Large Stroke Comb-Drive Actuators Using Reinforced, Clamped, Paired Double Parallelogram (C-DP-DP) Flexure

Abstract

This paper reports in-plane electrostatic comb-drive actuators with stroke as large as 245 μm, achieved by employing a novel Clamped Paired Double Parallelogram (C-DP-DP) flexure mechanism. For a given flexure beam length (L1), comb gap (G), and actuation voltage (V), this is currently the largest comb-drive actuator stroke reported in the literature. The C-DP-DP flexure mechanism design offers high bearing direction stiffness (Kx) while maintaining low motion direction stiffness (Ky), over a large range of motion direction displacement. The resulting high (Kx /Ky) ratio mitigates the on-set of sideways snap-in instability, thereby offering significantly greater actuation stroke compared to existing designs. Further improvement is achieved by reinforcing the individual beams in this flexure mechanism. While the traditional Paired Double Parallelogram (DP-DP) flexure design with G = 3 μm, L1 = 1 mm results in a 50 μm stroke before snap-in, the reinforced C-DP-DP design with G = 3μm achieves a stroke of 141 μm. The same C-DP-DP flexure design provides a 215 μm stroke with G = 4 μm, and a 245 μm stroke with G = 6 μm. The presented work includes closed-form stiffness values for the reinforced C-DP-DP flexure, a design procedure for selecting dimensions of the overall comb-drive actuator, micro-fabrication of some representative actuators, and experimental measurements demonstrating the large stroke.