Image Acquisition System with Phase-Shifted Pattern Projection
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Solution Overview
Problem
Existing image acquisition systems for obtaining height profiles of surfaces are complex, time-consuming, and prone to inaccuracies due to alignment issues and reliance on diffuse reflection, especially when dealing with larger surfaces or specular surfaces.
Innovation Solution
An image acquisition system comprising a projector and a camera with a means to generate relative motion between the sample and the projector-camera arrangement, using a pattern of sub-patterns projected onto the surface and detection fields defined to record light intensity information, allowing for the quick and reliable generation of height profiles without complex configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple patterns are projected one after the other, then height profile measurement is achieved, but measurement time increases and productivity decreases
Solution Approach 1:
The system employs periodic modulation of the light source intensity synchronized with the moving sample to encode height information in the temporal domain. By projecting patterns at different phases during periodic cycles and detecting the modulated reflected light, the system achieves phase shift measurement without requiring sequential projection of multiple static patterns, thereby maintaining measurement precision while improving throughput through continuous sampling.
2Adaptability or versatility
If a second detection device is added to detect specular reflection, then measurement capability on specular surfaces is improved, but device complexity increases
Solution Approach 1:
The detection function is segmented between spatial separation of detection fields and temporal separation of pattern phases. The single camera captures multiple detection fields simultaneously in space, while the periodic modulation separates different pattern phases in time. This eliminates the need for multiple simultaneous detection devices while maintaining the capability to measure both diffuse and specular surfaces through the moving sample technique.
Solution Approach 2:
The single detection device is designed with multi-functionality to perform both diffuse reflection detection and specular reflection detection by capturing light from different spatial fields and processing the periodic modulation signals appropriately. The system achieves universal measurement capability across different surface types without requiring specialized detection devices for each surface type.
3Area of stationary object
If multiple detection fields are used to cover larger surfaces, then measurement coverage is improved, but alignment errors increase and measurement precision deteriorates
Solution Approach 1:
The moving sample technique allows the system to self-align measurements across multiple detection fields. As the sample moves continuously through the detection region, each point on the sample surface is sequentially exposed to all detection fields in a predetermined sequence. The system uses the known motion trajectory and timing to automatically correlate measurements from different fields, eliminating manual alignment requirements and ensuring consistent precision across the entire measurement area.
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 solution enables efficient and accurate generation of height profiles by simplifying the setup and reducing alignment errors, allowing for quick and reliable surface analysis without the need for additional detection devices or complex calibration.
Implementation Method 1
A pattern is projected on the surface of interest. Depending on the height profile of the surface, these lines as projected on the surface are deformed with respect to the shape they would have if projected onto a plane
Implementation Method 2
a means to generate a relative motion between the sample on the one hand, and the camera and projector on the other hand
Data Source
AI summary
The invention relates to an image acquisition system and an image acquisition method, as well as to an inspection system having at least one such image acquisition system. A projector projects a pattern on a surface of a sample, a camera records light intensity information from within at least two detection fields defined by the camera on the surface of the sample. A relative motion between the sample on the one hand and the camera and projector on the other hand is generated. From the acquired at least one image a height profile of the surface of the sample may be inferred. The pattern may comprise a number of sub-patterns related to each other by a phase shift. Alternatively, the pattern may be a fringe pattern.