Technical Brief

A Continuum Model for Fiber-Reinforced Soft Robot Actuators

[+] Author and Article Information
Audrey Sedal

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

Daniel Bruder

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

Joshua Bishop-Moser

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

Ram Vasudevan

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

Sridhar Kota

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

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received September 22, 2017; final manuscript received January 18, 2018; published online February 12, 2018. Assoc. Editor: Andreas Mueller.

J. Mechanisms Robotics 10(2), 024501 (Feb 12, 2018) (9 pages) Paper No: JMR-17-1314; doi: 10.1115/1.4039101 History: Received September 22, 2017; Revised January 18, 2018

Fiber-reinforced elastomeric enclosures (FREEs) generate sophisticated motions, when pressurized, including axial rotation, extension, and compression, and serve as fundamental building blocks for soft robots in a variety of applications. However, most modeling techniques employed by researchers do not capture the key characteristics of FREEs to enable development of robust design and control schemes. Accurate and computationally efficient models that capture the nonlinearity of fibers and elastomeric components are needed. This paper presents a continuum model that captures the nonlinearities of the fiber and elastomer components as well as nonlinear relationship between applied pressure, deformation, and output forces and torque. One of the key attributes of this model is that it captures the behavior of FREEs in a computationally tractable manner with a minimum burden on experimental parameter determination. Without losing generality of the model, we validate it for a FREE with one fiber family, which is the simplest system exhibiting a combination of elongation and twist when pressurized. Experimental data in multiple kinematic configurations show agreement between our model prediction and the moments that the actuators generate. The model can be used to not only determine operational parameters but also to solve inverse problems, i.e., in design synthesis.

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Fig. 1

FREE behavior when relaxed (left) and pressurized (right) [17]

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Fig. 2

Motion of a point on the FREE wall. As the FREE inflates, the reference point changes coordinates (in the cylindrical coordinate system shown) from (R, Θ, Z) to (r, θ, z).

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Fig. 3

Torsional moment, rotation, and fiber angle sign conventions

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Fig. 4

Fiber direction on a continuum element of the FREE wall

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Fig. 5

Differential element of the FREE wall and associated stresses

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Fig. 6

The position-fixed test bed, which measures torsion at various deformation and pressure states

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Fig. 7

Predicted (-) and measured moment generation by pressure 60 deg design angle FREE

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Fig. 8

Predicted (-) and measured moment generation by pressure 40 deg design angle FREE

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Fig. 9

Predicted (-) and measured moment generation by pressure 30 deg design angle FREE

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Fig. 10

Torque by pressure curve for a FREE with design angle Γ=40 deg at various deformations

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Fig. 11

Torque-displacement profiles of a design set of FREEs at 40 kPa with feasible designs emphasized



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