A trajectory tracking control of a skid steer type mobile robot for vertical walls

Wall-climbing robots can be used for various dangerous works such as painting, inspecting and cleaning of vertical walls instead of human workers. The typical wall-climbing robots use a magnet or a vacuum suction device for travelling on the vertical wall. For a reliable and an efficient work, the robots should follow a desired path accurately. However, gravitational effect makes lower the performance of the trajectory control for the case of travelling on the vertical wall. In this paper, a trajectory tracking control law for a skid steer type wall-climbing robot is proposed considering the gravitational effect. The control law is a non-linear feedback one with compensation of gravity and wheels' rolling resistance. It is shown that a tracking error converges to zero using Lyapunov method. A window cleaning robot is used for an experiment of the trajectory tracking control. The experimental results confirm the validity of the proposed control method.