  In this paper we present control strategies for implementing reconfigurable
planar microassmbly using multiple stress-engineered MEMS microrobots
(MicroStressBots). A MicroStressBot is an electrostatic microrobot that
consists of an untethered scratch drive actuator (USDA) that provides forward
motion, and a steering-arm actuator that determines whether the robot moves in
straight line or turns. The steering-arm is actuated through electrostatic
pull-down to the substrate initiated by the applied global power delivery and
control signal. Control of multiple MicroStressBots is achieved by varying the
geometry of the steering-arm, and hence affecting its electrostatic pull-down
and/or release voltages. Independent control of many MicroStressBots is
achieved by fabricating the arms of the individual microrobots in such a way
that the robots move differently from one another during portions of the global
control signal. In this paper we analyze the scalability of control in an
obstacle free configuration space. Based on robust control strategies, we
derive the control signals that command some of the robots to make progress
toward the goal, while the others stay in small orbits, for several classes of
steering-arm geometries. We also present a comprehensive analysis and
comparison between the numbers of required independent pull-down and release
voltages, demonstrating significant improvement in terms of the efficiency as
well as the size of the control signal presented in past work. Our analysis
presents an important step for developing multi-microrobots control of
MicroStressBots.
