Decoupling controller for use with a process having two input variables and two output variables

Claim 1

A decoupling controller for use with a paper making machine process having two input variables (U 1 and U 2 ) which are dry stock flow and steam pressure and two output variables (X 1 and X 2 ) which are basis weight and moisture where in the process each input variable affects both output variables, such process having desired setpoints (S 1 , S 2 ) for said output variables such decoupling controller comprising: linked internal model controller means including two pairs of proportional, integral, derivative P.I.D. velocity units (C 11 , C 21 ; and C 12 , C 22 ) each pair respectively receiving from a first pair of difference junctions total process error, (et 1 , et 2 ) in a feedback loop for the process and producing said inputs (U 1 , U 2 ), which are control inputs to the process itself, such P.I.D. units taking into account loop, proportional, integral, and derivative gains of the feedback loop for both direct and cross-coupling; four first order transfer function units (K 11 , K 12 , K 21 , and K 22 ) for receiving as inputs U 1 , U 2 , said K 11 , K 22 units providing predicted values of X 1 , X 2 , said K 21 , K 12 units providing predicted outputs of X 1 , X 2 due to cross-coupling; means for feeding back to a pair of second summing junctions the outputs of K 11 , K 12 and K 22 , K 21 respectively; means for coupling the outputs of said second summing junctions, which are total predicted values of X 1 and X 2 taking into account cross-coupling, to a pair of third summing junctions; means for feeding the summed output of said third pair of summing junctions to said first pair of difference junctions, which have as the other difference input the setpoints S 1 , S 2 to provide said total process error inputs et 1 and et 2 to C 11 , C 21 and C 12 , C 22 , respectively; means for taking the deadtime of said process into account which is the lag time between the change of input variables and output variables, including four deadtime units, (D 11 , D 21 , and D 12 , D 22 ), having their inputs respectively connected to the outputs of K 11 , K 21 , K 12 , and K 22 , including a pair of fourth summing junctions having as outputs current estimated values (Y 1 , Y 2 ) of the X 1 , X 2 output variables where one of the pair of fourth summing junctions, sums the outputs of D 11 , D 12 and the other of the pair of summing junctions, sums the outputs of D 22 , D 21 ; means for coupling the outputs of said fourth pair of summing junctions, to a fifth pair of difference junctions to take the difference between the actual outputs X 1 , X 2 and the estimated values Y 1 , Y 2 , such differences being modeling error output signals; means for feeding back said modeling error output signals to said third pair of summing junctions; and where said K 11 the process gain for stock, is increased for an increase in the paper machine speed and said feed back loop gain of the correspondin a P.I.D. unit, C 11 , is decreased.