Design Exploration and Experimental Characterization of a 6 Degrees-of-Freedom Robotic Manipulator Powered by Cable-Driven Semi-Delocalized Magnetorheological Actuators

Collaborative robots need to work closely and safely with users while being fast and strong. Fulfilling both these needs simultaneously presents a significant challenge, if not a roadblock, for conventional geared motor technology. Magnetorheological (MR) actuation is an alternative technology that has the potential to exhibit both safety and speed at the same time in a compact and cost-effective envelope. MR actuation has demonstrated great potential for low-DOF mechatronic devices in close collaboration with humans such as exoskeletons and flight control systems but its potential for high-DOF collaborative robots remains widely unexplored. This paper presents the design and experimental validation of a 6 DOF manipulator prototype actuated by semi-delocalized MR clutches. The manipulator is designed with the objective of matching or exceeding the performance requirements of today's cobots in order to verify the potential of MR actuation for such applications. Experimental results show that the prototype has a mass in motion of 5.3 kg and can move a 4.5 kg payload at 1 m/s in a range of 0.885 m. Force bandwidth is above 50 Hz and backdriving forces less than 10% of the joints maximum torque, assuring excellent dynamic performance. Furthermore, the manipulator prototype is shown to be inherently safe and impact-tolerant. In all, results suggest that semi-delocalized MR actuation is a promising solution for high performance cobots although future work is needed for the MR technology to reach full-maturity in robotics.