JP2006145780A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize the reduction of power consumption by attaining the low heat capacity of an inner core without spoiling magnetic connection between a magnetic flux generating means at a part opposed to a magnetic shielding body and the inner core. <P>SOLUTION: In a state where a projecting core 2332C having maximum size width faces to a position where it is opposed to a center core 234, magnetic flux 401 flowing to the disposed part of the magnetic shielding body 2333A of a projecting core 2332A having A4 size width is induced toward a side core 235 by a magnetic flux induction core 801. Thus, the lowering of the magnetic connection between the side core 235 and the small-diameter core 2331 at a part opposed to the magnetic shielding body 2333A of the projecting core 2332A having A4 size width when A3 size recording paper 109 passes is eliminated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device that heats and fixes an unfixed image on a recording medium using electromagnetic induction heating type heating means, and more particularly to an image forming apparatus such as an electrophotographic type or electrostatic recording type copying machine, facsimile, and printer. The present invention relates to a fixing device that is useful for use.

  In an induction heating (IH) type fixing device, an eddy current is generated in a heating element by a magnetic field, and it is formed on a recording medium such as transfer paper and an OHP sheet by Joule heating of the heating element by the eddy current. The fixed unfixed image is heat-fixed on the recording medium.

  This electromagnetic induction heating type fixing device has an advantage that the heat generation efficiency is high and the rise time until heat is generated at a predetermined fixing temperature can be shortened as compared with a heat roller type fixing device using a halogen lamp as a heat source. Have.

  However, in a fixing device using a film-like fixing belt or sleeve having a small heat capacity as the heating element, even when the recording medium is passed, the heat of the heating element is taken away and the temperature of the sheet passing area is lowered. . Thus, in this type of fixing device, the heating element is heated in a timely manner so that the temperature of the sheet passing area is maintained at a predetermined fixing temperature. For this reason, in a fixing device using a heating element having a small heat capacity, when a recording medium having a small size is continuously fed, the heating element is continuously heated, and the temperature of the non-sheet passing area is changed. This causes a phenomenon that the temperature becomes abnormally higher than the temperature, that is, an excessive temperature rise phenomenon in a non-sheet passing region.

  In order to prevent the heating element from exceeding the heat-resistant temperature due to this excessive temperature rise in the non-sheet passing area, the number of sheets of the recording medium is limited and the interval between the sheets to be passed is increased. However, any of these measures reduces print efficiency (number of prints per unit time).

  Conventionally, as a fixing device for solving such a problem, only the magnetic flux acting on the non-sheet passing region of the heating element is moved in the heating width direction of the heating element among the magnetic flux of the magnetic flux generating means for causing the heating element to generate electromagnetic induction heat. What prevents the excessive temperature rise of a non-paper passing area | region by shielding with the possible magnetic flux shielding board is known (for example, refer patent document 1).

Further, as another fixing device for solving the above problem, a second magnetic core corresponding to the non-sheet passing region is disposed behind the first magnetic core of the magnetic flux generating means for generating heat by electromagnetic induction. One that changes the temperature distribution in the longitudinal direction of the heating element by changing the gap between the first magnetic core and the second magnetic core is known (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 10-74009 JP 2003-123961 A

  However, since the fixing device described in Patent Document 1 is configured to move the magnetic flux shielding plate forward and backward in the heat generation width direction with respect to the non-sheet passing region of the heating element, the magnetic flux shielding plate greatly protrudes from both ends of the magnetic flux generation means. There is a problem that the main body of the fixing device is enlarged.

  On the other hand, the fixing device described in Patent Document 2 does not change the distance between the first magnetic core and the heating element even when the second magnetic core is displaced with respect to the first magnetic core. The magnetic gap between the area and the non-sheet passing area is constant.

  For this reason, in the fixing device described in Patent Document 2, the magnetic flux wraps around from the end of the sheet passing area corresponding to the first magnetic core to the end of the non-sheet passing area corresponding to the second magnetic core. In addition, the effect of suppressing the magnetic flux in the non-sheet passing region of the heating element is lowered.

  As a result, in the fixing device described in Patent Document 2, when a small-sized recording medium is continuously fed, heat is accumulated in the non-sheet passing area of the heating element, and the excessive temperature rise is effectively suppressed. Is difficult. Further, since this fixing device can hold only the second magnetic core corresponding to the size of one recording medium, the sheet passing area width of the heating element is limited to the paper width of the two types of recording media, the maximum size and the small size. I cannot make it correspond.

  Accordingly, the applicant of the present invention has disclosed a sheet passing size of a recording medium capable of blocking the magnetic flux flowing in the non-sheet passing region of the heating element in the rotatable inner core disposed so as to face the magnetic flux generating unit with the heating element interposed therebetween. Has been proposed (Japanese Patent Application No. 2003-358023).

  According to the fixing device proposed by the present applicant, the magnetic shield corresponding to the paper passing size of the recording medium to be passed is brought to a position where the magnetic flux flowing in the non-sheet passing region of the heating element is blocked, thereby generating magnetic flux. The magnetic path between the means and the inner core can be shielded. As described above, in this fixing device, the magnetic path is shielded by the magnetic shield, thereby preventing the magnetic flux corresponding to the paper passing area of the heating element from entering the non-paper passing area. Therefore, in this fixing device, it is possible to effectively block the magnetic flux flowing in the non-sheet passing area by the magnetic shield and prevent an excessive temperature rise due to heat accumulation in the non-sheet passing area of the heating element.

