The local calibration method for robot inaccuracy compensation

Abstract

Abstract This article presents a local calibration method that is philosophically different from the more contemporary global calibration methods. Local methods seek models of robot performance at the robot distal link measured relative to parts in localized part regions. In contrast, global methods seek to model various sources of robot inaccuracy internal to the robot. For example, a significant global research area is the determination of the actual robot arm structural parameters. Given more accurate estimates of these parameters, global compensation methods propose perturbation techniques or improved kinematic models that can be used to control the as‐manufactured robot. To implement local calibration methods, calibration procedures have been developed to locate tool and sensor tool control frames (TCF's) and to measure robot inaccuracy in localized regions. Using the measured position and orientation (pose) data obtained by hardware sensors, the components of operational inaccuracy are integrated into compensation models. This article discusses compensating model effectiveness and considers the interactions between hardware sensors and part features necessary to extract robot pose measurements automatically and effectively. Applying the relative calibration methodologies presented in this article to a GMF S‐200 six‐axis robot, robot repeatability was reduced by 39% and average localized robot inaccuracy was reduced from 3.4 mm (0.134 inch) to less than 0.86 mm (0.034 inch). The compensated robot inaccuracy is near the unstructured robot repeatability.