Method of measuring non-coherent runout for a disk drive

Abstract

In a disk drive, a modified adaptive runout compensation algorithm is employed to measure non-coherent repeatable runout (RRO) of a track. The adaptive runout compensation algorithm is used to control the transducer head to follow the average RRO of adjacent tracks during the process of computing correction factors for non-coherent RRO for a given track. The adaptive runout compensation algorithm does not completely adapt to both the coherent and non-coherent RRO of a particular track because the transducer head is positioned over any one particular track for only a limited number of revolutions.

1 . In a disk drive that has a recording medium configured with multiple tracks and a transducer head controlled with a servo control signal, the servo control signal being generated based on an adaptive runout compensation algorithm, a method for determining non-coherent runout of each track in a group of adjacent tracks, comprising the steps of:
 (a) positioning a transducer head over a track in the group;   (b) allowing the adaptive runout compensation algorithm to adapt to a coherent runout of said track;   (c) determining a non-coherent runout of said track before the adaptive runout compensation algorithm adapts to the non-coherent runout of said track; and   (d) positioning the transducer head over an adjacent track in the group and repeating steps (b) and (c) for said adjacent track.   
     
     
         2 . The method according to  claim 1 , further comprising the step of repeating step (d) until the non-coherent runout of all tracks in the group has been determined. 
     
     
         3 . The method according to  claim 1 , further comprising the step of adapting the adaptive runout compensation algorithm to a coherent runout of one of the tracks in the group prior to step (a). 
     
     
         4 . The method according to  claim 3 , wherein the step of adapting includes:
 positioning the transducer head over a track in the group that is N tracks away from said one of the tracks and waiting for M revolutions of the recording medium; and   successively repositioning the transducer head over an adjacent track in the group that is closer to said one of the tracks and waiting for M revolutions of the recording medium,   wherein N is 2 to 5 times greater than the number of revolutions of the recording medium that is needed by the adaptive runout compensation algorithm to adapt to a particular track of the group and M is at least 10 times smaller than the number of revolutions of the recording medium that is needed by the adaptive runout compensation algorithm to adapt to a particular track of the group.   
     
     
         5 . The method according to  claim 1 , wherein, during step (c), the adaptive runout compensation algorithm is restricted to adapting only for a certain period of time. 
     
     
         6 . The method according to  claim 5 , wherein said step (c) of determining includes measuring position error signals, and the measured position error signals are representative of the non-coherent runout. 
     
     
         7 . The method according to  claim 6 , wherein, during step (c), the adaptive runout compensation algorithm is restricted to adapting only for a certain period of time. 
     
     
         8 . In a disk drive that has a recording medium configured with multiple tracks and a transducer head controlled with a servo control signal, the servo control signal being generated based on an adaptive runout compensation algorithm and correction factors, a method for determining the correction factors comprising the steps of:
 (a) successively positioning a transducer head over one or more tracks in the group and, for each track position, allowing the adaptive runout compensation algorithm to adapt to a runout of said track for a number of revolutions of the recording medium;   (b) after step (a), stepping the transducer head to be moved over one track and allowing the adaptive runout compensation algorithm to adapt to a runout of said track for a limited number of revolutions of the recording medium; and   (c) after step (b), determining the correction factors.   
     
     
         9 . The method according to  claim 8 , wherein said step of determining includes measuring position error signals, and the measured position error signals are representative of the correction factors. 
     
     
         10 . The method according to  claim 9 , wherein the adaptive runout compensation algorithm is restricted to adapting for a limited period of time while the correction factors are being determined. 
     
     
         11 . The method according to  claim 8 , further comprising the steps of:
 (d) stepping the transducer head to be moved over one track to a different track and allowing the adaptive runout compensation algorithm to adapt to a runout of said different track for a limited number of revolutions of the recording medium; and   (e) after step (d), determining the correction factors for said different track.   
     
     
         12 . The method according to  claim 11 , wherein steps (d) and (e) are repeated until correction factors for all tracks in the group have been determined. 
     
     
         13 . In a disk drive that has a recording medium and a transducer head controlled by a servo control signal that is generated in accordance with an adaptive runout compensation algorithm, a method for measuring non-coherent runout of a track, said method comprising the steps of:
 adapting the adaptive runout compensation algorithm to a coherent runout of said track;   positioning a transducer head over said track;   measuring position error signals while the transducer head is positioned over said track; and   determining the non-coherent runout of said track based on the position error signals.   
     
     
         14 . The method according to  claim 13 , wherein the step of adapting is carried out by allowing the adaptive runout compensation algorithm to adapt to a runout of multiple tracks that are near said track. 
     
     
         15 . The method according to  claim 14 , wherein the multiple tracks are adjacent tracks. 
     
     
         16 . The method according to  claim 15 , wherein the multiple tracks are located on an outer diameter region of the recording medium. 
     
     
         17 . The method according to  claim 15 , wherein the multiple tracks are located on an inner diameter region of the recording medium. 
     
     
         18 . The method according to  claim 13 , wherein the step of adapting includes successively repositioning the transducer head over different tracks near said track and allowing the adaptive runout compensation algorithm to adapt to each of the different tracks for at least one revolution of the recording medium. 
     
     
         19 . The method according to  claim 18 , wherein the number of different tracks is 2 to 5 times greater than the number of revolutions of the recording medium that is needed by the adaptive runout compensation algorithm to adapt to a particular track.