Evaluation Concept for Impedance Controlled Series Elastic Actuator Modules

Abstract

Compliant actuators, such as variable stiffness actuators (VSA), series elastic actuators (SEA), variable impedance actuators (VIA), etc., are increasingly used in robotics for applications requiring adaptability to different task requirements, energy efficiency, and safe interaction with humans and the environment. These actuators are widely employed in applications such as human-robot interaction, wearable assistive devices, and highly dynamic-legged robots. Among the various control strategies, impedance control has emerged as a favored approach for achieving safe and adaptive interaction. The upcoming humanoid robot in our institute, Claudia, designed with SEA-based flexible joints, highlights the integration of compliant actuation for energy-efficient and high-performance locomotion. This thesis primarily focuses on proposing concepts for evaluating impedancecontrolled SEA systems while also developing a new testbed for actuator parameter identification. Several metrics are introduced to assess system performance from three featured perspectives: apparent passive impedance, torque/velocity transmissibility, and energy efficiency under distrubance. The contributions of the concepts for evaluation include extending the passive impedance region (Z-region) from forcecascaded impedance control to the feedback equivalence based control (e.g., ESPi), enabling the parameter selection of impedance controller by direct and indirect retrieval methods based on Z-region, adapting the torque/velocity transmissiblity from force control to force cascaded impedance control, unification of torque/velocity transmissibility and Z-region for force cascaded impedance control. The findings provide a structured methodology for selecting optimal control parameters and actuator configurations, forming a foundation for future advancements in compliant robotic actuation.