Analysis and Modeling of Air-Core Monopole Linear Motor for Nanopositioning System

In the ultra-precision system, the multi-axis servo system is composed of air-core monopole linear motors (AMLM) for achieving nanopositioning. In the AMLM system, the thrust varies according to the changes of the relative position of motor's primary and secondary. In this paper, the concept of thrust stiffness is proposed in order to illustrate the phenomenon of varieties of thrust according to changes in position. By using the surface charge model, the air-gap magnetic flux density of AMLM is predicted. Based on this prediction, the whole winding's thrust, including straight and corner segments of winding, is calculated. Then, this winding thrust model is simplified to replace the original complicated analytical model. The accuracy of the simplified model is verified by the corresponding experimental tests. Thus, the thrust stiffness simplification model can be used in the feedforward compensation model in the control system of AMLM and efficiently decrease the calculation time of DSP.