JP2007133250A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device designed so as to prevent noise leakage, improve heat generation efficiency of a fixing body and prevent the adverse effect of a magnetic flux on a temperature detecting part. <P>SOLUTION: The magnetic flux generating body 3 of the fixing device includes a coil 31 and a magnetic body core 32 disposed so as to cover the coil 31. The magnetic body core 32 has such a shape that a face 51 opposite the temperature detecting part is located farther from the circumferential face of a fixing roller 1 than faces 52 opposite the coil. Accordingly, a magnetic flux generated by the coil 31 passes inside the magnetic body core 32 without leaking out, and further passes through the magnetic induction heat generation layer 13 of the fixing roller 1 without leaking out of the magnetic body core 32 from a space between the face 51 and the faces 52 and without passing though the temperature detecting part 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a laser printer, and a facsimile.

  Conventionally, as a fixing device, a fixing roller, a pressure roller in pressure contact with the fixing roller, an annular coil that is disposed outside the fixing roller and generates magnetic flux to generate heat from the fixing roller, and the fixing Some include a temperature detection unit that detects the temperature of the roller (see JP 2003-86344 A).

  The coil is disposed along the outer surface of the fixing body, and the temperature detection unit is disposed outside the fixing body so as to overlap the hole of the coil.

However, in this conventional fixing device, since there is no member covering the outside of the coil, the magnetic flux generated from the coil leaks to the outside, causing noise and reducing the heat generation efficiency of the fixing roller. . In addition, due to the influence of noise leaking from the coil, the temperature detection unit has been adversely affected by heat generation and the inability to detect an accurate temperature, or by causing a malfunction.
JP 2003-86344 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that prevents noise leakage, improves the heat generation efficiency of the fixing body, and prevents the adverse effects of magnetic flux on the temperature detection unit.

In order to solve the above-described problems, a fixing device according to the present invention includes a rotatable fixing member, a pressure member that presses against the fixing member, an outer side of the fixing member, and generates a magnetic flux to generate the fixing member. A magnetic flux generator that generates heat, and a temperature detector that detects the temperature of the fixing body,
The magnetic flux generator has an annular coil disposed along the outer surface of the fixing body, and a magnetic core disposed on the opposite side of the fixing body with respect to the coil so as to cover the coil.
The temperature detection unit is disposed between the fixing body and the magnetic core at a position overlapping the hole of the coil,
In the cross section orthogonal to the rotation axis of the fixing body, the magnetic core has a position where the temperature detecting portion facing surface facing the temperature detecting portion is farther from the outer surface of the fixing body than the coil facing surface facing the coil. It is formed in the shape which becomes.

  According to the fixing device of the present invention, since the magnetic flux generator has a magnetic core disposed so as to cover the coil, the magnetic core can prevent leakage of magnetic flux generated from the coil. In addition to preventing the generation of noise, the heat generation efficiency of the fixing body can be improved.

  In the cross section perpendicular to the rotation axis of the fixing body, the magnetic core has a temperature detecting portion facing surface facing the temperature detecting portion farther from the outer surface of the fixing body than a coil facing surface facing the coil. The magnetic flux flowing through the magnetic core is formed between the temperature detecting portion facing surface and the coil facing surface, which is a point far from the outer surface of the fixing body in the magnetic core. Therefore, the magnetic flux density at the center position of the hole of the coil can be reduced by flowing in the direction of the fixing body. For this reason, the magnetic flux passing through the temperature detection unit in the hole of the coil is reduced, and the adverse effect of the magnetic flux on the temperature detection unit is reduced, and the heat generation efficiency of the fixing body can be kept high. .

  Therefore, noise leakage is prevented, the heat generation efficiency of the fixing body is improved, and adverse effects due to the magnetic flux on the temperature detection unit are prevented.

  In the fixing device according to the embodiment, the temperature detection unit is arranged to have a length in the rotation axis direction of the fixing body.

  According to the fixing device of this embodiment, the temperature detection unit is arranged to have a length in the rotation axis direction of the fixing body, so that the temperature measurement region having a relatively large area is secured while the temperature detection unit is secured. The distance between the outer surface of the fixing body and the temperature detection unit can be accurately maintained.

