抄録
In recent years, there has been a growing demand for high-speed cutting work in the field of machining. The fundamental performance of the processing use spindle is normally evaluated by the magnitude of a DN value (spindle diameter × number of revolutions). In the case of the magnetic bearing, it is possible to provide a spindle of which the DN value surpasses the DN value of the ball bearing by making the best use of the features of non-contact rotation. However, it was discovered that magnetic bearing, which was expected to have small loss because of the non-contact structure, unexpectedly caused a great friction loss as the result of striving for higher DN value. The principal factor of the above result is the eddy current loss of the radial bearing. We proposed a new radial magnetic bearing structure to satisfy following (1) (2) at the same time. (1) High stiffness and a large loading capability can be kept. (2) The eddy current loss can be greatly decreased. Wide magnetic pole teeth are formed in the radial electromagnet. And, the both ends of the magnetic pole teeth have "a long rising interval" and "a long decelerating interval" of the magnetic flux density curve. This electromagnet was installed in the developed magnetic bearing spindle, and the evaluation experiment was done under the condition of the spindle diameter: D =Φ 90 mm, rotational speed: N = 50000 rpm, DN = 4.5 million and rising interval: α =10deg, uniformity interval: β =25deg, decelerating interval: γ =10deg. As a result, the temperature of bearing gap have decreased to about 1/2, and the motor power have decreased to 2/3 with the same radial stiffness maintained.
