Concept to separate wet end and dry end paper machine control through estimation of physical properties at the wire

摘要

Partitioning control of the wet end and dry end, by introducing estimates of physical properties such as dry weight: and percent ash at the wire, allows for machine direction (MD) controls to continue during loss of scanner measurements. A mathematical model estimates the controlled, variables, such as dry weight, basis weight, and ash percent at the wire, and these estimated values are then controlled. When scanner measurements resume, parameters in the model are recursively updated to compensate for any model errors and ensure an accurate model. MD controls consist of a cascade set-up where the estimated wire-dry weight or wire basis weight and estimated wire ash percent are controlled by manipulating stock flow and addition of filler to stock. When scanner measurements are available, they become the downstream variables in the cascade control and are controlled by manipulation of the setpoints for the estimated wire weight and ash.

主权项

1. A control system for a sheet making machine having a wet end that comprises a wire and a dry end, the wet end having manipulable elements which are adjusted to maintain properties of the sheet at the wet end, which properties effect measurable properties of the sheet that comprises paper at the dry end, and the dry end having sensors which develop electrical signals to convey quantitative information of the measurable properties, the control system comprising:
a dry end controller responsive to the measured values of properties of the sheet at the dry end developed by the sensors and operative to develop setpoint signals for properties of the sheet at the wet end, each of the setpoint signals quantitatively establishing a setpoint of a respective one of properties of the sheet at the wet end; a wet end controller responsive to the setpoint signals for the wet end properties and operative to manipulate the wet end elements commensurately with the setpoints; and an estimator responsive to the measurements developed by the sensors and to further signals which convey quantitative information of present values of the inputs to the wet end to develop estimated values of wet end properties at the wire and said estimator includes a wire dry weight estimator, a wire ash weight estimator and a percent ash calculator, said estimated wet end property signals being commensurate with an estimated dry weight and an estimated percent wire ash relating to the corresponding measurable properties of dry weight and ash percentage at the dry end; wherein in the event the setpoint signals are not currently available to establish the wet end setpoints the wet end controller being further responsive to the estimates of the wet end properties and operative to manipulate the wet end elements.