Piezo Valve Flow Control with Shaped Command Signal Rise
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Solution Overview
Problem
In pressure type flow rate control devices, particularly in semiconductor manufacturing equipment and chemical plants, the response to flow rate rise is delayed when the piezo valve is opened from a closed state, leading to distorted response waveforms and variations in control, especially at low set flow rates.
Innovation Solution
A flow rate control device with a control valve and a piezoelectric element, where an arithmetic processing circuit generates an internal command signal that rises with time from zero and converges to the target flow rate, with slopes at initial rise and convergence being smaller than the slope between them, effectively combining a first-order lag process and a ramp process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a piezo valve is used to control flow rate, then the response speed is improved, but the valve opening response is delayed due to biasing force
Solution Approach 1:
The arithmetic processing circuit generates a command signal that temporarily exceeds the target voltage value when opening the piezo valve from closed state. This preliminary over-voltage action overcomes the biasing force on the diaphragm valve element more quickly, reducing the valve opening delay while maintaining high response speed capability
2Speed
If the rate of change in command signal is increased to improve responsivity, then the flow rate rise speed is improved, but the response waveform becomes distorted especially at low flow rates
Solution Approach 1:
The arithmetic processing circuit dynamically adjusts the command signal characteristics based on the current flow rate state. When the flow rate is low, the circuit reduces the rate of change to prevent waveform distortion, while allowing faster response when the flow rate is higher, thus adapting the control strategy to the operating conditions
3Reliability
If the piezo valve is pressed against the valve seat by biasing means, then leakage prevention is improved, but the valve opening response is delayed
Solution Approach 1:
The arithmetic processing circuit applies a temporary over-voltage signal when opening the valve from closed state, providing enough force to overcome the biasing means that prevents leakage. This preliminary action allows the valve to open quickly despite the biasing force, resolving the contradiction between leakage prevention and fast response
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 smooth gas flow during flow rate rise, even at low settings, while maintaining stable control and responsivity, thereby improving the flow rate control performance.
Implementation Method 1
a piezoelectric element for moving the valve element
Data Source
AI summary
A flow rate control device (8) includes a control valve (6) having a valve element and a piezoelectric element for moving the valve element, and an arithmetic processing circuit (7) for controlling an operation of the control valve, wherein the arithmetic processing circuit is configured to receive an external command signal SE corresponding to a target flow rate when opening the control valve from a closed state so that a gas flows at the target flow rate, and to generate an internal command signal E1 output to a driving circuit for determining a voltage applied to the piezoelectric element based on the external command signal, the internal command signal is a signal that rises with time from zero and converges to a value of the external command signal, and is generated such that a slope at the time of initial rise and a slope immediately before convergence are smaller than a slope therebetween.