Most disk-drives currently use brushless spindle motors using Hall sensors for rotor position sensing. The primary objective is to minimise cost; however, the rotor position sensing mechanism can still cost a significant proportion of the motor cost. Disk-drive spindle system cannot use extensive or expensive drive systems. This paper describes sensorless systems which are simple, cheap and can be easily implemented using software control. The system uses the back-emf of the armature winding with simple and cheap components to accurately predict the rotor position for the inverter. The method allows the motor to start from stand-still when there is no back-emf. The paper also investigate other novel drive mechanisms for enhancing starting and running performance of the spindle motors - such an a 5-phase motor inverter set or a switch-coil motor using two-phase starting and single-phase running.
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