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) set-up. Experiments on this PoC set-up endorse the
feasibility of the SPEA concept. The results match the modeled
trend of a lowered motor torque and increased energy efficiency.