1、Sensitivity analysis of the 3-PRS parallel kinematic spindleplatform of a serial-parallel machine toola Department of Mechanical Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Road, Taipei, Taiwan, ROCb Department of Mechanical Engineering, Ming-Chi Institute of Technology, Taipei, Ta
2、iwan, ROCc School of Mechanical Engineering, Jiao Zhou College of Engineering, Henan, Chinad Mechanical Industry Research Laboratory, ITRI, Taichung, Taiwan, ROCReceived 1 April 2003; accepted 9 July 2003AbstractThe special configuration of a serial-parallel type machine tool possesses five degrees
3、of freedom and provides more flexibility in NC machining. The parallel spindle platform plays the key role in manipulating three directions of movement. In this study, the inverse kinematics analysis of the platform is derived first. A sensitivity model of the spindle platform subject to the structu
4、re parameters is then proposed and analyzed. All the parameters influencing the position and orientation of the spindle platform are discussed based on the sensitivity model and the simulated examples. Critical parameters to the accuracy of the cutter location can then be found, which are the slider
5、 position, the strut length, and the tool length. 2003 Elsevier Ltd. All rights reserved.Keywords: Kinematic analysis; Sensitivity analysis; 3-PRS spindle platform; Serial-parallel machine tool1. IntroductionTo obtain higher accuracy and greater dexterity, machine tool manufacturers are developing p
6、arallel type structures for the next generation of machine tools. It is always a goal to pursue an interesting development in the machine tool industry that holds great promise for improving accuracy. Machine tools with their high rigidity and accuracy are ideally suited for precision applications.
7、Parallel manipulator offers a radically different type of machine structure relative to the traditional serial type machines. It is believed that the inherent mechanical structure of the parallel type machines provides high dexterity, stiffness, accuracy and speed compared to the conventional multi-
8、axis structure 1,2.In the past, many comprehensive studies and works have been made in the area of parallel manipulators. The kinematic behavior of the parallel mechanism with extensible strut has been discussed in many literatures 3-5。Some reports dealt with the kinematics of threelegged parallel m
9、anipulators 6,7. Most of these articles focused on the discussion of both the analytical and the numerical methods to solve the kinematics of pure-parallel mechanisms 68. Some papers also discussed the accuracy analysis of the Stewart platform manipulators 911. A new type of serial-parallel machine
10、tool has been developed by the Mechanical Laboratory of ITRI in Taiwan. Simulation analysis and experimental tests have shown the necessity of its accuracy enhancement 12-14Even though many researches have made contributions to the theory and design of the parallel kinematic mechanism, however, comm
11、ercial applications of this potential parallel machine have not been widespread yet. The main obstacle to the applications of this kind of machine tool is their unsatisfactory accuracy. Similar to the traditional machine tool, there are several major factors, such as the structural imperfection, the
12、 elastic deformation and the thermal deformation, that will degrade the machine accuracy. In order to find out the essential error sources, sensitivity analysis of the spindle platform movement and error identification are neces sary for the purpose of accuracy enhancement of the machine tool.In thi
13、s paper, the kinematics model of parallel mechanism is derived in the first part. Sensitivity model of the spindle platform subject to structural and kinematic parameters is then proposed. All parameters influencing the position and orientation of the spindle platform are analytically estimated. Sim
14、ulated example are given to identify the most critical error sources.2. Machine tool configurationThe machine tool under investigation is called a serialparallel type machine tool. The configuration is shown in Fig. 1. It consists of a three-degree-of-freedom spindle platform and a conventional two-
15、degree-of-freedom XY table to form a five-axis structure. The spindle is assembled in the platform, which is connected to three struts of constant length by means of ball joints (or Ujoint)that are equally spaced at a nominal angle of 120. The other end of each strut is connected to a slider with a
16、rotational joint. Each slider can move up and down along the corresponding vertical slideway fixed to a column that is also spaced at nominal 120 angle from one another. The platform, such constructed, has one linear motion in the Z-axis and two angular rotations ( and ) in the X- and Y-axes, respectively. The XY table that supports the workpiece provides the linear motions of the workpiece in two horizontal directions. The features
