Robust control of underactuated manipulators: analysis and implementation

Underactuated manipulators are robot manipulators composed of both active and passive joints. The advantages of using such systems reside in the fact that they weigh less and consume less energy than their fully-actuated counterparts. Another interest reside in the reliability or fault-tolerant design of fully-actuated manipulators. The methodology proposed in this paper uses the dynamic coupling between the passive and the active joints in order to bring the passive joint angles to a desired set-point. Therefore, the control law and the performance of the system are completely dependent on the dynamic model. Since it is difficult to obtain the exact dynamic model of the system in general, considerable position errors and even instability can result in some cases. We propose a variable structure controller to provide the system with the robustness necessary to perform tasks regardless of the modelling errors