  Further, according to the fixing device proposed by the present applicant, the magnetic path of the magnetic flux can be interrupted or released by rotating the inner core with respect to the magnetic flux generating means. No increase in size in the direction.

  Further, according to the fixing device proposed by the present applicant, the magnetic flux flowing in the non-sheet passing region of the heating element can be blocked by the small magnetic shield that shields only the magnetic path between the magnetic flux generating means and the inner core. It is possible to provide a magnetic shield corresponding to the size width of the type of recording medium.

  Incidentally, as described above, in the fixing device in which the inner core is rotatably arranged so as to face the magnetic flux generation means with the heating element interposed therebetween, further energy saving of the fixing device is achieved by reducing the heat capacity of the inner core. (Reduction of power consumption) can be realized. This reduction in heat capacity of the inner core can be achieved, for example, by reducing the diameter of the inner core so that its volume is not smaller than that of the conventional one.

  However, in the fixing device having such a configuration, when the inner core is simply reduced in diameter to reduce the heat capacity of the inner core, the separation distance between the magnetic flux generating means and the inner core increases. Magnetic coupling will be weak. In particular, when the recording medium of the maximum size width is passed, the magnetic flux flowing along the inner core wraps around the inner core in the width direction (heating width direction) so as to avoid the magnetic shield disposed portion. The magnetic coupling between the magnetic flux generating means and the inner core at the portion facing the magnetic shield is weakened. As a result, the heat generation temperature in the width direction of the heating element becomes non-uniform, and particularly the temperature drop at both ends becomes remarkable, which adversely affects the image quality when the recording medium of the maximum size width is passed. End up.

  The present invention has been made in view of such a point, and the low heat capacity of the inner core without impairing the magnetic coupling between the magnetic flux generating means and the inner core, in particular, the magnetic coupling between the magnetic flux generating means and the inner core at a portion facing the magnetic shield. It is an object of the present invention to provide a fixing device that can reduce power consumption.

  In order to solve such a problem, a fixing device of the present invention includes a rotatable cylindrical heating element having a conductive layer, an inner core rotatably disposed inside the heating element, and an outer periphery of the heating element. An exciting coil for inductively heating the conductive layer disposed so as to cover a part; a center core disposed at a winding center of the exciting coil; a side core disposed at a side portion of the exciting coil; A plurality of convex cores provided on the inner core and having a size width corresponding to a sheet passing size of the recording medium, and selectively facing a position facing the center core by rotation of the inner core; A magnetic shield disposed on a side portion of the convex core having a size width smaller than the convex core having at least the maximum size width and blocking a magnetic flux flowing in a non-sheet passing region of the heating element; and provided on the inner core. A magnetic flux induction core that induces a magnetic flux that flows toward the arrangement portion of the magnetic shield in a state where the convex core of the maximum size width faces a position facing the center core. Take.

  According to the present invention, the magnetic flux that flows toward the magnetic shielding member in a state where the convex core of the maximum size width faces the position facing the center core can be guided toward the side core by the magnetic flux guiding core. The inner core can be reduced in size (lower heat capacity) without damaging the magnetic coupling between the side core and the inner core at the part facing the magnetic shield of the convex core, and heat is generated in the width direction when heated at the maximum size width. Power consumption can be reduced while achieving uniform temperature.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, components having the same configuration or function and corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  First, an image forming apparatus suitable for mounting a fixing device according to an embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus suitable for mounting a fixing device according to an embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 100 includes an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 101, a charger 102, a laser beam scanner 103, a developing device 105, a paper feeding device 107, and a cleaning device 113. And a fixing device 200.

  In FIG. 1, the surface of the photosensitive drum 101 is uniformly charged to a predetermined negative dark potential by the charger 102 while being rotated at a predetermined peripheral speed in the direction of the arrow.

  The laser beam scanner 103 outputs a laser beam 104 modulated in accordance with a time-series electric digital pixel signal of image information input from a host device such as an image reading device or a computer (not shown), and is uniformly charged. The surface of the photosensitive drum 101 is scanned and exposed by a laser beam 104. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 101 decreases to a bright potential, and an electrostatic latent image is formed on the surface of the photosensitive drum 101.

  The developing device 105 includes a developing roller 106 that is driven to rotate. The developing roller 106 is disposed to face the photosensitive drum 101, and a thin layer of toner is formed on the outer peripheral surface thereof. Further, a developing bias voltage whose absolute value is smaller than the dark potential of the photosensitive drum 101 and larger than the bright potential is applied to the developing roller 106.

  As a result, the negatively charged toner on the developing roller 106 adheres only to the light potential portion on the surface of the photosensitive drum 101, and the electrostatic latent image formed on the surface of the photosensitive drum 101 is reversely developed and developed. As a result, an unfixed toner image 111 is formed on the photosensitive drum 101.

  On the other hand, the paper feeding device 107 feeds the recording paper 109 as a recording medium one sheet at a time by the paper feeding roller 108. The recording paper 109 fed from the paper feeding device 107 passes through a pair of registration rollers 110 and is fed to the nip portion between the photosensitive drum 101 and the transfer roller 112 at an appropriate timing synchronized with the rotation of the photosensitive drum 101. As a result, the unfixed toner image 111 on the photosensitive drum 101 is transferred onto the recording paper 109 by the transfer roller 112 to which a transfer bias is applied.

