Paper Machine Basis Weight Control via Headbox Consistency Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing control systems for regulating the basis weight of a paper web have long dead times, leading to inaccuracies and increased operational effort, as they fail to account for consistency variations and backwater system influences, resulting in unsalable paper during setting times.
Innovation Solution
A control device with a pilot control system that dynamically adjusts the headbox setpoint using PI or PID controllers, considering consistency, target speed, and data from the return water system, and employing neural networks or fuzzy logic to optimize substance application, along with a measuring controller for real-time corrections and a limiter to prevent operational errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a control device measures basis weight at the end of the paper machine, then the basis weight can be measured, but the dead time becomes very long (several minutes)
Solution Approach 1:
The patent applies preliminary action by measuring the consistency of the fiber suspension in the headbox before the paper web is formed and dried. This early measurement allows the control system to predict and adjust the basis weight before the long dead time of traditional end-of-line measurement, thereby reducing the effective control delay and allowing salable paper to be produced during the setting time.
2Manufacturing precision
If the headbox is controlled by paper machine speed with delayed drive response, then the basis weight can be regulated, but errors in consistency measurement and chemical composition variations cause basis weight errors
Solution Approach 1:
The patent implements feedback control by continuously measuring the consistency of the fiber suspension in the headbox and using this measurement to dynamically adjust the amount of substance applied to the screen. This closed-loop feedback system compensates for variations in chemical composition and measurement errors, improving the reliability of basis weight regulation despite the challenges of consistency measurement.
3Device complexity
If the setpoint of the operating controller is statically defined, then the control is simple, but the influence of dead time on the headbox remains large
Solution Approach 1:
The patent applies dynamics by making the setpoint of the operating controller dynamically adjustable based on real-time consistency measurements and predicted basis weight. Instead of a static setpoint, the system continuously adapts the setpoint to current operating conditions, thereby reducing the influence of dead time while maintaining relatively simple control structure.
4Ease of operation
If no correction values are applied during setting time, then the control is straightforward, but unsalable paper is produced during this period
Solution Approach 1:
The patent applies preliminary action by calculating and applying correction values to the setpoint during the setting time based on early consistency measurements and predicted basis weight. This allows the control system to proactively compensate for deviations before they result in unsalable paper, maintaining both operational simplicity and productivity by automating the correction process.
Data Source
Figure 1
AI summary
The regulating device includes an operating regulator (1) for material flow from an outlet (3). The intended value is transmitted by a pre-control device (2). It also has an additional measuring regulator (8) to determine the actual value of the surface weight. The output weight value can be corrected by correction values (24, 25) from the pre-control device.