An Enhanced POE-Based Method with Identified Transmission Errors for Serial Robotic Kinematic Calibration

Abstract

This paper proposed an enhanced method on the basis of product of exponentials (POE) formula for open chain robotic kinematic calibration. The advantages of the method mainly lay in two aspects: Above all, both the joint offsets and the link length errors can be distinctly identified using the decoupling matrix B to constrain redundant degrees of freedom of POE-based model. Moreover, the absolute positioning accuracy can be further improved by identifying the errors of the reduction ratio and the coupling ratio, namely the transmission errors. Through this model, the following parameters can be identified: 1) the joint offsets, 2) the link lengths, 3) the transformation from measurement coordinate system to base, 4) the transformation from flange coordinate system to tool, and 5) the errors of joint reduction ratio and coupling ratio. The experimental results on a 6R type and a SCARA type manipulators revealed that there were significant improvements in the positioning accuracy after the calibration process: the 6R manipulator and the SCARA manipulator were enhanced from 2.175 mm to 0.291 mm, from 7.078 mm to 0.203 mm, respectively.