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.