• Industrial Engineering and Management Systems
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• v.1 no.1
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• pp.1-9
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• 2002

Among the state-space description of discrete vent systems, the max-plus algebra is known as one of the effective approach. This paper proposes a model predictive control (MPC) design method based on the max-plus algebra. Several studies related to these topics have been done so far under the constraints that system parameters are constant. However, in practical systems such as production systems, it is common and sometimes inevitable that system parameters vary by each event. Therefore, it is of worth to design a new MPC controller taking account of adjustable system parameters. In this paper, we formulate system parameters as adjustable ones, and they are solved by a linear programing method. Since MPC determines optimal control input considering future reference signals, the controller can be more robust and the operation cost can be reduced. Finally, the proposed method is applied to a production system with three machines, and the effectiveness of the proposed method is verified through a numerical simulation.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.2
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• pp.191-200
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• 2007

We propose the QoS (Quality of Service) assurance model for AMR (Adaptive MultiRate) voice users considering the capacity and service quality jointly in downlink WCDMA system. For this purpose, we introduce a new system performance measure and the number-based AMR mode allocation scheme. The proposed number-based AMR mode allocation can be operated only with the information of total number of ongoing users. Therefore, it can be more simply implemented than the existing power-based allocation. The proposed system performance measure considers the stochastic variations of AMR modes of ongoing users and can be analytically obtained using CTMC (Continuous Time Markov Chain) modeling. In order to validate the proposed analytical model, a discrete event-based simulation model is also developed. The performance measure obtained from the analytical model is in agreement with the simulation results and is expected to be useful for parameter optimization.

• Industrial Engineering and Management Systems
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• v.4 no.2
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• pp.117-122
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• 2005

An assembly system (AS), a valuable tool for mass production, is generally composed of a number of workstations and a transport system. While the workstations perform some preplanned operations, the transport system moves the assemblies by special designed pallets from one station to another. One common problem associated with automatic assembly systems is that some assembly operations may have relatively long cycle times. As a consequence, the productivity, as determined by the operations with the longest cycle time, can be reduced significantly. Therefore, special forms of parallel workstations were developed to improve the performance of an assembly system. In this paper, three most commonly used parallel stations: on-line, off-line and tunnel-gated stations in a free transfer assembly system are studied via discrete event simulation. Our findings revealed that the off-line parallel system has the best performance because the two independent parallel stations can lower the buffer requirement; reduce the sensitivity to variability of processing time and balance of a line. On-line parallel systems were found to have a relatively poor performance, because the operations of two parallel stations block each other, and higher buffer capacity is required to achieve similar capacity. The tunnel-gated system was more efficient than the on-line system since the first parallel station can operate independently. More importantly, we have quantified the productivity of the three different strategies mentioned. Engineers can choose the optimal strategies for installing parallel stations under their working environment.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.1
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• pp.101-108
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• 1997

The initial token value required to the optimal performance of discrete event systems can be decided by Sum of Delay Time and Synchronic Time ratio, which are new synchronic variables in Timed Place Petri Nets. For the system consisting of two Live-and-Bounded circuits(LB-circuits) fused in common Transition-Transition-Path or common Place-Place-Path, we prove that the Synchronic Time Ratio is the initial token ratio between two LB-circuits to optimally perform system functions. These results are generalized and formulated as a theorem. The initial tokens of a specific place can imply shared resources. Using the theorem, we can decide the minimum number of the shared resources to obtain the optimal performance, and minimize the idling time of resources. As an example, an automated assembly system is modeled by Timed Place Petri Net, and the initial tokens to achieve the optimal system performance are identified. All the values are verified by simulation.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.2
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• pp.22-31
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• 2004

A problem of task rescheduling using a coordinator in a structural decentralized control of supervisory control theory is formulated. we consider that the overall system is divided into a number of local systems. Using an example of a chemical batch reaction process, it has shown that after local supervisors have been established for a given task, a coordinator can be used to solve some rescheduling problems among local plants for new or modified tasks. The coordination system models the interactions of local plants, and is consisting of only the shared events of local plants, so simpler to synthesize. A coordinator is designed based on the specifications given for the coordination system. Under the 'structural' conditions developed in this paper, the combined concurrent actions of the coordinator with the existing local supervisors will achieve the rescheduling requirements. Again since the conditions are structural (not specification-dependent), once the coordination architecture has been established, it can be used for a number of different tasks without further verifications.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.5
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• pp.34-45
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• 2000

In this paper, a multiagent fault-tolerant supervisory control methodology is proposed for serial production systems under partial observation. To this end, the idea of multiagent control is incorporated with the fault-tolerant supervisory control of discrete event systems. Especially, the concept of mutual fault-tolerance between cascaded processes is established and the unobservable fault identification utilizing the difference information of the controlled results is investigated. Then the synthesis of agent supervisors is formulated based on the proposed concept. A case study of the fault-propagation control of polypropylene prepolymerization and polymerization processes is provided to illustrate the proposed control policy.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.116-123
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• 2018

These days, geographic information system has released in everyday life and industries. However, the shipyard only uses it to manage the layout of the yard. In this study, we apply the Geographic Information System to shipbuilding block logistics simulation to analyse the behavior of bogies and forklifts carrying blocks and materials in the shipyard. The shipyard manages daily block logistics plans at the execution planning stage. However, since it is a daily plan, it is difficult to respond to an unexpected situation immediately, and application to judge a certain value or higher value is insufficient. Therefore, a simulation model was created using the shape and attribute information inherent in the geographic information system to verify and improve the block logistics of the mid-and long-term yards. Through this simulation model, we will analyse loads on the workplace, stockyard, and road, and contribute to overall logistics improvement from the point of view of resource planning. In addition, the results of the simulation are reflected in the planning, to help support various decisions.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.269-277
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• 2009

The current paper focuses on the analysis of transient cavitating flow in pressurised polyethylene pipes, which are characterized by viscoelastic rheological behaviour. A hydraulic transient solver that describes fluid transients in plastic pipes has been developed. This solver incorporates the description of dynamic effects related to the energy dissipation (unsteady friction), the rheological mechanical behaviour of the viscoelastic pipe and the cavitating pipe flow. The Discrete Vapour Cavity Model (DVCM) and the Discrete Gas Cavity Model (DGCM) have been used to describe transient cavitating flow. Such models assume that discrete air cavities are formed in fixed sections of the pipeline and consider a constant wave speed in pipe reaches between these cavities. The cavity dimension (and pressure) is allowed to grow and collapse according to the mass conservation principle. An extensive experimental programme has been carried out in an experimental set-up composed of high-density polyethylene (HDPE) pipes, assembled at Instituto Superior T$\acute{e}$cnico of Lisbon, Portugal. The experimental facility is composed of a single pipeline with a total length of 203 m and inner diameter of 44 mm. The creep function of HDPE pipes was determined by using an inverse model based on transient pressure data collected during experimental runs without cavitating flow. Transient tests were carried out by the fast closure of the ball valves located at downstream end of the pipeline for the non-cavitating flow and at upstream for the cavitating flow. Once the rheological behaviour of HDPE pipes were known, computational simulations have been run in order to describe the hydraulic behaviour of the system for the cavitating pipe flow. The calibrated transient solver is capable of accurately describing the attenuation, dispersion and shape of observed transient pressures. The effects related to the viscoelasticity of HDPE pipes and to the occurrence of vapour pressures during the transient event are discussed.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1184-1189
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• 2003

Map building and position estimation capabilities are practically indispensable for a mobile robot to execute its given tasks in its working environments. An autonomous map building method and a smart localization method is proposed in our previous works. The experimental verifications are carried out in this paper. We applied the proposed algorithms to mobile service robots in large-scale indoor buildings. Experimental results show that our strategy is reliable and feasible in tough conditions like non-polygonal and dynamic environments. The advantages of the algorithms are well-illustrated through real experiments.

• Journal of Korean Society for Quality Management
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• v.18 no.2
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• pp.54-68
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• 1990

Contingency response in a FMS system requires that the system be able to identify and evaluate a number of alternatives. This paper is outlined that DSS completes with a problem processor in corporating Timed Petri Nets model, and a data base system. DSS enables the FMS user to get the maximum benefit from a FMS. The structure of this DSS parallels the organizational activities involved in running the FMS. In designing a shop floor controller for FMS, interactions between the different real time, discrete event functions must be established. The specification of the machine tool and material handling system functions working as a concurrent and cooperative system is given in terms of Timed Petri Nets. In addition, the basic concepts and uses of Petri Nets are surveyed. The system to be studied is first modelled by a Timed Petri Nets and then procedure for evaluating the FMS system performance are presented. Numerical examples are studied to illustrate a session of the FMS used-DSS interaction.