Patent ID: 6344625
Filing Date: 2002-02-05
Classification: B23K

Abstract:
A method for monitoring the size variation and the focus shift of a weld pool simultaneously or either the size variation or the focus shift of a weld pool in a laser welding, the method comprising the steps of:transmitting a laser beam through an aperture which limits a size of a laser beam; focusing transmitted laser beam with at least one lens with some chromatic aberration but minimum spherical aberration on a workpiece; measuring a thermal radiation from a weld pool through the at least one lens, and through the aperture or any other aperture limiting a size of a weld pool wherein the thermal radiation is measured; separating the thermal radiation and the laser beam reflected from the workpiece with a dichromatic mirror; splitting the thermal radiation with dichromatic beam splitters into at least three spectral bands; filtering each spectral band of the thermal radiation with a narrow band-pass optical filter; detecting each narrow band-pass filtered thermal radiation with a single-element detector as a electrical signal; sampling electrical signals as detector signals from the single-element detectors digitally; processing a plurality of digitized detector signals as processed signals so that the processed signals generator a digital signal, a size variation signal, and/or another digital signal, a focus shift signal; and generating, from the size variation signal and the focus shift signal, a size error signal representative of the size variation of a weld pool and/or a focus error signal representative of the focus shift of a weld pool from the image plane of the aperture formed by the at least one lens at the wavelength of the laser beam.