JP2013057840A - Fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which has a sufficiently high heating efficiency of a fixing rotating body by electromagnetic induction heating and further reduces heat-up time of the fixing rotating body, and to provide an image forming apparatus.SOLUTION: A fixing device comprises: a fixing rotating body 21 comprising a first heat generating layer which is heated by electromagnetic induction by an excitation coil part 25; and a heat generating member 23 comprising a second heat generating layer heated by electromagnetic induction by the excitation coil part 25, which faces it via the fixing rotating body 21. By making adjustable the magnetic flux density applied to the first heat generating layer of the fixing belt 21, switching is enabled between a first heating state in which the fixing rotating body 21 is heated by heating only the first heat generation layer by electromagnetic induction by the excitation coil part 25 and a second heating state in which the fixing rotating body 21 is directly heated by heating the first heat generating layer and the second heat generating layer of the heat generating member 23 by electromagnetic induction by the excitation coil part 25, and the fixing rotating body 21 is indirectly heated by the heat generating member 23.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof, and an electromagnetic induction heating type fixing device installed therein.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine and a printer, an electromagnetic induction heating type fixing device characterized by a short warm-up time and first print time is known (for example, Patent Documents 1 to 3). reference.).

  Patent Document 1 discloses an electromagnetic induction heating type fixing device in which the temperature-sensitive magnetic member is separated from the fixing belt until the temperature of the fixing belt (fixing rotator) reaches the fixing set temperature. A technique is disclosed in which a temperature-sensitive magnetic member in a heated state is brought into contact with a fixing belt after electromagnetic induction heating is performed and the temperature of the fixing belt reaches a fixing setting temperature.

Patent Document 2 discloses a fixing device of an electromagnetic induction heating method, and when the temperature of the heat generating roller is increased, a conductive member provided in the heat generating roller is moved to a position not facing the exciting coil, thereby fixing the fixing belt. A technique is disclosed in which the conductive member is moved to a position facing the exciting coil after the temperature of the (fixing rotator) reaches a predetermined temperature.
In Patent Documents 2 and 3, a heat generating roller (metal pipe) that is electromagnetically heated by an exciting coil is formed of a temperature-sensitive magnetic material having a predetermined Curie temperature. A technique for preventing temperature rise is disclosed.

The fixing device of Patent Document 1 described above performs electromagnetic induction heating of the fixing belt with the temperature-sensitive magnetic member separated from the fixing belt until the temperature of the fixing belt (fixing rotating body) reaches the fixing set temperature. However, since the temperature-sensitive magnetic member is always subjected to electromagnetic induction heating during that time, the heating efficiency of the fixing belt (fixing rotating body) by electromagnetic induction heating cannot be sufficiently increased.
Further, in the fixing devices of Patent Documents 2 and 3 described above, since the heat generating layer that is heated by electromagnetic induction and the temperature-sensitive magnetic layer that is formed to prevent the temperature increase are integrated, The temperature rise time of the fixing belt (fixing rotator), in which heat is not taken away by the temperature-sensitive magnetic layer, cannot be shortened sufficiently.

  The present invention has been made to solve the above-described problems, and the heating efficiency of the fixing rotator by electromagnetic induction heating is sufficiently high, so that the heating time of the fixing rotator is further shortened. An apparatus and an image forming apparatus are provided.

  According to a first aspect of the present invention, a fixing device includes a first heat generating layer that is electromagnetically heated by an exciting coil unit, and that also travels in a predetermined direction to heat and melt a toner image. A pressure rotator that forms a nip portion where the recording medium is conveyed by being pressed against the fixing rotator, and a second heat generation layer that is electromagnetically heated by the exciting coil portion that is opposed to the fixing rotator. A heating member formed so as to be able to heat the fixing rotator while being in contact with the fixing rotator, and changing the magnetic flux density acting on the first heat generating layer, A first heating state in which only the first heat generating layer is electromagnetically heated by the exciting coil unit to heat the fixing rotating body, and the first heat generating layer and the second heat generating layer are electromagnetically heated by the exciting coil unit. Before By the heat-generating member with directly heating the fixing rotary body and the second heating condition for indirectly heating the fixing rotator, in which is switched.

  According to the present invention, the magnetic flux density acting on the first heat generating layer of the fixing rotator is varied, so that the first heating state in which only the first heat generating layer is electromagnetically heated to heat the fixing rotator, and the first heat generation. The second heating layer is switched between a second heating state in which the fixing rotating body is heated directly by the heat generating member while the fixing rotating body is directly heated by electromagnetic induction heating of the layer and the second heating layer of the heating member. Accordingly, it is possible to provide a fixing device and an image forming apparatus in which the heating efficiency of the fixing rotator by electromagnetic induction heating is sufficiently high and the temperature rise time of the fixing rotator is further shortened.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a configuration diagram illustrating a fixing device installed in the image forming apparatus of FIG. 1. (A) The enlarged view which shows the 1st heating state by which the opposing distance with respect to the exciting coil part of a 1st ferromagnetic material and a 2nd ferromagnetic material was set short, (B) The exciting coil part of a 1st ferromagnetic material It is an enlarged view which shows the 2nd heating state to which only the opposing distance with respect to was set short. It is a graph which shows the relationship between the magnetic field and magnetic flux density which are formed in the 1st exothermic layer. 6 is a graph showing the temperature distribution in the width direction of the fixing belt when small-size paper is continuously fed. It is a block diagram which shows the fixing device of another form. It is a block diagram which shows the fixing device in Embodiment 2 of this invention. It is a figure which shows operation | movement of the heat generating member in the fixing device of FIG. FIG. 6 is a cross-sectional view showing a part of another type of fixing device in a width direction. 6 is a graph showing the temperature rise characteristics of the fixing rotator when the heating member separation control is performed at the time of start-up and when it is not performed. It is a table | surface figure which shows the contact-and-separation state of the heat generating member variably controlled by paper passing conditions. 6 is a graph showing a change in temperature of the fixing rotator when the heating member separation control is performed and when it is not performed when the print mode is switched. 6 is a graph showing a change in temperature of the fixing rotator when the heating member separation control is performed during overshooting of the fixing rotator and when it is not performed. FIG. 10 is a table showing conditions for controlling the separation of the heat generating member that is changed for each image forming apparatus having a different recording medium conveyance speed.

  Hereinafter, embodiments 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, reference numeral 1 denotes an apparatus main body of a copying machine as an image forming apparatus, 2 an original reading unit that optically reads image information of an original D, and 3 an exposure light L based on image information read by the original reading unit 2. Is exposed to the photosensitive drum 5, 4 is an image forming unit for forming a toner image (image) on the photosensitive drum 5, and 7 is a toner image formed on the photosensitive drum 5 on the recording medium P. A transfer unit 10 for transferring, a document transport unit for transporting the set document D to the document reading unit 2, 12 to 14 a paper feed unit storing a recording medium P such as transfer paper, and 20 on the recording medium P A fixing device for fixing an unfixed image, 21 is a fixing belt as a fixing rotator installed in the fixing device 20, and 31 is a pressure roller as a pressure rotator installed in the fixing device 20.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, the document D is conveyed from the document table in the direction of the arrow in the drawing by the conveyance roller of the document conveyance unit 10 and passes over the document reading unit 2. At this time, the document reading unit 2 optically reads the image information of the document D passing above.
Then, the optical image information read by the document reading unit 2 is converted into an electric signal and then transmitted to the exposure unit 3 (writing unit). Then, exposure light L such as laser light based on the image information of the electrical signal is emitted from the exposure unit 3 toward the photosensitive drum 5 of the image forming unit 4.

