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This paper investigates the dynamic behavior of a HDD spindle system with fluid dynamic bearings (FDBs) by solving the Reynolds equation and the equations of a motion of a HDD spindle system in five degrees of freedom. FEM is used to solve the Reynolds equation in order to calculate the pressure distribution in fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors of a HDD spindle system, such as the whirling and the tilting motion, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This paper also proposes two design methods to improve the dynamic characteristics of a HDD spindle system without increasing friction torque, i.e., optimization of the width of the lower and the upper journal bearings and the journal bearings with asymmetric grooves.

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Welding is one of the many important manufacturing processes for automotive, electronics, heavy industries, and the reliability of the products is influenced by that of the weld zone. Two types of weld inspection tests exist, which are destructive and non-destructive tests. Although the destructive test is far more reliable than the non-destructive test, the product must be destroyed. The non-destructive test such as ultrasonic or X-ray test is thus used to overcome this problem, but this test is not applied in real time inspection. In this study, visual inspection using laser vision sensor is proposed and verified with experiment for fast and economic inspection