Patent ID: 7405727

Claim:
A method for detecting a lift condition from an illuminated surface portion of an optical motion sensing device comprising a light source and a photodetector device, said method comprising the steps of: a) illuminating a surface portion with radiation by means of the light source; b) detecting radiation reflected from the illuminated surface portion by means of the photodetector device; c) detecting and measuring relative motion of said optical motion sensing device with respect to the illuminated surface portion; d) outputting motion reports representative of a magnitude of the detected relative motion; steps a) to d) defining a flash period and being repeated at a selected flash rate, the method also comprising the steps of: e) comparing the magnitude of the detected relative motion with a predetermined threshold and adjusting accordingly the flash rate; f) comparing the adjusted flash rate with a predetermined flash rate threshold and determining there from whether said optical motion sensing device is moving or not; g) extracting motion features from said detected relative motion and counting a total number of said motion features and providing a loss-of-focus signal if said total number of motion features is less than a predetermined loss-of-focus threshold; wherein the method further comprises the steps of: h) switching between a first loss-of-focus threshold if said optical motion sensing device is moving and a second loss-of-focus threshold greater than said first loss-of-focus threshold if said optical motion sensing device is not moving; i) entering a low consumption mode if said loss-of-focus signal is provided.