Passivity-Based Versus Disturbance Observer Based Robot Control: Equivalence and Stability

Disturbance observer based robot control algorithms provide good control performance while giving a straightforward method of gain selection. Unfortunately, the stability of these algorithms has not been shown rigorously for nonlinear systems such as robots. This paper demonstrates that a disturbance observer based algorithm can be made equivalent to the well-known passivity-based approaches of Sadegh and Horowitz, and Slotine and Li. This is accomplished by choosing a specific design of the Q(s) filter (described in the paper) of the disturbance observer. By doing so, the stability of the disturbance observer based approach can be proven rigorously. An additional benefit of the equivalence of the two approaches is the ability to combine an adaptive controller to the disturbance observer based approach.