Abstract
This paper presents a three-link direct drive robot arm for wafer handling application. This robot arm is directly driven by three permanent magnet synchronous motors which are designed with flat structures and large rated torques. The mechanical structures of the presented robot arm and the PM motors are introduced and their dynamic models are derived. The frequency responses obtained from experimental tests reveal serious coupling effect of the system. A decoupling method based on computed torque control is proposed and the test results validate the effectiveness of this method. Robust SISO controllers are developed to control the PM motors after the decoupling. The experimental results demonstrate satisfying dynamic, settling and static performances with the proposed robust decoupling control.