Interstage Buffer Research Articles

A Variable-Gain Low-Noise Amplifier for MedRadio Band Applications

A variable-gain 0.18 μm Complementary Metal- Oxide-Semiconductor (CMOS) Low-Noise Amplifier (LNA) for Medical Device Radiocommunications Service (MedRadio) applications has been designed and verified through simulations in Cadence IC5 with Silterra’s C18G CMOS technology Process Design Kit. Unlike other MedRadio LNAs from previous works, this proposed LNA can vary its gain from just above 10 dB to nearly 30 dB. It consists of three stages; the input-matching stage, the interstage buffer, and the gain-varying stage. The input-matching stage provides an input impedance match and drives the initial gain of the LNA. The inter-stage buffer isolates the input-matching stage from the gain-varying stage. The overall gain of the LNA can be varied and is determined by the variable biasing of the driving transistors of the gainvarying stage. On post-layout simulations with a sourcefollower output buffer, this LNA exhibits a wide-ranging gain from 11.2 dB at 0.49 mW DC power consumption to 29.1 dB at 1.34 mW DC power consumption.

Spare parts or buffer? How to design a transfer line with unreliable machines

In this paper, we study the design of a transfer line consisting of two unreliable machines in series and an interstage buffer. In addition to the buffer capacity, the system planner can decide on the inventory levels for spare parts in order to reduce the time to repair failed machines. Our work aims to find cost-efficient combinations of buffer capacity and spare parts inventory. We formulate discrete-time Markov chains for two different situations in order to analyse the trade-off between buffer capacity, spare parts inventory and throughput. By means of numerical examples, we illustrate that the effect of a spare part on the efficiency of a transfer line is much greater than the effect of additional buffer places. We conclude that it is necessary to optimize buffer capacity and spare parts inventory levels simultaneously. For systems with identical critical components, our results show that not only is there a pooling effect of safety stocks but also between the buffer places and spare parts inventory levels. We conclude that planners who select a standardised component for the system design and optimize spare parts levels as well as buffer capacity can significantly reduce costs or increase the throughput of a transfer line.

Studying unbalanced workload and buffer allocation of production systems using multi-objective optimisation

Numerous studies have investigated the effects of unbalanced service times and inter-station buffer sizes on the efficiency of discrete part, unpaced production lines. There are two main disadvantages of many of these studies: (1) only some predetermined degree of imbalance and patterns of imbalance have been evaluated against the perfectly balanced configuration, making it hard to form a general conclusion on these factors; (2) only a single objective has been set as the target, which neglects the fact that different patterns of imbalance may outperform with respect to different performance measures. Therefore, the aim of this study is to introduce a new approach to investigate the performance of unpaced production lines by using multiple-objective optimisation. It has been found by equipping multi-objective optimisation with an efficient, equality constraints handling technique, both the optimal pattern and degree of imbalance, as well as the optimal relationship among these factors and the performance measures of a production system can be sought and analysed with some single optimisation runs. The results have illustrated that some very interesting relationships among the key performance measures studied, including system throughput, work-in-process and average buffer level, could only be observed within a truly multi-objective optimisation context. While these results may not be generalised to apply to any production lines, the genericity of the proposed simulation-based approach is believed to be applicable to study any real-world, complex production lines.

Pipelining data-dependent tasks in FPGA-based multicore architectures

In recent years, there has been increasing interest in using task-level pipelining to accelerate the overall execution of applications mainly consisting of producer/consumer tasks. This paper proposes fine- and coarse-grained data synchronization approaches to achieve pipelining execution of producer/consumer tasks in FPGA-based multicore architectures. Our approaches are able to speedup the overall execution of successive, data-dependent tasks, by using multiple cores and specific customization features provided by FPGAs. An important component of our approach is the use of customized inter-stage buffer schemes to communicate data and to synchronize the cores associated with the producer/consumer tasks. We propose techniques to reduce the number of accesses to external memory in our fine-grained data synchronization approach. The experimental results show the feasibility of the approach in both in-order and out-of-order producer/consumer tasks. Moreover, the results using our approach reveal noticeable performance improvements for a number of benchmarks over a single core implementation without using task-level pipelining.

