A practical decoupled stabilizer for joint-position controlled humanoid robots

Efficient methods have so far been proposed for planning dynamically stable walking pattern for humanoid robots. However, to guarantee that the reference joint trajectory will produce a safe movement despite modeling errors and perturbations, a stabilizer needs to be implemented on the robot. Though this stabilizer constitutes an essential part of the control strategy of most advanced humanoid platform, it is usually not open-source and dedicated to the own robot characteristics. The goal of this paper is to propose a general and practical strategy for designing a stabilizer for joint-position controlled humanoid robots. The proposed method is based on a double inverted pendulum model and a decoupling approach thanks to which the position of the ZMP and the center of gravity can be controlled independently through the regulation of the ankle and hip joints. The stabilizer generates the expected stabilizing torques from the admissible joint position input. The resulting control algorithm is fast and can be easily executed on the robot. This algorithm was successfully implemented as real-time plugins for the OpenHRP simulator of the HRP2. Simulations showing the efficiency of the method are presented and discussed.