Free fall detection device
A free fall detection device capable of detecting a fall accompanied by rotation is provided. A fall accompanied by rotation is detected based on a waveform of an acceleration signal output from the acceleration detection unit and an angular velocity signal output from the angular velocity detection unit. A gravity center acceleration of the device to be protected is calculated from the acceleration detected by the acceleration detection unit and from the angular velocity detected by the angular velocity detection unit. Even when the device being protected rotates as it falls, the fall of the device can be detected from the detected acceleration or angular velocity. Further, by calculating the gravity center acceleration not affected by the rotation, it is possible to detect a fall of the device with high precision even if the device rotates as it falls.
1. A free fall detection device comprising:
an acceleration detection unit installed in the device to detect an acceleration of the device in each of three axial directions; and
a rotation decision unit to detect a fall, accompanied by a rotation of the device, from a waveform of the acceleration detected by the acceleration detection unit that has a substantially sinusoidal shape along one of the three axial directions, with a principal moment value of inertia that is an intermediate value among values corresponding to each of the three axial directions.
2. A free fall detection device according to claim 1 , wherein the waveform is a smooth, self-repeating waveform.
3. A free fall detection device according to claim 1 , further including a fall decision unit that detects a fall of the device when all of the accelerations in the three axial directions are almost zero.
4. A free fall detection device according to claim 3 , wherein the fall decision unit detects a fall of the device when all of the accelerations in the axial directions are smaller than a predetermined threshold.