Experimental study of contouring accuracy for CNC machines executing curved paths with constant and curvature-dependent feedrates |
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Authors: | Jeremy R Conway Aurelia L Darling Charlie A Ernesto Rida T Farouki Christine A Palomares |
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Affiliation: | Department of Mechanical and Aerospace Engineering, University of California, Davis, CA 95616, USA |
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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. |
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Keywords: | CNC machines Feedrate Curvature Contour error High-speed machining Open-architecture controller Real-time interpolator |
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