On The Analysis, Optimization And Control Of The Flexible Supported Stewart Platform

The research works of this dissertation are based on a major project of Chinese National Science Foundation, entitled by"Overall design and key technogies research of the five hundred meters aperture shperical radio telescope (FAST)". In view of the difficulty to realize the tracking precision of the feed source for the huge flexible wire driven parallel manipulator (WDPR), several key technological problems in the application of the six-degrees-of-freedom Stewart platform, which was used as a secondary stabilizing and tuning mechanism for achieving the specification of the feed source in FAST, were delt with. The mechatronic servo bandwidth, design optimization, software and hardware implementation, calibration and motion control were developed, which were validated by the experiments of the 50m scaled model of FAST. The main works can be described as follows.1. The definition of mechatronic servo bandwidth of the six-degrees-of-freedom Stewart platform was made in the beginning, which has the straightforward physical meaning and can be used to estimate the moving ripidity of the mechatronic system of the Stewart platform. The mechanical and control factors determining the mechatronic servo bandwidth were discussed in the kinematics and dynamics points of view. Given the configuration parameters, dynamical performace of the legs and load capacity of the universal and spherical joints, the general solution to the servo bandwidth is proposed. Besides, a case study was carried out.2. The multi-objective configuration optimization model of the Stewart platform was established, which integrated the kinematic, dynamic peformance and dynamical compliance degree with the flexbile base. The real-coded adaptive genetic algorithm was employed to solve the optimization problem. Under the conditioin of satisfying the dexterous and mechatronic servo bandwidth, the design parameters of the Stewart platform for higher dexterity and weaker dynamical compliance were obtained.3. Based on the SynqNet sychronized multi-axis network controller, the hardware and software control system of the Stewart platform were developed, and the following control of the typical trajectory was implemented. The smoothly moving trapezoidal mode was adopted to plan and realize the typical trajectory. Aiming at the constructed Stewart platform, experiments on the workspace, static positioning accuracy, and dynamical trajectory tracking accurcy and mechatronic servo bandwidth were carried out. Consequently, the optimized result was validated by experiments. 4. A decoupled tracking and prediction algorithm was presented, which laid a base for overcoming the effect of displacement response of the feed cabin by the external disturbance (wind load and dynamical compliance) and internal perturbation (the flexibility and lag of the flexible cables, the friction of the joints) on the feed platform. In this algorithm the three dimensional object was treated as the end-effector of a suppositional six degrees-of-freedom fully parallel manipulator. The lengths of actuating links are predicted in the decouled joint space, and then the future position of the object is obtained with forward kinematics of the suppositional parallel manipulator. Taking the two stage compound control model of FAST feed supporting and orienting system as an example, the numerical simulation shows the algorithm has the advantages of high predication accuracy and real time computation.5. In order to overcome the control difficulty of the flexible supported Stewart platform, the adaptive interactive PID controller, which utilized the adaptive interactive algorithm to adjust the parameters of conventional PID controller, was devised as the supervisory controller in the joint space of the Stewart platform. The supervisory controller was used to generate the control commands in the upper level of the electrical cylinders and improve the dynmical performance of the control process. Besides, in the lower level of the the electrical cylinders, the digital servo filters with feedforward were employed to track the desired trajectory accurately. The experiments of the FAST50m field model validate the effectiveness of the adaptive PID supervisory controller, accompanied with the motion predication of the feed cabin. The feed supporting, pointing and tracking system could meet the demands of positioning and orientating precision with the desired tracking velocity.