Posture control of two-link torque unit manipulator under condition of viscous friction

In this research, we study on posture control of a two-link torque unit manipulator under the condition of viscous friction. The torque unit is a module which consists of an electric motor and a reaction wheel, and it can be set at any arbitrary position as actuators to control a rotating link system with free joints. In this paper, we propose a control method using a kinetic energy of the reaction wheel. The viscous friction cannot be ignored in the real system. There arises a problem such that angular momentum remains in the reaction wheel of the torque units by the influence of the viscous friction. Then, we clarify the relation between angular momentum of the reaction wheels and rotation angles of the links. First, we try to control the first link to an arbitrary reference position without regard for the angle of the second link. The angle of the first link can be controlled by changing the viscous friction between the first link and the base. Next, we try to control the second link to an arbitrary reference position by using the residual angular momentum of the reaction wheel on the second link. Finally, we propose a control method based on these ideas, and we confirm the feasibility of the proposed method through the numerical simulations.