  The recording paper 109 to which the unfixed toner image 111 is transferred in this way is guided by the recording paper guide 114 and separated from the photosensitive drum 101, and then conveyed toward the fixing portion of the fixing device 200. The fixing device 200 heat-fixes the unfixed toner image 111 on the recording paper 109 conveyed to the fixing portion.

  The recording paper 109 on which the unfixed toner image 111 is heat-fixed passes through the fixing device 200 and is then discharged onto a paper discharge tray 116 disposed outside the image forming apparatus 100.

  On the other hand, the photosensitive drum 101 from which the recording paper 109 has been separated is subjected to the subsequent image formation repeatedly by removing residuals such as transfer residual toner on the surface thereof by the cleaning device 113.

  Next, a fixing device mounted on the image forming apparatus 100 described above will be described. FIG. 2 is a cross-sectional view showing a basic configuration of a fixing device mounted on the image forming apparatus shown in FIG.

  As shown in FIG. 2, the fixing device 200 includes a fixing belt 210 as a heating element, a support roller 220 as a belt support member, a coil unit 230 as electromagnetic induction heating means, a fixing roller 240, and an addition as belt rotation means. A pressure roller 250 is provided.

  In FIG. 2, the fixing belt 210 is suspended from a support roller 220 and a fixing roller 240. The fixing roller 240 is in pressure contact with the pressure roller 250 with the fixing belt 210 interposed therebetween.

  The pressure roller 250 is rotationally driven in the direction of the arrow by a drive source (not shown). The fixing roller 240 is driven to rotate while sandwiching the fixing belt 210 by the rotation of the pressure roller 250. As a result, the fixing belt 210 is sandwiched between the fixing roller 240 and the pressure roller 250 and rotated in the direction of the arrow. By the rotation of the fixing belt 210, a nip portion is formed between the fixing belt 210 and the pressure roller 250 for heating and fixing the unfixed toner image 111 on the recording paper 109.

  The coil unit 230 includes the IH type electromagnetic induction heating means, and includes an exciting coil 231 and a core 232 as shown in FIG. An exciting coil 231 serving as a magnetic flux generating means is disposed along the outer periphery of a portion of the fixing belt 210 suspended from the support roller 220.

  The core 232 includes a center core 234 made of a ferromagnetic material such as ferrite, a pair of side cores 235, and an arch core 236, and is disposed so as to cover the exciting coil 231. The inner core 233 built in the support roller 220 and positioned coaxially is made of a ferromagnetic material such as ferrite, and is disposed so as to face the excitation coil 231 with the fixing belt 210 and the support roller 220 interposed therebetween.

  The center core 234 of the core 232 is disposed (or integrally formed) at the center of the arch core 236. The pair of side cores 235 are disposed (or integrally formed) at both ends of the arch core 236, respectively.

  The exciting coil 231 is formed using a litz wire bundled with thin copper wires, and has a semicircular cross-sectional shape so as to cover the outer periphery of the fixing belt 210 suspended from the support roller 220.

  An excitation current having a predetermined drive frequency (for example, 30 kHz) is applied to the excitation coil 231 from an excitation circuit (not shown). As a result, an alternating magnetic field is generated between the core 232 and the inner core 233, and an eddy current is generated in the conductive layer of the fixing belt 210 as a heating element, so that the fixing belt 210 generates heat.

  In the fixing device 200, the fixing belt 210 is used as a heating element. However, the supporting roller 220 may be used as a heating element, and the heat of the supporting roller 220 may be transmitted to the fixing belt 210.

  The core 232 is provided at the center of the exciting coil 231 and a part of the back surface. As a material of the core 232, a material having high magnetic permeability such as permalloy can be used in addition to ferrite.

  As shown in FIG. 2, the fixing device 200 conveys the recording paper 109 on which the unfixed toner image 111 is transferred from the direction of the arrow so that the carrying surface of the unfixed toner image 111 is in contact with the fixing belt 210. Thus, the unfixed toner image 111 can be heat-fixed on the recording paper 109.

  A temperature sensor 260 made of a thermistor is provided on the back surface of the fixing belt 210 that has passed through the contact portion with the support roller 220. The temperature sensor 260 detects the temperature of the fixing belt 210 and outputs the detection result to a control device (not shown). The control device controls the power supplied to the exciting coil 231 via the exciting circuit based on the output of the temperature sensor 260, and the amount of heat generated by the fixing belt 210 is optimal for fixing the unfixed toner image 111. It is controlled to keep the temperature.

  A discharge guide 270 that guides the recording paper 109 that has been heat-fixed toward the discharge tray 116 is provided at a portion of the fixing belt 210 suspended from the fixing roller 240 on the downstream side in the conveyance direction of the recording paper 109. Is provided.

  The coil unit 230 is provided with a coil guide 237 as a holding member integrally with the exciting coil 231 and the core 232. The coil guide 237 is made of a resin having a high heat resistance such as PEEK material or PPS. The coil guide 237 functions to prevent the excitation coil 231 from being damaged due to the heat radiated from the fixing belt 210 in the space between the fixing belt 210 and the excitation coil 231.

  The support roller 220 in the fixing device 200 is made of a member that transmits the magnetic flux generated by the coil unit 230 without being shielded, for example, a nonmagnetic stainless material (SUS304) having a specific resistance of 72 μΩcm.

