Abstract
In this paper, we analyze a user-friendliness of wheelchair propulsion by using a dynamic index of the driving force. The index explains how much margin the user can take in joint moments to his maximum ability during wheelchair propulsion, and is expressed by the dynamic manipulating force ellipsoid (DMFE). The DMFE is illustrated from the measured values of maximum generated moments at the user's upper limb joints, and is used to understand quantitatively the margin of the user's ability for wheelchair propulsion. Based on the index, we have also proposed the concept of the driving force contribution figure (DFCF) to clarify how efficient the user accomplishes the wheelchair propulsion. The DFCF expresses the direction cosine of generated force on the handrim to the tangential direction. If the DFCF takes large value along the driving force direction, it means the applied force acts efficiently for wheelchair propulsion. In order to show the effectiveness of DMFE and DFCF, we measured the driving motion of the upper limb, hand force applied to the handrim, and the individual's muscular power characteristics for eight experienced wheelchair users. From the experimental data, it is shown that the users start driving the handrim at such posture where it is difficult to generate required hand force to drive the wheelchair. It is also shown that the user are driving the wheelchair taking the load of the upper limb and the efficiency of the wheelchair propulsion into consideration.
