Local Energy Smoothing and Singularity Avoidance Method of Five-axis Linear Toolpath
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摘要: 针对现行五轴加工中存在的路径拐角处平动轴减速过度, 奇异区域旋转轴角度变化剧烈的问题, 以AC双转台五轴机床为研究对象, 提出一种满足机床运动学约束的路径优化方法。该方法首先以刀心点光顺前后最大许用偏移量作为约束, 利用转角向量和双弦弓高进行建模, 寻求微小线段拐角处局部能量最优解。并对奇异范围内部和边缘的刀轴矢量点二次规划, 使得矢量末端刚好绕过单位球面上的奇异区域, 极大地保留原有加工特性。通过结合三角函数加减速控制算法, 对优化效果进行评估。仿真结果表明: 该路径优化方法在拟合偏差与弓高误差均没有超过许用值的同时, 平均进给速度提升了10.64%, 而且能有效避免加工中奇异现象的发生。可见本文所提出的方法在提高五轴加工效率和加工质量等方面具有较高的理论意义和实际应用价值。Abstract: Aiming at the problems existing in the current five-axis machining that the translation axis at the corner of the toolpath decelerates excessively and the angle of the rotation axis changes drastically in the singular area. This paper takes the AC dual-table five-axis machine tool as the research object and proposes a path optimization method that satisfies the kinematics constraints of the machine tool. Firstly, the method takes the maximum allowable offset before and after the smoothing of the tool center point as a constraint, and uses the corner vector and the double-chord bow height for modeling to seek the local energy optimal solution at the corner of the micro-line segment. Then the cutter axis vector points inside and at the edges of the singular range are planned again so that the end of the vector just bypasses the singular region on the unit sphere; thus the original machining characteristics are greatly preserved. Finally, the optimization effect is evaluated by the trigonometric function acceleration and deceleration control algorithm. The simulation results show that the path optimization method improves the average feed rate by 10.64% while the fitting deviation and bow height error do not exceed the allowable values, and can effectively avoid the occurrence of singularities in machining. Consequently, the proposed method has high theoretical significance and practical application value in improving the efficiency and quality of five-axis machining.
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Key words:
- five-axis machining /
- local energy smoothing /
- singular regions /
- motion control
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表 1 机床约束条件
Table 1. Constraint conditions of machine tool
参数 数值 最大进给速度vm 25 m/min 最大加速度am 3 000 mm/s2 许用弓高误差δmax 4×10-7 m 最大拟合偏差εmax 8×10-7 m 数控系统采样插补周期ΔT 0.02 s A、C轴最大角速度 0.73 rad/s A、C轴最大角加速度 30 rad/s2 权重系数λ 0.6 表 2 光顺前后拐点处的进给速度
Table 2. Feed rates at turning points before and after smoothing
拐点位置 光顺前进给速度/(m·min-1) 光顺后进给速度/(m·min-1) D1 9.382 20.987 D2 8.979 20.085 D3 8.624 19.291 D4 8.410 18.811 D5 9.411 21.051 D6 9.682 21.659 -
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