Model-free visual servoing on complex images based on 3D reconstruction

We present a way to achieve positioning tasks by model-free visual servoing in the case of planar and motionless objects whose shape is unknown. Emphasize is made on the algorithm of 3D reconstruction which allows to synthesize easily the control law. More precisely, the reconstruction phase is based on the measurement of the 2D displacements in a region of interest and on the measurement of the camera velocity. However, we will show that the proposed algorithm is robust with respect to inaccurate values of this velocity. 2D displacements rather than 2D motions are used to remove the assumption that the acquisition rate has to be high. In addition, a particular attention is paid to the complex case of large displacements to access high camera velocities. Once the parameters of the plane are sufficiently stable, a visual servoing scheme is used to control the orientation of the camera with respect to the object and to ensure that it remains in the camera field of view for any desired orientation. The 3D reconstruction phase is maintained active during the servoing to improve the accuracy of the parameters and, consequently, to obtain a small positioning error. Experimental results validate the proposed approach.