New Variable Stiffness Safety Oriented Mechanism for Cobots' Rotary Joints

Introducing compliance in stiff robots arises from different design paradigms, such as achieving explosive motion or enhancing cyclic motion. However, a great emphasis is laying on the safety aspect especially in collaborative robots (Cobots) design. Herein, we present a novel design V2SOM which stands for Variable Stiffness Safety Oriented Mechanism. This new device, as its name indicates, comes to ensure the safety of physical Human/Robot Interaction (pHRI) as well as to reduce the dynamics' drawbacks of making robots compliant. Due to its two continuously linked functional modes, high and low stiffness modes. V2SOM presents a high inertia decoupling capacity which is a necessary condition for a safe pHRI without compromising robot's dynamic performances. The high stiffness mode eases the control without compromising the safety aspect. Once a Human/Robot (HR) collision occurs, a spontaneous smooth shift to low stiffness mode is passively triggered to safely absorb the impact. In this work two complementary safety criteria of pHRI are considered. The impact force (ImpF) criterion and Head Injury Criterion (HIC) for external and internal damage evaluation of blunt shocks, respectively.