An approach to measure wheelchair stability. Concept and benefits.

Wheelchair stability is dependent on user's body characteristics that can shift significantly the original center of mass in the cases of limb amputation, severe skeletal deformities or obesity. The center of gravity may change with the installation of additional devices such as oxygen cylinders or ventilators on the wheelchair. Therefore, quantitative evaluation and prediction of the behavior of the user-wheelchair system in a variety of static and dynamic situations is essential for user's safety and for the optimal tuning of the human-wheelchair system. In this paper we discuss an approach for wheelchair stability assessment that only requires two inclinations and weight measurements. We also discuss the algorithm associated to the procedure based on the use of the reaction forces in the contact points of the wheels measured by the load cells. Further, the paper includes an analysis of the influence of the errors in measurement of the input parameters on the output results and demonstrates that the proposed approach possesses high accuracy. The advantage of the proposed approach is the use of a reliable procedure based on three simple steps and five weight measurements with four independent load scales which may lead to the design of an affordable and accurate measurement system.