Stress Athermalized Hard Contact Mount for Optical Elements
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Solution Overview
Problem
Optical systems face challenges due to differential thermal expansion between various materials used in transmissive optical elements and their metal barrels, leading to stress, deformation, or loosening at extreme temperatures, which conventional compliant members may not fully address without adding space or allowing motion under vibration and shock.
Innovation Solution
A stress-athermalized mounting technique using a double tangent mount with convex surfaces tangential to conical surfaces within the barrel components, allowing sliding motion to compensate for thermal expansion differences without a compliant member, ensuring consistent contact and minimizing temperature-dependent interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid aluminum barrel is used to hold optical elements, then mechanical strength and structural stability are improved, but differential thermal expansion causes stress, deformation, or loosening at extreme temperatures
Solution Approach 1:
The patent introduces axial play (movability) in the optical element along the optical axis, transforming the static rigid mounting into a dynamic system that can adapt to thermal expansion differences. The optical element is positioned with clearance in the axial direction, allowing it to move freely as temperature changes, thereby eliminating thermal stress while maintaining lateral mechanical support from the rigid barrel.
Solution Approach 2:
The patent separates the constraints into two independent directions: lateral constraint (radial direction) is maintained by the rigid barrel for mechanical strength, while axial constraint is released to allow thermal expansion. This segmentation of constraints resolves the contradiction by applying different degrees of freedom to different directions.
2Reliability
If a compliant member such as a spring or elastomer is used to absorb thermal expansion, then thermal stress is reduced, but the device complexity and space requirements increase
Solution Approach 1:
The patent extracts and eliminates the compliant member from the mounting structure entirely. Instead of adding a spring or elastomer to absorb thermal expansion, the design uses the inherent axial play in the optical element's positioning to naturally accommodate thermal effects, simplifying the overall structure while maintaining thermal stress reduction.
Solution Approach 2:
The optical element itself serves the dual function of maintaining optical function and accommodating thermal expansion through its axial movability. The system uses the optical element's own degree of freedom to compensate for thermal effects without requiring external compliant components.
3Reliability
If a compliant member is used to accommodate thermal expansion, then stress is reduced, but motion of the optical component under vibration and mechanical shock is allowed
Solution Approach 1:
The patent introduces controlled dynamics in the axial direction (allowing movement) while maintaining static stability in the lateral direction (fixed position). The optical element can move axially to accommodate thermal expansion but remains laterally constrained by the rigid barrel, preventing unwanted motion under vibration and shock.
Solution Approach 2:
The patent applies different constraint qualities to different spatial locations: the lateral surfaces of the optical element are firmly constrained by the rigid barrel for positional stability, while the axial ends are left with clearance for thermal accommodation. This localized differentiation of constraint quality resolves the contradiction between stress reduction and positional stability.
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 approach effectively minimizes stress and maintains optical system performance across temperature ranges by allowing axial motion of optical elements, thereby optically athermalizing the system without the need for compliant members, reducing stress and motion issues.
Implementation Method 1
the different thermal expansion coefficients of the lens and barrel materials... the aluminum expands more than the glass as the system temperature increases
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
There is disclosed an optical element having a first surface and a second surface bounded by a circular periphery. A rim having an inner surface may extend from the second surface proximate the periphery. At least a portion of the inner surface of the rim may be convex.