The surprising effectiveness of earliest operation due-date sequencing

In make-to order production, schedule reliability is very important but still not sufficiently accomplished in industrial practice by the vast majority of companies. It has been known for long that processing the orders at a workstation in the order of their operation due-dates can compensate for lateness in the arrival at the workstation within certain boundaries. The paper analyses the effectiveness of earliest operation due date (EODD) sequencing by comparing it to an optimistic theoretical boundary. The surprising result is that EODD can nearly fully exploit the theoretical potential. It should therefore be used in practice whenever schedule reliability is important, with only few exceptions. Its effectiveness though is increasing with the workstation’s WIP level and thus is in conflict with the objective to reduce WIP levels and throughput times. A simple forecasting model allows to assess the extent to which lateness can be compensated by EODD sequencing and which schedule compliance can be achieved.     

A Universal Appointment Rule in the Presence of No‐Shows and Walk‐Ins

This study introduces a universal “Dome” appointment rule that can be parameterized through a planning constant for different clinics characterized by the environmental factors—no‐shows, walk‐ins, number of appointments per session, variability of service times, and cost of doctor's time to patients’ time. Simulation and nonlinear regression are used to derive an equation to predict the planning constant as a function of the environmental factors. We also introduce an adjustment procedure for appointment systems to explicitly minimize the disruptive effects of no‐shows and walk‐ins. The procedure adjusts the mean and standard deviation of service times based on the expected probabilities of no‐shows and walk‐ins for a given target number of patients to be served, and it is thus relevant for any appointment rule that uses the mean and standard deviation of service times to construct an appointment schedule. The results show that our Dome rule with the adjustment procedure performs better than the traditional rules in the literature, with a lower total system cost calculated as a weighted sum of patients’ waiting time, doctor's idle time, and doctor's overtime. An open‐source decision‐support tool is also provided so that healthcare managers can easily develop appointment schedules for their clinical environment.     

中国劳动密集型制造业的生产力困境——企业社会责任的视角

在“用工荒”已经出现并将持续存在的情况下,中国劳动密集型制造业企业面临其特有的“生产力困境”.追求高度分工的运营策略虽然提高了企业的运营效率,但也使企业变得脆弱且反应迟钝,难以应对“用工荒”的挑战.本文尝试从企业社会责任的角度寻找帮助企业走出困境的办法.运用结构方程模型(SEM)通过对大样本(N=1185)企业员工问卷数据的分析,我们发现员工感知到的企业的社会责任努力能有效降低员工的离职意愿,同时提高其工作绩效;而且当企业采用高度分工策略时,上述关系变得更强.员工离职率的降低能有效提升企业应对“用工荒”的能力从而降低企业运营风险,员工工作绩效的提升将有助于改善企业整体运营效率.因此,我们认为企业的社会责任行为有助于缓解企业运营效率与运营灵活性之间的矛盾,帮助企业走出“生产力困境”.     

Extending Little’s Law to single order throughput times

It has long been established that the mean throughput time is a result from the relationship between the work in process (WIP) and output rate. In reality, however, throughput times are frequently dispersed broadly around this mean. With the aid of a model originally developed for lateness, it is now possible to describe the throughput times of individual orders. Accordingly, the throughput time can be divided into two components: WIP-dependent throughput time and sequence-dependent throughput time.     

An adaptation of the EOQ formula for JIT quasi-pull system production

This research demonstrates for the first time that in a just-in-time (JIT) quasi-pull production environment, a model adapted from the Economic Order Quantity and made up of two specific formulas can be employed for calculating an optimised lot size. The assumptions of our model are: a low level of defects, and insignificant shortage backordering and failure of the equipment. JIT quasi-pull production is the state typically reached by many manufacturing companies because it is almost impossible to achieve zero set-ups and zero work-in-process (WIPs) even in the best Lean Production implementations. In this model, finished products are shipped at once in a JIT way. The two developed formulas are specialised: one for balanced stations/processes and the other for unbalanced stations; the formulas allow calculation of an optimised lot size. Several applications of the formulas have been tested and discussed through a case study. Findings demonstrated that the optimised quantity of a lot size has to be smaller than the customer’s daily demand for the product. Moreover, in case of unbalanced stations with long cycle times, the formula forces the company to reduce its set-up times and the cycle times. The new model will be of interest to practitioners who are seeking a way to balance the costs of set-ups and the cost of holding some WIPs and offers interesting avenues for new research.     

