A High-Torque Density Compliant Actuator Design for Physical Robot Environment Interaction

Compared to the traditional industrial robots that use rigid actuators, the advanced robotic systems are mobile and physically interact with unknown and dynamic environments. Therefore, they need intrinsically safe and compact actuators. In the last two decades, Series Elastic Actuators (SEAs) have been one of the most popular compliant actuators in advanced robotic applications due to their intrinsically safe and compact mechanical structures. The mobility and functionality of the advanced robotic systems are highly related to the torque-density of their actuators. For example, the amount of assistance an exoskeleton robot can provide is determined by the trade-off between the weight and output-torque, i.e., torque-density, of its actuators. As the torque outputs of the actuators are increased, the exoskeleton can expand its capacity yet it generally becomes heavier and bulkier. This has significant impact on the mobility of the advanced robotic systems. Therefore, it is essential to design light-weight actuators which can provide high-output torque. However, this still remains a big challenge in engineering. To this end, this paper proposes a high-torque density SEA for physical robot environment interaction (p-REI) applications. The continuous (peak) output-torque of the proposed compliant actuator is 147Nm (467 Nm) and its weight is less than 2.5kg. It is shown that the weight can be lessened to 1.74, but it comes at cost. The performance of the proposed compliant actuator is experimentally verified.