Please cite this article in press as: Ahuett-Garza H, et al. Studies about the use of semicircular beams as hinges in large deflection planar compliant mechanisms. Precis Eng (2014), http://dx.doi.org/10.1016/j.precisioneng.2014.03.008 ARTICLE IN PRESS G Model PRE-6101; No. of Pages 17 Precision Engineering xxx (2014) xxx–xxx Contents lists available at ScienceDirect Precision Engineering jo ur nal ho me p age: www.elsevier.com/locate/precision Studies about the use of semicircular beams as hinges in large deflection planar compliant mechanisms Horacio Ahuett-Garza a,∗ , Oscar Chaides b , Pedro N. Garcia b , Pedro Urbina a a Department of Mechanical Engineering, Tecnológico de Monterrey, Campus Monterrey, Mexico b Center for Innovation in Design and Technology, Tecnológico de Monterrey, Campus Monterrey, Mexico a r t i c l e i n f o Article history: Received 17 September 2011 Received in revised form 29 October 2013 Accepted 28 March 2014 Available online xxx Keywords: Compliant mechanism design Mathematical modeling Precision machine design a b s t r a c t Conventional hinge designs in planar compliant mechanisms have a limited deformation range because of the high stresses induced during deflection. To improve the range of motion of these mechanisms, hinges that allow for large displacement are highly desirable. This paper explores the use of curved beams as large displacement hinges in planar compliant mechanisms. To facilitate design, analytic expressions that predict deflections under different types of loads are introduced. These expressions are used in pseudo rigid link models of compliant mechanism designs. Predictions made by the analytic expressions are compared with the results of FEA simulations. To validate the proposed models, two planar compliant mechanism designs were prepared and experimental measurements of deflections under loads were made. Overall, results showed that analytic models and FEA predictions lie within 10% of experimental data for the planar mechanism geometry in which pseudo rigid motion models apply. FEA models of the second case, a more complex mechanism, make predictions that lie within 15% of experimental measurements. Results and ways to improve accuracy of models and designs are discussed at the end of the article. © 2014 Elsevier Inc. All rights reserved. 1. Background In planar compliant mechanisms, weak sections are designed and built into a structure to produce specific motions of rigid parts of the mechanism. The weaker sections are commonly referred to as “elastic hinges”, and replace the revolute joints that are used in conventional rigid link mechanisms. Mechanism compliance is a direct result of the elastic response of the joints. Compliant mechanisms are inherently insensitive to the non- linearities and inaccuracies caused by conventional joints, a characteristic that makes them very attractive for high precision applications. To maintain geometric integrity, however, stresses induced by the deformation of the compliant mechanism have to be kept below the yield strength of the material. This limits the range of motion of compliant mechanisms, which in turn constitutes a limitation for their application. A number of studies have proposed hinge designs that improve the range of motion of compliant mechanisms. Of particular interest is the work of Trease [1], who introduced a variety of designs that allow for large deformations, and described some of the challenges ∗ Corresponding author. Tel.: +52 81 8358 2000; fax: +52 81 8358 2000. E-mail address: horacio.ahuett@itesm.mx (H. Ahuett-Garza). these designs need to overcome. In particular, Trease explains that besides an improved range of motion, the ideal design should reduce axis drift and stress concentration, and increase off-axis stiffness. This article introduces a hinge design that relies on semi cir- cular beams, which is particularly suitable for planar mechanisms. The proposed design combines a relatively well-localized center of rotation, comparable to those of conventional hinges, with deflec- tions that are more characteristic of long beams. To facilitate design, analytic models that can be used for mechanism synthesis in the manner proposed by Howell [2] are introduced and validated with FEA models. In general, good agreement was found. Experimen- tal tests with prototype planar compliant mechanisms that use semicircular beams as hinges are presented at the end of the article. 2. Literature review There is an extensive literature associated with common appli- cations of compliant mechanisms. The works by Howell [3], Smith [4] and Lobontiu [5] constitute excellent references for the design and analysis of compliant mechanisms. Traditionally, hinge designs have been used to allow small deflection of mechanisms and analysis has typically focused on the deformation of the hinge when subject to different types of http://dx.doi.org/10.1016/j.precisioneng.2014.03.008 0141-6359/© 2014 Elsevier Inc. All rights reserved.