Torque Unit Manipulator Driven by Control Moment Gyros

This paper deals with a space manipulator which is called Torque-Unit-Manipulator (TUM) : TUM separates its actuator called torque unit from its joints; i.e., torque unit is placed on an arbitrary place on a link, and each rotational joint is a free joint. The TUM proposed in the previous work, however, is driven by reaction wheels, and thus it has a problem to be solved : the angular velocity of the reaction wheel may saturate when external force disturbs the posture of the TUM repeatedly. The reason is that the reaction wheels accumulate angular momentum during the maneuver because of non-holonomic constraint for the free joints. Therefore, TUM driven by Control Moment Gyros (CMGs) is proposed in this paper. For the proposed TUM, an asymptotically stable controller can be designed through Lyapunov's approach, and besides the gimbal angular velocity of the CMG returns to zero after each maneuver. The dynamics of the proposed TUM is computed in numerical simulation, and the effectiveness of the designed controller is shown.