Is Active Impedance the Key to a Breakthrough for Legged Robots?

Part of the Springer Tracts in Advanced Robotics book series (STAR, volume 114)


This work addresses the question whether active impedance control is key to a breakthrough for legged robots. In this paper, we will talk about controlling the mechanical impedance of joints and legs with a focus on stiffness and damping control. In contrast to passive elements like springs, active impedance is achieved by torque-controlled joints allowing real-time adjustment of stiffness and damping. We argue that legged robots require a high degree of versatility and flexibility to execute a wide range of assistive tasks to be truly useful to humans and thus to lead to a breakthrough. Adjustable stiffness and damping in realtime is a fundamental building block towards versatility. Experiments with our 80 kg hydraulic quadruped robot HyQ demonstrate that active impedance alone (thus no springs in the structure) can successfully emulate passively compliant elements during highly-dynamic locomotion tasks (running and hopping); and, that no springs are needed to protect the actuation system. Here we present results of a flying trot, also referred to as running trot. To the authors’ best knowledge this is the first time a flying trot was successfully implemented on a robot without passive elements such as springs. A critical discussion on the pros and cons of active impedance concludes the paper. An extended version of this paper has been published in IJRR in 2015 [43].


Ground Reaction Force Stance Phase Joint Torque Duty Factor Active Impedance 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This research has been funded by the Fondazione Istituto Italiano di Tecnologia. The authors would like to thank CAPES for the scholarship granted to V. Barasuol (Grant Procs. 6463-11-8). T. Boaventura is partially funded through the EU Project BALANCE (Grant 601003 of the EU FP7 program). J. Buchli is supported by a Swiss National Science Foundation professorship. The authors would like to thank also the other members of the Dynamic Legged Systems Lab that contributed to the success of this project: M. Focchi, I. Havoutis, S. Bazeille, J. Goldsmith, H. Khan, B.Rehman, and our team of technicians.


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Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  1. 1.Department of Advanced RoboticsIstituto Italiano di Tecnologia (IIT)GenovaItaly
  2. 2.PPGEAS - Department of Automation and SystemsFederal University of Santa Catarina (UFSC)FlorianpolisBrazil
  3. 3.ETH ZurichAgile & Dexterous Robotics LabZürichSwitzerland

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