Position Control of a Planar Four-Link Underactuated Manipulator

A position control strategy by employing the model reduction and the cascade transformation is proposed for a planar four-link AAPA (Active-Active-Passive-Active) underactuated manipulator in this paper. First, a dynamics model of the system is built. Next, three controllers are designed based on the Lyapunov function to control the fourth active link from any initial angle to zero while the angles of the first and second active link remain their initial values, which makes the system is reduced to a planar virtual three-link AAP (Active-Active-Passive) underactuated manipulator. Then, we obtain the new inputs of the cascade system of the planar virtual three-link AAP underactuated manipulator. Finally, we can get the controllers of the active links to realize the system position control objective. Simulation results demonstrate the validity of the proposed control strategy.