Unreinforced Polymer Mirrors in High-G Optical Systems
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Solution Overview
Problem
Current gun-launched imaging infrared optical systems face challenges in achieving low cost and low mass while maintaining optical quality, as they often require expensive machining and suffer from thermal distortion due to mismatched coefficients of thermal expansion in materials.
Innovation Solution
The use of an imaging optical system comprising a primary and secondary mirror made of unreinforced polymer, optically coupled with a field lens, and a strut with cross-struts and mounting features, where the strut is made of reinforced polymer, and bonded using RTV and structural adhesive bonds to accommodate thermal expansion and provide structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fiber-reinforced polymer mirrors are used to reduce mass and cost, then manufacturing cost and mass are reduced, but surface finish becomes inadequate for mirror use due to reinforcing fibers
Solution Approach 1:
The patent divides the optical system into two distinct segments: fiber-reinforced polymer structural components (strut, retainers) and unreinforced polymer optical components (mirrors). This segmentation allows each component to be optimized for its specific function - structural parts gain strength from fibers while optical parts maintain smooth surfaces suitable for precision optics.
2Manufacturing precision
If unreinforced polymer mirrors are used to achieve adequate surface finish, then surface quality is improved, but strength and stiffness are insufficient for gun-launched systems
Solution Approach 1:
The patent divides the optical system into two distinct segments: fiber-reinforced polymer structural components (strut, retainers) and unreinforced polymer optical components (mirrors). This segmentation allows each component to be optimized for its specific function - structural parts gain strength from fibers while optical parts maintain smooth surfaces suitable for precision optics.
Solution Approach 2:
The patent employs composite materials strategy by using fiber-reinforced polymer for structural components that require high strength and stiffness to withstand launch shocks, while using unreinforced polymer for optical components where surface quality is paramount. This composite approach at the system level allows simultaneous achievement of structural integrity and optical precision.
3Strength
If filled Ultem polymer is used to increase stiffness and reduce CTE, then structural strength and thermal stability are improved, but surface roughness becomes too high for precision optics
Solution Approach 1:
The patent divides the optical system into two distinct segments: fiber-reinforced polymer structural components (strut, retainers) and unreinforced polymer optical components (mirrors). This segmentation allows each component to be optimized for its specific function - structural parts gain strength from fibers while optical parts maintain smooth surfaces suitable for precision optics.
4Strength
If conventional machined aluminum components are used, then structural strength and thermal stability are achieved, but mass and manufacturing cost increase
Solution Approach 1:
The patent changes the material parameters by transitioning from metal (aluminum) to polymer composites (fiber-reinforced Ultem). This parameter change enables significant mass reduction while maintaining structural strength through the fiber reinforcement, and reduces manufacturing cost through molding processes compared to precision machining.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for low-cost, low-mass optical systems that can withstand high acceleration and temperature variations without sacrificing optical quality, by segregating optical and structural functions and using athermal bond joints to minimize distortion.
Implementation Method 1
Optical distortion at high temperature is due to the difference in coefficients of thermal expansion (CTE) of multiple materials used in the optical system design
Data Source
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AI summary
Optical systems configured to withstand operation in high acceleration and varying temperature environments, and methods of assembling the same. In one example, an imaging optical apparatus includes a primary mirror made of an unreinforced polymer, a secondary mirror made of the unreinforced polymer and optically coupled to the primary mirror, a field lens optically coupled to the secondary mirror, and a strut having a plurality of cross-struts and mounting features configured to mount the primary mirror, the secondary mirror and the field lens. In some examples, the imaging optical apparatus further includes an outer retainer disposed behind the primary mirror and coupled to the strut, and an inner retainer disposed behind the field lens and coupled to the strut, the outer and inner retainers configured to structurally support the primary mirror and the field lens and to accommodate deflections of the primary mirror.