| The equipment of reflow oven plays an important part in welding equipment of surface-mount technology (SMT). The aim of this equipment is to control the temperature to the seting point following the temperature curve of the SMT components so as to the SMT components can fix on the soldering plate of PCB. The precision and stability of controlling on temperature is the key factor to ensure a well product can produced.Based on the existing equipment of reflow oven, this paper adopt microprocessor of ATmega 128 (L) as its controller to provide with high efficiency and performance, even as the high speed of operation, and employ K type thermocouple as front-end sampling tools of temperature, cooperating with the A/D conversion chip named MAX6675, which take the cold end compensation, and some other advantages such as high precision, reliability, strong transformation. The A/D will send the datas collecting from field parameters to microprocessor. According to control algorithm, the microprocessor will calculate the sampled datas and make a decision of controlling, and send the control orders to the unit used to execute orders-Solid-state relay (MGR-1 D4810) to control the resistance of power. The whole set of monitoring system has some advantages such as high performance of reliability, simple operation, easy to expand, facilitate the promotion and the transformation.In order to achieve more accurate control effect, it needs to establish a mathematical model of reflow oven, and then to design a controller based on this model.A accurate model can established by the equation of thermodynamic equilibrium, but it has to understand the process of the system.So the establishing models is relatively complicated and has not a strongly practicability, but it can be used to analyze the system from the mechanism, and easy to modify the equipment for the reflow oven; With the emergence and continuous development in recently years, the MATLAB gradually formed a lot of methods to solve practical problems. In the process of establishing a model, the MATLAB solves the disadvantage from repeated explorations, large amount of calculation, difficult to complete and so on, and firstly it only to obtain the data from the practice of the object and then test the data, choose a model structure, estimate the parameter and test this model, and finally get the mathematical model of the object through system identification theory, making the complex control system designing more convenient. During the process of identification using MATLAB, the veracity and reliability of the sampled data must be guarantee. And according to the experience to select a system structure, finally calculates model structure and parameters through MATLAB. As the research background in reflow oven, this paper combines with the modern temperature modeling study status of summary and analysis, then points out what the problems needed to be solved; Combined with MATLAB tool software, adopts the way of one-order inertial system modeling method and the toolbox of recognition and analysis to establish a mathematical modeling of reflow oven. Firstly this paper introduces the theory and method about the modeling avoiding analysis, and gives the realization and quick solutions of obtaining mathematic model of the system; then defines a data structure based on the system needed during the modeling process. After that, it introduces the basic principle of Dalin algorithm, and how to design the controller with this algorithm; Finally, test the model by experiments and the effectiveness of the designed controller. |
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