An improved formulation for scheduling an automated wet-etch station

Karimi, Iftekhar A.; Tan, Zerlinda Y. L.; Bhushan, Swarnendu

doi:10.1016/j.compchemeng.2004.07.007

Cited by 22 publications

(16 citation statements)

References 8 publications

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“…However, it is not clear, if a satisfactory resolution of this issue is possible. Though it is certainly beyond the scope of this work, we strongly believe that this critical issue, in addition to those mentioned by Karimi et al,51 must be taken care of in any numerical evaluation of MILP models. In our numerical evaluation, we have eliminated the effect of this factor.…”

Section: Numerical Evaluationmentioning

confidence: 95%

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A novel approach to scheduling multipurpose batch plants using unit‐slots

Susarla

Karimi

2009

AIChE Journal

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in Wiley InterScience (www.interscience.wiley.com).Several models for scheduling multipurpose batch plants exist in the literature. The models using unit-specific event points have shown better solution efficiency on various literature examples. This article presents a novel approach to scheduling multipurpose batch plants, which uses unit-slots instead of process-slots to manage shared resources such as material storage. We develop two slightly different models that are even more compact and simpler than that of Sundaramoorthy and Karimi, Chem Eng Sci. 2005;60:2679-2702. Although we focus on material as a shared resource, our multigrid approach rationalizes, generalizes, and improves the current multi-grid approaches for scheduling with shared resources. Our models allow nonsimultaneous transfers of materials into and out of a batch. We show by an example that this flexibility can give better schedules than those from existing models in some cases. Furthermore, our approach uses fewer slots (event-points) on some examples than even those required by the most recent unit-specific event-based model. Numerical evaluation using literature examples shows significant gains in solution efficiency from the use of unit-slots except where the number of unit-slots required for the optimal solution equals that of process slots. We also highlight the importance of constraint sequencing in GAMS implementation for evaluating mixed-integer linear programming based scheduling models fairly. V

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Section: Numerical Evaluationmentioning

confidence: 95%

“…A fair and an unbiased comparison demands careful attention on many factors51 such as hardware, operating system, and software. In our study, we used CPLEX 11/GAMS52 22.8 on a Dell precision PWS690 workstation with Intel® Xeon® 3 GHz CPU, 16 GB RAM, running Windows XP Professional x64 Edition.…”

Section: Numerical Evaluationmentioning

confidence: 99%

A novel approach to scheduling multipurpose batch plants using unit‐slots

Susarla

Karimi

2009

AIChE Journal

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“…A fair, well‐planned, extensive, and comprehensive procedure is essential49 for a reliable assessment of MILP models based on a numerical study. To achieve a solid comparison, we solve the three test problems (Examples 1, 2a, and 2b) for several numbers of partitions and several sets of grid‐point positions.…”

Section: Case Studiesmentioning

confidence: 99%

Piecewise MILP under‐ and overestimators for global optimization of bilinear programs

2008

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in Wiley InterScience (www.interscience.wiley.com).Many practical problems of interest in chemical engineering and other fields can be formulated as bilinear programs (BLPs). For such problems, a local nonlinear programming solver often provides a suboptimal solution or even fails to locate a feasible one. Numerous global optimization algorithms devised for bilinear programs rely on linear programming (LP) relaxation, which is often weak, and, thus, slows down the convergence rate of the global optimization algorithm. An interesting recent development is the idea of using an ab initio partitioning of the search domain to improve the relaxation quality, which results in a relaxation problem that is a mixed-integer linear program (MILP) rather than LP, called as piecewise MILP relaxation. However, much work is in order to fully exploit the potential of such approach. Several novel formulations are developed for piecewise MILP under-and overestimators for BLPs via three systematic approaches, and two segmentation schemes. As is demonstrated and evaluated the superiority of the novel models is shown, using a variety of examples. In addition, metrics are defined to measure the effectiveness of piecewise MILP relaxation within a two-level-relaxation framework, and several theoretical results are presented, as well as valuable insights into the properties of such relaxations, which may prove useful in developing global optimization algorithms.

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“…Bhushan and Karimi (2003) also adopt a Mixed Integer Linear Programming (MILP) approach to generate optimal schedules at a wet station; based on the MILP approach, a two-step heuristic approach is developed. A reformulation of their MILP model is available (Karimi, Tan, and Bhushan 2004). A MILP approach was also recently used by Aguirre, Méndez, and Castro (2011) to model the wet station scheduling problem with several robots; the model proved more efficient than the one developed by Bhushan and Karimi (2003) for solving medium-sized problems.…”

Section: Introductionmentioning

confidence: 99%

Using simulation and hybrid sequencing optimization for makespan reduction at a wet tool

Rotondo

Geraghty

Young

2012

Proceedings Title: Proceedings of the 2012 Winter Simulation Conference (WSC)

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When rigid scheduling rules apply to wet tools, the development of Cycle Time (CT) optimization strategies becomes a relevant challenge. The impact of sequencing optimization on makespan performance at a wet tool is investigated here by means of a hybrid optimization model that combines an exact optimization approach, based on an efficient permutation concept, and a heuristics, based on Genetic Algorithms (GAs). The model also includes a scheduling module that reproduces the control logics governing wet tools operating in a real semiconductor manufacturing plant and proves effective in generating efficient and detailed schedules in short computational times. The realistic assumptions on which the scheduling module is based allow the simulation of different tool configurations. The results obtained show that significant makespan reductions can be achieved by means of a mere sequencing optimization as parallel processing within the wet tools is better exploited.

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An improved formulation for scheduling an automated wet-etch station

Cited by 22 publications

References 8 publications

A novel approach to scheduling multipurpose batch plants using unit‐slots

A novel approach to scheduling multipurpose batch plants using unit‐slots

Piecewise MILP under‐ and overestimators for global optimization of bilinear programs

Using simulation and hybrid sequencing optimization for makespan reduction at a wet tool

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