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A Buckling Flexure-Based Force-Limiting Mechanism

[+] Author Affiliations
Jonathan T. Slocum, Kenneth Kamrin, Alexander H. Slocum

MIT, Cambridge, MA

Paper No. DETC2018-86388, pp. V05AT07A024; 8 pages
  • ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference
  • Volume 5A: 42nd Mechanisms and Robotics Conference
  • Quebec City, Quebec, Canada, August 26–29, 2018
  • Conference Sponsors: Design Engineering Division, Computers and Information in Engineering Division
  • ISBN: 978-0-7918-5180-7
  • Copyright © 2018 by ASME


A force-limiting buckling flexure has been created which can be used in a wide array of applications where excessive force from an implement can cause harm or damage. The buckling flexure is monolithic, contains no electronics, and can be manufactured using a single shot in an injection molding machine, making it extremely cost effective. In this paper, the design of this flexure is applied to a force-limiting toothbrush as an example of how this buckling flexure may be applied in a real-world technology. An overview of the buckling flexure is presented, and a structural model is shown to predict when the flexure will elastically buckle. This model is compared to data collected from flexures fabricated with varying buckling beam thickness. The data show that the force to buckle the flexure when applied at the tip can be predicted to within 20.84%. Furthermore, a preliminary model is presented which enables design of the buckling beam’s displacement, such that the total breakaway deformation can be maximized, making sensing the sudden deformation easier. As part of the application of the buckling flexure, an ergonomic, injection moldable toothbrush was created with the flexure built into the neck of the brush. When the user applies too much force while brushing, the flexure gives way and alerts the user when they have applied too much force and when the user lets off the force, the brush snaps back to its original shape. This design methodology is generalized and can be utilized in other force limited applications where an injection moldable, pre-set force, purely mechanical breakaway device is desired.

Copyright © 2018 by ASME



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