Study Of Variable-Gain Cross Coupling Control For Direct Drive X-Y Table Based On Genetic Algorithm

With the rising demand of high accuracy complicated surface parts process, contour precision has become one of the important precision indexes in CNC system. X-Y table directly driven by two permanent magnet linear synchronous motors eliminates the problems of traditional drive mode, such as slow reaction, large friction. X-Y table plays an important role in the CNC system to improve the machining precision and performance. Thus, improving the coordination between X and Y axis needs to design contour controller which can eliminate or improve the system contour error and the performance of X-Y table.The X-Y table directly driven by two permanent magnet linear synchronous motors is easily influenced by the nonlinear dynamic, system uncertainties and complicated contour error model of curve trajectory. Variable-gain cross coupling controller was used to compensate X,Y axis coupling error, and genetic algorithm was used to optimize PID controller parameters in order to improve the direct drive X-Y table servo system contour error.Firstly, X-Y table mathematical model was analyzed and established according to the working principle. The uniaxial speed and position controllers were designed to control the X,Y axis track errors to the minimum within controllable scope, then, the system contour error was decreased indirectly. Uniaxial separate feedback X-Y table traditional PID control was designed as a kind of contour control methods, in order to improve the system contour precision and dynamic performance. Eventually, the system simulation results were analyzed.Secondly, contour error model was analyzed and established according to the contour error characters of X-Y table. Variable-gain cross coupling controller was used between X,Y axis. The contour error models gain were corrected in the real-time according to the axis feedback information and interpolation value. Variable-gain cross coupling controller can find the optimum compensation rate and compensate the feedback modified information to each axis to compensate the contour error. Nonlinear tracking control was simulated and analyzed.Finally, genetic algorithm was used to optimize the variable-gain cross coupling controller PID parameters by which the parameters can be avoided falling into local optimal value and the global optimal value can be found directly without any initial information. Usually, the trial-and-error method was used to determine the variable-gain cross coupling controller PID parameters, which not only need professional experience and a lot of time, but also the search results are not necessarily system optimal value. Programs were written based on genetic algorithm, and the best PID controller parameters were put in the memory for different trajectory.KOLLMORGEN IC11-050 permanent magnet linear synchronous motors are considered as the controlled object, and MATLAB software is used to simulate and analyze of the control strategy. Theoretical analysis and simulation results show that variable-gain cross coupling control for two permanent magnet linear synchronous motor directly drive X-Y table based on genetic algorithm make the system possess high contour accuracy.