Process optimization controller for robotic laser machining

This work details the performance assessment of a high-bandwidth optical range sensor for local stand-off control of a robotically manipulated optical fiber laser beam delivery system. Consistent, repeatable high quality materials processing, using fiber optically delivered Nd3+-YAG laser radiation requires precise local control of stand-off distance. Unless specifically designed for laser processing applications, many robots produce a jerking incremental trajectory and usually suffer from position dependent displacement of the end effector. With the addition of a focal height servomechanism performance of the system can be considerably improved. The high-bandwidth optical range sensor described herein allows the use of such robots for fiber optically delivered laser beams enabling high quality laser cutting and welding operations using equipment that may already exist. Radiation from a low power laser diode is focused onto a workpiece surface; light reflected from the surface is collected through a main lens and directed into an astigmatic lens, which focuses the signal onto a quadrant photodiode. A differential amplifier is used to generate an output signal that determines the magnitude and direction of any workpiece displacement. The system facilitates a measuring range of ±5 mm; its effectiveness in controlling the stand-off distance for laser materials processing applications is assessed.