Closed form approximations for steady state probabilities of a controlled fork-join network

  • Authors:
  • Jonathan Billington;Guy Edward Gallasch

  • Affiliations:
  • Computer Systems Engineering Centre, School of Electrical and Information Engineering, University of South Australia, Mawson Lakes, SA, Australia;Computer Systems Engineering Centre, School of Electrical and Information Engineering, University of South Australia, Mawson Lakes, SA, Australia

  • Venue:
  • ICFEM'10 Proceedings of the 12th international conference on Formal engineering methods and software engineering
  • Year:
  • 2010

Quantified Score

Hi-index 0.00

Visualization

Abstract

Our work is motivated by just-in-time manufacturing systems, where goods are produced on demand. We consider a class of products made from two components each manufactured by its own production line. The components are then assembled, requiring synchronisation of the two lines. The production lines are coordinated to ensure that one line does not get ahead of the other by more than a certain number of components, N, a parameter of the system. We assume that the statistics of the processes follow exponential distributions, with requests to manufacture the product arriving at a rate λ0 and the two production lines having rates λ1 and λ2. Generalised Stochastic Petri Nets (GSPN) are used to model this system where N is the initial marking of a control place. TimeNET is used to calculate the stationary token distribution of the GSPN as N increases, revealing convergence of the steady state probabilities. We characterise the range of rates for which useful convergence occurs using a large number of TimeNET runs and show how these results can be used to approximate the steady state probabilities for arbitrarily large N, to a desired level of accuracy. Further, for λ0 min(λ1, λ2) we discover geometric progressions in the steady state probabilities once they have converged. We use these progressions to derive closed form approximations, the accuracies of which increase as N increases.