Static and cyclic performance evaluation of sensors for human interface pressure measurement

Abstract

Researchers and clinicians often desire to monitor pressure distributions on soft tissues at interfaces to mechanical devices such as prosthetics, orthotics or shoes. The most common type of sensor used for this type of applications is a Force Sensitive Resistor (FSR) as these are convenient to use and inexpensive. Several other types of sensors exist that may have superior sensing performance but are less ubiquitous or more expensive, such as optical or capacitive sensors. We tested five sensors (two FSRs, one optical, one capacitive and one fluid pressure) in a static drift and cyclic loading configuration. The results show that relative to the important performance characteristics for soft tissue pressure monitoring (i.e. hysteresis, drift), many of the sensors tested have significant limitations. The FSRs exhibited hysteresis, drift and loss of sensitivity under cyclic loading. The capacitive sensor had substantial drift. The optical sensor had some hysteresis and temperature-related drift. The fluid pressure sensor performed well in these tests but is not as flat as the other sensors and is not commercially available. Researchers and clinicians should carefully consider the convenience and performance trade-offs when choosing a sensor for soft-tissue pressure monitoring.

A Novel and Inexpensive Approach for Force Sensing Based on FSR Piezocapacitance Aimed at Hysteresis Error Reduction

“…Just with the exception of a new time constant, the analysis that led to (24) remains unchanged. Considering the new situation, (20) is rewritten as follows:…”

“…Unloading forces are applied when the FSR is released until σ = 0. During unloading forces, the FSR recovers its nondeformed state and the average filler interparticle distance returns from s f to s 0 , but this happens through a very different path [24].…”

Experimental characterization, modeling and compensation of hysteresis in force sensing resistors

“…The performance of the CMA to estimate F was comparatively evaluated with the linear regression model (1), which is the manufacturer recommended method. It must be noted that the linear regression model is the preferred method in research applications [4,5,[9][10][11][12][13]. Two sets of m and b constants were calculated using the triangle force profiles of Section III.B.…”

“…Since this paper focusses on reducing the force MSE through conductance readings only, capacitance measurements are not henceforth considered. For linearization purposes, conductance variations -measured through Vo1 -have been preferably used in several studies to estimate F [8,9,12,15]; this is possible by inverting the model of Fig. 1e, which yields:…”

“…Relevant works on this scope have been developed by Lebosse [9], Schofield [5], Dabling [12], Vecchi [13] and Urban [14]. Likewise, authors' previous work has demonstrated that the A201 sensors, working on the piezoresistive principle, are also capable of exhibiting a piezocapacitive response.…”