Lens Unit Thermal Expansion Compensation
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Solution Overview
Problem
In lens units with plastic lenses, the refractive index decrease with rising temperature causes a shift in the focal position, which is not effectively addressed by existing technologies.
Innovation Solution
A lens unit configuration with a meniscus-shaped plastic lens press-fitted into a holder, where the concave side portion of the lens abuts the holder's inner surface, and the holder has a smaller coefficient of thermal expansion than the lens, allowing the convex lens surface to deform and offset the refractive index decrease, thereby reducing focal position shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a plastic lens is employed in the lens unit, then the lens can be manufactured with ease and cost-effectiveness, but the refractive index decreases when ambient temperature rises, causing focal position shift
Solution Approach 1:
The invention changes the physical state parameters of the plastic lens by controlling its thermal expansion through the holder structure. The holder with smaller coefficient of thermal expansion than the plastic lens creates a differential expansion relationship that compensates for the refractive index decrease at high temperatures, thereby maintaining focal position stability while retaining the manufacturing advantages of plastic lenses
Solution Approach 2:
The invention utilizes thermal expansion principles by designing a holder with a smaller coefficient of thermal expansion than the plastic lens. When temperature rises, the plastic lens expands more than the holder, creating compressive stress on the lens that compensates for the refractive index decrease, thus offsetting the focal position shift toward the image side
2Reliability
If the convex lens surface deforms to offset refractive index decrease, then focal position shift is reduced, but the lens surface curvature changes
Solution Approach 1:
The invention intentionally allows parameter changes in the lens surface curvature as a compensation mechanism. The convex lens surface deforms to increase its curvature, which increases the lens power to compensate for the refractive index decrease, thereby maintaining focal position stability despite the shape change
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 effectively minimizes the shift in focal position at elevated temperatures by compensating for the decrease in refractive index with deformation of the convex lens surface, maintaining optical performance.
Implementation Method 1
the refractive index of the plastic lens decreases when the ambient temperature rises
Implementation Method 2
the convex lens surface of the single lens receives a reaction force of the force of expansion and deforms such that the curvature radius becomes smaller
Data Source
AI summary
A lens unit is provided capable of reducing the shift of the focal position when the temperature rises. The lens unit includes a plurality of lenses and a cylindrical holder configured to internally hold the plurality of lenses. The holder has a smaller coefficient of thermal expansion, compared to single lenses (i.e., the second lens and the third lens) that are meniscus-shaped plastic lenses. The side surfaces of the second lens and the third lens are press-fitted such that the concave side portions corresponding to the positions of the concave lens surfaces abut the inner surface of the holder, the second lens and the third lens including the concave lens surfaces and the convex lens surfaces. Therefore, when the ambient temperature rises, the refractive index of the plastic lens decreases but the convex lens surface deforms such that the curvature radius becomes smaller.