Investigation of Line-Scan Dispersive Interferometry for In-Line Surface Metrology

Advanced manufacturing techniques enable ultra-precision surfaces to be fabricated with various complicated and large-area structures. For instance, the cost-effectiveness of Roll-to-Roll (R2R) manufacturing technology has been widely demonstrated in industries making high volume as well as large-area foil products and flexible electronics. Evaluation of these fine surfaces by an expensive trial-and-error approach is unadvisable due to the high scrap rate. Therefore quality control using in-line metrology of the functional surface plays an important role in the success of employing R2R technology by enabling a high product yield whilst guaranteeing high performance and a long lifespan of these multi-layer products.
This thesis presents an environmentally robust line-scan dispersive interferometry (LSDI) technique that is suitable for applications in in-line surface inspection. Obtaining a surface profile in a single shot allows this interferometer to minimise the effect of external perturbations and environmental noise. Additionally, it eliminates the mechanical scanning and has an extended axial measurement range without the 2π phase ambiguity problem by dispersing the output of the spectrometer onto the camera. Benefiting from high-speed camera, general-purpose graphics processing unit and multi-core processor computing technology, the LSDI can achieve high dynamic measurement with a high signal-to-noise ratio and is effective for use on the shop floor.
Two proof-of-concept prototypes aimed at different applications are implemented. The cylindrical lens based prototype has a large lateral range up to 6 mm and can be used for characterisation of additively manufactured surface texture, surface form and surface blemish. The second prototype using a 4X microscope objective with a diffraction limited lateral resolution (~ 4 µm) is aiming at characterisation of surface roughness, micro-scale defects, and other imperfections of the ultra-precision surfaces. System design, implementation, fringe analysis algorithms and system calibrations are presented in detail in this thesis. Their performances are evaluated experimentally by measuring several standard step heights as well as Al2O3 coated polyethylene naphthalate (PEN) films. The measurement results acquired using both prototypes and a commercial available instrument (Talysurf CCI 3000) align with each other acceptably. This shows that the developed metrology sensors may potentially be applied to production lines such as R2R surface inspection where only defects present on the surface are concerned in terms of quality assurance. Implementation of these prototypes offers an attractive solution to improve manufacturing processing and reliability for the products in ultra-highprecision engineering.