Multipolar distributed material flow simulation of a virtual enterprise.

Popa, Cicerone Laurentiu ; Cotet, Costel Emil

1. INTRODUCTION

The virtual enterprise represents a temporary alliance of enterprises who wish to share resources and aptitudes for the purpose of making a product in the shortest time possible, at the smallesc price possible, and with the maximum satisfaction of the client (Camarinha-Matos et al., 1997). It is based on a technical infrastructure, represented by the informational technologies and by the computer communication networks (Dragoi, 2005).

Thus, the projection, planning of production and marketing, supplying, fabrication, services etc. can be realized anywhere in the country, the continent or the world, because of the facilities offered by the infrastructures which allow the change of information, goods and services (Ciobanu & Popa, 2004).

2. MULTIPOLAR DISTRIBUTED SIMULATION

The multipolar distributed simulation can be defined as an integrated system of monitoring more than two material flow simulations, interconnected inside the architecture of a virtual enterprise (Cotet & Dragoi, 2003).

In order to realize a simulation model of the material flow in the system, the first step is to define the necessary machine-tools, the work-pieces and the parts involved in the process on the level of each FMS (Flexible Manufacturing Systems). The inputs in the system are represented by the parameters of the machinetools, of the work-pieces and of the parts involved, and the output of the system is represented by the optimized architecture of the system. The main limitations of the system are: the realization plans, the available realization stages, and the capacity of the CAD-CAM-CAE system to analyze the behavior of the machinetools, the work-pieces and the parts in the work regime.

In the following study case three partners are found, organized under the shape of a virtual organization. Two of them represent product suppliers, and the third represents the enterprise where the assembling will take place, after which the final product will result.

Using specific solutions, each partner can realize a simulation in order to check the capability of its own system to fulfill the function traced in the virtual enterprise. After this, all these simulations can be integrated in a model of multipolar simulation in order to optimize the material flow in the entire system.

In the following we will define the three partners implicated in the system as being the three flexible fabrication systems, and thus FMS1 and FMS2 will represent the components supplier partners and FMS3 will be the system that makes their assembly.

3. CASE STUDY

In order to evaluate the architecture of the system, we used simulation models of the material flow for the three FMS, using the Witness software. The simulation of this project was realized in order to demonstrate and confirm the productivity of a fabrication process, based on the presentation of the proposed design and the operational data. Another purpose of the simulation was the identification of the ways to improve the configuration of the system in order to raise productivity.

The improving of productivity means the identification of the material flow concentrator for each FMS and for the virtual enterprise as a system, and the proposal of another manufacturing architecture that eliminates the concentrators.

According to the previous statements, FMS1 and FMS2 are diffused systems, and FMS3 is a concentrated system. Therefore, a concentrated FMS can be defined as a manufacturing architecture based on a single work point surrounded & assisted by transport, transfer & deposit facilities. A diffused FMS system can be defined as a manufacturing architecture with more than two work points connected by transport & transfer systems and using deposits at local or system level. (Cotet et al., 2004)

In figure 1 the FMS2 is presented during simulation. The parameters for each machine and conveyor were defined, and following the simulation, the place where the concentrators of the respective systems were identified.

The rapport regarding the activity of conveyor C2_1 is found in figure 2. We can observe the blocking of activity at this unit for 45% of the time, the conveyor is stopped for the intervention of the operator 5% of the time, and the machine works normally just 50% of the total time.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The FMS2 system was remodeled and a new simulation of the material flow in the system was made.In figure 3 the rapport regarding the activity of conveyor C2_1 after the remodeling is presented and we can observe the total disappearance of blockages found in the previous simulation. Thus, the conveyor is in function 55% of the time, 34% of the time it waits for parts arrival, and the time necessary for the intervention of the human resource is of 11%. In figure 4 the third manufacturing system is presented during the simulation. We can observe: the B1 and B2 buffers that are the inputs in system 3 and also the outputs of system 1 and 2; the two conveyors and the machine on which the final assembly is done (M3_1). Also, the two parts (P and P2) can be found, which come from the previous systems FMS1 and FMS2, the operator and the number of pieces being worked at the time of reporting. From the study of the rapports and from the localization of the concentrators, especially in conveyor C3_2, results the necessity of remodeling the system for eliminating the concentrators. This will be done for system 3, and if concentrators will be maintained it results the necessity of intervention over the inputs in the system, and therefore over systems 1 and 2, which through the results of their own outputs determine the two inputs of system 3.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Following the remodeling of system 3, according to the demands, the elimination of the concentrator in the case of conveyor C3_2. In the case of conveyor C3_2, according to the rapport presented in figure 5, the existing blockage is reduced from 84% to 19% of time. Thus, it results that it works normally 80% of the time, which indicates a major improvement of its activity and implicitly of that of the system.

4. CONCLUSION

If we want to optimize the architecture of a usual material flow inside a virtual enterprise, a simple simulation is not enough. This is the reason why we proposed as a solution, the multipolar simulation, capable of evaluating the performances on a virtual enterprise as an integrated system. The analysis of the multipolar simulation does much more than just concatenates the results of isolated simulations. The flow concentrator which results from the multipolar simulation can be any of the concentrators of isolated simulations, but it can also be a totally different one. Some of the main causes of this particularity are the difference in algorithms for diffuse, isolated algorithms. For this case study, the elimination of the material flow concentrator of FMS3 gives important improvements of production at the level of the entire virtual enterprise, but the most influent concentrator of the entire system is localized in FMS2.

5. REFERENCES

Camarinha-Matos, L.M.; Carelli, R.; Pellicer, J.; Martin, M. (1997). Towards the virtual enterprise in food industry, Proceedings of the ISIP'97 OE/IFIP/IEEE International. Conference on Integrated and Sustainable Industrial Production, ISBN 0-412-79950-2, Portugal, May 1997, Chapman & Hall, Lisboa

Ciobanu, L.F.; Popa, C.L. (2004). Simulation and CAD/CAM/CAE cooperative systems integration in virtual environments, Proceedings of the 7th Conference on Management of Innovative Technologies (MIT'2004), pp. 1518, ISBN 973-700- 028- 5, Constanta, Romania, October 2004, Ed. AIUS, Craiova

Cotet, C.E.; Abaza, B.F.; Carutasu, N.L. (2004). Multipolar distributed simulation for concentrate and difussed FMS, Proceedings of the International Conference on Manufacturing Systems (ICMaS 2004), pp. 647-650, ISBN 973-27-1102-7, Ed. Academiei Romane, Bucharest

Cotet, C.E.; Dragoi, G. (2003). Material flow management in validating concentrate and diffused FMS architectures. International Journal of Simulation Modelling IJSIMM, Vol. 2, No. 4, December 2003, pp.109-120, ISSN 1726-4529

Dragoi, G. (2005). Informational Infrastructure of modern enterprise (Infrastructura informationala si de comunicatii a intreprinderii moderne), Ed. Politehnica Press, ISBN 973-8449-73-1, Bucharest

POPA, C[icerone] L[aurentiu] & COTET, C[ostel] E[mil] *

* Supervisor, Mentor