Robust tracking of elastic joint manipulators using sliding mode control

Abstract

Tracking control of manipulators with joint flexibility is considered. Singular perturbation techniques are employed to decompose the system dynamics into reduced-order models in separate time-scales. Based on these reduced-order models, a two time-scale composite control strategy is adopted and three control laws developed: (i) Continuous Composite Control (CCC), (ii) Sliding Mode Composite Control (SMCC) and (iii) Extended Sliding Mode Composite Control (ESMCC). The SMCC controller enables accurate tracking to be maintained in the presence of payload variations which degrade the performance of the CCC controller, while the ESMCC controller also compensates for the effects of parameter variations on the fast system states, a problem which has not previously been addressed. Simulations of an RTX robot are employed to evaluate the relative performances of these control laws.