基于仿真的汽车发动机再制造生产线缓冲区容量优化

以汽车发动机核心部件为对象,以在制品数量(WIP)为主要评价指标,重点研究回收件到达率、可再制造率、加工时间等不确定因素对缓冲区容量的影响.基于离散事件仿真技术建立系统动态运行模型,采用正交试验设计方法完成了仿真试验的方案设计.通过仿真再制造生产线动态平衡及缓冲区容量的内在变化规律,获得生产线优化运行所需的最小缓冲区容量.案例研究表明,所提出的方法能有效确定再制造系统缓冲区的最佳容量.     

考虑役龄的预防性维修计划与缓冲区库存联合优化决策

针对生产系统中的预防性维修问题,提出考虑缓冲区库存和役龄回退的预防性维修策略,分析役龄对故障率的影响,推算出设备的故障次数,建立设备预防维修计划与缓冲区库存联合优化决策模型。该模型以预防性维修周期T和缓冲区库存量S为决策变量,以周期内单位时间总费用CT(T,S)为决策目标,并运用离散迭代算法进行算例仿真求解,获得最佳的缓冲区库存量及最优预防性维修周期,使单位时间总费用达到最低。算例对比分析证明了策略模型能有效节省生产成本。最后通过灵敏度分析得出相关参数对于策略模型的影响,验证模型的有效性,为维修计划提供理论指导。     

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。     

考虑运费的短生命周期产品供应链集成模型

一般的供应链集成问题都是忽略机器故障、产品检查以及运输成本,然而,这些因素对生产计划的制定也是有很大影响的。因此,在考虑机器故障、返修费用和担保费用,以及短生命周期产品库存成本随着时间呈非线关系的情况下,建立了短生命周期产品供应链集成模型,研究分析了运输费用、返修费用和担保费用对最优生产批量和单位时间总成本的影响,同时比较了考虑机器故障与运输费用对短生命周期产品在生产策略上的一些区别,得到了一些有价值的结论。     

约束理论在电磁阀生产计划中的应用

以电磁阀生产计划控制为研究对象,将约束理论引入生产系统.通过生产类型和工艺路线分析,对可能存在瓶颈工序部件的各个工序进行工时统计、生产能力负荷比较后,找出阀门生产中的瓶颈工序.运用DBR理论,对瓶颈工序建立"前拉后推"的生产计划编排方式,提高了瓶颈工序的生产效率,瓶颈工序的在制品堆积情况有所缓解,装配停工待料情况大大减少,电磁阀生产周期缩短了20%,使得阀门能够按时出厂.     

"按订单"生产方式下瓶颈资源的确定

分析了瓶颈资源、缓冲、生产提前期之间的关系，以及目前各种用于确定约束资源的方法。针对工序能力比较接近的情况，提出了一种利用Q—GERT仿真技术来分析单一产品模式和多产品模式下确定瓶颈资源的方法，既能真实体现生产中的实际情况，也能准确确定系统中的瓶颈资源，从而使企业在保证较短的生产提前期的同时，大大节省人力和物力。     

一种动态识别瓶颈机床的前向启发算法

为了解决作业车间调度问题中的瓶颈漂移和动态识别问题,提出了一种动态识别瓶颈机床的前向启发算法.该算法引入搜索空间的概率分析方法,通过工序开工概率、工序对机床的独立需求概率、机床累计需求概率和3个量化参数,构造了以竞争高峰时段的机床负荷量大小为判定依据的瓶颈机床识别启发规则.实验结果表明该方法能够有效识别瓶颈机床,使得大规模作业车间调度的求解复杂度显著降低.     

基于像素点的机器视觉系统能力评价

为保证形似矩形或形似椭圆形的不规则形状产品图像数据的可靠性,提出了拍摄该类不规则产品的机器视觉系统的一般性能力评价方法。通过图像处理技术对获取的原始图像数据进行处理,获取产品所在的目标区域,以目标区域所在像素点的个数S及区域边界像素点个数C,作为判断该产品是否合格的质量特性,并分析影响产品质量特性的各影响因素,评价机器视觉系统的能力。通过案例分析表明,该方法能有效且准确评价机器视觉系统能力。     

