Serpentine flux path for high torque MRF brakes in haptics applications

This research aimed to address two main goals in the development of a rotary magnetorheological fluid (MRF) brake: (1) design of a compact and powerful brake and (2) low friction sealing technique to reduce the off-state braking torque and prevent the fluid from leaking. Using magnetically conductive and non-conductive rings a serpentine flux path was developed to weave the magnetic flux through the MRF. Experimental results showed that, when compared to a commercial MRF brake, our 33% smaller prototype MRF brake could generate 2.7 times more torque (10.9 Nm). A ferro-fluidic sealing technique was developed that resulted in sealing in the fluid and decreased the off-state friction. Further reduction in the off-state torque was obtained by applying a reverse current pulse to collapse a residual magnetic field in the brake. A 1-DOF haptic interface employing the brake enabled crisp virtual wall collision and Coulomb friction simulations.