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We have developed an umbilical data-acquisition system for measuring pressures between the foot and shoe during walking. It consists of pressure sensors in the insoles of shoes, amplifier circuits, umbilical cables, an analog-to-digital converter, and a graphics display card in an IBM PC for real-time data collection and display. The applied pressure on a sensor decreases its resistance, which causes the output voltage of the amplifier circuit to increase. We attach seven sensors to the surface of each insole of a pair of extra-depth shoes and calibrate all the sensors in the insole before and after each test using a load cell as a reference. The IBM PC samples the outputs from the sensor and the load cell and stores a piecewise linear lookup table for use in compensation for the nonlinearity of the sensor. On the PC's graphics display, two programs provide displays of foot pressures as real-time bar graphs or as analog pressure versus time curves.
Zhu et al. (Mon,) studied this question.