Motion Control of a Four-wheel-drive Omnidirectional Wheelchair with High Step Climbing Capability

In recent years, aging problem has been arising to be among the most serious social issues world wide, especially in some European and Asian countries, involving Japan. It is reported in Japan that the population of over 65 years old would reach 30,000,000 in 2012 and grow over 30% of total population in 2025[1]. Electric wheelchairs, personal mobiles, scooters are currently commercially available not only for handicapped persons but also for elderly. However, such a rapid grow of aging populations suggest that requirements for electric mobile systems will soon increase dramatically for supporting mobility and activity of elderly people and reducing labor of care-givers. However, those mobile systems do not have enough functionalities and capabilities for moving around existing environments including step, rough terrain, slopes, gaps, floor irregularities as well as insufficient traction powers and maneuverability in crowded areas. Promotion of barrier-free environments will be required for a large number of users of wheelchairs and other electric mobile systems however, re-constructing of the existing facilities could not be a feasible solution because of the limitations in economy and time. For overcoming the problem, to improve the mobility of the electric mobile systems to adapt to existing environments could be one solution. For this objective, we propose a new type of wheelchair, four-wheel-drive (4WD) omnidirectional system, with enhanced step climb capability together with high maneuverability. In this chapter, omnidirectional control of a wheelchair with 4WD mechanism would be mainly discussed. The mobile systems realizing holonomic and omnidirectional motion is one of the important research area in mobile robots. It provide flexibility and high maneuverability to motion planners and human drivers. The holonomic and omnidirectional mobile capability is very convenient for human drivers since they do not have to understand drive mechanisms and its configuration at all. A human only commands the direction and velocity of motion he/her wants to perform since a holonomic and omnidirectional mechanism can start to move in any direction with any configuration of the mechanism such as directions of wheels. 4