A fuzzy-sliding mode controller for robust tracking of robotic manipulators

Considerable attention has been given to controller designs that utilize the variable structure system theory in order to achieve robust tracking performances of robotic manipulators subjected to parameter variations and extraneous disturbances. However, the theory has not had widespread acceptance in the practical control engineering community, due mainly to the worry of chattering which is inherent in the variable structure system. A new type of fuzzy-sliding mode controller to alleviate the chattering problem is presented. A sliding mode controller for robust tracking is firstly synthesized with an assumption that imposed system uncertainties satisfy matching conditions so that certain deterministic performances can be guaranteed. The controller is then incorporated with a fuzzy technique in which fuzzy variables are obtained from a relationship between predetermined sliding surfaces and the positions of representative points in the error state space. The discontinuous feedback gain of the fuzzy-sliding mode control system is to be properly adjusted according to the commanded fuzzy rules. A two degree-of-freedom robotic manipulator subjected to a variable payload and a torque disturbance is considered in order to demonstrate the superior tracking performances accrued from the proposed methodology. (C) 1997 Elsevier Science Ltd. All rights reserved.