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Research Papers

A Three-Spring Pseudorigid-Body Model for Soft Joints With Significant Elongation Effects

[+] Author and Article Information
Venkatasubramanian Kalpathy Venkiteswaran

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: kalpathyvenkiteswaran.1@osu.edu

Hai-Jun Su

Department of Mechanical and
Aerospace Engineering,
The Ohio State University,
Columbus, OH 43210
e-mail: su.298@osu.edu

1Corresponding author.

Manuscript received May 16, 2015; final manuscript received February 19, 2016; published online June 10, 2016. Assoc. Editor: Larry L. Howell.

J. Mechanisms Robotics 8(6), 061001 (Jun 10, 2016) (7 pages) Paper No: JMR-15-1116; doi: 10.1115/1.4032862 History: Received May 16, 2015; Revised February 19, 2016

Compliant mechanisms achieve motion utilizing deformation of elastic members. However, analysis of compliant mechanisms for large deflections remains a significant challenge. In this paper, a three-spring revolute–prismatic–revolute (RPR) pseudorigid-body (PRB) model for short beams used in soft joints made of elastomer material is presented. These soft joints differ from flexure-based compliant joints in which they demonstrate significant axial elongation effects upon tip loadings. The traditional PRB models based on long thin Euler beams failed to capture this elongation effect. To overcome this difficulty, a model approximation based on the Timoshenko beam theory has been derived. These equations are utilized to calculate the tip deflection for a large range of loading conditions. An optimization process is then carried out to determine the optimal values of the parameters of the PRB model for a large range of tip loads. An example based on a robotic grasper finger is provided to demonstrate how the model can be used in analysis of such a system. This model will provide a simple approach for the analysis of compliant robotic mechanisms.

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Figures

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Fig. 1

Joints fabricated using SDM at DISL at OSU

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Fig. 2

Cantilever beam with end loads

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Fig. 3

The three-spring PRB model after deformation

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Fig. 4

Optimal PRB parameters as functions of length-to-height ratio

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Fig. 5

Variation of error in PRB model with load (for the joint with L/h = 2)

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Fig. 6

Sensitivity of individual PRB parameters near the optimal point for RPR model

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Fig. 7

Schematic diagram of finger of compliant gripper in deformed position

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Fig. 8

Comparison of X and Y coordinates of tip of compliant finger as a function of the actuation force A(N), calculated using FEA and PRB models

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