On the other hand, in the image forming unit 4, the photosensitive drum 5 is rotated in the clockwise direction in the drawing, and image information is transferred onto the photosensitive drum 5 through a predetermined image forming process (charging process, exposure process, development process). An image (toner image) corresponding to is formed.
Thereafter, the image formed on the photosensitive drum 5 is transferred by the transfer unit 7 onto the recording medium P conveyed by the registration roller.

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 12, 13, and 14 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 12 is selected). To do.)
Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 12 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. Then, the recording medium P that has reached the position of the registration roller is conveyed toward the transfer unit 7 at the same timing in order to align with the image formed on the photosensitive drum 5.

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 21 and the pressure roller 31, and the image is fixed by the heat received from the fixing belt 21 and the pressure received from both members 21, 31. The The recording medium P on which the image is fixed is delivered from between the fixing belt 21 and the pressure roller 31 (a nip portion), and then discharged from the image forming apparatus main body 1.
Thus, a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing rotating body (fixing member), a fixing member 22 (nip forming member), a heating member 23, a ferromagnetic body 24 (magnetic flux adjusting member), and an excitation coil. A section 25 (induction heating section), a pressure roller 31 as a pressure rotator, a temperature sensor 40 as temperature detection means, guide plates 35 and 37, and the like.

  Here, the fixing belt 21 as a fixing rotator is a thin and flexible endless belt, and rotates (runs) in the arrow direction (clockwise) in FIG. The fixing belt 21 has a first heat generating layer (base material layer), an elastic layer, and a release layer sequentially laminated from the inner peripheral surface (the sliding contact surface with the fixing member 22 and the heat generating member 23) side. The overall thickness is set to 1 mm or less.

Here, the first heat generating layer (base material layer) of the fixing belt 21 is made of a low heat capacity conductive material having a layer thickness of about several microns to several hundred microns (preferably, about ten microns to several tens of microns). It functions as a heat generating layer heated by electromagnetic induction by the exciting coil unit 25.
The elastic layer of the fixing belt 21 has a layer thickness of about 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion are not formed, and heat is uniformly transmitted to the toner image T on the recording medium P, thereby suppressing the generation of a scum skin image. In the first embodiment, silicone rubber having a layer thickness of 200 μm is used as the elastic layer of the fixing belt 21.
The release layer of the fixing belt 21 has a layer thickness of about 10 to 50 μm, and includes PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, PES. (Polyether sulfide), etc. By providing the release layer, the releasability (peelability) for the toner T (toner image) is secured.

  A fixing member 22, a heat generating member 23, a ferromagnetic body 24, and the like are fixed inside the fixing belt 21 (inner peripheral surface side). An exciting coil unit 25 (induction heating unit) is disposed so as to face a part of the outer peripheral surface of the fixing belt 21 with a gap. Although not shown, a lubricant is applied to the inner peripheral surface of the fixing belt 21.

Here, the fixing member 22 is fixed so as to be in sliding contact with the inner peripheral surface of the fixing belt 21. Then, the fixing member 22 is pressed against the pressure roller 31 via the fixing belt 21 to form a nip portion where the recording medium P is conveyed. Although illustration is omitted, both ends of the fixing member 22 in the width direction are fixedly supported on the side plate of the fixing device 20. In addition, the fixing member 22 is formed of a material having a certain degree of rigidity so that the fixing member 22 does not bend greatly even if it receives pressure applied by the pressure roller 31.
The fixing member 22 is formed in a concave shape so that the surface facing the pressure roller 31 (sliding contact surface) follows the curvature of the pressure roller 31. Thereby, since the recording medium P is sent out from the nip portion so as to follow the curvature of the pressure roller 31, the problem that the recording medium P after the fixing process is not attracted to the fixing belt 21 and separated is suppressed. be able to.
In the first embodiment, the shape of the fixing member 22 that forms the nip portion is formed in a concave shape, but the shape of the fixing member 22 that forms the nip portion can also be formed in a planar shape. That is, the sliding contact surface of the fixing member 22 (the surface facing the pressure roller 31) can be formed in a planar shape. As a result, the shape of the nip portion is substantially parallel to the image surface of the recording medium P, and the adhesion between the fixing belt 21 and the recording medium P is increased, so that the fixing property is improved. Further, since the curvature of the fixing belt 21 on the exit side of the nip portion is increased, the recording medium P sent from the nip portion can be easily separated from the fixing belt 21.

With reference to FIG. 2, the heat generating member 23 is disposed so as to face the exciting coil portion 25 via the fixing belt 21 (fixing rotating body) and to contact the inner peripheral surface of the fixing belt 21. Although not shown, the heat generating member 23 is fixedly supported by the side plates of the fixing device 20 at both ends in the width direction.
The heat generating member 23 is formed with a second heat generating layer (formed of a conductive material) that is electromagnetically heated by the exciting coil unit 25, and is generated by an alternating magnetic field generated by the exciting coil unit 25. The fixing belt 21 is heated by electromagnetic induction heating (transfers heat). That is, the heating member 23 is directly heated by electromagnetic induction by the exciting coil unit 25, and the fixing belt 21 is indirectly heated via the heating member 23.
Here, as described above, since the fixing belt 21 is also provided with the first heat generating layer, the fixing belt 21 (first heat generating layer) itself is also directly applied by the alternating magnetic field generated by the exciting coil unit 25. Therefore, electromagnetic induction heating is performed. Therefore, the fixing belt 21 is directly heated by electromagnetic induction by the excitation coil unit 25 and indirectly heated by the heat generating member 23 (electromagnetic induction heating by the excitation coil unit 25). The heating efficiency of the fixing belt 21 is increased.

In the first embodiment, heat is applied to the toner image T on the recording medium P from the surface of the heated fixing belt 21.
The output control of the exciting coil unit 25 is performed based on the detection result of the belt surface temperature by the temperature sensor 40 (temperature detecting means) such as a thermistor or a thermopile facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the exciting coil unit 25.

  Referring to FIGS. 2 and 3, the excitation coil unit 25 (induction heating unit) includes an excitation coil 26, an excitation coil core 27, and the like. The exciting coil 26 is formed by winding a litz wire, which is a bundle of fine wires, on an exciting coil core 27 disposed so as to cover a part of the outer peripheral surface of the fixing belt 21, and in the width direction (in the direction perpendicular to the paper surface in FIGS. 2 and 3). It is extended. Then, when an alternating current is supplied from an alternating current power source (not shown) to the exciting coil 26, a magnetic flux is generated from the exciting coil portion 25 toward the first heat generating layer of the fixing belt 21 and the second heat generating layer of the heat generating member 23. Will be. The exciting coil core 27 is made of a ferromagnetic material such as ferrite (having a relative permeability of about 2500) and is efficient toward the first heat generating layer of the fixing belt 21 and the second heat generating layer of the heat generating member 23. It is for forming magnetic flux.

