The use of modelling and simulation in the design of flexible manufacturing systems.

Fota, Adriana

1. INTRODUCTION

The use of simulation models in the area of large-sized systems is nowadays very widespread. As far as the design of flexible manufacturing systems (FMS) is concerned, it is a frequently used modern procedure of modelling and simulation. In present, the simulation of flexible manufacturing systems is the most dynamic and controversial field of research in this area, (Abrudan, (1) (9) (9) (6) ). The absence of consecrated mathematical models in the design of flexible manufacturing systems makes the creation of such systems difficult, with consequences on their performances. In a previously paper (Fota, (2) (0) (0) (4) ) one can found elaborate mathematical models used in the dimensioning and the configuration of flexible manufacturing system for circular shafts. The algorithm and simulation program using the Delphi software product have been created through original approaches. The inner structure of flexible manufacturing systems of round shafts processing has been detailed, so that operating systems of all their subsystems may be calculated and computerized systematically, respecting precision and taking into consideration interactions with external environment.

The applicative research within the scientific research project will be performed through simulations on mathematic models. The applicative character of the project research theme is demonstrated simulating the flexible manufacturing system's performance for circular shafts processing. It is a dynamic simulation, performed in real environment and time, based on a reliable theoretical concept. The simulation models will be validated on the computer and on real flexible manufacturing system for real physical applications. After simulating the performance of the flexible fabrication system, the validity of the models will be confirmed, as well as their utility in the design and the management of the processes in real time and environment. Furthermore, it is considered the use of specific software, and programming languages for design and simulation (Delphi, Visual [C.sup.++], and Catia) and the development of new software applicable in the design of any flexible manufacturing system, and the development of new, specialized software, which can be applied in the flexible manufacturing systems design. As a dynamic system, the input function concerning the condition of flexible systems for round shafts processing, may be described as algorithms or complex procedures, which can describe as well as possible, the real function.

Using the software Delphi 7, on the base of dimensioning and modelling structures, a simulation program of flexible manufacturing systems for round shafts processing was drawn up. This simulation language contributes to the quality of the graphical animation, visualizing on the screens the simulating behaviour, except the encoded transcription of the simulation model. The programming language used hereby provides the dynamic simulation of discrete technical systems, where also flexible manufacturing systems for round shafts processing are attached.

2. ASSEMBLING PLAN OF A SIMULATION SYSTEM

On the base of the program conceived, the performance simulation in the case of flexible manufacturing systems for round shafts processing is done successively, in order to process the most complex real item (solid round shafts family), an intermediate item (lifting spindles family) and to process a simple item (axles and spindles family), (Boncoi & Fota 2001). Besides, a simulation of simultaneous processing of the three items above is performed--situation that is frequently met in real environments. Within the system, the three items that have been processed have their own technological flow, whose steps take specific times. In figure 1, a computer display capture during the simulation of the three items processing is shown. The whole system's function is described specifying different interactions between processes.

[FIGURE 1 OMITTED]

For flexible manufacturing systems, items in general interact with the other processes, what explains their movement within the system. Simulation is performed describing the movement of the parts, following different processes, according to the tool-machines, to the transporting and handling means, etc., (Tempelmaier, 2006).

The Delphi programming environment is able to supply automatically entities in the system, according to a predefined delivery sequence. This is possible by setting up lists of destination stations and an optional assignment of some properties or variables for each previously described station. In addition, processing times for each working station have been assigned. The simulation program has the following constraints: the choice of a minimum critical path-type trajectory, the selection of those machines of the station that are available, the choice of the most expensive machines of the station and high degrees of loading. Another limit concerns industrial logistic sub-systems belonging to stations that cannot be used. Other constraints are the full use of all handling stations and the achievement of a minimum path algorithm for robots' displacement within the system. Simulation provides definition of some aspects related to manufacturing management, definition of algorithms for transport methods and detection of "tight points" delaying manufacturing flow, or study of breakdown influence upon the process.

