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.
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