Dynamic characteristics of rotary magnetorheological fluid brake for use with air turbine spindle

Air turbine spindles are widely used in various machines, such as milling tools and aspherical lens generators. This study aimed to investigate the potential use of commercially available rotary magnetorheological fluid (MRF) brakes as components to effectively regulate the rotational speed of air turbine spindles in the low rotation-speed range from 100 to 500 min-1. The target speed was set as 300 min-1 with response time set to 20 s after the speed reached the target. Accordingly, a Hall Effect magnetic sensor was used to measure the low-to-high rotation speed of the air turbine spindle in addition to the magnetic induction generated by the current supply of the MRF brake. Tests were conducted to obtain the rotation speed, resistance torque, magnetic field, and electrical power supply in a commercial MRF brake used to control the shaft of the air turbine spindle. The results show that commercial MRF brake can effectively control the rotation speed in the low-speed region. However, the dynamic characteristic of the MRF brake cause undesirable oscillations.