Design and Analysis of a Small-Scale Magnetorheological Brake

This article presents the design and performance of a small-scale magnetorheological (MR) brake, with the fastest time constant and highest torque-to-mass ratio among small-scale MR brakes (i.e., those with a diameter less than 40 mm and a thickness less than 30 mm), which are typically designed for use in small haptic or robotic devices. By combining disk- and drum-type designs and incorporating the current-carrying coils into the rotor, this brake uses all three shear surfaces of the rotor to generate large braking torque. Additionally, a serpentine magnetic flux path that crosses the MR fluid shear surfaces a total of six times is used to achieve this torque in a small form factor. An FEM model is used to inform the dimensions of the brake components to increase the magnetic flux density within the MR fluid gap. This enables us to increase the shear force of the MR fluid, and thus, increase braking torque. To characterize brake performance and dynamic response, we measure the relationship between current and braking torque. We then compare the brake’s performance to various types of similarly sized commercial brakes and other small-scale MR brakes found in the literature.