  In this paper, a speed and separation monitoring (SSM) based safety
controller using three time-of-flight ranging sensor arrays fastened to the
robot links, is implemented. Based on the human-robot minimum distance and
their relative velocities, a controller output characterized by a modulating
robot operation speed is obtained. To avert self-avoidance, a self occlusion
detection method is implemented using ray-casting technique to filter out the
distance values associated with the robot-self and the restricted robot
workspace. For validation, the robot workspace is monitored using a motion
capture setup to create a digital twin of the human and robot. This setup is
used to compare the safety,performance and productivity of various versions of
SSM safety configurations based on minimum distance between human and robot
calculated using on-robot Time-of-Flight sensors, motion capture and a 2D
scanning lidar.
