Modeling and Active Balance Control of a Two-wheel-legged Inverted Pendulum Robot

This paper presents a kinematic and dynamic modeling and balance control of a two-wheel-legged robot (TWLR) which typically consists of bipedal legs, two wheels, and torso connecting the two parallel legs with three revolute joints respectively. The 5-DOF motion capability of the torso in task space is confirmed through the mobility analysis about the wheeled-parallel mechanism. The inverse kinematic solutions for the leg joints are given as a prerequisite for tracking task-space trajectories which define the posture of torso. The movement of the overall center of mass of the robot following the multi-joint motions is assumed as a 3-D inverted pendulum and the dynamic equation of motion is developed by applying Kane’s method. Finally, an active balance control method is followed with numerical experiments to show that the self-balancing performance of TWLR can be greatly enhanced by activating a counter mass equipped inside torso while the leg joints are tracking task space trajectories.