Experimental Validation of the Usage of Kinematic Singularities to Produce Periodic High-Powered Motion

Abstract

This paper reports on preliminary experimental results of recently proposed mechanism kinematics for a legged robot. The proposed kinematics creates a mapping from a series-elastic actuator to a foot motion that includes a pair of singularities within a fully rotatable kinematic circuit. Such a circuit is less common and only possible with certain multi-loop linkages. A slice of the configuration space displaying series-elastic rotation versus linear foot motion presents a characteristic “S” shape, motivating the name S-curve kinematics. Our experimental results show that S-curve kinematics can enhance the energetic output of a series-elastic actuator in a hopping task versus the usage of a conventional rotary-to-linear mechanism. This is possible because S-curve kinematics enable elastic energy storage outside of stance that is released through a mechanical reflex. Compared to a conventional rotary-to-linear actuator, S-curve kinematics demonstrated up to a 4x increase in kinetic output.