A differential-based dual actuator for a safe robot joint: Theory and experiments

This paper presents experiments with a prototype of the Parallel Force/Velocity Actuator (PFVA), a differential-based dual actuator that consists of a low gear ratio input (Force Actuator or FA) and a high-gear ratio input (Velocity Actuator or VA). These experiments show the PFVA´s safe response to obstacles and impact forces. A mode of operation of the actuator is experimentally demonstrated where the controlled backdriveability of the FA is used to yield safely to obstacles. Backdriveability of FA in response to collisions with approach velocity of 0.5m/s and also to impulse forces is demonstrated. The theory and experimental techniques developed and implemented in this paper are directly applicable to velocity-summing dual actuators such as differential screw mechanisms. These are also extensible to torque-summing dual actuators.