Overcoming the Variability of Fingertip Friction with Surface-Haptic Force-Feedback

International audienceTouch screens have pervaded our lives as the most widely used human-machine interface, and much research has focused recently on producing vivid tactile sensations on these flat panels. One of the main methods used for this purpose is based on ultrasonic vibration to controllably reduce the friction experienced by a finger touching a glass plate. Typically, these devices modulate the amplitude of the vibration in order to control the frictional force that the finger experiences without monitoring the actual output. However, since friction is a complex physical process, the open-loop transfer function is not stationary and varies with a wide range of external parameters such as the velocity of exploration or the ambient moisture. The novel interface we present here incorporates a force sensor which measures subtle changes of the frictional force on a wide frequency bandwidth including static forces. This force sensor is the basis for real time control of the frictional force of the finger, which reduces significantly the inherent variability of ultrasonic friction modulation while maintaining a noise level below human perception thresholds. The interface is able to render of precise and sharp frictional patterns directly on the user's fingertip

Mechanisms of tactile sensory deterioration amongst the elderly

It is known that roughness-smoothness, hardness-softness, stickiness-slipperiness and warm-cold are predominant perceptual dimensions in macro-, micro- and nano- texture perception. However, it is not clear to what extent active tactile texture discrimination remains intact with age. The general decrease in tactile ability induces physical and emotional dysfunction in elderly, and has increasing significance for an aging population. We report a method to quantify tactile acuity based on blinded active exploration of systematically varying micro-textured surfaces and a same-different paradigm. It reveals that elderly participants show significantly reduced fine texture discrimination ability. The elderly group also displays statistically lower finger friction coefficient, moisture and elasticity, suggesting a link. However, a subpopulation of the elderly retains discrimination ability irrespective of cutaneous condition and this can be related to a higher density of somatosensory receptors on the finger pads. Skin tribology is thus not the primary reason for decline of tactile discrimination with age. The remediation of cutaneous properties through rehydration, however leads to a significantly improved tactile acuity. This indicates unambiguously that neurological tactile loss can be temporarily compensated by restoring the cutaneous contact mechanics. Such mechanical restoration of tactile ability has the potential to increase the quality of life in elderly.