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Application of nine point controller in microwave sintering temperature control system of ceramic materials

1 introduction

microwave sintering is a kind of sintering of materials by microwave heating. The birth and development of microwave sintering technology has fundamentally changed the current situation of material sintering process, and has become the focus of material and control research in recent years. The control of sintering temperature will directly affect the quality and performance of new materials. However, due to the complexity of microwave sintering mechanism of ceramic materials, it is impossible to establish an accurate mathematical model for such a complex and difficult system to control the sintering temperature. Therefore, for this kind of system, the traditional PID control is difficult to meet the requirements, and for PID control, in the system design, the selection of control parameters is the core of the design, which increases the difficulty of system design and prolongs the research and development time

the energy measurement range of the drop hammer impact testing machine is 300j, and three experiments can be carried out: a method, B method and C method. In view of the above problems, in order to better meet the requirements of the rapidity and stability of temperature control, this paper adopts a fuzzy intelligent control method, that is, nine point controller, and carries out simulation research with MATLAB

2 principle of nine point controller

the basic control idea of the nine point controller is: when the output value of the controlled object deviates from the set value, the controller automatically adds a force in the opposite direction to force the system to respond quickly and return to the set value

the block diagram of the control system composed of nine point controller is shown in Figure 1:

Figure 1 the block diagram of nine point controller

in Figure 1, R (T) is the set value given by the system, y (T) is the output of the system, then the deviation e=r (T) -y (T), the deviation change rate = (ei-ei-1)/t, t is the sampling period, I and I-1 are the current sampling time and the last sampling time respectively, ± E0 is the allowable deviation of the system (where E0 is the upper limit of error and -e0 is the lower limit of error). The system deviation and the change rate of deviation are divided into three cases, and then nine working cases are combined with Pan Boolean algebra as the analysis tool. Each case represents a kind of operation mode of the system, which is called working condition. The controller adopts different control rules according to different working conditions. The determination of working conditions and the corresponding control rules are shown in the attached table: attached table nine point controller rule table

the nine point controller selects different working conditions according to the given deviation and deviation change rate of the system, and gives the corresponding control force ki to supplement and consume energy to the control object in time, so as to achieve the control purpose and tracking performance requirements

due to the one-to-one correspondence between the control rule table and the phase plane, the phase plane analysis method can be used for the auxiliary design of the nine point controller, mainly to set the parameters in the table, as shown in Figure 2:

Figure 2 the phase plane of the nine point controller

Figure 2 the areas sandwiched by L1 and L2 constitute the zero band of the expected deviation change rate e, and the areas sandwiched by L3 and L4 constitute the expected deviation. K4+, k3+, k2+, k1+, k4-, k3-, k2-, k1- and K0 correspond to the parameters of zone I, II,..., IX controllers respectively. When combined with the specific control object, from the phase plane analysis and experimental results, we can get: K0 control steady-state error; K4- control the negative overshoot and k4+ control the positive overshoot, which constitute two insurmountable limits of the allowable error range; K3+ controls the starting speed; K2+ affects the rise time of the system. Therefore, as long as their values are reasonably selected, the system can meet the requirements of stability, accuracy and rapidity at the same time, and its static and dynamic performance is better than PID controller. Therefore, the setting of the nine point controller is relatively easy

3 application of nine point controller in microwave sintering temperature control system of ceramic materials

in the microwave sintering process of ceramic materials, the temperature needs to be strictly controlled according to the process requirements from temperature rise to sintering, heat preservation and temperature reduction. Because the system uses microwave to heat, the microwave energy has the characteristics of power temperature instantaneous response, and the change of power can immediately change the temperature, Therefore, the control of sintering temperature is actually achieved by controlling the size of microwave power

in the past, most of them used computers to control power output, and Yunnan will speed up the construction of an automobile industry chain with a sales revenue of more than 100 billion yuan, supplemented by accurate temperature measurement, but it is still unable to make microwave sintering achieve a high degree of automation. In addition, in the sintering process, the temperature may be too high because the microwave power is not changed in time or the state of the resonator is not adjusted, which may lead to the melting or heating suspension of the material, or even the failure of sintering. Because it has high requirements for the rapidity and stability of temperature control. At the same time, the system also has the characteristics of large time delay. Based on the above control requirements, the nine point controller is now used to automatically control the equipment

the flow chart of microwave sintering temperature control system is shown in Figure 3. We use a nine point controller to control the thyristor of high-power power power electronic devices to realize the control of microwave power

Figure 3 flow chart of microwave sintering temperature control system

in the control area of the nine point controller, define the deviation e=1200 ℃ - actual temperature, the deviation change rate k3+>k2+>k1+, k4->k3->k2->k1-, and K0 is generally taken as a smaller value, so that the oscillation frequency of the system in steady state is small

it can be seen that the control strategy of the ceramic microwave sintering temperature control system based on the nine point controller is an intelligent control method with variable control strategy, which takes different proportional gains according to the change of system deviation and deviation change rate to realize different control strategies. Its control strategy is simple, easy to realize, and has strong robustness and real-time performance

4 simulation test

the nine point controller divides the control system into 9 different working conditions according to the deviation and deviation change rate, and adopts different control functions under different working conditions. As discussed earlier, complex industrial processes such as microwave sintering have the characteristics of nonlinearity, pure delay, random interference and so on. Its sintering mechanism is also very complex, so it is difficult to establish an accurate mathematical model. According to experimental experience, we assume that the control object is a first-order system with delay link, as shown in the following formula:

simulation research is carried out below to verify the effectiveness of the control algorithm. In the actual control process, the material control problem will be adjusted in real time according to the control situation: the compressive strength of materials in different industries is different, and the system reconstruction will be realized

for the hypothetical control object, after experimental calculation, set the proportional parameters k4+>k3+>k2+>k1+, K0, k1-, k2-, k3- and k4- of the nine point controller to take 65.7, 19.4, 13.5, 10.6, 1.4, -10.6, -13.5, -19.4 and -65.7 respectively, and the time constant to take 0.1 to promote the democratic process of Hong Kong to take a historic step S, and the deviation and deviation change rate are taken as 0.01 respectively. Simulate with Simulink. Figure 4 is the simulation block diagram of the nine point controller system

Figure 4 nine point controller system simulation block diagram

the simulation results are shown in Figure 5:

Figure 5 nine point controller control effect on temperature

it can be seen that the nine point controller has a good control effect on the temperature of the system. As long as the adjustment can well suppress the overshoot and control the temperature fluctuation of the system within the allowable error range

5 conclusion

for the whole system, the temperature control system is a time-delay system, and the parameters of the ordinary controller are not easy to set in the case of large time-delay, but the nine point controller used in this paper solves this problem very well. Using relatively simple control rules, and introducing the phase plane method into the analysis of the controller, using different control forces in different areas, the parameters are easy to set, and the control results also have good dynamic and static performance. The simulation results of microwave sintering temperature control of ceramic materials show that this treatment method is feasible and effective. (end)

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