印染设备的故障及现场管理探讨

印染行业的设备,大多机器都是连贯性作业,定期检修就显得有些力不从心了。如果采取定期维修的办法,需要停工操作,检修起来,也是很不便利的。而且也对生产有影响。为了避免机器出现故障,影响工时,减少设备的故障,提高工作效率,设备维修应提供现场维修。     

988B制动系统故障分析与判断

988B制动系统压力油不但要给机械提供制动液压力,还分别要给机具液压系统供给先导油压,和控制变速箱的腹中位系统控制油压以便使机器在工作时能够方便的进行前后运行,同时还要提供冷却系统的冷却油使液压油进行冷却,它的结构复杂,包括很多的控制阀和溢流阀,当每个部件出现故障都会影响机械的正常工作,因大多数抄作人员和维修人员没有通过系统的培训,当系统出现故障时不能及时的判断和排除故障,常会盲目的刚换配件,使维修成本提高,设备不能及时正常工作,严重的影响生产,在此向维修人员提供一些方法判断维修的方法     

Determination of buffer sizes for drum–buffer–rope (DBR)-controlled production systems

The present paper describes an analytical approach based on reliability analysis to determine the sizes of constraint buffer and assembly buffer in a drum–buffer–rope-controlled production system. Every machine in the system is modelled as a two-state named as up and down canonical model. Then, with these canonical models and the relationships between the feeder and fed machines, the models for determining constraint buffer and assembly buffer are constructed. To illustrate the approach's practical usefulness, a numerical example is presented. Based on the data analysis, we find that, for constraint buffer, the more feeder machines, the smaller the buffer size needed. And for assembly buffer, the more feeder machines the larger the buffer size needed. Then, two pieces of advice for the production managers to effectively use production-controlling policies are proposed.     

Modified drum–buffer–rope scheduling mechanism for a non-identical parallel machine flow shop with processing-time variation

The drum–buffer–rope (DBR) is a scheduling mechanism under the Theory of Constraints (TOC) philosophy. In DBR, ‘drum’ is a production schedule on the capacity-constrained resources (CCRs), which controls the speed of production for the whole system; ‘rope’ is a mechanism to release the required material to the CCRs; and ‘buffer’ is used to protect the CCRs from starvation due to statistical fluctuations. For a non-identical parallel machine flow-shop environment, estimating an efficient rope and time buffer for DBR implementation is not an easy task because of the complexity of non-identical parallel machine loading. This paper proposes a new scheduling method, which is called the modified DBR (MOD-DBR). It applies a backward finite capacity scheduling technique, including machine loadings and detail scheduling, instead of the rope mechanism in DBR. The scheduling performances of MOD-DBR are evaluated under variable processing time situations. The experimental results indicate that the MOD-DBR without a time buffer outperformed the DBR with a considerable level of buffer on the average flow time, while they have the same performance on tardiness, constraint resource utilization, and throughput.     

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.     

A dynamic WIP control strategy for bottlenecks in a wafer fabrication system

The performance of a wafer fabrication system is constrained by its bottlenecks, which are difficult to detect and improve due to the complexity within the system. To weaken the negative effects of bottlenecks, a work in process (WIP) strategy is proposed in this paper which focuses on offline target WIP level setting and online WIP control simultaneously. First, bottlenecks are detected and classified based on the constraint weights which are decided by the sensitivity of the system performance to the machine's fluctuant availability. Second, the target WIP level is allocated to the bottlenecks to avoid the process fluctuation caused by unpredictable events. Third, in real time scheduling, the upstream machine of the bottlenecks modifies its dispatching order to adjust the deviation of the WIP levels at the bottlenecks. Finally, a simulation platform is developed to validate the effectiveness of the proposed method.     

A segmentation approach for solving buffer allocation problems in large production systems

Buffer space allocation is an important step in production line design. In this paper, we focus on maximising the profit rate of a line subject to a production rate constraint. We describe a newly observed property of production line optimisation. The property is that the production rate constraint, if it is effective, allows an original line to be decoupled into several short lines for optimisation. An approximation method is developed from this property. Instead of optimising a long line, the method divides it into several short lines, optimises them separately and combines their optimal buffer distributions to find the optimal or near optimal buffer distribution of the original line. The method greatly improves the computation efficiency for solving buffer allocation problem for long lines, while ensuring the accuracy of the optimal buffer distribution. A heuristic explanation is proposed. Numerical experiments are provided to show the accuracy and efficiency of the method. The effect of the number and length of line segments on the performance of the method is discussed.     

