Estimation of Safe Distance from the Robot Arm as a Guide for Limiting Slow Speed of Robot Motions

The main objective of this laboratory study was to determine the minimum distance from the robot considered as safe for monitoring purposes, and the corresponding perception of danger for close interaction in robot teaching tasks. Five speed levels of robot motions, i.e.: 10, 20, 30, 40 and 50 cm/sec, were used. The three motion types of the robot arm were forward, swing (from right) and swing (from left), he response variables were the minimum distance from the robot that the subject selected as safe for monitoring purposes, and the perception of danger due to robot speed at the selected safe distances. The subjects selected significantly different values of safe distances from the robot arm moving at the speed of 10 cm/s, than they did for the range of robot speeds from 20 to 40 cm/s. The corresponding perception of danger due to the robot motions at the selected safe distances was the lowest for the speed of 10 cm/s, while the values of perceived danger for the speed range of 20-40 cm/s did not significantly differ between each other. The above results indicate that the range of slow speeds of robot motions from 20 to 40 cm/s is similarly perceived by the subjects with respect to the potential hazards from the moving robot arm. It was suggested that the safe slow speed of robot motions for teaching and programming purposes lies somewhere between 10 and 20 cm/s, and that current recommendation of 25.0 cm/s for safe reduced speed of robot motions should be redefined.