Research On Techniques Of NC Machining Oriented To Parallel Machine Tool

Parallel machine tool (PMT) is a creative application of parallel mechanism, NCtechnology and computer control technology in the area of NC machine tool. PMT hasmany advantages over traditional machine tool, and is suitable for machining parts withcomplicated surfaces.This paper focuses on the development of CAD/CAM system oriented to5-UPS/PRPU PMT and conducts research into the operation of a new solution foranalysis of parallel mechanisms. Topics includes general structure of CAD/CAM systemoriented to 5-UPS/PRPU PMT, techniques of NC postprocessing, orientation algorithm ofworkpiece coordinate system, algorithm of fast interference inspection, simulationtechniques of NC machining and a new solution for analysis of parallel mechanisms areanalyzed systemically. And experiments of machining are performed. This research aimsto resolve key programming techniques of NC machining, realize NC machining of partswith complicated surfaces by 5-UPS/PRPU PMT, push the industrialization andpracticality of PMT and also provide a new tool for analysis of parallel mechanisms. Themain contributions are as follows:The general structure of the CAD/CAM system oriented to 5-UPS/PRPU PMT is putforward, the information flow and key algorithm of the CAD/CAM system software ispresented. At the same time, the CAD/CAM system software is modularized andfunctionally described.A general model of miller is applied to perform tool path calculation, and the generaltool path calculation equations for 5-axis surface milling are deduced. By analysingkinematics of 5-UPS/PRPU PMT and cutter swing 5-DOF machine tool, the same qualityof two Euler angles of 5-UPS/PRPU PMT and two swing angle of cutter swing 5-DOFmachine tool is obtained.The design principle, function, general structure and process of NC postprocessingfor 5-UPS/PRPU PMT are introduced, and several key problems and relative algorithmsare analyzed in detail. Simulation is performed to verify the correctness of the methodbased on a 3D free surface machining.The importance and principle of orientation of workpiece coordinate system isintroduced. By analyzing dexterity measures of PMTs, two terms are defined, which arenamed comprehensive dexterity coefficient and comprehensive dexterity degree, andcomprehensive dexterity degree are applied in the layout of tool path. The orientation of5-UPS/PRPU PMT workpiece coordinate is treated as a nonlinear programming, that is,for a given cutter location data, they must be inside the PMT workspace and theircomprehensive dexterity degree is the least, the general procedure of the solution ofabove problem using complex method is given. The arithmetic is verified by theorientation of a free-form surface.The kinematic equation of 5-UPS/PRPU PMT is derived by means of open loopkinematic chain method. Using this equation all kinematic variables, including thelengths of bars, moving angles of spherical joints and hooke joints, can be obtained in theone-time kinematic calculation, therefore it is very suitable for fast interferenceinspection of PMTs. The related arithmetic of the method is put forward and verified.Basing on 3D CAD software----SolidWorks2000 and OLE interface, the method ofdeveloping the NC milling process computer simulation for 5-UPS/PRPU PMT waspresented, and the software is developed. Under object-oriented program circumstance,the idea of developing 3D standard parts library of cutter and holder based onSolidWorks2000 by using development tools of Visual Basic and Access was put forward,and the automatically changing cutter and rough in simulation-system are realized.Simulation example of NC machining and experiment of machining are performed.In order to obtain the solution for analysing kinematic of a parallel mechanismwithout the construction of mathematical model, a method of using assembly constraintand label dimension function of CAD software is presented. The results of computersimulation show that this method is not only straightforward and quick, but is alsoadvantageous from viewpoint of accuracy and the highly efficient solution for otherparallel mechanism. The realization process of motion simulation of 5-UPS/PRPU PMT,mapping from virtual axis to real axis space for 5-UPS/PRPU PMT, forward kinematicsanalysis for 5-UPS/PRPU PMT, velocity and acceleration analysis for 5-UPS/PRPU PMTare given in detail, and the correctness of the method is verified. The new method notonly complements the traditional method perfectly, but also has academic significanceand notable practical value.