On the Stiffness Selection for Torque-Controlled Series-Elastic Actuators

Wesley Roozing*, Jorn Malzahn, Navvab Kashiri, Darwin G. Caldwell, Nikos G. Tsagarakis

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

32 Citations (Scopus)


Series-elastic actuators are quickly becoming the core component of robots operating in real-world environments, allowing for robust, safe, torque-controlled robots. This letter investigates the influence of the selected stiffness and control parameters. By consolidating several analyses, it is shown two opposing criteria exist for the choice of stiffness: lowering stiffness increases actuator transparency, while increasing stiffness increases torque tracking bandwidth. This fact is used in the context of impedance rendering to propose an optimal stiffness selection criterion that maximizes the renderable impedance frequency. This provides a concrete method for choosing stiffness based on the application of the joint. Extensive simulation and experimental results are presented that validate the analyses.

Original languageEnglish
Article number7976385
Pages (from-to)2255-2262
Number of pages8
JournalIEEE Robotics and automation letters
Issue number4
Publication statusPublished - 1 Oct 2017
Externally publishedYes


  • compliance and impedance control
  • Compliant joint/mechanism
  • force control


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