Determination of economic order quantities (EOQ) in an integrated material flow system

The material flow system is the backbone of a manufacturing system as it provides both physical and operational structure. Each component (material handling, until load size, storage space, layout, etc) is a difficult problem to address on its own; however, it is imperative that components be addressed concurrently due to their interactions. This paper explores the relationships between the components in the material flow system with respect to determining the economic order quantity. This is in contrast to the traditional EOQ model, which considers only order cost, inventory cost, and demand, ignoring other material flow system issues. A multi-item economic order quantity (EOQ) model under a storage space limit is considered with respect to material handling equipment selection and requirements, unit load size, and flow path selection. The integrated material flow system problem is mathematically formulated as a large scale, nonlinear integer programming model and a heuristic solution procedure is developed. The impact of using an integrated approach to determine the EOQ is illustrated and solutions are compared to a lower bound. It is found that an integrated approach provides consistent and significant improvement in the overall solution quality.     

An integrated approach to the facilities and material handling system design

The facility layout problem involves the optimal location of manufacturing facilities into a workshop. The classical approach to the layout design is carried out in two separate steps: the first step is the construction of the block layout, i.e. the location of the departments into the workshop, and the second step is the design of the material handling system. The separate optimization of these two aspects of the problem leads to solutions that can be far from the total optimum. In this paper, an integrated approach to the facilities and material handling system design is proposed. Referring to a physical model, named the bay structure , and to a unidirectional AGV system, a genetic approach is proposed to individuate the locations of the departments, the positions of the pickup/delivery stations and the direction of the flow-path. The minimization of material handling cost is adopted as optimality criterion.     

Economic production quantity (EPQ) model with partial backordering and a discount for imperfect quality batches

Economic production quantity (EPQ) models are traditionally used in operations management. Despite the large number of papers that describe the models, the classic EPQ model does not consider either imperfect quality batches or shortages. However, some industries may be able to sell imperfect items for a lower price, reducing the total production cost. This paper proposes an EPQ model with partial backordering and discount for imperfect quality batches and an algorithm that returns optimal values for the problem. From a numerical example, it is possible to analyse how the changes in the variables affect each part of the total cost function, which provides a useful tool for strategic decision-making. We conclude that it is better to sell imperfect items as soon as possible because the savings in holding costs results in a total cost reduction. It is more profitable for the producer to have planned shortages considering that some costumers are willing to wait. Furthermore, the reduction of the goodwill cost does not necessarily reduce the total cost.     

An introduction to the segmented flow approach for discrete material flow systems

Due to increases in versatility and the complexity of demands in modern manufacturing systems a growing need has evolved t0 simplify the control of these systems while maintaining a high degree of efficiency and flexibility in operation. The segmented flow approach (SFT) suggested in this paper is a possible solution to these needs. This structure simplifies the control task by reducing the need for dispatching and by eliminating the need for routeing material handling devices and scheduling traffic at intersections. Each task involves only one material handling device and one possible route. This structure maintains a high degree of efficiency by operating material handling devices in a bidirectional mode and eliminates congestion and blocking by operating them on mutually exclusive tracks. This paper introduces a design procedure for an SFT implemented system using a minimum cost objective, and compares the throughput and time in system performance of this system to a conventional system and a tandem type system by means of simulation.     

An economic model for determining the optimal quality and process control policy in a queue-like production system

This paper interrelates and synthesizes the economic design of quality and process control policy and the management of a production system described in terms of an M/G/X queue. A mathematical model is developed to determine the optimal quality and process control policy when both the quality and quantity issues in the production system are considered. The optimal control policy is defined as the one that maximizes the expected profit per unit time over an infinite horizon. Hypothetical data is used to illustrate the impact of on-line control policies on the operating characteristics of the production process.

For a given control policy, it is shown that the expected profit per unit time of the production system can be increased by either improving the reliability of the production system, increasing the arrival rate of incoming jobs, increasing the system's processing rate, or shortening the system's shutdown time. The results also indicate that the larger the performance difference between the in-control and the out-of-control states, the greater the amount of effort should be involved in quality and process control. Finally, it is important for the capacity design of a production system to take into account the requirrments for both quality control and process adjustment.     

