Visual servoing for non-holonomic mobile robots

Although visual servoing is suitable for control of a mobile robot based on a single on-board camera image, wheeled vehicles have a non-holonomic property that the degree of freedom of the input is less than that of the configuration. Thus the visual servoing can not be directly applied to a camera system fixed on the vehicle. Furthermore there is no smooth and stable state feedback law for non-holonomic vehicles. To overcome these difficulties, the authors consider another situation, that the pan angle of camera is actuated and used as an input of visual servoing. The desired state is given as not a constant value but a trajectory represented in terms of image sequences of a gazed object. Based on this idea, the authors propose a method of realizing “teaching and playback” for a non-holonomic mobile robot. In the teaching mode, the robot tracks a landmark in the environment by a single on-board camera and stores its image sequences while running commanded by a human operator. In the playback mode, the robot tracks the desired trajectory with velocity commands for the vehicle and the pan angle for the camera determined from the stored and current images. The authors discuss the convergence to a desired state and moreover point out an additional feedback term, of a deviation of the pan angle works to improve the tracking performance. The effectiveness of the proposed method is shown by illustrating computer simulation results