五轴线性刀路的转接光顺及轨迹生成算法

A Corner Rounding and Trajectory Generation Algorithm for Five-axis Linear Toolpath

线性刀路是五轴加工中广泛采用的刀具路径形式。由于线性刀路的切向和曲率均不连续,容易引起机床振动,降低加工质量和加工效率。已有的方法仍然存在一些问题,同步参数化、误差控制以及实时性无法同时满足,在规划进给速度时没有考虑五轴机床的非线性运动学特性。为此,提出了一种新的路径光顺方法。该方法采用2条3次Bézier曲线对线性刀路进行转接光顺,提高几何连续性:一条Bézier曲线对刀尖点位置进行光顺;为了保证刀轴矢量单位化,用2个欧拉角表示刀轴矢量,从球面坐标系映射到平面笛卡尔坐标系,用另一条Bézier曲线对其光顺。接着,给出了基于转接光顺的轨迹生成算法。该算法考虑非线性运动学特性,结合前瞻技术和7段式S型速度规划方法,实时规划出满足伺服约束的平滑进给速度。仿真与试验结果表明:所提出的刀路光顺与轨迹生成算法能够规划出加速度连续的进给速度曲线,提高进给速度,生成的轨迹满足驱动约束,适用于实时环境。

Linear tool paths are still the most widely used format of tool path in five-axis machining. Tangential and curvature discontinuities of linear tool path may lead to vibration of the machine, which inevitably result in poor machining efficiency and quality. To solve this issue, different smoothing methods is developed in the existing literatures. There exist some problems such as parameter synchronization, error restriction and real-time that cannot be realized simultaneously, the nonlinear kinematics are not taken into account while feedrate scheduling. A novel local path smoothing for five-axis machine is proposed. Segment junctions of the linear tool path in the workpiece coordinate system are blended by two transition cubic-Bézier curves. One cubic Bézier curve is used to smooth the segment junction of tool tip position path. To ensure magnitude of the orientation vector always results in unit magnitude, it is represented by two Eular angles and mapped form spherical coordinates to Cartesian plane, where another Bézier curve is used. Then, a trajectory generation algorithm for local path smoothing is proposed. The proposed trajectory generation algorithm takes the nonlinear kinematics into account, and look-ahead and seven segment S-shape feedrate scheduling method is employed to schedule a feedrate profile while respecting drive constrains. Finally, the experiments are conducted to verify the feasibility and efficiency of the proposed algorithm.