In this paper, a closed-loop observer to extract the center of mass (CoM) of a bipedal robot is suggested. Comparing with the simple conversion method of just using joint angle measurements, it enables to get more reliable estimates by fusing both joint angle measurements and F/T sensor outputs at ankle joints. First, a nonlinear-type observer is constructed to estimate the flexible rotational motion of the biped in the extended Kalman filter framework. It adopts the flexible inverted pendulum model which is appropriate to address the flexible motion of bipeds, specifically in the single support phase. The predicted estimates of CoM in terms of the flexible motion observer are combined with measurements (that is, output of the CoM conversion equation with joint angles). Then, we have final CoM estimates depending on the weighting values which penalize the flexible motion model and the CoM conversion equation. Simulation results show the effectiveness of the proposed algorithm.
[1]
Marko B. Popovic,et al.
Ground Reference Points in Legged Locomotion: Definitions, Biological Trajectories and Control Implications
,
2005,
Int. J. Robotics Res..
[2]
Miomir Vukobratovic,et al.
Zero-Moment Point - Thirty Five Years of its Life
,
2004,
Int. J. Humanoid Robotics.
[3]
Youngjin Choi,et al.
Posture/Walking Control for Humanoid Robot Based on Kinematic Resolution of CoM Jacobian With Embedded Motion
,
2007,
IEEE Transactions on Robotics.
[4]
Shuuji Kajita,et al.
The Human-size Humanoid Robot That Can Walk, Lie Down and Get Up
,
2005,
Int. J. Robotics Res..