Locomotion control system for legged mobile robot

Abstract

A locomotion control system for a biped walking robot having a body and two legs each connected to the body through a hip joint and each having ankle joint adjacent to its foot portion. A walking patter is preestablished in advance in terms of a trajectory of IMP (Zero Moment Point) at which horizontal moment acting on the robot generated by the ground reaction force is zero, a trajectory of the body's attitude or the like. During walking, actual ground reaction force is detected to determine an actual ZMP position and detected position is compared with a target IMP position obtained from the IMP trajectory. When there is an error between the positions, the robot legs are driven in such a manner that the error decreases. More specifically, if the actual IMP position is shifted forward the target ZMP position, the moment produced therefrom causes the robot to tilt backward. Therefore, it is controlled such that the forward foot is lifted vertically, while the rearward foot is lowered vertically, thus producing a moment in the opposite direction to restore the stable attitude. The robot can therefore be simulated as an inverted pendulum so that constantly maintains a prescribed restoration force and control characteristics becomes liner. Various embodiments are proposed for the same purpose. Alternatively, output rate of time series data is changed in response to the robot's unstable attitude.