我国工业电力用户价值画像模型构建与应用研究

在新型冠状病毒感染肺炎疫情对我国电力市场造成巨大冲击的宏观背景下,为进一步提升我国供电企业营销服务资源配置效能,最大化撬动供电企业的综合效益,笔者开展了我国工业电力用户价值画像模型研究。本文对电力用户价值进行了分析和定义,从安全稳定价值(S)、经济效益价值(E)、契约信用价值(C)与有序用电价值(O)四个维度,构建了我国工业电力用户价值评级SECO指标模型,并集成智能算法中的RST(粗糙集理论)与数据挖掘技术中的PAM(围绕中心点切割聚类算法),构造了一种半监督自动化用户价值识别、预测与特征展示模型,模型包括基于RST的指标体系设计、基于Gower相异度系数与PAM的用户价值评级,以及基于用户画像的价值特征展示三大模块。其中,为增强聚类分析结果的科学性与可靠性,采用霍普金斯统计量进行聚类趋势判断,利用间隔统计量输出理论最佳聚类数目,运用轮廓系数评估模型效果与识别误判样本。以我国南方电网公司下属某供电企业电力用户数据进行模型测试与应用研究,得到具有较高解释性与区分度的用户细分方案,表明本模型是一套可行有效的用户价值评级与特征可视化工具。     

排污权价格随机情境下基于CVaR 准则的企业生产决策

面向排污权市场价格随机情境,通过提取理性企业在产品生产、污染削减、排污权交易等方面决策行为与排污权市场价格之间的关联性,推导了排污权市场价格随机情境下的企业随机利润函数;基于条件风险价值(CVaR)风险度量准则,推导了任意置信水平下随机利润的风险价值(VaR)解析表达式,建立了不同排污权预期价格和置信水平下的CVaR测度模型;基于此,深入论证了给定置信水平下实现随机利润CVaR最大化的企业最优决策及其特征,并系统分析了外部情景要素变动对最优决策及其优化结果的影响。主要结论表明：在企业分别作为排污权出售者与购买者两种情况下,随机利润CVaR的具体测度因利润下行风险存在的排污权市场价格区间不同而存在差异;基于CVaR准则,考虑决策风险的最优决策受到决策主体置信水平、排污权初始配额、排污权市场价格均值及标准差等多因素的复杂影响,进而系统性地偏离风险中性最优决策,并表现出风险规避特征;通过算例分析对所得结论进行全面验证,进一步说明该模型能较好地刻画与反映排污权交易企业决策风险及其现实决策行为。     

Information quality deficiencies in delivery schedules and their impact on production scheduling

The purpose of this paper is to explore how different delivery schedule characteristics affect the quality of shared delivery schedule information and, in turn, how deficiencies in quality affect a supplier’s production scheduling process. It describes a case study conducted in the Swedish automotive industry involving a supplier that operates as the first-, second- and third-tier supplier to an original equipment manufacturer. The study reveals how four delivery schedule characteristics – namely, receiving frequency, planning period, frozen period and demand variation – create information quality (IQ) deficiencies in five dimensions of IQ: completeness, conciseness, reliability, timeliness and credibility. At the same time, it demonstrates how such deficiencies affect the supplier’s production scheduling process by requiring additional rescheduling, reworking and follow-up activities as well as additional capacity problems, safety time, safety stock and backlogs. In effect, the paper extends previous IQ-related research by considering IQ in delivery schedules.     

高管权力与公司治理效率——基于国有上市公司高管变更的视角

本文基于国有企业的高管变更视角分析了高管权力对公司治理效率的影响.以2004 -2008年的国有上市公司为研究样本,实证发现:(1)总体上高管变更与公司业绩呈负相关,而高管权力的增强会降低其因业绩低劣而被强制性更换的可能性,表明国企高管的权力在高管变更决策中发挥了显著的职位堑壕效应;(2)发生了高管变更的公司其未来业绩有明显的提高,但这一促进效应仅在权力较小的高管被变更后出现,而权力较大的高管被变更后公司业绩并没有得到改进;(3)进一步的研究显示,政府控制层级的提升和制度环境的改善能够抑制国企高管的权力寻租行为.本文的研究结果有助于我们理解国有企业高管权力的经济后果,并为当前有关国企公司治理和高管选聘体制改革的政策导向提供了经验启示.     

