SMOOTH ROBUST ADAPTIVE SLIDING MODE CONTROL OF MANIPULATORS WITH GUARANTEED TRANSIENT PERFORMANCE

A systematic way to combine adaptive control and sliding mode control (SMC) for trajectory tracking of robot manipulators in the presence of parametric uncertainties and uncertain nonlinearities is developed. C ontinuous sliding mode controllers without reaching transients and cha ttering problems are first developed by using a dynamic sliding mode. Transient performance is guaranteed and globally uniformly ultimately bounded (GUUB) stability is obtained An adaptive scheme is also develo ped for comparison. With some modifications to the adaptation law, the control law is redesigned by combining the design methodologies of ad aptive control and sliding mode control. The suggested controller pres erves the advantages of both methods, namely, asymptotic stability of the adaptive system for parametric uncertainties and GUUB stability wi th guaranteed transient performance of sliding mode control for both p arametric uncertainties and uncertain nonlinearities. The control law is continuous and the chattering problem of sliding mode control is av oided. A prior knowledge of bounds on parametric uncertainties and unc ertain nonlinearities is assumed. Experimental results conducted on th e UCB/NSK SCARA direct drive robot show that the combined method reduc es the final tracking error to more than half of the smoothed SMC laws for a payload uncertainty of 6 kg, and validate the advantage of intr oducing parameter adaptation in the smoothed SMC laws.