Impact of Actuator Torque Density on Expected Robot Life - A Dynamic Model

Electric actuators not only add weight along an articulated robot arm, but they also have torque and speed limits that impose additional dynamic constraints. Further, the useful life of a robot depends on the extent to which each actuator operates at or near its torque ratings. Cumulative damage theory offers some means of quantifying how much wear a robot arm will sustain in real time as it executes a given trajectory. The dynamic performance as well as fatigue wear of a hypothetical dual-link robot arm are examined in the context of actuator torque density - the actuator's torque-to-mass ratio. The results show that the expected wear to the most stressed joint are approximately inversely proportional to the actuator's torque density. The model also suggests how expected robot life under one or more pre-defined trajectories could be used as an additional constraint in robot arm design and actuator choice.