  Further, in the fixing device according to an embodiment, the coil-facing surface of the magnetic core and the fixing body at the central position in the width direction in the rotation direction of the fixing body of the coil in a cross section orthogonal to the rotation axis of the fixing body. The distance between the outer surface and the outer surface of the fixing body is b, and the distance between the outer surface of the fixing body and the temperature detecting portion facing surface of the magnetic core at the center position in the width direction of the fixing member rotating direction of the fixing member is b. Then, b / a is 1.2 or more and 2.0 or less.

  According to the fixing device of this embodiment, since b / a is 1.2 or more and 2.0 or less, it is possible to reduce the size of the device while reducing the flow of magnetic flux into the temperature detection unit. it can. That is, if it is less than the lower limit value, the flow of magnetic flux into the temperature detection unit cannot be reduced, and if it exceeds the upper limit value, the apparatus becomes large.

  In one embodiment, the temperature detecting portion facing surface of the magnetic core is a curved surface that is concave on the opposite side of the temperature detecting portion.

  According to the fixing device of this embodiment, the temperature detecting portion facing surface of the magnetic core is a curved surface that is concave on the side opposite to the temperature detecting portion. Further away from the outer surface, it is possible to further reduce the flow of magnetic flux to the temperature detection unit and to secure a wide space for arranging the temperature detection unit.

  In one embodiment, the magnetic core has a protrusion that extends from between the temperature detection unit facing surface and the coil facing surface to between the temperature detection unit and the coil.

  According to the fixing device of this embodiment, the magnetic core has a protruding portion that extends from between the temperature detecting portion facing surface and the coil facing surface to between the temperature detecting portion and the coil. The magnetic flux flowing through the magnetic core can be guided to the fixing member side through the protrusion. Accordingly, the flow of magnetic flux to the temperature detection unit can be further reduced.

  According to the fixing device of the present invention, the magnetic core has a magnetic core disposed so as to cover the coil, and the magnetic core has a surface facing the temperature detection unit that is closer to the outer surface of the fixing body than the surface facing the coil. Since it is formed in a shape at a distant position, noise leakage is prevented, the heat generation efficiency of the fixing body is improved, and adverse effects due to magnetic flux on the temperature detection unit are prevented.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

(First embodiment)
FIG. 1 is a sectional view showing a first embodiment of a fixing device according to the present invention. The fixing device is disposed outside the fixing roller 1 and generates a magnetic flux while being disposed outside the fixing roller 1 as a rotatable fixing member, a pressure roller 2 as a pressure member in pressure contact with the fixing roller 1, and the fixing roller 1. And a magnetic flux generator 3 for generating heat from the fixing roller 1.

  Then, after the fixing roller 1 is heated by the magnetic flux of the magnetic flux generator 3, the recording material P to which the unfixed toner t is adhered is brought into contact with the mutual contact surface between the fixing roller 1 and the pressure roller 2. The unfixed toner t is melt-fixed (heat-fixed) on the recording material P while the recording material P is conveyed by the nip portion N to be formed.

  The fixing device constitutes an image forming apparatus such as a copying machine, a laser printer, or a facsimile together with an image forming unit (not shown) that forms an image by attaching unfixed toner t to the recording material P.

  The recording material P is, for example, a sheet such as paper or an OHP sheet, and the toner t is made of a material having heat melting properties such as a resin, a magnetic material, or a colorant.

  The fixing roller 1 and the pressure roller 2 are arranged to face each other in parallel, and both end sides thereof are rotatably supported by a bearing member (not shown). The pressure roller 2 is urged toward the shaft side of the fixing roller 1 by a pressure mechanism such as a spring (not shown), and is pressed against the outer surface of the fixing roller 1 with a predetermined pressure to form the nip portion N. .

  The fixing roller 1 is rotationally driven at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow by driving means such as a motor (not shown). The pressure roller 2 rotates following the rotation of the fixing roller 1 by the frictional force of contact with the fixing roller 1 at the nip portion N.

