Patent ID: 7458570

Claim:
A sheet-supplying device comprising: a sheet-accommodating tray having a bottom plate for supporting a plurality of sheets in a stacked arrangement, wherein the sheet has a surface including one end portion and another end portion; a raising/lowering unit for raising and lowering the sheet-accommodating tray in a stacked direction substantially perpendicular to the bottom tray; a first position sensor detector for detecting a first position indicating a position in the stacked direction of one end portion of a topmost sheet stacked in the sheet-accommodating tray; a second position sensor for detecting a second position indicating a position in the stacked direction of another end portion of the topmost sheet; a controlling unit for controlling the raising/lowering unit to raise or lower the sheet-accommodating tray, based on both the first position detected by the first position sensor and the second position detected by the second position sensor, wherein-one end portion of the topmost sheet in the stacked status is positioned at a prescribed position in the stacked direction; an air jetting unit for blowing air onto at least one of said one end portion of the topmost sheet detected by said first position sensor and said one end portion of the topmost sheet detected by said second position sensor in order to float one end portion of the topmost sheet; a sucking unit for sucking air in order to attract the topmost sheet, wherein only the topmost sheet in the floated status is attracted when one end of the topmost sheet in the stacked status is at the prescribed position; and a sheet-conveying unit for conveying the sheet attracted to the sucking unit; wherein the controlling unit is arranged to set a reference position value by controlling the raising/lowering unit to raise or lower the sheet-accommodating tray to a tray position at which the first position sensor detects a first position having a predetermined value and to stop the sheet-accommodating tray at said tray position, and by setting the reference position value based on the value of the second position detected by the second sensor with the tray at said tray position, and wherein the controlling unit is arranged for controlling the raising/lowering unit while the sheet-conveying unit conveys the sheet, based on comparing a second position value detected by the second position sensor to the reference position value.