Pressure sensing approach to measuring normal forces

-- MiguelPiedrahita? - 13 May 2004

Normal forces on the foot can be determined by connecting a pressure sensor to a fluid-filled chamber which undergoes compression when the foot is loaded.
A sealed polyurethane chamber was fabricated using SDM, as described in the figure below.

This cavity was then filled with water and connected to a Motorola pressure sensor.

Pressure Sensor used: Motorola MPXV5004
This sensor provides an analog output of 1.0 to 4.9 V, for pressures of 0 to 3.92 kPa.
Sensitivity: 1.0 V/kPa

Experiments showed large variation in the sensor performance from day to day, likely due to small amounts of air trapped in the system.
The data from a single day showed a strong linear relationship between normal force and pressure output, as well as fairly good repeatability. A plot of this data is shown here:

Further details can be found in this Powerpoint presentation: PressureSensorsandFutureWork5-12-04.ppt: