Analysis of a variable stiffness differential drive (VSDD)

In robotics, differential mechanisms are widely used when lightweightness and compactness are a requisite for the robot design. Moreover, the last decades have seen the rise of (variable) compliant acuators as important elements to perform safe interaction and dynamic tasks. This paper introduces a Variable Stiffness Differential Drive (VSDD), i.e., a differential transmissions with variable stiffness actuators (VSAs), and presents a dynamic analysis. The analysis shows that, when variable stiffness actuators are used in coupled differential transmissions, the allowable stiffness range at the output of the system depends on the position of the springs inside the device. In particular, independent output joint stiffness can be obtained by dislocating the actuation from the elastic elements.