  The fixing roller 1 includes a support layer 11, a heat insulating layer 12, an electromagnetic induction heat generating layer 13, an elastic layer 14, and a release layer 15 that are disposed in order from the inner side to the outer side in the radial direction. The fixing roller 1 has a Asker C hardness of 30 to 90 degrees, for example. In this embodiment, the fixing roller 1 includes the elastic layer 14 for accommodating color images. However, the fixing roller 1 includes at least the support layer 11, the heat insulating layer 12, and the electromagnetic induction heating layer. 13 and the release layer 15 may be provided.

  For the support layer 11, for example, an aluminum cored bar cylinder having an outer diameter of 40 mm and a thickness of 3 mm is used. The support layer 11 may be a heat-resistant molded pipe such as iron or PPS (polyphenylene sulfide), for example, as long as the strength of the material can be secured. However, the core metal generates heat. In order to prevent this, it is desirable to use a nonmagnetic material that is less affected by electromagnetic induction heating.

  The heat insulating layer 12 is for heat insulating and holding the heat generated in the electromagnetic induction heat generating layer 13, and a heat-resistant and elastic rubber or resin sponge (heat insulating structure) is used. As described above, by using a heat-resistant and elastic rubber or resin sponge (heat-insulating structure) for the heat-insulating layer 12, the electromagnetic induction heat-generating layer 13 can be reliably insulated and retained. The deflection of the induction heating layer 13 is allowed to increase the width dimension of the nip portion N, and the roller hardness of the fixing roller 1 is made smaller than that of the pressure roller 2 to improve the paper discharge performance and the recording material separation performance. Can be improved. For example, when a silicon sponge material is used for the heat insulation layer 12, the thickness is 2 to 10 mm, preferably 3 to 7 mm, and the hardness is set to 20 to 60 degrees, preferably 30 to 50 degrees with an Asker rubber hardness meter. Is done.

  The electromagnetic induction heat generating layer 13 is, for example, an endless nickel electroformed belt layer having a thickness of 10 to 100 μm, desirably 20 to 50 μm. As another material of the electromagnetic induction heat generating layer 13, a material having a relatively high magnetic permeability μ and an appropriate resistivity ρ such as a magnetic material (magnetic metal) such as magnetic stainless steel may be used. . Moreover, even if it is a nonmagnetic material, electroconductive materials, such as a metal, can be used by making a material into a thin film, for example. Further, the electromagnetic induction heat generating layer 13 may be a resin in which heat generating particles are dispersed. By using a resin-based material for the electromagnetic induction heat generating layer 13, the separation property of the recording material P can be improved. Can be better. The electromagnetic induction heat generating layer 13 is bonded to the heat insulating layer 12.

  In the electromagnetic induction heat generating layer 13, an eddy current is generated by the magnetic flux of the magnetic flux generator 3 to generate heat by Joule heat, and the fixing roller 1 is heated by this heat generation. This heating is called electromagnetic induction heating.

  The elastic layer 14 is made of a rubber material or a resin material having heat resistance and elasticity, and improves the adhesion between the recording material P and the surface of the fixing roller 1. As the elastic layer 14, for example, a heat-resistant elastomer such as silicon rubber or fluororubber that can be used at a fixing temperature is used. Various elastic fillers may be mixed in the elastic layer 14 for the purpose of thermal conductivity, reinforcement, and the like. Examples of the thermally conductive particles include diamond, silver, copper, aluminum, marble, and glass. Examples include silica, alumina, magnesium oxide, boron nitride, and beryllium oxide.

  The thickness of the elastic layer 14 is, for example, preferably 10 to 800 μm, and more preferably 100 to 300 μm. When the thickness of the elastic layer 14 is less than 10 μm, it becomes difficult to obtain elasticity in the thickness direction. On the other hand, when the thickness of the elastic layer 14 exceeds 800 μm, the heat generated in the electromagnetic induction heating layer 13 is It becomes difficult to reach the outer peripheral surface of the fixing roller 1, and the thermal efficiency tends to deteriorate.

