Ph.D.s' Dissertations A Study on Design of a Cooperative- Distributed Shop Floor Control System for Computer Integrated Manufacturing
2015.07.29 11:05
| year | 1994 |
|---|---|
| author | Namkyu Park |
| Keyword | Cooperative-Distributive Control System, Re-Negotiation, Shop Floor Control, On-line Monitoring and Control, Computer Integrated Manufacturing ( CIM ) |
| Abstract | A computer integrated manufacturing system(CIMS), which requires computer communication, information, and control technology, has characteristics such as sharing of manufacturing facilities, reduced setup time, dynamic event control, and real-time response. In this dissertation, a cooperative-distributive shop floor control system, MODERATO is proposed, and the performance of the proposed system is compared with an existing system. MODERATO system has a control architecture based on contract net models. It supports autonomy and intelligence of a manufacturing system, and system control through information sharing between control elements. To maintain robustness of this architecture, MODERATO system has 3 kinds of agents - order agent, resource agent, and communication forwarding agent. These 3 agents do the functions for real-time data acquisition, on-line monitoring, and control of system deadlock and dynamic situation. Each agent operates through message exchange. Order agent( OA )performs job allocation, dynamic event control, and can respond to interrupts by rush orders. It also passes messages, such as task information and resource selection, to RA and evaluates bids from RA. OA adopts ´maximize throughput´ as a main strategy for job dispatching and ´due data satisfaction´ as an auxiliary. Furthermore, OA can change dispatching control strategy by itself according to the system status. Resource agent(RA) is a decision maker for each resource. Each RA plays the role of task evaluation and sends a bid message. A bid is selected and awarded from the negotiation between OA and RA. Also presented is an architecture for re-negotiation among RAs using information on resource congestion, whereby resources already assigned can be reallocated. Communication forwarding agent(CFA) is a sort of information buffer that can help information exchange between OA and RA. CFA always maintains most current information on shop floor status. By modelling a flexible manufacturing system using the Petri net, and by incorporating information in CFA into this model, we suggest a methodology and algorithms to forecast, prevent, avoid and resolve system deadlocks. MODERATO system is based on a concept for client/server computing, and has a 2-layered architecture that hide decision making from information processing. All message between OA and RA is sent through CFA. In terms of information handling, OA and RA, as clients, are dedicated to decision making and are free from message exchange. And CFA is wholly dedicated to message handling. In this way, the control logic of an FMS can be made more transparent. To investigate the performance of the MODERATO system, we conducted simulation experiments using SNU-FMS that is installed and operated at ASRI( automation and systems research institute) in SNU( Seoul National University ). Experiment results show that the MODERATO system outperforms the existing system being compared. Especially the higher the congestion level of shop floor, the better the performance of the MODERATO system. |
| c | PhD |
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