Moshe Eben-Chaime

How far should JIT vendor–buyer relationships go?

Abstract In pull production management systems such as JIT, deliveries must be made on an as-needed basis only, and production begins only when requested. It is supposed to match customer demand, i.e., producing only enough to replenish what the customer has used or sold. In this work, we argue that there should be a certain degree of independence between successive links of the supply chain, to allow flexibility in production management in individual links. We attempt to identify the degree of independence and level of flexibility in terms of lot sizing and delivery scheduling in a single-vendor–single-buyer system. Toward this aim, appropriate two-sided vendor–buyer inventory–production models are formulated, some interesting conclusions from their analysis are drawn, and a numerical study, which compares relevant policies, is discussed. It shows that imposing a lot-for-lot production on the JIT supplier is strikingly un-economical. On the other hand, delivery on demand can be met without intervening in the suppliers operations, and where deviation from the optimal of the resulting joint total costs is tolerable.

Operations sequencing in automated warehousing systems

The block sequencing strategy, where retrievals are sequenced and executed in blocks, is commonly assumed in many works on operations management in automated warehousing systems. The nearest neighbour heuristic is a popular sequencing method. In this work, the destructive effects of block sequencing on the systems performance: waiting times and queue length, in a non-deterministic environment, is demonstrated. Dynamic application of the nearest neighbour as a dispatching rule is proposed as an alternative. The performance level of the dispatching nearest neighbour rule is surprisingly high

Capacitated location-allocation problems on a line

For economic and other reasons, distribution networks are often constructed in hierarchies, where, due to high costs, high-level distribution channels are built in straight lines from which low-level channel branch. Branching facilities, too, may incur high costs and thus, their number, locations along the lines, and allocation of destinations to them are important components in system design, which can be accomplished by solving a series of capacitated location-allocation problems on a line. This problem is studied here and its properties are discussed, and appropriate mathematical optimization models formulated and their properties and complexity are also considered. Heuristic solution schemes and lower bounds on objective values are proposed for the models. The efficiency and effectiveness of these schemes are evaluated and more insight into the models is gained through a numerical study. The major conclusion is that the hierarchical structure considered is highly restrictive and imposes high costs. Therefore, its use must be properly justified.

Optimizing desalinated sea water blending with other sources to meet magnesium requirements for potable and irrigation waters

Sea water desalination provides fresh water that typically lacks minerals essential to human health and to agricultural productivity. Thus the rising proportion of desalinated sea water consumed by both the domestic and agricultural sectors constitutes a public health risk. Research on low-magnesium water irrigation showed that crops developed magnesium deficiency symptoms that could lead to plant death, and tomato yields were reduced by 10-15%. The World Health Organization (WHO) reported on a relationship between sudden cardiac death rates and magnesium intake deficits. An optimization model, developed and tested to provide recommendations for Water Distribution System (WDS) quality control in terms of meeting optimal water quality requirements, was run in computational experiments based on an actual regional WDS. The expected magnesium deficit due to the operation of a large Sea Water Desalination Plant (SWDP) was simulated, and an optimal operation policy, in which remineralization at the SWDP was combined with blending desalinated and natural water to achieve the required quality, was generated. The effects of remineralization costs and WDS physical layout on the optimal policy were examined by sensitivity analysis. As part of the sensitivity blending natural and desalinated water near the treatment plants will be feasible up to 16.2 US cents/m(3), considering all expenses. Additional chemical injection was used to meet quality criteria when blending was not feasible.

Operations management of multiple machine automatic warehousing systems

Abstract Most operations management studies of automatic warehousing systems investigate single-machine systems in isolation of the total system which includes other related functions. In this paper, we overcome these limitations and investigate an integrative model of a warehouse, containing several storage/retrieval (S/R) machines, which is integrated within a total system. Moreover, whereas performance was previously analyzed, mostly, in terms of throughput and travel times of the S/R machines, this paper considers additional performance measures such as response times, queue lengths, and utilization of the S/R machines. A simulation of the integrative model is used to study the effects of various operations management tactics on performance. The results demonstrate that economic gains are possible while hardly sacrificing performance. The gains result from decreasing the number of S/R machines — up to 20%, and reducing building space as a consequence of shorter queues.

