六自由度数控铣床工件定位及后置处理系统_英文_.pdf

WORKPIECE LOCATING AND POST PROCESSING Received date 2005 10 11 revision received date 2006 02 18 E mail wrhit SYSTEMS ON 6 DOF CNC MILLING MACHINE Wang Rui Zhong Shisheng W ang Zhixing School of Mechatronics Engineering Harbin Institute of Technology Harbin 150001 P R China Abstract A conventional non computerized numerical control CNC machine is updated by mounting a six de gree of free DOF parallel mechanism on it thus obtaining a new CNC one The structure of this CNC milling machine is introduced and the workpiece locating system and the post processing system of the cutter location CL data file are analyzed The new machine has advantages of low costs simple structure good rigidity and high precision It is easy to be transformed and used to process the workpiece with a complex surface Key words parallel kinematic machine CNC milling machine workpiece locating system post processing sys tem CLCnumber TG543 T P391 73 Document code A Article ID 1005 1120 2006 02 00138 06 INTRODUCTION With the fast development of machine tools inmoderncomputerizednumericalcontrol CNC limitations of conventional three axis milling machines become obvious For example the conventional machine tool cannot mill some workpieces with complicated surfaces and these tasks need costly multi axis machining centers A Stewart parallel mechanism is a kind of the spatial structure possessing desirable workpieces with high accuracy high stiffness a high payload to weight ratio and good static stability 1 4 Harbin Institute of Technology is now researching on such a new kind of CNC milling machine which mounts a six degree of freedom DOF parallel mechanism on the base of a conventional non CNC milling machine Complicated workpieces such as turbine vanes can be processed by this kind of milling machine T he cost is less than that of a multi axis machining center In this pa per the structure of the milling machine the workpiece locating system and the post process ing system are analyzed 1 6 DOF MILLING MACHINE T he structure of the 6 DOF milling machine is shown in Fig 1 The milling head of the con ventional three axis milling is turned around the back side and the 6 DOF parallel mechanism is placed beneath the rotating spindle T he mecha nism has a movable platform connected to the fixed base by six identically extensible struts Each of these struts is attached to the movable platform by the 3 DOF universal joint and to the Fig 1 6 DOF milling machine Jun 2006Transactions of Nanjing University of Aeronautics 0 010 670 000 671 000 670 000 670 000 No141 2Wang Rui et al Workpiece Locating and Post Processing Systems 671 000 670 000 In this cam table 0 000 and 0 010 are the different time the following 668 000 669 000 668 000 668 000 669 000 668 000 represent six strut lengths T he time unit is second and the length unit is millimeter Finally the milling ma chine will complete the processing task using these cam tables 4 EXPERIMENTAL RESULTS Positioncoordinatesof3 DOFuniversal joints Biin the frame M and the position coordi nates of 2 DOF universal joints Aiin the frame S are listed in T able 1 In order to compute the origin position of the frame W in the frame M the following six vectors are collected p1S 3 796 72 444 674 578 p2S 29 204 64 444 674 808 p3S 29 204 90 444 674 569 p4S 29 204 102 115 692 539 p5S 12 796 103 721 692 539 p6S 40 394 83 761 692 539 and the vector o WMand transformation matrix T nWxM nW yM nW zM can be obtained o WM 48 556 38 10136 035 T Table1 Position coordinates of Biand Ai Jointxyz B1 192 518 3 170 040 20 000 0 B2192 339 2 169 936 80 036 5 B3243 398 9 81 636 70 024 3 B451 000 0251 484 90 046 0 B5 51 000 0251 514 40 040 8 B6 243 330 7 81 597 30 038 2 A1 128 500 0 407 577 30 000 0 A2128 500 0 407 615 90 010 4 A3417 423 092 620 30 062 1 A4288 826 8315 133 30 032 4 A5 291 663 9316 771 20 974 5 A6 420 456 794 371 71 065 1 T 0 9990 038 0 005 0 0380 9990 009 0 005 0 0091 000 By using the position vector o WM the trans formation matrix T nWxM nW yM nWzM and the post processing system of the CL data file the CL data file can be transformed to the CAM table in the form of strut lengths The transformation is shown in Fig 6 Fig 6 Transformation from CL data file to CAM table file 5 CONCLUSION The structure of the 6 DOF milling machine is analyzed based on a conventional one It pos sesses such merits as low cost good stiffness high accuracy high payload to weightratios and good static stability T he workpiece locating system and the post processing system of CL data file are introduced And now they are applied to a new kind of milling machine researc