[KenWittlief]

If you click on the advanced search option here on CD and search on

PID
or
Closed loop feedback

selecting 'search titles only' you will find a bunch of posts from previous years. most are locked so you cant reply to them, but lots of good info there.

PID stands for "proportional intergral differential". In motion terms that corresponds to a control system that looks at "position, velocity and acceleration" of where you are compaired to where you want to be.