Interferometric Position Measurement Calibration for Pressure Errors
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Solution Overview
Problem
Position-measuring systems in metrology face challenges in achieving high accuracy due to the influence of ambient air pressure changes, which conventional methods struggle to account for effectively, leading to measurement errors despite environmental control measures.
Innovation Solution
A method and system that utilize interferometry to measure sample stage movement and pressure changes in the measuring area, with a calibration rule established through multiple measurements at different pressures to correct for pressure-induced errors, allowing for improved position determination without requiring pressure regulation in the measuring area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensors and environmental control are used to determine refractive index and correct positions, then measurement accuracy is improved to some extent, but measurement precision remains insufficient due to unaccounted pressure-induced errors
Solution Approach 1:
The patent replaces mechanical/environmental control methods with an optical interference-based measurement system. The second measuring system uses optical interference to detect pressure-induced path length changes, substituting conventional mechanical pressure sensors and environmental control mechanisms with a more precise optical detection method that directly measures the relevant physical quantity.
Solution Approach 2:
The patent introduces a second measuring system as an intermediary that specifically measures pressure-induced path length changes. This intermediary system provides correction data that compensates for the errors in the primary position measurement system, acting as a mediator between the uncontrolled pressure environment and the position measurement accuracy requirement.
2Measurement precision
If pressure regulation is implemented in the measuring area, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent extracts the pressure measurement function from the position measurement system by introducing a separate, dedicated second measuring system. This allows the position measurement system to remain simple while the extracted pressure measurement component provides the necessary correction data, separating the two functions to avoid complexity.
Solution Approach 2:
The patent changes the measurement parameter from directly controlling pressure to measuring and compensating for pressure-induced optical path length changes. Instead of maintaining constant pressure through complex regulation, the system measures the path length changes caused by pressure variations and uses these measurements to correct position data, transforming a control problem into a measurement and compensation problem.
3Measurement precision
If multiple measurements at different pressures are performed to establish calibration rules, then pressure dependence is reduced, but measurement time increases
Solution Approach 1:
The patent performs preliminary calibration measurements at different pressures to establish the relationship between pressure and optical path length changes. This preliminary action creates a calibration model that can then be applied to correct subsequent measurements, allowing the time-consuming multi-pressure measurements to be performed once during calibration rather than repeatedly during normal operation.
Solution Approach 2:
The patent implements a feedback mechanism where the second measuring system continuously monitors pressure-induced path length changes and provides real-time correction data to the evaluation unit. This feedback loop allows the system to automatically compensate for pressure effects during position measurements without requiring continuous multi-pressure calibration measurements.
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 accuracy by accounting for pressure-induced influences, reducing errors and allowing for cost-effective production of position-measuring systems with high precision, even under large pressure fluctuations.
Implementation Method 1
a first measuring system which is arranged in the measuring area, measures, by use of interferometry, the movement of the sample stage in the at least one direction
Implementation Method 2
a second measuring system which measures a change in distance corresponding to a change in pressure of the gaseous medium in the measuring area
Data Source
AI summary
A method is provided for calibrating a position-measuring system which includes the following steps: a) multiple measurements of positions of a structure of a sample held by a sample stage at different pressures of the gaseous medium in which the sample stage is arranged, b) ascertaining the pressure dependence when determining actual positions by use of an evaluation unit, c) establishing a calibration rule based on the ascertained pressure dependence, and d) applying the calibration rule when determining the actual positions.