Performance evaluation of a make-tO-stock production line with a two-parameter-per-machine policy: the control point policy

This paper presents a decomposition method for evaluating the performance of a production line with finite buffers controlled by the Control Point Policy (CPP), a policy with two parameters per machine. (One parameter is the buffer size; the other is a local hedging point.) Policies with two parameters per machine show very good performance while remaining simple to use. However, decomposition methods have not yet been developed for their analysis. We consider a production line, with exponentially distributed processing, failure, and repair times, controlled by a CPP. We decompose this line into two-machine CPP-controlled lines, which considerably simplifies the decomposition equations. Furthermore, the information loops are then included in the building blocks, and can be solved numerically. A numerical study shows that the method is accurate.     

Performance evaluation of linear and non-linear multi-product multi-stage lines with unreliable machines and finite homogeneous buffers

More and more machines are increasing their flexibility so as to be able to produce different products with the same tooling. In this context, it is necessary to have fast and accurate methods to evaluate the system performance. This paper presents an approximate analytical method for the performance evaluation of production systems in which Z different types of products are produced. The proposed method is based on the decomposition of the complex system into a set of simpler building blocks, each one formed by two machines and Z homogeneous buffers. The set of building blocks models the whole behavior of the original system. The performance of each building block is evaluated by using the aggregation technique applied to two-machine lines in which the behavior of several products is modeled by an aggregate product, thus simplifying the complexity of the analysis. The numerical results reported in this paper prove the method provides accurate results.     

Exact analysis of a discrete material three-station one-buffer merge system with unreliable machines

In this paper, a model of a discrete material flow line consisting of three unreliable machines and one buffer of limited capacity is analysed. A similar system, but with continuous flow of material was examined by Helber and Mehrtens (2001) and Tan (2001). In our system it is assumed that the buffer has two immediate preceding machines, performing the same operations and one immediate succeeding machine that receives material from the buffer. For the case where the buffer reaches its own capacity, one of the two preceding machines has priority over the other to dispose its processed part into the buffer. Processing times are assumed to be deterministic and identical for all machines and are taken as the time unit. Geometrically distributed operation dependent failures at the machines are assumed. All possible transition equations for the examined model are derived and a recursive algorithm that generates the transition matrix for any value N of the storage level is developed. Once the transition matrix is known the performance measures of the model under consideration can be easily evaluated. This model may be used as a building block in a decomposition method to evaluate large production systems with split/merge operations (for example, flow lines with quality inspections and rework loops).     

Semiconductor nanowires: A platform for nanoscience and nanotechnology

Advances in nanoscience and nanotechnology critically depend on the development of nanostructures whose properties are controlled during synthesis. We focus on this critical concept using semiconductor nanowires, which provide the capability through design and rational synthesis to realize unprecedented structural and functional complexity in building blocks as a platform material. First, a brief review of the synthesis of complex modulated nanowires in which rational design and synthesis can be used to precisely control composition, structure, and, most recently, structural topology is discussed. Second, the unique functional characteristics emerging from our exquisite control of nanowire materials are illustrated using several selected examples from nanoelectronics and nano-enabled energy. Finally, the remarkable power of nanowire building blocks is further highlighted through their capability to create unprecedented, active electronic interfaces with biological systems. Recent work pushing the limits of both multiplexed extracellular recording at the single-cell level and the first examples of intracellular recording is described, as well as the prospects for truly blurring the distinction between nonliving nanoelectronic and living biological systems.     

Logical reconfiguration of reconfigurable manufacturing systems with stream of variations modelling: a stochastic two-stage programming and shortest path model

Designing flexible manufacturing systems in general, and flexible material handling system in particular, is a complex problem, typically approached through several stages. Here the focus is on the conceptual design stage during which valid approximation-based methods are needed. The segmented flow topology (SFT) AGV systems were developed to facilitate control of complex automated material handling systems. This paper introduces a decomposition method, directly derived from timed Petri nets (TPN) theories, to calculate the expected utilization of AGVs (as servers of SFT systems) and to derive simple operational decision rules leading to maximum system productivity at steady state, for a given deterministic routeing of discrete material through the manufacturing system.     

A station model for continuous materials flow production systems

This study develops a station model for continuous flow production systems. The most prominent use of the model is as a building block for a general and flexible decomposition method to analyse and design continuous materials flow production systems. Station breakdown and a finite capacity buffer are considered. Station inference caused by the blocking and starving phenomena is included in the station model. We assume that the time to station breakdown and station repair are exponentially distributed while the buffer is neither empty nor full. No restrictive assumptions are made about the distributions of the station breakdown and repair times when the station is blocked or starved, that is, while the buffer remains empty or remains full. The production rate and the expected level of the buffer are given in closed form. Numerical results that show the effects of the input parameters on the production rate along with an overview of the decomposition methods are presented.     

