Introduction: This paper presents the functional design and kinematic synthesis of a recent version of an electric stair-climbing wheelchair. Wheelchair.q: The proposed device represents the latest evolution of the ‘Wheelchair.q’ project and introduces several improvements over previous designs. This updated solution has greater stability during stair-climbing operation, and it satisfies the safety requirements introduced by ISO 7176-28:2012, “Requirements and test methods for stair-climbing devices”. The main improvement presented concerns the regularity of the user trajectory during stair-climbing, which ensures a more comfortable perception. This result has been achieved by introducing a cam mechanism between the frame connected to the locomotion unit and the seat frame, which properly manages the seat orientation. With an appropriate cam profile, it is possible to compensate for the oscillations that are introduced on the wheelchair during the climbing sequence and allow the user to obtain a translational trajectory. Results: The proposed design and its working principle are first described and illustrated through schematic and graphic representations. A brief explanation of the procedure for obtaining the cam profile is also given. Two different architectures for the cam mechanism are then compared, and the advantages and disadvantages for each solution are identified. Finally, the kinematic wheelchair performances are tested through a simulation conducted in the MSC-ADAMS multibody environment. Conclusions: The results obtained with the simulation show the effectiveness of the proposed solution. The wheelchair is able to climb a staircase in a safe and regular way. Following studies will complete the design of the wheelchair with the aim to build a prototype for demonstrating the proposed working principle.
stair-climbing wheelchair, architectural barriers, cam mechanism, wheelchair.qsubir escaleras, silla de ruedas, barreras arquitectónicas, mecanismo cam
 W. Lutz, W. Sanderson, and S. Scherbov, “The coming acceleration of global population ageing”, Nature, vol. 451, no. 7179, pp. 716-719, 2008.
 L. Bruzzone, and G. Quaglia, “Review article: locomotion systems for ground mobile robots in unstructured environments”, Mechanical Sciences, vol. 3, pp. 49-62, 2012.
 ISO 7176-28:2012, “Requirements and test methods for stair-climbing devices”.
 Y. Sugahara et al., “Walking up and down stairs carrying a human by a biped locomotor with parallel mechanism”, Proc. Int. Conf. on Intelligent Robots and Systems (IROS), 2005, Edmonton, Alberta, Canada, pp. 1489-1494.
 S. Yu et al., “Configuration and tip-over stability analysis for stair-climbing of a new-style wheelchair robot”, Proceeding of International Conference on Mechatronics and Automation (ICMA), 2010, Xi’an, China, pp. 1387-1392.
 Stair-climbing wheelchair, by R. T. Quigg, U.S. Patent No. 6,857,490, 22 Feb, 2005.
 Powered wheeled vehicle capable of travelling on level ground, over uneven surfaces and on stairs, by Hervé Marie Georges Le Masne, U.S. Patent No. 7,384,046, 10 Jun, 2008.
 J. Yuan, and S. Hirose, “Research on leg-wheel hybrid stair-climbing robot, Zero Carrier”, Proceeding of International Conference on Robotics and Biomimetics (ROBIO), 2004, Shenyang, China, pp. 654-659.
 M. J. Lawn, and T. Ishimatsu, “Modeling of a stair-climbing wheelchair mechanism with high single-step capability”, IEEE T. Neur. Sys. Reh., vol. 11, no. 3, pp. 323-332, 2003.
 A. González, E. Ottaviano, and M. Ceccarelli, “On the kinematic functionality of a fourbar based mechanism for guiding wheels in climbing steps and obstacles”, Mech. Mach. Theory, vol. 44, no. 8, pp. 1507-1523, 2009.
 A. Gonzalez et al., “Improving the mechanical design of new staircase wheelchair”, Ind. Robot, vol. 34, no. 2, pp. 110-115, 2007.
 G. Quaglia, L. Bruzzone, G. Bozzini, R. Oderio, and R. Razzoli, “Epi.q-TG: mobile robot for surveillance”, Ind. Robot, vol. 38, no. 3, pp. 282-291, 2011.
 U. Saranli, M. Buehler, and D. E. Koditschek, “RHex: A Simple and Highly Mobile Hexapod Robot”, Int. J. Robot Res., vol. 20, no. 7, pp. 616-631, July 2001.
 C. Chen, and H. Pham, “Design and fabrication of a statically stable stair-climbing robotic wheelchair”, Ind. Robot, vol. 36, no. 6, pp. 562-569, 2009.
 Y. Sugahara, N. Yonezawa, and K. Kosuge, “A novel stair-climbing wheelchair with transformable wheeled four-bar linkages”, Proceeding of International Conference on Intelligent Robots and Systems (IROS), 2010, Taipei, Taiwan, pp. 3333-3339.
 System and method for stair climbing in a cluster-wheel vehicle, by J. B. Morrell et al., U.S. Patent no. 6,311,794, 6 Nov, 2001.}  Battery powered stair-climbing wheelchair, by Kenneth Ray Cox, U.S. Patent No. 6484829, Nov. 26, 2002.
 G. Quaglia, W. Franco, and M. Nisi, “Evolution of Wheelchair.q, a Stair-climbing Wheelchair”, Proceedings of the 14th IFToMM World Congress, Taipei, Taiwan, 2015.
 G. Quaglia, W. Franco, and R. Oderio, “Wheelchair. q, a mechanical concept for a stair climbing wheelchair”, Proceeding of International Conference on Robotics and Biomimetics (ROBIO), 2009, Guilin, China, pp. 800-805.
 G. Quaglia, W. Franco, and R. Oderio, “Wheelchair. q, a motorized wheelchair with stair climbing ability”, Mech. Mach. Theory, vol. 46, no. 11, 2011, pp. 1601-1609.
 G. Quaglia, W. Franco, and M. Nisi, “Design of a reconfiguration mechanism for an electric stair-climbing wheelchair”, Proceeding of the International Mechanical Engineering Congress & Exposition (IMECE), 2014, Montreal, Quebec, Canada.
 G. Quaglia, W. Franco, and M. Nisi, “Analysis of the static stability for an electric stairclimbing wheelchair”, Proceeding of the International Conference on Robotics in Alpe-Adria-Danube Region (RAAD), 2016, Belgrade, Serbia.
 G. Quaglia, and M. Nisi, “Design and optimization of a self-leveling cam mechanism for a stair climbing wheelchair”, Manuscript submitted for publication.
 R. L. Norton, Design of machinery: an introduction to the synthesis and analysis of mechanisms and machines, New York: McGraw-Hill Professional, 2004.