Reflectance spectroscopy can obtain the optical properties such as reflective index and extinction coefficient, and the thickness of each layer in the multilayer optical model for contact surface. So we can analyze the properties of transformed layer and oil film. The carbonaceous coatings such as Diamond-Like Carbon (DLC) coating and amorphous Carbon Nitride (CN_x) coating are promising for high hardness, low friction property and affordability. Though it is reported that transformed layer is important to show low friction, it is still unclear that transformed layer makes an effect on low friction. To clarify the effect of transformed layer of CN_x on friction clearly, we proposed the in-situ observation method which observes the friction surface with a reflectance spectroscopy and measures friction force simultaneously. From the result, it can be seen that estimated friction coefficients follow observed friction coefficients. Also this in-situ observation method with a reflectance spectroscopy was tried to use to know the condition of two phase lubricants which is the mixture of two lubricants. Experimental results showed the possibility of the separation of two lubricants in lubricant film with the reflectance spectroscopy.

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Achieving mechanical systems with high safety and reliability requires performing appropriate maintenance according to the situation. For this reason, sensing technology that can accurately measure damage progression in situ is essential. Concerning tribological phenomena in particular, direct external access to the friction interface is difficult, and its state changes constantly over time. Therefore, it is not easy to measure and visualize changes in the friction interface in situ. Acoustic emission (AE) sensing is a useful in situ measurement method for diagnosing and evaluating conditions such as surface-to-surface contact and wear at friction interfaces of mechanical components by measuring and analyzing elastic stress waves generated by material deformation and fracture. AE sensing excels in detection sensitivity to phenomena, and since the measurement data contains abundant information on deformation and fracture, it provides insights unattainable by other measurement methods. Furthermore, correlating AE parameters with tribological phenomena (e.g., friction and wear modes and wear rates) makes it possible to visualize in real time the previously invisible changes in the state of friction interfaces. This article explains how AE sensing is a visualization technology that supports tribology. It focuses on diagnostic and evaluation techniques for contact states and damage conditions at friction interfaces and incorporates research examples.

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Lubricants not only reduce friction and wear in machinery but also reflect internal mechanical conditions. Conventional methods for evaluating lubricant degradation rely on offline oil sampling, which lacks real-time responsiveness. Recently, in-situ and on-line monitoring technologies have gained attention as more effective alternatives. This paper provides an overview of sensor technologies for visualizing lubricant degradation, focusing on optical and electrical approaches. Furthermore, a novel approach is proposed for monitoring lubricant degradation in machines without lubricant circulation systems. This method enables condition monitoring by utilizing sliding components themselves as sensors, offering a promising solution for real-time, non-invasive diagnostics in such systems.

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Demands for improved efficiency in automobiles have led to the use of low viscosity oils, which result in turn trends to cause the surface temperature of rolling bearings and gears to raise. The most common measuring method is to touch thermocouple against the targets. But, this method can only measure temperatures in a limited range. The author applied the Seebeck effect in which an electromotive force is generated when different metals are touched, which is called dynamic thermocouple method. This method makes it possible to directly measure the temperature changes of the surface. Using dynamic thermocouple method, it is possible to visualize temperature changes of gears and rolling bearings.

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The lightweighting and strengthening of automotive parts contribute to both environmental issues and the improvement of vehicle safety. Cold rolling is one of the processes used to manufacture thin sheets for such automotive parts. In the roll bite, where work-rolls grips steel strips, significant friction forces occur. Reducing the friction forces with lubricants contributes to improved productivity and stable operation. Therefore, the lubrication state within the roll bite is crucial for effectively reducing friction forces. However, measuring the oil film thickness on the friction surface is challenging, and many efforts have been made in this regard. This paper discusses recent technological trends in measurement technology of oil film thickness between solid surfaces.

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The friction coefficient characteristics of annular V type microgrooves that experienced running-in with a lubricant containing an acid phosphate ester additive were analyzed using a one-dimensional modified Reynolds equation that includes the effect of a high-viscosity surface layer due to additives. First, the lubrication mechanism of the annular groove was proposed, and the lubrication characteristics were analyzed by applying the tapered-land tapered bearing (TLTB) model in which the tangential inertia flow generated by the mating surface crosses the grooves diagonally. As a result, it was clarified that the friction coefficient has a minimum and a maximum value with respect to the circumferential sliding velocity. Next, it was shown that by appropriately selecting the design parameters of the TLTB, it is possible to theoretically evaluate the different characteristics of the friction coefficient after running-in with lubricants containing three types of additives on different annular groove test specimens. It was also clarified that the different characteristics of the friction coefficient after sufficient running-in using three types of additive lubricants for a specific test specimen can be evaluated. Finally, the friction coefficient after running-in using five base oils with different viscosities was compared with the analytical results, and the maximum friction coefficient and the corresponding speed showed good agreement, indicating the validity of the analytical model.

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[in Japanese]

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