Nonlinear dynamic model with varying hip trajectory for stable walking of biped robot

Publication Type:

Journal Article


International Journal of Robotics and Automation, Actapress, Volume 33, Issue 6 (2018)



This work addresses the planning and control of stable walking of a biped robot on an uneven terrain. The existing models used for gait planning of a biped robot, constrain the hip trajectory to be at a constant value or a pre-defined pattern. In this work, the robot is modelled as a non-linear 3D inverted pendulum, where the hip trajectory varies according to the terrain. The foot of the robot has three degrees of freedom in the sagittal plane to obtain proper ground contact points on an uneven terrain. The zero moment point (ZMP) is fixed at the centre of the support polygon formed by the contact points. The relationship between ZMP and centre of mass of the robot is derived, and a suitable reference centre of mass trajectory is dynamically planned at each step. A control law is derived to control the centre of mass position and is validated for a robot walking on a continuous uneven terrain through both simulation and experiments.