Architecture and Applications of the Bremen Autonomous Wheelchair 3 Safety Issues

The work described here is motivated by the necessities for safety and multi-functionality in rehabilitation robotics. The Bremen Autonomous Wheelchair will be presented as a platform for the realization of rehabilitation applications. This paper mainly focuses on safety issues. Thus, it presents the wheelchair's system architecture that contains a safety layer as its central module. Three applications realized on top of this layer will be outlined. 1 Motivation Due to the changed distribution of ages in future populations , more and more elder people, in addition to handicapped persons, will be forced to maintain their mobility with the help of rehabilitation technology. As there is a large number of possible disabilities, a wide range of support technologies has to be developed to provide an adequate assistance to the handicapped users, from simple mechanic wheelchairs and manually controlled power wheelchairs to sophisticated semi-autonomous robot systems that may even include robot arms. In order to maintain the user's mental activity, the transition between manual control and autonomy has to be uent, i.e. people should only get as much support as they really need. This implies that it is not possible to develop the semi-autonomous wheelchair that satisses the needs of all handicapped persons. Instead, a system should be modular in terms of software and hardware to allow to setup an adequate vehicle for each particular user. In recent years, a large number of service robotics applications has been developed, e.g. surveillance robots or autonomous vacuum-cleaners. As these robots often operate in environments in which people live and work, they have to satisfy very strict requirements with regard to dependability. In case of rehabilitation robots, e.g. manipulators, or intelligent wheelchairs, safety considerations become the dominating design issues. Accordingly , both trends|the increasing importance of safety as well as multi-functional platforms|have to be thoroughly taken into account when developing a rehabilitation robot. Considering these leitmotivs, the Bremen Autonomous Wheelchair is developed as a safe system that, due to its modular system architecture, can be adapted to various needs of speciic users. 2 The Wheelchair The basis for the Bremen Autonmous Wheelchair \Rol-land" is a commercial power wheelchair manufactured by Meyra (cf. Fig. 1). It is a non-holonomic vehicle that is driven by its front wheels and steered by its back wheels. This model already has two serial ports that allow to set the speed and the steering angle every 32 ms as well as …