| In today's world, the manufacturing industry has become a country's economic lifeline, while the CNC machine tools as the basis of the manufacturing industry has been unprecedented attention. Our government considers development the CNC machine tools as the key to revitalize the manufacturing industry, how to ensure the performance and the quality of CNC machine tools has become a major task of machine tool industry. In recent years, the level of CNC machine tools have been significantly improved, but compared to similar products in foreign countries there are still some gaps, the main difference is reflected in the row dependability and the high failure rate. Therefore, that is very critical for the China's machine tool industry to enhance the level of dependability of Chinese-made CNC machine tools. The paper puts forward for the State 863 Project topics -For life-cycle heavy-duty CNC equipment dependability modeling and analysis techniques. Based on depth studying the dependability engineering mathematics and systems development method, the paper has focused on researching and development the management information system of the CNC machine tools dependability, in order to achieve the modeling, analysis and evaluation of the CNC machine tools dependability. One: System Analysis and Overall DesignAccording to the specific characteristics of the study of the CNC machine tools dependability, the paper establishes a system goal, and analyzes the system feasibility of three aspects: the economic, technology and social environment. After investigating researchers of the CNC machine tools dependability in detail, the paper defines their diverse needs, and considering the difference of the system user identity, the paper carries out on the system requirements analysis. In accordance with the principles of system design and the results of system requirements analysis, the paper carries out on the overall system design, divides the system into seven function modules: user login module, system maintenance module, information processing module, dependability modeling module, failure statistics and analysis module and dependability assessment module. Based on the security of researching the CNC machine tools dependability, the paper establishes the LAN-based client/server architecture for the system. Finally, according to system requirements and the specific situations of developers, the paper chooses Visual Basic 6.0 Enterprise Edition as the system development tool, and configures the Access database which is simple and easy to master.Two: Database DesignIn view of the characteristic that the data from CNC machine tools dependability are complexity and dispersion, in order to alleviate the work of data management for researchers, the system establishes a database, and all the data are unified management and control by DBMS, to ensure data security, integrity and sharing. According the six steps of standardized design, the paper designs the database in detail. At the phase of requirements analysis, the paper analyzes the requirements of researchers from three aspects: information requirements, processing requirements and security and integrity requirements. At the phase of conceptual structure design, it adopts a down - top design strategy and establishes the entity relationship diagram of researches of CNC machine tools dependability. At the phase of logical structure design, it changes the entity relationship diagram into relational model, optimizes it, and establishes the database logical structure. At the phase of physical design, it selects the appropriate storage structure and storage methods for the relational model. At the phase of implementation and maintenance, it organizes the data into the database and then has a test run on the database, and finally, runs and maintains the database.Three: Detailed System Design Based on Dependability TheoryThe paper designs the six function modules divided in the overall design in detail, sets out the functions and purposes of function modules and researches the dependability theory in the process of system design.The design of user login module is based on the system security. When users log in, it identifies their identities via user ID and password, so it uses the classification set to achieve the security settings. At the same time, it is the most outer layer of security protection measures.Information processing module mainly designs for data collection staff, is composed of two parts: information input and information query.System maintenance module is designed mainly for responsible person, they can control user's authority, maintain the relevant dependability codes and have data backup. Dependability modeling module is the most crucial module of the entire system, is designed mainly for analysts, who can built the model of CNC machine tools dependability, which is the main purpose of the paper. Dependability modeling module is divided into four sub-modules: data selection module, machine dependability modeling module, sub-system dependability modeling module, and reliability influence of sub-system for machine modeling module. The design process of machine dependability modeling module and sub-system dependability modeling module is basically the same, by model selection, parameter estimation, hypothesis testing and model precedence to establish the model of CNC machine tools dependability and draw the corresponding curves finally. In the process of modeling, the paper applies a great deal of dependability engineering mathematics, for example, linear regression method, maximum likelihood estimation method and homogeneous markov method, based on entropy-fuzzy comprehensive evaluation method and etc.. At the same time, this is the first time to establish reliability influence model of sub-system, reliability model of sub-two-weibull distribution, maintenance model and all-index availability model.The main function of fault statistics is to count machine fault according fault location, the mode, the causes and the reasons type, to count sub-system fault according the mode, the reason and the reason type. By listing statistics table and drawing histogram to analyze the CNC machine tools fault, which is an important significance for improving the prioritization, the trade-off analysis or proposing the most effective approach to operations and etc..The main function of dependability assessment model is to assess the level of CNC machine tools dependability. It can assess the basic level of dependability by commonly used dependability indicators which are calculated by point estimation method. The main function of analysis results model is to achieve the upload and the query of the results of the analysis.Four: Examples of System ApplicationThis paper selects a group of dependability data from a Machining Center to applies the system. By running the system, it can establish machine dependability model and sub-system dependability model, do a statistics according failure location, failure mode, failure reason, reason type, identify the key factors that impact the dependability, and finally, it can assess dependability by calculating the MTBF, MTTR and Ai. |
