Yixi Chen, Evangelos Chatziandreou, Chase Mathews, Beau Johnson, and David J. Braun, Design of a Parallel Elastic Actuator with Continuously Adjustable Equilibrium Position, IEEE Robotics and Automation Letters, vol. 11, no. 6, pp. 6512-6519, 2026.
We present an adjustable-equilibrium parallel elastic actuator (AE-PEA) that combines a large direct-drive motor (DDM) and a 3D printed torsional spring with a small motor that can continuously adjust the equilibrium position of the actuator. We demonstrate that the AE-PEA achieves high torque control bandwidth like direct-drive actuators (DDAs), energy storage and shock mitigation like parallel elastic actuators (PEAs), and equilibrium position adjustment similar to series elastic actuators (SEAs). Owing to these features, we foresee the benefit of AE-PEAs in robot joints performing a variety of static load bearing and dynamic oscillatory motion.