Research On Error Model Building And Error Correcting Technique Of Coordinate Measuring Machines

Development of modern manufacturing has put forward higher speed and accuracy requirement for CMM. According to some research fruits of several research projects undertaken by the author, the dynamic error modeling and correcting technique of the medium precision CMM are systematically and deeply analyzed and researched by choosing the universal mobile bridge CMM as the project investigated. Those CMM having different structure have different demand of the measuring precision. There exists great difference among their error modeling and correcting technique. So the dynamic error modeling and correcting technique of high precision Nano CMM having miniature structure and the low precision on-line CMM are systematically researched. Main research work of the paper include: l)The influence to the static and dynamic precision of three type CMM created by their different structure are investigated. 2) Some static and dynamic error modeling problems of the CMM are deeply researched. 3) The error separating system are built and the effect of error model building and error correcting technique are verified by the error measuring data. Main research work and creative points of the paper are shown as follows:The static error sources of the CMM are analyzed and generalized. On the basis of researching structure characteristic and force analysis of Nano CMM and on-line CMM, error sources of static correlation of these two machines are analyzed. Each dynamic error source and their relationship of mobile bridge CMM are researched. The reasons causing the vibration of bridge frame are explored in principle. Theoretical relationship between dynamic deformation of CMM body and measurement error of CMM is deduced. The influence of dynamic property parameter of gauging head and grating dynamic property parameter on dynamic measuring precision of CMM are researched. Dynamic error sources of on-line CMM are specifically analyzed from inertia force, vibrating characteristics of rolling guide, and magnifying effect of cantilever. The influence of vibration characteristics of rolling guide on CMM vibration are researched theoretically. Representing forms of dynamic errors of on-line CMM are analyzed.According to different characteristics of CMM error distribution, single error measurement model is built by cubic spline principle and double cubic spline function. According to structure characteristics of on-line CMM and the property of non-coincident zero point, error correction model of CMM is built by homogeneous transformation matrix. In order to overcome the shortcomings of needing a large amount of sample data to build high-accuracy single-dimension dynamic error model, the theoretical basis and arithmetic of inserting standard quantity selectively of Bayesian theory are researched which will be used to build the dynamic error model of mobile bridge CMM in one direction. The characteristic and algorithm of BP net and LS-SVM are introduced which will be used to build the dynamic error correlative model of mobile bridge CMM on the different spatial measuring positions.In order to verify the effect of error model building and error correcting technique and to correct the static and dynamic error of the CMM and to improve the static and dynamic measuring precision, mobile bridge CMM dynamic error separation experiment equipment is built by the laser interferometer and aiding clamps. The relationship between dynamic accuracy of measuring system and each property parameter are analyzed. Concepts of optimum measuring speed and measuring space are presented. Dynamic error one-dimensional model of measuring system is built with the method of one-step predication, multi-steps predication, even interval inserting standard quantity and selectively inserting standard quantity of Bayesian theory. Dynamic error model of measurement system of mobile bridge CMM on the different spatial measuring positions is built with the method of double cubic spline curved face model-building, BP net and LS-SVM to compare the effect of model building. According to the structure and accuracy demand of Nano CMM, error separation experiment equipment is composed of triple light beam plane reflection laser interferometer SP2000-TR with the departure of measuring head and laser source. Separation solution of each single error of Nano CMM is designed. One-time separation of indication error and linear error is realized. Theoretical research on the influence of deflecting light path and absolute zero point on measuring result are carried out. Correlative preview experiment is designed to verify the influence. High-accuracy separation method of worktable guide error based on motion instant center is researched which considering that the actual rotating center is supposed to change with the time. The calculation formula of coordinate error of worktable speed center and random points are deduced theoretically and the corresponding error separation and correction method based on the speed instant center are designed theoretically. Error separation system of on-line CMM is built by using length measuring system and small-angle measuring system of laser interferometer, inductance measuring instrument, and angle ruler. Indicating error in X,Y and Z directions, beat and pitch error are measured. The obtained error data characteristics are analyzed. The single-axis positioning errors of CMM are corrected.