Determinants for Stiffness Adjustment Mechanisms

Variable stiffness actuators (VSAs) are a new generation of robotic drives that are developed to enhance the robot's ability to safely interact with unknown and dynamic environments. Furthermore, stiffness adjsutability can enhance energy efficiency in some particular applications, e.g. periodic motions with different frequencies. To adjust the stiffness, different mechanisms have been implemented in VSAs, each to fulfill the requirements of different applications with certain determinants. This paper explains these determinants and presents a comprehensive framework to systematically analyse performances of different stiffness adjustment mechanisms. First, a classification of different stiffness adjustment mechanisms is presented. Then, characteristics of each class regarding different determinants are evaluated and compared through numerical analysis. This will give additional insights into intrinsic pros and cons of different classes of stiffness adjustment mechanisms that enable a systematic future development of variable stiffness actuators and their applications.