A Compact Variable Stiffness Actuator for Agile Legged Locomotion

The legged robots with variable stiffness actuators (VSAs) can achieve energy-efficient and versatile locomotion. However, equipping legged robots with VSAs in real-world applications is usually restricted by 1) the redundant mechanical structure design, 2) limited stiffness variation range and speed, 3) high energy consumption in stiffness modulation, and 4) the lack of an online stiffness control structure with high performance. In this article, we present a novel variable-length leaf-spring actuator (VLLSA) designed for legged robots that aims to address the aforementioned limitations. The design is based on leaf-spring mechanism and we improve the structural design to make the proposed VSA 1) compact and lightweight in mechanical structure, 2) precise in theoretical modeling, and 3) capable of modulating stiffness with wide range, fast speed, low energy consumption, and high control performance. Hardware experiments including in-place and forward hopping validate the advantages of the proposed VLLSA.