Position control of a bio-inspired semi-active joint with direct inverse hysteresis modeling and compensation

Accurate position control of pneumatic artificial muscle actuated systems has always been difficult due to their inherent nonlinear hysteresis characteristics. This article designs a bio-inspired semi-active robotic joint that is synergistically driven by a pneumatic artificial muscle and an extension spring by imitating the mechanism of energy storage and return in animals and then studies its position tracking control with hysteresis compensation. To simplify the derivation of the inverse hysteresis model which functions as hysteresis compensator, a novel approach termed as direct inverse hysteresis modeling is adopted. With this method, the inversion of the asymmetric angle-pressure hysteresis of the semi-active joint is modeled directly from experimental measurements by a modified Prandtl-Ishlinskii model. On the basis, a closed-loop position tracking controller composed of forward hysteresis compensation and conventional proportional-integral-derivative control is designed for the joint. Experimental results indicate that the proposed controller can track the reference position signals with high accuracy.