A device for mimicking the contact force/contact area relationship of different materials with applications to softness rendering

In this paper a fabric yielding softness display (FYD-2) is proposed, where the stretching state is controlled using two motors, while the contact area is measured in real-time. In previous works, authors proposed a fabric-based device, with embedded contact area measurement system, which was proved to provide subjects with a compelling and naturalistic softness perception. Compared to it, FYD-2 exhibits reduced dimensions, a more accurate sensorization scheme and an increased actuation velocity, which allows to implement fast changes in the stretching state levels. These changes are mandatory, for example, to properly track typical quadratic force/area curves of real materials. Furthermore, FYD-2 is endowed with an additional degree of freedom that can be used to convey supplementary haptic cues, such as directional cues, which can be exploited to produce more immersive haptic interactions. In this work we describe the mechanical design and the mathematical model of the device. The reliability in real-time tracking of stiffness and force-area curves of real objects is also demonstrated.