Understanding the effect of sourcing voltage and driving circuit in the repeatability of measurements in force sensing resistors (FSRs)

Abstract

Force sensing resistors (FSRs) are manufactured by the vigorous mixing of conductive particles with an insulating polymer resulting in a conductive polymer composite (CPC). FSRs have found great acceptance in biomechanical applications due to their low profile and light weight. However, FSRs exhibit considerable amounts of hysteresis and repeatability error that currently limit their usage. In an attempt to overcome this limitation, the hysteresis and repeatability errors of FSRs were assessed under different conditions of sourcing voltages (VFSR) and driving circuits. It was found that the hysteresis error exhibits a strong dependency on VFSR; this observation opposes the general belief that FSRs’ performance is voltage independent. In general, it was observed that incremental VFSR results in lower hysteresis error. The phenomenon of sensitivity degradation (SD) was also studied at the aforementioned conditions; it was found that SD is also a voltage-related phenomenon occurring at large VFSR. An electrical model was presented for the voltage-dependent response of FSRs; such a model can explain—up to some extent—the different performance of FSRs in regard to voltage changes. In order to obtain representative results, the experimental tests comprised 32 specimens of commercial FSRs from the brands: FlexiForce A201-1 and Interlink FSR 402. Only the Interlink FSR 402 sensor showed a slight dependency between VFSR and the repeatability error.