Robert D. Collier
Dept. of Mech. Eng., Tufts Univ., Medford, MA 02155
Wheel chairs are being used increasingly in outdoor environments including paved and unpaved roads and sidewalks with widely varying roughness. Wheel chair design and development for active users is a lively field in which weight, stability, control, and comfort are important design criteria. An ongoing research project at Tufts includes baseline laboratory and field vibration measurements of both conventional and new prototype wheel chairs and associated bioresponse. A test track includes a range of roughness conditions. Representative results show: (1) wheel hub vibration levels on the order of 1--3 g (0--200 Hz) with impulse waveforms of 5--10 ms occurring several times a second; (2) frequency response functions of a standard wheel chair structure contain several low-frequency resonances below 100 Hz that are lightly damped; (3) cushions provide comfort but limited low-frequency vibration and shock isolation. A review of models of whole body vibration together with an analysis of wheel chair dynamics provide guidance for vibration isolation/stability design criteria for nonstationary impulsive forces. An isolator that can be installed on an existing chair has been designed and evaluated.