Patent ID: 7912671

Claim:
A method for determining coordinates of an arbitrarily shaped pattern on a surface in a deflector system, including: a) selecting a reference clock signal that defines a movement in a first direction (X), b) providing a micro sweep that repeatedly scans the surface in a second direction (Y), perpendicular to the first direction (X) c) selecting a measurement clock signal that is related to the signal used to start each micro sweep in the second direction (Y), d) adjusting the speed of the movement in the first direction (X) to determine the distance between the start of each micro sweep, e) performing a first run that include the steps of: e1) starting a first micro sweep at a starting position, e2) detecting at least one edge of the arbitrarily shaped pattern when the pattern is moved in the first direction (X) relative the deflector system, e3) generating at least one event if the edge of the pattern is detected, and e4) counting using a counter the number of micro sweeps performed until each event is generated, and f) calculating a coordinate of the edge, for each event, in the first direction (X) using the number of performed micro sweeps wherein more than one run as defined in step e) is performed, for each run the starting position in step e1) is pseudo randomly selected, thereby generating pseudo randomly distributed micro sweeps between each run.