Research On Control Strategy Of Shaftless Esta Coating System

With the fast development of automobile industry in China in recent fifteen years, the concern about the surface quality is more and more strict. As one of the most important check point of the carbody's surface, the coating quality is much concerned by all the manufacturers. This paper researches on the application of shaftless contour control in the ESTA coating.system, which is the most important process in car body coating. And some fruit conclusion is produced.The shaftless contour controlling is essentially a multi-axes motion control problem. But it is not just simple synchronization but to consider the position of all the servo motors as a whole system. This paper takes the ESTA coating system at BMW-Brilliance Co., Ltd. as an example to analyze the multi-axes contour control in the application of typical ESTA profile control system and exploratory research is taken.This paper first analyzes the synchronization structure of multi-axes motion control. And based on parallel structure, the transfer function and two typical contour curves are used to analyze the reason of contour error. So the control strategy of contour system is educed.Considering each servo loop, because the typical three-loop servo system is ripe at both theory and practice application, system transfer function is aware and the desired contour of ESTA coating is known beforehand. So the Zero Phase Error Tracking Control (ZPETC) with a optimal digital polynomial filter is taken to design a feedforward controller to further improve dynamic performance of each axis which can reduce contour error.Considering the contour error between each axis, the error at tangential direction is more crucial than tracking error at each axial direction. Cross-Coupling Control (CCC) is taken to transfer contour error from open loop to closed loop which can further improve contour precision. For Cross-Coupling Control strategy the Error Transfer Function is taken to transfer the cross-coupled system to an equivalent feedback system, and make the conclusion that there will be a time-variable and non-linear character after variable gain cross-coupling is educed to the parallel system. It means that the traditional PID controller is not able to reach satisfied performance. So a feedforward neural network PID based on improved BP training method is taken to be the cross-coupling controller. Through simulation it is proved that this controller can effectually reduce the typical contour of ESTA Coating control.