On the Efficient Control of Series-Parallel Compliant Articulated Robots

Abstract

The paper applies optimal control to investigate the efficacy of distinct torque distribution strategies on a redundant robot that combines the potential of asymmetric series-parallel compliant actuation branches and multi-articulation. An optimization based controller that can accommodate various quadratic cost functions to perform the non-trivial torque distribution among the dissimilar actuators is contrived. Three candidate criteria are composed and their performance during periodic squat motions are compared. From one set of experiments, it is learnt that by minimizing a criterion that takes into account the actuator hardware specifications, the gravity-driven phases can be lengthened. Thereby, the particular criterion results in slightly better performance than when adopting a strategy that maximizes the torque allocation to the higher efficiency actuators. Another set of experiments performed across a range of frequencies provide valuable insights such as the efficacy of maximum utilization of the highly-efficient but slow actuators decreases progressively at high frequencies.