Referring to FIG. 2, the ferromagnetic body 24 (inner core) as a magnetic flux adjusting member is disposed so as to face the exciting coil portion 25 through the fixing belt 21 and the heat generating member 23. The ferromagnetic body 24 is formed of a ferromagnetic material such as ferrite that can adjust the magnetic flux (for example, a material having a relative permeability of about 2500).
In the first embodiment, the ferromagnetic body 24 is formed so that the posture facing the exciting coil unit 25 can be changed by the drive unit 61 controlled by the control unit 60. The magnetic flux density acting on the first heat generating layer of the fixing belt 21 is varied by changing the attitude of the ferromagnetic body 24 with respect to the exciting coil unit 25 by the drive unit 61. This will be described in detail later.

  Referring to FIG. 2, a pressure roller 31 as a pressure rotator is obtained by forming an elastic layer 33 (layer thickness is about 3 mm) on a hollow cored bar 32. The elastic layer 33 of the pressure roller 31 (pressure rotator) is formed of a material such as foamable silicone rubber, silicone rubber, or fluororubber. A thin release layer made of PFA, PTFE or the like can be provided on the surface layer of the elastic layer 33. The pressure roller 31 is pressed against the fixing member 22 via the fixing belt 21 to form a desired nip portion between both members. Although not shown, the pressure roller 31 is provided with a gear that meshes with a drive gear of a drive mechanism (not shown), and the pressure roller 31 rotates in an arrow direction (counterclockwise direction) in FIG. Driven. Further, both ends of the pressure roller 31 in the width direction are rotatably supported on the side plate of the fixing device 20 via bearings. A heat source such as a halogen heater can be provided inside the pressure roller 31.

  When the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced. Further reduction can be achieved. Furthermore, since the heat insulation of the pressure roller 31 is enhanced and the heat of the fixing belt 21 is difficult to move to the pressure roller 31 side, the heating efficiency of the fixing belt 21 is improved.

  A guide plate 35 (inlet guide plate) for guiding the recording medium P conveyed toward the nip portion is provided on the inlet side of a contact portion (a nip portion) between the fixing belt 21 and the pressure roller 31. Is arranged. Further, a guide plate 37 (exit guide plate) for guiding the recording medium P fed from the nip portion is disposed on the outlet side of the nip portion. Both guide plates 35 and 37 are fixed to the frame (housing) of the fixing device 20.

The normal operation of the fixing device 20 configured as described above will be briefly described below.
When the power switch of the apparatus body 1 is turned on, an alternating current is supplied from an unillustrated AC power source (high frequency power source) to the exciting coil unit 25, and the pressure roller 31 is rotationally driven in the direction of the arrow in FIG. Be started. The fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31 at the position of the nip portion.
Thereafter, the recording medium P is fed from the paper feeding unit 12, and an unfixed color image is carried (transferred) on the recording medium P at the position of the transfer unit 7. The recording medium P carrying the unfixed image T (toner image) is conveyed in the direction of the arrow Y10 in FIG. 2 while being guided by the guide plate 35, and the nip portion between the fixing belt 21 and the pressure roller 31 in the pressure contact state. To be sent to.
The toner image T is fixed on the surface of the recording medium P by the heating by the fixing belt 21 in the heated state and the pressing force of the fixing belt 21 (fixing member 22) and the pressure roller 31. Thereafter, the recording medium P delivered from the nip portion is conveyed in the direction of arrow Y11.

Hereinafter, the characteristic configuration and operation of the fixing device 20 according to the first embodiment will be described in detail.
In the fixing device 20 according to the first exemplary embodiment, the ferromagnetic body 24 is moved by the driving unit 61 to change the posture of the ferromagnetic body 24 with respect to the exciting coil unit 25, thereby forming the first heating layer of the fixing belt 21. It is configured so that the acting magnetic flux density can be varied.

Referring to FIG. 3, the ferromagnetic body 24 is divided into a plurality of parts along the rotation direction of the fixing belt 21. Specifically, the ferromagnetic body 24 includes a first ferromagnetic body 24A and a second ferromagnetic body 24B. The first ferromagnetic body 24 </ b> A is disposed so as to face the central portion (range W <b> 2) of the exciting coil portion 25 along the rotation direction of the fixing belt 21. On the other hand, the second ferromagnetic body 24B has both ends of the exciting coil section 25 along the rotation direction of the fixing belt 21 (the first ferromagnetic body 24A in the range W1) so as to sandwich the first ferromagnetic body 24A. Is a range excluding the range W2). The divided ferromagnetic bodies 24A and 24B are both formed of the same material (a material such as ferrite that functions as a magnetic flux adjusting member).
Of the plurality of divided ferromagnetic bodies 24A and 24B, the second ferromagnetic body 24B is configured such that the opposing distance to the exciting coil section 25 can be varied by the drive section 61. Specifically, the first ferromagnetic body 24A is fixedly supported on the side plate of the fixing device 20 so that the facing distance between the fixing belt 21 and the exciting coil portion 25 via the heat generating member 22 is a predetermined distance H1. On the other hand, the second ferromagnetic body 24B is formed on the side plate of the fixing device 20 so that the opposing distance between the fixing belt 21 and the exciting coil portion 25 via the heat generating member 22 can be varied in the range of H1 to H2. It is held through the slide groove (which is a long hole extending in the vertical direction) and is slid up and down by the drive unit 61 controlled by the control unit 60.
As the drive unit 61 that moves the second ferromagnetic body 24B up and down, for example, a cam mechanism that contacts the second ferromagnetic body 24B biased downward by a tension spring or the like from below can be used.

  Then, by controlling the drive unit 61 so as to vary the magnetic flux density acting on the first heat generating layer of the fixing belt 21, only the first heat generating layer (fixing belt 21) is electromagnetically heated by the exciting coil unit 25. The first heating state in which the fixing belt 21 is heated and the first heating layer (fixing belt 21) and the second heating layer (heating member 23) are electromagnetically heated by the exciting coil unit 25 to directly fix the fixing belt 21. The second heating state in which the fixing belt 21 is indirectly heated by the heating member 23 while being heated is switched. That is, by controlling the drive unit 61 by the control unit 60 and changing the facing distance of the second ferromagnetic body 24B to the exciting coil unit 25 and changing the facing posture of the ferromagnetic body 24 to the exciting coil unit 25, The magnetic flux density acting on the first heat generating layer of the fixing belt 21 is varied to switch between the first heating state and the second heating state.

