Force Sensing Resistors (FSRs) are manufactured from a blend of conductive nanoparticles dispersed in an insulating polymer matrix. FSRs exhibit large amounts of hysteresis and drift error, but currently, a great effort is placed on improving their performance through different techniques applied during sensor manufacturing. In this article, a novel technique for improving the performance of FSRs is presented; the method can be applied to already-manufactured sensors, which is a clear benefit of the proposed procedure. The method is based on driving the sensors with a modified-astable 555 oscillator, in which the oscillation frequency is set from the sensor’s capacitance and resistance. Considering that the sensor’s capacitance and resistance have opposite signs in the drift characteristic, the driving circuit provides self-compensated force measurements over extended periods of time. The feasibility of the driving circuit to reduce hysteresis and to avoid sensitivity degradation is also tested. In order to obtain representative results, the experimental measurements from this study were performed over eight FlexiForce A201-25 sensors.

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.