On the uncertainties of decentralized controllers in a transfer production line

In this paper, an information theoretic approach is applied to analyze the performance of a decentralized control system. The control system plays the role of a correcting device which decreases the uncertainties associated with state variables of a production line by applying an appropriate “correcting signal” for each deviation from the target. In particular, a distributed feedback control policy is considered to govern a transfer production line, which consists of machines and buffers and processes a single part type in response to a stochastic demand. It is shown how the uncertainty of the demand propagates dynamically into the production system, causing uncertainties associated with buffer levels and machine production rates. The paper proposes upper estimates for these uncertainties as functions of the demand variance, parameters of the distributed controllers and some physical properties of the production line. The bounds are based on dynamic entropy measures of the system state and the control variables. Some practical implications into the area of decentralized controller design are proposed, an information-economical analysis is presented and a numerical study is performed.     

Event-driven model of unreliable production lines with storage

We have developed an event-driven algorithm for simulating a factory production line with storage. Using this algorithm a production line, with an arbitrary number of machines each processing items at different rates and with buffers of any size, can be modelled efficiently. The algorithm is based on computing the time to the next event for each buffer and machine, where the events are: a buffer becomes full, a buffer becomes empty, a machine fails and a machine is repaired. By collapsing the production line to exclude empty buffers that stay empty and full buffers that stay full, piece-by-piece computation is avoided. Computation time is reduced further by updating a buffer only when the input or output rate of that buffer changes or when the state of that buffer changes. The implementation of this model is compared to a piece-by-piece simulator.     

卷包机组设备效率评价指标体系的设计与实现

目的 针对烟草行业常见设备卷包机组,提出一种结合OEE的设备效率评价体系,实现对卷包机组设备运行状态的精确、实时、具体的反映.方法 通过分析离散制造与连续制造的差异,在传统离散制造OEE方法基础上,针对连续生产进行适应性改进,提出一套针对卷包机组的设备效率评价指标;在此基础上,通过分析卷包机组各运行单元结构特点,提出一套实时采集设备状态数据与动态分析效率状态的卷包机组设备效率评价体系.结果 将此体系部署于湖北中烟某车间6台卷包机上6个月进行实验验证,结果显示在该体系的支持下,设备净效能平均同比增长7.72％,证明本效率评价结果可以精准、全面、实时地反映设备运行情况和状态背后的影响因素,有助于提升卷烟机组设备效率.结论 文中提出的卷包机组设备效率评价指标体系使用户可以针对性、快速地调整设备运行状态,实现了精准管理,提高了生产作业效率,具有实际的推广价值.     

酒品包装生产中动态缓冲管理机制

考虑存在资源约束的流线式酒品包装生产车间,为了减少企业生产成本,提出了一种以控制在制品(WIP)库存为主要参考指标的动态缓冲管理方法。本方法通过实时监控缓冲区的WIP库存,根据在监控窗口中缓冲区出现WIP库存由高于安全下限变化到低于安全下限的频率以及随后是否出现WIP库存耗尽的情况,对库存安全上下限进行动态调节进而实现对缓冲的动态管理。为了验证方法的有效性,安排了3组不同的仿真实验。实验结果表明：与传统的缓冲管理策略相比,基于动态缓冲管理策略的控制方法在WIP库存控制方面存在22%以上的优势,采用该方法可以有效的控制生产系统中的在制品库存。     

A variance change point estimation method based on intelligent ensemble model for quality fluctuation analysis

For multivariable production process, knowing the first time of process really changes (change point) will help to accelerate the location of assignable causes and make measures for process adjustment. So effective estimating the change point is an important way to analyse the quality fluctuation of process. In the present study, an intelligent ensemble model for quality fluctuation analysis is proposed to estimate the variance change point in multivariable process. With the method, the process is decomposed based on moving window analysis, then different types of kernel functions are combined together to form the multi-kernel support vector machine model, which has combined the feature mapping capability of each basic kernel in the new feature space. The particle swarm optimisation is considered to search the optimised multi-kernel parameters. After that, each sub-characteristic is regarded as a pattern to be recognised to determine the change point by using the optimised intelligent ensemble model. Finally, a case study is conducted to evaluate the performance of proposed approach. It reveals that the method could estimate the time of variance change point in continuous production process accurately.