Precision Measurement Method of Misalignment, Cracks, Contours, and Gaps in Aerospace Industry

Precise measurement of surface defects is of critical importance in parts manufactured for the aerospace industry. The measurements of different characteristics of the testing samples are presented in this paper. They are measurement of (i) micro scratches, cracks, (ii) contours and (iii) gaps. The instrumentation setup for the measurement of the above parameters includes laser source, collimators, imaging and vision acquisition system, three axis (xyz) stage, graphical programming and computerized image analyzer. For measurement of the major geometrical dimensions of scratches and cracks a low power (2mW) Helium-Neon (HeNe) laser source has been used. Due to relatively high wavelength of the red photons irradiated from the HeNe laser source, the incident laser beam possesses a very high level of reflectivity and negligible penetration. The experiments listed in this paper explore unique optical methods using a line laser. The advantage for using this type of laser is that it generates low energy red photons having about two to three electron-volt energy and possessing perfect reflectivity. The low energy photons have negligible low penetration. The paper explains a methodology for non-contact measurement of radius of curvature on the finished surface of manufactured parts. In addition, a hybrid approach consisting of laser based triangulation, photogrammetry and edge detection techniques has been investigated to measure inner surfaces of parts that have limited access, especially where human presence is impossible. The system is capable of detecting and measuring misalignments, gaps, inclinations as well as surface variations such as cracks and dents. The system employs the accuracy and speed of measurement of triangulation systems and combines these with the mobility and cost effectiveness of photogrammetry and edge detection techniques. In addition to gap and alignment offset inspections, and the instrument enables angle measurements, surface texture examinations and other inspections needed to be done inside assemblies with narrow openings, with its compact body. This topical area provides an ongoing thesis topic for graduate engineering students at the masters level.