Ferro-Fluid Lubricated Bearings for a Polygon Mirror Motor

Abstract

Laser printers, which feature quiet, fast, high-quality printing, are evolving towards digital copiers with even faster and higher quality printing performance. This trend requires faster and more precise rotation of the polygon mirror motor of the laser beam scanning mechanism. Thus, bearings are becoming a key technology for the advancement of laser printers. This report proposes an integrated bearing unit that employs ferro-fluid for the bearing lubrication and seals in a new concept of leakage-free high-speed bearings. The intention is to take advantage of hydrodynamic oil-film bearings with high stiffness and damping characteristics to solve the oil leakage problem, and use them in place of ball-bearings or air bearings to get highly precise rotation. Leakage is completely prevented by using a compound seal of a ferro-magnetic seal and a viscous seal. The structural features of these bearings and experimental results concerning their lubrication and sealing performance and rotation accuracy when applied to a polygon mirror motor operating from 10000 to 30000 r/min are presented. The ferro-fluid bearings provide satisfactory friction torque and stiffness characteristics and the proposed bearing unit can be utilized with the polygon mirror motor.

Sliding bearings lubricated with magnetic fluids

“…To achieve high speed and precise rotation, the bearing performance must have excellent stiffness and damping characteristics. The stiffness characteristics of three types of bearings: precision ball bearings, air bearings and oil-film bearings are conceptually shown in Figure 1 (Nii et al, 1996).The oil-lubricated bearings have greater stiffness than ball bearings and gas bearings at rotation speeds above 10,000 rpm for small-sized bearings. The stiffness of these bearings increases with rotation speed because of the hydrodynamic effect of the oil film.…”

“…Magnetic fluids are stable colloids comprising a base liquid, ferromagnetic particles, and a stabilizing dispersing agent (surfactant) that suspends the particles in the base liquid. The advantages of the magnetic fluid bearing assemblies, over conventional ball bearings assemblies are extremely low non‐repetitive runout/high accuracy of rotation/, in addition to a high‐speed capability, very good damping properties and quietness of operation (Nii et al , 1996; Rosensweig, 1978; Perry, 1978; Berkovsky et al , 1993; Fertman, 1990; Orlov and Podgorkov, 1993; Berkovsky and Bashtovoy, 1996; Raj and Moskowitz, 1990; Nakatsuka, 1993; Ochonski, 2002, 2001).…”

“…The friction characteristics of ferrofluid and ball bearings are shown in Figure 2 (Nii et al , 1996). The ball bearings show a large fluctuation torque at high‐rotational speeds compared to the ferrofluid bearings.…”