Fall detection scheme using FFS

1. A disk drive comprising:

a disk;

a head; and

control circuitry comprising a servo control system operable to actuate the head over the disk, the control circuitry configured to:

determine a magnitude of acceleration readings, the acceleration readings involving at least three degrees of freedom,

confirm a free fall when a magnitude of the acceleration readings is less than a first threshold, and

confirm a tilt drop when the magnitude is between the first and a second threshold.

2. The disk drive of claim 1 , wherein the control circuitry is further configured to actuate the head to park on a ramp of the disk drive, and monitor a shock impact when the control circuitry confirms the free fall or the tilt drop.

3. The disk drive of claim 2 , wherein the control circuitry is further configured to:

monitor the shock impact until the magnitude is within a range of 1 g, and

when the magnitude is within the range, disable detection of the tilt drop for a preset period of time and unload the head from the ramp.

4. The disk drive of claim 1 , wherein the control circuitry is further configured to disable detection of the tilt drop when an integration based on a difference between the magnitude and 1 g is positive.

5. The disk drive of claim 4 , wherein the control circuitry is further configured to re-enable detection of the tilt drop when the magnitude is within a range of 1 g for another preset period of time.

6. The disk drive of claim 1 , wherein the acceleration readings comprise readings along an X, Y and Z axis.

7. A control circuitry comprising:

a servo control system operable to actuate a head over a disk; and

one or more integrated circuits configured to:

determine a magnitude of acceleration readings for a disk drive, the acceleration readings involving at least three degrees of freedom,

confirm a free fall when a magnitude of the acceleration readings is less than a first threshold, and

confirm a tilt drop when the magnitude is between the first and a second threshold.

8. The control circuitry of claim 7 , wherein the one or more integrated circuits are further configured to actuate the head of the disk drive to park on a ramp, and monitor a shock impact when the control circuitry confirms the free fall or the tilt drop.

9. The control circuitry of claim 8 , wherein the one or more integrated circuits are further configured to:

monitor the shock impact until the magnitude is within a range of 1 g, and

when the magnitude is within the range, disable detection of the tilt drop for a preset period of time and unload the head from the ramp.

10. The control circuitry of claim 7 , wherein the one or more integrated circuits are further configured to disable detection of the tilt drop when an integration based on a difference between the magnitude and 1 g is positive.

11. The control circuitry of claim 10 , wherein the one or more integrated circuits are further configured to re-enable detection of the tilt drop when the magnitude is within a range of 1 g for another preset period of time.

12. The control circuitry of claim 7 , wherein the acceleration readings comprise readings along an X, Y and Z axis of the disk drive.

13. A method comprising:

determining a magnitude of acceleration readings for a disk drive, the acceleration readings involving at least three degrees of freedom,

confirming a free fall when a magnitude of the acceleration readings is less than a first threshold, and

confirming a tilt drop when the magnitude is between the first and a second threshold.

14. The method of claim 13 , further comprising actuating a head of the disk drive to park on a ramp, and monitoring a shock impact when the free fall or the tilt drop is confirmed.

15. The method of claim 14 , further comprising:

monitoring the shock impact until the magnitude is within a range of 1 g, and

when the magnitude is within the range, disabling detection of the tilt drop for a preset period of time and unloading the head from the ramp.

16. The method of claim 13 , further comprising disabling detection of the tilt drop when an integration based on a difference between the magnitude and 1 g is positive.

17. The method of claim 16 , further comprising re-enabling detection of the tilt drop when the magnitude is within a range of 1 g for another preset period of time.

18. The method of claim 13 , wherein the acceleration readings comprise readings along an X, Y and Z axis of the disk drive.