Reconfigurable Flexible Haptic Interface Using Localized Friction Modulation

Current flexible haptic technologies struggle to render textures as effectively as rigid surfaces with friction reduction due to poor propagation of elastic waves in flexible substrates. Alternative solutions using different actuators have been explored, but their low density hampers fine renderings, and so texture rendering. To overcome these limits, we propose in this paper the development, the characterization, and the evaluation of an innovative haptic solution enabling localized or continuous texture rendering on a flexible surface. On the basis of previous work, the developed surface is composed of several haptic resonators vibrating at an ultrasonic frequency, driven by piezoelectric actuators, and associated with a polymer matrix. The solution combines the advantages of a rigid haptic surface, implementing friction modulation to obtain texture stimulation, and the conformability of a 75 $\mathrm{\mu }$m thick polymer sheet. By powering or not the actuators, it is possible to display simple tactile shapes. Tribological measurements confirm that the friction reduction matches the desired shape. Two studies demonstrated the device's effectiveness: participants identified simple geometric shapes with a 96$\%$ success rate and 14 s detection time, and two users simultaneously recognized independent tactile patterns, achieving 89$\%$ accuracy. This flexible device supports simple geometric shape display with texture rendering, multi-touch and multi-user interaction, offering potential for various applications.