US 9,309,625 B2Granted

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

AssigneeHoneywell ASCa Inc.

InventorsJohan Backstrom, Michael Forbes

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Abstract

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.

Claims16

Dependent claims

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.

2 more elements

A continuous control method for maintaining measurable properties close to setpoints for the measurable properties of a sheet of paper being formed in a sheet making machine which has a wet end that comprises a wire and a dry end, the wet end having manipulable inputs which are adjusted to affect properties of the sheet at the wet end affecting measurable properties of the sheet being formed at the dry end and the dry end having sensors which develop measurements of the properties of the sheet at the dry end, the method comprising steps of:

developing setpoint signals for the properties of the sheet at the wet end as a function of the setpoints of the measurements developed by the sensors;
manipulating the wet end inputs as a function of the setpoints signals;
developing estimates of properties of the sheet at the wet end at the wire relating to the measured properties at the dry end as a function of the measurements developed by the sensors and to further signals which convey quantitative information of present values of the inputs to the wet end wherein the estimated values of the wet end properties are commensurate with an estimated dry weight and an estimated percent wire ash relating to the corresponding measurements of dry weight and ash percentage at the dry end;
and
in the event the setpoint signals are not currently available to establish wet end setpoints manipulating the wet end inputs as a function of the estimates for the properties of the sheet at the wet end.

2 more elements

Dependencies are inferred from the claim text.