Variable structure control of a rodless pneumatic servoactuator with discontinuous sliding surfaces

A rodless pneumatic servoactuator undergoes disturbances that do not satisfy the matching condition. Standard variable structure control approach leads to a disturbance-contaminated sliding surface and loses the disturbance rejection attribute. A two-fold sliding modes approach is employed to resolve this problem. Integration of the two layers of sliding surfaces yields a single discontinuous surface, on which the unmatched disturbances can be rejected. Set point regulation and sinusoidal tracking experiments using both approaches as well as PID control are conducted and compared to demonstrate the effectiveness of the proposed method