Performance analysis of assembly/disassembly systems with unreliable machines and random processing times

This paper presents an efficient method to evaluate performance of tree-structured assembly/disassembly (AD) systems with finite buffer capacity. The times to failure, the times to repair, and the processing times are assumed to be exponentially distributed. The method is based on an extension of a decomposition method originally applied to performance evaluation of transfer lines. The method decomposes a K-machine tree-structured AD system to a system of K-1 two-machine lines and then finds the processing rates, failure rates and repair rates of the decomposed system that make performance of the two systems close to each other. To determine those rates of the decomposed system, we derive 6(K-1) equations based on interruption of flow, resumption of flow, and flow rate-idle time relations, and suggest two methods, which use the equations in different ways. Results from computational experiments show that the suggested decomposition methods give good estimates in a short time.     

Performance analysis of assembly/disassembly systems with unreliable machines and random processing times

This paper presents an efficient method to evaluate performance of tree-structured assembly/disassembly (AD) systems with finite buffer capacity. The times to failure, the times to repair, and the processing times are assumed to be exponentially distributed. The method is based on an extension of a decomposition method originally applied to performance evaluation of transfer lines. The method decomposes a K-machine tree-structured AD system to a system of K - 1 two-machine lines and then finds the processing rates, failure rates and repair rates of the decomposed system that make performance of the two systems close to each other. To determine those rates of the decomposed system, we derive 6(K - 1) equations based on interruption of flow, resumption of flow, and flow rate-idle time relations, and suggest two methods, which use the equations in different ways. Results from computational experiments show that the suggested decomposition methods give good estimates in a short time.     

Material flow analysis and volume distance sampling in heuristic line layout procedures

An empirical investigation is focused on the relationship between material flow patterns in a manufacturing system and the distribution of the volume distance values associated with all possible solutions to a line layout problem. Volume distance distribution for line layout problems are shown to follow roughly normal distribution for some common material flow patterns. Based on this result, sampling procedures are described for estimating the parameters of volume distance distributions and proposed as a basis for formulating satisficing criteria for use with heuristic line layout procedures. Subsequent empirical studies suggest relatively low levels of error are observed in the estimation of volume distance parameters for most material flow patterns. These results suggest that volume distance sampling and material flow analysis procedures may have practical value in the development of cost effective stopping criteria for heuristic line layout methods.     

Integrated analysis of quality and production logistics performance in manufacturing lines

This paper presents an analytical method for evaluating the performance of production systems, jointly considering in a unique framework quality and production logistics performance measures. In the literature, quality and production logistics have traditionally been investigated using independent approaches. Thus far, only a few recent contributions have focused on their mutual inter-relation, showing that benefits can be achieved from an integrated analysis. This paper contributes to this growing research by considering, for the first time, production systems in which the behaviour of the machines is monitored by statistical control charts. The control action performed by the quality control system on the machines is directly modeled. Moreover, the impact of the quality control action on the logistic flow of parts in the system is taken into account. In order to estimate the performance of such systems, an approximate analytical method based on the system decomposition technique is developed. The accuracy of the method is assessed by comparing the results with those obtained by simulation. Analysis of the results provides new insights into the relations among the quality and production logistics performance measures and paves the way to the development of integrated design techniques for improved configurations of the system as a whole.     

Modeling and Analysis of Assembly Systems with Unreliable Machines and Finite Buffers

An assembly line is a tree-structured manufacturing system in which some machines perform assembly operations. In this paper, we consider assembly lines with the following features: every operation is performed in a fixed amount of time, machines are unreliable, and buffers have finite capacity. Usually, the times to failures of machines are much larger than the processing times. This allows us to approximate the behavior of these systems by a continuous flow model. The behavior of this model is then analyzed using a decomposition technique which is an extension of an earlier technique proposed in the case of transfer lines. An efficient algorithm for calculating performance measures such as production rate and average buffer levels is derived. Experimental results are provided showing mat this approximate method is quite accurate.     

Approximate evaluation of semi-Markov chain reliability models

A property observed in high reliability fault-tolerant control systems is the relatively rare occurrence of component failures compared to the frequent occurrence of redundancy management decision events. This property leads to a temporal decomposition of the semi-Markov chain reliability model into two time-scales: a slow time-scale for failure events and a fast time-scale for FDI events. Conditions are described under which a semi-Markov chain reliability model of a high reliability fault-tolerant control system can be approximated by an enlarged Markov process, the parameters of which are derived from the parameters of the semi-Markov chain.     