  The elastic layer 14 has a JIS hardness of preferably 1 to 80 degrees, and more preferably 5 to 30 degrees. The elastic layer 14 has a fixability of the toner t while preventing a decrease in strength and poor adhesion. Defects can be prevented. In this case, the elastic layer 14 is preferably made of silicon rubber. Specifically, the silicon rubber is a one-component, two-component or three-component or more silicon rubber, LTV type, RTV type. Alternatively, HTV type silicon rubber, condensation type or addition type silicon rubber can be used. In this embodiment, the elastic layer 14 is silicon rubber having a JIS hardness of 10 degrees and a thickness of 200 μm.

  The release layer 15 enhances the releasability of the surface of the fixing roller 1, and can withstand use at a fixing temperature and has toner releasability. As the release layer 15, for example, silicon rubber, fluororubber, or fluororesin such as PFA, PTFE, FEP, and PFEP is used. 5-100 micrometers is preferable and, as for the thickness of the said mold release layer 15, 10-50 micrometers is more preferable. Further, in order to improve the interlayer adhesion, an adhesion treatment with a primer or the like may be performed. In addition, a conductive material, an abrasion resistant material, or a good heat conductive material may be added as a filler to the release layer 15 as necessary.

  The pressure roller 2 includes a support layer 21, a heat insulating layer 22, and a release layer 23 that are sequentially arranged from the inner side to the outer side in the radial direction. The support layer 21 is, for example, an aluminum cored bar having an outer diameter of 20 mm and a thickness of 3 mm. The heat insulating layer 22 is, for example, 3-10 mm silicon sponge rubber obtained by foaming silicon rubber. The release layer 23 is, for example, a fluorine resin such as PTFE or PFA having a thickness of 10 to 50 μm.

  As long as the material of the support layer 21 can secure the strength, for example, a pipe of a heat-resistant mold such as iron or PPS (polyphenylene sulfide) can be used, but in order to prevent the cored bar from generating heat. It is desirable to use a nonmagnetic material that is less affected by electromagnetic induction heating.

  The pressure roller 2 is pressed against the fixing roller 1 with a load of 300 to 500 N. In this case, the width dimension of the nip portion N (the dimension in the conveyance direction of the recording material P) is About 5 to 15 mm. Of course, the width dimension of the nip portion N may be changed by changing the load.

  The thermal conductivity of the heat insulating layer 22 of the pressure roller 2 is preferably 0.15 W / m · K or less. By setting the thermal conductivity in such a range, the amount of heat taken away by the pressure roller 2 from the fixing roller 1 can be kept small. For this reason, thermal efficiency can be improved, and a quick start of the fixing device is enabled.

  As shown in FIGS. 1 and 2, the magnetic flux generator 3 faces the fixing roller 1 along the longitudinal direction of the fixing roller 1. The magnetic flux generator 3 includes a bobbin 33 disposed along the outer surface of the fixing roller 1, an annular coil 31 disposed on the outer surface of the bobbin 33, and the coil 31 so as to cover the coil 31. A magnetic core 32 disposed on the opposite side of the fixing roller 1; In FIG. 2, the coil 31 is indicated by hatching in order to make the coil 31 easier to understand.

  The bobbin 33 is formed in a cup shape (trapezoidal shape) having a cross section that is widened and opened on the fixing roller 1 side. The bobbin 33 covers substantially half of the cross section of the fixing roller 1. The bobbin 33 has an opening facing the fixing roller 1 at the bottom.

  The coil 31 has a structure in which a conducting wire is wound along the outer surface of the bobbin 33 so as to be elongated in the axial direction of the fixing roller 1 and has a trapezoidal cross section. That is, the coil 31 is disposed along the outer surface of the fixing roller 1.

  More specifically, the coil 31 includes a pair of extending portions 31a and 31a extending in the axial direction of the fixing roller 1 and a pair of connecting portions respectively connecting both ends of the pair of extending portions 31a and 31a. Parts 31b and 31b.

  The magnetic core 32 is a long member having a length dimension substantially corresponding to the axial dimension of the fixing roller 1. A predetermined gap is formed between the magnetic core 32 and the bobbin 33, and the coil is formed in the gap. 31 is arranged.

