ATmega 128 소자를 이용한 자기베어링 제어시스템의 구축에 관한 연구

Abstract

This study deal with the magnetic bearing control system using the one board micro controller as the controller, and also a control system design method and a equation related to electromagnetic force were proposed. Because magnetic bearing supports levitating body without contact, wear, noise and vibration are very small comparing with mechanical bearings, it is very useful to high revolution machinery. The history of the magnetic bearings started with the success of one axis control by Beams, Black, Holmes of Virginia University in 1937, and afterwards the magnetic bearings were earnestly developed by Habermann, a French bearing company in 1976. The magnetic bearings are recently studied by Thomas, Chen, Matsumura and etc. and in Korea, a diversity of studies have been done by Ro, Lee, Choi, Kim, Jeong and etc.. Most of the studies involved the system performance evaluation of control algorithm or an electromagnetic actuator. The magnetic levitation system is inherently nonlinear and unstable. To control the position of the unstable system, the real time position feed back is required. The personal computers is often used or the DSP(digital signal processor) such as DS1003, DS1103PPC, TMS320C32, DSP VC33 and etc. are used widely for real-time control.

High performance control system using personal computer or expensive DSP is a good way to control the magnetic bearing system, but it is worth utilizing less expensive and widely used micro controllers. And the developed modern control theory could be applied to design the magnetic bearing control system. In this case, in spite of the effort to the mathematical modeling by linearization and the application of the difficult modern control theorems, good control performance can not be guaranteed, because modeling errors for linearization and uncertainty for system parameters still exist on the system modeling. So it is worth controlling the system with a PID controller because the PID controllers are trusted and popular in the industrial field.

In this study, magnetic bearing control system with satisfied control performance was constructed by the less expensive, convenience and widely used micro controller, 8 bits ATmega 128 in stead of more expensive micro processor. A control system design method and a equation related to electromagnetic force were proposed. The method repeats the simulation with application such as Simulink using the experimental results for the controlled system included non-linearity. This method is easy to apply at industrial field.

The contents of this paper is as followings. In the chapter I, the background and the brief contents of this study was represented. In the chapter II, the one board controller with a less expensive and widely used micro controller, ATmega 128, was designed and manufactured. And at the first step the possibility of the levitation control with real time PID control was reviewed. In the chapter Ⅲ, the actual magnetic bearing system was designed and manufactured. For the purpose of rotation of the magnetic bearing system, 3 phase induction motor was included in the center of the bearings. Thus the structure of the magnetic bearing system is to replace ball bearing with the magnetic bearing to both end of 3 phase induction motor. And the mathematical modelling of magnetic bearing, rotor shaft and current amplifier was conducted. In the chapter Ⅳ, a non linear related to electromagnetic force was proposed for electromagnet. And also a control system design method by simulation and experiments was proposed for non-linear controlled system. Then the simulation program contained discrete, quantization, non-linearity and time delay for calculation. While simulation was conducted and control performance was examined, the sampling time and the control gain was selected. And the one board controller used at chapter II was redesigned to control the magnetic bearing system manufactured in chapter IV through the expansion of input channel, output channel, DA converter and etc.. The control program of the one board controller utilized lookup table to reduce calculation time, and bit shifting for the integral calculus was used instead of floating point calculation. As the results, the controller carried out relatively high speed PID control of sampling time 0.25ms. At last the rotation test for the magnetic bearing system was carried out by 3 phase induction motor and air turbine. In chapter Ⅴ, the results of this study was reviewed synthetically.