USE A MACHINE'S FULL CAPABILITY by ProQuest

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									                                                                                                                                   process
                                                                                                                              control




                     By SHIH-CHIN CHEN, JONAS BERGGREN, and ANDREAS ZEHNPFUND

A multivariable CD control application approach may be
beneficial for certain applications; coordination is the key


USE A MACHINE’S
      FULL CAPABILITY

                             C
                                       ross-machine direction (CD) profile control has       CD control was designed to minimize the variation of the
                                       been a key area of advanced control applications      weighted profile [4,12]. The implementation was simple
                                       in the paper industry since the early 1970s [1-11].   and results were effective for specific applications.
                             In the past 30 years, the number of profile control ap-              In other cases where one profile is changed by
                             plications on paper machines has increased dramatically.        multiple sets of actuators, one approach [13] separates
                             The number of CD actuators installed between 1990 and           the input profile in multiple profiles based on the spatial
                             2007 exceeds 6,000 sets. As a result, many paper machines       frequency contents in the profile and then feeds one
                             today are equipped with multiple sets of CD actuators. It       separated profile to each actuator set. Each actuator set
                             is quite common that different CD actuators are added           controls the separated profile independently.
                             sequentially to existing machines for controlling particu-           Another approach [14,15] predicts profile changes
                             lar sheet property profiles.                                    based on the control actions derived for the first set of
                                  Therefore, many paper machines have multiple sets          actuators. The predicted profile changes are removed
                             of CD actuators working independently on the same               from the source profile. The difference profile is fed to
                             machine. Even though papermakers recognized that one            the second set of actuators for control. Similar steps are
                             set of actuators may influence multiple sheet properties        applied to multiple sets of CD actuators in cascade. The
                             and one sheet property may be affected by multiple sets         execution of control actions is synchronized. All these
                             of actuators, there is no easy way to coordinate multiple       approaches have had limited success and can only be
                             CD actuators through independent single-input, single-          applied to special cases.
                             output CD control applications.                                      While alternative solutions have been applied in the
                                  Early attempts to coordinate multiple CD actuators         past, the computing power and network communication
                             were severely restricted by the capabilities of quality         of industrial control systems have significantly evolved in
                             control systems (QCS) and 
								
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