Study On Self-Calibration And Error Compensation Of Articulated Arm Coordinate Measuring Machines

The Articulated Arm Coordinate Measuring Machine (AACMM) is a kind of multi-degree-of-freedom, non-Cartesian coordinate measuring instrument, with features of small size, light weight, flexibility and convenience to be applied in industrial field. Sopported by the Technologies R&D Program of Hangzhou Municipality "Development of flexible arm measuring machine based on embedded system", a six degree-of-freedom AACMM with its calibration and error compensation systems were developed. The rearsearch work of this dissertation was carried out through the methods of theoretical analysis, numerical simulation with experimental verification.In chapter 1, the background and significance of the research were introduced, the current research situations, key technologies and development trend of the AACMM were expatiated in detail, and then the research contents of this dissertation were proposed.In chapter 2, the kinematics model of the AACMM was established, and it was analyzed through the method of numerical calculation and graphical simulation. The error model of AACMMs was presented followed a thorough analysis of the error sources of AACMMs. Then the error distribution maps of joint angles, joint torsion angles and other linear parameters were plotted, and the influence of structure parameters on measurement precision was analyzed through the error distribution maps, which provide theoretical foundation for structural design, components selection and measurement area selection of AACMMs.In chapter 3, mechanical structure design of an AACMM was carried out based on the theoretical analysis in chapter 2, and its measurement space is achieved through simulation analysis. The deformation of the AACMM under the gravity and measuring force were analyzed with the software of ANSYS, and the results show that the strength and deformation meet the design requirements. The data acquisition system was built, which can realize real-time signal acquisition and high-speed transmission. The fit and evaluation methods of common geometric elements were studied, and a coordinate measuring software for AACMMs was developed based on Open Cascade CAD and multi-threading technology.In chapter 4, the composition and working principle of radial circular grating angle sensors were studied, and the measurement errors which caused by installation were analyzed. Then the angle sensors were calibrated respectively with coordinate measuring machines and autocollimators. From the calibration data the distribution of angle measurement errors was achieved. Afterwards two different forms of error compensation methods were proposed. One method predicts the measurement error of the angle sensors with radial basis function neural network at first, and then compensate the reading of the sensors by the predicting data. The other method is based on the spectrum analysis of the calibrating data. From the analysis result a sine function compensation model was proposed. Furthermore, a particle swarm optimization was used to identify the parameters of the compensation model, which can overcome the non-converge problem of the least-squares method and other traditional algorithms.In chapter 5, the principle and realization method of self-calibration for AACMMs were studied. A modified simulated annealing algorithm was proposed to identify the structural parameters of the AACMMs with the single point data acquisited from a cone-shape hole. The algorithm can keep the best solution during search, and reduce the search range when the solution approaches the global minimum, which can improve the search efficiency and accuracy.In chapter 6, the 6-DOF AACMM was used to carry out experimental tests to evaluate the calibration and error compensation methods, the results show that after compensation the measurement accuracy of circular grating sensors reaches 0.002°, and after calibration, length measurement and repeatability accuracy of the AACMM reaches 0.06mm and 0.05mm respectively.In chapter 7, the main work and innovations of this dissertation were summarized, and the further research subjects were proposed.