Geometrical analysis of a continuously variable transmission system designed for human-robot interfaces

Abstract

New robotic systems are placed out of their constrained workspaces in order to work alongside humans. Consequently, these applications call for robots monitoring and regulating physical human-robot interaction. These robots’ mechanical compliance should be varied when they are in physical contact with the human or their changing environments. This compliance variation can be achieved in a variety of ways. However, one common idea is the variation of joint stiffness mechanically, electromechanically or by control. The solution presented in this paper is an electromechanical way of varying the joint stiffness. Among the electromechanical methods for varying the joint stiffness, continuously variable transmission (CVT) systems can be used in human-robot interfaces if a set of design criteria are met. These criteria include backdrivability, independent output position and stiffness variation, shock absorbing and low mass/inertia. In this paper, a novel two-cone CVT design with a double spherical transmission element is introduced by taking into account the abovementioned criteria. Additionally, design parameters are identified via carrying out a geometrical analysis of this new CVT system.