Performing explosive motions using a multi-joint arm actuated by pneumatic muscles with quasi-DDP optimal control

Abstract

New actuators are expected to endow robots with the capability to execute explosive movements such as throwing, kicking or jumping. In the present paper, we present a ball throwing and kicking tasks performed by an anthropomorphic arm with each joint actuated by an agonist-antagonistic pair of Mckibben artificial muscles. Pneumatic actuators have inherent compliance and hence they are very interesting for applications involving interaction with environment or human. However, the control of such systems is known to be difficult. The paper presents an implementation of iterative Linear Quadratic Regulator (iLQR) based optimal control for such actuators. The method is applied to positioning tasks and generation of explosive throwing of a ball to a maximum distance and kicking a ball. It is then compared to traditional control strategies to justify that optimal control is effective in controlling the position in highly non-linear pneumatic systems. The algorithm validation is reported here by several simulations and hardware experiments in which the shoulder and elbow flexion are controlled simultaneously.