Seamless control between standing and repetitive hopping for legged robots based on dynamics morphing

Abstract

This paper presents a novel control strategy that enables seamless transitions between stationary standing and repetitive hopping in legged robots through dynamics morphing. At the core of the approach lies a stable nonlinear oscillator that can be continuously transformed into and from a regulator for vertical center of mass (COM) motion by adjusting a small set of key parameters. This unified controller allows the robot to operate in two distinct modes: regulating COM height for stable standing, and shaping stance-phase dynamics to achieve a target apex height during hopping. A parameter adjustment strategy is developed to maintain COM motion within the robot’s kinematic limits. Furthermore, the strategy ensures soft landings during transition from hopping to standing and in response to external disturbances during the flight phase. Numerical simulations demonstrate that the proposed controller achieves smooth transitions between standing and hopping, enables on-the-fly modification of the target apex height, and recovers from the applied external perturbations, all while consistently ensuring soft landings.