Research On The Kinematic Errors For Five-axis Machine Tool Rotary Axes Based On The Machining Tests In Error Sensitive Directions

With the increasing application of five-axis CNC machine tools in the high-precision machining, the improvement of the machining accuracy is a crucial demand in the market. Motion accuracy is the most basic indicators to develop high-precision Five-axis machine tools. Estimation of the kinematic errors is the basis to improve the motion accuracy. This thesis studies the kinematic errors identification method for five-axis machine tool rotary axes based on the machining tests in error sensitive directions, in support of the science and technology major project of advanced CNC machine tools and basic manufacturing equipment (2009ZX04014-026) and Zhejiang Provincial key scientific and technological innovation team of "advanced CNC machine tools and key technologies". The content and achievement of the thesis are summarized as follows:The different principle between Five-axis machine tool kinematic errors direct measurement and error identification was been studied comparatively. The advantages and disadvantages of the non-cutting kinematic errors identification method and machining tests identification method were summed up. Focused on the disadvantages of computational complexity, time-consuming of operation, high cost and weak versatility in the existing five-axis machine tool rotary axis kinematic error identification technology, combining with the actual need of the machine tool users and manufacturers, the method combined interpolation motion detection and working accuracy detection was proposed to design the machining tests based on a mathematical model of the interpolated motion, and then the rotary axes kinematic error sources were quickly identified from the machining errors of the test piece.A simple mathematical model of the machine tool was established by optimizing the coordinate system settings based on robot kinematics. The kinematic error mathematical formula of universal spindle head type and cradle five-axis machine tools, which both have two rotary axes superimposed together, are derived. According to the structural characteristics of universal head five-axis machine tools and cradle type five-axis machine tools, the mathematical expression of this model is simple, the physical meaning is clear. It is convenient to separate individual kinematic error from this model. The proposed model is a theoretical foundation for further kinematic error recognition.The machining tests based on error sensitive directions are proposed to identify the kinematic errors of five-axis machine tool. Error sensitive direction vectors are adopted in the machine tool kinematics model to carry out matrix calculation firstly. Then the functional relationship between the machining errors of the test piece and the kinematic errors in the rotation axes of five-axis machine tool is established. And then the machining errors can be obtained by CMM inspection from the finished workpiece to identify the kinematic errors from the machining errors. The method is divided into two steps. The first step is the kinematc errors detection with the movement of only the rotary axis of the table, and the second step is the detection with the simultaneous movement of the trunnion axis and rotary axis of the table. The machining tests contain a total of10machining modes. Experimental results demonstrate that the proposed method can reduce the complexity, cost and time-resuming substantially. The versatility of the proposed method is strong so that it does not depend on the type and size of the machine tools.In order to assess the credibility of the evaluation results of Five-axis machine tools kinematic errors based on machining tests, uncertainty analysis of five-axis machine tool kinematic error evaluation process was carried out by combining Monte Carlo simulation and analytic statistical method, the measurement uncertainty of the test piece machining errors are assigned to the uncertainty of individual kinematic errors. It can provide operational evaluation and certification processes for the popularization and application of the machining tests in the industry.