  Electro-hydraulic servo-systems 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 electro-hydraulic 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 a sliding mode controller with a neural network
compensation scheme for electro-hydraulic systems subject to an unknown
dead-zone input. The boundedness and convergence properties of the closed-loop
signals are proven using Lyapunov stability theory. Numerical results are
presented in order to demonstrate the control system performance.
