Scalability of Controlling Heterogenous Stress-Engineered MEMS Microrobots (MicroStressBots) through Common Control Signal using Electrostatic Hysteresis

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.