Heating device, fixing device, and image processing apparatus

Abstract

A heating device for heating a medium on which an image can be formed includes a cylindrical belt, a first heating unit, and a second heating unit. The first and second heating units are inside the cylindrical belt and face an inner circumferential surface of the belt. A controller is configured to control the heating units to generate heat. When the medium is to be heated to reach an image fixing temperature at which the image can be fixed to the medium, the controller controls the first and second heating units to both generate heat. After the medium is heated to the image fixing temperature, the controllers control the first heating unit to generate heat, but not the second heating unit.

1 . A heating device, comprising:
 a cylindrical belt;   a first heating unit and a second heating unit inside the belt, facing an inner circumferential surface of the belt, and extending along an axial direction of the belt, the second heating unit having a length in the axial direction that is greater than a length of the first heating unit in the axial direction; and   a controller configured to control the first and second heating units, wherein   when the medium is to be heated to reach an image fixing temperature, the controller controls both the first and second heating units to generate heat, and   after the medium has been heated to the image fixing temperature, the controller controls the first heating unit to generate heat and the second heating unit to not generate heat.   
     
     
         2 . The heating device according to  claim 1 , wherein
 the first and second heating units are arranged on a substrate extending along a longitudinal direction that is parallel to the axial direction of the cylindrical belt.   
     
     
         3 . The heating device according to  claim 2 , wherein
 the first heating unit generates heat in a first region of the cylindrical belt at a center thereof in the axial direction, and   the second heating unit generates heat in a second region of the cylindrical belt beyond the first region along the axial direction.   
     
     
         4 . The heating device according to  claim 3 , wherein the second heating unit also generates heat in the first region. 
     
     
         5 . The heating device according to  claim 4 , wherein the first and second heating units are arranged parallel to each other on the substrate. 
     
     
         6 . (canceled) 
     
     
         7 . The heating device according to  claim 1 , further comprising:
 a heat conduction member in contact with at least one of the first and second heating units.   
     
     
         8 . The heating device according to  claim 7 , wherein
 the heat conduction member is in contact with the first heating unit.   
     
     
         9 . The heating device according to  claim 1 , wherein a resistance temperature coefficient of the first heating unit is different from a resistance temperature coefficient of the second heating unit. 
     
     
         10 . The heating device according to  claim 9 , wherein the resistance temperature coefficient of the second heating unit is less than the resistance temperature coefficient of the first heating unit. 
     
     
         11 . A fixing device for fixing an image to a sheet, comprising:
 a cylindrical belt that contacts a sheet;   a first heating unit and a second heating unit inside the cylindrical belt, facing an inner circumferential surface of the cylindrical belt, and extending along an axial direction of the cylindrical belt, the second heating unit having a length in the axial direction that is greater than a length of the first heating unit in the axial direction; and   a controller configured to control the first and second heating units, wherein   when the sheet is to be heated to reach an image fixing temperature, the controller controls both the first and second heating units to generate heat, and   after the sheet is heated to the image fixing temperature, the controller controls the first heating unit to generate heat and the second heating unit not to generate heat.   
     
     
         12 . The fixing device according to  claim 11 , wherein an image is formed on the sheet with a toner. 
     
     
         13 . The fixing device according to  claim 11 , wherein
 the first and second heating units are arranged on a substrate extending along a longitudinal direction that is parallel to the axial direction of the cylindrical belt.   
     
     
         14 . The fixing device according to  claim 13 , wherein
 the first heating unit generates heat in a first region of the cylindrical belt at a center thereof in the axial direction, and   the second heating unit generates heat in a second region of the cylindrical belt beyond the first region along the axial direction.   
     
     
         15 . The fixing device according to  claim 13 , wherein the second heating unit also generates heat in the first region. 
     
     
         16 . An image processing apparatus, comprising:
 an image forming unit configured to form an image on a sheet;   a conveyance roller configured to convey the sheet to the image forming unit;   a cylindrical belt that contacts the sheet after the sheet is conveyed to the image forming unit;   a first heating unit and a second heating unit inside the cylindrical belt, facing an inner circumferential surface of the cylindrical belt, and extending along an axial direction of the cylindrical belt, the second heating unit having a length in the axial direction that is greater than a length of the first heating unit in the axial direction; and   a controller configured to control the first and second heating units, wherein   when the sheet is to be heated to reach an image fixing temperature, the controller controls both the first and second heating units to generate heat, and   after the sheet is heated to the image fixing temperature, the controller controls the first heating unit to generate heat and the second heating unit to not generate heat.   
     
     
         17 . The image processing apparatus according to  claim 16 , further comprising:
 a pressure roller contacting the cylindrical belt to form a nip.   
     
     
         18 . The image processing apparatus according to  claim 16 , wherein
 the first and second heating units are arranged on a substrate extending along a longitudinal direction that is parallel to the axial direction of the cylindrical belt.   
     
     
         19 . The image processing apparatus according to  claim 18 , wherein
 the first heating unit generates heat in a first region of the cylindrical belt at a center thereof in the axial direction, and   the second heating unit generates heat in a second region of the cylindrical belt beyond the first region along the axial direction.   
     
     
         20 . The image processing apparatus according to  claim 18 , wherein the second heating unit generates heat in the first region. 
     
     
         21 . The heating device according to  claim 2 , wherein the second heating unit is closer to an edge of the substrate in a direction crossing the longitudinal direction than the first heating unit.