A continuous model for supply planning of assembly systems with stochastic component procurement times

This paper studies a customized product assembly scenario where some components cannot be stocked due to high component cost and risk. We consider the case where these key components are ordered after a demand has been registered with a promised delivery date. Component lead-times are stochastic and associated distribution function is known in advance. The objective is to determine the ordering time for each component such as to minimize the sum of expected holding and backlogging costs. An approach to solve this problem is proposed and the algorithm is tested on a randomly generated data set.     

Design of the optimal feeding policy in an assembly system

This paper describes an innovative and integrated approach to component management optimization within a production/assembly system. In a mixed-models assembly process the handling of parts and components for each work station represents a substantial variable that can greatly affect job duration and efficiency. This paper is strictly related to Assembly to Order/Manufacturing to Order (ATO and MTO) systems, where lead time has to be very short and flexibility is at its maximum level. In Assembly to Order (ATO) or Make to Order (MTO) systems, the production is increasingly getting more customized in response to the demand, thanks to the progresses reached in both manufacturing and information technologies. It is becoming increasingly possible to assemble or make products specifically in response to the requests of either end customers or retailers. As a consequence of such customization, the design of the whole system must take into direct account several elements: parts warehouses location, feeding policies and feeding systems. In some cases the collection of parts and components required picking activities, in other the movement of entire units load.In several instances experts have analyzed the problems about material centralization/decentralization, storage policies and assembly feeding problem in different and independent ways, while the problem needs an integrated approach. While many researches regarding components allocation problems in ATO and MTO systems, did not consider feeding policies, material picking, packing activities and vehicles optimization, this paper cover focuses on filling such gap using an integrated framework that considers both aspects of the problem: the centralization/decentralization of components in order to minimize the total storage costs and the right feeding policies.Feeding problems in assembly lines are some of the most important aspects to consider during the analysis and design of an assembly system, to allow the maximization of efficiency and flexibility. To reach such goals, a multi-factorial analysis has been carried out during this experiment and will validate the introduced framework. An industrial application of the introduced framework is illustrated to explain its real significant production implication.     

Optimal time phasing and periodicity for MRP with POQ policy

This paper deals with component supply planning for assembly systems where several types of components are ordered from external suppliers to produce a single type of finished product. Actual component lead times are often different from those contracted because of random delays. An MRP approach with periodic order quantity (POQ) policy is used for the supply planning of components. Our aim is to find the optimal values of the order periodicity and planned lead times at the offsetting step of the MRP procedure. The goal is to minimise the sum of the average component holding, finished product backlogging and setup costs. Several theoretical properties of the objective function are proven and an efficient optimization algorithm is developed. The proofs of the explicit form and properties of the objective function as well as the development of the optimization algorithm occupy a large portion of this paper. The method developed can be used for the optimization of time phasing and periodicity for such an MRP system under lead time uncertainties.     

摩托车单向器自动装配机气动系统设计

针对当前摩托车单向器组件主要采用手工装配、装配效率低、随机性大、无法对装配过程实现有效管理控制的情况,为了易于对零件装配过程进行实时监测和提高生产效率,开发了一种智能摩托车单向器自动装配机。介绍了摩托车单向器自动装配机的上料系统、装配系统、检测系统和落料系统的机械结构,重点阐述了设备的气动系统设计,并进行了实验研究。结果表明,该设备可实现组成单向器的5种零件自动上料和装配,同时降低了操作人员的劳动强度,生产效率提高约50%。其气动系统噪音小、工作可靠,可应用于摩托车单向器的大批量生产。研究结果可为其他相似异形零件自动装配机的开发提供参考。     

The development from prototype construction to workshop production of an advanced underground locomotive: A case study

This paper reports on the problems encountered and their subsequent solution during the development and construction of an advanced locomotive from prototype to full production assembly. A fleet of these locomotives are to work in the UK National Coal Board's (NCB) Selby coalfield. In order to ensure that all the information was accurately recorded and could be applied to a reasonably precise point in the development process, visits were made to the company at intervals of about two weeks. In developing products of this nature a strongproblem solving capacity is a necessity and in the main it was found that engineering and theoretical design problems were solved quickly and once solved did not recur on subsequent units. Strong links between specialist suppliers and customers are vital, since components will often be used in unfamiliar applications and the customer may have to spend time carrying out applied development of suppliers' components. The development and production of the locomotive would have been aided by the NCB providing more accurate specifications, giving an indication of future volume requirements and being better prepared to site test the prototype after its delivery.     

