Patent ID: 7268866

Claim:
A method for inspecting a weld seam between two plastic parts of a workpiece made of weldable material, the method comprising producing the weld seam by using a laser beam, wherein one of the plastic parts of the workpiece is essentially transparent to laser radiation and the other plastic part absorbs the laser radiation, determining the quality of the weld seam produced in this way by optical means; the method further comprising after producing the weld seam by laser radiation, directing an electromagnetic control radiation against the weld seam; wherein one of the two plastic parts is also transparent to the control radiation, introducing the control radiation into the interior of the transparent plastic part such that the control radiation impacts the welding seam which has already solidified, wherein the control radiation is reflected at a contact surface between the plastic parts and at an interface of the weld seam and is partly transmitted back out of the workpiece; during the measurement of the exiting radiation, measuring only the reflected radiation emanating from an already solidified location of the weld seam and supplying the reflected radiation to an evaluation unit; conducting the control radiation emanating from the workpiece on its path to the measuring location partially along optical elements along which the laser light is also conducted in an opposite direction to the welding point in the workpiece; and, using the evaluation unit, detecting a disturbance of the measured exiting radiation caused by an imperfect weld and a reaction triggering a reaction in a monitoring device by the disturbance of the measured exiting radiation.