State Estimation for a Legged Robot With Multiple Flexibilities Using IMUs: A Kinematic Approach

Abstract

This letter presents a general state estimation method for legged robots having internal flexibilities. In details, the method is applicable to any robot with an arbitrary number of punctual deformations, during standing and walking phases on flat ground. Focused on balance applications, this estimator reconstructs the position relative to the contact foot, the absolute orientation and the world velocity of each robot body. It reconciles the rigid kinematics, given by joint encoders, with attitude measurements obtained from several IMUs, through a kinematic model incorporating the flexibilities. Compared to previous works, no dynamic model of the flexibilities is employed. For illustration, the estimator is successfully tested on the exoskeleton Atalante, both in static and while walking. It is then used in closed-loop to control the position of the flying foot during a quasi-static step.