Heating device with thermometers and thermostats alternately arranged on a heat conductor

Abstract

A fixing device which heats an image formed on a sheet to fix the image thereon, includes a cylindrical film supported in a rotatable manner and having an outer circumferential surface that comes into contact with the sheet, and a heater unit provided in an inner space of the cylindrical film to heat an inner circumferential surface thereof. The heater unit includes a plurality of first heating elements disposed along a longitudinal direction of the cylindrical film, and a first temperature sensor configured to measure a temperature of one of the plurality of first heating elements. The plurality of first heating elements and the first temperature sensor are connected in series by a first wiring.

What is claimed is: 
     
         1 . A fixing device which heats an image formed on a sheet to fix the image thereon, the fixing device comprising:
 a cylindrical film supported in a rotatable manner and having an outer circumferential surface that comes into contact with the sheet; and   a heater unit provided in an inner space of the cylindrical film to heat an inner circumferential surface thereof and including:
 a plurality of first heating elements disposed along a longitudinal direction of the cylindrical film, and 
 a first temperature sensor configured to measure a temperature of one of the plurality of first heating elements, wherein 
   the plurality of first heating elements and the first temperature sensor are connected in series by a first wiring.   
     
     
         2 . The fixing device according to  claim 1 , further comprising:
 a controller configured to electrically connect or disconnect the first wiring and to which the temperature measured by the first temperature sensor is input, wherein   the controller disconnects the first wiring when the measured temperature is an abnormal temperature higher than a target temperature.   
     
     
         3 . The fixing device according to  claim 1 , wherein
 the heater unit further includes:
 a second heating element by which a central portion of the cylindrical film in the longitudinal direction is heated, and 
 a second temperature sensor configured to measure a temperature of one of the second heating element and the central portion, 
   the plurality of first heating elements is a pair of heating elements by which end portions of the cylindrical film in the longitudinal direction are heated, and   the second heating element is connected to the plurality of first heating elements in parallel by a second wiring.   
     
     
         4 . The fixing device according to  claim 1 , wherein
 the heater unit further includes a second heating element by which a central portion of the cylindrical film in the longitudinal direction is heated, and   the plurality of first heating elements, the second heating element, and the first temperature sensor are connected in series by the first wiring.   
     
     
         5 . The fixing device according to  claim 1 , wherein the first temperature sensor is a thermostat. 
     
     
         6 . An image forming apparatus comprising:
 a transfer unit configured to transfer an image on a sheet; and   the fixing device according to  claim 1 , which fixes the transferred image on the sheet.   
     
     
         7 . A fixing device which heats an image formed on a sheet to fix the image thereon, the fixing device comprising:
 a cylindrical film supported in a rotatable manner and having an outer circumferential surface that comes into contact with the sheet; and   a heater unit provided in an inner space of the cylindrical film to heat a heated area thereof and including:
 a plurality of first heating elements disposed along a longitudinal direction of the cylindrical film, and 
 a first temperature sensor configured to measure a temperature of the heated area, wherein 
   the plurality of first heating elements and the first temperature sensor are connected in series by a first wiring.   
     
     
         8 . The fixing device according to  claim 7 , further comprising:
 a controller configured to electrically connect or disconnect the first wiring and to which the temperature measured by the first temperature sensor is input, wherein   the controller disconnects the first wiring when the measured temperature is an abnormal temperature higher than a target temperature.   
     
     
         9 . The fixing device according to  claim 7 , wherein
 the heater unit further includes:
 a second heating element by which a central portion of the heated area in the longitudinal direction is heated, and 
 a second temperature sensor configured to measure a temperature of the central portion of the heated area, 
   the plurality of first heating elements is a pair of heating elements by which end portions of the heated area in the longitudinal direction are heated,   the temperature measured by the first temperature sensor is a temperature of one of the end portions of the heated area, and   the second heating element is connected to the plurality of first heating elements in parallel by a second wiring.   
     
     
         10 . The fixing device according to  claim 7 , wherein
 the heater unit further includes a second heating element by which a central portion of the heated area in the longitudinal direction is heated, and   the plurality of first heating elements, the second heating element, and the first temperature sensor are connected in series by the first wiring.   
     
     
         11 . The fixing device according to  claim 7 , wherein the first temperature sensor is a thermostat. 
     
     
         12 . An image forming apparatus comprising:
 a transfer unit configured to transfer an image on a sheet; and   the fixing device according to  claim 7 , which fixes the transferred image on the sheet.   
     
     
         13 . A fixing device which heats an image formed on a sheet to fix the image thereon, the fixing device comprising:
 a cylindrical film supported in a rotatable manner and having an outer circumferential surface that comes into contact with the sheet; and   a heater unit provided in an inner space of the cylindrical film to heat a heated area thereof and a heat conductor, the heater unit including:
 a plurality of first heating elements disposed along a longitudinal direction of the cylindrical film, and 
 a first temperature sensor configured to measure a temperature of the heat conductor, wherein 
   the plurality of first heating elements and the first temperature sensor are connected in series by a first wiring.   
     
     
         14 . The fixing device according to  claim 13 , wherein the heat conductor is between the first temperature sensor and the plurality of first heating elements. 
     
     
         15 . The fixing device according to  claim 14 , wherein the heater unit further includes a substrate including a first surface on which the plurality of first heating elements are disposed and a second surface on which the heat conductor is disposed. 
     
     
         16 . The fixing device according to  claim 13 , further comprising:
 a controller configured to electrically connect or disconnect the first wiring and to which the temperature measured by the first temperature sensor is input, wherein   the controller disconnects the first wiring when the measured temperature is an abnormal temperature higher than a target temperature.   
     
     
         17 . The fixing device according to  claim 13 , wherein
 the heater unit further includes:
 a second heating element by which a central portion of the heated area in the longitudinal direction is heated, and 
 a second temperature sensor configured to measure a temperature of a part of the heat conductor corresponding to the central portion, 
   the plurality of first heating elements is a pair of heating elements by which end portions of the heated area in the longitudinal direction are heated,   the temperature measured by the first temperature sensor is a temperature of another part of the heat conductor corresponding to one of the end portions, and   the second heating element is connected to the plurality of first heating elements in parallel by a second wiring.   
     
     
         18 . The fixing device according to  claim 13 , wherein
 the heater unit further includes a second heating element by which a central portion of the heated area in the longitudinal direction is heated, and   the plurality of first heating elements, the second heating element, and the first temperature sensor are connected in series by the first wiring.   
     
     
         19 . The fixing device according to  claim 13 , wherein the first temperature sensor is a thermostat. 
     
     
         20 . An image forming apparatus comprising:
 a transfer unit configured to transfer an image on a sheet; and   the fixing device according to  claim 13 , which fixes the transferred image on the sheet.