Continuously Controllable Series Clutches for Efficient Robot Actuation

This paper investigates the energy efficiency potential of continuously controllable clutches between the motors and links of robot joints. Inspired by biological muscles, the clutch enables free, purely gravity driven robot link motion phases gradually disengaged from gear friction, not requiring motor effort. The concept combines the energetic benefits of direct drives during unforced motion phases with the high torque density of conventional and mature geared robotic drive technology during forced motion phases. The paper specifies the general functional principle of the clutch for energy saving independent of any particular clutch implementation. The feasible energy saving of up to 60 % is investigated for harmonic link motions with varying frequencies and with respect to different ratios of link weight to friction torque. The outcomes of the theoretical investigations are supported by first experimental results.