JP2006011294A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable fixing device and image forming apparatus such that a heat generating member never overheats even in the case that an electromagnetic induction heating type fixing device is abruptly stopped from being driven and so on. <P>SOLUTION: The fixing device 20 which heats a toner image to fix the toner image on a recording medium is equipped with an induction heating part 24 which produces magnetic flux, heat generating members 22 and 23 which are opposed to the induction heating part 24 and heated with the magnetic flux, and a shield member 40 which cuts off magnetic flux reaching the heat generating members 22 and 23 associatively with a stop of driving of the heat generating members 22 and 23. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and a fixing device installed therein, and more particularly to an electromagnetic induction heating type fixing device and an image forming apparatus. .

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines and printers, many use an electromagnetic induction heating type fixing device for the purpose of reducing the rise time of the apparatus and saving energy (for example, (See Patent Document 1).

  In Patent Document 1 and the like, an electromagnetic induction heating type fixing device includes a support roller (heating roller), a fixing auxiliary roller (fixing roller), a fixing belt stretched between the supporting roller and the fixing auxiliary roller, and a fixing belt on the supporting roller. An induction heating unit that faces the fixing auxiliary roller, a pressure roller that faces the fixing auxiliary roller via a fixing belt, and the like. The induction heating unit includes a coil unit (excitation coil) extending in the width direction (a direction orthogonal to the conveyance direction of the recording medium), a core facing the coil unit, and the like.

The fixing belt is heated at a position facing the induction heating unit. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, a magnetic field is formed around the coil portion, and an eddy current is generated on the surface of the support roller. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat. Note that the temperature on the fixing belt is detected by a temperature sensor in contact with the inner peripheral surface of the fixing belt.
Such an electromagnetic induction heating type fixing device is known as being capable of raising the surface temperature (fixing temperature) of the fixing belt to a desired temperature with a small energy consumption and a short start-up time.

  On the other hand, Patent Document 2 and the like disclose a technique of an electromagnetic induction heating type fixing device in which an endless belt is brought into contact with an outer peripheral surface of a heat generating member (fixing roller) facing an induction heating unit (magnetic flux generating means). Has been. This technique aims at optimizing the distance between the two members and preventing damage to the fixing roller by interposing an endless belt between the induction heating unit and the heat generating member.

JP 2002-82549 A JP 2003-15445 A

  In the conventional fixing device described above, when the device suddenly stops driving, a part of the fixing belt may overheat.

Details are as follows.
When a paper jam (jam) occurs in the conveyance path in the image forming apparatus, or when an abnormality occurs in the control, the driving in the fixing device is suddenly stopped. In such a case, the portion of the fixing belt facing the induction heating unit instantaneously overheats in a short time until the energization to the induction heating unit is cut off. This is because the heating time by the electromagnetic induction heating method is short. As described above, when an excessive temperature rise occurs in a part of the fixing belt, it is conceivable that the structural members such as the fixing belt and the coil portion of the induction heating unit are thermally damaged.

In order to solve such a problem, it is conceivable to install a temperature sensor such as a thermostat on the surface of the fixing belt or the support roller and detect the excessive temperature rise by the temperature sensor.
However, if the temperature sensor is installed in the vicinity of the induction heating unit, the temperature sensor may malfunction due to the magnetic flux generated from the induction heating unit, or the temperature sensor itself may malfunction due to excessive heating due to electromagnetic induction. A malfunction occurs.
On the other hand, if the temperature sensor is installed at a position away from the induction heating unit, the temperature sensor is installed at a position where the temperature is not overheated. Cannot be detected quickly.

  On the other hand, the technique disclosed in Patent Document 2 described above stabilizes the heat generation amount of the heat generating member by optimizing the distance between the two members by interposing an endless belt between the induction heating unit and the heat generating member. is there. Therefore, the effect of suppressing the excessive temperature increase of the fixing belt cannot be expected.

  The present invention has been made to solve the above-described problems, and even if the electromagnetic induction heating type fixing device suddenly stops driving, the heating member does not overheat. Another object of the present invention is to provide a fixing device and an image forming apparatus with high reliability.

  A fixing device according to a first aspect of the present invention is a fixing device that heats a toner image and fixes the toner image on a recording medium, and includes an induction heating unit that generates magnetic flux, and an induction heating unit. A heat generating member that is opposed and heated by the magnetic flux, and a shielding member that shields the magnetic flux reaching the heat generating member in conjunction with the stop of driving of the heat generating member are provided.

  A fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the shielding member releases the shielding of the magnetic flux in conjunction with driving of the heat generating member.

  A fixing device according to a third aspect of the present invention is the fixing device according to the first or second aspect, wherein the driving portion of the shielding member is connected to the driving portion of the heat generating member.

  The fixing device according to a fourth aspect of the present invention is the fixing device according to any one of the first to third aspects, wherein the shielding member is installed in the induction heating section.

  The fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, wherein the induction heating unit includes a coil unit to which an alternating current is applied, and the shield. The member is a belt-like member having an opening for opening the coil portion toward the heat generating member and a covering portion for covering the coil portion.

  According to a sixth aspect of the present invention, in the fixing device according to the fifth aspect, the shielding member is configured such that the encapsulating portion faces the heat generating member in conjunction with the driving stop of the heat generating member. Driven to the position, the drive is controlled so that the opening is moved to a position facing the heat generating member in conjunction with the driving of the heat generating member.

  The fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, wherein the shielding member is made of copper or aluminum.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to any one of the first to seventh aspects, wherein the shielding member is grounded.

  A fixing device according to a ninth aspect of the invention is the fixing device according to any one of the first to eighth aspects, wherein the heat generating member is a fixing member that melts a toner image.

  The fixing device according to a tenth aspect of the present invention is the fixing device according to the ninth aspect, wherein the fixing member is a fixing belt stretched in a circumferential shape, and the induction heating unit includes the fixing device. It is arrange | positioned so that the outer peripheral surface of a belt may be opposed.

  According to an eleventh aspect of the present invention, in the fixing device according to the tenth aspect, the fixing belt is stretched between a support roller and a fixing auxiliary roller, and the fixing auxiliary roller is conveyed. It is disposed so as to abut against a pressure roller for pressing the recording medium via the fixing belt.

  The fixing device according to a twelfth aspect of the present invention is the fixing device according to the eleventh aspect, wherein the support roller is disposed so as to face the induction heating unit via the fixing belt. Is.

  The fixing device according to a thirteenth aspect of the present invention is the fixing device according to the ninth aspect, wherein the fixing member is a fixing roller that abuts against a pressure roller that presses a conveyed recording medium, The induction heating unit faces the outer peripheral surface or inner peripheral surface of the fixing roller.

  According to a fifteenth aspect of the present invention, in the fixing device according to any one of the first to thirteenth aspects, the heating member is a heating member that heats the fixing member that melts the toner image. Is.

  According to a fifteenth aspect of the present invention, in the fixing device according to the fourteenth aspect, the fixing member is a fixing belt, and the heating member stretches the fixing belt together with a fixing auxiliary roller. The support roller is disposed so as to face the induction heating unit facing the outer peripheral surface of the fixing belt via the fixing belt, and the fixing auxiliary roller is conveyed. The recording medium is disposed so as to abut against a pressure roller that presses the recording medium via the fixing belt.

  An image forming apparatus according to a sixteenth aspect of the present invention includes the fixing device according to any one of the first to fifteenth aspects.

  The present invention is an electromagnetic induction heating type fixing device, and is provided with a shielding member that shields magnetic flux reaching the heat generating member in conjunction with the stop of driving of the heat generating member. Accordingly, it is possible to provide a highly reliable fixing device and image forming apparatus in which the heat generating member does not overheat even when the fixing device is suddenly stopped.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is detachably installed on the apparatus main body 1. A process cartridge as an image forming unit; 7, a transfer unit for transferring a toner image formed on the photosensitive drum 18 to a recording medium P; 10, a paper discharge tray on which an output image is placed; A paper feeding unit containing a recording medium P such as paper, 13 a registration roller for conveying the recording medium P to the transfer unit 7, 15 a manual paper feeding unit, 18 a photosensitive drum as an image carrier, and 20 a recording 1 shows a fixing device that fixes an unfixed image on a medium P;

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 toward the photosensitive drum 18 of the process cartridge 4. The photosensitive drum 18 rotates counterclockwise in the drawing, and a toner image corresponding to image information is formed on the photosensitive drum 18 through a predetermined electrophotographic process (charging process, exposure process, development process). Is done.
Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the recording medium P conveyed by the registration roller 13 in the transfer unit 7.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 11, 12, and 15 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 11 is selected). To do.) Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 11 is transported toward the position of the transport path K. Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the recording medium P that has reached the position of the registration roller 13 is conveyed toward the transfer unit 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt and the pressure roller, and the toner image is fixed by the heat received from the fixing belt and the pressure received from the pressure roller. The recording medium P on which the toner image has been fixed is sent from between the fixing belt and the pressure roller, and then is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10.
Thus, a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 20 in the image forming apparatus main body 1 will be described in detail with reference to FIG.
As shown in FIG. 2, the fixing device 20 mainly includes a fixing auxiliary roller 21, a fixing belt 22 (fixing member), a support roller 23, an induction heating unit 24, a pressure roller 30, a thermostat 37, a thermistor 38, and a shielding member 40. (Refer to FIG. 3), a guide plate 35, a separation plate 36, and the like.

  Here, the fixing auxiliary roller 21 is formed by forming an elastic layer such as silicone rubber on the surface of a cored bar made of stainless steel or the like. The elastic layer of the fixing auxiliary roller 21 has a thickness of 3 to 10 mm and an Asker hardness of 10 to 50 degrees.

  The support roller 23 (heating member) as a heat generating member includes a cylindrical portion made of iron, stainless steel, cobalt, nickel, aluminum or the like. The cylindrical portion of the support roller 23 is formed to have a thickness of about 0.6 mm. The support roller 23 is driven to rotate counterclockwise in FIG. 2 by a drive unit (not shown).

In the first embodiment, the support roller 23 is composed of only a metal material (metal layer). However, an elastic layer, a heat-resistant layer, or the like may be provided on the metal layer of the support roller 23.
In the first embodiment, depending on the material of the support roller 23, an inner core made of a ferromagnetic material such as ferrite can be installed inside the support roller 23. In that case, the inner core faces the coil portion 25 via the fixing belt 22.

2 and 3, the induction heating unit 24 includes a coil unit 25, a core 26, a coil guide 27 (frame), a shielding member 40, and the like.
Here, the coil portion 25 is wound around a width direction (in the direction perpendicular to the paper surface in FIGS. 2 and 3) by winding a litz wire bundled with thin wires so as to cover the outer peripheral surface of the fixing belt 22 wound around the support roller 23. It is extended. The coil guide 27 is made of a highly heat-resistant resin material or the like, and holds the coil part 25 and functions as a frame of the induction heating part 24. The core 26 is made of a ferromagnetic material such as ferrite having a relative permeability of about 2500, and is provided with a center core 26a and a side core 26b. The core 26 is installed so as to face the coil portion 25 extending in the width direction. The coil unit 25 is connected to a high frequency power supply unit (not shown), and an alternating current of 10 k to 1 MHz is applied from the high frequency power supply unit.

With reference to FIG. 3, the shielding member 40 of the induction heating unit 24 is an endless belt-like member made of a thin film metal such as copper or aluminum. The shielding member 40 is stretched and supported by three support shafts 41 while the coil portion 25 is sandwiched between the coil guide 27 and the surface facing the support roller 23 and the fixing belt 22. The shielding member 40 is grounded (grounded) by a static elimination brush or the like.
Further, the shield member 40 is connected with a drive unit that drives the shield member 40 in the counterclockwise direction of FIG. 3 and a tension spring 43 that biases the shield member 40 in the clockwise direction. With such a configuration, the shielding member 40 swings in both the clockwise and counterclockwise directions. The configuration and operation of the shielding member 40 will be described in detail later.

The fixing belt 22 as a heat generating member is stretched and supported by a support roller 23 and a fixing auxiliary roller 21. The fixing belt 22 is a multi-layered endless belt in which a heat generation layer, an elastic layer, and a release layer are formed on a base material.
The base material of the fixing belt 22 is made of a heat-resistant resin material. For example, polyimide, polyamideimide, PEEK (polyetheretherketone), PES (polyethersulfone), PPS (polyphenylene sulfide), fluororesin, or the like can be used. . As the heat generating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy made of a plurality of these metals, or the like can be used. As the elastic layer, silicone rubber, fluorosilicone rubber, or the like can be used. As the release layer, fluorine resins such as tetrafluoroethylene resin (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (FEP), or a mixture of these resins can be used.

