Fuser using endless belt and image forming apparatus

Abstract

According to one embodiment, a fuser includes a heat roller, an endless belt, a first press roller and a second press roller. The heat roller rotates and contacts a toner surface side of a sheet, and heats the sheet. The endless belt contacts a part of an outer peripheral surface of the heat roller. The first press roller contacts a part of an inner peripheral surface of the endless belt, and is provided at an insertion part of the sheet in a nip portion where the heat roller contacts the endless belt. The second press roller contacts a part of the inner peripheral surface of the endless belt, is provided at an exit part of the sheet in the nip portion, and has a lower rotational resistance than the first press roller.

What is claimed is: 
     
       1. A fuser comprising:
 a heat roller configured to rotate, contact a toner surface side of a sheet and heat the sheet;   an endless belt that contacts a part of an outer peripheral surface of the heat roller;   a first press roller that contacts a part of an inner peripheral surface of the endless belt and is provided at an insertion part of the sheet in a nip portion where the heat roller contacts the endless belt; and   a second press roller that contacts a part of the inner peripheral surface of the endless belt and is provided at an exit part of the sheet in the nip portion, wherein   the first press roller includes a first bearing at an end of a rotary shaft of the first press roller,   the second press roller include a second bearing at an end of a rotary shaft of the second press roller,   a bearing type of the second bearing is different from a bearing type of the first bearing, and   the second bearing has a rotational resistance lower than the first bearing.   
     
     
       2. The fuser according to  claim 1 , wherein the first press roller and the second press roller apply a specific tensile force to the endless belt and form the nip portion. 
     
     
       3. The fuser according to  claim 1 , wherein the first bearing of the first press roller is a sliding bearing assembly, and the second bearing of the second press roller is a ball bearing assembly. 
     
     
       4. The fuser according to  claim 1 , wherein the first bearing of the first press roller is a sliding bearing assembly, and the second bearing of the second press roller has a longer length in a rotary shaft direction than the first bearing of the first press roller. 
     
     
       5. The fuser according to  claim 1 , wherein
 the first bearing of the first press roller is provided at both ends of the rotary shaft of the first press roller, and   the second bearing of the second press roller is provided at both ends of the rotary shaft of the second press roller.   
     
     
       6. The fuser according to  claim 1 , wherein the first bearing of the first press roller is a sliding bearing assembly, and the second bearing of the second press roller has a longer length in a rotary shaft direction than the first bearing of the first press roller. 
     
     
       7. The fuser according to  claim 6 , wherein
 the first bearing of the first press roller has a grease different from that of the second bearing of the second press roller, and   a viscosity of the grease used for the first bearing of the first press roller is higher than a viscosity of the grease of the second bearing of the second press roller.   
     
     
       8. The fuser according to  claim 1 , wherein the rotary shaft of the first press roller has a diameter larger than a diameter of the rotary shaft of the second press roller. 
     
     
       9. The fuser according to  claim 2 , wherein a part of the endless belt is arranged between the heat roller and the first press roller in a state where the endless belt contacts both the heat roller and the first press roller. 
     
     
       10. The fuser according to  claim 9 , wherein a part of the endless belt is arranged between the heat roller and the second press roller in a state where the endless belt contacts both the heat roller and the second press roller. 
     
     
       11. The fuser according to  claim 2 , wherein a frictional resistance of a contact surface between an inside of the endless belt and the first press roller is higher than a frictional resistance of a contact surface between an outside of the endless belt and the heat roller. 
     
     
       12. An image forming apparatus comprising:
 a plurality of photoconductive bodies on each of which a latent image is formed;   a developing unit configured to supply a developer to the photoconductive bodies and form toner images on the photoconductive bodies;   a transfer unit configured to transfer the toner images formed on the photoconductive bodies by the developing unit to a sheet;   a heat roller configured to rotate, contact a toner surface side of the sheet and heat the sheet;   an endless belt that contacts a part of an outer peripheral surface of the heat roller;   a first press roller that contacts a part of an inner peripheral surface of the endless belt and is provided at an insertion part of the sheet in a nip portion where the heat roller contacts the endless belt; and   a second press roller that contacts a part of the inner peripheral surface of the endless belt and is provided at an exit part of the sheet in the nip portion, wherein   the first press roller includes a first bearing at an end of a rotary shaft of the first press roller,   the second press roller include a second bearing at an end of a rotary shaft of the second press roller,   a bearing type of the second bearing is different from a bearing type of the first bearing, and   the second bearing has a rotational resistance lower than the first bearing.   
     
