Sheet loading device, sheet post-processing device provided therewith, and image forming system

A sheet loading device comprising:

• a discharge roller pair which includes a drive roller and a driven roller which follows the drive roller to rotate, and which discharges a sheet;
• a loading tray which is arranged on a downstream side of the discharge roller pair with respect to a discharge direction of the sheet, and on which sheet discharged by the discharge roller pair is loaded;
• a paddle member which is arranged coaxial with the drive roller, and which rotates in a same direction as the drive roller to thereby come into contact, from above, with an upstream part, in the discharge direction, of the sheet discharged by the discharge roller pair;
• a sheet holding member which is arranged below the discharge roller pair, and which is swingable between a holding position at which the sheet holding member holds the upstream part, in the discharge direction, of the sheet loaded on the loading tray and a retraction position at which the sheet holding member releases holding of the sheet;
• a tray lifting-lowering drive portion which lifts and lowers the loading tray;
• a top surface detection sensor which switches between an on state in which the top surface detection sensor performs detection of a sheet loading surface of the loading tray or of a top surface of the sheet loaded on the sheet loading surface and an off state in which the top surface detection sensor does not perform the detection;
• and
• a control portion which controls the tray lifting-lowering drive portion,
• wherein
• the control portion which performs a lifting-lowering operation to arrange the loading tray at a reference position by lowering the loading tray with the sheet holding member arranged at the holding position to turn the top surface detection sensor into the off state, then lifting the loading tray to turn the top surface detection sensor into the on state, and then lowering the loading tray again to turn the top surface detection sensor into the off state and stopping the loading tray, and,
• with the loading tray at the reference position, a predetermined clearance is provided between the top surface of the sheet loaded on the loading tray and a rotational orbit of the paddle member.