Contrôle redondant de la position d'un robot par capteurs externes. Applications en milieux médical et industriel

Safety issues are of prime importance in using robots in some sensitive applications. We classify the possible incidents and the partial solutions that exist in various robotic elds. We particularly detail two applications of interest : the guiding of a medical intervention and the inspection of a steam boiler in a power plant. We aim at checking, in a global way, the correct accomplishment of the plani ed task. Thus we attempt to control the robot position by means of external sensors. That is why we study di erent kinds of position sensors that would be possible and then we suggest a solution that consists in drawing some passive markers on the robot and then in controlling their position by means of video cameras. To proceed so, it is necessary to rst calibrate the di erent components of the system. The intrinsic calibration of the cameras is studied in detail and we choose a method that uses two calibration planes. We extend this method to cameras with a variable focal length. Once the cameras are calibrated, their position in the environment has to be determined. We suggest one speci c solution for both of our applications. The last calibration step consists in determining the position of each marker with respect to the robot link it belongs to. This is a similar problem to the \hand-eye calibration". We particularly study two classic methods that we improve by minimizing a global error on a sizeable data set. By combining all these steps, we can predict the markers position, and then check it thanks to an appropriate image processing. Experiments have been conducted in order to prove the feasability of the project and to estimate the possible accuracy. key-words : vision, robotics, safety, position control, camera calibration, variable focal length, hand-eye calibration, subpixel detection