Design for Variable Stiffness Actuation based on Enumeration and Analysis of Performance

This paper presents a systematic enumeration and performance analysis of Variable Stiffness Actuators (VSAs). VSAs are becoming more and more popular in robotics, and many different prototypes have been recently proposed and built in the research community. In comparison with conventional geared motors, actuators with variable stiffness introduce the need for new specifications, requirements, and performance criteria, concerning e.g. the range of achievable stiffness, and the response time to stiffness reference changes. On the other hand, the mechanical construction of VSAs is also more complex. To address the problem of harnessing the increased complexity of VSA design, we consider in this article the enumeration of all possible arrangements of two prime movers (elementary motors), two harmonic-drive gears, the output shaft, and the interconnections (either rigid or elastic) between these elements. We propose an automated algorithm to search the large combinatorics of such enumeration, and present a reduced number of feasible basic designs which accomplish the objectives of VS actuation. Furthermore, we propose a quasi-static model of VS actuators which can be used for an analysis of their performance and we conclude by presenting some preliminary characteristics of one of the selected designs.