A Fully-Compliant, In-Plane Rotary, Bistable Micromechanism

A fully compliant bistable micromechanism (hereafter identified as an in-plane rotary bistable micromechanism or IPRBM) is designed to accomplish in-plane rotary motion with two stable positions. The micromechanism consists of four individually bistable mechanisms arranged in a cyclically symmetric geometry about a central proof mass. This class of bistable mechanism can be used in gate valve, optical shutter, and other switching applications. Two classes of IPRBMs are investigated in this paper. The bistable micromechanism size is less than 1 mm and fabricated by electroplating a soft magnetic material — Permalloy (80% Ni, 20% Fe) in a positive photoresist mold. Minimum feature size in the IPRBM, which corresponds to the width of flexible linkages, is 4 μm. The fabricated IPRBMs have been tested for their force-deflection response using an image based force sensing method. The test results were then compared with the simulated results obtained from a finite element model of the IPRBM. The IPRBM are shown to reversibly undergo 10 to 20 degrees of in-plane rotation and required a maximum torque of 1 to 2 μNm depending on the design. The experimental results showed good overall agreement with the design. A comparison within and between the two classes of IPRBM have been completed for three different design cases between which the tether width and aspect ratio was varied. The study showed a relative advantage of slender tethers with high aspect ratio in minimizing out-of-plane deflection. Also, the radial separation of the individual bistable mechanisms is important.