| The kinematic accuracy of computer numerical control(CNC)is the key factor affecting the machining quality,and also an important index to evaluate the comprehensive performance of CNC.The instrument detection is more efficient and convenient than the specimen cutting.However,it is somewhat limited and fussy to empty traditional instrument detection in motion accuracy of five axis machine tools.The RTCP(Rotation Tool Center Point)function is developed to transfer the programming object of the NC program to the point of the knife point,so the transformation of linear interpolation objects avoids the nonlinear error introduced by rotation axis,thus the machining accuracy of CNC machine tools has been improved.When RTCP is used to detect error,the tip point is still stationary relative to the workpiece coordinate system,while the tool rotation axis moves along the programming trajectory.Based on this characteristic,RTCP synchronous detector might achieve synchronous detection of tool posture and tool tip displacement,and the corresponding relation between the motion error and the position of each axis can be accurately obtained,which is beneficial to the tracing of the error of the machine tool and the improvement of error compensation.However,the errors introduced by factors such as processing and assembly will lead to the deviation of the detection data,compensation is an inexpensive way to decrease errors.In order to solve this problem,the following study is carried out in this paper.1)The error modeling and evaluation of the synchronous detector is shown.For the error evaluation index based on sensitivity analysis,the shortcomings of local sensitivity index and global sensitivity index are analyzed.Besides,the construction of comprehensive global sensitivity index and its fluctuation index is completed.According to the theory of multi-body system,the geometric error model of synchronous detector is established,and the key error of terminal error is defined by evaluation index.2)The design and implementation of the error measurement scheme is presented.According to the characteristics of the synchronous detector,the measurement error is analyzed.The relationship between the number of measurement points and the measurement accuracy of each measured geometry is analyzed based on Monte Carlo method,so as to identify the number of optimal measuring points.According to the characteristics of the components of the synchronous detector,the design and implementation of the error measurement scheme is completed.The spherical shape error and the comprehensive error are constructed from the measured data,and the uncertainty analysis of the error calibration is completed.3)The error compensation model is built.For spherical shape error,the method of confirm spherical and plane contact points is analyzed,and the compensation model is established by the actual contact points.For the comprehensive error,the shortcoming of the traditional methods of ignoring the nonlinear error is exhibited.The estimation accuracy of semi parametric regression and the least square method is compared,and the compensation model of the comprehensive error is built according to the basic form of the semi parameter model.The two stage estimation method is used to estimate the parameters of the model.4)The software development and experimental verification of the compensation function.Based on the completed error compensation model,relevant software development is carried out,and the accuracy of error compensation is verified by comparative test. |
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