JP2010085806A - Fixing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which the induction heating of the total width of a member to be heated is forcibly prevented when a magnetic flux shield part different in the shield width of a magnetic flux by a rotation position is freely turned, and to provide an image forming apparatus. <P>SOLUTION: In the fixing device capable of changing the width of the path of the magnetic flux by turning a center core 55 by a prescribed drive means, at least a shield part D1 where the shield width of the path of the magnetic flux acting on a heating roller 53 is the total width of the heating roller 53 is provided in the center core 55 and the position of the centroid 55g of the center core 55 and the position of the shield part D1 (total width shield part) in the center core 55 are set so that when the center core 55 is freely turned, the center core 55 may be turned by gravity until the shield part D1 (total width shield part) is interposed on the path of the magnetic flux between an induction coil 54 and the heating roller 53. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an induction heating type fixing device and an image forming apparatus including the same, and more particularly to a technique for changing the width of a heating target region of a member to be heated (such as a fixing roller) to be heated by induction. .

In general, an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine of these uses an induction heating type fixing device that heats a heated member such as a fixing roller by electromagnetic induction. Specifically, in the fixing device, an induction coil and a magnetic core are disposed so as to face the maximum sheet passing area of a heated member made of a magnetic material. A magnetic flux is generated by passing a high-frequency current through the induction coil. As a result, the magnetic flux generated by the induction coil is guided to the member to be heated through the magnetic circuit formed by the magnetic core, and the member to be heated is heated by the eddy current (induction current) generated by electromagnetic induction by the magnetic flux. The
Conventionally, in such an induction heating type fixing device, when a paper having a size smaller than the maximum paper passing area is passed, in order to maintain the paper passing area through which the paper passes at a predetermined fixing temperature, There is a problem that overheating occurs in a non-sheet passing region near the end of the heated member through which the sheet does not pass. Therefore, a configuration in which the width of the heating target region in the heated member can be changed according to the paper size has been studied.
For example, Patent Document 1 discloses that the width of the heating target region is changed by changing the width of the magnetic flux acting on the member to be heated from the induction coil with a magnetic flux shielding member. Specifically, the width of the magnetic flux acting on the member to be heated is adjusted by changing the rotation position of the arc-shaped magnetic flux shielding plates having different widths.
JP-A-2005-208624

However, an abnormality such as a gear breakage occurs in a drive system such as a drive motor for rotating the magnetic flux shield member or a transmission mechanism for transmitting the drive force of the drive motor, and the magnetic flux shield member is rotated. If it cannot be moved, the heated member may be overheated depending on the position of the magnetic flux shielding member at that time.
For example, in a state where the magnetic flux shielding member is rotated to a position where the A3 size width is set as the heating target region and printing is performed using B5 size paper, the magnetic flux shielding member is set to the B5 size width. It is necessary to rotate to a position to be a heating target area. However, at this time, the magnetic flux shielding member cannot be rotated due to an abnormality in the drive system of the magnetic flux shielding member, and if the magnetic flux shielding member is maintained at a position where the width of the A3 size is the heating target area, In the paper printing process, induction heating is continuously performed with the A3 size width as the heating target area, and thus overheating occurs in the non-sheet passing area.
In addition, when an abnormality occurs in the drive system of the magnetic flux shielding member and the magnetic flux shielding member becomes rotatable, the magnetic flux shielding member may be rotated by its own weight. The position of the magnetic flux shielding member is not particularly determined with intention. For this reason, after the magnetic flux shielding member is rotated by its own weight, it is not specified how the heating target area of the heated member is adjusted by the magnetic flux shielding member, and in some cases, the heated member may be overheated. There is.
Accordingly, the present invention has been made in view of the above circumstances, and the object of the present invention is that when a magnetic flux shielding member having a different magnetic flux shielding width depending on the rotational position becomes rotatable, the heated member An object of the present invention is to provide a fixing device and an image forming apparatus in which full width induction heating is forcibly prevented.

