Reaction disturbance cancellation for a magnetically levitated ladder arm of clean-room robot

This paper treats a disturbance cancellation problem for minimizing the effects of reaction forces on position accuracy of a clean-room robot applied with magnetic bearings. The robot is composed of a main body and a ladder arm, and moves without friction at joints owing to magnetic support. The support stiffness is, however, weaker than the conventional bearings, and the ladder arm moves in reaction to rotary motion of the main body. A feedforward controller is designed to compensate the effects of the reaction forces, and implemented successfully to reduce the transverse displacements of the ladder arm when the main body rotates.