Characterization of nonlinearity in servo patterns

Patent metadata

Field	Value
Publication number	US-10657997-B2
Application number	US-201916398030-A
Country	US
Kind code	B2
Filing date	Apr 29, 2019
Priority date	Jul 24, 2018
Publication date	May 19, 2020
Grant date	May 19, 2020

Abstract

A method according to one embodiment includes applying a static head skew to a magnetic tape head, positioning the first reader at a first y-position relative to a servo pattern in a servo band, and measuring y-positions of the second reader relative to the servo pattern in the servo band while the first reader is at the first y-position. A y-position value is calculated for the second reader based on the measured y-positions. The following process is repeated several times: moving the first reader to a next y-position, measuring y-positions of the second reader while the first reader is at the next y-position, and calculating a y-position value of the second reader based on the measured y-position of the second reader. A unique nonlinearity value of the servo pattern in the servo band is calculated for each of the calculated y-position values of the second reader.

First claim

What is claimed is:

1. A method, comprising:
applying a static head skew to a magnetic tape head for misaligning first and second readers in a direction perpendicular to a tape travel direction thereacross;
positioning the first reader at a first y-position relative to a servo pattern in a servo band;
measuring y-positions of the second reader relative to the servo pattern in the servo band while the first reader is at the first y-position;
calculating a y-position value for the second reader based on the measured y-positions;
repeating the following process several times:
moving the first reader to a next y-position,
measuring y-positions of the second reader while the first reader is at the next y-position, and
calculating a y-position value of the second reader based on the measured y-position of the second reader while the first reader is at the next y-position;

calculating a unique nonlinearity value of the servo pattern in the servo band for each of the calculated y-position values of the second reader using the respective calculated y-position value of the second reader; and
storing and/or outputting the calculated nonlinearity values.

2. The method as recited in claim 1 , wherein the next y-position corresponds to an average y-position of the second reader during the immediately previous measuring.

3. The method as recited in claim 1 , wherein calculating a unique nonlinearity value of the servo pattern in the servo band for each of the calculated y-position values of the second reader includes calculating a difference between the respective calculated y-position value of the second reader and a corresponding linearized y-position.

4. The method as recited in claim 3 , wherein the linearized y-positions are calculated based on the first y-position of the first reader and a last calculated y-position value of the second reader.

5. The method as recited in claim 4 , wherein each of the linearized y-positions correspond to a different position along a linear function that extends between the first y-position of the first reader and the last calculated y-position value of the second reader.

6. The method as recited in claim 1 , wherein the process stops when an end of the servo band is reached.

7. The method as recited in claim 1 , wherein the next y-position corresponds to a predefined step size from the y-position of the first reader during the immediately previous measuring.

8. The method as recited in claim 1 , where the servo pattern is a timing-based servo (TBS) pattern that comprises bursts of servo stripes, or a high-density (HD) servo pattern containing multiple HD tracks having a repeating periodic waveform.

9. A computer program product for characterizing nonlinearity in a timing-based servo pattern, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions readable and/or executable by a controller to cause the controller to:
apply, by the controller, a static head skew to a magnetic tape head for misaligning first and second readers in a direction perpendicular to a tape travel direction thereacross;
position, by the controller, the first reader at a first y-position relative to a servo pattern in a servo band;
measure, by the controller, y-positions of the second reader relative to the servo pattern in the servo band while the first reader is at the first y-position;
calculate, by the controller, a y-position value for the second reader based on the measured y-positions;
repeat, by the controller, the following process several times:
move, by the controller, the first reader to a next y-position,
measure, by the controller, y-positions of the second reader while the first reader is at the next y-position, and
calculate, by the controller, a y-position value of the second reader based on the measured y-position of the second reader while the first reader is at the next y-position;

calculate, by the controller, a unique nonlinearity value of the servo pattern in the servo band for each of the calculated y-position values of the second reader using the respective calculated y-position value of the second reader; and
store and/or output, by the controller, the calculated nonlinearity values.

10. The computer program product as recited in claim 9 , wherein the next y-position corresponds to an average y-position of the second reader during the immediately previous measuring.

11. The computer program product as recited in claim 9 , wherein calculating a unique nonlinearity value of the servo pattern in the servo band for each of the calculated y-position values of the second reader includes calculating a difference between the respective calculated y-position value of the second reader and a corresponding linearized y-position.

12. The computer program product as recited in claim 11 , wherein the linearized y-positions are calculated based on the first y-position of the first reader and a last calculated y-position value of the second reader.

13. The computer program product as recited in claim 12 , wherein each of the linearized y-positions correspond to a different position along a linear function that extends between the first y-position of the first reader and the last calculated y-position value of the second reader.

14. The computer program product as recited in claim 9 , wherein the process stops when an end of the servo band is reached.

15. The computer program product as recited in claim 9 , wherein the next y-position corresponds to a predefined step size from the y-position of the first reader during the immediately previous measuring.

16. The computer program product as recited in claim 9 , wherein the servo pattern is a timing-based servo (TBS) pattern that comprises bursts of servo stripes, or a high-density (HD) servo pattern containing multiple HD tracks having a repeating periodic waveform.

17. An apparatus, comprising:
a controller configured to:
apply a static head skew to a magnetic tape head for misaligning first and second readers in a direction perpendicular to a tape travel direction thereacross;
position the first reader at a first y-position relative to a servo pattern in a servo band;
measure y-positions of the second reader relative to the servo pattern in the servo band while the first reader is at the first y-position;
calculate a y-position value for the second reader based on the measured y-positions;
repeat the following process several times:
move the first reader to a next y-position,
measure y-positions of the second reader while the first reader is at the next y-position, and
calculate a y-position value of the second reader based on the measured y-position of the second reader while the first reader is at the next y-position;

calculate a unique nonlinearity value of the servo pattern in the servo band for each of the calculated y-position values of the second reader using the respective calculated y-position value of the second reader; and
store and/or output the calculated nonlinearity values.

18. The apparatus as recited in claim 17 , wherein the next y-position corresponds to an average y-position of the second reader during the immediately previous measuring.

19. The apparatus as recited in claim 17 , wherein calculating a unique nonlinearity value of the servo pattern in the servo band for each of the calculated y-position values of the second reader includes calculating a difference between the respective calculated y-position value of the second reader an

Assignees

• IBM

Inventors

• Judd Kevin B
• Furrer Simeon
• Pantazi Angeliki
• Lantz Mark A

Classifications

• G11B5/584

  for track following on tapes · CPC title

• G11B5/00817 Primary

  on longitudinal tracks only, e.g. for serpentine format recording · CPC title

• G11B5/588 Primary

  by controlling the position of the rotating heads (by controlling the speed of the record carrier G11B15/467; by controlling speed of the heads G11B15/473; {by moving the transducing part of the head relative to the headwheel, in the direction of the scanning movement G11B15/1841}) · CPC title