Intermittent walking controller with holonomic constrained trajectory forming a conservative system

Abstract Reduced-order models encapsulating complex whole-body dynamics have facilitated stable walking in various bipedal robots. These models have enabled intermittent control methods by applying control inputs intermittently (alternating between zero input and feedback input), allowing robots to follow natural dynamics and provide energetically and computationally efficient walking. However, due to their inability to derive closed-form solutions for the angular momentum generated by swing motions and other dynamic actions, constructing a precise model for the walking phase with zero input is challenging, and controlling walking behavior using an intermittent controller remains problematic. This paper proposes an intermittent controller for bipedal robots, modeled as a multi-mass system consisting of an inverted pendulum and an additional mass representing the swing leg. The proposed controller alternates between feedback control during the double support (DS) phase and zero-input control during the single support (SS) phase. By deriving a constrained trajectory, the system behaves as a conservative system during the SS phase, enabling closed-form solutions to the equations of motion. This constraint allows the robot to track the target behavior accurately, intermittently adjusting energy during the DS phase. The effectiveness of the proposed method is validated through simulations and experiments with a bipedal robot, demonstrating its capability to accurately and stably track the target walking velocity using intermittent control.