Development of Outdoor Navigation for a Robotic Wheelchair System

Holly A. Yanco

Abstract: The goal of this research is the creation of a complete robotic wheelchair system to be used by people unable to drive standard powered wheelchairs. A complete robotic wheelchair system must be able to navigate indoor and outdoor environments and should switch automatically between navigation modes. For the system to be useful, it must be easily customized for the specific access methods required for each user. This abstract focuses on the vision system being developed for outdoor navigation and the method for selecting whether to use the indoor navigation mode or the outdoor navigation mode. A report of the indoor navigation mode and user interface can be found in (Yanco In press). Navigation is divided into two classes: indoor and outdoor. In both navigation modes, the user gives a high-level command (“forward,” “left,” “right,” and “backward”) through the graphical user interface which has been customized to accommodate the user’s access method. The system carries out the user’s command using common sense constraints such as obstacle avoidance. Since the user must be able to successfully navigate novel environments immediately, the system does not use maps or environment modification. The navigation problem in an indoor environment is simplified by regularities such as level floors and walls. A vision system can be used in an indoor environment, but it is not necessary. Robots navigating indoors can use sonar and infrared sensors to avoid obstacles. Outdoor navigation is not feasible using only sonar and infrared sensors. To facilitate navigation in outdoor environments, a vision system with one camera is being added to the wheelchair. Initial image processing is aimed at finding and navigating sidewalks, crosswalks, curb cuts and handicapped ramps. To stay on sidewalks and in crosswalks, the vision system will detect long straight lines that head towards the vanishing point. Ground-plane constraint or optical flow using successive frames will be used to approximate the distance of