Investigation of the position error signal of an operating hard disk drive due to varying temperature conditions

Abstract

Electromechanical analysis was employed to investigate how variations of hard disk drive (HDD) temperature affect the position error signal of the read/write head. Electromagnetic fields of the spindle motor and voice coil motor were analyzed by solving time-stepping finite element equations. The motional analysis of the rotating spindle and actuator was performed using the Newton-Euler equation of motion. The control actions of the disk speed and track following motion of actuator are included for the numerical description of the data access. The simulation results showed how the operating temperature dependence of HDD variables such as the coil resistances, magnetization of the permanent magnet, fluid viscosity in the fluid dynamic bearing and thermal expansion of the structures, affect the electromechanical characteristics of the HDD system. Also, the results showed that the increased position error signal of the head at an elevated operating temperature was mainly caused by increased disk run-out. The latter phenomenon was due to a degradation of performance in the fluid dynamic bearing in the rotating disk-spindle system. These results were verified by experimental testing.