Modelling and control of a 2 D.O.F. high-precision positionning system

Abstract

We present a hierarchical controller for a set of two linear synchronous motors with permanent magnets moving in two orthogonal directions for a two degree of freedom high-precision positionning system developed by Newport-France. This system is supposed to realize relatively fast linear displacements from 1 count (4 nm) to 400 mm. A linear displacement of 25mm must be achieved in less than 0.2 s with maximum acceleration of 1 g and current and voltage limitations, and with an error in the final position less than 1 count. A nonlinear model of the plant is obtained, consisting of two independent subsystems, representing the two linear drive dynamics. Flatness based motion planning and tracking design are proposed. Each motor's tracking controller is then realized in a hierarchical way by a high level force control loop and a low level current loop.