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1.
Counting the number of units is not always practical during the sampling of particulate materials: it is often much easier to sample a fixed volume or fixed mass of particles. Hence, a class of sampling designs is proposed which leads to samples that have approximately a constant mass or a constant volume. For these sampling designs, estimators were derived which are a ratio of arbitrary sample totals. A Taylor expansion was used to obtain a first-order approximation for the expected value and variance in the limit of a large batch-to-sample size ratio. Furthermore, a π -estimator for a ratio of batch totals was found by deriving expressions for the first- and second-order inclusion probabilities. Practical application of the π -estimator is limited because it requires inaccessible batch information. However, when the denominator of the estimated batch ratio is the batch size, the π -estimator becomes equal to a sample total divided by the sample size in the limit of a large sample-to-particle size ratio. As a consequence, the obtained sample ratio becomes an unbiased estimator for the corresponding batch ratio. Retaining unbiasedness, the Horvitz–Thompson estimator for the variance, which also contains inaccessible batch information, is replaced by an estimator containing sample information only. Practical application of this estimator is illustrated for the sampling of slag, produced during the production of steel.  相似文献   

2.
This paper describes the concepts of statistical batch process monitoring and the associated problems. It starts with an introduction to process monitoring in general which is then extended to batch process monitoring. The performance of control charts for batch process monitoring is discussed by means of two performance indices: the overall type I error and the action signal time. Problems associated with the existing approach are discussed and highlighted. Improvements are suggested and checked with the performance indices. To evaluate the effect of the proposed improvements as well as to assess the performance of the existing approach, an industrial batch production process is used.  相似文献   

3.
Certain manufacturing systems, notably those in high technology precision casting and integrated circuit production suffer from process yield losses which are both significant in quantity terms and are also highly unpredictable. This poses special problems for the provisioning of materials to support a manufacturing program and for the detailed scheduling necessary to update the priorities of work in process batches as losses occur. This paper establishes a framework of analysis to handle this problem in MRP logic. It describes the mechanisms available and discusses their relevance to the market environments in which the company is operating.The key conclusion of this paper is that different solutions are required for different market circumstances. The four key strategies developed are:
1. A: For continuous schedules, make-for-stock: Use mean yield rate and fixed buffer stocks.
2. B: For continuous schedules, make-to-order: Use mean yield rate, fixed buffers and a yield to finish monitoring system.
3. C1: For single batch production make-to-order: As for B but using a desired service level yield rate.
4. C2: For multiple batch production, make-to-order: As B but using a variable yield rate by batch.
The implementation of each of these is described in relation to the business objectives of cost effectiveness and customer satisfaction.  相似文献   

4.
The accuracy of the determination of the amount of solids in bread.
Of a loaf with a nominal weight of 800 grams only about 480 grams remains after complete drying. This so-called 'amount of solids in bread' is regularly checked by samples. From a batch of loaves a group of at least 5. but usually more, are taken at random and weighed. From this group one is selected with a weight as nearly as possible equalling the average weight of the whole group; for two slices of this sample loaf the decrease in weight upon drying is determined in the laboratory, and is considered as representative for the entire batch.
The accuracy of these determinations is analysed on the basis of 35 samples which were investigated in 3 different laboratories. The standard error is estimated at 5 grams per loaf. The influence of various factors, such as the method of sampling which may be altered in many ways, is briefly considered, while in a final section the results obtained are discussed from a practical point of view.  相似文献   

5.
In this paper we analyse a multi-server batch-service queueing model. Customers arrive one by one according to a Poisson process. They are served in batches under the following threshold policy: when a server becomes available a new batch of waiting customers is taken into service as soon as their number reaches a threshold a . The maximum allowable batch size is equal to b . Two classes of batch service time distributions are considered: Coxian-2 and Erlang- r distributions. In both cases the queueing model can be described by a Markov process. For this process it is shown that the equilibrium probabilities for states with all servers busy can be expressed as a finite sum of geometric terms. This form is used to derive a closed form expression for the waiting time distribution.  相似文献   

6.
为了解决当前业务数据处理中客户群庞大、业务数据大、人工操作繁杂、重复性高等问题,针对现有核心系统构架并非针对完全连线化的设计,提出了同一Job内批次作业平行处理的通用批处理作业系统框架模型,采用断点续接、参数化和模块化设计等实现了该系统。研究结果表明:通过调节参数,Batch循环流程控制,以满足气象、电信等不同业务的需要,系统能为其提供业务数据的快捷处理手段,提高了操作效率,减少了人工误操作率,达到了通用批处理作业的效果。  相似文献   

7.
基于谱分析的连续加工过程检验批量的确定   总被引:2,自引:0,他引:2  
在连续加工过程中 ,合理地确定检验批量 ,不仅可以反映加工过程的稳定性 ,而且也是确定抽样检验方案及检验频次的基础。本文主要利用时间序列的谱分析方法对连续加工过程的质量检测数据进行周期划分 ,从而确定抽样检验的批量 ,并根据周期分析结果 ,指出了导致加工质量产生波动的一些原因。  相似文献   

