Ball bearings are usually used for the spindle system of machine tools under preloading to achieve high stiffness of the main spindles. However, in the case of high speed cutting, too high a degree of preloading results in excessive temperature rise and, consequently, bearing seizure. Therefore, several mechanisms have been proposed to adjust the preload on bearings. Most of them, however, have some problems. In this study, a simple and practical mechanism for preload adjustment is developed using piezoelectric actuators, and the preload is successively adjusted while the spindle in rotation.
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