In order to achieve the above object, the present invention provides an induction coil for generating a magnetic flux for induction heating of a heated member, and a portion interposed on a magnetic flux path between the induction coil and the heated member. A magnetic flux shielding member having a different shielding width for shielding the path of the magnetic flux, and rotating the magnetic flux shielding member by a predetermined driving means to change a portion of the magnetic flux shielding member interposed on the magnetic flux path. A fixing device comprising a magnetic flux width changing means for changing the width of the path, wherein the magnetic flux shielding member is provided with at least a full width shielding portion in which the shielding width of the magnetic flux path is the full width of the heated member. When the magnetic flux shielding member becomes rotatable, the magnetic flux shielding member rotates by its own weight until the full width shielding portion is interposed on the magnetic flux path between the induction coil and the heated member. You As configured as a fixing device, characterized in that the position of the full width shielding portion at the center of gravity position and the magnetic flux shielding member of the magnetic flux shielding member are thus determined.
According to the present invention, when the magnetic flux shielding member becomes rotatable, the magnetic flux shielding member reaches a position where the full width shielding portion is interposed on the magnetic flux path between the induction coil and the heated member. Is rotated by its own weight, and the action of the magnetic flux on the full width of the heated member is forcibly blocked by the full width shielding portion. Therefore, for example, when an abnormality occurs in the predetermined driving means and the magnetic flux shielding member becomes rotatable, overheating (abnormal heating) of the heated member can be prevented. In addition, as will be described later, it is possible to forcibly prevent induction heating of the member to be heated by forcibly turning the magnetic flux shielding member when an abnormality occurs.

Specifically, the induction coil and the magnetic flux shielding member are arranged vertically above the heated member, and the magnetic flux shielding member is formed between the rotation center of the magnetic flux shielding member and the full width shielding portion. It is conceivable that the center of gravity is eccentric so that it is located between them. As a result, when the magnetic flux shielding member becomes rotatable, the magnetic flux shielding member is rotated by its own weight, and the full width shielding portion is positioned vertically downward so that the induction coil and the heated member Therefore, induction heating of the full width of the member to be heated can be prevented.
The magnetic flux shielding member is provided on a magnetic core that forms a magnetic circuit between the induction coil and the heated member, and an outer peripheral surface of the magnetic core. It is conceivable to include a magnetic flux shielding plate having a different shielding width for shielding the magnetic flux path by a portion interposed on the magnetic flux path therebetween. In such a configuration, for example, the center of gravity of the magnetic flux shielding member can be decentered by providing a hollow portion inside the magnetic core. Further, the center of gravity of the magnetic flux shielding member can be decentered by weights provided at one or both side end portions of the magnetic core.

Further, there is a predetermined abnormality in the holding unit that holds the magnetic flux shielding member in a position after being rotated by the predetermined driving unit, and the fixing device and / or the image forming apparatus in which the fixing device is mounted. It is conceivable that it further comprises holding release means for releasing the holding of the magnetic flux shielding member by the holding means so that the magnetic flux shielding member can be rotated on the condition that it has occurred. Thereby, when the abnormality occurs, the magnetic flux to the member to be heated is shielded by the full width shielding portion, and induction heating of the member to be heated is forcibly blocked.
By the way, the present invention may be understood as an invention of an image forming apparatus including the fixing device configured as described above.

According to the present invention, when the magnetic flux shielding member becomes rotatable, the magnetic flux shielding member reaches a position where the full width shielding portion is interposed on the magnetic flux path between the induction coil and the heated member. Is rotated by its own weight, and the action of the magnetic flux on the full width of the heated member is forcibly blocked by the full width shielding portion. Therefore, for example, when an abnormality occurs in the predetermined driving means and the magnetic flux shielding member becomes rotatable, overheating (abnormal heating) of the heated member can be prevented.
It is also possible to forcibly prevent induction heating of the heated member by forcibly turning the magnetic flux shielding member when an abnormality occurs in the fixing device or the image forming apparatus. .

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of a copying machine X according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a schematic configuration of a fixing device 5 according to the embodiment of the present invention, and FIG. FIG. 6 is a schematic diagram for explaining the structure of a center core 55 provided in the fixing device 5 according to the embodiment of the present invention.
First, a schematic configuration of the copying machine X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, a copying machine X according to an embodiment of the present invention includes an operation display unit 1, an image reading unit 2, an image processing unit 3, an image forming unit 4, a fixing device 5, a control unit 6, and the like. In general, it is structured. The copying machine X has various other constituent elements that a general electrophotographic copying machine has, but since these are not different from the conventional ones, description thereof is omitted here. The present invention is not limited to the copying machine X, and can also be applied to, for example, an electrophotographic image forming apparatus such as a printer apparatus, a facsimile apparatus, and a multifunction machine having these functions and a scanner function.
The control unit 6 includes a CPU, peripheral devices such as a ROM and a RAM, and executes the process according to a predetermined program stored in the ROM while developing the copy machine X on the RAM. Control all over.

The operation display unit 1 includes a liquid crystal display that displays various types of information according to instructions from the control unit 6, a touch panel for performing operation input to the control unit 6, and the like.
The image reading unit 2 reads an image of a document set on a document table or an ADF (automatic conveyance device), and the image data read by the image reading unit 2 is input to the image processing unit 3. The
The image processing unit 3 performs various operations on image data of a document read by the image reading unit 2 and image data of a document input from an information processing apparatus (not shown) via a communication network such as a LAN. Image processing is performed. The image data that has been subjected to image processing by the image processing unit 3 is input to the image forming unit 4.
The image forming unit 4 includes a photosensitive drum, a charger, a developing device, an LSU, and the like. A toner image (developer) is applied to a sheet based on image data of a document input from the image processing unit 3. To form.
The fixing device 5 melts and fixes the toner image on the paper on which the toner image is formed by the image forming unit 4. The copying machine X according to the embodiment of the present invention is characterized by the configuration and operation related to the fixing device 5 and will be described in detail below.

As shown in FIG. 2, the fixing device 5 includes a fixing roller 51 and a pressure roller that rotate while pressing a sheet conveyed on the sheet conveying path 50 after the toner image is transferred in the image forming unit 4. A heating roller 53 (an example of a member to be heated) that is rotationally driven by a driving force transmitted from the fixing roller 51 via a fixing belt 52 stretched between the fixing roller 51 and the fixing roller 51; An induction coil 54 that generates a magnetic flux for induction heating the roller 53, and a center core 55 (a magnetic core core) that forms a magnetic circuit (see the thick arrow in FIG. 2) between the induction coil 54 and the heating roller 53. An external core 56).
The fixing roller 51 is connected to driving means such as a stepping motor (not shown), and is rotationally driven by the driving means. When the fixing roller 51 is rotationally driven, the fixing belt 52 travels by the driving force, and the heating roller 53 rotates by the driving force transmitted from the fixing belt 52.
The heating roller 53 is made of a magnetic material such as iron or a magnetic shunt alloy. In addition, the induction coil 54 and the center core 55 are disposed vertically above the heating roller 53.

The induction coil 54 is wound in the direction of the rotation axis (the depth direction in FIG. 2), which is the width direction of the heating roller 53, and has a longitudinal width (substantially the same as the maximum sheet passing width). The width is substantially the same as the width.
The center core 55 and the outer core 56 are made of a ferromagnetic material such as ferrite, and are formed to have a width substantially the same as the width of the heating roller 53 in the same manner as the induction coil 54. Yes.
Here, the center core 55 is a cylindrical roller member disposed to face the heating roller 53 through a hollow portion of the induction coil 54, and is interposed between the outer core 56 and the heating roller 53. A magnetic circuit is formed. Further, as shown in FIG. 2, the outer core 56 is composed of a pair of U-shaped and inverted U-shaped magnetic cores surrounding both sides of the heating roller 53 and the center core 55. A magnetic circuit that passes outside the induction coil 54 is formed between the heating roller 53 and the center core 55. As described above, in the fixing device 5, a magnetic circuit (see the thick arrow in FIG. 2) is formed between the induction coil 54 and the heating roller 53 by the center core 55 and the external core 56.
The outer core 56 is not limited to the one continuously formed over the entire longitudinal width of the heating roller 53 and the center core 55. For example, the outer core 56 is not limited to the longitudinal direction of the heating roller 53 and the center core 55. It may have a plurality of plate-like cores arranged at predetermined intervals over the entire width.

