A Novel Passive Parallel Elastic Actuation Principle for Load Compensation in Legged Robots

This work introduces a novel parallel elastic actuation principle designed to provide torque compensation for legged robots. Unlike existing solutions, the proposed concept leverages a nitrogen N<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> gas spring combined with a cam roller module to generate a highly customizable torque compensation profile for the target leg joint. An optimization-based design approach is employed to derive the specifications of the gas spring and optimize the cam module to produce a compensation torque profile closest to the desired one. The proposed load compensation concept and related mechanism are experimentally evaluated and practically integrated into the knee joint of a two-DoF monopedal robot actuated by cycloid actuators. The experimental results demonstrate that the proposed principle can effectively generate the required compensation torque profile and achieve significant benefits for the prototyped monopedal robot system by reducing 71.92<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> of the additional energy consumption caused by the payload. The entire system is compact, easy to integrate, and highly customizable, enabling the creation of nonlinear torque compensation profiles as needed. The work provides a promising solution to load compensation in legged robots.