An extended inverse kinematic model of the HEXA-parallel-robot for calibration purposes

Geometric calibration is a well known technique to improve absolute accuracy of robotic structures. For spatial parallel robots most research activities in this area are limited to calibration of existing robot models which are based on ideal geometry and can be said to be simplified as they neglect geometrical effects such as axes offset in cardan or spherical joints. Complete models consider these effects. However, these models are complex so that an analytic solution of the inverse kinematics is not possible as usually the case for "ideal parallel robot" models. As real time inverse kinematics need to be guaranteed for control purposes, an analytic solution is preferable due to short and constant evaluation tunes. This paper presents an inverse kinematic model for the HEXA-parallel-robot which contains an increased number of geometric parameters compared to the ideal geometry models while still being analytical solvable. As it is presumed that the calibration result is the more accurate the more geometric parameters are considered the solution is a way to improve robot calibration with the more sophisticated robot model.