Three-dimensional displacement and force transducer

A nonintrusive method which has been developed for measuring triaxial forces within footwear, developed particularly for use in the design of footwear for diabetics, is described. The technique uses four coils, one for excitation and the other three for sensing, embedded into a rubber insole. The voltages induced in the sensing coils can be processed to give displacements in three orthogonal directions. Given an appropriate material for the insole, forces can also be measured using the technique. The coils and electronic processing are briefly described, but the emphasis is on the computer processing which is used to extract the normal and shear displacement components from the voltage measurements. A number of approaches are proposed and analysed, and their performance contrasted by a comprehensive set of experimental results.