Interstage Buffers Research Articles

Evaluation of Unreliable Flow Lines with Limited Buffer Capacities and Spare Part Provisioning

We consider a model of an N-stage flow line with stochastic processing times and interstage buffers that decouple adjacent production stages. Machine downtimes are induced by failures of critical machine components. Each machine is assumed to have exactly one of these failure-prone components. To achieve high machine availability, it is assumed that spare parts for those failure-prone critical components are kept in stock. Failed components are immediately replaced with new, functioning components, and a one-for-one replenishment policy is applied for the restocking of those spare parts. We present a novel decomposition approach to approximate the average throughput and inventory for a system with an arbitrary number of machines, buffers, and spare parts. With a detailed numerical study, we analyze the impact of different parameter constellations on the approximation quality. We demonstrate the remarkable accuracy of our method by comparing our results with both exact and simulated values. Using our method, we further study the complex interaction and partial substitution effects between buffer sizes and spare part base-stock levels on the logistical performance of the flow line.

A dual encoding-based meta-heuristic algorithm for solving a constrained hybrid flow shop scheduling problem

Though scheduling problems have been largely investigated by literature over the last 50years, this topic still influences the research activity of many experts and practitioners, especially due to a series of studies which recently emphasized the closeness between theory and industrial practice. In this paper the scheduling problem of a hybrid flow shop with m stages, inspired to a truly observed micro-electronics manufacturing environment, has been investigated. Overlap between jobs of the same type, waiting time limit of jobs within inter-stage buffers as well as machine unavailability time intervals represent just a part of the constraints which characterize the problem here investigated. A mixed integer linear programming model of the problem in hand has been developed with the aim to validate the performance concerning the proposed optimization technique, based on a two-phase metaheuristics (MEs). In the first phase the proposed ME algorithm evolves similarly to a genetic algorithm equipped with a regular permutation encoding. Subsequently, since the permutation encoding is not able to investigate the overall space of solutions, a random search algorithm equipped with an m-stage permutation encoding is launched for improving the algorithm strength in terms of both exploration and exploitation. Extensive numerical studies on a benchmark of problems, along with a properly arranged ANOVA analysis, demonstrate the statistical outperformance of the proposed approach with respect to the traditional optimization approach based on a single encoding. Finally, a comprehensive comparative analysis involving the proposed algorithm and several metaheuristics developed by literature demonstrated the effectiveness of the dual encoding based approach for solving HFS scheduling problems.

On the search of workstations arrangement in pull production systems

This research presents a model to determine the workstation arrangement and kanban number for pull production systems. Several practical production line characters are considered, and evolutionary algorithms are utilized to obtain the optimal/near-optimal result. The proposed system is a flow-shop, pull production line with N unreliable workstations and N − 1 inter-stage buffers. Workstations may be allocated to any stage in the production line and have a different processing rate at each stage. Workstations will breakdown/recover at fixed rates, and the operating-breakdown-recovery process is formulated as a Markov process in this model. The size of the inter-stage buffers varies according to the arrangements of workstations. A model is established on the objective of minimizing the total production cost per item of the finished product. The costs considered in the system contain the allocation of workstations, operations, inventory, and production shortage costs. An evolutionary algorithm, genetic algorithm, is used to obtain the allocation of workstations in the production line.

Analysis and design of split and merge unpaced assembly systems by metamodelling and stochastic search

The study presents a new approach in optimal interstage buffer allocation problem of split-and-merge unpaced open assembly systems, which are increasingly being used in modern manufacturing systems, particularly in automotive industries. Allocations of interstage buffers to accommodate the work-in-process inventories are optimized in an attempt to maximize the overall system production rate. A simulation model developed is used in conjunction with genetic algorithms (GA) to find optimal interstage buffer configurations yielding a maximum production rate. However, simulation is extremely time-consuming due to lengthy computational requirements, especially when used in a stochastic search algorithm. In an attempt to overcome this problem, an alternative approach in simulation metamodelling based on artificial neural networks (ANN) is developed. The optimization problem previously conducted through simulation and GA is reconsidered by integrating the metamodelling approach into the GA, replacing the simulation model. The new ANN-GA approach not only gives solutions with no statistically significant difference in comparison with the original simulation GA approach, but also demands significantly less computational time. The proposed methodology intends to help practising system design engineers to take quicker decisions regarding the assembly system design parameters. The potential of metamodelling to solve manufacturing systems problems are also discussed.

THROUGHPUT ANALYSIS USING ALTERNATING RENEWAL PROCESS IN BALANCED SERIAL PRODUCTION LINES WITH NO INTERSTAGE BUFFERS

ABSTRACT This paper presents a closed form method with exponential function to calculate performance measures, such as expected value and variance of the transient throughput, and the probability that measures the delivery in time for a balanced serial production with no interstage buffers. Such approach is based on the assumptions that 1) each machine alternates between Normal and Failed, 2) up times and down times are i.i.d. (but with exponential distributions required in closed form method) and 3) all machines have the same production rate μ. Numerical experiments that compare values of such performance measures by different methods are presented in terms of a balanced serial production with no interstage buffer cited from literature. The results were found that: for T > 10, both E(πT) and Var(πT) increase by decreasing α (1/MTTF). That is, it seems to indicate that the system performance can not be improved by choosing smaller α. On the contrary, we can achieve that both E(πT) increases and Var(πT) decreases by increasing β (1/MTBF).

