Articulated Arm Coordinate Measuring Machine Calibration Technique

AACMM (Articulated Arm Coordinate Measuring Machine) has broad application prospect as a portable coordinate measurement system. It has the advantages of wide measurement range and flexible based on the characteristics of the mechanical structure. But the measurement accuracy is difficult to be improved, this limit its application and usefulness. Calibration is one of its key technologies to ensure its accuracy. The main contents of this thesis are revolving around AACMM calibration technologies, including the following:1)Existing calibration methods are analyzed and compared both from the theoretical and practical aspects, which provides a basis for selecting the calibration method. First, experimental analysis was made to them on the basis of summing up the process of the calibration. The relationship between the precision (standard deviation) and the angle measurement accuracy was gained by analyzing the affection of sampling data, sample size and angle measurement accuracy to the calibration effect. Secondly, a simple classification of the standard amount used for parameter calibration was made and the advantages and disadvantages of some standards were pointed out. Their error's nature of the gauge block, cone and standard bar was analyzed and the structural design and error analysis of the physical constraints standard parts were made. Finally, the commonly used algorithm for the calibration of AACMM were researched and analyzed. The adaptability, advantages and disadvantages of the Genetic Algorithm, Simulated Annealing and Nonlinear Least Squares Methods were pointed out, and the performance of the three algorithms in acquiring the structure parameters of AACMM was compared through experiments. From the experimental results, nonlinear least square represented by the LM algorithm are more appropriate.2)The parameters can be calibrated based on the measurement model; AACMM was kinematics modeled by using the DH method, after then the measurement model of the AACMM was given. The process of kinematics modeling was discussed, including modeling under different pose and structure of the measuring machine; Non-redundant parameter model was put forward based on study of the probe's parameters; On this basis, the parameters errors of the measuring machine were carefully analyzed; In order to meet the demand of portable coordinate measurement, the probe parameters calibration were studied after the probe of the AACMM was replaced, and its theoretical basis was given and the probe parameters calibration program was edited.3)In this thesis, cone and standard bar were used as a calibration standard parts, this method has the advantages of high precision and adaptability. The common 6-DOF AACMM was calibrated. Some preparatory works were carried out before the calibration, including programming calibration software system, verifying and correcting the angle errors of the joints. They were calibrated by use of cone and standard bar first after the above preparation, and then the affection of the standard bar length and sampling coverage error to the calibration results was analyzed. The designed physical constraints standard parts were calibrated by using the laser tracker. Physical restraint standard parts is an ideal calibration standard parts, in addressing the problems of its own calibration can greatly improve the calibration efficiency.4)The seven-axis AACMM was modeled and calibrated in this thesis. After the kinematic modeling to it using D-H method, the special problems of the seven-axis AACMM were found by the simulation. Then a calibration method was given. Measured data show that the calibration method can effectively solve calibration problems of the seven-axis AACMM and can ensure the accuracy.