Modeling and identification of serial two-link manipulator considering joint nonlinearities for industrial robots control

This paper presents modeling and identification of a serial two-link manipulator considering joint nonlinearities for industrial robot control. In order to achieve the desired performance using model-based control approaches, it is important to obtain relevant models of both kinematics and dynamics including the nonlinear effects. The main nonlinear components which result in trajectory tracking errors of typical multi-axis industrial robot, are joint nonlinearities in each axis and dynamic coupling effects between different axes. A parametric modeling approach is presented to reproduce behaviors of a serial two-link manipulator with joint nonlinearities. Nonlinear stiffness, angular transmission errors, and friction in these two links are directly identified as joint nonlinearities. As a case study, this approach is applied for the serial two-link arm of a typical multi-axis industrial robot, which has low frequency vibration modes and significantly affect to the trajectory performance. Effectiveness of the modeling is verified by comparative studies with numerical simulations and experiments. Finally, a simple 2-degrees-of-freedom controller on the basis of the identified dynamic model has been applied to improve the performance of trajectory tracking and residual vibration suppression.