Closed-Loop CD Alignment Identification in Papermaking
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Solution Overview
Problem
Current methods for monitoring and controlling cross-directional alignment in sheetmaking systems, such as papermaking machines, are inefficient and often result in production losses due to misalignment issues, as they require open-loop tests and disrupt normal production processes.
Innovation Solution
A closed-loop cross-directional alignment system that detects misalignment through actuator picketing detection and uses a novel PRBS test for real-time alignment identification, allowing for online deployment and minimizing disruptions to production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If open-loop bump tests are used to identify CD alignment, then alignment identification can be performed, but normal production is disrupted and productivity decreases
Solution Approach 1:
The patent implements closed-loop alignment identification by continuously monitoring actuator responses during normal operation and comparing them against expected responses. The system uses feedback from the running system to detect misalignment conditions and trigger identification procedures without stopping production, thereby maintaining both measurement accuracy and productivity
Solution Approach 2:
The system performs preliminary baselining operations to establish reference responses before normal operation begins. This preliminary characterization of actuator responses enables the system to detect alignment issues during running conditions without requiring additional open-loop tests that would disrupt production
2Manufacturing precision
If frequent open-loop realignment tests are performed, then alignment accuracy is maintained, but production loss increases and time is wasted
Solution Approach 1:
The system continuously monitors actuator responses during normal closed-loop operation and compares them against baseline responses. When deviations indicating misalignment are detected, the system automatically triggers identification procedures, eliminating the need for frequent scheduled open-loop realignment tests and reducing time loss while maintaining alignment accuracy
Solution Approach 2:
The system performs self-diagnosis by automatically detecting misalignment conditions through continuous monitoring of actuator responses. When misalignment is detected, the system autonomously initiates closed-loop identification and updates alignment parameters without requiring production stoppage or manual intervention, thereby maintaining precision while minimizing time loss
3Ease of operation
If traditional edge detection methods are used to compensate for sheet wander, then sheet position control is improved, but shape change of shrinkage profiles cannot be detected
Solution Approach 1:
The system uses actuator response monitoring to achieve multiple functions simultaneously: it controls sheet wander through traditional edge detection while also detecting shape changes in shrinkage profiles. By analyzing the responses of actuators to controlled perturbations, the system extracts both position and shape information from the same measurement channel, eliminating the need for separate detection systems
Data Source
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AI summary
Alignment is a critical component for modeling a cross-directional (CD) papermaking process. It specifies the spatial relationship between individual CD actuators to paper quality measurements. Misalignment can occur unexpectedly due to sheet wander or CD shrinkage variation. In certain applications and circumstances, a misalignment of one third (1/3) actuator zone width can result in significant paper quality degradation. Detecting a misalignment and identifying CD alignment in closed loop are highly demanded in paper mills but these are nontrivial problems. A technique for maintaining proper CD alignment in sheetmaking systems entails monitoring the alignment online, triggering closed loop identification if misalignment is detected, and then deploying the new alignment. No personnel intervention is required.