Validation and mathematical model of workspace Measuring and Positioning System as an integrated metrology system for improving industrial robot positioning

Abstract

This article aims to improve the absolute accuracy of an individual industrial robot by means of integrating itself with the workspace Measuring and Positioning System, which is currently under development at Tianjin University, China. We found that the absolute positioning error persists in the robot base frame, whereas the errors, both in position and orientation, can be reduced by changing the reference frame from the robot to the integrated metrology system, that is, the workspace Measuring and Positioning System. What it needs more is several additional corrective movements. And this correction work just needs roughly calibrated parameters between the robot frame and the workspace Measuring and Positioning System frame. To validate it, we present the experiment which demonstrates that the absolute error of the industrial robot can be less than 0.2 mm by virtue of the workspace Measuring and Positioning System and the convergent corrective movements. Aiming to explain the results, this study deduces the mathematical model in detail about the integration of the robot with the workspace Measuring and Positioning System. The model explains why the integration of the robot with the workspace Measuring and Positioning System applies. First, the model tells that there exists a low requirement, that is, the tolerable rough level of the parameters between the robot frame and the workspace Measuring and Positioning System frame, for assuring the convergence of the corrective movements. Second, the relationship among the relevant factors in the corrective process is given. Finally, besides the workspace Measuring and Positioning System, this model is of general significance for any available metrology systems with which the industrial robot can integrate, and it may also provide theoretical instructions for the improvement of the robot off-line programming, that is, the robot can work at a higher accuracy provided by the integrated metrology system.