Abstract

Consistent, repeatable high quality materials processing, using fibre 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 the high-bandwidth optical range sensor described herein allows the use of such robots for fibre manipulation and hence facilitates high quality laser cutting and welding operations using equipment that may already exist. Radiation from a low power laser beam is focussed onto a workpiece surface, light reflected from the surface is collected through a main lens and directed into an imaging lens, which focuses the signal to two positions after being split by a beam splitter. The irradiances of the two beams are detected by photodiodes placed behind pinhole apertures positioned fore and aft of the two focal positions. 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 ±6 mm, its effectiveness in controlling the stand-off distance for laser materials processing applications is assessed.

© 1994 IEEE