Real-time Scheduling Method Research Articles

Multi-agent-based scheduling methods for hybrid cellular production lines in semiconductor industry

This article addresses scheduling problems for the hybrid cellular production lines in the semiconductor industry, in which the hybrid cellular production line is defined as the production system composed of both single-functional and multi-functional cellular layouts. Detailed system configuration and material flow of a hybrid cellular production line are presented, and then, the scheduling problems in the hybrid cellular production line are separated into an inter-cell scheduling problem and intra-cell scheduling problems. A multi-agent-based scheduling method is proposed for the inter-cell scheduling problem, and a real-time heuristic scheduling method is proposed for the intra-cell scheduling problem. In the simulation experiments, various scenarios have been compared under the proposed inter-cell and intra-cell scheduling methods with the hybrid cellular production line composed of six cells.

A real-time scheduling method for the cluster tool with wafer transfer delay

In this study, we propose an effective real-time scheduling method based on the timetabling technique for the cluster tool. Instead of considering the no-wait assumption generally adopted in almost all of the previous literature, we take wafer transfer delay into consideration, which implies that a wafer can stay at the current chamber for a certain, limited time before proceeding to the next chamber. In order to improve the total cycle time, an additional pulling procedure to the timetabling is introduced and applied. Numerical examples show that the proposed method gives effective schedules in real time even for practical-sized problems.

A comparison of three heuristics on a practical case of sub-daily staff scheduling

Sub-daily personnel planning, which is the focus of our work offers considerable productivity reserves for companies in certain industries, such as logistics, retail and call centres. However, it also creates complex challenges for the planning software. We compare particle swarm optimisation (PSO), the evolution strategy (ES) and a constructive agent-based heuristic on a set of staff scheduling problems derived from a practical case in logistics. All heuristics significantly outperform conventional manual full-day planning, demonstrating the value of sub-daily scheduling heuristics. PSO delivers the best overall results in terms of solution quality and is the method of choice, when CPU-time is not limited. The approach based on artificial agents is competitive with ES and delivers solutions of almost the same quality as PSO, but is vastly quicker. This suggests that agents could be an interesting method for real-time scheduling or re-scheduling tasks.

Study on Optimal Real-Time Feedback Scheduling of Networked Collaborative Design Project under Uncertainty

Aimed at resource-restrained project scheduling problem under uncertainty which is a hot research spot, a kind of real-time feedback scheduling method is presented in this paper. Before a project is executed, the scheduling plan of all subtasks is made according to ascertain condition. The running procedure of the project is monitored by a workflow management system. When a situation, in which the finish time of the project will be delayed by changed running condition, is detected, the related information is fed back to a scheduling controller; And the controller calculates the controlling data according to optimal objective and then sends it to object scheduled; And then the old plan is rescheduled The concept model for real-time feedback scheduling of cooperative design project with resource-restrained is setup. When only the finish time of subtask is influenced and it is described as interval number, its corresponding mathematic model is setup and converted to an ascertain one by possibility-level, and solve it by GA(Genetic Algorithm). The structure of this GA is given, and a method of chromosome coding, that is the chromosome is segmented according to resources and gene is sorted in task-series, is presented in this paper. A computational example is studied in this paper, the results reveal that the method presented is valid.

DRX-Aware Scheduling Method for Delay-Sensitive Traffic

The Long Term Evolution (LTE) system adopts Discontinuous Reception (DRX) in the link level for power saving to extend the battery life of the User Equipment (UE). A novel real-time DRX-aware scheduling method is proposed for delay-sensitive services in wireless downlink systems. In the scheme, DRX parameters are introduced into the scheduling determinants, so as to reduce packet loss caused by the sleeping process during DRX. Simulation results show that, significant performance gain in terms of packet loss rate and power consumption, can be achieved by the proposed scheme compared with traditional schemes.