Specifically, as shown in FIG. 3A, the opposing distance between the first ferromagnetic body 24A and the second ferromagnetic body 24B is the first distance H1 (a relatively short distance). Thus, when the position of the second ferromagnetic body 24B is set by the drive unit 61, a magnetic flux is formed over almost the entire range W1 where the ferromagnetic body 24 faces the fixing belt 21, and the first heat generating layer (fixing) The magnetic flux density acting on the belt 21) is reduced. In such a state, the magnetic flux generated by the exciting coil unit 25 (indicated by a broken line arrow) reaches only the first heat generating layer (fixing belt 21) and the second heat generating layer (heat generating member 23). Therefore, only the first heat generating layer (fixing belt 21) is heated by electromagnetic induction by the exciting coil unit 25 (in the first heating state). At this time, the magnetic flux from the exciting coil section 25 acts intensively only on the first heat generating layer (fixing belt 21), so that the first heat generating layer (fixing belt 21) can be rapidly heated. In the first heating state, the heat of the fixing belt 21 is transferred to the heat generating member 23, but the contact area of the heat generating member 23 (in the circumferential direction, not in the entire circumferential direction with respect to the fixing belt 21). Is not so large and the heat capacity is small, so the loss of the heating efficiency of the fixing belt 21 is extremely small.
On the other hand, as shown in FIG. 3B, the facing distance of the second ferromagnetic body 24B is the second distance H2 (greater than the first distance H1 and a relatively long distance). When the position of the second ferromagnetic body 24B is set by the driving unit 61 and only the first ferromagnetic body 24A is opposed to the exciting coil unit 25 at a short distance H1, the ferromagnetic body 24 is fixed to the fixing belt 21. Magnetic flux is concentrated in the adjacent and facing range W2 (<W1), and the magnetic flux density acting on the first heat generating layer (fixing belt 21) is increased. In such a state, the magnetic flux generated by the exciting coil unit 25 (shown by a broken arrow) penetrates the first heat generating layer (fixing belt 21) and enters the second heat generating layer (heat generating member 23). In addition to the first heat generating layer (fixing belt 21), the second heat generating layer (heat generating member 23) is also electromagnetically heated by the exciting coil unit 25 (in the second heating state). is there.). At this time, the magnetic flux from the exciting coil section 25 also acts on the second heat generating layer (heat generating member 23) in a distributed manner, so that the heat generating member 23 has a temperature so as to compensate for the temperature drop of the fixing belt 21 in the heated state. Heat is transferred to the fixing belt 21.
Note that the same coil magnetic field is formed in the exciting coil section 25 in both the first heating state and the second heating state. The magnetic flux density acting on the first heat generating layer (fixing belt 21) in the second heating state is higher by about W1 / W2 than that in the first heating state. In other words, the magnitude of the magnetic flux density that acts on the first heat generating layer by the exciting coil unit 25 is inversely proportional to the range of the ferromagnetic body 24 that is close to and faces the fixing belt 21.

As described above, the region (skin depth) in which the magnetic flux acts in the first heat generating layer differs depending on the magnetic flux density acting on the first heat generating layer (fixing belt 21). The “skin depth” is the characteristic of the heat generating layer. This is because, in proportion to the resistance, it is inversely proportional to the permeability of the heat generating layer and the frequency of the alternating current exciting the heat generating layer. That is, since the magnetic flux density acting on the heat generating layer is inversely proportional to the magnetic permeability of the heat generating layer (variable by the change in the orientation of the ferromagnetic body 24 facing the exciting coil portion 25), the “skin depth” is applied to the heat generating layer. It is proportional to the acting magnetic flux density.
In this manner, by configuring the first heating state and the second heating state to be switchable, the fixing belt 21 is heated in an appropriate heating state according to the temperature rise state of the fixing belt 21. be able to. That is, the heating efficiency of the fixing belt 21 due to electromagnetic induction heating is sufficiently high, and the temperature raising time of the fixing belt 21 can be further shortened.

Specifically, in the first exemplary embodiment, the driving unit 61 sets the first heating state when the fixing device 20 (device main body 1) is started up and the second heating state when the continuous paper is passed. The ferromagnetic material 24 is controlled (movement control of the second ferromagnetic material 24B is performed).
As a result, the fixing belt 21 that has been left in the morning for a long time and the temperature has decreased is heated in the first heating state, so that the fixing belt 21 can be rapidly heated (started up). Become. Further, during continuous paper passing, the heat of the fixing belt 21 is gradually taken away by the recording medium P through which the continuous paper is passed, but the heat of the heat generating member 23 is transferred to the fixing belt 21 so as to complement it. Therefore, it is possible to reduce the occurrence of defective fixing images due to a decrease in the temperature of the fixing belt 21 during continuous paper feeding.

Here, in the first embodiment, the ferromagnetic body 24 is configured such that the magnetic flux density acting on the first heat generating layer (the fixing belt 21) is smaller than the saturation magnetic flux density of the first heat generating layer in the first heating state. The posture facing the exciting coil unit 25 is varied, and in the second heating state, the posture facing the exciting coil unit 25 is such that the magnetic flux density acting on the first heat generating layer is larger than the saturation magnetic flux density of the first heat generating layer. It will be variable.
FIG. 4 shows a magnetic field (coil magnetic field) generated in the vicinity of the first heat generation layer when the first heat generation layer is formed of a ferromagnetic material such as iron, nickel, cobalt, or an alloy thereof. It is a graph which shows the relationship with the magnetic flux density which acts on a heat generating layer. As shown in FIG. 4, the magnetic flux density acting on the first heat generating layer increases as the magnetic field increases, but the magnetic flux density becomes saturated when the magnetic field increases to some extent (saturated magnetic flux density C Reach). Then, by moving and controlling the ferromagnetic body 24 (second ferromagnetic body 24B) so that the magnetic flux density B1 smaller than the saturation magnetic flux density C acts, the magnetic flux generated by the exciting coil unit 25 is changed to the first. It acts only on the first heat generation layer without penetrating the heat generation layer (the state shown in FIG. 3A is the first heating state). On the other hand, by controlling the movement of the ferromagnetic body 24 (second ferromagnetic body 24B) so that the magnetic flux density B2 larger than the saturation magnetic flux density C acts, the magnetic flux generated by the exciting coil unit 25 is It penetrates through the first heat generating layer and also acts on the second heat generating layer (heat generating member 23) (the state shown in FIG. 3B is the second heating state).

Here, the first heat generating layer of the fixing belt 21 is made of a ferromagnetic material such as iron, nickel, cobalt, or alloys thereof (preferably iron, nickel, silicon, boron, niobium, copper). , Zirconium, cobalt, or an alloy thereof such as a magnetically tunable metal material that changes from ferromagnetic to paramagnetic.
In that case, by setting the Curie temperature of the first heat generating layer in the vicinity of the fixing temperature, the temperature of the fixing belt 21 does not exceed the fixing temperature, so that the temperature ripple of the fixing belt 21 during continuous paper passing becomes small, A fixed image having stable fixing properties and glossiness can be obtained. Further, by setting the Curie temperature of the first heat generation layer to be equal to or lower than the heat resistance temperature of the fixing belt 21, even when a small size paper (a recording medium P having a small size in the width direction) is continuously passed, It is possible to suppress a problem that the non-sheet passing region of the fixing belt 21 is excessively heated beyond the heat resistance temperature.
FIG. 5 is a graph showing the temperature distribution in the width direction of the fixing belt 21 during the continuous passage of small-size paper. The alternate long and short dash line Q0 shows the temperature distribution when the first heat generating layer is formed of a normal metal material. A solid line Q1 indicates a temperature distribution when the first heat generating layer is formed of a magnetically tunable metal material. From FIG. 5, it can be seen that when the first heat generating layer is formed of a magnetically tunable metal material, the belt temperature is suppressed in the vicinity of the fixing set temperature TM even in the non-sheet passing region of small size paper.

