Experimental study of contouring accuracy for CNC machines executing curved paths with constant and curvature-dependent feedrates

Authors:
Jeremy R. Conway;Aurelia L. Darling;Charlie A. Ernesto;Rida T. Farouki;Christine A. Palomares
Affiliations:
Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616, USA;Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616, USA;Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616, USA;Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616, USA;Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616, USA
Venue:
Robotics and Computer-Integrated Manufacturing
Year:
2013

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Abstract

Experiments to measure and improve the contouring accuracy of CNC machines executing curved paths with strong curvature and variations of curvature at high feedrates are reported, using P and PI controllers with a wide range of gains. The experiments are based on test curves exhibiting (a) a steady increase of curvature; (b) a periodic curvature variation between fixed minima and maxima; and (c) a sudden ''spike'' in the curvature profile. For the P controller, the curvature-dependent feedrate yields a diminution of the contour error by up to an order of magnitude, compared to constant feedrate. The curvature-dependent feedrate appears to be most advantageous in situations exemplified by case (c), since it affords a dramatic suppression of local contour error with a modest increase in traversal time. Moreover, the improvement in contour accuracy is relatively insensitive to the P gain. The results are less predictable when the curvature-dependent feedrate is used in conjunction with PI control, because of its more ''active'' response to the excitation arising from the varying path geometry and feedrate.