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.

Operational capacity allocation for unreliable module-based assembly systems

This paper discusses the operational capacity allocation (OCA) problem in an unreliable module-based assembly (MOBA) system. MOBA systems stem from pervasive applications of agile manufacturing. A MOBA system consists of a number of assembly stations in series, each of which is fed by a sub-fabrication line. Each assembly station performs one assembly operation which requires one workpiece pulled from the upper stream station and one module supplied from its sub-fabrication line. The inter-station buffers are small. The assembly stations are subject to random breakdowns and repairs. OCA for throughput maximization is a key issue in the design and operation of a MOBA system. We develop a set of rules for allocating a finite amount of operational capacity of the production system so that its throughput is maximized. Simulation results show that this policy is robust and applicable to systems with more than three stages and with general processing times. Through numerical experiments, we discuss the impacts of the system parameters on the optimal allocation policy. We then propose the concept of soft and rigid throughput bottlenecks and explore criteria for identifying the soft throughput bottleneck of a system. We believe our work provides a basis for a promising approach for OCA in complex and unreliable assembly systems.

Performance Analysis of Banyan Switch Architecture

The advancement in the field of computer technology, communication and the increasing user demand in terms of bandwidth and speed, the future communication network is rolling towards the BISDN with optical technology. The high speed ATM network is one of the major tool used for BISDN. In turn, the efficiency of the ATM network relies on the switching fabric. Hence, the switching fabric of future telecommunication systems should have a very low cell loss and delay performance. In this paper, the simulation results of Sort Banyan architecture of size 8 × 8 are presented. The simulation of Sort Banyan network is performed along with four different methods in view of enhancing the throughput of the Sort Banyan switch network. The cell loss and delay performance versus the cell arrival rate for the four schemes viz, Input buffer, Interstage buffer, Shared output buffer and Regeneration of cells using FEC method are presented for both Poisson and Self-similar traffic models.

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).

Throughput, flow times, and service level in an unreliable assembly system

This paper considers an unreliable assembly network where different types of components are processed by two separate work centers before being merged at an assembly station. The operation complexity of the system is a result of finite inter-station buffers, uncertain service times, and random breakdowns that lead to blocking at the work centers and starvation at the assembly station. The objective of this study is to gain an understanding of the behavior of such systems so that we can find a way to maximize the system throughput while maintaining the required customer service level. By constructing appropriate Markov processes, we obtain the probability distribution of the production flow time and derive formulas for throughput, the loss probability of type-2 workpieces, and the mean flow time. We present expressions for average work-in-process (WIP) and study their monotone properties. Using the distribution of the flow time, a customer service level can be defined and computed. We then formulate a system optimization model that can be used to maximize the throughput while maintaining an acceptable service level.

Modelling and scheduling of an asynchronous cyclic production line with multiple parts

In this study, we model and analyse a production line with asynchronous part transfers, processing time variability, and cyclic scheduling in the same framework. We consider a production line with multiple parts and finite interstation buffers. The line produces a batch of n jobs repetitively using the same order of jobs in every batch. The processing time of a job on a station is a random variable and is assumed to have a phase-type distribution. Parts are transferred between the stations in an asynchronous manner. We first present a continuous time Markov chain model to analyse the performance of this system for a given sequence. A state-space representation of the model and the associated rate matrix are generated automatically. The steady state probabilities of the Markov chain are determined by using a recursive method that exploits the special structure of the rate matrix. The cycle time, the production rate, and the expected Work-In-Progress (WIP) inventory are used as the main performance measures. We then present an approximate procedure to determine the cyclic sequence that minimises the cycle time. We then investigate the effects of operating decisions, system structure, processing time variability, and their interaction in the same framework. Numerical results for the performance evaluation and scheduling of cyclic production lines are also presented.

