Positive and negative pressure continuous control system based on vacuum pump

The PID control method discusses the system characteristics in detail and tests. The simulation and experimental results show that the positive and negative pressure continuous control system based on the vacuum pump has good dynamic and static characteristics, strong robustness, a certain flexibility on the system parameter changes, and can better meet the requirements of high precision and high response of the system. . The test results also prove the correctness of the system mathematical model.

0刖g Various space vehicles will be directly affected by the space vacuum environment during the space flight. Therefore, it is necessary to set up a test device for simulating the flight environment of aircraft on the ground. B can only eliminate various hidden dangers in flight by only understanding the conditions and characteristics of the spacecraft working in the space before the various aircraft have passed through the ground. To achieve the purpose of flight control. The positive and negative pressure continuous control system is a system that simulates the variation of the flying height of the aircraft by controlling the gas pressure.

Vacuum pumps are devices that use mechanical, physical, chemical, or physicochemical methods to obtain, improve, and maintain vacuum in enclosed spaces. They are often used in vacuum technology. At present, vacuum technology has been widely used in the industrial sectors such as machinery, electronic appliances, aerospace and cryogenics and scientific and technological research. The vacuum system constructed using a vacuum pump is mainly used for open-loop control applications. The adjustment of the working negative pressure employs a simple switch control, but it cannot achieve a high-precision and high-response continuous closed-loop control of the vacuum in a closed chamber.

An air pump is used as the negative pressure source to combine the vacuum system and the pneumatic servo control system organically. The positive and negative pressure continuous control system based on the vacuum pump is established and the fuzzy PID controller is used to control the system. The study has drawn some useful conclusions and laid the foundation for the in-depth study of the combination of pneumatic technology and vacuum technology.

1 system composition and mathematical description 1.1 system composition and working principle Vacuum pump based on positive and negative pressure continuous control system schematic diagram as shown, which is mainly by the vacuum pump, positive pressure gas source, positive and negative pressure adjustment device and vacuum chamber and other parts composition. By adjusting the positive and negative pressure adjustment devices, positive and negative pressure high precision and high response continuous control can be achieved.

The vacuum pump positive and negative pressure continuous control system working conditions include a positive pressure inflation state and a negative pressure suction state. Under negative pressure pumping, the vacuum pump evacuates through the vacuum chamber and positive and negative pressure regulators. In the positive pressure inflated state, the positive pressure gas source is inflated by the positive and negative pressure regulating devices, and the positive and negative pressure regulating devices are closed to the inlet of the vacuum gas chamber, and the vacuum pump extracts gas from the vacuum gas chamber.

1.2 Systematic Mathematical Model Based on the above analysis of the working principle of the continuous positive and negative pressure control system based on vacuum pump, the flow of gas in the positive and negative pressure continuous control system is a very complicated thermodynamic process, in the two fields of pneumatic technology and vacuum technology. The relevant theories, respectively, from the positive pressure inflation and negative pressure pumping two kinds of working conditions on the system model for a detailed derivation. The mathematical description of the system here is briefly described as follows.

Time table simulation calculation parameter parameter value positive pressure air source pressure/VkPa400 vacuum chestnut limit pressure; vPa200 vacuum chamber volume r/m30.000 2 gas temperature 77K293 gas constant. Mkg1K, 2871 Gas adiabatic index Female 1.4 Flow coefficient 0.6H Proportional coefficient v/On.V1) 0.0001 Nominal diameter d/m 0.006 Vacuum pump Nominal pumping speed V (m3IT1) 3 It can be seen that other parameters of the system remain unchanged When the volume of the vacuum chamber becomes larger, the response of the system becomes slower. If the oscillation occurs when the pressure difference is too large when moving from the positive pressure source to the negative pressure source, it may be considered to appropriately increase the vacuum chamber volume for buffering. However, this should take into account the influence on the system response.

(2) Positive pressure inflated state 1) Above 2) The above equation (1) (4) is a mathematical model for describing a positive and negative pressure continuous control system based on a vacuum pump.

2 simulation research simulation time / s vacuum chamber volume on the system performance 1. vacuum chamber is 0.1L2. vacuum chamber is 0.2L (2) vacuum pump parameters on the system performance. From the simulation results, the vacuum pump performance also has an impact on the system, the greater the nominal pumping speed of the vacuum pump, the faster the system response. The smaller the ultimate pressure, the faster the system responds. The lower the pressure in the chamber, the slower the change in pressure. This is due to the fact that the actual pumping speed of the vacuum pump becomes smaller as the pressure in the chamber approaches the ultimate pressure. Obviously, the system response of a vacuum pump with a high nominal pumping speed and a small limit pressure is relatively faster.

