Design and characterization of a miniaturized low inertia and low viscous friction magnetorheological clutch using 3D metal printing for human-robot applications

Robotic actuators such as geared MR actuators must improve their torque capacities and reduce their size to increase system integration density. MR clutches are at the heart of geared MR actuators and conventional machining is a major hurdle to downsizing because it requires having close tolerance for machining and assembling a large number of small parts. This paper studies the potential of nested 3D printed MR clutches to improve the torque density of geared MR actuators at small scales. Nested 3D printed MR clutches are multi-disk MR clutches where the rotor and stator are fabricated simultaneously on a single 3D print. A prototype is designed, built, tested and compared to similar conventionally made MR clutches. The prototype weighs 84 g and can transmit a maximum torque of 0.88 N.m. The fabrication process is fast and simple, and the performance levels well surpass those of comparable machined MR clutches. The manufactured prototype doubles the torque density and multiply respectively by 4 and by 10 the torque-to-inertia and torque-to-viscosity ratios compared to equivalent machined MR clutches. Results show that nested 3D printing of MR clutches is an effective manufacturing process and opens the door to a new generation of high-performance mechanical transducer.