Frequency-Scanning Interferometry Distance Tracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Frequency-scanning interferometry (FSI) systems face accuracy and precision issues due to sensitivity to errors in phase measurement and 'drift error' when measuring long distances, especially when the distance changes during measurement, as they struggle to simultaneously determine absolute distance and the rate of change with respect to laser frequency.
Innovation Solution
The method involves using two lasers with varying frequencies, allowing independent measurement of interferometer phases to solve for both the absolute distance and the rate of change, eliminating the need to hold the distance constant and reducing error magnification, enabling precise tracking of distance changes during measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If frequency-scanning interferometry is used to measure long distances, then the measurement range is extended, but measurement precision deteriorates due to sensitivity to phase measurement errors and drift error
Solution Approach 1:
The measurement process is segmented into multiple frequency sweeps, with each sweep providing a partial measurement. The final distance is obtained by combining results from multiple sweeps, which reduces the impact of phase measurement errors and drift in any single sweep.
Solution Approach 2:
The system performs periodic frequency sweeps across the laser frequency range. By conducting multiple periodic sweeps and averaging the results, the system reduces random errors and drift effects while maintaining the ability to measure long distances.
2Measurement precision
If the distance is held constant during measurement, then measurement accuracy is improved, but the ability to track distance changes is reduced
Solution Approach 1:
The system uses feedback from multiple frequency sweep measurements to continuously update the distance measurement. This allows the system to track distance changes while maintaining accuracy through iterative refinement of the measurement results.
Solution Approach 2:
The system performs preliminary frequency sweeps to establish a baseline measurement before tracking distance changes. This preliminary action allows subsequent measurements to focus on detecting changes while maintaining overall accuracy.
3Productivity
If fast frequency tuning is used, then measurement speed is improved, but measurement precision deteriorates due to increased sensitivity to drift error
Solution Approach 1:
The fast frequency tuning is segmented into multiple smaller sweeps rather than one large sweep. This segmentation reduces the total frequency range covered in each sweep, thereby reducing drift error accumulation while maintaining high measurement speed through parallel processing of multiple sweeps.
Solution Approach 2:
The system uses periodic frequency sweeps at high speed, with each sweep covering a limited frequency range. The periodic repetition allows averaging of results to reduce drift effects while maintaining the high measurement speed enabled by fast laser tuning.
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 measurement precision and reduces technical requirements for the lasers, allowing for higher accuracy and faster measurement rates while minimizing errors caused by distance changes, and enabling the use of slowly tuned lasers.
Implementation Method 1
The significant property of an interferometer is that the intensity of the detected light waves with changes in the relative lengths of the arms, due to interference between the portions of waves that have propagated along each arm.
Implementation Method 2
when the frequency of the waves is varied, the resulting change in the phase of the detected intensity in each interferometer is proportional to the optical path difference between the arms of that interferometer
Data Source
Figure 1~3
Figure 2(a)~2(b)
Figure 4(a)~4(b)
AI summary
A method of tracking the position of an object, comprising using reference interference data from first output beam, reference interference data from a second output beam, measurement interference data from the first output beam, measurement interference data from the second output beam, and knowledge of the difference between the absolute phase offset of the first output beam and the absolute phase offset of the second output beam for both a reference interferometer(15') and a measurement interferometer (15) to calculate a parameter indicative of the absolute phase offset of the measurement interferometer (15) for the first output beam. The calculated parameter is used to calculate the ratio of the optical path differences of the measurement interferometer (15) and the reference interferometer (15').