Method and apparatus for offset control in a disk drive

Abstract

According to one embodiment, a disk drive capable of performing a dynamic offset control (DOC) is provided. The disk drive has an offset module and an updating module. The offset module calculates an offset value that changes during a one-rotation period of a disk, from the offset-measuring position data recorded in the disk. The updating module updates the offset value to a new one if a disk shift has occurred.

1 . A disk drive comprising:
 a disk comprising a servo region configured to store servo data;   a magnetic head comprising a write head and a read head configured to maintain a distance of a prescribed offset, the write head configured to write data in the disk, and the read head configured to read data from the disk;   a head-position controller configured to position the magnetic head at a target position over the disk, in accordance with the servo data read by the read head;   an offset calculator configured to write offset-measuring position data for measuring an offset value between the read head and the write head, on a locus of the write head corresponding to a locus of a data track in a predetermined region of the disk other than the servo area, and configured to calculate the offset value from the offset-measuring position data read by the read head;   a controller configured to store the offset value calculated by the offset calculator and to control an offset dynamically using the offset value;   a determination module configured to determine whether a disk shift has occurred after the offset calculator calculated the offset value; and   an updating module configured to update the offset value when the determination module determines that a disk shift has occurred.   
   
   
       2 . The disk drive of  claim 1 , wherein
 the offset-measuring position data comprise burst signals corresponding to servo-burst signals in the servo data; and   the offset calculator is configured to adjust the position of the read head by a distance equivalent to the prescribed offset, to calculate the position error of the read head as an offset error from the offset-measuring position data read by the read head, and to add the prescribed offset to the offset error thereby calculating the offset value.   
   
   
       3 . The disk drive of  claim 1 , wherein
 the offset-measuring position data comprise burst signals corresponding to servo-burst signals in the servo data; and   the offset calculator is configured to adjust the position of the read head by a distance corresponding to a change of the offset value during a one-rotation period of the disk, to calculate the position error of the read head as an offset error from the offset-measuring position data read by the read head, and to add the prescribed offset to the offset error thereby calculating the offset value.   
   
   
       4 . The disk drive of  claim 1 , wherein the offset-measuring position data comprise burst signals corresponding to servo-burst signals in the servo data; and
 the offset calculator is configured to use a position change of the read head while the write head is writing the offset-measuring position data during a one-rotation period of the disk, to adjust the position of the read head by the prescribed offset to a locus of the write head while the write head is writing the offset-measuring position data, to calculate the position error of the read head as an offset error from the offset-measuring position data read by the read head, and to add the position change of the write head, the prescribed offset and the offset error, thereby calculating the offset value.   
   
   
       5 . The disk drive of  claim 1 , wherein the determination module is configured to use the offset value stored in the memory, to cause the controller to dynamically control the offset of the read head, and to determine whether a disk shift has occurred from the position error calculated from the read out offset-measuring position data. 
   
   
       6 . The disk drive of  claim 1 , wherein the determination module is configured to determine that no disk shift has occurred when the position error in the offset-measuring position data is smaller than a preset threshold value, and to determine that a disk shift has occurred when the position error exceeds the threshold value. 
   
   
       7 . The disk drive of  claim 1 , wherein the determination module and the updating module are configured to start operating after the magnetic head is moved from a standby position to any position over the disk and before data is either recorded in from the disk or reproduced from the disk. 
   
   
       8 . The disk drive of  claim 1 , wherein the determination module and the updating module are configured to start operating when the disk drive is detected to be subjected to impact or vibration. 
   
   
       9 . An offset calculating method of a disk drive that comprises a disk comprising a servo region configured to store servo data and a magnetic head comprising a write head and a read head configured to maintain a distance of a prescribed offset, the write head configured to write data in the disk, and the read head configured to read data from the disk, the method comprising:
 positioning the magnetic head in accordance with the servo data read by the read head and writing offset-measuring position data for measuring an offset value between the read head and the write head, on a locus of the write head corresponding to a locus of a data track in a predetermined region of the disk other than the servo area;   calculating the offset value from the offset-measuring position data read by the read head;   storing the offset value in a memory;   controlling an offset dynamically using the offset value stored in the memory;   determining whether a disk shift has occurred after the calculation of the offset value; and   updating the offset value when a disk shift has occurred.   
   
   
       10 . The method of  claim 9 , further comprising:
 reading the offset-measuring position data using the offset value stored in the memory by the dynamically offset controlled read head; and   determining whether the disk shift has occurred from a position error calculated from the offset-measuring position data.   
   
   
       11 . The method of  claim 9 , further comprising:
 determining that no disk shift has occurred when a position error calculated from the offset-measuring position data is smaller than a preset threshold value; and   determining that a disk shift has occurred when the position error exceeds the preset threshold value.   
   
   
       12 . The method of  claim 9 , wherein the determining whether a disk shift has occurred and the updating the offset value occur after the magnetic head is moved from a standby position to any position over the disk and before data is either recorded in the disk, or reproduced from the disk. 
   
   
       13 . The method of  claim 9 , wherein the determining whether a disk shift has occurred and the updating the offset value are configured to start when the disk drive is detected to be subjected to impact or vibration.