Development of a Multilayered Magnetorheological Brake for Knee Orthosis Applications

Traditional passive knee orthoses support patients to walk. However, they cannot enable patients achieve a regular walking rhythm. Conventional active knee orthoses (AKOs) can apply motors to help patients walk smoothly; however, their heavy weight, high cost, and high power consumption are not suitable for most consumers. This study developed a novel multilayer magnetorheological (MR) brake (MRB) for knee orthoses with variable resistance. This MRB overcomes the drawbacks of conventional knee orthoses and motor-driven AKOs. The MRB primarily comprises a rotor, stator, and single magnetic pole and MR layers. The rotor and stator have multiple discs; both sides of the discs are surrounded by MR fluid layers. This multilayer structure provides a relatively high torque density during braking. The proposed brake was optimized through electromagnetic simulations. Subsequently, an MRB prototype was fabricated, and its performance characteristics were experimentally examined to confirm the design requirements. The results showed that the proposed MRB achieved a torque and torque-volume ratio (TVR) of 12.5 N．m and 46 N．m/dm^3, respectively. Because of the high TVR, this brake is more suitable than existing MRBs in AKO applications. Additionally, this brake exhibits advantages of rapid response (response time: 170 ms), easy control, low weight, and low power consumption.