摘要:

We present and compare a number of branch and bound algorithms for minimizing the total weighted tardiness in job shops. There are basically two types of branching schemes. The first one inserts operations in a partial schedule, while the second one fixes arcs in the disjunctive graph formulation of the problem. The bounding schemes are based on the analysis of precedence constraints, and on the solution of nonpreemptive single machine subproblems that are subject to so-called delayed precedence constraints. We obtain optimal solutions for all the instances with ten jobs and ten machines that we consider, including three tardiness versions of a well-known 10 × 10 instance introduced by Muth and Thompson [1] in 1963.

ISSN:0740-817X    

DOI:10.1080/07408179808966443

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper we present an emergency repair model. We model a situation where failed parts arrive at a repair shop according to a Poisson process. If the stock on hand of serviceable spare parts exceeds a given emergency trigger level, the failed part is sent into normal repair. Otherwise the failed part is sent into an alternative emergency repair channel. Upon arrival failed parts are exchanged for serviceable spare parts, if available. Otherwise the demand is backordered. A backorder is filled with the first part that becomes available from either one of the repair processes. The repair times (including transportation time) are assumed to be exponentially distributed. We analyze the impact of using emergency repair on two service measures: the fraction of demand that is satisfied from stock on hand and the expected duration of a backorder. We calculate the initial stock level and the emergency trigger level that minimize the total cost for a given emergency repair rate. The proposed policy is compared with two other policies: (1) emergency repair is not used and (2) emergency trigger level is zero. We find that significant service improvements and cost reductions can be obtained by using our emergency repair policy. We also present simulation results showing that the distribution of the repair times has a negligible effect on the relevant service measures. Finally, we compare our results with the results of an emergency supply model by Muckstadt and Thomas [1] Again we observe significant cost reductions when using our policy.

ISSN:0740-817X    

DOI:10.1080/07408179808966444

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Empty-vehicle travel time plays an important role in the design and control of automated guided vehicle systems (AGVSs). However, many analytical models of these systems assume the amount of empty-vehicle travel time is the same as the loaded-vehicle travel time. This paper examines empty-vehicle travel time in AGVSs with low traffic intensity. The model uses a discrete-time Markov chain based on vehicle location and represents dispatching rules in the one-step transition matrix. The model can be used to compute moments and cumulative probabilities for the empty-vehicle travel time. Coupled with the loaded-vehicle travel time and the loading/unloading time, similar results can be obtained for the time to service a load request.

ISSN:0740-817X    

DOI:10.1080/07408179808966445

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Previous work by Armstrong and Atkins examined age replacement and spare ordering decisions for a system which contained one machine subject to random failure and with only one spare machine in stock or on order at any one time. In this technical note we consider several extensions to that work which generalize the cost terms and the order lead time while retaining the one-machine one-spare structure of the original paper.

ISSN:0740-817X    

DOI:10.1080/07408179808966446

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This research examines the lead-time setting, capacity utilization, and pricing decisions facing a firm serving customers that are sensitive to quoted lead-times. We model the firm's operations as an M/M/1 queue and treat the demand as being linear in price and quoted lead-time. We analyze the quoted lead-time, capacity utilization, and price that maximize revenues less total variable production costs, WIP holding costs, and lateness penalty costs. We use this analysis to show that the capacity utilization should be lower when (1) customers are more sensitive to lead-times and/or (2) the firm incurs higher congestion related costs and/or (3) the penalty for lateness is higher. Further, we study the robustness of optimal profit contributions when the model parameters are mis-estimated.

ISSN:0740-817X    

DOI:10.1080/07408179808966447

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Motivated by an application in semiconductor manufacturing, we study the problem of minimizing total tardiness on a batch processing machine with incompatibl8e job families, where all jobs of the same family have identical processing times and jobs of different families cannot be processed together. We present a dynamic programming algorithm which has polynomial time complexity when the number of job families and the batch machine capacity are fixed. We also examine various heuristic solution procedures which can provide near optimal solutions in a reasonable amount of computation time.

ISSN:0740-817X    

DOI:10.1080/07408179808966448

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a new algorithm for the flexible manufacturing system (FMS) scheduling problem. The proposed algorithm is a heuristic based on filtered beam search. It considers finite buffer capacity, routing and sequence flexibilities and generates machine and automated guided vehicle (AGV) schedules for a given scheduling period. A new deadlock resolution mechanism is also developed as an integral part of the proposed algorithm. The performance of the algorithm is compared with several machine and AGV dispatching rules using mean flow time, mean tardiness and makespan criteria. It is also used to examine the effects of scheduling factors (i.e., machine and AGV load levels, routing and sequence flexibilities, etc.) on the system performance. The results indicate that the proposed scheduling algorithm yields considerable improvements in system performance over dispatching rules under a wide variety of experimental conditions.

ISSN:0740-817X    

DOI:10.1080/07408179808966449

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We consider the bicriteria scheduling problem of minimizing flowtime and maximum earliness on a single machine. The problem is known to be NP-hard. We develop heuristic procedures for generating all efficient sequences for the cases where machine idle time is either allowed or not allowed. For both cases we also discuss an algorithm that finds the best of the approximately efficient sequences for a given objective function by generating only a small subset of those sequences. We present computational results which demonstrate that the heuristic procedures and the algorithms perform very well.

ISSN:0740-817X    

DOI:10.1080/07408179808966450

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor