Patent ID: 7723883
Filing Date: 2010-05-25
Classification: F01D,F04D,F05D,F16C,F25B,H02K

Abstract:
1. A motor built-in magnetic bearing device which comprises: a main shaft; a flange shaped thrust plate coaxially mounted on the main shaft so as to extend perpendicular to the main shaft and made of a ferromagnetic material; a rolling bearing unit for supporting a radial load; a magnetic bearing unit for supporting one or both of an axial load and a bearing preload and having an electromagnet fitted to a spindle housing so as to confront the thrust plate, on a non-contact basis; a motor for driving the main shaft and having a motor rotor mounted on the main shaft and a motor stator arranged in face-to-face relation with the motor rotor, the main shaft being driven by a magnetic force or a Lorentz force developed between the motor rotor and the motor stator; a sensor for detecting an axial force acting on the rolling bearing unit; and a controller for controlling the electromagnet in response to an output from the sensor; wherein a stiffness of a composite spring formed by the rolling bearing unit and a support system for the rolling bearing unit is higher than a negative stiffness of a composite spring of a motor part comprised of the motor and the electromagnet.