We introduce a principled method for multi-robot coordination based on a general model (termed a MacDec-POMDP) of multi-robot cooperative planning in the presence of stochasticity, uncertain sensing, and communication limitations. A new MacDec-POMDP planning algorithm is presented that searches over policies represented as finite-state controllers, rather than the previous policy tree representation. Finite-state controllers can be much more concise than trees, are much easier to interpret, and can operate over an infinite horizon. The resulting policy search algorithm requires a substantially simpler simulator that models only the outcomes of executing a given set of motor controllers, not the details of the executions themselves and can solve significantly larger problems than existing MacDec-POMDP planners. We demonstrate significant performance improvements over previous methods and show that our method can be used for actual multi-robot systems through experiments on a cooperative multi-robot bartending domain.

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We introduce a principled method for multi-robot coordination based on a generic model (termed a MacDec-POMDP) of multi-robot cooperative planning in the presence of stochasticity, uncertain sensing and communication limitations. We present a new MacDec-POMDP planning algorithm that searches over policies represented as finite-state controllers, rather than the existing policy tree representation. Finite-state controllers can be much more concise than trees, are much easier to interpret, and can operate over an infinite horizon. The resulting policy search algorithm requires a substantially simpler simulator that models only the outcomes of executing a given set of motor controllers, not the details of the executions themselves and can to solve significantly larger problems than existing MacDec-POMDP planners. We demonstrate significantly improved performance over previous methods and application to a cooperative multi-robot bartending task, showing that our method can be used for actual multi-robot systems.

Adhesion and friction during physical contact of solid components in microelectromechanical systems (MEMS) often lead to device failure. Translational stages that are fabricated with traditional silicon MEMS typically face these tribological concerns. This work addresses these concerns by developing a MEMS vertical translation, or focusing, stage that uses electrowetting-on-dielectric (EWOD) as the actuating mechanism. EWOD has the potential to eliminate solid-solid contact by actuating through deformation of liquid droplets placed between the stage and base to achieve stage displacement. Our EWOD stage is capable of linear spatial manipulation with resolution of 10 μm over a maximum range of 130 μm and angular deflection of approximately ±1°, comparable to piezoelectric actuators. We also developed a model that suggests a higher intrinsic contact angle on the EWOD surface can further improve the translational range, which was validated experimentally by comparing different surface coatings. The capability to operate the stage without solid-solid contact offers potential improvements for applications in micro-optics, actuators, and other MEMS devices. KEYWORDS: Electrowetting on Dielectric (EWOD), Microelectromechanical Systems (MEMS), Tribology, Lab-on-a-Chip 2The efficacy and longevity of actuation-based microelectromechanical systems (MEMS) are limited by tribological issues such as friction and adhesion.1 Adhesion typically occurs between small asperities when nominally smooth solid surfaces come into contact, and friction is the result of this adhesion during motion of the surfaces relative to each other. In some cases, the forces from adhesion and friction are comparable to the forces actuating the device, rendering it unusable. In the presence of water vapor, these concerns are amplified; formation of a thin liquid film on solid surfaces and the corresponding capillary and viscous effects that come into play when these surfaces interact lead to stiction, a phenomenon that increases the adhesion between solid asperities and causes small features to stick together due to exceptionally high friction. 1-3These reactive forces at the physical contact of solid components lead to wear and removal of material, reducing device lifetime. 1,4,5

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