Ulrich Borgolte Helmut Hoyer Christian Bühler Helmut Heck Ralf Hoelper Architectural Concepts of a Semi-autonomous Wheelchair. 233-253 1998 22 Journal of Intelligent and Robotic Systems 3-4 http://dx.doi.org/10.1023/A:1007944531532 db/journals/jirs/jirs22.html#BorgolteHBHH98