Classical approaches to layout design problem tend to maximise the efficiency of layout, measured by the handling cost related to the interdepartmental flow and to the distance among the departments. ...However, the actual problem involves several conflicting objectives hence requiring a multi-objective formulation. Multi-objective approaches, recently proposed, in most cases lead to the maximisation of a weighted sum of score functions. The poor practicability of such an approach is due to the difficulty of normalising these functions and of quantifying the weights. In this paper, this difficulty is overcome by approaching the problem in two subsequent steps: in the first step, the Pareto-optimal solutions are determined by employing a multi-objective constrained genetic algorithm and the subsequent selection of the optimal solution is carried out by means of the multi-criteria decision-making procedure Electre. This procedure allows the decision maker to express his preferences on the basis of the knowledge of candidate solution set. Quantitative (handling cost) and qualitative (adjacency and distance requests between departments) objectives are considered referring to a bay structure-based layout model, that allows to take into account also practical constraints such as the aspect ratio of departments. Results obtained confirm the effectiveness of the proposed procedure as a practicable support tool for layout designers.
The quality of a product greatly depends on the quality of its components. This requires that manufacturing specifications have to be met in the manufacturing environment and as a consequence ...inspection stations are present in many manufacturing systems and inspection policies must be adopted. One problem, which has been widely investigated, concerns the detection of the inspection points in the hypothesis that the action to be taken is known when a defective part is detected. If different jobs are to be produced, then operation scheduling becomes yet another complex problem needing to be solved. And while the problem of scheduling has received a great amount of attention from researchers, to our knowledge the interaction between the two problems has not been treated in job-shop environment. In the present paper three different control policies are preliminarily examined: they differ both in terms of the number of operations that are inspected, and with regard to the type of intervention carried out on detection of a defect. Each control policy affects the optimal inspection locations, which, in their turn, influence operation scheduling. As will be shown in the present paper, a sequential decision process based on separate optimization steps can lead to very poor final results. For this reason, an integrated approach is proposed, in an attempt to identify an optimal solution using a genetic algorithm.
The problem of facility layout design is discussed, taking into account the uncertainty of production scenarios and the finite production capacity of the departments. The uncertain production demand ...is modelled by a fuzzy number, and constrained arithmetic operators are used in order to calculate the fuzzy material handling costs. By using a ranking criterion, the layout that represents the minimum fuzzy cost is selected. A flexible bay structure is adopted as a physical model of the system while an effective genetic algorithm is implemented to search for a near optimal solution in a fuzzy contest. Constraints on the aspect ratio of the departments are taken into account using a penalty function introduced into the fitness function of the genetic algorithm. The efficiency of the genetic algorithm proposed is tested in a deterministic context and the possibility of applying the fuzzy approach to a medium-large layout problem is explored. PUBLICATION ABSTRACT
Transit services quality has long been recognized as an important factor in influencing travellers' behaviour and a terminal's architectural quality is certainly part of it. As a matter of fact a ...number of transit promotion policies explicitly based on qualitative factors and specifically high architectural standards are being adopted in designing new railways stations. Several examples of remarkable architecture applied to railways stations can be found all round the world. The aim of this paper is to estimate and compare the \"catchment area" of both traditional metro stations and high architectural quality ones, taking advantage of the metro Line 1 in Naples (Italy), also called \"Metro dell'arte" (art in the Metro). This metro line is a high quality line where many international level architects were involved to ensure high aesthetic quality standards for the new stations. The originality of the experiment field is that the rail network including both traditional and new metro lines (and stations) connect homogeneous areas of the city, either for transport system accessibility (same service frequency and same mode/service alternative) and for socio-economic aspects (same population density, income and employment, average age etc.). Graham's scan algorithm was used to estimate the catchment areas of the Naples metro stations through transportation surveys conducted in 2013. The estimation results show that the \"catchment area" of the high quality station is greater than a traditional one, of approximately 99%. These results suggest that high architectural standards for railways stations should be considered as an explicit design variable in transportation planning.
Robots are being used more and more extensively as material-handling systems for automated manufacturing systems. This is especially true for dual-gripper robots whose in-process buffer (the robot's ...second gripper) constitutes a further element of flexibility. When the number of stations to be served is high and the set of activities the robot must execute is great, the system throughput may depend on robot capability rather than on process times. In such conditions, the use of several robots leads to an increase in system productivity. Obviously, the design and the management of such a handling system becomes more complex: the minimum number of robots required, the work stations to be served by each of them and the robot move cycles must be all determined so as to minimize the cycle time of a multi-robot serial system. Since the aim of minimizing the cycle time could lead to a non-univocal configuration, a secondary objective may be pursued. To this aim, the classic case of a single dual-gripper robotic cell is preliminarily revisited, using a practical rather than a theoretical approach, to show that, under the conditions of minimum cycle time, it is possible to take into account both the reduction of the WIP and that of the length of the transitory periods.
Software routers based on personal computer (PC) architectures are becoming an important alternative to proprietary and expensive network devices. However, software routers suffer from many ...limitations of the PC architecture, including, among others, limited bus and central processing unit (CPU) bandwidth, high memory access latency, limited scalability in terms of number of network interface cards, and lack of resilience mechanisms. Multistage PC-based architectures can be an interesting alternative since they permit us to i) increase the performance of single- software routers, ii) scale router size, iii) distribute packet-manipulation and control functionality, iv) recover from single-component failures, and v) incrementally upgrade router performance. We propose a specific multistage architecture, exploiting PC-based routers as switching elements, to build a high-speed, large-size, scalable, and reliable software router. A small-scale prototype of the multistage router is currently up and running in our labs, and performance evaluation is under way.
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