Cold-Rolling Line Thickness Control via Upstream Measurement
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Solution Overview
Problem
In multi-stand cold rolling mills, thickness errors in intermediate roll stands are difficult to correct due to dead time in the control system, leading to low controller dynamics, especially in skin-pass mode C where the last roll stand operates with constant rolling force, resulting in only low-frequency disturbances being adequately corrected.
Innovation Solution
Implementing an operating method that includes additional thickness measurement upstream of the last roll stand, recording strip speeds, and using these data to determine set values for thickness control, allowing dynamic correction of strip thickness errors by acting on the penultimate roll stand, and optionally incorporating force control and tension regulation to enhance control dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the last roll stand operates with constant rolling force in skin-pass mode C, then the rolling force control is simplified and stable, but the thickness errors pass through undamped and controller dynamics are reduced to low frequency only
Solution Approach 1:
The patent measures the strip thickness upstream of the last roll stand before the strip enters the stand. This preliminary measurement allows the control system to predict and compensate for thickness errors before they propagate through the system, enabling high-frequency disturbance correction while maintaining constant rolling force operation
Solution Approach 2:
The patent implements a feedback control loop where the upstream thickness measurement is fed back to the last roll stand's actuator. This feedback enables dynamic adjustment of the roll gap based on actual thickness conditions, providing damping action and improving controller dynamics without sacrificing the stability of constant rolling force mode
2Device complexity
If thickness measurement is performed only behind the last roll stand, then the measurement system is simplified, but the dead time in control increases and thickness errors are noticed too late for effective correction
Solution Approach 1:
The patent places the thickness measurement device upstream of the last roll stand to perform measurement before the strip passes through the stand. This preliminary measurement eliminates the dead time associated with measuring after the strip has already passed through, enabling real-time control intervention
Solution Approach 2:
The patent introduces an intermediate measurement point between the last roll stand and the final product. This intermediary measurement location provides early detection of thickness errors without requiring complex downstream measurement systems, enabling timely control action
3Manufacturing precision
If the monitor control acts on the penultimate roll stand to correct thickness errors, then the control action is applied earlier in the process, but the large dead time between intervention and measurement limits correction to low-frequency disturbances only
Solution Approach 1:
By measuring thickness upstream of the last roll stand, the system performs the measurement action before the strip enters the controlled stand. This eliminates the transport time dead time between control intervention on the penultimate stand and measurement, enabling high-frequency disturbance correction
Solution Approach 2:
The upstream thickness measurement creates a short-feedback loop where thickness errors are detected immediately and control action is applied to the last roll stand with minimal delay. This feedback mechanism enables dynamic correction of high-frequency disturbances that would be lost in the longer dead time of traditional downstream measurement systems
Data Source
Figure 1~5
Figure 2
Figure 3
AI summary
In a multi-staged cold-rolling line, a strip (5) is rolled. An actual rolling force (F) of a last rolling stage (4) of the cold-rolling line is detected using a rolling force detection apparatus (14) and fed to a force control unit (15). The force control unit (15) determines at least one control parameter (δsl*, δv'*) using the actual rolling force (F) and a target rolling force (F*) fed to it and outputs the at least one control parameter. An actual thickness (d) of the strip (5) is detected using a thickness measurement unit (10) directly downstream of the last rolling stage (4) of the cold-rolling line and this thickness is sent to a thickness control unit (11). The thickness control unit (11) acts on the last rolling stage (4) of the cold-rolling line. Another actual thickness (d’) of the strip (5) is detected using another thickness measurement unit (16) directly upstream of the last rolling stage (4) of the cold-rolling line. Speeds (v', v) at which the strip (5) enters the last rolling stage (4) of the cold-rolling line and exits the last rolling stage (4) of the cold-rolling line are detected using speed detection units (19, 20). The detected speeds (v', v) and a pre-determined final thickness (d*) which the strip (5) should have following the last rolling stage (4) of the cold-rolling line are fed to a setpoint determination unit (18). The setpoint determination unit (18) determines a target thickness (d'*) as a function of the parameters (v', v, d*, d) fed to it. Another thickness control unit (H’) acting on the next to last rolling stage (3) of the cold-rolling line receives the target thickness (d'*) as a setpoint (d'*) and the other actual thickness (d') as an actual value (d').