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Robust Bipedal Locomotion Based on a Hierarchical Control Structure

Published online by Cambridge University Press:  01 March 2019

Jianwen Luo
Affiliation:
Department of Mechanical and Energy Engineering, Southern University of Science and Technology, Shenzhen, China. E-mail: luojw@sustc.edu.cn Department of Computer Science, Stanford University, Stanford, CA, USA
Yao Su
Affiliation:
Mechanical and Aerospace Engineering Department, University of California, Los Angeles, CA, USA. E-mails: yaosu@g.ucla.edu, ruanlecheng@ucla.edu
Lecheng Ruan
Affiliation:
Mechanical and Aerospace Engineering Department, University of California, Los Angeles, CA, USA. E-mails: yaosu@g.ucla.edu, ruanlecheng@ucla.edu
Ye Zhao
Affiliation:
Woodruff School of Mechanical Engineering, Georgia Institute of Technology. E-mail: ye.zhao@me.gatech.edu
Donghyun Kim
Affiliation:
Mechanical Engineering Department, Massachusetts Institute of Technology, MA, USA. E-mail: robot.dhkim@gmail.com
Luis Sentis
Affiliation:
Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, TX, USA. E-mail: lsentis@austin.utexas.edu
Chenglong Fu*
Affiliation:
Department of Computer Science, Stanford University, Stanford, CA, USA
*
*Corresponding author. E-mail: fucl@sustc.edu.cn

Summary

To improve biped locomotion’s robustness to internal and external disturbances, this study proposes a hierarchical structure with three control levels. At the high level, a foothold sequence is generated so that the Center of Mass (CoM) trajectory tracks a planned path. The planning procedure is simplified by selecting the midpoint between two consecutive Center of Pressure (CoP) points as the feature point. At the middle level, a novel robust hybrid controller is devised to drive perturbed system states back to the nominal trajectory within finite cycles without chattering. The novelty lies in that the hybrid controller is not subject to linear CoM dynamic constraints. The hybrid controller consists of two sub-controllers: an oscillation controller and a smoothing controller. For the oscillation controller, the desired CoM height is specified as a sine-shaped function, avoiding a new attractive limit cycle. However, this controller results in the inevitable chattering because of discontinuities. A smoothing controller provides continuous properties and thus can inhibit the chattering problem, but has a smaller region of attraction compared with the oscillation controller. A hybrid controller merges the two controllers for a smooth transition. At the low level, the desired CoM motion is defined as tasks and embedded in a whole body operational space (WBOS) controller to compute the joint torques analytically. The novelty of the low-level controller lies in that within the WBOS framework, CoM motion is not subject to fixed CoM dynamics and thus can be generalized.

Information

Type
Articles
Copyright
© Cambridge University Press 2019 

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