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An approach to improvement of HDD spindle motor efficiency

To improve the efficiency of HDD spindle motor, reducing air gap length (AGL) and raising magnetic energy product (MEP) of magnetic material are considered to be efficient methods. However some disadvantages are introduced concomitantly, such as the increase of cogging torque (CT) and unbalanced magnetic pull (UMP). This paper investigates both positive and negative effects of reduction of AGL and improvement of MEP on motor characteristics and proposes methods to decrease or avoid the negative effects. Then, an optimal design which can achieve a trade-off between high efficiency and increase of CT and UMP is proposed.