Design, modeling and testing of a compact variable stiffness mechanism for exoskeletons

In this paper, the mechanical design of a novel variable stiffness mechanism (VSM) with reconfigurability is presented. The design of VSM is based on a zero-length base link four-bar linkage, integrated with a linear spring. The VSM is able to achieve variable stiffness in adjustable ranges, due to its reconfigurable design. Compared with other similar designs, the new VSM is compact and light weight, and can be used as a standalone module, or integrated with electric motor to build variable stiffness actuator which can be further applied in wearable exoskeletons. In the paper, mathematical models are developed for VSM to reveal the stiffness/torque performance limits. The mathematical models are validated experimentally with a prototype in both static and dynamic tests. The proposed VSM is finally integrated in a wearable elbow exoskeleton.