JP2008003473A - Image forming apparatus and fixing device used for it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which a coil is cooled inexpensively in a space-saving manner and fixing efficiency can be increased as a result, and to provide a fixing device used for it. <P>SOLUTION: The image forming apparatus has an image forming part forming a toner image and transferring it to a sheet and a fixing part fixing the toner image transferred to the sheet by heating, wherein the fixing part is provided with a cylindrical heating roller 21, an exciting coil 31 applying a magnetic field to the heating roller 21, a giant magnetostrictive element 34 generating mechanical driving force by receiving the magnetic field generated by the exciting coil 31 and a fin 33 rocked by receiving force from the giant magnetostrictive element 34. The giant magnetostrictive element 34 extends/contracts by the magnetic field, thereby a free end of the fin 33 is rocked as in fanning. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and an induction heating type fixing device used therefor. More specifically, the present invention relates to an image forming apparatus that prevents overheating of a coil and a fixing device used therefor.

  In the induction heating type fixing device, an alternating magnetic field is generated by applying an alternating voltage to the coil of the coil unit. The generated magnetic field causes eddy currents to be generated in the heat generation target according to the electromagnetic induction law. As a result, the heat generation target generates Joule heat. The induction heating type fixing device can intensively generate heat to be generated by the above mechanism. From this, it is generally known that the warm-up time is short and the followability of the control is good.

  For alternating current, the coil exhibits a large resistance value due to the skin effect. On the other hand, the electrical resistance can be reduced by using a thin wire having a large surface area. Nevertheless, heat is unavoidable due to the electrical resistance of the coil conductor itself. When the coil generates heat, the resistance further increases. For this reason, when the coil generates heat, the heat generation amount of the heat generation target is reduced accordingly, and the efficiency of the fixing device is lowered.

Conventionally, there is a method of cooling with a fan or the like in order to suppress the temperature rise of the coil. For example, Patent Document 1 discloses a technique in which a coil unit is provided outside a heating roller and cooled by an air cooling fan or a heat radiating fin. Patent Document 2 discloses a technique for cooling a coil by passing a cooling pipe through a litz wire and circulating a refrigerant.
JP 2002-116644 A JP 2003-84588 A

  However, the conventional techniques described above have the following problems. As in Patent Document 1, in order to provide a fan around the fixing device, a space for the fan and a duct for guiding the wind without impairing the air volume and the wind pressure as much as possible are necessary. For this reason, there is a problem that the apparatus becomes larger. In addition, a control unit for appropriate control and a harness for supplying power to the fan are required, which is not preferable because it causes high costs. Further, the technique of Patent Document 2 has a problem that the fixing unit is enlarged although the cooling effect is high.

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide an image forming apparatus that can cool a coil and increase the fixing efficiency in a space-saving and low-cost manner, and a fixing device used therefor.

  In order to solve this problem, an image forming apparatus according to the present invention includes an image forming unit that forms a toner image and transfers the toner image onto a sheet, and a fixing unit that fixes the toner image transferred onto the sheet by heating. The fixing unit includes a cylindrical heating conductor, an excitation coil that applies a magnetic field to the heating conductor, and a driving member that generates a mechanical driving force by receiving the magnetic field generated by the excitation coil And an oscillating member that oscillates by receiving a force from the driving member.

  According to the image forming apparatus of the present invention, the fixing unit applies a magnetic field to the heat generating conductor by the exciting coil, and the heat generating conductor generates heat. Furthermore, a mechanical driving force is generated by the driving member in response to the magnetic field generated by the exciting coil. Examples of such a drive member include a magnetostrictive element that extends due to a magnetic field and a permanent magnet that is attracted by a magnetic field. In general, since the voltage applied to the exciting coil of the fixing unit is an alternating voltage, the driving force of the driving member is a reciprocating driving force. The swing member is swung by receiving this reciprocating drive force. Therefore, it is not necessary to add a new driving device for driving the driving member, and the coil can be cooled in a small space and at a low cost.

