Abstract
In this paper, a new controller for an operating manipulator work in the space microgravity environment is proposed. First, on the basis of the load variation caused by microgravity, a sliding mode control method is used to model the gravity term, and the logistic function is introduced as the approaching function. An improved sliding mode reaching law is proposed to control the manipulator effectively, and Lyapunov theory is used to deduce its closed-loop stability. A friction compensation scheme, which regards friction as disturbance, is introduced to the microgravity environment, and a space disturbance observer (SDO) is designed from the viewpoint of disturbance suppression to identify the friction characteristics of the control system accurately. To model the lagging friction phenomenon caused by velocity inversion during operation tasks, an adaptive compensation scheme based on the LuGre model is proposed. Finally, the design of a manipulator system, which consists of a robot arm, dexterous hand, teleoperation system, central controller, and visual system, is presented. On-orbit maintenance and capture experiments are carried out successively. The effectiveness and reliability of the controller are verified, and the on-orbit operation tasks are completed successfully.
Highlights
Space technology is the realization of human’s infinite yearning to explore the universe
The dynamic equation of the manipulator consists of three parts: inertia term, Coriolis and centripetal force term, gravity term, an effective control strategy is needed to preprocess the gravity term while compensating for the friction of the space manipulator to account for the differences between space and ground conditions
Space manipulator system is responsible for on-orbit servicing missions, such as space capture tasks and maintenance of electrial connection, so the core of system is a 6-DOF humanoid robotic arm
Summary
Space technology is the realization of human’s infinite yearning to explore the universe. The change in mechanical motion behavior and control performance caused by the microgravity environment has become an unavoidable problem in the design of space technology. Because of the space microgravity environment, the ideal model is entirely different from the actual model, and this divergence seriously affects the final control accuracy of the space robot manipulator. The dynamic equation of the manipulator consists of three parts: inertia term, Coriolis and centripetal force term, gravity term, an effective control strategy is needed to preprocess the gravity term while compensating for the friction of the space manipulator to account for the differences between space and ground conditions
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