  More specifically, the magnetic core 32 is disposed on both sides of the coil 31 in the rotation direction of the fixing roller 1 and extends in the axial direction of the fixing roller 1. And a plurality of main body cores 32a that are fixed at both ends to the support cores 32b and 32b so as to bridge the pair of support cores 32b and 32b and are arranged side by side in the axial direction of the fixing roller 1.

  The main body core 32 a has a trapezoidal cross section and extends in the rotation direction of the fixing roller 1 so as to cover the coil 31. The plurality of main body cores 32a are arranged so that the central portion in the axial direction of the fixing roller 1 in the magnetic core 32 is sparse, and the end portions in the axial direction of the fixing roller 1 in the magnetic core 32 are densely arranged. Yes. Accordingly, the magnetic flux density at the end of the fixing roller 1 in the axial direction is increased in response to the temperature drop due to heat radiation from the end of the fixing roller 1, and the temperature distribution in the axial direction of the fixing roller 1 is made uniform. Can be.

  The magnetic core 32 has a high magnetic permeability and low loss. The magnetic core 32 is used for improving the efficiency of the magnetic circuit and for magnetic shielding. As the material of the magnetic core 32, a ferrite core is usually used. However, when an alloy such as permalloy is used, the eddy current loss inside the magnetic core 32 increases at a high frequency. Also good. Note that when a resin material in which magnetic powder is dispersed is used, the magnetic permeability is relatively low, but the shape can be freely set.

  A protrusion (not shown) that protrudes toward the fixing roller 1 may be provided at the central portion of the magnetic core 32 in the rotation direction of the fixing roller 1 except for the temperature detection unit facing surface 51. For example, the protruding portion is arranged side by side in the axial direction of the fixing roller 1 except for the temperature detecting portion facing surface 51. Therefore, the heat generation efficiency of the fixing roller 1 can be improved. Note that the magnetic circuit portions of the coil 31 and the magnetic core 32 may omit the protruding portion when there is a means capable of sufficient magnetic shielding.

  The coil 31 is connected to the high frequency converter 4 and supplied with high frequency power of 100 to 2000 W, for example. For this reason, the coil 31 is made of a litz wire formed by bundling several tens to several hundreds of thin wires, and is coated with a heat resistant resin in consideration of the case where heat is transferred to the winding. Use things.

  A temperature detection unit 6 for detecting the temperature of the fixing roller 1 is disposed outside the fixing roller 1 and inside the magnetic core 32 so as to overlap the central hole of the coil 31. The temperature detector 6 is attached to the bobbin 33 at the axial center position of the fixing roller 1. The temperature detector 6 is, for example, a non-contact thermistor, and is disposed so as to be close to or in contact with the surface of the fixing roller 1.

  A controller 5 is connected to the temperature detector 6, and the controller 5 controls the high-frequency converter 4 on the basis of the surface temperature detection signal of the fixing roller 1 from the temperature detector 6, and the high-frequency converter 4. The converter 4 automatically controls the surface temperature of the fixing roller 1 to be a predetermined constant temperature by increasing / decreasing the power supply to the coil 31.

  The temperature detection unit 6 has a substantially rectangular parallelepiped shape, and the long side of the temperature detection unit 6 is disposed in parallel with the rotation axis of the fixing roller 1. In other words, the temperature detection unit 6 is arranged to have a length in the rotation axis direction of the fixing roller 1. The length of the temperature detection unit 6 in the axial direction of the fixing roller 1 is longer than the gap between the main body cores 32 a and 32 a adjacent to the magnetic core 32.

  More specifically, the temperature detector 6 extends in the axial direction of the fixing roller 1 and has a box having an opening on the fixing roller 1 side, and is disposed inside the box and has the above-described structure. A sensor unit that receives heat from the surface of the fixing roller 1 from the opening. The box is made of metal, for example. The sensor unit includes, for example, a metal or a semiconductor.

