Dynamic Formulation and Controller Design of a Novel 3-PRS Parallel Manipulator

• Main Author: 袁偉翔
• Other Authors: 蔡孟勳
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/21952427397478397350

碩士 === 國立中正大學 === 機械系 === 90 === A novel machine tool composed of a 3-PRS (3-Prismatic-Revolute-Spherical) parallel manipulator and X-Y table was designed by the Industry Technology Research Institute (ITRI) in Taiwan. The X-Y table is used to achieve large working space, while the parallel 3-PRS mechanisms is designed to achieve high-precision and high-speed performances. In this thesis, fundamental analyses on the 3-PRS mechanism such as degrees of freedom, position analysis, inverse and forward kinematics problems are performed first. The dynamic equation of the 3-PRS mechanism is formulated based on Lagrange approach. Due to the kinematics constraints, three Lagrange multipliers are introduced. The forward dynamic analysis is performed to understand the characteristics of the 3-PRS mechanism. Because the resultant dynamic equations consists of nonlinear differential equations and algebraic constraint equations, some modification on the constraint equations must be carried out for computer simulation. As for the controller design, a PID controller based on the concept of decentralized joint control is first analyzed. It is found that although the 3-PRS parallel manipulator is highly nonlinear and with complicated dynamic equations, the PID controller still works if the coupling between the servo actuator and the parallel manipulator is small. To improve the system performance, a disturbance observer is adopted to perform better disturbance rejection and to achieve system robustness when the system is subjected to parameter variation. Two different kinds of disturbance observers are analyzed. One is based on the concept of inverse model while the other uses predicted velocity error to on-line observe the disturbance. These two types are proved to be identical from the point of view of transfer function. Also the integration of the disturbance observer with variable-structure control technique is analyzed.