In the fixing device 5, the magnetic flux generated in the induction coil 54 by supplying power to the induction coil 54 is guided to the heating roller 53 by the center core 55 and the outer core 56, and is applied to the surface of the heating roller 53. When the eddy current (inductive current) is generated, the heating roller 53 is heated.
When the heating roller 53 is heated, the fixing belt 52 is heated by heat conduction from the heating roller 53 to the fixing belt 52 thermally coupled to the heating roller 53. As a result, on the paper contacting the fixing belt 52, the toner adhering to the paper is melted and fixed. A configuration in which the fixing belt 52 is made of a magnetic member and the fixing belt 52 is directly heated by the magnetic flux from the induction coil 54 is also conceivable. It is also conceivable that the fixing roller 51 is directly induction-heated by the magnetic flux from the induction coil 54 without the heating roller 53 or the fixing belt 52. In these cases, the fixing belt 52 and the fixing roller 51 to be heated correspond to the heated member.

Further, the fixing device 5 employs a configuration for changing the heating target area of the heating roller 53.
Here, FIGS. 3A to 3C are schematic views of the main part for explaining the relationship between the rotational position of the center core 55 and the heating target area of the heating roller 53, and the right side is a diagram. The figure which looked at the said center core 55 from the front, and the figure on the left side are the figures which looked at the said center core 55 from the left side. In FIG. 3, the downward direction is a portion facing the heating roller 53.
As shown in FIG. 3, the outer peripheral surface 55a of the center core 55 is provided with a magnetic flux shielding plate 60 having a shape in which the width in the longitudinal direction of the heating roller 53 changes in a plurality of stages. The magnetic flux shielding plate 60 is a silver foil, copper foil, aluminum foil or the like that shields the magnetic flux, and shields the magnetic flux path by a portion interposed on the magnetic flux path between the induction coil 54 and the heating roller 53. Different shielding widths are used.

Specifically, as shown in FIG. 3A, the magnetic flux shielding plate 60 includes a shielding part D1 (corresponding to the full width shielding part) corresponding to the full width region of the center core 55, and an A4 side (short side of A4). ) Having a shielding portion D3 corresponding to a region excluding the width of the vertical portions B2 and B5 (long side of A3) corresponding to the region excluding the width of. Further, the magnetic flux shielding plate 60 has a non-shielding portion D0 corresponding to the width A3 (short side of A3), which is the entire width of the heating roller 53, on the outer peripheral surface 55a of the center core 55. Attached to the outer peripheral surface 55a so as to leave as a region not shielded by 60.
Therefore, in the fixing device 5, the part of the center core 55 interposed on the magnetic flux path between the induction coil 54 and the heating roller 53 is either the shielding part D1 to D3 or the non-shielding part D0. Depending on how, the shielding width in which the path of the magnetic flux is shielded is different. Here, in the present embodiment, the center core 55 and the magnetic flux shielding plate 60 are considered as an example of a magnetic flux shielding member.

For example, as shown in FIG. 3A, when the shielding part D1 is interposed at a position facing the heating roller 53 (downward in FIG. 3A), the induction coil The shield width of the magnetic flux path between 54 and the heating roller 53 is the entire width of the heating roller 53, and the entire heating roller 53 is not heated.
On the other hand, as shown in FIG. 3B, when the shielding portion D3 is interposed at a position facing the heating roller 53 (downward in FIG. 3B), the heating roller 53 The area to be heated becomes a width of B5 vertical size, and the non-shielding portion D0 is interposed at the position facing the heating roller 53 (downward in FIG. 3C) as shown in FIG. If it is, the heating target area of the heating roller 53 has a width of A3 horizontal size.

The magnetic flux shielding plate 60 may further have a multi-stage shielding portion, and may have a shielding portion corresponding to each arbitrary size without being limited to each paper size. Further, the magnetic flux shielding plate 60 has a hypotenuse for continuously changing the shielding width of the magnetic flux path from the center core 55 to the heating roller 53 according to the rotational position of the center core 55. It is also possible to become.
In this embodiment, the description will be made on the assumption that the sheet is conveyed so that the center of the sheet is aligned with the center of the fixing belt 52 in the width direction. The present invention is also applicable to a configuration in which the paper is conveyed so that one end of the paper is along one end. In this case, the magnetic flux shielding plate 60 may be formed so that the region shielded by the magnetic flux shielding plate 60 is aligned with one end thereof.
Furthermore, a configuration in which the magnetic flux shielding plate 60 can be rotated independently of the center core 55 is also conceivable as another embodiment. In this case, the magnetic flux shielding plate 60 corresponds to a magnetic flux shielding member.

