Development of Elastomer-Strain Gauge Composite for On-Body Dynamic Force Measurement

Sensing force on the body is useful for a variety of aerospace applications. In extravehicular activity (EVA) suits, sensing force on the body is important to determine when and where a rigid suit structure comes into contact with the astronaut. In intravehicular activity (IVA) compression garments, real-time force sensing could help improve current garment performance, or even enable new forms of compression therapy. In this paper we describe the development of a novel elastomer-strain gauge composite designed to unobtrusively measure contact force on the body. The sensor, which combines a strain-sensitive conductive cover-stitched trace with a compliant elastomer matrix, is engineered to respond to normal force by inducing repeatable and predictable strain in the conductive trace. Consequently, the electrical resistance of the trace changes with applied force, leading to useful sensing capability. A parametric design study of two manufacturing methods and elastomer material stiffnesses (Shore value) was performed to assess the effects of these parameters on the elastomer-strain gauge composite performance. The two manufacturing methods differ in terms of ease of manufacturing. The results of this study indicated that the ‘direct-stitched’ manufacturing method with a lower Shore value had greater performance than the ‘layered-assembly’ manufacturing method in terms of sensor characteristics, evaluated based on polynomial model fitting and long term-repeatability. This type of novel elastomer-strain gauge composite enables unobtrusive on-body normal force sensing, which can benefit astronauts during IVA/EVA, as well as additional applications where on body force sensing is valuable.