Study On Geometric Parameters Identification Of Hybrid Machine Tool's Parallel Mechanism And Machining Of Internal Spherical Surface

The hybrid machine tool is a novel type machine tool developed in the recent years. It is combined serial mechanism with parallel mechanism so that it can obtains the advantages of great travel and rotational angle of the serial parts, as well as high stiffness, high accuracy and high feed speed of the parallel parts. The birth of the hybrid machine tool is a great revolution of the machine tool industry, which also represents the development trend of the new generation machine tool. However, the machining accuracy still is an important factor which restricts the commercialization of the hybrid machine tool and its popularization and application in industrial production. In this case, how to improve the machining accuracy of the hybrid machine tool has become the key that relates to that whether it can be put into practice or not.The Kinematic Calibration is a high-efficiency and low-cost method that can improve the geometric accuracy of the hybrid machine tool. In this thesis, the Geometric error sources of the six-axis hybrid boring and milling NC machine tool 6PM2's parallel mechanism are analyzed. Space coordinate systems are established, and then the posture of the motion platform is described with the solution of coordinate transformation. Then, the geometric parameters' identification model is constructed according to the relationship between the posture errors of the motion platform and the geometric errors that is given out by the inverse model. With the calibration of parallel bars' original length being taken for instance, the posture information of the motion platform is measured and the identification equations are solved by considering the structural parameters as unknowns so that the real value of the parallel bars' original length can be obtained. Finally, the control model parameters of the parallel mechanism are corrected. In this way, the kinematic calibration of the hybrid machine tool is preliminarily accomplished.With the machining of internal spherical surface being taken for example, the kinematic calibration of the hybrid machine tool is proved effectively. The generating principle of internal spherical surface is analyzed, based on which the machining method of combining the motion of cylinder milling cutter interpolating the section circular arc of the internal spherical surface with the motion of the workpiece rotating on its own axis is chosen. As it is possible that the milling cutter would interfere with the machined surface while machining the internal spherical surface, the minimum value formula of the spindle's inclination angle is deduced. The time-slicing circular interpolating method is used to accomplish the rough interpolation of the section circular arc of the internal spherical surface, while a certain motion mode of the multi-axis motion controller PMAC is used for the precise interpolation.