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Self-calibration of the HEXA-parallel-structure

In order to enhance absolute accuracy of the HEXA-parallel-robot this paper presents a technique to calibrate the structure by means of redundant angular sensors added to its passive joints. Compared to traditional calibration strategies which are based on pose-measurement by external measurement devices the so-called self calibration approach possesses several advantages. Besides a derivation of the kinematic transformation equations of the system under consideration it is shown how to formulate an appropriate residual function that has to be minimized in order to identify the geometric parameters of the robot manipulator. An important difference to previous work on the topic of calibration is the fact, that only angular measurements are available from both the actuator encoders as well as passive joint sensors, making HEXA-self-calibration more elaborate. Simulation studies finally indicate efficiency of the proposed strategy. In order to consider the effect of measurement inaccuracies, noise has been taken into account.