Hybrid control of biped robots to increase stability in locomotion

This article proposes a new hybrid control method, a combination of impedance control and computed-torque control, to control biped robot locomotion. The former is used for the swinging (or unconstrained) leg and the latter for the supporting (or constrained) leg. This article also suggests that the impedance parameters be changed depending on the gait phase of the biped robot. To reduce the magnitude of the impact and to guarantee a stable footing during foot contact with the ground, the damping of the leg is increased drastically at the moment of contact. Computer simulations of a biped robot, with 3 DOF in each leg and the environment represented by a 3-DOF environment model composed of linear and nonlinear compliant elements, were performed. Simulation results show that the performance of the proposed controller is superior to that of the computed-torque controller, especially in reducing impact and stabilizing the footing. They also show that the proposed controller makes the biped robot more robust to the uncertainties in its own parameters as well as in its environment.