In this paper, we aim at achieving accurate positioning control of a pneumatic actuation mechanism of antagonist-type by means of the simple adaptive control (SAC) method. Since this plant does not satisfy the ASPR-ness condition, we introduce a parallel feedforward compensator (PFC) so that the SAC strategy can be applied. However, the introduction of PFC leads to performance deterioration and in particular causes a steady state error. To suppress the steady-state error while keeping the fundamental structure of the SAC system, we introduce a “constant scaling” to the SAC system. We also consider a “dynamic scaling” so that the transient response of the controlled system can be improved. Through experiments, we show that the SAC strategy with these scalings is indeed effective in achieving accurate positioning control.
