Title: Energetics of passivity-based running with high-compliance series elastic actuation

Authors: C. David Remy; Keith Buffinton; Roland Siegwart

Addresses: Autonomous Systems Lab, Institute of Robotics and Intelligent Systems, Swiss Federal Institute of Technology (ETHZ), Tannenstr, 3/CLA-E-32.1 8092 Zurich, Switzerland. ' Department of Mechanical Engineering, Bucknell University, 701 Moore Avenue Lewisburg, PA 17837, USA. ' Autonomous Systems Lab, Institute of Robotics and Intelligent Systems, Swiss Federal Institute of Technology (ETHZ), Tannenstr, 3/CLA-E-32.1 8092 Zurich, Switzerland

Abstract: The efficiency of running gaits in nature results in large part from passive elastic oscillations on springy legs. In this paper, this principle is applied to robotic systems by endowing them with high compliance series elastic actuators in which the electric motors are decoupled from the joints by elastic elements. Periodic motor inputs excite the natural dynamic motion of the robot and create a passivity-based running motion. An optimisation algorithm minimised energy expenditure and estimated the necessary initial model states and the coefficients of a parameterised excitation function for the simulations of a two-dimensional hopping monopod and a planar bounding quadruped. Gait synthesis within this framework was analysed with respect to energy consumption, particularly as a function of running speed. Different solution groups were found, each of them corresponding to a characteristically different movement which proved to be most efficient for the corresponding speed range. This shines a different light on the meaning of 'gait' in the context of robotics, and directly contributes to a better understanding of the creation and exploitation of different modes of locomotion in legged robotics.

Keywords: legged robots; gait creation; robot gait; running gaits; elastic energy storage; locomotion efficiency; legged locomotion; optimal control; passivity-based running; high-compliance; series elastic actuation; monopedal hopping; quadrupedal bounding; passive elastic oscillations; elastic actuators; running speed; robot running; robot control.

DOI: 10.1504/IJMMS.2012.046526

International Journal of Mechatronics and Manufacturing Systems, 2012 Vol.5 No.2, pp.120 - 134

Available online: 12 Apr 2012

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