Spherically Mounted Retroreflector Runout Error Compensation
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Solution Overview
Problem
Current methods for measuring spherically mounted retroreflectors (SMRs) face challenges due to errors in vertex centering and sphere diameter, leading to measurement inaccuracies, especially with open-air cube corner retroreflectors, which are costly to correct and limit the accuracy of three-dimensional coordinate measurements.
Innovation Solution
The solution involves a spherically mounted retroreflector design with a reference point placed on the SMR to minimize runout error by aligning the axis of symmetry with the beam of light, using a reference ray and reference angle to correct for centering errors, and incorporating a temperature sensor to account for thermal expansions, allowing for more accurate 3D measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If open-air cube corner retroreflectors are used in SMRs, then manufacturing cost is reduced, but measurement precision deteriorates due to vertex centering errors
Solution Approach 1:
The patent replaces mechanical alignment methods with optical methods. Instead of relying on precise mechanical centering of the cube corner retroreflector vertex, the system uses optical detection to identify the vertex position and calculates correction factors. The laser tracker optically detects the retroreflector position and uses computational algorithms to compensate for centering errors, eliminating the need for expensive mechanical precision in SMR manufacturing.
Solution Approach 2:
The patent changes the approach from controlling physical dimensions to controlling measurement parameters. Instead of requiring the vertex to be mechanically centered within tight tolerances, the system measures the actual vertex position parameters, calculates deviation from the ideal sphere center, and applies computational corrections to the measurement data, transforming a manufacturing precision problem into a data processing solution.
2Measurement precision
If expensive high-accuracy SMRs are used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent enables the use of inexpensive SMRs by compensating for their imperfections through computational methods. Instead of requiring expensive, precisely manufactured SMRs with accurately centered retroreflectors, the system uses cheap SMRs and corrects their inherent errors through optical detection and mathematical compensation algorithms, making high-precision measurement accessible with standard, affordable equipment.
Solution Approach 2:
The patent introduces computational algorithms as an intermediary between the imperfect SMR and the measurement system. The correction factor calculation software acts as a mediator that translates the raw, error-containing measurements from inexpensive SMRs into accurate measurement data, bridging the gap between low-cost hardware and high-precision measurement requirements.
3Ease of manufacture
If the vertex is not precisely centered in the sphere, then manufacturing is easier, but measurement accuracy deteriorates due to runout errors
Solution Approach 1:
The patent implements a feedback mechanism where the laser tracker optically detects the actual position of the retroreflector vertex, calculates the deviation from the ideal sphere center position, and uses this feedback information to apply real-time correction factors to the measurements. This closed-loop approach continuously compensates for centering errors without requiring precise mechanical centering during manufacturing.
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 of 3D coordinate measurements by correcting for centering and radius errors, improving the precision of SMR-based measurements without the need for expensive high-accuracy SMRs, and maintaining accuracy across varying temperatures.
Implementation Method 1
The laser tracker sends a laser beam to a retroreflector target. As long as the beam of light strikes the vertex, the beam of returning beam of light retraces the path of the outgoing beam of light back to the tracker.
Data Source
AI summary
A spherically mounted retroreflector (SMR) having a reference point placed on a body of the SMR in a fixed and predetermined relationship to a runout error vector as given in a manufacturer's data sheet. A method for aligning the reference point to minimize measurement error.