The effects of moisture on fingertip skin deformation during loading and slipping
39th Annual Meeting of the Society for Neuroscience, Chicago, USA, 2009.download pdf
During tactile interaction, skin deformation stimulates the mechanoreceptors, enabling the nervous system to become aware of the properties of the touched surface. Even on perfectly smooth, glassy surfaces, the fingertip skin deforms in complicated ways when slip occurs. The aim of the present study is to assess the effects of moisture content and interaction forces on the fingertip skin deformation occurring in this condition.
Twelve subjects having a large range of skin moisture (from dry to wet) participated in this study. They were asked to exert a constant normal force against a glass surface with the index fingertip and to increase the tangential force until slip occurs. Each subject performed five slippages for six different levels of normal force (0.2, 0.5, 1, 2, 5, 10N). Forces and moisture were measured with a force-torque sensor (ATI F/T Mini40) and a moisture evaluator (Corneometer®), respectively. Skin deformation at the contact surface was acquired with a specifically designed optical apparatus that allowed the evaluation of the relative sizes of the slipping and sticking regions.
The area of the sticking region decreased when the tangential force increased. It varied linearly with the ratio of net tangential/normal force components. The slope of this relationship was strongly influenced by both the normal force exerted and the moisture content of the skin. Finally, the static coefficient of friction could be extracted when the sticking regions vanished and the slipping region spread to the whole surface of contact.
This study described the deformation of the skin occurring during interaction with smooth surfaces and evaluated the effect of interaction force components and moisture on this deformation. A skin deformation model that takes into account these two parameters is presently being developed. This research was supported by a grant from Prodex (contract numbers 90063, 90064, 90231, 90232), ESA (European Space Agency), PAI, FNRS, FRSM, ARC, and NANOBIOTACT-project (EU-FPG-NMP-033287).