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In building a human-robot cooperative system, it is an important issue to reduce the harm caused by contact with the robot. A protective measure for a robot with a sharp and highly rigid surface is to smoothen the surface shape and reduce the rigidity in order to increase the contact area, and protection with a soft covering is effective. In this research, we focus on the event when the edge of the robot contacts the human body, especially the outer arms or legs. In order to design an appropriate soft covering, it is necessary to estimate the contact pressure between each part of the human body and the edge covered with the soft covering. The contact pressure can be derived from a contact model that considers the curved surface shape of the human body, the radius of curvature of the soft covering and edges, and the stress balance that considers the elastic modulus that hardens the hardness of the human body and the soft covering according to the compressive strain. Then, the validity of the proposed method was confirmed by material experiments to grasp the material properties and experiments simulating contact, using appropriate materials for the contact model targeted in this research. The proposed method can contribute to understanding the tendency of contact pressure by arbitrarily estimating the curvature radius of the edge and the hardness and thickness of the protective covering that covers the surface when applying the soft covering to the edge of the robot surface.

Dynamic contact behavior occurs between wheels and rails while the train is running, it is an unsteady phenomenon and becomes more complicated when passing through a curved section. To examine the mechanism of this phenomenon, the authors have developed a dynamic rolling contact tool, called “Wheel/Rail rolling contact simulator,” using a large-scale parallel finite element method (FEM). This tool uses the Lagrange multiplier method to calculate the contact force in the normal direction between the wheel and the rail, and it is possible to obtain a precise contact force distribution within the contact surface. In this paper, we introduce a developed algorithm to make the finite element (FE) model of the curved section automatically. Then, we reproduce the rolling behavior in the curved section with one bogie model for validation of the developed numerical simulation method and discuss the behavior in the contact patch of each wheel. As a result, the calculated summation of the wheel load and lateral force of all wheels indicate a quantitatively good agreement in comparison to the initial condition. Moreover, the dynamic behavior of the bogie during the rolling from the straight section to the transition curve section has been qualitatively good. In the future, improvement of the boundary conditions such as the bottom of the rail, and the use of fine mesh on the wheel/rail contact surface model will be carried out to do the quantitative comparison with the actual phenomenon.

This paper presents a numerical analysis of adhesion contact due to meniscus between a sphere and a flat considering the elastic deformation of the contacting surfaces. Analytical model and basic equations for numerical analysis are explained first. Meniscus contact characteristics are presented for a 2-mm-radius glass contact on a magnetic disk coated with submonolayer mobile lubricant, and 2-μm and 20-nm-radius asperity contacts on mobile and bonded lubricant layer with a low elasticity. It was found that the sphere-flat contact with submonolayer liquid meniscus shows Derjaguin-Muller-Toporov theory-like behavior to Johnson-Kendall-Roberts theory-like one as the mobile layer thickness decreases from 1 nm to 0.3 nm. There is a critical liquid film thickness below which the meniscus length becomes zero so that the meniscus liquid cannot be transferred to the mating surface. This numerical method can be used for the rigorous analysis of various meniscus adhesion contact problems. Some of the experimental adhesion characteristics between a glass sphere and a magnetic disk are discussed from the aspect of the calculated results of elastic meniscus contact.