Pair pole asymmetry compensation in back electromotive force zero cross detection

Abstract

Disk drive spindle jitter is comprised of electrical noise, error due to pair pole asymmetry, and random disk speed variances. Error caused by pair pole asymmetry can be identified and compensated for by detecting over a single rotation of a rotor a plurality of zero cross signals. These signals can be statistically analyzed over a period of a plurality of revolutions of the rotor so as to identify the systematic error caused by pair poles. Once identified, this pair pole error can be used to modify zero cross signals and/or modify commutation signal driving the disk so as to arrive at a more accurate determination of disk speed and to precisely control the speed of the disk.

1 . A system for reducing pole pair asymmetry in disk drive jitter computations comprises:
 a commutation circuit and a back EMF detection circuit for coupling to a disk drive;   a pole pair asymmetry compensation device coupled to the commutation circuit; and   a spindle speed controller coupled to the pole pair asymmetry compensation device.   
     
     
         2 . The system of  claim 1  wherein the pole pair asymmetry compensation device comprises a memory for storing back EMF data from a plurality of zero cross signal readings. 
     
     
         3 . The system of  claim 1  wherein the pole pair asymmetry compensation device comprises a memory capable of storing executable code or instructions. 
     
     
         4 . The system of  claim 3  wherein the pole pair asymmetry compensation device comprises a microprocessor capable of performing computations directed by the stored code or instructions. 
     
     
         5 . The system of  claim 1  wherein the back EMF detection circuit gathers zero cross signals from each of the pole pairs as a rotor rotates above a stator in the disk drive. 
     
     
         6 . A system for reducing pole pair asymmetry in disk drive jitter computations comprises:
 a commutation circuit and a back EMF detection circuit coupled to a disk drive including a stator and a rotor;   a pole pair asymmetry compensation device coupled to the commutation circuit; and   a spindle speed controller coupled to the pole pair asymmetry compensation device.   
     
     
         7 . The system of  claim 6  wherein the pole pair asymmetry compensation device comprises a memory for storing back EMF data from a plurality of zero cross signal readings. 
     
     
         8 . The system of  claim 6  wherein the pole pair asymmetry compensation device comprises a memory capable of storing executable code or instructions. 
     
     
         9 . The system of  claim 8  wherein the pole pair asymmetry compensation device comprises a microprocessor capable of performing computations directed by the stored code or instructions. 
     
     
         10 . The system of  claim 6  wherein the back EMF detection circuit gathers zero cross signals from each of the pole pairs as the rotor rotates above the stator. 
     
     
         11 . A computer system for controlling a disk drive motor assembly wherein the disk drive motor assembly includes a rotor having a plurality of pole pairs and a stator, the computer system comprising:
 a device capable of detecting for each rotation of the rotor a plurality of zero cross signals; and   a machine having a first portion for removing pole pair asymmetry from each of the plurality of zero cross signals forming a plurality of corrected zero cross signals, a second portion to determine rotor speed based on at least one of the plurality of corrected zero cross signals, and a third portion to generate a plurality of commutation steps based on at least one of the plurality of corrected zero cross signals.   
     
     
         12 . The computer system of  claim 11  wherein the plurality of zero cross signals includes at least one zero cross signal from each of the plurality of pole pairs associated with the rotor. 
     
     
         13 . The computer system of  claim 11  wherein each of the plurality of zero cross signals is associated with one of the plurality of pole pairs associated with the rotor. 
     
     
         14 . The computer system of  claim 11  wherein each of the plurality of pole pairs is associated with two or more of the plurality of zero cross signals. 
     
     
         15 . The computer system of  claim 11  wherein each zero cross signal is generated from a back electromotive force signal associated with one of the plurality of pole pairs. 
     
     
         16 . The computer system of  claim 11  wherein the first portion of the machine includes means for determining for each rotation of the rotor a plurality of electrical periods based on the plurality of zero cross signals. 
     
     
         17 . The computer system of  claim 16  wherein the first portion of the machine includes means for averaging separately the plurality of electrical periods responsive to a plurality of rotor revolutions forming a plurality of separate averages. 
     
     
         18 . The computer system of  claim 17  wherein the first portion of the machine includes means for averaging the plurality of separate averages to form an electrical period mean. 
     
     
         19 . The computer system of  claim 18  wherein the first portion of the machine includes means for modifying each of the plurality of zero cross signals based on a comparison the plurality of separate averages and the electrical period mean. 
     
     
         20 . The computer system of  claim 11  wherein the machine comprises a spindle speed controller.