JP2010091592A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing a drastic change in magnetic flux upon changing the width of the magnetic flux applied from an induction coil to a member to be heated, and to provide an image forming apparatus. <P>SOLUTION: Regarding a magnetic flux shielding plate 60 for shielding the magnetic flux path between the induction coil and the member to be heated, an opening for magnetic flux leakage 61 for gradually changing the magnetic flux to be applied from the induction coil to the member to be heated upon changing two adjacent shielding parts D1 and D2 is formed on the side of the shielding part D2 whose shielding width from a boundary P between the shielding parts D1 and D2 is larger than that of the shielding part D1, and in an area corresponding to the shielding width difference between the two adjacent shielding parts D1 and D2. Concretely, the opening for magnetic flux leakage 61 is a plurality of slits 61a to 61c whose length in a direction advancing from the boundary P toward the shielding part D2 having the larger shielding width, and also, whose length in the width direction of the member to be heated become gradually smaller. <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 describes 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 rotating an arc-shaped magnetic flux shielding plate having a plurality of stages of shielding portions with different widths.
JP-A-2005-208624

However, when the shielding width of the magnetic flux from the induction coil to the heated member is changed by moving the magnetic flux shielding plate and switching the shielding portion, if the magnetic flux changes abruptly, on the energizing circuit to which the induction coil is connected, There is a possibility that a counter electromotive voltage is generated and an overcurrent flows.
Therefore, the present invention has been made in view of the above circumstances, and its object is to prevent a sudden change in magnetic flux when changing the width of the magnetic flux acting on the member to be heated from the induction coil. Another object of the present invention is to provide a fixing device and an image forming apparatus that can be used.

To achieve the above object, the present invention provides an induction coil for generating a magnetic flux for induction heating of a member to be heated, and a plurality of different shielding widths for shielding a magnetic flux path between the induction coil and the member to be heated. A magnetic flux shielding member having a shielding portion and a magnetic flux width for changing a width of the magnetic flux path by moving the magnetic flux shielding member by a predetermined driving means and changing the shielding portion interposed on the magnetic flux path The magnetic flux shielding member is on the shielding portion side having a larger shielding width from the boundary between the two adjacent shielding portions. In order to gradually change the magnetic flux acting on the member to be heated from the induction coil when the two shielding portions are changed by the magnetic flux width changing means in the region corresponding to the difference in shielding width between the two shielding portions. Magnetism Configured as a fixing device, characterized in that in which the leakage opening is formed.
As a result, when the shielding width for shielding the magnetic flux path between the induction coil and the heated member is changed by moving the magnetic flux shielding member and switching the shielding portion, the change is performed slowly. Therefore, it is possible to suppress the occurrence of back electromotive force on the energization circuit to which the induction coil is connected, and to prevent overcurrent.

Specifically, the magnetic flux leakage opening includes a plurality of magnetic fluxes that gradually decrease in length in the same direction or in the width direction of the heated member in a direction from the boundary toward the shielding portion having the large shielding width. It may be a leakage slit. Thereby, when the magnetic flux shielding member is moved, a sudden change in magnetic flux can be prevented by gradually changing the amount of magnetic flux leaking from the magnetic flux leakage opening.
Further, for example, the magnetic flux shielding member is provided on the outer peripheral surface of a cylindrical magnetic core that forms a magnetic circuit between the induction coil and the heated member. In this case, it is conceivable that the predetermined driving means rotates the magnetic flux shielding member by rotating the magnetic core.
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 shielding width for shielding the magnetic flux path between the induction coil and the heated member is changed by moving the magnetic flux shielding member and switching the shielding portion, the change is slow. Therefore, the generation of back electromotive force on the energization circuit to which the induction coil is connected can be suppressed, and overcurrent can be prevented.

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. It is a schematic diagram for demonstrating the magnetic flux shielding board 60 provided in the fixing apparatus 5 which concerns on embodiment of this 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 relating to the fixing device 5 and will be described in detail below with reference to FIGS.

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, a center core 55 (an example of a magnetic core) that forms a magnetic circuit that guides the magnetic flux generated by the induction coil 54 to the heating roller 53, and 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.

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 substantially the same width as that of the heating roller 53 in the same manner as the induction coil 54. Has been. The center core 55 and the outer core 56 form a magnetic circuit (see a thick arrow in FIG. 2) that guides the magnetic flux generated by the induction coil 54 to the heating roller 53.
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 the surface of the heating roller 53 is swirled. When the 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.

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.
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.