For the vacuum-pump-based positive and negative pressure continuous control system, MATLAB simulation software was used to solve the differential equations (1) and (4) with the fourth-order Runge-Kutta method, and the vacuum pump-based positive and negative pressure continuous control system operating characteristics were analyzed. Simulation parameters such as Table (1) vacuum chamber volume on the system performance. From the island time / / s vacuum pump performance on the system 2 nominal pumping speed 3m3 / h, the limit pressure is 200Pa 2.2 system tracking signal expected response performance (1) system tracking step signal response. a is the simulation result of the system tracking 10 kPa step signal, and b is the simulation result of the system tracking the 40 kPa step signal. By comparing the simulation curves of the two graphs, it can be seen that the size of the step signal tracked by the system has a large impact on the system response time, and the higher the expected pressure, the shorter the response time of the system.

The simulation time of the simulation time//s system tracking step signal shows that the system tracking rising signal is obviously faster than the falling signal response.

This is because under positive pressure working conditions, the pressure in the chamber is significantly different from the pressure in the positive pressure source, and the inflation process is rapid, so the system can respond quickly. In the negative pressure working condition, the working point is closer to the ultimate pressure of the negative pressure source vacuum pump. The smaller the actual pumping speed of the vacuum pump, the slower the response of the system.

(3) The system tracks the sinusoidal signal response. In the system, when the system traces the sine wave, there is a small ripple in the rising curve. This is because the pressure of the positive pressure gas is very large compared with the pressure in the chamber. The flow rate through the positive and negative pressure regulators is the speed of sound and the inflation speed is too fast. To. Curve 2 Compared with curve 1, the operating point of the system is closer to the pressure of the positive pressure source, and the ripple phenomenon of the rising curve is relatively insignificant.

Considering that the positive and negative pressure continuous control system based on the vacuum pump is a strong non-linear system, according to the above analysis of the system simulation study, the system parameters and system operating point changes affect the performance of the system.

In order to realize the high response and high precision of the positive and negative pressure continuous control system based on the vacuum pump, a fuzzy PID controller as shown is proposed. Fuzzy control is adopted within a large error range, and the response speed is fast, and the overshoot is small, and the system is robust. PID control is used when the error is very small, that is, almost close to the fuzzy control zero, to reduce the system's steady-state error and improve the system's control accuracy. In the experimental research process, the influence of system structural parameters and different expected signal sizes on the system performance was mainly studied. The test results are respectively shown in Fig. 11. Simulation time "s system tracking square wave signal simulation results PID controller controlled object chamber 7 fuzzy The higher the negative pressure of the PID control structure, the faster the system response.0 is the response curve of the system tracking square wave signal.When the system tracks square wave, the rising curve is over-tuned, and from the falling curve, the response curve is flat.The above test results It is basically consistent with the results of system simulation research. This also proves the correctness of theoretical analysis and simulation research.

Simulation time f/s step signal is 40kPa. Simulation curve is the test curve of step signal when the volume of vacuum chamber is different. The larger the volume of the vacuum chamber, the slower the system response. n is the system step response curve with the same system parameters but different step signals. Obviously, the larger the step signal, that is, the desired test result also shows that the system adopts fuzzy PID control method to respond quickly, and has strong adaptability to systematic parameter changes and system operating point changes and has good robustness. High precision, to meet the requirements of high precision and high response of the system. When the system tracks step signals, it has good rapidity, and the control effect is almost the same at different working points. From the absolute pressure of lOOkPa to OkPa, the transition time is 2.8s, and the steady-state error does not exceed 50Pa. For the system to track the response curve of the sinusoidal signal, from the curve can also be seen, the system using fuzzy PID control has good tracking, when the tracking frequency is 1Hz, the amplitude of 0.2kPa sine signal, its amplitude error is 2.04 %, the phase-frequency error is 1.2794°.

4 Conclusions A new idea of ​​vacuum positive control and vacuum continuous control system was proposed. The results show that the system consists of a reasonable therapeutic formula. The fuzzy PID control method is feasible for positive and negative pressure continuous control systems based on vacuum pumps and can achieve positive and negative pressures. High precision and high response continuous control. When the absolute pressure drops from 100kPa to 10kPa, the K transition time is 2.8s, the steady-state error does not exceed 50Pa, and the tracking frequency is 1Hz. When the amplitude is 0.2kPa sinusoidal signal, the K-amplitude error is 2.04%. Phase frequency The error is 1.279 The positive and negative pressure continuous control system based on the vacuum pump is a strong non-linear system. The change of the system parameters and the change of the system E have a greater impact on the system performance.

The results of the simulation and experimental research of the positive and negative pressure continuous control systems based on the vacuum pump are basically the same, which proves the correctness of the given system mathematical model.

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