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Design Innovation

A Unidirectional Series-Elastic Actuator Design Using a Spiral Torsion Spring

[+] Author and Article Information
Brian T. Knox

Department of Mechanical Engineering, Ohio State University, Columbus, OH 43210knox.81@osu.edu

James P. Schmiedeler

Department of Aerospace and Mechanical Engineering, University of Notre Dame, South Bend, IN 46556

J. Mech. Des 131(12), 125001 (Nov 09, 2009) (5 pages) doi:10.1115/1.4000252 History: Received December 11, 2008; Revised September 09, 2009; Published November 09, 2009; Online November 09, 2009

This paper presents a novel series-elastic actuator (SEA) design that uses a spiral torsion spring to achieve drivetrain compliance in a compact and efficient mechanism. The SEA utilizes electromechanical actuation and is designed for use in the experimental biped robot KURMET for investigating dynamic maneuvers. Similar to helical torsion springs, spiral torsion springs are particularly applicable for legged robots because they preserve the rotational motion inherent in electric motors and articulated leg joints, but with less drivetrain backlash and unwanted coil interaction under load than helical torsion springs. The general spiral torsion spring design equations are presented in a form convenient for robot design, along with a detailed discussion of the mechanism surrounding the spring. Also, the SEA mechanism has a set of unidirectional hardstops that further improves the position control by allowing series-elasticity in only one rotational direction.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Photograph of the experimental biped KURMET with four SEAs located in the torso

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Figure 2

Schematic of a spiral torsion spring illustrating the important design variables

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Figure 3

Exploded view of a solid model of the SEA mechanism

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Figure 4

A solid model of the adjustable pulley hardstop showing (a) the hardstop’s adjustable range and (b) hardstop protruding through the face of the drive pulley intersecting the arbor hardstop

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Figure 5

A photograph of the SEA mechanism assembled on KURMET

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Figure 6

Motor and joint angles of (a) the knee joints and (b) the hip joints for two consecutive two-legged vertical jumps of the biped robot KURMET. In (a), “RK” and “RKM” indicate the right knee joint and the right knee motor angles. Similarly, “L” indicates left for both plots, and H indicates hip in (b).

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