INTEGRATING STATISTICAL PROCESS CONTROL AND ENGINEERING PROCESS CONTROL the discrete parts areas,cutting tool manufacturers ndwhieaoig (y nipulate the t Of co on of The coutrol action of eguation (3)is based on us the MMSE coutroller as dise ssed by Box and lent in the process industries.are now being applied Jenkins (1976).MacGregor(1990)showed that this in the parts industrics as well whe some graph Yi =u+n+et (1) where Y ist i the encouteouorsntrolastistas s riod t These resu 59m that the are no wiegnable tionn.is the ellect of the underly an from equation (2)and the and e is an indepen ent ra random disturbance terme inequation(1).We now el. zero and the that thi of the .is the position of the funnel after the(1 control action,and is the underlying external changes (i.c. drop.The quant assigmable causcs).If however,either the model is one (e()T inappropriate,such as mis-specifie ame the mo m om-1+at (2) where-1<d<1 and the at's are randomn variables n tar with mean zero and variance that are independent to be of one oft d if the gnable causes are eliminated,consider able reduction in output variability can be obtain of which model (2)is an examp The as signable causes take the form r a st M( the pro an or a t thSPC.It should be mentioned that EPC crib such as is s (eg a tren rrelation in the mean gnable causcs are typ an described by equation(1and (2),MacGrego case in the developtnents (1990)suggested the control action 4=4-1-(中-0)Y (3) An ExamDle We first show a simple example and then give the ()) esults of a more comprelensive simulation study Figure 1 shows the output for 500 model in equation (2)is co mbined with the white e pr the by mdredet 197G n n (3) The parameter volues are=0.95 and MacGregor and HIarris (1993,p.110).These 0=0.4,which are the same as those used by Mac authors point out that the sumn of an AR(1)process Gregor (1990).The values of t Vol.26,No.April 1994 Journalof Quality Technology