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

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Book cover Robotics Research

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

Abstract

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].

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Notes

  1. 1.

    Compliance is the inverse of stiffness.

  2. 2.

    Reduction gears are required to amplify the low output torque of electric motors.

  3. 3.

    Note that we recently increased the hydraulic system pressure of the HyQ robot to 20 MPa, increasing the maximum torque of the hip and knee flexion/extension joints to 181 Nm.

  4. 4.

    Note that the fact that models are required for good performance does not address the question where the model comes from. For robots it can sometimes be derived from CAD data, sometimes must be estimated/learned. For humans models are typically acquired by learning.

  5. 5.

    It is worthwhile discussing these issues in the control theoretic notions of nominal behavior and disturbance reaction.

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Acknowledgments

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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Authors and Affiliations

  1. Department of Advanced Robotics, Istituto Italiano di Tecnologia (IIT), via Morego, 30, 16163, Genova, Italy

    Claudio Semini & Marco Frigerio

  2. PPGEAS - Department of Automation and Systems, Federal University of Santa Catarina (UFSC), Florianpolis, SC, Brazil

    Victor Barasuol

  3. ETH Zurich, Agile & Dexterous Robotics Lab, John-von-Neumann-Weg 9, 8093, Zürich, Switzerland

    Thiago Boaventura & Jonas Buchli

Authors
  1. Claudio Semini
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  2. Victor Barasuol
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  4. Marco Frigerio
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  5. Jonas Buchli
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Correspondence to Claudio Semini .

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Editors and Affiliations

  1. Creative Informatics, The University of Tokyo, Tokyo, Japan

    Masayuki Inaba

  2. School of Electrical Engineering and Com, Queensland Univ of Technology, Brisbane, Queensland, Australia

    Peter Corke

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Semini, C., Barasuol, V., Boaventura, T., Frigerio, M., Buchli, J. (2016). Is Active Impedance the Key to a Breakthrough for Legged Robots?. In: Inaba, M., Corke, P. (eds) Robotics Research. Springer Tracts in Advanced Robotics, vol 114. Springer, Cham. https://doi.org/10.1007/978-3-319-28872-7_1

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  • DOI: https://doi.org/10.1007/978-3-319-28872-7_1

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