Study Of Iterative Learning Control Method For XY Table System

Because there is no transmission device when linear motor direct drive XY table NCsystem, the system is sensitive to disturb, and linear motor has some feature such asnonlinear, coupling, time varying, it is difficult to control. The contour of XY table iscompounded by double-axis’s linear motion, when one of the axis position error is so largethat let the contour error decline very much. For these problem, iterative learning controllerbased on disturb observer is to enhance each axis robustness, hybrid error contourcontroller is to control XY table contour motion, ensure the contour precision.Firstly, the development of direct drive XY table was introduced, permanent magnetlinear synchronous motor(PMLSM) mathematical model was set up, and analysis thedisturb and some factor that influence the contour precision base on the character of directdrive XY table. Because of PMLSM’s construction, PMLSM produce thrust ripple wavewhich vary period. Load disturb is random, it impose non-repetitive disturbance to system.The friction is influenced by velocity and load, it impose non-repetitive disturb to system.Secondly, for the repetitive and non-repetitive disturb, the iterative learning controllerbased on DOB was designed. DOB feedback disturb to the input port, so that ensurerobustness of system. The error of DOB nominal model will let the observed disturb is notaccurate either, influence the precision of system, but iterative learning controller can learnthe error between nominal model and practical control object at the iteration, andcompensate the error.Last, hybrid error iterative learning controller was designed. Now, most of the contourerror calculate method demand tracking error much less than the contour’s radius ofcurvature. The hybrid error iterative learning controller in this article, only control contourwhen tracking error is smaller than the contour’s radius of curvature, control position ofeach axis when tracking error is larger.