Optical Coherence Tomography for Non-Contact Evaluation of Fastener Flushness

Abstract

Outside of the medical field, spectral domain optical coherence tomography (SD-OCT) is sparsely used. As such, we explored the possibility and practicality of using SD-OCT as a tool to evaluate fastener flushness and countersink surface profiles. A SD-OCT device was built with a handheld galvanometer scanner that weighed only 0.5 lb. Not only it does not require scan center alignment, but it is also capable of quickly producing measurements of fastener flushness, radius, slant angle, countersink edge radius, and surface angle. With the X-Y two-line scanning method, measurements take only 90 ms. The SD-OCT device used to obtain these measurements uses a lens with 60 mm focal length and a broadband light source of 840 nm center wavelength and 45 nm spectral bandwidth. With these components, the SD-OCT device is able to provide an axial depth resolution of 8.5 μm and a lateral resolution of 19 μm. The axial depth resolution can be improved by using a wider bandwidth light source. Furthermore, the device is able to produce 3D surface profiles of fasteners and countersinks using multi-line scans.