NL-WCS: A Novel Data-Driven Algorithm for Extracting the Dynamics of Serial Robots Considering Non-Linear Friction

Recently, developed data-driven SINDy-based techniques can identify the dynamic model of serial robots without simplifying assumptions nor pre-knowledge of all kinematics and geometric details. However, these techniques cannot handle non-linear friction models, which significantly affects the precision of the dynamic model identification. This study proposes a novel data-driven approach for dynamic model identification considering the non-linear friction model along with SINDy concept. This approach is termed as non-linear-weighted-constrained SINDy (NL-WCS). The SINDy concept is extended to accommodate any non-linear friction model by efficiently incorporating the Levenberg-Marquardt (LM) algorithm. Weighted L1 regularization is combined with the physics and the data constraints, to promote sparsity in the recovery of the dynamic equations. Moreover, this combination makes the approach robust against the regression matrix’s ill-conditionality and noise. LM is integrated with the robot’s SIMULINK model to get initial values for the non-linear friction empirical parameters. NL-WCS is experimentally evaluated by utilizing three distinct trajectories to validate the extracted dynamic model of 6-DOF UR10 and 7-DOF KUKA robots. In addition, five non-linear friction models are compared. NL-WCS outperforms all the previous SINDy-data-driven methods since it reduced the RMSE significantly up to 60.65%. NL-WCS also demonstrated robustness when tested against different levels of noise. Note to Practitioners—High-performance serial robot model-based controllers need precise dynamic model identification. The classical analytical methods for modeling serial robots rely on deriving the dynamic equations with simplified assumptions and then identifying the inertial parameters. Specifically, they assume that all the robot’s geometric details are known. Furthermore, there are uncertainties in geometric parameter values due to manufacturing/assembly errors. Data-driven-based SINDy methods can derive the dynamic model without pre-knowledge of the geometric parameters of the robot. However, it can’t incorporate non-linear friction models. Thus, this paper proposed a novel data-driven technique to extract the dynamic model of any serial manipulator by coupling SINDy approach with the nonlinear friction models which is the realistic case. The practitioners can benefit from a technique like that, in such a way of applying NL-WCS to different types of industrial robots, particularly, those that have missing manufacturer data sets or sheets. Simple and reliable dynamic models can be derived only by running the robot with various trajectories. Also, this helps eliminate any uncertainties in the dynamic model discovery/building process. Furthermore, Incorporating the non-linear friction model in the derivation process enhances the dynamic modeling accuracy as it effectively takes into account all friction characteristics. The proposed approach can be converted into a software package that the practitioners can use to derive the dynamics without getting their heads around the overwhelming robot’s kinematic details.