Passive momentum observer for mechanical systems

In this paper, we propose a hybrid momentum observer for mechanical systems that has the momentum estimate error as a passive output. It is shown that, in the absence of additional input terms, the proposed observer is exponentially stable with a tunable rate of convergence. Then, by interconnecting the observer with the plant, the momentum estimate is shown to be a passive output from the combined plant and observer systems. Using this property, asymptotic stability of the closed-loop system is possible via negative feedback using the momentum estimate. The approach is demonstrated on a planar 2 degree-of-freedom robotic manipulator.