Asymptotic variance rate of the output in production lines with finite buffers

Production systems that can be modeled as discrete time Markov chains are considered. A state‐space‐based method is developed to determine the variance of the number of parts produced per unit time in the long run. This quantity is also referred to as the asymptotic variance rate. The block tridiagonal structure of the probability matrix of a general two‐station production line with a finite buffer is exploited and a recursive method based on matrix geometric solution is used to determine the asymptotic variance rate of the output. This new method is computationally very efficient and yields a thousand‐fold improvement in the number of operations over the existing methods. Numerical experiments that examine the effects of system parameters on the variability of the performance of a production line are presented. The computational efficiency of the method is also investigated. Application of this method to longer lines is discussed and exact results for a three‐station production line with finite interstation buffers are presented. A thorough review of the pertinent literature is also given.

Busy Period Analysis of A Two-Stage Multi-Product System with Interstage Buffer

This paper examines the transient behaviour of a two-stage multi-product production system with an interstage buffer. The system is described by a stochastic method and is analysed by employing the state-space model and regenerating point technique. Explicit expressions are obtained for certain essential system characteristics and a cost analysis is carried out using some of the characteristics. A particular case is investigated to illustrate some features of this production system.

Asymptotic variance rate of the output of a transfer line with no buffer storage and cycle-dependent failures

In this study the variability properties of the output of transfer lines are investigated. The asymptotic variance rate of the output of an N-station synchronous transfer line with no interstation buffers and cycle-dependent failures is analytically determined. Unlike the other studies, the analytical method presented in this study yields a closed-form expression for the asymptotic variance rate of the output. The method is based on a general result derived for irreducible recurrent Markov chains. Namely, the limiting variance of the number of visits to a state of an irreducible recurrent Markov chain is obtained from the n-step transition probability function. Thus, the same method can be used in other applications where the limiting variance of the number of visits to a state of an irreducible recurrent Markov chain is of interest. Numerical results show that the asymptotic variance rate of the output does not monotonically increase as the number of stations in the transfer line increases. The asymptotic variance rate of the output may first increase and then decrease depending on the station parameters. This property of the production rate is investigated through numerical experiments and the results are presented.

Optimality of the Symmetric Workload Allocation in a Single-Server Flow Line System

This paper provides a proof of the symmetrical allocation property (SAP), conjectured in an earlier work on the workload allocation problem for a manufacturing flow line system. The system consists of N single-Erlang servers in series having a common interstation buffer capacity. SAP says a symmetric workload allocation exists among the optimal solutions. We first show the reciprocal of the throughput is increasing and jointly convex, not component-wisely, in workloads. Then we apply the line reversibility property to obtain an alternative optimal allocation symmetric for any optimal workload allocation that is asymmetric. A sufficient condition for SAP to hold is also given, which relaxes the hypothesizing assumptions on the service-time distribution and interstation buffer capacities.

An analytical formula for variance of output from a series-parallel production system with no interstation buffers and time-dependent failures

This paper presents a method to determine the mean and the variance of the amount of materials produced in a fixed time interval by a continuous materials flow production system with N stations in series and M stations in parallel and no interstation buffers. Unreliable stations with exponential failure and repair times, time dependent failures, and deterministic processing times are considered. Closed-form expressions for the asymptotic mean and variance of the amount of materials produced per unit time are given for series, parallel, and series-parallel production systems with identical stations. It is shown that the distribution of the amount of materials produced in a fixed time is asymptotically normal. By using this property, effects of variability on the due-date performance are investigated by considering the probability of meeting a customer order on time. Numerical experiments that explore some relationships among performance measures and production system parameters are also presented.

Effects of variability on the due-time performance of a continuous materials flow production system in series

In this study, we consider a specific continuous materials flow production system with N unreliable stations in series and no interstation buffers. Processing times of the stations are deterministic and identical. We assume that the failures are time-dependent and the time to failure and time to repair distributions are exponential and two-phase balanced coxian ( C 2: b ), respectively. The effects of repair time variability on the performance of the production system are investigated by changing the parameters of C 2: b distribution. We obtained closed-form expressions for the asymptotic mean and variance of the amount of materials produced in this production system. It is shown that the amount of materials produced in a fixed time interval is normal as time approaches infinity. The asymptotic distribution of the amount of materials produced is used to derive the probability of meeting a customer order on time. We used this probability to evaluate the due-time performance of the production system. Numerical experiments that investigate some relationships among the performance measures and the system parameters are also presented.

