Mechanics of vibrotactile sensors for applications in skin-interfaced haptic systems

Recent advances in haptic interfaces support a range of options in adding sensations of touch to virtual and augmented reality experiences. A fundamental understanding of the mechanics associated with coupling between vibro-tactile actuators and the skin is important in considering device designs and interpreting sensory perceptions. Here, we investigate vibrational dynamics induced by the three main classes of such actuators in bilayer elastomer structures that capture essential mechanical properties of human skin. The measurements rely on three dimensional digital image correlation methods, with corresponding simulations based on finite element analysis techniques. Studies examine the effects of key parameters relevant to the mechanics and resulting sensations, such as those related to contact area, actuation amplitude and spatio-temporal distributions of displacements in terms of both surface and body waves. Results reveal that tactor type actuators operate in a power efficient mode to produce deformations largely oriented out of the plane of the skin, for robust sensations that can, however, depend strongly on mounting strategy. Actuators based on eccentric rotating motors yield deformations with similar magnitudes but with substantial in-plane components and reduced sensations. Key attractive features of these actuators are in small, lightweight designs that facilitate mounting on the skin and deployment into large arrays. A third type of device, linear resonant actuators, produce the weakest sensations and the lowest power efficiencies, with limited potential for practical applications.