Clustering algorithms to optimize the tool handling system management in an FMS

Tool management is recognized as a critical issue in flexible manufacturing facilities management. This article addresses the issue of tool management in a flexible system installed in an avionics components factory. The system is composed of two machining centers equipped with local tool magazines of limited capacity. A tool handling system is in charge of tool movements between the tool room and the two machines. Each machine is able to perform any operation, provided that it is equipped with the suitable tool. In this kind of installation, tool allocation must be determined, and tool movements must be synchronized in order to minimize operating costs, or, equivalently, maximize the productivity of the system. We propose an approach to production planning based on a clustering algorithm, which takes into account the tool requirements of each part program in the production batch. We also propose two different heuristics for the scheduling problem. A case study was conducted on the facility mentioned above. Two conflicting objectives can be identified for this kind of production system: the reduction of tools to be shared among machines and the reduction of workload unbalance. The tests and comparison made demonstrate how the proposed procedure leads to superior results in terms of both objectives.     

Experimental investigation of an FMS due-date scheduling problem: Evaluation of machine and AGV scheduling rules

Although extensive research has been conducted to solve design and operational problems of automated manufacturing systems, many of the problems still remain unsolved. This article investigates the scheduling problems of flexible manufacturing systems (FMSs). Specifically, the relative performances of machine and automated guided vehicle (AGV) scheduling rules are analyzed against various due-date criteria. First, the relevant literature is briefly reviewed, and then the rules are tested under different experimental conditions by using a simulation model of an FMS. The sensitivity to AGV workload, buffer capacity, and processing-time distribution is also investigated to assess the robustness of the scheduling rules.     

A comparative study of FMS tool allocation and part type selection approaches for a varying part type mix

Hankins and Rovito (1984) examined the impact of different tool policies on cutting tool inventory levels and spindle utilization for a flexible manufacturing system (FMS). This study provides a broader perspective of the impact of tool allocation approaches on flow times, tardiness, percent of orders tardy, machine utilization, and robot utilization. Part type selection procedures have been suggested for the FMS prerelease planning problem. However, very little research has specifically evaluated the part type selection procedures across different tool allocation approaches. Also, with the exception of Stecke and Kim (1988, 1991) no other known study has provided any insights on what tool allocation approaches are appropriate when processing different mixes of part types. This research is devoted to addressing those issues. Three tool allocation approaches, three production scheduling rules, and three levels of part mix are evaluated in this study through a similation model of a flexible manufacturing system. The specific impacts of the tool approaches, their interaction effects with the part type selection rules, and their effectiveness at different part type mix levels are provided through the use of a regression metamodel.     

A mixed dispatching rule approach in FMS scheduling

Short-term scheduling in flexible manufacturing systems (FMSs) is a difficult problem because of the complexities and dynamic behavior of FMSs. To solve this problem, a dispatching rule approach is widely used. In this approach, however, a single dispatching rule is usually assigned for all machines in a system during a given scheduling interval. In this paper, a mixed dispatching rule which can assign a different dispatching rule for each machine is proposed. A search algorithm which selects an appropriate mixed dispatching rule using predictions based on discrete event simulation is developed for this approach. The search algorithm for the mixed dispatching rule is described in detail. The effectiveness (in meeting performance criteria) of the mixed dispatching rule and the efficiency of the search algorithm relative to exhaustive search (complete enumeration) is demonstrated on an FMS model. The mixed dispatching rule approach performs up to 15.9% better than the conventional approach, and is 4% better on average. The statistical significance of the results is dicussed.     

Matrotrophy in the cave molly: an unexpected provisioning strategy in an extreme environment