An integrative model for automatic warehousing systems

Automatic warehouses, for the most part, have been studied in isolation. This paper departs from this approach by proposing an integrative model in which warehouse activities interact with other functions of the total system. The model has been simulated under three modes of operation: Single command, dual command (DC), and hybrid. Simulation results confirm that the length of stay of unit loads outside the warehouse affects performance and also suggests that, under the DC mode, the warehouse may lose stability. Hence, the hybrid mode is proposed as an alternative. The hybrid mode outperforms the DC mode on most performance measures, except that the length of the storage queue at high throughput levels is longer. Finally, saving opportunities, via a reduction in the number of storage/ retrieval machines, are discussed.

A note on: the economic effects of quality improvements

‘If we have quality problems and therefore a defect rate greater than zero, the total costs of production actually decrease.’ Furthermore, ‘although at first this might sound surprising, the decreasing total costs of production for poorer quality levels are to be expected.’ This was concluded in a paper published in this journal. In this note it is argued that this conclusion is misleading in suggesting that poor quality might be of economical advantage. The contrary is demonstrated – production costs actually grow dramatically due to poor quality.

Circuit Partitioning Via Set Partitioning and Column Generation

In this paper, a new application of the methodology of set partitioning formulation augmented with heuristic column generation is presented. An efficient method for the partitioning of large-scale electronic circuits is developed based on this methodology. Circuit partitioning constitutes a major step of the physical design phase of electronic circuits, the fundamental components of electronic products. The major advantage of the scheme presented here is to provide a framework for an effective integration of most existing circuit partitioning methods. Another attractive feature of the current approach is the incorporation of interactive optimization: The circuit designer controls the operation of the procedure and enhances its performance by suggesting and/or requiring specific partitions. Following the development of the model, the solution approach is presented and computational results are reported for several benchmark circuits.

The queuing theory machine interference model: use and application

Abstract This paper aims at making the queuing theory machine interference model a usable tool for process designers, production managers, and others who face decisions regarding the number of machines and the size of crew to operate/maintain them. The model is presented conceptually and compared with other existing models. Next, the model is analysed, and parameter calculations are detailed: a ready-to-implement procedure is given to carry out these calculations. Finally, the use of the model and its application in the work-study context are illustrated by examples.

Hand-held computers to increase accuracy and productivity in agricultural work study

Purpose - – Labor is the largest single cost contributor in agriculture. Accurate estimation of labor requirements is, thus, a key to cost reduction. Work measurement is the professional discipline for this type of estimations, in the industrial engineering domain. Horticulture, however, lays a substantial barrier to work and, thus, to work measurement. Till harvesting, its products – fruits/flowers, are in fixed positions, and for all tasks the workers have to arrive at the plant. The purpose of this paper is to develop, test and analyze a system to perform horticultural work study in agricultural environments in order to accurately estimate the required amount of labor for each activity and to improve productivity. Design/methodology/approach - – In this paper, the development of an advanced system for work study on a hand-held computer (HHC) platform for horticultural work measurement is presented and an experimental study was conducted. The methodology consists of characteristics of the system platform including hardware, interface and software, development of a dedicated measuring software, a controlled experiment in agricultural environment and a statistical analysis. Findings - – The study shows that a single surveyor who uses traditional tools is subject to measurement errors, which can be reduced only with the assistance of a second surveyor. The study further shows that the HHC platform enables to avoid this second surveyor – a single surveyor who uses the HHC platform performs as accurate as two surveyors who use traditional tools. Of course, being computers, the HHC platform maintains the advantage of error free data transfer, in practically negligible time. Originality/value - – This paper presents a unique approach to perform work study in agricultural environment and contributes to minimize the errors accumulated in the process and the manpower required to perform the measurements.