Study On The Analysis Of Accuracy And Error Compensation For NC Machine Tools

The machining accuracy is one of the most important performance indexes for machine tools. Firstly, this dissertation details the accurate problems of the multi-axis CNC machine tool based on the precision analysis theory of kinematics for multi-body system (MBS) systemically. Secondly, it lays the strong emphases on the researches of the error analyzing and 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 work pieces are opened out, their machining accuracy predicted and their errors compensated based on software to increase their machining accuracy. The following issues are mainly studied and addressed in this thesis:1. The commonly used measurement of the parallel machine and corresponding measure tool were studied. The measurement theory and application methods of some advanced measure instruments were analyzed, which are DBB (double ball bar); the dual frequency laser interferometer,2. Due to taking full advantages of the development results of computers, the MBS theories have coruscated out of new magic power, showing their good universality, systematization and convenience for the researches of the kinematics and dynamics of MBS. Thus, this paper gives 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.3. 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 the machine tool to influence its machining accuracy. The recognized strategies of error measurements and evaluations for machine tools are introduced. After that, this paper has detailed a new method defined as twelve-line method for the sake of making the most of double-frequency laser interferometers to measure and evaluate 21 geometric errors of three-axis system. 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.4. This paper put forward index systems of machining contour errors, expatiated the mapping relation from position errors to contour errors, and established the idle 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 this software error compensation is that how to obtain the numerical control instructions to compensate the known errors. Selecting the model, identifying the parameters and transferring the NC command with the help of the dialogue model between human and computer. The transfer of NC command can be directly turned into the files of NC command compensated by the computer, so it is operated very conveniently.According to the error compensation of this technology, all kinds of the errors of the NC have been lower than before, reaching the aim of approving the accuracy of processing of NC. But the results of the programmer have not been used in practice, in the near future of researching, we have to do lots of experiments, and get a large quantity of useful dates in order to make the foundation of future practical application of this method.