Flow Control Device Feed Forward Feedback Decoupling
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Solution Overview
Problem
Existing flow control devices for semiconductor manufacturing processes face challenges in responsiveness, particularly due to the dominance of PID control, which limits response speed, and the complexity of adjusting feed forward and feedback parameters, requiring significant manhours for calibration.
Innovation Solution
A flow control device that separates feed forward and feedback current generation, allowing for independent adjustment of control voltages, thereby improving responsiveness without mutual interference between control components, and utilizing analog circuits for stable control despite slow response sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PID control is used for flow control, then stability is improved, but response speed deteriorates
Solution Approach 1:
The control signal is segmented into three separate components: feed forward signal (provides immediate response), proportional signal (provides stability), and integral signal (eliminates steady-state error). Each component is generated independently and then combined, allowing the system to achieve both fast response and stable control without the trade-off present in traditional PID control
2Manufacturing precision
If feed forward and feedback parameters are adjusted together, then control precision is improved, but adjustment complexity increases
Solution Approach 1:
The adjustment process is segmented into independent stages: first adjust the feed forward gain (affecting response speed), then adjust proportional and integral gains (affecting stability). This segmentation eliminates the need for complex correlated adjustments of multiple parameters simultaneously, reducing adjustment complexity while maintaining control precision
Solution Approach 2:
The feed forward component is adjusted first as a preliminary action to establish the desired response characteristics. This preliminary adjustment simplifies subsequent adjustments of the feedback components, as the system's basic response behavior is already optimized, reducing the overall complexity of the tuning process
Data Source
AI summary
In a flow control device 100, a comparator 40 outputs a first control voltage Vref based on a comparison of an instruction value signal Vi1 of the flow volume and a signal Vi2 according to the sensor output signal Vs. A feedback current generator 30 generates a feedback current Ifb according to a difference between the sensor output signal Vs and a signal Vi2 according to the instruction value signal Vi1. A feedback voltage generator 50 is a resister. A feed forward current generator 20 generates a feed forward current Iff according to the instruction value signal Vi1. A synthesis unit 60 generates a second control voltage Vdrv* obtained by adding to the feedback voltage Vfb a voltage according to a sum of the feedback current Ifb and the feed forward current Iff. The valve unit 90 is controlled according to the first and the second control voltage Vref, Vdrv*.