Exploration of vibro-acoustic characteristics of HDD spindle motors using electro-magnetic frequency-swept excitation

In this paper, an approach of modal testing to investigate the vibro-acoustic characteristics of a three-phase motor with fluid dynamic bearings used in hard disk drives (HDD) is proposed. The motor is excited by varying the frequency of the electrical current input on one of the three phases to ensure constant amplitudes of electro-magnetic (EM) excitations for all various audible frequencies. Compared with the conventional mechanical excitation, the EM excitation is more relevant to the actual EM forces which are the major source of acoustic noises in the motor operation. With the proposed EM-excitation method, the frequency response functions (FRFs) between the measured mechanical vibrations at exterior of the motor structure and the motor current input were obtained with good repeatability. The vibro-acoustic resonances of the motor and their corresponding mode shapes were determined from both the experimental FRFs and the sound spectra of the running motor. The results clearly show the critical vibro-acoustic modes that induce the acoustic noises in HDD motor.