Dec 13, 2021
Automating STOP Analysis with Ansys Solutions
In many applications stress and heat loads can significantly impact the performance of an optical system. Although structural thermal optical performance (STOP) analysis has traditionally been considered an important part of the design process for precision applications in aerospace and defense and laser manufacturing, the effects of structural and thermal perturbations are becoming increasingly important in a variety of applications outside of these traditional markets, from medical imaging to mixed reality, from automotive displays to autonomous vehicle sensors. As optical component size continues to shrink, the methods used to manufacture these components (such as plastic molding and 3D printing) can add additional stress on the optics that creates a further need for detailed STOP analysis as a part of the product design process.
However, conducting robust and accurate STOP analysis can be both challenging and time consuming. This analysis often requires multiple iterations between the software tools used to design the optics and those tools used to conduct finite element analysis (FEA) for calculating the impacts of heat and stress loads on those optics. Transferring results between these tools requires data conversion and data translation; conversion that enables the optical package to interpret the FEA results (and vice versa), and translation to align those results between the different coordinate systems used by optical and FEA packages. When results are manually transferred, these data conversions and data translations are susceptible to error. Significant effort is then required by the design team to validate and verify results during each iterative step in the design process. Thus, although designing an optical system for manufacture may take many weeks, a complete STOP analysis could take many months or even longer.
In 2021 Zemax introduced the OpticStudio STAR Module1 to streamline communication between FEA tools and OpticStudio. STAR allows data from any FEA package to be converted and translated into a format for direct use in OpticStudio. STAR also provides a critical set of validation and verification tools that enable the design team to readily assess that the structural and thermal data calculated by the FEA package are accurately represented in the optical model. The data required by STAR is provided through text files that can be manually exported from the FEA package, but scripts have also been created using the Ansys Customization Toolkit (ACT)2 and the Ansys Parametric Design Language (APDL)3 to automate this data export from Ansys Mechanical4. These scripts can then be used in conjunction with the OpticStudio API (ZOS-API)5 to create a fully automated workflow between Ansys Mechanical, STAR, and OpticStudio for comprehensive STOP analysis of a single design.
An important benefit to this fully automated workflow is the ability to simulate multiple designs for variation analysis and optimization. A proof-of-concept (PoC) demonstrating such an analysis was presented at the Ansys WOST conference in June 20216-7. In this PoC, the workflow was driven using Ansys optiSLang8, a standalone software tool for conducting robust variation analysis and design optimization of engineering systems. A connection between OpticStudio and optiSLang was already in place9 for investigating the impact that various optical parameters have on system performance for both imaging and non-imaging designs. The recent PoC extended this connection to STAR and Ansys Mechanical, enabling the automated analysis and optimization of optical system performance in the presence of structural and thermal loads10. This automation also provides an opportunity to investigate the temporal behavior of the design, as it allows results from different time slices of the finite element analysis to be programmatically imported into OpticStudio for dynamic characterization. This is critical for applications such as autonomous vehicle camera sensors in which structural and thermal loads will vary in time as the vehicle is moving and experiencing different environmental conditions.
For too long STOP analysis has been restricted to the domain of select experts working on specific applications. But as structural and thermal loads influence and impact the behavior of more and more optical systems, it is critical that STOP analysis become an integrated part of the design process. This is now possible using the OpticStudio STAR Module along with workflow automation provided by Ansys optiSLang. The result will be a next generation of optical products that are more robust, accurate, and reliable than ever before!
Chief Technology Officer
Zemax An Ansys Company