Paper Machine Control Mechanism for Caliper Profile Recovery
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Solution Overview
Problem
Paper sheet breaks during manufacturing disrupt the control of sheet-making machines, leading to production of sheets with caliper profiles far from target values, resulting in time and material losses as the machine operates to regain control.
Innovation Solution
Implementing a control mechanism with two modes: a fast mode for aggressive setpoint changes after a break to quickly recover the caliper profile and a slow mode for conservative adjustments once the profile is near the target or after a specified time, using a control law unit to determine and output setpoint changes to actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If larger or more frequent setpoint changes are made after a sheet break, then the caliper profile recovers faster, but the risk of excessive control actions and instability increases
Solution Approach 1:
The control system dynamically switches between two operational modes (first mode with larger/frequent setpoint changes and second mode with smaller/less frequent changes) based on the recovery state. This dynamic adaptation allows the system to optimize recovery speed when needed while maintaining stability when the caliper profile is near target, resolving the contradiction between fast recovery and control stability.
Solution Approach 2:
The invention changes the control parameters (setpoint change magnitude and frequency) based on the operational mode. In the first mode, aggressive parameter changes enable fast recovery, while in the second mode, conservative parameter changes ensure stability. This parameter adaptation resolves the technical contradiction by adjusting the control aggressiveness according to system state.
2Manufacturing precision
If the machine operates to regain control after a break, then sheet properties return to target values, but time and material losses occur
Solution Approach 1:
The control system initiates aggressive caliper profile recovery actions immediately upon detecting a sheet break, rather than waiting for the system to naturally stabilize. By taking preliminary corrective action at the moment of disruption, the system minimizes the duration of non-conforming production, thereby reducing time and material losses while ensuring quality recovery.
Solution Approach 2:
The dynamic switching between control modes enables the system to rapidly respond to breaks with aggressive correction, then transition to conservative control once recovery is achieved. This dynamic approach minimizes the time spent producing non-conforming sheets while preventing excessive control actions, thus resolving the contradiction between quality recovery and production time loss.
3Manufacturing precision
If the machine operates to regain control after a break, then sheet properties return to target values, but material losses occur
Solution Approach 1:
By immediately initiating aggressive caliper recovery control upon sheet break detection, the system minimizes the duration of non-conforming production. This preliminary action reduces the amount of unusable paper produced during recovery, thereby reducing material waste while ensuring quality standards are met.
Solution Approach 2:
The control system rushes through the recovery process by applying larger and more frequent setpoint changes in the first mode, quickly eliminating the effects of the sheet break. This approach minimizes the time spent producing non-conforming sheets, thereby reducing material waste associated with extended recovery periods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Facilitates faster recovery of the caliper profile, reducing time and material losses by quickly eliminating the effects of a sheet break and preventing excessive control actions, ensuring the produced sheets meet desired quality standards.
Implementation Method 1
The pressure applied by the rolls to the paper sheet is typically controlled by varying the temperature of the rolls
Implementation Method 2
heating the rolls typically causes the diameter of the rolls to expand, decreasing the size of the nip and increasing the pressure applied to the paper sheet
Data Source
AI summary
A method includes determining one or more setpoint changes for one or more actuators in a process control system. Determining the one or more setpoint changes includes making larger or more frequent setpoint changes when operating in a first mode and making smaller or less frequent setpoint changes when operating in a second mode. The method also includes outputting the one or more setpoint changes to the one or more actuators. The method could further include entering the first mode after a paper sheet has broken and been rethreaded through a paper machine. The method could also include entering the second mode (i) after a specified amount of time has elapsed since entering the first mode or (ii) after the first mode has been entered and a caliper profile of the paper sheet is within a specified threshold of a desired caliper profile.