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A method of expanding the on-track operational range of a disk drive based upon detection of an external vibration condition. The method involves detecting that a vibration state exists and, while the existence of the vibration state is detected, modifying the default on-track-declaration algorithm

A method of expanding the on-track operational range of a disk drive based upon detection of an external vibration condition. The method involves detecting that a vibration state exists and, while the existence of the vibration state is detected, modifying the default on-track-declaration algorithm such that a data transfer operation can be completed in less time than if the default on-track-declaration algorithm was in use.

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1. A method of expanding an on-track operational range of a disk drive that is subject to being in a vibration state that is initiated by an external vibration force, wherein the disk drive comprises a control system, the control system using a default on-track-declaration algorithm for analyzing se

1. A method of expanding an on-track operational range of a disk drive that is subject to being in a vibration state that is initiated by an external vibration force, wherein the disk drive comprises a control system, the control system using a default on-track-declaration algorithm for analyzing servo samples and determining whether or not a data transfer operation is warranted, the method comprising the steps of:detecting that the vibration state exists;modifying the default on-track-declaration algorithm while the existence of the vibration state is detected; andcompleting the data transfer operation in less time than if the default on-track-declaration algorithm was in use. 2. The method of claim 1 wherein the data transfer operation is a read operation and wherein the on-track-declaration algorithm is a read-related algorithm. 3. The method of claim 1 wherein the data transfer operation is a write operation and wherein the on-track-declaration algorithm is a write-related algorithm. 4. The method of claim 3 wherein the default on-track-declaration algorithm comprises a write-unsafe (WUS) limit that is specified in terms of an off-track percentage that when exceeded in any one servo sample indicates that writing should stop. 5. The method of claim 3 wherein the default on-track-declaration algorithm comprises a write-settle window that is specified in terms of an off-track percentage that when achieved for predetermined number of successive servo samples indicates that writing may start. 6. The method of claim 3 wherein the detecting step is accomplished by directly detecting that the vibration state exists by monitoring a sensor. 7. The method of claim 6 wherein the sensor is an accelerometer. 8. The method of claim 3 wherein the detecting step comprises indirectly detecting that the vibration state exists. 9. The method of claim 8 wherein the detecting step comprises indirectly detecting that the vibration state exists by monitoring a control system metric. 10. The method of claim 9 wherein the control system metric is PES. 11. The method of claim 9 wherein the control system metric is a raw error rate experienced during read operations. 12. The method of claim 9 wherein the control system metric is frequency of ECC correction. 13. The method of claim 9 wherein the detecting step is accomplished by:receiving a plurality of n most recent servo samples that each correspond to an off-track percentage;multiplying each of the plurality of n most recent servo samples by a weighting factor;summing the plurality of n most recent servo samples to produce a weighted sum; anddetermining that a vibration state is detected when the weighted sum exceeds a vibration threshold value. 14. The method of claim 13 wherein the step of receiving plurality of n most recent servo samples is accomplished by the step of receiving a running plurality of n most recent servo samples and wherein the steps of multiplying, summing and determining are performed with respect to successively updated ones of the running plurality of n most recent servo samples. 15. The method of claim 14 wherein the step of receiving a running plurality of n most recent servo samples is accomplished by storing each of the n most recent servo samples and, for each new servo sample, adding the new servo sample while removing a new-nth servo sample. 16. The method of claim 15 wherein the step of receiving a running plurality of n most recent servo samples is accomplished with a circular buffer. 17. The method of claim 15 wherein the weighting factor increases in magnitude as a function of increasing off-track percentage in order that the weighted sum increases more rapidly in the presence of a vibration state than the weighted sum decreases in the absence of a vibration state. 18. The method of claim 9 wherein the detecting step comprises monitoring a control system metric over a running period of time. 19. The method of claim 18 wherein the detecting step further comprises determining that a vibration state exists when the monitored control system metric exceeds a pre-determined threshold value. 20. The method of claim 18 wherein the control system metric is a contiguous servo sample set representative of an off-track percentage. 21. A method of expanding an on-track operational range of a disk drive that is subject to being in a vibration state that is initiated by an external vibration force, wherein the disk drive comprises a control system, the control system using a default on-track-declaration algorithm for analyzing servo samples and determining whether or not a data transfer operation is warranted, the method comprising the steps of:detecting that the vibration state exists; andmodifying the default on-track-declaration algorithm while the existence of the vibration state is detected. 22. The method of claim 20 further comprising the step of completing the data transfer operation in less time than if the default on-track-declaration algorithm was in use.