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Chapter 5

Robust Control of

Robotic Manipulators

In this chapter we discuss the control of robots when their dynamical model
is uncertain. This may arise because the robot is carrying an unknown load
or because the exact evaluation of the robot’s dynamics is too costly. The
robust controllers in this chapter are obtained from modifications to the
controllers designed in Chapter 4.

5.1 Introduction

The control of uncertain systems is usually accomplished using either an
adaptive control or a robust control philosophy. In the adaptive approach,
one designs a controller that attempts to “learn” the uncertain parameters
of the system and, if properly designed, will eventually be a “best” controller
for the system in question. In the robust approach, the controller has a fixed
structure that yields “acceptable” performance for a class of plants which
include the plant in question. In general, the adaptive approach is applicable
to a wider range of uncertainties, but robust controller are simpler to
implement and no time is required to “tune” the controller to the particular
plant. In this chapter we review different robust control designs used in
controlling the motion of robots. The adaptive control approach is discussed
in Chapter 6. The robust control methods presented in this chapter may be
used to analyze the performance of the simple controllers used by robot
manufacturers which were discussed in Chapter 4, and to suggest
improvements and modifications. In fact, we are able to determine the range

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Copyright © 2004 by Marcel Dekker, Inc.