Chattering in Sliding Mode Control of Robotic Manipulators

Many Sliding Mode Control (SMC) algorithms are developed and tested on robotic manipulators based on the premise that finite-time convergence can be achieved in practical systems. However, this idealistic approach only works theoretically, as parasitic dynamics (unmodeled dynamics) in real systems lead to non-vanishing oscillations instead of convergence to an equilibrium point. In this work, we argue this fundamental point for the case of robotic manipulators. Two SMC techniques—conventional and Terminal SMC—are analyzed using Describing Function analysis and the Locus of Perturbed Relay Systems on a SOPDT model and a two-link manipulator. Findings confirm that chattering, caused by parasitic dynamics, challenges the feasibility of SMC’s finite-time convergence in real-world applications.