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research-article

Optimal Stiffness Design for an Exhaustive Parallel Compliance Matrix in Multiactuator Robotic Limbs

[+] Author and Article Information
Nathan M. Cahill

Student Researcher National Science Foundation Fellow Department of Mechanical Engineering Arizona State University Tempe, Arizona 85281
nathan.m.cahill@asu.edu

Thomas Sugar

Professor Senior Member, ASME Department of Mechanical Engineering Arizona State University Tempe, Arizona 85281
thomas.sugar@asu.edu

Yi Ren

Professor Member, ASME Department of Mechanical Engineering Arizona State University Tempe, Arizona 85281
yiren@asu.edu

Kyle Schroeder

Researcher SpringActive inc. Tempe, Arizona, 85281
kyle.schroeder@springactive.com

1Corresponding author.

ASME doi:10.1115/1.4039772 History: Received May 09, 2017; Revised February 28, 2018

Abstract

Comparatively slow growth in energy density of both power storage and generation technologies has placed added emphasis on the need for energy efficient designs in legged robots. This paper explores the potential of parallel springs in robot limb design. We start by adding what we call the Exhaustive Parallel Compliance Matrix (EPCM) to the design. The EPCM is a set of parallel springs which includes a parallel spring for each joint and a multi-joint parallel spring for all possible combinations of the robot's joints. Then we carefully formulate and compare two performance metrics which improve various aspects of the system performance. Each performance metric is analyzed and compared, their strengths and weaknesses being rigorously presented. The performance benefits associated with this approach are dramatic. Implementing the spring matrix reduces the sum of square power exerted by the actuators by up to 47 percent, the peak power requirement by almost 40 percent, the sum of squared current by 55 percent, and the peak current by 55 percent. These results were generated using a planar robot limb and a gait trajectory borrowed from biology. We use a fully dynamic model of the robotic system including inertial effects. We also test the design robustness using a perturbation study which shows that the parallel springs are effective even in the presence of trajectory perturbation.

Copyright (c) 2018 by ASME
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