Research On The Geometric Errors Of Five-axis Horizontal Machining Centers

The performance of five-axis CNC machine tools determines the development level of a country's manufacturing industry.Ranging from high-efficiency and precision machining of complex parts in the national defense industry,to the mobile phone parts that we use at any time,these products with exquisite appearance and precise processing are all processed by precision machine tools.However,in the aspect of high precision manufacturing,although our country uses functional components of the same specifications as foreign countries,and also has domestic advanced CNC system,the machining accuracy of machine tools is still inferior to foreign highprecision machine tools,and it is not self-sufficient to achieve the same machining accuracy.The machining accuracy of machine tool is affected by many factors,such as machining error and assembly error of machine components,cutting heat and cutting vibration in cutting process,thermal offset caused by high-speed rotation of spindle,etc.In order to improve the machining accuracy of machine tools,all possible error sources must be considered.This paper mainly analyzes the geometric errors of the machine tools,and mainly focuses on the five-axis horizontal machining centers developed by Sichuan Pshning Jiang Co.,Ltd.This paper researches the modeling,identification,compensation and detection technology of the geometric errors of the machine tools.Precision detection usually refers to the use of different precision detection instruments with different detection methods to measure the geometric error of machine tools,and then the measured data is substituted into the relevant geometric error modeling methods and identification algorithms to carry out the research on the geometric error of machine tools.At the same time,the ultimate goal of precision detection is compensation,so geometric error compensation is also a closely related research direction in this field.The main research work and achievements are as follows:(1)In the first part,the kinematics modeling theory of CNC machine tool is studied.Based on the theory of multi-body system and the method of multiplication of homogeneous transformation matrix,the kinematic model of machine tool is established,including the kinematic modeling of ideal situation and geometric error modeling.Geometric error modeling includes two methods,one is based on tool tip coordinates,the other is based on kinematic chain transmission.The physical meaning and mathematical relationship of the two models are analyzed.Finally,a five-axis horizontal machining center is taken as an example,the topological structure,low order body array and characteristic matrix are analyzed,and the establishment processes of the actual and ideal kinematics models of the machine tool are described in detail.(2)In the second part,the structure of a new R-test is optimized.A new precision testing device R-test is designed,and its structure is modularized and the key components involved are selected.According to the technical indexes and design criteria of the R-test,the measurable space and sensitivity of the R-test are analyzed,and the mathematical relationship between the measurable space and sensitivity and its structural parameters is established through its mathematical model.The sensitivity of the device is the best when the three sensors are in the orthogonal state.Compared with traditional R-test,two positioning datums A and B and a manual sliding table are added to this new R-test,so the calibration of the R-test can be realized on the worktable.The positioning error can be reduced by using the improved R-test,and the position and orientation of the sensors can be adjusted more conveniently,which provides convenience for geometric error identification.(3)In the third part,a systematic geometric error identification algorithm is proposed,and the geometric errors of the rotary axis is detected by using the R-test.Firstly,the differences and relations between left matrix multiplication and right matrix multiplication of error matrix are analyzed,and combined with the above two geometric error modeling methods,four geometric error identification algorithms are obtained,which are the most comprehensive identification algorithms based on multibody system theory.The effectiveness and feasibility of the identification algorithm are verified by using the new R-test.The calibration method of the R-test in the experimental process and the post-processing algorithm of the measured data are described in detail.(4)In the fourth part,the compensation algorithm based on RTCP function is proposed,and it is verified by the experiment with the double ballbar.In this paper,two methods of measuring the accuracy of rotary axis of machine tools by using double ballbar are proposed under the condition that RTCP function is on and off.The analysis shows that when RTCP function is turned on,the NC code is more concise and more consistent with the actual production and processing conditions.A geometric error compensation algorithm based on RTCP function is proposed in the paper.The geometric errors are compensated by modifying the NC code.Finally,the geometric errors of the rotary axis are identified and the error compensation is carried out for the measuring points in the experiment.The results show that the volumetric errors all decrease after compensation,which proves the reliability of the compensation algorithm.