Contour control for direct drive XY table

The combined contour control strategy of H_inf velocity feedback control, zero phase error tracking control (ZPETC) and normal cross-coupled control is proposed. It reduces the influences of load interference, mechanical time delay and parameter mismatch between two axes on the contour accuracy of XY table directly driven by two permanent magnet linear synchronous motors (PMLSM). H_inf velocity feedback control has the advantages of fast responding and suppressing interference. ZPETC implements precise tracking based on zero-pole and phase cancellations. With the contour error as the direct controlled variable, normal cross-coupled control improves the contour accuracy by real-time compensation between two axes. Compared with the conventional method, the contour error is decreased much and the controller design is simplified. Simulation results show that the designed control system possesses good tracking performance, strong robustness and high contour accuracy.