System and method for detecting head instability
View Patent ↗Embodiments of the present invention relate to systems, methods, and computer readable media for calibrating storage devices such as hard drives. A testing system is connected to a group of storage devices that are being prepared for release and eventual sale. Alternately, a storage device may be connected to an end-user system for which it is in use. The storage devices are tested for head instability. A lower frequency test pattern is performed, which induces a stronger magnetic field. A measurement of servo gain control is taken while reading from a disk and compared to a baseline for servo gain control. If the variance is larger than a predetermined amount, then the read/write head is determined to be unstable.
1. A method for detecting a read/write head that is prone to instability, the method comprising:
determining gain control values when not reading from a rotatable storage medium;
performing read operations on the rotatable storage medium; and
varying a magnetic field in a test pattern while performing the read operations, wherein the magnetic field is varied at a low frequency, the low frequency configured to cause excitation of a free layer of the read/write head.
2. The method of claim 1 , wherein the low frequency is less than 1/(16T) wherein T is a cycle of a data clock.
3. The method of claim 1 , further comprising:
determining gain control values while performing the read operations on the rotatable storage medium.
4. The method of claim 3 , further comprising:
determining a variance in the gain control values while performing the read operations on the rotatable storage medium.
5. The method of claim 4 , further comprising:
determining that a read/write head is unstable when the variance is larger than a predetermined amount.
6. The method of claim 5 , wherein the variance is a result of the test pattern.
7. The method of claim 1 , wherein the frequency is less than 1/(4T) wherein T is a data clock cycle.
8. The method of claim 1 , wherein the frequency is less than 1/(8T) wherein T is a data clock cycle.
9. A machine readable medium having instructions stored thereon that when executed by a processor causes a system to:
determine gain control values when not reading from a rotatable storage medium;
perform read operations on the rotatable storage medium; and
vary a magnetic field in a test pattern while performing the read operations, wherein the magnetic field is varied at a low frequency, the low frequency configured to cause excitation of a free layer of the read/write head.
10. The machine readable medium of claim 9 , wherein the low frequency is less than 1/(16T) wherein T is a cycle of a data clock.
11. The machine readable medium of claim 9 , further comprising instructions that when executed by the processor cause the system to:
determine gain control values while performing the read operations on the rotatable storage medium.
12. The machine readable medium of claim 11 , further comprising instructions that when executed by the processor cause the system to:
determine a variance when performing read operations in the test pattern.
13. The machine readable medium of claim 12 , further comprising instructions that when executed by the processor cause the system to:
determine that a read/write head is unstable when the variance is larger than a predetermined amount.
14. The machine readable medium of claim 13 , wherein the variance is a result of the test pattern.
15. The machine readable medium of claim 9 , wherein the frequency is less than 1/(4T) wherein T is a data clock cycle.
16. The machine readable medium of claim 9 , wherein the frequency is less than 1/(8T) wherein T is a data clock cycle.
17. A method for detecting a read/write head that is prone to instability, the method comprising:
determining gain control values when not reading from a rotatable storage medium;
performing read operations on the rotatable storage medium;
varying a magnetic field in a test pattern while performing the read operations, wherein the magnetic field is varied at a low frequency;
determining gain control values while performing the read operations on the rotatable storage medium;
determining a variance when performing the read operations in the test pattern on the rotatable storage medium; and
determining that a read/write head is unstable when the variance is larger than a predetermined amount.
18. The method of claim 17 , wherein the low frequency is less than 1/(16T) wherein T is a cycle of a data clock.
19. The method of claim 17 , wherein the frequency is less than 1/(4T) wherein T is a data clock cycle.
20. The method of claim 17 , wherein the frequency is less than 1/(8T) wherein T is a data clock cycle.
21. A storage device comprising:
a rotatable storage medium; and
a read/write mechanism configured to read from and write to the rotatable storage
medium, the read/write mechanism comprising a read/write head; and
a controller configured to:
determine gain control values when the read/write mechanism is not reading from the rotatable storage medium;
direct the read/write mechanism to perform read operations on the rotatable storage medium; and
vary a magnetic field in a test pattern while the read/write mechanism is performing the read operations, wherein the magnetic field is varied at a low frequency, the low frequency configured to cause excitation of a free layer of the read/write head.
22. A system for detecting unstable heads, the system comprising:
a test system configured to transmit testing instructions to hard drives;
a storage device comprising:
a rotatable storage medium;
a read/write mechanism configured to read from and write to the rotatable storage medium, the read/write mechanism comprising a read/write head; and
a controller, responsive to the testing instructions, configured to:
determine gain control values when the read/write mechanism is not reading from the rotatable storage medium;
direct the read/write mechanism to perform read operations on the rotatable storage medium; and
vary a magnetic field of a test pattern while the read/write mechanism is performing the read operations, wherein the magnetic field is varied at a low frequency, the low frequency configured to cause excitation of a free layer of a read/write head.