High-precision sensitivity error analysis and compensation method for on-machine measurements of large aperture optical surfaces

Large-aperture optical components are widely used in various fields. On-machine measurement systems can improve the measurement efficiency of optical surfaces during grinding. However, the measurement accuracy on the machine is limited by the accuracy of the machine tool and cannot meet the requirements. Currently, three-coordinate offline measurements are used for optical surfaces during grinding. However, offline measurements are inefficient. Therefore there is an immediate need for a high-precision on-machine measurement method. This study proposes a high-precision sensitivity error analysis and compensation method for on-machine measurements of large-aperture optical surfaces to replace coordinate measuring machine. The on-machine measurement precision of large-aperture optical surfaces was improved in two approaches. First, owing to the difficulty of directly compensating for all geometric errors of the machine tool, a sensitivity error model for surface measurements was established to identify the main sources of geometric errors. Second, an accurate error measurement and compensation method based on the Abbe principle was developed to ensure that no additional Abbe errors were introduced during the measurement process. Finally, the validity of the proposed method was verified using an on-machine measurement system to conduct precision tests on an aspheric surface with a diameter of 500 mm, and the results were compared with those obtained using a commercial profilometer. The measurement error was PV = 1.6 μm, RMS = 0.2 μm. Further on-machine measurements and machining experiments were performed on surfaces with the same diameter. The results show that the proposed method can effectively improve both the machining precision and efficiency, as demonstrated by the 50 % increase in the measurement efficiency compared to that achieved by coordinate measuring machine.