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Evaluation of Optical Distortion Measurement Techniques for Curved Optical Surfaces
Completed
TRL 4 (started at 3, targeting 4)
Description
The Applied Physics Lab created a computer based image processing system to allow inspection of the new visors being developed for the Artemis Program. This system was based on an ASTM standard where the distortion of an image is used to determine the optical aberrations in a visor, but this approach is restricted to small fields-of-view (small areas of the visor) and is limited in its ability to reliably detect and measure distortion. From our experience with flat surface inspection, we know that other optical techniques can offer higher sensitivity and accuracy. This project would be to explore these other approaches, compare and contrast them to one another, and adapt at least one to curved surface inspection. The end goal is to offer better optical metrology for the evaluation of visors and other curved optical components.
Benefits
We were asked to look at characterizing the distortion in terms of diopter variations in newly manufactured Artemis visors (see Figure 1 below). There was no off the shelf tool to automate the inspection process so we developed a method of performing this measurement using a backlit grid of dots, a high resolution digital lab camera, and image acquisition/ machine vision software. We were able to achieve accuracy required by the customer but with little to room to spare. We will look at options to adapt our flat pane distortion measurement techniques to curved surfaces and then test and characterize these methods. While we automated the image comparison method described in ASME and ISO standards, there may be room for some further improvements through proper grid selection, changes in optics, and test geometry. Moiré interferometry/ Schlieren techniques are an improvement over image comparison for flat windows and the same may hold true for inspection of curved surfaces. The challenge will be to come up with the proper geometry to allow the rays of light to follow the radius of curvature and strike normal to the curved surface. Locating the curved surface under test closer to the focus of the spherical mirror should help enable this measurement using the moiré technique previously explored.
Details
| Technology area | Ground, Test, and Surface Systems > Test and Qualification Environments |
| Program | Center Innovation Fund: KSC CIF (KSC CIF) |
| Lead organization | Kennedy Space Center, Kennedy Space Center, FL |
| Start date | 2020-10-01 |
| End date | 2021-09-30 |
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