  Although the core 232 has a semicircular cross-sectional shape, the core 232 does not necessarily have to have a shape that follows the shape of the exciting coil 231. It may be.

  Next, the configuration of the inner core 233 of the fixing device 200 will be described. FIG. 3 is a schematic perspective view showing the configuration of the inner core in the fixing device shown in FIG.

  As shown in FIG. 3, the inner core 233 of the fixing device 200 has three convex cores 2332A, 2332B, and 2332C protruding from the circumferential surface on the circumferential surface (outer circumferential surface) of a small-diameter core 2331 formed in a cylindrical shape. It has the structure which formed. The inner core 233 has a configuration in which two sets of magnetic shields 2333A and 2333B are disposed on the circumferential surface of the small-diameter core 2331.

  Here, the positions of the convex cores 2332A, 2332B, and 2332C and the magnetic shields 2333A and 2333B are determined by the inner core 233 on the small-diameter core 2331 according to the sheet passing reference of the recording paper 109.

  In the fixing device 200, the sheet passing reference of the recording paper 109 is the center reference, and as shown in FIG. 3, the convex cores 2332A, 2332B, and 2332C are arranged at the center portion of the small-diameter core 2331. Magnetic shields 2333A and 2333B are disposed on both side portions of the respective convex cores 2332A and 2332B.

  Each of the convex cores 2332A, 2332B, and 2332C is made of a ferromagnetic material such as ferrite, and has a width corresponding to each size width of the plurality of recording sheets 109 that can be passed. In the fixing device 200 of this example, the convex core 2332A has an A4R size width corresponding to the size width of the short side of the A4 size recording paper 109. The convex core 2332 </ b> B has a B4 size width corresponding to the size width of the short side of the B4 size recording paper 109. Further, the convex core 2332C has an A3 size width corresponding to the size width of the short side of the A3 size recording paper 109.

  On the other hand, the magnetic shields 2333A and 2333B are made of a material (for example, a copper plate having a thickness of 1 mm) that can block the magnetic flux flowing in the non-sheet passing region of the recording paper 109 of each size of the fixing belt 210. . Further, the magnetic shields 2333A and 2333B are respectively disposed on the circumferential surface of the small-diameter core 2331 so as to face the non-sheet passing area of the recording paper 109 of each size of the fixing belt 210. That is, the magnetic shield 2333A is disposed on both side portions of the convex core 2332A having an A4R size width. The magnetic shield 2333B is disposed on both sides of the convex core 2332B having a B4 size width.

  The fixing device 200 including the inner core 233 having such a configuration is configured to heat a heating element (here, referred to as a fixing belt 210) in accordance with the size width of the recording paper 109 to be passed (hereinafter referred to as “paper width”). Control heating ”).

  FIG. 4 is a schematic cross-sectional view showing a cross-section of a paper passing area when performing paper width control heating in accordance with the A3 size width of the fixing device shown in FIG. FIG. 5 is a schematic cross-sectional view showing a cross section of the sheet passing area when the paper width control heating in accordance with the B4 size width of the fixing device shown in FIG. 2 is performed. FIG. 6 is a schematic cross-sectional view showing a cross section of the sheet passing area when the paper width control heating according to the A4R size width of the fixing device shown in FIG. 2 is performed.

  As shown in FIG. 4, in the fixing device 200, when performing paper width control heating in accordance with the A3 size width, the inner core 233 is rotated by a driving means (not shown), and the convex core 2332C having the A3 size width is turned into the center core 234. It is in a state of facing the opposite position.

  In this state, when an excitation current having a predetermined drive frequency is applied from the excitation circuit to the excitation coil 231, an alternating magnetic field is generated between the core 232 and the convex core 2332 </ b> C of the inner core 233, and the conductive layer of the fixing belt 210. An eddy current is generated in the fixing belt 210, and a sheet passing region facing the convex core 2332C having an A3 size width generates heat.

  That is, in this case, as indicated by an arrow in FIG. 4, the magnetic flux 401 circulates from the center core 234 through the convex core 2332C having an A3 size width, and from the small-diameter core 2331 to the center core 234 through the side core 235 and the arch core 236. To do.

  As shown in FIG. 5, in the fixing device 200, when performing paper width control heating in accordance with the B4 size width, the inner core 233 is rotated by a driving means (not shown), and the convex core 2332B having the B4 size width is replaced with the center core. The state facing the position 234 is set.

  In the case of the paper width control heating in accordance with the B4 size width, as shown in FIG. 5, the magnetic shields 2333B disposed on both side portions of the convex core 2332B having the B4 size width are formed by the center core 234 and the inner core. It is in a state where it faces a position where the magnetic path in the non-sheet-passing area with 233 is shielded.

  In this state, when an exciting current having a predetermined driving frequency is applied from the exciting circuit to the exciting coil 231, an alternating magnetic field is generated between the core 232 and the convex core 2332 B of the inner core 233, and the conductive layer of the fixing belt 210 is formed. An eddy current is generated in the fixing belt 210, and only the sheet passing region facing the convex core 2332B having a B4 size width generates heat.

  That is, in this case, as indicated by an arrow in FIG. 5, the magnetic flux 501 circulates from the center core 234 through the convex core 2332B having a width of B4, and from the small-diameter core 2331 to the center core 234 through the side core 235 and the arch core 236. The magnetic flux 501 passing through the magnetic path in the non-sheet passing region between the side core 234 and the inner core 233 is shielded by the magnetic shield 2333B.

