Sheet feeding device and image forming apparatus

A sheet feeding device which feeds a sheet, comprising:

• a tray which supports the sheet and is capable of being lifted up and down;
• a driving mechanism which lifts up and down the tray;
• a sheet feeding portion which feeds a sheet at a topmost position of a sheet stack supported by the tray;
• an air loosening device which blows air to an end portion of the sheet stack supported by the tray;
• an upper limit detection sensor which is turned ON as the topmost sheet reaches an upper limit position of a feeding enabled range while lifting up the tray;
• a lower limit detection sensor which is turned ON as the topmost sheet reaches a lower limit position of a feeding enabled range while lifting up the tray;
• and
• a control device which controls the driving mechanism,
• wherein after the upper limit detection sensor is turned ON by a sheet floated by air from the air loosening device, the control device controls driving mechanism to lower the tray until the upper limit detection sensor is turned OFF, and
• when the air loosening device starts to blow air, counting of a pulse number is started, and
• in the case that the upper limit detection sensor is turned OFF and the counting of pulse member is larger than a predetermined pulse number, the control device controls the driving mechanism to raise the tray to a position corresponding to the predetermined pulse number, and in the case that the upper limit detection sensor is turned OFF and the counting of pulse member is smaller than the predetermined pulse number, the control device controls the driving mechanism to stop the tray.