On the other hand, 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 a magnetic member is provided between the outer core 56 and the heating roller 53. A circuit is formed. The center core 55 is rotatably supported by a core rotation mechanism (not shown) that drives the center core 55 to rotate independently of the heating roller 53.
The core rotation mechanism (not shown) includes a transmission system such as a rotation shaft and a gear connected to the center core 55, and a drive system such as a stepping motor and a servo motor connected to the rotation shaft and the gear. Yes. The presence / absence of drive of the core rotation mechanism (not shown), the drive amount, and the like are controlled by the control unit 6 and the like. Specifically, when a stepping motor that rotates by a predetermined amount according to the number of steps input is used as the drive system, the rotation amount of the center core 55 can be controlled by the number of steps input to the stepping motor. it can.

Further, in the fixing device 5, the longitudinal width of the heating roller 53 changes in a plurality of stages on the outer peripheral surface of the center core 55 on the path of the magnetic flux acting on the heating roller 53 from the induction coil 54. A magnetic flux shielding plate 60 (an example of a magnetic flux shielding member) having a shape is provided.
The magnetic flux shielding plate 60 is made of a material such as silver, copper, or aluminum that shields the magnetic flux, and rotates when the center core 55 is rotated by the core rotating mechanism (not shown). Here, the core rotating mechanism (not shown) is an example of a predetermined driving unit that rotates and moves the magnetic flux shielding plate 60. As another embodiment, the magnetic flux shielding plate 60 is rotatably supported independently of the center core 55 and is rotated by a predetermined drive motor (an example of a predetermined drive means).

Here, the magnetic flux shielding plate 60 will be described with reference to FIG. 3A is a perspective view of the center core 55 and the magnetic flux shielding plate 60, and FIG. 3B is a development view of the magnetic flux shielding plate 60. FIG.
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.
As shown in FIG. 3, the magnetic flux shielding plate 60 has shielding portions D1, D2 (shaded portions in FIG. 3) having different positions and widths that shield the magnetic flux path from the center core 55 to the heating roller 53. is doing. Here, the shielding portions D1 and D2 are adjacent to each other across the boundary P in the circumferential direction of the center core 55. In the fixing device 5, since the sheet passing through the fixing device 5 is passed along the center of the fixing belt 52, the magnetic flux shielding plate 60 is connected to the center core 55. It is divided into left and right.
Each of the shielding portions D1 and D2 corresponds to the case where the size of the paper passing through the fixing device 5 is A3 and A5, respectively, and acts on the width corresponding to the passage area of the paper. The magnetic flux outside the paper passage area is shielded. Here, for convenience of explanation, the case where the magnetic flux shielding plate 60 is provided with two-stage shielding portions D1 and D2 corresponding to the A3 and A5 sizes will be described as an example. In order to realize the change of the width, a configuration in which more shielding portions are provided may be used. For example, it is conceivable that a shielding portion corresponding to each paper size used in the copying machine X is provided. Furthermore, the shielding width of each shielding part is not limited to the one corresponding to the paper size, and may be any predetermined size.

Further, when the magnetic flux shielding plate 60 is rotated to switch the shielding portions D1 and D2, if the width of the magnetic flux acting on the heating roller 53 from the induction coil 54 changes abruptly, the induction coil 54 is connected. A back electromotive voltage may be generated on the energizing circuit, and overcurrent may flow.
Therefore, as shown in FIG. 3, the magnetic flux shielding plate 60 is arranged on the side of the shielding part D2 having a larger shielding width from the boundary P between the two shielding parts D1 and D2 adjacent to each other. In the region R corresponding to the difference in the shielding width between the two shielding parts D1 and D2, the induction coil 54 acts on the heating roller 53 when the control part 6 changes the two shielding parts D1 and D2. A magnetic flux leakage opening 61 for gradually changing the magnetic flux is formed. In the configuration in which the magnetic flux shielding plate 60 further includes a multi-stage shielding portion, the magnetic flux leakage opening is provided on each of the multi-stage shielding portions from the boundary between two adjacent shielding portions to the shielding portion having a large shielding width. 61 is provided.
The magnetic flux leakage opening 61 has the same length in the width direction of the heating roller 53, but a plurality of slits whose length in the same direction gradually decreases in the direction from the boundary P toward the shielding portion D2. 61a, 61b, 61c (an example of a magnetic flux leakage slit). The slits 61 a to 61 c are rectangular openings whose longitudinal direction is the axial direction of the center core 55. The magnetic flux leakage opening 61 may be, for example, a circular hole or a slit formed in an oblique direction.

