摘要:

In this paper, we consider the FMS planning problem of determining optimal machine workload assignments in order to rninimizemean part flow time. We decompose this problem into the subproblems of first forming machine groups and next assigning operations to these groups. Three types of grouping configurations—no grouping, partial grouping and total grouping—are considered. In bothno groupingandpartial grouping, each machine is tooled differently. While each operation is assigned to only one machine in no grouping, partial grouping permits multiple operation assignments. On the other hand,total groupingpartitions the machines into groups of identically-tooled machines; each machine within a group is capable of performing the same set of operations. Within this grouping framework, we consider three machine loading objectives—minimizing the total deviation from the optimal group utilization levels, minimizing part travel and maximizing routing flexibility, for generating a variety of system configurations.

ISSN:0740-817X    

DOI:10.1080/07408179408966624

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We examine the effect of variability on the performance of an assembly system where two stations feed another station and a competing system where two independent stations are fed by a single station. We study the impact of variability in processing times, variability due to unreliable workstations, and variability due to imperfect yield. The above impact is examined for both PUSH and PULL manufacturing environments. We also discuss design features of the two configurations that could be used to recover part of the output lost due to variability.

ISSN:0740-817X    

DOI:10.1080/07408179408966625

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A robust schedule is defined as a schedule that is insensitive to unforeseen shop floor disturbances given an assumed control policy. In this paper, a definition of schedule robustness is developed which comprises two components: post-disturbance make-span and post-disturbance makespan variability. We have developed robustness measures and robust scheduling methods for the case where a “right-shift” control policy is used. On occurrence of a disruption, the right-shift policy maintains the scheduling sequence while delaying the unfinished jobs as much as necessary to accommodate the disruption. An exact measure of schedule robustness is derived for the case in which only a single disruption occurs within the planning horizon. A surrogate measure is developed for the more complex case in which multiple disruptions may occur. This surrogate measure is then embedded in a genetic algorithm to generate robust schedules for job-shops. Experimental results show that robust schedules significantly outperform schedules based on makespan alone.

ISSN:0740-817X    

DOI:10.1080/07408179408966626

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the first part of this review [62] we described the characteristics of semiconductor manufacturing environments and reviewed research on system performance evaluation and production planning. In this paper we focus on shop-floor control problems. We classify research to date by the solution techniques used, and discuss the relative advantages and disadvantages of the various approaches. We discuss the relationship between shop-floor control and production planning and suggest future research directions.

ISSN:0740-817X    

DOI:10.1080/07408179408966627

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper discusses thefractional operator problem, which involves the production of many parts on several parallel machines. In this problem, operators can monitor more than one adjacent machine subject to the operator requirements of the parts being produced on those machines. Thus, the combination of parts being produced determines the number of operators required. We consider minimizing the average setup and holding costs subject to a constraint on the number of operators available. We describe planning- and control-level versions of the problem and give formulations that provide a basis for future work.

ISSN:0740-817X    

DOI:10.1080/07408179408966628

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Among recent studies considering the splitting of an order among several suppliers (i.e., in “multiple sourcing”), one group considered only the favorable effect of multiple suppliers on the effective lead time demand and required safety stock, but its effects on the annual order and holding cost components have been ignored. Another group that considers the effect of using two suppliers on all relevant cost components imposes severe restrictions on the suppliers' lead-time distributions as well as the proportion of order-split between the suppliers. Our primary purpose is to present easily-solvable decision models for minimizing the sum of annual holding and ordering costs with two suppliers, subject to a maximum allowable stockout risk; restrictions on lead-time distributions and order-split proportion are completely eliminated. Solving these models gives the optimal total order quantity, reorder point and proportion of split between the two suppliers. Numerical results from our models reveal some unexpected observations; e.g.: (i) In using two suppliers, die reduction of inventory carrying cost (a hitherto unrecognized component) is at least as important, and often considerably more important than the effect of safety-stock-cost reduction, (ii) Although intuitively one might use suppliers with the shortest (mean) lead times, it is actually better to have two suppliers such mat the second supplier's mean lead time is “suitably” larger man the first's; this could mean excluding the one with lowest mean lead times among the candidates for the second supplier, (iii) The optimal proportion of split varies with, among other factors, the difference in the suppliers' mean lead times.

ISSN:0740-817X    

DOI:10.1080/07408179408966629

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this paper we consider a single machine scheduling problem with two criteria; minimizing both maximum tardiness and the number of tardy jobs. We present both heuristic and branch-and-bound algorithms to find the schedule which minimizes the number of tardy jobs among all schedules having minimal maximum tardiness. Computational results show that problems with up to 40 jobs can be solved in less than one minute of computer time, and solution difficulty tends to increase as the range of due dates increases relative to the total processing time. We extend our results to generate all nondominated schedules for the two criteria. Computational experiments indicate that all non-dominated solutions to problems with 40 jobs can be generated. However, solution difficulty for these problems is highly dependent on problem parameters.

ISSN:0740-817X    

DOI:10.1080/07408179408966630

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We consider the problem of lot sizing when learning results in decreasing setup costs. Finding optimal lot sizes requires information about future setup costs and also the horizon length, which can be difficult to forecast. We analyze an intuitively appealing and well knownmyopic policy(Part Period Balancing). This policy sets the current lot size such that the current setup cost equals the holding cost for the current lot. It is easy to implement and does not require information on future setup costs. It is shown that the number of setups in the myopic policy is at most one greater than the optimal number of setups. Using this bound, we show that the myopic policy costs no more than 6/(3 + min(l, 1.5R)) times the optimal cost, whereRis the ratio of the minimum setup cost to the initial setup cost. Computational experiments show that its average performance is good even for horizons as short as eight times the initial reorder interval. Further, our study shows that the average performance improves withR.

ISSN:0740-817X    

DOI:10.1080/07408179408966631

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor