The Dynamic Analysis of Series-Parallel Machine Tool with Flexible Links and Joints

• Main Authors: Yun-Jie Jheng, 鄭運傑
• Other Authors: Ting-Nung Shiau
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/05154806408537396356

碩士 === 國立中正大學 === 機械系 === 93 === The novel machine tool composed of a 3-Prismatic-Revolute-Spherical parallel (3-PRS) 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 mechanism is designed to achieve high-precision and high-speed performance. The link length of the parallel manipulator is one of the most sensitive parameters influencing the cutter location. The joint stiffness of parallel manipulator is weaker than the traditional machine tool. Thus the dynamic behavior influenced by the flexible links and joints is discussed in the study. The dynamic equation of the 3-PRS mechanism is formulated based on Lagrange approach. The natural frequency of the system, the position of the tool tip and the transmitting forces of the joints are discussed under the influence of flexible links and joints. For the motion analysis of the system with flexible links and joints, the relation between the feed of the spherical screw and the tool tip profile is first derived by the inverse kinematics. And then it is substituted into the equations of motion of the system with rigid links and flexible joints and other equations of motion of this system with flexible links and joints respectively. The dynamic behavior influenced by different stiffness of links and joints are discussed. According to the numerical results, the response of the system with flexible links and joints is compared with the response of the system with rigid links and flexible joints. The difference of each position is calculated as compared with these two systems. The difference of the tool tip position in x-direction is greatly affected by the difference of the tool tip rotational position in -direction. The difference of the tool tip position in y-direction is greatly affected by the difference of the tool tip rotational position in -direction. When the stiffness of the links or the stiffness of the joints is changed, the variation of the position in z-direction is much larger than the variation of the position in other directions. The effect of the spherical-joint stiffness ks on the sensitivity of the natural frequency of the 3-PRS mechanism is larger than that of the revolute-joint stiffness kr on the sensitivity of the natural frequency of the 3-PRS mechanism. When the stiffness of the joint is changed, the variations of transmitting forces of spherical joints are smaller than those of revolute joints. To regulate the natural frequency of the 3-PRS mechanism, a change of the stiffness of the spherical joints is better than that of the revolute joints.