Turning characteristics and stability of manual wheelchairs on a slope

Abstract

Abstract-Wheelchairs will be in ever greater demand in a rapidly aging society. Because of the special needs of aging users, due to frailty and reduced reflexes in many cases, it is important to give careful consideration to rather fundamental design properties. Inter alia it is very important to define, clarify and design running, turning and stability properties of the highest standards in manual wheelchairs. In particular we discuss these matters in regard to wheelchair behavior on sloping surfaces. In the present paper we report on an analytical model for a 4 wheel manual wheelchair which shows good correlation with the existing experimental data relating to torque and speed when the wheelchair is moving on a level plane and when climbing a 3 degree slope. The rolling stability of the wheel chair on a slope is also discussed. Keywords -Wheelchair, Dynamic characteristics , Stability I. INTRODUCTIONIn a rapidly aging society, wheelchairs are used a lot as support devices for independent movement. The environment where they are used is not necessarily free of barriers. Many roads have a slope in Japan. Some roads are a plane but others are designed also to rise from the curb towards the center. This design feature is for improved drainage. Such roads have to be crossed and also have to be used up and down their length for any journey. Accordingly it is important to clarify the dynamic characteristics and stability properties of manual wheelchairs from the point of users and providers. Yoneda etc.[1] and Tanaka etc.[2] have undertaken a lot of empirical research in this area.In the present study, the dynamic characteristics of manual wheelchairs were studied from a theoretical point of view based on Shung etc. [3], for powered wheelchairs. The models fitted the existing experimental results for 4 wheelchairs on a level plane and on a downhill slope. Cooper's work [4]-[6] on the stability of wheelchairs on a downhill slope was also considered.The authors considered the stability conditions for a violent fall and the direction hold stability of the wheelchair on a downhill slope.On the stability conditions for a violent fall , the influence of the center of gravity of the rider/wheelchair system is greater before than an axle line is considered and the stable judgement equation is proposed.Furthermore, we studied the direction hold stability on a downhill slope in relation to torque, pitch and drive distance in a search for the relationship between necessary torque and slope angle, to travel in a straight line, because it is difficult to travel in a straight line where there is a slope affecting pitch. II. METHODOLOGYAlthough the modeling of the wheelchair on a down hill slope is based on a powered wheelchair of Shung [3], the following points are changed and simplified to clarify the principles. (a) A surface of a slope is assumed to be plat. (b) The coordinate system of the wheelchair on a slope depends on at least the properties shown in Figure 1. (c) The moving direction is defined as a positive irrespective ...