Due to scaling laws and ease of fabrication, electrostatic actuation offers a promising

opportunity for actuation in small-scale robotics. This dissertation presents several novel

actuator and motor designs as well as new techniques by which to characterize electrostatic

gap closing actuators.

A new motor architecture that uses in-plane electrostatic gap-closing actuators along

with a flexible driving arm mechanism to improve motor force density is introduced, optimized,

manufactured, and tested. This motor operates similarly to other inchworm-based

microactuators by accumulating small displacements from the actuators into much larger

displacements in the motor. Using an analytical model of the inchworm motor based on

the static force equilibrium condition, optimizations of a full motor design were performed

to maximize motor force density. In addition, force losses from supporting flexures were

included to calculate the theoretical motor efficiency for different motor designs. This force

density optimization analysis of the gap-closing actuators and supporting motor structures

provided the basis for designing and manufacturing inchworm motors with flexible driving

arms and gap-closing actuators. The motor required only a single-mask fabrication and

demonstrated robust performance, a maximum speed of 4.8mm/s , and a maximum force on

the shuttle of 1.88mN at 110V which corresponds to area force density of 1.38mN/mm2. In

addition, instead of estimating motor force based on drawn or measured dimensions which

often overestimates force, the demonstrated maximum motor force was measured using calibrated

springs. The efficiency of the manufactured motor was measured at 8.75% using

capacitance measurements and useful work output.

To further increase force output from these motors, several new designs were proposed,

analyzed, and tested. Thick film actuators that take advantage of a through-wafer etch offered

a promising opportunity to increase force given the linear increase in force with actuator

thickness. However, fabrication challenges made this particular approach inoperable with

current manufacturing capabilities. New actuator designs with compliant and zipping electrodes

did demonstrate significant increases in force, but not the order of magnitude increase

promised by modeling and analysis. In order to study and understand this discrepancy, several

new techniques were developed to electrically and electromechanically characterize the

force output of these new actuator designs. The first technique identifies parameters in an

equivalent circuit model of the actuator, including actuator capacitance. By monitoring

change in capacitance along the travel range of the motor, electrostatic force in equilibrium

can be estimated. Charge transferred to and from the actuator can also provide an estimate

of actuator efficiency. The second technique uses a constant rate spike to more thoroughly

explore the rapid dynamics of actuator pull-in and zipping.

New characterization methods allowed for collecting large amounts of data describing

performance of motors with zipping and compliant electrodes. The data was used to back

up the main hypothesis of force output discrepancy between theory and practice. Also, it

was used to highlight extreme sensitivity of proposed motors toward manufacturing process

and its tolerances.