Development of contactless dynamic spindle testing using an eddy current brake

Abstract

It is important to determine the dynamic stiffness of machine tools in terms of chatter vibration. Although a hammering test is widely used to measure the dynamic stiffness, it is difficult to measure a moving object at high speed because the method requires direct contact. In particular, the dynamic stiffness of milling spindles that can rotate at high speed changes considerably between the resting and rotating states. Therefore, it is essential to develop a contactless dynamic spindle test (CDST) method. Although a few CDST methods have been proposed, a conclusive method has not yet been established because of the problem of convenience. The present study proposes a novel CDST method that uses the concept of an eddy current brake. The proposed method offers advantages in that it does not require a power supply or external control, although the excitation frequency depends on the rotation speed. The present paper first introduces the principle of the proposed method. Next, the measurement results obtained by a conventional hammering test and those obtained by the proposed method are compared in order to confirm the reliability and effectiveness for an actual milling spindle.