Paper Machine Control via Wet End Property Estimation
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Solution Overview
Problem
Papermaking machine direction controls are disrupted during sheet breaks or scanner malfunctions, leading to process deviations and production interruptions due to the loss of measurable variables like basis weight and ash content.
Innovation Solution
A control system that separates wet end and dry end paper machine control by estimating physical properties at the wire, using a mathematical model to maintain target values for dry weight, basis weight, and ash percent, allowing continuous operation even without scanner measurements, and updates parameters recursively for accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If scanner measurements are used to control paper properties at the dry end, then manufacturing precision is improved, but productivity deteriorates due to production interruptions during sheet breaks or scanner malfunctions
Solution Approach 1:
The patent introduces an estimator as an intermediary component that predicts paper properties (basis weight, ash content) at the wire section based on wet end process variables. This estimator serves as a mediator between wet end control and dry end measurements, allowing the control system to function during sheet breaks when scanner measurements are unavailable, thus maintaining productivity while preserving manufacturing precision through continuous control
Solution Approach 2:
The control system performs preliminary action by using the estimator to predict paper properties before the sheet reaches the scanner. This advance estimation allows the control system to maintain active control during sheet breaks and malfunctions, preventing production interruptions and maintaining both manufacturing precision and productivity
2Manufacturing precision
If MD controls are deactivated during sheet breaks to avoid using unreliable scanner data, then manufacturing precision is maintained, but productivity deteriorates due to loss of control and subsequent rethreading requirements
Solution Approach 1:
The estimator acts as a reliable intermediary that provides continuous paper property predictions during sheet breaks. By relying on the estimator's predictions based on wet end variables rather than unavailable or unreliable scanner measurements, the control system maintains active control throughout the sheet break event, eliminating downtime and preventing rethreading while preserving manufacturing precision
Solution Approach 2:
The patent ensures continuity of useful action by maintaining active MD control during sheet breaks through the estimator. The control system continuously adjusts wet end variables based on estimator predictions, ensuring unbroken control action that prevents process deviations and eliminates the need to shut down control during sheet breaks, thereby eliminating loss of time
3Manufacturing precision
If the control system waits for scanner measurements to become available again after a sheet break, then manufacturing precision is restored, but productivity deteriorates due to the time required to rethread and reestablish measurements
Solution Approach 1:
The estimator performs preliminary action by continuously predicting paper properties during the rethreading period. This allows the control system to maintain active control and keep paper properties on target during the time when scanner measurements are unavailable, eliminating the need to wait for measurements and maintaining both manufacturing precision and productivity during rethreading operations
Data Source
AI summary
A system for controlling properties of a sheet of material to be manufactured on a sheet-making machine. The wet end is controlled by setpoints developed by a dry end controller based on properties such as ash content and dry weight, measured at the dry end, and estimated values of wet end properties, such as headbox flow, consistency, ash content, wire speed and slice width, based on those properties measured at the dry end.