On the other hand, the first heat generating layer of the fixing belt 21 is formed of a nonmagnetic metal material such as gold, silver, copper, aluminum, zinc, tin, lead, bismuth, beryllium, antimony, or an alloy thereof. You can also.
In this case, even if the facing distance between the exciting coil unit 25 and the fixing belt 21 changes, the amount of magnetic flux penetrating the fixing belt 21 does not change greatly, so that uneven heating in the width direction of the fixing belt 21 is less likely to occur. . Further, even when the fixing belt 21 is shifted in the width direction while the fixing belt 21 is running, uneven heating in the width direction of the fixing belt 21 is less likely to occur.

Further, the first heat generating layer of the fixing belt 21 may be formed so that its layer thickness is smaller than the skin depth when an alternating current having a predetermined frequency flows through the exciting coil section 25 (exciting coil 26). preferable. Here, the “skin depth” means, as described above, the specific resistance and permeability of the heat generation layer, the frequency of the alternating current that excites the heat generation layer (in the first embodiment, the AC current output from the AC power supply). Is set within a range of 20 kHz to 100 kHz.).
In the configuration of the fixing device 20 according to the first embodiment, the first heating layer is formed so that the thickness of the first heat generating layer is smaller than the skin depth, so that the magnetic flux of the exciting coil unit 25 is reliably ensured in the second heating state. The second heat generating layer (heat generating member 23) is reached.

Furthermore, the second heat generating layer of the heat generating member 23 is formed of a magnetically tunable metal material that changes from ferromagnetic to paramagnetic, such as iron, nickel, silicon, boron, niobium, copper, zirconium, cobalt, or alloys thereof. can do.
In that case, by setting the Curie temperature of the second heat generating layer higher than the fixing temperature and not higher than the heat resistance temperature of the fixing belt 21, it is possible to prevent the fixing belt 21 from being overheated.

On the other hand, the second heat generating layer of the heat generating member 23 can be formed of a ferromagnetic metal material such as iron, nickel, cobalt, or the like.
In this case, even in the second heating state, the magnetic flux from the exciting coil unit 25 does not penetrate the second heat generating layer.

  In the first embodiment, the heat generating member 23 is a single-layer structure formed of only the second heat generating layer. However, the heat generating member 23 may be a multilayer structure including the second heat generating layer. For example, the front and back layers of the heat generating member 23 may be formed of a second heat generating layer (electromagnetic induction heating layer), and the intermediate layer may be formed of a high heat conductive material such as aluminum, iron, and stainless steel.

In the first embodiment, the heat generating member 23 is formed in a semi-cylindrical shape. On the other hand, as shown in FIG. 6A, the heat generating member 23 can be formed in a cylindrical shape.
Further, in the first embodiment, the heat generating member 23 is disposed so as to contact the inner peripheral surface of the fixing belt 21, and the exciting coil portion 25 is disposed so as to face the outer peripheral surface of the fixing belt 21. On the other hand, as shown in FIG. 6B, the heat generating member 23 is disposed so as to contact the outer peripheral surface of the fixing belt 21, and the exciting coil portion 25 is opposed to the inner peripheral surface of the fixing belt 21. It can also be arranged.
Even in these cases, the ferromagnetic body 24 (second ferromagnetic body 24B) is moved and controlled so as to vary the magnetic flux density acting on the first heat generating layer of the fixing belt 21, and the first heating state and the first heating state are changed. By switching between the two heating states, the same effect as in the first embodiment can be obtained.
Although not shown, the fixing device 20 shown in FIGS. 6A and 6B also applies to the second embodiment described later (which separates the heat generating member 23). You can also.

  As described above, in the first embodiment, only the first heat generating layer (fixing belt 21) is electromagnetically changed by changing the magnetic flux density acting on the first heat generating layer of the fixing belt 21 (fixing rotating body). A first heating state in which the fixing belt 21 (fixing rotator) is heated by induction heating, and the first heat generation layer (fixing belt 21) and the second heat generation layer (heat generation layer 23) are electromagnetically heated to cause the fixing belt 21 to heat. And the second heating state in which the fixing belt 21 is indirectly heated by the heat generating member 23 is switched. As a result, the heating efficiency of the fixing belt 21 by electromagnetic induction heating is sufficiently high, and the temperature raising time of the fixing belt 21 can be further shortened.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 7 is a configuration diagram showing the fixing device 20 in the second embodiment, and corresponds to FIG. 2 in the first embodiment. FIG. 8 is a diagram illustrating the operation of the heat generating member 23 in the fixing device. Further, FIG. 9 is a sectional view showing a part of another type of fixing device in the width direction.
The fixing device according to the second embodiment is configured such that the heat generating member 23 can be separated from the fixing belt 21. The heat generating member 23 is in contact with and fixed to the fixing belt 21. It differs from that of Form 1.

Referring to FIG. 7, the fixing device 20 in the second embodiment also has a fixing belt 21 (fixing rotating body), a fixing member 22, a heat generating member 23, and a ferromagnetic body 24, as in the first embodiment. (Magnetic flux adjusting member), exciting coil unit 25, pressure roller 31 (pressure rotating body), temperature sensor 40 (temperature detecting means), and the like.
Further, in the fixing device 20 according to the second embodiment, similarly to the first embodiment, the ferromagnetic body 24 includes the first ferromagnetic body 24A and the second ferromagnetic body along the rotation direction of the fixing belt 21. The magnetic flux density acting on the first heat generating layer (fixing belt 21) can be varied by controlling the movement of the ferromagnetic material 24 (second ferromagnetic material 24B) by the drive unit 61. Thus, the first heating state and the second heating state are switched.

Here, the fixing device 20 according to the second embodiment is provided with a separation mechanism that separates the heat generating member 23 from the fixing belt 21 at a predetermined timing, unlike the fixing device 20 according to the first embodiment. Then, in the state where the heat generating member 23 is separated from the fixing belt 21 (the state shown in FIGS. 7 and 8B), the first heat generating layer (fixing belt 21) is heated by the exciting coil unit 25. The heating state can be switched. In the third heating state, even if the magnetic flux from the exciting coil unit 25 reaches the second heat generating layer (heat generating member 23) in the separated state through the first heat generating layer (fixing belt 21), the second heat generation is performed. The heating efficiency of the layer is lowered, and heat conduction is not performed between the heat generating member 23 and the fixing belt 21. By using such a third heating state at a predetermined timing, the heating state of the fixing belt 21 can be finely adjusted.
As the separation mechanism that separates the heat generating member 23 from the fixing belt 21, for example, a cam mechanism that contacts the heat generating member 23 biased in a predetermined direction can be used.

