Performance evaluation experiments on a laser spot triangulation probe

Laser triangulation probes are increasingly used for dimensional measurements in a variety of applications. At the National Institute of Standards and Technology, we have recently explored the use of laser spot triangulation probes to determine dimensional features such as height and width of channels in a fuel cell plate. To assess the suitability of the probes for performing these dimensional measurements, we designed several experiments that highlighted different error sources in the probes. This report is a summary of those experiments. Numerous studies have been reported in the literature on error sources in laser triangulation probes utilizing artifacts of varying shape (form), color, reflectivity, surface finish, etc. However, our experiments are targeted towards establishing bounds on errors when measuring simple linear dimensions such as height and width on prismatic objects of a single color and material. Our scope is indeed narrow, but intentionally so; it is our objective to highlight the influence of a number of “hidden performance attributes” [1] that impact accuracy of even simple linear dimensional measurements so that it may be of use to others who perform similar measurements.

► Study error sources in laser triangulation probes and their effect on dimensional measurements.
► Document effect of probe spot size on width measurements.
► Quantify the effect of side wall and secondary reflections on width measurements.
► Study the influence of material and optical properties of the part on height and width measurements.
► Summary: errors of the order of hundreds of micrometers to several millimeters are possible.