Approximation of single-class queueing networks with downtime-induced traffic variability

Queuing networks have been used with partial success for analytical modelling of manufacturing systems. In this paper, we consider a tandem system with high traffic variability caused by downtime events in the first queue. We propose improved approximation for departure variability in order to predict the waiting duration at the bottleneck queue located last in the line. We demonstrate that existing methods do not properly approximate such systems and provide some reasons and insights. Thus, a new decomposition method which employs the variability function principles is proposed. We differentiate between two components of the departure variability in multi-class systems: the ‘within-class effect’ – the variability caused by the class’ own inter-arrival and service time distributions – and the ‘between-class effect’ – the variability caused by interactions with other classes. Our analysis shows that the first effect can be approximated by existing multi-class decomposition methods, while the second effect requires a new development. Our proposed approximation for between-class effect is based on simulating a proper sub-system. The method enables modelling different policies of downtimes (e.g. FCFS, Priority). Numerical experiments show relative errors much smaller vs. existing procedures.     

Product quality inspection in Bernoulli lines: analysis,bottlenecks, and design

This paper is devoted to serial production lines consisting of producing and inspection machines that obey the Bernoulli reliability and Bernoulli quality models. Such production lines are encountered in automotive assembly and painting operations where the downtime is relatively short and the defects are due to uncorrelated random events. For these systems, this paper develops analytical methods for performance analysis, bottleneck identification, and design. In addition, insights into the nature of bottlenecks in such systems are provided, and an empirical rule for placing an inspection machine that maximises the production rate of non-defectives is formulated.     

Integrated analysis of quality and production logistics performance in manufacturing lines

This paper presents an analytical method for evaluating the performance of production systems, jointly considering in a unique framework quality and production logistics performance measures. In the literature, quality and production logistics have traditionally been investigated using independent approaches. Thus far, only a few recent contributions have focused on their mutual inter-relation, showing that benefits can be achieved from an integrated analysis. This paper contributes to this growing research by considering, for the first time, production systems in which the behaviour of the machines is monitored by statistical control charts. The control action performed by the quality control system on the machines is directly modeled. Moreover, the impact of the quality control action on the logistic flow of parts in the system is taken into account. In order to estimate the performance of such systems, an approximate analytical method based on the system decomposition technique is developed. The accuracy of the method is assessed by comparing the results with those obtained by simulation. Analysis of the results provides new insights into the relations among the quality and production logistics performance measures and paves the way to the development of integrated design techniques for improved configurations of the system as a whole.     

Downtime variability: the impact of duration–frequency on the performance of serial production systems

It is intuitively appealing to measure downtime in terms of total time lost (i.e. frequency times duration). However, the same total downtime can be produced by an infinite number of frequency/duration combinations. This study reports the findings of a computer simulation study on the impact of varying combinations of downtime frequency/duration pairs on performance of serial production systems. The research reported here clearly shows that different downtime frequency/duration combinations affect serial production lines differently even when the total downtime remains equal. Analysis suggests that long duration, infrequently occurring variation has a much more negative impact on system performance than short duration, frequently occurring variation.     

Simulation study of a bottleneck-based dispatching policy for a maintenance workforce

Maintenance is important for production operations and for continuous improvement. Appropriate dispatching of the maintenance workforce to quickly respond to equipment failures and carry out preventive services can improve system productivity. The first-come-first-served policy is typically used in many manufacturing industries. In this paper, we present a priority-based dispatching policy, a dynamic bottleneck policy, based on the analysis of real-time data. In such a policy, priority is assigned to the bottleneck machine after a fixed time period, and the maintenance worker will service the high-priority machine (i.e. bottleneck machine) first when multiple service requests are received. It is shown by extensive simulation experiments that this policy can lead to a greater improvement in system throughput compared with the first-come-first-served policy. To implement such a policy, the appropriate time period for data collection and the frequency for carrying out bottleneck analysis are investigated. In addition, a sensitivity study suggests that the results obtained are insensitive to machine downtime, efficiency, and reliability models.     

服务作业系统设计技术路线及方法体系的研究

服务项目实施需要特定的设施和作业系统。阐述了服务作业系统的特征，以工业工程和市场营销等多学科为指导，探讨了该类系统的设计目标和原理，提出了完整服务作业系统设计技术路线和方法体系。     

Performance analysis of multi-server tandem queues with finite buffers and blocking

In this paper we study multi-server tandem queues with finite buffers and blocking after service. The service times are generally distributed. We develop an efficient approximation method to determine performance characteristics such as the throughput and mean sojourn times. The method is based on decomposition into two-station subsystems, the parameters of which are determined by iteration. For the analysis of the subsystems we developed a spectral expansion method. Comparison with simulation shows that the approximation method produces accurate results. So it is useful for the design and analysis of production lines.     

非遗文化服务设计中的接触点优化方法研究

目的 为提升用户服务体验,探索服务设计接触点的优化方法,扩展服务设计理论。方法 首先,以服务流程分析为基础,识别非遗文化服务过程的接触点,由用户对服务接触点满意度评价计算引申重要性后,分析并确定关键服务接触点;其次,进行关键服务接触点失效分析,嵌入用户感知评价作为三种风险因素权重计算关键服务接触点风险值,输出改进优先级排序矩阵;最后,依据分析结果对非遗文化服务设计方案进行制定与验证评价。结论 搭建服务接触点优化设计方法,通过福州漆艺文化服务设计为例验证表明,该方法可以有效评估关键接触点,全面分析关键服务接触点的失效性,提供服务接触点优化设计方向,进而改善用户体验流畅感,提高服务品质,藉此为非遗文化服务设计提供方法借鉴。     

服务产品设计质量保证的质量功能展开集成方法

为处理服务产品设计中散乱的模糊顾客需求信息,客观反映用户质量需求,解决传统质量功能展开方法中判断一致性差和整体满意度的展开精度低等问题,将模糊聚类分析、模糊层次分析法和质量屋方法集成,引入到服务产品设计的质量保证中。通过模糊聚类对顾客质量要求进行层次划分,在此基础上使用模糊层次分析法确定顾客质量需求权重,继而在质量屋关系矩阵中引入模糊集进行评判,从而将自然语言与模糊数相联系,更加准确地把握顾客需求。同时采用模糊数表示权重分析和关系度评判结果,提高了评判的精度和稳定性,为满足服务产品质量设计阶段质量保证工作提供一种量化分析方法。     

Kanban-based pull systems with advance demand information

This paper investigates the benefits of integrating advance demand information (ADI) with Kanban-based pull production and inventory control systems (PICS). Predicting the impact of several PICS design parameters such as Kanban card limits, base stock levels, demand information lead times, and the quality of ADI on performance measures such as throughput, inventory holding costs and customer service levels, presents a complex yet important problem. Since efficient analytical models for performance evaluation studies of these systems are unavailable, simulation experiments are used for the study. The study shows that in many situations, integrating ADI with Kanban-based pull systems provides opportunities for efficiencies that might be significantly greater than that available using pull systems alone. Further, the study also investigates the performance sensitivity of these systems to the quality of information shared and information asymmetry.     

Queuing network analysis approach for estimating the sizes of the time buffers in Theory of Constraints-controlled production systems

The present paper describes an open queuing network modelling approach to estimate the size of the time buffers in production systems controlled by the Theory of Constraints philosophy. Workstations in the production network are modelled as GI/G/m queues and a queuing network analysis multiproduct open queuing network modelling method is used to estimate the average flow time to the time buffer origin and the standard deviation of flow time. Using these two values together with an assumption of normally distributed flow times and a chosen service level, the final time buffer length is determined. The queuing network analysis method has been modified to enable the modelling of production networks with machine failures, batch service and varying transfer batch sizes. The modelling approach has also been incorporated in a computerized tool that uses product specific information such as bill-of-material and routing data, and production network information such as resource data to estimate the sizes and location of the necessary time buffers for each product. Simulation experiments indicate that the procedure is sufficiently accurate to provide an initial quick estimate of the needed time buffer lengths at the design stage of the line.     

Global quality: Linking ergonomics and production

The globalization of commerce has combined with the new dominance of customer demands and the need for shareholder value to force the pace of change in manufacturing and service industries. Production now entails fitting of a productive process to the needs of remote customers and demanding shareholders, while ensuring the correct mix of human and technology in the production process. Production now encompasses service industries, which provide the majority of employment in the industrialized countries. The human in the production process implies ergonomics. Pressures from globalization, customer and shareholder appear to be in conflict but, in fact, all are demanding a combination of function, reliability, price and productivity. The combination desired might change between stakeholders, but the overriding metric is quality. Quality is a function of technological and human factors, and is greatly influenced by ergonomics in its broadest sense. Errors in the process can arise from many human/system interactions and result in product unreliability, poor productivity or even injury to the workforce or product user. This paper shows examples of quality as the system goal that can drive systems to meet the global demands, and of how quality and ergonomics are intimately related in production systems.     