  As shown in FIG. 6, in the fixing device 200, when performing paper width control heating in accordance with the A4R size width, the inner core 233 is rotated, and the convex core 2332 A having the A4R size width is opposed to the center core 234. It is in a state where it is exposed to.

  In the case of the paper width control heating in accordance with the A4R size width, as shown in FIG. 6, the magnetic shields 2333A disposed on both side portions of the convex core 2332A having the A4R size width are formed by the center core 234 and the inner core. It is in a state where it faces a position where the magnetic path in the non-sheet-passing area with 233 is shielded.

  In this state, when an exciting current having a predetermined driving frequency is applied to the exciting coil 231, an alternating magnetic field is generated between the core 232 and the convex core 2332 A having an A4R size width of the inner core 233, and the conductive layer of the fixing belt 210. An eddy current is generated in the fixing belt 210, and only the sheet passing area facing the convex core 2332A having the A4R size width of the fixing belt 210 generates heat.

  That is, in the case of the paper width control heating in accordance with the A4R size width, as indicated by an arrow in FIG. 6, the magnetic flux 601 passes from the center core 234 through the convex core 2332A having the A4R size width and from the small diameter core 2331 to the side core 235. The magnetic flux 601 that circulates to the center core 234 through the arch core 236 and passes through the magnetic path in the non-paper passing region between the side core 234 and the inner core 233 is shielded by the magnetic shield 2333A.

  As described above, in the fixing device 200, the fixing belt 210 can be heated and controlled in accordance with the size width of the recording paper 109 to be passed, and the size is smaller than the maximum size of the recording paper 109 that can be passed. Overheating in the non-sheet passing area of the fixing belt 210 when the recording paper 109 is continuously fed can be suppressed.

  Further, in the fixing device 200, the convex cores 2332A, 2332B, and 2332C are provided in the portion of the small-diameter core 2331 that faces the center core 234. Therefore, the outer diameter of the inner core 233 is not increased, that is, the heat capacity of the inner core 233 is increased. The magnetic coupling between the center core 234 and the inner core 233 of the coil unit 230 can be improved without increasing the size.

  By the way, the inner core 233 having a reduced heat capacity as described above is a convex core having an A3 size width as shown in FIG. 7 when the recording paper 109 having the maximum size (A3 size in this example) is passed. The magnetic flux 401 flowing along the small-diameter core 2331 from 2332C wraps around the inner side of the inner core 233 in the width direction (heating width direction) so as to avoid the location of the magnetic shield 2333A of the convex core 2332A having an A4 size width. End up.

  For this reason, in the fixing device 200 using the inner core 233 having such a configuration, when the A3 size recording paper 109 is passed, the side core 235 at a portion facing the magnetic shield 2333A of the A4 size width of the convex core 2332A. And the small-diameter core 2331 are weakly magnetically coupled.

  Therefore, as shown in FIG. 8, in the fixing device 800 according to the embodiment of the present invention, the magnetic flux is applied to the side portion of the magnetic shield 2333A of the convex core 2332A having the A4 size width of the small-diameter core 2331 of the inner core 233. The induction core 801 is provided.

  In the fixing device 800 of this example, the angle θ1 formed by the magnetic flux guiding core 801 and the convex core 2332A having an A4 size width is set to 78 °. The opening angle θA of the magnetic shield 2333A of the convex core 2332A having an A4 size width was 116 °. Further, the opening angle θB of the magnetic shield 2333B of the convex core 2332B having a B4 size width was set to 87 °.

  In fixing device 800 according to the present embodiment, as shown in FIGS. 9 and 10, a convex core having an A4 size width in a state where convex core 2332 </ b> C having the maximum size width faces a position facing center core 234. The magnetic flux 401 flowing toward the portion where the magnetic shield 2333A of 2332A is disposed can be guided toward the side core 235 by the magnetic flux guiding core 801.

  Therefore, in the fixing device 800 according to the present embodiment, the side core 235 and the small-diameter core 2331 at a portion facing the magnetic shield 2333A of the convex core 2332A having an A4 size width when the A3 size recording paper 109 is passed. The decrease in magnetic coupling can be eliminated.

  Next, a specific configuration of the inner core 233 in the fixing device 800 according to the present embodiment will be described. FIG. 11 is a schematic cross-sectional view showing a specific configuration of the inner core in the fixing device according to the embodiment of the present invention. Here, as shown in FIG. 11, the supporting roller 220 is a heating element, the outer diameter of the small-diameter core 2331 of the inner core 233 is D1, the inner diameter of the supporting roller 220 is D2, and each of the convex cores 2332A, 2332B, and 2332C is The distance between the top and the support roller 220 will be described as G, and the width of each of the convex cores 2332A, 2332B, and 2332C will be described as W.

  First, in the fixing device 800 of this example, the optimum separation distance G between the tops of the respective convex cores 2332A, 2332B, and 2332C of the inner core 233 (hereinafter referred to as “convex tips”) and the heating element (support roller 220). Will be described.

  In the fixing device 800 of this example, if the above-described separation distance G is too large, the magnetic coupling between the convex cores 2332A, 2332B, and 2332C of the center core 234 and the inner core 233 is reduced, and if the separation distance G is too small, There is a possibility that the cores 2332A, 2332B, 2332C and the heating element (supporting roller 220) come into contact with each other.

