Research On Integrated Control Of Trajectory Tracking And Vibration Suppression Of A Space Flexible Manipulator System Using Piezoelectric Actuators

Trajcectory tracking of space flexible manipulators together with suppressing their vibrations during their operation has been the main concern of many recent stuies in aeronautics and robotics. This thesis is mainly concerned with trajcectory tracking and vibration suppression control of a typical space flexible manipulator system using piezoelectric actuators. Funded by National Natural Science Foundation, dynamic modeling of the flexible manipulator system, optimal placing of the actuators/sensors, optimal trajectory planning for vibration suppression of the manipulator and the integrated control strategies for trajcectory tracking and vibration suppression of the system are studied deeply in this dissertation. The main contents of this dissertation are as follows:In chapter1. scientific backgrounds and siganificances of this thesis are presented. Then, state-of-art for several key technologies concerning this field are elaborated. The structure and main contents of this dissertation are depicted.In chapter2. a dynamic model of the space flexible manipulator system is drived using extended Hamilton’s principle with discretization by the assumed mode method. In addition, introduced the friction torque and the coupling torque between the motor and the flexible manipulator, dynamics of the driving set-up(sevo-motor and harmonic gear)is described. In the end. a further verification of the dynamic characterics of the system is made through numerical simulation.The objective of chapter3is to determine the optimal locations of multiple distributed actuators/sensors. The dynamic model in chapter2is converted to state space form for control design. To find the optimal location of piezoelectric sensor/actuator pairs, a hybrid optimization strategy combined with minimization of the input energy, maximization of the transferring energy and minimization of natural frequencies changes is proposed. The performance criterion is composed of two parts:(1)a LQR performance criterion including flexible vibration energy, rigid motion energy and driving energy of the motor.(2) The change ratio of the natural frequencies. To solve this complex multi-objective optimization problem, a modified Multi-Island Genetic Algorithm (MIGA) is developed for identifying optimal sizing and location of piezoelectric patches as well as the optimal feedback control gains. Also, a series of comparable research is implemented in different conditions.In chapter4. an optimal trajectory planning technique for suppressing vibrations of the system is proposed. At first, vibrations responses of the manipulator between polynomial and cycloidal motions are compared. Then, the principle of optimal trajectory planning technique for suppressing vibrations of the flexible manipulator system, which is controlled by the sevo-motor and piezoelectric actuators, are elucidated, and a performance criterion considering the exciting torque for the flexible part and the driving torque for the rigid part is presented. In order to get the displacement, the five order polynomial functions, which arouses less vibrations, is used to constructe and interpolate the discrete displacements. And the optimal trajectory is found using Multi-Island Genetic Algorithm (MIGA), again. It is confirmed from the simulation results that the proposed trajectory planning technique is effective in suppressing vibrations of the flexible manipulator.In Chapter5, it deals with the integrated control strategies of trajectory tracking and vibration suppression for the space flexible manipulator system with PZT actuators. Using the singular perturbation theory, the flexible-rigid-coupled dymanics of the system, is separated into flexible and rigid subsystems, by considering the fact that it takes place in two time scales. And then, a composite control strategy consisting of a fuzzy sliding controller for slow subsystem and a hierarchical fuzzy PID controller for fast subsystem is developed. According to the numerical simulation results, it can be concluded that the proposed integrated control strategies have a suitable and efficient performance for trajectory tracking and suppressing vibrations of the flexible manipulator in different intial contiditons and trajectories. Both motion precision and operation efficiency are improved.In chapter six. experimental system of the space flexible manipulator is set up, and the corresponding software and hardware are summarized. Experimental studies on system dynamics, optimal locations of multiple distributed piezoelectric actuators/sensors, optimal trajectory planning for suppressing vibrations and the integrated control strategies of trajectory tracking and vibration suppression are elaborated respectively.Conclusions and prospects are briefly depicted at the end of this thesis.