Large-scale complex optical?mechanical systems are widely applied in high-tech fields like aerospace, space remote sensing, and lithography. As the apertures of ground-based astronomical telescopes and space-based complex optical systems keep increasing, optical systems show characteristics such as large-scale non-coplanar spatial structures, multi-load integrated optical layouts, multi-band shared apertures, and higher precision requirements. Meanwhile, the extensive application of novel design structures and special optical elements has exponentially increased the difficulty and complexity of aligning and assembling optomechanical systems, posing new challenges to the assembly process. The assembly precision of large optomechanical systems is one of the key factors affecting imaging quality and performance metrics, and it is also a critical aspect in determining whether a theoretical design can be successfully transformed into a high-performance optical device. The design and alignment of optical systems usually center around the optical axis. However, due to the invisibility of the optical axis, specific alignment techniques are needed for the initial alignment of complex optomechanical systems. Currently, initial alignments often rely heavily on the experience of assembly personnel, which brings in significant human errors, resulting in unstable measurement results and poor image quality. This also increases labor costs and assembly time. Moreover, measurement devices are relatively independent, lacking interconnection, and their data cannot be unified. Therefore, it has become more and more urgent to research digital and data-traceable assembly processes for complex optomechanical systems.

To address the issues of complex spatial layout, difficult alignment and adjustment, and the hard characterization of optical axes in off-axis and eccentric multi-reflection optical systems, we propose a quantitative characterization method for optical axes based on multi-system collaborative measurements. First, we establish a digital multi-system collaborative measurement field model to unify different measurement coordinate systems and ensure coordination and consistency among systems. Second, we realize the quantitative characterization of the optical axis and the transmission of the mechanical?optical reference in the measurement field by using a point-source microscope. Based on this transferred optical reference, we adjust the position and orientation of the mirror group to ensure the precision and reliability of system assembly. Furthermore, through in-depth accuracy analysis, we assess and optimize the errors in the optical axis quantification, resulting in a validated and mature alignment and adjustment process. This method not only significantly improves assembly efficiency but also reduces human errors, ensuring the overall imaging quality and system performance. Additionally, the method creates a data-traceable digital assembly by tracking the attitude information of optical components during the assembly process, ensuring the consistency of measurement and analysis among different subsystems. The accuracy of the optical axis calibration is further validated, with a position error of less than 25 μm and a decentering accuracy better than 10″, meeting the current optical system calibration requirements.

We construct a digital collaborative measurement field for large-scale complex optical-mechanical systems. In this field, the measurement coordinate systems of different subsystems are transformed into a global coordinate system through common points. This enables us to track the attitude information of optical components during assembly, ensuring that the systems are no longer independent. By using the digital measurement field to trace the measurement data of each optical component, we can reverse-engineer, review, and track the process of adjustments and equipment calibration in real-time, allowing for quick identification and troubleshooting of issues during assembly. We use devices such as point-source microscopes, theodolites, and laser trackers to digitally represent the virtual optical axis of the optomechanical system. We propose a method to transfer the mechanical reference to the optical reference using SMR target balls and point-source microscopes, replacing the traditional mechanical reference used in assembly. Then, the transferred optical reference is used for the alignment of the optomechanical system. Based on the small displacement screw theory, we develop a mathematical model for optical axis characterization error. By combining the error from the laser tracker during positioning, we analyze the accuracy of the optical axis quantification. The results show that the optical axis calibration position error is less than 25 μm, and the decentering accuracy is better than 10″, meeting the current optical axis calibration requirements.

We propose a multi-system collaborative measurement method to digitally represent the virtual optical axis. Based on this, the SMR target ball is used to transfer the mechanical?optical reference. We derive the theoretical model of optical axis characterization, providing an effective method for the digital representation of the optical axis. We evaluate the optical axis positioning accuracy using the small displacement screw theory, comprehensively assessing the errors of each instrument in the optical axis representation. It is determined that the optical axis calibration position error is less than 25 μm, and the decentering accuracy is better than 10″, meeting the current requirements for optical systems.