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Research Papers

Experimental Characterization and Static Modeling of McKibben Actuators

[+] Author and Article Information
Curt S. Kothera

 Techno-Sciences, Inc., Beltsville, MD 20705kotherac@technosci.com

Mamta Jangid

Department of Aerospace Engineering, Smart Structures Laboratory, University of Maryland, College Park, MD 20742

Jayant Sirohi

Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, TX 78712jayant.sirohi@mail.utexas.edu

Norman M. Wereley1

Department of Aerospace Engineering, University of Maryland, College Park, MD 20742wereley@umd.edu

1

Corresponding author.

J. Mech. Des 131(9), 091010 (Aug 19, 2009) (10 pages) doi:10.1115/1.3158982 History: Received March 19, 2008; Revised April 30, 2009; Published August 19, 2009

McKibben actuators are pneumatic actuators with very high force to weight ratios. Their ability to match the behavior of biological muscles better than any other actuators has motivated much research into the characterization and modeling of these actuators. The purpose of this paper is to experimentally characterize the behavior of McKibben artificial muscles with basic geometric parameters, and present a model that is able to predict the static behavior accurately in terms of blocked force and free displacement. A series of experiments aimed at understanding the static behavior of the actuators was conducted. The results for three different lengths (4 in., 6 in., and 8 in.), three diameters (1/8 in., 1/4 in., and 3/8 in.), and one wall thickness (1/16 in.) at pressures ranging from 10 psi to 60 psi illustrate the key design trends seen in McKibben actuator geometry. While existing models predict this static behavior, there are varying degrees of accuarcy, which motivates the present study. Using knowledge gained from the experimental study, improvements for the two modeling approaches were explored, including effects from elastic energy storage, noncylindrical shape, and variable thickness. To increase model accuracy, another set of experiments was used to characterize the elasticity of the rubber tubes and fibers of the braid. Comparisons of the measured data to the improved model indicate that the ability to accurately predict the static behavior of McKibben actuators has increased.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Experimental setup for McKibben actuator characterization

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Figure 2

Blocked force as a function of pressure—linear increase (actuator 5c)

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Figure 3

Free contraction as a function of pressure—nonlinear increase (actuator 5c)

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Figure 4

Free contraction ratio as a function of pressure—nonlinear decrease (actuator 5c)

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Figure 5

Blocked force as a function of actuator length—independent (actuator 5x)

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Figure 6

Free contraction as a function of actuator length—linear increase (actuator 5x)

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Figure 7

Free contraction ratio as a function of actuator length—independent (actuator 5x)

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Figure 8

Blocked force as a function of actuator diameter—quadratic increase (actuator Xc)

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Figure 9

Free contraction as a function of actuator diameter—increasing (actuator Xc)

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Figure 10

Free contraction ratio as a function of actuator diameter—decreasing (actuator Xc)

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Figure 11

Blocked force as a function of t/D—nonlinear decrease (actuator Xc)

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Figure 12

Free contraction as a function of t/D—linear decrease (actuator Xc)

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Figure 13

Free contraction ratio as a function of t/D—linear increase (actuator Xc)

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Figure 14

Blocked force as a function of braid angle—increase (actuators 2a and 3a)

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Figure 15

Free contraction as a function of braid angle—increase (actuators 2a and 3a)

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Figure 16

Free contraction ratio as a function of braid angle—decrease (actuators 2a and 3a)

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Figure 17

Blocked force of elastic energy models compared with experimental data (actuator 5A)

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Figure 18

Free contraction of elastic energy models compared with experimental data (actuator 5A)

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Figure 19

Freebody diagram for force balancing model (27)

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Figure 20

Blocked force of force balance models compared with experimental data (actuator 5A)

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Figure 21

Free contraction of force balance models compared with experimental data (actuator 5A)

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Figure 22

Blocked force predictions using force balance model (actuator Xa)

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Figure 23

Free contraction predictions using force balance model (actuator 5x)

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