Pressure observer-controller design for pneumatic cylinder actuators

Recent research has shown that robust and precise high-speed control of pneumatic actuators is practicable, by application of advanced control techniques such as model-based adaptive and sliding-mode control. However, the resulting need for full state-based feedback and feedforward control-in particular, the measurement of air pressures-increases both the cost and complexity of the overall system. In this paper, we consider the problem of design of observers to estimate the chamber pressure variables in a cylinder actuator. Since the cylinder pressures are not simultaneously observable because of the nature of cylinder dynamics, we first propose a continuous gain observer in which the pressure on one side of the cylinder is measured and the pressure on the other side is estimated. Next, we propose a sliding-mode observer where numerically estimated acceleration is used in order to observe both pressures, with ultimate bounded stability. A sliding-mode controller is proposed, whose sensitivity to errors under the sliding-mode observer is studied. The proposed observers are simple, effective and easy to implement. Results of experimental implementation illustrate the practical effectiveness of the new observers.