Experimental study of contouring accuracy for CNC machines executing curved paths with constant and curvature-dependent feedrates
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.
cnc machines curvature feedrate contour error high-speed machining open-architecture controller real-time interpolator