The equivalence of two-station closed and open serial production systems with finite buffers

This note presents a simple method for transforming any two-station closed serial production system with finite buffers into an equivalent two-station open system by the appropriate removal of job carriers or buffers.     

The equivalence of two-station closed and open serial production systems with finite buffers

This note presents a simple method for transforming any two-station closed serial production system with finite buffers into an equivalent two-station open system by the appropriate removal of job carriers or buffers.     

Control of deadlock and blocking for production systems with unreliable workstations

Over the past decade, the development of supervisory controllers for automated manufacturing systems has been an active area of research with particular attention focusing on deadlock avoidance. Most work to date assumes that system workstations do not fail. This paper considers deadlock and blocking problems in systems with one unreliable workstation, the objective being to develop supervisory control policies that allocate workstation buffer space so that failure of the workstation server does not propagate through blocking to effectively stall other portions of the system. In short, when a workstation fails, the system should automatically continue producing all part types not requiring that workstation. To accomplish this, the supervisory controller must simultaneously avoid deadlock and buffer allocation states that are not feasible initial states for the 'reduced' system resulting from workstation failure. When the workstation fails, the controller must then simultaneously avoid both deadlock and buffer allocation states that are not feasible initial states for the original system so that transition to normal operation is smooth when the failed workstation is restored. This paper shows this class of problems through several examples, identifies properties that controllers must satisfy to deal effectively with these problems and develops a polynomial control policy that satisfies these properties.     

The impact of restricting the flow of inventory in serial production systems

This research uses simulation technique to compare the output performance of pull production systems with different inter-station storage capacities (ISSC) under various levels of total inventory (INV) in the system, station coefficient of variation (CV), and station down-time (DT). There are two primary findings from this study. First, it shows pull systems with larger ISSC yield a significantly higher output at all levels of INV in the system, station CV, and station DT. Second, it shows that lines using a strict kanban-based pull system can increase output while decreasing WIP inventory simply by allowing the inventory to flow freely between stations. These are major findings considering that the modifications necessary in the system to achieve these results are fairly uncomplicated and should require minimal investment.     

Design of material transportation system for tandem automated guided vehicle systems

A new design concept of materialtransportation system is proposed on the basis of tandem automated guided vehicle (AGV) systems. The first design stage is to find the one and only one optimal transfer point for each traffic zone. All in-process parts to be moved into and out of a zone must go through the specified transfer point and parts can be moved directly to their destinations. The second design stage is to link all transfer points as a 'transportation centre' by several bidirectional tracks. This design concept can simplify material transportation system and provides accurate estimation of traffic load in a zone.     

Location and sequencing of imperfect inspection operations in serial multi-stage production systems

An integrated approach to the problem of allocation of inspection effort in multistage production systems is presented. The problem addresses multiple inspection operations, different disposition policies and inspection, production and repair errors. Quality and cost transfer functions are developed to model production operations and different types of inspection operations in a unified manner and to facilitate the recursive computations required to evaluate alternative system configurations. We formulate the combined inspection location and sequencing problem as a nonlinear mathematical programming problem and solve it with a branch and bound technique, using a heuristic to generate a feasible solution and upper bound. These developments are illustrated with a numerical example.     

Optimal leadtimes planning in serial production systems with earliness and tardiness costs

We consider a production system consisting of N processing stages. The actual leadtimes at the stages are stochastic. The objective is to determine the planned leadtimes at each stage so as to minimize the expected total inventory costs, tardiness penalties, and a backlog penalty for not meeting demand due date at the last stage. Recursive relationships are used for automatic generation and efficient computation of the objective function. The efficiency of the proposed algorithms allows us to obtain new insights regarding operating policies, leadtime delivery reliability, and production line design. The problem is formulated as a convex non-linear programming problem. The latter is then solved using classical convex optimization algorithms. For the special case of exponentially distributed leadtimes, the objective function is derived in a closed form.     

生产浮动性对产线的影响分析及仿真

将生产线分成无缓存区、有缓存区两类,分别建立仿真模型,编写计算程序得到生产时间和产量等数据;结合图表分析数据,得到生产浮动性对单件生产时间及整体生产效率的影响特点;对比分析有无缓存区两种生产线,得到缓存区的设置对提高生产效率具有积极作用,以及在制品数量、总体生产效率随时间的变化趋势等结果;给出了对这些结果的解释,并用Flexsim软件对结果进行了验证.     

Performance analysis for automated storage and retrieval systems

Automated storage and retrieval (AS/R) systems have had a dramatic impact on material handling and inventory control in warehouses and production systems. A unit-load AS/R system is generic and other AS/R systems represent its variations. Common techniques that are used to predict performance of a unit-load AS/RS are a static analysis or computer simulation. A static analysis requires guessing a ratio of single cycles to dual cycles, which can lead to poor prediction. Computer simulation can be time-consuming and expensive. In order to resolve these weaknesses of both techniques, we present a stochastic analysis of a unit-load AS/RS by using a single-server queueing model with unique features. To our knowledge, this is the first study of a stochastic analysis of unit-load AS/R systems by an analytical method. Experimental results show that the proposed method is robust against violation of the underlying assumptions and is effective for both short-term and long-term planning of AS/R systems.     

