3D Coordinate Measurement With Retroreflector Context Matching
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Solution Overview
Problem
Laser trackers face limitations in complexity, maintenance, resistance to shock, and identifying target objects, particularly when an object blocks the laser beam path, requiring a reset of the distance reference or the use of additional components like absolute distance meters.
Innovation Solution
A coordinate measuring device with a housing, motors to direct a light beam, angle measuring devices, and locator camera assemblies to determine 3D coordinates, using shape-and-context matching of retroreflector spots and background objects, and incorporating features like infrared cameras and filters to enhance target identification and beam tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an interferometer is used without an absolute distance meter, then the device complexity is reduced, but the reliability deteriorates when the laser beam path is blocked requiring manual reset
Solution Approach 1:
The patent introduces an absolute distance meter as an intermediary component that works alongside the interferometer. The ADM provides absolute distance measurements that serve as a reference when the interferometer loses tracking due to beam blockage, eliminating the need for manual reset operations while maintaining relatively simple device architecture.
Solution Approach 2:
The system implements feedback by continuously monitoring the interferometer's tracking status and automatically initiating reset procedures when beam blockage is detected. The ADM measurements provide feedback reference values that enable the system to recover from lost tracking conditions without operator intervention, thereby maintaining reliability while keeping the core interferometer architecture simple.
2Reliability
If an absolute distance meter is added to the tracker, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The patent merges the ADM and interferometer systems into a unified coordinate measurement platform. Both distance measurement technologies share common components such as the laser source, beam steering mechanism, and control system, thereby achieving improved reliability through redundancy while minimizing the increase in overall device complexity through resource sharing.
3Ease of operation
If shape-and-context matching is used for retroreflector identification, then the ease of operation is improved, but the device complexity increases due to additional processing requirements
Solution Approach 1:
The system performs preliminary action by pre-storing reference images and characteristics of retroreflectors and background objects in memory. During operation, the shape-and-context matching algorithm compares real-time camera images against these pre-stored references, enabling rapid and accurate target identification without requiring complex real-time processing, thus improving ease of operation while keeping computational requirements manageable.
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
The solution improves the ability to track retroreflectors in complex environments, reduces maintenance needs, and enhances resistance to mechanical shocks, providing accurate 3D coordinate measurements without the need for additional components like absolute distance meters.
Implementation Method 1
A common type of retroreflector target is the spherically mounted retroreflector (SMR), which comprises a cube-corner retroreflector embedded within a metal sphere.
Implementation Method 2
The distance is measured with a distance-measuring device such as an absolute distance meter or an interferometer.
Implementation Method 3
The angles are measured with an angle-measuring device such as an angular encoder.
Implementation Method 4
A gimbal mechanism within the laser tracker may be used to direct a laser beam from the tracker to the SMR.
Data Source
AI summary
A coordinate measuring device is provided having a light source that emits a beam of light. A distance meter measures a distance to a target. A first locator camera assembly includes a first camera and first lights. A second locator camera assembly includes a second camera and second lights. The processor matches retroreflectors in a first image of the first camera and a second image of the second camera based on a shape-and-context matching of retroreflector spots in the first and second image and on an area-context-matching of background objects in the first and second image. The retroreflector spots in the first image produced by illumination of the retroreflectors by the first lights, the retroreflector spots in the second image produced by illumination of the retroreflectors by the second lights. The processor provides a third image that includes both the background objects and markers indicating the matched retroreflectors.