  The pressure roller 30 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on a cylindrical member made of aluminum, copper, stainless steel or the like. The elastic layer of the pressure roller 30 has a thickness of 1 to 5 mm and an Asker hardness of 20 to 50 degrees. The pressure roller 30 is in contact with the fixing auxiliary roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion between the fixing belt 22 and the pressure roller 30.
A separation plate 36 that guides the conveyance of the recording medium P and promotes the separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30. Yes.

  An oil application roller 34 is in contact with the outer peripheral surface of the fixing belt 22. The oil application roller 34 supplies oil such as silicone oil onto the fixing belt 22. Thereby, the toner releasability on the fixing belt 22 is further ensured. The oil application roller 34 is in contact with a cleaning roller 33 that removes dirt on the surface.

A thermostat 37 is in contact with the inner peripheral surface of the fixing belt 22. When the temperature of the fixing belt 22 detected by the thermostat 37 exceeds a predetermined temperature, the energization to the induction heating unit 24 is cut by the thermostat 37.
A thermistor 38 is in contact with the outer peripheral surface of the fixing belt 22 and upstream of the fixing nip portion. The thermistor 38 detects the surface temperature (fixing temperature) on the fixing belt 22 and adjusts the output in the induction heating unit 24 including an inverter circuit and the like. Thus, the fixing temperature on the fixing belt 22 is kept constant.

The fixing device 20 configured as described above operates as follows during a normal fixing process (during driving).
As the support roller 23 is driven to rotate, the fixing belt 22 rotates in the direction of the arrow in FIG. 2, the auxiliary fixing roller 21 also rotates counterclockwise, and the pressure roller 30 also rotates in the direction of the arrow. The fixing belt 22 is heated at a position facing the induction heating unit 24.

  Specifically, a high-frequency alternating current of 10 kHz to 1 MHz is caused to flow from a high-frequency power supply unit (not shown) to the coil unit 25, thereby surrounding the coil unit 25 (a range including a part of the fixing belt 22 and the support roller 23). It is formed so that the magnetic field lines are alternately switched in both directions. By forming an alternating magnetic field in this way, an eddy current is generated on the surface of the support roller 23 and the heat generating layer 22b of the fixing belt 22, and Joule heat is generated by the electric resistance of the support roller 23 and the heat generating layer 22b. The support roller 23 and the heat generating layer 22b are heated. In this way, the fixing belt 22 is heated by the heat received from the heat-generating support roller 23 and the heat generated by the heat generating layer 22b.

Thereafter, the surface of the fixing belt 22 that generates heat by the induction heating unit 24 passes through the position of the thermistor 38 and reaches a contact portion with the pressure roller 30. Then, the toner image T on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35 (indicated by the arrow Y). It is movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

The surface of the fixing belt 22 that has passed through the position of the pressure roller 30 sequentially passes through the positions of the oil application roller 34 and the thermostat 37 and then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

Hereinafter, the configuration / operation of the shielding member 40, which is characteristic in the first embodiment, will be described in detail with reference to FIGS.
FIG. 4 is a partial view showing the vicinity of the shielding member 40 described above with reference to FIG. 3, and shows a state in which the fixing device 20 has stopped driving (a state in which the support roller 23 is not rotationally driven). is there. FIG. 5 is a view showing the shielding member 40 in a state where the fixing device 20 is driven (the support roller 23 is rotationally driven). FIG. 6 is a front view of the shielding member 40 viewed from the support roller 23 side in the state of FIG. 5 (during driving).

  4 to 6, a gear 51 is installed on the shaft of the support roller 23. A relay gear 52 is meshed with the gear 51 of the support roller 23, and a gear 53 with a driving roller 54 integrated is meshed with the relay gear 52. Here, the rotation center axis of the gear 51 and the relay gear 52 of the support roller 23 is supported by a housing of the fixing device via a bearing. On the other hand, the gear 53 provided with the drive roller 54 is configured such that the center axis of rotation thereof is inserted into a guide groove provided in the housing and swings along the pitch circle of the relay gear 52. . The gear 53 provided with the drive roller 54 is provided with a tension spring 55 that urges the drive roller 54 and the gear 53 in the right direction in FIG. 4 (the direction in which the drive roller 54 is retracted from the shielding member 40). The gears 51 to 53 and the drive roller 54 function as a drive unit for the shielding member 40.

  4 to 6, the shielding member 40 is provided with an opening 40a. And the position of the opening part 40a also moves because the shielding member 40 is driven by the drive parts 51-54. As a result, the coil portion 25 facing the fixing belt 22 and the support roller 23 is covered with the enveloping portion 40b of the shielding member 40 (the state shown in FIG. 4), or opened at the opening 40a of the shielding member 40. (The state shown in FIGS. 5 and 6). In addition, with reference to FIG. 6, the encapsulation part 40b of the shielding member 40 is a part other than the opening part 40a.

  Specifically, when the drive shown in FIG. 4 is stopped, since the drive unit of the support roller 23 is in a stopped state, drive transmission to the drive units 51 to 54 of the shielding member 40 is not performed. At this time, the drive roller 54 and the gear 53 are in a position where they are retracted from the shielding member 40 by the urging force of the tension spring 55 (locked at one end of a guide groove not shown). The shielding member 40 is in a position where the opening 40a is retracted from the coil portion 25 by the urging force of the tension spring 43 (locked by a stopper (not shown)).

  At this time, the coil part 25 will be in the state covered with the shielding member 40 (encapsulation part 40b). Thereby, the magnetic flux generated from the induction heating unit 24 is blocked or attenuated by the shielding member 40. That is, since the magnetic flux reaching the fixing belt 22 and the support roller 23 as a heat generating member is shielded, the fixing belt 22 and the support roller 23 are not heated even when the induction heating unit 24 is energized. In addition, since the shielding member 40 is grounded, electromagnetic induction heating of the shielding member 40 itself is suppressed, and the temperature rise in the shielding member 40 is prevented.

  On the other hand, at the time of driving shown in FIG. At this time, the drive roller 54 and the gear 53 move to the shielding member 40 side following the rotation of the relay gear 52 against the urging force of the tension spring 55. The drive roller 54 and the gear 53 are locked at a position where the drive roller 54 contacts the support shaft 41. Furthermore, the drive roller 54 and the gear 53 continue to rotate clockwise in FIG.

  When the drive roller 54 rotates in the clockwise direction, the support shaft 41 rotates in the counterclockwise direction by the frictional force with the support shaft 41 in contact with the drive roller 54. As a result, the shielding member 40 moves in the direction of the broken line arrow (counterclockwise) against the urging force of the tension spring 43. And the shielding member 40 stops in the position where the opening part 40a opens the coil part 25 (it latches with the stopper not shown). At this time, the rotating drive roller 54 is idled while being in contact with the support shaft 41.

  Thus, when the opening 40a moves to the position of the coil part 25, the coil part 25 is released from the shielding state by the shielding member 40 (encapsulated part 40b) (see FIG. 6). . As a result, the magnetic flux generated from the induction heating unit 24 reaches the fixing belt 22 and the support roller 23 as heating members, as described above with reference to FIG. Then, the fixing belt 22 and the support roller 23 are heated by the induction heating unit 24, so that a normal fixing process is performed.

  Thereafter, when the fixing process is finished and the driving of the fixing device 20 is stopped, the fixing device is again in the state of FIG. That is, the drive transmission of the shielding member 40 to the drive parts 51 to 54 is stopped, and the driving roller 54 and the gear 53 are moved again to the position where they are retracted from the shielding member 40 by the urging force of the tension spring 55. Accordingly, the shielding member 40 is moved to a position where the opening 40 a is retracted from the coil portion 25 by the urging force of the tension spring 43. Thus, the coil part 25 is again covered by the encapsulating part 40b of the shielding member 40.

  As described above, the shielding / releasing operation of the shielding member 40 is interlocked with the rotational driving of the support roller 23. In other words, when the constituent members such as the support roller 23 and the fixing belt 22 are driven, the shielding member 40 moves so as to release the shielding of the coil portion 25 and promotes the heating of the support roller 23 and the fixing belt 22. On the other hand, when the structural members such as the support roller 23 and the fixing belt 22 are stopped, the shielding member 40 moves so as to shield the coil portion 25 and restricts the heating of the support roller 23 and the fixing belt 22. To do.

  With such a configuration, when the paper jam (jam) occurs in the conveyance path K in the image forming apparatus main body 1 or when an abnormality occurs in the control, the driving in the fixing device 20 is suddenly performed. Even when it is stopped, the shielding member 40 moves from the state of FIG. 5 to the state of FIG. As a result, the fixing belt 22 and the support roller 23 as the heat generating members are heated in a short time until the energization to the induction heating unit 24 is cut off, and the portion of the fixing belt 22 facing the induction heating unit 24 is The problem of overheating instantaneously is prevented.

