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# magnetic circuit optimization in spindle motors for minimization of vibration and acoustics

IP.com Disclosure Number: IPCOM000023856D
Publication Date: 2004-Apr-01
Document File: 3 page(s) / 231K

## Publishing Venue

The IP.com Prior Art Database

## Abstract

Disclosed is an improved spindle motor stator design with a smaller slot angle to reduce magnetic excitation forces. This reduces RRO (repeatable run-out) and acoustic noise of hard disk drive system generated by magnetic forces between the stator and the stator. This applies to all hard disk drive spindle motor pole/slot configutrations as long as the stator has slots.

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magnetic circuit optimization in spindle motors for minimization of vibration and acoustics

Magnetic force exists as long as there is eccentricity (regardless of the number of slots) because a portion of stator is closer to magnet than the rest of the stator. This force is DC component in eccentric stator case and 1X (the same as the rotational frequency) component in eccentric rotor case.

1. Stator eccentricity: the portion closer to magnet (region A in Fig. 1) is stationary and the force is DC component (no vibration) in nature. As the rotor rotates portion A sees different magnet polarity Np times per revolution (Np is the number of magnet poles), which leads to integer*Np harmonics.

2. Rotor eccentricity: portion B rotates with the rotor in Fig. 1. Accordingly the magnetic force rotates with the rotor leading to 1X magnetic force harmonic. If the stator has slots, this rotating force is modulated by the stator slots and the resulting force will have harmonic components of frequencies integer*Ns +/- 1 (Ns is the number of slots in stator).

In the above two eccentricity cases DC component and 1X component are inevitable as long as there is eccentricity. The major harmonics such as 7X and 8X, however, will be zero (in rotor eccentricity) or significantly reduced (in stator eccentricity) if there is no slot in the stator (perfect-cylinder stator) because perfect-cylinder stator sees minimal change in magnetic configuration as the rotor rotates. In other words, in...