五轴数控加工中旋转轴运动引起的非线性误差分析及控制

五轴数控(Computer numerical control,CNC)加工中,刀具路径规划阶段与实际加工阶段对旋转轴运动采用的插补方式存在差异,其中刀具路径规划阶段是根据零件的几何信息进行插补,而实际加工中则根据机床信息进行插补,这种差异将引起原理性加工误差。针对五轴数控加工中旋转轴的运动,分析采用线性插补方式控制两个旋转轴进行加工时刀具姿态变化引起的原理性误差,进一步研究不同加工情况下由此产生的在垂直于走刀方向的平面内的非线性误差。通过分析旋转轴运动过程中线性插补引起的刀轴偏差角,证明刀具在相邻两刀位点运动过程的中间时刻处刀轴偏差角取得最大值,并得到由该最大值的显式表达式,在此基础上分析最大偏差角的影响因素。提出通过限制相邻两刀位点间刀轴夹角来控制此非线性误差的方法,并给出实例验证。

Analysis and Control of Tool Path Interpolation Error in Rotary Axes Motions of Five-axis CNC Milling

In five-axis computer numerical control(CNC) machining,the interpolation modes for rotary axes motions are different between tool path planning stage which interpolates with geometry of parts and real machining stage which interpolates with the configuration of machine tools.A tool path interpolation error in the rotary axes motions of real five-axis CNC machining is analyzed in this work.In the plane orthogonal to the tool path direction,the error model is constructed by taking into account deviation of the tool orientation.The maximum error is proven in the middle of two consecutive cutter locations,and its close-form equation is derived.A practical approach to inserting cutter locations in the tool path with the tool orientation and the interpolation errors under a specified limit is proposed.This approach is verified with several empirical examples.