     
       13. The apparatus according to  claim 12 , wherein the first press roller and the second press roller apply a specific tensile force to the endless belt and form the nip portion. 
     
     
       14. The apparatus according to  claim 12 , wherein the first bearing of the first press roller is a sliding bearing assembly, and the second bearing of the second press roller is a ball bearing assembly. 
     
     
       15. A fuser for fusing a toner on a surface of a sheet, comprising:
 a rotary member configured to rotate and contact a toner receiving side of a sheet;   an endless belt contacting an outer peripheral surface of the rotary member;   a first roller contacting an inner peripheral surface of the endless belt, the first roller provided at an insertion location of a sheet into a nip portion of the fuser formed where the rotary member contacts the endless belt;   a second roller contacting the inner peripheral surface of the endless belt at an exit location of a sheet from the nip portion; and   a heater configured to heat the sheet, wherein   the first roller includes a first bearing and the second roller includes a second bearing, and   the first bearing is of a type having a first rotational resistance and the second bearing is of a type having a second rotational resistance that is lower than the first rotational resistance such that the surface speed of the first roller surface which contacts the endless belt is lower than the surface speed of the second roller surface which contacts the endless belt.    
     
     
       16. The fuser of claim 15, wherein the first bearing and the second bearing are different bearing types.  
     
     
       17. The fuser of claim 16, wherein the second bearing is a roller bearing and the first bearing is a bearing type other than a roller bearing having a rolling resistance greater than a roller bearing.  
     
     
       18. The fuser of claim 15, wherein the first bearing is a roller bearing of a first size and the second bearing is a roller bearing of a second size, and the first size is greater than the second size.  
     
     
       19. The fuser of claim 15, wherein the first and second rollers have a central longitudinal axis, and the first bearing is longer in a central longitudinal axis direction than the length of the second bearing in the central longitudinal axis direction.  
     
     
       20. The fuser of claim 15, wherein the first bearing is lubricated with a first grease and the second bearing is lubricated with a second grease that is different from the first grease.  
     
     
       21. The fuser of claim 20, wherein the first grease has a viscosity higher than a viscosity of the second grease.  
     
     
       22. The fuser of claim 15, wherein the first bearing is a sliding bearing of a first length along a rotational axis of the first roller and the second bearing is a sliding bearing of a second length along a rotational axis of the second roller, the first length being greater than the second length.  
     
     
       23. A fuser for fusing a toner on a surface of a sheet, comprising:
 a rotary member configured to rotate and contact a toner receiving side of a sheet;   an endless belt contacting an outer peripheral surface of the rotary member;   a first roller contacting an inner peripheral surface of the endless belt, the first roller provided at an insertion location of a sheet into a nip portion of the fuser formed where the rotary member contacts the endless belt;   a second roller contacting the inner peripheral surface of the endless belt at an exit location of a sheet from the nip portion; and   a heater configured to heat the sheet, wherein   the first roller includes a first bearing assembly having a first grease type applied thereto,   the second roller includes a second bearing assembly having a second grease type applied thereto, and   the first grease type has a higher viscosity than the second grease type such that the surface speed of the first roller surface which contacts the endless belt is lower than the surface speed of the second roller surface which contacts the endless belt.    
     
     
       24. A fuser for fusing a toner on a surface of a sheet, comprising:
 a rotary member configured to rotate and contact a toner receiving side of a sheet;   an endless belt contacting an outer peripheral surface of the rotary member;   a first roller contacting an inner peripheral surface of the endless belt, the first roller provided at an insertion location of a sheet into a nip portion of the fuser formed where the rotary member contacts the endless belt;   a second roller contacting the inner peripheral surface of the endless belt at an exit location of a sheet from the nip portion; and   a heater configured to heat the sheet, wherein   the first roller includes a first bearing that is a first size type and the second roller includes a second bearing that is a second size type that is different from the first size type, and   the second bearing has a rotational resistance that is lower than a rotational resistance of the first bearing.    
     
     
       25. The fuser of claim 24, wherein the surface speed of the first roller surface which contacts the endless belt is lower than the surface speed of the second roller surface which contacts the endless belt.  
     
     
       26. The fuser of claim 24, wherein the first size type has an inner diameter that is larger than an inner diameter of the second size type.