Patent ID: 8132808

Claim:
A sheet conveying device, comprising: a sheet container to contain a sheet stack including an uppermost sheet of multiple recording sheets on a sheet stacking tray; an elevator to raise and lower the sheet stacking tray; a sheet attraction and conveyance unit to attract the uppermost sheet placed on top of the sheet stack and convey the attracted uppermost sheet to an image forming device in which an image is formed and transferred onto a sheet; a first detector disposed downstream of the sheet container in a sheet conveying direction to detect a position of the uppermost sheet without contacting the uppermost sheet before the uppermost sheet is attracted to the sheet attraction and conveyance unit; a second detector disposed upstream of the sheet container in the sheet conveying direction to detect position of the uppermost sheet in a vertical direction, the second detector comprising: a driven contact roller contactable with the upstream end of an upper surface of the uppermost sheet in the sheet conveying direction and rotatably driven with a movement of the uppermost sheet; a top surface position detection member swingably disposed to support the driven contact roller; and an angle detector to detect an angle of the top surface position detection member so that the position of the uppermost sheet can be obtained based on the angle; and a controller comprising a processing unit to cause the first detector to detect the uppermost sheet, the elevator to lift and stop the sheet stack at a position where the sheet attraction and conveyance unit attracts the uppermost sheet thereto, and the second detector to detect the position of the uppermost sheet of the stopped sheet stack and store the detection result as a reference position in the controller, the controller performing a primary operation in which the sheet attraction and conveyance unit attracts the uppermost sheet for a given number of times and conveys the uppermost sheet while the second detector is contacting the uppermost sheet that is located at the reference position, and the controller calculates a variation amount of the angle detected by the second detector to convert to a thickness of M sheets, where “M” represents a positive number, and stores the result, and a secondary operation in which the driven contact roller of the second detector is retreated from a detecting position where the driven contact roller contacts the uppermost sheet to a non-detecting position where the driven contact roller is spaced from the uppermost sheet, and, each time the sheet attraction and conveyance unit attracts the uppermost sheet by a thickness of N sheets from the sheet stack and conveys the N sheets, where “N” represents a positive integer, the elevator moves up the sheet stack by a sheet amount calculated based on the thickness of M sheets stored in the controller, satisfying a relation of N=XM, where “X” indicates a positive number equal to or greater than 1.