EVALUATION OF SPATIAL RESOLUTION AND THE NON-LINEARITY ANALYSIS FOR 3-D METROLOGY

Structured light systems (SLS) have become increasingly important for three-dimensional shape measurements. A quantitative evaluation of the spatial resolution is also becoming increasingly important. The spatial frequency response of the instrument is a reasonable metric for resolution and is commonly referred to as the instrument transfer function (ITF). We used the ITF to determine the capability of a commercial SLS the EinScan-pro using a step artifact. The ITF is similar to the modulation transfer function (MTF) of an imaging system, which describes how well the system images an object as a function of spatial frequency. Similarly, ITF describes the instrument response to the spatial frequency on the surface to be measured. Many optical measurement instruments use a camera for data acquisition and the optical transfer function will necessarily impose a limit on the instrument resolution. The ITF and the MTF metrics rely on the linearity of the measurement. Only a liner and shift invariant system can be used to uniquely define ITF/MTF. In this dissertation, we describe the use of the step artifact to determine the spatial resolution of a commercial SLS the EinScan-Pro. We check the use of the ITF over the MTF of the imaging system. We present a methodology to check the combined uncertainty for the ITF measurements including a method to check the applicability of the step artifact for the ITF measurements, the impact of the use of step artifact with different surface finishes, and the effect of the tilt and disposition of the artifact during the measurement. We also, present the use of the bispectrum for the non-linearity check of any kind of measurement which is applicable for both ITF/MTF measurements.