CLOSED-LOOP CONTROL OF A PARALLEL-PLATE MICROACTUATOR BEYONDTHE PULL-IN LIMIT

摘要

In this paper, we present a controller design for servoing theposition of a parallel-plate electrostatic microactuator beyond itsopen-loop instability point. Controller design considers nonlinearitiesfrom both the parallel-plate actuator and the parallel-plate positionsensor, to ensure robust stability within the feedback loop.Desired transient response is achieved by a pre-filter added in frontof the feedback loop to shape the input command. The microactuatoris characterized by static and dynamic measurements, with aspring constant of 0.17 N/m, mechanical resonant frequency of12.4 kHz, and effective damping ratio from 0.55 to 0.35 for gapsbetween 2.3 to 2.65 μm. The minimum input-referred noise capacitancechange is measured at a gap of 5.5 μm, corresponding to aminimum input-referred noise displacement of 0.2 nm/√Hz. Resultsof the servo test show excellent agreement with design specifications(Rise time < 2 ms, overshoot = 0, and settling time < 5 ms) forthe intended application as a magnetic probe tip actuator for datastorage. Actuator displacement servoed as far as 55% of the gap ismeasured, which surpasses the static pull-in limit of one-third of thegap.