An approach to computer integrated production management

A new paradigm is proposed for the realization of computer integrated production management. Computer integrated manufacturing (CIM) can never be constructed just by combining the automated devices available at present, such as CAD, CAM, CAPP and MRP systems. To realize successful CIM, the automation of friendly communication between experts is required, which plays a most important role in the integration of the various functions of production management. This points to the importance of computer integrated production management. In order to confirm the validity of the paradigm proposed in this paper, a prototype in process planning has been developed which aims at integration with CAD.     

An integrated system for controlling shop loading and work flow

Effective management of loading and work flow is becoming increasingly important in manufacturing. However, research has not addressed the associated dynamic internal performance issues as effectively as possible. This paper investigates an integrated approach to input and shop floor control under conditions of controlled delivery performance. Several new mechanisms are developed, including a method of dynamically adjusting buffer sizes based on system loads. Lead time and several measures related to the level and distribution of work in the system are used to evaluate performance. Results show that performance can be improved by taking loading and work flow issues into consideration when input release, dispatching and buffer space decisions are being made.     

An integrated approach for production and distribution planning in supply chain management

Many firms have been trying to optimize their production and distribution systems separately, but using this approach limits any possible increase in profit. Thus, it is becoming more important to analyse these two systems simultaneously. This paper presents the solutions for integrated production and distribution planning and investigates the effectiveness of their integration through a computational study, in a multi-plant, multi-retailer, multi-item, and multi-period logistic environment where the objective is to maximize the total net profit. Computational results on test problems using the proposed heuristic confirm the substantial advantage of the integrated planning approach over the decoupled one. Sensitivity analysis on the input parameters indicates that, under the right conditions, the effectiveness of integrating production and distribution functions can be extremely high.     

An economic model for raw material selection

An economic model for raw material selection is presented and a case analysis is given. The model considers two decision factors: initial raw material cost and additional manufacturing costs incurred due to inappropriateness of raw material quality. This additional manufacturing cost may include items such as: extra operator cost, extra machine cost and extra quality cost.     

An integrated model for inventory and production planning in a two-stage hybrid production system

A two-stage hybrid flow-shop production system is considered. The first stage is a process production system and the second stage is a job-shop production system. The two stages are separated by an intermediate warehouse to introduce flexibility (some independence) in the planning of production at both stages. The inventory level at the warehouse should be optimized to provide a trade-off between the cost of carrying the inventory of the semi-finished products, the minimum batch size requirement in the first stage, and the required service level at the second stage. An integrated model for planning the production in these hybrid flow-shop production systems types is developed. The objectives of optimizing the production and inventory costs at the two stages of the system, including the warehouse, while satisfying customer demands, are considered. An algorithm to solve the suggested model is described in detail, and a solution is provided for a real world case, which has inspired the study. A computational study to measure the performance of the approach was also carried out and the results are reported.     

A compactly integrated flow cell with a chemiluminescent FIA system for determining lactate concentration in serum

We have fabricated an integrated flow cell as a total microanalysis system (microTAS). This flow cell (size, 15 x 20 mm; total inner volume, 12.2 microL) was designed for a rational analyzing system of lactate determination for serum. This cell was made by micromachining techniques and consisted of two hollows of a lactate oxidase (LOD) reactor and a mixing cell, a spiral groove, and three penetrated holes. To form the reactor and capillary, these patterns, etched on a silicon wafer, were attached to a glass plate by the anodic bonding method. A photodiode was put under part of the spiral capillary. The compactly accumulated devices were integrated into a flow injection analysis (FIA) system. In the flow cell, lactate was catalyzed to pyruvate and hydrogen peroxide at the LOD reactor; subsequently, hydrogen peroxide reacted with the luminol-ferricyanic reagent at the mixing cell. The resulting chemiluminescent light was detected by the photodiode. Using the miniaturized flow cell, the sample volume for one measurement was greatly reduced to 0.2 microL. The response to lactate was obtained within 30 s and was linear between 0.5 and 5.0 mM (4.5 and 45 mg/dL) lactate with excellent correlative variances of 3.2% (average of three measurements at 5.0 mM). For practical application, the lactate concentration in control human serum was determined using this system. The results showed a good correlation coefficient (r = 0.979) with the results obtained by the spectrophotometric reference method. No difference in sera (normal or pathological) was found. Consequently, this integrated flow cell shows potential as a clinical device for lactate determination in serum. In this article, the effect of the design on the chemiluminescent FIA system is also described.     