Integrated inventory models with controllable lead time and backorder discount considerations

Many companies use time as a means of differentiating themselves in the marketplace. In many literatures, the controllable lead time is regarded as a decision variable and decomposed into several components, each having a crashing cost function for the respective reduced lead time. When an item is out of stock, the loyal, patient and captive customers will wait until the outstanding orders arrive and are served from them. To compensate for the inconvenience of backordering and to secure orders, the supplier may offer a price discount on the stockout item. In this paper, an integrated inventory system in which shortage is allowed and both lead time and backordering are negotiable is investigated. The lead time crashing cost is represented as a function of reduced lead time and the quantities in the orders. There are two inventory models proposed in the paper, one with normally distributed demand, and another with generally distributed demand.     

Optimal safety stock levels of subassemblies and manufacturing components

In order to control the time to market and manufacturing costs, companies produce and purchase many parts and components before receiving customer orders. Consequently, demand forecasting is a critical decision process. Using modular product design and super bills of materials are two effective strategies for developing a reliable demand forecasting process. They reduce the probability of stockouts in diversified production contexts. Furthermore, managing and controlling safety stocks for pre-assembled modules provide an effective solution to the problem of minimizing the effects of forecast errors. This paper develops, evaluates, and applies innovative cost-based analytical models so that the optimal safety stock of modular subassemblies and components in assembly to order and manufacturing to order systems, respectively, can be rapidly quantified. The implementation of the proposed models in two industrial case applications demonstrates that they significantly reduce the safety stock inventory levels and the global logistical cost.     

The benefits and potential costs of a digital economy

Computerisation, or more generally, digitisation, of an economy has brought about substantial benefits. It has greatly increased productivity. It has significantly advanced both the pace and the scope of economic globalisation and international division of labour. However, digitisation can also enable, through the collection and assembly of individual-consumer-specific information, price discrimination by a seller of a product, which results in the consumer surplus of the buyer being appropriated. Moreover, the widespread use of email and other message application platforms operated by profit-making private enterprises also facilitates the collection and assembly of vast amounts of individual-consumer-specific private information without the explicit and specific consent of the individual consumer, information which can be used to his or her detriment. Possible remedial measures are proposed.     

Questions about Change over Time in Cross-Cultural Organizational Research

Conceptually, the phenomena of interest in many organizational research questions are in fact about changes and processes that unfold in various ways over time. Unfortunately, longitudinal studies that explicitly assess change over time is generally lacking in organizational research and virtually absent in cross-cultural organizational research. The large majority of the literature on cross-cultural measurement in organizational research is focused exclusively on cross-sectional data, addressing cross-cultural differences in measurement and constructs without examining the temporal dimension of measurement and constructs. This article explicates nine fundamental questions about change over time and applies them to the study of changes over time in cross-cultural organizational research.     

Measuring the efficiency of assembled printed circuit boards with undesirable outputs using data envelopment analysis

The printed circuit board (PCB) assembling production process is generally optimized to ensure very low levels of errors (defects) so as to produce the higher quality product. The evaluation of efficiency of different types of PCB (cards) could help the management in identifying the quality of assembly process to work out appropriate interventions to prevent failures. This study uses the technique of data envelopment analysis to assess the efficiency of cards across all assembly units as well as within its respective assembly unit in the presence of undesirable outputs under the assumption of weak disposability. In our case, the three types of errors, viz., machine error, manual errors and other errors that occur in the defective assembled PCBs are considered as the undesirable outputs. In-depth analysis has been carried out through jackknifing analysis to check the robustness of DEA efficiency scores. The best practice group of cards for each inefficient card has been identified which eventually facilitate the management to derive the level of undesirable outputs to be reduced and desirable output to be improved so as to achieve the level of efficiency at par with its practice group.     

