A versatile and safe mobility assistant

he Bremen Autonomous Wheelchair project covers a variety of research issues that include spatial cognition, safe systems, and mobility assistance for the handicapped. Emphasizing one or the other of these cornerstones provides various views of the wheelchair Rolland (Fig. 1). Within the framework of the priority program " Spatial Cognition " of the Deutsche Forschungsgemeinschaft, the main topics are navigation, landmark recognition, and space representation [7]. Moreover, the wheelchair serves as a case study for the development of safe systems based on formal methods [8]. The third determinant of the Rolland project is the aspect of rehabilitation [13]; i.e., to develop a support tool that can help handicapped and elder people to control a wheelchair. These seemingly divergent topics complement each other to build a robust and safe wheelchair system. Rolland is based on the commercial power wheelchair Genius 1.522 manufactured by the German company Meyra. The wheelchair is a nonholonomic vehicle that is driven by its front axle and steered by its rear axle. The human operator can control the system with a joystick. The wheelchair is equipped with a standard PC (Pentium 233, 64 MB RAM) and sensors to perceive its environment. The principal idea behind such an assistive system is to wiretap the connection between the joystick and the motor. If the human operator issues a command that may lead to a collision with an obstacle , the wheelchair changes the dangerous target command into a safe one. This article shows how the tasks of reliably detecting obstacles in the environment and safely avoiding these obstructions are solved in the Bremen Autonomous Wheelchair. In addition , it deals with the problems that arise due to the fact that, in contrast to most research robots, the wheelchair is a shared-control system; i.e., it is jointly controlled by the software modules and the human operator. This is primarily important for the obstacle avoidance skill as well as for the mobility assistant. Being able to ensure safe traveling of an assistive power wheelchair requires several preconditions to be met. First, the importance of safety issues has to be accepted and rigorously taken into account during system design. Second, methods to satisfy the safety requirements have to be found. This section motivates the meaning of safety aspects in service robots and presents the main components of the safety layer of the Bremen Autonomous Wheelchair—a local obstacle map that represents measurements of …