Sheet feeding

Abstract

A sheet feeding device includes a tray to store a stack of sheets, and a sheet elevation mechanism provided at the bottom of the tray to lift the stack of sheets until a top sheet of the stack of sheets reaches a predetermined height position. A paper feed roller is disposed above the tray to come in contact with the top sheet having reached the predetermined height position and rotated by a motor to deliver the top sheet from the tray. Additionally, the sheet feed device includes a controller to control the sheet elevation mechanism based on a drive torque of the motor to adjust the height position of the stack of sheets, after delivery of the first sheet from the tray by the paper feed roller and upon delivery of a second sheet by the paper feed roller. The frictional force to be produced between the second sheet and the paper feed roller is substantially equal to the frictional force produced between the first sheet and the paper feed roller during delivery of the first sheet.

1 . A sheet feeding device comprising:
 a tray to store a stack of sheets;   a sheet elevation mechanism provided at a bottom of the tray to lift the stack of sheets until a top sheet of the stack of sheets reaches a predetermined height position;   a paper feed roller disposed above the tray to come in contact with the top sheet having reached the predetermined height position and rotationally driven by a motor to deliver the top sheet from the tray; and   a controller to control the sheet elevation mechanism based on a drive torque of the motor to adjust the height position of the stack of sheets, after delivery of the first sheet from the tray by the paper feed roller and upon delivery of a second sheet by the paper feed roller, such that the frictional force produced between the second sheet and the paper feed roller is substantially equal to the frictional force produced between the first sheet and the paper feed roller during delivery of the first sheet.   
     
     
         2 . The sheet feeding device according to  claim 1 , comprising a current detection circuit to measure a current value of the motor indicative of the drive torque of the motor,
 the controller to measure a first current value of the motor with the current detection circuit during delivery of the first sheet,   the controller to measure a second current value of the motor with the current detection circuit during delivery of the second sheet,   the controller to control the sheet elevation mechanism to lift the stack of sheets when the second current value is less than a reference current value determined based on the first current value by more than a predetermined threshold value; and   the controller to control the sheet elevation mechanism to halt the movement of the stack of sheets when the absolute value of a difference between the second current value and the reference current value is not greater than the predetermined threshold value.   
     
     
         3 . The sheet feeding device according to  claim 2 ,
 the controller to control the sheet elevation mechanism to lower the stack of sheets when the second current value is greater than the reference current value by more than the predetermined threshold value.   
     
     
         4 . The sheet feeding device according to  claim 1 , comprising a leading edge sensor to detect delivery of sheets from the tray,
 the controller to selectively deliver the second sheet when the leading edge sensor has detected that the first sheet has been delivered from the tray.   
     
     
         5 . The sheet feeding device according to  claim 2 ,
 the controller to measure the first current value of the motor with the current detection circuit after a predetermined waiting time has passed from the start of delivery of the first sheet, and   the controller to measure the second current value of the motor with the current detection circuit after the predetermined waiting time has passed from the start of delivery of the second sheet.   
     
     
         6 . The sheet feeding device according to  claim 5 ,
 the controller to measure the first current value of the motor with the current detection circuit a plurality of times after the predetermined waiting time has passed from the start of delivery of the first sheet, and   the controller to determine the reference current value based on the measured plurality of first current values.   
     
     
         7 . The sheet feeding device according to  claim 1 , comprising an upper limit sensor to detect that the top sheet of the stack of sheets has reached the predetermined height position. 
     
     
         8 . The sheet feeding device according to  claim 2 ,
 the controller to halt the motor when the second current value is less than a predetermined non-feeding detection value or greater than a predetermined double-feeding detection value.   
     
     
         9 . A method comprising:
 lifting, with a sheet elevation mechanism, a stack of sheets from the bottom of a tray until a top sheet of the stack of sheets reaches a predetermined height position and a paper feed roller disposed above the tray makes contact with the top sheet;   rotationally driving the paper feed roller by a motor to deliver the top sheet from the tray by the paper feed roller; and   controlling the sheet elevation mechanism based on a drive torque of the motor to adjust the height position of the stack of sheets, after delivery of the first sheet from the tray by the paper feed roller and upon delivery of a second sheet by the paper feed roller, such that the frictional force to be produced between the second sheet and the paper feed roller is substantially equal to the frictional force produced between the first sheet and the paper feed roller during delivery of the first sheet.   
     
     
         10 . The method according to  claim 9 , wherein controlling the sheet elevation mechanism based on the drive torque of the motor comprises:
 measuring a first current value of the motor indicative of the drive torque of the motor during delivery of the first sheet;   measuring a second current value of the motor indicative of the drive torque of the motor during delivery of the second sheet;   controlling the sheet elevation mechanism to lift the stack of sheets when the second current value is less than a reference current value determined based on the first current value by more than a predetermined threshold value; and   controlling the sheet elevation mechanism to halt the movement of the stack of sheets when the difference between the second current value and the reference current value is not greater than the predetermined threshold value.   
     
     
         11 . The method according to  claim 10 , wherein controlling the sheet elevation mechanism based on a drive torque of the motor comprises controlling the sheet elevation mechanism to lower the stack of sheets when the second current value is greater than the reference current value by more than the predetermined threshold value. 
     
     
         12 . The method according to  claim 10 , wherein measuring the first current value of the motor indicative of the drive torque of the motor during delivery of the first sheet includes measuring the first current value of the motor after a predetermined waiting time has passed from the start of delivery of the first sheet, and
 wherein measuring the second current value of the motor indicative of the drive torque of the motor during delivery of the second sheet includes measuring the second current value of the motor after the predetermined waiting time has passed from the start of delivery of the second sheet.   
     
     
         13 . The method according to  claim 12 , wherein measuring the first current value of the motor after the predetermined waiting time has passed from the start of delivery of the first sheet includes measuring the first current value of the motor a plurality of times after the predetermined waiting time has passed from the start of delivery of the first sheet, and
 wherein determining the reference current value based on the measured first current value includes determining the reference current value based on the measured plurality of first current values.   
     
     
         14 . The method according to  claim 10 , comprising halting the motor when the second current value is less than a predetermined non-feeding detection value or greater than a predetermined double-feeding detection value. 
     
     
         15 . The method according to  claim 9 , wherein the delivery of the second sheet is selectively performed when the first sheet has been delivered from the tray.