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I am developing novel methods for the control of microrobots, which are under 1 mm in size. The small size of these microrobots could enable them to have potential applications in healthcare, microfluidics or micro-scale factories. My work focuses on addressing the challenges in microrobot motion and the manipulation of objects at the micro-scale in confined spaces. Microrobot actuation is accomplished by computer-controlled magnetic fields, supplied by a set of magnetic coils. This enables "crawling"-type motion on 2D surfaces as well as levitation in fluids for 3D motion.
This work introduces new strategies for fluid-based manipulation of micro-scale objects using rotating magnetic micro-robots at low Reynolds numbers. By rapidly spinning the micro-robots, rotational fluid flow is induced which acts to move the micro-objects by fluidic drag. Acting in parallel, teams of these micro-robots work together to rapidly move micro-objects along planned "virtual channels" to goal positions. As the micro-robots are themselves highly mobile, the manipulation trajectories are controlled to achieve accurate, fast manipulation of multiple micro-objects in 2D environments.
One significant challenge in micro-robotics is the simultaneous control of multiple untethered agents. This is difficult with current micro-robotic systems because driving signals are typically uniform in the workspace, so all agents receive identical control inputs. Methods to address individual micro-robots must be developed for the full control of multiple micro-robots.
I have explored the use of unique microrobots which respond differently to the same driving fields. Using this method, I have shown the independent positioning of 2-3 microrobots moving on a planar 2D surface and levitating in 3D.
Addressable Magnetic Actuation for Robotics and Microfluidics
Remotely and selectively turning on and off the magnetization of many micro-scale magnetic actuators could be a great enabling feature in fields such as microrobotics and microfluidics. We have developed an array of addressable sub-mm micropumps made from a composite material whose net magnetic moment can be selectively turned on or off by application of a large magnetic field pulse. The material is made from a mixture of micron-scale neodymium-iron-boron and ferrite particles, and can be formed into arbitrary actuator shapes using a simple molding procedure.
By selectively controlling the orientation of each of an array of micro-actuators prior to the application of the field pulse, the magnetic on/off state of each can be controlled independently. The micropumps are actuated by weak rotating magnetic fields to pump liquid through 100 μm fluid channels. A distinct transition between the on and off states is seen by application of pulsed large magnetic fields. We have shown the performance of groups of up to five of these micropumps, and are extending the capabilities to mobile untethered microrobots.
Micro-Scale Reconfigurable Robots
The field of reconfigurable robotics propos
es versatile robots that can reform into various configurations depending on the task at hand. These types of robotic systems consist of many independent and often identical modules, each capable of motion, and capable of combining with other modules to create assemblies. These modules can then be disassembled and reassembled into alternate configurations.
A primary challenge in the field of reconfigurable robotics is scaling down the size of individual robotic modules. This project has developed a novel set of permanent magnet modules that are under 1 mm in all dimensions for use in a reconfigurable micro-system. The modules are actuated by oscillating external magnetic fields of several mT in strength, and are capable of locomoting on a 2-D surface. Multiple modules are controlled by using an electrostatic anchoring surface, which can selectively prevent specific modules from being driven by the external field while allowing others to move freely. We address the challenges of both assembling and disassembling modules. Assembly is performed by bringing two modules sufficiently close that their magnetic attraction causes them to combine. Disassembly is performed by electrostatically anchoring one module to the surface, and applying magnetic torques from external sources to separate the unanchored module. We have also investigated stronger bonds by heat-activated adhesives.
Micro-scale swimming robots are attractive for biological and biomedical applications because much of the human body is filled with fluids. Some of the potential biomedical applications for swimming micro-robots are kidney stone removal, minimally invasive surgery, early stage disease screening, biopsy, and highly localized drug delivery. Microorganisms swim with beating cilia or helical flagella, which are efficient due to the nature of fluid dynamics at the small scale.
This project aims to develop bacteria-inspired swimming microrobots which move using artificial flagella. We are investigating the use of different helical or soft flagella designs, and the use of multiple flagella for increased propulsion.
More information on micro-scale robotics can be found at the NanoRobotics Lab website.
In the Biologically Inspired Robotics Lab at Case Western Reserve University I developed a hexapod climbing robot named DIGbot. DIGbot's name comes from its utilization of Distributed Inward Gripping (DIG) to generate adhesive forces. DIG allows robots to climb on surfaces of any orientation with respect gravity, including ceilings, or in zero gravity environments.
DIGbot is driven by 19 servomotors which allows the robot to execute complex climbing manuevers such as turns and transitions from vertical to horizontal climbing at any angles.