Robust Control of Space Robot Paying Attention to Nonlinearity

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An attitude control algorithm of a free-flying space robot with thrusters is proposed. It is well known that the motion of the manipulator attached to the main body of a space robot causes the attitude deviation of the main body because of dynamic interaction, and an effective attitude control algorithm is desired. An equation of motion for the attitude of the space robot is derived using the Lagrange equation. The proposed disturbed torque compensation algorithm, which is a kind of feedforward control is as follows. The inertia force, which is calculated from the equation of motion, is considered as the disturbance torque for the main body. Thrusters act to compensate the impulse of the disturbance torque. The proposed algorithm is compared with the time optimal control and time-fuel optimal control algorithms. Simulation results of attitude deviations and input energy are discussed.Also, this research proposes the effectiveness of the computer based discrete time sliding mode control algorithm to compensate the attitude deviation of the main body of a free-flying space robot, which is caused by both the motion of manipulators on it, and the disturbance caused by capturing a flying target such as space debris. The controller design methodology using discrete time sliding mode control algorithm is developed. And the performance of it is compared with those current discrete time PD control algorithm and continuous time sliding mode control algorithm causes no chattering that is often observed in the case of the continuous time sliding mode control algorithm. It is clarified that the discrete time sliding mode control algorithm is the highest performance and robustness than other control algorithm.