Laser Tracker and Structured Light Scanner 3D Coordinate Registration
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Solution Overview
Problem
Existing coordinate measurement devices face challenges in accurately registering images acquired by scanner devices, particularly when dealing with large flat or curved surfaces, as existing techniques struggle to properly align images taken by handheld scanners.
Innovation Solution
A method utilizing a six degree-of-freedom (DOF) laser tracker and a portable structured light scanner, which includes a projector, cameras, and a processor, projects a pattern of light onto the object surface, and uses epipolar constraints to determine and store three-dimensional coordinates of points on the surface, improving image registration through a predetermined geometric arrangement of cameras and projectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feature matching is used to register images from handheld scanners, then registration works well 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 placed on the surface being measured. The retroreflector provides high-contrast, easily detectable features that enable accurate image registration even on surfaces that lack sufficient natural features. The retroreflector acts as a mediator between the scanner and the surface, ensuring consistent registration accuracy across all surface types.
Solution Approach 2:
The patent changes the parameters of the measurement system by using a retroreflector with specific optical properties (high reflectivity, spherical geometry) that fundamentally alter how features are detected. This parameter change enables the system to detect and register images on surfaces that would otherwise be difficult to measure, expanding the system's adaptability to different surface types.
2Measurement precision
If a laser tracker is used to measure distance and position, then accurate three-dimensional coordinates are obtained, but the measurement process is slower compared to triangulation systems
Solution Approach 1:
The patent merges two measurement systems: a laser tracker for accurate position and orientation measurement, and a structured light scanner for rapid surface scanning. The laser tracker provides precise six-degree-of-freedom pose information, while the structured light scanner quickly captures surface geometry. By combining these systems, the patent achieves both high measurement precision and improved productivity.
Solution Approach 2:
The laser tracker performs preliminary measurement of the retroreflector's position and orientation before the structured light scanner captures the surface data. This preliminary action establishes an accurate reference frame that guides the subsequent rapid scanning process, ensuring both speed and precision in the overall measurement workflow.
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 registration of images acquired by scanner devices, particularly for handheld scanners, by accurately determining and storing three-dimensional coordinates, thereby improving the tracking and measurement of objects with complex surfaces.
Implementation Method 1
A TOF system such as a laser tracker, for example, directs a beam of light such as a laser beam toward a retroreflector target positioned over a spot to be measured
Implementation Method 2
a triangulation system such as a scanner projects either a line of light (e.g. from a laser line probe) or a pattern of light (e.g. from a structured light) onto the surface
Implementation Method 3
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 of determining three-dimensional coordinates of an object surface with a laser tracker and structured light scanner. The method includes providing the scanner having a body, a pair of cameras, a projector, a retroreflector and a processor. The projector and cameras are positioned in a non-collinear arrangement. The projector is configured to project a pattern onto the surface. The method also includes providing the tracker which emits a beam of light onto the retroreflector and receives a reflected beam of light. The first location and orientation is measured with the tracker. The first surface pattern is projected onto the surface. A pair of images of the surface pattern is acquired with cameras. The processor determines the 3D coordinates of a first plurality of points in the tracker frame of reference.