Computational Design Method to Control Touch Feeling of Mattress With Geometric Surface-Shape

Foam material is one of the ingredients that are frequently used for controlling of touch feeling on the contacting part of various products like bed mattresses. For better sleep, it is necessary to design to control the touch feeling of the mattresses. Touch feeling depends on various properties of the foam material, and the shape characteristics of the contact part also give humans various and complicated feelings. According to previous studies, it was possible to easily quantify the physical properties of foam materials by using indentation test. Furthermore, it is necessary to analyze the change in touch feeling due to the shape of contact part of foams for better mattress design. Then, the purpose of this study is to evaluate the touch feeling with multiple shape parameters of foam surface on the contacting point. Here, this become the contact problem between the foam material with the shape change and the human body which is modelled by simplicial ball in the first step of this study. The contact problem is modelled by unit cells in FEM. By thinking for periodic unit cell, it is mathematically approximated to push the foam uniformly as the curvature of the contact surface is large. FE model was developed by approximating the unit cells. Using the analysis model, vertical compress analysis by rigid plate was performed to get the relationship between displacement and reaction force.　 The result is the reaction force behavior of the entire contact surface with the human body. For this purpose, all the reaction forces for the indentation amount at each point were added. As a result, the reaction force behavior of the human body with respect to the pushing amount can be understood. In this study, it was assumed that the human body was pushed in the hip. Then, it is the reaction force behavior was analyzed for the design. The result was made a new softness parameter. From the behavior of the parameters, it was found that peaks occur at the beginning of pushing by causing the tip shape even in the same material. Then, the push stroke until the peak occurs is shortened as the tip shape is pointed. The maximum value of the peak becomes larger as the tip shape becomes sharper. The click ratio can be calculated from the maximum and minimum values of the peak. It was found that the click ratio increased by making the tip shape take.