Further, the separation mechanism described above also functions as a moving unit that moves the heat generating member 23 along the circumferential direction of the fixing belt 21 to a position not facing the exciting coil unit 25. Specifically, the heat generating member 23 is positioned by the separation mechanism so as to face the exciting coil unit 25 (the position shown in FIG. 8B), and the position not facing the exciting coil unit 25 (the position shown in FIG. 8A). ) Can be moved (moving in the direction of the double arrow in FIG. 7). And the magnetic flux of the exciting coil part 25 does not act on the heat generating member 23 completely by moving the heat generating member 23 to the position of FIG. Such a state is useful when it is not desired to completely heat the heat generating member 23 by electromagnetic induction heating.
In addition, as a separation mechanism (moving means) for moving the heat generating member 23, for example, a gear mechanism that meshes with a gear installed on a support shaft that supports the heat generating member 23 can be used.

Specifically, in the second embodiment, when the fixing device 20 (device main body 1) is started up, the first heating state (the state shown in FIG. 8B or FIG. 8A) is set. In addition, the separation mechanism of the heat generating member 23 is controlled. As a result, the fixing belt 21 that has been left for a long time in the morning and the temperature of the fixing belt 21 is intensively heated without being deprived of heat by the heat generating member 23. (Launch) is possible.
In the first heating state (the state shown in FIG. 8B or FIG. 8A), the posture of the ferromagnetic body 24 (second ferromagnetic body 24B) is the state shown in FIG. The drive unit 61 is controlled so that

FIG. 10 is a graph showing the temperature rise characteristics of the surface of the fixing belt 21 when the separation control of the heat generating member 23 is performed at the time of start-up and when it is not performed.
In FIG. 10, the solid line graph shows the temperature rise characteristic of the fixing belt 21 when the heat generating member 23 is separated at the time of starting the apparatus (the state shown in FIG. 8B or FIG. 8A). The broken line graph shows the temperature rise characteristic of the fixing belt 21 when the heat generating member 23 is brought into contact with the apparatus when the apparatus is started up (in the state shown in FIG. 8C).
From the result of FIG. 10, it can be seen that the temperature of the fixing belt 21 can be rapidly raised (started up) by performing the separation control of the heat generating member 23 at the time of starting up.

On the other hand, the separation mechanism of the exciting coil unit 25 and the heat generating member 23 is controlled so that the second heating state (the state shown in FIG. 8C) is switched when the paper is passed. At this time, the heat generating member 23 (second heat generating layer) is positively heated by electromagnetic induction by the exciting coil unit 25. Then, heat is transferred between the fixing belt 21 and the heat generating member 23 so as to supplement the heating of the fixing belt 21 in a state where the temperature has been sufficiently raised by the operation at the time of start-up.
In the second heating state (the state shown in FIG. 8C), driving is performed so that the posture of the ferromagnetic body 24 (second ferromagnetic body 24B) is in the state shown in FIG. 3B. The unit 61 is controlled.

When the temperature detected by the temperature sensor 40 (temperature detection means) is below a predetermined value, the contact state (FIG. 8C) is changed from the separated state (the state shown in FIG. 8B). When the temperature detected by the temperature sensor 40 reaches a predetermined value by controlling the separation mechanism of the heat generating member 23 so that it can be switched to the state of FIG. 8 (C). .) Can be controlled so as to be switched from the separated state (the state shown in FIG. 8B).
By performing such control, even when the paper is passed, the heat of the fixing belt 21 is lost by the recording medium P through which the paper is passed and the belt temperature is lowered, so that the heat generating member 23 is complemented. Is brought into contact with the fixing belt 21 and the heat of the heat generating member 23 is transferred to the fixing belt 21, so that it is possible to reduce the occurrence of defective fixing images due to a decrease in the temperature of the fixing belt 21 during paper passing. Further, when the temperature of the fixing belt 21 does not decrease, the heat generating member 23 is separated from the fixing belt 21 and the heat generating member 23 is stored by electromagnetic induction heating.
It should be noted that such control during paper passing can be performed in the same way during continuous paper passing.

Further, when thin paper is passed as the recording medium P (when the recording medium P having a thickness equal to or smaller than a predetermined value is conveyed to the nip portion), the heat generating member 23 is separated from the fixing belt 21. Thus, the separation mechanism can also be controlled (so that the state shown in FIG. 8B is obtained). This is because when the thin paper is passed, the heat of the fixing belt 21 taken away by the recording medium P is small, so that the heat generating member 23 is brought into contact with the fixing belt 21 and the heat of the heat generating member 23 is transmitted to the fixing belt 21. This is because the temperature of the fixing belt 21 can be stabilized without heating.
The image forming apparatus according to the first embodiment is a monochrome image forming apparatus. However, when a color image forming apparatus is used and the monochrome image mode is executed (a monochrome image is not fixed without fixing the color image). When fixing, the separation mechanism can be controlled so that the heat generating member 23 is separated from the fixing belt 21 (so that the state shown in FIG. 8B is reached). This is because in the monochrome image mode, the heat of the fixing belt 21 taken away by the toner image on the recording medium P is smaller than in the color image mode. This is because the temperature of the fixing belt 21 can be stabilized without transferring heat to the fixing belt 21.

FIG. 11 is a table showing the contacting / separating state of the heat generating member variably controlled according to these sheet passing conditions (the thickness of the recording medium P to be passed and the print mode). Specifically, when the recording medium P to be passed is thin paper (basis weight is 80 g / cm ² or less), the heating member 23 is in the monochrome image mode or in the color image mode. Is separated from the fixing belt 21. When the recording medium P to be passed is plain paper (basis weight of 81 to 105 g / cm ² ), the heating member 23 is separated from the fixing belt 21 in the monochrome image mode, and in the color image mode. The heat generating member 23 is brought into contact with the fixing belt 21. Further, when the recording medium P to be passed is thick paper (basis weight is 106 g / cm ² or more), the heat generating member 23 is fixed in both the monochrome image mode and the color image mode. It abuts on the belt 21.
By performing these controls, deterioration due to sliding contact between the fixing belt 21 and the heat generating member 23 can be reduced.
As a means for detecting the thickness of the recording medium P to be passed, a paper thickness sensor is installed in the conveyance path of the recording medium P or in the paper feeding units 12 to 14 to directly determine the thickness of the recording medium P. Alternatively, the thickness of the recording medium P may be indirectly detected based on the information of the recording medium P input by the operation of the operation panel of the apparatus main body 1 by the user. Then, based on the thickness information of the recording medium P detected in this way, the above-described control is performed.

Further, in the second embodiment, a printing mode (for example, a case where thick paper is passed as the recording medium P in which the temperature of the fixing belt 21 is controlled to the first target value, and the fixing belt 21 is passed. Is a high-temperature mode in which the temperature of the recording medium P is set to a high temperature) to a second target value lower than the first target value (for example, thin paper is passed as the recording medium P). In this case, the heat generating member 23 is separated from the fixing belt 21 when the mode is switched to the low temperature mode in which the temperature of the fixing belt 21 is set to be low (see FIG. 8B). The separation mechanism can also be controlled so that it is in a state.
This is because when the heat from the heat generating member 23 is transferred to the fixing belt 21 while the heat generating member 23 is in contact with the fixing belt 21 when the high temperature mode is switched to the low temperature mode, the fixing belt in the high temperature state is transferred. This is because it takes time to control the temperature of 21 to be lower. That is, by performing such control, the time (waiting time) during which the high temperature mode is switched to the low temperature mode can be shortened.

