Improving contouring accuracy by tuning gains for a bi-axial CNC machine

Contour errors in continuous-path computer numerical control (CNC) systems usually result from unmatched axial dynamics and undesirable nonlinearities. The errors due to unmatched dynamics can be largely reduced by using a simple controller so as to keep the order of axial dynamics low and by tuning appropriately the proportional gains to match the dynamics. Experimental results show that the resulting matched axial dynamics can, on one hand, effectively eliminate the linear contour errors, and, on the other hand, largely reduce the circular contour errors due to unmatched axial dynamics. On the basis of the matched axial dynamics, circular contours will be made circular with accuracies greatly improved. However, because of limitation in the bandwidths of the axial dynamics, there will be radial contour errors. The radial contour error can be further reduced by a simple approach of feedforward compensation. Experiments conducted show the effectiveness of feedforward compensation in improving circular contouring accuracies.