Small TOF Lens System Reducing Tolerance Sensitivity
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Solution Overview
Problem
Conventional small lens systems for Time of Flight (TOF) cameras have high f-numbers and are sensitive to tolerance, making it difficult to provide accurate 3D information and resulting in low performance and productivity.
Innovation Solution
A small lens system comprising three lenses with specific thickness and refractive power relationships, where the second lens has a low refractive power and aspherical surfaces, and the f-number is set to less than 1.7, reducing tolerance sensitivity and improving lens sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the f-number is reduced to increase lens sensitivity, then measurement precision is improved, but device complexity increases due to stricter tolerance requirements
Solution Approach 1:
The patent applies parameter changes by optimizing the refractive indices and thicknesses of the lens components. Specifically, the first lens has a refractive index of 1.866 and the second lens has a refractive index of 1.641, with carefully controlled thickness ratios (0.7 ≤ ct1/(ct3+ct5) ≤ 1.3). These parameter adjustments enable the system to achieve low f-number (high lens sensitivity) while maintaining tolerance insensitivity through the balanced optical design.
2Length of moving object
If the lens system is miniaturized to reduce total track length, then device size is reduced, but manufacturing precision becomes more difficult to maintain
Solution Approach 1:
The patent uses parameter changes by establishing specific thickness ratio relationships: 0.7 ≤ ct1/(ct3+ct5) ≤ 1.3 and 0.4 ≤ ct1/ct3 ≤ 2.0. These parameter constraints enable miniaturization while maintaining manufacturing feasibility. The controlled thickness ratios ensure that even in a compact design, the lenses remain insensitive to tolerance variations, solving the contradiction between size reduction and manufacturing precision.
3Length of moving object
If the refractive power of the second lens is increased to reduce total track length, then device size is reduced, but tolerance sensitivity increases
Solution Approach 1:
The patent applies parameter changes by carefully controlling the refractive power of the second lens through its refractive index (1.641) and thickness parameters. The thickness ratio constraints (0.4 ≤ ct1/ct3 ≤ 2.0) ensure that the second lens does not have excessive refractive power, thereby reducing tolerance sensitivity while still achieving a compact total track length. This balanced parameter selection resolves the contradiction between size reduction and tolerance sensitivity.
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 solution provides a small, lightweight lens system with improved accuracy and productivity for TOF cameras by reducing tolerance sensitivity and enhancing lens sensitivity, enabling the capture of accurate depth information.
Implementation Method 1
a first lens, a second lens, and a third lens which are sequentially disposed from an object along an optical axis... the refractive power (P2) of the second lens satisfies −0.01 mm−12−1
Data Source
AI summary
Disclosed is a small lens system including a first lens, a second lens, and a third lens sequentially arranged from an object along an optical axis, wherein the thickness (ct1) of the first lens, the thickness (ct3) of the second lens, and the thickness (ct5) of the third lens satisfy ct1/ct3>1.5 and ct1/(ct3+ct5)>0.8, the refractive power (P2) of the second lens satisfies −0.01<P2<0.01, the lens thickness (et) at a predetermined height and the center thickness (ct) of the second lens thereof satisfy |et−ct|<5 μm up to 30% of the height of the rear effective diameter thereof and satisfy et−ct<−20 μm at 70% of the height of the rear effective diameter thereof, and the f-number of the lens system is less than 1.7.