The center core 55 is rotatably supported by a core rotation mechanism (not shown) that rotates the center core 55 independently of the heating roller 53.
The core rotation mechanism includes a transmission system such as a rotation shaft and a gear that rotatably supports the center core 55, and a stepping motor and servo for rotating the center core 55 by applying a driving force to the transmission system. A drive motor such as a motor, and a connection switching mechanism that switches the connection between the drive motor and the transmission system are provided. The presence / absence and drive amount of the drive motor and the operation of the connection switching mechanism are controlled by the control unit 6 and the like.
Here, in the core rotation mechanism, when the drive motor and the transmission system are connected by the connection switching mechanism, the center core 55 is in a position after being rotated by the drive motor. It is held by the holding force of the drive motor. Here, the drive motor when the holding force for holding the center core 55 in the rotating position is exhibited is an example of the holding means. On the other hand, when the connection between the drive motor and the transmission system is released by the connection switching mechanism, the holding of the center core 55 by the drive motor is released, and the center core 55 is rotatable. It becomes.
For example, the connection switching mechanism connects the drive motor and the center core 55 when energized to enable transmission of driving force from the drive motor to the center core 55, and when not energized, the drive motor and the center core. It is conceivable that the mechanism is a mechanism using a clutch, a solenoid, or the like that releases the connection of 55 and interrupts transmission of the driving force from the drive motor to the center core 55.

In the fixing device 5 configured as described above, the control unit 6 controls the drive motor to rotate the center core 55, and is interposed on the magnetic flux path from the induction coil 54 to the heating roller 53. The width of the path of the magnetic flux acting on the heating roller 53 can be changed by changing the part of the center core 55 to be one of the non-shielding part D0 and the shielding parts D1 to D3. The said control part 6 when performing the magnetic flux width change process which concerns here corresponds to a magnetic flux width change means.
For example, in the copying machine X, the control unit 6 rotates the center core 55 according to the size of the paper on which image formation is performed, and adjusts the heating target area of the heating roller 53 to the paper size. The overheating of the area corresponding to the non-sheet passing area in the heating roller 53 is prevented.
However, as described above, the rotation of the center core 55 cannot be controlled when an abnormality occurs in the drive motor or the connection switching mechanism in the core rotation mechanism in the fixing device 5. The heating roller 53 may be overheated.
At this time, if the abnormality occurring in the core rotation mechanism is, for example, that the connection between the drive motor and the transmission system by the connection switching mechanism is released, the center core 55 due to the holding force of the drive motor The holding of the rotation position is released, and the center core 55 is in a rotatable state.
Therefore, in the embodiment of the present invention, when the center core 55 is rotatable, the center core 55 is placed on the magnetic flux path between the induction coil 54 and the heating roller 53. The position of the center of gravity of the center core 55 and the position of the shielding part D1 in the center core 55 are determined so that the center core 55 rotates by its own weight until it is interposed. Specific examples will be described below.

As shown in FIG. 3, the center core 55 is formed from the rotation center 55c of the center core 55 (the center of the circle of the center core 55) toward the side opposite to the shielding portion D1 of the magnetic flux shielding plate 60. A semicircular (D-shaped) hollow portion 55b is provided. The hollow portion 55b is formed over the entire length of the center core 55 in the longitudinal direction. Accordingly, the center core 55 is eccentric so that the center of gravity 55g is located between the rotation center 55c and the shielding part D1 of the magnetic flux shielding plate 60. The shape of the hollow portion 55b may be another shape as long as the center of gravity 55g of the center core 55 can be determined as described above.
Thus, if the hollow portion 55b is formed in the center core 55, the center of gravity 55g of the center core 55 can be decentered without deforming the shape of the outer peripheral surface of the center core 55 through which magnetic flux passes. The hollow portion 55b may be used as an insertion port through which a D-cut rotation shaft connected to the center core 55 is inserted, for example.

In the fixing device 5 configured as described above, for example, as shown in FIGS. 3B and 3C, the center of gravity 55g of the center core 55 is not positioned vertically downward. When an abnormality occurs in the core rotation mechanism and the center core 55 becomes rotatable, the center core 55 is rotated by the rotational force generated when the rotation center 55c and the center of gravity 55g are separated (FIG. 3B, (C), the center of gravity 55g rotates until it is positioned vertically downward.
That is, the center core 55 rotates by its own weight until the shielding portion D1 is interposed on the magnetic flux path between the induction coil 54 and the heating roller 53.
Accordingly, since the magnetic flux that should act on the entire width of the heating roller 53 is shielded by the shielding portion D1, induction heating of the heating roller 53 is forcibly blocked, and overheating of the heating roller 53 is prevented. can do.

