3D Collision-Force-Map for Safe Human-Robot Collaboration

The need to guarantee the safety of collaborative robots limits their performance, in particular, their speed and hence cycle time. In this work, we measure the forces exerted by two collaborative manipulators (UR10e and KUKA LBR iiwa) on an impact measuring device. Our contributions are the following: (i) a new data-driven model predicting impact forces from velocity, distance from robot base, and, newly, the height in the workspace; (ii) demonstration that the model can be trained on a limited number of data points; (iii) analysis of the force evolution upon impact. The standard ISO/TS 15066 defines the Power and Force Limiting operation mode and prescribes force thresholds that a moving robot is allowed to exert on human body parts during impact (for the back of the hand, 280 N for transient and 140 N for quasi-static contact), along with a simple formula to obtain maximum allowed speed of the robot in the whole workspace. Applying this to our scenario where the impact has a clamping nature, the allowed end effector speed on the whole robot workspace would be only 0.13 and 0.16 m/s for the UR10e and KUKA LBR iiwa, respectively. Our measurements reveal that if the task is performed for example 0.8 m away and 0.4 m above the robot base, speeds of 0.16 m/s (UR10e) and 0.20 m/s (KUKA LBR iiwa) can be safely operated, staying within the prescribed force limit. Furthermore, the force evolution during impact for the UR10e reveals that clamping never occurs. With the 280 N limit, 0.36 m/s will still be safe with the UR10e. The formulas relating robot mass, velocity, and impact forces from ISO/TS 15066 are insufficient -- leading both to significant underestimation and overestimation of velocities/forces, and thus to unnecessarily long cycle times or even dangerous applications.