Effectiveness of the DIDIM method with respect to the usual CLOE method. Application to the dynamic parameters identification of an industrial robot

The Usual Closed Loop Output Error (CLOE) method for dynamic parameters identification of robots has several drawbacks: slow convergence, sensitivity to initial conditions and the calculation of significant parameters is not easy-to-run. Recently a new CLOE method called as DIDIM for Direct and Inverse Identification Model needing only actual forces/torques data was validated on rigid robots. This method avoids the drawbacks of the usual CLOE method. With the DIDIM method, the optimal parameters minimize the 2-norm of the error between the actual forces/torques and the simulated ones. It is based on a closed-loop simulation of the robot using the direct dynamic model, the same structure of control-law and the same reference trajectory for both the actual robot and the simulated one. The DIDIM method simplifies dramatically the non-linear Least Squares problem by using the Inverse Dynamic Model in order to obtain an analytical expression of the simulated forces/torques which are linear in the parameters. This explains why the DIDIM method has a fast convergence. In this paper, the DIDIM method is compared with the usual CLOE method which uses the actual positions as output. Experiments are performed on a 6 degrees of freedom robot Stäubli TX40.