| Since the numerical control technique was developed in 1950's there have beenmany developments, the CNC (computerized numerical control) system has been thecore part of the modern manufacturing systems. However, contemporary most CNCmachines are still programmed in the ISO 6983 "G and M code" language, which makesmany limitations in current CNC machines. Today a new model of data transfer betweenCAD/CAM systems and CNC machines, called ISO 14649 (informally known asSTEP-NC), is being developed under the ISO technical Committees TC184sub-committees SC1 and SC4 based on the ISO 10303 known as STEP. With the newstandard advent, a new CNC controller called STEP-CNC (STEP-NC based CNC)receives worldwide attention. The STEP-NC not only is the basis for development ofthe next generation of CNC controller that possesses intelligent, flexible and opencharacters, but also gives CAM and CNC vendors the opportunity to integrate theCAD/CAM system with a new bread of intelligent CNC controllers. This paper presentsa careful and detailed research on STEP-NC and its application for CAPP, CAM, CNCand the integration between CAx systems and CNC system. The key issues andimportant conclusions deduced in the dissertation are as follows:(1) The STEP-NC_based CNC system was studied. An intelligent and openSTEP-CNC system function frame was proposed and its hardware structure based onIPC & PMAC with double CPUs was also designed. Compared with the currentdeveloped STEP-CNC systems, this new CNC system not only includes all functions ofthe conventional CNC system, but also possesses three distinct advantages as follows: 1)well expansibility, convenient transplantablity and maneuverability, 2) intelligentfunctions, 3) supports the WEB based manufacturing.(2) The STEP-NC program structure was studied and a STEP-NC programinterpreter was developed. Since the tool path design should be completed bySTEP-CNC system, the tool path automatic generation technique was investigated. Thefundamental principle of the tool path design is object-oriented view in terms ofmanufacturing features, and the objects in this case are manufacturing features and theirassociated working steps.(3) Taking the NURBS as an example of free surface machine in the STEP-CNC system, a method of fixed parameter for tool path automatic generation andinterpolation technology based on constant arc increment were discussed in detail.Correction and validity of algorithms were verified through the real example machinesimulation.(4) A simple and effective method of intervention detection and disposal wasstudied. This method can be applied into any complex surface machining.(5) The data model features of STEP-NC decide that the process planning in theSTEP-CAPP (CAPP based on STEP-NC) system is non-linear process planning, whichcan generate multi-process routes at the same time. In this paper the course and methodsof non-linear process planning in STEP-CNC system are presented.(6) Genetic algorithm based on elite choice for the optimization of working stepssequence was developed. In the conventional manufacturing the working procedure isused as machining unit, while under the application of STEP-NC the working step is asmachining unit and the machining is numerical control machining center-oriented. Theoptimization goal is to find the best working steps sequence according to the leastassistant machining time consumed by the part location transform and tool replacing. ASTEP-CAPP prototype system was designed and the course and methods of non-linearprocess planning were demonstrated, and the algorithm for optimization of workingsteps sequence was tested in this prototype system.(7) A method of information integration is proposed based on STEP-NC and XML,and a CAD/CAPP/CNC integrated system model was established. Furthermore, the keyintegration technologies including manufacturing features modeling, manufacturingprocess information modeling based on STEP-NC, and expression and exchangetechnique of information by the XML are detailed discussed in this paper.
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