Chemical Flow Rate Control Using Model Switching Under Microbubbles
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Solution Overview
Problem
Ultrasonic flowmeters used in semiconductor and flat panel display manufacturing processes face reduced measurement sensitivity due to microbubbles in the chemical solutions, leading to errors in flow rate measurement.
Innovation Solution
A flow rate control apparatus that includes a flow rate measuring unit with dual ultrasonic sensors, a flow rate control unit with a PID controller and constant pressure valve, and a processor that switches between two modes based on flow rate thresholds, using a smoothing switching algorithm and a flow rate estimation model for accurate control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an ultrasonic flowmeter is used to measure flow rate from outside the flowmeter, then non-contact measurement is achieved, but microbubbles in the chemical solution are collected around the ultrasonic sensor reducing measurement sensitivity
Solution Approach 1:
The system dynamically switches between two operational modes: using actual measured flow rate data when measurement quality is high, and switching to estimated flow rate data from a flow rate estimation model when measurement quality degrades due to microbubble interference. This dynamic adaptation resolves the contradiction by adjusting the measurement strategy based on real-time conditions.
Solution Approach 2:
A flow rate estimation model acts as an intermediary when direct ultrasonic measurement becomes unreliable. The model provides alternative flow rate data when microbubbles interfere with sensor measurements, maintaining system reliability without requiring direct contact between the sensor and the chemical solution.
2Reliability
If actual measured flow rate is used for control, then accurate real-time control is achieved, but measurement errors occur when microbubbles are present
Solution Approach 1:
The system implements feedback through a mode determination unit that continuously monitors measurement quality and switches between measurement modes. When ultrasonic measurements become unreliable due to microbubbles, the feedback mechanism triggers a switch to the flow rate estimation model, maintaining control reliability despite degraded measurement precision.
Solution Approach 2:
The system changes the parameter source from actual measured flow rate to estimated flow rate based on the determination of measurement quality. This parameter change allows the control system to maintain reliability by using appropriate data sources depending on the presence of microbubbles.
3Reliability
If flow rate control is switched between different modes, then measurement reliability is improved, but system complexity increases
Solution Approach 1:
The system performs self-service by automatically determining measurement quality and selecting the appropriate operational mode without external intervention. The mode determination unit autonomously switches between using actual measured data and estimated data based on the presence of microbubbles, improving reliability while keeping the automation logic relatively simple.
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
The apparatus provides improved reliability in flow rate control by minimizing errors caused by microbubbles, ensuring stable and accurate measurement and control of chemical solution flow rates.
Implementation Method 1
The ultrasonic flowmeter transmits and receives an ultrasonic signal (or an ultrasonic beam) from an ultrasonic sensor and calculates the time difference to measure the flow rate
Implementation Method 2
calculates the time difference to measure the flow rate
Data Source
AI summary
A flow rate control apparatus with improved reliability is provided. The flow rate control apparatus comprises a flow rate measuring unit for measuring a flow rate of chemical solution in a chemical solution supply line, a flow rate control unit for comparing a preset target flow rate profile and an applied flow rate profile, and controlling the flow rate of the chemical solution so that the applied flow rate profile matches the target flow rate profile, and a processor for switching the flow rate control unit to a first mode in response to a signal for the flow rate of the chemical solution measured by the flow rate measuring unit being less than a preset level, wherein, in the first mode, the applied flow rate profile includes a profile of a flow rate estimation model simulated using a flow rate of chemical solution measured by the flow rate measuring unit.