The synthesis of manufacturing task in flexible manufacturing systems.

Fota, Adriana

1. INTRODUCTION

The first stage in the design of any flexible manufacturing system is the manufacturing task analysis (Askin & Standrige, 1993). The importance of the manufacturing task analysis and its complexity derive from the fact that flexible manufacturing systems are destined to small series production, characterised by a typological diversity and instability in time. It is estimated, that about 70% of the actual production is realised by methods, which are specific to small / individual series production. For now, however, in the entire speciality literature, especially in the documentation oriented towards technology, a fabrication task is considered given, and known, exclusively by an old linguistic classification, based on a "morphologic analysis method" (Opitz, 1970). It is considered that the references family, the version, or the reference as technological entity, which is manufactured by mechanical processes have a configuration--geometrical and technological properties given, and known from execution drawings. Alternatively, while designing any flexible fabrication system, the designer has sometimes a partial typology, undefined significantly, insufficiently relevant, and taken from execution drawings, which are available. Under these conditions, the analysis of a manufacturing task opens a large research area, and for now, nobody has elaborated any analytical model of the manufacturing task for the synthesis of flexible manufacturing systems.

Lack of consecrated mathematical models in the design of flexible fabrication systems makes the creation of such systems difficult, with consequences upon their performance. Because it the new property of production systems--"flexibility", is imposed, there can appear some conception errors, and designers cannot anticipate precisely the optimal flexibility degree. As far as the approach method of the large topic of flexible manufacturing systems is concerned, it must be remarked the fact that there have been and there still are different methods and interpretations, but no model practically confirmed has been imposed. The modelling of flexible fabrication systems functioning represents currently the most dynamic and controversial research area in this field, (Tempelmeier & Khun, 1993).

In this paper, the simulation model for real manufacturing items drawn up, and the "Shafts" program having on its grounds, the generalized analytical model of the manufacturing task conceived in paper (Boncoi & Fota, 2000). The "Shafts" program was realised in Visual [C.sup.++] programming language. Essential in simulation modelling, the logical element is set up by data structures that are convenient for the performance of an event.

2. THE MOST LIMITED DATABASE

The geometrical--constructive configuration of the generalized item is obtained from the logical characteristic function by using the database. Before graphical transposition, the logical function is submitted to constraints (conditions and restrictions). Conditions are imposed by construction, functionality, and the assembling process of the real item overall. The main condition is precedence, which requires writing the components of the characteristic logical function strictly ordered. The precedence condition requires only ordering in a monotonously increasing/ decreasing sequence of the diameters conveniently chosen by the designer; lengths of sections result from the constructive--functional conditions following a randomly, unpredictable distribution.

The conditions' question is one of heuristically engineering and expert system. Restrictions are imposed by the same construction or functionality but also by new rules, imposed by the complex synthesis process of the generalized item. There are some important categories of restrictions. The main category of restrictions to precedence restrictions is related. A second category of restrictions is that imposed by the synthesis process.

Lying on the grounds of flexible manufacturing systems design for round shafts processing, the generalized manufacturing task before, has been fixed according to the typological nucleus, which includes the whole range of possible items belonging to an item class, family or variant, limited by restrictions to a required area, in the paper (Abrudan, 1999). There have been followed the stages below. The synthesis method of the current manufacturing task has been drawn up by the analysis and mathematical structure of the items' features. On the base of the generalized analytical and global synthesis model of the manufacturing task for designing any flexible system for the round shafts processing, generalized item models, hypothetical and representative items for the family or variant of particular real items have been set up. The generalized item includes all the constructive-geometrical elements belonging to the multitude of real, factual items in the family or variant described.

