixing member in a non-rotating / stationary state and the abnormal temperature detecting means is made smaller than that at the time of rotation, the surface of the fixing member is not scratched.

FIG. 2 is a schematic diagram for explaining a configuration of an image forming apparatus using a fixing device according to the present invention. FIG. 2 is an explanatory diagram showing an embodiment of a fixing device of the present invention. It is explanatory drawing which shows another embodiment of the fixing device of this invention. FIG. 2 is an explanatory diagram showing an embodiment of a fixing device of the present invention. FIG. 2 is an explanatory diagram showing an embodiment of a fixing device of the present invention. It is explanatory drawing which shows another embodiment of the fixing device of this invention. It is explanatory drawing which shows an example of the fixing device which has the conventional structure.

First, the configuration of an image forming apparatus to which the fixing device of the present invention is applied will be described with reference to FIG.
The image forming apparatus shown in FIG. 1 is a color printer using a tandem system in which image forming units for forming a plurality of color images are juxtaposed along the belt extending direction. However, the present invention is not limited to this system. It is also possible to target not only copying machines and facsimile machines.

  In the image forming apparatus 100, photosensitive drums 20Y, 20C, 20M, and 20Bk as image carriers that can form images as images corresponding to colors separated into yellow, cyan, magenta, and black are arranged in parallel. The installed tandem structure is adopted.

  In the image forming apparatus 100 having the illustrated configuration, the visible images formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk are transferred to the photosensitive drums 20Y, 20C, 20M, and 20Bk by executing the primary transfer process. A recording medium on which an endless belt that can move in the direction of the arrow A1 while facing it is superimposed and transferred to an intermediate transfer member (hereinafter referred to as a transfer belt) 11 and then an image on the intermediate transfer member is a recording sheet or the like. The batch transfer is performed on S by executing the secondary transfer process.

  Around each photosensitive drum, an apparatus for image forming processing is arranged according to the rotation of the photosensitive drum. The photosensitive drum 20Bk that performs black image formation will be described as an example. A charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk that perform image forming processing are arranged along the rotation direction of the photosensitive drum 20Bk. Has been. An optical writing device 8 is used for writing performed after charging of the photosensitive drum.

  In the superimposing transfer to the transfer belt 11, the visible image formed on each photoconductive drum 20 </ b> Y, 20 </ b> C, 20 </ b> M, 20 </ b> Bk is transferred to the same position on the transfer belt 11 in the process of moving the transfer belt 11 in the A1 direction. As shown in the figure, the voltage is applied by the primary transfer rollers 12Y, 12C, 12M, and 12Bk disposed opposite to the photosensitive drums 20Y, 20C, 20M, and 20Bk with the transfer belt 11 interposed therebetween, and thereby the upstream side in the A1 direction. The timing is shifted from downstream to downstream.

  The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 20Y, 20C, 20M, and 20Bk is provided in an image station for forming yellow, cyan, magenta, and black images, respectively.

  The image forming apparatus 100 is disposed so as to face four image stations that perform image forming processing for each color and above each of the photosensitive drums 20Y, 20C, 20M, and 20Bk, and includes a transfer belt 11 and a primary transfer roller 12Y. , 12C, 12M, and 12Bk, a secondary transfer roller 5 that is a transfer roller as a transfer member that is arranged to face the transfer belt 11 and that is driven by the transfer belt 11 and rotates. An intermediate transfer belt cleaning device 13 disposed opposite to the transfer belt 11 for cleaning the transfer belt 11, and an optical writing device 8 serving as an optical writing device disposed below these four image stations. And have.

  The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, a rotating polygon mirror as a deflecting means, and the like, and each of the photosensitive drums 20Y, 20C, 20M, Write light Lb corresponding to each color with respect to 20 Bk (in FIG. 1, for the sake of convenience, a reference is given only to the image station of the black image, but the same applies to the other image stations), and the photosensitive drum An electrostatic latent image is formed on 20Y, 20C, 20M, and 20Bk.

