Study On The Flexible Multibody Dynamics Of The Virtual Axis Hybrid Polishing Machine Tool

The metal cutting machine tool develops until now, in a word their basic construction has no what to change. It is generally adopted the layout of asymmetry "C" to be set up by the bed, the column, the headstock and the table. This kind of layout makes machine tool organization complicated, the being forced deformation and the thermal deformation is asymmetrical and the accumulation error enlarged. However, the virtual axis machine tool (the parallel machine tool) breaks thoroughly since two centuries the principle of the construction for the machine tool and the kinematics, based on the straight-line displacement of Cartesian coordinate. It is combined with the robot technique and the machine tool construction technique. Based on the space parallel mechanism (the parallel robot), the part of hardwares is replaced by the software and the parts of mechanical transmission are replaced by the electrical device and appliance. It has some merit such as the simple construction, the short transmission chain, the good environment adaptability and the high additional value of technology.The virtual axis machine tool is developed for 10 years up to now, many kinds of the constructions of the special machine tool was developed in the world. In it, some have already carried into the practical phrase. Totally, the virtual axis machine tool has the high extent of modularization, apting to reforming and the simple mechanical construction. But the machine tool has also existed some shortages obviously, namely it has the obvious disfigurement in the rigidity, precision and workspace and so on. Therefore, how to develop the new applied field of the virtual axis machine tool by growing the advantage and avoiding the shortage, become the strategy choice, which has the important research value in this field. In the development of the virtual axis hybrid machine tool is developed by our group, the new field of the automatic and precision machining on the mold curved surface is looked for and expanded. To make use of the characteristics of the flexibility machiningwell and to design flexible polishing tool system skillfully, it is applied in the polishing on the free curved surface. The exploration of this paper opens up a new road to develop the applied field of the virtual axis hybrid machine tool.The virtual axis hybrid polishing machine tool is a complex multibody system, which contains many closed-loop chain structures. It is complex and difficult to build the dynamic equations compared with the traditional series mechanism. Different from robots, the virtual axis hybrid polishing machine tool itself has many features in the dynamics aspects. Especially, for such a special machining process of polishing of free-form surfaces, the vibration of the machine and cutting stability is the key problem. So it is the key to analyze the dynamics of the virtual axis hybrid polishing machine tool in order to improve the dynamic characteristics of the system. At present the dynamic equations of virtual axis hybrid polishing machine tool are mostly built by taking the machine tool as rigid multibody system. By the methodology of rigid multibody dynamics, the dynamic equations for each leg and platform can be built by regarding each leg and platform of the virtual axis hybrid polishing machine tool as the independent sub-structure. Then based on the constraint conditions of sub-structure, the constraint dynamic equations for the system are built. Because rigidity of each part is different, for example, the rigidity of each leg is weaker than that of the moving and fixed platform, the deformation of legs can not be ignored during the process of moving. Meanwhile the deformation of each leg is acting or coupling with the rigid movement of the whole virtual axis hybrid polishing machine tool.Based on the above analysis, this paper applies the modeling method of dynamics of flexible multibody systems into the dynamic analysis of virtual axis hybrid polishing machine tool and builds the dynamic equations of spatial rigid-flexible coupling multibody syste...