The MPS parameterization under lead time uncertainty

The supply planning of assembly systems under lead times uncertainty is studied. The used criteria is the sum of the average holding cost for the components, the average backlogging cost for the finished product, and the setup cost. The decision variables are the planned lead times of components and the periodic ordering quantity. A new generalized Newsboy model gives the optimal solution under the assumption that the lead times of the different types of components follow the same distribution probability, and that the holding costs per period of the ordered quantities are the same.     

基于BIM的装配式建筑施工场地布置研究

考虑预制构件的布置和安全问题对施工现场布局的影响,通过建立预制建筑施工现场BIM模型,找出施工过程存在的碰撞冲突,减少不必要的二次搬运。在此基础上根据施工效率、成本优化、安全和可持续目标形成多个施工场地布置方案,通过层次分析与模糊综合评价相结合的方法评选出最优场地布置方案,为提高装配式建筑场地布置水平提供有效借鉴。     

Heuristics for operational fixed job scheduling problems with working and spread time constraints

Operational fixed job scheduling problems select a set of jobs having fixed ready and processing times and schedule the selected jobs on parallel machines so as to maximize the total weight. In this study, we consider working time and spread time constrained versions of the operational fixed job scheduling problems. The working time constraints limit the total processing load on each machine. The spread time constraints limit the time between the start of the first job and the finish of the last job on each machine. For the working time constrained problem, we present a filtered beam search algorithm that evaluates the promising nodes of the branch and bound tree. For the spread time constrained problem we propose a two phase algorithm that defines the promising sets for the first jobs and finds a solution for each promising set. The results of our computational tests reveal that our heuristic algorithms perform very well in terms of both solution quality and time.     

Impact evaluation of child nutrition programmes

A review of current practices and recent developments regarding impact evaluation of nutrition programs for preschool children in developing countries is presented. Nutrition education, food suplementation, and nutrition rehabilitation, the 3 major components of intervention in child nutrition, generally focus on food consumption and are directed at individual cases. Impact evaluations are generally confronted with situations where different programs operate in a variety of cultural settings, where the effects of the interventions are small, and where methodological difficulties usually weaken the evaluations. Definitions of impact evaluation generally include reference to the measurement of program effects by "objective" and "systematic" means. The 1st refers to the use of reliable measuring instruments with standard routines; the 2nd to the comparison of different groups of recipients (and nonrecipients) in such a way that it reveals the impact of the intervention, irrespective of other factors that influence child nutrition. Impact evaluation has 2 major components the indicators selected to reflect program impact, and the design used for the comparison of different groups of recipients. Both the interventions and evaluations have to operate under restricting conditions, and different strategies to accomodate this situation are mentioned. It is argued that the contribution of evaluation is not so much in the nature of being a final arbiter, but rather in the nature of helping to seek the optimal combination of local conditions and type of assistance offered.     

An efficient hybrid genetic algorithm for the multi-product multi-period inventory routing problem

The inventory routing problem (IRP) addressed in this study is a many-to-one distribution network consisting of an assembly plant and many distinct suppliers where each supplies a distinct product. We consider a finite horizon, multi-periods, multi-suppliers and multi-products where a fleet of capacitated homogeneous vehicles, housed at a depot, transport products from the suppliers to meet the demand specified by the assembly plant in each period. The demand for each product is deterministic and time varying. A mathematical formulation of the problem is given and CPLEX 9.1 is run for a finite amount of time to obtain lower and upper bounds. A hybrid genetic algorithm, which is based on the allocation first route second strategy and which considers both the inventory and the transportation costs, is proposed. In addition to a new set of crossover and mutation operators, we also introduce two new chromosome representations. Several medium and small sized problems are also constructed and added to the existing data sets to show the effectiveness of the proposed approach.     

