Overcoming actuator performance degradation caused by non-smooth nonlinearities

In this paper, we outline our design efforts to control the output of a pneumatic actuator. The actuator in hand exhibits significant coulomb friction and hysteresis type characteristics, both of which harden the control problem-especially when the reference signal becomes small in magnitude. Additionally, the pneumatic actuator responds differently for increasing and decreasing values of the pressure within the chamber. The major design constraints are: 1) to avoid significant overshoot while; and 2) maintaining close tracking for a wide class of reference signals. A variable structure controller (together with some feedforward terms) is utilized to achieve the design specifications.