Triple push-pull optical tracking system
View Patent ↗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.
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.