Maternal provisioning of animal embryos may be entirely through yolk deposited in the unfertilized egg (lecithotrophy) or may include post-fertilization nutrient transfer (matrotrophy) in varying degrees. Current theory suggests that the extent of post-fertilization provisioning is resource-dependent, with higher levels of matrotrophy being advantageous in more productive environments. In this study, we investigated post-fertilization embryo provisioning in a livebearing fish, Poecilia mexicana, from two different habitats (a toxic cave and a non-toxic surface habitat) that impose different energetic demands and therefore differ in resources available for reproduction. We predicted that fish in the benign habitat would be more matrotrophic than those from the toxic cave. We used two different techniques for this assay: (1) the matrotrophy-index analysis (MI) for field-collected fish and (2) both MI and radio-tracer assay for laboratory-reared females. According to the interpretation of the matrotrophy index, both populations are purely lecithotrophic, while the radio-tracer assay found females from both populations to actively transfer nutrients to developing embryos at approximately the same rate. Our results suggest that P. mexicana, which was traditionally classified as lecithotrophic, is capable of incipient matrotrophy, and that matrotrophy can contribute to embryo provisioning even in populations from resource-limited environments. Furthermore, the analysis of laboratory-reared animals provides evidence for a genetic component to the large offspring size in cave mollies, which had so far only been described from the field. Specifically, our results suggest matrotrophy occurs in species interpreted as lecithotrophic using the MI approach. Hence, to avoid misclassification, both techniques should ideally be employed in concert, rather than individually. Finally, our results provide further insights into the possible evolutionary pathway from lecithotrophic oviparity to matrotrophic viviparity.     

An Evaluative Study of Operation Grouping Policies in an FMS

The increased use of flexible manufacturing systems to provide customers with diversified products efficiently has created a significant set of operational challenges for managers. This technology poses a number of decision problems that need to be solved by researchers and practitioners. In the literature, there have been a number of attempts to solve design and operational problems. Special attention has been given to machine loading problems, which involve the assignment of job operations and allocation of tools and resources to optimize specific measures of productivity. Most existing studies focus on modeling the problem and developing heuristics in order to optimize certain performance metrics rather than on understanding the problem and the interaction between the different factors in the system. The objective of this paper is to study the machine loading problem. More specifically, we compare operation aggregation and disaggregation policies in a random flexible manufacturing system (FMS) and analyze its interaction with other factors such as routing flexibility, sequencing flexibility, machine load, buffer capacity, and alternative processing-time ratio. For this purpose, a simulation study is conducted and the results are analyzed by statistical methods. The analysis of results highlights the important factors and their levels that could yield near-optimal system performance.     

A new hypothesis on cell provisioning in solitary wasps

Like many other eumenid wasps, Pachodynerus nasidens (Latr.) generally stores more provisions in female–producing cells than in male–producing cells. According to the proposed hypothesis the provisioning of more or less food is determined by the variation in the time available for storing; this in turn, is caused by the slower or more rapid development respectively of female or male eggs.     

A case study in FMS production planning and dispatching

The speedy development and extensive application of computers have helped play a significant role in a new technological revolution. The importance of FMS flexibility in producing a variety of products and adapting rapidly to customer requirements makes FMSs attractive. Further, FMSs are most appropriate for largevariety and medium- to high-volume production environments. However, the module of the FMS production planning system is not perfect. This paper focuses on a new scheme for FMS production planning and dispatching under the realistic assumptions promoted by a particular flexible manufacturing factory. Some practical constraints such as fixture uniqueness, limited tool magazine capacity, and a given number of pallets are considered. The simulation results indicate that the scheme provides a good production plan, according to the short-term plans from the MIS Department. Some conclusions are drawn and a discussion is presented.     

XPN-FMS: A CAD tool for FMS modeling,analysis, animation,and simulation using Petri nets and X window

Flexible Services and Manufacturing Journal - We propose a CAD tool, XPN-FMS, which is primarily based on a unique Petri net (PN) synthesis method, called the knitting technique, developed by the...     

Laboratory observation of siblicide with hatching asynchrony in an insect with parental provisioning

We report laboratory observation of siblicide with hatching asynchrony in the passalid beetle Cylindrocaulus patalis. Parents construct a breeding gallery in rotten logs and show complex care of offspring, including provisioning. Clutch sizes are extremely small, and only a single offspring is raised in a colony in each breeding season. We introduced field-collected colonies into an artificial gallery and recorded the behaviour of colony members. Eggs hatched at 2- to 10-day intervals in each colony. Fatal fighting invariably occurred among the larvae soon after hatching of the junior larva, and a single larva, usually the senior one, survived.     

