Research On The Key Technology Of Networked STEP-NC Controller

With globalization of the modern manufacturing industry, the open and networked machining devices are urgently needed. Machine tools are the key devices for manufacturing industry, and should meet these requirements. Thus the Numerical Control (NC) system is demanded to possess a good networked architecture and an intelligent, effective machining data model. A good networked architecture means the NC system should have a unified cross-platform Internet interface that can link and communicate with other devices, and a bus network in a fieldbus level. Real-time Ethernet (RTE) is the new developing trend of the fieldbus. Comparing to traditional fieldbuses, it has faster communication speed, better compatibility to Ethernet, bigger data packets, less deployment wiring and cost. As to the machining data model, the traditional G&M code that is a low level machining description language loses a lot of up level design information, and thus restricts the development of machine tools. Meanwhile, the birth of STEP-NC model provides a brand new machining data model, which supports bi-directional and the whole life cycle machining dataflow. This thesis rationally combines the up level interface, Real-time Ethernet and STEP-NC, and proposes an open and networked STEP-NC controller solution. This controller has three buses:one is the hardware bus-Real-time Ethernet, one is the up level network interface-MTConnect, and the last is the data bus-STEP-NC.Refering to the Real-time Ethernet, a improved RTE-EtherMAC is provided based on NC requirements. RTE based NC system have a modulized and extendible hardware bus. Comparing to other RTE, EtherMAC adopts a mechanism that uses the latch signal to trigger the up transferring package, in order to reduce the awaiting time between the feedback data and the instruction data; analyzes the transmission delay and signal jitter from the electronic components, and proposes a synchronization method that can give high synchronization accuracy especially for a few nodes. Thus, EtherMAC is suitable for NC systems. EtherMAC provides solutions based on Windows NT to cover more NC applications. The work process and fault handling of EtherMAC are addressed. The realization of EtherMAC on FPGA is given, including the data link layer and some NC control interface modules. At last, its real-time performance are tested and verified.MTConnect is used as the up layer interface of the NC system. It is a new device interconnecting standard that is cross-platform and royalty-free. The structure, workflow, data format and device description methods of MTConnect are demonstrated. According to the definitions in MTConnect, an MTConnect based machine tool model is constructed and saved as a XML document. This is the essential procedure for monitoring. MTConnect does not support monitor the STEP-NC controller, so methods of interfacing STEP-NC with MTConnect are provided. Also provided is the realization of MTConnect Agent and Client, which is based on the.NET platform. This realization is then used for monitor the information of tool path, swithes and feedrate of the machine tool.As there is no commercial CAM software that can generate STEP-NC machining files, to test the STEP-NC controller, this thesis provides a2D CAM module that can generate STEP-NC files and can also be regard as an embedded CAM module for STEP-NC controller. The CAM module reads ECAD files (Gerber files), a tool definition file and machine tool model information, then makes process planning and defines STEP-NC machining features, machining operations and the workingstep order. STEP-NC does not support centerline based profiles in Gerber, the CAM module can map these graphics into STEP AP210ARM, and then converts them to machining features in STEP-NC. During these process, a self-defined entity "Closed_profile_with_styles" are defined. The thesis describes the STEP-NC compliant process planning for circuit board milling process. The process planning gives a new machining strategy that uses multi-cutters. To describe this situation, according to STEP AP238, an improment is made to ISO14649to support the case that multi-cutters share the same final feature. This new machining strategy is in fact a combined strategy of "Contour_parallel" and "Bidirectional". As to the tool path generation, a pixel-based algorithm is used to calculate contour parallel tool paths for "Contour_parallel" strategy. Algorithm for "Bidirectional" machining strategy is also provided.At last, the realization of the application layer of the STEP-NC controller is provided, which together with the realization of EtherMAC and MTConnect compose the whole networked STEP-NC controller. The STEP Java libraries provided by ST-Developer software are used to manipulate STEP entities and instances, and IKVM.NET is used for the interactive call between Java and.NET. Then STEP-NC controller can be realized in.NET platform. The STEP-NC core includes the following modules:general STEP interpreter, tool path generation, machining management, simulation and machine tool model. The general STEP interpreter utilizes the architecture of STEP classes provided by ST-Developer, the polymorphism of objected oriented programming, reflection mechanism and iteration, and can be used as the basic component for distributed STEP applications. The controller provides2D/3D simulation, and the3D simulation uses CADability. At last, the simulation and machining results are given.