Non-linear pressure observer design for pneumatic actuators

The robust precision dynamic control output of pneumatic systems requires model-based control techniques such as sliding mode and adaptive control. These controllers require full state knowledge of the system, viz. pressure, position, and velocity. For measuring two of the states, a pneumatic servo system requires two expensive pressure sensors per axis, and hence it makes the system economically non-competitive with most electromagnetic types of actuation. This paper presents the development of two Lyapunov-based pressure observers for the pneumatic actuator system. The first method shows that an energy-based stable pressure observer can be developed with the state equations. The other method incorporates the output error to control the convergence of the observed pressures. Simulation and experimental results are presented that demonstrate and validate effectiveness of the proposed observers