Real-time scheduling for twin RMGs in an automated container yard

This paper proposes heuristic-based and local-search-based real-time scheduling methods for twin rail-mounted gantry (RMG) cranes working in a block at an automated container terminal. The methods reschedule the cranes in real time for a given fixed-length look-ahead horizon whenever an RMG finishes a job. One difficulty with this problem is that sometimes additional rehandling of containers needs to be carried out in order to complete a requested job, especially when other containers are stacked on top of the target container. These rehandlings are the main cause of the delay of the crane operations, leading to extended waiting of automated guided vehicles (AGVs) or external trucks that co-work with the cranes. By treating the rehandling operations as independent jobs in our solution methods, we can greatly facilitate the cooperation between the two RMGs. Through this cooperation, the workload of the two RMGs can be better balanced and interference can be more easily avoided, thereby maximizing crane utilization. Simulation experiments show that the waiting times of AGVs and external trucks are significantly reduced due to the increased utilization through cooperation.

Simulation modeling and analysis for production scheduling using real-time dispatching rules: A case study in canned fruit industry

This paper considers a production scheduling problem frequently found in many industries whose raw materials are agricultural products. The study focuses on a production system in processed canned fruit industry as a case study. Common characteristics of the system include: (1) high uncertainties of agricultural raw materials (fresh fruits), both in terms of quality and quantity, which significantly affect the production schedule that is usually planned in advance, (2) multiple types of finished products (can sizes and fruit types), sharing the same resources, thus makes their scheduling interdependent, and (3) the shared resources (retorts) are non-identical which exist to provide services to the bottleneck operation (sterilization) in parallel. The paper has two interrelated objectives: to propose the use of real-time scheduling methods based on dispatching rules for such systems, and to demonstrate the use of computer simulation modeling to imitate the actual production system and how to conduct computational experiment on the simulation model to determine a set of appropriate dispatching rules for the case study industry. Nine real-time, setup dependent, dispatching rules are compared using two types of performance measures: flow time and tardiness. The results show the effectiveness of this approach to supporting the decision-making process in production scheduling of canned fruit products.

Real-time scheduling method for networked discrete control systems

This paper proposes a new scheduling method to obtain a maximum allowable delay bound for a scheduling of networked discrete control systems. The proposed method is formulated in terms of linear matrix inequalities (LMI) and can give a much less conservative delay bound than the existing methods. An event based network scheduling method is presented based on the delay bound obtained through the proposed method, and it can adjust the sampling period to allocate identical utilization to each control loop. The presented method can handle sporadic emergency data, periodic data, and non-real-time data.

2202 人に優しい自律分散型生産システムに関する研究 : 作業者の希望を考慮したリアルタイムスケジューリング(OS2-2 スケジューリングII)

Recently, new distributed architectures of manufacturing systems are proposed, aiming at realizing more flexible control structures of the manufacturing systems. However, the human operators have not yet been discussed for the autonomous components of the distributed manufacturing systems. A real-time scheduling method is proposed, in this research, to select suitable combinations of the human operators, the resources and the jobs for the manufacturing processes. The proposed scheduling method consists of following three steps. In the first step, the human operators select their favorite manufacturing processes which they will carry out in the next time period, based on their preferences. In the second step, the machine tools and the jobs select suitable combinations for the next machining processes. In the third step, the automated guided vehicles and the jobs select suitable combinations for the next transportation processes.

A Study on Real-Time Scheduling of Holonic Manufacturing Systems (5th Report, Estimation Method of Future Status Without Decision Criteria of Other Holons)

This paper deals with a real-time scheduling system of the holonic manufacturing systems (HMS). In the previous papers, real-time scheduling processes have been proposed based on the utility values of the candidate holons. A simulation based procedure has also been implemented to estimate the future status of HMS and to determine the utility values based on the estimated future status. However, it was assumed that the simulation models for estimation include the model representing the decision criteria of all the holons. A new simulation based real-time scheduling method is proposed, in the present paper, to improve the estimation process, which enable all the holons to estimate the future status of the HMS without decision criteria of other holons. An estimation process is developed for the individual job holons and resource holons to estimate the future status of HMS through the simulation. Some case studies of the real-time scheduling are carried out to verify the effectiveness of the proposed method. It is shown, through case studies, that the proposed methods are effective to improve the objective function values of the individual holons.

