Magnetorheological-Actuators: An Enabling Technology for Fast, Safe and Practical Collaborative Robots

Collaborative robots are more and more used in ap- plications requiring robots and humans to work in proximity or direct contact. However, conventional collaborative robots powered by servo-geared actuators are intrinsically dangerous due to their high reflected inertia. Recent studies have shown that low inertia and high bandwidth (> 30 Hz) magnetorheological (MR) actuators have the potential to improve the safety of collaborative robots without reducing their force and speed capabilities. The main contribution of this article is to provide a quantitative assessment of how MR actuators can contribute to reducing the impact forces with humans, and thus increase the safety of collaborative robots. Dynamic models, validated with simplified 1 degrees-of-freedom (experiments, show that the safety level of collaborative robots can be increased by a factor up to 3 only by changing the conventional servo-geared actuator architectures for MR actuators with no other changes. The article also presents a simple, reliable, and fast colli- sion detection method based on joint angular velocity band-pass filtering, a method exploiting the unique low inertia and clean dynamics properties of MR actuators. Finally, an experimental comparison of representative collaborative robots demonstrates an impactforcereductionof10timesusingMRactuators,fastcollision detection, and passive foam padding.