High torque, low speed joint actuator based on PM brushless motor and magnetic gearing

An approach to joint actuation for space applications is presented. This electric actuator is capable of directly operating a robot arm, with the low speed, high torque, good smoothness, and intrinsic safety brake ability required by a typical space application. The actuator consists of a PM (permanent magnet) brushless motor and a high-efficiency magnetic gearbox built into the motor airgap, with no backlash but finite stiffness and quasisinusoidal torque vs. position characteristic. A complete finite element analysis has been carried out to verify the mechanical feasibility and to optimize the actuator design. The test design, with total mass of 3 kg including the sensor, reaches a torque density greater than 9 Nm/kg with an overall motor plus reducer efficiency of 63% at 150 W power level