A simple and accurate approximation for the order fill rates in lost-sales Assemble-to-Order systems

In this paper we consider an Assemble-to-Order system with multiple end-products. Demands for an end-product follow a Poisson process and each end-product requires a fixed set of components. We are interested in the order fill rates, i.e., the percentage of demands for which all requested components are available from stock. Requested components that are not in stock are supplied via an emergency shipment and the demand for these components is lost for the stockpoint under consideration. The component lead times are deterministic and may differ per component. The inventory of each component is controlled via a base stock policy. We show that the system decomposes into subsystems which can be analyzed independently. Each subsystem can be approximated by a subsystem with exponentially distributed lead times, for which an exact evaluation exists. For big subsystems, however, this method requires considerable computational effort. Therefore, we formulate a simple and accurate approximation for the order fill rates. Our approximation uses two estimates of which one generally gives an underestimation of the order fill rate and the other one an overestimation. A weighing factor is used to combine these two estimates into an approximate value. The approximation is shown to be accurate and requires little computational effort.     

Time compression (dis)economies: An empirical analysis

Research Summary: To investigate time compression diseconomies (TCD), this study estimated time–cost elasticities using 459 oil and gas global investment projects (1997–2010). Results show that the average cost of accelerating investments is negative: a firm could cut $6.3 million in costs of a single project by accumulating asset stocks 1 month faster. About 88% of the projects exhibit negative time–cost elasticities with over 39% of unrealized economies of time compression. Only 12% of the projects are subject to TCD. These time inefficiencies or frictions do not negate the existence of TCD, but suggest they are less prevalent than assumed in the literature. Management experience, R&D investment, firm size, economic development, and political stability are shown to be associated with greater time compression efficiency. Managerial Summary: How fast should firms invest? The conventional view is that acceleration increases market revenues but also inflates costs. However, there is no recent empirical evidence of this tradeoff. Our article systematically investigates the costs of compressing time in investment projects. Results show that most firms in the oil and gas industry are significantly time inefficient in their operations. Specifically, by accelerating investments, firms would also substantially decrease costs. We estimate the magnitude of these time inefficiencies for specific oil and gas industries and firms and study which strategies might mitigate this problem. This fine‐grained analysis should help firms assess their financial incentives to accelerate projects and prove informative to stock market analysts’ valuations of firm investment timing.     

基于主成分分析的我国房地产业周期波动研究

运用主成分分析法构造房地产业景气综合指标（主成分）,第一主成分贡献率为0．96829,说明它保留了原始变量96．829％的信息,在房地产业周期波动分析中就可以把其他主成分舍弃。第一主成分与原始变量的相关系数p称为因子负荷量为0．70632,表明第一主成分反映了商品房销售额指标70．632％的信息。选择商品房销售额指标作为代表,来研究房地产业周期变动的特征和规律性是可行的。运用时间序列加法模型和乘法模型分析了我国房地产业周期波动的特征和规律性,我国房地产业循环波动的周期为12-13年。     

Ant colony optimization for the single model U-type assembly line balancing problem

An assembly line is a production line in which units move continuously through a sequence of stations. The assembly line balancing problem is defined as the allocation of tasks to an ordered sequence of stations subject to precedence constraints with the objective of optimizing a performance measure. In this paper, we propose ant colony algorithms to solve the single-model U-type assembly line balancing problem. We conduct an extensive experimental study in which the performance of the proposed algorithm is compared against best known algorithms reported in the literature. The results indicate that the proposed algorithms display very competitive performance against them.     

基于网络DEA交叉效率模型的我国商业银行效率评价研究

本文从商业银行的实际情况出发，将其经营过程划分为资金筹措与资金运营两个阶段。结合网络DEA与权重平衡交叉效率思想，并利用熵值法处理交叉效率的集结问题，构建了商业银行各子系统及链形系统的交叉效率评价模型。将上述模型应用于我国16家商业银行的效率评价，发现这16家商业银行的效率普遍不高，且城市商业银行的系统平均交叉效率高于国有银行，国有银行的系统平均交叉效率略高于股份制银行。