  Furthermore, in the present invention, the swinging member has one end as a fixed end and the other end as a free end, and receives a force from the drive member at a position between the fixed end and the free end, and the free end swings. It is desirable to be. In this way, the free end of the rocking member performs an air blowing operation. Accordingly, wind is generated from the rocking member, whereby the exciting coil can be cooled.

Furthermore, in the present invention, the driving member is preferably a magnetostrictive element. The magnetostrictive element expands and contracts in the direction upon receiving a magnetic field. Therefore, the swing member can be swung by using the expansion / contraction force as a mechanical driving force.
Alternatively, in the present invention, the driving member may be a ferromagnetic material. Ferromagnetic materials are attracted and separated by a magnetic field. Therefore, the swing member can be swung using this magnetic force as a mechanical driving force.

  Furthermore, in the present invention, the magnetic path of the magnetic flux passing outside the exciting coil is formed, the outer core is located outside the heat generating conductor and has a gap, and the exciting coil, the oscillating member, and the driving member are heated. The direction that is located between the outer surface of the body and the outer core and connects the fixed end of the swinging member and the free end is the direction that intersects the axial direction of the heat generating conductor. It is desirable that a part of the exciting coil is disposed in front of the heading direction. By doing so, air is caused to flow in the direction intersecting the axial direction of the heat generating conductor by the swing of the free end of the swing member, and is exchanged with the external air through the gap of the outer core. In addition, since a part of the exciting coil is arranged immediately leeward of the swing member, the exciting coil is efficiently cooled.

  Alternatively, in the present invention, the exciting coil, the swinging member, and the driving member are located inside the heat generating conductor, and the direction connecting the fixed end and the free end of the swinging member is parallel to the axial direction of the heat generating conductor. It may be a thing. In the case where the exciting coil, the swinging member, and the driving member are located inside the heat generating conductor, air hardly flows in the direction intersecting the axial direction of the heat generating conductor. Thus, by doing so, air can flow in parallel with the axial direction of the heat generating conductor.

  Furthermore, in the present invention, it is preferable that the inner core has a magnetic path of magnetic flux passing through the inside of the exciting coil, and the fixed end of the swing member is attached to the end face of the inner core. In this way, the magnetic field generated by the exciting coil can be reliably received, and a part of the exciting coil is disposed in front of the free end.

  Furthermore, in the present invention, it is desirable to have a voltage application unit that applies a voltage in which a high frequency voltage and a low frequency voltage are superimposed on the excitation coil. When the responsiveness of the driving member is lower than the frequency of the high frequency voltage, the driving member can be driven by the low frequency voltage in this way.

  The present invention is also a fixing device for fixing a toner image transferred on a sheet by heating, and includes a cylindrical heating conductor, an excitation coil for applying a magnetic field to the heating conductor, and an excitation coil. The present invention also extends to a fixing device having a driving member that generates a mechanical driving force by receiving a magnetic field and a swinging member that swings by receiving a force from the driving member.

  According to the image forming apparatus of the present invention and the fixing device used therefor, the coil can be cooled and the fixing efficiency can be increased in a space-saving and low-cost manner.

"First form"
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus using an induction heating type fixing device.

  In the image forming apparatus 1 of this embodiment, as shown in FIG. 1, image forming portions 10Y, 10M, 10C, and 10K for Y, M, C, and K colors are arranged along the intermediate transfer belt 11. In the image forming units 10Y, 10M, 10C, and 10K for the respective colors, toner images of the respective colors are formed and transferred onto the intermediate transfer belt 11 in an overlapping manner. Further, a recording medium is supplied from the paper supply unit 12, and the superimposed toner images are transferred to the recording medium by the secondary transfer device 13. The toner image transferred to the recording medium is fixed by being heated and pressed by the fixing device 14. The recording medium on which the image is fixed is discharged out of the apparatus by the paper discharge device 15. In this embodiment, any part other than the fixing device 14 may be a general device, and is not limited to the shape shown in the drawing.

