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research-article

Ring-based stiffening flexure applied as a load cell with high resolution and large force range

[+] Author and Article Information
Jocelyn M. Kluger

Graduate Research Assistant, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
jociek@mit.edu

Alexander Slocum

Professor Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
slocum@mit.edu

Themistoklis Sapsis

Associate Professor Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
sapsis@mit.edu

1Corresponding author.

ASME doi:10.1115/1.4037243 History: Received September 12, 2016; Revised June 07, 2017

Abstract

This paper applies linear elastic theory and Castigliano's first theorem to design nonlinear (stiffening) flexures used as load cells with both large force range and large resolution. Low stiffness at small forces causes high sensitivity while high stiffness at large forces prevents over-straining. With a standard 0.1 $\mu$m deflection sensor, the nonlinear load cell may detect 1\% changes in force over 5 orders of force magnitude. In comparison, a traditional linear load cell functions over only three orders of magnitude. We physically implement the nonlinear flexure as a ring that increasingly contacts rigid surfaces with carefully chosen curvatures as more force is applied. We analytically describe the load cell performance as a function of its geometry. We describe methods for manufacturing the flexure from a monolithic part or multiple parts. We experimentally verify the theory for two load cells with different parameters.

Copyright (c) 2017 by ASME
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