Structured Light 3D Measurement via Defocus-Degree Unwrapping
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Solution Overview
Problem
Existing structured light 3D measurement methods are susceptible to wrapped phase errors due to excessive or insufficient defocusing, leading to inaccuracies in phase unwrapping and failing to achieve high-precision 3D measurements.
Innovation Solution
A structured light 3D measurement method and device based on defocus-degree-based unwrapping, which involves acquiring a fringe image after defocused projection, calculating the defocus degree, and using a calibrated defocusing phase function to obtain a normalized reference phase for phase unwrapping, thereby reducing the influence of phase errors and achieving high-accuracy 3D measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If binary fringe defocused projection is used to achieve high efficiency and wide application range, then measurement efficiency is improved, but wrapped phase error increases due to excessive or insufficient defocusing
Solution Approach 1:
The patent changes the parameter of defocus degree from a fixed value to a variable parameter that is optimized for different depth ranges. By dynamically adjusting the defocus degree according to the depth of the object being measured, the system maintains high measurement efficiency while minimizing wrapped phase errors that occur with fixed defocus settings.
Solution Approach 2:
The patent introduces dynamic adjustment of defocus degree based on depth information. The defocus degree is no longer static but varies according to the depth range of the measurement target, allowing the system to adapt to different measurement scenarios and maintain optimal phase accuracy across varying depths while preserving measurement efficiency.
2Measurement precision
If multi-frequency phase unwrapping method is used, then phase unwrapping is performed, but the method is susceptible to wrapped phase error and fails to achieve high-precision measurement
Solution Approach 1:
The patent introduces depth information as an intermediary element that mediates between the wrapped phase and the final unwrapped phase. By using depth information to guide the phase unwrapping process, the system can reliably resolve phase ambiguities even in the presence of wrapped phase errors, significantly improving robustness while maintaining measurement precision.
Solution Approach 2:
The patent implements a feedback mechanism where depth information obtained from the measurement process is fed back into the phase unwrapping algorithm. This feedback allows the system to continuously adjust the unwrapping strategy based on actual depth variations, making the process highly resistant to wrapped phase errors and achieving reliable high-precision measurement.
3Shape
If excessive defocusing is applied to blur binary fringe into standard sinusoidal fringe, then fringe quality is improved, but defocus degree cannot be accurately controlled leading to increased unwrapping error
Solution Approach 1:
The patent performs preliminary calibration to establish the relationship between defocus degree and fringe quality before actual measurement. By pre-determining the optimal defocus settings and creating lookup tables or calibration curves, the system eliminates the need for real-time manual adjustment, thereby improving both fringe quality and the ease of controlling defocus degree during operation.
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 allows for high-accuracy 3D measurements even with large phase errors, due to its independence from phase accuracy, effectively overcoming the limitations of existing methods by using a defocus-degree-based method to reconstruct 3D point clouds.
Implementation Method 1
acquiring, by a camera, a fringe image generated after defocused projection of binary fringes varying in fringe width onto an object to be measured
Implementation Method 2
the binary fringe is blurred into a standard sinusoidal fringe by means of defocusing effect
Data Source
AI summary
A structured light 3D measurement device and method based on defocus-degree-based unwrapping. Binary fringes varying in fringe width are projected onto an object, and a corresponding fringe image is collected by a camera, and then subjected to phase demodulation to calculate a wrapped phase. The defocus degree is calculated according to modulation degrees of the binary fringes. The defocus degree is plugged into the defocusing phase function to obtain a normalized reference phase. The wrapped phase is subjected to phase unwrapping based on the normalized reference phase to obtain an absolute phase to reconstruct a 3D point cloud.