Enhancing the Repeatability of Pressure-Mapping Insoles by Choosing an Appropriate Driving Circuit and Sourcing Voltage

Force Sensing Resistors (FSRs) are obtained by randomly dispersing conductive nanoparticles in an insulating polymer matrix. The low-profile and low-weight characteristics of FSRs have been exploited in the manufacturing of pressure-mapping insoles. However, FSRs exhibit low repeatability which limits the extensive usage of such devices in certain applications that require high levels of accuracy and repeatability. In order to enhance the performance of FSRs, a custom-designed insole has been manufactured from commercial FSRs. The purpose of this study is to assess the influence of the sourcing voltage (V_s) and the driving circuit on the repeatability of pressure measurements when collecting gait data. It was found that setting a low V_s improves the repeatability of the system, whereas setting a large sourcing voltage causes a degradation of sensors' sensitivity. Some possible reasons for sensitivity degradation are discussed on the basis of modelling sensor dynamics with equations for quantum tunneling conduction and constriction resistance. Enhancing the repeatability of FSRs opens the way for a broader usage of such devices in applications demanding accurate pressure measurements, such as: rehabilitation and object manipulation in robotics.