자동화 컨테이너 터미널의 복수 장치장 크레인을 위한 실시간 작업 계획 수립

본 논문은 교행이 불가능한 두 대의 자동화 크레인을 운영하는 자동화 컨테이너 터미널의 장치장을 대상으로 국지적 탐색 알고리즘을 이용해 실시간 작업계획을 수립하는 방안을 제안한다. 제안방안은 실시간 제약조건을 만족시키기 위해 현재 이후 일정 시간의 작업만을 작업 계획의 대상으로 삼으며, 장치장의 동적인 작업 특성을 고려하여 새로운 작업이 요청될 때마다 작업 계획을 다시 수립한다. 또한, 교행이 불가능한 두 대의 크레인을 운영할 때 발생할 수 있는 크레인 간의 작업 부하 불균형을 해소하기 위해 작업 계획 과정에서 상대 크레인에 의한 사전 재취급과 사전 이적을 통한 두 크레인 간의 협업을 가능하게 하였다. 시뮬레이션을 이용한 실험 결과 제안 방안이 휴리스틱 방안에 비해 우수하며, 크레인 간의 협업이 작업 효율 향상에 도움이 됨을 확인하였다. This paper proposes a realtime scheduling method using local search algorithm for non-crossable yard cranes in automated container terminal. To take into consideration the dynamic property of yard crane operation and satisfy the real time constraint, the proposed method repeatedly builds crane schedule for the jobs in a fixed length look-ahead horizon whenever a new job is requested In addition, the proposed method enables the co-operation between yard cranes through prior re-handling and re-positioning in order to resolve the workload imbalance problem between the two cranes, which is one of the primary causes that lower the performance of yard cranes. Simulation-based experiments have shown that the proposed method outperforms the heuristic based methods, and the cooperation scheme contributes a lot to the performance improvement.

A Study on Real-Time Scheduling of Holonic Manufacturing Systems (4th Report, Multi-objective Optimization Process for Individual Holons and Whole HMSs)

This paper deals with a real-time scheduling system of HMSs (Holonic Manufacturing Systems). A scheduling process based on the utility values have been proposed and applied to the realtime scheduling problems of the HMSs in the previous report. It was shown that the proposed methods generate suitable schedules from the view point of the objective functions of the individual holons in the HMSs. A new real-time scheduling method is proposed, in the paper, to consider both the objective functions of the individual holons and the whole HMSs. In this method, all the pareto optimal combinations of the resource holons and the job holons are generated based on the objective function values of the individual holons. Following this, a most suitable combination is selected from the pareto optimal ones, based on the objective functions of the whole HMSs, such as total make span and total tardiness. It is shown, through case studies, that the proposed method is effective to improve the production schedules from the viewpoint of the objective functions of the whole HMSs in comparison with the previous method.

2108 ホロニック生産システムにおけるシミュレーションに基づくリアルタイムスケジューリング(OS2 生産スケジューリング)

This paper deals with a real-time scheduling system of the Holonic Manufacturing Systems (HMSs). In the previous papers, real-time scheduling processes based on the utility values have been proposed and applied to the HMSs. A simulation based procedure has also been implemented to estimate the future status of HMSs and to determine the utility values aiming at improving scheduling method. However, it was assumed that only one holon in the HMSs carries out the estimation, in the previous research, for the ease of the estimation process. A simulation based real-time scheduling method is newly proposed, in the paper, to improve the objective function values by estimating the future status of HMSs by all the holons. Some case studies of the real-time scheduling are carried out to verify the effectiveness of the proposed method.

201 ホロニック生産システムにおける強化学習を用いたリアルタイムスケジューリング手法(S81 生産システムの新展開I,S81 生産システムの新展開I)

This paper deals with a real-time scheduling system of the Holonic Manufacturing Systems (HMSs). In the previous papers, real-time scheduling method based on the utility values have been proposed and applied to the HMSs. In this method, individual job holons and resource holons determine the utility values for the next machining operation based on their own decision criteria. Reinforcement learning is applied to the job holons, in the paper, in order to make the suitable decision criteria for determination of utility values. Some case studies of the real-time scheduling are carried out to verify the effectiveness of the proposed method.

Advanced Performance Enhancing Mechanisms for Supporting Real-Time Services on DVB-RCS System Environments

This paper describes two way satellite system environments on geostationary orbit (GEO) and performance enhancement mechanisms which reduces round trip time (RTT) and supports real-time services. We use performance enhancing proxy (PEP) for reducing round trip time and user-level real-time scheduler for reducing deadline violation tasks. The user-level real-time scheduling method classifies priority of user process into four types and those are reflected in kernel. With these dual performance enhancement mechanisms, we can improve quality of service (QoS) of end-user who connects to the DVB-RCS system.

