Research On Precision Contour Tracking Control Strategy Of Biaxial Motion Table

XY motion table is key functional component for realizing multi-axis high-end CNC plane XY coordinated motion. Precision contour control is the inevitable demand and trends for improving CNC workspeed and precision. The dissertation is supported by National Natural Science Foundation of China “Trajectory Planning and Accurate Contour Control based Velocity field for Direct Drive XY Table” and Province National Natural Science Foundation “Research on Precision Contour Tracking Control Strategy of biaxial linear motor”. Permanent magnet linear synchronous motor(PMLSM) direct drive XY motion table servo system is the main study object, and theory and experiment researches were proposed for improving contour accuracy.Firstly, contour error model is important for biaxial XY table contour control. Contrally, contour error model is built using time domain, and biaxial coordinate control is realized by cross-coupling control.However, building accurate contour error model is difficult on time because of complex curve trajectories. Most contour error model using equvilent error will not satisfy high precision and high speed performance. In this dissertation, time domain is changed to position domain. A new position domain mathematical model was developed, and the stability analysis was conducted based on Lyapunov function method. For developed the control stragegy, a biaxial motion is treated as a master-slave cooperative motion system. Then a new control law was adapted for improving contour precision by new dynamical model using time and position domain translation.Secondly, contour precision depends on controller. The control strategy based on position domain mathematical model was proposed to improve the contour tracking performance. For X-axis and Y-axis tracking control, adaptive ZPETC was used for tracking fast, and PDFF was used for fast track and robustness.Hybrid controller of adaptive ZPETC+PDFF+PD was proposed for high precision motion. The method has excellent performance and fast tracking.The master motion(X axis) is sampled equidistantly and used as an independent variable, while the slave motion(Y axis) is expressed as function of the master motion according to desired contour requirement. A dynamic model of the biaxial motion system represented in position domain is proposed based on the master motion through one to one mapping from time to position domain. In the proposed position domain model, the master motion will yield zero tracking error for the position domain as it is used as referene,and only the slave motion tracking error will affect the final contour error. Simulation results are demonstrated by time domain and position domain comparision.Thirdly, in order to further improve the contour performance, adaptive feedrate control strategy was proposed in position domain. Contour error increases when curvature is big. And federate will affect performance of contour precision, and contour control quality.To further reduce the contour error when curvature is big, an adaptive feedrate scheme is proposed, which utilizes the predicted contour error to adjust the feedrate online. The control method interpolates on line with adaptive feedrate, and varial feedrate is good for steady and transient periods because of adaptive parameters.The proposed adaptive feedrate scheme is capable of significantly reducing the transient contour error at high feedrates, while maintaining comparable tracking performance at low feedrates. Simulation analyses are done for adaptive federate and constant feedrate.Lastly, contour control system for direct drive XY experimental table was built. Control strategies in time domain, in position domain, based on adaptive feedrate, was compared in the experiments under the circumstances of the loop. The comparative experimental results verified the validity of control strategies proposed in theoretical analysis and simulation.