  The image forming apparatus 100 includes a sheet feeding device 61 as a sheet feeding cassette on which a recording medium S conveyed between the photosensitive drums 20Y, 20C, 20M, and 20Bk and the transfer belt 11 is stacked, and a sheet feeding device. The transfer section between the photosensitive drums 20Y, 20C, 20M, and 20Bk and the transfer belt 11 at a predetermined timing that matches the recording timing of the toner image formed by the image station with the recording medium S conveyed from the feeding device 61. And a sensor (not shown) for detecting that the leading edge of the recording medium S has reached the registration roller pair 4.

  The image forming apparatus 100 also includes a roller fixing type fixing device 200 for fixing the toner image to the recording medium S to which the toner image is transferred, and a recording medium S on which the toner image has been fixed. A paper discharge roller 7 that discharges to the outside of the main body, a paper discharge tray 17 that is disposed in the upper part of the main body of the image forming apparatus 100 and loads the recording medium S discharged to the outside of the main body of the image forming apparatus 100 by the discharge roller 7; Located below the paper discharge tray 17 are provided toner bottles 9Y, 9C, 9M and 9Bk filled with toners of yellow, cyan, magenta and black.

  The transfer belt unit 10 includes a drive roller 72 and a driven roller 73 around which the transfer belt 11 is wound, in addition to the transfer belt 11 and the primary transfer rollers 12Y, 12C, 12M, and 12Bk.

  The driven roller 73 also has a function as tension urging means for the transfer belt 11, and for this purpose, the driven roller 73 is provided with urging means using a spring or the like. The transfer belt unit 10, the primary transfer rollers 12 Y, 12 C, 12 M, and 12 Bk, the secondary transfer roller 5, and the cleaning device 13 constitute a transfer device 71.

  The sheet feeding device 61 is disposed at the lower part of the main body of the image forming apparatus 100, and includes a feeding roller 3 as a feeding roller that contacts the upper surface of the uppermost recording medium S. 3 is rotated counterclockwise so that the uppermost recording medium S is fed toward the registration roller pair 4.

  Although not shown in detail, the cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade disposed so as to face and contact the transfer belt 11. The transfer belt 11 is cleaned by scraping and removing foreign matter such as residual toner on the top with a cleaning brush and a cleaning blade.

  The cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the residual toner removed from the transfer belt 11.

FIG. 2 is a sectional view showing the fixing device of the present invention.
The fixing device 200 includes a fixing belt 201 as a fixing member and a pressure roller 203 as a pressure member. A halogen heater 202 serving as a heat source is provided in the fixing belt 201, whereby the fixing belt 201 is directly heated by radiant heat from the inner peripheral side. Further, a nip forming member 206 that forms a nip with the pressure roller 203 via the fixing belt 201 is disposed on the side of the fixing belt 201 facing the pressure roller 203, and directly or unillustrated on the inner surface of the fixing belt. It slides indirectly through the moving seat.

  In the configuration of FIG. 2, the shape of the nip portion is flat, but may be a concave shape or other shapes. By forming the concave nip, the discharge direction of the front end of the recording medium is closer to the pressure roller, and the separation of the recording medium from the fixing belt is improved, so that jamming is suppressed.

  The fixing belt 201 is an endless belt (or film) using a metal belt such as nickel or SUS or a resin material such as polyimide. The surface layer of the belt has a release layer made of tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA) or tetrafluoroethylene resin (PTFE), and has a releasability so that toner does not adhere. It is There may be an elastic layer formed of a silicone rubber layer or the like between the belt substrate and the PFA or PTFE layer. When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved. However, when the unfixed image is crushed and fixed at the nip portion, minute irregularities on the belt surface are transferred to the image, resulting in a solid image portion. In this case, there is a problem that a glossy unevenness (skin image) remains on the skin. In order to improve this, it is necessary to provide a silicone rubber layer of 100 μm or more. Due to the deformation of the silicone rubber layer, minute irregularities are absorbed, and the skin image is improved.

