Spherical Brake with MR Fluid as Multi Degree of Freedom Actuator for Haptics

This research explored design of a magnetorheological (MR) spherical brake as a multi-DOF actuator. To the best of our knowledge, our design is the first ever multi-DOF spherical brake using MR fluid. The primary goal was to design a compact but powerful brake using the serpentine flux path approach. An optical position measurement system was also designed to eliminate the gimbal mechanisms that are typically used in spherical joints for position measurement. It was found that the braking torque scales up proportionally to the cube of the brake radius. This enables making much more powerful brakes without increasing the overall size significantly. A prototype spherical brake was built with 76.2 mm diameter and 3.7 Nm braking torque. Experiments were conducted to identify the characteristics of the prototype brake and to test it in virtual wall collision, damping and Coulomb friction simulations for haptics. A joystick was built as a haptic device using the MR spherical brake. Virtual wall collision experiments showed crisp reaction force at initial contact and very high rigidity during the contact.