Mass Flow Controller Gain Switching for Crosstalk Reduction
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Solution Overview
Problem
In semiconductor manufacturing, existing mass flow controllers face challenges in controlling flow rates without excessive response to pressure changes, leading to crosstalk issues when one supply channel is closed or its flow rate changes significantly, affecting other channels.
Innovation Solution
A mass flow controller with a flow rate sensor, control valve, and calculation section that distinguishes between a 'changing period' and a 'stable period' for proportional control, using different gain functions to quickly follow flow rate setting changes while minimizing responses to disturbances like pressure changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a related art PID control method with a single gain function is used, then the flow rate can be controlled, but the flow rate excessively responds to pressure changes when pressure changes beyond a certain level, causing crosstalk between supply channels
Solution Approach 1:
The patent applies dynamics by switching between two different gain functions based on the operational state. When the flow rate setting value is changing, a first gain function is used that allows larger gain values for faster response. When the flow rate setting value is stable, a second gain function is used that employs smaller gain values to suppress excessive response to pressure disturbances. This dynamic switching resolves the contradiction between maintaining control stability and preventing excessive response to pressure changes.
Solution Approach 2:
The patent changes the control parameter (gain value) based on the operational condition. By substituting the flow rate setting value into different functions, the gain value dynamically adapts: higher gains during transient periods for fast tracking, and lower gains during steady states for disturbance rejection. This parameter change strategy effectively addresses the technical contradiction.
2Speed
If the gain value is increased to quickly follow flow rate setting changes, then the speed of response improves, but the flow rate becomes more sensitive to pressure changes and disturbances
Solution Approach 1:
The patent dynamically adjusts the gain value by switching between two functions based on whether the flow rate setting value is changing or stable. During changing periods, the first function provides larger gain values for fast response. During stable periods, the second function provides smaller gain values for stability. This dynamic approach resolves the contradiction between speed and stability.
Solution Approach 2:
The control system operates in periodic phases: a changing period when the flow rate setting value is changing, and a stable period when it is stable. During the changing period, aggressive control with higher gain is applied. During the stable period, conservative control with lower gain is applied. This periodic switching of control strategies resolves the speed-stability contradiction.
Data Source
AI summary
A mass flow controller has: a flow rate sensor section that measures the flow rate of a fluid and outputs a flow rate measurement signal indicating the measurement value; a flow rate control valve disposed upstream or downstream of the flow rate sensor section; a calculation section that calculates a feedback control value to be supplied to the flow rate control valve by performing at least a proportional calculation on the deviation of the flow rate measurement value indicated by the flow rate measurement signal from a flow rate setting value; and an opening control signal output section that generates an opening control signal based on the feedback control value and outputs the opening control signal to the flow rate control valve. The function used for calculating the gain value in the proportional calculation differs between a changing period and a stable period.