On the Controllers Based on Time Delay Estimation for Robotic Manipulators

Assurance of asymptotic trajectory tracking in robotic manipulators with a continuous control law in the presence of unmodeled dynamics or external disturbance is a challenging problem. Recently, it is asserted that this aim is achieved by designing a traditional model-free controller together with time delay estimation (TDE) such that neither dynamical parameters nor conservative assumptions on the external disturbance are required. In this note, the purpose is to show that this claim is wrong. Additionally, modification of this method for some special cases is presented.