| The aerospace field has always been the top priority of our country’s research,and it is also a key Racetrack for competition among countries.From the rising of China’s first artificial satellite to the successful launch of the first manned spacecraft,to today’s "Beidou" satellite network,space station,lunar exploration mission,etc.,China’s aerospace field has been making continuous progress and achievements.And the important carrier for completing these tasks is the rocket.As the world’s attention to environmental protection increases,China also pays more and more attention to the safety and environmental protection of rocket fuel.HAN（hydroxylamine nitrate）-based rocket fuel is a kind of "green" fuel that can replace hydrazine propellants.In order to study the rocket engine thruster structure suitable for its combustion,Various research institutes in my country,such as the 801 Space Propulsion Research Institute,have built platforms for the combustion of rocket engines.In order to study the fuel atomization effect sprayed by the injector in the experiment,the measurement instrument needs to perform precise movement of millimeter level in the experimental cabin to sample the droplet distribution.The displacement accuracy of the stepper motor directly affects the observation of the fuel atomization effect and plays as a vital role in the design of the sprayer structure.In precise positioning,the stepping motor is especially suitable for the application scenario of one step one millimeter in the experimental measurement system.In order to solve the problems above,this article has studied its process control of the stepper motor in precise positioning.On the basis of fuzzy PID control,a neural network is used to optimize its reasoning process to establish a controller whose control parameters can be updated to precisely control the displacement of the stepper motor.Based on this research,a 3D displacement platform based on stepper motor was designed and the control algorithm was verified.The main work of this paper is as follows:First of all,this paper has researched the control strategies and driving methods of stepper motor.By searching for relevant information and reading research literatures,we has known that the pitch angle of the stepper motor can be further reduced by current subdivision control without changing the motor structure to improve the positioning accuracy.And a control strategy combining intelligent control and PID control algorithm is determined.Secondly,the working principle of stepper motor is discussed,especially the principle and realization of subdivision control are studied.On this basis,some complex factors are reasonably ignored,and the voltage balance equation,torque balance equation and motion equation are established for the two-phase hybrid stepper motor to derive transfer function.Besides fuzzy control theory and adaptive neural network theory are studied.According to this,an intelligent control algorithm combining fuzzy neural network structure with PID control is applied to the closed-loop control system of stepper motor.The weight adjustment of the network is similar to that of BP network,which uses Hybrid learning rules to combine gradient descent and least squares to determine a set of weight parameters in the form of back propagation.By injecting a large number of training samples,the connection weights such as membership function parameters,fuzzy rules and applicability of Fuzzy rules are optimized continuouslyThe model of position closed-loop subdivision control system for stepper motor is built on the simulation platform based on this intelligent control algorithm and the mathematical model of motor already established.The result shows that the FNN-PID controller makes the system better robustness and dynamic response which can adapt to adjust the parameters and reduces the adjustment time,reduces the overshot,and improves the stability of the system.Compared with the traditional PID control algorithm and fuzzy control,the FNN-PID controller has a better control performance.Finally,the hardware selection of the three-dimensional displacement platform includes: STM32 main control chip,three stepper motor driver chips,three two-phase hybrid stepper motor with encoder,switching power supply,screw slide,etc.,and the relevant circuits are designed.Use the STM32 Cube MX assistant software to design the program on the Keil integrated development platform and simulated on the Proteus platform so that the stepper motor can perform precise point displacement in three directions with millimeter intervals.This paper provides an effective and feasible solution for the automatic measurement system of the aerospace engine fuel spray experimental platform. |
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