Image forming device modifying nip pressure of nip formed in fixing device before motor is halted

Abstract

In an image forming device, a first fixing member has a roller. A second fixing member has a belt to form a nip together with the first fixing member. A pressure modifying mechanism modifies a nip pressure at the nip to selected one of a first nip pressure and a second nip pressure smaller than the first nip pressure. A controller drives the first motor to drive the roller and fixes the developer image on a sheet in a state that the nip pressure is the first nip pressure. The controller modifies the nip pressure from the first nip pressure to the second nip pressure while driving the first motor in a case where a final sheet among one or more sheets fixed according to a print job has passed the nip, and halts the first motor after the nip pressure is modified to the second nip pressure.

What is claimed is: 
     
         1 . An image forming device comprising:
 a sheet tray configured to accommodate a sheet;   a sheet feeder configured to feed the sheet from the sheet tray;   a first photosensitive drum;   a first developing roller configured to supply developer to the first photosensitive drum;   a second photosensitive drum;   a second developing roller configured to supply developer to the second photosensitive drum;   a transfer unit including a belt configured to move in a moving direction, the transfer unit being in contact with the first photosensitive drum located at a first position, the transfer unit being in contact with the second photosensitive drum located at a second position downstream of the first position in the moving direction, the transfer unit configured to transfer developer images formed on the first photosensitive drum and the second photosensitive drum to the sheet;   a switch mechanism configured to: switch a state of the first developing roller between a first contact state in which the first developing roller is in contact with the first photosensitive drum and a first separated state in which the first developing roller is separated from the first photosensitive drum; and switch a state of the second developing roller between a second contact state in which the second developing roller is in contact with the second photosensitive drum and a second separated state in which the second developing roller is separated from the second photosensitive drum;   a first fixing rotator;   a heater configured to heat the first fixing rotator;   a second fixing rotator to form a nip together with the first fixing rotator;   a pressure modifying mechanism configured to modify a nip pressure at the nip to selected one of a first nip pressure and a second nip pressure smaller than the first nip pressure; and   a controller configured to perform:
 in a case where a final sheet among one or more sheets is printed according to a print job,
 switching, after the sheet feeder feeds the final sheet, the state of the first developing roller to the first separated state from the first contact state by using the switching mechanism; 
 switching, after the state of the first developing roller is switched to the first separated state, the state of the second developing roller to the second separated state from the second contact state by using the switching mechanism; and 
 modifying, after the final sheet passes the nip, the nip pressure to the second nip pressure from the first nip pressure by using the pressure modifying mechanism. 
 
   
     
     
         2 . The image forming device according to  claim 1 , wherein the controller is configured to further perform:
 halting the rotation of the first fixing rotator after the modifying the nip pressure to the second nip pressure from the first nip pressure is completed.   
     
     
         3 . The image forming device according to  claim 1 , further comprising:
 a first motor configured to drive the first fixing rotator; and   a second motor configured to drive the pressure modifying mechanism.   
     
     
         4 . The image forming device according to  claim 3 , wherein the second motor is configured to further drive the first developing roller and the second developing roller. 
     
     
         5 . The image forming device according to  claim 4 , wherein the controller is configured to further perform:
 controlling the second motor to rotate in forward to drive the first developing roller and the second developing roller; and   controlling the second motor to rotate in reverse to drive the pressure modifying mechanism so that the pressure modifying mechanism modifies the nip pressure to the second nip pressure from the first nip pressure.   
     
     
         6 . The image forming device according to  claim 3 , wherein the second motor is configured to further drive the switch mechanism. 
     
     
         7 . The image forming device according to  claim 1 , further comprising:
 a third photosensitive drum; and   a third developing roller configured to supply developer to the third photosensitive drum,   wherein the transfer unit is in contact with the third photosensitive drum located at a third position between the first position and the second position in the moving direction,   wherein the switch mechanism is configured to further switch a state of the third developing roller between a third contact state in which the third developing roller is in contact with the third photosensitive drum and a third separated state in which the third developing roller is separated from the third photosensitive drum,   wherein the controller is configured to further perform:
 switching, after the state of the first developing roller is switched to the first separated state, the state of the third developing roller to the third separated state from the third contact state by using the switching mechanism, 
   wherein after the state of the third developing roller is switched to the third separated state from the third contact state, the controller switches the state of the second developing roller to the second separated state from the second contact state by using the switching mechanism.   
     