  As described above, the temperature detection unit 6 is arranged so as to have a length in the rotation axis direction of the fixing roller 1, so that a temperature measuring region having a relatively large area is secured and the temperature of the fixing roller 1 is increased. The distance between the outer surface and the temperature detection unit 6 can be accurately maintained. In other words, even if the outer surface of the fixing roller 1 is curved in the rotational direction, the temperature detecting unit 6 is elongated along the axis of the fixing roller 1, so that the temperature detecting unit 6 is not connected to the fixing roller 1. 1 is less affected by the curved surface of the outer surface.

  In the cross section perpendicular to the rotation axis of the fixing roller 1, the magnetic core 32 has a temperature detecting portion facing surface 51 that faces the temperature detecting portion 6 more than the coil facing surface 52 that faces the coil 31. 1 is formed in a shape that is far from the outer surface.

  That is, in the cross section orthogonal to the rotation axis of the fixing roller 1, the coil facing surface 52 of the magnetic core 32 and the outer surface of the fixing roller 1 at the center position in the width direction of the fixing roller rotation direction of the coil 31. And the distance between the temperature detecting portion facing surface 51 of the magnetic core 32 and the outer surface of the fixing roller 1 at the center position in the width direction of the fixing roller rotating direction of the temperature detecting portion 6. If b, then a <b.

  The center position in the width direction of the coil 31 in the rotation direction of the fixing roller refers to the center position of the width of the extending portion 31 a of the coil 31. The center position in the width direction of the fixing roller rotation direction of the temperature detection unit 6 refers to the center position of the width of the box of the temperature detection unit 6.

  Note that b / a is preferably 1.2 or more and 2.0 or less, and desirably b / a is 1.5 or more and 1.8 or less. For example, when the distance a is 10 mm, the distance b is 12 to 20 mm, preferably 15 to 18 mm.

  The temperature detector facing surface 51 and the coil facing surface 52 are flat surfaces provided on the main body core 32 a of the magnetic core 32. Of all the main body cores 32a, at least in the main body core 32a facing the temperature detection unit 6, the temperature detection unit facing surface 51 is further away from the outer surface of the fixing roller 1 than the coil facing surface 52. It only has to be.

  The operation of the magnetic flux generator 3 configured as described above will be described. For example, an AC current of 10 to 100 kHz is applied to the coil 31 by the high frequency converter 4. The magnetic flux induced by the alternating current passes through the inside of the magnetic core 32 without leaking to the outside as indicated by a broken line B in FIG. 1, and the temperature detecting unit facing surface 51 and the coil facing surface 52 And from the support core 32b to the outside of the magnetic core 32, penetrate the electromagnetic induction heat generating layer 13 of the fixing roller 1, and an eddy current flows through the electromagnetic induction heat generating layer 13 to The electromagnetic induction heat generating layer 13 itself generates Joule heat. The fixing roller 1 is heated by the heat generated by the electromagnetic induction heat generating layer 13.

  According to the fixing device having the above-described configuration, the magnetic flux generator 3 has the magnetic core 32 disposed so as to cover the coil 31, so that leakage of magnetic flux generated from the coil 31 by the magnetic core 32. Thus, noise generation can be prevented and the heat generation efficiency of the fixing roller 1 can be improved.

  The magnetic core 32 has a shape in which the temperature detection unit facing surface 51 is farther from the outer surface of the fixing roller 1 than the coil facing surface 52 in a cross section orthogonal to the rotation axis of the fixing roller 1. Since the magnetic core 32 is formed, the magnetic flux flowing through the magnetic core 32 is between the temperature detecting portion facing surface 51 and the coil facing surface 52 which is a point far from the outer surface of the fixing roller 1 in the magnetic core 32. Thus, the magnetic flux density at the center position of the hole of the coil 31 can be reduced by flowing in the direction of the fixing roller 1.

  For this reason, the magnetic flux passing through the temperature detection unit 6 in the hole of the coil 31 is reduced to reduce the adverse effect of the magnetic flux on the temperature detection unit 6 and to increase the heat generation efficiency of the fixing roller 1. Can keep.

  The adverse effect due to the magnetic flux on the temperature detection unit 6 means that the temperature detection unit 6 generates heat due to the magnetic flux and cannot detect an accurate temperature, or the temperature detection unit 6 has an adverse effect such as a malfunction caused by the magnetic flux. is there.

