Simple closed-loop control has been used for decades to perform machine tool contouring. But a number of refinements are increasingly used in industry today. These refinements are usually aimed at handling special control applications that may include synchronization of multiple axes or web presses. Additional improvements handle high-speed precision positioning and changing loads and inertias when positioning the joints in robot arms.
Common variations on the basic closed-loop techniques often concern four specific areas: filtering, synchronization of multiple axes, handling instabilities caused by gear backlash, and obtaining low position error during acceleration and deceleration.