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Design Innovation Paper

Variable Stiffness Mechanism for Suppressing Unintended Forces in Physical Human Robot Interaction

[+] Author and Article Information
Sri Sadhan Jujjavarapu

Human In the Loop System Lab., University at Buffalo, SUNY, Buffalo, New York 14260
srisadha@buffalo.edu

Amirhossein Hajiagha Memar

Human In the Loop System Lab., University at Buffalo, SUNY, Buffalo, New York 14260
ahajiagh@buffalo.edu

M. Amin Karami

IDEAS Laboratory, University at Buffalo, SUNY, Buffalo, New York 14260
karami@buffalo.edu

Ehsan T Esfahani

Human In the Loop System Lab., University at Buffalo, SUNY, Buffalo, New York 14260
ehsanesf@buffalo.edu

1Corresponding author.

ASME doi:10.1115/1.4042295 History: Received October 16, 2018; Revised December 12, 2018

Abstract

This paper presents the design of a two degrees of freedom variable stiffness mechanism and demonstrates how the adjustable compliance can enhance the robustness of physical human-robot interaction. The compliance in the proposed design is achieved using repulsive magnets in pre-loaded configuration as nonlinear springs in each of the degrees of freedom. The mechanism handle is attached to a passive slider placed in between actuated magnets. By adjusting the air gaps between the outer magnets the stiffness of the mechanism in each direction can be adjusted. The capability of the proposed design in suppressing unintended interaction forces is evaluated in two different experiments. In the first experiment, the improper adjustment of an admittance controller gains leads to unstable interaction, whereas in the second case, high-frequency involuntary forces are caused by tremor.

Copyright (c) 2018 by ASME
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