Path Optimization And Robust Tracking Control For Space Manipulator

Space manipulators are expected to perform important tasks in future space mission-s, for instance, satellite maintenance, refueling and replacing the orbit replacement unit. These missions are performed for the benefit of extending on orbit lifetime, so as to reduce cost and raise efficiency. Path optimization and tracking control are foundations for space manipulators to realize these missions, and also the key technology in space missions. Such operations will encounter challenges because space manipulators have some unique characteristics unfound on ground-based robots, such as, dynamic coupling between ma-nipulator and space manipulator for working without a fixed base, limited energy supply and so on.Free-floating and attitude-controlled are two most commonly used work modes when executing assignments. Therefore, research on path optimization and robust tracking con-trol of these two modes are significant to theoretical study and practical applications. This thesis will take free-floating and attitude-controlled space manipulators as research back-ground, and focus on solving some challenging problems during path optimization and robust tracking control. The following contents are mainly considered.The problem of path optimization for free-floating space manipulator is solved based on the Gauss pseudospectral method; the factors of distinct nodes that affect computing time and accuracy are analyzed. Aimed at minimizing time, fuel and perturbations to the base, we derive the optimization path from initial pose to target pose under physical lim-itations and environmental constraints. Costate mapping theorem ensures the rationality of the algorithm. By comparing proposed performance index, computing time, and errors with various objectives and distinct nodes, we draw conclusions that the accuracy can be improved by increasing the number of nodes, however, the increase in nodes number leads to the increment of the state differential matrix dimension, computational complexity and computing time.The problem of path optimization for free-floating space manipulator is solved based on the multiphase Gauss pseudospectral method and adaptive pseudospectral method. The multiphase Gauss pseudospectral method is performed by implementing pseudospectral method on each segmental, less nodes are needed on high accuracy segmental, so as to reduce the total number of nodes, and the nonlinear programming problem can be solved speedily by means of the sparseness of Jacobian matrix. Furthermore, the adaptive Gauss pseudospectral method which dynamically adjusts the node number and distribution is proposed based on the evaluation of relative error distribution and the method of refin-ing mesh. Compared with three pseudospectral methods, we find that the multiphase pseudospectral method has shorter computing time and higher accuracy than Gauss pseu-dospectral method, the adaptive pseudospectral method has less nodes and higher effi-ciency than multiphase pseudospectral method, what is more, the demand of real time for path optimization is satisfied.The robust model reference tracking controller and robust second order model refer-ence tracking controller based on the parameterized theory are proposed for free-floating space manipulator to tracking the optimized path in Chapter3. Based on the parameter-ized theory, the model reference controller can be divided into two parts:state feedback controller and feedforward tracking controller, these controllers provide all free degrees, by optimizing these free parameters the controller with optimized robust performance in-dex and error is obtained. The problem of robust tracking control for base attitude and end-effector pose is solved, what is more, the problem of robust point to point tracking control for dual-arm space manipulator is solved too. Furthermore, a robust second order model reference tracking controller is proposed according to the second order nonlinear model of space manipulator. The method avoids matrix inversion, provides good numeri-cal stability. The stability and convergence of closed-loop system are proved. Simulation results show that the proposed method is efficient and robust to different types of uncer-tainties and disturbances.We propose robust trajectory tracking control methods to tracking the optimized path in Chapter4based on the improved state dependent Riccati equation for attitude-controlled space manipulators with uncertainty and disturbance. For space manipulators with uncertainty, a robust performance index is derived based on the uncertainty analysis, then the robust tracking controller is proposed by optimizing the performance index. The optimization problem can be solved by state dependent Riccati equation according to the linear-like structure of space manipulator. For space manipulators with disturbance, we assume that the bound of the disturbance is known, based on a new sliding surface, a robust optimal tracking controller is proposed by combining the sliding controller theory and state dependent Riccati equation, the local asymptotic stability and convergence of closed loop system are proved. Simulations are performed by tracking the optimized path and show that the proposed method is efficient and robust to different types of uncertain-ties and disturbances.