Free fall detection system for protecting hard drives in mobile devices
In a method for detecting free fall, a first acceleration parallel to a first axis, a second acceleration parallel to a second axis perpendicular to the first axis, and a third acceleration parallel to a third axis perpendicular to the first axis and to the second axis are measured. A sum of a first absolute value of the first acceleration, a second absolute value of the second acceleration, and a third absolute value of the third acceleration is calculated, and the free fall is detected as a function of the sum.
1. A method for detecting a free fall of a mobile device, comprising:
recording a first acceleration of the mobile device provided by a first acceleration sensor, the first acceleration being parallel to a first axis;
recording a second acceleration of the mobile device provided by a second acceleration sensor, the second acceleration being parallel to a second axis perpendicular to the first axis;
recording a third acceleration of the mobile device provided by a third acceleration sensor, the third acceleration being parallel to a third axis perpendicular to the first axis and to the second axis;
determining first, second and third absolute values of the first, second and third accelerations, respectively;
determining a sum of the first, second and third absolute values;
detecting the free fall of the mobile device solely as a function of the sum; and
generating a warning signal responsive to detecting the free fall.
2. The method as recited in claim 1 , wherein the first acceleration, the second acceleration, and the third acceleration are recorded from a triple-axis acceleration sensor.
3. The method as recited in claim 2 , wherein the triple-axis acceleration sensor is configured to generate digital signals.
4. The method as recited in claim 1 , further comprising:
comparing the sum to a predetermined threshold value.
5. The method as recited in claim 4 , further comprising:
generating the warning signal if the sum is below the threshold value.
6. The method as recited in claim 5 , wherein the warning signal indicates that the free fall is present.
7. The method as recited in claim 6 , further comprising:
locking a write-read head of a hard drive of the mobile device if the free fall is detected.
8. A device for detecting a free fall of a mobile device, comprising:
a triple-axis acceleration sensor configured to generate:
a first acceleration of the mobile device parallel to a first axis,
a second acceleration of the mobile device parallel to a second axis perpendicular to the first axis, and
a third acceleration of the mobile device parallel to a third axis perpendicular to the first axis and to the second axis; and
an evaluation circuit configured to:
record the generated first, second and third accelerations,
determine first, second and third absolute values of the first, second and third accelerations, respectively,
determine a sum of the first, second and third absolute values, and
detect the free fall of the mobile device solely as a function of the sum.
9. The device as recited in claim 8 , wherein the device is implemented as a microelectromechanical system.
10. The device as recited in claim 9 , wherein the triple-axis acceleration sensor and the evaluation circuit are integrated in a sensor housing.
11. The device as recited in claim 8 , further comprising:
a lock for locking a write-read head of a hard drive of the mobile device if the free fall is detected.
12. The method of claim 1 , wherein the first, the second, and the third acceleration sensors are part of a single triple axis acceleration sensor.