  As shown in FIG. 2, the fixing device 14 of this embodiment includes a heating roller 21 and a pressure roller 22. A heating device 30 is provided in close proximity to the heating roller 21, and the heating roller 21 is heated by the heating device 30. Moreover, it has the voltage application part 23 for applying a voltage to the heating apparatus 30. FIG.

  Here, only the heat generating layer 21a is shown as the heating roller 21, but a metal core, an elastic layer, or the like may be further provided. Further, a release layer or the like may be provided on the outer periphery of the heat generating layer 21a. The heating layer 21a of the heating roller 21 is preferably formed of a material having high magnetic permeability and low resistance. Further, although the pressure roller 22 is illustrated as having the elastic layer 22b provided on the outer periphery of the cored bar 22a, a release layer or the like may be provided on the outer periphery of the elastic layer 22b. Hereinafter, the rotation axis direction (the depth direction in FIG. 2) of the heating roller 21 is simply referred to as an axial direction.

  The heating device 30 includes an exciting coil 31 and a magnetic core 32 as shown in FIG. The exciting coil 31 has a long and thin conductive wire wound in the axial direction. Generally, the exciting coil 31 is a litz wire formed by bundling copper thin wires within a range of several tens to several hundreds. Further, the excitation coil 31 is connected to a voltage application unit 23 such as a high frequency inverter, and high frequency power of 100 W to 2000 W is supplied.

  The magnetic core 32 is made of ferrite having high magnetic permeability and high electrical resistance. As shown in FIG. 2, the magnetic core 32 is formed in a polygonal shape or a curved shape approximately along the outer shape of the heating roller 21, and a convex portion 32 a toward the central axis of the heating roller 21 is provided at the center. ing. The magnetic core 32 is divided into a plurality of ribs in the axial direction as shown in FIG. 3 as viewed from above in FIG. In addition, there is a certain gap between the ribs. Furthermore, the ribs are densely arranged near both ends and roughly arranged near the center.

  Further, in the heating device 30 of this embodiment, as shown in FIG. 2, the fin 33 and the giant magnetostrictive element 34 are provided at the lower end of the convex portion 32 a of the magnetic core 32, that is, near the center of the winding of the exciting coil 31. It has been. The fins 33 are formed of a non-magnetic material, a high resistance material, a laminated material, or the like, and are substantially U-shaped (U-shaped falling to the right) and are long members in the axial direction. The upper side of the fin 33 in the figure is fixed in close contact with the convex portion 32 a of the magnetic core 32. On the other hand, the lower side of the fin 33 in the figure is slightly longer in the right direction in the figure than the upper side and is not fixed. Accordingly, at the lower side of the fin 33 in the figure, the left end in the figure is a fixed end and the right end in the figure is a free end.

  The giant magnetostrictive element 34 is formed of a member that extends in the direction of the magnetic field when it receives a magnetic field, such as a Tb-Fe alloy or a Dy-Fe alloy. The giant magnetostrictive element 34 is disposed between the upper and lower sides of the fin 33 and bonded to the inside of both sides. Accordingly, when the giant magnetostrictive element 34 expands and contracts in the vertical direction in FIG. 2, the distance between the sides of the fin 33 is opened and closed. Since the upper side of the fin 33 in the figure is fixed, the free end side of the lower side in the figure is swung by the expansion and contraction of the giant magnetostrictive element 34. Note that the position of the giant magnetostrictive element 34 with respect to the lower side of the fin 33 in the horizontal direction in FIG. 2 is preferably a position where the vibration of the fin 33 excited by the giant magnetostrictive element 34 does not become a standing wave vibration.

