Planar Illumination Device Reflector Fixing for Thermal Stability
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Solution Overview
Problem
Planar illumination devices used in vehicles face light loss due to gaps between the reflector and substrate, and temperature changes cause the reflector to detach from the substrate due to differing linear expansion coefficients.
Innovation Solution
A planar illumination device design that includes a substrate with light sources, a reflector, and a bottom frame, featuring a first fixing member to secure the reflector's center portion to the bottom frame and a second fixing member, such as double-sided tape, with varying adhesive strength along the reflector's length to stabilize the reflector-substrate assembly during temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the reflector is fixed to the substrate using double-sided tape along outer peripheries, then light loss is suppressed by eliminating gaps, but the reflector detaches from the substrate during temperature changes due to differential thermal expansion
Solution Approach 1:
The patent applies different fixing methods to different regions of the reflector-substrate assembly. The center portion uses a pin-based mechanical fixing member that allows thermal expansion, while the peripheral portions use double-sided tape to prevent light loss. This local differentiation resolves the contradiction by allowing each region to address its specific functional requirement.
Solution Approach 2:
The fixing system is segmented into multiple independent fixing members: a first fixing member (pin) at the center portion and second fixing members (double-sided tape) at peripheral portions. This segmentation allows each fixing member to perform its specialized function without interfering with the thermal expansion needs of other regions.
2Ease of manufacture
If uniform adhesive strength is applied across the reflector, then manufacturing is simplified, but the reflector cannot accommodate differential thermal expansion and detaches
Solution Approach 1:
The adhesive strength varies by location: strong mechanical fixing with pins at the center and weaker peripheral fixing with double-sided tape at the edges. This local quality differentiation allows the assembly to accommodate thermal expansion while maintaining overall reliability.
Solution Approach 2:
The fixing strength parameter is changed across different locations of the reflector. The center portion has high fixing strength via pins, while peripheral portions have lower fixing strength via tape, allowing controlled flexibility for thermal expansion.
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
The design effectively stabilizes the reflector to the substrate, preventing detachment and light loss even under temperature fluctuations, ensuring consistent illumination performance.
Implementation Method 1
a second fixing member configured to fix the one surface of the substrate and the reflector. A force of the second fixing member restricting the substrate and the reflector is greater at a center portion of the reflector in the longitudinal direction than at a portion of the reflector separated in the longitudinal direction from the center portion
Implementation Method 2
a linear expansion coefficient of the reflector and a linear expansion coefficient of the substrate (or frame with the substrate fixed to the frame) are different in a usage environment of a planar illumination device mounted to a vehicle. Therefore, when a temperature change in the vehicle occurs, a length (amount of change) of the reflector in a longitudinal direction and a length (amount of change) of the substrate in the longitudinal direction differ
Data Source
AI summary
In a planar illumination device according to an embodiment, a reflector can be stably fixed to a substrate even when a temperature change occurs. A planar illumination device includes a substrate provided with a plurality of light sources at one surface side, a reflector provided at the one surface side of the substrate, a bottom frame provided at a surface side of the substrate opposite to the one surface side, a first fixing member configured to fix a center portion of the reflector in a longitudinal direction to the bottom frame, and a second fixing member configured to fix the one surface of the substrate and the reflector. A force of the second fixing member restricting the substrate and the reflector is greater at a center portion of the reflector 4 in the longitudinal direction than at a portion of the reflector 4 separated in the longitudinal direction from the center portion.