Research On Method Of Static Geometric Error Identification Of Five-axis Cnc Machine Tool

With the increasing market demand for surface processing,more and more domestic five-axis CNC machine tools are being designed,manufactured and applied.The static geometric errors caused by the assembly of the machine tool,especially the measurement and calibration of the axis position deviation of the rotating shaft,become the key to improve the precision of the CNC machine tools.There are many researches on the measurement and identification of static geometric errors based on the ballbar,but they have not been well popularized and applied in the industrial field.The error modeling method,the measurement track design and the identification algorithm design all affect the practicability of the measurement scheme.In this dissertation,experimental research is done on the shortcomings of the existing measurement and identification methods of static geometric errors based on the ballbar.In this dissertation,kinematics modeling of five-axis CNC machine tools is based on screw theory,and the ideal kinematics and the actual kinematics models are established respectively.The Jacobian matrix estimation is used to establish the approximate linear relationship between the position error of the tool tip and the static geometric error terms.The derivation process of Jacobian matrix function is given,the static geometric error model is simplified,and the simplified model is simulated.The relationship between the telescoping amount of the ballbar and the error vectors of the kinematics twists of each axis is deduced.Through the error separation,each static geometric error is identified and the identification algorithm is simulated.Based on the measuring principle of the ballbar and the characteristics of the motion control of the CNC machine tool,the factors influencing the measuring accuracy of the ballbar are analyzed through the experiment and the simulation so that the details of the ballbar measuring experiment can be further improved.In view of the contradiction that the ballbar can only measure the distance variations based on the time sampling while the identification algorithm requires obtaining the position information of each axis corresponding to each sampling point,this paper puts forward a method to acquire the real-time position of each axis in the measurement of the ballbar by means of numerical control system,making the position information of each moving axis more accurate and the identification result more reliable in the process of error identification.At the same time,the measurement error caused by following error can be eliminated in the identification step according to the obtained actual position of each moving axis,which reduces the influence of the measurement errors.The feasibility and practicability of the overall scheme are verified by the actual measurement experiments on a five-axis CNC machine tool with dual turntables.