Table 1 shows the relationship between the configuration of the inner core 233 and the coupling coefficient k.

  As shown in Table 1, when only the small-diameter core 2331 having an outer diameter D1 of 12 mm (φ12) = 250 g was used as the inner core 233, the coupling coefficient k was 0.67. The coupling coefficient k is 0 when the inner core 233 in which the convex cores 2332A, 2332B, and 2332C are formed on the small-diameter core 2331 having the outer diameter D1 = 12 mm (φ12), that is, the inner core 233 having φ12 + convex core = 300 g is used. .70. Incidentally, the coupling coefficient k in the case of using the inner core 233 having an outer diameter of 16 mm (φ16) = 400 g was 0.72.

  FIG. 12 shows the separation distance and coupling coefficient when the width W of the convex portion of the inner core in the fixing device according to one embodiment of the present invention is fixed to 4 mm and the separation distance between the tip of the convex portion and the heating element is changed. It is a graph which shows the relationship.

  Here, the coupling coefficient k necessary for heat generation of the heating element (supporting roller 220) needs to be 0.685 or more in consideration of the ease of entering power into the exciting coil. In order to satisfy this relationship, as is apparent from FIG. 12, it is preferable that the separation distance G between the tip of the convex portion of the inner core 233 and the heating element is 3 mm or less.

  Further, in the fixing device 800 configured as in this example, in order to prevent contact between the protrusion of the inner core 233 and the heating element (supporting roller 220) due to variations in parts processing accuracy, assembly errors, and the like, It is preferable to secure a separation distance G between the protrusion tip and the heating element of at least 0.5 mm or more.

  Therefore, in the fixing device 800 of this example, it is preferable that the separation distance G between the protrusion tip of the inner core 233 and the heating element is in the range of 0.5 to 3 mm.

  Next, the width W of each convex core 2332A, 2332B, 2332C of the inner core 233 in the fixing device 800 of this example will be described.

  FIG. 13 shows the width of the convex core when the distance between the tip of the convex portion of the inner core and the heating element in the fixing device according to the embodiment of the present invention is fixed to 2 mm and the width of the convex core is changed. It is a graph which shows the relationship between a coupling coefficient.

  As shown in FIG. 13, the distance G between the convex ends of the convex cores 2332A, 2332B, and 2332C of the inner core 233 and the heating element is fixed to 2 mm, and the width W of each convex core 2332A, 2332B, and 2332C is set. When changed, the coupling coefficient k indicates k = 0.69 or more necessary for heat generation of the heating element if the width W of each of the convex cores 2332A, 2332B, and 2332C is 1 mm or more.

  Therefore, in the fixing device 800 of this example, the width W of each of the convex cores 2332A, 2332B, and 2332C is preferably in the range of 1 to 6 mm, and handling (handling property) of each of the convex cores 2332A, 2332B, and 2332C is considered. And 2 mm or more and 6 mm or less are preferable.

  In the fixing device 800 of the present example, the outer diameter D1 of the small-diameter core 2331 is preferably in the range of 10 to 14 mm (φ10 to φ14) due to the above.

  Next, an inner core having another configuration used in the fixing device 800 of this example will be described. FIG. 14A is a plan view of an inner core having another configuration used in the fixing device according to the embodiment of the present invention. FIG. 14B is a front view of the inner core. FIG. 14C is a right side view of the inner core. FIG.14 (d) is sectional drawing which fractured | ruptured the inner core shown in FIG.14 (c) by line segment XX.

  As shown in FIGS. 14A, 14B, and 14D, the inner core 1433 is composed of a fixing belt 210 as a heat generating element of a convex core 2332B having a B4 size width and a convex core 2332C having an A3 size width. The height of the top portions 2332b and 2332c of the portion facing the non-sheet-passing region having the maximum width (corresponding to the width of the magnetic shield 2333A) is higher than the height of the tip of the convex portion of the other portion. ing.

  The inner core 1433 configured as described above can increase the magnetic coupling between the top portion 2332c of the convex core 2332C and the center core 234, and can increase the magnetic flux in the non-sheet passing region when the A3 size recording paper 109 is passed. . Further, in a state where the convex core 2332C having an A3 size width faces the position facing the center core, the convex core 2332B forms a magnetic path of magnetic flux, and the top portion 2332b of the convex core 2332B is higher by one step. As a result, the magnetic flux in the non-sheet passing area when the A3 size recording sheet 109 is passed can be increased.

  Therefore, in the fixing device 800 using the inner core 1433, both ends of the fixing belt 210 caused by a decrease in magnetic flux due to the influence of the magnetic shield 2333A disposed on both sides of the convex core 2332A having an A4R size width. The heat generation temperature in the width direction of the fixing belt 210 can be made uniform by correcting the temperature drop.

  Next, an inner core having still another configuration used in the fixing device 800 of this example will be described. FIG. 15 is a side view of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention.

  The inner core 1533 shown in FIG. 15 has the magnetic shields 2333A, 2333A, 2233A, 2333A, 2233A, 2333A, 2C, 2C, 2C, 2C, 2C, 2C, 2C, 2C, 2C, 2C, and 2C so 2333B is provided. In the fixing device 800 of this example, the same effect can be obtained even when the inner core 1533 having such a configuration is used.

