Study On Error Model And Calibration Technology Of Measurement-Oriented Motion Mechanism With Multi-Joint

With the development of the automobile manufactory, universal industrial robot flexible and on-line vision inspection systems, which are based on motion mechanism with multi-joint, play an important role in quality monitoring and control of car body assembly and sub assembly. In order to ensure the measurement accuracy, it is necessary to calibrate every part of the system. Two of the most critical steps are calibration of the robot itself, which is to establish the correct mapping from the joint variables to the end-effector at arbitrary posture by exact identification of the model parameters, and on-field calibration, which is to accomplish coordinate systems unification on complex industrial field with small accuracy loss in coordinate transformations. The main work of the thesis is as follows:1. Summarization of the application domains of industrial robots with visual function in flexible manufacturing. Enumeration of the present application situation of flexible and on-line visual inspection systems in the world. Explanation of the common and key technologies exhaustively.2. Analysis and Comparison of different robot forward kinematics. MDH model was adopted to deduce positioning error model and compensation model of the robot because of the drawbacks of DH model.3. Compensation model for robot positioning error which was based on relative position error. Errors in three directions were included in the vector which represents relative position. Therefore, this method was suitable for complex filed with simplified process.4. Analysis of structure of the robot with parallelogram mechanism. The propagation error was taken into consideration in robot positioning error model through the other transformation path of the four-bar. The calibration results were compared with those without four-bar mechanism in compensation model.5. Analysis of regularity of the robot compliance errors. The flexible deformations of cantilever beam imposed on stress were discussed. Flexible joint model was established based on external loads experiments. Compensation models for compliance errors due to external loads and manipulator's gravity were established.6. Effective compensation for thermal errors due to manipulator motion. Link parameters, which were affected by temperature variation significantly and contribute most to thermal errors, were selected by Multivariate Liner Regression analysis and compensation model for thermal errors was established accordingly.7. On-filed calibration of BIW (Body-In-White) flexible and on-line visual inspection system and accuracy analysis of measurement data. Two global calibration methods which were based on measuring posture and robot forward kinematics respectively were introduced. Car body coordinates were established dynamically by using coordinate registration method based on Singular Value Decomposition. On-line and dynamic compensation for robot thermal errors was implemented by taking spheres which were made of silicon carbide as reference.