Booming demand for high speed and high accuracy 3D inspection, especially in the area of manufacturing of electronic devices and components, causes fast progress in research related to this area and significant improvement in these systems capabilities, specification and features. Accuracy can be considered as one of the most important features for 3D machine vision inspection systems, probably along with speed and robustness.
Phase shift based systems are believed to be among the most accurate 3D measurement systems with resolution at sub-micron level, though to achieve such a high resolution and accuracy considerable efforts should be made and various physical effects should be taken into consideration.
3D accuracy problems comprise of 2D accuracy problems, such as camera radial and perspective distortions, subpixel measurement problems, etc. combined with special issues related specifically to the phase-shift measurement profilometry. Among them there are distortions of the projected light pattern, including projector radial, perspective distortions and non-sinusoidality of the projected pattern (harmonic distortion) and dynamic range problems caused by camera's signal to noise ratio and by constraints of limited digitized signal bit width. To eliminate or minimize negative influence of the above mentioned factors, a number of measures should be carried out when making 3D measurement head design followed by compensation and calibration procedures. Experimental results on various accuracy problems based on real 3D measurement system developed by authors as well as simulation results are presented in this paper.