New control strategy for CNC machines via STEP-NC
The contemporary product design and manufacturing environment requires a bidirectional and seamless data flow throughout all stages of data transactions. The establishment of STEP (STandard for Exchange of Product data) offers manufacturers a new method to exchange product data in the entire product life cycle. As an extension to STEP, STEP-NC provides the potential to finally close the gap between design and manufacturing in the drive for a complete, integrated product development environment. The STEP-NC data model is a long overdue improvement in the domain of computer numerical controls (CNC) where G-codes have been in use for more than half a century. STEP-NC brings richer information to CNCs presenting an opportunity for the development of more intelligent, interoperable and informative machining. The research work documented in this thesis introduces a fully STEP-compliant CNC system with an aim to solve the problems faced by the current CNC systems, e.g. disconnection with the upper-stream activities. The research is based on the premise that a STEP-NC program can document “generic” manufacturing information (whatto- do). This way, a STEP-NC program can be made machine-independent and has an advantage over the conventional G-code based NC program that is always generated for a specific CNC machine. The core of the STEP-compliant CNC system is the mapping mechanism which accepts STEP-NC data and translates it into the type of G-code that a specific controller can understand. The STEP-compliant CNC system has two principal elements, a STEP-NC Adapter and a STEP-NC Converter. The STEP-NC Adapter takes a generic STEP-NC program as its input and produces a more specific version of the STEP-NC program by “adapting” it to a local manufacturing environment and capabilities. This native STEP-NC file is a localised version of the generic STEP-NC file. It may be re-adapted to another manufacturing environment. The STEP-NC converter takes a native STEP-NC file and converts it to the required machine control data, i.e. G-codes that are ready to be loaded to the targeted CNC controller. The conversion process is also called a mapping or translating process that utilises the manufacturing environment databases developed for specific machine tools, or rather CNC controllers. The use of function block (IEC 61499) technology gives the system robustness and modularity. The STEP-NC adapter and converter are so developed that they can be embedded into a future CNC controller, making it a STEP-NC enabled controller. The system offers ample benefits to the CNC users by providing an interface for the STEP-NC data that carries rich information and the interface itself is also more userfriendly. It realises a long-awaited paradigm of common interface for CNC machine tools. With this system in place, one generic STEP-NC program can be made to drive different CNC machine tools, making NC programs portable and universally compatible. This system supports the scenario of “design anywhere and build anywhere”.
Networked Digital Library of Theses and Dissertations