Patent ID: 7400317

Claim:
An input device comprising: a captive disc movably suspended over a sensor, said captive disc having an active surface facing said sensor, the active surface having a predetermined pattern; wherein said sensor is adapted to take successive images of the predetermined pattern of the active surface of said captive disc and compare the successive images of the predetermined pattern to determine movement of said captive disc; a horizontal spring allowing resistive movement of said captive disc in horizontal directions; and a vertical spring allowing resistive movement of said captive disc in vertical directions; wherein; the horizontal spring returns said captive disc to a horizontal rest position when said captive disc is released; the vertical spring returns said captive disc to a rest plane when said captive disc is released; said sensor determines the movement of said captive disc by taking the successive images of the active surface when said captive disc, in response to finger pressure, is proximal to a focal plane below the rest plane so that the active surface is in focus for said sensor; and said sensor does not determine the movement of said captive disc when said captive disc is released, by removal of the finger pressure, from the focal plane so that the active surface becomes out of focus for said sensor; wherein; said active surface comprises a navigation area having a first pattern and a border area having a second pattern generally surrounding said navigation area; and the pattern of the border area has a lower density than the pattern of the navigation area so the border area becomes out of focus for the sensor faster than the navigation area when said captive disc moves from the focal plane to the rest plane.