Analysis of production control systems kanban and CONWIP

In this paper we describe and classify different pull production systems. The production control systems kanban and CONWIP are then analysed with respect to production rate and average W1P. We examine single product flow lines with exponential service time distributions and unlimited demand at the final buffer (saturated lines). We show that the distribution of cards (kanbans) has a significant effect on the performance of kanban systems. Different types of kanban control mechanisms show equivalent performance data, if the distribution pattern is adapted accordingly. Our research shows that the kanban system is more flexible with respect to a given objective than the CONWIP system, because in addition to the total card number the card distribution is a control parameter. Moreover for a given production rate the average WIP is lower in a kanban system than in a CONWIP system. We identify the average WIP in the interstage buffers as important parameter and describe the ‘WIP bowl phenomenon’ as result of optimum card distributions. Concluding remarks and directions for future research conclude the paper.

Analysis of behaviour of an unreliablen-stage transfer line with (n− 1) inter-stage storage buffers

This paper develops an efficient method to analyse the behaviour of an unreliable n-stage transfer line with (n − 1) finite inter-stage storage buffers. The n-stage line is decomposed into (n − 1) aggregate two-stage lines, for which analytical solutions are available. The method is developed through the examination of the steady state behaviour of the n-stage line and the decomposed lines, and the relationship between the failure and repair rates of the individual stages and the aggregate stages. Numerical and simulation experiments show that the method is efficient in computation and performs quite well.

Two-level solution method for Markov chain modelling transfer lines with unreliable servers and finite buffers

Transfer lines with inter-stage buffers and unreliable servers are often modelled by means of Markov chains. Because of the large number of states, solving the steady-state equations of the chain is not a trivial task. This paper proposes a two-level iterative scheme for computing the steady-state probability distribution. In the framework of non-negative matrix theory some general results are proved which guarantee the convergence of the proposed procedure. Moreover, numerous numerical experiments are given, which show that the two-level iterative scheme enjoys a very good rate of convergence. The method also works suitably for solving the steady-state probability equation of chains modelling systems with more than three stages.

A multistage ATM switch with interstage buffers

AbstractAsynchronous transfer mode (ATM) is the transport technique for the broadband ISDN recommended by CCITT (I.121). Many switches have been proposed to accommodate the ATM that requires fast packet switching capability.1‐8 The proposed switches for the broadband ISDN can be classified as being of input queueing or output queueing type. Those of the input queueing type have a throughput performance which is approximately 58 per cent that of the output queueing type. However, output queueing networks require larger amounts of hardware than input queueing networks. In this paper, we propose a new multistage switch with internal buffering that approaches a maximum throughput of 100 per cent as the buffering is increased. The switch is capable of broadcasting and self‐routeing. It consists of two switching planes which consist of packet processors, 2 x 2 switching elements, distributors and buffers located between stages and in the output ports. The internal data rate of the proposed switch is the same as that of the arriving information stream. In this sense, the switch does not require speed‐up. The switch has log2 N stages that forward packets in a store‐and‐forward fashion, thus incurring a latency of log2 N time periods. Performance analysis shows that the additional delay is small.

Study on GaAs monolithic dynamic divider

AbstractThe GaAs monolithic dynamic divider, a high speed divider for microwave phase locked oscillators, has been studied. It can be operated at a higher speed than static dividers. The load in the inverter section is a passive resistor. Improved circuit topology at interstage buffers and reduction of gate resistance by the Au/WSi self‐aligned process have been used for superior characteristics of a single FET. For a 1 μm gate length, both division and frequencies ranging from 4.3 GHz to 7.3 GHz have been observed. As a system application, the divider has been implemented in a 13 GHz frequency synthesizer of oscillator‐multiplier type. The divider has been operated in the 6.5 GHz band and an operation with 1 MHz steps has been confirmed at the 13 GHz band. The phase noise has been 90 dBc/Hz at the off‐carrier frequency of 10 kHz. This value is sufficient for conventional microwave circuits.

The effect of inequality of interstage buffer capacities and operation time variability on the efficiency of production line systems

It has now been generally established that the output rate of balanced production lines having variable operation times can be improved by deliberately unbalancing the line through assigning proportionately lower operation times to the middle station(s). Nevertheless, a production line may be balanced in terms of mean operation times at the respective stations yet unbalanced in the sense that the interstage buffer capacity allocation or the operation time variability are not equal for all stations. This paper attempts to study the effect that the latter types of imbalance have on the output rate and average number of work units in the system for some production line situations. Computer simulation experimentation results confirm that inequality of variability of operation times have the same general effect on output rate as inequality of operation times but little effect on the number of units in the system. Inequality of interstage buffers, on the other hand, affects the average number of units in the system but has little effect on the output rate.