PRELOAD ADJUSTING DEVICE FOR MAIN SHAFT BEARING

PURPOSE:To provide a correct actual preload value without affected by thermal displacement in an axial direction due to the temperature rise of a bearing by providing a preload detection device for detecting an actual preload value on an axis same as that of the preload giving device for pressing the bearing through the side surface of an outer wheel body to give a preload. CONSTITUTION:In a preload giving device 5 such as a piezo actuator, an outer wheel body 4a is pushed from a side surface against the energizing force of an energizing means 9 to give a preload. An actual preload value, given by the preload giving device 5, is determined by arithmetically processing a detected signal from a preload detection device 6 such as a pressure sensor provided coaxially with the preload giving device 5. The optimum preload value in accordance with a main shaft rotation frequency is read out in a comparison circuit from a memory in a control device to be compared with an actual preload value. When both the sides do not conform, the drive of the preload giving device 5 is controlled by a compared result to increasingly/decreasingly adjust a preload value given to the outer wheel body 4a to make the actual preload value optimum in accordance with the rotation frequency of a main shaft 2.