FIG. 12 shows the case where the separation control of the heating member 23 is performed and the case where the heating member 23 is not performed at the time of switching the printing mode (when switching from the thick paper passing mode to the plain paper passing mode). 6 is a graph showing a change in the surface temperature of the fixing belt 21.
In FIG. 12, the solid line graph shows the temperature change of the fixing belt 21 when the heat generating member 23 is separated at the time of switching the printing mode (the state shown in FIG. 8B or FIG. 8A), and the broken line. The graph shows a change in the temperature of the fixing belt 21 when the heat generating member 23 is brought into contact with the print mode (in the state shown in FIG. 8C). Note that the target value of the fixing temperature (first target value) in the thick paper passing mode is set to 180 ° C., and the target value (second target value) of the fixing temperature in the plain paper passing mode is 165. It is set to ℃.
Also from the result of FIG. 12, the time (waiting time) during which switching from the high temperature mode (thick paper passing mode) to the low temperature mode (plain paper passing mode) is performed by performing the separation control of the heat generating member 23 when switching the printing mode. Can be shortened.

  In the second embodiment, the heating member 23 is in contact with the fixing belt 21 (the state shown in FIG. 8C), and the temperature of the fixing belt 21 is a predetermined value. (When overshoot of the fixing belt 21 is detected by the temperature sensor 40), the heating member 23 is separated from the fixing belt 21 by the separation mechanism as shown in FIG. 8B. It is preferable to control. As a result, the heat of the heat generating member 23 is not transferred to the fixing belt 21, so that the temperature of the fixing belt 21 in an excessively high temperature state is easily lowered.

FIG. 13 is a graph showing a change in the surface temperature of the fixing belt 21 when the separation control of the heat generating member 23 is performed during the overshoot of the fixing belt 21 and when it is not performed.
In FIG. 13, the solid line graph shows the temperature change of the fixing belt 21 when the heat generating member 23 is separated during overshoot (the state shown in FIG. 8B or FIG. 8A), and the broken line graph is The temperature change of the fixing belt 21 when the heat generating member 23 is brought into contact with the overshoot (the state shown in FIG. 8C) is shown. The overshoot of the fixing belt 21 is likely to occur during the cardboard paper passing mode in which the surface temperature of the fixing belt 21 is set high (180 ° C.), and the surface temperature of the fixing belt 21 is a heat resistant limit temperature 225. When the temperature sensor 40 detects that the surface temperature of the fixing belt 21 exceeds a predetermined value (for example, 195 ° C.) so that the temperature sensor 40 does not reach ° C., it is assumed that the heating member 23 is in an overshoot state and the heating member 23 is separated. Control takes place.
From the results shown in FIG. 13, it can be seen that the occurrence of thermal damage to the fixing belt 21 can be prevented by controlling the separation of the heat generating member 23 during overshoot.

In addition, the fixing device 20 according to the second embodiment is installed in the image forming apparatus main body 1 (an apparatus having different printing productivity) having a different conveyance speed (process linear speed) of the recording medium P (commonization). In the case where the heat generating member 23 is separated from the fixing belt 21 by the separation mechanism, the condition (the condition in which it is in the state of FIG. 8B) can be varied.
This is because the heat of the fixing belt 21 taken away by the conveyed recording medium P is smaller in the image forming apparatus having a low conveying speed of the recording medium P than in the image forming apparatus having a high conveying speed of the recording medium P. This is because the temperature of the fixing belt 21 can be stabilized to some extent without contacting the member 23 with the fixing belt 21 and transferring the heat of the heat generating member 23 to the fixing belt 21.
By making such a setting, the common fixing device 20 can be used without problems even for image forming apparatuses having different printing speeds.

FIG. 14 is a table showing conditions for controlling the separation of the heat generating member 23 that is changed for each image forming apparatus in which the conveyance speed of the recording medium P is different.
Specifically, in the image forming apparatus A (the apparatus that conveys 31 A4 size recording media P per minute) with the slowest conveyance speed of the recording medium P, the recording medium P to be passed is thin paper (tsubo). the amount is of 80 g / cm ² or less.) with a heating member 23 is separated from the fixing belt 21 in the case of, but the recording medium P to be fed is plain paper (basis weight 81~105g / cm ² In the case of the above, the heat generating member 23 is separated from the fixing belt 21 and the recording medium P to be passed is thick paper (basis weight is 106 g / cm ² or more). It is brought into contact with the fixing belt 21. Further, in the image forming apparatus B (the apparatus that conveys 41 A4-sized recording media P per minute) with a medium conveyance speed of the recording medium P, the recording medium P to be passed is thin paper. When the heat generating member 23 is separated from the fixing belt 21 and the recording medium P to be passed is plain paper, the heat generating member 23 is brought into contact with the fixing belt 21 and the recording medium P to be passed is thick paper. Also, the heat generating member 23 is brought into contact with the fixing belt 21. Further, in the image forming apparatus C (the apparatus that conveys 51 A4-sized recording media P per minute) with the fastest conveying speed of the recording medium P, regardless of the thickness of the recording medium P to be passed. The heat generating member 23 is brought into contact with the fixing belt 21.
By performing these controls, the common fixing device 20 can be used without problems even for image forming apparatuses having different printing speeds.

Furthermore, in the second embodiment, as shown in FIG. 9, the heat generating members 23A and 23B are divided into a plurality of width directions in accordance with the recording medium P having different width direction sizes, and are conveyed to the nip portion. It is also possible to control the separation mechanism so as to vary the separation state of the heat generating members 23A and 23B divided into a plurality according to the width direction of P with respect to the fixing belt 21.
Specifically, as shown in FIG. 9, the first heat generating member 23 </ b> A is installed in the central portion in the width direction so as to be able to contact and separate in accordance with the passing area of the small size paper, and the passing area ( The second heat generating member 23B is installed at both ends in the width direction so as to be able to contact and separate. The first heat generating member 23A and the second heat generating member 23B are configured to be able to contact and separate independently from the fixing belt 21 by the separation mechanism. Then, the first heat generating member 23A and the second heat generating member 23B are independently contacted and separated according to the size of the recording medium P to be passed, so that the small size paper can be passed. Overheating of the fixing belt 21 in the non-sheet passing region can be suppressed (see FIG. 5).
For example, in the state shown in FIG. 9B (when the heat generating members 23A and 23B are separated from each other), when the small size paper is passed immediately after the large size paper is continuously passed, the small size is left as it is. Since the heat at both ends of the fixing belt 21 corresponding to the non-sheet passing area of the size paper is not taken away by the paper, the temperature rises excessively. On the other hand, as shown in FIG. 9A, the heat of the non-sheet passing area of the fixing belt 21 is caused to be generated by bringing the heat generating members 23B at both ends into contact with the non-sheet passing area of the fixing belt 21. The excessive temperature rise at both ends of the fixing belt 21 can be prevented.
The operation of the heat generating members 23A and 23B described above is an example, and the two heat generating members 23A and 23B can be independently contacted and separated according to various situations. In FIG. 9, the heat generating members 23A and 23B are divided according to the recording media P of two sizes, but the heat generating members can be divided according to the recording media P of three or more sizes.

