Continuously Variable Transmission and Stiffness Actuator Based on Actively Variable Four-Bar Linkage for Highly Dynamic Robot Systems

This letter presents a novel actuation mechanism that combines a continuously variable transmission (CVT) mechanism with a variable stiffness actuator (VSA) for highly dynamic robot systems such as legged robots. The CVT effectively changes the input-output transmission ratio of the system, thereby extending the operational torque-speed range. Concurrently, the VSA adjusts the system stiffness, altering its compliance characteristics. Both CVT and VSA are seamlessly integrated into a single four-bar linkage mechanism, with their active features enabled by an actively variable link within this linkage. This CVT-VSA mechanism offers a range of dynamic advantages by inversely varying transmission ratio and stiffness, which includes impact mitigation, torque or speed amplification, and expanded control bandwidth. The implementation and efficacy of the CVT-VSA mechanism in a legged robot were tested and validated through a series of experiments.