A Fundamental Limitation of Passive Spring Rendering With Series Elastic Actuation

• Published in: IEEE transactions on haptics Vol. 16; no. 4; pp. 1 - 6
• Main Authors: Kenanoglu, Celal Umut, Patoglu, Volkan
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.10.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Actuation; Actuators; Controllers; coupled stability; Damping; Elastic limit; Fundamental limitations of interaction control; haptic rendering of springs; High frequency; Impedance; Linear systems; passivity; Rendering; Rendering (computer graphics); series (damped) elastic actuation; Springs; Stiffness; velocity-sourced impedance control; Viscous damping
• ISSN: 1939-1412; 2329-4051
• DOI: 10.1109/TOH.2023.3260063

We establish a fundamental limitation of stiffness rendering with series elastic actuation by rigorously proving that no causal controller can passively render virtual stiffness levels that are higher than the stiffness of the physical series elastic element. To relax this bound, we propose the addition of a viscous damping term parallel to the elastic element to form series damped elastic actuation (SDEA). We show that there exist LTI controllers for SDEA that can relax the passivity bound on the virtual stiffness, and derive the necessary and sufficient conditions for the passive stiffness rendering with SDEA under such a controller. We experimentally verify the relaxed passive stiffness rendering bounds for SDEA, by studying the coupled stability of interactions with most destabilizing environments.