Development of an E-maintenance System for a CNC System

Globalization and rapid growth of network technologies have changed the traditional patterns of device maintenance. E-maintenance has emerged and is widely used in many manufacturing systems. In this paper, a new architecture of an E-maintenance system is proposed, which consists of E-maintenance centre, embedded CNC gateway and CNG terminal. The E-maintenance centre provides the technical support and service for customers based on Internet and communication technologies. The embedded CNC gateway serves as an agent between the public and plant device network, and provides web-based access for the CNC system. A reconfigurable CNC terminal is highly desired in a signal measuring and analysing system, which is built on the top of component and software bus based models. Finally, the E-maintenance system for the CNC machine is implemented and the experiments show that the architecture of an E-maintenance system can effectively reduce the downtime of devices, the responding time of maintenance work, and increase both the quality and the productivity of enterprises.     

Toward a probabilistic design of reinforced concrete durability: application to a marine environment

This work aims to propose a complete design methodology for concrete durability problems based on a probabilistic method including an original chloride diffusion modelling compatible with the new performance-based approaches. This is illustrated by the study of a concrete immersed in sea water. The physical and chemical processes that lead to the corrosion of the concrete reinforcement bars are presented first. A chloride penetration model based on Fick’s second law is proposed. Next, the durability modelling parameters chosen among the durability indicators (Baroghel-Bouny, Concrete design for structures with predefined service life—durability control with respect to reinforcement corrosion and alkali–silica reaction, 2004; Alexander et al., Mater Struct 41:921–936, 2008) are assessed. They depend on the concrete formulation and the chemical composition of the cement. These indicators are characterized by their statistical distributions, which are realistically specified from a wide literature review. The whole probabilistic modelling is included in a Bayesian network so that it can be easily updated to include new experimental data. The evaluation of the time dependant corrosion risk is estimated for two types of cement: CEM I and CEM I with silica fume. The result shows the effect on the Lind–Hasofer reliability index of the type of cement, the concrete quality and the design options. The quality is integrated through the mean value and the standard deviation of the modelling parameters. The method could be used either directly for cover design or for semi-probabilistic design code calibration.     

Failure event prediction using the Cox proportional hazard model driven by frequent failure signatures

The analysis of event sequence data that contains system failures is becoming increasingly important in the design of service and maintenance policies. This paper presents a systematic methodology to construct a statistical prediction model for failure event based on event sequence data. First, frequent failure signatures, defined as a group of events/errors that repeatedly occur together, are identified automatically from the event sequence by use of an efficient algorithm. Then, the Cox proportional hazard model, that is extensively used in biomedical survival analysis, is used to provide a statistically rigorous prediction of system failures based on the time-to-failure data extracted from the event sequences. The identified failure signatures are used to select significant covariates for the Cox model, i.e., only the events and/or event combinations in the signatures are treated as explanatory variables in the Cox model fitting. By combining the failure signature and Cox model approaches the proposed method can effectively handle the situation of a long event sequence and a large number of event types in the sequence. Its effectiveness is illustrated by a numerical study and analysis of real-world data. The proposed method can help proactively diagnose machine faults with a sufficient lead time before actual system failures to allow preventive maintenance to be scheduled thereby reducing the downtime costs.     

A SIL quantification approach based on an operating situation model for safety evaluation in complex guided transportation systems

Safety analysis in guided transportation systems is essential to avoid rare but potentially catastrophic accidents. This article presents a quantitative probabilistic model that integrates Safety Integrity Levels (SIL) for evaluating the safety of such systems. The standardized SIL indicator allows the safety requirements of each safety subsystem, function and/or piece of equipment to be specified, making SILs pivotal parameters in safety evaluation. However, different interpretations of SIL exist, and faced with the complexity of guided transportation systems, the current SIL allocation methods are inadequate for the task of safety assessment. To remedy these problems, the model developed in this paper seeks to verify, during the design phase of guided transportation system, whether or not the safety specifications established by the transport authorities allow the overall safety target to be attained (i.e., if the SIL allocated to the different safety functions are sufficient to ensure the required level of safety). To meet this objective, the model is based both on the operating situation concept and on Monte Carlo simulation. The former allows safety systems to be formalized and their dynamics to be analyzed in order to show the evolution of the system in time and space, and the latter make it possible to perform probabilistic calculations based on the scenario structure obtained.     

