| Plasma cutting as one of the main way of sheet metal hot cutting has been widely applied in industrial sheet metal cutting production. Fine plasma cutting is ordinary plasma cutting upgrade, which has greatly improvement in the aspect of energy consumption, cutting quality and cutting efficiency. Plasma cutting power supply is plasma cutting power plant and cutting current and cutting gas are important process parameters which affect the cutting quality. Therefore, this paper mainly research the fine plasma cutting power supply control system to achieve the precise control of cutting current and cutting gas.Based on plasma cutting technology, it introduced the basic operating principle of fine plasma cutting. It designed the fine plasma cutting power supply hardware, which was structured based on master-slave PLC control system. It selected the model of main electrical components, including electromagnetic directional valve, check valve and current sensor.Through studying the characteristics of plasma arc, it designed two control strategies of cutting current, open-loop control and closed-loop control. Based on the research of output characteristic for plasma cutting power supply, it established a open-loop control system for cutting current, which the core is current calibration. Based on the research of the step response for plasma cutting power supply, it established PI control model for plasma cutting current. With the help of MATLAB, it did the simulation experiment of the PI control. and then to experiment of two kinds of control strategy for cutting current, the experimental results showed that PI control is better than open-loop control In the aspect of waveform quality and stability.Through the analysis of the six kinds of gas process requirement of fine plasma cutting, it designed the schematic diagram of the gas control and gas console, and compiled gas control process tables. By analyzing the working principle of electric proportional valve and the control algorithm, the cutting gas control system which the core is electrical proportional valve was constructed. Finally, by testing the cutting gas control system, it verified the feasibility of cutting gas control system.It distributed the input and output points of the PLC controller, which the paper selected. it designed the main circuit of the control system of the fine plasma cutting, and the connection circuit, in which the electric proportional valves and current sensors are connected to the simulation module of the PLC. It designed the communication circuit, in which the host PLC communicates with the touch screen. According to the fine plasma cutting process, it designed the PLC control system software of the main program and subroutine.To complete the design of human-computer interface software, it included Include monitoring interface, process selection interface, debugging interface, alarm interface and help interface. It could carry out cutting process monitoring, process setting and selection, system debugging, alarm records, and real-time communication. It improved the automation and operational simplicity of the fine plasma cutting power supply control system.Finally, combined with the principle prototype of fine plasma cutting power supply to carry out cutting process experiment, it verified the feasibility of the system. At the same time, by detecting the cutting precision and cutting quality, the result showed that the system meets the design requirements. |
