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Control of legged robots with optimal distribution of contact forces


Conference Paper



The development of agile and safe humanoid robots require controllers that guarantee both high tracking performance and compliance with the environment. More specifically, the control of contact interaction is of crucial importance for robots that will actively interact with their environment. Model-based controllers such as inverse dynamics or operational space control are very appealing as they offer both high tracking performance and compliance. However, while widely used for fully actuated systems such as manipulators, they are not yet standard controllers for legged robots such as humanoids. Indeed such robots are fundamentally different from manipulators as they are underactuated due to their floating-base and subject to switching contact constraints. In this paper we present an inverse dynamics controller for legged robots that use torque redundancy to create an optimal distribution of contact constraints. The resulting controller is able to minimize, given a desired motion, any quadratic cost of the contact constraints at each instant of time. In particular we show how this can be used to minimize tangential forces during locomotion, therefore significantly improving the locomotion of legged robots on difficult terrains. In addition to the theoretical result, we present simulations of a humanoid and a quadruped robot, as well as experiments on a real quadruped robot that demonstrate the advantages of the controller.

Author(s): Righetti, L. and Buchli, J. and Mistry, M. and Schaal, S.
Book Title: 2011 11th IEEE-RAS International Conference on Humanoid Robots
Pages: 318--324
Year: 2011
Publisher: IEEE

Department(s): Autonomous Motion, Movement Generation and Control
Bibtex Type: Conference Paper (inproceedings)

DOI: 10.1109/Humanoids.2011.6100832

Address: Bled, Slovenia
URL: https://ieeexplore.ieee.org/abstract/document/6100832/


  title = {Control of legged robots with optimal distribution of contact forces},
  author = {Righetti, L. and Buchli, J. and Mistry, M. and Schaal, S.},
  booktitle = {2011 11th {IEEE}-{RAS} {International} {Conference} on {Humanoid} {Robots}},
  pages = {318--324},
  publisher = {IEEE},
  address = {Bled, Slovenia},
  year = {2011},
  url = {https://ieeexplore.ieee.org/abstract/document/6100832/}