An investigation of output flow control,bottleneck flow control and dynamic flow control mechanisms in various simple lines scenarios

Flow control mechanisms have been a topic of academic research for several years. With the growth of business-wide information systems such as enterprise resource planning and supply chain, better planning, scheduling and control of the business transformation process is required in order to achieve increased throughput, reduced inventories, shorter lead times and reduced tardiness. This research compares two new approaches to flow control, output flow control and bottleneck flow control to a real-time flow control system, dynamic flow control. Both output and bottleneck flow control mechanisms are much simpler to implement and manage than dynamic flow control in that they do not require continual feedback and rescheduling. Line characteristics, such as location of breakdowns with respect to the bottleneck, the location of the bottleneck when breakdowns occur, and the impact of variability of processing times on the performance measures (output, WIP level, lateness, and number of tardy jobs) for these three flow control mechanisms are compared. Both output and bottleneck flow control mechanisms perform favourably (particularly bottleneck) under different scenarios and warrant further study across a wider range of scenarios (mixed models, job shops, etc.).     

Hierarchical production planning at a multiproduct multiprocessor fibreglass manufacturing facility

Abstract

Abstract. A hierarchical production planning model is developed for a forming facility of a major fibreglass manufacturer. The model establishes aggregate quarterly quantities for families of products, monthly disaggregate production quantities for end-items within these families, and a weekly sequencing schedule of end-items. A key feature of the planning system is its ability to decompose total set-up cost into primary and secondary components and to account appropriately for each component at a distinct level of the planning hierarchy. The mathematical programming formulations, the accompanying solution algorithms, and the results of their application to nine months of actual company demand and cost data are presented.     

The Effects of Employee-Led Process Design on Welder Set-Up Intervals

This study focused on improving manufacturing efficiency and production by designing new steps to the work process with an employee focus group. The set-up behaviors of two regular stock welders at a medium-size metal furniture manufacturer were observed via video recordings. The videos of the welders completing their tasks were reviewed in an employee focus group, during which it was determined that designing the welding process to include the use of walkie-talkies would successfully alter the contingencies surrounding set-up behaviors, thereby leading to a decrease in average set-up time. Results for the two welders combined showed a decrease in average set-up time of 2.27 min, with Welder A exhibiting a larger decrease overall and Welder B’s set-up time showing a greater reduction in variability.     

基于柔性资源约束的前摄性项目调度优化研究

不确定环境中，项目进度计划鲁棒性的高低直接影响项目能否顺利实施。本文研究了具有随机活动工期的柔性资源约束下的前摄性项目调度优化问题，目标是在柔性资源和项目工期的约束下，借助对活动开始时间合理的进行安排进而得到拥有最大鲁棒性的进度计划。首先对研究问题进行界定；随后构建优化模型，并根据问题NP-hard属性和模型特点设计了双层嵌套禁忌搜索启发式算法，通过内外两层交互搜索寻找满意解；最后通过一个实际案例对本文研究进行说明，并分析关键参数对进度计划鲁棒性的影响，得到如下结论：相对于资源无柔性情况下的项目进度计划而言，资源具备柔性后得到的项目进度计划的鲁棒性更高，具有更强的抗干扰能力，能够保证项目稳定执行；同时，项目进度计划鲁棒性分别随着项目工期的延长、资源可用量的增加或资源柔性的提高而上升。     

Adjexpectile风险测度的性质、优化及资产配置的应用

金融风险的度量和识别是风险管理的重要内容,常用的风险度量工具是标准差、VaR、ES,但存在很多缺陷,expectile的提出弥补了这些不足,在理论界得到广泛的讨论和应用。本文扩展了expectile进行资产配置,提出Adjexpectile的概念,并讨论和分析了Adjexpectile的一致性风险度量、随机占优性、凸性,与标准差、VaR、shortfall的关系,风险贡献及风险分解的性质。通过对六个资产指数：上证国债指数、上证企业债指数、上证180指数、深圳100指数、深成长40p指数和黄金现货指数的复合周收益率数据进行组合优化配置,发现Adjexpectile在非对称性收益数据、组合前沿、风险分散方面具有一定的优越性。     

