Rolling Mill Stand Control Using Frequency-Split Contour Adjustment
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Solution Overview
Problem
In multi-stand rolling mills, maintaining the contour and flatness of rolled metal strips is challenging due to the interdependence of these parameters, which leads to difficulties in adjusting the contour quickly and accurately, especially in larger rolling trains, resulting in flatness errors and material cross-flow issues.
Innovation Solution
The implementation of an operating method where the control device determines provisional manipulated variables for upstream rolling stands through frequency filtering, shifting rapid contour changes to rear stands and slower changes to front stands, while using intermediate variables and correction variables to account for previous stand adjustments, thereby achieving high dynamics and minimizing flatness errors in intermediate stand areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the contour of the rolled material is adjusted quickly in rear rolling stands, then the dynamics of contour control is improved, but flatness errors occur in intermediate stand areas
Solution Approach 1:
The control signal for contour adjustment is segmented into different frequency components, with each rolling stand processing specific frequency ranges. Rear stands handle high-frequency (rapid) changes while front stands handle low-frequency (slow) changes, preventing flatness errors in intermediate areas
Solution Approach 2:
The system dynamically distributes control tasks across rolling stands based on frequency content of the contour adjustment signal. The cutoff frequencies are assigned progressively from rear to front stands, allowing the system to adapt rapidly to contour changes while maintaining flatness
2Manufacturing precision
If contour adjustments are made in front rolling stands, then the contour control is achieved, but material cross-flow occurs due to thick strip
Solution Approach 1:
The control system performs preliminary frequency analysis of the contour adjustment signal before distribution. By identifying the frequency content in advance, the system can assign appropriate stands to handle specific frequency ranges, avoiding cross-flow in front stands where the strip is still thick
Solution Approach 2:
Different rolling stands are assigned different functional roles based on their position in the train. Rear stands are optimized for high-frequency contour adjustments while front stands handle low-frequency changes, matching the local material conditions at each position
3Manufacturing precision
If the roll gap profile of one rolling stand is modified to maintain flatness, then the flatness is improved, but the contour changes and affects subsequent stands
Solution Approach 1:
The system uses feedback from downstream stands to adjust upstream stands. When flatness errors are detected, the control signal is propagated upstream with frequency filtering to compensate while maintaining contour integrity
Solution Approach 2:
Frequency filtering acts as an intermediary mechanism between flatness control and contour control. It mediates the interaction between upstream and downstream stands by selectively transmitting different frequency components of the control signal
Data Source
Figure 1~2
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AI summary
A metal stock (2) is rolled in rolling stands (3a to 3f) of a rolling mill (1). Based on a characteristic value (δQ) for the change in the cross-section with which the stock (2) is to exit from a specific rolling stand (3e) of the rolling mill (1), preliminary control variables (Sb to Se) are initially determined for this rolling stand (3e) and for upstream rolling stands (3b to 3d). These preliminary control variables then inform final control variables (Sb' to Se'), which influence the cross-section with which the stock (2) exits the respective rolling stand (3b to 3e). The rolling stands (3b to 3e) are controlled accordingly. The preliminary control variables (Sb to Sd) for the upstream rolling stands (3b to 3d) are determined by frequency filtering of the characteristic value (δQ) or a respective intermediate value (Zb to Zd) derived from it.The frequency filters are designed such that only frequency components of the characteristic quantity (δQ) below a given cutoff frequency (fb to fd) are included in the determination of the respective preliminary control variable (Sb to Sd). The cutoff frequency (fb to fd) remains the same or increases from one rolling stand (3b to 3d) to the next (3b to 3e). The preliminary control variable (Se) for the specific rolling stand (3e) is determined such that at least those frequency components of the characteristic quantity (δQ) above the cutoff frequency (fd) of the rolling stand (3d) immediately upstream of the specific rolling stand (3e) are included in its calculation.