Further, here, the prevention of overheating of the heating roller 53 when the center core 55 becomes rotatable due to an abnormality occurring in the core rotation mechanism has been described. However, the present invention relates to a home position of the center core 55, for example. It is also suitable for determining.
For example, the control unit 6 energizes the connection switching mechanism only when the heating roller 53 performs induction heating, and after the induction heating is completed or when the induction heating is not performed, the connection switching mechanism is switched to. It is conceivable to stop the energization. As a result, the rotational position of the center core 55 is maintained during the induction heating of the heating roller 53, but after the induction heating is completed or when the induction heating is not performed, the center core 55 is rotated. The holding of the moving position is released and the center core 55 can rotate, and as described above, the center core 55 rotates by its own weight until it is positioned vertically downward.
Therefore, when the induction heating of the heating roller 53 is started next, the center core 55 is always in a state where the shielding portion D1 is positioned vertically downward. The process of detecting the position of the center core 55 at the start of the induction heating and the sensor arrangement therefor can be omitted. Further, since the rotation of the center core 55 can always be started from the same position, compared to a configuration in which the center core 55 is once returned to a preset home position and then moved to a predetermined position, the induction heating is started. It is also possible to shorten the time required for.

By the way, in the copying machine X, if the connection between the drive motor and the transmission system by the connection switching mechanism is intentionally cut off to make the center core 55 rotatable, the center core 55 is rotated by its own weight. It is possible to forcibly prevent induction heating over the entire width of the heating roller 53 by moving the heating roller 53.
Therefore, on the condition that a predetermined abnormality that has occurred in the copying machine X or the fixing device 5 has occurred, the holding of the center core 55 by the drive motor is released and the center core is released. It is conceivable to make 55 a rotatable state. For example, the abnormality may be that a maintenance door for performing maintenance of the image forming unit 4 or the fixing device 5 provided in the copying machine X has been opened, or that the heating roller 53 in the fixing device 5 has a high temperature. It may be abnormal. Hereinafter, the latter case will be described as an example. In the former case, the opening / closing of the maintenance door may be interlocked with OFF / ON of a relay contact 78 described later.

FIG. 4 is a block diagram for explaining an example of the heating control unit 7 provided in the fixing device 5.
As shown in FIG. 4, the heating control unit 7 includes a CPU 71, an IGBT gate drive circuit 72, a gate power supply control circuit 73, an IGBT 74, a fixing high temperature detection circuit 75, a relay coil 76, relay contacts 77 and 78, a thermistor 79, a rotary. The control circuit includes an encoder 80 and the like.
In the heating control unit 7, the CPU 71 executes predetermined control processing (arithmetic processing) based on a control program and various parameters stored in a ROM or RAM (not shown) to control each component. Is done. The CPU 71 controls a heating operation in the fixing device 5 based on a control instruction from the control unit 6. Further, the processing function of the CPU 71 may be achieved by the control unit 6 and the CPU 71 may be omitted.

The rotary encoder 80 is mounted on the rotating shaft of the heating roller 53 and rotates in synchronization with the heating roller 53, and a photo interrupter that outputs a pulse signal in response to detection of each slit formed in the encoder. And the presence or absence of rotation of the heating roller 53 is detected. The detection result by the rotary encoder 80 is input to the CPU 71 and the gate power supply control circuit 73.
For example, when the rotary encoder 80 detects that the heating roller 53 is stopped, the CPU 71 performs control for rotating the fixing roller 51 by a predetermined driving unit. Therefore, it is determined that an abnormality has occurred in the transmission system of the driving force to the heating roller 53. At this time, the CPU 71 executes a process for displaying the fact on the operation display unit 1 and a process for stopping the input of the switching signal to the IGBT gate drive circuit 72.

