A shape memory alloy based tendon-driven actuation system for biomimetic artificial fingers, part II: modelling and control

In this paper, the dynamics and biomimetic control of an artificial finger joint actuated by two opposing oneway shape memory alloy (SMA) muscle wires that are configured in a double spring-biased agonist-antagonist fashion is presented. This actuation system, which was described in Part I, forms the basis for biomimetic tendon-driven flexion/extension and abduction/adduction of the artificial finger. The work presented in this paper centres on thermomechanical modelling of the SMA wire, including both major and minor hysteresis loops in the phase transformation model, and co-operative control strategy of the agonist-antagonist muscle pair using a pulse-width-modulated proportional-integral-derivation (PWM-PID) controller. Parametric analysis and identification are carried out based on both simulation and experimental results. The performance advantage of the proposed cooperative control is shown using the metacarpophalangeal joint of the artificial finger.