Iterative Reconstruction Method With Auto-Updated Seed Point of Monoscopic Deflectometry for Off-Axis Aspheric

Abstract

The complex surface characteristics and misalignment of the geometric and optical axes of off-axis aspherical surfaces pose major challenges in the work to develop a measurement technique that is accurate, effective, and simple. Phase measurement deflectometry (PMD) is a more convenient and cost-effective method than interferometry for measuring specular objects. Nevertheless, monocular PMD necessitates complicated processes or costly additional equipment to resolve height-slope problems, whereas binocular PMD requires more time-consuming matching calculations. In this article, a novel iterative strategy based on monocular PMD technology with an automatically updated seed point during the iterative process is proposed, which only requires an approximate estimation about the height of one point (either the lowest, middle, or highest) on the measured off-axis aspheric component. The lowest, middle, or highest point of the reconstructed surface is used as the target of the auto-updated seed point in the iterative process, and the surface’s overall height information is then updated until the difference between two neighboring surface profiles is less than a certain threshold. Finally, the off-axis aspherical surface result is sent out. The proposed monocular PMD method is more straightforward, cost-effective, and simple, requiring only basic and low-cost tools to estimate the initial height of the measured component without the need to obtain the seed point’s 3-D coordinate. An experiment was performed to evaluate the feasibility and accuracy of the proposed method with the results of high-precision contact measurements as benchmarks. The results also indicated that even the uncertainty in the estimated initial height using common Vernier calipers has little effect on the measured surface shape, since it only leads to a small offset in the whole surface location.