Triple push-pull optical tracking system

• US 6,940,676 B1
• Filed: 06/07/2000
• Issued: 09/06/2005
• Est. Priority Date: 06/07/2000
• Status: Expired due to Fees

• Current Assignee: Quantum Corporation (Chi Ko Investment Co., Ltd.)
• Original Assignee: Quantum Corporation (Chi Ko Investment Co., Ltd.)
• Inventors: Tylock, James, Lee, Tzuo-Chang
• Primary Examiner(s): Tran, Sinh
• Assistant Examiner(s): WONG, KIN C
• Application Number:
  US09/588,891
• Time in Patent Office: 1,917 Days
• Field of Search: 360/77.12, 360/72.1, 360/77.03, 360/75, 360/78.02, 369/112, 369/44.17, 369/44.23, 369/44.11, 369/14, 369/44.37, 369/44.38, 369/112.24, 369/97, 369/44.31
• US Class Current: 360/72.1
• CPC Class Codes: G11B 15/602 for track selection, acquisition or following
• CPC Class Codes: G11B 5/584 for track following on tapes

Abstract

A method of generating a composite signal in a closed loop servo signal system of a data recording system used to drive a recording head to any given position within a dynamic range of a servo tracks includes an optical pickup system for generating optical spots focused on a recording medium, the spots separated by equal distances across a track, the optical pickup system receiving a set of reflectances from the spots, a media system for providing the servo tracks responsive to optical spot illumination, an electric system for generating a set of filtered signals from the reflectances and for generating a set of S-curves by pair wise subtraction of the filtered signals, a processing system to generate a composite servo position signal from the S-curves and filtered reflectances, and a servo system for driving the recording head to a desired position by comparing the desired position to a measured position from the composite servo position.

Claims

1. A triple push pull optical tracking method comprising:

receiving a set of three reflectance values from three optical spots on a recording medium in an optical pickup system;

generating three S-curves by pair-wise subtraction of reflectance values;

generating a linear position estimate by processing the S-curves; and

servoing the optical pickup system to the recording medium.

2. The method of claim 1 wherein the three reflectance values are digitized.

3. The method of claim 1 wherein equal distances separate the three optical spots across a track.

4. The method of claim 1 wherein servoing the optical pickup system comprises comparing a desired position of the optical pickup system to a measured position from the linear position estimate.

5. The method of claim 1 wherein the recording medium is a linear magnetic tape.

6. The method of claim 5 wherein the three optical spots result from servo tracks on a magnetic side of the linear magnetic tape.

7. The method of claim 5 wherein the three optical spots result from servo tracks on a non-magnetic side of the linear magnetic tape.

8. The method of claim 1 wherein the recording medium is an optical disk.

9. A triple push-pull system for generating a composite signal in a closed loop servo signal of a data recording system comprising:

optical pickup system for generating three optical spots focused on a recording medium, the spots separated by equal distances across a track, the optical pickup system receiving a set of reflectances from the three spots;

media means for providing the servo tracks responsive to optical spot illumination;

electronic means for generating a set of three filtered signals from the three reflectances and generating a set of three S-curves by pair-wise subtraction of the filtered signals;

processing means to generate a composite servo position signal from the S-curves and filtered reflectances; and

servo means for driving the optical pickup system to a desired position by comparing the desired position to a measured position from the composite servo position.

10. The system of claim 9 wherein the media means is a linear magnetic tape system.

11. The system of claim 10 wherein the servo tracks are provided on a magnetic side of a recording medium of the linear magnetic tape system.

12. The system of claim 10 wherein the servo tracks are provided on a non-magnetic side of a recording medium of the linear magnetic tape system.

13. The system of claim 9 wherein the optical spots are separated by one-third track pitch in a direction across the servo tracks.

14. The system of claim 10 wherein a servo track comprises a series of marks in a form of depressed pits on a back coating of the recording medium.

15. The system of claim 12 wherein a servo track comprises a series of marks in a form of depressed pits on a back coating of the recording medium.

16. The system of claim 9 wherein each reflectance value maximum amplitude is normalized to a constant value.

17. The system of claim 9 wherein processing means to generate a composite servo position signal from the S-curves and filtered reflectances comprise:

choosing the pair of reflectance values with the largest amplitude gradient; and

adjusting the chosen s-curve position estimate for the zone based on a slope and an offset.

18. The system of claim 9 wherein individual s-curve position estimates are blended together to generate a continuous position estimate as individual linear sections are traversed.

19. The system of claim 9 wherein the closed loop servo system comprises a digital processor, the digital processor used to perform the composite servo position calculations from the reflectance values, derive a position error signal based on the position estimate and a commanded position, compensate the error signal in such a way as to reduce the lateral tape motion, and command an actuator to follow the lateral tape motion.

20. A method of generating a composite signal in a closed loop servo signal of a data recording system comprising:

generating in an optical pickup system three optical spots focused on a recording medium, the spots separated by equal distances across a track;

receiving a set of reflectances from the three spots;

generating a set of three filtered signals from the three reflectances;

generating a set of three S-curves by pairwise subtraction of the filtered signals;

generating a composite servo position signal from the S-curves and filtered reflectances; and

driving the optical pickup system to a desired position by comparing the desired position to a measured position from the composite servo position.

21. The method of claim 20 wherein the recording medium is a linear magnetic tape system.

22. The method of claim 21 wherein servo tracks are provided on a magnetic side of the recording medium of the linear magnetic tape system.

23. The method of claim 21 wherein servo tracks are provided on a non-magnetic side of a recording medium of the linear magnetic tape system.

24. The method of claim 20 wherein the optical spots are separated by one-third track pitch in a direction across servo tracks.

25. The method of claim 20 wherein a servo track comprises a series of marks in a form of depressed pits on a back coating of the recording medium.

26. The method of claim 23 wherein a servo track comprises a series of marks in a form of depressed pits on a back coating of the recording medium.

27. The method of claim 20 wherein generating the set of three filtered signals comprises:

converting electronic current from the reflectances to voltages;

generating the S-curves; and

reducing noise in the S-curves.

28. The method of claim 20 wherein each reflectance value maximum amplitude is normalized to a constant value.

29. The method of claim 20 wherein generating a composite servo position signal from the S-curves and filtered reflectances comprise:

choosing the pair of reflectance values with the largest amplitude gradient; and

adjusting the chosen s-curve position estimate for the zone based on a slope and an offset.

30. The method of claim 20 wherein individual s-curve position estimates are blended together to generate a continuous position estimate as individual linear sections are traversed.