Legged Robot Running on Rough Terrains Based on Norm Regulation of Spring-Loaded Inverted Pendulum Model

Legged locomotion is a complex control problem involving multi-linkage, underactuation, and hybrid dynamics. To traverse through a compliant surface, the inclusion of uncertainties and unstructured disturbances aggravates the problem. A responsive and robust controller is essential, which may not be guaranteed by pure numerical methods such as learning-based and optimisation-based methods. In this paper, we investigate the running behaviour of a legged robot on a rough terrain with height and stiffness variation by proposing a control framework which comprises i) a limit-cycle-based state feedback controller to regulate the norm of the leg length, ii) a hip velocity controller, and a landing angle controller so that the robot can continuously control the energy and state to achieve the desired running height and speed even on a compliant surface. We demonstrate the effectiveness and robustness of the proposed method on a monoped and a biped in simulation and hardware, respectively.