Research On Paramenters Identification And Experimental Platform Of Large-scale Space Manipulator Joints

With the accelerated pace of the building of the China Space Station, developmentof the large-scale space manipulators should be put into practice desirably. Jointsworking in large temperature, high vacuum, hard radiation environment are keycomponents of the large-scale space manipulator, whose performance will directlyaffect the entire implementation of the orbital mission. Therefore, with the support ofthe laboratory autonomous program “Development on the large-scale spacemanipulators” the HIT large-scale space manipulator joint performance test platform aredeveloped and the joint dynamic parameters identification is thoroughly studied in thetest platform.The positioning accuracy and the load capacity are the two most important indicesof performance. So it is very important to check if indices of performance satisfy designindices. For satisfying this requirement, the HIT large-scale space manipulator jointperformance test platform is designed, which integrates a torque sensor, a positionsensor, a gear increaser and a magnetic particle brake for loading. So the indices of thejoint are completely measured.Harmonic drive is the core transmission part of the joint, whose stiffness andfriction nonlinearity will cause the nonlinearity of the joint. So the dynamic model ofthe HIT large-scale space manipulator joint is established, according to the nonlinearityof the dynamic model for the harmonic drive.The accuracy of the sensors in the joints will directly influence the accuracy ofparameters identification. High accuracy sensors can greatly increase efficiency ofparameters identification. For the reason the sensors in the joint are calibrated, includingthe resolver, the torque sensor, the current sensor and the encoder. The problem of thelow accuracy of the resolver will be solved by an error compensation method based onBP neural network. For many compensation experiments it is proved that this methodcan improve the accuracy of the resolver greatly.The exact dynamic parameters can greatly improve the joint control accuracy. Forthis reason in the control mode of the current close-loop and the position close-loopcontrol parameters identification is researched on the HIT large-scale space manipulatorjoint. The research on the coulomb-hydraulic friction model, the cubic polynomialfriction model and Stribeck friction model are done, experimental results show that theStribeck model can reflect the actual joint damping better. Experimental results of thestiffness identification show that the stiffness is less than the harmonic drive’s samplevalues, which is caused by deformation of the torque sensor and connectors of the joint.Then the off-line parameters identification of the overall dynamic model using theleast-squares method is obtained, and experimental results show that the identified stiffness is closer to the actual joint stiffness, considering the damping torque. Finally,on-line parameters identification of the joint is carried out using the modified recursiveleast-squares algorithm, considering the error model based on a forgetting factor. Theexperimental results show that the parameters can converge to the relative stable valueswhich are near to the off-line identification parameters.