| On-machine measurement system of CNC(Computerized Numerical Control)machine tools can realize to complete all or most of the machining and measurement work by one-time clamping,which ensure the workpieces’ machining accuracy and improve the products’ quality.The on-machine measurement system mainly adopts the measurement method of"CNC machine tool+probe",which uses the reading system(grating measurement system)on the machine tool itself,supplemented by the probe trigger,to realize the accurate measurement of the size and shape of the workpiece on the clamping position.but there is the problem of "ontology processing,ontology measurement".However,there is the problem of "ontology processing,ontology measurement",which does not meet the basic criterion of measurement system accuracy that must be three times higher than the part processing accuracy.In order to improve and ensure the measurement accuracy of the machine measurement system,the error compensation technology must be used to compensate the machine measurement system error.In this paper,the on-machine measurement system of three-axis CNC machine tools is taken as the research object to further solve the problems in the existing research results,such as error correlation under different influencing factors,insufficient consideration of dynamic influence,inaccurate compensation method of motion error of guideway worktable,and poor practicability of comprehensive error compensation model.The main work is summarized as follows:(1)The dynamic and static characteristics of the XY worktable are analyzed,and the calculation model of dynamic positioning error is derived based on the structural characteristics and working characteristics of the XY worktable of CNC machine tools.The results show that the motion speed,the weight of the measured workpiece,the installation position of the workpiece,the friction force,and the temperature are the main factors affecting the dynamic characteristics of the XY worktable.The dynamic positioning error experimental verification under the influence of different speeds,loads and positions is carried out by the self-designed XY correlation error experimental platform.The results show that the dynamic positioning error of XY table of CNC machine tool is related to the running speed and the load borne by the table,and there is an "optimal measuring speed",at which the positioning error of the table can be minimized.(2)On the basis of error correlation analysis,a concept of instantaneous rotation center of guideway system(referred to as the instantaneous center)is put forward.The theoretical position was determined by ADAMS kinematics simulation software,and the actual position determination method was studied by the self-designed CNC machine tool XY correlation error experimental platform.The Abbe positioning error compensation experiment of the worktable based on the instantaneous rotation center is completed.The experimental results show that compared with the original maximum measurement value of the positioning error,the positioning error data corrected by the instantaneous center Abbe arm is more accurate than that by the traditional Abbe error method,and the positioning error compensation accuracy of the machine tool body is improved.(3)Considering the influence of temperature,speed,position,and other working conditions on the on-machine measurement system error of three-axis CNC machining center,the comprehensive error modeling method based on differential transformation is studied,and its comprehensive model is established by using the concepts of thermal deformation critical point and instantaneous rotation center,which effectively improves the single-point measurement accuracy of on-machine measurement system.(4)A concept of "optimal measurement area" is put forward,which means that when the measurement is completed in this space,the on-machine measurement accuracy is the highest.The method of determining the optimal measuring area of three-axis CNC machining center is studied.Aiming at the VMC850E three-axis CNC machining center,the distribution law of the spatial point measurement error of the on-machine measurement system is analyzed.A genetic optimization algorithm(SA-GA)based on simulated annealing is proposed.The objective function model of point-oriented in-machine measurement system was used to solve the optimal measurement area.The experimental results show that the SA-GA algorithm has the fastest convergence speed and less time-consuming for single optimization,so it is suitable for solving the optimal measurement area of point-oriented measurement.(5)An experimental scheme for solving the optimal measurement area of on-machine measurement system for point measurement is designed,and the experiments of the optimal measurement area for point measurement are carried out in the designated measurement space of 304.487mm≤X≤475.487mm,-179.042mm≤Y≤-44.042mm,-315mm≤Z≤-235mm in VMC850E three-axis CNC machining center in this paper.The optimal measurement areas are 331.487mm≤X≤340.487mm,-116.042mm≤Y≤-107.042mm,-305mm≤Z≤-295mm and the minimum value of the maximum measurement error is 4 μm.The results show that the optimal measurement area can help to improve the measurement accuracy of onboard measurement system,and the measurement accuracy can be improved by 94%to the maximum extent.Figure[67]table[12]reference[144]... |
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