Finite Element Analysis: Weight Optimization for Optical Systems

Thermal Management and Mechanical forces addressed using FEA

balance-resized-600As we discussed in our previous blog, optomechanical engineers use Finite Element Analysis (FEA) to establish proper considerations and tests to address issues such as thermal management and mechanical forces. However, using FEA to optimize the weight of a structure is often overlooked. The ultimate optical system design will weigh as little as possible, yet still withstand the required shock, vibration, and thermal loads.

Optomechanical Engineering

Optomechanical engineers use FEA to determine if an optical system can withstand certain conditions without needing extra material to bolster it. In certain cases, a structure requires additional materials to meet stress requirements, but the additional materials do not optimize weight. Although optomechanical engineers and mechanical engineers use FEA tools to evaluate the design, creating weight optimization solutions require specialized techniques.  The systems are complicated, and require engineering teams to complete the design, testing, and analysis.

One of the least understood design methods for achieving a sound design without sacrificing weight is to use “flexures”. Highly experienced optomechanical engineers use flexures to design optical systems to absorb thermal, stress, and shock loads while addressing weight issues. For example, in some mirror mount designs, flexures can be added as passive mechanical devices, which isolate components from mechanical forces and thermal loads.

Most flexures are designed with compliance in one direction, but stiffness in the remaining two orthogonal directions. For instance, mirror mounts have a three point mounting interface around the perimeter; they need to be constrained in such a way to have the flexibility to absorb thermal expansions and still be able to handle shock loads. If a mirror mount structure is too stiff it can cause costly fractures to the mirror. Optomechanical engineers can use flexures to avoid these types of problems. Understanding what materials can be used for flexures in a particular application is also key to a successful design.

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