A Two-way Hausdorff Distance Evaluation Method of Chord Error using NURBS Curve Interpolation
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摘要: 数控系统中采用插补方法进行复杂曲线加工会引入弓高误差。利用密切圆(Osculating circle,OC)近似法和单向Hausdorff距离近似法可以获取弓高误差并对其进行后续补偿,但弓高误差求解与补偿精度较低。基于弓高误差的双向Hausdorff距离定义,提出了一种弓高误差的迭代评估算法。该算法能在不考虑曲线复杂度的情况下提升弓高误差的求解精度,并获取满足误差限制要求的最大插补步长,从而进一步生成精确的进给速度限制,防止加工精度及效率因引入其它误差而下降。最后利用该算法对‘∞’形和花瓣形NURBS曲线进行仿真,仿真结果验证了算法的性能及其有效性。
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关键词:
- 插补法 /
- OC近似法 /
- 弓高误差 /
- 双向Hausdorff距离 /
- NURBS曲线
Abstract: In numerical control system, interpolation is often used to realize complex curve machining, which will introduce some chord errors. The commonly used Osculating Circle(OC) method and single-direction Hausdorff distance method can obtain estimated chord errors, then make subsequent compensations, but they both introduce other errors in the estimation process. For this problem, based on the both-direction Hausdorff distance definition of the chord error, an iterative evaluation algorithm is proposed in this paper. This algorithm can improve the estimation precision of chord error without considering the flexibility of curves, and obtain the maximum interpolation step length that satisfies the error limitation, thereby further generating the accurate feed rate constraints to prevent the reduction of both machining accuracy and efficiency due to the introduction of other errors. Finally, it is simulated by '∞'-shaped and petal-shaped NURBS curves, the simulation results verify the performance and the effectiveness of the proposed algorithm.-
Key words:
- interpolation /
- OC method /
- chord error /
- both-direction Hausdorff distance /
- NURBS curve
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表 1 仿真系统参数表
参数名称 数值 插补周期Ts 1 ms 最大允许弓高误差δmax 0.001 mm 最大允许进给速度vmax 100 mm/s 最大允许加速度amax 3 000 mm/s2 最大允许加加速度jmax 60 000 mm/s3 最大允许轴向速度vxmax, vymax 100 mm/s 最大允许轴向加速度axmax, aymax 3 000 mm/s2 最大允许轴向加加速度jxmax, jymax 60 000 mm/s3 向心加速度系数M 0.2 表 2 弓高误差评估超限测试点的分析统计表(‘∞’形)
弓高误差评估方法 超限测试点数量 超限测试点占比/% 最大弓高误差/mm OC法 504 50.4 0.194 884 本迭代算法 49 4.9 0.001 013 表 3 弓高误差评估超限测试点的分析统计表(花瓣形)
弓高误差评估方法 超限测试点数量 超限测试点占比/% 最大弓高误差/mm OC法 519 51.9 0.469 542 本迭代算法 67 6.7 0.001 019 -
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