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When rolling bearings are used under light loads and high rotational speeds, their life may be determined by cage wear rather than raceway flaking. Under these operating conditions, the life and reliability of the bearings can be improved by reducing cage wear. To reduce cage wear, it is necessary to measure and analyze the contact forces acting on the cage due to the interactions between the roller and the cage pocket. In this paper, a measurement system capable of measuring “the contact forces between the roller and the cage pocket” and “the cage center displacement” at the same time has been constructed. Measurements have been conducted using this system for a cylindrical roller bearing at various rotational speeds. As a result of measuring the contact forces, it has been found that “the force to accelerate the cage” is generated continuously in the load zone of the bearing, while “the force to decelerate the cage” is generated intermittently in the non-load zone of the bearing. Since the contact forces are not constant during one rotation of the cage, the impulses due to the interactions have been calculated to evaluate not only the contact force but also the contact time. Results indicate that the impulses per rotation of the cage caused by each force show a tendency to decrease up to 2000 min-1 of rotational speed and not to almost change at higher speeds. In addition, it has been found that the cage center displacement measured becomes a constant velocity circular motion when the rotational speed exceeds 2000 min-1. These findings suggest that the contact between the roller and the cage can be easily modeled when the rotational speed exceeds 2000 min-1. The analysis based on this model created is in general agreement with the impulses obtained from the measurement results.

This study discussed design criteria for suppressing stick-slip using dynamic vibration absorber. First, a simplified analytical model that can quantify the effect of the dynamic vibration absorber on the occurrence and nonoccurrence conditions of stick-slip was proposed. The model comprises of two vibration systems, i.e., the primary vibration and additional mass systems. In the primary vibration system, stick-slip occurs due to the difference of static and kinetic friction acting on a sliding surface between a primary mass and driven rigid plane. In the additional mass system, an additional mass is connected to the primary mass in the primary vibration system by a linear spring and a dashpot. From the numerical simulations using this analytical model, it was verified that the presence of the additional mass is effective in suppressing stick-slip occurring in the primary vibration system. Secondary, based on the previous studies, i.e., the theories of stick-slip and dynamic vibration absorber, the discriminant equation of the boundary conditions for the occurrence and nonoccurrence of stick-slip was analytically derived. Through some numerical simulations, the validity of the discriminant equation proposed was discussed. It was confirmed that the proposed discriminant equation can accurately formulate the design guideline of the dynamic vibration absorber for suppressing stick-slip. Finally, as a conclusion of this study, the basic design strategy of the dynamic vibration absorber for suppressing stick-slip occurring in mechanical systems were discussed.

In this study, in-situ observations of a contact interface between a transparent rubber hemisphere made of PDMS (poly dimethyl siloxane) and a smooth plate made of PMMA (polymethyl methacry- late) were performed. Using a reflective optics, the space distribution of real contact regions formed in the apparent contact region was visualized. Additionally, the normal load dependence of friction force that acts on the contact interface was also investigated. As a result, it was found that the classical Amontons' friction law breaks down in this system; friction coefficient gradually decreased with increasing normal load. Based on Persson's contact theory, we discussed the mechanism of the normal load dependence of real contact area and friction coefficient. Finally, a novel method for estimating the real contact area and shear strength in sliding friction of a rubber like material was developed. The use of this method allows to estimate the real contact area and shear strength without any optical measurements of contact interfaces.