S. Wadhwa et al., PERFORMANCE OF A HYSTERESIS BASED CONTROL STRATEGY FOR A FLEXIBLE MACHINE OPERATING UNDER A PERIODIC STATUS MONITORING POLICY, Computers & industrial engineering, 32(3), 1997, pp. 557-574
The role of on-line control strategies is crucial for exploiting the f
lexibility within discrete part manufacturing systems. When studying t
heir impact on system performance, researchers have mostly assumed the
presence of real-time information availability. Such assumption may n
ot always be valid in real world manufacturing situations since on-lin
e control strategies base their decisions on information that may enta
il significant rime delays depending upon the extent of computer based
automation and information integration employed. We refer to these de
lays as information delays. In the domain of discrete part manufacturi
ng systems with defined levels of flexibility, it is essential explici
tly to model and analyze the effect that information delays have on th
e performance of a given on-line control strategy. In this paper we co
nceptualize three basic modes of information delays and indicate the n
eed to model them explicitly in order to assess their impact on the pe
rformance of on-line control strategies. One of these basic forms of i
nformation delay is caused due to a review period based status monitor
ing policy. We propose and characterize a hysteresis based on-line con
trol strategy (HCS) to cope with information delays. The study system
chosen represents the simplest possible manifestation of machine flexi
bility and resembles the two-queue single server case for which prior
research results indicate the superiority of the alternating priority
(AP) rule when average job flowtime is the measure of performance. We
use computer simulation to compare the behaviour of HCS with the AP ru
le in a real-time as well as the information delay mode. The best HCS
setting in the real-time mode fails to remain consistent in the inform
ation delay case, thus clearly indicating the need to explicitly model
delays when developing suitable control strategies. Further, when com
pared with the AP rule, HCS shows consistently superior performance to
AP. (C) 1997 Elsevier Science Ltd.