Structured Light 3D Measurement Using Multi-Frequency Heterodyne
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Solution Overview
Problem
Existing structured light three-dimensional measurement methods face challenges with poor stability of phase-unwrapping due to limited frames and high computational complexity, especially when using single-frequency phase-shifting fringe images.
Innovation Solution
A structured light three-dimensional measurement method based on joint multi-frequency heterodyne and time-gated overlapping coding strategy, which generates sinusoidal fringe images with different spatial frequencies, extracts wrapped phase maps using time-gated overlapping coding, and unwraps phases using multi-frequency heterodyne method to improve stability and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-frequency phase-shifting fringe images are used, then measurement speed is improved, but phase-unwrapping stability deteriorates
Solution Approach 1:
The patent changes the spatial frequency parameter by using multiple frequency groups (low, medium, high frequencies) instead of a single frequency. This allows the system to maintain fast measurement speed while improving phase-unwrapping stability through the complementary information provided by different frequency components.
Solution Approach 2:
The patent combines multiple frequency components to form a composite measurement approach. By synthesizing phase information from low, medium, and high frequency fringe patterns, the system achieves both speed and stability that neither single-frequency method could provide alone.
2Measurement precision
If Gray code pattern is used for phase unwrapping, then phase unwrapping is achieved, but computational complexity increases
Solution Approach 1:
The patent replaces the complex Gray code decoding mechanism with a multi-frequency phase-shifting approach. Instead of using binary-coded spatial patterns that require complex decoding algorithms, the system uses temporal phase-shifting at multiple frequencies, which simplifies the computational process while maintaining phase unwrapping capability.
Solution Approach 2:
The patent employs periodic phase-shifting actions at different frequencies to encode depth information. By capturing a small number of fringe images at multiple frequency rates, the system extracts phase information more efficiently than Gray code methods, reducing computational burden.
3Productivity
If limited frames are used in one measurement, then high-speed three-dimensional topography is achieved, but phase-unwrapping stability deteriorates
Solution Approach 1:
The patent changes the temporal sampling strategy by using multiple frequency groups with a fixed number of phase-shifting steps. This allows the system to capture sufficient phase information within limited frames while maintaining high measurement speed, resolving the contradiction between frame limitation and unwrapping stability.
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 proposed method enhances the stability of phase-unwrapping and improves measurement accuracy, while maintaining high-speed three-dimensional topography recording and reducing computational complexity, thus promoting measuring speed and hardware efficiency.
Implementation Method 1
projecting images collected from the sinusoidal fringe image set onto an interrogated target
Implementation Method 2
synchronously capturing fringe images modulated by a surface of the target
Data Source
AI summary
Disclosed is a structured light three-dimensional measurement method based on joint multi-frequency heterodyne and time-gated overlapping coding strategy. Specifically, fringe images modulated by a target surface are firstly collected and processed to obtain corresponding wrapped phase maps according to the phase-shifting method. Then, the wrapped phase maps are re-organized following the time-gated overlapping coding strategy, and further proceeded to obtain corresponding multi-frequency heterodyne unwrapped phase maps. With the unwrapped phase maps, a corresponding three-dimensional point cloud can be derived with the calibration parameters. The present application uses multi-frequency heterodyne method for phase unwrapping, promising high stability of phase-unwrapping and high measurement accuracy. Furthermore, the temporal correlation among the fringe images is fully exploited by the proposed time-gated overlapping coding strategy to further improve the measurement accuracy. Besides, only a few sinusoidal fringe images need to be used to complete one single measurement, highly promoting the measuring speed.