A new design of small-sized magnetorheological brakes based on the mixed mode operation for high torque efficiency

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A small-sized brake generating the torque less than 0.5 Nm is very attractive to achieve desired dynamic motions in many different fields such as medical haptic and auto door closure. In this work, a controllable compact-sized brake utilizing a magnetorheological fluid (MRF) is proposed and its effectiveness is validated through simulation and experiment. Unlike conventional shear mode magnetorheological brake (MRB), a mixed mode MRB (M-MRB) featuring both the flow and shear mode operations is designed to obtain high torque efficiency in which both the key shape and ring shape structures play the significant role. Through these structures, the proposed M-MRB can provide higher torque with the relatively less amount of MRF than conventional shear mode MRB. The key shape structure is fixed to the rotor and shaft of MRB and rotates in same direction. Then, MRF on the front and back of the barrier is subjected to the pressure difference resulting in the field-dependent torque generation. To demonstrate the effectiveness of the proposed design concept, a small-sized M-MRB is designed and manufactured considering the required torque level and space constraint of auto door closure applicable to autonomous vehicle systems. It is identified through a reasonable comparison between the proposed M-MRB and conventional MRB that the proposed one can improve controllable torque range up to 325% with less MR fluid than conventional MRB.