Patent ID: 8445815

Claim:
A method of monitoring performance of a circular lens in a laser processing machine head monitoring system, the method comprising: obtaining a circular lens designed to transmit a processing laser beam and comprising two broad surfaces bounded by a peripheral surface, wherein a portion of the peripheral surface comprises a delineated surface segment bounded on either side by a circular portion of the peripheral surface, and wherein the delineated surface segment is arranged to reflect or transmit a light beam through the lens along a path substantially perpendicular to an axis of the processing laser beam; inserting the circular lens in a lens holder, which is arranged in the laser processing machine and comprises a lens retaining device, by aligning the delineated surface segment of the lens with the lens retaining device; coupling a beam of light into the lens through the peripheral surface at a first location, through the lens, and toward the peripheral surface at a second location; monitoring light that is internally reflected from the second location of the peripheral surface to determine lens performance; determining, based on a change in intensity of the reflected light, whether lens performance has decreased; if lens performance has decreased, removing the lens from the lens holder to clean or replace the lens; and inserting a cleaned or new circular lens into the lens holder by aligning the delineated surface segment of the lens with the lens retaining device; wherein the delineated surface segment comprises the first location or the second location of the peripheral surface or both.