Free Model Control for Semi-passive Biped Robot

We have presented a free model control strategy to control a semi-passive biped robot at three the joints in this paper. First we describe complicated problem of the under actuated robot. Then using free model, we proposed walking control algorithm to ensure an asymptotically stable gait for the under-actuated robot according to open-loop oscillating control method. The walking control algorithm means two stages control strategy. In the first stage, the passive joint angle of swing leg is brought to its desired position by regulating oscillating torque at the hip joint. In the second stage, imparting input force or torque, i.e. u = 0, at the same time, the knee is stopper without affecting the position of the passive joint, the semi-passive biped robot is governed by itself gravity.