Form error on-line estimation and compensation for non-circular turning process

Parts with non-circular profiles are widely used in the automobile, navigation and aerospace areas, such as camshafts and convex ellipse pistons etc. The form accuracy of non-circular profiles directly affects the transmission accuracy and efficiency. However, existing non-circular turning studies mainly focused on improving the positioning accuracy of fast radial servo drives but neglected the form accuracy caused by the mismatch motions among all feed drives. In order to improve the form accuracy of non-circular turning, this paper proposes a novel control structure which treats the form error as a direct objective. The form error is estimated in real time at first within preset tolerance of calculation error. Then an on-line control strategy is designed to reduce form error through compensating the motion commands of the fast radial servo drive. The control loops of individual drives are decoupled and only position commands of the fast radial servo drive are compensated without touching the inside velocity and current loops. Comparisons with traditional contouring error control structure based on cross-coupled compensations of all axes show that the proposed error compensation strategy has better dynamic performance. Experimental results on the in-house developed non-circular turning prototype show that the proposed form error estimation and compensation methodology significantly improves the contouring accuracy than traditional controllers which only focused on tracking error control of individual drives.