Study On Flexible Joint Control System With High Precision For Space Manipulator

With the gradual development of space cause and deepening in exploration to deep space, space manipulators are more and more applied in space operation instead of astronauts, such as constructions and maintenance of the space station, on-orbit capture and repair of artificial satellites, tending of experimental facilities, planet surface exploration and so on. As the core component of space manipulators,joint is facing challenge on design of the sensor system and control system, dynamic modeling and control, which are the important research direction in the field of space technology. This paper is supported by National Basic Research Program of China "space mechanisms reliability and its dynamics and system control" and "xxx space manipulator" project from PLA, and mainly focus on design of the sensor system and control system, dynamic modeling and control strategies for the space manipulator joint with harmonic drive. The main work of this paper is as follows:Firstly, in order to solve the problem of low accuracy in simplified dynamic model of joint with harmonic drive for space missions, the research in effects of natural nonlinear characteristics existing in harmonic gears is carried out, with presenting a detailed dynamic model and corresponding parameter identification method based on comprehensive consideration of nonlinear stiffness, hysteresis,transmission error and friction. Furthermore, a joint performance test platform is designed and constructed. In order to solve the drawback of axial force disturbances for the joint torque sensor based on shear spoke-type structure, a torque sensor with bend spoke-type structure is proposed, then the optimized design scheme of flexure and strain gauges for space environment, and data preprocessing algorithm are further given. Eventually performance indexes such as linearity, hysteresis,resolution and repeatability are given from static calibration data of the proposed torque sensor. Then the experiment of parameter identification is carried out based on the test platform designed before. This part of work could provide basic information for high precision control on position servo systems of the joint.Secondly, based on the detail dynamic model, problems of position accuacry and smoothness of motion at the output terminal caused by complicated dynamic characteristics in the joint are studied, and a cascade compound controller including position loop with error compensation and velocity loop with adaptive notch filter is further proposed. The experimental results show that the controller could improve position control precision of the joint, and achieve vibration suppression by means of online detection of resonant frequency.Thirdly, constraint conditions existing in the space manipulator joint are analyzed, and the problem of design methods for the joint controller subjected to multiple constraints are studied. Then a model predictive control strategy based on hybrid system dynamic model of hysteresis is proposed. A universal modeling method aiming at strongly and weakly nonlinear characteristics on the basis of hybrid system theory is put forward first, and the joint predictive model including hysteresis, transmission error and friction is further built.Next, aiming at the problem of high calculation complexity for both online and offline condition of the control strategy, this thesis transforms a N step mp-QP problem into N mp-QP problem using theories of multi-parametric programming and dynamic programming to reduce the complexity of solving. The experimental results show that the controller could satisfy the physical constraint conditions and safety limitations of the electrical drive variables while guaranteeing control accuracy and smoothness of motion of the joint.Finally, an experimental prototype of the space manipulator is developed. Furthermore, a micro gravity test platform based on air floatation is designed and constructed. Through analyzing the main influence factors of the positioning accuracy of the end-effector, this thesis establishes the error model of the end position, and then compares the variable quantity of the end position error between spatial movement condition(6 DOF) and planar movement(4 DOF) condition. Eventually the experimental research on positioning and trajectory tracking of space manipulator based on micro gravity test platform is carried out. The experimental results demonstrate the effectiveness of the proposed control strategy.