Design and Analysis of a Comb-Drive Actuator for Large Displacement

Comb-drive electrostatic actuators have been widely applied to steer a gripper, an acceleratometer, a scanning mirror, and a xy-stage because their output forces are easily controlled and capacitively sensed. To obtain large displacement with low drive voltage, a comb-drive actuator has to be designed with narrower gap and larger overlapping area between two electrodes. As a result, it will induce the instability or side sticking during operation; that is, the stationary and the moving electrodes will stick together and the actuator fails to operate. Furthermore, due to the asymmetric electrodes caused by inevitably imperfect fabrication of the actuator, the comb-drive actuator may be unstable for a large displacement, resulting from the unbalanced electrostatic forces between two electrodes. We report a novel design, which utilizes a set of extra electrode structure to compensate the unbalanced electrostatic forces. Simulation results demonstrated that the larger displacement is achieved while the size of the comb-drive actuator keeps the same. For better performance, the design of electrode structure and the number of electrodes are discussed in this report.