Abstract
A capacitive transducer has been developed for continuously measuring the vertical component of foot-forces during walking. The transducer is shaped like a insole and consists of two sub-transducer units, the front and rear. The outputs of the two units are summed up to give the total force exerted by the foot.
Each unit has a multi-layered structure. The basic layer is a 2mm neoprene sponge sheet sandwiched between two 50μm copper foils. These, as a whole, form a capacitor. The other two layers comprise the driving shield and the static shield, which minimize the effect of stray capacitance and the power line noise, respectively. The transducer is thin (3.8mm), lightweight (90g) and flexible. Thus, it does not hinder the natural gait pattern. It can be attached to the shoe-sole easily by elastic bands and Velcro straps.
The accuracy of the transducer is well within ±10% of the full scale. An error analysis has been made to clarify the change in sensitivity due to a localized load. The result is utilized to compensate for the inherent nonlinearity of the transducer units.
