Serpentine Flexures





Overview


A serpentine (or meander) flexure shown in the figure above, is made of four serpentine springs. Several micromechanical suspension designs use serpentine flexures [Tang, Nguyen, and Howe; Tang]. Compliant serpentine flexures can be designed with compact springs. The width of the meanders is adjusted to give the desired stiffness ratio. Residual stress and extensional axial stress are relieved through bending of the meanders.
Serpentine springs get their name from the meandering snake-like pattern of the beam segments. Each meander is of length a, and width b, except for the first and last meanders, which are of width c. The beam segments that span the meander width are called span beams, or spans. The beam segments that connect the spans are called connector beams, or connectors. In some spring designs, the width of the first and last meanders is half that of the other meanders (c=b/2) [Zhang and MacDonald]. An optical microshutter uses serpentine meanders made of two beams across the width and connected by a rigid truss [Jaecklin, Linder, and de Rooij]. In the following spring-constant analysis, we assume that all spans are equal (c=b).

Spring Constants


n even:





where ~a=I_z,b a/I_z,a.

n odd:





Approximations for large n, defined as n much greater than 3b/(~a+b) are:



The spring constant equation is simplified for n much greater than 3b/((GJ_b/EI_x,a)a+b).



Definition of terms used in flexure equations:




CMU MEMS Lab Home
Revised: July 3, 1996 by fedder@ece.cmu.edu