Retroreflector Orientation Determination via Mark Segmentation
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Solution Overview
Problem
Existing coordinate-measuring devices, particularly laser trackers, face limitations in accurately determining the three orientational degrees of freedom of retroreflectors, especially when using glass cube-corner retroreflectors, due to sensitivity issues at large angles of tilt and overlapping marks in camera images.
Innovation Solution
A method involving a programmable control device that obtains a 2D image of markings on a glass prism retroreflector, determines a 2D mathematical representation of these markings, extracts coordinates, and adjusts guess values for orientation angles to improve the figure of merit, using a device with an image sensor, light source, and display to enhance orientation angle determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional laser tracker methods are used to measure retroreflector orientation, then the measurement process is simple, but measurement precision deteriorates at large tilt angles due to mark overlap and sensitivity issues
Solution Approach 1:
The patent divides the retroreflector into multiple distinct marking features (cube corner vertex, front face center, intersection points of reflecting surfaces) that can be individually detected and used to calculate orientation angles. This segmentation of the target object provides multiple reference points for accurate measurement even at large tilt angles where traditional single-mark methods fail.
Solution Approach 2:
The patent transitions from 2D mark detection to 3D spatial coordinate detection by using a camera to capture the spatial positions of multiple features on the retroreflector. By analyzing the 3D coordinates of the vertex, face centers, and intersection points, the system can accurately determine orientation angles without the mark overlap problems that plague 2D methods at large tilt angles.
2Manufacturing precision
If glass cube-corner retroreflectors are used, then manufacturing precision can be improved, but measurement precision deteriorates due to sensitivity to large tilt angles and mark overlap in camera images
Solution Approach 1:
The patent applies preliminary marking to the glass cube-corner retroreflector during manufacturing, placing high-contrast markers at specific geometric locations (vertex, face centers, intersection points) before the measurement process. This preliminary action ensures that the measurement system has reliable reference features to detect, eliminating the sensitivity issues that arise from trying to detect unmarked or poorly marked glass surfaces at large tilt angles.
Solution Approach 2:
The patent uses high-contrast color markings on the glass retroreflector surfaces to enhance detectability. By applying markers with contrasting colors to the glass cube corner features, the camera system can reliably detect the position and orientation of the retroreflector even at large tilt angles where unmarked glass would be difficult to distinguish from the background or mounting structure.
3Ease of manufacture
If simple mark patterns are used on retroreflectors, then ease of manufacture is improved, but measurement precision deteriorates due to mark overlap in camera images
Solution Approach 1:
The patent employs asymmetric mark placement on the retroreflector, positioning markers at specific non-symmetric locations such as the vertex, front face center, and intersection points of reflecting surfaces. This asymmetric arrangement ensures that the pattern remains distinguishable and non-overlapping from various viewing angles, allowing accurate orientation determination while maintaining relatively simple manufacturing processes.
Solution Approach 2:
The patent introduces computational image processing algorithms as an intermediary between the simple physical marks on the retroreflector and the final orientation measurement. These algorithms automatically detect the mark positions, calculate spatial coordinates, and determine orientation angles, thereby achieving high measurement precision even with simple, easily manufactured mark patterns that would otherwise be prone to overlap interpretation errors.
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 improves the accuracy and reliability of determining the three orientational degrees of freedom of retroreflectors, reducing measurement errors associated with large tilt angles and mark overlap, thereby enhancing the precision of coordinate measurements.
Implementation Method 1
obtain a two-dimensional (2D) image of markings on a retroreflector
Data Source
AI summary
A program storage device having instructions that cause a programmable control device to obtain a two-dimensional (2D) image of markings on a retroreflector, determine a 2D mathematical representation of the markings on the retroreflector, extract a first collection of 2D coordinates from the 2D mathematical representation and a corresponding second collection of 2D coordinates from the 2D image of markings, determine a figure of merit, and adjust guess values for three orientation angles of the retroreflector to improve the figure of merit.