On the structure and logic of typical material flow systems†

A queueing network technique (Solberg's CAN-Q) and a flow control simulator (SINDECS) are applied to investigate general, fundamental performance properties of material flow systems (MFS). The effects of a system's structure and flow logic on performance are compared for three typical flow systems: transfer line, recirculating conveyor loop, and job shop. The concepts of Most Economical MFS for a given performance level, Iso-Performance MTS combinations, and Overall MFS Configuration Measures are introduced.     

建筑结构基于LMI的鲁棒非脆弱H∞控制

考虑一维地震动作用和结构参数不确定性影响,提出一种基于线性矩阵不等式(Linear Matrix Inequalities, LMI)的鲁棒非脆弱H_∞控制方法。引入工程中常用的二次型最优指标,并应用线性矩阵不等式减小求解的复杂度,使得控制器的性能指标容易衡量,设计相对简单,便于工程应用。以一个三层剪切型结构模型为例进行数值分析,并与传统H_∞控制方法进行对比,仿真结果初步表明:1) 所提方法具有很好的控制效果和鲁棒性;2) 合理地计算结构参数值,可使控制系统在具有最优反应品质的前提下,获得相对更好的鲁棒性和非脆弱性。     

Generischer Steuerungs-Algorithmus zur Erstellung von Modulen für die Steuerungssoftware von ortsfesten Materialflusssystemen

Automated material handling systems are increasingly used in industry due to short process times and high throughputs. These systems have to be custom-built in order to utilize their full potential and therefore require individually created control software. To create this individual control software extensive manual programming is required, since a modular structure of the control algorithm with predefined modules is often missing. We fill this gap and describe such a modular control structure, which is based upon a two-layer architecture separating the hardware control from the material flow control. Our control structure uses a five-phase generic control algorithm, which represents a template by which the modules can be worked out. We describe this five-phase generic control algorithm, implement it for a demonstrator scenario and show its proper functionality. We show that with our two-layer architecture and the generic control algorithm predefined modules for the conveyor hardware and material flow elements can be created and then assembled in the needed configuration. Therefore, the presented method allows to create the control software for a custom-built material handling system by arranging predefined modules, thus without manual programming.     

Comparison of DBR with CONWIP in an unbalanced production line with three stations

The recently developed alternatives to traditional production planning and control systems such as material requirement planning (MRP) and Kanban are the drum–buffer–rope (DBR) and CONWIP (CONstant Work In Process) systems. Each system is best described as a combination push (like an MRP)/pull (like a Kanban) logistical procedure. Materials are pulled into the shop via the appropriate logic, and once released, materials are then pushed to subsequent workcentres. The performance of the DBR and CONWIP control policies are analysed and compared in a three-stage unbalanced tandem production line. Using a continuous Markov process model, steady-state probability distributions for the systems are derived, and then the performance measures of the systems can be evaluated. To compare the two systems, an optimization model for each system is proposed. From sensitivity analyses for the optimization models, the proposed models are validated, the differences of the two systems are investigated, and it is found that DBR is better than CONWIP under the proposed performance measures.     

An efficient evolutionary structural optimization method with smooth edges based on the game of building blocks

Although bi-directional evolutionary structural optimization (BESO) has the advantages of a simple concept and clear-cut solutions, the edges of the optimal solution are normally non-smooth. This article proposes an approach that directly represents the smooth structure using finite elements. The pseudo-auxiliary line is introduced to make the staggered boundary approach a smooth one, and a rule is presented to make the boundary element deformable to describe the structure’s edges. To improve the efficiency, the game of building blocks is incorporated into the classical BESO algorithm. A set of basic blocks is predefined and is positioned in a suitable location to assemble the optimal structure. In this way, the optimal structure has better mechanical performance and smooth edges with acceptable computational cost. The roundness of corners is easily controlled by adjusting the configuration of the basic blocks. Several two- and three-dimensional numerical examples investigate the effects of the parameters of auxiliary lines and the shape of basic blocks on the boundary smoothness and optimization performance. The efficiency of the proposed method is justified through these examples.     

面向生产系统重构的物流仿真

指出了物流在生产系统中的重要性,提出了通过物流来重构生产系统的思想,在这个思想的基础上给出了递阶层次控制结构和基于时间优先级的任务队列的物流控制方法,同时规范化了3种物流运输策略,最终建立了面向生产系统重构的物流仿真平台,为物流系统重构提供了可靠依据,能满足市场多变的要求。