Optical Surface Inspection Using Phase-Shifted Light Patterns
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Solution Overview
Problem
Current methods for inspecting shiny surfaces under industrial conditions are not automated enough, requiring high a priori knowledge and struggling with measurement speed, reliability, and adaptability to changing conditions such as temperature, dust, and noise.
Innovation Solution
A device with a variable pattern generator and a camera system that moves relative to the object, using a coherent chronological sequence of light-dark patterns with defined intensity profiles and phase shifts to inspect surfaces efficiently and accurately, allowing for flexible adaptation to different surfaces and conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If visual inspection by experienced persons is used, then inspection reliability is maintained, but automation degree remains low
Solution Approach 1:
The patent replaces the mechanical visual inspection system (human eyes and brain processing) with an optical measurement system using structured light projection and camera-based deflectometry. The system projects light-dark patterns onto the surface and uses camera recordings to automatically determine local surface inclinations, substituting human visual judgment with automated optical measurement and evaluation algorithms.
Solution Approach 2:
The evaluation algorithm automatically processes the camera recordings to determine local surface inclinations and detect defects without requiring human inspection. The system performs self-evaluation by comparing measured surface properties against reference values, enabling fully automated quality control that serves itself rather than relying on external human inspectors.
2Productivity
If multiple phase-shifted stripe patterns are generated simultaneously with different colors, then measurement speed is improved, but device complexity increases
Solution Approach 1:
The patent uses periodic phase-shifting of light-dark patterns where at least three patterns have the same intensity profile but differ in phase position. This periodic variation allows the system to encode multiple measurement states in a sequential manner, enabling rapid successive measurements of the same surface point with different pattern phases, thereby improving measurement speed through time-multiplexed periodic action.
Solution Approach 2:
The system employs a variable pattern generator that can dynamically change the phase position of light-dark patterns in chronological sequence. This dynamic capability allows the same pattern generator to produce multiple phase-shifted patterns over time, achieving multi-state measurements without requiring multiple static pattern generators, thus improving speed while managing device complexity through dynamic reconfiguration.
3Measurement precision
If the camera records only partial sections of the surface, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent segments the surface inspection task by having the camera record only partial sections at any given time, while the workpiece holder systematically moves the object to bring different surface points into the camera's field of view. This segmentation allows the camera to maintain high measurement precision on small areas while the automated positioning system ensures complete surface coverage through sequential inspection of segmented regions.
Solution Approach 2:
The system maintains continuous useful action by coordinating the camera's partial section recording with continuous workpiece holder movement. As the workpiece holder moves the object to present new surface points, the camera continuously records partial sections, ensuring that the inspection process flows without interruption. This continuous coordination maintains high productivity despite the camera's limited field of view at any instant.
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 rapid, automated, and precise surface inspection with reduced measurement inaccuracies, capable of handling varying surface properties and conditions, improving the inspection speed and reliability of shiny surfaces.
Implementation Method 1
Deflectometry is a promising concept for at least partially reflective surfaces, in which a light-dark pattern is recorded and evaluated with a camera over the surface to be inspected
Data Source
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AI summary
A device for optically inspecting a surface (28) of an object (26) has a pattern generator (12) to produce variable light-dark patterns (16a, 16b). The surface (28) comprises a plurality of surface points (54, 58, 62) distributed along a direction. A camera (32) is directed at a section of the surface (28). A workpiece holder (20) is configured to move the object (26) relative to the camera (32) in such a way as to capture the surface points (54, 58, 62) sequentially with the camera (32). A control and evaluation unit (34) is configured to control the pattern generator (12), the workpiece holder (20) and the camera (32) such that each surface point from the multitude of distributed surface points (54, 58, 62) is recorded with a multitude of different light-dark patterns (16a, 16b), wherein the pattern generator (12) generates the different light-dark patterns (16a,16b) in a continuous temporal sequence, and wherein the camera (32) is always directed at the same surface point (54, 58, 62) during the continuous temporal sequence, wherein the light-dark patterns (16a, 16b) each have an intensity profile (22) with a defined and identical period (24), wherein at least three light-dark patterns (16a, 16b) of the sequence have the same intensity profile (22), and wherein the three light-dark patterns (16a, 16b) differ in that the intensity profile (22) is arranged with different phase positions.