Measurement and monitoring of hard disk drive spindle motor bearing parameters using position error signal

Current methods used for the measurement of stiffness and damping of spindle motor bearings used in hard disk drives use a vibration base driven by an external actuator. Acceleration sensors and displacement sensors installed onto the vibration base are then used to measure the acceleration and the spindle runout, respectively. Outputs from these sensors are analysed and used for the calculation of the stiffness and damping. The method, used for direct measurement and monitoring of total stiffness and damping, and proposed in this article does not require the use of any additional external sensors, neither does it require a vibration base driven by an external actuator. Vibration is generated by introducing a known value of imbalance onto the spindle motor. The vibration generated is then measured by reading and analysing the position error signal written on the disk surface and subsequently, used to calculate the total stiffness and damping. Experimental results verifying the proposed method are presented.