  Therefore, noise leakage is prevented, the heat generation efficiency of the fixing roller 1 is improved, and adverse effects due to the magnetic flux on the temperature detection unit 6 are prevented.

  In addition, since the temperature detection unit 6 is disposed so as to overlap the hole of the coil 31, it is possible to reduce the size of the apparatus by using a dead space. On the other hand, when the temperature detection unit 6 is arranged outside the coil 31, the apparatus becomes large and it is difficult to secure a sheet passing path for the recording material P.

  Further, since b / a is 1.2 or more and 2.0 or less (preferably 1.5 or more and 1.8 or less), the apparatus can reduce the flow of magnetic flux into the temperature detection unit 6 while reducing the flow of the magnetic flux. Can be miniaturized. That is, if it is less than the lower limit value, the flow of magnetic flux into the temperature detection unit 6 cannot be reduced, and if it exceeds the upper limit value, the apparatus becomes large.

  Next, FIG. 3 shows a comparative example of the fixing device.

  This fixing device is different from the fixing device of the present invention (FIG. 1) in the configuration of the magnetic flux generator. In the magnetic flux generator 3 ′ of the fixing device in FIG. 3, the magnetic core 32 ′ has an arc shape along the outer surface of the fixing roller 1. That is, the distance a between the coil facing surface 52 ′ of the magnetic core 32 ′ and the outer surface of the fixing roller 1, the temperature detecting portion facing surface 51 ′ of the magnetic core 32 ′, and the fixing roller 1. The distance b from the outer surface is the same.

  Therefore, the magnetic flux flowing inside the magnetic core 32 ′ reaches the temperature detecting portion facing surface 51 ′ and then flows into the fixing roller 1 side as indicated by a broken line B ′ in FIG. 3. That is, the magnetic flux passes through the inside of the temperature detection unit 6.

  Therefore, the temperature detector 6 may generate heat due to the magnetic flux and cannot detect an accurate temperature, or may malfunction due to the magnetic flux. Further, since the magnetic flux flows through the temperature detection unit 6, the heat generation efficiency of the fixing roller 1 is reduced.

  Although not shown in the drawings, as another comparative example of the fixing device, referring to FIG. 2, the main body core 32a adjacent to the magnetic core 32 so that the magnetic core 32 does not overlap the temperature detector 6. , 32a has a disadvantage that the magnetic flux distribution becomes non-uniform, the heat generation efficiency decreases, and the temperature distribution becomes non-uniform.

  Although not shown in the drawings, as another comparative example of the fixing device, referring to FIG. 2, the main body core in a portion overlapping the temperature detection unit 6 so that the temperature detection unit 6 does not overlap the magnetic core 32. When 32a is notched, there is a drawback that magnetic flux leaks to the outside.

(Second Embodiment)
FIG. 4 shows a second embodiment of the fixing device of the present invention. The difference from the first embodiment (FIG. 1) will be described. In the second embodiment, the temperature detection unit facing surface 151 of the magnetic core 132 of the magnetic flux generator 103 is connected to the temperature detection unit 6. The curved surface is concave on the opposite side.

  Specifically, the main body core 132a of the magnetic core 132 facing the temperature detection unit 6 is formed such that a portion facing the temperature detection unit 6 is curved, and as a whole, substantially C It is formed in a letter shape.

  Therefore, the distance b between the temperature detecting portion facing surface 151 of the magnetic core 132 and the outer surface of the fixing roller 1 is set between the coil facing surface 152 of the magnetic core 132 and the outer surface of the fixing roller 1. The distance a can be further increased.

  As described above, the temperature detection unit facing surface 151 can be further away from the outer surface of the fixing roller 1, and the flow of magnetic flux to the temperature detection unit 6 can be further reduced as shown by a broken line B in FIG. In addition, a wide space for arranging the temperature detection unit 6 can be secured.

  In addition, since the surface between the temperature detection unit facing surface 151 and the coil facing surface 152 can be formed smoothly, the magnetic flux can flow smoothly through the magnetic core 132.

