Safety-Aware Hierarchical Passivity-Based Variable Compliance Control for Redundant Manipulators

Youssef Michel, Christian Ott, Dongheui Lee

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


This article presents a hierarchical passivity-based compliance controller that exploits robot redundancy and aims at achieving an impedance behavior with a time-varying stiffness on all the priority levels. Unfortunately, this gives rise to certain control actions that lead to the loss of the safety-critical passivity feature. To deal with this problem, we employ the concept of virtual energy tanks that keep track of the passivity violating energy in the system, ensuring that it remains bounded. This restores the passivity in the system, which guarantees the stable interaction with any passive environment. Furthermore, we augment our controller with an additional safety layer, which ensures that the energy injected through the tank into the system remains below a safe limit, defined based on the maximum kinetic energy allowed in the system. Finally, our approach is validated in terms of performance during task execution and safety both in simulations and on real-robot hardware.

Original languageEnglish
Pages (from-to)3899-3916
Number of pages18
JournalIEEE Transactions on Robotics
Issue number6
StatePublished - 1 Dec 2022
Externally publishedYes


  • Compliance and impedance control
  • passivity-based control
  • redundant robots
  • robot safety


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