The use of similarity coefficients in production flow analysis

In production flow analysis, routings are the basic data from which interrelations between operations in a functionally structured production system may be found.

A quantitative analysis of these interrelations permits operations to be grouped into cells in such a way that interdependencies between cells fulfill certain conditions. One possibility of describing interrelations between operations is by using similarity coefficients. The definition of a similarity coefficient determines the specific cell structure based upon its application. Several definitions of similarity coefficients are proposed and their application for the design of cell structures is demonstrated.     

Markovian models for deadlock analysis in automated manufacturing systems

Deadlocks constitute a major issue in the desing and operation of discrete event systems. In automated manufacturing systems, deadlocks assume even greater importance in view of the automated operation. In this paper, we show that Markov chains with absorbing states provide a natural model of manufacturing systems with deadlocks. With illustrative examples, we show that performance indices such as mean time to deadlock and mean number of finished parts before deadlock can be efficiently computed in the modelling framework of Markov chains with absorbing states. We also show that the distribution of time to deadlock can be computed by conducting a transient analysis of the Markov chain model.     

The impact of buffering strategies on the performance of production line systems

This paper investigates the effect of different buffering strategies on the performance of production line systems. Three models of different buffering strategies are studied. Each buffering strategy represents a different degree or flexibility of the storage buffers in the system. We first prove the analytical result that system throughput increases with the degree of flexibility for the three models in this study. Simulation results are then presented to compare the performance of the three models under different system configurations. The results provide useful information for evaluating different design alternatives for a production line.     

Trends in the development of automated control systems in the production of optoelectronic equipment

Automated systems for monitoring the physical parameters and controlling the processes involved in the design and fabrication of optoelectronic equipment is analyzed. Various techniques for implementing such systems and the trends in the further development and improvement of such systems are pointed out. Translated from Izmeritel'naya Tekhnika, No. 7, pp 36–39, July, 1996.     

Formal specification and analysis of production systems

This paper discusses how formal methods can be integrated with existing simulation techniques to specify and analyse production systems. Simulation is very well suited for performance analysis of production systems, such as cycle time or throughput approximations. However, it fails with respect to behavioural analysis of these systems, such as deadlock and livelock detection. Formal methods are mathematical notations and techniques especially designed for behavioural analysis. We show that it is possible to integrate a particular formal methods technique, called model checking , with existing simulation based techniques. The resulting mix provides powerful tools to analyse both performance and behavioural properties of production systems, which will be shown by two examples.     

The effect of machine breakdowns and interstage storage on the performance of production line systems

Both machine breakdowns and interstage storage can significantly affect the efficiency of a production line. In this paper we use an exact analytic model to conduct a detailed study of how these two factors affect the throughput of a line. Based on the empirical results, a simple heuristic method is given to estimate the amount of storage space required to offset the negative effect of machine breakdowns. The results provide useful guidelines for designing or analysing production line systems.     

Multi-job production systems: definition,problems, and product-mix performance portrait of serial lines

This paper pursues two goals: (a) Define a class of widely used in practice flexible manufacturing systems, referred to as Multi-Job Production (MJP) and formulate industrially motivated problems related to their performance. (b) Provide initial results concerning some of these problems pertaining to analysis of the throughput and bottlenecks of MJP serial lines as functions of the product-mix. In MJP systems, all job-types are processed by the same sequence of manufacturing operations, but with different processing time at some or all machines. To analyse MJP with unreliable machines, we introduce the work-based model of production systems, which is insensitive to whether single- or multi-job manufacturing takes place. Based on this model, we investigate the performance of MJP lines as a function of the product-mix. We show, in particular, that for the so-called conflicting jobs there exists a range of product-mixes, wherein the throughput of MJP is larger than that of any constituent job-type manufactured in a single-job regime. To characterise the global behaviour of MJP lines, we introduce the Product-Mix Performance Portrait, which represents the system properties for all product-mixes and which can be used for operations management. Finally, we report the results of an application at an automotive assembly plant.     

Analytical models for analysis of automated warehouse material handling systems

Automated storage and retrieval systems (AS/RSs) and autonomous vehicle storage and retrieval systems (AVS/RSs) are two competing technologies for the handling, storage and retrieval of unit-loads in the reserve section of an automated warehouse. In this paper, we model variants of the two systems as an open queuing network (OQN) and use an existing tool for the analysis of OQNs, called the manufacturing system performance analyser (MPA), for analysing the performance of the AS/RS and AVS/RS. Experimental results are provided to show that MPA is a better choice than simulation to quickly evaluate alternate configurations of the two systems. We use MPA to answer a series of design questions for AS/RS and AVS/RS design conceptualisation.     

The metrological characteristics of automated magnetic measuring systems

Automated systems for precision measurements of the magnetic characteristics and parameters of samples of soft magnetic materials are considered. A list of their metrological characteristics is proposed. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 36–39, November, 1999.