Robust walking control of a planar spring mass biped robot

The variable spring-loaded inverted pendulum (V-SLIP) model captures characteristic properties of the hip or COM motion in human locomotion. A control strategy consists of a leg stiffness controller and a foot placement controller is proposed for a biped walker. Some restrictions are considered in the control strategy, e.g. the friction and the ability of the actuator. A novel trajectory function is designed for stance phase control. The function not only can approximate the nominal trajectory with error in the order of sub-millimeter, but also can preserve the restriction on vertical velocity in spite of the horizontal velocity. To validate the control strategy and the trajectory function, simulations are implemented on a virtual ideal biped walker. The walker starts walking with a low velocity, by taking a few steps it comes to the desired walking cycle. With the proposed control strategy the walker is able to recover from a disturbance up to 20 N*m.