Using Skin Micro-Displacements to Create Vibrotactile Signals for Mobile Touchscreen Displays

This paper investigates the possibility of providing one-directional micro-displacement-based tactile feedback for touchscreen displays on mobile devices, utilizing the existing haptic actuators and transducers. Most existing systems use a generic vibration signal, transmitted throughout the entire device, irrespective of the point of interaction. This low-resolution generic haptic feedback mechanism also does not account for variations caused during signal propagation through various density components and ignores specific skin-receptor constraints. Therefore, tactile information delivered to the point of contact is usually distorted and inconsistent with reference to the original signal and its meaning, creating phase shifts and signal integration as well as dead zones, throughout the device. This research tries to redefine vibrotactile feedback by utilizing the micro-displacements of a screen overlay on top of the touchscreen as the core haptic feedback mechanism. To achieve this, we have developed a custom setup to test and deliver one-directional micro-displacements on a mobile device (Nokia Lumia 710) with the help of a transparent 100-μm-thick PET film overlay. Utilizing four generic vibrotactile actuators, to generate skin micro-displacements, at various frequencies, we have measured each actuator's ability to create one-directional displacement of the screen overlay and concluded that it is indeed possible to evolve from an inefficient, entire-device-based vibration haptic system, to a simple screen overlay micro-displacement mechanism for delivering onscreen tactile feedback utilizing the existing actuators. Furthermore, we also specify additional parameters that need to be considered in designing any touchscreen-based haptic system.