Reconfigurable Magnetic Micro-Modules (Mag-μMods)
Scaling down the size of modules in reconfigurable robotic systems using micro-robotics technologies.

Goal: To employ magnetic micro-robot (Mag-μBot) technologies to create micron-scale modules for a reconfigurable system. To demonstrate reconfiguring systems at the micron-scale, which can give rise to high-resolution synthetic reality, as described by the Carnegie Mellon Claytronics Project.

Approach: Multiple Mag-μBots are capable of independently locomoting on a two-dimensional surface; addressably of individual Mag-μBots is enabled by the use of a surface with several independently controlled electrostatic anchoring pads, which can selectively prevent specific Mag-μBots from translating. Positioning two Mag-μBots close enough together (about 2-3 body lengths) will cause them to jump together and assemble, as their magnetic attraction far exceeds any other forces.

To facilitate disassembly, the inter-magnet attractive force is reduced by encasing the Mag-μBot inside a shell, giving rise to the magnetic micro-module, or Mag-μMod for short. The Mag-μMod locomotes on a two-dimensional surface like the Mag-μBot using stick-slip motion, although at slower velocities. Assembly is performed by simply bringing two Mag-μMods close enough together such that their magnetic attraction will cause them to jump-into each other. Only magnetically stable configurations are possible due to the nature of permanent magnets, which can restrict the types of assemblies formed, and will require pre-planning and intermediate steps to reach final magnetically-stable assemblies. Some magnetic assemblies are also capable of locomoting on the surface, as the stick-slip dynamics has not fundamentally changed.

Disassembly can be performed by electrostatically anchoring the Mag-μMod assembly, and unanchoring the module desired to be disassembled. By the application of strong magnetic field gradients applied from external sources, the unanchored module can be pulled off the assembly. Alternatively, magnetic torques can be applied from external sources to rotate the unanchored module into a configuration that repulses it from the assembly; in this configuration, the unanchored module can simply walk away using the standard stick-slip actuation technique. The method of magnetic torques is advantageous as weak magnetic fields can disassemble the module, and can be operated by the electromagnets used to locomote the Mag-μMods.

Both the Mag-μBots and Mag-μMods can be batch fabricated using soft-lithographc processes, which is conducive towards creating many modules for a large-volume reconfigurable system. Polyurethane is typically mixed with magnetic particles, and molded into a mold that contains the desired shapes of Mag-μBots. Shells are fabricated without the magnetic particles. After inserting the Mag-μBot inside a shell, it is magnetized in a magnetizer.

Benefits: Mag-μMods can pave the way for reconfigurable robotics at the micron-scale. This can lead to high-resolution assemblies of micron-scale robots, and high-resolution synthetic reality. Being essentially simple permanent magnets with a plastic casing, Mag-μMods can be fabricated inexpensively in large volumes. Additionally they are robust to the environment and do not break easily, and can be handled simply by using tweezers. Because Mag-μMods are based on permanent magnets, no additional power is required to maintain an assembly of Mag-μMods; power is only required to initially create the assembly or disassemble and reconfigure modules.

Videos: (newest to oldest)

• Experimental video of two Mag-μMods assembling and disassembling (2009) [YouTube video] [MP4 video]
• Experimental video of four 500 μm Mag-μMods assembling, reconfiguring and disassembling (2010) [YouTube video]

Members: Eric Diller, Metin Sitti

Past Members: Steven Floyd, Chytra Pawashe
Publications:

• Adhesion/friction data from reconfigurable paper (2011) dataAppendix.pdf
• E. Diller, C. Pawashe, S. Floyd, and M. Sitti, ''Assembly and Disassembly of Magnetic Mobile Micro-Robots towards Deterministic 2-D Reconfigurable Micro-Systems,'' International Journal of Robotics Research, vol 31, 1667-1680, 2011. link.
• C. Pawashe, E. Diller, S. Floyd, and M. Sitti, ''Assembly and Disassembly Methods for Magnetic Micro-Robots towards 2-D Reconfigurable Micro-Systems,'' IEEE Conference on Robotics and Automation, Shanghai, China, pp. 261-266, May 2011.
• C. Pawashe, S. Floyd, and M. Sitti, ''Assembly and Disassembly of Magnetic Mobile Micro-Robots towards 2-D Reconfigurable Micro-Systems,'' International Symposium on Robotics Research, 2009.