  Next, the fixing operation in the fixing device 14 of the present embodiment will be described. The excitation coil 31 is applied with an alternating voltage having a predetermined frequency and amplitude by the voltage application unit 23. And it is excited by the electric current by it and generates a magnetic force line W as shown by a thick line in FIG. The magnetic core 32 captures the magnetic lines of force W generated by the exciting coil 31 and guides it to the heating roller 21. At this time, since the resistance of the magnetic core 32 is sufficiently high, almost no eddy current is generated. On the other hand, an eddy current is generated in the heat generating layer of the heating roller 21, and heat is generated by Joule heat. Similarly, the exciting coil 31 also generates heat slightly due to Joule heat.

  The recording medium P on which the toner image is formed is conveyed to the nip between the heating roller 21 and the pressure roller 22 as shown in FIG. The recording medium P is sandwiched in the nip so that the toner image faces the heating roller 21. As a result, the toner image is heated and pressurized and fixed to the recording medium P. The recording medium P that has been subjected to the fixing process at the nip is separated from the fixing device 14 and carried out.

  At this time, the lines of magnetic force W generated by the exciting coil 31 are strong alternating magnetic fields. Since the giant magnetostrictive element 34 has good response to a magnetic field, it is expanded and contracted in the vertical direction in FIG. 2 by this high frequency alternating magnetic field. Thereby, both sides of the fin 33 are opened and closed, and the free end of the fin 33 is swung. That is, the giant magnetostrictive element 34 drives the fin 33 at a frequency twice that of the alternating magnetic field.

  The movement of the fin 33 by the giant magnetostrictive element 34 is similar to the fanning operation, and this causes an air flow from the free end of the fin 33 to the right in FIG. Since the fins 33 are disposed between the excitation coils 31, the generated wind is directly applied to the excitation coils 31 and takes heat from the excitation coils 31. Here, since the magnetic core 32 has gaps between the ribs as shown in FIG. 3, the air that has cooled the exciting coil 31 can flow out of the magnetic core 32. At the same time, outside air that has not yet been warmed is introduced. Thus, since the air flow is generated by the fins 33, the exciting coil 31 can be efficiently cooled. Note that since the fin 33 is formed of an insulator, no eddy current is generated.

  Here, the axial length of the fin 33 is preferably substantially the same as that of the exciting coil 31. Also, the giant magnetostrictive element 34 only needs to be able to move up and down over the entire axial direction of the fin 33, and may be slightly shorter than the fin 33. For example, as shown in FIG. 4, the giant magnetostrictive element 34 may be simply press-fitted while the fins 33 are bent, and it is not always necessary to bond them.

  Alternatively, in addition to fitting, as shown in FIGS. 5 and 6, a fin may be formed to hold the giant magnetostrictive element 34. In this way, there is no possibility that the giant magnetostrictive element 34 is displaced in the direction intersecting the axial direction even if it is not bonded. When not bonded in this manner, the fin 33 is opened by the extension of the giant magnetostrictive element 34 and closed by the elastic force of the fin 33 itself.

  Alternatively, as shown in FIG. 7, the fins 35 may be divided into a plurality of parts in the axial direction. This figure is a view from the bottom side in FIG. Further, as shown in FIG. 7, the both ends in the axial direction of the fin 35 can be fixed to the magnetic core 32 or a holding member for holding it by screwing. This point can also be applied to the fins 33 that are not divided. In this figure, the divided parts have the same size and are arranged at equal intervals. However, the heat radiation efficiency can be changed depending on the position in the axial direction by appropriately changing the size and interval.

  As described above in detail, according to the image forming apparatus 1 of the present embodiment, the fins 33 are provided inside the heating device 30 of the induction heating type fixing device 14. Further, the fin 33 is moved up and down by the giant magnetostrictive element 34 and its free end side is swung. Thereby, wind is raised and the exciting coil 31 is cooled. Here, since the giant magnetostrictive element 34 expands and contracts due to a magnetic field generated when the heating device 30 performs a heating operation, a separate driving device is not required. Therefore, the coil can be cooled and the fixing efficiency can be increased in a space-saving and low-cost manner. Further, since it is driven only during the heating operation of the fixing device 14, control by a control unit or the like is unnecessary.

