Accelerometer-based differential free fall detection system, apparatus, and method and disk drive protection mechanism employing same
Embodiments of the present invention employ differential acceleration computations for detecting free fall conditions. The differential acceleration computations can be based on two-axis or three-axis acceleration measurements, and therefore can be implemented using a two-axis accelerometer or a three-axis accelerometer (or combinations of accelerometers that enable acceleration measurements in two or three axes). When a free fall condition is detected, an appropriate signal can be generated, for example, to place a HDD in a protected state before damage is likely to occur. Differential acceleration measurements can also be used to detect a “safe” condition following a free fall condition.
1. A method for signaling a free fall condition, the method comprising:
measuring acceleration for each of a plurality of axes in each of a plurality of successive sample periods;
computing an acceleration delta for each axis for each of the plurality of successive sample periods, wherein each acceleration delta represents a change in acceleration between two successive sample periods;
computing, for each of the plurality of successive sample periods, a sum of the squares of the acceleration deltas from that sample period; and
signaling a free fall condition, if the sum falls within a first predetermined range for each of a first predetermined number of consecutive sample periods.
2. A method according to claim 1 , wherein the plurality of axes consists of two axes.
3. A method according to claim 1 , wherein the plurality of axes consists of three axes.
4. A method according to claim 1 , wherein the first predetermined range includes values exceeding a first predetermined threshold.
5. A method according to claim 1 , further comprising:
placing a device in a protected state based upon such signal.
6. A method according to claim 5 , wherein the device is a hard drive.
7. A method according to claim 1 , further comprising:
subsequent to signaling the free fall condition, testing for a safe condition and signaling the safe condition, wherein the safe condition is characterized by the sum falling within a second predetermined range for each of a second predetermined number of consecutive sample periods.
8. A method according to claim 7 , wherein the second predetermined range includes values less than or equal to a second predetermined threshold.
9. A method according to claim 7 , further comprising:
prior to testing for the safe condition, testing for an impact condition in which the sum falls within a predetermined impact range for at least one sample period and testing for the safe condition only after detecting the impact condition.
10. Apparatus comprising:
an accelerometer arrangement providing acceleration outputs for each of a plurality of axes;
a free fall detector in communication with the acceleration outputs, wherein the free fall detector is configured to measure acceleration for each of the plurality of axes in each of a plurality of successive sample periods based on the acceleration outputs; compute an acceleration delta for each axis for each of the plurality of successive sample periods, wherein each acceleration delta represents a change in acceleration between two successive sample periods; compute, for each of the plurality of successive sample periods, a sum of the squares of the acceleration deltas from that sample period; and signal a free fall condition if the sum falls within a first predetermined range for each of a first predetermined number of consecutive sample periods.
11. Apparatus according to claim 10 , wherein the accelerometer arrangement includes a single two-axis accelerometer for providing acceleration outputs for each of two axes.
12. Apparatus according to claim 10 , wherein the accelerometer arrangement includes a single three-axis accelerometer for providing acceleration outputs for each of three axes.
13. Apparatus according to claim 10 , wherein the accelerometer arrangement includes a plurality of accelerometers for providing acceleration outputs for each of the plurality of axes.
14. Apparatus according to claim 10 , wherein the first predetermined range includes values exceeding a first predetermined threshold.
15. Apparatus according to claim 10 , further comprising:
a device operably coupled to enter a protected state in response to the signal indicating the free fall condition.
16. Apparatus according to claim 15 , wherein the device is a hard drive.
17. Apparatus according to claim 10 , wherein the free fall detector is further configured to test for a safe condition subsequent to signaling the free fall condition and signal the safe condition, wherein the safe condition is characterized by the sum falling within a second predetermined range for each of a second predetermined number of consecutive sample periods.
18. Apparatus according to claim 17 , wherein the second predetermined range includes values less than or equal to a second predetermined threshold.
19. Apparatus according to claim 17 , wherein the free fall detector is further configured to test for an impact condition prior to testing for the safe condition and test for the safe condition only after detecting the impact condition, wherein the impact condition is characterized by the sum falling within a predetermined impact range for at least one sample period.
20. Apparatus according to claim 10 , wherein the apparatus is one of:
a portable computer;
a portable media player; and
a handset.
21. Apparatus comprising a computer readable medium having embodied therein a computer program for detecting a free fall condition, the computer program comprising:
first program code for measuring acceleration for each of a plurality of axes in each of a plurality of successive sample periods;
second program code for computing an acceleration delta for each axis for each of the plurality of successive sample periods, wherein each acceleration delta represents a change in acceleration between two successive sample periods;
third program code for computing, for each of the plurality of successive sample periods, a sum of the squares of the acceleration deltas from that sample period; and
fourth program code for signaling a free fall condition, if the sum falls within a first predetermined range for each of a first predetermined number of consecutive sample periods.
22. Apparatus according to claim 21 , further comprising:
fifth program code for testing for a safe condition subsequent to signaling the free fall condition and signaling the safe condition, wherein the safe condition is characterized by the sum falling within a second predetermined range for each of a second predetermined number of consecutive sample periods.
23. Apparatus according to claim 22 , further comprising:
sixth program code for testing for an impact condition and enabling such testing for the safe condition only after the impact condition is detected, wherein the impact condition is characterized by the sum falling within a predetermined impact range for at least one sample period.