Hybrid Profilometry Apparatus for Depth Range and Precision
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Solution Overview
Problem
Conventional three-dimensional profilometry methods face challenges in achieving high accuracy and large measurable depth range due to phase ambiguities and time-consuming decoding processes, particularly when dealing with surface discontinuities and varying depth resolutions.
Innovation Solution
A method and apparatus that synchronously or asynchronously project random speckle and structured fringe patterns onto an object, using two different wavelengths, and combine absolute and relative phase information from detected images to eliminate 2π ambiguities and improve depth measuring accuracy while maintaining a large measurable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-shifting profilometry is used to achieve high measurement precision, then surface depth analysis accuracy is improved, but multiple interference images need to be acquired which reduces inspection efficiency
Solution Approach 1:
The patent combines absolute phase measurement (random speckle) and relative phase measurement (structured fringe) into a single hybrid projection system. This merging allows both absolute depth range and high precision to be achieved simultaneously in one-shot measurement, resolving the contradiction between measurement precision and inspection efficiency.
Solution Approach 2:
The patent segments the measurement function into two complementary components: random speckle projection for absolute phase information (depth range) and structured fringe projection for relative phase information (measurement precision). This segmentation allows each component to optimize its specific function while working together to eliminate the time-consuming multi-image acquisition requirement.
2Measurement precision
If phase-shifting profilometry is used to achieve high measurement precision, then surface depth analysis accuracy is improved, but 2π phase ambiguities occur when surface discontinuity exceeds 1/4 of the projected period
Solution Approach 1:
The patent introduces random speckle projection as an intermediary mechanism that provides absolute phase information. This intermediary resolves the 2π phase ambiguities inherent in structured fringe projection by establishing the correct fringe order through correlation-based absolute phase measurement, ensuring reliable profiling results even for large surface discontinuities.
Solution Approach 2:
The patent creates a composite measurement approach by combining two different projection methods (random speckle and structured fringe) with complementary characteristics. The random speckle component handles absolute depth range without phase ambiguity, while the structured fringe component provides high precision relative measurements, together forming a reliable hybrid system.
3Reliability
If gray code profilometry is used to eliminate phase ambiguity, then surface profile detection without phase ambiguity is achieved, but multiple structural grey-code patterns need to be projected which increases time consumption
Solution Approach 1:
The patent extracts the absolute phase measurement function from the time-consuming multi-pattern gray code sequence and implements it through random speckle projection with correlation-based decoding. This extraction eliminates the need for multiple structured pattern projections while maintaining the ability to resolve phase ambiguities, significantly reducing measurement time.
Solution Approach 2:
The patent replaces the mechanical sequence of multiple gray code pattern projections with a single random speckle projection followed by computational correlation analysis. This substitution transitions from a time-sequential mechanical process to a parallel computational approach, eliminating the time-consuming multi-pattern projection requirement.
4Length of stationary object
If random speckle profilometry is used to achieve large depth measuring range, then depth of field is improved, but depth resolution and accuracy are reduced due to small lens apertures
Solution Approach 1:
The patent merges random speckle projection (providing large depth range) with structured fringe projection (providing high depth resolution) into a hybrid system. This combination allows the system to achieve both the large measurable depth range from random speckle and the high precision from structured fringes simultaneously, resolving the trade-off between depth range and depth resolution.
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 enhances the accuracy and range of surface profile measurement, overcoming limitations of existing methods by eliminating phase ambiguities and allowing for one-shot measurements with improved depth resolution.
Implementation Method 1
a random-speckle generating module, generating a random-speckle light beam projecting onto a tested object for forming a reflecting random-speckle beam
Implementation Method 2
generating a random-speckle light beam projecting onto a tested object for forming a reflecting random-speckle beam
Implementation Method 3
a structured fringe generating module, generating a structured fringe light beam projecting onto the tested object for forming a reflecting structured fringe beam
Implementation Method 4
an image acquiring module, detecting the reflecting random speckle beam and the structured reflected fringe beam for generating a random-speckle image and a structured fringe image
Implementation Method 5
determining a profile (depth) information of a tested surface of the object according to the random-speckle image and structured fringe image
Data Source
AI summary
The present invention provides measuring apparatus and method for three-dimensional profilometry of an object, wherein a random-speckle beam and a structured fringe beam are projected onto the object and reflected therefrom for forming deformed random-speckle beam and structured fringe beams that are separately acquired by an image acquiring device thereby obtaining a random-speckle image utilized to determine an absolute phase information of each position on the surface of the object, and a structured fringe image utilized to determine a relative phase information for each position of the surface of the object. Each absolute phase information and each relative phase information corresponding to each position are converted into an absolute depth and a relative depth, respectively. Finally, the depth information of each position on the surface of the object is calculated by combining the corresponding absolute depth and the relative depth whereby the surface profile of the object can be established.