Dipartimento d'Ingegneria

07 Mar

The Assembly Line Simulator Project Featured

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ALS (Assembly Line Simulator), is a Java based simulator for mixed model assembly lines. ALS is the result of the ALS Research Project, and has been developed with the scope to be usable by researchers and practitioners.  

line sketch

ALS home page


ALS guiTo evaluate performances of a mixed model assembly line may be complicated. This complication is a result of blockage and starvation caused by the arrival of different models to the line, having different assembly time requirements at each station. Considering the throughput as the main operational design objective, the effects of these phenomena on line throughput are very difficult to evaluate. 
Unfortunately its evaluation is fundamental in almost all procedures and algorithms developed to solve MALBP (Mixed-model Assembly Line Balancing Problem), since the estimation of objective functions that includes performance indicators is often required. The delicacy of this issue has been accurately outlined by [Bukchin 1998]. He argued that the only practical method to accurately evaluate throughput is a simulation study, which is very time consuming and hard to perform, and that for this reason, instead, various performance measures are usually used in order to evaluate and compare design alternatives. These performance measures are required to be highly correlated with the objective in question (i.e. throughput).

The aim of this project is to overcome the limit of using performance measures instead of simulated throughput, by developing a parametric simulator for mixed model lines that can quickly simulate different line configurations and can be used iteratively in algorithms and procedures.
The Process Oriented VersionAt this scope, an object-oriented assembly line simulator has been developed in Java. This first version was developed using the "process oriented" approach, which provides a natural way of describing complex systems and oft
en leads to more compact code than the event-oriented view.Final results of the research activity, that leads to the construction of a simulator [Tiacci and Saetta, 2007], allow to state that the process oriented approach makes possible to easily and effectively model an assembly line by the use of an intuitive correspondence of process to system entities. Unfortunately many programming environments, including the two Java packages that were analyzed in the study (JavaSimulation and SSJ), implement processes as true threads from the operating system.
This adds significant overhead, prevents the use of a very large number of processes in the simulation and slows the simulation execution, so that the model cannot be effectively coupled to those algorithms and procedures where numerous variants of a base system may have to be simulated, and the evaluation of a fitness function has to be performed several times.ALS - The Event Oriented VersionStarting from the results obtained by the process oriented version, the project aims to identify programming languages and architectures that, maintaining the object-oriented structure (which allows the desired degree of flexibility of the model) avoid the use of the process oriented approach. One appealing possibility is to combine object-oriented simulation with the event-oriented simulation approach, in which the simulation run is performed only by events scheduling, rescheduling, cancelling, avoiding the use of processes and thus keeping execution times very low. The construction of parametric simulation models through the event-oriented approach, while will ensure faster execution times, on the other hand will require a considerable modeling effort.The result of the project is 'ALS' [Tiacci 2012], an event and object oriented simulator able to fast evaluate operational objectives of mixed model assembly lines problems.

Bukchin, J., 1998, "A comparative study of performance measures for throughput of a mixed model assembly line in a JIT environment", International Journal of Production Research, 36, 2669-2685.

Tiacci, L. , Saetta, S., 2007, "Process-oriented simulation for mixed-model assembly lines", 2007 Summer Simulation Multiconference, 14 - 19 Luglio, San Diego, CA, USA, pp. 1250-57, ISBN: 1-56555-316-0.

Tiacci, L., 2012. Event and object oriented simulation to fast evaluate operational objectives of mixed model assembly lines problems, Simulation Modelling Practice and Theory, 24, 35–48. http://dx.doi.org/10.1016/j.simpat.2012.01.004

Read 223519 times Last modified on Wednesday, 30 April 2014 17:24
Tiacci Lorenzo

Website: impianti.dii.unipg.it/tiacci

Additional Details

  • Phone
    075 585 3741
  • Role
    Professore associato - Associate professor
  • Area
    Impianti industriali meccanici - Industrial plants

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