Research On Architecture And Key Technologies Of STEP-NC Based NC System

STEP(Standard for the Exchange of Product Data) has been the main standard in production data exchange. On such background, STEP has extended to NC(Numerical controller) machining in floor shop. A new ISO standard(ISO 14649) named STEP-NC was developed by vendors, user and academic institutes in word wide to provide a standard data interface model between CAxs(Computer Aid for X) and CNC. STEP-NC has broken the bottle-neck of information transfer between CAxs and CNC. In this thesis, a new standard type STEP-NC CNC architecture had been put forward, and some key technologys had been studied. The main research content included:STEP-NC data model and open NC architecture were introduced firstly. Then the system function model was put forward based on function requirement. Information stream model was structured succedently. And it was divided into three parts by real-time characteristic, there were non-real-time information, weak real-time information and strong real-time information. So the STEP-NC based NC system is divide three layers, there were model application layer, manufacture plan layer and real-time controller layer. By referencing existing NC system topology structure, especially the PC based soft type CNC, a two layers standard type STEP-NC NC architecture which combined PC system and embed system was put forward.STEP-NC machining program information extraction was the precondition and basic of controller development. A SDAI based STEP-NC machining program information extraction system was developed. The system includes two sects: data transfer and feature reconstruct. In the data transfer proceeding, there included dictionary data construct, entity instance construct, machining program tree construct and entity-instance match. In the feature reconstruct proceeding, four types feature need reconstruct. There were manufacture feature reconstructing, technology feature reconstructing, execute stream listing and resource reconstructing.Tool path generation on surface is the key technology of NC. A tool path generation algorithmic which can meet three demands simultaneously was put forward. Three demands included Arbitrary boundary conformed, change meeting second order PDEs rule and ISO-parameter. This algorithmic can apply on compound surface. In the tool path generation proceeding, surface was dispersed firstly, then generating lead lines on discrete surface by steady heat transferring principle, subsequently, global subsection geodesic lines was constructed base on lead lines and discrete surface using MMP algorithm. Then generate tool path on global subsection geodesic lines using iso-parameter method. There sever advance in which STEP-NC replaced G code as NC data model interface standard. It was not the simply function moving from CAxs to STEP-NC NC. By the some function and model were realized in STEP-NC NC controller, the system became complicated, Especially in real-time function and system dynamic stability. In the STEP-NC system, the real-time requirement in different models was widely. It will be unfitting the STEP-NC system demand if we used traditional real-time scheduling technology in NC. So real-time schedule method and closed loop real-time manufacture processing in STEP-NC NC system was considered.A real time scheduling mechanism meeting STEP-NC numerical control system is put forward. Because there were wide real-time requirement between different models, it was not suitable using precise timing technology, such as based on WCET(Worst-Case Execute Time). By analyzed PC OS(operation system) scheduling characteristic and STEP-NC NC model real-time reminding, a weak real-time scheduling method on PC base on integrate resource restriction was put forward. The method included real-time scheduling frame and algorithm. The frame was constructed by scheduling cell, scheduling serve and resource management. The scheduling algorithm met scheduling cell PRI alterable, serve application etc.Real-time close loop manufacture process included manufacture programming, strategy optimize. It was one of remarkable change in STEP-NC NC system compared with G code based NC. Current part manufacture process in CAxs and CNC was analyzed firstly. It is difficult in realizing closed loop between in CAxs and CNC for low interface standard-G code. But it is not exist when STEP-NC was used as NC data interface standard. So a Real-time close loop manufacture process model in STEP-NC NC system was put forward.The emergence of STEP-NC will influence NC manufacture technology and other technology such as e-manufacturing widely. STEP-NC NC system is the basic and important equipment, it is the new key part of the numerical manufacture process. The thesis was aim to develop the controller of STEP-NC and solve the some key technology.