Study On The Methods Of Precision Modeling And Error Compensation For Multi-Axis CNC Machine Tools

The machining accuracy is one of the most important performance indexes for machine tools. Firstly, this dissertation details the accuracy problems of the multi-axis CNC machine tool based on the precision analysis theory of kinematics for multi-body system(MBS) systemically. Afterward, it lays the strong emphases on the researches of the error analyzing and precision modeling and the studying of the error identifying, machining accuracy predicting, software error compensating and so on. With the precision model of the multi-axis CNC machine tools, their error transferability rules from the parts to the machined workpieces are opened out, their machining accuracy predicted and their errors compensated based on software to increase their machining accuracy.Due to taking full advantage of the development results of the computers, the MBS theories have coruscated out of new magic power, showed their good universality, systematization and conveniency for the researches of the kinematics and dynamics of MBS. That the MBS kinematics theories are applied to study the accuracy of nonideal kinematics develops a new usage field of them. Though these researches began to be think much of till in the last few years, they have already displayed their mighty vitality. Thus, this paper makes a systematic and in-depth study on the MBS kinematics theory and the methods of precision modeling, error identification, accuracy prediction, and error compensation based on the studied theory.The kernels of MBS theories are that the number arrays of low-order body are used to describe the topological structures which are taken to generalize and refine MBS, and the characteristic matrixes are employed to represent the relative positions and gestures between any two bodies in MBS. These kernels are the foundation of the kinematics analyzing and modeling for machine tools and have been detailed. This paper has established a kind of universal precision model for all multi-axis CNC machine tool according to the proposed MBS kinematics theory. After that, the paper has given the concrete expressions of ideal kinematic model, nonideal kinematic model and volumetric error model for a three-axis machine tool and a five-axis machine tool taken for examples.After establishing the precision model of machine tools, the measurement and evaluation of their error parameters have been started. There are many kinds of error parameters in a machine tool to influence its machining accuracy, for example, geometric errors, heat deformation errors and force deformation errors etc.. The recognized strategiesof error measurements and evaluations for machine tools are introduced. After that, this paper has detailed nine-line method, but also proposed and probed into a new method defined as twelve-line method for the sake of the making the most of double-frequency laser interferometries to measure and evaluate 21 geometric errors of three-movement-axis system in a multi-axis machine tool. In order to identify 6-freedom errors of turning-axis, this paper has detailed the identification mechanism of these errors according to radial errors, axile errors and turning errors. Based on these researches, the problems of the error measurement and evaluation of machine tools in the application process of MBS theories are resolved perfectly.After completed error modeling and error identification, machining accuracy predicting and error compensating can been carried through with that. This paper has put forward of index systems of machining contour errors, expatiated the mapping relation from position errors to contour errors, and established the mapping model from the errors of the components of machine tools to machining errors so that the machining accuracy estimates can be realized accurately.A key point of software error compensation is that how to obtain the numerical control instructions to compensate the known errors. This paper has expounded several direct calculation methods and adding additional instruction methods. Taking a three-axis machine tool...