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Research Papers

Kinematics of a Generalized Class of Pneumatic Artificial Muscles

[+] Author and Article Information
Girish Krishnan

Industrial and Enterprise Systems Engineering,
University of Illinois Urbana-Champaign,
Urbana, IL 61801
e-mail: gkrishna@illinois.edu

Joshua Bishop-Moser

Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: joshbm@umich.edu

Charles Kim

Mechanical Engineering,
Bucknell University,
Lewisburg, PA 17837
e-mail: charles.kim@bucknell.edu

Sridhar Kota

Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: kota@umich.edu

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1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received May 20, 2014; final manuscript received January 22, 2015; published online April 6, 2015. Assoc. Editor: Robert J. Wood.

J. Mechanisms Robotics 7(4), 041014 (Nov 01, 2015) (9 pages) Paper No: JMR-14-1115; doi: 10.1115/1.4029705 History: Received May 20, 2014; Revised January 22, 2015; Online April 06, 2015

Fluid filled fiber reinforced elastomeric enclosures (FREEs) have been a popular choice for actuators in prosthetics and soft robots owing to their high power density and cost effective manufacturing. While a narrow class of FREEs known as McKibben's actuators have been extensively studied, there is a wide unexplored class that could be potentially used as actuators and soft structural members. This paper analyzes the mobility of generalized FREEs based on simple geometric relationships that result from the inextensibility of fibers and fluidic actuation. The analysis conducted can be classified into instantaneous kinematics and global or large deformation kinematics. Instantaneous kinematics reveals that the most general deformation pattern of the FREE is a screw motion about the axis of its cylinder, whose pitch is a function of fiber orientations. Furthermore, a set of fiber angles, which do not deform under volumetric actuation were identified as the locked manifold (LM). Global kinematic analysis revealed that every FREE continued to deform until its fiber configuration approached the LM. These insights were corroborated with finite element analysis (FEA) and testing for a small sample of FREE actuators.

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Figures

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Fig. 1

FREEs consist of an elastomeric hollow cylinder pressurized with fluids, reinforced by two families of helical fibers. FREEs are inspired by (a) hydrostatic skeletons observed in squids and worms (reproduced with permission from Vogel [2], copyright 2003 by Princeton University Press), which in most cases have (b) equal and opposite fiber angles such that α = −β. (c) Spiral growth patterns of grapevine tendrils [5] and (d) mammalian penises (reproduced with permission from Kelly [3], copyright 1997 by Wiley) where it is shown that armadillo penis consists of fiber configurations with α = 0 deg and β = 90 deg) are shown to contain (e) asymmetric arrangement of fibers α ≠ −β.

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Fig. 3

(a) Commercial examples of FREEs with equal and opposite fiber angle configurations, commonly known as McKibben pneumatic muscles2 and (b) potential applications of asymmetric fiber configurations demonstrated in manipulation

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Fig. 5

Deformation parameters of a cylindrical FREE wrapped with a single family of helical fibers

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Fig. 6

Design space spanned by the two helix angles with example geometries in various quadrants

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Fig. 8

The instantaneous normalized pitch for quadrants I and II configurations

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Fig. 9

Trajectory taken by the various initial fiber configurations toward the LM

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Fig. 12

Verifying the large deformation behavior of FREEs using FEA and prototype testing (a) undeformed and (b) deformed configurations

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Fig. 13

Fiber angle deformed trajectory comparison between kinematic analysis, FEA, and prototype testing

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