Error Prediction And Compensation Of Cradle Five-axis Machine Tools

Five axis NC machine tools are widely applied in the field of complex free-form surface machining.With the rapid development of NC technology,the machining accuracy of five axis NC machine tools is put forward higher requirements.The geometric error is an important factor affecting the machining accuracy of NC machine tools.Therefore,the modeling,identification and compensation methods of geometric error of five axis machine tool are studied in this paper,and the experiments of modeling,measurement,identification and compensation of translational shaft error are carried out.Firstly,according to the basic structure of the five axis machine tool,the topology of the machine tool and the low order body array are established by using the basic representation method of the multi-body system.The homogeneous coordinate transformation matrix is used to describe the coordinate transformation of the individual in the machine tool,and the feature matrix table is set up.Based on the forming function and motion constraint equation,the comprehensive spatial geometric error model of the five axis machine tool is established.Secondly,based on the advantages of simple,unconditional hypothesis and no error model to participate in calculation,the 9 line method is used to identify the geometric error of the translational axis of the five axis machine tool,and the traditional error identification method is used to identify the rotation axis error.By the advantage of BP neural network in nonlinear data fitting,the discrete data of basic geometric error after identification are fitted.Thirdly,the Levenberg-Marquardt algorithm which has global characteristics and fast convergence rate is used as the learning algorithm of BP neural network.The mapping between forming motion point and NC machining instruction point is established by using neural network,that is,the error compensation model.Finally,the geometric error modeling,measurement,identification and compensation experiments of the translational axis are carried out by using the five axis machine tool.The samples are processed with NC program before and after compensation,and the geometric error modeling,identification and compensation method of the five axis NC machine tool are verified.