A control strategy for SLIP-based locomotion under lateral impact in 3D space

Lateral impact disturbances upon a legged running locomotion can result in the generation of an unexpected lateral velocity, consequently cause the deviation of the locomotion from its original direction of movement, even falling down to destroy the system. Dealing with the influence of lateral impact disturbances greatly increases the complexity of control in 3D space. Inspired by biomechanical studies, this paper constructs a control strategy based on the spring-loaded inverted pendulum principle (SLIP) for legged locomotion under lateral impact disturbances. This strategy, named 3D-HFC, is composed of three core modules: touchdown angle control, body attitude angle control and energy compensation. The first module regulates the forward/lateral running velocities such that lateral velocity recovers to zero after impact, the second maintains the body posture without being influenced by external forces, and the third compensates energy loss to ensure a desired hopping height. These three parts operate commonly to achieve the APEX state variables converging to the desired value in each running cycle, so as for the system to keep stable periodic motion. The simulations of running systems bearing different force impacts are conducted to verify the effectiveness of the 3D-HFC strategy, indicating that the proposed approach can reject impact disturbances effectively.