MPEG-2 디코딩을 위한 멀티미디어 시스템에서 우선순위에 의한 태스크 스케쥴링 기법

In this paper, we propose an efficient real-time scheduling method of multimedia tasks for decoding frames of MPEG-2 video streams. In our task model, each frame is decoded by a separate multimedia task. The decoding task for each frame is assigned to the priority according to the precedence and importance of frames in a video stream. We use a priority-based scheduling policy in order to effectively allocate the CPU bandwidth to multimedia tasks for MPEG-2 decoding. We show how to dynamically control the fraction of the CPU bandwidth allocated to each multimedia task according to the priority. The primary purpose of our scheduling method is to enhance the real-time performance of the multimedia system by minimizing the number of decoding tasks that have missed their deadlines while reducing the decoding times of these multimedia tasks. The performance of this scheduling method is compared with that of similar mechanisms through simulation experiments.

Genetic-algorithm-based real-time task scheduling with multiple goals

This paper presents and evaluates a new method for real-time task scheduling in multiprocessor systems. Its objectives are to minimize the number of processors required and the total tardiness of tasks. The minimization is carried out through a multiobjective genetic algorithm (GA), because the problem has non-commensurable and competing objectives to be optimized. The experimental results showed that when compared to five methods used previously, such as list-scheduling algorithms and a specific GA, the performance of our algorithm was comparable or better for 178 out of 180 randomly generated task graphs. Also shown is the impact of the sparsity of a task graph on the performance of our algorithm.

Simplification methods for accelerating simulation-based real-time scheduling in a semiconductor wafer fabrication facility

This paper presents a real-time scheduling methodology in a semiconductor wafer fab that produces multiple product types with different due dates. In the suggested real-time scheduling method, lot scheduling rules and batch scheduling rules are selected from sets of candidate rules based on information obtained from discrete event simulation. Since a rule combination that gives the best performance may vary according to the states of the fab, a selected rule combination is employed for a certain period of time and then a new combination is selected and employed. Since multiple simulation runs should be made in the simulation-based real-time scheduling (SBRTS) method, it may take excessively long computation time to react to unexpected events. To reduce response time, we suggest three techniques for accelerating rule comparison. We test these techniques as well as other operational policies that can be used in the SBRTS method through computational experiments on a number of test problems.

Real-Time Manipulation of Alternative Routeings in Flexible Manufacturing Systems: A Simulation Study

This paper presents the results of a simulation study of a typical flexible manufacturing system (FMS) that has routeing flexibility. The objective is this study is to test the effectiveness of the dissimilarity maximisation method (DMM) for real-time FMS scheduling. DMM is an alternative process plan selection method developed for routeing selection in off-line FMS scheduling. An integrated framework that consists of a computer simulation model, which mimics a physical system, a C++ + module, and a linear program solver is used to evaluate the effects of various operational control rules on the system performance. The hypothetical FMS employed in this study consists of seven machining centres, a loading and an unloading area, and six different part types. Owing to the existence of identical machining centres in the system, the part types have alternative routeings. For selecting an incoming part and later routeing it to a machining centre for its next operation, three control rules, namely, first-in first-out/first available (FIFO/FA), equal probability loading (EPL), and dissimilarity maximisation method/first-in first-out (DMM/ FIFO) are used. In this study, DMM is 1. Used as a real-time decision-making tool to select routeings for the parts that are in the system. 2. Tested and benchmarked against FIFO/FA and EPL. The results show that DMM/FIFO outperforms FIFO/FA and EPL on system throughput. Other measures such as average waiting time, average transportation time, and percentage utilisation rates are also investigated to provide insights for the effectiveness of the DMM rule for real-time FMS control applications.

Stability of On-line Compensated Real-time Scheduled Control Tasks

Real-time scheduling methods introduce various types of jitter in task instance execution. For real-time computer-controlled systems, the introduced sampling jitter and sampling-actuation delays may degrade the system performance and even lead to instability in the system. The degradation of the system performance can be compensated on-line by updating the controller parameters at each controller task instance execution, in what we call the compensation approach. In this paper we present stability analysis for controller tasks that perform the compensation approach.