In the first embodiment, the shielding member 40 is driven by the frictional force between the drive roller 54 and the support shaft 41. However, a gear is provided on the drive roller 54 side and meshed with the gear provided on the support shaft 41 side. Thus, the shielding member 40 can be driven. In this case, a torque limiter or the like is installed on the gear provided on the drive roller 54 side, and the gear is idled in the state shown in FIG.
Further, in the first embodiment, the tension spring 43 is directly installed on the shielding member 40, but a winding spring or the like is installed on the support shaft 41 to urge the shielding member 40 in the same manner as the tension spring 43. it can.

  As described above, in the first embodiment, the electromagnetic induction heating type fixing device 20 is a shielding member that shields the magnetic flux reaching the heat generating members 22 and 23 in conjunction with the stop of driving of the heat generating members 22 and 23. 40 is provided. Thereby, even when the fixing device 20 suddenly stops driving, it is possible to prevent overheating of the heat generating members 22 and 23.

  In the first embodiment, the induction heating unit 24 is disposed at a position facing the support roller 23 via the fixing belt 22. On the other hand, the induction heating unit 24 can be disposed at a position facing the outer peripheral surface of the fixing belt 22 from the support roller 23 to the auxiliary fixing roller 21. Even for such a fixing device, the same effect as in the first embodiment can be obtained by installing the shielding member 40 that can be shielded / released in the induction heating unit 24.

  In the first embodiment, the fixing belt 22 having the heat generating layer and the support roller 23 are used as the heat generating members. On the other hand, only one of the fixing belt 22 and the support roller 23 can be used as the heat generating member. In such a case, the same effect as in the first embodiment can be obtained.

  In the first embodiment, the fixing device 20 is configured so that the pressure roller 30 contacts the auxiliary fixing roller 21 via the fixing belt 22. In contrast, the fixing device 20 is configured such that the pressure roller 30 contacts the surface of the fixing belt 22 from the heating roller 23 (or the fixing auxiliary roller 21) to the fixing auxiliary roller 21 (or the heating roller 23). You can also. In such a case, the same effect as in the first embodiment can be obtained.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 7 is a cross-sectional view showing the fixing device according to the second embodiment. The fixing device of the second embodiment is different from that of the first embodiment in that the fixing roller 31 is used as a heat generating member.

As shown in FIG. 7, the fixing device 20 according to the second embodiment mainly includes a fixing roller 31 (fixing member) as a heat generating member, a pressure roller 30, an induction heating unit 24, a shielding member 40, and the like.
The fixing roller 31 includes a heat generating layer 31a made of nickel or the like, an elastic layer made of silicone rubber or the like, a release layer made of fluorine compound or the like.

  The induction heating unit 24 includes the coil unit 25, the core 26, the coil guide 27, the shielding member 40, and the like as in the first embodiment. Then, by supplying an alternating current of 10 k to 1 MHz to the coil unit 25, magnetic lines of force are formed around the coil unit 25 (a range including a part of the fixing roller 31), and the fixing roller is electromagnetically induced. 31 is heated. In this way, the heated fixing roller 31 heats and melts the toner image on the recording medium P conveyed from the direction of the arrow and fixes the toner image on the recording medium P.

Also in the second embodiment, as in the first embodiment, the shielding member 40 that is driven in conjunction with the rotational driving of the fixing roller 31 is provided in the dielectric overheating portion 24.
That is, when the fixing roller 31 is being driven, the shielding member 40 having the opening 40 a moves so as to release the shielding of the coil portion 25, thereby urging the fixing roller 31 to be heated. On the other hand, when the driving of the fixing roller 31 is stopped, the shielding member 40 moves so as to shield the coil portion 25, and the heating of the fixing roller 31 is suppressed.

  As described above, in the second embodiment, the electromagnetic induction heating type fixing device 20 is provided, and the shielding member 40 that shields the magnetic flux reaching the heat generating member 31 in conjunction with the stop of the driving of the heat generating member 31 is provided. Yes. As a result, even if the fixing device 20 suddenly stops driving, it is possible to prevent overheating of the heat generating member 31.

  In the second embodiment, in the fixing device 20, the induction heating unit 24 is opposed to the outer peripheral surface of the fixing roller 31. On the other hand, the induction heating unit can be opposed to the inner peripheral surface of the fixing roller 31. That is, the coil portion 25 can be installed inside the fixing roller 31 and the fixing roller 31 can be heated by electromagnetic induction. Also for such a fixing device 20, the same effect as in the second embodiment can be obtained by installing a shielding member 40 that can be shielded and released around the coil portion 25.

