Sheet stacking apparatus having tray that is lifted and lowered and image forming apparatus

A sheet stacking apparatus on which sheets received from an image forming apparatus are stacked, comprising:

• a stacking unit that stacks sheets thereon;
• a drive unit configured to drive said stacking unit to be lifted and lowered;
• a determination unit configured to determine a lifted or lowered state of said stacking unit;
• and
• a control unit configured to, in a case where said determination unit determines that said stacking unit is not lowered when said control unit controls said drive unit to lower said stacking unit, control said drive unit to lift said stacking unit, and in a case where said determination determines that said stacking unit is not lifted, decide that said drive unit is abnormal, whereas in a case where said determination determines that said stacking unit is lifted, decide that said drive unit is free from abnormality.

An image forming apparatus comprising:

• an image forming unit configured to form an image on a sheet based on an input job;
• a stacking unit that stacks thereon sheets each having an image formed thereon by said image forming unit;
• a drive unit configured to drive said stacking unit to be lifted and lowered;
• a determination unit configured to determine a lifted or lowered state of said stacking unit;
• and
• a control unit configured to, in a case where said determination unit determines that said stacking unit is not lowered when said control unit controls said drive unit to lower said stacking unit, suspend the job, control said drive unit to lift said stacking unit, and in a case where said determination determines that said stacking unit is lifted, resume the job.