摘要:

This paper synthesizes recent work by the author and his colleagues on the performance analysis of manufacturing systems and on real-time scheduling methods. It describes a decentralized scheduling/control policy and proposes a method for analyzing the performance of systems that are operated according to the policy. It presents three views of the production system: surplus-based, time-based, and token-based; and shows how they are equivalent in special cases. While there are no assurances of optimality, experience suggests that the policy has desirable characteristics. The paper also suggests how the physical resources and the control policy can be designed together.

ISSN:0740-817X    

DOI:10.1080/07408170008967448

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper proposes and tests an approximation of the solution of a class of piecewise deterministic control problems, typically used in the modeling of manufacturing flow processes. This approximation uses a stochastic programming approach on a suitably discretized and sampled system. The method proceeds through two stages: (i) the Hamilton-Jacobi-Bellman (HJB) dynamic programming equations for the finite horizon continuous time stochastic control problem are discretized over a set of sampled times; this defines an associated discrete time stochastic control problem which, due to the finiteness of the sample path set for the Markov disturbance process, can be written as a stochastic programming problem; and (ii) the very large event tree representing the sample path set is replaced with a reduced tree obtained by randomly sampling over the set of all possible paths. It is shown that the solution of the stochastic program defined on the randomly sampled tree converges toward the solution of the discrete time control problem when the sample size increases to infinity. The discrete time control problem solution converges to the solution of the flow control problem when the discretization mesh tends to zero. A comparison with a direct numerical solution of the dynamic programming equations is made for a single part manufacturing flow control model in order to illustrate the convergence properties. Applications to larger models affected by the curse of dimensionality in a standard dynamic programming techniques show the possible advantages of the method.

ISSN:0740-817X    

DOI:10.1080/07408170008967449

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The importance of finite-capacity schedulers is increasing, with respect to the widespread MRP packages, due to their ability to model the shop floor more accurately. However, this very advantage may turn into a disadvantage, since it is quite difficult to devise a high-quality general purpose scheduler able to cope with the technological peculiarities of different production environments. Furthermore, a detailed schedule is prone to disruptions due to the uncertainty affecting the shop floor. Hence, we need both a modular approach to devise and assemble local schedulers, and a way to link predictive and real time scheduling. To cope with both requirements, we propose a scheduling architecture inspired by the well-known Shifting Bottleneck method. The knowledge needed to cope with technological peculiarities is pushed down the decision hierarchy, to the level of local schedulers. A material coordinator negotiates a reference trajectory with the local schedulers, by deriving local due dates which can be used as targets to drive real time dispatching. The modularity of the architecture is illustrated through an object-oriented conceptual model based on the Unified Modeling Language.

ISSN:0740-817X    

DOI:10.1080/07408170008967450

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Most planning and optimization methods in manufacturing logistics assume centralized or hierarchical decision-making using monolithic models. Motivated by the increasing needs to coordinate diverse decision processes and systems, we investigate an auction-theoretic mechanism for production coordination in a supply chain. Our effort focuses on structural mappings between mathematical decomposition and iterative auction mechanisms wherein agents compete based on their local utilities, announced conflict pricing, and production targets. Building upon the rich literature in optimization and auction-theoretic analysis, we investigate the advantages and limitations of this distributed decision scheme on a large set problem in supply chain production planning. Experimental results show that the proposed auction mechanism provides impressive improvement over the traditional monolithic method without significant degradation to the solution quality.

ISSN:0740-817X    

DOI:10.1080/07408170008967451

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper investigates possible implementations of the autonomous agents concept in flexible manufacturing control. The implementation issues and the effectiveness of different control architectures and algorithms are analyzed by means of a simulation model of a flexible job shop. Extensive experimental results are reported, allowing the evaluation of the trade-off between the degree of autonomy and system performance.

