International Journal of Planning and Scheduling (6 papers in press)
Simultaneous Scheduling and Lot-Sizing with Earliness/Tardiness Penalties
by Parinaz Vaez, Mehdi Bijari, Ghasem Moslehi
Abstract: The problem investigated in this paper is one of the simultaneous lot-sizing and scheduling problem with earliness/tardiness penalties along with the sequence-dependent setup time and cost. Minimizing earliness and tardiness is of interest both in just-in-time production systems and in make-to-order ones. A mathematical model is presented similar to the travelling salesman problem. The problem objective is to determine the production lot-size and their schedules. In spite of its wide applications, this problem has not yet been reported in the literature. To solve the problem, two meta-heuristic algorithms: Tabu Search and Ant Colony System are presented. The efficiencies of the algorithms are investigated for different sets of problems. The results show that each of the Ant Colony System and the Tabu Search obtained optimal solutions for 196 and 203 problems, respectively, out of among the 333 problem instances. Despite the differences between these two methods, neither can be statistically preferred.
Keywords: Scheduling; Lot-sizing; Earliness/Tardiness; Tabu Search; Ant Colony System.
Analyses of the phase I postanesthesia care unit baseline capacity and effect of disruptions to its beds or nurse availability on operating room workflow.
by Franklin Dexter, Danial Khorasanian, Ghasem Moslehi
Abstract: When there is not a free bed or nurse in the phase I postanaesthesia care unit (PACU), the patient recovers in the operating room, preventing the start of subsequent case(s), until capacity is available in the PACU. We report some real examples of situations in which the capacity of the PACU decreases unexpectedly, and analyse their implications on the operating room workflow. For this purpose, first, different surgical suite sizes are simulated, considering the important factors observed in real time. The baseline capacities of PACU beds and nurses are determined. Then, the characteristics of some situations with less capacity than the baseline are investigated, caused by disruptions of either decreasing the number of beds or nursing hours in the PACU. For example, when the number of PACU beds in 8-OR surgical suites decreases to half of the baseline, the percentage of days with delay increases from 0.22% to 86.79%.
Keywords: Operating room workflow; PACU beds and nurses; Capacity; Disruption; Analytics.
A Survey and Classification of Service-Staff Scheduling Models that Address Employee Preferences
by John Loucks
Abstract: Scheduling service workers in operations that require staffing over long days and a long week, oftentimes 24/7, is a problem that continues to grow in importance and applicability. As research in this area progresses, proposed scheduling models are increasingly including consideration of employee preferences. Roughly 325 articles containing workforce scheduling models were examined, of which 48 (about 15%) explicitly address worker preferences. Findings suggest an upward trend over time in the number of scheduling models with preference consideration. Shift and days-off preferences are most often addressed, with task assignment, total hours scheduled, and work location preferences receiving much less attention. This study brings much needed organization to, and hence a better picture of, the research of this type published to date. The models surveyed are classified by types of preferences considered, source of the preferences (i.e. individual or staff), and priority criterion in satisfying the preferences.
Keywords: Staff scheduling; workforce scheduling; scheduling models; employee schedule preferences; worker preferences; schedule preferences; shift preferences; days-off preferences; task assignment preferences; employee satisfaction.
Material-Handling-System-based Input Control Policy for Wafer Fabrication
by Subhash C. Sarin
Abstract: In this paper, a new input control strategy is proposed for wafer fabrication facilities. This strategy is an adaptation of workload regulating and CONWIP, and comprises of two sequential steps: 1) determination of operational lot sizes; and 2) release of lots based on a material handling system-based CONLOAD approach. We show the superiority of our strategy over a CONWIP-based policy via simulation of a real-life wafer fab. An approach for determining target workload levels for the proposed strategy is also presented.
Keywords: input control; lot sizing; CONWIP; shop floor control; wafer fabrication; simulation.
New Heuristics For The Balanced K-Chinese Postmen Problem
by Yasemin Limon, Meral Azizoglu
Abstract: In this study, we consider a directed k-Chinese Postmen Problem that aims to balance the costs of the postmen, while maintaining the total cost as small as possible. We formulate the problem as a pure integer nonlinear programming model. We propose three solution algorithms that use efficient incorporation of the heuristic subtour elimination constraints. Our computational results have revealed the satisfactory performances of our heuristic solution algorithms.
Keywords: k-Chinese Postmen Problem; Pure Integer Nonlinear Program; Heuristic Solution Algorithms.
A Two-Stage Stochastic Programming Model for Production Lot-Sizing and Scheduling Under Demand and Raw Material Quality Uncertainties
by Guiping Hu
Abstract: Production planning and scheduling focus on efficient use of resources and are widely used in the manufacturing industry, especially when the system operates in an uncertain environment. The goal of this paper is to provide a two-stage stochastic programming framework for a multi- period, multi-product, lot-sizing and scheduling problem considering uncertainties in both demand and the quality of raw materials. The objectives are to determine the number of units to be produced and the production sequence so that the total production costs are minimized. The decisions made in the first stage include the basic production plan along with the production quantities and sequences, which are later updated with recourse decisions on overtime production made in the second-stage. To demonstrate the proposed decision-making framework, a case study for a manufacturing facility producing braking equipment for the automotive industry was conducted. The results show that the stochastic model is more effective in production planning under the uncertainties considered. The managerial insights derived from this study will facilitate the decision-making for determining optimal production quantities and sequences under uncertainties.
Keywords: Stochastic Programming; Production Planning; Uncertainty; Scheduling.