A computer controlled robot system for positioning a patient for radiation therapy or other medical procedures and the like. The robot is mounted at the top of a vertical shaft extending from the treatment room floor and includes horizontal arms arranged to maximize the available work envelope and eliminate “dead spots” in the envelope that the robot cannot reach. A double redundant coupling system for coupling devices to the robot is provided. A vision based docking system is employed for automatically coupling devices to the robot. Various enhanced safety features are provided, including device specific collision avoidance.