On the other hand, the IGBT gate drive circuit 72 is a transistor, FET, IGBT, or the like, and switches whether or not a switching signal is input from the CPU 71 to the IGBT 74. The IGBT 74 is a switching means for performing a switching operation for switching whether or not a DC voltage supplied from a primary power supply (not shown) is supplied to the induction coil 54 in accordance with a switching signal input from the CPU 71. A transistor or FRT may be used instead of the IGBT 74.
The gate power supply control circuit 73 switches the establishment of the power supply path from a predetermined power supply to the IGBT gate drive circuit 72 according to the detection result input from the rotary encoder 80, thereby driving the IGBT gate drive. The presence or absence of a switching signal input to the IGBT 74 by the circuit 72 is switched. Specifically, the gate power control circuit 73 shuts off the power supply path to the IGBT gate drive circuit 72 on condition that the rotary encoder 80 detects that the heating roller 53 is stopped. The input of the switching signal to the IGBT 74 by the IGBT gate drive circuit 72 is stopped.
Therefore, in the fixing device 5, when the heating roller 53 is stopped due to some abnormality, the input of the switching signal from the IGBT gate drive circuit 72 to the IGBT 74 is stopped, and the power supply to the induction coil 54 is stopped. By being cut off, local abnormal heating of the heating roller 53 is prevented.

The thermistor 79 is a contact-type temperature sensor that detects the temperature of the heating roller 53 by bringing a heat-sensitive portion into contact with the outer peripheral surface of the heating roller 53. The detected temperature is detected by the CPU 71 and the fixing high-temperature detection circuit 75. To enter. The CPU 71 executes fixing temperature control for maintaining the temperature of the fixing belt 52 at a predetermined fixing temperature by controlling a switching signal output to the IGBT 74 based on the temperature detected by the thermistor 79.
On the other hand, the fixing high temperature detection circuit 75 determines whether or not the temperature of the heating roller 53 detected by the thermistor 79 has reached a preset upper set temperature or higher, and has reached the upper set temperature or higher. On the condition that the relay coil 76 is energized. The upper limit set temperature is set in advance as a temperature for detecting an abnormal heating state of the heating roller 53.
The relay coil 76 is a relay provided on a power supply path following the induction coil 54 from the primary power source (not shown) through the IGBT 74 in accordance with the presence or absence of energization controlled by the fixing high temperature detection circuit 75. ON / OFF of the contact 77 and the relay contact 78 provided on the power supply path following the connection switching mechanism is switched.

Specifically, the fixing high temperature detection circuit 75 cuts off the power supply to the induction coil 54 by cutting off the power supply to the relay coil 76 when the heating roller 53 is abnormally heated. Stop induction heating.
Further, when the heating roller 53 is abnormally heated, the fixing high temperature detection circuit 75 cuts off the power supply to the connection switching mechanism to release the connection between the drive motor and the transmission system, and the drive motor performs the connection. By releasing the holding of the center core 55, the center core 55 is brought into a rotatable state. Here, the fixing high temperature detection circuit 75 when performing such an operation corresponds to the holding release means.
As a result, the center core 55 is rotated by its own weight until a position where the magnetic flux to the heating roller 53 is shielded at the full width, that is, until the shielding portion D1 is located at a portion facing the heating roller 53, and the heating is performed. Induction heating of the roller 53 is prevented. Therefore, for example, even when an abnormality occurs in which the energization to the induction coil 54 is not interrupted, the heating roller 53 can be prevented from being abnormally heated, and the safety of the fixing device 5 can be improved. Of course, when the rotation of the heating roller 53 is stopped by the rotary encoder 80, the energization to the relay coil 76 is cut off to switch the relay contact 78 and the energization to the connection switching mechanism is cut off. It is possible.

In the second embodiment, another configuration example of the center core 55 will be described. In addition to the configuration described here, it is possible to decenter the center of gravity 55g by the outer peripheral shape of the center core 55 and to decenter the center of gravity 55g by the weight of the magnetic flux shielding plate 60.
FIG. 5 is a view for explaining a center core 155 which is another example of the structure of the center core 55. In addition, about the structure similar to the said center core 55, the same code | symbol is attached | subjected and the description is abbreviate | omitted.
As shown in FIG. 5, the center of gravity 55g is located between the rotation center 55c and the shielding part D1 at both ends of the center core 155, and the center core 155 is connected to the induction coil 54 and the heating coil. A weight 55d for decentering the center of gravity 55g of the center core 155 is provided so as to rotate by its own weight until the shielding portion D1 is interposed on the path of the magnetic flux between the rollers 53. The weight 55d is provided at a position deviated from the rotation center 55c of the center core 155 toward the shielding portion D1 at both end portions of the center core 155. The weight 55d may be provided only on one side end of the center core 155. The shape of the weight 55d is not particularly limited.

