Control of underactuated manipulators with uncertain static friction

In this paper the control of 2R underactuated planar manipulator with uncertain static friction is considered. The control process is divided into two phases. In the first phase, terminal sliding mode control is used to stabilize the passive joint to the desired position in finite time; during this phase the motion of the active joint is regarded as mechanical disturbance. In the second phase, the dynamic equation of the active joint becomes a linear equation with a limited control input and a parameter containing the uncertain static friction of the passive joint. A two-dimension fuzzy controller, the domain of which is dynamically adjusted, is applied to stabilize the active joint to the desired position, while the passive joint remains at its desired position all the time. The simulation results indicate that the control scheme proposed in this paper is valid.