  Further, a support member 207 that is a stay for supporting the nip portion is provided inside the fixing belt 201 to prevent the nip forming member 206 that receives pressure from the pressure roller 203 from being bent, and in the axial direction (perpendicular to the paper surface). ) To obtain a uniform nip width. The support member 207 is held and fixed to a holding member 208 that is a flange at both ends, and is positioned. Further, a reflection member 209 is provided between the heat source 202 and the support member 207, and this reflects the radiant heat from the heat source 202, thereby suppressing energy waste due to the support member 207 being heated by radiant heat or the like. .

  Here, the same effect can be obtained even if the surface of the support member 207 is subjected to heat insulation treatment or mirror treatment instead of including the reflection member 209. Although the illustrated halogen heater may be used as the heat source 202, a resistance heating element, a carbon heater, or the like may be used.

  The pressure roller 203 includes a metal core 205, an elastic rubber layer 204 provided on the metal core, and a release layer (PFA or PTFE layer) provided on the surface in order to obtain releasability. The pressure roller 203 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus 100 via a gear. The pressure roller 203 is pressed against the fixing belt 201 by a spring or the like (not shown), and has a predetermined nip width when the elastic rubber layer 204 is crushed and deformed.

  The pressure roller 203 may be a hollow roller, and may have a heating source such as a halogen heater inside the pressure roller 203. The elastic rubber layer 204 may be solid rubber, but if there is no heater inside the pressure roller 203, sponge rubber may be used. Use of sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 201 is hardly taken away.

The fixing belt 201 rotates with the pressure roller 203. In the case of the fixing device 200 of FIG. 2, the pressure roller 203 is rotated by a driving source (not shown), and the driving force is transmitted to the fixing belt 201 through the nip portion N, whereby the fixing belt 201 rotates. The fixing belt 201 is sandwiched and rotated at the nip portion N, and travels while being guided by the holding member 208 at both ends other than the nip portion. The recording medium S is heated and pressurized as it passes through the nip N, and a fixing process is performed.
With the above configuration, it is possible to realize a fixing device that is inexpensive and has a short warm-up time.

FIG. 3 is a configuration diagram showing another embodiment of the fixing device of the present invention.
In the fixing device of FIG. 2, the heat source 202 is composed of one halogen heater, whereas in the present embodiment, the heat source 202 is composed of three halogen heaters. Thereby, it is possible to cope with various paper widths without reducing productivity.

  Next, referring to FIGS. 4 and 5, the thermostat as the fixing belt abnormal temperature detecting means, and the electromagnetic clutch as the position changing means for adjusting the gap between the thermostat and the fixing belt according to the rotation / non-rotation state of the fixing belt. The configuration and operation will be described.

  The fixing device in FIGS. 4 and 5 is also of the fixing belt direct heating method, similar to the fixing device in FIGS. Here, the heater 202 is disposed slightly below the center of the fixing belt 201, and the pressure stay 207 for supporting the nip portion is formed in a flat shape, but the basic configuration is the same. Therefore, the operation of the thermostat 210 can be applied to the fixing device shown in FIGS.

  The fixing belt direct heating method greatly improves the heat transfer efficiency, and the temperature rise performance is remarkably high. Accordingly, in the rotation state of the fixing belt 201, heat spreads over the entire circumference of the fixing belt 201, and the pressure roller 203 draws heat from the fixing belt 201, so that the temperature rise itself becomes relatively gentle. However, in the non-rotating state of the fixing belt 201, the fixing belt is locally heated by the heater 202. Therefore, in the unlikely event that the temperature control runs out of control, only the temperature rises abnormally, and the fixing belt is thermally deformed. Since there are few inclusion members, there is a risk of immediate ignition.

  Therefore, in the present invention, when the fixing belt 201 is in a non-rotating state, the gap between the thermostat 210 and the fixing belt 201 can be reduced by starting the electromagnetic clutch 211. A thermostat 210 for detecting the temperature of the fixing belt 201 is attached to an actuator such as an electromagnetic clutch 211 fixed to a unit frame or the like on the outside of the fixing belt 201 so as to face the fixing belt 201. It is arranged to be movable at a position facing the heater 202. That is, the thermostat 210 can take a position approaching the heater 202 and the fixing belt 201 (FIG. 5) and a position away from the fixing belt 201 (FIG. 4) when the electromagnetic clutch 211 is activated.

