Robust Performance of the Multiloop

A novel perturbation attenuation method is proposed for robust performance of mechanical systems. First, we give a uni- fied view on a class of existing perturbation observers and define the residual perturbation. In terms of the view and the definition, a new perturbation compensator with multiloop structure is devel- oped. It effectively compensates the perturbation (i.e., model un- certainty and external disturbance) to the plant in a hierarchical and recursive fashion. In the multiloop perturbation compensator (MPEC) proposed, as the number of loops increases, the external disturbance condition for system stability is greatly relaxed and the perturbation attenuation performance is gradually enhanced but the robust stability margin on the modeling error becomes more strict. A recursive algorithm for general -loop case of the MPEC is derived. By combining the developed robust perturbation com- pensator with a nominal feedback controller, a robust motion con- troller is synthesized. Experimental results for XY positioner and 2-DOF robot arms demonstrate the excellent robust tracking per- formance in spite of arbitrary large perturbation inputs.