Collimating Lens Thermal Stability via Refractive Index Tuning
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Solution Overview
Problem
Collimating lenses used in 3D imaging technology experience significant changes in focal length and light angle due to temperature fluctuations, leading to errors in contour restoration and reduced sharpness of three-dimensional objects.
Innovation Solution
A collimating lens design comprising a sequence of lenses with specific refractive powers and aspherical surfaces, where the refractive index change rates with temperature are carefully managed to maintain a stable focal length, ensuring minimal variation in the angle and spot size of projected light across temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional lens is used for collimating laser light in 3D imaging, then the lens can project light onto the to-be-measured object, but the focal length changes significantly with temperature, causing the angle of projected light to change and reducing measurement accuracy
Solution Approach 1:
The patent changes the material parameter (refractive index temperature coefficient) by selecting specific glass types with different (dn/dt) values for each lens element. The first lens uses glass with (dn/dt)1 between -80 to -110×10^-6/°C, the second lens uses glass with (dn/dt)2 between -110 to -130×10^-6/°C, the third lens uses glass with (dn/dt)3 between -90 to -110×10^-6/°C, and the fourth lens uses glass with (dn/dt)4 greater than -10×10^-6/°C. This parameter selection compensates for thermal expansion effects and stabilizes the overall focal length across temperature variations.
Solution Approach 2:
The patent employs a composite lens system where each lens element is made from different glass materials with specifically selected refractive index temperature coefficients. This composite structure combines materials with different thermal-optical properties to achieve overall thermal stability of the focal length, transforming the temperature sensitivity issue into a controllable parameter through material composition.
2Measurement precision
If the focal length changes with temperature, then the angle of the projected light changes, but this causes errors in the calculation of the entire system and affects contour restoration accuracy
Solution Approach 1:
The patent stabilizes the optical information by carefully selecting the refractive index temperature coefficients of the lens materials. The specific ranges of (dn/dt) values for each lens element are chosen to compensate for thermal effects, ensuring that the focal length and consequently the projected light angle remain stable. This maintains the integrity of the optical information used for 3D contour restoration calculations.
3Measurement precision
If the temperature changes, then the imaging point of the collimating lens becomes larger, but this reduces the sharpness of the three-dimensional object
Solution Approach 1:
The patent addresses the imaging point size issue by selecting lens materials with specific refractive index temperature coefficients. The combination of materials with different (dn/dt) values compensates for thermal expansion and refractive index changes, keeping the imaging point size stable across temperature variations. This maintains image sharpness and resolution in the 3D imaging system.
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 achieves a focal length stabilization of less than 0.0005 mm per 10 degrees Celsius, maintaining consistent optical information and enhancing the suitability of the 3D structured light algorithm with a larger focal length and smaller field of view angle.
Implementation Method 1
a first lens L1 with positive refractive power, including a convex object side surface; a second lens L2 with negative refractive power, including a concave object side surface and a concave image side surface; a third lens L3 with positive refractive power; a fourth lens L4 with positive refractive power, including a convex image side surface
Implementation Method 2
as the ambient temperature changes, the focal length f of a lens changes greatly... due to the refractive index of each lens is distributed reasonably with temperature, an effect of the thermal expansion the lens itself and the structural components can be offset
Data Source
AI summary
The disclosure provides a collimating lens. In order from a laser transmitter side to a to-be-measured object side, the collimating lens includes a first lens, a second lens, a third lens, a fourth lens and an aperture stop. The aperture stop is on the to-be-measured object side, and optical centers of each lens being on a same line. The collimating lens satisfying the following conditions: (dn/dt)1<−50×10−6/° C., (dn/dt)2<−50×10−6/° C., (dn/dt)3<−50×10−6/° C., (dn/dt)4>−10×10−6/° C. A refractive index of each lens is usually distributed reasonably with temperature, the focal length can be stabilized and applied to different temperature occasion. Under the same size laser emitter, the focal length of the system is larger, and the field of view angle is smaller.