These constructive-geometrical components have been ordered in a logical and natural sequence. Thus, six types of generalized item models have been set up, according to the structure and size of the flexible manufacturing system for processing round shafts. These models are the following:

1. The model of a generalized item of compact, typical, asymmetrical, externally configured round shafts family

2. The model of a generalized item of round gap shafts family;

3. The model of a generalized idem of polygonal/ conic round shafts;

4. The model of a generalized item of axles and spindles family

5. The model of a generalized item of threaded shafts family;

6. The model of a generalized item of spherical shafts family Each item's family or variant represents an ordered literary-numeric (alphanumeric) sequence. All the restrictions associated with the families of the corresponding class have been written, which also will be introduced in the database, next to the corresponding symbol.

3. RESULTS

For the generalized manufacturing task computer simulation, an "assembling" program is set up, which has to associate different database figures, expressing the symbols of the ordered sequences. The program converts the alphanumeric ordered sequence into a succession, joining geometric figures that comply with this ordered sequence.

Running this program on the computer, more item families of the same class, in different variants will be obtained. These variants may be real or theoretical. From an item family the most complex variant is chosen, generally theoretical, hypothetical, fictive, including all the accordingly family features, all the geometrical elements of all variants belonging to the accordingly item family.

3.1 How to Use the Simulation Program

The computer program has been realised in the Visual [C.sup.++] programming language. A database--DB has been conceived, containing the sizes and features of all the elements belonging to the previously fixed round shafts families. The main stages of the program usage are as follows. Through the decision block, called <option> the user may automatically select, at any time, from the database, from the six generalized items, the generalized shafts family he or she wants to use. The two windows are visualised on the screen (figure 1):

--the generalized shaft window, called "generalized shaft" including generalized items for the six round axles' family types;

--the real shaft window, called "client axle" which may be automatically generated from the generalized item.

[FIGURE 1 OMITTED]

Pressing the key "outlining," the program will automatically generate in the "generalized shaft" window:

1. The family selected (example, family round gap shafts;

2. The code bare corresponding to the assigned functions to the elementary geometric components of the database items made and keeping the same symbols (for example: radial-axial bearing section, polygonal section, narrow thread, key transmission, belt canal, grooved section, spacing section, teeth, flange, etc.);

3. From the generalized item any real item type, represented by a model graph, as the ordered sequence determined by the assigned functions to some elementary geometric figures from the database may be obtained.

Generation of real shaft, also called client shaft is performed in the window "client shaft." Initialization of the client shaft elements is performed by selecting the current element of the "generalized shaft" window. From the figure below (figure 1) one application window has been extracted, for exemplifying the construction of any real item type resulted from the generalized items of round shafts families included in the database of the program's that has been used.

4. CONCLUSION

The first essential aspect in using computer simulation of real manufacturing items refers to confronting the flexible manufacturing system designer with a huge volume of information, sometimes unpredictable, uncertain, depending on time, incomplete, which under uncertainty conditions may be appreciated as irrelevant and, consequently, eliminated from the configuring process. Therefore, the need of a strong program is imperious, a program that can be used for a computer network, replacing the classical design method of machine parts and of corresponding technologies. Another advantage of this simulation program use consists in the fact that through the available, easily accessible graphic database, the processing time is considerable reduced, thus reducing the number of designers too. The simulation program contains a database concerning standardized entities and conditions of the flexible manufacturing systems for processing round shafts, providing easy attachment or removal of structures that perform applications. The simulating program realized in this paper has as objective the application of flexible manufacturing systems for processing round shafts, area in which the speciality literature does not offers information.

5. REFERENCES

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

Askin, R. G. & Standrige C. R. (1993)--Modeling and analysis of Manufacturing Systems, Publisher Wiley Inter-science, ISBN 978-0471514183, New York

Boncoi, Gh. & Fota, A. (2000)--Family, Variant and Individual Feature Analysis of the Reference Component Parts of the Manufacturing Task for FMS, International Conference ICMas 2000, University Polytechnic of Bucharest, pp. 413 -424, ISBN 973-31-1492-8, Bucharest.

Opitz, H. (19700--A Classification System to Describe Work Pieces, Pergamon Press Ltd., Oxford

Tempelmaier, H. & Kuhn, H. (1993)--Flexible Manufacturing Systems, John Wiley &Sons, Inc., ISBN 78-04713307277, New York.