[+] Author and Article Information
Jonathan T. Slocum

77 Massachusetts Avenue Cambridge, MA 02139 jtslocum@mit.edu

Kenneth Kamrin

77 Massachusetts Ave, Room 1-310 Cambridge, MA 02139 kkamrin@mit.edu

Alexander H. Slocum

77 Mass Ave Rm 3-445 Rm 3-445 Cambridge, MA 02139-4301 slocum@mit.edu

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received September 3, 2018; final manuscript received March 20, 2019; published online xx xx, xxxx. Assoc. Editor: Guimin Chen.

ASME doi:10.1115/1.4043317 History: Received September 03, 2018; Accepted March 21, 2019


A force-limiting buckling flexure has been created which can be used in a wide range 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 a design study to show its application in a real-world technology. An overview of the buckling flexure is presented, and a structural model is to predict when the flexure will elastically buckle. Flexures of different geometries were tested and buckled. The data show that model can predict buckling of the flexure with an error of 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 applications where injection-moldable, force-limiting, and purely mechanical breakaway devices are desired.

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