Method of Measuring Relative Movement of an Object and an Optical Input Device Over a Range of Speeds

摘要

A method and optical module for measuring relative movement of an input device and object ( 15 ) along at least one measuring axis. A laser device ( 3 ) having a laser cavity is provided for generating a measuring beam ( 13 ) in respect of each measuring axis. The measuring beam ( 13 ) is used to illuminate the object ( 15 ) and measuring beam radiation reflected from the object ( 15 ) and re-entering the laser cavity generates a self-mixing effect in the laser and causes changes in operation of the laser cavity. A detector ( 4 ) is used to generate a measurement signal representative of these changes and an electronic processing circuit ( 18 ) selects, in dependence on the speed of relative movement, one of at least two parameters of the measurement signal for use in determining the speed and direction of relative a movement.