Steady Schedule Research Articles

Tourism Color Run Party Event Management in Ngawi

With every city, big or small, hosting a steady schedule of fresh events each year, events or festivals have become an integral element of Indonesian culture. A prime example is Ngawi City, East Java's Color Run Party. Even then, this event brings up several concerns, including the buildup of trash and the degradation of Indonesian culture due to the absence of regional components. The impact of the Color Run Party on society and culture, as well as destination and visitor management, are covered in this article. A qualitative technique is employed as the primary instrument in this research method, which describes the object's natural state. Findings indicate that although destination management and other event-related factors have been well-organized, some areas, such as trash management and the absence of regional cultural components, still need improvement. So that this event not only concentrates on quantity but also considers the effects on the environment and culture, more cautious management is required. Keywords: local culture, tourism destination management, Color Run Party, festival, and event management.

Integrated Scheduling of a Dual-Armed Cluster Tool for Maximizing Steady Schedule Patterns

A cluster tool consists of several single-wafer processing chambers and a wafer handling robot. A wafer has to wait within a chamber after being processed there until it is unloaded by the robot. Such wafer delays may cause wafer quality degradation or variability due to residual gases and heat in the chamber. The tool operation schedule has to maintain identical timing patterns or schedules for each cycle so as to keep wafer delays constant for every wafer. However, at the beginning of the tool operation, the tool is in an empty state and hence we need to make the tool reach such steady schedule by loading wafers into the tool. In this article, we develop a method of scheduling the robot tasks during the start-up period of a cluster tool to reach a target steady schedule quickly as possible. To do this, we model the behaviors of a cluster tool using timed Petri nets and linear system matrices in the max-plus algebra. By analyzing the matrices, we first identify a class of steady schedules which can be reached from the empty tool. We develop the matrices that explain the schedule evolution of the start-up period before reaching the steady period. By examining the matrices, we develop a method of choosing the most desirable one from such class of reachable steady schedules that can be achieved in the minimum time. We also prove that the schedule also minimizes the time duration of the close-down. Finally, we present computational experiments.

Eficiência e governança portuária: evidência do sistema portuário brasileiro

Dada a importância dos portos brasileiros para o desenvolvimento da economia nacional, o presente trabalho buscou avaliar a eficiência dos portos brasileiros em função do sistema de governança portuária. Para tal, avaliou-se a eficiência portuária através da Análise Envoltória de Dados (DEA) orientada a insumos. Foram considerados tanto retornos de escala constantes como retornos variáveis. Os resultados apontam que a eficiência portuária, considerando o tempo de espera dos navios para atracação, é reduzida, indicando a necessidade de investimentos tanto em termos estruturais como na relação entre os atores envolvidos nas operações portuárias.

양팔 클러스터장비의 초기 전이 기간 스케줄링

A cluster tool used in many kinds of semiconductor processes for improving the performance and the quality of wafers has a simple configuration, but its schedule is not easy because of its parallel processing module, a lack of intermediate buffers, and time constraints. While there have been many studies on its schedule, most of them have focused on full cycles in which identical work cycles are repeated under constant task times. In this research, we suggest strategies of start-up transient scheduling which satisfies time constraints and converges into a desirable steady schedule for full work cycle. The proposed schedules are expected robust under the stationary stochastic task times. Finally, we show that the strategies make schedules enters the desirable steady schedule and robust using the simulation.

Schedule Restoration for Single-Armed Cluster Tools

The idle time between two consecutive tasks may seriously affect the wafer quality in some wafer fabrication processes requiring high temperature and pressure. Hence, a cluster tool provides high wafer quality and predictability when operated at a steady schedule, which means that every cycle repeats the same pattern considering not only a sequence but also timing. However, multiple process modules per step can cause the fluctuation of wafer quality even under the same sequence since different modules have different wafer delays. It is known that a dual-armed cluster tool can always have a steady schedule that can be established via a timed event graph and (max, +) algebra. We extend this result to a single-armed cluster tool and generalize the method to establish its steady schedule. Although a cluster tool is initially set on a steady schedule, the schedule can become unsteady after disruptive events, such as wafer alignment failures, and it cannot always return to it. We develop strategies that change the system dynamics of a cluster tool by appropriately delaying some tasks such that any disrupted schedule pattern is stabilized in a finite time. Finally, we examine how they help to flatten wafer delays after a disruption or when tasks have stochastic time fluctuation.

Scheduling start-up and close-down periods of dual-armed cluster tools with wafer delay regulation

Cluster tools have been increasingly used for semiconductor manufacturing. While there have been many studies on cluster tool scheduling, most of them have focused on full work cycles in which identical work cycles are repeated. However, in reality, there are significant transient periods during which an empty tool begins to process new wafers or finishes processing and becomes empty. We should minimise the lengths of transient periods, so that a cluster tool quickly enters a desirable steady schedule for full work cycles or finishes operations quickly. We should also regulate wafer delays within chambers, because they cause wafer quality variation or failures. In this paper, we propose scheduling strategies for transient periods to meet those requirements. We prove that for the close-down period, the earliest starting policy that starts each operation as soon as the preceding operations complete minimises the close-down period while regulating the wafer delays. We also show that for the start-up period, the latest starting policy that starts each operation as late as possible while meeting the deadlines specified by the starting times of the given steady schedule minimises the start-up period. Finally, we suggest a way of minimising the total makespan by optimising the steady schedule.

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Spotlight

A Closed-Form Solution for Schedulability and Optimal Scheduling of Dual-Arm Cluster Tools With Wafer Residency Time Constraint Based on Steady Schedule Analysis

Because of wafer residency time constraints for cluster tools, it is very difficult to schedule them. This paper addresses their scheduling issues and conducts their schedulability and scheduling analysis. A Petri net (PN) model is developed to model them. With this model, to schedule a dual-arm cluster tool with wafer residency time constraints is to determine when and how long the robot should wait for. Based on the model, necessary and sufficient conditions under which the system is schedulable are presented. The conditions can be checked analytically. Meanwhile, an algorithm is developed for the optimal scheduling of dual-arm cluster tools. The algorithm finds an optimal periodic schedule with closed form expressions if it is schedulable. A method is also presented for the implementation of the obtained cyclic schedule by appropriately controlling the initial transient process. Examples are presented to show the application and power of the theory and algorithm.

An Extended Event Graph With Negative Places and Tokens for Time Window Constraints

We introduce places with negative holding times and tokens with negative token counts into a timed event graph in order to model and analyze time window constraints. We extend the enabling and firing rules for such an extended event graph named a negative event graph (NEG). We develop necessary and sufficient conditions based on the circuits for which the NEG is live, that is, an infinite sequence of feasible firing epochs exist for each transition. We prove that the minimum cycle time is the same as the maximum circuit ratio of the circuits with positive token counts. We also show that when there exists circuits with negative token counts, the maximum cycle time is bounded and the same as the minimum circuit ratio of such circuits. A scheduling example for a robot-based cluster tool with wafer residency time constraints for semiconductor manufacturing is explained. Note to Practitioners-Scheduling and control problems for modern man-made systems, including automated manufacturing systems such as cluster tools for semiconductor manufacturing, microcircuits, and real-time software systems, are usually modeled as discrete event systems. Such systems often have strict time constraints on timings of some events. Our results can be used for identifying whether there can be a feasible schedule that satisfies all time constraints, computing the range of the feasible cycle times, and determining a steady schedule with the minimum cycle time. By using the feasibility condition, we also can accommodate the system configuration, the task times, and the task sequence so that the system can satisfy the time constraints while meeting the target cycle time. Such practice is already used for real cluster tool engineering. We have more results on implementing a real-time scheduler and controller for time constrained systems.