Variance of the throughput of an N-station production line with no intermediate buffers and time dependent failures

In this study, the variance of the throughput of an N-station production line with no intermediate buffers and time dependent failures is analytically determined. Time to failure and time to repair distributions are assumed to be exponential. The analytical method yields a closed-form expression for the variance of the throughput. The method is based on determining the limiting variance of the total residence (sojourn) time in a specific state of an irreducible recurrent Markov process from the probability of visiting that state at time t given an initial state. This probability function is the instantaneous availability of a production system in the reliability context. A production line with no interstation buffers and time-dependent failures is basically a series system with hot standby. The same procedure can be applied to determine the variance of the throughputs of various arrangements of workstations including series, parallel, series-parallel systems provided that the instantaneous availabilities of these systems can be written explicitly. Numerical experiments show that, although the expected throughput decreases monotonically, the variance of the throughput may increase and then decrease as the number of stations in the line increases depending on the system parameters. Numerical experiments that investigate this phenomenon and also the dependence of the coefficient of variation on the number of stations are also presented in this study.

Analysis of multistation production systems with limited buffer capacity part 2: The decomposition method

We seek efficient techniques to evaluate the performance of multistation production systems with limited interstation buffers and station breakdown. Our ultimate objective is to develop a practical computer implementation that can be used for analysis and design. A flexible decomposition framework is developed. This approach allows the analysis of multistation production systems with various structures including series arrangements, network topologies, and rework (feedback) systems. The efficient solution techniques for the subsystems developed in Part 1 are used at each iteration of the decomposition method. It is the generality and efficiency of the subsystem model as well as the flexibility and robustness of the decomposition approach that distinguish our study from earlier work.

Analysis of multistation production systems with limited buffer capacity part 1: The subsystem model

We seek efficient techniques to evaluate the performance of multistation production systems with limited interstation buffers and station breakdown. Our ultimate objective is to develop a practical computer implementation that can be used for analysis and design. Practically implies two design considerations: flexibility and computational efficiency. The approach must be flexible enough to be applicable to production systems with various topologies and station characteristics. These include series arrangements of production systems, as well as network topologies and rework (feedback) systems. Similarly, the technique must be computationally expedient. Our approach is based on a framework to model single-buffer subsystems to be used within a decomposition technique to evaluate the performance of the entire system. The first part presents a quasi-birth-death process model for the subsystems. Exploiting the spectral characteristics of the associated matrix polynomial, we develop a novel solution procedure for the steady-state probabilities where the computational effort is independent of the buffer size. The solution procedure is applicable to quasi birth-death processes. The efficient solution procedure developed in this part is used as a building block in decomposing and analyzing multistation production systems with various topologies in the second part of the study.

Control policies for multi-product multi-stage manufacturing systems: An experimental approach

We investigate the behaviour of a multi-product, multi-stage pull-type production/ inventory system operating under a variety of manufacturing control policies. The system consists of multiple stages in series with finite interstage buffer space and a single processor. The first stage has always sufficient amount of raw material to work on and the last stage is followed by a finite-capacity warehouse. Demand for a product follows a compound Poisson distribution. Any unsatisfied portion of the demand is backordered. The inventory level as well as the production process of each product at each stage are controlled through the use of an (R, r) continuousreview inventory control policy. A set-up is involved whenever a switch-over takes place to another product at any stage. Using a particular test case, we have evaluated various manufacturing strategies and switching policies under static as well as dynamic priority structures. We have compared the operating regimes by observing a set of performance measures such as the average inventory levels, the average backorder size, the average backorder levels, the probability of backorder and the average number of set-ups. We conclude proposing control policies for better customer service level for given scenarios.