# US 8,571,458 B2 · Fixing device with a plurality of core bodies and image forming apparatus including the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,571,458 B2 - Document ID: US8571458B2 - Status: Granted - Kind: B2 - Application number: 13/013,868 - Filed: 2011-01-26 - Published: 2011-07-28 - Granted: 2013-10-29 - Earliest claimed: 2010-01-28 - Assignees: KYOCERA Document Solutions Inc. - Applicants: Seiji Okada - Inventors: Seiji Okada - Web page: https://patentgrep.com/patent/US8571458B2 ## CPC - G03G 15/2053: {Structural details of heat elements, e.g. structure of roller or belt, eddy current, induction heating} - G03G 2215/2032: the belt further entrained around additional rotating belt support members - G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY ## Abstract A fixing device includes a coil disposed along an outer surface of a heating member and configured to generate magnetic flux for heating the heating member through induction heating; and a core unit being configured to constitute a part of a magnetic path around the coil. The core unit includes a plurality of core bodies arranged in a width direction of a recording medium to be conveyed, the core bodies being made of magnetic material; and a shaft having an outer surface on which the core bodies are arranged, a length of the outer surface being longer than a sum of lengths of the core bodies arranged thereon, the core body lengths including axial tolerances of the core bodies. A gap is provided between any adjacent ones of the core bodies. ## Claims ### Claim 1 A fixing device that fixes an image on a recording medium, the fixing device comprising: a coil disposed along an outer surface of a heating member and configured to generate magnetic flux for heating the heating member through induction heating; and a core unit being configured to constitute a part of a magnetic path around the coil, wherein the core unit includes a plurality of core bodies arranged in a width direction of the recording medium to be conveyed, the core bodies being made of magnetic material; and a shaft having an outer surface on which the plurality of core bodies are arranged, a length of the outer surface being longer than a sum of lengths of the plurality of core bodies arranged on the outer surface, the core body lengths including axial tolerances of the plurality of core bodies, wherein a gap is provided between any adjacent ones of the plurality of core bodies arranged on the shaft, and wherein the gap is located in or around a center of a sheet passing region of a recording medium having a minimum printable size. ### Claim 2 (depends on 1) The fixing device according to claim 1, wherein the plurality of core bodies are arranged on the shaft with reference to both axial ends of the outer surface. ### Claim 3 (depends on 1) The fixing device according to claim 1, wherein the gap is provided with an elastic member in contact with the adjacent core bodies. ### Claim 4 (depends on 3) The fixing device according to claim 3, wherein the elastic member is a spring member. ### Claim 5 (depends on 4) The fixing device according to claim 4, further comprising caps, wherein the shaft has a shaft core; the caps engage with and are secured to respective ends of the shaft core; of the plurality of core bodies arranged on the shaft, the outermost core bodies in an axial direction of the shaft engage with and are secured to the respective caps; and the core bodies arranged inside the outermost core bodies are secured in position by being pressed toward the corresponding caps by the spring member. ### Claim 6 (depends on 1) The fixing device according to claim 1, further comprising caps, wherein the shaft has a shaft core; the caps engage with and are secured to respective ends of the shaft core; and of the plurality of core bodies arranged on the shaft, the outermost core bodies in an axial direction of the shaft engage with and are secured to the respective caps. ### Claim 7 (depends on 6) The fixing device according to claim 6, wherein the core bodies arranged inside the outermost core bodies are sequentially bonded and secured to the outermost core bodies. ### Claim 8 (depends on 1) The fixing device according to claim 1, wherein a length of the gap is about 6.0 mm or less. ### Claim 9 (depends on 1) The fixing device according to claim 1, wherein the length of the gap is approximately equal to or greater than the sum of the axial tolerances of the plurality of core bodies. ### Claim 10 An image forming apparatus comprising: an image forming section including at least one image bearing member bearing a toner image thereon; a transfer unit configured to transfer a toner image formed on the image bearing member onto a recording medium; and a fixing device configured to fix the toner image on the recording medium, the toner image having been transferred onto the recording medium by the transfer unit, wherein the fixing device includes a coil disposed along an outer surface of a heating member and configured to generate magnetic flux for heating the heating member through induction heating; and a core unit being configured to constitute a part of a magnetic path around the coil, wherein the core unit includes a plurality of core bodies arranged in a width direction of the recording medium to be conveyed, the core bodies being made of magnetic material; and a shaft having an outer surface on which the plurality of core bodies are arranged, the outer surface being longer than a sum of lengths of the plurality of core bodies arranged on the outer surface, the core body lengths including axial tolerances of the plurality of core bodies wherein a gap is provided between any adjacent ones of the plurality of core bodies arranged on the shaft, and wherein the gap is located in or around a center of a sheet passing region of a recording medium having a minimum printable size. ### Claim 11 (depends on 10) The image forming apparatus according to claim 10, wherein the plurality of core bodies are arranged on the shaft with reference to both axial ends of the outer surface. ### Claim 12 (depends on 10) The image forming apparatus according to claim 10, wherein the gap is provided with an elastic member in contact with the adjacent core bodies. ### Claim 13 (depends on 12) The image forming apparatus according to claim 12, wherein the elastic member is a spring member. ### Claim 14 (depends on 13) The image forming apparatus according to claim 13, further comprising caps, wherein the shaft has a shaft core; the caps engage with and are secured to respective ends of the shaft core; of the plurality of core bodies arranged on the shaft, the outermost core bodies in an axial direction of the shaft engage with and are secured to the respective caps; and the core bodies arranged inside the outermost core bodies are secured in position by being pressed toward the corresponding caps by the spring member. ### Claim 15 (depends on 10) The image forming apparatus according to claim 10, further comprising caps, wherein the shaft has a shaft core; the caps engage with and are secured to respective ends of the shaft core; and of the plurality of core bodies arranged on the shaft, the outermost core bodies in an axial direction of the shaft engage with and are secured to the respective caps. ### Claim 16 (depends on 15) The image forming apparatus according to claim 15, wherein the core bodies arranged inside the outermost core bodies are sequentially bonded and secured to the outermost core bodies. ### Claim 17 (depends on 10) The image forming apparatus according to claim 10, wherein a length of the gap is 6.0 mm or less. ### Claim 18 (depends on 10) The image forming apparatus according to claim 10, wherein the length of the gap is approximately equal to or greater than the sum of the axial tolerances of the plurality of core bodies. ### Claim 19 A fixing device that fixes an image on a recording medium, the fixing device comprising: a coil disposed along an outer surface of a heating member and configured to generate magnetic flux for heating the heating member through induction heating; and a core unit being configured to constitute a part of a magnetic path around the coil, wherein the core unit includes a plurality of core bodies arranged in a width direction of the recording medium to be conveyed, the core bodies being made of magnetic material; and a shaft having an outer surface on which the plurality of core bodies are arranged, a length of the outer surface being longer than a sum of lengths of the plurality of core bodies arranged on the outer surface, the core body lengths including axial tolerances of the plurality of core bodies, wherein a gap is provided between any adjacent ones of the plurality of core bodies arranged on the shaft, and wherein the gap is provided with an elastic member in contact with the adjacent core bodies.