| High speed and accuracy five axis machine tools,movable gantry five axis machine tools,high torque machining center are urgently needed in the aircraft,automobile and die&mould industry.Meanwhile possessing the movable and rotary axis,five axis machine tools can process the backbone structural with complex structural characteristics and the higher accuracy demanded.Machines equipped with high speed motorized spindle simultaneously have the large margin cutting ability and can satisfy the demands of high material removal rate.There are two types of methods to improve the accuracy of machine tool:Error Avoidance and Error Compensation.Although error avoidance is an effective machining method to improve workpiece precise,it existed definitely limitation especially for higher precision and ultraprecision machining.It is difficult to machine a part whose accuracy is higher than the machine tool in the technical aspect and the cost is very high,or even unacceptance.In order to realize the high precision machining,error compensation must be used.Using software technology,error Compensation can enhance the precision,not only for the new machine tool but also the used machine tool,and can be realized easily at low cost.Now,the errors acquiring for software compensation mainly focused on the linear axis.Even though,the error measured for rotation axis is only position error.The other errors of rotation axis and the perpendicularity between the rotation axis and linear axis are seldom considered.Furthermore,whether the distribution and numbers of measure points and the precision of the measurement system meet the requirement of the accuracy of machine tool is not considered qualitative in the measuring process.In addition,thermal-elastic effect of thermal errors is not considered in the thermal error model for motorized spindle.Aiming at error compensation of high speed and accuracy five axis machine tool of large aerospace backbone structure manufacture,error sources analysis,error elements efficient measurement,synthetical error model establishing on dimensional points and error compensation system implement have been researched in this paper.The main research results in this paper are as follows:Using multi-body kinematics and homogeneous coordinates transformation theory,the synthetical error modeling of the working space points in machine tool is researched by analyzing the structure and the main error sources of double-swivel head spindle five-axis machine tools in this paper.After the relationship between tool and workpiece has be analyzed as the relationship between "tool-machine body" chain which is from tool to machine body and "workpiece-machine body"chain which is from workpiece to machine body.Based on micro-angle assumption,then the synthesis models is derived by the homogeneous coordinate transformation method which provides a theory base for the error measurement and compensation.Aimed at different error elements,several effective measurement methods had proposed.Based the analysis of the relationship between the accuracy and the numbers of measuring,the error measuring numbers of the X,Y,and Z slides are determined.The measurement system accuracy meet the requirement of machine tool through the assessing the uncertainty.The laser interferometer and electronic level meter are used for the 21 error of 3 linear axes.For the geometric errors of rotation axis,a laser interferometer is first used to measure the rotation angle position error and then the rest errors can be identified through following circle measurement in different locations with laser tracker.The laser tracker is used to measure the parallelism error between the rotation axis and the linear axis according to its effectivnes and quickly use.The laser translation sensor is used to identify thermal deformation error of motorized spindle through following circle measurement.Compared with the other research,more error elements can be measured in this paper and compensation effect can be enhanced further.Thermal error is a key factor that influenced the accuracy of the machine tools.Thermal error of each axis in stable condition when warmed up was summaried to geometric accuracy in the paper.According to the structural features of motorized spindle,its thermal deformation characteristics were analyzed in detail based on the analysis of the relationship betweenthe heat generated quantity by heat source and rotational speed.Combined the advantages of neural network and Wavelet Transform theory,a method of thermal error modeling using local recurrent wavelet neural network was proposed.The traditional thermal error model only for the real-time temperature on the key points directly connected with thermal deformation.The results of experiment showed that the method can improved the forecast accuracy of motorized spindle thermal error model effectively.A forecast method of any point space errors in machine tool working region is presented based on shape function interpolation according to the required of the compensation points and the accuracy of the interpolation.Two different methods,finite element interpolation and meshless methods interpolation,have been analyzed.Based on the comparison between the advantages and disadvantages of two methods,a space error forecast method of coupling finite element interpolation and meshless methods interpolation for complex shape was presented.Based on the coupling characteristics of simultaneous movements of movable axis and rotary axis,a step-by-step compensation strategy was presented:first to compensate posture error by adjusting actual posture of tool to ideal posture through the rotation movements of rotary axis;then compensate position error through linear movements of movable axis.Through simulation analysis and body diagonal CNC precision testing of no-load maching,the error compensation system was verified effectively.Final the processing accuracy was obviously improved for the experiment of compensation processing on S curved surface part machining on a five axis machine tool.The experiment's results showed the error compensation mathematical model is feasibility and validity. |
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