  In this manner, when the fixing belt 201 is locally rotated by the heater and the fixing belt 201 is not rotated, the thermostat functioning as a safety device is reduced by reducing the gap between the thermostat 210 and the fixing belt 201 as shown in FIG. 210 operates more reliably at the rated temperature, and safety can be improved. That is, when the thermostat 210 detects an abnormal temperature rise of the fixing belt 201, the current of the heater 202 is quickly cut off to avoid dangers such as abnormal temperature rise and ignition.

  When the fixing belt is in a rotating state (FIG. 4), it is necessary to take a larger gap in consideration of some running fluctuation of the belt, but when the fixing belt is in a non-rotating state (FIG. 5), the fixing is performed. Since the positional relationship of the belt deviates only within the range of component tolerance accumulation, the gap can be made smaller than in the case of the rotation state. Further, since the fixing belt is stationary and does not have a sliding mark or the like, the thermostat 210 may be brought into contact with the fixing belt 201. As a result, the thermostat can be reliably operated at the rated temperature, and the safety of the temperature control of the fixing belt can be enhanced. Since the fixing belt 201 has elasticity and has no members inside, there is no problem even if some contact pressure is generated between the fixing belt 201 and the thermostat 210.

  A plurality of thermostats 210 may be arranged in the longitudinal direction of the fixing belt 201. As a result, even in a fixing device in which a plurality of heaters are arranged in accordance with the paper width, thermostats can be arranged corresponding to the respective heaters to improve the safety of temperature control of the fixing belt. Moreover, safety can be improved by using a thermostat that has a mechanically interrupting ability as the abnormal temperature detecting means.

Next, another embodiment of the fixing device of the present invention will be described with reference to FIG.
In the fixing device 200, a pressing unit 224 that presses the pressure roller 203 to press the fixing belt 201 is provided. The pressure means 224 is a mechanism for reducing the compression set of the pressure roller 203, and is a cam 218 as a second cam that can rotate around the camshaft 216, a lever 220 that contacts the cam 218 at one end, and a lever 220. It consists of a spring 222 connected to the other end. FIG. 6 shows the rotation state of the pressure roller and the fixing roller in the pressure state. The cam 218 presses the lever 220 against the urging force of the spring 222, so the lever 220 presses the core of the pressure roller 203 and presses the pressure roller 203 against the fixing belt 201 side.

  On the other hand, in the depressurized state and the non-rotating state (not shown) of the pressure roller and the fixing roller, the lever 220 is tilted by the urging force of the spring 222 as the cam 218 rotates, the pressing force is released, and the pressure roller 203 is fixed. The belt is separated from the belt 201.

  The thermostat 210 is connected to the outer side of the fixing belt 201 so as to face the cam belt 212 as a position changing means that can rotate around the cam shaft 212, and the fixing belt 201 is rotated as the cam 214 rotates. It is possible to move at a position facing the heater 202 via. That is, as the cam 214 rotates, the thermostat 210 can take a position (not shown) that approaches the heater 202 and the fixing belt 201 and a position (FIG. 6) that moves away.

Here, for example, by attaching a cam 214 for moving the thermostat 210 up and down to the camshaft 216 of the pressurizing means 224 (in FIG. 6, the camshaft 216 and the camshaft 212 are not coaxial), the pressurizing means 224 is used. The depressurization of the pressure roller 203 and the approach of the thermostat 210 to the fixing belt 201 can be synchronized. In FIG. 6 showing the pressurization, the thermostat 210 is separated from the heater 202 and the fixing belt 201 by the rotation of the cam 214 in synchronization with the pressurization of the pressurizing roller 203, and the gap becomes large. At the time of depressurization (not shown), the thermostat 210 approaches the heater 202 and the fixing belt 201 by the rotation of the cam 214 in synchronization with the pressure of the pressure roller 203, and the gap becomes small. With this configuration, the gap can be adjusted without adding an actuator such as an electromagnetic clutch.

