LED Optical Plate Mounting for Thermal Expansion Alignment
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Solution Overview
Problem
LED engines face misalignment issues due to thermal expansion differences between aluminum PCBs and polymethylmethacrylate or polycarbonate optical plates, leading to mechanical stress and potential cracks, which can result in early lifetime failure.
Innovation Solution
The use of fasteners with a wide portion and a resilient washer that allows for thermal expansion compensation, where the fastener extends through a through hole with a tapered or stepwise narrowing, enabling the optical plate to shift resiliently and return to its original position, reducing mechanical constraints and preventing cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the optical plate is fixedly mounted onto the PCB using fasteners to maintain alignment, then the alignment between LEDs and lenses is improved, but the mechanical constraints increase leading to cracks and early failure
Solution Approach 1:
The through hole geometry is changed from a uniform cylinder to a tapered structure with a wide upper portion and a narrow lower portion. This geometric parameter change allows the fastener to move freely in the upper portion while being constrained at the narrow lower portion, accommodating thermal expansion while maintaining alignment.
Solution Approach 2:
A resilient washer is introduced as an intermediary element between the fastener head and the optical plate. The washer deforms elastically under thermal stress, absorbing expansion forces and preventing them from being transmitted to the PCB and optical plate, thus avoiding cracks while maintaining fastener positioning.
2Stability of the object's composition
If rigid fixation is used to counteract thermal expansion misalignment, then alignment stability is improved, but mechanical stress increases causing potential cracks
Solution Approach 1:
The through hole is designed with varying cross-sectional area along its length, creating a tapered geometry. This allows the fastener to have freedom of movement in the upper portion to accommodate thermal expansion while being positioned by the narrow lower portion, achieving both stability and stress reduction.
Solution Approach 2:
The resilient washer is positioned beforehand between the fastener and the optical plate to provide cushioning. When thermal expansion occurs, the washer deforms to absorb the stress before it can be transmitted to the rigid components, preventing cracks while maintaining alignment stability.
3Manufacturing precision
If the fastener is tightly secured to maintain fixed position, then alignment precision is improved, but thermal expansion accommodation is reduced
Solution Approach 1:
The through hole cross-sectional area is varied along its length, being large at the top and small at the bottom. This allows the fastener to have translational freedom in the upper portion to accommodate thermal expansion while being laterally constrained by the narrow lower portion to maintain alignment precision.
Solution Approach 2:
The through hole is effectively segmented into two functional zones: an upper wide portion that allows thermal movement and a lower narrow portion that maintains positioning. This segmentation enables the fastener to simultaneously achieve both adaptability to thermal expansion and precision alignment.
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 solution effectively mitigates the misalignment and mechanical stress caused by thermal expansion differences, enhancing the longevity and reliability of LED engines by allowing local shifts during heating and returning to alignment during cooling.
Implementation Method 1
each fastener extends through said through hole with play S in a plane P parallel to said PCB main surface and rests on a respective, associated resilient washer seated in the wide portion of said associated through hole
Data Source
AI summary
An illumination device comprising an optical plate extending over a plurality of LEDs arranged on a PCB main surface of a PCB. In a mounted configuration said PCB and optical plate are mutually connected by fasteners. Each fastener extends with play in a plane parallel to said PCB main surface through a through hole in the optical plate in a direction transverse to said PCB main surface. The through hole has a wide portion extending over a depth D from a first main surface of the optical plate facing away from the PCB towards a second main surface of the optical plate facing towards the PCB, and said through hole is narrowed to a neck portion at said depth D. Furthermore, each fastener rests on a resilient washer seated in the wide portion of said through hole.