A truthful online mechanism for virtual machine provisioning and allocation in clouds

We address the problem of online virtual machine (VM) provisioning and allocation with multiple types of resources. Formulating this problem in an auction-based setting, we propose an accurate mathematical model incorporating the ability to preempt and resume a given task for the sake of best overall use of resources. Our objective is to efficiently provide and allocate multiple VMs to maximize social welfare and encourage users to declare truthful requests. We first design an offline optimal mechanism based on the VCG mechanism; this mechanism has full knowledge of all users and offers ideal solutions. We also design an online greedy mechanism that considers only current knowledge while offering near-optimal solutions instead. Our proposed greedy mechanism consists of winner determination and payment algorithms. Furthermore, we show that the winner determination algorithm is monotonic and that the payment algorithm implements the critical payment. Both our allocation methods offer incentives to users providing true values for the sake of obtaining the best utility. We performed extensive experiments to investigate the performance of our proposed greedy mechanism compared to the optimal mechanism. Experimental results demonstrate that our proposed greedy mechanism obtains near-optimal solutions in a reasonable time.

     

The behavioural ecology of provisioning in birds

Ydenberg, R. 2000. The behavioural ecology of provisioning in birds. Ostrich 71 (1): 361.

In this talk I outline the idea of provisioning, stressing the difference between feeding and delivery. Foraging studies have just begun to recognise this distinction, and to explore some of its implications for behaviour. I outline a basic model of provisioning, based on central place foraging, in which the forager must spend some extra time on each excursion to gather enough energy to cover the excursion's energetic costs. I describe studies of provisioning pertinent to this framework, and go on to consider risk-sensitive provisioning, the role of predation danger in provisioning, and the question of how hard provisioners should work.     

Analytical models for FMS design optimization: A survey

This paper surveys the analytical methods that have been developed for optimizing the design of flexible manufacturing systems. A classification of the design issues into six groups is proposed first. The two main mathematical tools used for performance analysis are presented briefly. Then, the literature is analyzed critically according to the problem classification given. Suggestions for further work within each area are given throughout the paper and some general remarks concerning the whole field are finally made.     

Experimental provisioning increases play in free-ranging meerkats

The sensitivity of play to variations in food availability has been cited as evidence of the costliness of play, since energetically stressed animals dispense with costly behaviours. However, the causality of the relationship between nutrition and play has not been adequately tested. Using weight gain as a measure of food intake, we documented the food consumption of free-ranging meerkat, Suricata suricatta, pups and found that long-term nutritional status (weight gain over a 6-week period) was positively correlated with rates of play. We confirmed the causality of this relationship by conducting long-term (4-8 weeks) provisioning experiments that raised the nutritional status of experimental pups, subadults and adults. Experimental animals more than doubled their rate of play compared with their nonprovisioned controls. Short-term variations in food consumption (daily weight gain) were not correlated with subsequent rates of play, and we used a short-term feeding experiment to document the transitory effects of hunger satiation. We established that an increase in available energy contributed to the increase in rates of play, rather than the animals simply having more time available to play as a result of being released from the constraints of foraging. We conclude that play in meerkats was energetically costly, and must be adaptive given that the cost of play to juveniles (in terms of future reproductive success) was potentially high. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Iterative screening LCA in an eco-design tool

A screening and simplified LCA method, is essential necessary to include environmental aspects in the stage of Research and Development (R&D) of products and processes. An interactive, iterative and integrative eco-design tool using the top-down approach in the identification of advanced materials is being developed in a joint project performed by six research institutes. The principles and methods as well as some examples for the validation of the screening LCA as well as its application in eco-design in case studies are presented in this article.     

Immunomodulators as an antimicrobial tool

The spectrum of infectious diseases has shifted in the past 50 years to include those caused by microbes that cause disease predominantly in immunocompromised individuals. This phenomenon has underscored the dependence of microbial virulence on the immune status of the host. The limited efficacy of the available antimicrobial armamentarium in immunocompromised individuals, combined with increasing resistance to these agents, has led to an urgent need for new therapies for infectious diseases. Immunomodulation represents a novel approach to antimicrobial therapy that depends on bolstering host immunity, rather than direct antimicrobial activity. Immunomodulators can be divided into those that are specific to pathogens (pathogen-specific) and those that are not specific to pathogens (non-specific). However, to date only a few immunomodulators have been evaluated for their efficacy as antimicrobial tools.