CMMs (Coordinate Measuring Machines) can measure the geometric tolerances of various mechanical components, but even the most accurate CMM have submicron accuracy, which makes it difficult to use them for evaluating optical components. On the other hand, more accurate μ-CMMs that can measure small optical components have also been developed. Our μ-CMM (UA3P) has three high-precision plane mirrors to construct three-dimensional orthogonal XYZ coordinates and uses a frequency-stabilized HeNe laser as the length scale. By scanning the surface of the object with a tactile-type probe, it is possible to measure the profile of optical components such as aspherical or free-form mirrors and lenses with an accuracy of less than 50nm. In this paper, by using a high accurate flat bar mirror whose profile has been measured by National Institute of Advanced Industrial Science and Technology (AIST) and making error table to correct the profile of the Z reference mirror installed in the machine, we could reduce the profile error of Z reference mirror within 24nm on the 400mm square in the XY plane. For tactile-type measurement machine, if the measurement range is large, the measurement time may be over an hour. Even in such the case of long-time measurements, we verified a method of configuring the profile of measured surfaces by referring to base axis data measured in a short period of time, and confirmed that profile waviness can be detected with 10nm precision by comparison with an interferometer. The advantage of a mechanical tactile measuring machine is that it can evaluate the profile without being influenced by the profile of the object. This means that our μ-CMM can perform highly accurate absolute profile measurement and evaluation for large-area free-form samples that are difficult to measure with an interferometer.
Latest advancements in XR devices or the application of autonomous driving technology, the number of complicated freeform optical design components are increasing. And the demand for accurate measurement and evaluation is invaluable. In addition to standard form evaluation, there is an increasing demand for surface to surface decenter evaluation for optical characteristics, I.E.: bi-aspherical surfaces. We believe a standardized evaluation solution is lacking in the market. We are proposing a method for axial center evaluation between lens surfaces by synthesizing coordinate system using three reference spheres.In this research, we have developed decenter and rotational misalignment evaluation method for freeform bi-aspheric optical components by the Ultrahigh Accurate 3-D Profilometer (UA3P) and by coordinate system synthesis method. Using a fixture that can evaluate both bi-aspheric surfaces, the rotational deviation was calculated between outline standard and the actual surfaces measurements from the UA3P. The result of regression line inter free-form rotational deviation against the mechanical rotational deviation has a slope of 0.9737 and a coefficient of determination of 0.9995.
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