Abstract
In the machining progress of free-form surface, tool path is presented as continuous small line segments. To achieve high machining speed and fine machining quality, the tool path needs to be smoothed. This study presents a smooth tool path generation algorithm based on B-spline curves for small line segments machining. The algorithm includes two modules: smooth tool path generation module and real-time look-ahead interpolation module. In the smooth tool path generation module, the tool path is divided into non-fitting regions and fitting regions by three conditions: the length of small line segments, the angle of adjacent small line segments, and the change rate of the length and angle. To control contour error and get fine machining quality, the fitting regions are corrected by circle correction method and fitted into B-spline curves, while the non-fitting regions are smoothed with B-spline curves. In this module, the gained tool path has continuous curvature. In the interpolation module, the seven-phase jerk-limited look-ahead planning is adopted to generate smooth machining velocity, while the calculation accuracy of interpolation point generated by the interpolation period crossing two adjacent tool path is controlled. Simulations and experimental results demonstrate that the proposed algorithm is able to reduce the amount of numerical control codes, achieve high machining speed, and improve machining quality.
Highlights
In conventional computer numerical control (CNC) machining progress, the free-form surfaces designed by computer-aided design/computer-aided manufacturing (CAD/CAM) systems have to be converted into G codes, and this method has certain problems: heavy transfer load between CAD/CAM system and CNC system, long machining time, and poor machining surface quality.[1]
Advances in Mechanical Engineering et al.,[5] but the Akiama spline only has G1 continuity between consecutive curves, which means the machining velocity and machining quality would be affected at the junction of curves, otherwise the Akiama spline cannot be adjusted by the weight of control points
To verify the performance of the proposed algorithm, the tool path shown in Figure 10(a) is implemented on SMTCL VMC850E machining center, which is equipped with an open CNC system developed by the authors.[25]
Summary
In conventional computer numerical control (CNC) machining progress, the free-form surfaces designed by computer-aided design/computer-aided manufacturing (CAD/CAM) systems have to be converted into G codes, and this method has certain problems: heavy transfer load between CAD/CAM system and CNC system, long machining time, and poor machining surface quality.[1]. Yau and Wang[9] utilized a cubic Bezier interpolator to generate smooth tool path with G1 continuity, while Lin et al.[10] proposed a NURBS conversion method with C1 continuity. To generate smooth tool path with continuous curvature, quintic B-splines method[14] and cubic Bsplines[15,16] were proposed, but the curvature extreme of these methods cannot be calculated analytically,[14,15] while the construction of the transition curve is timeconsuming, complex, and the amount of data becomes larger.[16] To overcome these problems and obtain smooth machining velocity profile, the B-spline transition method based on five control points[17] and the velocity planning method with limited jerk[18,19] were given, but the accuracy of the calculated interpolation points cannot be guaranteed, as the method calculates the parameters of the interpolation points based on Taylor’s expansion of only one certain curves
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