Additive Manufacturing Volume Optimization for Athermal Optics

Additive manufacturing (AM) is a rapidly advancing area in which new mechanical design techniques can be used to greatly benefit optical sensor designs. Emerging technologies now allow us to utilize many different materials to print three-dimensional structures in complex, accurate shapes. This enables designers to build volumes with optimal material distributions, allowing them to tailor a structure's response to temperature or vibration. Introduction of these methods provides an excellent opportunity for a designer of optical sensors to make significant for harsh and varied environments. The Army is currently funding research of a Robust Seeker Optomechanics project to design novel mechanical structures promising to athermalize and vibration-isolate a missile seeker's imaging components. The structures would eliminate the need for moving parts or expensive components such as gimbals or complex lenses. Methods for topology optimization allow a computer algorithm to fill the volume around a missile seeker lens and camera focal plane with a uniquely shaped composite material. These uniquely constructed spaces can both move or maintain the position of the imaging components when the missile experiences large temperature variations and vibrations thus improving performance. Army Aviation and Missile Research and Development Center (AMRDEC) lens designers teamed with Materials Sciences Corporation (MSC) to develop topology optimization algorithms based on frequency tailoring of structures specific to another project underway. The initial phase of this effort is to demonstrate mechanical athermalization of a simple long-wave infrared camera in a small, 2.75-inch-diameter missile seeker configuration. MSC created a series of volume optimizations and algorithm refinements to study the solution space for a 45mm, F/1.4, 14-degree lens and a FUR Quark2 640 sensor between -35 degrees C and +50 degrees C. The example problem provides a relevant, achievable athermalization goal as well as an opportunity to include vibration damping in later phases. The results of initial volume optimization reveal that one can achieve a buildable athermalized design by separating the detector mount structure from the lens retention structures. The study also showed that mechanical and optical design need to be coupled into a common optimization solution to achieve the best results. MSC measured the mechanical properties of many additively-produced metals and plastics to use in the optimization. The team produced a lens in a prototype housing, and will measure it for thermal stability soon after this paper is submitted.