Error Synthetic Compensation Technique And Application For NC Machine Tools

In this dissertation, based on fully understanding and deeply analyzing the current status of the research and application of the NC machine tool error compensation technique, some theories and techniques concerned have been studied, some new methods are used to save the machine error compensation technique from laboratories to plants, and more than 100 CNC turning centers are implemented successfully by the error compensation technique.In chapter 1, a survey of the important role of NC machine tool error compensation in industry production application is given, and the review of the current status of the research and application of the NC machine tool error compensation technique is provided. Finally, the maincontents of the dissertation are presented.In chapter 2, the error synthesis models of a CNC turning center and a NC twin-spindle lathe are derived by the homogeneous coordinate transformation method, which cover not only the geometric errors but also the thermal errors.In chapter 3, new theories and methods of thermal error modeling are discussed. Because of fully depending on modeling data, the models which are set up by current methods are not very robust, and one model couldn't be used by several machine tools even though the machine tools are the same type and used to machine the same parts. Two new modeling methods, the synthesis least squares approach and the orthogonal experiment design approach, are proposed, which possess the characteristics of combining the statistic theory with machine's structures, engineering judgments and surrounding temperatures, so they can make the thermal error models more robust and accurate.In chapter 4, the thermal sensor location optimization is studied. By thermal dynamical analysis, study and simulation, it can be obtained for a spindle that: (1) one thermal sensor is enough to be used to express a spindle's thermal expansion;(2) there exists at least one point along the length of a spindle whose temperature reading has a linear relationship with the spindle thermal expansion;(3) the temperature-expansion relationship is linear when sensor is located around one third of a spindle length from the heat source end. For the three dimensions of thermal sensor locations on a machine tool, six tactics are put forward, which are main element tactic, observable tactic, non-correlation tactic, minimum sensor number tactic, maximum sensitivity tactic, and most linear tactic.In chapter 5, real time thermal error compensation on a CNC turning center is introduced, which is a production project under the sponsorship of General Motors Windsor Transmission Plant. First, the major thermal error sources and modes are analyzed for the purpose of selecting best thermal sensor locations. Then, the errors are detected and modeled. Last, a thermal error compensation system is developed and extensive experiments are completed. After the compensation cutting results show the effectiveness on the first CNC turning center, a large number (more than 100) of CNC turning centers are implemented by the thermal error compensation technique based on the two new modeling methods discussed in chapter 4, in which all the CNC turning centers share just two thermal error models, and almost all machines get good compensation results, so, good financial and social profits are obtained. It could say that this is the first successful example for machine error compensation in the world.In chapter 6, real time compensation of geometric and thermal errors on a NC twin-spindle lathe is introduced, which is also a production project under the sponsorship of US Saginaw Machine Systems Inc., the difficulties of which are not only compensation for thermal errors but also geometric errors, and the machining accuracy of two spindles are inter-affected. Geometric errors and thermal errors are separated on the basis of their different properties, that is, the geometric errors have the position property and the thermal errors have the temperature property. A set of strategies are presented for modeling different types of error components according to their properties. Compensation cutting tests are conducted to verify the effectiveness of this method and the accuracy of the machine is improved significantly.Finally, in chapter 7, the conclusions deduced from this dissertation and prospects for future research will be suggested.