A Cutter Orientation Modification Method Based On Machine Rotary Axes For Five-axis Sculptured Surface Machining

In five-axis CNC machining,tool orientations need to be planned smoothly in order to avoid the drastic changes of angular velocity or acceleration.In fact,for better kinematics performances and better quality of finished surface,the problem of tool orientations smoothing should be settled properly,or else the cutter accessibility,machining efficiency and machined surface quality can be deteriorated,especially for surface with complex shape.The optimization of tool axis vector is reflected in smoothness and singularity avoidance.The smooth change of tool orientations is the precondition for the improvement of kinematics performance of machine rotary axes.On the other hand,the avoidance of singularity may directly affect the machined surface quality,and the kinematics performance of machine rotary axes.Therefore,this paper focuses on the tool orientations smoothing method and singularity avoidance in five-axis machining.Taking 5-axis machine of table-tilting type as an example,this paper proposes one tool orientation smoothing method and provide a solution for singularity avoidance based on machine coordinate system(MCS),aiming to obtain the smooth tool orientations without singularity.In 5-axis CNC milling,it is important to avoid the drastic change of tool orientation for improving the kinematics performance of the rotary axes and achieving the good machining surface quality.For this purpose,a smoothing method with drive limits is proposed to plan the tool orientations.In this method,with several representative tool orientations(RTOs),the initial tool orientations are planned efficiently along the path curve by using quaternion interpolation while ensuring no machining interference.Then,the planned tool orientations are checked whether the angular accelerations of the rotary axes exceed their drive limits,and the areas not meeting the drive limits are determined.At these areas,a tool orientation smoothing method conducted in the machine coordinate system(MCS)is implemented to locally adjust the tool orientations in order to improve the kinematics performance of the rotary axes.Finally,the performed experiments demonstrate that the proposed method can significantly improve the dynamic characteristics of the rotary axes while guaranteeing no machining interferences.For the singularity in five-axis machining,an adjustment method based on the shape modification of five-order B-spline curve is adopted in the machine coordinate system.To settle the modification of cutter axis vector,one only needs to modify the shape of B-spline curve,which simplifies the singularity problem.By taking the minimum strain energy of error curve as the objective and the kinematic characteristics of machine tool as the constraint,the objective function with linear constraint is established,so as to eliminate the singularity problem possibly arisen in five-axis machining.The experimental results show that the optimization method can improve the smoothness of cutter axis vector without interference,optimize the kinematic performance of machine rotary axes,and avoid the singularity in five-axis machining.The effectiveness of the proposed method: tool orientation smoothing method and singularity avoidance method,is verified by experiments.