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Magnetically Actuated Micro-Robots (Mag-μBot)
Harnessing magnetic fields to control mobile micro-scale robots.
Also see: Reconfigurable Magnetic Micro-Modules (Mag-μMod)
Goal
To employ external magnetic fields to controllably position and orient a magnetic micro-robot. We demonstrate this approach in the 2007 and 2008 RoboCup Nanogram Demonstrations.
Approach
Six electromagnetic coils surround a working volume, wherein the magnetic micro-robot (Mag-μBot) resides. The four upright coils create in-plane magnetic fields with the micro-robot, and the top and botom coils provide an orthoganal clamping force. DC magnetic field gradients are developed using the coils, which exerts a force and torque onto the micro-robot orienting it, however is insufficient to translate it due to surface friction. By nonuniformly oscillating the magnetic field, the micro-robot experiences a nonuniform rocking motion. This, in effect, induces stick-slip behavior in the robot resulting in translation. By varying the pulsing frequency and waveform shape, control of micro-robot velocity is achieved. Maximum velocities observed are over 16 mm/s in air (about 60 body lengths per second) and 7 mm/s underwater.
A Mag-μBot is a Neodymium-Iron-Boron permanent magnet. It is machined using a laser micro-machining system to a desired shape, typically a rectangular solid with approximate dimensions 250x130x50 microns.
Visual servoing is possible using computer vision to track the Mag-μBot. Motion tasks can be planned and executed using path-planning techniques from a computer. Control strategies will be implemented to ensure stability of manipulation, and will be implemented for task-based guided micromanipulation.
Multiple Mag-μBots can be operated with the additional use of electrostatic anchoring pads. The surface is covered with individually addressable electrostatic cells, and Mag-μBots can be locked down selectively. Anchored robots do not move in the presenece of a driving magnetic field, but unclamped robots do. This allows for the serial uncoupled positioning of multiple Mag-μBots, or the parallel symmetric motion of multiple Mag-μBots.
Advantages and Benefits
Externally controlled magnetic actuation for micro-scale robots benefits from the ability of operation on arbitrary surfaces. Most surfaces are feasible, provided that they are not magnetically active and not overly sticky. Examples of valid surfaces are glass, silicon, hard plastics, and machined aluminum; in observation, the micro-robot operates better on slightly rough surfaces, likely due to decreased adhesive forces to the surface. In comparison, approaches such as electrostatic actuation for micro-robots requires a specialized surface with electrodes. Without these constraints, Mag-μBot motion on arbitrary surfaces can be realized, as actuation is independent of the surface.
In addition the Mag-μBot can operate in a fluid environment, provided the fluid is not too viscous such that it impedes the micro-robot's motion. In experiment, fluids up to 50 cSt in viscosities can be used, however the micro-robot experiences velocity reductions due to fluid damping. Fluid environments are advantageous as micro-scale stiction forces are reduced, which can improve the reliability of micro-scale manipulation tasks.
As the Mag-μBot is simply a permanent magnet, it is not fragile and is physically robust, capable of being handled in harsh environments. Susceptibility to dirt, contamination, and humidity fluctuations are minimal with this design, when compared to other micro-robot approaches.
Videos
A Mag-μBot moving on a glass slide in air with a US dime for scale reference (2008) [YouTube video] [WMV video]
A Mag-μBot moving on a dime underwater, traversing across the 50 to 100 micron features on the coin (2008) [YouTube video] [WMV video]
A Mag-μBot pushing 50-micron polystyrene beads underwater (2008) [YouTube video] [WMV video]
High-speed video of the side-view of a Mag-μBot in translation, displaying stick-slip motion, taken at 200 fps (2008) [YouTube video] [WMV video]
Demonstration of three Mag-μBots with micro-sphere manipulation (on MIT Technology Review), [video], [link]
Interview of magnetic micro-robot system at EngineeringTV.com [link]
Members
Steven Floyd,
Chytra Pawashe,
Metin Sitti
Former Members
Brad Camburn
In the news
"Precision Control of Micro Machines" on MIT Technology Review, [link]
"The Works: Robots" on the History Channel, September 2008, [iTunes Link]
Engineering TV episode, "Magnetically Actuated Micro-Robots", June 2008, [Link]RoboCup Nanogram Demonstration Competition, 2007 and 2008, [Link], [CNN YouTube Video]
Publications
S. Floyd, C. Pawashe, M. Sitti, ''Two-Dimensional Contact and Non-Contact Micro-Manipulation in Liquid using an Untethered Mobile Magnetic Micro-Robot,'' IEEE Transactions on Robotics, 2009, in press. [link]
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, invited paper, to appear, 2009.
S. Floyd, C. Pawashe, and M. Sitti, ''Microparticle Manipulation using Multiple Untethered Magnetic Micro-Robots on an Electrostatic Surface,'' IEEE/RSJ Int. Conf. Robots and Intelligent Systems, St. Louis, USA, 2009. Best Paper Award. [pdf]
C. Pawashe, S. Floyd, M. Sitti, ''Modeling and Experimental Characterization of an Untethered Magnetic Micro-Robot,'' International Journal of Robotics Research, Vol. 28, No. 8, 2009, invited paper. [link]
C. Pawashe, S. Floyd, M. Sitti , ''Multiple Magnetic Microrobot Control using Electrostatic Clamping," Applied Physics Letters, 94, 164108 (2009). [pdf] [link]
Pawashe, C., Floyd, S., Sitti, M., "Dynamic Modeling of an Untethered Magnetic Micro-Robot," Robotics: Science and Systems, Zurich, Switzerland, 2008. [pdf]
Floyd, S., Pawashe, C., Sitti, M., "An Untethered Magnetically Actuated Micro-Robot Capable of Motion on Arbitrary Surfaces," IEEE Int. Conf. on Robotics and Automation, 2008. [pdf]
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