Study On Operational Reliability Analysis And Maintenance Policy For Manufacturing System

As modern manufacturing systems developed towards larger size, higherautomation, more flexible, more efficient and higher precision continuously, the partsand equipments in systems greatly increase, and the structures are more complicated.As a result the probability of system failures will be increased significantly undercomplex working conditions and circumstances, and therefore how to ensure theoperational reliability of manufacturing systems has become a major problem facingthe users of manufacturing systems. Conventional reliability analysis methods formanufacturing systems are limited and weak, because of diverse manufacturingmissions, dynamic manufacturing environment and extremely complex degradationmechanism during the operation of modern manufacturing systems. For thedeficiencies that exist in the current researches, in this paper, various random events inthe universal external environment and performance degradation of manufacturingsystems caused by intrinsic degradation mechanism are treated as a starting point, thenbrittleness theory of complex system and theory of multi-state system are introduced instudy on operational reliability analysis and maintenance policy for manufacturingsystem, the mechanism of accumulation and propagation of brittleness effect inmanufacturing systems is studied, the technical framework of operational reliabilityanalysis and the predictive model of performance degradation for manufacturingsystems based on R-E system are established, and the improvement interval universalgenerating function for reliability evaluation is proposed considering brittleness effect.According to the operational reliability analysis above, the dynamic predictivemaintenance policy is formulated to ensure the operational reliability of manufacturingsystems, and the maintenance policy is optimized with the largest benefit output in theoperational phase as target in the end. The theoretical method system presented in thispaper evaluates operational reliability of manufacturing systems from micro and macroaspects, analyses maintenance policies of manufacturing systems from qualitative andquantitative aspects, overcomes the difficulties and deficiencies of conventionalreliability analysis methods and maintenance policies in the applications to someextent, and provides a new approach for analysis of operational reliability andformulation of maintenance strategy for manufacturing systems. Topics covered in thispaper are as follows： (1) Some basic theories about manufacturing system and its operational reliabilityare introduced, the development and the status of researches on reliability andmaintenance policy of manufacturing system are discussed, and the source, the mainworks and frame of this paper are illustrated here. For the characteristics of morecomplicated structure, more failure sources, varied manufacturing missions, and variedperformance, multi-state reliability theory, brittleness theory of complex system andsystem engineering of man-machine-environment are introduced to discuss theformation mechanism of multi-state during the operation phase, describe themechanism of failure evolution and propagation, analyze the universal externalenvironment of manufacturing systems, and propose technical framework ofoperational reliability analysis for manufacturing system based on R-E system. Theseworks provide a theoretical support for evaluation of operational reliability andformulation of maintenance strategy for manufacturing system.(2) The accumulation and propagation model of brittleness effect inmanufacturing systems under universal external environment is studied. Firstly, thetheory of factor space is introduced to describe the physical stimulation of dynamicfactors in universal external environment, and the mapping model between brittlenesseffect in manufacturing systems and the dynamic external factors is constructed. Then,brittleness degree is given to express the direct and indirect impact of each brittlenessmotivators on system degradation, and the algorithms for risk degree and couplingdegree of brittleness motivators are analyzed systematically. Finally, according to thebrittleness mechanism of physical stimulation and flow stimulation, the brittlenesspropagation models of equipment layer and manufacturing system layer are established,and the improved ant colony algorithm is used to search propagation path of brittlenesseffect with maximum intensity. These works provide a new method for analysis ofevolution and propagation mechanism of concrete failures in manufacturing systems.(3) Operational reliability evaluation of manufacturing system based onbrittleness effect is studied. Firstly, state space model is introduced to describe the stateevolution of manufacturing system under the impact of brittleness motivators,following the establishment of state evolution predictive model of manufacturingsystem. Moreover, the improved universal generating function for reliability evaluationof manufacturing is proposed considering brittleness effect, and the interval extensionof reliability value is made on the basis of the interval analysis theory and affinearithmetic to evaluate the interval-valued operational reliability. The result shows the heterogeneity and dynamic uncertainty of manufacturing systems under differentmanufacturing missions, and makes reliability evaluation more accurate and reliable.(4) The selection algorithm for maintenance policies of manufacturing systemunder universal external environment is studied. Firstly, the basic theory ofmaintenance and its policies of manufacturing system are summarized. Secondly, forthe heterogeneity and dynamic uncertainty existed in manufacturing systems underuniversal external environment, decision-making attributes for maintenance are given,and the selection process of optimum maintenance policy is summarized. Then, themaintenance policies of manufacturing system are ranked by fuzzy AHP (subjectiveweighting) and information entropy method (objective weighting), and the optimummaintenance policy is selected by the fuzzy Borda method combining with fuzzy AHPand information entropy. This method effectively overcomes the problems aboutsubjectivity and ambiguity existed in conventional selection algorithms, and improvesthe accuracy and rationality of ranking selection of maintenance policies. Finally, usingthis method, the optimum maintenance policy for machining center that is keyequipment in manufacturing system should be predictive maintenance.(5) The factor-driven dynamic predictive maintenance policy for manufacturingsystem is studied. Firstly, in view of incomplete consideration to the influence ofdynamic environment events on manufacturing system degradation in conventionalmaintenance policies, the predictive maintenance policy under universal externalenvironment is analyzed and the cost-effective evaluation model of maintenance policyis established based on brittleness theory and state evolution predictive model ofmanufacturing system. In addition, as the dynamic maintenance decision thresholdvalue was given and the buffer contents and the maintenance sources were limited, themaintenance policy optimization flow of the manufacturing system based on GeneticAlgorithm is built with the largest benefit output in the operational phase as target.Finally, an example of manufacturing system in one domestic manufacture enterprise istaken to prove the usability and validity of the method mentioned after thebenchmarking analysis. This study of maintenance policy has potential reference valueto improve the operational reliability, economical efficiency and capability ofmanufacturing equipments in China.