(Third embodiment)
FIG. 5 shows a third embodiment of the fixing device of the present invention. The difference from the second embodiment (FIG. 4) will be described. In the third embodiment, the magnetic core 232 of the magnetic flux generator 203 includes the temperature detecting portion facing surface 151 and the coil facing surface 152. A protrusion 32c extending between the temperature detector 6 and the coil 31.

  More specifically, the main body core 132a of the magnetic core 232 facing the temperature detection unit 6 has a pair of protrusions 32c and 32c located on both sides of the temperature detection unit 6 in the fixing roller rotation direction. Have

  Therefore, the magnetic flux flowing through the magnetic core 232 can be guided to the fixing roller 1 side via the protrusion 32c as shown by a broken line B in FIG. The flow of magnetic flux can be further reduced.

  In addition, this invention is not limited to the above-mentioned embodiment. For example, the fixing roller 1 includes a support layer 11, a heat insulating layer 12, an electromagnetic induction heat generating layer 13, an elastic layer 14, and a release layer 15, but of course, other layers may be included. is there.

  Further, a fixing belt may be used as the fixing body instead of the fixing roller 1. Instead of the pressure roller 2, a pressure belt or a vibrating body such as an ultrasonic vibrator or a piezoelectric element may be used as the pressure body. As the temperature detection unit, a thermostat for ensuring safety may be used instead of the thermistor.

1 is a cross-sectional configuration diagram illustrating a first embodiment of a fixing device of the present invention. It is a top view of FIG. FIG. 6 is a cross-sectional configuration diagram illustrating a comparative example of a fixing device. It is a cross-sectional block diagram which shows 2nd Embodiment of a fixing device. It is a cross-sectional block diagram which shows 3rd Embodiment of a fixing device.

Explanation of symbols

1 Fixing roller (fixing body)
2 Pressure roller (Pressure body)
3, 103, 203 Magnetic flux generator 6 Temperature detector 11 Support layer 12 Heat insulation layer 13 Electromagnetic induction heat generation layer 14 Elastic layer 15 Release layer 21 Support layer 22 Heat insulation layer 23 Release layer 31 Coil 32, 132, 232 Magnetic core 32a, 132a Main body core 32b Support core 32c Projection part 33 Bobbin 51, 151 Temperature detection part facing surface 52, 152 Coil facing surface P Recording material t Toner

Claims (5)

A rotatable fixing member;
A pressure member that is in pressure contact with the fixing member;
A magnetic flux generator that is disposed outside the fixing body and generates a magnetic flux to heat the fixing body; and
A temperature detection unit for detecting the temperature of the fixing body,
The magnetic flux generator is
An annular coil disposed along the outer surface of the fixing body;
A magnetic core disposed on the opposite side of the fixing body with respect to the coil so as to cover the coil;
The temperature detection unit is disposed between the fixing body and the magnetic core at a position overlapping the hole of the coil,
In the cross section orthogonal to the rotation axis of the fixing body, the magnetic core has a position where the temperature detecting portion facing surface facing the temperature detecting portion is farther from the outer surface of the fixing body than the coil facing surface facing the coil. A fixing device characterized by being formed into a shape. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the temperature detection unit is arranged to have a length in a rotation axis direction of the fixing body. The fixing device according to claim 1,
In the cross section orthogonal to the rotation axis of the fixing body, a is a distance between the coil facing surface of the magnetic core and the outer surface of the fixing body at the center position in the width direction of the fixing body rotation direction of the coil, When the distance between the temperature detecting unit facing surface of the magnetic core and the outer surface of the fixing member at the center position in the width direction of the fixing member rotating direction of the temperature detecting unit is b,
b / a is 1.2 or more and 2.0 or less. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the temperature detecting portion facing surface of the magnetic core is a curved surface that is concave on the side opposite to the temperature detecting portion. The fixing device according to claim 1,
The fixing device according to claim 1, wherein the magnetic core has a projecting portion extending from between the temperature detecting portion facing surface and the coil facing surface to between the temperature detecting portion and the coil.

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