In such a configuration, the center of gravity 55g of the center core 155 is vertical as shown in FIGS. 5 (b) and 5 (c), as in the case of using the center core 55 described in the embodiment. If the center core 155 becomes rotatable due to an abnormality in the core rotation mechanism without being positioned in the downward direction, the center core 155 is separated from the center of rotation 55c and the center of gravity 55g. The center of gravity 55g is rotated by the rotational force generated by That is, the center core 155 rotates by its own weight until the shielding part D1 is interposed on the magnetic flux path between the induction coil 54 and the heating roller 53.
Accordingly, since the magnetic flux that should act on the entire width of the heating roller 53 is shielded by the shielding portion D1, induction heating of the heating roller 53 is forcibly blocked, and overheating of the heating roller 53 can be prevented. it can.

1 is a block diagram showing a schematic configuration of a copier according to an embodiment of the present invention. 1 is a schematic diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. FIG. 4 is a schematic diagram for explaining a structure of a center core provided in the fixing device according to the embodiment of the present invention. The block diagram for demonstrating an example of a heating control part. The figure for demonstrating the other structural example of a center core.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Operation display part 2 ... Image reading part 3 ... Image processing part 4 ... Image forming part 5 ... Fixing device 6 ... Control part 50 ... Paper conveyance path 51 ... Fixing roller 51a ... Pressure roller 52 ... Fixing belt 53 ... Heating roller 54 ... induction coils 55, 155 ... center core 55a ... outer peripheral surface 55b ... hollow portion 55c ... rotation center 55d ... weight 55g ... center of gravity 56 ... outer core 60 ... magnetic flux shielding plate D0 ... non-shielding portions D1-D3 ... shielding portion X ... Copier

Claims (7)

A magnetic flux shield for generating a magnetic flux for inductively heating the member to be heated, and a shielding width for shielding the magnetic flux path depending on a portion interposed on the magnetic flux path between the induction coil and the member to be heated. And a magnetic flux width changing means for changing the width of the magnetic flux path by rotating the magnetic flux shielding member by a predetermined driving means to change a part of the magnetic flux shielding member interposed on the magnetic flux path. A fixing device comprising:
The magnetic flux shielding member is provided with at least a full width shielding portion in which the shielding width of the magnetic flux path is the full width of the heated member,
When the magnetic flux shielding member becomes rotatable, the magnetic flux shielding member is rotated by its own weight until the full width shielding portion is interposed on the magnetic flux path between the induction coil and the heated member. The fixing device is characterized in that the position of the center of gravity of the magnetic flux shielding member and the position of the full width shielding portion in the magnetic flux shielding member are determined. The induction coil and the magnetic flux shielding member are arranged vertically above the heated member,
The fixing device according to claim 1, wherein the magnetic flux shielding member is eccentric so that a center of gravity is located between a rotation center of the magnetic flux shielding member and the full width shielding portion.   The magnetic flux shielding member is provided on a magnetic core forming a magnetic circuit between the induction coil and the member to be heated, and an outer peripheral surface of the magnetic core, and between the induction coil and the member to be heated. 3. The fixing device according to claim 1, further comprising: a magnetic flux shielding plate having a different shielding width that shields the magnetic flux path by a portion interposed on the magnetic flux path.   The fixing device according to claim 3, wherein the center of gravity of the magnetic flux shielding member is eccentric by a hollow portion provided inside the magnetic core.   The fixing device according to claim 3, wherein the center of gravity of the magnetic flux shielding member is decentered by weights provided at one or both side end portions of the magnetic core.   A predetermined abnormality has occurred in the holding unit that holds the magnetic flux shielding member in a position after being rotated by the predetermined driving unit, and the fixing device and / or the image forming apparatus in which the fixing device is mounted. 6. The apparatus according to claim 1, further comprising holding release means for releasing the holding of the magnetic flux shielding member by the holding means to make the magnetic flux shielding member rotatable. Fixing device.   An image forming apparatus comprising the fixing device according to claim 1.

Images