Figure: Composite optical micrograph of experimental microassembly using four microrobots. This figure shows docking of robot D₂ (left) to subsassembly G₁, forming assembly G₄, while robot D₁ follows a limit cycle (closed-loop orbit - upper right). Each microrobot is approximately 245 µm × 60 µm × 10 µm in size, and they move simultaneously within a single operating environment.

Notation: µm = micrometers.

Summary of paper: We present control strategies that implement planar microassembly using groups of stress-engineered MEMS microrobots (MicroStressBots) controlled through a single global control signal. The global control signal couples the motion of the devices, causing the system to be highly underactuated. In order for the robots to assemble into arbitrary planar shapes despite the high degree of underactuation, it is desirable that each robot be independently maneuverable (independently controllable).

To achieve independent control, we fabricated robots that behave (move) differently from one another in response to the same global control signal. We harnessed this differentiation to develop assembly control strategies, where the assembly goal is a desired geometric shape that can be obtained by connecting the chassis of individual robots. We derived and experimentally tested assembly plans that command some of the robots to make progress toward the goal, while other robots are constrained to remain in small circular trajectories (closed-loop orbits) until it is their turn to move into the goal shape.

Our control strategies were tested on systems of fabricated MicroStressBots. The robots are 240-280 µm × 60 µm × 7-20 µm in size and move simultaneously within a single operating environment. We demonstrated the feasibility of our control scheme by accurately assembling five different types of planar microstructures.

Videos: See videos of our microrobots, and see more of these microassemblies, on our our lab's YouTube channel: www.youtube.com/user/labdonald/videos,