In the copying machine X configured as described above, the shield part D1, D2 of the magnetic flux shield plate 60 is interposed in the facing part where the heating roller 53 and the center core 55 are closest to each other. By rotating the magnetic flux shielding plate 60, it is possible to change the position and width of the path of the magnetic flux acting from the center core 55 to the heating roller 53, that is, the heating target area of the heating roller 53. At this time, the magnetic flux shielding plate 60 is rotated so that one of the centers C1 and C2 (see FIG. 3B) of the shielding portions D1 and D2 is located at a portion facing the heating roller 53.
Specifically, in the copying machine X, the control unit 6 includes a temperature sensor (not shown) that detects the size of the sheet on which image formation is performed, the toner transfer area on the sheet, and the temperature of the heating roller 53. Depending on the detection result and the like, the core rotating mechanism (not shown) rotates the center core 55 to rotate the magnetic flux shielding plate 60, thereby shielding the magnetic roller on the path of the magnetic flux to the heating roller 53. The magnetic flux width changing process for changing the part to any one of the shielding parts D1 and D2 is executed. Thereby, the width of the path of the magnetic flux acting on the heating roller 53 from the center core 55, that is, the heating target area of the heating roller 53 is changed. The said control part 6 when performing the magnetic flux width change process which concerns here corresponds to a magnetic flux width change means.

At this time, in the fixing device 5, when the magnetic flux width changing process is executed by the control unit 6, the magnetic flux shielding plate 60 is rotated, and the magnetic flux path from the induction coil 54 to the heating roller 53. When the shielding portions D1 and D2 of the magnetic flux shielding plate 60 interposed above are switched, the amount of magnetic flux shielded by the magnetic flux shielding plate 60 is gradually changed by the slits 61a to 61c formed in the region R. Will do. Specifically, when switching from the shielding part D1 to the shielding part D2, the magnetic flux leaking from the magnetic flux leakage opening 61 in the region R and acting on the heating roller 53 gradually decreases, and conversely, the shielding part At the time of switching from D2 to the shielding part D1, the magnetic flux acting on the heating roller 53 gradually increases.
Therefore, the back electromotive force generated on the energization circuit of the induction coil 54 at the time of switching between the shielding portions D1 and D2 can be suppressed, and an overcurrent on the energization circuit can be prevented.

Here, the case where the magnetic flux leakage opening 61 has the three slits 61a to 61c is described as an example. However, a configuration having a large number of slits that become smaller in multiple stages may be used.
The slits 61 a to 61 c of the magnetic flux leakage opening 61 gradually decrease in length in the direction from the boundary P toward the shielding part D <b> 2, but the present invention is not limited to this. The length in the width direction may gradually decrease.
Furthermore, the slits 61a to 61c are gradually reduced in length in the direction from the boundary P toward the shielding part D2 and in the width direction of the heating roller 53. Also good.

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 magnetic flux shielding member provided in the fixing device according to the embodiment of the present invention.

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 coil 55 ... center core (an example of a magnetic core)
56 ... Outer core 60 ... Magnetic flux shielding plate (an example of magnetic flux shielding member)
61 ... Magnetic flux leakage openings 61a to 61c ... Slit (an example of magnetic flux leakage slit)
D1, D2 ... shielding part X ... copying machine (an example of an image forming apparatus)

Claims (4)

An induction coil that generates a magnetic flux for induction heating the member to be heated, a magnetic flux shielding member having a plurality of shielding portions with different shielding widths that shield a magnetic flux path between the induction coil and the member to be heated, and a predetermined A fixing device comprising: a magnetic flux width changing means for changing the width of the magnetic flux path by moving the magnetic flux shielding member by the driving means to change the shielding portion interposed on the magnetic flux path;
In the region corresponding to the difference in the shielding width between the two shielding portions, the magnetic flux shielding member is on the shielding portion side having a large shielding width from the boundary between the two shielding portions adjacent to each other. A fixing device having a magnetic flux leakage opening for gradually changing the magnetic flux acting on the member to be heated from the induction coil when the two shielding portions are changed by the magnetic flux width changing means. .   A plurality of magnetic flux leaks in which the magnetic flux leakage opening gradually decreases in length in the same direction and / or in the width direction of the heated member in a direction from the boundary toward the shielding portion having the large shielding width. The fixing device according to claim 1, wherein the fixing device is a slit for use. The magnetic flux shielding member is provided on an outer peripheral surface of a cylindrical magnetic core that forms a magnetic circuit between the induction coil and the heated member;
The fixing device according to claim 1, wherein the predetermined driving unit is configured to rotate the magnetic flux shielding member by rotating the magnetic core.   An image forming apparatus comprising the fixing device according to claim 1.

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