1. H.G. Rau, Personal mobility vehicle, U.S. Patent 2003/0121705, Jul. 3, 2003.
2. J.M. Pagett, Invalid's wheelchair and like conveyances, U.S. Patent 4564080, Jan. 14, 1986.
3. Environment adaptation of a new staircase-climbing wheelchair;Morales;Autonomous Robots,2007