Post-processing apparatus and image forming apparatus

A post-processing apparatus comprising:

• an ejection tray configured to receive a recording medium that is ejected;
• an elastic member configured to urge the ejection tray upward in a vertical direction;
• a moving mechanism configured to cause the ejection tray to move up and down in the vertical direction;
• and
• a driving source configured to drive the moving mechanism,
• wherein the moving mechanism comprises a holding plate,
• wherein the ejection tray is fixed to the holding plate,
• wherein the elastic member is configured to urge the holding plate upward in the vertical direction,
• wherein the post-processing apparatus further comprises:
• a detector configured to detect a position of the ejection tray;
• and
• at least one processor configured to execute a controller configured to estimate a weight of a recording medium placed on the ejection tray using a position detected by the detector,
• wherein the controller is configured to control vertical movement of the ejection tray when power is supplied to the driving source,
• wherein the post-processing apparatus is configured such that, when the moving mechanism is not being driven by the driving source, the position of the ejection tray is moved by a total weight of the ejection tray and the recording medium placed on the ejection tray, and
• wherein the detector includes:
• a member that has a plurality of holes having different widths and that is configured to move as the ejection tray moves;
• and
• an optical sensor that is fixed to an apparatus body and that is configured to measure the widths of the plurality of holes.