Optimization of a bend-twist-and-sweep compliant mechanism

Joseph Calogero, Mary Frecker, Aimy Wissa, James E. Hubbard

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Scopus citations

Abstract

The overall goal of this research is to develop design optimization methodologies for compliant mechanisms that will provide passive shape change. Our previous work has focused on designing two separate contact-aided compliant elements (CCE): one for bend-and-sweep deflections, called the bend-and-sweep compliant element (BSCE), and another for twist deflection, called the twist compliant element (TCE). In the current paper, all three degrees of freedom, namely bending, twist, and sweep, are achieved simultaneously using a single passive contact-aided compliant mechanism. A new objective function for a contact-aided compliant mechanism is introduced and the results of the optimization procedure are presented. A bend-twist-and-sweep compliant element (BTSCE) can be inserted into the leading edge spar of an ornithopter, which is an avian-scale flapping wing un-manned air vehicle. The multiple objective functions of the optimization problem presented in this paper are: for upstroke, maximize tip bending and sweep deflections, maximize twist angle, and minimize the mass and peak von Mises stress in the BTSCE, and for downstroke, minimize tip bending and sweep deflections, minimize twist angle, and minimize the mass and peak von Mises stress in the BTSCE. This allows a designer to select a CCE from a set of optimal designs to accomplish all three displacement goals. The BTSCE was modeled using a commercial finite element program and optimized using NSGA-II, a genetic algorithm. The results for a single angled compliant joint (ACJ) for quasi-static upstroke loading conditions are presented. Two optimal designs are discussed and compared, one with a moderate peak stress and moderate deflections, the other with a high peak stress and large deflections. The optimization results are then compared to the previous results for the two independent CCEs. A design study showed that the angle of the ACJ needs to be obtuse to achieve a positive twist angle during upstroke, and an acute contact angle reduces peak stress. The deflection objective functions were relatively insensitive to eccentricity for upstroke and downstroke compared to the other parameters, and a high stress penalty was paid for any gains in deflection. The downstroke objective functions were relatively insensitive to all parameters compared to the upstroke objective functions, and were much smaller in magnitude. The optimization showed that under simplified upstroke loading conditions, the BTSCE with a single ACJ allowed bending deflection near 30% of the length of the BTSCE, twist angle near 0.14 radians, and sweep deflection near 5% of the length of the BTSCE.

Original languageEnglish (US)
Title of host publicationASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014
PublisherWeb Portal ASME (American Society of Mechanical Engineers)
ISBN (Electronic)9780791846155
DOIs
StatePublished - 2014
EventASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014 - Newport, United States
Duration: Sep 8 2014Sep 10 2014

Publication series

NameASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014
Volume2

Other

OtherASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014
CountryUnited States
CityNewport
Period9/8/149/10/14

All Science Journal Classification (ASJC) codes

  • Biomaterials
  • Civil and Structural Engineering

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    Calogero, J., Frecker, M., Wissa, A., & Hubbard, J. E. (2014). Optimization of a bend-twist-and-sweep compliant mechanism. In ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014 (ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2014; Vol. 2). Web Portal ASME (American Society of Mechanical Engineers). https://doi.org/10.1115/SMASIS20147518