Structured Light Scanner Retroreflector Tracking
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Solution Overview
Problem
Existing coordinate measurement systems face challenges in accurately registering images acquired by scanner devices, particularly when dealing with featureless or large flat/curved surfaces, leading to registration issues and potential drift in image alignment.
Innovation Solution
A method utilizing a structured light scanner with a six degree of freedom retroreflector and a laser tracker, where the scanner is calibrated and tracked to determine its position and orientation, allowing for accurate registration of image frames without relying on object features, using a fixture and predetermined movement patterns to maintain contact and record coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feature matching technique is used to register sequential images, then registration accuracy is improved for objects with many features, but registration fails for large flat or curved surfaces with few features
Solution Approach 1:
The patent introduces a retroreflector as an intermediary object attached to the scanner. The retroreflector serves as a reliable registration feature that works independently of the scanned object's surface features. The coordinate measurement device tracks the retroreflector's position and orientation, providing a stable reference frame for registering sequential images even when the object itself lacks sufficient features.
Solution Approach 2:
The system separates the registration reference from the scanned object by attaching a distinct retroreflector to the scanner. This segmentation allows the registration process to rely on the retroreflector's known geometry and tracked position rather than features of the scanned object, enabling consistent registration across different object types including flat and curved surfaces.
2Measurement precision
If a laser tracker is used to measure distance with high accuracy, then measurement precision is improved, but scanning speed decreases compared to triangulation systems
Solution Approach 1:
The patent merges the advantages of both laser tracker and triangulation scanner by combining them into a hybrid system. The scanner uses triangulation for rapid capture of surface geometry, while the laser tracker simultaneously tracks the retroreflector for precise position and orientation measurement. This combination allows the system to achieve both high scanning speed and high measurement precision.
Solution Approach 2:
The retroreflector serves multiple functions: it provides a tracking target for the laser tracker to determine scanner position and orientation, and it serves as a registration feature for aligning sequential images. This multi-functionality allows the system to achieve both fast scanning and accurate registration without requiring separate systems.
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 precise registration of image frames and determination of three-dimensional coordinates on the object surface, even in featureless regions, improving the accuracy and reliability of coordinate measurement systems.
Implementation Method 1
a six degree of freedom retroreflector coupled to a second side of the body... configured to send a first beam of light to the retroreflector and to receive a second beam of light from the retroreflector
Implementation Method 2
A triangulation system such as a scanner... projects either a line of light (e.g. laser line probe) or a pattern of light (e.g. structured light) onto the surface... The light/pattern emitted from the projector is reflected off of the surface and detected by the camera
Data Source
AI summary
A method is provided for determining the three dimensional coordinates of points on the surface of an object. The method includes providing a structured light scanner and a coordinate measurement device. The coordinate measurement device tracks the location and orientation of the structured light scanner during operation. The location and orientation data is combined with image frames captured by the scanner to allow registration of the image frames relative to each other. The three-dimensional coordinates of points on the surface of the object may then be determined in the frame of reference of the coordinate measurement device.