摘要:

We introduce a zero-one integer programming model for the simultaneous solution of the cell formation and operation allocation problem in cellular manufacturing. We assume that there is a set of existing machines in a manufacturing shop and that there is a set of part types to be processed on these machines. Each part type is assumed to have more than one process plan, and each operation of a part type may be performed on more than one machine. The objective of the model is to simultaneously form machine groups (cells) and allocate operations of the part types to the regrouped machines in such a way as to minimize the sum of operation costs, refixturing costs and transportation costs. Computational results are provided to demonstrate the viability of the model.

ISSN:0020-7543    

DOI:10.1080/00207549508930134

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This research explored in depth the integration of a machinist's concept of manufacturing precedence among part features with a complete and explicit graph representation for alternative process plans, A precedence graph that captures the implicit predecessor-successor cost for any directed pair of features observed in the part replaces the state space representation adopted by AI based search strategies. The Hamiltonian path (HP) analogy for a process plan was developed and the Latin multiplication method (LMM) for constrained enumeration of all feasible HP's was implemented in a Turbo Pascal program running on a 486/25 PC. The program was tested using several examples of actual industrial parts obtained from the literature. The experimental results showed that severe constraints are imposed on problem size due to memory limitations imposed by the DOS environment, that the computational burden of using constrained enumeration is heavy and that there is need for using randomly generated alternative feasible plans and iteratively reducing their overall cost. It was observed that the sparseness and connectivity properties of individual precedence graphs improved program execution time. The thrust of this research was bidirectional—incorporating the machinist's heuristic knowledge of manufacturing precedences and implicit costs to make generative CAPP software viable in practice, and systematically generating and ranking several feasible process plans which the planner may not have even considered in the first

ISSN:0020-7543    

DOI:10.1080/00207549508930135

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In a continuous-review or re-order level inventory control (Q,R) system, the safety stock is maintained to protect the system from the risk of stockouts during the replenishment lead time. Most inventory models assume that the lead time is ‘fixed’, and calculate the optimal level of safety stock on the basis of this assumption. We question this ’fixed lead time’ assumption. We recognize from the literature that manufacturing lead time is a function of lot size in many manufacturing environments, and explicitly consider the impact of lot size on the lead time and safety stock requirement. In so doing, we attempt to demonstrate that significant savings can occur if firms consider the interrelationships between the lot size and safety stock decisions. This paper begins with a discussion of the relationship between lot size and lead time. We then present an iterative algorithm that determines lot size and safety stock simultaneously, and compare it against a more conventional sequential approach. An example is provided to clarify the iteration proccedure, and a sensitivity analysis is used to test the performance of the proposed algorithm.

ISSN:0020-7543    

DOI:10.1080/00207549508930136

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An experimental investigation of factors affecting the scheduling of a system of non-identical, parallel processors using a series of experimental designs was carried out. System variables included were processor capacity relationships, sequencing and assignment rules, job size, and product demand distributions. The effect of the variables was measured by comparing mean flow times, proportion of jobs tardy, and processor utilization spread. Results showed that system loading and set-up times play a major role in system performance. Grouping jobs by product will minimize set-up times and hence mean flow time and tardiness at the expense of controlling individual processor usage. Factors involving processor capacities and assignment rules tend to have no effect on any of the system performance measures. Variability in job size and product demand tended to give flexibility in controlling individual processor utilization.

ISSN:0020-7543    

DOI:10.1080/00207549508930137

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We present solution methods to the problem of synchronizing parallel machining operations in order to avoid overlapping tool changes. The proposed algorithm utilizes results from the economic lot scheduling problem and modifies the machining speeds of the various operations in accordance with the minimum machining cost objective. The procedure is demonstrated through a numerical example.

