Variable stiffness control and implementation of hydraulic SEA based on virtual spring leg

SLIP model with compliance describes human locomotion very well. A Legged robot's variable stiffness joint could produce an equivalent virtual spring leg, which is the foundation for SLIP model's physical implementation. This paper presents a single leg with knee joint actuated by hydraulic SEA and proposes a variable stiffness control method that is applied to the virtual spring leg. The experiment results prove the effectiveness of proposed control method and also present that the designed hydraulic SEA could realize virtual spring leg with stiffness adjustable from 5KN/m to 20KN/m, which is the stiffness needed in human's normal walking. The robot's single leg weighs about 6kg and could burden at least 60kg load, which provides a way to realize the heavy load legged robot with variable stiffness joint.