The Research On Pre-compensation Metod Of Contour Error In Five-axis Machining Based On Model Prediction

The development of high speed and high precision machining in multidimensional space conforms to the widespread application trend of complex curve and surface parts in the manufacturing industry.In addition to the improvement of processing speed,the improvement of parts processing quality is also the most important concern of many scholars and researchers.Because the quality of the workpiece depends more on the difference between the actual contour and the desired contour.Therefore,the modeling,prediction,pre-compensation and cutter feed rate customization of contour error are used as an important means to improve the quality of the workpiece in the subject.Based on the detailed analysis of the causes of contour error,this paper discusses the control and compensation scheme for improving the contour error of five axis NC machine tools when machining complex curve and surface parts.Considering the tracking error and contour error modeling method of machining,trajectory prediction model,five axis machine tool parametric spline interpolation method,contour error pre-compensation scheme,the tool feed rate of linear programming,based on ensuring the contour error of precision control in the process of implementation,the tool path with C~3continuity fitting,maximum improve processing speed and machining accuracy.The main contents and achievements of this paper including:First,the study of five axis machine tool parametric spline interpolation algorithm,the contour error control key technology,control strategy and parameter optimization theory and application,do a good job of theoretical foundation for the following chapters about puting forward C~3five continuous spline interpolation,contour error prediction and compensation and tool feed rate of the linear programming.Second,according to the problem of five axis machining process,discrete cutter location data provided by the CAD system,and the tool path to a first-order discontinuity,resulting in cutting process,velocity,acceleration discontinuity,influence the workpiece quality,put forward respectively for the tip locus and cutter axis orientation five parametric spline fitting scheme,this scheme guarantees the spline interpolation of C~3continuous,the spline function of displacement,velocity and acceleration are continuous,avoid the spline discontinuity caused by machine oscillation and contour error value is too large due to excessive wear of machine.In view of the problem that the axis direction of the cutter is not directly related to the displacement of the machining trajectory,the interpolated spline is re-parameterized to ensure the minimum jerk.The experiment shows that the algorithm can get a more smoother parameter fitting spline,reduce the vibration of machine tool and improve the quality of the machining parts.Third,in the process of five-axis machining,a method for modeling and compensating contour errors is proposed due to the coupling between the tool path locus and the tool axis caused by the presence of the rotating shaft.Fitting a reference instruction with a continuous C~3spline curve gives an analytical representation of the reference instruction.Use continuous reference commands as input to the servo drive to solve linear differential equations for tracking error modeling.Based on the tracking error prediction,an iterative method is used to calculate the contour error of the tool tip position and tool axis direction.After the contour error is calculated,the two-phase algorithm is executed to compensate for the contour error in the tool axis direction and the tool nose point,respectively.Since the tool axis direction error is decoupled from the linear axis,the rotation command is first modified to compensate for the contour error in the tool axis direction.Next,to compensate for the position contour error,this sequence of compensation ensures that the compensated direction is not affected.Fourth,the high-performance multi-axis machining feed process planning needs to consider the high efficiency,smooth,small impact,and always within the scope of the capacity of machine tools.In view of the conflict between the high-speed machining of five-axis machine tool and the movement limitation of the machine tool,this article has limited the feed rate of the machine tool from aspects of geometric accuracy,kinematics,driving characteristics of the machine tool,etc.,it stipulates the range of speed,acceleration and jerk during the movement of the tool.It ensures that the machine tool can process the part to the maximum extent without exceeding the motion limit of the machine tool.And the linearity of the feed rate of the machine tool is planned according to these comprehensive requirements.In summary,based on the tracking error modeling and prediction,this paper proposed a five-spline fitting discrete position for multi-axis machining to obtain a smooth reference command,combined with the kinematics formula for the contour error modeling,forecast and pre-compensation.And in order to ensure high-speed machining speed,acceleration,jerk within the scope of the capacity of the machine tool,the tool feed rate linear programming.Finally,the proposed method and model are simulated to verify its effectiveness.