Ferrofluid Levitated Micro/Milli-Robots

In this article, we study the use of ferrofluids for levitating magnetic micro/milli-robots. With the addition of a ferrofluid, the robots improved their weight-carrying ability (xI2, >12 grams) and precision (x2 ~5 um) without any associated increase in actuation power of the robot relative to sliding versions without the ferrofluid. To better understand the longterm stability of a ferrofluid on the micro/milli-robot, we perform motion cycle testing on two different surfaces (graphite and Teflon), ultimately achieving a motion repeatability and pose angular stability of 5 um and 0.05 °, close to the limits of our measurement setup. The underdamped motion of the ferrofluid robot showed a natural resonance of ~58-60 Hz. Through careful control of the evaporation of the ferrofluid, we show long-term stability of a ferrofluid micro/milli-robot over the course of >11 hours. While the performance of the robot does change due to evaporation of the particular ferrofluid used, we also show that robots can easily be replenished with new ferrofluid after mechanically cleaning away the remaining ferrofluid. Overall, the application of ferrofluids toward magnetically actuated micro/milli-robots can enable low-cost and high-precision motion for future high-precision micro-manipulation or positioning tasks.