Design and Control of 3-DOF Reluctance-force-type Magnetic Levitator Module for Fine-positioning Short-stroke Stage

This paper presents the design and control of a three degrees-of-freedom (3-DOF) magnetic levitation module for fine-positioning short-stroke actuators to be serially connected to high-acceleration long-stroke stages. The 3-DOF levitator module consists of two stator assemblies with iron-cores having actuating coils and permanent magnets (PMs) along the magnetic path. The levitating target is an U-shaped rotor with its weight passively compensated by the PM-biased flux and the lateral-direction force is balanced out by the symmetric structure. In such a magnetic levitator design, the PM-biased flux is superposed with the current-driven flux, enabling to control the reluctance forces in both the levitational and lateral directions in a decoupled manner to achieve active 3-DOF motion control. The control performance of the proposed 3-DOF magnetic levitator is experimentally validated to have RMS (root-mean-square) position tracking errors of 4.3 µm for the translation motions and 5.97 µdeg for the rotational motion. These control performances show a great potential of the magnetic levitation module to be utilized for fine-positioning short-stroke actuators that can overcome high inertial forces generated by serially-connected long-stroke actuators such as high-throughput linear stages and robotic arms.