Design, fabrication, and characterization of a compliant shear force sensor for a human–machine interface

Abstract

The determination of shear forces acting on a body is of crucial importance in decubitus ulcer prevention. The commercially available shear force sensors are generally costly and due to their properties (compliance, design of the deformation element, etc.) often unsuitable for this specific application.In this paper we propose and characterize the principle of a novel compliant shear force sensor for use in an anti-decubitus system. The sensor consists of conductive and non-conductive silicone elastomers, and includes a hermetically closed cavity which is continuously supplied with an internal pressure. The dependence of the distance between the two conductive sensor components (1) on the acting shear force and (2) on the internal pressure allows the magnitude, and the direction of the shear force to be determined by measuring the internal pressure when opening or closing the electrical contact.The sensor principle was characterized by analytical calculation and finite element method (FEM) analysis. Finally, the functional model was evaluated with metrological tests. Thereby, it was supplied with an internal pressure ranging from 0 to 0.045MPa in 0.005MPa increments and simultaneously loaded with a shear force. Depending on the pressure and the direction in which the shear force was applied, the minimum shear force required to activate the detection circuit was in the range 2.6–6.8N. The determined sensor characteristic showed a high linearity (R2>0.998).