Tariq A. Aldowaisan

A review of scheduling research involving setup considerations

The majority of scheduling research assumes setup as negligible or part of the processing time. While this assumption simplifies the analysis and/or reflects certain applications, it adversely affects the solution quality for many applications which require explicit treatment of setup. Such applications, coupled with the emergence of production concepts like time-based competition and group technology, have motivated increasing interest to include setup considerations in scheduling problems. This paper provides a comprehensive review of the literature on scheduling problems involving setup times (costs). It classifies scheduling problems into batch and non-batch, sequence-independent and sequence-dependent setup, and categorizes the literature according to the shop environments of single machine, parallel machines, flowshops, and job shops. The suggested classification scheme organizes the scheduling literature involving setup considerations, summarizes the current research results for different problem types, and finally provides guidelines for future research.

New heuristics for no-wait flowshops to minimize makespan

This paper addresses the m-machine no-wait flowshop scheduling problem to minimize makespan. We propose two heuristics that are based on simulated annealing and Genetic Algorithm techniques. We also propose improvement procedures to these heuristics. Extensive computational experiments show that the simulated annealing heuristic outperforms the best two existing heuristics. They also show that the improvement procedures, applied to the Simulated Annealing and Genetic Algorithm, result in significant reduction in error, about 750% error reduction to Simulated Annealing and about 1960% to Genetic Algorithm.

Total flowtime in no-wait flowshops with separated setup times

Abstract An important class of scheduling problems is characterized by a no-wait constraint where the jobs have to be processed continuously without waiting between or on consecutive machines. This constraint of no-waiting arises from the characteristics of the processing technology itself. Considering setup times separate from processing times of the jobs forms another important class of scheduling problems. This is particularly important when the ratio of the setup time to the processing time is non-negligible. This paper addresses a scheduling problem which falls in the combined category of no-wait and separate setup times. The performance measure considered is the total flowtime. This paper addresses the two-machine no-wait flowshop problem where the setup time of a job is separated from its processing time. The performance measure considered is the total flowtime. An elimination criterion is developed and optimal solutions are obtained for two special cases. For the generic case, a heuristic algorithm is provided. Computational experience shows that the algorithm yields good solutions.

A new heuristic and dominance relations for no-wait flowshops with setups

Abstract The two-machine no-wait flowshop problem, where setup times are considered separate from processing times and sequence independent, is addressed with respect to minimizing total flowtime. A local and a global dominance relation are developed and a new heuristic is provided. Furthermore, a lower bound is obtained and used along with the dominance relations in a branch-and-bound algorithm in order to evaluate the efficiency of the heuristic. Computational experience demonstrates the superiority of the local dominance relation and the new heuristic. Scope and purpose No-wait flowshop problems, where jobs have to be processed without interruption between consecutive machines, represent an important area in scheduling. There are several industries where the no-wait flowshop problem applies including the metal, plastic, and chemical industries. For instance, in the case of steel production, the heated metal must continuously go through a sequence of operations before it is cooled in order to prevent defects in the composition of the material. Another important area arises when setup time is considered separate from processing time. Such a consideration is particularly justified when the ratio of setup to processing time is non-negligible. Many applications warrant separate consideration of setup; examples include the re-tooling of multi-tool equipment. Other applications can be found in textile, plastic, chemical, and semi-conductor industries. This paper develops a new heuristic and dominance relations for the two-machine no-wait separate setup flowshop problem, where the performance criterion is total flowtime.

Business process reengineering : an approach for process mapping

The goal of business process reengineering (BPR) is to achieve dramatic improvements in business measures of performance by radically changing the process design. This paper provides a structural definition of the redesign search space using the number of employee types and the number of activities. A systematic approach that combines some linear programming tools with unique BPR principles is then proposed to support the technical redesign of the current process. The approach is illustrated using a public firm process.

No-wait flowshops with bicriteria of makespan and maximum lateness

Abstract We address the m-machine no-wait flowshop scheduling problem with a weighted sum of makespan and maximum lateness criteria, known as bicriteria. The problem reduces to the single criterion of makespan or maximum lateness when a weight of zero is assigned to makespan or maximum lateness. There are many heuristics for the single criterion of makespan. However, no heuristic has been reported in the literature on the single criterion of maximum lateness or the bicriteria problem. We propose a hybrid simulated annealing and a hybrid genetic heuristics, which can be used for the single criterion of makespan or maximum lateness, or the bicriteria problem. We also propose a dominance relation (DR) and a branch-and-bound algorithm. Extensive computational experiments show that the proposed heuristics perform much better than the best existing heuristics for makespan, and perform very well for the single criterion of maximum lateness and the bicriteria problem. The experiments also show that the DR and the branch-and-bound algorithm are quite efficient.

Minimizing total completion time in a no-wait flowshop with sequence-dependent additive changeover times

This paper addresses the problem of minimizing total completion time in a two-machine no-wait flowshop where setup times of the jobs are sequence-dependent. Optimal solutions are obtained for two special flowshops and a dominance relation is developed for the general problem. Several heuristic algorithms with the computational complexity of O(n2) and O(n3) are constructed. The heuristics consist of two phases: in the first phase a starting list is developed and in the second a repeated insertion technique is applied. Computational experience demonstrates that the concept of repeated insertion application is quite useful for any starting list and that solutions for all starting lists converge to about the same value of less than 1% after a few iterations.

No-wait flowshops with bicriteria of makespan and total completion time

We consider the m-machine no-wait flowshop scheduling problem with the objective of minimizing a weighted sum of makespan and total completion time. For the two-machine problem, we develop a dominance relation and embed it within a proposed branch-and-bound algorithm. For the m-machine problem, we propose a heuristic. Computational experiments show that the proposed heuristic outperforms the best existing multi-criteria heuristics and the best single criterion heuristics for makespan and total completion time. The efficiency of the dominance relation and branch-and-bound algorithm is also investigated and shown to be effective.

TWO-MACHINE FLOWSHOP SCHEDULING PROBLEM TO MINIMIZE MAKESPAN OR TOTAL COMPLETION TIME WITH RANDOM AND BOUNDED SETUP TIMES

This paper addresses the two-machine flowshop scheduling problem with separate setup times to minimize makespan or total completion time (TCT). Setup times are relaxed to be random variables rather than deterministic as commonly used in the OR literature. Moreover, distribution-free setup times are used where only the lower and upper bounds are given. Global and local dominance relations are developed for the considered flowshops and an illustrative numerical example is given.

Minimizing total tardiness in no-wait flowshops

Abstract We address the m-machine no-wait flowshop scheduling problem; where the objective is to minimize total tardiness. To the best of our knowledge, the considered problem has not been addressed so far. We propose heuristic solutions since the problem is NP-hard. Initially, we consider a number of dispatching rules commonly used for the considered objective in other scheduling environments. We identify through computational experiments the best performing dispatching rule; and then propose simulated annealing (SA) and genetic algorithms (GA) by using the best performing dispatching rule as an initial solution. This achieves at least 50% improvement in the SA and GA performances. Next, we propose enhanced versions of SA and GA and show through computational experiments that the enhanced versions provide over 90% further improvement. The performance of enhanced GA is slightly better than that of enhanced SA; however, the computation time of enhanced GA is about 10 times that of enhanced SA. Therefore, we conclude that the enhanced SA outperforms the enhanced GA.