Research On Coordinated Operation Of Multi-Arm Freeflying Space Robot

Multi-arm Free-Flying Space Robot can be called robot satellite, it is composed of main body and several manipulators assembled on main body, this robot can fly or float in space freely, the dangerous extra vehicular activities can be finished by the robot instead of astronaut. The position and attitude of main body will be disturbed by the motion of parts of manipulators, because there isn't a fixed foundation in the multi-arm FFSR system. The normal functions of solar collector and satellite antenna would be disabled by the change of main body attitude, if main body attitude angle exceed the range limits prescribed. In this paper, the work space of multi-arm FFSR was discussed, at first. The character of main body attitude stability was studied when FFSR carried out space duty, such as catching object free floating in space, secondly. Main body attitude disturbance character was researched when the object was grasped by manipulators mounted on main body and the attitude adjusting equipment didn't work, and the affection caused by external force to multi-arm coordination were researched deeply. The fuzzy VSSC method was given in the control system of multi-arm FFSR, at last. Through simulation, the method was proved that it is robust to external disturbance and change of system parameters.In this paper, kinematics and inverse kinematics model of multi-arm FFSR was constructed based on the augment body method of multi-body system dynamics, the structure and singularity of Generalized Jacobin Matrix got from multi-arm FFSR kinematics was analyzed, and the definition of dynamics singularity of multi-FFSR was given. Because multi-arm FFSR is nonintegrated constraint system, this character results in that the dynamics singularity of task space is associated with path of manipulators. Through the analysis of work spaces of multi-arm, the definitions of reachable, path independent and guarantee work space were given. The variation of manipulators work space was analyzed when the object was grasped by a manipulator of multi-arm FFSR, the workspace of manipulators affected by object mass was analyzed, the path plan foundation of object was established.The kinematics and dynamics model were constructed based on redundancy resolution methods. The burden of reaction wheel was released through multiple arm coordinated operation. Utilizing its redundant character and zero space of Generalized Jacobin Matrix of multi-arm FFSR, the joint angle acceleration calculating method was got when manipulators move along desired path, and the joint torques calculate method during object grasping was given. The torque calculating was carried out on acceleration level, the joint torque of FFSR was optimized utilizing vector norm minimum principle, power consumed by joint motor to drive manipulators of FFSR was reduce to minimum.The kinematics model was established when the object was grasped firmly by manipulators and closed kinematics chains was formed. Through kinematics character simulation of coordinated operation, the coordinate operating relation between manipulators and main body position and attitude disturbance character caused by mass of different components was got. The dynamics coordinated operation model was constructed utilizing Newton-Euler equation, in this method, calculating partial derivative of Lagrange energy function was avoided, the calculated speed was raised. In order to guarantee the motion identical character of manipulators and keep contact force between object and manipulators during the object was coordinated operated to track desired path. The tracking error model of object position and inertial force was set up, they are simulated under simulink environment and proved true.The equivalent sliding mode controller was designed based on the dynamics model of Multi-arm FFSR coordinated operation. The advantage of sliding mode various structure controller, which is its strong robustness to unsure factor of FFSR system and external disturbance is combined with the advantage of fuzzy logic controller, which is its intelligent judgment and inference to control signal. To fast the duration getting into sliding mode predefined and reduce its vibration, the sliding mode controller gain and slope of sliding surface was switched dynamically according to fuzzy control theory. through simulation, the performance of PID controller, traditional sliding mode controller and fuzzy sliding mode control was compared, the conclusion is that any kinds of fuzzy sliding mode controller is best among these controller, and the performance the gain and slope adjusted dynamic according to fuzzy theory is the best among these three fuzzy sliding controller, and the robust performance to external disturbance and variation of system parameters is proved.In order to verify character of coordinated operation kinematics, dynamics and main body position and attitude disturbance caused by external force, it is necessary to establish micro-gravity environment on the ground. Air cushion was used to simulate two dimension micro-gravity environment, which can make dual-arm FFSR prototype floats freely on the platform. The position and attitude disturbance experiments of main body and main body position variation caused by external force was carried out in this environment.