3. DELPHI SIMULATION PROGRAM FOR FLEXIBLE MANUFACTURING SYSTEM

Some specialists consider Delphi a version of Rapid Application Development--RAD of Borland Pascal programming environment (Ispas & Mohora 2001). One of the first things to be understood when working in a RAD environment refers to the fact that a Rapid Application Development environment is technology, offering solutions to several IT related questions, based on a series of concepts, components, and protocols concerning their use (Law & Kelto 1991).

Essential in simulation modelling, the logical element is set up by data structures that are convenient for the event's performance. The object oriented modelling outlook first introduces fundamental model categories by counting key model types of each category and, secondly, it specifies the way of getting programmed objects, starting from the real ones.

The object oriented functional networks methodology has been developed in order to incorporate all the aspects concerning a system: structure, functionality, and behaviour. The model has also been developed to provide the user a neat control at any level of a complex system, without losing any aimed aspect. It is also the case of the flexible manufacturing system that has been conceived. This modelling strategy provides graphical representations by visualizing the model. The structure of such a model is based on the concept according to which any real system can be described as an informational part or an acting part.

Subsequently the main data structures that are used will be described, in order to finish simulation. For a better explanation of an object's features, we hereby provide a short example in Delphi (figure 2).

The concept on which this program is based is described below. Each part follows a technological trajectory. In each working station, a processing time is set (each working station has timing devices). When time is out, a warning sound is heard. The program includes a warning manager.

The moment of the warning, the processes find all the useful information about the part that triggered the warning (the part, the active location, the next working station that has to arrive). After having discovered all information, a robot is involved in the process. It takes over the information needed in order to perform the task, from the warning manager.

Fig. (2) Sequence from Delphi simulation program for FMS

Unit Unit1;
Interface
Uses Windows, Messages, SysUtils, Variants, Classes,
Graphics, Controls, Forms, Dialogs;
Type

 Tform1=class (TForm)
 Private
 {Private declarations}
 Public
 {Public declarations}
 End;
Variable
 Form1: Tform1;
Implementation
{$R *.dfm}
End

4. CONCLUSIONS

The simulation program includes a database concerning parts and conditions of the flexible manufacturing systems for processing round shafts, under a standard structure, providing easy attachment or removal of structures that accomplish the applications. We consider that the research, which will be developed, will produce useful results with impact upon the industrial reality, thus it will restrain the gap between theory and practice, and it will open new directions to research, having as cumulate effect a less degree of uncertainty in the area of flexible manufacturing.

The researches performed within this paper will be directed to the study of flexible manufacturing systems, in order to know their behaviour and their performances very well, and if it is possible, before their physical manufacturing and in order to establish on scientific bases dimensioning models, representation and simulation of flexible manufacturing systems, with direct application in the domain of round shafts. In order to perform the research there will be used software and modern equipment. Moreover, by the project are identified the possibilities of consolidating research of applying it in industry on the purpose of issuing possible further contracts. The researches will be also extended in the field of FMS management and control in real and virtual environment. There will be developed aspects concerning programming with the aid of flexible manufacturing system virtual reality.

The implementing of a flexible manufacturing system in an integrate fabrication system, represents an important result, which leads to the optimization of the entire material and informational flux of the enterprise.

5. REFERENCES

Abrudan, I. (1996)--Flexible Manufacturing Systems. Design concept and management, Dacia Publishing House, ISBN 973-5-0568-4, Cluj-Napoca

Boncoi, Gh. & Fota, A. (2001)--Production Systems, "Transilvania" University Publishing House, ISBN-973-9474-896, Brasov

Fota, A. (2004)--Machines Systems Design. Simulation and Modelling, "Transylvania" University Publishing House, ISBN 973-635-331-1, Brasov

Law, A. M. & Kelto, W. D. (1991)--Simulation, modelling and analaysis, McGraw-Hill Book Company, Singapore

Ispas, C. & Mohora, C. (2001)--Simulation of Product Systems, Romanian Academy Publishing House, ISBN 973-27-0868-9, Bucharest

Tempelmaier, H. (2006) Material Logistik. Grundlagen der Bedarfs und Losgrossenplanung in PPS--Systems, Springer-Verlag, ISBN 978-540-70906-0, Berlin