High-precision motion control of a stage with pneumatic artificial muscles

Pneumatic artificial muscles (PAMs) have been applied in bionic robots, welfare devices, and parallel manipulators because of their many advantages over traditional actuators; such advantages include their high power-to-weight ratio, high power-to-volume ratio, high degree of safety, and stick-slip-free operation. However, significant nonlinearities in PAMs cause low controllability and limit their application. This research aims to provide a practical controller design method for high-precision motion of PAM mechanisms, and this paper proposes a simple and practical controller design method. This controller is designed based on our previous positioning controller and includes a phase-lead element that reduces residual vibration and a simple modified feed-forward element that improves its following ability. The proposed controller design procedure can be easily implemented in PAM mechanisms without an exact dynamic model. This system's motion control performance was evaluated experimentally. The positioning results indicate that the maximum steady-state error is reduced to 0.7 μm and that the transient response's overshoot is eliminated using a reconstructed step-like reference signal. The experimental results show that the maximum errors are less than 2 and 5 μm under 0.1- and 0.5-Hz sinusoidal tracking control, respectively. Moreover, the designed control system's robustness for positioning and tracking was examined in experiments using an additional mass.