3D Shape Measurement Using Composite Pattern Deflectometry
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Solution Overview
Problem
Conventional 3D shape measurement techniques for freeform surfaces using deflectometry face challenges in accuracy due to external vibrations and environmental changes, particularly when measuring objects with non-linear sensitivity features, leading to measurement errors.
Innovation Solution
A system and method employing composite patterns with different frequencies are projected onto a measurement object, using Fourier transforms to obtain wrapped phases, which are then unwrapped to accurately analyze the 3D shape, incorporating regularization and spatial-carrier frequency phase-shifting methods to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional deflectometry with single-frequency patterns is used, then the measurement process is simple, but measurement precision deteriorates due to external vibrations and environmental changes
Solution Approach 1:
The patent segments the measurement process by using multiple frequency components in composite patterns. Instead of using a single frequency pattern, the system employs composite patterns containing multiple frequencies (e.g., fundamental frequency and harmonic frequencies), allowing the measurement to be divided into multiple frequency-based analyses that collectively improve precision while managing complexity through systematic processing.
Solution Approach 2:
The patent changes the frequency parameters of the projected patterns by using composite patterns with different frequency components. This parameter change allows the system to capture surface information at multiple frequency scales, improving measurement precision by providing redundant information that can be processed to compensate for vibrations and environmental disturbances.
2Productivity
If high-speed phase measurement is implemented, then productivity improves, but measurement precision may worsen due to simplified processing
Solution Approach 1:
The patent employs periodic action by using phase-shifting techniques with multiple frequency components. The composite patterns are projected with periodic phase shifts, and the reflected light is captured in multiple frames corresponding to different phase states. This periodic measurement approach enables high-speed data acquisition while maintaining precision through the systematic processing of periodic signals using Fourier transform and phase unwrapping algorithms.
3Measurement precision
If non-linear sensitivity features of displays are used to enhance visual recognition, then ease of operation improves, but measurement precision deteriorates due to non-linear distortion
Solution Approach 1:
The patent extracts the linear sinusoidal signal components from the non-linear display output by using Fourier transform analysis. The system projects composite patterns and captures the reflected light, then extracts the fundamental frequency and harmonic components through spectral analysis. This extraction process separates the useful linear measurement information from the non-linear display characteristics, eliminating the distortion effect while preserving the measurement capability.
Solution Approach 2:
The patent introduces an intermediary processing step using Fourier transform and phase-shifting algorithms between the display output and the final measurement result. This intermediary processing converts the non-linear display output into linear phase information by analyzing the frequency components and their phase relationships, effectively mediating the transformation from non-linear display characteristics to precise linear measurement data.
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 enables rapid and accurate 3D shape measurement of freeform surfaces by reducing measurement errors caused by external factors, improving the precision and reliability of the measurement process.
Implementation Method 1
a detector for acquiring images of a deformed composite pattern reflected from the measurement object
Data Source
AI summary
The present disclosure is related to a system and a method for 3D shape measurement of a freeform surface based on high-speed deflectometry using composite patterns. More particularly, a system for profile measurement based on high-speed deflectometry using composite patterns includes: a composite pattern generation part to project a composite pattern generated by synthesizing patterns having different frequencies to a measurement object; a detector to acquire images of a deformed composite pattern reflected from the measurement object; and a phase acquisition part to acquire wrapped phases by each frequency from the composite pattern and unwrapped phases from the respective wrapped phases.