  Here, as shown in FIG. 16, the height of the surface of each magnetic shield 2333A, 2333B is preferably formed to be lower than the height of the convex tip of each convex core 2332A, 232B. The inner core 1633 shown in FIG. 16 can release the heat generated in the magnetic shields 2333A and 2333B to the small-diameter core 2331, and suppresses the radiation generated in the magnetic shields 2333A and 2333B to the heating element side. Can do.

  Next, an inner core having still another configuration used in the fixing device 800 of this example will be described. FIG. 17 is a schematic perspective view of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention.

  As shown in FIG. 17, the inner core 1733 is disposed on both sides of the magnetic shielding body 2333A disposed on both sides of the convex core 2332A having an A4R size width and the convex core 2332B having a B4 size width. The magnetic shield 2333B is provided with through holes 2333a and 2333b.

  The inner core 1733 configured as described above can reduce the heat capacities of the magnetic shield 2333A and the magnetic shield 2333B. Therefore, in the fixing device 800 using the inner core 1733, the rise (warm-up) time until the fixing belt 210 generates heat to a predetermined fixing temperature can be shortened, and the power consumption can be further reduced. it can. Note that the through holes of the magnetic shield 2333A and the magnetic shield 2333B may be provided only in one.

  Next, an inner core having still another configuration used in the fixing device 800 of this example will be described. FIG. 18 is a schematic perspective view of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention.

  As shown in FIG. 18, this inner core 1833 has a configuration in which magnetic flux guiding auxiliary cores 1801A and 1801B are provided at the portions of the through holes 2333a and 2333b of the respective magnetic shields 2333A and 2333B.

  As shown in FIG. 9, the fixing device 800 using the inner core 1833 has a magnetic shield 2333 </ b> B with the convex core 2332 </ b> C having the maximum size width (here, A3 size width) facing the center core 234. The magnetic flux 401 ′ flowing toward the arrangement site can be guided toward the side core 235 by the magnetic flux guiding auxiliary core 1801B. However, in the case of the configuration shown in FIG. 18, the magnetic flux induction auxiliary core 1801A does not function as a magnetic flux induction auxiliary core but functions as a heat capacity correction core described below. The magnetic flux induction auxiliary core 1801A functions as a magnetic flux induction auxiliary core only when the arrangement of the magnetic flux induction auxiliary cores 1801A and 1801B is switched.

  On the other hand, since the convex cores of each size width have a heat capacity, the heat of the heating element is easily taken away by the convex cores, but the maximum size width (here In the state where the convex core 2332C of (A3 size width) faces the position facing the center core 234, the heat generation temperature tends to be uneven within the maximum size width with respect to a predetermined fixing temperature. However, the magnetic flux induction auxiliary cores 1801A and 1801B correct the difference in heat capacity depending on the length of each convex core, and the heat generation temperature within the maximum size width is made uniform with respect to a predetermined fixing temperature.

  Therefore, in the fixing device 800 using the inner core 1833, the both ends of the fixing belt 210 are caused by the decrease in magnetic flux due to the influence of the magnetic shield 2333A disposed on both sides of the convex core 2332A having an A4R size width. The temperature drop is corrected, and further, the difference in heat capacity due to the length of each convex core is corrected, and the heat generation temperature in the width direction of the fixing belt 210 can be made uniform. Only one of the magnetic flux induction auxiliary cores 1801A and 1801B may be provided.

  FIG. 19A is a schematic plan view of a main part of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention. FIG. 19B is a cross-sectional view of the inner core shown in FIG. 19A taken along line YY. An inner core 1933 shown in FIG. 19B is obtained by forming a magnetic shield 2333A and a magnetic shield 2333B with litz wires.

  As described above, the inner core 1933 in which the magnetic shield 2333A and the magnetic shield 2333B are formed of litz wire can suppress heat generation by the magnetic shield 2333A and the magnetic shield 2333B while maintaining the shielding effect of the magnetic flux. it can.

  FIG. 20 is a schematic side view of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention. An inner core 2033 shown in FIG. 20 is obtained by arranging a magnetic shield 2333A and a magnetic shield 2333B in close contact with a small-diameter core 2331 using an adhesive 2001 having high heat resistance and high heat conductivity.

  As described above, the inner core 2033 in which the magnetic shield 2333A and the magnetic shield 2333B are disposed so as to be in close contact with the small-diameter core 2331 using the adhesive 2001 having high heat resistance and high heat conductivity is used. Joule heat generated in 2333B can be transmitted to the small-diameter core 2331.

  Therefore, in the fixing device 800 using the inner core 2033, the heat generation of the magnetic shield 2333A and the magnetic shield 2333B can be more effectively suppressed.

  The fixing device according to the present invention can guide the magnetic flux flowing toward the magnetic shielding member in a state where the convex core having the maximum size width faces the center core toward the side core by the magnetic flux guiding core, Since the inner core can be reduced in size (lower heat capacity) without reducing the magnetic coupling between the portion of the convex core facing the magnetic shield and the inner core, the power consumption can be reduced. It is useful as a fixing device for an image forming apparatus such as an electrostatic recording type copying machine, a facsimile, and a printer.

