Technical Brief

Contractile Pneumatic Artificial Muscle Configured to Generate Extension

[+] Author and Article Information
Benjamin K. S. Woods, Shane M. Boyer, Erica G. Hocking

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

Norman M. Wereley

Minta Martin Professor and
Department Chair
Fellow ASME
Smart Structures Laboratory,
Department of Aerospace Engineering,
University of Maryland,
College Park, MD 20742
e-mail: wereley@umd.edu

Curt S. Kothera

Senior Research Engineer
InnoVital Systems, Inc.,
Beltsville, MD 20705

1Present address: Senior Research Officer, Swansea University, Swansea, Wales SA2 8PP, United Kingdom.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received August 4, 2012; final manuscript received December 15, 2013; published online January 29, 2014. Assoc. Editor: Nariman Sepehri.

J. Dyn. Sys., Meas., Control 136(3), 034501 (Jan 29, 2014) (3 pages) Paper No: DS-12-1248; doi: 10.1115/1.4026308 History: Received August 04, 2012; Revised December 15, 2013

Pneumatic artificial muscles (PAMs) are comprised of an elastomeric bladder surrounded by a braided mesh sleeve. When the bladder is inflated, the actuator may either contract or extend axially, with the direction of motion dependent on the orientation of the fibers in the braided sleeve. Contractile PAMs have excellent actuation characteristics, including high specific power, specific work, and power density. Unfortunately, extensile PAMs exhibit much reduced blocked force, and are prone to buckling under axial compressive loading. For applications in which extensile motion and compressive force are desired, the push-PAM actuator introduced here exploits the operational characteristics of a contractile PAM, but changes the direction of motion and force by employing a simple internal mechanism using no gears or pulleys. Quasi-static behavior of the push-PAM was compared to a contractile PAM for a range of operating pressures. Based on these data, the push-PAM actuator can achieve force and stroke comparable to a contractile PAM tested under the same conditions.

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Fig. 1

Schematic of a push-PAM in its resting (top) and actuated (bottom) configurations

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Fig. 2

Actuators characterized in this study (contractile PAM above, and push-PAM for extensile motion below)

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Fig. 3

Comparison of measured actuator load lines at operating pressures of 207, 414, and 621 kPa, (a) Full experimental results and (b) Average force within hysteresis loop

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Fig. 4

Blocked force as a function of actuation pressure. The intercept of the line fit to the data with the actuation pressure axis determines the pressure dead-band.




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