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Control Lyapunov Functions for Compliant Hybrid Zero Dynamic Walking

Reher, Jenna and Ames, Aaron D. (2021) Control Lyapunov Functions for Compliant Hybrid Zero Dynamic Walking. . (Unpublished)

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The ability to realize nonlinear controllers with formal guarantees on dynamic robotic systems has the potential to enable more complex robotic behaviors -- yet, realizing these controllers is often practically challenging. To address this challenge, this paper presents the end-to-end realization of dynamic bipedal locomotion on an underactuated bipedal robot via hybrid zero dynamics and control Lyapunov functions. A compliant model of Cassie is represented as a hybrid system to set the stage for a trajectory optimization framework. With the goal of achieving a variety of walking speeds in all directions, a library of compliant walking motions is compiled and then parameterized for efficient use within real-time controllers. Control Lyapunov functions, which have strong theoretic guarantees, are synthesized to leverage the gait library and coupled with inverse dynamics to obtain optimization-based controllers framed as quadratic programs. It is proven that this controller provably achieves stable locomotion; this is coupled with a theoretic analysis demonstrating useful properties of the controller for tuning and implementation. The proposed theoretic framework is practically demonstrated on the Cassie robot, wherein 3D walking is achieved through the use of optimization-based torque control. The experiments highlight robotic walking at different speeds and terrains, illustrating the end-to-end realization of theoretically justified nonlinear controllers on dynamic underactuated robotic systems.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Reher, Jenna0000-0002-8297-3847
Ames, Aaron D.0000-0003-0848-3177
Additional Information:Paper in preparation for submission to IEEE Transactions on Robotics (T-RO). This research was supported under NSF Grant Numbers 1544332, 1724457, 1724464 and Disney Research LA. The authors would like to thank Claudia Kann for her help in the early discussions of the ID-CLF-QP approach, and Wen-Loong Ma and Noel Csomay-Shanklin for experimental assistance.
Funding AgencyGrant Number
Subject Keywords:hybrid systems, zero dynamics, control Lyapunov functions, inverse dynamics
Record Number:CaltechAUTHORS:20210722-222549674
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109987
Deposited By: Tony Diaz
Deposited On:26 Jul 2021 19:22
Last Modified:26 Jul 2021 19:22

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