Accordingly, the fixing device shown in FIG. 6 operates as follows.
(1) The cam 218 is rotated to the pressure position, the pressure roller 203 is pressed against the fixing roller 201 to form a nip portion, and at the same time, the thermostat 210 is separated from the fixing belt by a predetermined gap by the rotation of the cam 212. .
(2) The pressure roller is rotated to turn on the heater 202 to heat the fixing belt.
(3) The recording medium with unfixed toner adhered is fixed at the nip portion and conveyed.
(4) After the print job is finished, the heater is turned off, and the fixing belt is rotated to some extent in anticipation of the overshoot of the fixing belt to lower the temperature of the fixing belt, and then the rotation of the pressure roller is stopped.
(5) The cam 218 is rotated to the depressurization position, the pressure roller is depressurized, and at the same time the rotation of the cam 212 brings the thermostat closer to the fixing belt to reduce the gap.
(6) Transition to standby heating mode.

  In the above operation, the fixing belt does not rotate during the standby heating, and the heater output is lowered and heated slowly to keep the entire belt warm and prepare for the next print job. If the temperature control goes out of control in this standby heating mode, according to the present invention, the thermostat 210 can detect the abnormal temperature rise of the fixing belt 201 more reliably.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 200 Fixing apparatus 201 Fixing belt (fixing member)
202 Halogen heater (heat source)
203 Pressure roller (Pressure member)
210 Thermostat (Abnormal temperature detection means)
211 Electromagnetic clutch (position changing means)
214 cam (position changing means)
N nip S Recording medium

JP 2004-286922 A Japanese Patent No. 2861280 JP 2007-334205 A

Claims (8)

A fixing member that has a heat source and is rotatable; a pressure member that is rotatable by a driving source and presses the fixing member to form a nip; and a fixing member disposed at a position facing the fixing member. An abnormal temperature detecting means for detecting abnormal temperature rise and a position changing means for changing the position of the abnormal temperature detecting means with respect to the fixing member, and directly heating the fixing member without a heat conductor by the heat source A fixing device for performing a fixing process on a recording medium passing through the nip,
The gap between the abnormal temperature detecting means and the fixing member when the fixing member is not rotated is set smaller than that when the fixing member is rotated by the position changing means ,
A pressurizing unit that pressurizes the pressurizing member and presses the pressurizing member against the fixing member;
When the pressing means separates the pressing member from the fixing member, the fixing member is in a non-rotating state,
The position changing means for the abnormal temperature detecting means is configured to make the gap between the abnormal temperature detecting means and the fixing member smaller than that during rotation in synchronization with the separation of the pressure member by the pressure means. A fixing device characterized. Wherein during non-rotation of the fixing member, the fixing device according to claim 1, wherein the abnormal temperature detecting means is equal to or in contact with the fixing member. 3. The fixing device according to claim 1, wherein a plurality of the abnormal temperature detection units are arranged in a longitudinal direction of the fixing member. The fixing device according to any one of claims 1 to 3, wherein the abnormal temperature detecting means is a thermostat. The position changing means is a cam, and the cam rotates in synchronization with the separation of the pressure member by the pressure means to reduce the gap between the abnormal temperature detection means and the fixing member, and synchronizes with the pressure. The fixing device according to claim 1, wherein the fixing device is rotated to increase the gap. The fixing device according to claim 5, wherein the pressurizing unit has a second cam rotatable around a camshaft, and the cam for moving the abnormal temperature detecting unit is attached to the camshaft. The position changing means fixing device according to any one of claims 1 to 4, characterized in that an electromagnetic clutch. An image forming apparatus comprising: an image forming unit that forms an image on a recording medium; and a fixing unit that performs a fixing process on the recording medium on which the image is formed by the image forming unit. an image forming apparatus comprising mounting a fixing device according to any one of 1 to 7.

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