Meaning
Optical measurement techniques use structured light to create a three dimensional map of a surface with high precision. In fringe pattern projection a series of black and white stripes is projected onto a component and the resulting distortion is captured by a camera. This method is widely used for the inspection of solder paste deposits and the flatness of printed circuit boards.
Phase Shifting
Movement of the stripes across the object allows the system to calculate the height at every pixel with sub micron resolution. The fringe pattern projection software uses the phase information to reconstruct the surface geometry even when the material is reflective or dark. This technique is more accurate than simple laser triangulation for complex shapes.
Surface Reconstruction
Mathematical models turn the 2D images of the distorted patterns into a 3D cloud of points. The fringe pattern projection system compares this cloud against the CAD model of the part to identify any deviations in height or volume. This analysis is performed in real time as the boards move through the inspection machine.
Resolution Limit
Density of the stripes and the resolution of the camera sensor determine the smallest detail that the system can detect. Fringe pattern projection is limited by the optical properties of the lens and the quality of the light source. Improving the contrast of the patterns and reducing the noise in the sensor can extend the performance to even smaller components.
