Energy-Efficient Design and Motion Control of Leg Mechanisms Using Redundant Drive Systems and Parallel Elasticity

Abstract

This paper examines a planar, two-degree-of-freedom leg utilizing a redundant drive system consisting of mono- and bi-articular motors, and parallel elasticity. Based on the drivetrain energy model, a closed-form redundant torque-allocation solution using a copper loss minimization criterion is derived and shown to be feasible for real-time implementation. A dynamic model that includes the drivetrain was then used to design the leg-length ratio and the parallel elasticity in accordance with the allocation rule. We built a single-leg prototype with a streamlined redundant drive mechanism, ensuring the bi-articular element improves energy efficiency while preserving the base leg's nominal motion. Experiments spanning static holding, drop landing, and hopping (vertical/forward) demonstrate that the complementary effects of the bi-articular element and the parallel elasticity consistently reduce peak torques and electrical energy, with suppression of absolute consumption during the stance phase identified as the primary contributor to total savings. These results provide a redundancy-allocation design methodology for articulated leg robots that jointly achieves energy efficiency and implementation simplicity.