updated 10:35 am EST, Tue December 11, 2007
Freefall sensor patent
Apple has today been granted a patent by the US Patent and Trademark Office, for a submission called Method and apparatus for detecting free fall. Many notebooks, and smaller devices as well, use hard drives which park their heads when a fall is detected; this prevents the heads from scratching or punching through storage platters. Sensing when to do this requires an accelerometer, and it is here that Apple has laid claim to two different concepts.
On a basic level, the concepts both work on the principle of breaking a closed circuit. When sitting in a stable position, an electrical switch remains closed, allowing uninterrupted flow; a sudden change in gravitational pull opens the switch, triggering head movement to a secure position.
In the first concept, the sensor is a conductive tube, with a beam or wire inserted. The insert is flexible, and normally remains in contact with the tube; once gravitational force lessens however, the insert leaves contact at one end of the tube, opening the circuit. The second concept changes the tube into a closed cylinder, with a beam fixed to its base. Partial insulation keeps the beam in place, but it is also touching a sphere, which in turn touches an oblique surface. Should the sensor start freefalling, the sphere will lose contact with the beam and/or the other surface, once again opening a circuit.
The patent is attributed to Paul James Wehrenberg, and was originally filed for in July of 2004.