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This Note presents a new asymmetric flexure design, the double parallelogram-tilted-beam double parallelogram (DP-TDP) flexure, that enables two times higher stroke in electrostatic comb-drive actuators, compared to the traditional symmetrically paired double parallelogram (DP-DP) flexure, while maintaining the same device footprint. Because of its unique kinematic configuration, the DP-TDP flexure provides an improved stiffness ratio between the bearing and actuation directions, thus delaying the on-set of sideways instability. Experimental testing of micro-fabricated comb-drive actuators with flexure beam length 1 mm and comb gap 5 μm demonstrates a stroke of 149 μm (at 86 V) for the proposed DP-TDP flexure, in comparison to 75 μm (at 45 V) for the traditional DP-DP flexure.

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. For a given flexure beam length, comb gap, and actuation voltage, 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 while maintaining low motion direction stiffness over a large range of motion direction displacement. The high stiffness ratio between the bearing and motion directions mitigates the on-set of sideways snap-in instability, thereby offering significantly greater actuation stroke compared to existing designs.

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.