Performance Analysis of Series Elastic Actuator Based on Maximum Torque Transmissibility

Abstract

Series elastic actuators (SEAs) have had sound contributions in the robotics field, and significant breakthroughs have been achieved. Despite this fact, there are still drawbacks to their performance. The elastic spring, which provides compliance, limits the SEA’s performance by lowering the bandwidth of force/torque generation, and this bandwidth decreases even further when the SEA has to render large torques. This problem originates from the constraints in motor and motor driver, such as torque and velocity limits. In this brief, the mathematical tools to analyze how these limitations influence the force control performance of SEA are proposed. To this end, a novel criterion called maximum torque transmissibility (MTT) is defined to assess the ability of SEA by fully utilizing the SEA dynamics, a maximum continuous torque, and permissible velocity of the servo motor. Further, based on MTT, a new concept called the maximum torque bandwidth that can indicate the frequency limit in which SEA can generate the maximum torque is proposed. Various design parameters, including the load condition and mechanical and controller design parameters of SEA, are evaluated. Experimental results verify that MTT can indicate the limitation of the performance of SEA precisely.