Research And Development On Knowledge-based Maintenance And Service System For CNC Machine Tools

Product manufacturers are extending their responsibilities in the whole life cycle by providing services to their customers.In recent years,product service system has become an important research topic to address the special requirements in the new service driven business model.High value machine tools in modern manufacturing factories are special products:they are regarded as ’products’ from maintenance point of view,and they also manufacture other products.In the new business model,the quality and behavior of a machine tool not only affect the quality of the parts it manufactures,but also affect the profits of the machine tool’s manufacturer.To ensure the effective performance and efficient maintenance of high-value machine tools,information and knowledge from their lifecycle should be collected and reused.However,in the research area of product service systems and related computerized maintenance systems,there is a lack of investigation into the special nature,problems and requirements of high value machine tool maintenance,especially the consistency and sharing problem with product design and configuration information from former phase,which are very important in modern digitized manufacturing systems.This project investigated the CNC machine tool product,by regarding the maintenance and service as one of many phases in the product lifecycle,and focusing on the management of stakeholders,process and knowledge during maintenance and service processes.A collaborative maintenance and service system for CNC machine tools between different stakeholders has been proposed.After analyzing the requirements for knowledge management,communication and collaborative decision making during maintenance and service processes,the system functions has been designed,and the implementation route has been provided and the method for selecting maintenance and service strategy is provided.And the key technologies have been extracted.The maintenance and service process for CNC machine tools,especially the collaborative maintenance and service process between stakeholders has been anaylised and modelled.According to the characteristics of product maintenance and service,a product maintenance and service system model based on product lifecycle has been proposed,and the relationships between stakeholders have been analyzed.The modelling for knowledge and process provides theoretical foundation for the next knowledge reusing method.The maintenance and service knowledge has been represented by ontology.A Knowledge Meta-Space Model has been proposed to describe knowledge and the mapping relationship between ontology,knowledge resource and knowledge meta-space has been given.A two-dimensional classification method has been adopted for maintenance and service knowledge.Then,the maintenance knowledge has been represented through description units,after which some examples of CNC machine tool’s rotary working-table have been given to verify the knowledge representation method.A knowledge reuse method based on semantic similarity and relevancy has been proposed to support the knowledge reuse.In this thesis,a case is devided into several description units,within which the concepts are described as ontology;then the similarity and relevancy for description units is calculated as local similarity,which can be summed with coefficient to generate the similarity between current case and historical cases.Then the retrieved historical cases whose adaptability are above the threshold will be taken as the one to be revised as the new solution for the current case,a new knowledge is thus generated.This method has been validated through an example.This research also explored the potential application of advanced content management systems,which are widely implemented in the financial,business and government organizations,in the manufacturing engineering domain which has been dominated by traditional engineering information systems.A prototype knowledge-based collaborative maintenance and service system is proposed and developed.After anaylising the development essentials,and selecting appropriate system development tools,the system architecture and functional modules have been described in detail.The chosen development tools are:Open Source Papyrus as SysML modelling tool,OSF as ontology editor,Open Source content management system Drupal as the development platform.Drupal is connected with OSF through RESTful Web service to achieve the integration between knowledge in Drupal and the ontology in OSF,such that the knowledge management and sharing can be achieved.The prototype system has been evaluated using an example machine tool.The system implementation functions include stakeholder module,product knowledge module,scheduled maintenance module,preventive maintenance module and knowledge sharing module.It indicates that the content management technology has a number of advantages over the traditional engineering information systems,such as computer aided engineering,product data and lifecycle management,and enterprise resource planning systems,in managing machine tool maintenance and service information including dynamic and unstructured knowledge.