MODAL FRAMEWORK FOR CLOSED-LOOP ANALYSIS OF OVER-ACTUATED MOTION SYSTEMS

A large class of motion systems used in precision applications is required to meet increasing levels of tracking performance whereas costs should not rise drastically. Allowing for more actuators and sensors than rigid-body modes, which is called over-actuation, higher levels of performance can be obtained without increasing mechanical stiffness. However, the design of MIMO controllers for motion systems is not straightforward and a better understanding of the modal behavior in closedloop would be valuable. In this paper we introduce a new framework to analyze multivariable controllers for over-actuated motion systems in modal form. This approach enables us to analyze various closed-loop properties, such as modal tracking behavior and modal disturbance attenuation. Both feedback and feedforward performance is evaluated at the same time, using a global performance measure. The new approach is illustrated by an example.