Open Architecture CNC System For Closed-loop Machining Based On Standard Of STEP-NC

Closed-loop machining method is suitable for small-batch production due to its openness, interoperability and intelligence. Machining process control is an effective way to reduce production costs, improve efficiency and product quality. There are two key issues in realizing machining process control in closed-loop machining system. The first is to transferring high-level product machining information rapidly. The second is to analyze product machining information it in real-time. The mechanism for transferring complete product machining information integratedly in a closed-loop data flow is proposed based on STEP-NC standard in this paper. Methods for analyzing high-level product machining information and realizing machining process control are studied in order to fill the information gap between shop floor and other process planning system.In this paper, function of closed-loop machining system and mechanism for integrating and interoperating product machining information are analyzed according to the demand of machining process control. The closed-loop data flow is built based on the descriptive and implementation methods of STEP-NC standard. Architecture of closed-loop machining system is built based on open STEP-NC controller, in which the procedures of product design, process planning, machining, process control and machining knowledge management are linked with each other dynamically. Integration definition method is used to build the functional model of closed-loop machining system.Software kernel of open architecture STEP-NC controller based on modular structure is proposed to interpret STEP-NC files directly. The functions of STEP-NC file interpretation, task generation, task transmission and interpolation calculating are encapsulated as software modules by using the technology of dynamic link library, component object model and application program interface, which make the software kernel portable and scalable. Mechanism of parsing STEP-NC file, extracting and generating tool path online are built based on the proposed open architecture STEPNC controller by using object oriented, multithread and shared memory technology, which interprets STEP-NC files directly without post-processor, so that integrated and closed-loop data flow contains only high-level product information in machining system can be realized.In order to realize and integrate machining process control based on open STEPNC controller, reparation of planar face is took as an example to analyze the implementation of online inspection and machining process control, while the control of milling force is took as an example to analyze the impl ementation of real-time machining process control. Data model for transferring information of machining process control tasks, machining process condition and inspection results are built by using descriptive method of STEP-NC standards and integrated with other product machining information, which can be used to solve the problem of transferring integrated high-level information in machining system. Approaches for identifying and repairing error area and fuzzy control algorithms for constant force milling are designed. The mechanism for transmitting and analyzing machining process control information is built by using multithread, shared memory and finite state machine technology, in which the integration level and real-time performance of machining process control can be guaranteed.Implementation of proposed closed-loop machining system architecture, open architecture STEP-NC controller, online machining process control methods and realtime machining process control methods are studied based on the hardwa re and software platform, in which the functions of STEP-NC file interpretation, machining, online inspection, real-time monitoring, machining process control and data output are developed and embedded. Experiments of interpreting and executing STEP-NC file contains multiple manufacturing features, online error area identification and reparation based on STEP-NC and constant force milling based on STEP-NC are carried out to verify the proposed STEP-NC data model, function of open architecture STEP-NC controller and implementation methods of online and real-time machining process control. The implementation methods developed and built in this paper provides an experimental platform for studies of machining process control based on STEP-NC.