SMARTHUB and SMARTCASTOR: force and moment sensing wheelchair wheels

The SMART^HUB and SMART^CASTOR are two new strain-gage based sensors designed to measure the reaction forces and moments at the rear axle and castor spindle, respectively. Both are five degree-of-freedom sensors, which measure all three force components and the two moment components perpendicular to the axes of rotation. These sensors will be used to improve wheelchair designs by allowing advanced engineering techniques such as finite element analysis to be applied with greater confidence. Both sensors are highly linear. When calibrated the lowest correlation coefficient was 0.9965 (N=21) and the cross-axes sensitivity was always less than 5%. Preliminary data are presented for two wheelchair users propelling over an indoor course and a non-wheelchair user traversing an outdoor course. The indoor data was transferred from a microcontroller-based signal conditioning board to a host PC through a high-speed serial port. For the outdoor data, the microcontroller was programmed to sample the data and to generate a histogram of force and moment frequencies, which was subsequently downloaded