"Second form"
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus using an induction heating type fixing device.

  As shown in FIG. 8, the fixing device of this embodiment includes a fin 41 and a ferromagnetic material 42 inside the heating device 40. The fin 41 is a plate member bent into a U-shape, and the upper side in the figure is fixed to the lower end part in the figure of the convex part 32 a of the magnetic core 32. The right side in FIG. 8 at the lower side of the figure is a free end, and a ferromagnetic body 42 such as a permanent magnet or a material having high permeability is fixed near the tip. In this embodiment, the giant magnetostrictive element 34 provided in the first embodiment is not provided. Other parts are the same as those in the first embodiment.

  It should be noted that the strength of the magnetic field is not uniform at the location where the ferromagnetic material 42 is disposed. That is, the closer to the convex portion 32a of the magnetic core 32, the stronger the magnetic field, and the farther away, the weaker the magnetic field. In FIG. 8, the ferromagnetic body 42 is attached to the lower surface of the fin 41 in the figure, but may be on the upper surface side, or a hole or the like may be provided in a part of the fin 41 and embedded therein. Good.

  In the fixing device 40 of this embodiment, when an alternating voltage is applied for heating, the ferromagnetic body 42 receives a force by the generated alternating magnetic field. That is, it is vibrated in the vertical direction in FIG. 8 because it is attracted or released according to the direction of the magnetic field. As a result, the fins 41 are swung, and a wind is generated because of the fan motion.

  In the configuration of this embodiment, due to the inertia of the ferromagnetic body 42, there is a possibility that sufficient amplitude of the fin 41 cannot be secured only by this alternating magnetic field. Therefore, in the present embodiment, the superimposed voltage as shown in FIG. That is, in addition to the high-frequency alternating voltage for heating, a voltage in which a low-frequency alternating voltage is superimposed is applied. In this way, at least oscillation due to the amplitude of the low frequency alternating voltage can be secured. In this case, the ratio of the amplitude between the high frequency voltage and the low frequency voltage may be always kept constant. In this way, an air volume proportional to the amount of heat generated by the exciting coil 31 can be obtained. Even after the fixing process is completed, the excitation coil 31 can be further cooled by applying only the low frequency voltage.

  As described above in detail, even in the image forming apparatus using the fixing device of the present embodiment, the coil can be cooled and the fixing efficiency can be increased at a low cost and at a low cost.

"Third form"
Hereinafter, a third embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an image forming apparatus using an induction heating type fixing device.

  As shown in FIG. 10, the fixing device of this embodiment is provided with a heating device 50 inside the heating roller 21. The heating device 50 includes an exciting coil 51 and a magnetic core 52. The magnetic core 52 of this embodiment is formed in conformity with the inner peripheral shape of the heating roller 21 and is housed inside the heating roller 21 together with the excitation coil 51. Further, the magnetic core 52 has a convex portion 52a formed at the central portion of the winding of the exciting coil 51, and a fin 53 and a giant magnetostrictive element 54 are attached to the tip portion (lower portion in the figure).

  Here, the heating roller 21 has a cylindrical shape and does not have a hole through which air can flow in the direction crossing the axial direction. Therefore, there is a possibility that a sufficient cooling effect cannot be obtained even if the fan is fanned in the direction crossing the axial direction as in the first and second embodiments. Therefore, in this embodiment, the fins 53 are arranged so that the free end side of the lower side of the U-shape is the front side in FIG. Thereby, an air flow can be caused in the axial direction. Furthermore, as shown in FIG. 11, a plurality of bent portions may be formed in the axial direction, and the giant magnetostrictive element 54 may be attached to each of the bent portions. As a result, a more reliable cooling effect can be obtained.

  As described above in detail, even in the image forming apparatus using the fixing device of the present embodiment, the coil can be cooled and the fixing efficiency can be increased at a low cost and at a low cost.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the giant magnetostrictive element 34 and the ferromagnetic body 42 are described as a single member in the axial direction, but may be divided into a plurality of members. As long as the fins 33 and 41 can be driven appropriately, the fins 33 and 41 may be provided in places in the axial direction. Moreover, as shown in FIG. 7, in the fin divided | segmented into the axial direction, you may form a reverse direction fin, for example by turns. In the third embodiment, a giant magnetostrictive element is used, but it can be driven in the same manner by attaching a ferromagnetic material to each fin portion. Furthermore, the present invention can be applied to a fixing device having a fixing belt.

It is sectional drawing which shows the image forming apparatus which concerns on this form. 1 is a cross-sectional view illustrating a fixing device according to a first embodiment. FIG. 2 is a plan view showing a fixing device. It is explanatory drawing which shows the example of how to attach a giant magnetostrictive element. It is explanatory drawing which shows the example of how to attach a giant magnetostrictive element. It is sectional drawing which shows the example of how to attach a giant magnetostrictive element. It is a perspective view which shows another example of the shape of a fin. It is sectional drawing which shows the fixing device which concerns on a 2nd form. It is explanatory drawing which shows the example of an applied voltage. It is sectional drawing which shows the fixing device which concerns on a 3rd form. It is a perspective view which shows another example of the shape of a fin.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10Y, 10M, 10C, 10K Image forming part 14 Fixing device 21 Heating roller 23 Voltage application part 31,51 Excitation coil 32,52 Magnetic body core 33,41,53 Fin 34,54 Giant magnetostrictive element 42 Ferromagnetic body

Claims (9)

In an image forming apparatus having an image forming unit that forms a toner image and transfers the toner image onto a sheet, and a fixing unit that fixes the toner image transferred onto the sheet by heating, the fixing unit includes:
A cylindrical heating conductor;
An exciting coil for applying a magnetic field to the heating conductor;
A driving member that receives a magnetic field generated by the exciting coil and generates a mechanical driving force;
An image forming apparatus comprising: a swinging member that swings by receiving a force from the driving member. The image forming apparatus according to claim 1, wherein the swing member is
One end is a fixed end and the other end is a free end;
Receiving a force from the drive member at a position between the fixed end and the free end;
An image forming apparatus, wherein the free end swings. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein the driving member is a magnetostrictive element. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein the driving member is a ferromagnetic material. The image forming apparatus according to claim 2,
A magnetic path of magnetic flux passing through the outside of the exciting coil, and an outer core with a gap located outside the heat generating conductor;
The exciting coil, the swinging member, and the driving member are located between an outer surface of the heat generating conductor and the outer core;
The direction connecting the fixed end and the free end of the swing member is a direction intersecting the axial direction of the heat generating conductor,
An image forming apparatus, wherein a part of the exciting coil is disposed in front of the swinging member in a direction from a fixed end toward a free end. The image forming apparatus according to claim 2,
The exciting coil, the swinging member, and the driving member are located inside the heat generating conductor;
An image forming apparatus, wherein a direction connecting the fixed end and the free end of the swing member is parallel to an axial direction of the heat generating conductor. In the image forming apparatus according to any one of claims 1 to 6,
An inner core that forms a magnetic path of magnetic flux passing through the inside of the exciting coil;
An image forming apparatus, wherein a fixed end of the swing member is attached to an end surface of the inner core. In the image forming apparatus according to any one of claims 1 to 7,
An image forming apparatus comprising: a voltage applying unit that applies a voltage in which a high frequency voltage and a low frequency voltage are superimposed on the excitation coil. In a fixing device for fixing a toner image transferred on a sheet by heating,
A cylindrical heating conductor;
An exciting coil for applying a magnetic field to the heating conductor;
A driving member that receives a magnetic field generated by the exciting coil and generates a mechanical driving force;
A fixing device having a swinging member that swings by receiving a force from the driving member.

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