Large Stroke Electrostatic Comb-Drive Actuators Enabled by a Novel Flexure Mechanism

This paper presents in-plane electrostatic comb-drive actuators with stroke as large as 245 μm that is achieved by employing a novel clamped paired double parallelogram (C-DP-DP) flexure mechanism. 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 onset of sideways snap-in instability, thereby offering significantly greater actuation stroke compared with 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 comb gap G = 3 μm and flexure beam length L₁ = 1 mm results in a 50- μm stroke before snap-in, the reinforced C-DP-DP design with the same comb gap and flexure beam length achieves a stroke of 141 μm. Furthermore, this 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 expressions for the reinforced C-DP-DP flexure, a design procedure for selecting dimensions of the overall comb-drive actuator, microfabrication of some representative actuators, and experimental measurements demonstrating the large stroke.