Optimal Design of Fluid Dynamic Bearings to Reduce Vibration of a Polygon Mirror Motor

Abstract

Fluid dynamic bearings (FDBs) has advantages for vibration and noise characteristics, because FDBs uses a lubricant as a sliding element between the rotor and stator. Especially, pressure, which is generated by wedge effect due to geometric difference between shaft and sleeve, can support rotating parts without external pressurization. Film pressure between shaft and sleeve have stiffness and damping effects, and maintain stability of rotating system by absorbing external shock. Because of these advantages, many researchers have studied to replace the ball bearings of polygon mirror scanner motor with FDBs. Application of FDBs to polygon mirror scanner motor contributes to prolong the life of polygon mirror scanner motor by reducing vibration, noise, and fatigue failure. In this paper, we have applied FDBs to polygon mirror scanner motor in order to reduce vibration of motor, and developed initial FDBs that can stably support rotating parts. Also, we optimized FDBs with improved stability assuming that in case of 50% and 100% oil-filled in FDBs. We used optimal Latin hypercube design (OLHD) with superior space-filling and Kriging suitable for non-linear problem method to optimize FBDs. In the optimization formulation, the objective function was set to maximize critical mass with constraints equations of radial load capacity, stiffness and damping coefficients for x, y, and z directions. We compared vibration responses at rotating and half-speed whirl frequencies of FDBs supporting rotating parts for initial and optimal model through harmonic analysis in external force. Also vibration reduction have experimentally verified by measuring displacement of rotating parts of polygon mirror scanner motor at rotating frequency.