Stabilization of underactuated two-link gymnast robot by using trajectory tracking strategy

This paper concerns the stabilization of an underactuated two-link gymnast robot called acrobot. A trajectory tracking control strategy is presented. First, we carry out a homeomorphous coordinate transformation on the acrobot system that transforms it into a new simplified nonlinear system. And then, a desired motion trajectory is designed for the new system. Finally, we use an equivalent-input-disturbance (EID) method to design a controller that makes the new system asymptotically track the desired trajectory. This enables the acrobot to be swung up from the downward position and to be stabilized at the upright position. The proposed strategy changes the stabilization of the nonlinear acrobot system into that of a linear time-invariant error dynamic system with an artificial disturbance. And it uses a single controller to accomplish the motion control objective of the acrobot. These makes the strategy simple and efficient. Simulation results demonstrate its validity and its superiority over others.