  As described above, also in the second embodiment, similarly to the first embodiment, the first heat generation is achieved by varying the magnetic flux density acting on the first heat generation layer of the fixing belt 21 (fixing rotating body). The first heating state in which only the layer (fixing belt 21) is heated by electromagnetic induction to heat the fixing belt 21 (fixing rotating body), the first heat generating layer (fixing belt 21), and the second heat generating layer (heat generating layer 23). The fixing belt 21 is directly heated by electromagnetic induction heating, and the second heating state in which the fixing belt 21 is indirectly heated by the heat generating member 23 is switched. As a result, the heating efficiency of the fixing belt 21 by electromagnetic induction heating is sufficiently high, and the temperature raising time of the fixing belt 21 can be further shortened.

  In each of the above embodiments, the present invention is applied to a fixing device using a pressure roller as a pressure rotator and a fixing belt as a fixing rotator. The present invention can also be applied to a fixing device using a fixing device and a fixing device using a fixing film or a fixing roller as a fixing rotator. In this case, the same effects as those of the above embodiments can be obtained.

  In each of the above embodiments, the present invention is applied to the fixing device 20 installed in the monochrome image forming apparatus 1. However, the present invention is naturally applied to the fixing device installed in the color image forming apparatus. The invention can be applied.

In each of the above embodiments, the ferromagnetic body 24 is divided into the first ferromagnetic body 24A and the second ferromagnetic body 24B, and the second ferromagnetic body 24B is moved up and down by the drive unit 61. The first heating state in which only the first heat generating layer (fixing belt 21) is heated by the exciting coil unit 25 by changing the attitude of the ferromagnetic body 24 with respect to the exciting coil unit 25, and the first by the exciting coil unit 25. The second heating state in which the heat generating layer (fixing belt 21) and the second heat generating layer (heat generating member 23) are heated can be switched.
However, the mode of dividing the ferromagnetic body 24 and the mode of changing the attitude of the ferromagnetic body 24 with respect to the exciting coil section 25 are not limited to those of the above-described embodiments, but the first heat generating layer (fixing belt). 21), the first heating state in which only the first heat generating layer (fixing belt 21) is heated by the exciting coil unit 25, and the first heat generating layer (by the exciting coil unit 25). Various modes can be used as long as the fixing belt 21) and the second heating state in which the second heating layer (heating member 23) is heated can be switched.
In this case, the same effects as those of the above embodiments can be obtained.

  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 embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 image forming apparatus body (apparatus body),
20 fixing device,
21 fixing belt (fixing rotating body),
22 fixing member,
23 Heat generating member,
24 Ferromagnetic material (magnetic flux adjusting member),
24A first ferromagnet, 24B second ferromagnet,
25 Excitation coil section (induction heating section),
31 Pressure roller (pressure rotating body),
40 temperature sensor,
61 Drive unit, P recording medium.

JP 2009-282413 A Japanese Patent No. 3527442 Japanese Patent No. 3900692

Claims (14)

A fixing rotator that includes a first heat generating layer that is electromagnetically heated by an exciting coil unit, and that travels in a predetermined direction to heat and melt a toner image;
A pressure rotator that forms a nip portion in which a recording medium is conveyed in pressure contact with the fixing rotator; and
A second heat generation layer that is electromagnetically heated by the exciting coil portion that is opposed to the fixing rotating body, and that is configured to be able to heat the fixing rotating body in contact with the fixing rotating body. Members,
With
A first heating state in which only the first heat generating layer is electromagnetically heated by the exciting coil unit to heat the fixing rotating body by varying a magnetic flux density acting on the first heat generating layer, and the exciting coil A second heating state in which the first heat generating layer and the second heat generating layer are heated by electromagnetic induction to heat the fixing rotator directly and the heat generating member indirectly heats the fixing rotator. , And a fixing device characterized by being switched. A ferromagnetic body formed so as to face the excitation coil unit via the fixing rotator and the heat generating member, and to change a posture facing the excitation coil unit;
The fixing device according to claim 1, wherein the magnetic flux density acting on the first heat generating layer is changed by changing a posture of the ferromagnetic body. The ferromagnetic body is divided into a plurality along the rotation direction of the fixing rotator,
The magnetic flux density acting on the first heat generating layer is varied by varying a facing distance of the at least one ferromagnetic material of the plurality of ferromagnetic materials from the exciting coil unit. The fixing device according to 1.   In the first heating state, the ferromagnetic body has a posture that is opposed to the exciting coil unit so that a magnetic flux density acting on the first heat generating layer is smaller than a saturation magnetic flux density of the first heat generating layer, The posture facing the exciting coil section is varied so that a magnetic flux density acting on the first heat generating layer is larger than a saturation magnetic flux density of the first heat generating layer in the second heating state. The fixing device according to claim 2 or 3.   5. The apparatus according to claim 1, wherein the first heating state is controlled when the apparatus is started up, and the second heating state is controlled when the sheet is continuously fed. Fixing device.   The fixing device according to claim 1, wherein the heat generating member is separated from the fixing rotator at a predetermined timing by a separation mechanism.   The fixing device according to claim 6, wherein the separation mechanism is controlled so that the heat generating member is separated from the fixing rotator when the device is started up.   The separation mechanism is used to fix the monochrome rotating image without fixing the color image, and / or when the recording medium having a thickness equal to or less than a predetermined value is conveyed to the nip portion. The fixing device according to claim 6, wherein the heat generating member is controlled to be separated.   The separation mechanism is controlled so that the temperature of the fixing rotator is controlled to be a first target value, and the second target value lower than the first target value is controlled. 9. The fixing device according to claim 6, wherein the heat generating member is controlled to be separated from the fixing rotator when the fixing rotation body is switched to.   When the heat generating member is in contact with the fixing rotator, and the temperature of the fixing rotator exceeds a predetermined value, the heat generation is performed on the fixing rotator by the separation mechanism. 10. The fixing device according to claim 6, wherein the member is controlled to be separated. The heat generating member is divided into a plurality in the width direction according to recording media having different width sizes,
7. The separation mechanism is configured to vary a separation state of the plurality of heat generating members divided into the fixing rotating body according to a width direction size of a recording medium conveyed to the nip portion. The fixing device according to claim 10.   The separation mechanism separates the heat generating member from the fixing rotator and moves the heat generating member along a circumferential direction of the fixing rotator to a position not facing the exciting coil unit. The fixing device according to claim 6.   The condition for separating the heat generating member from the fixing rotator by the separation mechanism is varied when the recording medium is installed in different image forming apparatus main bodies. The fixing device according to claim 12.   An image forming apparatus comprising the fixing device according to claim 1.

Images