Delivery mechanism, fixing device and image forming apparatus

Abstract

A sheet delivery mechanism including: a first roll; a second roll; and a plurality of convexes formed circumferentially for pushing a rear end of a sheet to be delivered, wherein: a sheet delivery roll pair comprises the first roll and the second roll in contact with each other; at least one of the first roll and the second roll is provided with the plurality of convexes; and one of the plurality of convexes is arranged to be more inside radially than the tangential line drawn from the radial tip of another convex upstream adjacent in the rotating direction to the one convex at issue to the outer periphery of the roll.

1 . A sheet delivery mechanism comprising: 
 a first roll;    a second roll; and    a plurality of convexes formed circumferentially for pushing a rear end of a sheet to be delivered, wherein:    a sheet delivery roll pair comprises the first roll and the second roll in contact with each other;    at least one of the first roll and the second roll is provided with the plurality of convexes; and    one of the plurality of convexes is arranged to be more inside radially than the tangential line drawn from the radial tip of another convex upstream adjacent in the rotating direction to the one convex at issue to the outer periphery of the roll.    
   
   
       2 . The sheet delivery mechanism according to  claim 1 , wherein 
 a portion more upstream than the radial tip of the one convex has a tapered shape with a gradient approximately equal to the tangential line drawn from the radial tip of another convex upstream adjacent in the rotating direction to the one convex to the outer periphery of the roll.    
   
   
       3 . The sheet delivery mechanism according to  claim 1 , wherein 
 the distance from the root of the one convex to a rotation center is shorter than the outer diameter of the roll.    
   
   
       4 . A sheet delivery mechanism comprising: 
 a first roll;    a second roll; and    a plurality of convexes formed circumferentially for pushing the rear end of a sheet to be delivered to shift inwardly in the radial direction through their elastic deformation, wherein    a sheet delivery roll pair comprises the first roll and the second roll in contact with each other;    at least one of the first roll and the second roll is provided with the plurality of convexes on its roll body;    where a sheet which receives pressure not lower than a predetermined pressure when it passes a nip passes the nip, the convex passing the same position as the nip in the rotating direction shifts inwardly in the radial direction; and    where the sheet which receives the pressure lower than the predetermined pressure when it passes the nip passes the nip, the convex keeps its normal convex shape.    
   
   
       5 . The sheet delivery mechanism according to claim  4 , wherein 
 the roll body and the convexes are integrally formed of resin, and the convexes are formed in a lightening shape or a shape with recesses on both ends in the axial direction    
   
   
       6 . The sheet delivery mechanism according to  claim 4 , wherein 
 the roll body and the convexes are formed separately from each other and made of different materials from each other    
   
   
       7 . The sheet delivery mechanism according to  claim 6 , wherein 
 the roll body comprises at least one of a tetrafluoroethylene-perfluoroalkylvinylether copolymer, a polytetrafluoroethylene and a tetrafluoroethylene-ethylene copolymer.    
   
   
       8 . The sheet delivery mechanism according to  claim 6 , wherein 
 the convexes comprises at least one of a polyacetal, a polypropylene and a polycarbonate.    
   
   
       9 . The sheet delivery mechanism according to  claim 1 , wherein 
 the sheet delivery roll pair serves as an inverting roll for duplex printing.    
   
   
       10 . A fixing device comprising: 
 a heating roll and a pressurizing roll for fixing a developer image on a sheet; and    a sheet delivery mechanism including: a first roll; a second roll; and a plurality of convexes formed circumferentially for pushing a rear end of the sheet to be delivered, wherein:    the heating roll and the pressurizing roll transport the sheet toward the sheet delivery mechanism;    a sheet delivery roll pair comprises the first roll and the second roll in contact with each other;    at least one of the first roll and the second roll is provided with the plurality of convexes; and    one of the plurality of convexes is arranged to be more inside radially than the tangential line drawn from the radial tip of another convex upstream adjacent in the rotating direction to the one convex at issue to the outer periphery of the roll.    
   
   
       11 . An image forming apparatus comprising: 
 a recording medium feeding unit for feeding a sheet;    a fixing device for fixing a developer image on the sheet; and    a transporting path that is arranged from the recording medium feeding unit to the fixing device, wherein    the fixing device includes a sheet delivery mechanism including: a first roll; a second roll; and a plurality of convexes formed circumferentially for pushing a rear end of the sheet to be delivered;    a sheet delivery roll pair comprises the first roll and the second roll in contact with each other;    at least one of the first roll and the second roll is provided with the plurality of convexes; and    one of the plurality of convexes is arranged to be more inside radially than the tangential line drawn from the radial tip of another convex upstream adjacent in the rotating direction to the one convex at issue to the outer periphery of the roll.