Large displacement linear actuator

The design and performance of a large-force, large-amplitude electrostatic actuator that exhibits the best features of previous electrostatic actuator designs are described. A tangential drive (T-drive) polysilicon, linear actuator is presented. It produces large-magnitude tangential motion by flexing a microstructure in an essentially straight line with moderate input voltage. These devices are designed, fabricated, and successfully tested to have substantial displacements even for static positioning. The working principle of the T-drive is that the strong electrostatic forces of attraction between a fixed bar and a free bar are converted to large-amplitude tangential motion by the parallelogram flexural suspension of the free bar. Operating devices are capable of tangential displacements as great as 32 mu m. This displacement is stable and easily varied, because the tangential displacement can be controlled by adjusting the potential between the fixed electrode and the traversing bar. Static displacements are detectable for voltages as low as 15 VDC. Typical T-drives have free bars 200 mu m long and 12 mu m wide, with flexural suspensions 450 mu m long and 2 mu m wide. All component thicknesses are 2 mu m. Theoretical models for both the flexural suspension and electrostatic forces are derived, and they predict the relation between tangential displacement and excitation voltage.<
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