  Electrohydraulic servosystems are widely employed in industrial applications
such as robotic manipulators, active suspensions, precision machine tools and
aerospace systems. They provide many advantages over electric motors, including
high force to weight ratio, fast response time and compact size. However,
precise control of electrohydraulic actuated systems, due to their inherent
nonlinear characteristics, cannot be easily obtained with conventional linear
controllers. Most flow control valves can also exhibit some hard nonlinearities
such as dead-zone due to valve spool overlap. This work describes the
development of an adaptive fuzzy controller for electrohydraulic actuated
systems with unknown dead-zone. The stability properties of the closed-loop
systems was proven using Lyapunov stability theory and Barbalat's lemma.
Numerical results are presented in order to demonstrate the control system
performance.
