Study on the control of a flexible manufacturing cell (FMC) using a multi-processing controller

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Study on the control of a flexible manufacturing cell (FMC) using a multi-processing controller

 

Author: Kwong, Wing-cheong
Title: Study on the control of a flexible manufacturing cell (FMC) using a multi-processing controller
Degree: M.Sc.
Year: 1994
Subject: Flexible manufacturing systems
Computer integrated manufacturing systems
Hong Kong Polytechnic -- Dissertations
Department: Multi-disciplinary Studies
Pages: 119 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1164478
URI: http://theses.lib.polyu.edu.hk/handle/200/3237
Abstract: The flexible manufacturing cell controllers developed by Loughborough University of Technology and National Institute of Standards and Technology respectively use high level languages or commercially available software packages for the FMC integration with a local area network architecture. This is the most popular technique of implementing the control of the FMC. However there are the peer-to-peer communication problems because of the hard-wired communication links among the machines and the cell controller in the FMC. When there is only one common material handling device for a group of a CNC or NC machine in the FMC which is a new classification scheme and a tightly-coupled production system, more traffic is required in the communication links. Some researchers suggested to have separate control and data paths. They recognized that more sophisticated computing and communication technologies would be forthcoming. It is proposed in this study to use a multi-processing controller which provides the multi-tasking architecture and can control up to a maximum of five processes or machines at the same time. All of these processes are only logically separated and the multi-processing controller provides their CNC functions as well as the control of its related automation hardwares in the FMC. Instead of using high level languages and ladder logic for the cell control, part programs running simultaneously in the machines/processes respectively are used in the multi-processing controller. The part program in process 1 which is for the material handling device, plays the role of the scheduling and control of the parts through other machining processes. Although other processes execute different part programs, they only respond to the process 1 through its synchronization directives (wait, execute, send, relieve) entered into the respective part programs as required. This FMC control relies mainly on the single part program for the material handling device in process 1. The ladder logic program which is commonly used for the central control of the FMC, is now used to start and stop of up to five separate processes and its related automation only. Therefore the software architecture of this FMC control is not only centralized (a single ladder logic and part program in process 1 as the master) but also hierarchical (other processes for machining as the slave). Hence the communications links between processes in the FMC is through the internal architecture of the processor and the peer-to-peer communication problem is resolved. Also the part programs for each process of the FMC can be tested in a graphic mode by setting at fast rapid feedrates, and the scheduling and control of the FMC for different part routings can thus be simulated on the graphic display of the operator panel. The same part programs can also be used for the actual FMC control when the controller is set at run mode because the part programs are mainly for the CNC machining. This is different from other simulation programs for FMC/FMS control which are not normally used for the actual cell control. The advantages of having the simulation and controlling the FMC by one multi-processing controller are that there is no discrepancy between the simulation and actual control, the effort of developing the simulation and control programs is less and there are no significant variations in data transfer rates between processes as in LAN which is sometimes very busy at a tightly-coupled FMC. Finally the part programs are used as the software model to find out the best possible part routings, shortest cycle times, deadlocking detection and prevention, and optimal number of buffer stations for the FMC design and control.

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