8.
K. Murari 《Metrika》1972,19(1):201-208
This paper considers the transient behaviour of queueing problem in which (i) the arrivals occur in batches of variable size (ii) the arrival and no arrival of a batch at two consecutive transition marks are correlated (iii) the service time distribution for each, unit is general with probability density functionD(x). TheLaplace transform of various probability generating functions of queue length are obtained and some particular cases are derived therefrom.  相似文献   

9.
在信息管理系统实际应用中,批量数据导入导出技术是提高数据录入速度和方便用户将数据库信息以多种报表方式予以输出的有效途径。文章详细介绍基于VC#开发平台实现Excel表格与SQLServer数据库之间批量数据导入导出技术的流程、步骤和实现方法。  相似文献   

10.
高等学校积极构建创业实践体系,是培养高水平创新创业型人才的关键。本文提出了一个中心、一个平台,个性辅导与批量创业相结合,校、院、系三级创业指导网络的模式,以指导学生创业实践活动。  相似文献   

11.
This study investigates how process choice relates to production planning and inventory control decisions. We empirically examine the validity of deductively derived patterns about these types of decisions. More importantly, we look for normative insights by exploring how production planning and inventory control decisions affect operations performance. Our findings show that production line and continuous flow plants use more of a level production strategy, and carry less raw material and work-in-process inventory. The performance drivers for these plants, through which the operations function excels, are effective utilization of equipment, reduced finished goods inventory, and reduced setup down time. To gain forward demand visibility and batching economies, job and batch shops rely much more on backlogs in their planning process. These plants use more of a production chase strategy and position inventory lower in the bills of materials. Four performance drivers for top-performing job and batch shops are to find ways that better anticipate customers' orders, have a more responsive chase strategy, carry less raw material or purchased inventory, and shorten production planning horizon, partly through less reliance on backlogs. It is intriguing that top-performing plants not only do the expected things, given their choice of process, but also excel in selected dimensions—some of which fit the profile normally associated with a different process choice. To monitor and continuously improve operations, evaluation ‘scorecards’ should pay particular attention to performance drivers, which change depending on the plant's process choice.  相似文献   

12.
This article presents a model for scheduling activities that are required to manufacture a product batch in a multistage process. The activities include setups, operations, and load movements between operations. In this model, setups may or may not require a unit from the preceding operation; each operation must be performed continuously on the batch once it has started, and capacity constraints apply to transportation activities. Within this context, two productivity-related objectives are sought. The primary objective is to minimize the total production time for the batch; the secondary is to minimize the number of load movements.Considering the capacity constraints, a maximum number of units per load is specified for each “vehicle” and one vehicle is dedicated to each transportation activity. The simplicity of the vehicle restriction facilitates the examination of scheduling interactions among activities, and the results of the research into this model may serve as a foundation for treating more general representations of capacity constraints.The model is used to investigate the scheduling implications of capacity-constrained load movements. It brings into focus interactions between these movements and the other activities in the process. After each operation, units must be grouped and moved in the fewest loads that permit the succeeding operation to begin as soon as possible, while observing setup and continuity requirements for this operation. Further, the departure times of loads depend on the availability of units and the vehicle. The formation of loads that must conform with the vehicle's capacity limit affects the times at which the loads are ready for movement, while the scheduling of previous movements from the operation affects the times at which the vehicle is available.A procedure is developed for scheduling activities that have this complex set of interactions. Computational requirements on test problems indicate that practical-sized applications can be handled with this procedure. These applications would be designed to assist in making production planning decisions by experimenting with factors such as vehicle capacity limits and sequencing of operations to determine their effect on production time requirements and numbers of load movements.The article develops a branch-and-bound routine to solve subproblems of scheduling transportation activities. The efficiency of this routine that results from exploiting the specific structure of the subproblems is critical for the success of the overall procedure. While the subproblems can be solved as zero-one mixed-integer programs, this approach is too computationally burdensome for all but the smallest of problems.  相似文献   

13.
《Statistica Neerlandica》1948,2(5-6):228-234
Summary  (Sample size for a single sampling scheme).
The operating characteristic of a sampling scheme may be specified by the producers 1 in 20 risk point ( p 1), at which the probability of rejecting a batch is 0.05, and the consumers 1 in 20 risk point ( p 2) at which the probability of accepting a batch of that quality is also 0.05.
A nomogram is given (fig. 2) to determine for single sampling schemes and for given values of p1 and p 2 the necessary sample size ( n ) and the allowable number of defectives in the sample ( c ).
The nomogram may reversedly be used to determine the producers and consumers 1 in 20 risk points for a given single sampling scheme.
The curves in this nomogram were computed from a table of percentage points of the χ2 distribution. For v > 30 Wilson and Hilferty's approximation to the χ2 distribution was used.  相似文献   

