Effect of additional harmonics of driving current on torque ripple and unbalanced magnetic force in HDD spindle motors with stator and rotor eccentricity

This paper mathematically investigates the characteristics of torque ripple and unbalanced magnetic force (UMF) caused by additional harmonics of the driving current in hard disk drive (HDD) spindle motors with stator and rotor eccentricities. It shows that additional harmonics of the driving current, stator eccentricity, and rotor eccentricity independently affect torque ripple. It also shows that UMF is not generated in an ideal HDD spindle motor even when the driving current has additional harmonics. However, additional harmonics of the driving current generate additional harmonics of UMF in an HDD spindle motor with stator or rotor eccentricities. The characteristics of torque ripple and UMF caused by additional harmonics of the driving current were indirectly verified by measuring the acoustic noise and vibration of an HDD spindle motor with stator and rotor eccentricities