| The compressibility of gas it makes difficult to accurately control the position of the cylinder in the pneumatic valve positioner. Try to solve this problem, the paper carries outs the following studies:1.The working principle of the valve positioned has been analyzed, especially for the piezoelectric valve. By application of the STC12C5A60S2 microprocessor the hardware design of control system has proceeded, including the microprocessor I/O resource allocation, power supply circuit, Ⅰ/Ⅴ converter circuit, AD sampling circuit, the piezoelectric valve drive circuit, valve position feedback detection circuit, and buttons and LCD circuit etc.2.According to the characteristics of the piezoelectric valve and pneumatic actuator, a PID control algorithm is proposed based on the portion control and positive & negative PWM pulse. The fuzzy control technology has been adopted to improve the control properties.3. Based on the algorithm above, the application program based on the uC/OS-II real-time operating system has been developed; it includes the main control module and configuration module. The main control module is applied to controlling piezoelectric valve, and to adjusting the gas flow in and out of the cylinder; and the configuration module assumes the task of parameter setting and parameter self-tuning function. The fuzzy PID control algorithm bas on positive & negative PWM pulse has been applied to the smart valve positioners.The control system of smart valve designed in this paper is convenient to use; and it runs stably and accurately. |
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