Impact force measurement of an actuator arm of a hard disk drive

Impact forces of an actuator arm of a hard disk drive (HDD) are measured by means of modifying the levitation mass method (LMM) whose basic concept was proposed by the first author. In the LMM, force is measured as the inertial force of a mass levitated with sufficiently small friction using an aerostatic linear bearing. The Doppler frequency shift of the laser beam reflecting from the mass is accurately calculated from the waveform recorded using a digitizer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. In the experiments, the mechanical response of an actuator arm of a HDD against an impact load and the inertial force of the actuator arm in free oscillation are measured. The importance and the problems concerning the present knowledge on the impact force of an actuator arm of a HDD are also discussed.