     
         8 . An image forming device comprising:
 a sheet tray configured to accommodate a sheet;   a sheet feeder configured to feed the sheet from the sheet tray;   a first photosensitive drum;   a first developing roller configured to supply developer to the first photosensitive drum;   a second photosensitive drum;   a second developing roller configured to supply developer to the second photosensitive drum;   a transfer unit including a belt configured to move in a moving direction, the transfer unit being in contact with the first photosensitive drum located at a first position, the transfer unit being in contact with the second photosensitive drum located at a second position downstream of the first position in the moving direction, the transfer unit configured to transfer developer images formed on the first photosensitive drum and the second photosensitive drum to the sheet;   a switch mechanism configured to: switch a state of the first developing roller between a first contact state in which the first developing roller is in contact with the first photosensitive drum and a first separated state in which the first developing roller is separated from the first photosensitive drum; and switch a state of the second developing roller between a second contact state in which the second developing roller is in contact with the second photosensitive drum and a second separated state in which the second developing roller is separated from the second photosensitive drum;   a fixing roller;   a first motor configured to drive the fixing roller;   a fixing belt to form a nip together with the fixing roller;   a pressure modifying mechanism including a cam, the pressure modifying mechanism being configured to modify a nip pressure at the nip to selected one of a first nip pressure and a second nip pressure smaller than the first nip pressure;   a second motor configured to drive the cam; and   a controller configured to perform:
 in a case where a final sheet among one or more sheets is printed according to a print job,
 switching, after the sheet feeder feeds the final sheet, the state of the first developing roller to the first separated state from the first contact state by using the switching mechanism; 
 switching, after the state of the first developing roller is switched to the first separated state, the state of the second developing roller to the second separated state from the second contact state by using the switching mechanism; and 
 modifying, after the final sheet passes the nip, the nip pressure to the second nip pressure from the first nip pressure by controlling the second motor to drive the cam. 
 
   
     
     
         9 . The image forming device according to  claim 8 , wherein the controller is configured to further perform:
 halting the rotation of the fixing roller by halting the first motor after the modifying the nip pressure to the second nip pressure from the first nip pressure is completed.   
     
     
         10 . The image forming device according to  claim 8 , wherein the second motor is configured to further drive the first developing roller and the second developing roller. 
     
     
         11 . The image forming device according to  claim 10 , wherein the controller is configured to further perform:
 controlling the second motor to rotate in forward to drive the first developing roller and the second developing roller; and   controlling the second motor to rotate in reverse to drive the pressure modifying mechanism so that the pressure modifying mechanism modifies the nip pressure to the second nip pressure from the first nip pressure.   
     
     
         12 . The image forming device according to  claim 8 , wherein the second motor is configured to further drive the switch mechanism. 
     
     
         13 . The image forming device according to  claim 8 , further comprising:
 a third photosensitive drum; and   a third developing roller configured to supply developer to the third photosensitive drum,   wherein the transfer unit is in contact with the third photosensitive drum located at a third position between the first position and the second position in the moving direction,   wherein the switch mechanism is configured to further switch a state of the third developing roller between a third contact state in which the third developing roller is in contact with the third photosensitive drum and a third separated state in which the third developing roller is separated from the third photosensitive drum,   wherein the controller is configured to further perform:
 switching, after the state of the first developing roller is switched to the first separated state, the state of the third developing roller to the third separated state from the third contact state by using the switching mechanism, 
   wherein after the state of the third developing roller is switched to the third separated state from the third contact state, the controller switches the state of the second developing roller to the second separated state from the second contact state by using the switching mechanism.   
     
     
         14 . The image forming device according to  claim 8 , further comprising:
 a nip forming member configured to press the fixing belt toward the fixing roller so that the fixing roller and the fixing belt form the nip.   
     
     
         15 . The image forming device according to  claim 14 , wherein the nip forming member includes a pad made of a rubber. 
     
     
         16 . The image forming device according to  claim 14 , further comprising a holder holding the nip forming member,
 wherein the holder is movable in a prescribed direction orthogonal to an axial direction of the fixing roller.   
     
     
         17 . The image forming device according to  claim 8 , further comprising a heater configured to heat the fixing roller.