A coupled relationship between control toques is constructed for an underactuated four-link gymnast robot (UFGR). It changes the nonlinear UFGR system into a cascade-connected system.
We transform the stabilization of the UFGR into that of an underactuated two-link acrobot.
An energy-based stabilizing controller is designed for the two-link acrobot.
The structure of the proposed control system is simple. And our proposed strategy is easy to extend to the stabilization control of n-DOF (n>4) underactuated manipulator.