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research-article

A Fixed Structure Gain Selection Strategy for High Impedance Series Elastic Actuator Behavior

[+] Author and Article Information
Kenan Isik

Dept. of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712
kisik@utexas.edu

Gray Thomas

Dept. of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712
gray.c.thomas@utexas.edu

Luis Sentis

Dept. of Aerospace Eng. and Eng. Mechanics, University of Texas at Austin, Austin, Texas 78712
lsentis@austin.utexas.edu

1Corresponding author.

ASME doi:10.1115/1.4041449 History: Received February 06, 2018; Revised August 24, 2018

Abstract

Series Elastic Actuators are widely used for impact protection and compliant behavior, but they typically fall short in tasks calling for accurate position control. In this paper, we propose a simple and effective heuristic for tuning series elastic actuator controllers to a high impedance position control behavior which compares favorably with previous publications. Our approach considers two models, an ideal model and a non-ideal model with time delays and filtering lag. The ideal model is used to design cascaded PD-type outer impedance and inner force loops as a function of critically-damped closed-loop poles for the force and impedance loops. The non-ideal model provides an estimate of the phase margin of the position controller for each candidate controller design. A simple optimization algorithm finds the best high-impedance behavior for which the non-ideal model meets a desired phase margin requirement. In this way, the approach automates the tradeoff between force and impedance bandwidth. The effect of important system parameters on the impedance bandwidth is also analyzed and the proposed method verified with a physical actuator.

Copyright (c) 2018 by ASME
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