ISSN:0020-7543    

DOI:10.1080/00207549508930138

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Group technology (GT) offers many advantages to firms engaged in batch manufacturing, including lower setup times, reduced lot sizes, lower lead times, and easier production planning and control. Period Batch Control (PBC) has been proposed in the literature as a simple production planning and control system for a GT environment, based on the choice of a cycle length. Unfortunately, there are no published studies providing guidelines for the choice of an optimal cycle length. In this paper we develop a cost minimization model for examining the choice of cycle length, and demonstrate its use by applying it to four published data sets. The analysis shows that the cell design itself directly affects total inventory and overtime costs and the choice of cycle length; that demand increases can be very expensive for a given cell design; and that the degree of demand uncertainty is an important factor in PBC design. The key managerial consideration is the amount of slack capacity to build into the cell designs to handle demand uncertainty. Finally, we studied the effect of safety stocks on costs and cycle lengths. Results indicate that safety stocks can reduce both total cost and cycle length.

ISSN:0020-7543    

DOI:10.1080/00207549508930139

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Machine vision has the potential to significantly impact both quality and productivity in computer integrated manufacturing, due to its versatility, flexibility and relative speed. Unfortunately, algorithmic development has not kept pace with advances in vision hardware technology, particularly in the areas of inspection and decision making. This paper deals with the development of machine vision algorithms for automated inspection of production parts. The inspection system presented in this work consists of three parts in series: segmentation, recognition and analysis. The input of this system is a set of ordered boundary data extracted from the object, and the output includes the identity of this object, and its pose, dimension and out-of-profile error, Computer experiments have shown the proposed algorithms to be consistently accurate and extremely fast. These algorithms can be easily programmable lo inspect different types of shapes, which makes the vision system generic and flexible. Furthermore, these algorithms were developed based on the current definitions of dimensioning and tolerancing standards provided by ANSI YI4-5M-I982, so that the results generated by the system are unique and interpretable.

ISSN:0020-7543    

DOI:10.1080/00207549508930140

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Master production scheduling is complicated by demand uncertainty. The problem from uncertain forecasts is scheduling either too few or too many components relative to actual demand. To cope with this problem, schedulers often form judgments about future forecasts and they adapt production schedules to reflect beliefs and opinions about forecast errors. The research literature on scheduling has largely ignored formal methods for capturing these informal judgments and injecting them explicitly, rather than informally, into the master scheduling process. The current research demonstrates a method for using subjective assessments of forecast accuracy to improve master scheduling. First, a production loss function is derived using performance data from computer simulations of the production environment. Second, subjective assessments of forecasts errors are integrated with the loss function to reveal how forecasts should be adjusted to minimize expected scheduling losses. The procedure enhances intuitive judgmental scheduling; it reveals how managerial beliefs can be formally used to intentionally and optimally bias forecasts. In applying the procedure to 44 simulated MRP configurations, the optimally-biased forecasts are superior to unadjusted forecasts and provide an objective benchmark for using judgmental adjustments. The results demonstrate opportunities for enhancing master schedules by using subjective assessments of forecasts compared with scheduling without subjective assessments.

ISSN:0020-7543    

DOI:10.1080/00207549508930141

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The job shop scheduling literature deals with problems characterized by a fixed linear process plan for each job: it is assumed that the process planning problem has been solved before scheduling, and no flexibility in the process plan is considered. Our aim here is to propose a solution approach for a joint process plan selection and job shop scheduling problem, taking both operations cost and makespan into account within a multi-objective framework. Due to the complexity of the problem, a two-phase hierarchical method is proposed. In the first phase, a relaxed version of the problem is solved, yielding an approximation of the set of efficient process plans with respect to cost and load balancing objectives. Each process plan is then considered and the corresponding scheduling problem is solved by tabu search; the process plan selection is improved by a two-level hierarchical tabu search algorithm.

ISSN:0020-7543    

DOI:10.1080/00207549508930142

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Here we formulate the facilities layout design optimization problem for a single loop material flow path configuration. Because of the NP-bard nature of the overall search space, we employ a genetic approach to sample the decomposed search spaces. In addition we analyse the following features of the problem: (1) we estimate lower bounds for the unidirectional flow problem along the loop by analysing the bidirectional flow problem; (2) we intelligently sample the search space by designing a knowledge-augmented genetic operator for layout cases with very low flow path dominance because the regular genetic search does not perform very well in such cases; and (3) we exploit qualitative constraints for reducing travel distances in highly circuitous flow paths.

ISSN:0020-7543    

DOI:10.1080/00207549508930143

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor