In this Letter, we study linear control of Euler-Lagrange (EL) systems. We
prove that there exists a linear proportional-integral-derivative control s
uch that any state of the EL system can be stabilized for any compact set o
f initial conditions. Basically, we show that integral control is necessary
to attain the control objective in the face of model uncertainties and non
linearities. We discuss some implications of our results on the control of
physical systems, e.g., control of human and animal motions. (C) 2000 Elsev
ier Science B.V. All rights reserved.