The robot working space protection system presented is based on visual perception. In this system any intrussion in the working area are detected by their movement. The evaluation of the collision risk is based on the analysis of the information given by the vision system and that corresponding to the position of the robot which is acquired by its own sensors The vision system differentiates among the movements of the robot itself, those of the tools and those of the usual scene components from those of unexpected events in order to detect them. Then the system studies the possible intersection of the bounding rectangles containing the mobile elements seen during the trainning phase and the detected objects. The tracking of the robot trajectory allows to foresee in advance their future movements and thus to foresee the collision risk. This allows the system to generate the stopping order with time enough in case the invaded zone has to be occtpiedsoon by the robot. The robot won't be sttoped if its trajectory is not in conflict with the detected obstacle. The system might be useful either in the coordination of several robots in a working cell doing not syncronised tasks, or in the protection of a robot working in a machine tool environment.