Research On Trajectory Interpolation Of Non-Circular Turning And Contour Error

Non-circular parts are widely used in textile machinery,automotive engines,light industry equipment and aerospace.In traditional turning,the tool is fixed to tool-holder mechanism,and is coordinated with the spindle with constant speed.In this way,the noncircular profiles will cause periodically variable cutting angles and feedrates,which leads to fluctuating cutting forces and is detrimental to cutter life and surface quality.Based on the shortcomings of traditional methods,a real-time variable angle compensation turning method is proposed,and trajectory interpolation and contour error analysis are carried out on this basis.In this paper,the kinematics analysis of the whole prototype system is carried out on the platform of non-circular turning prototype.The coordinate transformation analysis based on D-H method is developed on the platform structure.The homogeneous transformation matrix of the whole motion chain from the workpiece coordinate system to the tool is obtained,and the expression equation of the tool pose and position in the workpiece coordinate system is established.Based on the forward kinematics and inverse kinematics,the kinematic relationship between each axis drive commands and tool pose is obtained under the premise that the cutting angle constant is 0.At the same time,trajectory interpolation algorithm is developed for non-circular and irregular contour spline.First,Simpson method is used to calculate the length of the profile spline,then the seven polynomial is used to interpolate to guarantee velocity and acceleration.The length of the profile spline is discrete into a section line segment which is connected.Finally,the trapezoid acceleration is used to plan the velocity of the head and end part of the interpolation spline to guarantee the profile spline's uniform tangential feedrate,so as to improve the surface quality of workpiece.In order to apply the axis drive commands generated by the trajectory interpolation algorithm to the actual turning experiment,the software development of the computer is developed on TwinCAT.It is mainly used for data conversion,command transmission and data acquisition.The relevant useful data collected are analyzed,and the effect of the variable angle compensation method and the traditional turning method is compared.Finally,based on the collected data,we calculate the error of the final contour of the two turning experiments to verify the contour accuracy of which turning method is better.Through the final analysis of the turning experiment data,the real time variable angle compensation turning method can lead to lower cutting load fluctuations,higher tracking and contour accuracy when compared with traditional turning method.