Surface Shape Measurement Using Overlapping Interference Regions
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Solution Overview
Problem
Conventional surface shape measurement techniques using interferometers face accuracy limitations due to restrictions on the number of terms in polynomials for expressing system errors, leading to reduced measurement accuracy and increased calculation times or memory shortages.
Innovation Solution
A method involving the division of the target surface into overlapping regions, where an image sensor detects interference patterns to generate average data, correction data, and combine these to accurately separate and correct system errors, thereby improving measurement accuracy without excessive computational burden.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of terms of polynomials for expressing system error is increased to improve measurement accuracy, then measurement precision improves, but calculation time increases and computer memory capacity becomes insufficient
Solution Approach 1:
The patent divides the target surface into multiple measurement regions and processes each region separately. By segmenting the measurement data and using overlapping regions to establish relationships between regions, the system can achieve high measurement accuracy without requiring an excessive number of polynomial terms, thus avoiding excessive calculation time and memory usage.
Solution Approach 2:
The patent introduces a new dimension of processing by dividing the surface into multiple regions and using the overlap between regions as an additional constraint. This regional division approach transforms the problem from a global polynomial fitting challenge into localized measurements that can be combined, reducing the overall computational burden while maintaining accuracy.
2Measurement precision
If the number of terms of polynomials for expressing system error is increased to improve measurement accuracy, then measurement precision improves, but computer memory capacity becomes insufficient
Solution Approach 1:
By dividing the measurement into multiple regions and processing each region independently with fewer polynomial terms, the patent reduces the size of the matrices that need to be stored in memory. The segmentation allows the system to achieve high accuracy through regional measurements and overlap constraints rather than through a single large-scale polynomial model.
3Productivity
If the number of terms of polynomials for expressing system error is limited to reduce calculation time and memory usage, then productivity improves, but measurement precision deteriorates
Solution Approach 1:
The patent achieves high measurement precision with limited polynomial terms by segmenting the surface into multiple regions. The overlap between adjacent regions provides additional constraints that enable accurate determination of system errors and alignment errors even when using fewer polynomial terms per region, thus maintaining productivity while improving precision.
Solution Approach 2:
The patent uses the overlapping regions between adjacent measurement regions as feedback to refine the measurement results. By comparing measurements in overlapping areas and adjusting the polynomial coefficients accordingly, the system can achieve high accuracy even with limited terms, as the overlap information provides corrective feedback that compensates for the limited polynomial representation.
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 enables precise surface shape measurement by effectively averaging measurement results across overlapping regions, reducing system error impact and enhancing accuracy while managing computational constraints.
Implementation Method 1
causing an image sensor to detect an interference pattern formed by measurement light reflected by the measurement target region and reference light reflected by a reference surface
Data Source
AI summary
The present invention provides a method of calculating a surface shape of a target surface, including the steps of defining, as a measurement target region, each of a plurality of regions on the target surface in which adjacent regions overlap each other, and obtaining data that give the heights at the plurality of positions in each of the plurality of regions, and removing, for each of the plurality of regions, an average data from the data that are obtained in the step of obtaining the data and give the heights at the plurality of positions in each of the plurality of regions, thereby generating correction data for each of the plurality of regions.