Specular Surface Measurement Using Pattern-Coded Deflectometry
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Solution Overview
Problem
Existing methods for optically measuring specular and partially specular surfaces face challenges such as height ambiguity, requiring complex setups, additional equipment, and high costs, which hinder efficient full-surface measurement.
Innovation Solution
A method using a pattern generator to produce a two-dimensional pattern with varying optical properties, allowing differentiation of points or groups of points, and a correspondence function to determine geometric properties of the reflective surface based on differential geometric properties, eliminating height ambiguities with a single camera.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If phase-measuring deflectometry is used to measure specular surfaces, then measurement capability for reflective surfaces is achieved, but height ambiguity occurs making unique surface normal determination impossible
Solution Approach 1:
The patent applies local quality by varying optical properties (such as brightness, color, or phase) in different regions of the pattern. This creates local distinctions that allow each point or group of points to be uniquely identified, resolving the height ambiguity problem while maintaining measurement capability for specular surfaces.
2Measurement precision
If a second measurement with shifted screen position is used to resolve height ambiguity, then unique beam direction determination is achieved, but device complexity and measurement time increase
Solution Approach 1:
The patent segments the pattern into multiple regions with different optical properties. This segmentation allows the system to encode multiple pieces of information (including height information) within a single static pattern, eliminating the need for dynamic screen shifting mechanisms while achieving unique beam direction determination.
3Measurement precision
If additional independent measurement methods are used to determine object position, then height ambiguity is resolved, but cost and installation space increase
Solution Approach 1:
The patent makes the single pattern serve multiple functions: it provides both the directional information needed for surface normal calculation and the height information needed to resolve ambiguity. This multi-functionality eliminates the need for additional independent measurement methods while maintaining measurement precision.
4Measurement precision
If direction coded deflectometry with screen mapped to infinity is used, then unique direction assignment is achieved, but lens size and space requirements become impractical
Solution Approach 1:
The patent changes the parameters of the pattern (optical properties such as brightness, color, or phase) to encode directional and height information. This allows the system to achieve unique direction assignment without requiring the screen to be mapped to infinity or using space-consuming telecentric optics.
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
Enables efficient full-surface measurement of specular and partially specular surfaces with low equipment complexity and cost, using a single camera without additional mechanisms, by distinguishing points or groups of points through optical property variations.
Implementation Method 1
at least parts of the pattern are reflected by a reflective surface of the object as a reflected pattern onto a detector of a camera unit
Data Source
AI summary
The invention relates to a method for optically measuring an object having a reflective and/or partially reflective surface. According to the invention, by means of a pattern generator (1), a planar pattern (13) is generated which is varied in at least one optical property such that, at least in partial regions (10), a plurality of different points (p) or a plurality of different groups of points are distinguishable from each other. At least parts of the pattern (13) are reflected by a reflective surface (2) of the object (3) as a reflected pattern onto a detector (14) of a camera unit (4), wherein the reflected pattern is converted by the detector (14) into a camera image (9). A connection between points (q) of the camera image (9) and corresponding points (p) of the pattern (13) can be described by means of a correspondence function which is dependent on geometric properties of the reflective surface (2) of the object (3). At least one of the geometric properties of the reflective surface (2) of the object (3) is determined by using differential geometric properties of a transformation given by the correspondence function. The invention furthermore relates to a corresponding system and a corresponding measuring arrangement.