| As the basic equipment in the manufacturing sector,CNC machine tool is an important manifestation of the national industrial productivity.However,the geometric error problem has always been the bottleneck of domestic CNC machine tools,which has seriously affected the market competitiveness of our machine tools.Therefore,it is necessary to carry out theoretical research for the geometric error formation mechanism and evolution process of CNC machine tools,so as to have a positive impact on the development of our CNC machine tools industry.Meta-Action theory interprets the movement essence of complex electromechanical products from a new perspective,and lays a general technical foundation for the multiple quality characteristics research of CNC machine tools in quantitative analysis and collaborative design.Based on the original Meta-Action theory,the Function-Movement-Action-Part(FMAP)structural decomposition method is proposed,the function of CNC machine tools is decomposed into multiple motion chains including several Meta-Actions(MA).Taking the Meta-Action Unit(MAU)as the most basic motion unit,the error relationship model between the intra-MAU and the inter-MAU is distinguished.A multi-level error mapping model is established,which includes geometric error of parts,error transmission of inter-MAUs and error accumulation of components.In order to analyze the formation process and fluctuation reasons for geometric errors of CNC machine tools,the random error sources and time-varying error sources are analyzed in detail.And the comprehensive evaluation model for geometric error uncertainty of CNC machine tools is proposed by using the solution method for uncertainty problem.To analyze and control the influence factors on machining error,the guarantee strategy of CNC machine tools manufacturing process is studied.Finally,a theoretical research method is provided to improve the geometric error level of domestic CNC machine tools in the aspects of analysis modeling and evaluation control.The specific research contents include the following aspects:(1)Due to the complex structure of CNC machine tools,the expression model is not precise and cannot contain more error sources when modeling the error of CNC machine tools in the traditional method.A new FMAP structural decomposition method is proposed,which takes the MAU as the minimum granularity of CNC machine tools motion,and it can provide a reasonable balance between the subordinate relationship of parts and machine.Considering the structural characteristics of MAU,the output error of MA is represented as the deviation of the trajectory of the power take-off.Based on the small displacement torsors(SDT),the space pose expression matrix and torsor parameter constraint model for typical characteristic errors of components are given.And the output error formation process of MA is analyzed,which provides expression basis for output error quantitative calculation of MA.(2)The homogeneous coordinate transformation matrix is used to describe the process that the spatial position and pose of the power output part in MAU changes with the assembly sequence.By analogy the assembly process of MAU to a multi-stage linear system,the assembly cumulative error of MA actuator in the theoretical space rectangular coordinate system is solved based on the state space model.At the same time,the characteristic error of power input and power output with complex geometry is analyzed in detail.Thus,the quantitative expression model of MAU output error is obtained,which is composed of the spatial pose error and geometric error of the power output and the geometric error of the power input.Taking the worktable rotation MAU in the rotary table is as an example,the error of each part is simulated and calculated,which is the theoretical base of modeling inter-MAU error transmission.(3)The main reason affecting the MAU assembly error is the geometric dimension of manufactured parts,and the main influencing factors of error propagation from the previous MAU to the next MAU are relative position error,relative motion error and contact strain of the two MAUs.Because of the nonlinear and difficult to measure coupling error,the error transmission model of MA chain is established based on radial basis function(RBF)neural network.The simulation results show that the average relative error between the predicted value and the real value is 7.8% and 10.6%respectively,which verifies the feasibility of this method.The traditional motion axis measurement methods have lower precision because of ignoring small angle errors.To obtain complete geometric errors of multi-axis machine tools,a multi-component integrated geometric error modeling based on coupling and decoupling measurement method is proposed in this paper.Thereby a new error mapping model from parts to the machine tool is formed,which can not only describe the process of error transfer accumulation more accurately,but also include more comprehensive error types without complicated calculation process.The geometric error modeling of CNC grinder is taken as an example to verify the advantages of this method.(4)In order to quantitatively evaluate the probability of geometric error of CNC machine tools to meet the allowable error within a specified time,the uncertainty error source causing the fluctuation of output error is discussed from the perspective of Meta-Action.The uncertainty function of MA output error including initial random error and time-varying wear of components is established,and the function is modified based on stochastic processes discretization method.Furthermore,the mechanism of error transmission between two MAUs in different layers is analyzed.Combining with the conditional random field model,the precision multi-state reliability of the downstream MAU under the influence of the upstream MAU accuracy state is evaluated.Thus,a comprehensive evaluation model for the precision reliability is established according to the multi-layer chain structure of CNC machine tools.The limitation of random errors in previous modeling is solved,and the precision reliability evaluation under the comprehensive influence of multi-level random error sources is realized.It provides a more reasonable model basis for maintenance decision and tolerance design of CNC machine tools.(5)In view of the lack of systematic and comprehensive quantitative analysis tools in the past total quality management,in order to achieve the purpose of guaranteeing the manufacturing process by controlling the influencing factors on random error sources of CNC machine tools,a multi-index quantitative evaluation system for the manufacturing process of CNC machine tools is established.The influence factors in manufacturing process are analyzed and evaluated,and the calculation steps of process factor expectation index and manufacturing process expectation index are given based on hesitant fuzzy theory and multi criteria decision making method.And the expectation indexes are divided into five grades.The state of the manufacturing process is directly reflected by the numerical form.The multi-dimensional comprehensive evaluation and analysis of product production from process to result is realized combining with processing capability index method.Thereupon then,the process variables can be controlled to improve the quality,and the process management is evaluated comprehensively based on process status and processing results.And a new guarantee strategy is provided for the manufacturing process management of CNC machine tools. |
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