Variable Recruitment of Parallel Elastic Elements: Series–Parallel Elastic Actuators (SPEA) With Dephased Mutilated Gears

The development and control of variable stiffness actuators (VSAs) led to the capability of embodying physical principles of safety and energy-efficiency compared to traditional stiff servomotors. However, the output torque range and efficiency of servomotors and VSAs are still insufficient which hinders the development of machines with performances comparable to a human. We have developed a novel compliant actuation concept, series-parallel elastic actuation (SPEA), that addresses these problems. The novelty being the variable recruitment of parallel elastic elements and adaptive load cancellation. In this paper, we propose the use of multiple dephased mutilated gears with locking ring and plate, as intermittent mechanisms, linked in parallel to the motor. As a result, the motor torque requirements can be lowered, as such the motor can be downscaled and the efficiency can be drastically increased. After an abstract description of the SPEA concept and an outline of the biological basis, we present the first unidirectional SPEA proof of concept (PoC) setup. Experiments on this PoC setup endorse the feasibility of the SPEA concept. The results match the modeled trend of a lowered motor torque and increased energy efficiency.