Profilometer Lighting Symmetry for Non-Uniform Reflectance
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Solution Overview
Problem
Existing surface profiling techniques using color highlight and illuminance difference methods face accuracy issues when dealing with non-uniform reflectance properties, especially when the reflectance property of the measuring target differs from the reference object, and struggle to handle imperfect mirror surfaces.
Innovation Solution
A lighting device with a specific light source distribution that mimics a perfect mirror surface is used, where the radiance of the light source distribution is designed to coincide with regular reflection, allowing for accurate calculation of normal information even with non-uniform reflectance properties, by employing light source distributions that linearly change with respect to longitude or latitude, and overlapping different light source distributions to cancel out the influence of diffuse reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If color highlight method is used to measure surface profile, then measurement can be performed on mirror surfaces, but measurement fails on objects with non-uniform reflectance property and accuracy lowers on imperfect mirror surfaces
Solution Approach 1:
The invention changes the lighting parameters by using a specific light source distribution L(θ) that satisfies the symmetry condition L(θs-a) + L(θs+a) = 2×L(θs). This parameter change in illumination geometry allows the system to handle objects with non-uniform reflectance properties while maintaining measurement accuracy on mirror surfaces.
Solution Approach 2:
The invention applies asymmetry in the light source distribution relative to the specular reflection direction. By creating a symmetric light source distribution around the specular reflection angle θs, the system compensates for asymmetric reflectance variations in the measured object, enabling accurate measurement of both uniform and non-uniform reflectance surfaces.
2Adaptability or versatility
If illuminance difference stereo method is used, then objects with uniform reflectance property can be measured, but accuracy in normal calculation lowers when reflectance property is not uniform or differs from reference object
Solution Approach 1:
The invention changes the illumination parameter from conventional omnidirectional or multi-directional lighting to a specific angular distribution L(θ) centered on the specular reflection direction. This parameter change enables the system to measure both uniform and non-uniform reflectance objects with high accuracy by aligning the light source distribution symmetry with the measurement geometry.
Solution Approach 2:
The invention creates a universal measurement system that can handle multiple types of surfaces (perfect mirror, imperfect mirror, uniform reflectance, non-uniform reflectance) using a single lighting configuration. The symmetric light source distribution around the specular reflection angle provides multi-functionality across different object types.
3Reliability
If conventional lighting is used for imperfect mirror surfaces, then diffuse reflection causes measurement errors, but no solution exists to cancel lobe influence
Solution Approach 1:
The invention converts the harmful diffuse reflection (lobe) into a beneficial effect by using a light source distribution that is symmetric around the specular reflection direction. The symmetric lighting ensures that diffuse reflection components from symmetric angles cancel each other out, transforming the harmful scattering into a neutral or beneficial contribution to measurement accuracy.
Solution Approach 2:
The invention applies preliminary anti-action by pre-configuring the light source distribution to counteract the expected diffuse reflection effects. By setting L(θs-a) + L(θs+a) = 2×L(θs) before measurement, the system preemptively cancels the influence of lobe from symmetric directions, preventing measurement errors before they occur.
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 approach enables accurate calculation of normal information and observation of reflected light irrespective of reflectance uniformity, allowing for precise surface profiling even with unknown reflectance properties, and reduces measurement errors associated with imperfect mirror surfaces.
Implementation Method 1
a lighting device for irradiating the measuring target with light having a first light source distribution and light having a second light source distribution
Data Source
AI summary
An observing apparatus includes a lighting device for irradiating a surface of a measuring target with light having a first light source distribution, and an imaging section for imaging the surface of the measuring target. Considering a first plane passing through a measurement point, the first light source distribution is set such that: (1) a radiance L11(θ) changes in a continuous or stepwise manner according to an angle θ, and (2) the radiance L11(θ) is not zero in a local region of a predetermined range of ±σ having a point located at a predetermined angle θc as a center on the first plane when viewed from the measurement point, and the following equation substantially holds for arbitrary a satisfying 0<a≦σ; L11(θc−a)+L11(θc+a)=2×L11(θc).