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Stator design for robust rotor-position detction in inductive sense spin-up

IP.com Disclosure Number: IPCOM000023406D
Publication Date: 2004-Mar-30
Document File: 5 page(s) / 363K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is an improved spindle motor stator design with a smaller stator stem width for easier spin-up using inductive sense algorithm. This stator design enhances the sensitivity of winding inductance to motor magnet polarity and makes it easier to detect rotor position. This applies to all hard disk drive spindle motor configurations as long as inductive sense algorithm is used for spin-up.

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Stator design for robust rotor-position detction in inductive sense spin-up

Typical hard disk drive spindle motor has three phase windings as shown in fig. 1. At any instant only two of the three phases are energized depending on the rotor position, which is called commutation or current switching. In order for a three-phase motor to start from its standstill position the initial rotor position must be known so that proper commutation sequence can be determined. Previously hall-effect sensors were installed inside the motor to detect rotor position, which has disadvantages such as additional cost and less accurate rotor position detection at high speeds.

Fig. 1. Three phase motor winding diagram.

Inductive sense spin-up technique is widely used in small brushless DC motors including hard disk drive spindle motors for its advantage of saving hall sensors. The inductance of motor stator winding varies as the rotor position changes. The magnetic flux generated by the current in the stator winding can increase or decrease the flux density level in the stator depending on the rotor position, leading to decrease or increase in inductance due to saturation of stator. By applying positive and negative current and measuring the difference in inductance, it can be determined whether the phase winding is facing S-pole or N-pole of the permanent magnet. Rotor position can now be determined by repeating the procedure on all three phases.

The success of this algorithm strongly depends on how sensitive the inductance of phase winding to the applied current. Unlike Indy TSD motor whose start-up retrial rate is zero, Indy 2-disk RSS motor shows a high retrial rate, meaning that inductive sense-up algorithm is not successful. Finite element modeling on the existing Indy RSS and TSD motors show that the inductance difference of Indy RSS between positive current excitation and negative current excitation is smaller than that of Indy TSD. Figure 2 is a chart obtained through FEM showing the inductance of phase winding for positive excitation and negative excitation. The chart shows that the Inductance difference of Indy RSS is only one-third of that of Indy TSD.

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Fig. 2. Ind...