Optimization of Two-Level Disassembly/Remanufacturing/Assembly System with an Integrated Maintenance Strategy

International audienceWith an increase of environmental pressure on economic activities, reverse flow is increasingly important. It seeks to save resources, eliminate waste, and improve productivity. This paper investigates the optimization of the disassembly, remanufacturing and assembly system, taking into account assembly-disassembly system degradation. An analytical model is developed to consider disassembly, remanufacturing of used/end-of-life product and assembly of the finished product. The finished product is composed of remanufactured and new components. A maintenance policy is sequentially integrated to reduce the system unavailability. The aim of this study is to help decision-makers, under certain conditions, choose the most cost-effective process for them to satisfy the customer as well as to adapt to the potential risk that can perturb the disassembly-assembly system. A heuristic is developed to determine the optimal ordered date of the used end-of-life product as well as the optimum release dates of new external components. The results reveal that considering some remanufacturing and purchase components costs, the proposed model is more economical in comparison with a model without remanufactured parts. Numerical results are provided to illustrate the impact of the variation of the ordering cost and quality of the used end-of-life product on the system profitability. Finally, the risk due to system repair periods is discussed, which has an impact on managerial decision-making

Integrated Maintenance and Service Policies Definition for Urban Ropeway Transport System

International audienceThis work proposes a stochastic model for integrating service and maintenance policies in order to address the queuing problem and the cost of maintenance for public transport systems. The authors adopt the following approaches: (i) a cost-model that considers the uncertainty of passengers’ plans to compute the waiting time; (ii) a maintenance cost-model which take into account two different maintenance policies (periodic block-type and age-based); and (iii) a bi-objective optimisation process to bring together the service and maintenance policies. Finally, the proposed work is applied to a massive-urban ropeway belonging to a public transportation system, in which the current service policy has been evaluated, considering the established transportation operation

Geometric Approach and Taboo Search for Scheduling Flexible Manufacturing Systems

This paper addresses the scheduling and deadlock avoidance of a class of automated manufacturing systems. In such systems, a set of jobs is to be performed on a set of resources and each job requires several operations- . An operation may require several types of resources with several units of each type. Further, upon the completion of an operation, its related resources cannot be released until resources needed for the next operation become available. One important characteristic of such systems is the possibility of deadlock. The scheduling problem deals with the allocation of resources such that jobs are completed within a minimal makespan and deadlocks are avoided. We extend the classical geometric approach to solve the two­job case of our model. A greedy algorithm based on this result and the taboo search heuristic is then developed for the general case. Numerical results show that the proposed algorithm is fast and provides good schedules

Optimal integrated maintenance/production policy for randomly failing systems with variable failure rate

International audienceThis article deals with the combined production and maintenance plans for a manufacturing system satisfying a random demand. We first establish an optimal production plan which minimises the average total inventory and production cost. Second, using this optimal production plan, and taking into account the deterioration of the machine according to its production rate, we derive an optimal maintenance schedule which minimises the maintenance cost. A numerical example illustrates the proposed approach, this analytical approach, based on a stochastic optimisation model and using the operational age concept, reveals the significant influence of the production rate on the deterioration of the manufacturing system and consequently on the integrated production/maintenance policy

No-wait scheduling of a two-machine flow-shop to minimize the makespan under non-availability constraints and different release dates

International audienceIn this paper, we consider the two-machine no-wait flow-shop scheduling problem, when every machine is subject to one non-availability constraint and jobs have different release dates. The non-availability intervals of the machines overlap and they are known in advance. We aim to find a non-resumable schedule that minimises the makespan. We propose several lower bounds and upper bounds. These bounding procedures are used in a branch-and-bound algorithm. Computational experiments are carried out on a large set of instances and the obtained results show the effectiveness of our method

Bisphenol-A and Sleep Adequacy Among Adults in the National Health and Nutrition Examination Surveys

Study Objectives: To evaluate bisphenol-A (BPA) level and its relationship to sleep adequacy in a nationally representative sample of U.S. adults. Methods: A population-based cross-sectional study was conducted using 2005-2010 National Health and Nutrition Examination Survey whereby data were collected using in-person interviews, physical examination and laboratory testing. BPA level was measured in urine samples and analyzed as loge-transformed variable and in quartiles (\u3c 0.9 ng/mL; 0.9 to \u3c 1.9 ng/mL; 1.9 to \u3c 3.7 ng/mL; 3.7+ ng/mL). Sleep adequacy was operationalized with three questions: How much sleep do you usually get at night on weekdays or workdays? , Have you ever told a doctor or other health professionals that you have trouble sleeping? and Have you ever been told by a doctor or other health professional that you have a sleep disorder? Sleep duration was further categorized as (\u3c 6 h, ≥ 6 h); (\u3c 7 h, 7-8 h, \u3e 8 h); (\u3c 5 h, 5-6 h, 7-8 h, ≥ 9 h). Linear, binary, and ordinal logistic regression models were constructed. Results: Loge-transformed BPA level was inversely related to sleep duration defined, in hours, as a continuous variable, a dichotomous variable (≥ 6, \u3c 6), or an ordinal variable (≥ 9, 7-8, 5-6, \u3c 5), after adjustment for confounders. Help-seeking behavior for sleep problems and diagnosis with sleep disorders were not significantly associated with loge-transformed BPA level in fully adjusted models. Conclusions: Loge-transformed BPA level may be associated with fewer hours of sleep among U.S. adults, with implications for prevention. Further research involving diverse populations are needed to confirm these study findings