Method and apparatus for achieving a fast cross direction caliper control recovery time

In a sheet making process using a machine having a system responsive to control actions for cross direction feedback caliper control of actuators associated with a calender stack mounted on said machine, a method for recovering caliper control performance during startup of said machine after a sheet break comprising:

• using calender stack conditioning with said cross direction feedback caliper control suspended using setpoints corresponding to a heating gradient of said calender stack prior to said sheet break when a duration of said sheet break exceeds a predetermined period of time and said system for cross direction feedback caliper control of actuators can use said control actions comprising:
• suspending said cross direction feedback caliper control;
• and
• executing said calender stack conditioning for a specified time duration when said machine starts up comprising:
• reapplying to setpoints of said actuators saved before said sheet break that represent said heating gradient for conditioning said calender stack to achieve a previously determined caliper profile, said setpoints reapplied to said actuators with a preselected dynamic compensation.

An apparatus for controlling a sheet making machine comprising:

• a system including a computing unit for cross direction (CD) feedback caliper control of actuators associated with a calender stack mounted on said sheet making machine;
• a sensor for measuring caliper of a sheet being made by said sheet making machine;
• and
• a storage medium readable by said computing unit containing a program runnable by said computing unit to execute a method of providing fast CD caliper control recovery of said sheet making machine in the event of a break of said sheet, said method comprising:
• monitoring during operation of said sheet making machine in absence of said sheet break a performance of said CD feedback caliper control and storing CD setpoints corresponding to a CD profile that has a reduction in variability of a caliper error profile;
• monitoring the duration of said sheet break;
• and
• executing when said sheet making machine starts up and said sheet break duration exceeds a predetermined time period either a conditioning of said calender stack with said CD feedback caliper control in a suspend state and using stored CD setpoints or a conditioning with said CD feedback caliper control in a suspend state of said measurement from said caliper sensor or both said calender stack conditioning and said caliper sensor measurement conditioning.

In a sheet making process using a machine having a system for cross direction (CD) feedback caliper control of actuators associated with a calender stack mounted on said machine, a method for recovering caliper control performance during startup of said machine after a sheet break comprising:

• monitoring during operation of said machine in absence of said sheet break the performance of said CD feedback caliper control and storing CD setpoints corresponding to a CD profile that has a reduction in variability of a caliper error profile;
• monitoring the duration of said sheet break;
• and
• executing when said machine starts up and said sheet break duration exceeds a predetermined time period either a conditioning of said calender stack with said CD feedback caliper control in a suspend state and using said stored CD setpoints or a conditioning with said CD feedback caliper control in a suspend state of a measurement from a caliper sensor or both said calender stack conditioning with said CD feedback caliper control in a suspend state and using stored CD setpoints and said caliper sensor measurement conditioning with said CD feedback caliper control in a suspend state.

An apparatus for controlling a sheet making machine comprising:

• a system including a computing unit for cross direction feedback caliper control of actuators associated with a calender stack mounted on said sheet making machine;
• a sensor for measuring caliper of a sheet being made by said sheet making machine;
• a PI controller for providing feedback caliper control of said actuators;
• and
• a storage medium readable by said computing unit containing a program usable by said computing unit to provide one or more operations for recovering caliper control performance to be selectably performed during startup of said sheet making machine after a sheet break, said selectable operations selected from a group consisting of:
• a conditioning of said calender stack with said cross direction feedback caliper control in a suspend state and using setpoints corresponding to a heating gradient of said calender stack prior to said sheet break and
• a conditioning with said cross direction feedback caliper control in a suspend state of said measurement from said caliper sensor.