Investigation on the interaction mechanism between the compound motion and speed reduction performance of a miniature MR brake

The performance of miniature mechatronic systems can be significantly improved by incorporating the magnetorheological (MR) fluid-based rotary brake. However, the small-size effect becomes evident in the process of miniaturization. Our observation indicates that a miniature MR brake exhibits a slight eccentricity of 0.43 mm when its rotational axis is runs at a speed of 16,000 rpm. The maximum torque error between compound motion model and calculated dynamic torque based on experimental rotation speed n reached 47.4%, and the average torque error rate is only 8.5%. The paper proposes a comprehensive dynamic model to explain the interaction mechanism between the compound motion and speed reduction performance of a miniature MR brake. A high-speed camera-based dynamic performance testing system is developed to capture the motion state of the shaft and test the speed reduction performance. The dynamic magnetic field distribution under different eccentric distances is calculated by finite element method. The compound motion of rotation and eccentricity is observed when the rotational speed is above 3500 rpm. Results show that the behavior of the miniature MR brake can be well explained by the proposed comprehensive model. At a desired speed of 14,000 rpm, the maximum error of this model (87 rpm) is much smaller than the error of practical models in recent years (1338 rpm). We believe this work is significant for precisely describing the dynamics of miniature MR brake and promoting its application in miniature mechatronic systems.