Functional properties of throughput in tandem lines with unreliable servers and finite buffers

optimization;queueing theory;production

Sample-Path Optimization of Buffer Allocations in a Tandem Queue - Part I:Theoretical Issues

This is the first of two papers dealing with the optimal bu er allocation problem in tandem manufacturing lines with unreliable machines.We address the theoretical issues that arise when using sample-path optimization, a simulation-based optimization method, to solve this problem.Sample-path optimization is a recent method to optimize performance functions of stochastic systems.By exploiting the fact that the performance function we want to optimize is the almost sure limit of a sequence of random functions, it overcomes some of the di culties from which variants of stochastic approximation methods su er.We provide a mathematical framework that makes use of a function space construction to model the dependence of throughput on bu er capacities and maximum ow rates of machines.Using this framework we prove various structural properties of throughput and show how these properties, along with a niceness condition on the steady-state, can be used to prove that the sample-path optimization method converges almost surely when applied to the bu er allocation problem.Among the properties established, monotonicity in bu er capacities and in ma- chine ow rates are especially important.Although monotonicity results of this nature have appeared in the literature for discrete tandem lines, as far as we are aware the kind of analysis we present here has not yet been done for continuous tandem lines.

Adaptive policy of buffer allocation and preventive maintenance actions in unreliable production lines

Abstract The buffer allocation problem is an NP-hard combinatorial optimization problem, and it is an important design problem in manufacturing systems. The research proposed in this paper concerns a product line consisting of n unreliable machines with n − 1 buffers and a preventive maintenance policy. The focus of the research is to obtain a better trade-off between the buffer level and the preventive maintenance actions. This paper proposes a dynamic control of the buffers' level and the interval between two consecutive preventive actions. The set of the parameter of the proposed policy allows choosing the reduction in the costs or the increment of the throughput rate. A simulation model is developed to test the proposed model to the solution proposed in the literature. The proposed policy leads to better results in terms of total costs reduction keeping high production rate, while the design of a fixed level of buffer works better for lower production rates required

Performance Evaluation of Remanufacturing Systems

Implementation of new environmental legislation and public awareness has increased the responsibility on manufacturers. These responsibilities have forced manufacturers to begin remanufacturing and recycling of their goods after they are disposed or returned by customers. Ever since the introduction of remanufacturing, it has been applied in many industries and sectors. The remanufacturing process involves many uncertainties like time, quantity, and quality of returned products. Returned products are time sensitive products and their value drops with time. Thus, the returned products need to be remanufactured quickly to generate the maximum revenue. Every year millions of electronic products return to the manufacturer. However, only 10% to 20% of the returned products pass through the remanufacturing process, and the remaining products are disposed in the landfills. Uncertainties like failure rate of the servers, buffer capacity and inappropriate preventive maintenance policy would be highly responsible the delays in remanufacturing. In this thesis, a simulation based experimental methodology is used to determine the optimal preventive maintenance frequency and buffer allocation in a remanufacturing line, which will help to reduce the cycle time and increase the profit of the firm. Moreover, an estimated relationship between preventive maintenance frequency and MTBF (Mean Time Between Failure) is presented to determine the best preventive maintenance frequency for any industry. The solution approach is applied to a computer remanufacturing and a cell phone remanufacturing industry. Analysis of variance and regression analysis are performed to denote the influential factors in the remanufacturing line, and optimization is done by using the regression techniques and ANOVA results

Buffer allocation in stochastic flow lines via sample-based optimization with initial bounds

The allocation of buffer space in flow lines with stochastic processing times is an important decision, as buffer capacities influence the performance of these lines. The objective of this problem is to minimize the overall number of buffer spaces achieving at least one given goal production rate. We optimally solve this problem with a mixed-integer programming approach by sampling the effective processing times. To obtain robust results, large sample sizes are required. These incur large models and long computation times using standard solvers. This paper presents a Benders Decomposition approach in combination with initial bounds and different feasibilitycutsfortheBufferAllocationProblem,whichprovidesexactsolutionswhile reducing the computation times substantially. Numerical experiments are carried out to demonstrate the performance and the flexibility of the proposed approaches. The numerical study reveals that the algorithm is capable to solve long lines with reliable and unreliable machines, including arbitrary distributions as well as correlations of processing times

The line balancing algorithm for optimal buffer allocation in production lines

Cataloged from PDF version of article.Buffer allocation is a challenging design problem in serial production lines that is often faced in the industry. Effective use of buffers (i.e. how much buffer storage to allow and where to place it) in production lines is important since buffers can have a great impact on the efficiency of the production line. Buffers reduce the blocking of the upstream station and the starvation of the downstream station. However, buffer storage is expensive both due to its direct cost and the increase of the work-in-process inventories it causes. Thus, there is a trade-off between performance and cost. This means that the optimal buffer capacity and the allocation of this capacity have to be determined by analysis. In this thesis, we focus on the optimal buffer allocation problem. We try to maximize the throughput of the serial production line by allocating the total fixed number of buffer slots among the buffer locations and in order to achieve this aim we introduced a new heuristic algorithm called “Line Balancing Algorithm (LIBA)”applicable to all types of production lines meaning that there is no restriction for the distributions of processing, failure and repair times of any machine, the disciplines such as blocking, failure etc. and the assumptions during the application of LIBA in the line.Selvi, ÖmerM.S

Performance evaluation of the remanufacturing system prone to random failure and repair

Implementation of new environmental legislation and public awareness has increased the responsibility of manufacturers. Remanufacturing has been applied in many industries and sectors since its introduction. However, only 10% to 20% of the returned products pass through the remanufacturing process, and the remaining products are disposed in the landfills. Uncertainties like high failure rates of the servers, buffer capacities, and inappropriate preventive maintenance policies would be responsible for most of the delays in remanufacturing operations. In this paper, a simulation-based experimental methodology is used to determine the optimal preventive maintenance frequency and buffer allocation in a remanufacturing line. Moreover, an estimated relationship between preventive maintenance frequency and Mean Time Between Failure (MTBF), is presented to determine the best preventive maintenance frequency. The solution approach is applied to computer remanufacturing industry. Analysis of variance (ANOVA), and regression analysis are performed to denote the most influential factors to remanufacturing cycle time (performance measures). A case study is used to show the applicability of the modelling approach in assessing and improving the cycle time, and the profit of a remanufacturing line . Managerial insights are highlighted to support managers and decision-makers in their quest for more efficient and smooth operation of the remanufacturing system