创新人才胜任力模型实证研究

利用开放式问卷调查、关键事件访谈等方法,设计创新人才胜任力调查量表,从人才供应—需求视角出发,对我国一些研究型大学、科研院所和科技型企业进行调研。基于此,运用探索性因素分析和验证性因素分析,构建了由27个胜任特征项目构成创新知识、创新品德、创新能力、创新精神、创新人格五大胜任力维度的创新人才胜任力结构模型。该模型具有良好的信度和效度,丰富了胜任力理论体系,为大学、企业等组织创新人才选拔、培养和评价工作提供决策参考。     

First-Order Reliability Analysis of Public Health Risk Assessment

This paper demonstrates a new methodology for probabilistic public health risk assessment using the first-order reliability method. The method provides the probability that incremental lifetime cancer risk exceeds a threshold level, and the probabilistic sensitivity quantifying the relative impact of considering the uncertainty of each random variable on the exceedance probability. The approach is applied to a case study given by Thompson et al. ⁽¹⁾ on cancer risk caused by ingestion of benzene-contaminated soil, and the results are compared to that of the Monte Carlo method. Parametric sensitivity analyses are conducted to assess the sensitivity of the probabilistic event with respect to the distribution parameters of the basic random variables, such as the mean and standard deviation. The technique is a novel approach to probabilistic risk assessment, and can be used in situations when Monte Carlo analysis is computationally expensive, such as when the simulated risk is at the tail of the risk probability distribution.     

Scheduling with Sequencing Flexibility*

This study examines the effects of sequencing flexibility on the performance of rules used to schedule operations in manufacturing systems. The findings show that taking advantage of even low levels of sequencing flexibility in the set of operations required to do a job results in substantial improvement in the performance of scheduling rules with respect to mean flowtime. Differences in the mean flowtime measure for various rules also diminish significantly with increasing sequencing flexibility. Performance improvements additionally result for such due-date related performance measures as mean tardiness and the proportion of jobs tardy. At high levels of sequencing flexibility, some nonparametric scheduling rules outperform the shortest processing time rule in terms of the mean flowtime criterion. Rules based on job due dates also outperform rules based on operation milestones in terms of tardiness related criteria at high levels of sequencing flexibility. The implications of these findings for the design of manufacturing systems and product design are noted.     

A comparison of several approximations to the lead time demand distribution

Several distributions have been used for approximating the lead time demand distribution in inventory systems. We compare five distributions, the normal, the logistic, the lognormal, the gamma and the Weibull for obtaining the expected number of back orders, the reorder levels to have a given protection and the optimal order quantity, reorder levels in continuous review models of (Q, r) type. The normal and the logistic distributions are inadequate to represent the situations where the coefficient of variation (the ratio of the standard deviation to the mean) of the lead time demand distribution is large. The lognormal, the gamma and the Weibull distributions are versatile and adequate; however the lognormal seems to be a viable candidate because of its computational simplicity.     

REDUTEX: a hybrid push–pull production system approach for reliable delivery time in knitting SMEs

The textile sector is composed of small and medium enterprises (SMEs) worldwide. Nowadays there is a shortage of technological knowledge in SMEs. Lead time is a critical indicator in any productive company organisation. The aim of this research was to provide an approach, called REDUTEX, based on theoretical concepts of lean and synchronous manufacturing in order to help to understand the behaviour of SMEs and to improve the manufacturing process by reducing the customer lead times. The integration of these philosophies is the basis of REDUTEX; a hybrid push–pull production system approach to knitting SMEs. With this approach, it is possible to obtain a process reliability when the restrictive resource capacity (RRC) is identified, optimised and protected. By synchronising all activities to the rhythm of RRC, through a continuous flow, it is possible to obtain high-impact results through a dual automated system and product quality, through a visual control. REDUTEX uses a push system from the RRC to the location of the supermarket, where accumulated inventory may be distributed in the internal assembly department and external family workshops, making a pull system. Subsequent re-assembly processes use a push system until the end of the product. The stages of REDUTEX are explicitly described and applied to real data, so that the staff of SMEs can easily understand the behaviour of the process and implement it. One of the advantages of REDUTEX is that it does not need highly trained staff. The research methodology was conducted as a case of study in twelve SMEs and validated and implemented in three textile companies of the southern area of the state of Guanajuato in Mexico, obtaining reliable delivery times and very promising results.     

Exchange curves for fixing batch quantities

The problem considered is that of choosing batch quantities to minimize costs, subject to the constraints that neither overall set-up costs nor overall set-up time can be increased beyond certain limits. Theoretical and graphical solutions are obtained for two possible formulations of the problem, and a simple practical procedure is suggested.