14.
深入学习实践科学发展观,是解放思想、深化改革、解决新时期学院团学工作所面临问题的必然要求,是推动学院团学工作上水平的重大举措。文章就开展学习实践科学发展观活动的重大意义、现实紧迫性以及如何结合实际努力践行科学发展观进行探讨。  相似文献   

15.
Material requirements planning (MRP) is a planning and information system that has widespread application in discrete-parts manufacturing. The purpose of this article is to introduce ideas that can improve the flow of material through complex manufacturing systems operating under MRP, and that can increase the applicability of MRP within diverse manufacturing environments.MRP models the flow of material by assuming that items flow from work station to work station in the same batches that are used in production. That is, once work starts on a batch of a certain item at a certain work station, the entire batch will be produced before any part of the batch will be transported to the next work station on its routing plan. Clearly, efficiency can be increased if some parallelism can be introduced. The form of parallelism investigated here is overlapping operations.Overlapping operations occurs when the transportation of partial batches to a downstream work station is allowed while work proceeds to complete the batch at the upstream work station. The potential efficiencies to be gained are the following:
• Reduced work-in-process inventory
• Reduced floor space requirements
• Reduced size of transfer vehicles
Additional costs may accrue through additional cost of transportation of partial batches and through additional costs of control.Some MRP software vendors provide the data processing capability for overlapping operations. However, the user is given little or no guidance on overlapping percentages or amounts. It is our intent to provide a simple, robust technique to MRP users who would like to overlap operations and gain some or all of the above efficiencies.An optimal lot-sizing technique is derived by considering a generic two work station segment of a manufacturing system. Under the assumptions of constant demand and identical production rates, a cost function that considers setup costs, inventory holding costs and transportation costs is derived. This cost function is minimized subject to the constraint that the production batch is an integer multiple of the transfer batch. We solve for the optimal production batch, the optimal transfer batch, and the integer number relating them. Solutions are obtained as closed form, easy to-evaluate formulas.By introducing more parallelism, overlapping operations can reduce lead time. However, this will not happen without modification of MRP logic to accommodate such reduced lead time. We derive a formula that shows how a significant lead time compression can easily be obtained and implemented in MRP.We consider an example to illustrate the application of the technique on typical data from the electronics industry. The outcome showed a cost savings of approximately 22.5% over the standard MRP approach.Overlapping operations allows the applicability of MRP to an increasing number of situations that are not modeled faithfully by conventional MRP logic. Three such situations that occur often are the following:
• Limited size of transfer vehicles dictate that several transfers should be planned.
• Lead time requirements prohibit nonoverlapped operations.
Our analysis suggests how to accommodate these difficult practical situations into MRP.Overlapping operations in material requirements planning provides an enhancement that allows wider applicability, shortened lead times, and lower total costs. It may be applied selectively to any two work stations where it is deemed appropriate. Due to the structure of the cost function, it is possible to make the transfer lot-sizing decisions independent of the production lot-sizing decisions. Therefore, significant improvements can be made through overlapping with minimum disruption to the existing MRP system machinery. It is our conviction that overlapping operations is an important concept that can and will impact MRP. We suggest the approach presented here as a systematic way to implement overlapping.  相似文献   

16.
苏翔  朱丽 《价值工程》2012,31(24):200-202
本文针对多产品批处理实际生产中加工时间不确定的情况,基于鲁棒调度的思想,提出了一种将加工时间用区间范围表示的鲁棒模型和方法,并使用遗传算法实现该方法。最后,仿真实验的结果表明该鲁棒调度模型和算法的有效性。  相似文献   

17.
Quality & Quantity - The best evaluation for the proportion of defective units in a batch of fruits and vegetables can be achieved by an exhaustive checking of all the boxes in the batch, that...  相似文献   

18.
生鲜食品的二级补货系统优化研究   总被引:1,自引:1,他引:1  
针对连锁超市的配送网络。建立一个两级的库存系统模型,其中包括一个中心仓库和若干门店,每个门店面对的是随机的相互独立的需求,该需求服从正态分布。该库存系统是采用基于连续检测的再订货点方法管理。本文针对超市的生鲜食品补货的特征,增加对于过剩成本的考虑,采用分散库存控制权的方法,按照从门店到配送中心的思路。优化总库存成本,从而得出最佳的订购批量,同时也得出最佳的产品供给水平、再订货点等。  相似文献   

19.
20.
Abstract  The class of weighted M-estimators is defined. The ratio of the asymptotic variance of the weighted estimator to the asymptotic variance of the optimally weighted estimator is defined as the inefficiency. A K antorovich inequality is proved, its implications are investigated for the misweighted mean and misweighted median, and the results are applied to a batch of demographic data.  相似文献   

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