Patent ID: 7994468

Claim:
A method of determining movement and/or distance of an input device and object relative to each other along a measuring axis transverse to an action plane, the method comprising the steps of supplying a modulated drive current to a laser device and illuminating an object surface with a measuring laser beam emitted from the laser cavity of said laser device, generating a measurement signal representative of changes in operation of the laser cavity, said changes being due to laser self-mixing interference of measuring beam radiation re-entering said laser cavity and an optical wave in said laser cavity and being representative of said movement along said measuring axis, and said measurement signal including a rising portion and a falling portion in each period thereof on which is superposed undulations having an offset frequency, the method further comprising determining distance and/or movement of said object and said input device relative to each other along said measuring axis by summing said offset frequency of a rising portion and a falling portion of said measurement signal, generating an electric signal representative of said distance and/or movement, and determining from the result of summing of said offset frequency of a rising and falling portion of said measurement signal if said input device is at a distance from said action plane and, if not, using a parameter of said measurement signal to measure speed and/or direction of movement in a measuring axis in said action plane of said input device and object relative to each other.