A new approach for determining the hidden material parameters of a honeycomb

An optimization method to obtain the cell wall properties of Nomex honeycomb material is presented. There, the outcomes of physical experiments and micromechanical simulations are compared in an effort to identify the geometric or/and material parameters for the best match. Only the cell wall thickness and Young’s modulus, called here as the hidden parameters, are used in the matching as the Young’s modulus is difficult measure reliably. The mean values and standard deviations of the geometric parameters of the cell structure model are obtained through image analysis. In the micromechanical model used, the cell walls are considered as linearly elastic Bernoulli beams. The optimum hidden parameter values for the Nomex case turn out not to be unique but they appear in a combination known as the bending stiffness.     

An inverse method for determining elastic material properties and a material interface

A numerical procedure which integrates optimization, finite element analysis and automatic finite element mesh generation is developed for solving a two-dimensional inverse/parameter estimation problem in solid mechanics. The problem consists of determining the location and size of a circular inclusion in a finite matrix and the elastic material properties of the inclusion and the matrix. Traction and displacement boundary conditions sufficient for solving a direct problem are applied to the boundary of the domain. In addition, displacements are measured at discrete points on the part of the boundary where the tractions are prescribed. The inverse problem is solved using a modified Levenberg-Marquardt method to match the measured displacements to a finite element model solution which depends on the unknown parameters. Numerical experiments are presented to show how different factors in the problem and the solution procedure influence the accuracy of the estimated parameters.     

An integrated fluorescence detection system in poly(dimethylsiloxane) for microfluidic applications

This paper describes a prototype of an integrated fluorescence detection system that uses a microavalanche photodiode (microAPD) as the photodetector for microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS). The prototype device consisted of a reusable detection system and a disposable microfluidic system that was fabricated using rapid prototyping. The first step of the procedure was the fabrication of microfluidic channels in PDMS and the encapsulation of a multimode optical fiber (100-microm core diameter) in the PDMS; the tip of the fiber was placed next to the side wall of one of the channels. The optical fiber was used to couple light into the microchannel for the excitation of fluorescent analytes. The photodetector, a prototype solid-state microAPD array, was embedded in a thick slab (1 cm) of PDMS. A thin (80 microm) colored polycarbonate filter was placed on the top of the embedded microAPD to absorb scattered excitation light before it reached the detector. The microAPD was placed below the microchannel and orthogonal to the axis of the optical fiber. The close proximity (approximately 200 microm) of the microAPD to the microchannel made it unnecessary to incorporate transfer optics; the pixel size of the microAPD (30 microm) matched the dimensions of the channels (50 microm). A blue light-emitting diode was used for fluorescence excitation. The microAPD was operated in Geiger mode to detect the fluorescence. The detection limit of the prototype (approximately 25 nM) was determined by finding the minimum detectable concentration of a solution of fluorescein. The device was used to detect the separation of a mixture of proteins and small molecules by capillary electrophoresis; the separation illustrated the suitability of this integrated fluorescence detection system for bioanalytical applications.     

An economic model for integrated APC and SPC control charts

As suggested by Box and Kramer [1] and others, it is possible to reduce both the special cause and common cause variations by applying Statistical Process Control (SPC) methods to monitor the output of an Automatic Process Control (APC) controlled process. In this paper, we develop an economic model for SPC monitoring of APC controlled processes. We also develop an economic loss-based criterion, the Average Quality Cost (AQC), to evaluate the performance of SPC charting methods. The AQC and the traditional average run length of three common SPC charts are investigated and compared.     

Design procedures and implementation of the segmented flow topology (SFT) for discrete material flow systems

In this paper, both the single pick-up and delivery station (SPDS) and the multiple pick-up and delivery station (MPDS) cases of the segmented flow topology (SFT) system configuration are presented. These system's configurations serve as the backbone of a heuristic design procedure for SFT. This design procedure consists of an upper and lower bound calculation and a search procedure that minimizes the total system cost (transportation, setting up pick-up and/or delivery stations, and material handling devices). Two examples of the implementation of the procedure are given.     

An economic model for optimizing the production life of measuring instruments

Translated from Izmeritel'naya Tekhnika, No. 1, pp. 58–59, January, 1991.