A highly-geared haptic actuator using 3D printed magnetorheological clutches

Abstract Advanced robotic systems such as humanoid robots need actuators with high torque density but yet, with good haptic abilities, in order to interact transparently with people. Combining these two requirements presents an important challenge for conventional gearmotors due to a gearing design conflict where gearing increases torque density but only at the cost of reduced haptic performance. Recent research suggests that magnetorheological (MR) actuators have the potential to greatly reduce the gearing design conflict by introducing a small fluidic clutch between the “gear” and the “motor” which allows maintaining excellent haptic performance at high gearing. Fully extracting the benefits of MR actuators requires pushing gearing ratios above 100:1 in combination with miniature low friction and inertia clutches which presents serious manufacturing challenges. This paper presents a manufacturing solution for such miniature, low friction and inertia, 3D printed MR clutch design and integration in an actuator with 120:1 gearing ratio. An extensive experimental characterisation is conducted on a fully-functional actuator showing excellent backdrivability and frequency response even with such high gearing levels thus opening the door to a future generation of torque-dense, but yet haptic robot actuators.