# Three-Band Spectral Camera Structure Design Based on the Topology Optimization Method
## 3 Three-Band Optimization Results
### Parameter Optimization Results  
To eliminate redundant mass during topology optimization, methods such as rib reinforcement and hole design are commonly used. However, the topology optimization results often fail to fully meet practical design requirements. Based on the original topology optimization, the structure was parameterized, with parameters such as the thickness and diameter being further optimized. After the skinning treatment in topology optimization, preliminary analysis and verification showed that the inherent fundamental frequency of the housing was around 126 Hz. Although this frequency is close to some external vibration frequencies, the rigid design of the housing was proven to sufficiently meet the vibration resistance requirements of the system. Additionally, the external excitation energy within the 126 Hz frequency range was relatively low, meaning that its impact on the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **Housing** & **A, B, C, D, E** \\ \hline \multirow{2}{*}{Mass/kg} & Initial & \(8.84\pm 0.01\) & \(0.72\pm 0.01\) \\  & Optimization & \(5.08\pm 0.13\) & \(0.50\pm 0.03\) \\ \multirow{2}{*}{First Modal/Hz} & Initial & \(312.52\pm 3.75\) & \(546.04\pm 8.19\) \\  & Optimization & \(126.01\pm 1.20\) & \(492.55\pm 4.48\) \\ \multirow{2}{*}{Z-Deformation/nm} & Initial & \(2.37\pm 0.07\) & \(5.52\pm 0.12\) \\  & Optimization & \(6.15\pm 0.1\) & \(6.80\pm 0.15\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters before and after topology optimization of housing and support structure. Figure 5: Topology optimization result: (**a**) topology optimization results of housing; (**b**) topology optimization results of structure A; (**c**) topology optimization results of structure B; (**d**) topology optimization results of structure C; (**e**) topology optimization results of structure D; (**f**) topology optimization results of structure E.  
overall system's performance was limited. Thus, no further optimization of the housing was necessary. For the support structure, its inherent fundamental frequency was designed to far exceed the requirements, reaching approximately 500 Hz. To further enhance the lightweight performance of the system, the support structure underwent parameter optimization to reduce its mass while ensuring its load-bearing capacity and structural stability. This ultimately achieved an optimized balance between overall system performance and weight, improving the comprehensive performance of the multispectral camera. In the optimization design of optical-mechanical structural parameters, the number of parameters is relatively large. Including all of them as design variables in the optimization model would make the optimization process overly complex, create difficulties in convergence, and significantly increase the computational workload, thereby affecting the overall efficiency and accuracy. Therefore, it is necessary to screen the most important design variables. The selected design variables should not affect the original structure while influencing the optimization objectives, such as the mass and fundamental frequency. As shown in Figure 6, L1 and L2 represent the thickness dimensions of the support modules in the optical system. L3 and L4 refer to the thickness and outer diameter of the support module plates for the small semi-transparent and semi-reflective components in the beam-splitting system. L5 and L6 represent the outer diameter and thickness dimensions of the support module plates for the large semi-transparent and semi-reflective components in the beam-splitting system. L7 and L8 correspond to the outer diameter and thickness dimensions of the support modules for the mid-wave infrared system's lens barrel. By setting these as variables, targeted parameter optimization can be performed. Combining this approach with multi-objective optimization methods improves both the efficiency and feasibility of the optimization results [28].