Dynamic Manipulability for a Two-Link Manipulator Driven By Pneumatic Artificial Muscles and Passive Springs

Abstract

In the case of manipulators actuated by unidirectional pneumatic artificial muscles (PAMs) and passive restoring springs, the system parameters and spring stiffness affect the reachable workspace and the dynamic manipulability. A two-link planar manipulator actuated by PAMs and passive springs was designed and fabricated to analyze the limitations of its dynamic manipulability. Kinematic analysis and forward dynamics simulations show the influence of parameters of passive springs, such as spring stiffness and spring prestretch, on workspace and trajectory tracking performance. Simulation results prove the limitations on the dynamic motion ability of a manipulator with passive springs in certain regions of its workspace as compared to that of bidirectional actuated manipulators. These motion limitations cannot be improved by optimizing the controller. Experimental results show the trajectory tracking performance similar to those obtained in the simulations, thus validating the simulations and the dynamic manipulability analysis. Consequently, we propose a task-based optimization formulation for determining the system parameters, such as stiffness and prestretch of passive springs, to track a given trajectory accurately.