An Application of Mu-Synthesis to the Elevation Axis Control of a Gun-Pointing System

Dr. Vince Marcopoli
General Dynamics Land Systems

This talk describes how the mu-synthesis control design method has been applied to the M1A2 tank elevation system. It is meant to be tutorial in nature, and after a brief description of the general system and goals of the control problem, describes the application of the robust control framework. Particular attention is given to the practical issues of 1) design-oriented modeling, 2) defining realistic nominal performance objectives, and 3) defining appropriate robustness objectives to address model imperfections and plant variations. To elaborate, design-oriented modeling refers to a method of depicting the physical system that facilitates the application of modern robust control techniques. This involves defining performance, robustness, and controller inputs and outputs. Nominal performance objectives are defined in mu-synthesis via H-infinity constraints on certain frequency weighted transfer functions. Unfortunately, selection of the frequency weights is difficult in general. This work illustrates how an existing classical control system has been used to establish such frequency weights. Finally, robustness objectives are also addressed via frequency weighted transfer functions. As in performance specification, these frequency weights are generally difficult to obtain, due to their interpretation as uncertainty bounds. This issue is addressed here using the classical system as a guide, and gives rise to an iterative approach of arriving at such weights. An example of the iteration process is shown to illustrate this approach.