  In the second embodiment, the fixing roller 31 is used as a fixing member facing the induction heating unit 24. However, a cylindrical fixing belt 22 may be used as a fixing member facing the induction heating unit 24. In this case, a holding member that holds the fixing belt 22 in a cylindrical shape is brought into contact with the inner peripheral surface of the fixing belt 22. Further, in order to form an appropriate fixing nip between the fixing belt 22 and the pressure roller 30, a pressure member is brought into contact with a position on the inner peripheral surface of the fixing belt 22 facing the pressure roller 30. Become. Also for such a fixing device 20, the same effect as in the second embodiment can be obtained by installing a shielding member 40 that can be shielded / released in the induction heating unit 24.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view illustrating a fixing device in the image forming apparatus of FIG. 1. FIG. 3 is a cross-sectional view showing an arrangement of shielding members in the fixing device of FIG. 2. It is the schematic which shows the state at the time of the drive stop in the shielding member of FIG. It is the schematic which shows the state at the time of the drive in the shielding member of FIG. It is the front view which looked at the shielding member of Drawing 5 from the support roller side. It is sectional drawing which shows the fixing device in Embodiment 2 of this invention.

Explanation of symbols

1 image forming apparatus main body (apparatus main body), 3 exposure unit,
4 process cartridge (image forming section), 18 photosensitive drum,
20 fixing device, 21 fixing auxiliary roller,
22 fixing belt (heating member, fixing member), 23 support roller (heating member),
24 induction heating unit, 25 coil unit, 26 core,
27 Coil guide, 30 Pressure roller,
31 fixing roller (heating member, fixing member), 31a heating layer,
40 shielding member, 40a opening, 40b enveloping part,
41 support shaft, 43, 55 tension spring, 51-53 gear,
54 Driving roller, P recording medium, T toner image.

Claims (16)

A fixing device that heats a toner image and fixes the toner image on a recording medium,
An induction heating unit for generating magnetic flux;
A heating member that faces the induction heating unit and is heated by the magnetic flux,
A shielding member that shields the magnetic flux reaching the heat generating member in conjunction with the drive stop of the heat generating member;
A fixing device comprising: The fixing device according to claim 1, wherein the shielding member releases shielding of the magnetic flux in conjunction with driving of the heat generating member. The fixing device according to claim 1, wherein the driving unit of the shielding member is connected to the driving unit of the heat generating member. The fixing device according to claim 1, wherein the shielding member is installed in the induction heating unit. The induction heating unit includes a coil unit to which an alternating current is applied,
The said shielding member is a belt-shaped member which has the opening part which opens the said coil part toward the said heat generating member, and the encapsulation part which covers the said coil part, The any one of Claims 1-4 A fixing device according to claim 1. The shielding member is moved to a position where the enveloping part faces the heat generating member in conjunction with the driving stop of the heat generating member, and the opening faces the heat generating member in conjunction with the driving of the heat generating member. The fixing device according to claim 5, wherein the driving is controlled so as to be moved to a position. The fixing device according to claim 1, wherein the shielding member is made of copper or aluminum. The fixing device according to claim 1, wherein the shielding member is grounded. The fixing device according to claim 1, wherein the heat generating member is a fixing member that melts a toner image. The fixing member is a fixing belt stretched around a circumference,
The fixing device according to claim 9, wherein the induction heating unit is disposed so as to face an outer peripheral surface of the fixing belt. The fixing belt is stretched between a support roller and a fixing auxiliary roller,
The fixing device according to claim 10, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. The fixing device according to claim 11, wherein the support roller is disposed so as to face the induction heating unit via the fixing belt. The fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed,
The fixing device according to claim 9, wherein the induction heating unit faces an outer peripheral surface or an inner peripheral surface of the fixing roller. The fixing device according to claim 1, wherein the heat generating member is a heating member that heats a fixing member that melts a toner image. The fixing member is a fixing belt,
The heating member is a support roller that stretches the fixing belt together with a fixing auxiliary roller,
The support roller is disposed to face the induction heating unit facing the outer peripheral surface of the fixing belt via the fixing belt,
The fixing device according to claim 14, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. An image forming apparatus comprising the fixing device according to claim 1.

Images