Numerical Modeling and Analysis to Formulate Mechanical and Tactile Behavior of Skin

Tactile sensation by touching motion is one of the basic functions for human beings to recognize the characteristics and information of objects. It is known that information about touched objects is recognized through deformation of the skin, but it is difficult to physically clarify the mechanism of such sensations. In addition, there are several types of mechanoreceptors related to tactile sensation in human skin, and it is necessary to digitize the sensation in consideration of its response characteristics. The purpose of this study is to propose a product design method that recalls physical properties from mechanical information inside the skin in order to evaluate the relationship between human skin deformation and physical properties of touched objects. Humans can recognize the shape and softness of an object by pressing the skin against the surface of the object. The behavior inside the skin can be discussed by modeling the contact between human skin and a rigid sphere and analyzing it mechanically by numerical simulation. Finite element method (FEM) was adopted as a numerical analysis method for this elucidation, and a three-layer laminated solid having the epidermis, dermis, and subcutaneous was developed as a numerical model, and mechanical information inside the skin was discussed. Here, the skin model is configured with different elastic coefficients and thicknesses in each layer, and mechanical information inside the skin model in contact with the object is evaluated for each distance from the contact surface. At this time, parameters used for the evaluation were discussed about stress, pressure, and strain, and the objective validity of each parameter was verified by observing a change in distribution generated inside the skin. Here, a depth from a contact surface suitable for observation is proposed by comparing distribution changes using a plurality of theories in numerical analysis. Furthermore, distribution changes using a plurality of theories obtained from the analysis results are observed with a contour diagram for each parameter, so that evaluation parameters dominant in deformation of human skin are objectively compared. Further, pressure is adopted as an objective evaluation parameter of the sensory mechanism from the relationship between the distribution of general mechanoreceptors and the depth from the adopted contact surface, and is used for analysis. From these facts, it is considered that the human tactile sensation can be objectively treated as an evaluation index by focusing on the pressure applied to the skin and the distance from an appropriate contact surface.