Energy-Efficient Bipedal Running Using Parallel Elastic Couplings

This contribution examines the integration of parallel elastic couplings into a bipedal robot to enhance energy efficiency while running. Hybrid zero dynamics control is used to achieve periodic running on both rigid and compliant surfaces. A planar robot model that consists of five rigid segments interconnected by four electrically actuated joints is considered. Elastic couplings are positioned parallel to the joints either between the thighs or between the upper body and the thighs. Energy efficiency is improved by optimizing both the gait parameters and the nonlinear characteristics of the elastic couplings. Optimization results indicate a potential efficiency increase of up to 60 % on rigid surfaces and 30 % on compliant surfaces. Energy storage during phases of deceleration and subsequent release during acceleration significantly diminishes actuator deceleration losses and minimizes net mechanical work by the actuators, without compromising gait stability. Given that ground deformation is already leveraged to enhance efficiency, the added benefit of elastic couplings between segments is limited on compliant surfaces compared to rigid ones.