带缓冲区的基于时间延迟的可修设备联合优化

考虑到设备停机时间较长对企业经济效益的影响,在设备间设置缓冲区;同时考虑到设备单目标维修决策模型的不足,以及故障次数表达的精确程度对决策的影响,借用了时间延迟理论,建立了可修复设备的联合决策模型。为了满足设备的生产要求,以及最优化缓冲区生产系统的费用水平,将分别以平均单位时间的总停机时间、平均单位时间的总费用作为目标函数,来进行研究。通过时间延迟理论,分析了故障形成的过程,并表达出故障次数。借用更新报酬定理,来表达两目标函数。由离散迭代算法,求解得到：最优的检查周期和额定库存分别为25 d、1 195件时,总费用率在停机时间率为0.199时最小为22 739.95元。另外,进行了敏感性分析来验证最优解,最后由求解结果来指导生产线维修管理。     

Capacity estimation of a multi-product unreliable production line

This paper addresses the problem of capacity estimation of a multi-product production line composed of m unreliable workstations and ( m - 1) intermediate buffers. A simulation-based experimental design methodology is proposed to improve the performance of this flexible production line, which is expressed as the cycle time. The modelling approach integrates, in a more representative manner, the many parameters that impact the capacity of the manufacturing system. These are: workstation failure, repair, and set-up as product type changes. An experimental optimization to judiciously locate/allocate buffers between workstations is used to determine the maximum contribution of buffers on the overall performance of this serial manufacturing system. A case study is presented to show the modelling steps and to assess the contribution of each buffer. Analysis of the results shows the trade-offs between the different levels of buffers and the cycle time of the production line. The results present the percentage of workstations' operation, set-up, downtime, blocking and starving. In addition, for each combination of buffer sizes, the bottleneck workstation is identified. Changing a buffer size impacts directly the cycle time and, in some cases, a new bottleneck workstation evolves. The results provide insights into the performance of the system, including detection of important interactions and critical parameters. Considering various design scenarios, our methodology helps to identify the best strategy of buffer location/allocation that ensures a minimum cycle time, while considering other criteria. This could be achieved with less experimental effort and the manager could make the selection of the best design scenario. An analysis of the dynamic behaviour of buffers and their effectiveness is also given and commented upon.     

Optimization of cost and downtime for replacement model following the expiration of warranty

This paper deals with the optimal replacement policies following the expiration of warranty: renewing warranty and non-renewing warranty. If the system fails during its warranty period, it is replaced with a new one and if the system fails after the warranty period is expired, then it is minimally repaired at each failure. The criterion used to determine the optimality of the replacement period is the overall value function, which is established based on the expected downtime and the expected cost rate combined. Firstly, we develop the expected downtime per unit time and the expected cost rate per unit time for our replacement model when the cost and downtime structures of maintaining the system are given. The overall value function suggested by Jiang and Ji [Age replacement policy: a multi-attribute value model. Reliab Eng Syst Saf 2002;76:311–8] is then utilized to determine the optimal maintenance period based on the expected downtime and the expected cost rate. Numerical examples are presented for illustrative purpose.     

Performance analysis of open general queuing networks with blocking and feedback

Queuing network models have been extensively used for performance evaluation in many modern manufacturing and communication systems. The phenomenon of feedback reflects many practical situations, e.g. reworking in the production systems. However, existing research on open queuing network with feedback mainly concentrates on the models with infinite buffers or the models with finite buffers but exponentially distributed inter-arrival and service times. Research on open queuing networks with finite buffers, feedback and general inter-arrival and service times has not been reported. In this paper, a Rate Iterative Method embedded with the Generalised Expansion Method, is proposed for modelling this type of queuing network. System performance measures include the mean throughput, work-in-process and sojourn time all calculated by the proposed method. The accuracy and the efficiency of the proposed method are tested by comparing the results with other methods or simulation results from the experiments. Finally, a case study of a practical production system used in the manufacturing industry is studied and illustrates the applications of the proposed method. The results in this paper can be used as a basis for system design analysis and resource planning.