ISSN:0740-817X    

DOI:10.1080/07408170008967452

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, an information theoretic approach is applied to analyze the performance of a decentralized control system. The control system plays the role of a correcting device which decreases the uncertainties associated with state variables of a production line by applying an appropriate “correcting signal” for each deviation from the target. In particular, a distributed feedback control policy is considered to govern a transfer production line, which consists of machines and buffers and processes a single part type in response to a stochastic demand. It is shown how the uncertainty of the demand propagates dynamically into the production system, causing uncertainties associated with buffer levels and machine production rates. The paper proposes upper estimates for these uncertainties as functions of the demand variance, parameters of the distributed controllers and some physical properties of the production line. The bounds are based on dynamic entropy measures of the system state and the control variables. Some practical implications into the area of decentralized controller design are proposed, an information-economical analysis is presented and a numerical study is performed.

ISSN:0740-817X    

DOI:10.1080/07408170008967453

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Research studies on multi-agent systems have been recently boosted by manufacturing and logistics with deep motivations like the presence of independent human deciders with individual goals, the aspiration to dominate the complexity of decision-making in large organizations, the simplicity and robustness of self-reacting distributed systems. After a survey of the multi-agent paradigm and its applications, the paper introduces the notion of hybrid holonic system to study the effect of supervision on a system whose elements negotiate and cooperate in a rule-settled environment to obtain resources for system operation. The supervisor can spur or disincentive agents by assigning/denying resources to them. A simple single-decider optimization model referred to a real application is described, and solution methodologies for optimal resource allocation fitting different scenarios (centralized, distributed, multi-agent) are discussed, identifying ranges of autonomy, quantifying rewarding and defining a negotiation protocol between the agents and the supervisor. Aim of the paper is to describe through an example a general methodology for quantitative decision-making in multi-agent organizations.

ISSN:0740-817X    

DOI:10.1080/07408170008967454

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

There has been a considerable amount of research done on the “cell formation” problem, in which machining cells are designed to process a family of components. More recently, it has been suggested that machining cells should be designed so that they take advantage of the flexibility for processing parts that have alternate, or multiple machine routing possibilities. It is argued that such flexibility will improve machine utilization as well as other measures of cell performance and may reduce the need for centralized cell loading and scheduling algorithms. Unfortunately, if the cell is automated, routing flexibility requirements can create a complex control problem for the cell controller. In this paper we implement a cell controller designed to handle the requirements of the flexible routing of parts and compare the performance of the cell to the case in which each part has only one routing. We find that significant improvements occur when the cell design is capable of processing parts with flexible routings.

ISSN:0740-817X    

DOI:10.1080/07408170008967455

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Aggregate models of detailed scheduling problems are needed to support aggregate decision making such as customer order acceptance. In this paper, we explore the performance of various aggregate models in a decentralized control setting in batch chemical manufacturing (no-wait job shops). Using simulation experiments based on data extracted from an industry application, we conclude that a linear regression based model outperforms a workload based model with regard to capacity utilization and the need for replanning at the decentralized level, specifically in situations with increased capacity utilization and/or a high variety in the job mix.

ISSN:0740-817X    

DOI:10.1080/07408170008967456

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In assembly manufacturing systems there are points in the production process where several component parts are put together in areas called assembly cells so as to form more complex parts called subassemblies. In this paper, we present and compare two variants of the Extended Kanban Control System (EKCS) - a recently developed pull production control mechanism that combines base stock and kanban control - for the production coordination of assembly manufacturing systems. In both variants, the production of a new subassembly is authorized only when an assembly kanban is available. Assembly kanbans become available when finished subassemblies are consumed. If an assembly kanban is available, in the first variant, each component part of a subassembly is released into the assembly cell as soon asitis available (independent release). In the second variant, however, it is released only whenallother component parts also become available (simultaneous release). In both variants, when a component part is released into the assembly cell, it releases its kanban, thus authorizing the production of a new component part.

ISSN:0740-817X    

DOI:10.1080/07408170008967457

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor