The Research and Design of NC System for 6-UPU Parallel Machine Tool
|School||Shandong University of Technology|
|Course||Mechanical Manufacturing and Automation|
|Keywords||PMT NC System Interpolation algorithm Cutter radius compensation|
Parallel Machine Tool is a new type of machine tool developed in the past decades. Compared with traditional machine tools, Parallel Machine Tool has many advantages, such as high stiffness-weight ratio, good dynamic performance, high level of modularize-tion, high additional technology value, etc. It’s necessary to develop a type of PMT as well as CNC suited to education, in order to make college students understand the structure, function, control theory and control methods of this new machine tool as soon as possible and edit control programs for processing various complex mechanical elements’ patterns with this type of machine tool. An in-depth research on PMT’s NC system is carried out in this paper taking account of structural features and application requirements of the 6-UPU instructional PMT. The main researched contents are as follows:A general design of the NC system for PMT is presented. The hardware structure of "PC+Kinematics Controller", object-oriented programming techniques and modular thinking of the development of NC software are ensured. In addition, a friendly user interface of software is designed in this paper.The kinematic analysis of the 6-UPU instructional PMT is carried out in this paper. The selection of excess degrees of freedom is simplified at the request of five degree of freedom. A new descriptive method of spatial position of moving platform is presented based on tool vector. With the new descriptive method the inverse kinematics model of PMT is built.The structure and style of NC program adopted in PMT is presented, designing and developing the corresponding compiled modules. Some problems about the nonlinear error of PMT are researched in this paper, and a tool-vector-based subdivision method which can decrease the nonlinear error is presented. Based on the subdivision method, the spatial linear interpolation, the spatial circle interpolation and the spatial corner interpolation are realized. At the same time a algorithm for fine interpolation, Slope-based Pulse Distribution, is presented. All of the interpolation algorithms are confirmed by manufacture experiments.C cutter radius compensation of PMT is studied in this paper. The method to determine joint type of adjacent track segments and the specific steps to calculate the joint vector making use of the tool bias vector are presented. Then the process of programming implementation and simulation results are also presented. Finally, All of the algorithm are confirmed by manufacture experiments.