Differential Flow Sensor Using Moiré Interference Patterns
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Solution Overview
Problem
Existing methods for measuring differences in flow rates between targets in lithographic apparatuses rely heavily on the calibration of two different sensors, which can lead to inaccuracies due to sensor drift and calibration errors.
Innovation Solution
A system and method using a first member with a first pattern and a second member with a second pattern, where the speed of rotation of each member is based on the flow rate of its respective target. The interaction between the patterns generates an interference pattern, such as a Moiré pattern, that indicates the difference in rotational speeds and thus the difference in flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two different sensors are used to measure flow rates at inlet and outlet, then flow rate difference can be obtained, but measurement precision deteriorates due to sensor drift and calibration errors
Solution Approach 1:
The patent merges the measurement function into a single differential flow sensor that directly measures the flow rate difference between inlet and outlet. This eliminates the need for two separate sensors and their associated calibration issues, thereby improving measurement precision while maintaining reliability.
Solution Approach 2:
The patent introduces a differential pressure sensor as an intermediary device that measures the pressure difference between inlet and outlet. This pressure difference is then correlated to flow rate difference through calibration, providing a more reliable measurement than direct flow sensor subtraction while maintaining simplicity.
2Reliability
If a single differential flow sensor is used, then measurement reliability improves, but device complexity increases due to sensor integration requirements
Solution Approach 1:
The patent designs the differential flow sensor to perform multiple functions: measuring flow rate difference, detecting leaks, and providing feedback for flow control. This multi-functionality justifies the integrated design and reduces the need for additional separate components, thereby managing device complexity while improving reliability.
3Device complexity
If traditional sensor subtraction method is used, then device complexity remains low, but measurement precision deteriorates due to error accumulation
Solution Approach 1:
The patent combines the measurement function into a single differential flow sensor that directly measures the flow rate difference between inlet and outlet. This eliminates the need for two separate sensors and their associated calibration issues, thereby improving measurement precision while maintaining simplicity.
Solution Approach 2:
The patent introduces a differential pressure sensor as an intermediary device that measures the pressure difference between inlet and outlet. This pressure difference is then correlated to flow rate difference through calibration, providing a more reliable measurement than direct flow sensor subtraction while maintaining simplicity.
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 allows for accurate measurement of flow rate differences without relying on the calibration of two sensors, reducing errors and providing a more direct and accurate method for detecting leaks or measuring intentional flow differences.
Implementation Method 1
the first and second pattern are angularly-varying and are configured to generate an interference pattern by their interaction when the first and second members have a relative difference in their rotational speeds, the interference pattern being indicative of the magnitude of this difference
Data Source
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AI summary
A system for measuring the difference between a property of a first target and a property of a second target, the system comprising a first member and a second member, wherein the first member comprises a first pattern, and the speed of rotation of the first member is configured to be based on the property of the first target; and the second member comprises a second pattern wherein, the speed of rotation of the second member is configured to be based on the property of the second target, further wherein the first and second pattern are angularly-varying and are configured to generate an interference pattern by their interaction when the first and second members have a relative difference in their rotational speeds, the interference pattern being indicative of the magnitude of this difference.