Paper feeder and image forming device incorporating same

Abstract

A paper feeder including: a push-up mechanism that pushes up an end portion of a tray below a leading end of a stack of sheets; a paper feed roller that intersects a locus fitted to motion of the end portion of the tray or an extension of the locus in the direction of the motion, and applies a conveying force to a sheet that the push-up mechanism presses against the paper feed roller to move the sheet in a conveyance direction; a separation member that forms a nip with the paper feed roller and applies a resistance force in a direction opposite the conveyance direction to the sheet; and an auxiliary roller upstream in the conveyance direction from the locus that applies a conveying force in the conveyance direction to the sheet, maintaining a state of contact between the sheet and the paper feed roller.

What is claimed is: 
     
         1 . A paper feeder that feeds out a sheet from a stack of sheets stacked on a tray, the paper feeder comprising:
 a push-up mechanism that pushes up an end portion of the tray below a leading end of the stack;   a paper feed roller including an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction;   a separation member that forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller; and   an auxiliary roller including an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller.   
     
     
         2 . The paper feeder of  claim 1 , wherein
 the conveying force and a sheet feed amount of the auxiliary roller are designed to be less than the conveying force and a sheet feed amount of the paper feed roller, respectively.   
     
     
         3 . The paper feeder of  claim 1 , wherein
 the conveying force of the auxiliary roller is designed with an upper limit such that, if the leading end of the sheet is prevented from proceeding at the nip between the paper feed roller and the separation member, the auxiliary roller slips on a surface of the sheet.   
     
     
         4 . The paper feeder of  claim 1 , further comprising
 a support mechanism that moves the auxiliary roller between a pressure contact position where the outer circumferential surface of the auxiliary roller intersects a movable range of the sheet when the push-up mechanism pushes up the end portion of the tray and a retracted position where the outer circumferential surface of the auxiliary roller is positioned outside the movable range.   
     
     
         5 . The paper feeder of  claim 4 , wherein
 the support mechanism maintains the auxiliary roller at the pressure contact position during rotation of the paper feed roller and moves the auxiliary roller to the retracted position when the paper feed roller stops.   
     
     
         6 . The paper feeder of  claim 4 , wherein
 the support mechanism maintains the auxiliary roller at the pressure contact position while the push-up mechanism pushes up the end portion of the tray and moves the auxiliary roller to the retracted position when the push-up mechanism lowers the end portion of the tray.   
     
     
         7 . The paper feeder of  claim 4 , wherein
 a magnitude of a component in the normal direction of the sheet of a force applied to the sheet by the outer circumferential surface of the auxiliary roller at the pressure contact position is determined by a total weight of the auxiliary roller and components of the support mechanism including a bearing of the auxiliary roller.   
     
     
         8 . The paper feeder of  claim 4 , wherein
 the support mechanism includes   an actuator and   a link mechanism that moves the auxiliary roller by using output of the actuator.   
     
     
         9 . The paper feeder of  claim 1 , wherein
 the auxiliary roller includes a torque transmission mechanism that transmits to the auxiliary roller a portion of drive torque acting on the paper feed roller to synchronize rotation of the auxiliary roller with rotation of the paper feed roller.   
     
     
         10 . The paper feeder of  claim 9 , wherein
 the torque transmission mechanism includes a belt that is suspended between a shaft of the auxiliary roller and a shaft of the paper feed roller and rotates the auxiliary roller as the paper feed roller rotates.   
     
     
         11 . The paper feeder of  claim 1 , wherein
 the separation member includes an elastic material pad that forms a nip with the paper feed roller.   
     
     
         12 . The paper feeder of  claim 1 , wherein
 the separation member includes a separation roller with a torque limiter and forms a nip with the paper feed roller.   
     
     
         13 . The paper feeder of  claim 1 , wherein
 the tray is a manual feed tray.   
     
     
         14 . An image forming device comprising:
 a paper feeder that feeds out a sheet from a stack of sheets stacked on a tray;   a conveyance section that conveys the sheet fed from the paper feeder; and   a printer that forms an image on the sheet conveyed by the conveyance section,   the paper feeder comprising:   a push-up mechanism that pushes up an end portion of the tray below a leading end of the stack;   a paper feed roller including an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction;   a separation member that forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller; and   an auxiliary roller including an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller.