Measurement and modeling of orientation error of a six-axis robot

Abstract

Numerous research efforts have been reported in the literature on the positioning accuracy of a six-axis robot, but very few research have studied its orientation accuracy. Especially in robot machining, the end effector’s orientation accuracy plays a major role in the surface finish of the work piece. Typically, the surface of the work piece machined by a robot can be significantly worse than that the CNC milled surface, and it is to some extent attributable to the robot’s orientation errors.This research first measures the orientation accuracy of a six-axis robot by the following two different measurement schemes. The static and dynamic orientation error over a single line is measured using a laser interferometer. Then, the orientation error over the entire workspace is measured using an electronic level. The results obtained are compared with that of the simulated model based on the model developed by the authors’ group, which contains the angular positioning deviations of rotary axes as error sources, in addition to the Denavit-Hartenberg parameters in the conventional model. The performance of the present model in predicting the end effector orientation errors is validated by experiment.