1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus suitable for mounting a fixing device according to an embodiment of the present invention. Sectional drawing which shows the basic composition of the fixing device mounted in the image forming apparatus shown in FIG. FIG. 2 is a schematic perspective view showing a configuration of an inner core in the fixing device shown in FIG. FIG. 2 is a schematic cross-sectional view showing a cross section of a sheet passing area when performing paper width control heating in accordance with the A3 size width of the fixing device shown in FIG. FIG. 2 is a schematic cross-sectional view showing a cross section of a sheet passing area when performing paper width control heating in accordance with the B4 size width of the fixing device shown in FIG. FIG. 2 is a schematic cross-sectional view showing a cross section of a sheet passing region when performing paper width control heating in accordance with the A4R size width of the fixing device shown in FIG. The main part perspective view for demonstrating the behavior of the magnetic flux which flows along a small diameter core from the convex core of A3 size width of the inner core of the fixing device shown in FIG. Sectional drawing which shows the structure of the principal part of the fixing device which concerns on one embodiment of this invention. 1 is a schematic side view for explaining the flow of magnetic flux in a fixing device according to an embodiment of the present invention. 1 is a perspective view of a main part for explaining a flow of magnetic flux in a fixing device according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing a specific configuration of an inner core in a fixing device according to an embodiment of the present invention. The relationship between the separation distance and the coupling coefficient when the width of the protrusion of the inner core in the fixing device according to the embodiment of the present invention is fixed to 4 mm and the separation distance between the tip of the protrusion and the heating element is changed is shown. Graph In the fixing device according to the embodiment of the present invention, the width of the convex core and the coupling coefficient when the distance between the convex end of the inner core and the heating element is fixed at 2 mm and the width of the convex core is changed. Graph showing the relationship (A) is a plan view of an inner core of another configuration used in the fixing device according to the embodiment of the present invention, (b) is a front view of the inner core, (c) is a right side view of the inner core, (D) is sectional drawing which fractured | ruptured the right side surface of the said inner core shown to (c) by line segment XX. The side view of the inner core of the further another structure used with the fixing device which concerns on one embodiment of this invention. FIG. 6 is a schematic side view of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention. The schematic perspective view of the inner core of the further another structure used with the fixing device which concerns on one embodiment of this invention. The schematic perspective view of the inner core of the further another structure used with the fixing device which concerns on one embodiment of this invention. (A) is a schematic top view of the principal part of the inner core of the further another structure used with the fixing device which concerns on one embodiment of this invention, (b) is the inner core shown to (a) by line segment YY. Broken cross section FIG. 6 is a schematic side view of an inner core having still another configuration used in the fixing device according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Photosensitive drum 102 Charging device 103 Laser beam scanner 105 Developing device 107 Paper feeding device 109 Recording paper 110 Registration roller 112 Transfer roller 113 Cleaning device 200,800 Fixing device 210 Fixing belt 220 Support roller 230 Coil unit 231 Excitation coil 232 Core 233, 1433, 1533, 1633, 1733, 1833, 1933, 2033 Inner core 234 Center core 235 Side core 236 Arch core 240 Fixing roller 250 Pressure roller 260 Temperature sensor 401, 401 ', 501, 601 Magnetic flux 801 Magnetic flux induction core 1801A, 1801B Magnetic flux induction auxiliary core 2001 Adhesive 2331 Small diameter core 2332A, 2332B, 2332C Convex core 2332b, 2 32c top 2333A, 2333B magnetic shield 2333a, 2333b through hole

Claims (9)

A rotatable cylindrical heating element having a conductive layer;
An inner core rotatably disposed inside the heating element;
An exciting coil for inductively heating the conductive layer disposed so as to cover a part of the outer periphery of the heating element;
A center core disposed at the winding center of the exciting coil;
A side core disposed on a side portion of the exciting coil;
A plurality of convex cores provided in the inner core and having a size width corresponding to a sheet passing size of a recording medium and selectively facing a position facing the center core by rotation of the inner core;
A magnetic shield that is disposed on a side portion of the convex core having a smaller size width than the convex core having the maximum size width among the plurality of convex cores and blocks magnetic flux flowing in the non-sheet passing region of the heating element. Body,
A magnetic flux induction core that is provided on the inner core and that induces a magnetic flux that flows toward the arrangement portion of the magnetic shield in a state where the convex core having the maximum size width faces a position facing the center core, toward the side core; And a fixing device.   The fixing device according to claim 1, wherein a height of a surface of the magnetic shield is formed to be lower than a height of a top portion of the convex core.   The height of the top part of each convex core which is opposed to the maximum width non-sheet passing region of the heating element is formed higher than the height of the top part of the other part. Fixing device.   The fixing device according to claim 1, wherein a through hole is provided in the magnetic shield.   Magnetic flux that flows toward the magnetic shield placement site in a state where the convex core of the maximum size width faces the center core at a location of the through hole of the magnetic shield of the inner core. The fixing device according to claim 4, further comprising a magnetic flux guiding auxiliary core that guides toward the head.   The fixing device according to claim 1, wherein the magnetic shield is formed of a litz wire.   The fixing device according to claim 1, wherein the magnetic shield is bonded to the inner core using an adhesive having high heat resistance and high heat conductivity.   The fixing device according to claim 1, wherein a distance between the top of the convex core and the heating element is in a range of 0.5 to 3 mm. An image forming apparatus including a fixing unit that fixes an unfixed image formed on a recording medium,
An image forming apparatus using the fixing device according to claim 1 as the fixing unit.

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